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.

Photocatalytic degradation of 2,4-dichlorophenol using nanomaterials silver halide catalysts

In this study, the photocatalytic activity of nanomaterials Ag/AgX (X = Cl, Br, I) is reported. Highly efficient silver halide (Ag/AgX where X = Cl, Br, I) photocatalysts were synthesized through a hydrothermal method. The samples were characterized using a range of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) to check their structural, morphology, textural and optical properties. In addition, the photocatalytic activity of photocatalysts was evaluated through the degradation of 2,4-dichlorophenol (2,4-DCP) under UV and visible light irradiation. XRD analysis confirmed the presence of a single-phase structure (pure phase) in the synthesized photocatalysts. SEM micrographs showed agglomeration with a non-uniform distribution of particles, which is a characteristic of surfactant-free precipitation reactions in aqueous media. The Ag/AgBr photocatalyst exhibited the best degradation efficiency, resulting in 83.37% and 89.39% photodegradation after 5 h of UV and visible light irradiation, respectively. The effect of catalyst loading, initial solution pH, and 2,4-DCP concentration was investigated for the best-performing Ag/AgBr photocatalyst. The degradation kinetics were best described by the pseudo-first-order Langmuir-Hinshelwood model. The photocatalytic capacity of Ag/AgBr decreased by 50% after five reuse cycles. SEM images revealed heightened levels of photodegradation on the catalyst surface. The study proved the feasibility of using simple synthesis methods to produce visible light active photocatalysts capable of degrading refractory phenolic pollutants in aqueous systems.

UV and solar-based photocatalytic degradation of organic pollutants from ceramics industrial wastewater by Fe-doped ZnS nanoparticles

UV and solar-based photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) as an organic contaminant in ceramics industry wastewater by ZnS and Fe-doped ZnS NPs was the focus of this research. Nanoparticles were prepared using a chemical precipitation process. The cubic, closed-packed structure of undoped ZnS and Fe-doped ZnS NPs was formed in spherical clusters, according to XRD and SEM investigations. According to optical studies, the optical band gaps of pure ZnS and Fe-doped ZnS nanoparticles are 3.35 and 2.51 eV, respectively, and Fe doping increased the number of carriers with high mobility, improved carrier separation and injection efficiency, and increased photocatalytic activity under UV or visible light. Doping of Fe increased the separation of photogenerated electrons and holes and facilitated charge transfer, according to electrochemical impedance spectroscopy investigations. Photocatalytic degradation studies revealed that in the present pure ZnS and Fe-doped ZnS nanoparticles, 100% treatment of 120 mL of 15 mg/L phenolic compound was obtained after 55- and 45-min UV-irradiation, respectively, and complete treatment was attained after 45 and 35-min solar light irradiation, respectively. Because of the synergistic effects of effective surface area, more effective photo-generated electron and hole separation efficiency, and enhanced electron transfer, Fe-doped ZnS demonstrated high photocatalytic degradation performance. The study of Fe-doped ZnS's practical photocatalytic treatment capability for removing 120 mL of 10 mg/L 2,4-DCP solution made from genuine ceramic industrial wastewater revealed Fe-doped ZnS's excellent photocatalytic destruction of 2,4-DCP from real industrial wastewater.

Actinobacteria isolated from wastewater treatment plants located in the east-north of Algeria able to degrade pesticides

The pollution of water resources by pesticides poses serious problems for public health and the environment. In this study, Actinobacteria strains were isolated from three wastewater treatment plants (WWTPs) and were screened for their ability to degrade 17 pesticide compounds. Preliminary screening of 13 of the isolates of Actinobacteria allowed the selection of 12 strains with potential for the degradation of nine different pesticides as sole carbon source, including aliette, for which there are no previous reports of biodegradation. Evaluation of the bacterial growth and degradation kinetics of the pesticides 2,4-dichlorophenol (2,4-DCP) and thiamethoxam (tiam) by selected Actinobacteria strains was performed in liquid media. Strains Streptomyces sp. ML and Streptomyces sp. OV were able to degrade 45% of 2,4-DCP (50 mg/l) as the sole carbon source in 30 days and 84% of thiamethoxam (35 mg/l) in the presence of 10 mM of glucose in 18 days. The biodegradation of thiamethoxam by Actinobacteria strains was reported for the first time in this study. These strains are promising for use in bioremediation of ecosystems polluted by this type of pesticides.

A Kinetic Study of Photocatalytic Degradation of Phenol over Titania–Silica Mixed Oxide Materials under UV Illumination

A set of titania–silica mixed oxide materials were prepared by a cosolvent-induced gelation method using ethanol and toluene as solvent and cosolvent, respectively. These materials were extensively characterized by utilizing several characterization techniques and assessed for phenol degradation under UV illumination. The degradation of phenol follows first-order kinetics, and fragmented products formed during the phenol degradation were qualitatively identified by using high performance liquid Chromatographic (HPLC) and atomic pressure chemical ionization mass spectroscopic (APCI-MS) techniques. The complete mineralization of phenol was further evidenced by the measurement of the total organic contents that remained in the solution after irradiation. The pore diameter of the materials was found to be the key factor for phenol degradation, whereas surface area and pore volume play a role among the mixed oxide materials. In addition, in the mixed oxide system there was an inverse correlation obtained with the particle size of the materials and the degradation efficiency. The smaller particle size of titania in the mixed oxide material was found to be a requirement for an effective degradation of phenol.

Facile synthesis of nano-Zn/Bi–reduced graphene oxide for enhanced photocatalytic elimination of chlorinated organic pollutants under visible light

A Zn/Bi–RGO co-assembly was synthesized by a simple co-precipitation followed by hydrothermal process, and it exhibited enhanced visible light photocatalytic activity on remediation of chlorophenols.

Enhanced photocatalytic activity of V₂O₅-ZnO composites for the mineralization of nitrophenols

In an effort to enhance the photocatalytic activity of ZnO in natural sunlight, V2O5-ZnO nanocomposites were synthesized by co-precipitation technique. The characterization of the synthesized powders by FESEM, XRD and UV-visible diffuse reflectance spectroscopy (DRS) revealed that the both V2O5 and ZnO retain their individual identity in the composites but the increasing concentration of V2O5 affect the particle size of ZnO. As estimated by photoluminescence spectroscopy, in comparison to pure ZnO, the presence of V2O5 significantly suppressed the charge carrier's recombination process. The photocatalytic activity of the synthesized powders was evaluated for the degradation/mineralization of three potential nitrophenol pollutants (2-nitrophenol, 4-nitrophenol, and 2,4-dinitrophenol). The synthesized composites showed significantly higher activity for both degradation and mineralization of nitrophenols compared to pure ZnO. The progress of the degradation process was evaluated by HPLC while mineralization was monitored by TOC analysis. The degradation/mineralization route was estimated by identifying the intermediates using GC-MS. The correlation of the experimental data revealed that the position of NO2 group in 2- and 4-nitrophenol significantly affect the rate of degradation. The identification of hydroxyl group containing intermediates in the degradation of 4-NP confirmed the formation and vital role of hydroxyl radicals in degradation process. The rapid mineralization of nitrophenol substrates pointed out superoxide anions as major contributors in degradation and mineralization process. The assessment of the release of relevant ions (NO2(-), NO3(-), ONOO(-) and NH4(+)) during the degradation process assisted in identifying the plausible interaction sites.

Photocatalytic degradation of p-cresol by zinc oxide under UV irradiation

Photocatalytic degradation of p-cresol was carried out using ZnO under UV irradiation. The amount of photocatalyst, concentration of p-cresol and pH were studied as variables. The residual concentration and mineralization of p-cresol was monitored using a UV-visible spectrophotometer and total organic carbon (TOC) analyzer, respectively. The intermediates were detected by ultra high pressure liquid chromatography (UPLC). The highest photodegradation of p-cresol was observed at 2.5 g/L of ZnO and 100 ppm of p-cresol. P-cresol photocatalytic degradation was favorable in the pH range of 6–9. The detected intermediates were 4-hydroxy-benzaldehyde and 4-methyl-1,2-benzodiol. TOC studies show that 93% of total organic carbon was removed from solution during irradiation time. Reusability shows no significant reduction in photocatalytic performance in photodegrading p-cresol.