Synthesis of Fe3O4/CdS-ZnS nanostructure and its application for photocatalytic degradation of chlorpyrifos pesticide and brilliant green dye from aqueous solutions

Photocatalytic Degradation of Organic Dyes by Magnetite Nanoparticles Prepared by Co-Precipitation

Iron oxide nanoparticles were synthesized by co-precipitation using three different iron salt stoichiometric mole ratios. Powder X-ray diffraction patterns revealed the inverse cubic spinel structure of magnetite iron oxide. Transmission electron microscopic images showed Fe3O4 nanoparticles with different shapes and average particle sizes of 5.48 nm for Fe3O4-1:2, 6.02 nm for Fe3O4-1.5:2, and 6.98 nm for Fe3O4-2:3 with an energy bandgap of 3.27 to 3.53 eV. The as-prepared Fe3O4 nanoparticles were used as photocatalysts to degrade brilliant green (BG), rhodamine B (RhB), indigo carmine (IC), and methyl red (MR) under visible light irradiation. The photocatalytic degradation efficiency of 80.4% was obtained from Fe3O4-1:2 for brilliant green, 61.5% from Fe3O4-1.5:2 for rhodamine B, and 77.9% and 73.9% from Fe3O4-2:3 for both indigo carmine and methyl red. This indicates that Fe3O4-2:3 is more efficient in the degradation of more than one dye. This study shows that brilliant green degrades most effectively at pH 9, rhodamine B degrades best at pH 6.5, and indigo carmine and methyl red degrade most efficiently at pH 3. Recyclability experiments showed that the Fe3O4 photocatalysts can be recycled four times and are photostable.

Advanced photocatalytic materials based degradation of micropollutants and their use in hydrogen production - a review

The use of pharmaceuticals, dyes, and pesticides in modern healthcare and agriculture, along with expanding industrialization, heavily contaminates aquatic environments. This leads to severe carcinogenic implications and critical health issues in living organisms. The photocatalytic methods provide an eco-friendly solution to mitigate the energy crisis and environmental pollution. Sunlight-driven photocatalytic wastewater treatment contributes to hydrogen production and valuable product generation. The removal of contaminants from wastewater through photocatalysis is a highly efficient method for enhancing the ecosystem and plays a crucial role in the dual-functional photocatalysis process. In this review, a wide range of catalysts are discussed, including heterojunction photocatalysts and various hybrid semiconductor photocatalysts like metal oxides, semiconductor adsorbents, and dual semiconductor photocatalysts, which are crucial in this dual function of degradation and green fuel production. The effects of micropollutants in the ecosystem, degradation efficacy of multi-component photocatalysts such as single-component, two-component, three-component, and four-component photocatalysts were discussed. Dual-functional photocatalysis stands out as an energy-efficient and cost-effective method. We have explored the challenges and difficulties associated with dual-functional photocatalysts. Multicomponent photocatalysts demonstrate superior efficiency in degrading pollutants and producing hydrogen compared to their single-component counterparts. Dual-functional photocatalysts, incorporating TiO2, g-C3N4, CeO2, metal organic frameworks (MOFs), layered double hydroxides (LDHs), and carbon quantum dots (CQDs)-based composites, exhibit remarkable performance. The future of synergistic photocatalysis envisions large-scale production facilitate integrating advanced 2D and 3D semiconductor photocatalysts, presenting a promising avenue for sustainable and efficient pollutant degradation and hydrogen production from environmental remediation technologies.

Recent updates on remediation approaches of environmentally occurring pollutants using visible light-active nano-photocatalysts

Photocatalysis emerges as a potential remedy for the issue of an unreliable light source. Recognized as the most dependable and potent energy source sustaining life on Earth, sunlight offers a promising solution. Sunlight is abundant and free, operational costs associated with running photocatalytic system using nanoparticles are often lower compared to system relying on artificial light source. The escalating problem of water pollution, particularly in highly industrialized nations, necessitates effective wastewater treatment methods. These methods aim to combat elevated pollution levels, encompassing pharmaceuticals, dyes, flame retardants, and pesticide components. Advanced oxidation processes within photocatalytic wastewater treatment exhibit substantial promise for removing complex organic pollutants. Doped nanomaterials, with their enhanced properties, enable efficient utilization of light. Coupled nanomaterials present significant potential in addressing both water and energy challenges by proficiently eliminating persistent pollutants from environment. Photocatalysis when exposed to sunlight can absorb photons and generate e- h + pairs. This discussion briefly outlines the wastewater treatment facilitated by interconnected nanomaterials, emphasizing their role in water-energy nexus. In exploring the capabilities of components within a functional photocatalyst, a comprehensive analysis of both simple photocatalysts and integrated photocatalytic systems is undertaken. Review aims to provide detailed explanation of the impact of light source on photon generation and significance of solar light on reaction kinetics, considering various parameters such as catalyst dosage, pH, temperature, and types of oxidants. By shedding light on these aspects, this review seeks to enhance our understanding of intricate processes involved in photocatalysis and its potential applications in addressing contemporary environmental challenges.

Denim industry wastewater treatment by a heterogeneous solar-Fenton process catalyzed by Fe supported on recycled polyethylene terephthalate (PET) by ultrasonic modification

The textile industry is an important economic sector; however, its wastewater generates a great impact on the environment. A heterogeneous solar Fenton (HSF) process was evaluated for denim wastewater treatment. The catalyst was obtained through ultrasonic modification of recycled polyethylene terephthalate (PET) with Fe nanoparticles (PET/NPs- Fe3O4). The SFH process was optimized using surface response methodology with a face-centered central composite design considering the effects of the hydraulic retention time (10, 25, and 40 min), hydrogen peroxide dosage (500, 1000, and 1500 mg/L), and mass of the packed catalyst (4, 6 and 8 g) on the color, COD, and turbidity removal efficiencies. The operating conditions for maximum COD removal were H2O2 541.7 mg/L, HRT 33.9 min, and PET/NPs- Fe3O4 dose 7.9 g with solar radiation. The removal of 91.2% COD, 86.2% color, 90.4% turbidity, and 81.9% TOC was obtained at 14.2 kJ/L QUva. PET modification yielded 1.6 mg Fe/g PET, and the modification method does not allow Fe leaching. The effluent obtained from the SFH process complies with the maximum permissible limits in Mexican legislation in terms of COD, TOC, turbidity, and color and allows the reuse of PET.

Biodegradation mechanism of chlorpyrifos by Bacillus sp. H27: Degradation enzymes, products, pathways and whole genome sequencing analysis

Chlorpyrifos (CP) is a pesticide widely used in agricultural production. However, excessive use of CP is risky for human health and the ecological environment. Microbial remediation has become a research hotspot of environmental pollution control. In this study, the effective CP-degrading strain H27 (Bacillus cereus) was screened from farmland soil, and the degradation ratio was more than 80%. Then, the degradation mechanism was discussed in terms of enzymes, pathways, products and genes, and the mechanism was improved in terms of cell motility, secretory transport system and biofilm formation. The key CP-degrading enzymes were mainly intracellular enzymes (IE), and the degradation ratio reached 49.6% within 30 min. The optimal pH for IE was 7.0, and the optimal temperature was 25 °C. Using DFT and HPLC‒MS analysis, it was found that degradation mainly involved oxidation, hydrolysis and other reactions, and 3 degradation pathways and 14 products were identified, among which TCP (3,5,6-trichloro-2-pyridinol) was the main primary degradation product in addition to small molecules such as CO2 and H2O. Finally, the whole genome of strain H27 was sequenced, and the related degrading genes and enzymes were investigated to improve the metabolic pathways. Strain H27 had perfect genes related to flagellar assembly and chemotaxis and tended to tolerate CP. Moreover, it can secrete esterase, phosphatase and other substances, which can form biofilms and degrade CP in the environment. In addition, CP enters the cell under the action of permeases or transporters, and it is metabolized by IE. The degradation mechanism of CP by strain H27 is speculated in this study, which provided a theoretical basis for enriching CP-degrading bacteria resources, improving degradation metabolic pathways and mechanisms, and applying strain H27 to environmental pollution remediation.

Photocatalytic degradation of chlorpyrifos using Ag nanoparticles-doped g-C3N5 decorated with dendritic CdS

In this work, g-C3N5/CdS dendrite/AgNPs nanocomposite was synthesized using a mixed method consisting of hydrothermal, ultrasonic and chemistry reduction with sodium borohydride. The characterization of the as-prepared nanocomposite was done using infrared spectroscopy, X-ray, scanning electron microscopy, transmission electron microscopy, BET, and DRS methods was performed. The DRS results showed that the g-C3N5/CdS dendrite/AgNPs nanocomposite nanocomposite has a band gap of 1.08 eV. This band gap indicates the good capability of this nanocomposite as a photocatalyst. Accordingly, the photocatalytic degradation of chlorpyrifos (CPS) in was performed in an aqueous solution of the synthesized nanocomposite. The results showed that almost 95.3% of this poison, a concentration of 50 mg L-1 was degraded in the presence of 0.05 g L-1 of nanocomposite at pH = 5 in a 60 min. Hydroxide radicals and holes play a significant role in the photocatalytic process. The reusability of the nanocomposite with excellent performance in the degradation of photocatalytic toxins caused by the reduction in the electron-hole recombination and the high surface area of the nanocomposite are among the unique features of this work.

Unleashing the power of solar light: WO3 nanorods decorated onto BiVO4 dendrites for tetracycline detoxification and water splitting

The coupling of different oxide materials in a nanohybrid enables the customization of their optical and charge transport properties, leading to improved interfacial charge segregation and migration. In this study, BiVO4/WO3 (BVW), a sunlight-driven photocatalyst with distinct mole ratios was synthesized via a facile hydrothermal approach. The resultant catalyst exhibits a nanorods shape morphology decorated onto dendrite-like matrix and is studied for photocatalytic elimination of tetracycline (TC) and photoelectrocatalytic (PEC) H2 production. The effect of illumination time, solution pH, photocatalyst concentration, and mole ratios of BiVO4 to WO3 on the photocatalytic abatement of TC were tested sequentially as effective operating factors. Under optimal condition, 3:1 BiVO4:WO3 (31BVW) nanohybrid demonstrated a maximum degradation efficacy of 96.2% (rate constant ~0.0241 min-1), which is much better than its individual components and commercial TiO2-P25 (50.9%). The resultant by-products of TC decomposition were analyzed using GC-MS to explain the degradation mechanism. Moreover, as a photoanode, 31BVW showed a high photocurrent density of 0.64 mA/cm2 at 1.23 V vs RHE and a steady photocurrent for ~6 h under chronoamperometry study at1.23 V vs RHE. However, bare BiVO4 and WO3 exhibited the photocurrent density of 0.001 mA/cm2, and 0.015 mA/cm2, respectively at 1.23 V vs RHE. The Mott-Schottky analysis of 31BVW confirms their n-type behavior, with a calculated flat band potential of -0.067 V. The hydrogen production rate was theoretically calculated as 4.56 mmolcm-2 s-1 from chronoamperometric measurements. The photocatalyst's efficacy in TC degradation was further established via its reusability upto 7 cycles. Post degradation characterization of catalyst confirms its stability in lieu of practical usage. Comparative studies with existing literature revealed the superiority of reported photocatalysts in both applications. Overall, the binary BVW photocatalyst shows great potential for removing detrimental contaminants as well as H2 production via PEC water splitting due to efficient charge separation, reduced recombination, high surface area, and widen absorption window of the nanohybrid.

Utilization of the copper recovered from waste printed circuit boards as a metal precursor for the synthesis of TiO2/magnetic-MOF(Cu) nanocomposite: Application in photocatalytic degradation of pesticides in aquatic solutions

In this study, a number of leaching solutions (H2SO4, CuSO4 and NaCl) and an electrochemical method were used together for the separation of Cu from waste printed circuit boards. Secondly, the magnetic-MOF(Cu) was synthesized using the Cu recovered from waste printed circuit boards. Thereafter, TiO2/mag-MOF(Cu) composite was prepared and its photocatalytic activity was assessed in the photo degradation of two prominent organophosphorus pesticides, namely malathion (MTN) and diazinon (DZN). The catalytic structure of the MOF-based composite was fully characterized by various analyses such as XRD, SEM, EDAX, FT-IR, VSM and UV-vis. The obtained analyses confirmed the successful synthesis of TiO2/mag-MOF(Cu) composite. The synthesized composite exhibited highly efficient in the degradation of both pollutants under the following conditions: pH 7, contaminant concentration 1 mg/L, the catalyst dosage of 0.4 g/L, visible light intensity 75 mW/cm2 and reaction time of 45 min. First order kinetic model was best suited with the experimental results (R2: 0.97-0.99 for different MTN and DZN concentrations). Trapping studies revealed that superoxide radicals (O2•-) played an important role during the degradation process. Furthermore, the catalyst demonstrated a superb recovery as well as high stability over five cyclic runs of reuse. In addition, the total organic carbon (TOC) analysis showed over 83% and 85% mineralization for MTN and DZN, respectively. The combined system of TiO2/mag-MOF(Cu)/Vis also exhibited a great level of efficiency and feasibility in the treatment of tap water and treated wastewater samples. It is concluded that TiO2/mag-MOF(Cu) could be used as an excellent catalyst for the photodegradation of MTN and DZN in aqueous solution.

Facile synthesis and physicochemical characterization of κ-Carrageenan-silver-bentonite based nanocatalytic platform for efficient degradation of anionic azo dyes

Water pollution due to textile industry effluents is a global concern that warrants versatile research solutions for degrading them, and for a sustainable environment. In the present work, by using the imperative role of nanotechnology, a facile one-pot synthesis has been devised to generate κ-carrageenan capped silver nanocatalyst (CSNC), and was immobilized on 2D bentonite (BT) sheets to generate nanocatalytic platform (BTCSNC) for the degradation of anionic azo dyes. The nanocomposite(s) were physicochemically characterized using UV-Vis, DLS, TEM, FESEM, PXRD, ATR-FTIR, TGA, BET and XPS etc., to obtain insights into the nanocomposite composition, structure, stability, morphology and mechanism of interaction. The obtained CNSC are monodispersed, spherical with a size of 4 ± 2 nm, and were stabilized by the functional groups (-OH, COO‾, and SO3‾) of κ-Crg. The broadening of peak corresponding to basal plane (001) of BT montmorillonite in PXRD spectra established its exfoliation upon addition of CSNC. XPS and ATR-FTIR data evidenced the absence of covalent interactions between CSNC and BT. The catalytic efficiency of CSNC and BTCSNC composites were compared for the degradation of methyl orange (MO) and congo red (CR). The reaction followed a pseudo first order kinetics, and immobilization of CSNC on BT resulted in a 3-4 fold enhancement in degradation rates. The rates achieved for the degradation kinetics are: MO degradation within 14 s (Ka 9.86 ± 2.00 min-1), and CR degradation within 120 s (Ka of 1.24 ± 0.13 min-1). Further, a degradation mechanism has been proposed by analyzing the products identified through LC-MS. The reusability studies of the BTCSNC evidenced the complete activity of the nanocatalytic platform for six cycles, and gravitational separation method for catalyst recycling. In a nutshell, the current study provided an environmentally friendly, sizable, and sustainable nano catalytic platform" for the remediation of industrial wastewater contaminated with hazardous azo dyes".

Metal sulphides and their heterojunctions for photocatalytic degradation of organic dyes-A comprehensive review

Water pollution caused by organic dyes is one of the greatest threats to the ecosystem. The removal of dyes from water has remained a challenge for scientists. Recently, metal sulphides have emerged as a potential candidate for water remediation applications. The efficient charge transportation, greater surface-active sites, and low bandgap of metal sulphides make them an excellent choice of semiconductor photocatalysts for degradation of dyes. This review summarises the potential application of metal sulphides and their heterojunctions for the photocatalytic degradation of organic dyes from wastewater. A detailed study has been presented on the synthesis, basics of photodegradation and heterojunctions and photocatalytic activity. The effect of the use of templates, doping agents, synthesis route, and various other factors affecting the photocatalytic activity of metal sulphides have been summarised in this review. The synthesis techniques, characterisation techniques, mechanism of degradation of organic dyes by Z-scheme heterojunction photocatalyst, reusability and stability of metal sulphides, and the scope of future research are also discussed. This study indicates that Scopus-based core gathered data could be used to give an objective overview of the global dye degradation research from 2008 to 2023 (15 years). All data (articles, authors, keywords, and publications) is compiled in the Scopus database. For the bibliometric study, 1962 papers relevant to dye photodegradation by sulfide-based photocatalysts were found, and this number rises yearly. A bibliometric analysis provides a 15-year evaluation of the state-of-the-art research on the impact of metal sulfide-based photocatalysts on the photodegradation of dyes.

Heterogeneous photocatalytic oxidation for the removal of organophosphorus pollutants from aqueous solutions: A review

Organophosphorus pollutants (OPs), which are compounds containing carbon‑phosphorus bonds or phosphate derivatives containing organic groups, have received much attention from researchers because of their persistence in the aqueous environment for long periods of time and the threat they pose to human health. Heterogeneous photocatalysis has been widely applied to the removal of OPs from aqueous solutions due to its better removal effect and environmental friendliness. In this review, the removal of OPs from aqueous matrices by heterogeneous photocatalysis was presented. Herein, the application and the heterogeneous photocatalysis mechanism of OPs were described in detail, and the effects of catalyst types on degradation effect are discussed categorically. In particular, the heterojunction type photocatalyst has the most excellent effect. After that, the photocatalytic degradation pathways of several OPs were summarized, focusing on the organophosphorus pesticides and organophosphorus flame retardants, such as methyl parathion, dichlorvos, dimethoate and chlorpyrifos. The toxicity changes during degradation were evaluated, indicating that the photocatalytic process could effectively reduce the toxicity of OPs. Additionally, the effects of common water matrices on heterogeneous photocatalytic degradation of OPs were also presented. Finally, the challenges and perspectives of heterogeneous photocatalysis removal of OPs are summarized and presented.

Porous Ag3VO4/KIT-6 composite: Synthesis, characterization and enhanced photocatalytic performance for degradation of Congo Red

Novel Ag3VO4/KIT-6 nanocomposite photocatalyst has been successfully fabricated by a newly-designed simple hard-template induction process, in which the particles of Ag3VO4 were grown on the KIT-6 surface and inside the porous framework of the silica matrix. The developed porous framework nanocomposite was characterized by several techniques including N2-Physiosorption analysis. The obtained nanocomposite revealed a high surface area (273.86 m2/g) along with the possession of monoclinic Ag3VO4, which is highly responsive to visible light (with distinct intensity at about 700 nm). The UV-Vis DRS reveals that the Ag3VO4/KIT-6 photocatalyst bears a bandgap of 2.29 eV which confirms that the material has a good visible light response. The synthesized nanocomposite was tested for its superior physicochemical properties by evaluating its degradation efficiency for Congo Red (CR). The novel composite exhibited superior degradation capability of CR, reaching up to 96.49%, which was around three times the pure Ag3VO4. The detailed kinetic study revealed that the as-prepared material followed a pseudo first order kinetic model for the CR degradation. The study includes a comprehensive parametric study for the formulation of the optimized reaction conditions for photocatalytic reactions. The commercial applicability of the composite material was investigated by a regeneration and recyclability test, which revealed extraordinary results. Furthermore, the possible degradation pathway for CR was also proposed.

Reusable catalysts based on CeO2/cellulose derivative with visible light photocatalytic activity tuned by noble metal nanoparticles inclusion

For environmental preservation, it is crucial to effectively remove organic waste from water. Several approaches have been put forth, but photocatalysis stands out as a quick and effective solution. In this study, some hybrid polymeric structures that were created by photopolymerizing cellulose acetate/castor oil urethane methacrylates with embedded CeO₂ nanoparticles (NPs) and in situ photogenerated noble metal nanoparticles (Ag, Au, Pd) are characterized, and photochemically thoroughly evaluated. The effective modification of cellulose acetate with urethane methacrylate sequences and the degree of functionalization were first observed using ¹H NMR and FTIR spectra. Additionally, scanning and transmission electron microscopy, X-ray diffraction, FT-IR and UV-visible spectroscopy were utilized to analyse the resultant nanocomposites. The homogeneous dispersion of CeO₂ NPs (10-40 nm) into an organic matrix with the suitable functionalities, namely urethane and hydroxyl groups, favour the interfacial charge transfer reducing the E_g up to 2.85 eV. Moreover, noble metal nanoparticles (5-15 nm), such as Ag, Au and Pd introduction in nanocomposites, significantly lowered the E_g: 2.1 eV for CeAg samples, 1.7 eV for CeAu films and 1.5 eV for CePd films, respectively. This opens up new avenues for the creation of flexible cellulose-based photocatalysts that are active in visible light.

Adsorption and Photocatalytic Degradation of Pesticides into Nanocomposites: A Review

The extensive use of pesticides in agriculture has significantly impacted the environment and human health, as these pollutants are inadequately disposed of into water bodies. In addition, pesticides can cause adverse effects on humans and aquatic animals due to their incomplete removal from the aqueous medium by conventional wastewater treatments. Therefore, processes such as heterogeneous photocatalysis and adsorption by nanocomposites have received special attention in the scientific community due to their unique properties and ability to degrade and remove several organic pollutants, including pesticides. This report reviews the use of nanocomposites in pesticide adsorption and photocatalytic degradation from aqueous solutions. A bibliographic search was performed using the ScienceDirect, American Chemical Society (ACS), and Royal Society of Chemistry (RSC) indexes, using Boolean logic and the following descriptors: "pesticide degradation" AND "photocatalysis" AND "nanocomposites"; "nanocomposites" AND "pesticides" AND "adsorption". The search was limited to research article documents in the last ten years (from January 2012 to June 2022). The results made it possible to verify that the most dangerous pesticides are not the most commonly degraded/removed from wastewater. At the same time, the potential of the supported nanocatalysts and nanoadsorbents in the decontamination of wastewater-containing pesticides is confirmed once they present reduced bandgap energy, which occurs over a wide range of wavelengths. Moreover, due to the great affinity of the supported nanocatalysts with pesticides, better charge separation, high removal, and degradation values are reported for these organic compounds. Thus, the class of the nanocomposites investigated in this work, magnetic or not, can be characterized as suitable nanomaterials with potential and unique properties useful in heterogeneous photocatalysts and the adsorption of pesticides.

Pesticide pollutants in the environment - A critical review on remediation techniques, mechanism and toxicological impact

The excessive and unorganised utilisation of pesticides have posed negative impacts on soil and water at higher levels. Pesticides are a major class of persistent organic compounds with high resistance to natural biodegradation and enhanced tendency to bio accumulate. The severe health hazards imposed on the living organisms hinder the ecosystem and lead to chronic and irreversible health issues. Photocatalytic method is reported as a potential alternative with a variety of techniques and materials that are safer, easier, durable, cost-effective and efficient. Nanomaterials play a key role in this domain due to their versatility. In particular, nanostructured materials of organized shapes and morphological properties have gained enormous attention in research and real-time applications. Specifically, nanomaterials like nanotubes, nanorods and nanowires have unique properties and anisotropic structure that make them more suitable for treating pesticide wastes with photocatalysis. Variety of tuning methods and materials are emerging to enhance the activity of titanium and zinc based nanocatalysts in remediation methods. In the present article, four pesticides, namely, atrazine, chlorpyrifos, paraquat and naphthalene are chosen due to their common occurrence and usage in agricultural applications. These pesticides are highly toxic and need special attention to explore appropriate remediation methods. The report also details the latest innovations reported by several research studies in exploring the potential of specially synthesised nanoparticles for photocatalytic removal of pesticide pollutants from environment. For zinc-based hybrid nanomaterials, the maximum disintegration reported were 99%, 98%, 73.3% and 92.3% for atrazine, chlorpyrifos, paraquat and naphthalene, respectively.

Green synthesis of rGO-AgNP composite using Curcubita maxima extract for enhanced photocatalytic degradation of the organophosphate pesticide chlorpyrifos

In this study, Curcubita maxima leaves are used as a novel source for green synthesis of reduced graphene oxide - silver nanoparticle composite in a single pot. Characterization of the novel phyto source-driven composite was performed by UV-visible spectroscopy, Fourier transform infrared analysis, X-ray diffraction analysis, and field emission scanning electron microscopic methods. The assessment of degradation effect of chlorpyrifos by the synthesized nanocomposite was performed. The photocatalytic activity of the composite was demonstrated through two different processes as adsorption under room temperature and photocatalysis in the presence of sunlight. Different parameters such as pH, time, photocatalyst dose and pesticide concentration were optimized. The adsorption isotherms governing the photocatalytic adsorption process were investigated to predict the adsorption capacity of the synthesized nanocomposite. In addition, the results of antimicrobial activity of the nanocomposite against gram-positive, gram-negative bacteria and antifungal activity were also been found to be highly promising to utilize this composite for the removal of microbial contaminations in wastewater treatment.

Light driven Aspergillus niger-ZnS nanobiohybrids for degradation of methyl orange

Inorganic-microbial hybrid systems have potential to be sustainable, efficient and versatile chemical synthesis platforms by integrating the light-harvesting properties of semiconductors with microbial cells. Here, we demonstrate light-driven photocatalytic semiconducting Aspergillus niger cells-ZnS nanoparticles for enhanced removal of the dye methyl orange. Chemically synthesized ZnS nanoparticles exhibited a zinc blende pattern in X-ray diffraction, had a dimension of 20-90 nm with a band gap (E_bg) of 3.4 eV at 1.83 × 10¹⁸ photons/second. Biologically synthesized ZnS nanoparticles of 40-90 nm showed a hexagonal pattern in the X-ray powder diffraction spectra with an E_bg 3.7 eV at 1.68 × 10¹⁸ photons/second. At a methyl orange (MO) concentration of 100 mg/L, dosage of 0.5 × 10⁵ mol catalyst and pH 4, a 97.5% and 98% removal efficiency of MO was achieved in 90 min and 60 min for, respectively, chemically and biologically synthesized ZnS nanobiohybrids in the presence of UV-A light. The major degradation products of photocatalysis for chemically synthesized ZnS nanobiohybrids were naphtholate (C₁₀H₇O m/z 143) and hydroquinone (C₉H₅m/z 113). For the biologically synthesized ZnS nanobiohybrids, the degradation products were hydroquinone (C₉H₅m/z 113) and 2-phenylphenol (C₁₂H₁₀O m/z 170).

Recent developments in photocatalysis of industrial effluents ։ A review and example of phenolic compounds degradation

Industrial expansion and increased water consumption have created water scarcity concerns. Meanwhile, conventional wastewater purification methods have failed to degrade recalcitrant pollutants efficiently. The present review paper discusses the recent advances and challenges in photocatalytic processes applied for industrial effluents treatment, with respect to phenolic compounds degradation. Key operational parameters including the catalyst loading, light intensity, initial pollutants concentration, pH, and type and concentrations of oxidants are evaluated and discussed. Compared to the other examined controlling parameters, pH has the highest effect on the photo-oxidation of contaminants by means of the photocatalyst ionization degree and surface charge. Furthermore, major phenolic compounds derived from industrial sources are comprehensively presented and the applicability of photocatalytic processes and the barriers in practical applications, including high energy demand, technical challenges, photocatalyst stability, and recyclability have been explored. The importance of energy consumption and operational costs for realistic large-scale processes are also discussed. Finally, research gaps in this area and the suggested direction for improving degradation efficiencies in industrial applications are presented. In the light of these premises, selective degradation processes in real water matrices such as untreated sewage are proposed.

Lignocellulosic Nanocrystals from Sawmill Waste as Biotemplates for Free-Surfactant Synthesis of Photocatalytically Active Porous Silica

This work presents a new approach for more effective valorization of sawmill wastes (Beech and Cedar sawdusts), which were used as new sources for the extraction of lignin-containing and lignin-free cellulose II nanocrystals (L-CNCs and CNCs). It was shown that the properties of the extracted nanocrystals depend on the nature of the used sawdust (softwood or hardwood sawdusts). L-CNCs and CNCs derived from Beech fibers were long and thin and also had a higher crystallinity, compared with those obtained from Cedar fibers. Thanks to their interesting characteristics and their high crystallinity, these nanocrystals have been used without changing their surfaces as template cores for nanostructured hollow silica-free-surfactant synthesis for photocatalysis to degrade methylene blue (MB) dye. The synthesis was performed with a simple and efficient sol-gel method using tetraethyl orthosilicate as the silica precursor followed by calcination at 650 °C. The obtained materials were denoted as B/L-CNC/nanoSiO2, B/CNC/nanoSiO2, C/L-CNC/nanoSiO2, and C/CNC/nanoSiO2, when the used L-CNC and CNC cores are from Beech and Cedar, respectively. By comprehensive analysis, it was demonstrated that the nanostructured silica were quite uniform and had a similar morphology as the templates. Also, the pore sizes were closely related to the dimensions of L-CNC and CNC templates, with high specific surface areas. The photocatalytic degradation of MB dye was about 94, 98, 74, and 81% for B/L-CNC/nanoSiO2, B/CNC/nanoSiO2, C/L-CNC/nanoSiO2, and C/CNC/nanoSiO2, respectively. This study provides a simple route to extract L-CNCs and CNCs as organic templates to prepare nanostructured silica. The different silica structures showed excellent photodegradation of MB.

Titanium dioxide based nanocomposites - Current trends and emerging strategies for the photocatalytic degradation of ruinous environmental pollutants

Many ruinous pollutants are omnipresent in the environment and among them; pesticides are xenobiotic and pose to be a bio-recalcitrance. Their detrimental ecological and environmental impacts attract attention of environmental excerpts and the surge of stringent regulations have endows the need of a technically feasible treatment. This critical review emphasizes about the occurrence, abundance and fate of structurally distinct pesticides in different environment. The practiced remedial strategies and in particular, the advanced oxidation processes (AOPs) those utilize the photo-catalytic properties of nano-composites for the degradation of pollutants are critically discussed. Photo-catalytic degradation utilizes many composite materials at nano-scale level, wherein synthesis of nano-composites with appropriate precursors and other adjoining functional moieties are of prime importance. Therefore, suitable starter materials along with the reaction conditions are prerequisite for effectively tailoring the nano-composites. The aforementioned aspects and their customized applications are critically discussed. The associated challenges, opportunities and process economics of degradation using photo-catalytic AOP techniques are highlighted and in addition, the review tries to explain how best the photo-degradation can be a stand-alone tool with a societal importance. Conclusively, the future prospects for undertaking new researches in photo-catalytic breakdown of pollutants that can be judiciously sustainable.

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.

Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review

Over the last few years, industrial and anthropogenic activities have increased the presence of organic pollutants such as dyes, herbicides, pesticides, analgesics, and antibiotics in the water that adversely affect human health and the environment worldwide. Photocatalytic treatment is considered a promising, economical, effective, and sustainable process that utilizes light energy to degrade the pollutants in water. However, certain drawbacks like rapid recombination and low migration capability of photogenerated electrons and holes have restricted the use of photo-catalysts in industries. Hence, despite the abundance of lab-scale research, the technology is still not much commercialized in the mainstream. Several structural modifications in the photo-catalysts have been adopted to enhance the pollutant degradation performance to overcome the same. In this context, the present review article outlines the different advanced heterostructures synthesized to date for improved degradation of three major organic pollutants: antibiotics, dyes, and pesticides. Moreover, the article also emphasizes the degradation kinetics of photo-catalysts and the publication trend in the past decade along with the roadblocks preventing the transfer of technology from the laboratory to industry and new age photo-catalysts for the profitable implications in industrial sectors.

Tailored functional materials as robust candidates to mitigate pesticides in aqueous matrices-a review

Pesticides are among the top-priority contaminants, which significantly contribute to environmental deterioration. Conventional techniques are not efficient enough to remove pollutants from environmental matrices. The development of functional materials has emerged as promising candidates to remove and degrade pesticides and related hazardous compounds. Furthermore, the nanohybrid materials with unique structural and functional characteristics, such as better material anchorage, mass transfer, electron-hole separation, and charged interaction make them a versatile option to treat and reduce pollutants from aqueous matrices. Herein, we present the current progress in the development of functional materials for the abatement of toxic pesticides. The physicochemical characteristics and pesticide-removal functionalities of various metallic functional materials (e.g., zirconium, zinc, titanium, tungsten, and iron), polymer, and carbon-based materials are critically discussed with suitable examples. Finally, the industrial-scale applications of the functional materials, concluding remarks, and future directions in this important arena are given.

Boosted sono-oxidative catalytic degradation of Brilliant green dye by magnetic MgFe2O4 catalyst: Degradation mechanism, assessment of bio-toxicity and cost analysis

The magnetic MgFe₂O₄ nanoparticles (NPs) were fabricated via a facile co-precipitation technique and was comprehensively characterized by XRD, FTIR, SEM, EDX and VSM. The prepared NPs were used as catalyst in presence of ultrasound (US) irradiation to activate persulfate (PS) for generation of sulfate radicals (SO₄^·-) for boosted degradation of toxic Brilliant Green (BG) dye. Preliminary experiments revealed that highest BG dye degradation efficiency of 91.63% was achieved at MgFe₂O₄ catalyst dose of 1.0 g/L, PS dose of 300 mg/L, and initial dye concentration of 70 ppm within 15 min of US irradiation. However, only US, US in presence of PS oxidation and US in presence of MgFe₂O₄ catalyst have shown 20.2%, 83.6% and 45.0% of BG dye removal, respectively. Furthermore, response surface methodology (RSM) based central composite design (CCD) was executed to investigate the effect of interaction between independent variables such as MgFe₂O₄ catalyst dose (0.5-1.5 g/L), PS dose (150-350 mg/L), initial BG dye concentration (50-150 ppm) and US irradiation time (4-12 min). The RSM based quadratic model was used to predict the experimental data, and the prediction accuracy was confirmed by analysis of variance (R² = 0.98). The established RSM model has predicted the optimum experimental conditions as MgFe₂O₄ catalyst dose of 0.75 g/L, PS dose of 300 mg/L, initial dye concentration of 75 ppm and sonication time of 10 min. Subsequently, the treatment cost analysis was performed for all thirty experimental runs of CCD, and the RSM predicted response was found to be evidently optimum as this has delivered best economic condition (140 $/kg of BG removed) with respect to relative dye removal (%). COD removal and residual sulfate analysis have demonstrated satisfactory reduction of COD (90.31%) as well as sulfate ions (42.87 ppm) in the dye solution after treatment. Results of degradation pathway analysis portrayed the transformation of BG molecule (M/Z ratio 385) into simpler fractions with M/Z ratio of 193, 161, 73, and 61. Moreover, the toxicity analysis revealed that sono-catalytically activated PS system has efficiently reduced the toxicity level of BG dye from 93.9% to 5.13%.

Data mining for pesticide decontamination using heterogeneous photocatalytic processes

Pesticides are chemical compounds used to kill pests and weeds. Due to their nature, pesticides are potentially toxic to many organisms, including humans. Among the various methods used to decontaminate pesticides from the environment, the heterogeneous photocatalytic process is one of the most effective approaches. This study focuses on artificial intelligence (AI) techniques used to generate optimum predictive models for pesticide decontamination processes using heterogeneous photocatalytic processes. In the present study, 537 valid cases from 45 articles from January 2000 to April 2020 were filtered based on their content collected and analyzed. Based on cross-industry standard process (CRISP) methodology, a set of four classifiers were applied: Decision Trees (DT), Bayesian Network (BN), Support Vector Machines (SVM), and Feed Forward Multilayer Perceptron Neural Networks (MLP). To compare the accuracy of the selected algorithms, accuracy, and sensitivity criteria were applied. After the final analysis, the DT classification algorithm with seven factors of prediction, the accuracy of 91.06%, and sensitivity of 80.32% was selected as the optimal predictor model.

Adsorptive Separation of Brilliant Green Dye from Water by Tartaric Acid-Treated Holarrhena antidysenterica and Citrullus colocynthis Biowaste

Holarrhena antidysenterica (Ha) and Citrullus colocynthis (Cc) biowaste from indigenous Pakistan resources was used to remove toxic brilliant green (BG) dye from aqueous solutions in a batch mode. Tartaric acid chemical modification gave promising results than the nonmodified forms of biowaste. Surface characterization was carried out by FT-IR and SEM. The optimum conditions for (BG) dye elimination by Ha-tartaric acid modified (Ha-Ta) were 1.8 g, 45 minutes, 4.0 pH; 40°C, and 100 rpm and with Cc-tartaric acid modified (Cc-Ta) were 1.6 g, 45 minutes, 6.0 pH; 40°C, and 150 rpm dye solution shaking rate, which gave optimum results. Equilibrium data of raw and chemically modified biowaste followed the Langmuir model indicating monolayer chemisorption. Qmax values were found to be 55.24 mg/g, 112.35 mg/g, 50.50 mg/g, and 79.36 mg/g for Ha, Ha-Ta, Cc, and Cc-Ta. Kinetics followed the pseudo-second-order kinetic model. Dye removal involved surface and intraparticle mode of diffusion. Thermodynamic studies proved the process to be spontaneous and exothermic one. The adsorbents can be effectively utilized for the removal of toxic basic dyes, such as BG from wastewaters.

Insights into the microbial degradation and catalytic mechanisms of chlorpyrifos

Chlorpyrifos is extensively used worldwide as an insecticide to control various insect pests. Long-term and irregular applications of chlorpyrifos have resulted in large-scale soil, groundwater, sediment, and air pollution. Numerous studies have shown that chlorpyrifos and its major intermediate metabolite 3,5,6-trichloropyridinol (TCP) accumulate in non-target organisms through biomagnification and have a strong toxic effect on non-target organisms, including human beings. Bioremediation based on microbial metabolism is considered an eco-friendly and efficient strategy to remove chlorpyrifos residues. To date, a variety of bacterial and fungal species have been isolated and characterized for the biodegradation of chlorpyrifos and TCP. The metabolites and degradation pathways of chlorpyrifos have been investigated. In addition, the chlorpyrifos-degrading enzymes and functional genes in microbes have been reported. Hydrolases can catalyze the first step in ester-bond hydrolysis, and this initial regulatory metabolic reaction plays a key role in the degradation of chlorpyrifos. Previous studies have shown that the active site of hydrolase contains serine residues, which can initiate a catalytic reaction by nucleophilic attack on the P-atom of chlorpyrifos. However, few reviews have focused on the microbial degradation and catalytic mechanisms of chlorpyrifos. Therefore, this review discusses the deep understanding of chlorpyrifos degradation mechanisms with microbial strains, metabolic pathways, catalytic mechanisms, and their genetic basis in bioremediation.

Synthesis and application of magnetic materials-barium ferrite nanomaterial as an effective microwave catalyst for degradation of brilliant green

In this work, magnetic separably barium ferrite nanomaterial (BaFeO) was synthesized via citrate acid assisted sol-gel combustion method. Subsequently, X-ray diffraction (XRD), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were applied for its structural, morphological, and electromagnetic characterization. In addition, microwave (MW) absorption and thermal conversion test results indicated the BaFeO had electrothermal rather than magnetothermal conversion capacity. Meanwhile, the synthesized BaFeO showed satisfactory performance in both eliminating and mineralization of a typical triphenylmethane dye, brilliant green (BG), in MW-induced catalytic oxidation (MICO) process without extra oxidant addition. Besides, changes in element valence and content of BaFeO before and after MICO process investigated with XRD, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed its relatively stable properties. Furthermore, transition oxygen species involved in MICO process was deduced as lattice oxygen species. Then, the possible degradation pathway of BG was proposed as demethylation, open-loop of triphenylmethane, releasing one ring, formation of the benzene ring and the ultimate mineralization based on the degradation intermediates tentatively identified by gas chromatography mass spectrometry (GC/MS) and liquid chromatography mass spectrometry (LC/MS), respectively. Finally, ecotoxicity analysis by ecological structure activity relationships (ECOSAR) showed that both the acute and chronic toxicity of these intermediates were lower than that of parent BG. These findings are important regarding the development of efficient catalysts in MICO process for degradation of BG analogues in wastewater.

Recent Strategies for Environmental Remediation of Organochlorine Pesticides

The amount of organochlorine pesticides in soil and water continues to increase; their presence has surpassed maximum acceptable concentrations. Thus, the development of different removal strategies has stimulated a new research drive in environmental remediation. Different techniques such as adsorption, bioremediation, phytoremediation and ozonation have been explored. These techniques aim at either degrading or removal of the organochlorine pesticides from the environment but have different drawbacks. Heterogeneous photocatalysis is a relatively new technique that has become popular due to its ability to completely degrade different toxic pollutants—instead of transferring them from one medium to another. The process is driven by a renewable energy source, and semiconductor nanomaterials are used to construct the light energy harvesting assemblies due to their rich surface states, large surface areas and different morphologies compared to their corresponding bulk materials. These make it a green alternative that is cost-effective for organochlorine pesticides degradation. This has also opened up new ways to utilize semiconductors and solar energy for environmental remediation. Herein, the focus of this review is on environmental remediation of organochlorine pesticides, the different techniques of their removal from the environment, the advantages and disadvantages of the different techniques and the use of specific semiconductors as photocatalysts.