Enhanced photocatalytic degradation of RhB dye from aqueous solution by biogenic catalyst Ag@ZnO

Emerging bismuth stannate semiconductor and its photocatalytic applications in pollutant degradation via Z/S-scheme heterostructures

Bismuth stannate (Bi2Sn2O7) has emerged as a promising compound for heterostructure applications due to its outstanding photocatalytic, structural, and optical properties. As a pyrochlore-type semiconducting material, Bi2Sn2O7 demonstrates a suitable bandgap, strong visible-light absorption, and high chemical stability, making it attractive for environmental remediation. Heterostructures based on Bi2Sn2O7 have gained significant attention because of their enhanced charge carrier separation efficiency, improved charged carrier mobility, and synergistic effects that boost photocatalytic performance. Different strategies have been utilized to construct Bi2Sn2O7-based heterostructures, including doping, vacancies generation, coupling with other semiconductors to form Z-scheme and S-scheme heterojunctions. These engineered interfaces effectively reduce charge recombination, thereby enhancing photocatalytic efficiency for pollutant degradation. Furthermore, various synthesis techniques have been reviewed viz. hydrothermal, solvothermal solid-state reaction method, in-situ, and co-precipitation, etc for Bi2Sn2O7 photocatalyst in which the hydrothermal method was most preferable due to yield efficiency, crystallinity, morphology, cost-effectiveness, eco-friendly, and energy conserving. This review highlights the structural, and optical properties, synthesis, modification strategies, and application of Bi2Sn2O7-based heterostructures in environmental technologies. The challenges as well as future prospects of these materials are also analyzed, emphasizing their potential for next-generation photocatalysts. Further research is required to optimize material stability, enhance charge transport, and develop scalable synthesis methods for commercial applications.

Simultaneous H2 production and water purification with surface-modified nanostructured TiO2 photoelectrodes

The removal of emerging contaminants from water and production of green energy are some of the pressing needs of today's world. The use of water pollutants for the production of H2 can be a powerful strategy for solving both these problems. Several approaches have been proposed for this purpose, such as photocatalysis, electrocatalysis and photoelectrocatalysis. In this context, TiO2 is the most commonly used material, but it has several performance limitations. However, they can be improved with appropriate surface modifications. In this work, the inner surfaces of nanostructured TiO2-based films were modified to improve their photoelectrocatalytic and photocatalytic performances, with an aim to simultaneously remove a water pollutant (rhodamine B dye) and generate H2 in a custom-designed dual-chamber reactor. For this purpose, the TiO2 nanostructure, which can be used as a photoanode in photocatalytic and photoelectrocatalytic experiments, was functionalized by introducing a zirconium phosphate monolayer (ZP modification). The excellent performances of the ZP-modified photoanodes in simultaneously achieving photoelectrocatalytic dye removal and H2 evolution indicate that they are interesting candidates for attaining sustainable and circular solutions for environmental protection.

Triple-Phase Interfacial Freestanding Fluffy Pine Needle Structures for Efficient Self-Powered Photoelectrocatalysis

Approximately 2 billion people still lack access to clean drinking water. Extensive efforts are underway to develop semiconductor photocatalysts for water disinfection and environmental remediation, but conventional liquid-solid diphase interfacial photocatalysts face challenges like low diffusion coefficients and limited solubility of dissolved oxygen. This study introduces freestanding copper oxide fluffy pine needle structures (CO-FPNs) with tunable water pollutants-gas-solid (WGS) triple-phase interfaces that enhance oxygen enrichment and reactive oxygen species (ROS) production. Three differently structured CO-FPNs-microdendrites, hierarchical dendrites, and nanowires-are designed. The hierarchical CO-FPN/WGS, predominantly in the Cassie-Wenzel coexistence state, showed a 1.81- to 1.91-fold higher reaction rate than the micro- and nanostructured CO-FPNs due to increased interfacial O2 levels and high adsorption capability. Under illumination, the hierarchical CO-FPN/WGS achieved 99.999% sterilization by preventing pathogen adhesion and enhancing ROS generation. Additionally, a self-powered photoelectrocatalytic system is constructed using nickel-iron oxide-deposited bismuth vanadate (NiFeO/BiVO4) with hierarchical CO-FPN/WGS, achieving 1.45 times higher than the hierarchical CO-FPN/WGS alone, due to superior oxidation kinetics of NiFeO/BiVO4 and improved oxygen reduction via atmospheric oxygen from the hierarchical CO-FPN/WGS. This study demonstrates the first example of a triple-phase interfacial self-powered platform for efficient photoelectrocatalysis.

Recent advances and challenges of the green ZnO-based composites biosynthesized using plant extracts for water treatment

Recently, there has been a notable rise in the prevalence of persistent pollutants in the environment, posing a significant hazard due to their toxicity and enduring nature. Conventional wastewater treatment methods employed in treatment plants rarely address these persistent pollutants adequately. Meanwhile, the concept of green synthesis has garnered considerable attention, owing to its environmentally friendly approach that utilizes fewer toxic chemicals and solvents. The utilization of materials derived from sustainable sources presents a promising avenue for solving pressing environmental concerns. Among the various sources of biological agents, plants stand out for their accessibility, eco-friendliness, and rich reserves of phytochemicals suitable for material synthesis. The plant extract-mediated synthesis of zinc oxide nanoparticles (ZnONPs) has emerged as a promising solution for applications in wastewater treatment. Thorough investigations into the factors influencing the properties of these green ZnONPs are essential to establish a detailed and reliable synthesis process. Major weaknesses inherent in ZnONPs can be addressed by changing the optical, magnetic, and interface properties through doping with various semiconductor materials. Consequently, research efforts to mitigate water pollution are being driven by both the future prospects and limitations of ZnO-based composites. This review underscores the recent advancements of plant extract-mediated ZnONP composites for water treatment.

A novel approach for immobilizing Ag/ZnO nanorods on a glass substrate: Application in solar light-driven degradation of micropollutants in water

One of the main challenges in applying photocatalysts for water treatment is the complex separation and recycling process. In this study, we developed highly stable, porous zinc oxide nanorods (ZnO NRs) immobilized on glass vials using a solvent exchange process (SEP) and hydrothermal calcination. Key parameters, including oleic acid concentration and hydrothermal growth time, were optimized to maximize the active surface area, significantly enhancing photodegradation performance. Under the best conditions, ZnO NRs-coated vials achieved nearly 100% degradation of sulfamethoxazole (SMX) in 10 h of simulated solar irradiation. Depositing silver nanoparticles on the surface of ZnO NRs (Ag/ZnO NRs) further improved performance, reducing degradation time to 4 h and increasing photocatalyst stability. The Ag/ZnO NRs-coated vials, optimized with an Ag precursor concentration of 0.05 M, also demonstrated high degradation rates (>99%) for eight organic micropollutants at environmentally relevant concentrations over multiple reuse cycles and with minimal metal leaching. This study presents an innovative, tunable method for immobilizing photocatalysts on glass substrates, offering high surface area, excellent photocatalytic activity, and mechanical properties, making it highly suitable for water treatment applications.

Biogenic fabrication of NiO-ZnO-CaO ternary nanocomposite using Azadirachta Indica (Neem) leaves extract with proficient photocatalytic degradation of rhodamine B dye

In the current study, a ternary nanocomposite (NiO–ZnO–CaO) was successfully synthesized through the co-precipitation method using Azadirachta Indica (neem) leaves extract as green approach. The characterization of prepared nanocomposite was conducted using FT-IR, XRD, SEM and EDS to determine the metal oxides absorption bands, structural properties, elemental composition, and surface morphology of the nanocomposite. FT-IR analysis revealed characteristic vibrational peaks at 621, 684, and 721 cm−1, corresponding to Ni-O, Zn-O, and Ca-O bond vibrations, respectively. XRD patterns showed distinct diffraction peaks, indicative of the hexagonal structure of ZnO and the cubic structures of NiO and CaO. EDS analysis confirmed the presence of calcium, nickel, zinc, and oxygen with weight percentages of 9.2%, 14.4%, 15.1%, and 20.9%, respectively. SEM images displayed an irregular cube like morphology with noticeable clustering within the nanocomposite. The ternary nanocomposite was employed as photocatalyst and exhibited degradation efficiency (97%) against rhodamine B dye under 180 min of irradiation time. The kinetic studies of dye on the photocatalyst surface were accurately explained by a first-order kinetics model, with all R2 > 95, signifying a strong correlation between time and dye concentration. The potocatalytic degradation mechanism of ternary nanocomposite was proposed based on band positions of of NiO, ZnO and CaO forming double type II heterojunction. Furthermore, species trapping experiments employing different scavengers were carried out, revealing the active participation of OH● and O2●─ radicals in the degradation mechanism.

Decolorization of RhB on three-dimensional porous CeO2/LaFeO3/SrTiO3 catalyst via photo-fenton-like catalysis

The catalysts with three-dimensional porous (3DP) CeO2, LaFeO3 and SrTiO3 are synthesized by sol-gel method and chemical precipitation method. The resulting multi-component 3DP CeO2/LaFeO3/SrTiO3 composite material featured a high specific surface area (26.08 m2/g), which can provide more surface active sites to improve adsorption capacity and catalytic performance. The photocatalytic, Fenton-like, photo-Fenton-like performance of the catalyst are studied on decolorization of RhB under UV irradiation, respectively. 3DP CeO2/LaFeO3/SrTiO3 exhibits high catalytic performance. Compared with photocatalytic or Fenton-like performance, 3DP CeO2/LaFeO3/SrTiO3 catalyst exhibits higher photo-Fenton-like performance, facilitating efficient decolorization of the rhodamine B. Moreover, the initial reaction rate on decolorization of RhB with 3DP CeO2/LaFeO3/SrTiO3 is 10.55, 5.52, 3.67 and 1.51 times higher than that with SrTiO3, LaFeO3, 3DP CeO2 and 3DP CeO2/LaFeO3, respectively. Meanwhile, 3DP LaFeO3/CeO2/SrTiO3 has a wider pH usage range in the synergistic reaction. Finally, a catalytic mechanism for the decolorization of rhodamine B is proposed. The continuous cycling of Fe3+/Fe2+ and Ce4+/Ce3+ and the production of active substances are achieved under the photo-Fenton-like effect of the catalyst.

On the diverse utility of Cu doped ZnS/Fe3O4 nanocomposites

The global water crisis is a growing concern, with water pollution from organic dyes being a significant issue. Photocatalysis has emerged as a sustainable and renewable method for removing organic pollutants from wastewater. The study synthesized innovative (2.5, 5 and 10 wt%) Cu doped zinc sulfide/iron oxide nanocomposites using a sonochemical method, which have versatile applications in adsorption and photocatalytic degradation of organic pollutants in wastewater. The nanocomposites underwent comprehensive characterization using powder X-ray diffraction, fourier-transform infrared spectroscopy, photoluminescence spectroscopy, Ultraviolet-Visible spectrophotometer, field emission scanning electron microscopy combined with energy dispersive X-ray spectroscopy and Mott-Schottky analysis. The synthesized samples demonstrate strong adsorption ability to remove RhB and MB dyes. Afterward, we evaluated their capability to degrade Rhodamine B (RhB) dye under UV light exposure. The greatest photocatalytic efficiency was noticed when employing a UV-C lamp in combination with the 10 wt% Cu doped ZnS/Fe3O4 nanocomposite as photocatalyst (98.8% degradation after 60 min irradiation). The Langmuir-Hinshelwood model can be used to describe the pseudo first order kinetics of RhB dye photodegradation. The calculated ban gap values are 4.77, 4.67, and 4.55 eV, for (2.5, 5 and 10 wt%) Cu doped ZnS/Fe3O4, respectively. Furthermore, 10 wt% Cu doped ZnS/Fe3O4 showed good recyclability, with a degradation rate of 89% even after five cycles. Consequently, prepared samples have outstanding photocatalytic activity and can be used as useful adsorbents in water purification.

WO3-x nanorods/rGO/AgBiS2 Z-scheme heterojunction with comprehensive spectrum response and enhanced Fenton and photocatalytic activities

Tetracycline (TC) antibiotics and dyes are the prevalent water contaminants, and their removal from the water through photocatalysis is a plausible approach. However, most semiconductors in their pristine form need to be improved to be exploited in photocatalysis owing to poor photoresponse, intense carrier recombination, and inertness without irradiation. Herein, we demonstrate the modification of defective WO3-x by rGO and AgBiS2 in the form of WO3-x/rGO/AgBiS2 (R2). It exploits the superior conductivity and synergism of rGO to inhibit carrier recombination; thereby, Z-scheme heterojunction with AgBiS2 provides high redox potential. Defects in WO3-x enable electron (e-) storage in R2, which decomposes H2O2 to generate ROS without irradiation. Owing to these essences and broad-spectrum response, it removed 93.72, 82.77, and 84.82% of TC during photo-Fenton (PFR), night-Fenton (NFR), and photocatalytic (PCR) reactions, respectively. Its removal rates reached 94.74, 81.54, and 87.50% against rhodamine B (RhB) during PFR, NFR, and PCR, respectively. It is superior to memory catalysis (MC) and conventional Fenton reactions (CFR) because it can perform without and with irradiation across a broader pH range. So, this work is conducive to designing WO3-x-based catalysts to combat environmental and energy crises.

Enhanced photocatalytic efficiency of porous ZnO coral-like nanoplates for organic dye degradation

ZnO nanomaterials have been extensively used as photocatalysts for the removal of pollutants in aqueous environments. This study explores the enhanced photocatalytic performance of porous ZnO coral-like nanoplates synthesized via a one-pot wet-chemical method and subsequent annealing treatment. Characterization through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, photoluminescence (PL) spectroscopy, and Brunauer-Emmett-Teller (BET) measurements confirmed the nanoplates' porous structure, single-crystal structure, 100 nm thickness, and 80 nm pore size. These unique structural characteristics of the ZnO coral-like nanoplates enabled effective photodegradation of the organic dye rhodamine B (RhB) under visible light irradiation. Under simulated sunlight, the ZnO photocatalyst exhibited exceptional performance, achieving a 97.3% removal rate of RhB after 210 minutes of irradiation. The prepared ZnO photocatalyst also showed remarkable photostability and regeneration capability for RhB photodegradation with a decreased efficiency of less than 15% after eight testing cycles. The potential mechanism of the ZnO photocatalyst toward RhB degradation was also studied and is discussed in detail.

Photocatalytic decomposition of metronidazole by zinc hexaferrite coated with bismuth oxyiodide magnetic nanocomposite: Advanced modelling and optimization with artificial neural network

The objective of the present study was to employ a green synthesis method to produce a sustainable ZnFe12O19/BiOI nanocomposite and evaluate its efficacy in the photocatalytic degradation of metronidazole (MNZ) from aqueous media. An artificial neural network (ANN) model was developed to predict the performance of the photocatalytic degradation process using experimental data. More importantly, sensitivity analysis was conducted to explore the relationship between MNZ degradation and various experimental parameters. The elimination of MNZ was assessed under different operational parameters, including pH, contaminant concentration, nanocomposite dosage, and retention time. The outcomes exhibited high a desirability performance of the ANN model with a coefficient correlation (R2) of 0.99. Under optimized circumstances, the MNZ elimination efficiency, as well as the reduction in chemical oxygen demand (COD) and total organic carbon (TOC), reached 92.71%, 70.23%, and 55.08%, respectively. The catalyst showed the ability to be regenerated 8 times with only a slight decrease in its photocatalytic activity. Furthermore, the experimental data obtained demonstrated a good agreement with the predictions of the ANN model. As a result, this study fabricated the ZnFe12O19/BiOI nanocomposite, which gave potential implication value in the effective decontamination of pharmaceutical compounds.

Investigation of the Photocatalytic Performance, Mechanism, and Degradation Pathways of Rhodamine B with Bi2O3 Microrods under Visible-Light Irradiation

In the present work, the photodegradation of Rhodamine B with different pH values by using Bi2O3 microrods under visible-light irradiation was studied in terms of the dye degradation efficiency, active species, degradation mechanism, and degradation pathway. X-ray diffractometry, polarized optical microscopy, scanning electron microscopy, fluorescence spectrophotometry, diffuse reflectance spectra, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, UV-visible spectrophotometry, total organic carbon, and liquid chromatography-mass spectroscopy analysis techniques were used to analyze the crystal structure, morphology, surface structures, band gap values, catalytic performance, and mechanistic pathway. The photoluminescence spectra and diffuse reflectance spectrum (the band gap values of the Bi2O3 microrods are 2.79 eV) reveals that the absorption spectrum extended to the visible region, which resulted in a high separation and low recombination rate of electron-hole pairs. The photodegradation results of Bi2O3 clearly indicated that Rhodamine B dye had removal efficiencies of about 97.2%, 90.6%, and 50.2% within 120 min at the pH values of 3.0, 5.0, and 7.0, respectively. In addition, the mineralization of RhB was evaluated by measuring the effect of Bi2O3 on chemical oxygen demand and total organic carbon at the pH value of 3.0. At the same time, quenching experiments were carried out to understand the core reaction species involved in the photodegradation of Rhodamine B solution at different pH values. The results of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffractometer analysis of pre- and post-Bi2O3 degradation showed that BiOCl was formed on the surface of Bi2O3, and a BiOCl/Bi2O3 heterojunction was formed after acid photocatalytic degradation. Furthermore, the catalytic degradation of active substances and the possible mechanism of the photocatalytic degradation of Rhodamine B over Bi2O3 at different pH values were analyzed based on the results of X-ray diffractometry, radical capture, Fourier-transform infrared spectroscopy, total organic carbon analysis, and X-ray photoelectron spectroscopy. The degradation intermediates of Rhodamine B with the Bi2O3 photocatalyst in visible light were also identified with the assistance of liquid chromatography-mass spectroscopy.

Robust Biobased Membrane: Self-Entangled Cellulose Nanofibrils-ZnO-Ag Composite with High Photocatalytic Performance for Efficient Dye-Contaminated Water Treatment

This study presents a simple and effective method for fabricating a porous photocatalyst composite membrane with excellent wet strength, utilizing cellulose nanofibril (CNF) and zinc oxide-silver (ZnO-Ag) nanorod (NRs) for treating dye-contaminated water. The self-standing CNF membrane with a high wet strength was prepared by NaOH treatment. Besides wet strength, NaOH treatment also controlled the pore characteristics of the CNF membrane, which could tightly attach NRs in them. The photocatalyst composite was prepared by simply drop-drying ZnO-Ag NRs onto the CNF membrane, ensuring attachment within the pores. The photocatalytic activity of the composite was evaluated for the degradation of the methylene blue dye under visible light. Despite the straightforward drop-drying method used to cast the ZnO-Ag NRs onto the CNF membrane, the NRs were not washed out when in contact with water, resulting in a composite that exhibited both high photocatalytic activity and high wet strength. This exceptional performance can be attributed to the tight attachment of the photocatalytic ZnO-Ag NRs to the porous structure of the CNF. Furthermore, the composite demonstrated satisfactory reusability, as no significant deterioration in the photocatalytic performance was observed even after being reused for three cycles. Given its simple preparation method, impressive photocatalytic performance, and durability, we expect that our composite will hold significant value for practical applications in wastewater treatment.

Aminated graphene quantum dots/CdS nanobelts for enhanced photocatalytic degradation of RhB dye under visible light

CdS nanoparticles have wide applications as photocatalysts for degradation of organic pollutants, but due to their limited turnover number and off-pathway charge recombination processes, their degradation efficiency is low. Herein, aminated graphene quantum dots/CdS (GQDs/CdS) nanobelts were successfully fabricated by solvothermal and hydrothermal processes. The prepared GQDs/CdS were characterized by physical methods to investigate their structure, morphology, optical properties, specific surface area, element composition, and chemical state. GQDs/CdS materials promoted efficient charge separation, and showed high efficiency in the photocatalytic degradation of the organic dye Rhodamine B (RhB) under visible light. The degradation efficiency of RhB samples over 0.05 g of catalysts reached 97.40% after 150 min, a much higher efficiency in comparison to pure CdS. Electron paramagnetic resonance (EPR) spectroscopy provided direct evidence for ˙OH and ˙O2- as the reactive oxidative species using DMPO as a spin trap. Consistent with the experimental results, a possible mechanism of RhB photocatalytic degradation by GQDs/CdS under visible light was proposed. This work may provide environmentally friendly photocatalysts for degrading organic dyes and purifying water.

Recent progress on plant extract-mediated biosynthesis of ZnO-based nanocatalysts for environmental remediation: Challenges and future outlooks

The plant extract mediated green synthesis of nanomaterials has attracts enormous interest due to its cost-effectiveness, greener, and environmentally friendly. It is also considered as an alternative and facile method in which the phytochemicals can be used as a natural capping and reducing agents and helped to produce nanomaterials with high surface area, different sizes, and shapes. One of the materials fabricated using green methods is zinc oxide (ZnO) semiconductor due to its enormous applications in different field areas. In this review, an overview of recent progress on green synthesized ZnO-based catalysts and various modification methods for the purpose of enhancing the catalytic activity of ZnO and the corresponding structural-activity and interactions towards the removal of pollutants are highlighted. Particularly, the plant extract mediated ZnO-based photocatalysts application for the removal of pollutants via photocatalytic degradation, reduction reaction, and adsorption mechanism are demonstrated. Besides, the opportunities, challenges, and future outlooks of ZnO-based materials for environmental remediation with green and sustainable methods are also included. We believe that this review is a timely and comprehensive review on the recent progress related to plant extract mediated ZnO-based nanocatalysts synthesis and applications for environmental remediation.

Highly Efficient Solar Light Driven g-C3N4@Cs0.33WO3 Heterojunction for the Photodegradation of Colorless Antibiotics

This study facilitates the synthesis of a graphitic carbon nitride/cesium tungsten oxide (g-C₃N₄@Cs_0.33WO₃) heterojunction using a solvothermal method. The photocatalytic activities of the prepared samples were examined for the photodegradation of colorless antibiotics, namely tetracycline, enrofloxacin, and ciprofloxacin, as well as cationic and anionic dyes, such as methyl orange, rhodamine B, neutral red, and methylene blue, under full-spectrum solar light. We have purposely selected different kinds of wastewater pollutants of colorless antibiotics and cationic and anionic organic dyes to investigate the potential application of this heterojunction toward different groups of water pollutants. The results revealed that the g-C₃N₄@Cs_0.33WO₃ heterojunction showed an outstanding photocatalytic activity toward all the pollutants with concentrations of 20 ppm each at pH 3 by photocatalytically removing 97% of tetracycline within 3 h, 98% of enrofloxacin within 2 h, 97% of ciprofloxacin within 2.25 h, 98% of methylene blue in 1 h, 99% of rhodamine B within 2 h, 99% of neutral red in 1.25 h, and 95% of methyl orange in 2 h. These findings indicate that the developed photocatalyst possesses excellent photocatalytic properties toward seven different water pollutants that make it a universal photocatalyst. The developed g-C₃N₄@Cs_0.33WO₃ oxide heterojunction also presented a photocatalytic performance better than those of reported solar light active photocatalysts for photodegradation of rhodamine B and tetracycline. The efficient photocatalytic performance of the heterojunction can be ascribed to its extended light-absorbing ability, effective charge separation and fast charge transfer properties, and a high surface area. Moreover, an active species detection experiment also confirmed that superoxide radicals, hydroxyl radicals, and holes played significant roles in the photocatalysis of the organic dyes and tetracycline.