Elimination of rhodamine B from textile wastewater using nanoparticle photocatalysts: A review for sustainable approaches

Rhodamine B, an organic environmental pollutant induces reproductive toxicity in parental and teratogenicity in F1 generation in vivo

This study investigated the reproductive toxicity of rhodamine B in zebrafish and its transgenerational effects on the F1 generation. In silico toxicity predictions revealed high toxicity of rhodamine B, mainly targeting pathways associated with the reproductive and endocrine systems. In vivo experiments on zebrafish demonstrated that rhodamine B exposure at a concentration of 1.5 mg/L led to significant impairments in fecundity parameters, particularly affecting females. Histopathological analysis revealed distinct changes in reproductive organs, further confirming the reproductive toxicity of rhodamine B, with females being more susceptible than males. Gene expression studies indicated significant suppression of genes crucial for ovulation in rhodamine B-treated female fish, highlighting hormonal imbalance as a potential mechanism of reproductive toxicity. Furthermore, bioaccumulation studies showed the presence of rhodamine B in both adult fish gonads and F1 generation samples, suggesting transgenerational transfer of the dye. Embryotoxicity studies on F1 generation larvae demonstrated reduced survival rates, lower hatching rates, and increased malformations in groups exposed to rhodamine B. Moreover, rhodamine B induced oxidative stress in F1 generation larvae, as evidenced by elevated levels of reactive oxygen species and altered antioxidant enzyme activity. Neurotoxicity assessments revealed reduced acetylcholinesterase activity, indicating potential neurological impairments in F1 generation larvae. Additionally, locomotory defects and skeletal abnormalities were observed in F1 generation larvae exposed to rhodamine B. This study provides comprehensive evidence of the reproductive toxicity of rhodamine B in adult zebrafish and its transgenerational effects on the F1 generation.

Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

Enhanced dye sequestration with natural polysaccharides-based hydrogels: A review

Due to the expansion of industrial activities, the concentration of dyes in water has been increasing. The dire need to remove these pollutants from water has been heavily discussed. This study focuses on the reproducible and sustainable solution for wastewater treatment and dye annihilation challenges. Adsorption has been rated the most practical way of the several decolorization procedures due to its minimal initial investment, convenient utility, and high-performance caliber. Hydrogels, which are three-dimensional polymer networks, are notable because of their potential to regenerate, biodegrade, absorb bulky amounts of water, respond to stimuli, and have unique morphologies. Natural polysaccharide hydrogels are chosen over synthetic ones because they are robust, bioresorbable, non-toxic, and cheaply accessible. This study has covered six biopolymers, including chitosan, cellulose, pectin, sodium alginate, guar gum, and starch, consisting of their chemical architecture, origins, characteristics, and uses. The next part describes these polysaccharide-based hydrogels, including their manufacturing techniques, chemical alterations, and adsorption effectiveness. It is deeply evaluated how size and shape affect the adsorption rate, which has not been addressed in any prior research. To assist the readers in identifying areas for further research in this subject, limitations of these hydrogels and future views are provided in the conclusion.

Effective activation of peroxymonosulfate by CoCr-LDH for removing organic contaminants in water: from lab-scale to practical applications

In this study, CoCr layered double hydroxide material (CoCr-LDH) was prepared and used as an effective catalyst for peroxymonosulfate (PMS) activation to degrade organics in water. The prepared CoCr-LDH material had a crystalline structure and relatively porous structure, as determined by various surface analyses. In Rhodamine B (RhB) removal, the most outstanding PMS activation ability belongs to the material with a Co:Cr molar ratio of 2:1. The removal of RhB follows pseudo-first-order kinetics (R2 > 0.99) with an activation energy of 38.23 kJ/mol and efficiency of 98% after 7 min of treatment, and the total organic carbon of the solution reduced 47.2% after 10 min. The activation and oxidation mechanisms were proposed and the RhB degradation pathways were suggested with the key contribution of O2•- and 1O2. Notably, CoCr-LDH can activate PMS over a wide pH range of 4 - 9, and apply to a wide range of organic pollutants and aqueous environments. The material has high stability and good recovery, which can be reused for 5 cycles with a stable efficiency of above 88%, suggesting a high potential for practical recalcitrant water treatment via PMS activation by heterogeneous catalysts.

Ni, Co-Embedded MOF-Derived N-Doped Bimetallic Porous Carbon for Adsorption-Photocatalytic Degradation of Organic Dyes and Antibiotics

An efficient protocol for photocatalytic degradation of organic dyes and antibiotics has been successfully established via MOF-derived (MOF = metal-organic framework) Ni, Co-embedded N-doped bimetallic porous carbon nanocomposites (NiCo/NC). Such a NiCo/NC nanocomposite features well-distributed structures, suitable specific surface areas, and more active sites determined by various characterization analyses. The catalyst exhibits higher photocatalytic performance and stability toward the liquid-phase degradation of methylene blue (MB) under visible light irradiation for 60 min, after the adsorption-desorption equilibrium and the thorough degradation into H2O and CO2. Radical quenching experiments further confirmed the dominant effect of electron holes h+ and superoxide radical anions ·O2- for the MB photodegradation process. NiCo/NC was also appropriate for the degradation of Rhodamine B, methyl orange, tetracycline hydrochloride, and norfloxacin. Moreover, NiCo/NC is robust, and its photocatalytic activity is basically maintained after 8 cycles. This work is expected to provide additional information for the design of MOF-derived carbon material with more excellent properties and lay the foundation for further industrial applications.

Plasmonic photocatalytic nanocomposite of in-situ synthesized MnO2 nanoparticles on cellulosic fabric with structural color

The textile industry produces 20 % of the industrial water pollution containing toxic substances mostly dyes. Reducing material consumption and developing more efficient and scalable textile waste-water treatment methods such as photocatalytic degradation is essential. In this work, manganese dioxide nanoparticles (MnO2 NPs) were synthesized on the cotton fabric via a facile in-situ process. The preparation process was optimized for the highest photocatalytic activity under sunlight and color change originating from the plasmonic structural color of the nanoparticles. This promotes the photocatalytic activity by delocalization of the hot electrons while demonstrating the best washing and light fastness by using the least chemicals, and energy in a short time. In this way, the fabric was colored without any dye and possessed robust photocatalytic activity. Further, no dye-containing waste-water is made, and also accomplished to degrade dyes in a few hours under sunlight which is substantial for sustainable development. The treated fabrics indicated favorable mechanical properties, enhanced thermal stability, and perfect biocompatibility.

Synthesis and efficiency comparison of reed straw-based biochar as a mesoporous adsorbent for ionic dyes removal

The reed straw is assessed as a potential source of widely available renewable biomass for biochar production and compared with two other waste-based biomasses, namely fruit stones blend, and brewery spent grains. The biochars were activated via steam and CO2. While steam activation yielded 12 % carbon from reed biomass, CO2 activation resulted in biomass degradation. The characterization of reed biochar showed a mesoporous structure and a high surface area of 514 m2/g. The adsorption tests displayed a decent adsorption capacity of biochar, with values of 92.6 mg/g for methylene violet dye and 35.7 mg/g for acid green dye. Only 1 g/L dosage of reed biochar was able to remove 99 % of the 50 mg/L methylene violet solution in 15 min and 60 % of the 50 mg/L acid green solution in 10 min. The obtained results demonstrate reed biomass as a suitable source for biochar production as well as reed-based biochar as a promising dye adsorbent.

Phospholipid-derived Au and Au-Cu suspensions as efficient peroxide and borohydride activators for organic molecules degradation: Performance and sustainable catalytic mechanism

In the contemporary context, executing light-oxidant- and reductant-driven reactions in solution-phase processes remains challenging mainly due to the lack of general tools for understanding the reactive potential of nano-functional catalysts. In this study, dual-active nanometals (Au and Cu doped with Au) capped within soy lecithin (SL), were developed and characterized, combining flexibility with the catalytic advantages and stability of liquid-phase catalysts. The as-synthesized SL-Au (LG) and SL-Au-Cu (LGC) catalysts were efficiently degraded rhodamine B (RB, 100%) in the presence of H2O2 under light irradiation (350 W lamp) at wide pH range (3-7) within 4.5 h and p-nitrophenol (p-NP, >90% degradation at pH 7) in the presence of NaBH4 under normal stirring with slower kinetics (∼72 h). RB degradation followed a pseudo-second-order kinetic model with a higher r2, and p-NP degradation followed first-order kinetics. The active sites embedded within the structural order of SL arrangement displayed elevated catalytic activity, which was further enhanced by the movement of intermediate/excited states and charged elements within the metal suspended in the phospholipid (LG and LGC). The self-regulating tunability of the physicochemical characteristics of these catalysts provides a convenient and generalizable platform for the transformation of modern dual-active (redox) catalysts into dynamic homogeneous equivalents.

Polyol synthesis of one-dimensional Ag nanowires for the photocatalytic degradation of textile dye and effective removal of microbes

Due to the excess release of hazardous pollutants to the environment, the quest for the synthesis of effective nanomaterials for wastewater treatment is never-ending. Present study reports the polyol synthesis of Ag NWs of ~ 85 nm diameter and average length of 4.08 µm using PVP and ethylene glycol. The experimental data on the methylene blue dye degradation substantiated the photocatalytic efficiency of Ag NWs (88% degradation in 120 min). Furthermore, the Ag NWs exhibited microbial load reducing property in air conditioner condensate water (ACW) within a time period of 60 min. Also, the anti-bacterial effect of Ag NWs was estimated using two human pathogenic bacterial strains, namely Staphylococcus aureus and Bacillus cereus. The antibacterial potential of Ag NWs against Staphylococcus aureus and Bacillus cereus was revealed significant with an inhibition zone size of 14 ± 0.1 mm and 9 ± 0.1 mm, respectively. Hence, the present work validates the potential efficiency of Ag NWs in the degradation of textile dyes and reduction of microbial population.

Graphitic carbon nitride-adorned PDMS self-cleaning floating photocatalyst for simultaneous removal of Rhodamine B, Crystal Violet and Malachite Green from a ternary dye mixture

Graphitic carbon nitride-adorned polydimethylsiloxane (PDMS) floating catalyst was prepared by a simple procedure. The prepared catalyst was utilized for the simultaneous mitigation of recalcitrant organic pollutants such as Rhodamine B, Crystal Violet and Malachite Green from their ternary mixture for the first time. Derivative spectroscopic method was used to calculate the degradation efficiencies of individual dyes in the mixture. The prepared catalyst showed a consistent degradation performance up to 4 cycles inducing a degradation of 94.02%, 92.1% and 97.13% of Rhodamine B, Crystal Violet and Malachite Green, respectively, in a dye(s) solution with a catalytic loading of 0.5 g L-1. A kinetic analysis of the dye(s) degradation under visible light was carried out during the course of this work up to 120 min. A detailed characterization of the surface of this novel catalyst was carried out in this study by SEM, EDX, XRD, DRS, DTG, FTIR, Raman spectroscopy and UV-Vis spectroscopy and provided the experimental proof for the catalyst presenting high hydrophobicity, self-cleaning ability, good recyclability and high chemical stability.

Ba2-xHoxSr2-yNiyFe12O22 and its composite with MXene: synthesis, characterization and enhanced visible light mediated photocatalytic activity for colored dye and pesticide

The rapid recombination of charges of photogenerated electrons and holes severely limits single semiconductor photocatalytic applications. In this study, a simple and facile sol-gel approach was used to synthesize Ba2-xHoxSr2-yNiyFe12O22 (x = 0, 0.1 and y = 0, 0.5). The composite of holmium-nickel doped barium-strontium ferrite with MXene (Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene) was synthesized by ultrasonication method. These synthesized samples were subsequently used to photodegrade rhodamine B (RhB) and pendimethalin under visible light illumination. The results of the experiments demonstrated that MXene, as a cocatalyst, considerably reduces the rate of recombination of charges and broadens absorption of visible light by providing increased surface functional groups to improve the photocatalytic activity of synthesized samples. MXene is thermally stable, have high electrical conductivity, have adjustable bandgap, and hydrophilic in nature. The optimized Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene composite demonstrated an excellent photocatalytic rate by degrading 78.88% RhB and 75.59% pendimethalin in 140 minutes. Moreover, the scavenging experiment revealed that photogenerated electrons and holes were the primary active species involved in RhB and pendimethalin photodegradation, respectively. Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene showed increased photocatalytic behavior because it has increased surface area which decreases rate of recombination of electron and hole pair, hence photocatalytic activity increases. It is observed that Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene has potential application in photocatalytic degradation of harmful pollutants.

Fabricating BiOCl Nanoflake/FeOCl Nanospindle Heterostructures for Efficient Visible-Light Photocatalysis

Fabricating heterostructures with abundant interfaces and delicate nanoarchitectures is an attractive approach for optimizing photocatalysts. Herein, we report the facile synthesis of BiOCl nanoflake/FeOCl nanospindle heterostructures through a solution chemistry method at room temperature. Characterizations, including XRD, SEM, TEM, EDS, and XPS, were employed to investigate the synthesized materials. The results demonstrate that the in situ reaction between the Bi precursors and the surface Cl- of FeOCl enabled the bounded nucleation and growth of BiOCl on the surface of FeOCl nanospindles. Stable interfacial structures were established between BiOCl nanoflakes and FeOCl nanospindles using Cl- as the bridge. Regulating the Bi-to-Fe ratios allowed for the optimization of the BiOCl/FeOCl interface, thereby facilitating the separation of photogenerated carriers and accelerating the photocatalytic degradation of RhB. The BiOCl/FeOCl heterostructures with an optimal composition of 15% BiOCl exhibited ~90 times higher visible-light photocatalytic activity than FeOCl. Based on an analysis of the band structures and reactive oxygen species, we propose an S-scheme mechanism to elucidate the significantly enhanced photocatalytic performance observed in the BiOCl/FeOCl heterostructures.

Recent Advances in Nanocellulose Aerogels for Efficient Heavy Metal and Dye Removal

Water pollution is a significant environmental issue that has emerged because of industrial and economic growth. Human activities such as industrial, agricultural, and technological practices have increased the levels of pollutants in the environment, causing harm to both the environment and public health. Dyes and heavy metals are major contributors to water pollution. Organic dyes are a major concern because of their stability in water and their potential to absorb sunlight, increasing the temperature and disrupting the ecological balance. The presence of heavy metals in the production of textile dyes adds to the toxicity of the wastewater. Heavy metals are a global issue that can harm both human health and the environment and are mainly caused by urbanization and industrialization. To address this issue, researchers have focused on developing effective water treatment procedures, including adsorption, precipitation, and filtration. Among these methods, adsorption is a simple, efficient, and cheap method for removing organic dyes from water. Aerogels have shown potential as a promising adsorbent material because of their low density, high porosity, high surface area, low thermal and electrical conductivity, and ability to respond to external stimuli. Biomaterials such as cellulose, starch, chitosan, chitin, carrageenan, and graphene have been extensively studied for the production of sustainable aerogels for water treatment. Cellulose, which is abundant in nature, has received significant attention in recent years. This review highlights the potential of cellulose-based aerogels as a sustainable and efficient material for removing dyes and heavy metals from water during the treatment process.

Sustainable consideration for traditional textile handloom cluster/village in pollution abatement - A case study

Decentralized handlooms are being traditionally practised throughout India. Siripuram village known for traditional Pochampally/Ikat work was considered as a case study for detailed investigation towards providing a sustainable solution. Nearly 65% of village population solely depend on weaving and dyeing works as primary occupation based on the household survey and generated wash water of 127 KLD on an average from the dyeing operations. Initially, a topographical survey (Aerial drone; PHANTOM 4 RTK UAV) was carried out to understand the drainage pattern, elevations, contours and interlinked with domestic and dyeing functions. The characteristics of combined wastewater and dye wash water were studied at lab scale using sequential batch (SBR) operation under aerobic (SBRAe) and aerobic-anoxic (SBRAex) microenvironments. SBRAex microenvironment showed effective organic and nutrients removal due to infused anoxic microenvironment. Treatment studies depicted 76.2% of organic fraction, 73.3% of phosphate, and 81.6% of nitrate removal. Based on the lab scale studies a closed-loop decentralized effluent treatment system was designed to ensure zero-liquid discharge (ZLD).

Algal Extracts for Green Synthesis of Zinc Oxide Nanoparticles: Promising Approach for Algae Bioremediation

Zinc oxide nanoparticles (ZnO-NPs) possess unique properties, making them a popular material across various industries. However, traditional methods of synthesizing ZnO-NPs are associated with environmental and health risks due to the use of harmful chemicals. As a result, the development of eco-friendly manufacturing practices, such as green-synthesis methodologies, has gained momentum. Green synthesis of ZnO-NPs using biological substrates offers several advantages over conventional approaches, such as cost-effectiveness, simplicity of scaling up, and reduced environmental impact. While both dried dead and living biomasses can be used for synthesis, the extracellular mode is more commonly employed. Although several biological substrates have been successfully utilized for the green production of ZnO-NPs, large-scale production remains challenging due to the complexity of biological extracts. In addition, ZnO-NPs have significant potential for photocatalysis and adsorption in the remediation of industrial effluents. The ease of use, efficacy, quick oxidation, cost-effectiveness, and reduced synthesis of harmful byproducts make them a promising tool in this field. This review aims to describe the different biological substrate sources and technologies used in the green synthesis of ZnO-NPs and their impact on properties. Traditional synthesis methods using harmful chemicals limit their clinical field of use. However, the emergence of algae as a promising substrate for creating safe, biocompatible, non-toxic, economic, and ecological synthesis techniques is gaining momentum. Future research is required to explore the potential of other algae species for biogenic synthesis. Moreover, this review focuses on how green synthesis of ZnO-NPs using biological substrates offers a viable alternative to traditional methods. Moreover, the use of these nanoparticles for industrial-effluent remediation is a promising field for future research.

Porous Materials for Water Purification

Water pollution is a growing threat to humanity due to the pervasiveness of contaminants in water bodies. Significant efforts have been made to separate these hazardous components to purify polluted water through various methods. However, conventional remediation methods suffer from limitations such as low uptake capacity or selectivity, and current water quality standards cannot be met. Recently, advanced porous materials (APMs) have shown promise in improved segregation of contaminants compared to traditional porous materials in uptake capacity and selectivity. These materials feature merits of high surface area and versatile functionality, rendering them ideal platforms for the design of novel adsorbents. This Review summarizes the development and employment of APMs in a variety of water treatments accompanied by assessments of task-specific adsorption performance. Finally, we discuss our perspectives on future opportunities for APMs in water purification.

Activation of peroxymonosulfate by Co-Mg-Fe layered doubled hydroxide for efficient degradation of Rhodamine B

Reactive species serve as a key to remediate the contamination of refractory organic contaminants in advanced oxidation processes. In this study, a novel heterogeneous catalyst, CoMgFe-LDH layered doubled hydroxide (CoMgFe-LDH), was prepared for an efficient activation of peroxymonosulfate (PMS) to oxidize Rhodamine B (RhB). The characterization results showed that CoMgFe-LDH had a good crystallographic structure. Correspondingly, the CoMgFe-LDH/PMS process exhibited good capacity to remove RhB, which was equivalent to degradation performance as homogeneous Co(II)/PMS process. The RhB oxidation in the CoMgFe-LDH/PMS process was well described with pseudo-first-order kinetic model. Additionally, the oxidation process presented an excellent stability, and only 0.9% leaching rate was detected after six sequential reaction cycles at pH 5.0. The effects of initial pH, CoMgFe-LDH dosage, PMS concentration, RhB concentration, and inorganic anions on the RhB degradation were discussed in detail. Quenching experiments showed that sulfate radicals (SO₄^•-) acted as the dominant reactive species. Further, the removal of RhB from simulated wastewater was explored. The removal efficiency of RhB (90 μM) could reach 94.3% with 0.8 g/L of catalyst and 1.2 mM of PMS addition at pH 5.0, which indicated the CoMgFe-LDH/PMS process was also effective in degrading RhB in wastewater.

G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants

In this paper, a facile hydrothermal approach was used to integrate graphitic carbon nitride dots (CNDs) with hetaerolite (ZnMn2O4) at different weight percentages. The morphology, microstructure, texture, electronic, phase composition, and electrochemical properties were identified by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), ultraviolet-visible diffuse reflectance (UV-vis DR), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), and photocurrent density. The results of XRD, FT-IR, EDX, and XPS analyses confirmed the synthesis of CNDs/ZnMn2O4 (20%) nanocomposite. As per PL, EIS, and photocurrent outcomes, the binary CNDs/ZnMn2O4 nanocomposite revealed superior features for interfacial transferring of charge carriers. The developed p–n heterojunction at the interface of CNDs and ZnMn2O4 nanoparticles partaken a significant role in the impressive charge segregation and migration. The binary nanocomposites were employed for the photodegradation of several dye pollutants, including rhodamine B (RhB), fuchsin, malachite green (MG), and methylene blue (MB) at visible wavelengths. Amongst the fabricated photocatalysts, the CNDs/ZnMn2O4 (20%) nanocomposite gave rise to about 98% RhB degradation efficiency within 45 min with the rate constant of 747 × 10−4 min−1, which was 66.5-, 3.44-, and 2.72-fold superior to the activities of CN, CNDs, and ZnMn2O4 photocatalysts, respectively. The impressive photodegradation performance of this nanocomposite was not only associated with the capacity for impressive visible-light absorption and boosted separation and transport of charge carriers, but also with its large surface area.

Thermocatalytic Performance of LaCo1−xNixO3−δ Perovskites in the Degradation of Rhodamine B

Perovskite-type LaCo1−xNixO3−δ (x = 0, 0.2, 0.4, 0.6, and 0.8) powders were synthesized by solution combustion synthesis. The crystal structure, morphology, texture, and surface were characterized by X-ray powder diffraction combined with Rietveld refinement, scanning electron microscopy, N2-adsorption, X-ray photoelectron spectroscopy, and zeta-potential analysis. The thermocatalytic properties of the perovskites were investigated by UV–Vis spectroscopy through degradation of rhodamine B in the temperature range 25–60 °C. For the first time, this perovskite system was proven to catalyze the degradation of a water pollutant, as the degradation of rhodamine B occurred within 60 min at 25 °C. It was found that undoped LaCoO3−δ is the fastest to degrade rhodamine B, despite exhibiting the largest energy band gap (1.90 eV) and very small surface area (3.31 m2 g−1). Among the Ni-doped samples, the catalytic performance is balanced between two main contrasting factors, the positive effect of the increase in the surface area (maximum of 12.87 m2 g−1 for 80 mol% Ni) and the negative effect of the Co(III) stabilization in the structure (78% in LaCoO3 and 89–90% in the Ni-containing ones). Thus, the Co(II)/Co(III) redox couple is the key parameter in the dark ambient degradation of rhodamine B using cobaltite perovskites.

Casting Zinc Oxide Nanoparticles Using Fagonia Blend Microbial Arrest

Physical and chemical methods for production of nanoparticles (NPs) are not only harmful for environment but also toxic for living organism. The present study attempts to synthesize ZnO NPs using the natural plant extract of Fagonia cretica. The phytochemical screening of F. cretica water extract was performed to check the presence of biologically active compounds like alkaloids, tannins, carbohydrates, proteins, phenols, saponins, flavonoids, and steroids. Well-prepared ZnO NPs given sharp absorption peak at 362 were confirmed by UV-visible. XRD analysis showed the ZnO NPs having wurtzite hexagonal structure with crystalline form. TEM analysis endorses flower-shaped ZnO nanoparticles ~ 100-1000 nm. FTIR spectrum suggested the involvement of phenolic groups and amino acids and amide linkages in protein performs as the stabilizing agent in the synthesis of ZnO NPs. The ZnO NPs showed strong antibacterial behavior against two bacterial strains Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli. In addition, ZnO NPs exhibited strong antioxidant activity of 79%:85.6%:89.9% at 5 μg/mL:10 μg/mL:5 μg/mL concentration of ZnO NPs respectively. This work indicates that Fagonia is considered to be appropriate and promising candidate for extending the innovative applications in the field of medicine and industry and also helpful and useful to the scientific communities.

Synthesis of Co3O4 Nanoparticles-Decorated Bi12O17Cl2 Hierarchical Microspheres for Enhanced Photocatalytic Degradation of RhB and BPA

Three-dimensional (3D) hierarchical microspheres of Bi₁₂O₁₇Cl₂ (BOC) were prepared via a facile solvothermal method using a binary solvent for the photocatalytic degradation of Rhodamine-B (RhB) and Bisphenol-A (BPA). Co₃O₄ nanoparticles (NPs)-decorated BOC (Co₃O₄/BOC) heterostructures were synthesized to further enhance their photocatalytic performance. The microstructural, morphological, and compositional characterization showed that the BOC microspheres are composed of thin (~20 nm thick) nanosheets with a 3D hierarchical morphology and a high surface area. Compared to the pure BOC photocatalyst, the 20-Co₃O₄/BOC heterostructure showed enhanced degradation efficiency of RhB (97.4%) and BPA (88.4%). The radical trapping experiments confirmed that superoxide (^•O₂^-) radicals played a primary role in the photocatalytic degradation of RhB and BPA. The enhanced photocatalytic performances of the hierarchical Co₃O₄/BOC heterostructure are attributable to the synergetic effects of the highly specific surface area, the extension of light absorption to the more visible light region, and the suppression of photoexcited electron-hole recombination. Our developed nanocomposites are beneficial for the construction of other bismuth-based compounds and their heterostructure for use in high-performance photocatalytic applications.

Facilitated Photocatalytic Degradation of Rhodamine B over One-Step Synthesized Honeycomb-Like BiFeO3/g-C3N4 Catalyst

In the present work, a facile one-step methodology was used to synthesize honeycomb-like BiFeO₃/g-C₃N₄ composites, where the well-dispersed BiFeO₃ strongly interacted with the hg-C₃N₄. The 10BiFeO₃/hg-C₃N₄ could completely degrade RhB under visible light illumination within 60 min. The degradation rate constant was remarkably improved and approximately three times and seven times that of pristine hg-C₃N₄ and BiFeO₃, respectively. This is ascribed to the following factors: (1) the unique honeycomb-like morphology facilitates the diffusion of the reactants and effectively improves the utilization of light energy by multiple reflections of light; (2) the charged dye molecules can be tightly bound to the spontaneous polarized BiFeO₃ surface to form the Stern layer; (3) the Z-scheme heterojunction and the ferroelectric synergistically promoted the efficient separation and migration of the photogenerated charges. This method can synchronously tune the micro-nano structure, surface property, and internal field construction for g-C₃N₄-based photocatalysts, exhibiting outstanding potential in environmental purification.

g-C3N4-Based Direct Z-Scheme Photocatalysts for Environmental Applications

Photocatalysis represents a promising technology that might alleviate the current environmental crisis. One of the most representative photocatalysts is graphitic carbon nitride (g-C3N4) due to its stability, cost-effectiveness, facile synthesis procedure, and absorption properties in visible light. Nevertheless, pristine g-C3N4 still exhibits low photoactivity due to the rapid recombination of photo-induced electron-hole (e−-h+) pairs. To solve this drawback, Z-scheme photocatalysts based on g-C3N4 are superior alternatives since these systems present the same band configuration but follow a different charge carrier recombination mechanism. To contextualize the topic, the main drawbacks of using g-C3N4 as a photocatalyst in environmental applications are mentioned in this review. Then, the basic concepts of the Z-scheme and the synthesis and characterization of the Z-scheme based on g-C3N4 are addressed to obtain novel systems with suitable photocatalytic activity in environmental applications (pollutant abatement, H2 production, and CO2 reduction). Focusing on the applications of the Z-scheme based on g-C3N4, the most representative examples of these systems are referred to, analyzed, and commented on in the main text. To conclude this review, an outlook of the future challenges and prospects of g-C3N4-based Z-scheme photocatalysts is addressed.

Bimetallic Fe/Al-MOF for the adsorptive removal of multiple dyes: optimization and modeling of batch and hybrid adsorbent-river sand column study and its application in textile industry wastewater

Bimetallic metal organic framework (MOF) has garnered interest over the years with its applications in industrial wastewater treatment. In this work, Fe-Al-1,4-benzene-dicarboxylic acid (FeAl(BDC)) MOF was synthesized, and adsorptive removal of Rhodamine B dye in batch and unique hybrid FeAl (BDC)-river sand fixed-bed column was studied. The experimental data from the batch studies corroborated well with the pseudo-second-order (PSO) (R²: 0.97) and Freundlich adsorption isotherm models (R²: 0.98) and achieved a maximum adsorption capacity of 48.59 mg/g in 90 min. Furthermore, a fixed-bed column study was conducted to assess the effect of varying flow rate (2, 5, 8 mL/min), bed height (5, 9, 13 cm), and feed concentration (10, 20, 30 mg/L) on the adsorption performance of FeAl(BDC) in continuous mode of operation. A uniform mixture of river sand and FeAl(BDC) by weight ratio (9:1) was packed into the column. The sand-FeAl(BDC) fixed-bed column could achieve the maximum adsorption capacity (q_exp) of 113.05 mg/g at a 5 mL/min flow rate, feed concentration of 20 mg/L, and a bed height of 13 cm. The experimental data of the column study were successfully fitted well with BDST, Thomas (q_cal: 114.94 mg/g), Yoon-Nelson, and dose-response models (q_cal: 113.41 mg/g) and R²: 0.97-0.99. The fitting parameter values from the BDST model raise the scope of viable upscaling of the fixed-bed column. In all, it is proposed that these river sand-FeAl(BDC)-based filters can be widely used in areas facing critical contamination and in poor communities with a high demand for water.

Microwave-assisted preparation of cotton stem-derived activated carbon for dye removal from synthetic wastewater

Cotton stem is used to produce the high-efficient adsorbent (CSA) for Rhodamine B (RB) dye removal from wastewater, and hydrogen rich fuel gas via on-pot method using microwave heating. The adsorption data indicate that RB adsorption behavior follows the Langmuir model with the maximum adsorption capacity of 265.96 mg/g, whereas the adsorption kinetics follows the pseudo-second-order model. Thermodynamic calculations indicate that RB adsorption on CSA is spontaneous and endothermic process. The adsorption data are fitted to the Thomas and Yoon-Nelson model to predict the breakthrough curve in the column experiment. The RB removal could still be maintained at 71.22% of the original value after five cycles, demonstrating the reusability of CSA. The chemical functional groups, electrostatic interaction, and pore filling of CSA are found to be responsible for high RB adsorption capability. CSA exhibits excellent RB removal efficiency in treating actual water. The major components of byproduct gases collected from activation process are H₂ and CO.

Photocatalytic Efficiency of Titanium Dioxide for Dyes and Heavy Metals Removal from Wastewater

The hazardous toxicity of dye materials, even in low concentrations, harms ecological systems. It releases a large number of contaminants into the water, resulting as waste water. Dyes prevent the process of photosynthesis by obstructing light passage, lowers the oxygen levels dissolved in the water. Also, a good number of the dyes and heavy metals are carcinogenic and mutagenic to human beings. Heterogeneous photocatalysis is a promising technology for removing organic, inorganic, and microbial pollutants from water and wastewater. It is preferable to other conventional wastewater treatment approaches due to its benefit, such as low cost, environmental friendliness, ability to proceed at ambient temperature and pressure conditions, and to completely degrade pollutants into environmentally safe products with suitable measures. The titanium oxide (TiO2) is one of the most promising material that has gained enormous importance in the field of energy and environmental applications. The unique physicochemical properties of TiO2 make it one of the best candidates among existing photocatalysts. This review provides an overview of strategies employed to augment its catalytic performance as well as the impact of different operational parameters on the removal proficiency of various organic and inorganic pollutants in water and wastewater treatment. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Emerging bismuth-based direct Z-scheme photocatalyst for the degradation of organic dye and antibiotic residues

Organic dye and antibiotic residues are some of the key substances that can contaminate the environment due to their wide usage in various industries and modern medicine. The degradation of these substances present in waterbodies is essential while contemplating human health. Photocatalysts (PSs) are promising materials that develop highly reactive species instantly by simple solar energy conversion for degrading the organic dye and antibiotic residues and converting them into nontoxic products. Among numerous semiconductors, the bismuth (Bi)-containing PS has received great attention due to its strong sunlight absorption, facile preparation, and high photostability. Owing to the technology advancement and demerits of the traditional methods, a Bi-containing direct Z-scheme PS has been developed for efficient photogenerated charge carrier separation and strong redox proficiency. In this review, a synthetic Bi-based Z-scheme heterojunction that mimics natural photosynthesis is described, and its design, fabrication methods, and applications are comprehensively reviewed. Specifically, the first section briefly explains the role of various semiconductors in the environmental applications and the importance of the Bi-based materials for constructing the Z-scheme photocatalytic systems. In the successive section, overview of Z-scheme PS are concisely discussed. The fourth and fifth sections extensively explain the degradation of the organic dyes and antibiotics utilizing the Bi-based direct Z-scheme heterojunction. Eventually, the conclusions and future perspectives of this emerging research field are addressed. Overall, this review is potentially useful for the researchers involved in the environmental remediation field as a collection of up-to-date research articles for the fabrication of the Bi-containing direct Z-scheme PS.

Aspartic Acid- and Glycine-Functionalized Mesoporous Silica as an Effective Adsorbent to Remove Methylene Blue from Contaminated Water

In this work, aspartic acid- and glycine-functionalized mesoporous silica nanoparticles (Asp-MSNs and Gly-MSNs) were successfully prepared and applied as adsorbents for removal of methylene blue (MB) from contaminated water. The mesoporous structure of the fabricated nanomaterials was confirmed by nitrogen adsorption/desorption with specific surface area of ca. 700 m2/g and pore volume of 0.9 cm3/g for both Asp-MSNs and Gly-MSNs. The average size of the nanoadsorbents was estimated to be ca. 290 nm as characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The physical and chemical properties of the Asp-MSNs and Gly-MSNs were also characterized by Fourier transform infrared (FTIR) spectroscopy, zeta potential, and elemental analysis. Asp-MSNs and Gly-MSNs exhibited good adsorption performance for removal of cationic organic dyes (MB). The equilibrium adsorption capacity of Asp-MSNs and Gly-MSNs was found to be 55 mg·g−1 and 43 mg·g−1, respectively, under the optimal conditions. The Langmuir model and pseudo-second-order equation exhibited good correlation with the isotherm and adsorption kinetic data for MB, respectively.

Z-Scheme Heterojunction of 3-Dimensional Hierarchical Bi3O4Cl/Bi5O7I for a Significant Enhancement in the Photocatalytic Degradation of Organic Pollutants (RhB and BPA)

In this study, we report the synthesis of a 3-dimensional (3D) hierarchical Bi3O4Cl/Bi5O7I (BOC/BOI) heterostructure for the photocatalytic degradation of Rhodamine-B (RhB) dye and colorless Bisphenol-A (BPA) pollutant under visible light. The heterostructure was prepared using in situ solvothermal and calcination methods. BOC/BOI exhibits a 3D hierarchical structure constructed with thin nano-platelets. The photocatalytic performance of the BOC/BOI photocatalyst demonstrated that the degradation efficiencies of RhB and BPA were 97% and 92% after light illumination within 90 and 30 min, respectively. In comparison, bare BOC and BOI efficiencies were only 20% and 10% for RhB dye, respectively, and 2.3% and 37% for BPA aqueous pollutants, respectively. Moreover, radical trapping measurements indicated that •O2− and •OH radicals played prominent roles in RhB and BPA degradation into mineralization. Analysis of band structures and photochemical redox reactions of BOC/BOI revealed a Z-scheme charge transfer between BOC and BOI by an internal electric field formed at the interface. Therefore, the highly improved photocatalytic performance of the BOC/BOI heterostructure is attributed to the synergetic effects of large surface area, high visible-light absorption, and the enhanced separation and transport of photo-excited electron–hole pairs induced by the hierarchical and Z-scheme heterojunction of the BOC/BOI.

Invasive plants as biosorbents for environmental remediation: a review

Water contamination is an environmental burden for the next generations, calling for advanced methods such as adsorption to remove pollutants. For instance, unwanted biowaste and invasive plants can be converted into biosorbents for environmental remediation. This would partly solve the negative effects of invasive plants, estimated at 120 billion dollars in the USA. Here we review the distribution, impact, and use of invasive plants for water treatment, with emphasis on the preparation of biosorbents and removal of pollutants such as cadmium, lead, copper, zinc, nickel, mercury, chromate, synthetic dyes, and fossil fuels. Those biosorbents can remove 90-99% heavy metals from aqueous solutions. High adsorption capacities of 476.190 mg/g for synthetic dyes and 211 g/g for diesel oils have been observed. We also discuss the regeneration of these biosorbents.

The application of photoelectrocatalysis in the degradation of rhodamine B in aqueous solutions: a review

The pollution of the water environment by industrial effluents is an ongoing challenge due to the rate of industrialisation and globalisation. Photoelectrocatalysis (PEC), an electrochemical advanced oxidation process, has proven to be an effective method for removing organics from wastewater. Photoelectrocatalysis is environmentally benign, cost-effective and easy to operate. In this present review, we examine the recent progress in the removal of rhodamine B dye, a common constituent of textile effluent released into the environment, through photoelectrocatalytic degradation. We present a detailed discussion on the use of different kinds of unmodified and modified photoanodes that have been explored for the photoelectrocatalytic removal of this dye. More importantly, discussions are presented on the mechanisms and kinetics of the degradation of rhodamine B dye using these photoanodes. Hence, this review will be beneficial for researchers in developing future projects in the area of wastewater treatments through photoelectrocatalysis.

The pollution of the water environment by industrial effluents is an ongoing challenge due to the rate of industrialisation and globalisation.

Enhanced photocatalytic activities of a hierarchical ZnO/V2C MXene hybrid with a close coupling heterojunction for the degradation of methyl orange, phenol and methylene blue dye

A hierarchical ZnO/V2C MXene hybrid exhibited enhanced photocatalytic performance due to its close coupling heterojunction facilitating photo-generated carrier transfer.