Visible-light-driven photocatalytic degradation of Metalaxyl by reduced graphene oxide/Fe3O4/ZnO ternary nanohybrid: Influential factors, mechanism and toxicity bioassay

Using NaOH@Graphene oxide-Fe3O4 as a magnetic heterogeneous catalyst for ultrasonic transesterification; experimental and modelling

Burning fossil fuels causes toxic gas emissions to increase, therefore, scientists are trying to find alternative green fuels. One of the important alternative fuels is biodiesel. However, using eco-friendly primary materials is a main factor. Sustainable catalysts should have high performance, good activity, easy separation from reaction cells, and regenerability. In this study, to solve the mentioned problem NaOH@Graphene oxide-Fe3O4 as a magnetic catalyst was used for the first time to generate biodiesel from waste cooking oil. The crystal structure, functional groups, surface area and morphology of catalyst were studied by XRD, FTIR, BET, and FESEM techniques. The response surface methodology based central composite design (RSM-CCD) was used for biodiesel production via ultrasonic technique. The maximum biodiesel yield was 95.88% in the following operation: 10.52:1 molar ratio of methanol to oil, a catalyst weight of 3.76 wt%, a voltage of 49.58 kHz, and a time of 33.29 min. The physiochemical characterization of biodiesel was based to ASTM standard. The magnetic catalyst was high standstill to free fatty acid due to the five cycle's regeneration. The kinetic study results possess good agreement with first-order kinetics as well as the activation energy and Arrhenius constant are 49.2 kJ/min and 16.47 * 1010 min-1, respectively.

Oxidative treatment of micropollutants present in wastewater: A special emphasis on transformation products, their toxicity, detection, and field-scale investigations

Micropollutants have become ubiquitous in aqueous environments due to the increased use of pharmaceuticals, personal care products, pesticides, and other compounds. In this review, the removal of micropollutants from aqueous matrices using various advanced oxidation processes (AOPs), such as photocatalysis, electrocatalysis, sulfate radical-based AOPs, ozonation, and Fenton-based processes has been comprehensively discussed. Most of the compounds were successfully degraded with an efficiency of more than 90%, resulting in the formation of transformation products (TPs). In this respect, degradation pathways with multiple mechanisms, including decarboxylation, hydroxylation, and halogenation, have been illustrated. Various techniques for the analysis of micropollutants and their TPs have been discussed. Additionally, the ecotoxicity posed by these TPs was determined using the toxicity estimation software tool (T.E.S.T.). Finally, the performance and cost-effectiveness of the AOPs at the pilot scale have been reviewed. The current review will help in understanding the treatment efficacy of different AOPs, degradation pathways, and ecotoxicity of TPs so formed.

Study on diazinon toxicity reduction by electro-Fenton process: A bioassay using daphnia magna

The realm of diazinon reduction from polluted water has witnessed a surge in the significance of advanced oxidation processes (AOPs) in recent times. However, there is a dearth of research focusing on the mitigation of its toxicity through AOPs. Thus, the primary objective of this study was to evaluate the effectiveness of the Electro-Fenton process (EFP) in the eradication and detoxification of diazinon in aqueous solutions. Synthetic wastewater samples with concentrations of 2, 2.5 and 3 mg/L were prepared. A total of 27 samples were determined using Box Behnken Design. Reaction time, pH and iron to hydrogen peroxide ratio (Fe2+/H2O2) were examined as operational parameters under a constant current of 5.4 amps. The quantification of diazinon concentration was performed using High-Performance Liquid Chromatography (HPLC). To evaluate the detoxification of diazinon, the Daphnia magna bioassay was employed as a methodology in this study. According to the results, the EFP could reduce the diazinon to zero and the LC50 values are increased by applying the process. The LC50 values for diazinon were determined using the Daphnia magna bioassay, considering initial concentrations of 2, 2.5, and 3 mg/L at a pH of 5, a reaction time of 15 min, and an iron to hydrogen peroxide molar ratio of 2. The recorded LC50 values were 3.039, 3.076, and 3.106, respectively, indicating the lowest frequency of cumulative death in Daphnia magna. In this case, after 96 h, only 3 cases (30%) of Daphnia magna death were observed. However, for all the mentioned concentrations of diazinon, after 96 h of exposure to samples without applying the Daphnia Magna death process, it was observed between 60 and 100%. Reducing the diazinon concentration and increasing the 96-h LC50 showed that the EFP can reduce the toxicity of diazinon on Daphnia Magna at the same time. Therefore, EFP can be considered a superior method with low ecotoxicity.

Photocatalytic removal of organophosphorus pesticide by the WO3-Fe3O4/rGO photocatalyst under visible light

The WO3-Fe3O4/reduced graphene oxide (rGO) composite was synthesized with a hydrothermal method for the photocatalytic removal of diazinon (DZ) in visible light. The influence of catalyst concentration (0.5-1.5 g L-1), pH (5-9), and initial pollutant value (5-15 mg L-1) on the pesticide degradation was studied. The performance of the WO3-Fe3O4/rGO nanocomposite for DZ degradation under visible light shows 94% degradation of 5 mg L-1 DZ for 100 min with 1 g L-1 nanocomposite, and the degradation kinetic was modeled in pseudo-first order (PFO) and the maximum kobs was 0.0248 min-1. The photocatalytic mechanism and the intermediates of DZ degradation were identified. In addition, the WO3-Fe3O4/rGO catalyst showed reusability after 4 runs. The results of this work illustrate that the WO3-Fe3O4/rGO nanocomposite can be applied for real use owing to its high catalytic performance.

Degradation of Pesticides Using Semiconducting and Tetrapyrrolic Macrocyclic Photocatalysts-A Concise Review

Exposure to pesticides is inevitable in modern times, and their environmental presence is strongly associated to the development of various malignancies. This challenge has prompted an increased interest in finding more sustainable ways of degrading pesticides. Advanced oxidation processes in particular appear as highly advantageous, due to their ability of selectively removing chemical entities form wastewaters. This review provides a concise introduction to the mechanisms of photochemical advanced oxidation processes with an objective perspective, followed by a succinct literature review on the photodegradation of pesticides utilizing metal oxide-based semiconductors as photosensitizing catalysts. The selection of reports discussed here is based on relevance and impact, which are recognized globally, ensuring rigorous scrutiny. Finally, this literature review explores the use of tetrapyrrolic macrocyclic photosensitizers in pesticide photodegradation, analyzing their benefits and limitations and providing insights into future directions.

A Review on the Use of Metal Oxide-Based Nanocomposites for the Remediation of Organics-Contaminated Water via Photocatalysis: Fundamentals, Bibliometric Study and Recent Advances

The improper disposal of toxic and carcinogenic organic substances resulting from the manufacture of dyes, drugs and pesticides can contaminate aquatic environments and potable water resources and cause serious damage to animal and human health and to the ecosystem. In this sense, heterogeneous photocatalysis stand out as one effective and cost-effective water depollution technique. The use of metal oxide nanocomposites (MON), from the mixture of two or more oxides or between these oxides and other functional semiconductor materials, have gained increasing attention from researchers and industrial developers as a potential alternative to produce efficient and environmentally friendly photocatalysts for the remediation of water contamination by organic compounds. Thus, this work presents an updated review of the main advances in the use of metal oxide nanocomposites-based photocatalysts for decontamination of water polluted by these substances. A bibliometric analysis allowed to show the evolution of the importance of this research topic in the literature over the last decade. The results of the study also showed that hierarchical and heterogeneous nanostructures of metal oxides, as well as conducting polymers and carbon materials, currently stand out as the main materials for the synthesis of MON, with better photocatalysis performance in the degradation of dyes, pharmaceuticals and pesticides.

Recent progress in semiconductor/graphene photocatalysts: synthesis, photocatalytic applications, and challenges

The presence of an increasing number of organic pollutants in water now poses serious risks to both human health and ecological systems. Many of these pollutants are persistent and non-biodegradable. The contamination of fresh water by harmful substances has compelled researchers to develop innovative, efficient, and cost-effective water remediation techniques and materials. Thus, photocatalysis has long been recognized as a promising approach to tackle both environmental remediation and the energy crisis. However, semiconductor photocatalysts frequently suffer from defects such as photo-generated charge carrier recombination, poor visible light response, and slow surface reaction kinetics, which can be remedied by modifications with appropriate co-catalysts. Therefore, graphene and its derivatives have widely been used as supports for semiconductors and photocatalysts due to their distinctive optical, physicochemical, and electrical features. This critical review addresses the current progress in the design and synthesis of graphene/semiconductor photocatalysts, as well as their use in photocatalytic degradation of organic pollutants and hydrogen production. Several influencing parameters are addressed, including pH, photocatalyst loading, initial pollutant concentration, light wavelength, and oxidizing species, all of which could have a significant impact on the rate of organic pollutant's degradation. Furthermore, the recyclability of the catalyst and its photocatalytic activity mechanisms are thoroughly discussed. Numerous case studies are systematically presented. Moreover, future prospects and major challenges are highlighted.

Phyto-mediated photocatalysis: a critical review of in-depth base to reactive radical generation for erythromycin degradation

Erythromycin (ERY), designated as a risk-prioritized macrolide antibiotic on the 2015 European Union watch list, is the third most commonly used antibiotic, most likely due to its ability to inhibit the protein. ERY has revealed record-high aquatic concentrations threatening the entire ecosystem and hence demands priority remedial measures. The inefficiency of various conventional ERY degradation methodologies opened up a gateway to advanced technologies. The conventional approach comprising of a chemically formulated, single photocatalyst has a major drawback of creating multiple environmental stresses. In this context, photocatalysis is grabbing tremendous attention as an efficient and cost-effective antibiotic treatment approach. Several studies have ascertained that ZnO, TiO₂, Fe₃O₄, and rGO nanoparticles possess remarkable pollution minimizing operational capabilities. Additionally, composites are found much more effective in antibiotic removal than single nanoparticles. In this review, an attempt has been made to provide a comprehensive baseline for efficient reactive radical production by a phyto-mediated composite kept under a certain source of irradiation. Considerable efforts have been directed towards the in-depth investigation of rGO-embedded, phyto-mediated ZnO/TiO₂/Fe₃O₄ photocatalyst fabrication for efficient ERY degradation, undergoing green photocatalysis. This detailed review provides photocatalytic nanocomposite individualities along with a hypothetical ERY degradation mechanism. It is assumed that derived information presented here will provoke innovative ideas for water purification incorporating green photocatalysis, initiating the construction of high-performance biogenic hierarchical nanocatalysts.

One-step preparation of RGO/Fe3O4-FeVO4 nanocomposites as highly effective photocatalysts under natural sunlight illumination

The study used a one-step hydrothermal method to prepare Fe3O4-FeVO4 and xRGO/Fe3O4-FeVO4 nanocomposites. XRD, TEM, EDS, XPS, DRS, and PL techniques were used to examine the structurally and morphologically properties of the prepared samples. The XRD results appeared that the Fe3O4-FeVO4 has a triclinic crystal structure. Under hydrothermal treatment, (GO) was effectively reduced to (RGO) as illustrated by XRD and XPS results. UV-Vis analysis revealed that the addition of RGO enhanced the absorption in the visible region and narrowed the band gap energy. The photoactivities of the prepared samples were evaluated by degrading methylene blue (MB), phenol and brilliant green under sunlight illumination. As indicated by all the nanocomposites, photocatalytic activity was higher than the pure Fe3O4-FeVO4 photocatalyst, and the highest photodegradation efficiency of MB and phenol was shown by the 10%RGO/Fe3O4-FeVO4. In addition, the study examined the mineralization (TOC), photodegradation process, and photocatalytic reaction kinetics of MB and phenol.

Degradation of toxic agrochemicals and pharmaceutical pollutants: Effective and alternative approaches toward photocatalysis

Emerging concern regarding the remediation of environmental pollution has expanded tremendously in recent years. Pharmaceutical industries and agricultural sectors release an enormous amount of residues containing toxic pollutants at trace levels which poses a serious impact on the environment and human health. To cope with the effect of hazardous and toxic contaminants, numerous methodologies have been developed for the treatment of effluents released from the agrochemical and pharmaceutical industries. Amongst them, photocatalysis has gained much more attention for the degradation of pollutants due to its low cost, higher capability, green and eco-friendly approaches. Photocatalysts are the substrate that plays a key role in pollutant removal through photocatalysis by accelerating the necessary chemical reactions using a light source. In this review, the recent progress on photocatalysis and its fundamental mechanism in agrochemicals and pharmaceutical pollutant degradation was summarized. This review concisely discusses the incorporation of various metal oxides and nanomaterials into semiconductors for the effective degradation of contaminants. The current status and future research on different sectors and the difficulties in the photocatalytic removal of agrochemical and pharmaceutical pollutants are also reviewed in detail.

Studies on the removal of acid violet 7 dye from aqueous solutions by green ZnO@Fe3O4 chitosan-alginate nanocomposite synthesized using Camellia sinensis extract

In the present study, ZnO-Fe₃O₄ nanoparticles were synthesized using the leaves of Camellia sinensis and immobilized in crosslinked alginate-chitosan polymer beads and tested for their photocatalytic applications. The prepared nanocomposite was used for the simultaneous adsorption and photocatalytic degradation of acid violet 7 (AV7) dye. The optimization of reaction conditions ensured higher dye removal efficacy up to 94.21 ± 1.02% using the nanocomposite under UV-C irradiation of 365 nm. The kinetics of the adsorption study fitted well with the pseudo-first-order reaction. The Langmuir model fitted better to the adsorption isotherms compared to the Freundlich and Temkin models. The mechanism of degradation was studied by analyzing the treated AV7 solution. The removal efficiency in tap water, groundwater, and lake water was 83.23 ± 0.4%, 69.13 ± 1.6%, and 67.89 ± 0.3%, respectively. The residual toxicity of the degraded AV7 solution was tested on model organisms like freshwater algae, Scenedesmus sp., and plant model, Allium cepa, demonstrating the lower toxicity of the degraded AV7 product. Finally, a cost-benefit analysis of the experiments was also carried out.

Sonochemical preparation and characterization of Sm-doped GO/KSrPO4 nanocomposite photocatalyst for degradation of methylene blue dye

The present work pertains to synthesis of Sm-doped GO/KSrPO4 (GO/KSrPO4:Sm) nanocomposite using ultrasound-assisted method. Successful decoration of graphene oxide sheets with the KSrPO4:Sm3+ phosphor was confirmed using analysis techniques including SEM, EDS, UV/visible spectrometry, XRD, and FTIR of the prepared GO/KSrPO4:Sm nanocomposite. Further, photocatalytic activity of this nanocomposite material was studied by examining degradation of methylene blue (MB) dye from water. The effects of several parameters like concentration of Sm3+ in KSrPO4:Sm3+ phosphor within the GO/KSrPO4:Sm nanocomposite photocatalyst, photocatalyst loading, initial dye concentration, pH, and preparation method were evaluated. At a higher concentration of Sm3+ in the photocatalyst (1 mol.%), higher photocatalyst loading (1.5 mg/ml), lesser dye concentration (20 mg/L), and higher pH (11.4), the GO/KSrPO4:Sm nanocomposite photocatalyst prepared using ultrasound-assisted method showed higher dye removal compared to other conditions. A maximum of 83.35% removal of MB dye was achieved by the use of ultrasonically prepared GO/KSrPO4:Sm nanocomposite photocatalyst having a concentration of 1 mol.% of Sm3+ in the KSrPO4:Sm3+ phosphor at a loading of 1.5 mg/ml, initial dye concentration of 20 mg/L, and a pH of 11.4. Rate constant for MB dye degradation using the GO/KSrPO4:Sm nanocomposite photocatalyst synthesized by ultrasonic-assisted method was found to be 0.0053 min-1. PRACTITIONER POINTS: GO/KSrPO4:Sm nanocomposite photocatalyst prepared by ultrasonic-assisted method. Higher Sm3+ doping in nanocomposite with the use of ultrasound assisted method showed better performance of photocatalyst. A maximum removal of 83.35% of methylene blue dye was achieved.

Simple fabrication and unprecedented visible light response of NiNb2O6/RGO heterojunctions for the degradation of emerging pollutants in water

Utilization of environmentally friendly and effective synthesis methods to fabricate visible light responsive photocatalysts with impressive catalytic performance is desirable in photocatalytic water treatment.

Fabrication, characterization, and application of ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite for photodegradation of tetracycline in aqueous solutions

We aim at fabricating a ternary magnetic recyclable Bi₂WO₆/BiOI@Fe₃O₄ composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe₃O₄ loading ratio on the Bi₂WO₆/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi₂WO₆/BiOI@5%Fe₃O₄ composite has the highest TC removal (97%), as compared to the Bi₂WO₆ (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.

Efficiency of Candida tropicalis for Potential Degradation of Metalaxyl in the Aqueous Media

Biodegradation of pesticides by bacteria, fungi, algae, and other organisms is an eco-friendly, efficient, and economical method of detoxification. This study was conducted to evaluate the efficiency of Candida tropicalis for potential degradation of metalaxyl in the aqueous media. The yeast fungus from soil with a historical application of metalaxyl has been isolated. The identification of isolated fungus was carried out using 28S rRNA. The effect of pH, temperature, and metalaxyl concentration on the growth of C. tropicalis and its ability for metalaxyl degradation was also investigated. The isolated fungus was identified as C. tropicalis based on the sequencing of D1D2 region of the 28S rRNA and BLAST search of the nucleotide sequences. The growth of C. tropicalis in the presence of metalaxyl was significantly higher than in the absence of it. A temperature of 30 °C, a pH value of 7, and metalaxyl concentration of 5 mg/L were the optimal conditions for C. tropicalis to grow and to obtain the highest degradation rate of metalaxyl. At the optimum conditions, the degradation rate and the half-life value of metalaxyl were 0.065 d-1 and 10.7 days, respectively. Under the optimum conditions, a 98% degradation of metalaxyl initial concentration obtained within 36 days. This report is novel in showing the biodegradation of metalaxyl in water by the yeast C. tropicalis, which can be a promising method in this regard.