Adsorptive removal and photocatalytic degradation of organic pollutants using metal oxides and their composites: A comprehensive review

Achieving remarkable piezo-photocatalytic activity in Sr2Bi4Ti5O18/BiOCl sandwich ferroelectric heterojunction with continuous semi-coherent interfaces via selective etching of Aurivillius perovskite solid

Constructing ferroelectric hetrojuction and utilizing its piezo-photocatalytic performances is a promising approach for environmental remediation and sustainable energy conversion. However, challenges such as electron-hole recombination and interfacial instability limit the performance of piezoelectric heterojunction photocatalysts. In this study, a novel sandwich-structured heterojunction with a lattice-matched interface constructed by Sr2Bi4Ti5O18 (SBTO) bismuth Aurivillius phase ferroelectric material and BiOCl (BOC) was developed via a selective etching strategy. This approach minimizes interfacial defects and stress, while ferroelectric polarization modulates charge distribution, enhancing redox activity. Finite element simulations and experimental results demonstrate that the SBTO/BOC heterojunction leverages intrinsic and interfacial electric fields to form dual electron transport pathways, significantly improving charge separation in both bulk and interface regions. The optimized SBTO/BOC heterojunction achieves a piezo-photocatalytic degradation rate of 0.285 min-1 for Rhodamine B, approximately twice that of Sr2Bi4Ti5O18 under piezo-photocatalysis (0.147 min-1) and 13 times higher than photocatalysis alone (0.022 min-1). The heterostructure also efficiently degrades dyes, antibiotics, and Cr(VI), offering a robust design for high-performance piezo-photocatalytic systems.

Machine Learning Reveals Key Adsorption Mechanisms for Oxyanions Based on Combination of Experimental and Published Literature Data

The development of new adsorbents for water treatment often involves complex adsorption mechanisms, whose individual contributions are unclear, thereby limiting the understanding of adsorption driving forces, making it difficult to achieve precise design of adsorbents. Machine learning (ML) has been used to uncover the impacts of these mechanisms through feature engineering, but progress is limited by the data quality for training. Herein, we developed a universal ML strategy for precisely predicting the adsorption capacity of polymers for oxyanions and identifying the adsorption driving force based on the combination of experimental and published literature data. The adsorption mechanism was explored through classification of RDkit descriptors with different SHAP importance values, and electrostatic interaction was found to be the driving force in the oxyanion adsorption process, which was further verified by theoretical calculations, adsorption experiments, and effective targeted adsorbent design. In comparison, analysis relying on a separate literature data source led to decreased model performance, some biased conclusions, and invalid targeted adsorbent design. Overall, this study proposed a strategy for data set optimization as well as dominant mechanism identification, which could shed light on better treatment of oxyanions in wastewater.

Chalcogenide Materials in Water Purification: Advances in Adsorptive and Photocatalytic Removal of Organic Pollutants

Chalcogenide-based materials, known for their unique physicochemical properties, emerge as promising solutions for the removal of hazardous organic pollutants, such as dyes, pharmaceuticals, pesticides, and herbicides, from water and wastewater. This review examines the latest developments in the synthesis, structural optimization, and application of chalcogenide materials for environmental remediation. The past decade has witnessed remarkable advances in controlling the composition and structure of chalcogenide materials at the atomic level. The development of precise synthetic methods enables the creation of complex hierarchical structures, heterojunctions, and hybrid materials, leading to significant improvements in photocatalytic efficiency, stability, and selectivity for various environmental applications. Key emphasis is placed on adsorption and photocatalysis as green technologies, offering efficient pathways for pollutant removal. Mechanistic insights into the interactions between chalcogenide materials and contaminants are explored, providing a comprehensive understanding of their performance. Furthermore, challenges such as toxicity, scalability, and operational stability are discussed alongside future prospects for integrating these materials into industrial-scale water treatment systems. This review aims to inspire continued innovation in sustainable water purification technologies using chalcogenides.

Recent advances in titanium dioxide bio-derived carbon photocatalysts for organic pollutant degradation in wastewater

Water pollution from organic pollutants such as dyes and pharmaceuticals poses severe threats to ecosystems and human health, demanding effective remediation strategies. Conventional water treatment methods fall short in eliminating these contaminants, prompting interest in photocatalysis, which uses light energy to degrade pollutants into harmless substances such as carbon dioxide and water. This sustainable approach offers efficient pollutant removal with recyclable photocatalysts but faces challenges such as rapid charge recombination and limited electron-hole migration. Research aims to enhance photocatalytic efficiency under UV, visible, and solar light through metal doping and binary oxide systems, particularly titanium dioxide, which improves charge carrier migration and delays recombination. Coupling titanium dioxide with bio-derived carbon shows promise in enhancing electron-hole separation and visible light absorption. This review explores advances in photocatalyst synthesis, degradation mechanisms, adsorption reactions, and economic value of bioderived photocatalysts, emphasizing the potential of photocatalysis for efficient wastewater treatment.

Carbon-based metal oxide nanocomposites for water treatment by photocatalytic processes

The increasing contamination of water by emerging contaminants and the need for more efficient and sustainable treatment methods have prompted the exploration of advanced materials and technologies, with a particular focus on photocatalysis. Carbon-based metal oxide nanocomposites are a promising solution for the treatment of polluted water. This paper aims to review the current state of research on the application of these nanocomposites as photocatalysts for complete water treatment, describing breakthroughs in contaminant removal from 2019 through 2024 and milestones in water disinfection from 2016 through 2024. It includes discussion on the utilization of nanocomposites of Metal Oxides (MOs) with carbon materials to improve photocatalytic efficiency and addresses the advantages and drawbacks of these materials, including electron-hole recombination and agglomeration. The review focuses on the photocatalytic mechanisms of these nanocomposites and highlights the importance of heterostructures formed between metal oxides and carbon materials (e.g., graphene, carbon nanotubes, and carbon quantum dots), which enhance light absorption and hydroxyl radical generation, thereby increasing the efficiency of pollutant degradation and water disinfection. The review describes the properties of different MOs (n-type and p-type), exploring synergies between MOs and carbon materials and discussing the benefits and challenges of their application in wastewater treatment and pathogen inactivation. The review ends with a scientometric analysis of research trends in this field.

Enhanced Photocatalytic Activity of CQDs-Modified Layered g-C3N4/Flower-like ZnO Heterojunction for Efficient Degradation of Ciprofloxacin

Photocatalytic degradation has the advantages of high efficiency and stability compared with traditional antibiotic treatment. Therefore, the development of efficient and stable photocatalysts is essential for antibiotic degradation in water treatment. In this study, layered g-C3N4/flower-like ZnO heterojunction loaded with different amounts of CQDs (Cx%CNZO (x = 1, 2, 3, 4)) were precisely synthesized at room temperature. The as-prepared photocatalyst showed enhanced performance in degrading ciprofloxacin (CIP). The heterojunction with CQDs loaded at 3 wt% (C3%CNZO) achieved a 91.0% removal rate of CIP at 120 min under a sunlight simulator illumination, and the photodegradation reaction data were consistent with the first-order kinetic model. In addition, cycling experiments confirmed that the C3%CNZO heterojunction had good reusability and photocatalytic stability after four cycles. According to the experimental results, superoxide radical (•O2-) was the main active species involved in CIP degradation. Furthermore, C3%CNZO was found to conform to a type II electron transfer pathway. Finally, the possible degradation pathways of CIP were analyzed. This work may provide an effective strategy for the removal of various antibiotics in water treatment.

Highly efficient PMS activation by synergistic effects of FeS2/CoS2 for rapid diuron degradation: Advanced oxidation and mechanism

Diuron is an organic pollutant (herbicide). For the first time, a solvothermal method was used to prepare FeS2/CoS2 catalysts to activate peroxymonosulfate (PMS) for the degradation of diuron. The material characteristics of FeS2/CoS2-3 before and after use were analyzed. The study tested the impact of various factors on the degradation efficiency of diuron in solution. The electron transport phenomenon between FeS2 and CoS2 enhanced the activation efficiency of PMS and increased the degradation rate of diuron. After 8 h of dynamic cycling, FeS2/CoS2-3 could still activate PMS to efficiently degrade diuron. Singlet oxygen (1O2) plays an important role in the degradation of diuron in the presence of hydroxyl radical (OH•), sulfate radical (SO4•-), superoxide radical (O2•-), and high-valent metals. FeS2/CoS2-3 also effectively degraded methylene blue, neutral red, and sulfamethoxazole, and its degradation of diuron in various environments remained effective. The electrostatic potential, molecular bond energy, and frontier molecular orbitals of the diuron molecule were studied for the first time. A variety of potential degradation pathways for diuron were investigated, and the biotoxicity of the resulting intermediates was simulated and assessed. In addition, the primary mechanism by which FeS2/CoS2-3 activates PMS to degrade diuron has been proposed.

Advancements in functional adsorbents for sustainable recovery of rare earth elements from wastewater: A comprehensive review of performance, mechanisms, and applications

Rare earth elements (REEs) are crucial metallic resources that play an essential role in national economies and industrial production. The reclaimation of REEs from wastewater stands as a significant supplementary strategy to bolster the REEs supply. Adsorption techniques are widely recognized as environmentally friendly and sustainable methods for the separation of REEs from wastewater. Despite the growing interest in adsorption-based REEs separation, comprehensive reviews of both traditional and novel adsorbents toward REEs recovery remain limited. This review aims to provide a thorough analysis of various adsorbents for the recovery of REEs. The types of adsorbents examined include activated carbons, functionalized silica nanoparticles, and microbial synthetic adsorbents, with a detailed evaluation of their adsorption capacities, selectivity, and regeneration potential. This study focuses on the mechanisms of REEs adsorption, including electrostatic interactions, ion exchange, surface complexation, and surface precipitation, highlighting how surface modifications can enhance REEs recovery efficiency. Future efforts in designing high-performance adsorbents should prioritize the optimization of the density of functional groups to enhance both selectivity and adsorption capacity, while also maintaining a balance between overall capacity, cost, and reusability. The incorporation of covalently bonded functional groups onto mechanically robust adsorbents can significantly strengthen chemical interactions with REEs and improve the structural stability of the adsorbents during reuse. Additionally, the development of materials with high specific surface areas and well-defined porous structures is benifitial to facilitating mass transfer of REEs and maximizing adsorption efficiency. Ultimately, the advancement of the design of efficient, highly selective and recyclable adsorbents is critical for addressing the growing demand for REEs across diverse industrial applications.

Metal oxides and their composites for the remediation of organic pesticides: advanced photocatalytic and adsorptive solutions

Metal oxide nanoparticles and their composites have garnered significant attention in water treatment and environmental cleanup due to their unique physicochemical properties. These materials exhibit distinct crystalline structures, tunable morphologies, large surface areas, versatile surface chemistry, and widespread availability. These features make nanostructured metal oxides and their composites highly effective for the selective removal of organic pollutants from the environment, either by adsorption or photodegradation. This article focuses on recent advances, challenges, and opportunities in the use of metal oxides and their composites for the targeted removal of organic contaminants, including insecticides, phenolic compounds, organic dyes, and similar pollutants. The discussion encompasses a broad range of metal oxides and their composites, highlighting their diverse structural, crystallographic, and morphological characteristics that influence their adsorption and photocatalytic performance. Emphasis is placed on the photocatalytic and adsorptive capabilities of these materials, including their photo-stimulation properties and mechanisms. Metal oxides are highlighted as outstanding photocatalysts due to their high photodegradation efficiency, cost-effective synthesis methods, and optimized bandgap engineering. This review serves as a valuable resource for researchers exploring the photocatalytic and adsorptive applications of metal oxide-based materials, particularly in the remediation of hazardous organic pollutants such as pesticides.

Selenium-based nanomaterials: green and conventional synthesis methods, applications, and advances in dye degradation

The rapidly expanding industrialization and global increase in economic activities have drawn attention to the concerning accumulation of waste. The textile industry plays a significant role in environmental pollution, especially in and water pollution. Harmful dyes used during the fabrication process are mixed with water bodies through sewage or wastewater ejected from industrial factories. These toxic dyes are not only applied in textile industries but also used in other industries like pharmaceutical companies and rubber manufacturing. Therefore, scientists have adopted alternative techniques for the degradation of organic dyes because of eliminating the drawbacks from the traditionally used techniques. Catalytic degradation of organic dyes with the help of a safe and easy nanocatalyst is one of the best alternatives. Accordingly, the use of biomaterials or waste materials offers an easy, cost-effective and eco-friendly approach for the synthesis of such nanocatalysts. Several nanocatalysts have been used for the degradation of dyes present in industrial wastewater. The well-known semi-conductor selenium has several important properties, viz., optoelectronic, photovoltaic, thermoconductivity, and anisotropy, and has drawn significant research attention for its catalytic application in dye degradation. Considering all these points, selenium nanoparticles synthesized via green techniques provide the best possible alternative catalyst for the degradation of organic dyes in industrial wastewater. The current review covers various aspects of the biosynthesis of selenium nanoparticles; their application as a catalyst for the degradation of harmful organic dyes, viz., methylene blue, methyl orange, rhodamine B, alizarin S, malachite green, sunset yellow, fuchsin, safranin T, Congo red, and bromothymol blue; and their mechanism for the degradation process. This review will also shed light on the importance of using green chemistry towards the synthesis of selenium nanoparticles and different biosynthesis procedures and explores all aspects of the interesting catalytic activity towards the dye degradation mechanism. Hence this article will be beneficial to both industrialists and acdemicians bridging the gap between industrial and academic sceintists.

Three different methods for ZnO-RGO nanocomposite synthesis and its adsorption capacity for methylene blue dye removal in a comparative study

Water is one of the vital needs of life. However, due to rapid industrialization, urbanization and lack of awareness, the world population now facing the threat of water shortage. To ensure that future living conditions are preserved, it is crucial to reduce water pollution and protect the ecosystem. Zinc oxide- reduced graphene oxide (ZnO-RGO) nanocomposite is used in this study as an adsorbent for the adsorption of methylene blue (MB) dye from an aqueous solution. An easy strategy was used for the synthesis of reduced graphene oxide nanoparticles (RGO), Zinc oxide nanoparticles (ZnO) and ZnO-RGO nanocomposite. The synthesis of reduced graphene oxide (RGO) was accomplished through the exothermic reaction of a modified Hummer's method. In a novel approach, zinc oxide nanoparticles (ZnO NPs) were synthesized using the green Leidenfrost technique. This study presents a comparative investigation of ZnO-RGO nanocomposite synthesis employing both green and chemical methods. Three distinct approaches were utilized to prepare the ZnO-RGO nanocomposite: (1) the innovative Leidenfrost green method for composite A1, (2) a chemical precipitation method for composite A2, and (3) a physical mixing sonication method for composite A3. This research marks the first application of the Leidenfrost technique in the synthesis of ZnO-RGO nanocomposites, contributing to the growing body of knowledge in this field. X-ray diffraction (XRD), Burnauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), Zeta potential, transmittance electron microscope (TEM) and scanning electron microscope (SEM) analyses are conducted for synthesized sample characterization. Comparing the XRD patterns of the three synthesis methods, it is notable that the intensity peaks of composite A3 were the highest when ZnO was synthesized using a green method, indicating a higher degree of crystallinity. FTIR analysis approves that combining ZnO with RGO affects the functional groups of the three nanocomposite surfaces. The SEM analysis shows ZnO NPs and RGO sheets are incorporated together. In the case of A1 composite sharp angles make a flower shape was observed due to the unique synthesizing method. The surface area for A2 composite is the highest (7.29 m2/g) compared with A1 (2.91 m2/g) and A3(1.90 m2/g). A comparison study is made among the three nanocomposites for MB dye removal. The effect of adsorbent dose, pH, contact time and initial dye concentration on dye adsorption has been studied. The results show that A1 and A2 nanocomposites removed 85.5 and 87.5% of MB at the optimum adsorbent dose of 0.15 g/100 ml at pH8 and A3 removed 95% of MB at the optimum dose of 0.1 g/100 ml at pH 2. All three composites exhibited adherence to the Langmuir isotherm model, with correlation coefficients (R2) of 0.9858, 0.9904, and 0.9959 for A1, A2, and A3, respectively. Kinetic study results demonstrated that the pseudo-second-order model best described the adsorption process for all three composites, yielding R2 values of 0.9998, 0.9988, and 1.0000 for A1, A2, and A3, respectively. The A3 nanocomposite shows the highest adsorption capacity (104.5 mg/g) compared to the other composites (87.7 and 97.5 mg/g for A1 and A2, respectively). Desorption experiments revealed that the dye removal percentages varied with the ratio of the ethanol-water mixture used. Absolute ethanol achieved a 90% removal compared with 1:1 and 1:2 aqueous ethanol solutions (87.5% and 80%, respectively).

Effective removal of rhodamine B dyestuff using colemanite as an adsorbent: Isotherm, kinetic, thermodynamic analysis and mechanism

Removal of Rhodamine B (RhB) from aqueous solutions was performed by the batch adsorption process. Colemanite was characterized as an adsorbent by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF). The effects of contact time, the effect of the initial concentration of the dye, the amount of adsorbent and temperature parameters on the removal of RhB were investigated. Equilibrium adsorption data of RhB on colemanite were analyzed using the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. It was found that the isotherm that showed the highest correlation with experimental data was the Langmuir isotherm. Using the Langmuir isotherm, the theoretical adsorption capacity was calculated as 42.02 mg/g. Adsorption kinetics were analyzed with Pseudo-First-Order, Pseudo-Second-Order and Intraparticle diffusion models. As a result of the calculations, it was determined that the most appropriate kinetic model was the Pseudo-Second-Order kinetic model. Thermodynamic studies have shown that adsorption is a physical, non-spontaneous, exothermic process in which randomness at the solid-liquid interface decreases. According to the results obtained, it can be said that colemanite can be used as a suitable adsorbent in the removal of Rhodamine B dye from wastewater.

Transformation of Natural Organic Matter in Simulated Abiotic Redox Dynamic Environments: Impact on Fe Cycling

Redox fluctuations within redox dynamic environments influence the redox state of natural organic matter (NOM) and its interaction with redox-active elements, such as iron. In this work, we investigate the changes in the molecular composition of NOM during redox fluctuations as well as the impact of these changes on the Fe-NOM interaction employing Suwannee River Dissolved Organic Matter (SRDOM) as a representative NOM. Characterization of SRDOM using X-ray photoelectron spectroscopy and Fourier transform infrared spectrometry showed that irreversible changes occurred following electrochemical reduction and reoxidation of SRDOM in air. Changes in the redox state of SRDOM impacted its interaction with iron with higher rates of Fe(III) reduction in the presence of reduced and reoxidized SRDOM than in the presence of the original SRDOM. The increased rate of Fe(III) reduction in the presence of reduced SRDOM was due to the formation of reduced organic moieties on SRDOM reduction. The Fe(II) oxidation rate also increased in the presence of reduced SRDOM due to the formation of redox-active moieties that were capable of oxidizing Fe(II). Overall, our study provides useful insights into the changes in SRDOM that may occur in redox dynamic environments and the associated impact of these changes on Fe transformations.

A state-of-the-art review on lignocellulosic biomass-derived activated carbon for adsorption and photocatalytic degradation of pollutants: a property and mechanistic study

A promising water treatment method involves using biomass-derived activated carbon (AC) to remove emerging pollutants from wastewater due to its adsorption capacity, cost-effectiveness, and sustainability. Notwithstanding, the existing literature lacks comprehensive studies that specifically focus on removing contaminants in water by comparing the effectiveness of adsorption and photocatalytic degradation methods. Additionally, there is not much emphasis on analyzing the combined processes of adsorption-photocatalytic degradation utilizing AC. Herein, this paper investigates the intricacies of adsorption-photocatalytic degradation mechanisms and contributing variables in the enhancement of performances using biomass-derived AC. Furthermore, this review paper presents a comprehensive examination of different biomass sources employed in the synthesis of AC. It also discusses the diverse techniques utilized for the fabrication of AC, including physical and chemical activation methods. Finally, the shortcomings and future prospects of biomass-derived AC have been addressed. This study offers significant insights for the development of future biomass-derived AC, with the goal of improving their efficiency and expanding their uses in wastewater treatment.

Green Synthesis of Titanium Dioxide Nanoparticles Using Maerua oblongifolia Root Bark Extract: Photocatalytic Degradation and Antibacterial Activities

The root bark extract of the Maerua oblongifolia plant in the green synthesis of titanium dioxide nanoparticles (TiO2 NPs) for photocatalytic degradation of toxic pollutants and antibacterial activities was implemented in this study. The root bark extract served as a novel capping and reducing agent for the first time. Characterization of the TiO2 NPs was conducted by using visual observation, ultraviolet visible spectrometry (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques, confirming their successful synthesis. The TiO2 NPs exhibited maximum absorbance at 323 nm and an average particle size of 19.58 nm; the conjugations and existences of Ti-O and OH vibrational bands were revealed by the FTIR spectrum. The photocatalytic activities of the TiO2 NPs were investigated by using solar irradiation as an energy source for aqueous solutions of methyl orange (MO) and methylene blue (MB) dyes. The TiO2 NPs showed strong photocatalytic activities by degrading 97.23% MB and 91.8% MO under optimized conditions. Degradation behavior was investigated by isotherms and kinetics models, with the Langmuir isotherms (R2: 0.996, 0.979) and Langmuir-Hinshelwood (R2: 0.998, 0.997) highest correlation coefficients for MB and MO, respectively. Moreover, the antibacterial efficacy of the green-synthesized TiO2 NPs and the results indicated higher antibacterial activities on Gram-negative bacteria (27 ± 0.52).

Hierarchical Ordered Mesoporous Sr2Bi4Ti5O18 Microflowers with Rich Oxygen Vacancies In Situ Assembled by Nanosheets for Piezo-Photocatalysis

The Aurivillius phase layered perovskite ferroelectric material Sr2Bi4Ti5O18 (SBTO) exhibits spontaneous polarization and piezoelectric properties, which confer significant potential for piezo-photocatalysis. Its ability to enhance electron-hole separation while providing excellent fatigue resistance positions it as a promising candidate in this field. Defects were introduced to improve the structural polarization and photoelectrochemical properties of SBTO. SBTO nanocrystals, featuring a mixed structure of hierarchically ordered mesoporous microflowers and nanosheets, were successfully synthesized via the hydrothermal method. The SBTO sample synthesized at a lower hydrothermal temperature displayed optimal oxygen vacancy concentration and exhibited superior piezoelectric-photo synergistic degradation activity for organic pollutants. Additionally, corona polarization increases the macroscopic polarization of the SBTO photocatalyst, promoting the separation of photogenerated carriers. Finite element simulations confirmed that a single flower-like SBTO structure generates a higher piezoelectric potential compared to a sheet-like morphology. In conclusion, integrating self-assembled hierarchical structure design, ferroelectric polarization, and defect engineering forms an effective strategy for achieving high-performance SBTO-based layered perovskite piezo-photocatalysts.

Synthesis and characterization of nano iron oxide biochar composite for efficient removal of crystal violet from water

In the present study, Coconut Husk Biochar (CHB) was synthesize from widely available, locally sourced agro waste, coconut husk and characterized using different techniques like scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). CHB was tested for its ability to adsorb crystal violet (CV), a commonly used cationic dye, from water. It was capable of adsorbing more than 98 % of CV from water and follows Freundlich isotherm model with pseudo second order kinetics though the overall process was unfavourable. Moreover, separation of CHB from water after adsorption is a cumbersome process. Thus, unmodified CHB is not suitable for use as an adsorbent for CV. Magnetic nano iron oxide Biochar Composite (MBC) was synthesized by deposition of nano iron oxide (Fe3O4) onto its surface by co-precipitation method and characterized using SEM, XRD and FTIR. SEM analysis provided visual evidence of this deposition which was further confirmed by XRD and FTIR analysis. MBC was also effective in adsorbing more than 90 % of CV from aqueous solution though a decrease in adsorption capacity was observed. Adsorption data followed Langmuir isotherm model and pseudo second order kinetics. MBC is superparamagnetic and is strongly attracted to a small bar magnet, facilitating easy removal from water after CV adsorption.

Zirconium and cerium dioxide fabricated activated carbon-based nanocomposites for enhanced adsorption and photocatalytic removal of methylene blue and tetracycline hydrochloride

Activated carbon (AC) is a porous, amorphous form of carbon known for its strong adsorption capacity, making it highly effective for use in wastewater treatment. In this investigation, AC-based nanocomposites (NCs) loaded with zirconium dioxide and cerium dioxide nanoparticles (ZrO2/CeO2 NPs) were successfully synthesized for the effective elimination of methylene blue (MB) and tetracycline hydrochloride (TCH). The AC-ZrO2/CeO2 NCs have a size of 231.83 nm, a zeta potential of -20.07 mV, and a PDI value of 0.160. The adsorption capacities of AC-ZrO2/CeO2 NCs for MB and TCH were proved in agreement with the Langmuir isotherm and pseudo 1st order kinetic model, respectively. The maximum adsorption capacities were determined to be 75.54 mg/g for MB and 26.75 mg/g for TCH. Notably, AC-ZrO2/CeO2 NCs exhibited superior photocatalytic degradation efficiency for MB and TCH under sunlight irradiation with removal efficiencies reaching up to 97.91% and 82.40% within 90 min, respectively. The t1/2 for the photo-degradation process of MB and TCH were 11.55 min and 44.37 min. Analysis of active species trapping confirmed the involvement of hole (h+), superoxide anion (•O2-), and hydroxyl radical (•OH) in the degradation mechanism. Furthermore, the residual solution post-contaminant removal exhibited minimal toxicity towards Artemia salina and NIH3T3 cells. Importantly, the NCs did not exhibit antibacterial activity against tested pathogens post-absorption/degradation of TCH. Thus, AC-ZrO2/CeO2 NCs could be a promising nanomaterial for wastewater treatment applications.

Studying the properties of green synthesized silver oxide nanoparticles in the application of organic dye degradation under visible light

In present study the green synthesis of silver oxide nanoparticles has been effectively achieved using novel plant extract Phragmanthera Macrosolen. This method provides sustainable alternative for nanoparticle synthesis, demonstrating the potential of Phragmanthera Macrosolen as a reducing and stabilizing agent in the production of Ag2O NPs. The synthesized nanoparticles were characterized for their structural, morphological, and optical properties, confirming their successful formation and potential applications in various fields. The effects of different pH values and annealing temperature of the samples on the properties of Ag2O NPs formations, as well as photo-catalytic activities towards Toluidine Blue dye degradations, were studied. Powder XRD reveals that the crystallite natures of Ag2O NPs a long with crystalline size ranges from 25.85 to 35.90 nm. FIB-SEM and HR-TEM images displayed that the Ag2O NPs as spherical shapes. UV-vis spectroscopy displayed that Ag2O NPs belong to a direct-band gap of 2.1-2.6 eV. FTIR- study shown that the green synthesized Ag2O NPs may be steadied via the interfaces of -OH as well as C = O groups in the carbohydrate, flavonoid, tannin, as well as phenolic acid existing in P. macrosolen L. leaf. The chemical states, electron-hole recombinations and purity of Ag and O in the synthesized Ag2O NPs were confirmed through X-ray Photoelectron Spectroscopy (XPS) and PL analysis respectively. Fascinatingly, the synthesized Ag2O NPs at pH 12 displayed high photo-catalytic degradations for TB dyes. The photo-catalytic degradations of the TB dyes were monitored spectro-photo-metrically in wave-length ranges of 200-900 nm, as well as high efficiency (98.50%) with half-life of 9.5798 min and kinetic rate constant of 0.07234 min-1, was obtained after 45 min of reactions. From this study, it can be concluded that Ag2O NPs synthesized from Phragmanthera Macrosolen aqueous extract are promising in the remediation of environmental pollution and water treatment. In this light, the study reports that Phragmanthera Macrosolen green synthesis of Ag2O NPs can effectively address environmental pollution in cost-effective, eco-friendly, and sustainable ways.

Experimental and theoretical insights into the adsorption mechanism of methylene blue on the (002) WO3 surface

This work investigates the efficiency of green-synthesized WO3 nanoflakes for the removal of methylene blue dye. The synthesis of WO3 nanoflakes using Hyphaene thebaica fruit extract results in a material with a specific surface area of 13 m2/g and an average pore size of 19.3 nm. A combined theoretical and experimental study exhibits a complete understanding of the MB adsorption mechanism onto WO3 nanoflakes. Adsorption studies revealed a maximum methylene blue adsorption capacity of 78.14 mg/g. The pseudo-second-order model was the best to describe the adsorption kinetics with a correlation coefficient (R2) of 0.99, suggesting chemisorption. The intra-particle diffusion study supported a two-stage process involving surface adsorption and intra-particle diffusion. Molecular dynamic simulations confirmes the electrostatic attraction mechanism between MB and the (002) WO3 surface, with the most favorable adsorption energy calculated as -0.68 eV. The electrokinetic study confirmed that the WO3 nanoflakes have a strongly negative zeta potential of -31.5 mV and a uniform particle size of around 510 nm. The analysis of adsorption isotherms exhibits a complex adsorption mechanism between WO3 and MB, involving both electrostatic attraction and physical adsorption. The WO3 nanoflakes maintained 90% of their adsorption efficiency after five cycles, according to the reusability tests.

Unlocking solar energy's potential: Dual photocatalytic activities of g-C3N4/Sb2S3 for hydrogen evolution and tetracycline degradation in sunlight

This study focuses on developing a g-C3N4/Sb2S3 heterojunction photocatalyst with different g-C3N4 to Sb2S3 weight ratios (1:1, 1:3, and 3:1) for degrading tetracycline (TC) pollutants. The 1:3 ratio (13 GS) exhibited optimal photocatalytic performance, achieving 99% TC degradation under sunlight within 120 min, compared to 78.4% under visible light and 38% under UV light. The 13 GS catalyst demonstrated strong reusability, maintaining 80% degradation efficiency after six cycles. Scavenger experiments identified hydroxyl radicals as crucial for TC degradation, with DMSO reducing activity by 30%. The photocatalyst also showed high hydrogen production with an apparent quantum efficiency (AQE) of 19.8% under standard conditions, and improved AQE in acidic (23%) and basic (22.7%) conditions, and with CH3OH (23.2%). This g-C3N4/Sb2S3 heterojunction offers a promising solution for degrading toxic contaminants and has the potential for solar-powered applications.

Co3O4/CuO@C catalyst based on cobalt-doped HKUST-1 as an efficient peroxymonosulfate activator for pendimethalin degradation: Catalysis and mechanism

Pendimethalin (PM) is an organic pollutant (herbicide), and systematic studies on PM degradation are scarce. The efficient degradation of PM in water remains a challenge that requires to be addressed. Herein, for the first time, elemental Co was doped into HKUST-1 using a solvothermal method to generate Co3O4/CuO@C via pyrolysis. The as-prepared catalyst was used to activate peroxymonosulfate (PMS) for PM degradation, obtaining a PM degradation efficiency of 98.2 % after 30 min. The assessment of the effects of various factors on the degradation efficiency revealed that 1O2 dominated PM degradation, whereas the contribution of SO4•- was negligible. Although 3Co3O4/CuO@C exhibited a good degradation performance against other organic pollutants, its degradation performance in real water was poor. The carbon layer reduced metal-ion leaching (Co and Cu), and the synergistic interactions between Co3O4 and CuO promoted PMS activation. The roles of the components of 3Co3O4/CuO@C in PM degradation by activated PMS were investigated in the presence of CoIV and Co-OOSO3-. Two possible PM degradation pathways were systematically proposed, and the toxicity of the intermediates was analyzed. Finally, a mechanism for PM degradation by 3Co3O4/CuO@C-activated PMS was proposed.

Solvothermal synthesis of 3D rod-shaped Ti/Al/Cr nano-oxide for photodegradation of wastewater micropollutants under sunlight: a green way to achieve SDG:6

Waterbodies are day-by-day polluted by the various colored micropollutants, e.g., azo dyes enriched (carcinogenic, non-biodegradable) colored wastewater from textile industries. Water pollution has become a serious global issue as ~ 25% of health diseases are prompted by pollution as reported by WHO. Around 1 billion people will face water scarcity by 2025 and this water crisis is also a prime focus to the UNs' sustainable development goal 6 (SDG6: clean water and sanitation). To prevent the water pollution caused by micropollutants, a mesoporous, 3D rod-like nano-oxide Ti/Al/Cr (abbreviated as TAC) has been synthesized via the solvothermal method. TAC degraded all classes of azo dyes (mono, di, tri, etc.) with > 90% efficiency under renewable energy source solar irradiation within the pH range 2-11. The detailed study was done on the photodegradation of carcinogenic di-azo dye Congo red (CR) which is banned in many countries. TAC showed 90.64 ± 2% degradation efficiency for CR at pH 7. The proposed photodegradation mechanism of CR was confirmed by the high-resolution liquid chromatography-mass spectroscopy (HRLC-MS) analysis obeying the Pirkanniemi path. The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to successive 5 cycles which can be an efficient tool to meet the UNs' SDG:6.

Plant biomass-based nanoparticles for remediation of contaminants from water ecosystems: Recent trends, challenges, and future perspectives

Green nanomaterials can mitigate ecological concerns by minimizing the impact of toxic contaminants on human and environmental health. Biosynthesis seems to be drawing unequivocal attention as the traditional methods of producing nanoparticles through chemical and physical routes are not sustainable. In order to utilize plant biomass, the current review outlines a sustainable method for producing non-toxic plant biomass-based nanoparticles and discusses their applications as well as recent trends involved in the remediation of contaminants, like organic/inorganic pollutants, pharmaceuticals, and radioactive pollutants from aquatic ecosystems. Plant biomass-based nanoparticles have been synthesized using various vegetal components, such as leaves, roots, flowers, stems, seeds, tuber, and bark, for applications in water purification. Phyto-mediated green nanoparticles are effectively utilized to treat contaminated water and reduce harmful substances. Effectiveness of adsorption has also been studied using variable parameters, e.g., pH, initial contaminant concentration, contact time, adsorbent dose, and temperature. Removal of environmental contaminants through reduction, photocatalytic degradation, and surface adsorption mechanisms, such as physical adsorption, precipitation, complexation, and ion exchange, primarily due to varying pH solutions and complex functional groups. In the case of organic pollutants, most of the contaminants have been treated by catalytic reduction and photodegradation involving the formation of NaBH4, H2O2, or both. Whereas electrostatic interaction, metal complexation, H-bonding, π- π associations, and chelation along with reduction have played a major role in the adsorption of heavy metals, pharmaceuticals, radioactive, and other inorganic pollutants. This review also highlights several challenges, like particle size, toxicity, stability, functional groups, cost of nanoparticle production, nanomaterial dynamics, and biological interactions, along with renewability and recycling of nanoparticles. Lastly, this review concluded that plant-biomass-based nanoparticles provide a sustainable, eco-friendly remediation method, utilizing the unique properties of nanomaterials and minimizing chemical synthesis risks.

Metal oxide-based photocatalysts for the efficient degradation of organic pollutants for a sustainable environment: a review

Photocatalytic degradation is a highly efficient technique for eliminating organic pollutants such as antibiotics, organic dyes, toluene, nitrobenzene, cyclohexane, and refinery oil from the environment. The effects of operating conditions, concentrations of contaminants and catalysts, and their impact on the rate of deterioration are the key focuses of this review. This method utilizes light-activated semiconductor catalysts to generate reactive oxygen species that break down contaminants. Modified photocatalysts, such as metal oxides, doped metal oxides, and composite materials, enhance the effectiveness of photocatalytic degradation by improving light absorption and charge separation. Furthermore, operational conditions such as pH, temperature, and light intensity also play a crucial role in enhancing the degradation process. The results indicated that both high pollutant and catalyst concentrations improve the degradation rate up to a threshold, beyond which no significant benefits are observed. The optimal operational conditions were found to significantly enhance photocatalytic efficiency, with a marked increase in degradation rates under ideal settings. Antibiotics and organic dyes generally follow intricate degradation pathways, resulting in the breakdown of these substances into smaller, less detrimental compounds. On the other hand, hydrocarbons such as toluene and cyclohexane, along with nitrobenzene, may necessitate many stages to achieve complete mineralization. Several factors that affect the efficiency of degradation are the characteristics of the photocatalyst, pollutant concentration, light intensity, and the existence of co-catalysts. This approach offers a sustainable alternative for minimizing the amount of organic pollutants present in the environment, contributing to cleaner air and water. Photocatalytic degradation hence holds tremendous potential for remediation of the environment.

Fabrication of a reusable carbon quantum dots (CQDs) modified nanocomposite with enhanced visible light photocatalytic activity

In awareness of industrial dye wastewater, carbon quantum dots (CQDs) and cobalt zinc ferrite (CZF) nanocomposites were synthesised for the making of carbon quantum dots coated cobalt zinc ferrite (CZF@CQDs) nanophotocatalyst using oxidative polymerization reaction. The results of TEM, zeta potential value, and FTIR confirm highly dispersed 1-4 nm particles with the - 45.7 mV carboxylic functionalized surface of CQDs. The results of the synthesised CZF@CQDs photocatalyst showed an average particle size of ~ 15 nm according to TEM, SEM, and XRD. The photocatalyst showed a 1.20 eV band gap, which followed the perfect visible light irradiation. TGA and DTA revealed the good thermal stability of the nanophotocatalyst. VSM was carried out, and the saturation magnetisations for CZF and CZF@CQDs were 42.44 and 36.14 emu/g, respectively. A multipoint study determined the BET-specific surface area of the CZF@CQDs photocatalyst to be 149.87 m2/g. Under visible light irradiation, the final CZF@CQDs nanophotocatalyst demonstrated remarkable efficiency (~ 95% within 25 min) in the photocatalytic destruction of Reactive Blue 222 (RB 222) and Reactive Yellow 145 (RY 145) dyes, as well as mechanical stability and recyclability. Even after the recycling of the degradation study, the nanophotocatalyst efficiency (~ 82%, 7th cycles) was predominantly maintained. The effects of several parameters were also investigated, including initial dye concentration, nanophotocatalyst concentration, CQD content, initial pH of the dye solution, and reaction kinetics. Degradation study data follow the first-order reaction rate (R2 > 0.93). Finally, a simple and low-cost synthesis approach, rapid degradation, and outstanding stability of the CQD-coated CZF nanophotocatalyst should make it a potential photocatalyst for dye wastewater treatment.

Customizing Cerium Oxide Particle Synthesis with Hybrid Polyion Complex Templates for Enhanced Oxidation Performance in Photo-Fenton Processes

Hybrid poly-ion complexes were synthesized through the complexation of a double hydrophilic copolymer with Ce(III) ions. These colloids act as reservoirs for cerium ions, enabling the synthesis of cerium-based Prussian blue nanoparticles with a cubic structure, a narrow size distribution around 100 nm, and good colloidal stability in water. Upon high-temperature calcination, these nanoparticles are transformed into a cerium/iron-based metal oxide catalyst (CeO2/Fe2O3). The resultant composite catalyst demonstrates superior performance in the photo-Fenton oxidation of methylene blue pollutants, achieving a conversion efficiency that rivals other metal-based oxides and cerium-based catalysts.

Straightforward Creation of Multishell Hollow Hybrids for an Integrated Metabolic Monitoring System in Disease Management

Multidimensional metabolic analysis has become a new trend in establishing efficient disease monitoring systems, as the constraints associated with relying solely on a single dimension in refined monitoring are increasingly pronounced. Here, coordination polymers are employed as derivative precursors to create multishell hollow hybrids, developing an integrated metabolic monitoring system. Briefly, metabolic fingerprints are extracted from hundreds of serum samples and urine samples, encompassing not only membranous nephropathy but also related diseases, using high-throughput mass spectrometry. With optimized algorithm and initial feature selection, the established combined panel demonstrates enhanced accuracy in both subtype differentiation (over 98.1%) and prognostic monitoring (over 95.6%), even during double blind test. This surpasses the serum biomarker panel (≈90.7% for subtyping, ≈89.7% for prognosis) and urine biomarker panel (≈94.4% for subtyping, ≈76.5% for prognosis). Moreover, after attempting to further refine the marker panel, the blind test maintains equal sensitivity, specificity, and accuracy, showcasing a comprehensive improvement over the single-fluid approach. This underscores the remarkable effectiveness and superiority of the integrated strategy in discriminating between MN and other groups. This work has the potential to significantly advance diagnostic medicine, leading to the establishment of more effective strategies for patient management.

In-situ Hf/Zr co-doped Fe2O3 nanorod decorated with CuOx/CoOx: Enhanced photocatalytic performance for antibacterial and organic pollutants

Herein, we successfully synthesized Hf/Zr co-doping on Fe2O3 nanorod photocatalyst by a hydrothermal process and quenching methods. The synergistic roles of Hf and Zr double-doping on the bacteria inactivation test and decomposition of organic pollutants were investigated in detail for the 1 wt% CoOx loaded Hf/Zr-Fe2O3 NRs and CuOx/CoOx loaded Hf/Zr-Fe2O3 NRs photocatalyst. Initially, the rod-like porous morphology of the Hf/Zr-doped Fe2O3 NRs was produced via a hydrothermal method at various Hf co-doping (0, 2, 4, 7 and 10)%. Further, CoOx and CuOx loaded by a wet impregnation approach on the Hf/Zr-Fe2O3 NRs and a highly photoactive Hf(4)/Zr-Fe2O3 [CoOx/CuOx] NRs photocatalyst were developed. After the Hf(4)/Zr-Fe2O3 [CoOx/CuOx] NRs photocatalyst treatment, the Bio-TEM imagery of bacterial cells showed extensive morphological deviations in cell membranes. Hf(4)/Zr-Fe2O3 NR achieved 84.1% orange II degradation upon 3 h illumination, which is higher than that of Hf-Fe2O3 and Zr-Fe2O3 (68.7 and 73.5%, respectively). Additionally, the optimum sample, Hf(4)/Zr-Fe2O3 [CoOx/CuOx] photocatalyst, exhibited 95.5% orange II dye degradation after light radiation for 3 h. Optimized Hf(4)/Zr-Fe2O3 [CoOx/CuOx] catalysts exhibited 99.9% and 99.7% inactivation of E. coli and S. aureus with 120 min, respectively. Further, scavenger experiments revealed that the electrons are the primary responsible species for photocatalytic kinetics. This work will provide a rapid method for the development of high photocatalytic performance materials for bacterial disinfection and organic degradation.

Innovations in metal-organic frameworks (MOFs): Pioneering adsorption approaches for persistent organic pollutant (POP) removal

Adsorption is a promising way to remove persistent organic pollutants (POPs), a major environmental issue. With their high porosity and vast surface areas, MOFs are suited for POP removal due to their excellent adsorption capabilities. This review addresses the intricate principles of MOF-mediated adsorption and helps to future attempts to mitigate organic water pollution. This review examines the complicated concepts of MOF-mediated adsorption, including MOF synthesis methodologies, adsorption mechanisms, and material tunability and adaptability. MOFs' ability to adsorb POPs via electrostatic forces, acid-base interactions, hydrogen bonds, and pi-pi interactions is elaborated. This review demonstrates its versatility in eliminating many types of contaminants. Functionalizing, adding metal nanoparticles, or changing MOFs after they are created can improve their performance and remove contaminants. This paper also discusses MOF-based pollutant removal issues and future prospects, including adsorption capacity, selectivity, scale-up for practical application, stability, and recovery. These obstacles can be overcome by rationally designing MOFs, developing composite materials, and improving material production and characterization. Overall, MOF technology research and innovation hold considerable promise for environmental pollution solutions and sustainable remediation. Desorption and regeneration in MOFs are also included in the review, along with methods for improving pollutant removal efficiency and sustainability. Case studies of effective MOF regeneration and scaling up for practical deployment are discussed, along with future ideas for addressing these hurdles.

Synergistic adsorption and photocatalytic degradation of tetracycline using a Z-scheme kaolin/g-C3N4/MoO3 nanocomposite: A sustainable approach for water treatment

This research focuses on the synthesis and application of a novel kaolin-supported g-C3N4/MoO3 nanocomposite for the degradation of tetracycline, an important antibiotic contaminant in water systems. The nanocomposite was prepared through a facile and environmentally friendly approach, leveraging the adsorption and photocatalytic properties of kaolin, g-C3N4 and MoO3 nanoparticles, respectively. Comprehensive characterization of the nanocomposite was conducted using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and optical spectra. The surface parameters were studied using N2 adsorption-desorption isotherm. The elemental composition was studied using X-ray photoelectron spectroscopy. The efficiency of the developed nanocomposite in tetracycline degradation was evaluated and the results revealed an efficient tetracycline degradation exhibiting the synergistic effects of adsorption and photocatalytic degradation in the removal process. The tetracycline degradation was achieved in 60 min. Kinetic studies and thermodynamic analyses provided insights into the degradation mechanism, suggesting potential applications for the nanocomposite in wastewater treatment. Additionally, the recyclability and stability of the nanocomposite were investigated, demonstrating its potential for sustainable and long-term application in water treatment.

Ag-Incorporated Cr-Doped BaTiO3 Aerogel toward Enhanced Photocatalytic Degradation of Methyl Orange

A novel Cr-doped BaTiO3 aerogel was successfully synthesized using a co-gelation technique that involves two metallic alkoxides and a supercritical drying method. This freshly prepared aerogel has a high specific surface area of over 100 m2/g and exhibits improved responsiveness to the simulated sunlight spectrum. Methyl orange (MO) was chosen as the simulated pollutant, and the results reveal that the Cr-doped BaTiO3 aerogel, when modified with the noble metal silver (Ag), achieves a pollutant removal rate approximately 3.2 times higher than that of the commercially available P25, reaching up to 92% within 60 min. The excellent photocatalytic performance of the Ag-modified Cr-doped BaTiO3 aerogel can be primarily attributed to its extensive specific surface area and three-dimensional porous architecture. Furthermore, the incorporation of Ag nanoparticles effectively suppresses the recombination of photo-generated electrons and holes. Stability and reusability tests have confirmed the reliability of the Ag-modified Cr-doped BaTiO3 aerogel. Therefore, this material emerges as a highly promising candidate for the treatment of textile wastewater.

Unraveling the Impact of Adsorbed Molecules on Photocatalytic Processes: Advancements in Understanding Facet-Controlled Semiconductor Photocatalysts

This work aims to demonstrate that the Fe2O3 nanocrystals' adsorptive and photocatalytic properties can be adjusted by exposing the crystal facets that are functionalized. To this end, cube- and disc-like structures were synthesized using a metal ion-mediated hydrothermal route. Thereafter, some of the samples were annealed at 500 °C for 3 h. Our paper combines the experimental part with theoretical calculations of the obtained materials' band edge positions. The results reveal that-aside from hematite-the as-synthesized discs also contain γ-FeOOH and β-Fe2O3 phases, which transform into α-Fe2O3 during annealing. The hydrodynamic diameter, zeta potential, and adsorption kinetics measurements show that the cube-like samples exhibit the highest affinity for cationic, whereas the discs have an affinity for anionic dye. Measurements of the wall zeta potential also reveal that annealing the discs modifies their surface state and ability to adsorb molecules. Photocatalytic tests show that the as-synthesized powders have better photocatalytic performance toward methylene blue decomposition than the annealed ones. The observed small changes in the concentration of the MO during illumination result from the energy band structure of the cube-like crystal orientation.

Imine-Decorated Copper-Based Metal-Organic Framework for the Photodegradation of Methylene Blue

A low cost imine-decorated linker, 4,4'-(hydrazine-1,2-diylidenedimethylylidene)dibenzoic acid was utilized for the preparation of copper-based metal-organic framework (MOF) denoted as Cu-L via a solvothermal technique. The synthesized MOF material has been fully characterized by different analytical techniques such as Fourier-transform infrared (FT-IR) spectroscopy, powder X-Ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-Ray spectroscopy (EDX), nitrogen adsorption-desorption isotherm analysis, and thermogravimetric analysis (TGA). It has been found that the coordination of Cu2+ with L considerably reduced the band gap of the L of nearly about 1 eV, which is approximately 26% decline in total. Notably, a narrow band gap of the photocatalyst is an essential requirement for the proficient photodegradation of organic contaminants. An excellent optical properties and narrow band gap of (2.8 eV) of Cu-L ensure their suitability as a photocatalyst for the degradation of methylene blue (MB) dye. In the presence of Cu-L photocatalyst, 84.22% degradation of MB dye was observed after 150 min under sunlight exposure. It is the first time that imine-functionalized MOF was utilized for the degradation of MB dye under sunlight irradiation. For understanding the photodegradation of MB dye by the Cu-L photocatalyst, all the plausible mechanistic studies have been carried out in detail. Both theoretical (with the help of density functional theory (DFT) calculations) as well as experimental studies have been conducted to justify the possible mechanisms for the photodegradation of MB dye by Cu-L. The current work may open a new opportunity to construct a cheap MOF-based photocatalysts for fast degradation of dye contaminants.

Comparison of the antimicrobial photocatalytic activities of SiO2 and Au@SiO2 nanostructures in water decontamination

Photocatalytic disinfection of Escherichia coli suspension by silicon dioxide nanoparticles and silicon dioxide/gold nanocomposite in a batch reactor is investigated experimentally and results are compared. Silica nanoparticles were synthesized by Stöber method and pulsed laser ablation method was employed to prepare gold nanoparticles in distilled water. Composition of two nanoparticles species was carried out, using the second harmonic pulse of Nd:YAG laser, whose wavelength is in the absorption spectra of gold nanoparticles. Results confirm a decrease in the bandgap energy of silica nanoparticles after composition. Escherichia coli were selected as an indicator of the microbial water contamination. Disk diffusion method was used to evaluate the antimicrobial potential of SiO2 and Au@SiO2 nanostructures. Photocatalytic activities of both nanostructures were examined in dark, and under the irradiation of UV and visible light. In all conditions, the performance of Au@SiO2 nanocomposites was higher than SiO2 nanoparticles. In dark condition the higher biocidal nature and activity of Au nanoparticles and for the case of UV radiation, decreasing the bandgap energy and recombination rate of SiO2 nanoparticles after composition with Au increased the efficiency. For the case of visible light radiation, surface plasmon resonances effects, and local heat of Au nanoparticles were responsible for increasing the efficiency. RESEARCH HIGHLIGHTS: Doping large bandgap semiconductors nanostructures, such as silica with metal nanoparticles, such as gold will improve their photocatalytic activity to work in visible light. In this mechanism, gold nanoparticles act as effective traps to prevent the recombination of photogenerated electron-hole pairs. Other mechanisms, such as Schottky barrier formation, surface plasmon resonance absorption of gold nanoparticles, and biocidal nature of the gold nanoparticles are effective in increasing the efficiency of Au doped silica nanostructures.

Crosslinked chitosan-montmorillonite composite and its magnetized counterpart for the removal of basic fuchsin from wastewater: Parametric optimization using Box-Behnken design

Treating wastewater polluted with organic dyestuffs is still a challenge. In that vein, facile synthesis of a structurally simple composite of chitosan with montmorillonite (CS-MMT) using glutaraldehyde as a crosslinker and the magnetized analogue (MAG@CS-MMT) was proposed as versatile adsorbents for the cationic dye, basic Fuchsin (FUS). Statistical modeling of the adsorption process was mediated using Box-Behnken (BB) design and by varying the composite dose, pH, [FUS], and contact time. Characterization of both composites showed an enhancement of surface features upon magnetization, substantiating a better FUS removal of the MAG@CS-MMT (%R = 98.43 %) compared to CS-MMT (%R = 68.02 %). The surface area analysis demonstrates that MAG@CS-MMT possesses a higher surface area, measuring 41.54 m2/g, and the surface analysis of the magnetized nanocomposite, conducted using FT-IR and Raman spectroscopies, proved the presence of FeO peaks. In the same context, adsorption of FUS onto MAG@CS-MMT fitted-well to the Langmuir isotherm model and the maximum adsorption capacities (qm) were 53.11 mg/g for CS-MMT and 88.34 mg/g for MAG@CS-MMT. Kinetics investigation shows that experimental data fitted well to the pseudo-second order (PSO) model. Regeneration study reveals that MAG@CS-MMT can be recovered effectively for repeated use with a high adsorption efficiency for FUS.

Enhanced photocatalytic degradation of Rhodamine B using gold nanoparticles decorated on BaTiO3 with surface plasmon resonance enhancement

This study focused on synthesizing and applying gold nanoparticle (Au NP) decorated barium titanate (BaTiO3) nanoparticles for photocatalytic purposes. BaTiO3 NPs were synthesized using a facile hydrothermal method. Various techniques were employed to characterize the structure and morphological characteristics of the prepared materials. The photocatalytic degradation of Rhodamine B over the Au NPs-modified BaTiO3 photocatalysts was studied. Trapping experiments were conducted using different scavengers to elucidate the degradation mechanism and the involvement of photogenerated species. The incorporation of an appropriate amount of Au NPs into the composites resulted in a significant improvement in photocatalytic activity, attributed to the combined effect of Schottky junction at the interface and the surface plasmon resonance of Au NPs.

Recent advances in photoelectrochemical platforms based on porous materials for environmental pollutant detection

Human health and ecology are seriously threatened by harmful environmental contaminants. It is essential to develop efficient and simple methods for their detection. Environmental pollutants can be detected using photoelectrochemical (PEC) detection technologies. The key ingredient in the PEC sensing system is the photoactive material. Due to the unique characteristics, such as a large surface area, enhanced exposure of active sites, and effective mass capture and diffusion, porous materials have been regarded as ideal sensing materials for the construction of PEC sensors. Extensive efforts have been devoted to the development and modification of PEC sensors based on porous materials. However, a review of the relationship between detection performance and the structure of porous materials is still lacking. In this work, we present an overview of PEC sensors based on porous materials. A number of typical porous materials are introduced separately, and their applications in PEC detection of different types of environmental pollutants are also discussed. More importantly, special attention has been paid to how the porous material's structure affects aspects like sensitivity, selectivity, and detection limits of the associated PEC sensor. In addition, future research perspectives in the area of PEC sensors based on porous materials are presented.

Tungsten oxide encapsulated phosphate-rich porous alginate composites for efficient U(VI) capture: Insights into synthesis, adsorption kinetics and thermodynamics

In this work, novel monoclinic tungsten oxide (WO3)-encapsulated phosphate-rich porous sodium alginate (PASA) microspherical hydrogel beads were prepared for efficient U(VI) capture. These macroporous and hollow beads were systematically characterized through XRD, FTIR, EDX-mapping, and SEM-EDS techniques. The O and P atoms in the PO and monoclinic WO3 offered inner-spherical complexation with U(VI). The in situ growth of WO3 played a significant role inside the phosphate-rich biopolymeric network to improve its chemical stability, specific surface area, adsorption capacity, and sorption rate. The phytic acid (PA) served for heteroatom doping and crosslinking. The encapsulated WO3 mass ratio was optimized in different composites, and WO3/PASA3 (the microspherical beads with a mass ratio of 30.0 % w/w) exhibited remarkable maximum sorption capacity qm (336.42 mg/g) computed through the best-fit Langmuir model (R2 ≈ 0.99) and rapid sorption equilibrium, teq (150 min). The isothermal sorption studies were conducted at different temperatures (298, 303, and 308 K) and thermodynamic parameters concluded that the process of U(VI) sorption using WO3/PASA3 is endothermic and feasible having ΔHo (8.19 kJ/mol), ΔGo (-20.75, -21.38, and - 21.86 kJ/mol) and proceeds with a minute increase in randomness ΔSo (0.09 kJ/mol.K). Tungsten oxide (WO3)-encapsulated phosphate-rich porous microspherical beads could be promising material for uranium removal.

Promoting the suitability of graphitic carbon nitride and metal oxide nanoparticles: A review of sulfonamides photocatalytic degradation

The widespread consumption of pharmaceutical drugs and their incomplete breakdown in organisms has led to their extensive presence in aquatic environments. The indiscriminate use of antibiotics, such as sulfonamides, has contributed to the development of drug-resistant bacteria and the persistent pollution of water bodies, posing a threat to human health and the safety of the environment. Thus, it is paramount to explore remediation technologies aimed at decomposing and complete elimination of the toxic contaminants from pharmaceutical wastewater. The review aims to explore the utilization of metal-oxide nanoparticles (MONPs) and graphitic carbon nitrides (g-C3N4) in photocatalytic degradation of sulfonamides from wastewater. Recent advances in oxidation techniques such as photocatalytic degradation are being exploited in the elimination of the sulfonamides from wastewater. MONP and g-C3N4 are commonly evolved nano substances with intrinsic properties. They possessed nano-scale structure, considerable porosity semi-conducting properties, responsible for decomposing wide range of water pollutants. They are widely applied for photocatalytic degradation of organic and inorganic substances which continue to evolve due to the low-cost, efficiency, less toxicity, and more environmentally friendliness of the materials. The review focuses on the current advances in the application of these materials, their efficiencies, degradation mechanisms, and recyclability in the context of sulfonamides photocatalytic degradation.

Bio-based matrix photocatalysts for photodegradation of antibiotics

Antibiotics development during the last century permitted unprecedent medical advances. However, it is undeniable that there has been an abuse and misuse of antimicrobials in medicine and cosmetics, food production and food processing, in the last decades. The pay toll for human development and consumism is the emergence of extended antimicrobial resistance and omnipresent contamination of the biosphere. The One Health concept recognizes the interconnection of human, environmental and animal health, being impossible alter one without affecting the others. In this context, antibiotic decontamination from water-sources is of upmost importance, with new and more efficient strategies needed. In this framework, light-driven antibiotic degradation has gained interest in the last few years, strongly relying in semiconductor photocatalysts. To improve the semiconductor properties (i.e., efficiency, recovery, bandgap width, dispersibility, wavelength excitation, etc.), bio-based supporting material as photocatalysts matrices have been thoroughly studied, exploring synergetic effects as operating parameters that could improve the photodegradation of antibiotics. The present work describes some of the most relevant advances of the last 5 years on photodegradation of antibiotics and other antimicrobial molecules. It presents the conjugation of semiconductor photocatalysts to different organic scaffolds (biochar and biopolymers), then to describe hybrid systems based on g-C3N4 and finally addressing the emerging use of organic photocatalysts. These systems were developed for the degradation of several antibiotics and antimicrobials, and tested under different conditions, which are analyzed and thoroughly discussed along the work.

Advancements in TiO2-based photocatalysis for environmental remediation: Strategies for enhancing visible-light-driven activity

Researchers have focused on efficient techniques for degrading hazardous organic pollutants due to their negative impacts on ecological systems, necessitating immediate remediation. Specifically, TiO2-based photocatalysts, a wide-bandgap semiconductor material, have been extensively studied for their application in environmental remediation. However, the extensive band gap energy and speedy reattachment of electron (e-) and hole (h+) pairs in bare TiO2 are considered major disadvantages for photocatalysis. This review extensively focuses on the combination of semiconducting photocatalysts for commercial outcomes to develop efficient heterojunctions with high photocatalytic activity by minimizing the e-/h+ recombination rate. The improved activity of these heterojunctions is due to their greater surface area, rich active sites, narrow band gap, and high light-harvesting tendency. In this context, strategies for increasing visible light activity, including doping with metals and non-metals, surface modifications, morphology control, composite formation, heterojunction formation, bandgap engineering, surface plasmon resonance, and optimizing reaction conditions are discussed. Furthermore, this review critically assesses the latest developments in TiO2 photocatalysts for the efficient decomposition of various organic contaminants from wastewater, such as pharmaceutical waste, dyes, pesticides, aromatic hydrocarbons, and halo compounds. This review implies that doping is an effective, economical, and simple process for TiO2 nanostructures and that a heterogeneous photocatalytic mechanism is an eco-friendly substitute for the removal of various pollutants. This review provides valuable insights for researchers involved in the development of efficient photocatalysts for environmental remediation.

Surface modification of chitin nanofibers with dopamine as efficient nanosorbents for enhanced removal of dye pollution and metal ions

The development of environmentally friendly and low-cost adsorbents with high adsorption capacity remains a challenge. Herein, chitin nanofiber-polydopamine composite materials (CNDA) have been obtained by surface modification of chitin nanofiber using dopamine. According to the results of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), and X-ray photoelectron spectrometer (XPS), polydopamine have been successfully coated on the surface of chitin nanofiber (ChNF). The ability to remove methylene blue (MB) has been analyzed via standard adsorption experiments, indicating that the maximum adsorption capacity (qmax) can reach 196.6 mg/g at MB initial concentration of 50 mg/L. Most importantly, the adsorption kinetics, isotherm, and thermodynamics were used to investigate the MB adsorption mechanism on composites. This indicated that the polydopamine on the surface of chitin nanofiber (ChNF) plays an important role in the MB dye adsorption. Moreover, the removal ability of CNDA to metal ions has also been investigated, indicating high capacities for Fe3+, Mn2+, Cu2+, and Ni2+. Based on their biodegradability and good adsorption capacity, the CNDA composite material can be considered a promising adsorbent for wastewater treatment.

Effect of biocomposite production factors on the development of an eco-friendly chitosan/alginate-based adsorbent with enhanced copper removal efficiency

Nowadays, wastewater treatment is a critical concern, particularly regarding the removal of heavy metals through adsorption methods. Extensive research has been conducted on obtaining high-yield and environmentally friendly adsorbents. Natural polymer adsorbents especially have shown promise in ion and organic molecule adsorption. To enhance the practical applicability of adsorbents, the combination of biopolymers to form biocomposites is a promising alternative. In this study, adsorbents based on a 1:1 wt./wt. of chitosan (CS) and alginate (SA) were prepared. The influence of the regeneration route and drying conditions on the copper adsorption capacity was investigated, along with reaction parameters such as contact time, adsorbent particle size, and pH. The highest adsorption capacity was observed in the composite material obtained through a one-pot regeneration process and freeze-dried. The CSAR3L sample exhibited a remarkable adsorption capacity of 288 mg Cu(II)/g after 360 min at 25 °C. The synergistic effect between the CS and SA precursors was confirmed by analyzing the individual precursors and their mechanical mixture. The initial adsorption rates at pH 6 followed the order: CSAR3-L > Bk-CSR3L > Bk-SAR3L + Bk-CSR3L > Bk-SAR3L. The physicochemical and morphological properties of the materials were studied by FTIR, XRD, DLS, XPS, optical microscopy, EDS-SEM, elemental chemical analysis, and TGA-DTG. The utilization of different drying methods resulted in the formation of calcium carbonate crystalline phases in the as-prepared materials, thus creating substantial adsorption active sites. After the adsorption process, hydroxylated copper sulfate phases and a significant decrease in calcium concentration were observed, indicating that an ion exchange adsorption mechanism occurred. The analysis of adsorption kinetics and the shape of the adsorption isotherms, in agreement with the characterization results, suggested the presence of multiple active sites and the formation of a chemisorption monolayer.

A comparison of endosulfan removal by photocatalysis process under UV-A and visible light irradiation: optimization, degradation byproducts and reuse

In this study, the removal efficiency of endosulfan as a persistent organic pollutant and formation of its metabolites were investigated using Ag/TiO2/Fe3O4 photocatalyst under visible and UV-A light. Light intensity, catalyst amount, initial endosulfan concentration, initial pH and time were determined as controllable factors for Taguchi experimental design. The highest removal efficiencies of endosulfan were achieved as 86.14% and 85.46% for visible and UV-A light sources, respectively. According to the greatest best criterion, the level at which the highest S/N ratio was obtained for each parameter was accepted as the optimum value. As a result of the validation experiments, 94.2% and 91.9% efficiency were obtained for visible and UV-A light, respectively. The metabolite formations of endosulfan (endosulfan sulfate, ether, and lactone) remained below 7% in all experiments on a concentration basis. In the reuse experiments of the magnetically recovered photocatalyst, high removal efficiency of around 80% was obtained after four cycles. The removal efficiencies were found to be 86.7% and 84.8%, for real samples taken from the drinking water treatment plant inlet and the spring water network injected with endosulfan under optimal photocatalysis experimental conditions, respectively. It has been shown that nitrate and sulfate anions, which are in significant concentrations in raw water samples, have very little effects on endosulfan removal. The overall results showed that the Ag/TiO2/Fe3O4 photocatalyst was produced successfully, the catalyst was highly effective in the mineralization of endosulfan in synthetic and real water samples under UV and visible light, and effective yields could be obtained even with reuse.

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-023-00864-z.

Two-Dimensional Cu-Porphyrin Metal-Organic Framework Nanosheet-Supported Flaky TiO2 as an Efficient Visible-Light-Driven Photocatalyst for Dye Degradation and Cr(VI) Reduction

A series of 2D M(Cu, Zn, Co, and Mn)-TCPP MOFs/TiO2 binary nanocomposites (TCPP = tetrakis(4-carboxyphenyl)porphyrin) were constructed by solvothermal in situ loading of flaky TiO2 on the surface of 2D metal-organic frameworks (MOFs). The influence of different coordination metals on the catalytic activity was studied, and it was found that the 2D Cu-TCPP MOFs/TiO2 nanocomposite exhibited the best photo-Fenton performance. The superior property can be attributed to the high absorption coefficient and ultrathin two-dimensional structure of the 2D Cu-TCPP MOFs nanosheets. Meanwhile, the 2D Cu-TCPP MOFs/TiO2 II heterostructure can effectively promote the separation and transfer of photoformed carriers. Moreover, under visible irradiation, the optimized 2D Cu-TCPP MOFs/TiO2 composite can convert 99.9% of Cr(VI) to Cr(III) within 60 min with methanol as the hole scavenger at pH 3.14. Also, the photocatalytic performance of 2D Cu-TCPP MOFs/TiO2 was maintained after five reaction cycles. Furthermore, the proposed visible-light-driven photocatalysis mechanism of the 2D Cu-MOFs/TiO2 composite was reasonably derived according to experimental results. This study demonstrates the potential of building efficient TiO2-based visible light photocatalysts with 2D metal-porphyrin MOFs.

ZnO nanostructured matrix as nexus catalysts for the removal of emerging pollutants

Water pollution stands as a pressing global environmental concern, elevating the significance of innovative, dependable, and sustainable solutions. This study represents an extensive review of the use of photocatalytic zinc oxide nanoparticles (ZnO NPs) for the removal of emerging pollutants from water and wastewater. The study examines ZnO NPs' different preparation methods, including physical, chemical, and green synthesis, and emphasizes on advantages, disadvantages, preparation factors, and investigation methods for the structural and morphological properties. ZnO NPs demonstrate remarkable properties as photocatalysts; however, their small dimensions pose an issue, leading to potential post-use environmental losses. A strategy to overcome this challenge is scaling up ZnO NP matrices for enhanced stability and efficiency. The paper introduces novel ZnO NP composites, by incorporating supports like carbon and clay that serve as photocatalysts in the removal of emerging pollutants from water and wastewater. In essence, this research underscores the urgency of finding innovative, efficient, and eco-friendly solutions for the removal of emerging pollutants from wastewater and highlights the high removal efficiencies obtained when using ZnO NPs obtained from green synthesis as a photocatalyst. Future research should be developed on the cost-benefit analysis regarding the preparation methods, treatment processes, and value-added product regeneration efficiency.

Graphene-based photocatalysts for degradation of organic pollution

Compared with the traditional wastewater treatment technology, semiconductor photocatalysis is a rapidly emerging environment-friendly and efficient Advanced Oxidation Process for degradation of refractory organic contaminants. Single-component semiconductor photocatalysts exhibit poor photocatalytic performance and cannot meet the requirements of wastewater treatment. The combination of semiconductor photocatalysts and Graphene can effectively improve the photocatalytic activity and stability of semiconductor photocatalysts. This review focuses on the synergistic effect of several types of semiconductors with Graphene for photocatalytic degradation of organic pollutants. After a brief introduction of the photodegradation mechanism of semiconductor materials and the basic description of Graphene, the synthesis, characterization and degradation performance of various Graphene-based semiconductor photocatalysts are emphatically introduced.

Phase stabilization and optical response in the ultraviolet range, due to terbium concentration in hafnium oxide nanoparticles

This work reports the influence of terbium trivalent ions on growing kinetics and the phase in hafnium oxide nanoparticles, as well as response to radiation in the range from 256 to 286. The nanoparticles were obtained by the hydrothermal route maintaining the temperature constant and varying the reaction time and the terbium concentration. The results show a gradual change in the phase with the concentration of terbium trivalent ions, going from the monoclinic phase, present at low concentrations, to the tetragonal phase, which appears from dopant concentrations greater than 5% at., increasing in amount with concentration of dopant. These phases appear as two perfectly defined morphologies. Furthermore, there is a significant change in radiative lifetimes when the tetragonal phase appears.

Probing size-dependent defects in zinc oxide using synchrotron techniques: impact on photocatalytic efficiency

In the present study, synchrotron-based X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray excited optical luminescence (XEOL) have been used to investigate the induced defect states in metal oxide nanomaterials. Specifically, two synthesis approaches have been followed to develop unique nano-sized peanut-shaped (N-ZnO) nanostructures and micron-sized hexagonal rods (M-ZnO). XANES analysis at the Zn K-edge revealed the presence of defect states with a divalent oxidation state of zinc (Zn2+) in a tetrahedral structure. Furthermore, XAS measurements performed at the Zn L3,2-edge and O K-edge confirm higher oxygen-related defects in M-ZnO, while N-ZnO appeared to have a higher concentration of surface defects due to size confinement. Moreover, the in-line XEOL and time dependent-XEOL measurements exposed the radiative excitonic recombination phenomena occurring in the band-tailing region as a function of absorption length, X-ray energy excitation, and time. Based on the chronology developed in the defect state improvement, a possible energy band diagram is proposed to accurately locate the defect states in the two systems. Furthermore, the increased absorption intensity at the Zn L3,2-edge and the O K-edge under the UV lamp suggests delayed recombination of electrons and holes, highlighting their potential use as photo catalysts. The photocatalytic activity degrading the rhodamine B dye established M-ZnO as a superior catalyst with a rapid degradation rate and significant mineralization. Overall, this work provides valuable insights into ZnO defect states and provides a foundation for efficient advanced materials for environmental or other optoelectronic applications.