An efficient ternary photocatalyst Ag/ZnO/g-C3N4 for degradation of RhB and MG under solar radiation

An insight decipher on photocatalytic degradation of microplastics: Mechanism, limitations, and future outlook

Plastic material manufacturing and buildup over the past 50 years has significantly increased pollution levels. Microplastics (MPs) and non-biodegradable residual plastic films have become the two most pressing environmental issues among the numerous types of plastic pollution. These tiny plastic flakes enter water systems from a variety of sources, contaminating the water. Since MPs can be consumed by people and aquatic species and eventually make their way into the food chain, their presence in the environment poses a serious concern. Traditional technologies can remove MPs to some extent, but their functional groups, stable covalent bonds, and hydrophobic nature make them difficult to eliminate completely. The urgent need to develop a sustainable solution to the worldwide contamination caused by MPs has led to the exploration of various techniques. Advanced oxidation processes (AOPs) such as photo-catalytic oxidation, photo-degradation, and electrochemical oxidation have been investigated. Among these, photocatalysis stands out as the most promising method for degrading MPs. Photocatalysis is an environmentally friendly process that utilizes light energy to facilitate a chemical reaction, breaking down MPs into carbon dioxide and water-soluble hydrocarbons under aqueous conditions. In photocatalysis, semiconductors act as photocatalysts by absorbing energy from a light source, becoming excited, and generating reactive oxygen species (ROS). These ROS, including hydroxyl radicals (•OH) and superoxide ions ( [Formula: see text] ), play a crucial role in the degradation of MPs. This extensive review provides a detailed exploration of the mechanisms and processes underlying the photocatalytic removal of MPs, emphasizing its potential as an efficient and environmentally friendly approach to address the issue of plastic pollution.

The Synthesis of carbon dots//zincoxide (CDs/ZnO-H400) by using hydrothermal methods for degradation of ofloxacin antibiotics and reactive red azo dye (RR141)

The development of photocatalytic powders to remove contaminants from air solutions is an important field of research in the field of environmental conservation. CD/ZnO-H400, a heterogeneous photocatalytic production, is utilized to degrade the reactive red dye and the antibiotic ofloxacin found in wastewater. This study explains the synthesis of carbon dots (CDs) derived from coconut air and zinc oxide (ZnO) using a hydrothermal method at a temperature of 180 °C with a duration of 4 h and subsequently calcinated at a 400 °C temperature for 4 h. This shows a significant improvement in photocatalytic performance due to improved delivery efficiency at the interface. The cost-efficient use of solar energy allows the comprehensive elimination of harmful pollutants through detoxification. The removal of the contaminant takes place through the first-order reaction, with RR141 showing the highest constant rate at 0.03 min-1, while ofloxacin has a constant speed at 0.01 min-1. The photocatalytic stability is measured after five cycles. The study also tested the impact of sunlight on degradation, showing a degrading rate of 98% for RR141 and 96% for ofloxacin. This study displays a new catalyst powder synthesized from carbon dots derived from the air, coconut and ZnO, showing remarkable photoactivity to completely remove harmful dyes and antibiotics from the surrounding environment.

Cellulose nanocrystals doped silver nanoparticles immobilized agar gum for efficient photocatalytic degradation of malachite green

The present study involves the synthesis of green functional material based on the silver nanoparticle (Ag NPs) doped cellulose nanocrystals (CNC) immobilized agar gum (AA) biopolymer using chemical coprecipitation method. The stabilization of Ag NPs in cellulose matrix and functionalization of the synthesized material through agar gum was analyzed using various spectroscopic techniques such as Fourier Transform Infrared (FTIR), Scanning electron microscope (SEM), Energy X-Ray diffraction (EDX), Photoelectron X-ray (XPS), Transmission electron microscope (TEM), Selected area energy diffraction (SAED) and ultraviolet visible (UV-Vis) spectroscopy. The XRD results suggested that the synthesized AA-CNC@Ag BNC material is composed of 47 % crystalline and 53 % amorphous nature having distorted hexagonal structure due to capping of Ag NPs by amorphous biopolymer matrix. The Debye-Scherer crystallite sized was calculated as 18 nm which is found in close agreement with TEM analysis (19 nm). The SAED yellow fringes simulates the miller indices values with XRD patterns and supported the surface functionalization of Ag NPs by biopolymer blend of AA-CNC. The XPS data supported the presence of Ag⁰ as indexed by Ag3d orbital corresponding to Ag3d_3/2 at 372.6 eV and Ag3d_5/2 at 366.6 eV. The surface morphological results revealed a flaky surface of the resultant material having well distributed Ag NPs in the matrix. The EDX and atomic concentration results given by XPS supported the presence if C, O and Ag in the bionanocomposite material. The UV-Vis results suggested that the material is both UV and visible light active having multiple SPR effects with anisotropy. The material was explored as a photocatalyst for remediation of wastewater contaminated by malachite green (MG) using advance oxidation process (AOP). Photocatalytic experiments were performed in order to optimize various reaction parameters such as irradiation time, pH, catalyst dose and MG concentration. The obtained results showed that almost 98.85 % of MG was degraded by using 20 mg of catalyst at pH 9 for 60 min of irradiation. The trapping experiments revealed that ^•O₂^- radicals played primary role in MG degradation. This study will provide new possible strategies for the remediation of wastewater contaminated by MG.

Doped graphitic carbon nitride (g-C3N4) catalysts for efficient photodegradation of tetracycline antibiotics in aquatic environments

Tetracyclines (TCs) antibiotics are very common and often used in both human and veterinary medicines. More than 75% of TCs are excreted in an active condition and released into the environment, posing a risk to the ecosystem and human health. Residual antibiotics are in global water bodies, causing antibiotic resistance and genotoxicity in humans and aquatic organisms. The ever-increasing number of multi-resistant bacteria caused by the widespread use of antibiotics in the environment has sparked a renewed interest in developing more sustainable antibiotic degradation processes. In this regard, photodegradation technique provides a promising solution to resolve this growing issue, paving the way for complete antibiotic degradation with the generation of non-toxic by-products. As a fascinating activity towards visible light range shown by semiconductor, graphitic carbon nitride (g-C₃N₄) has a medium bandgap, non-toxicity, chemically stable complex, and thermally great strength. Recent studies have concentrated on the performance of g-C₃N₄ as a photocatalyst for treating wastewater. Pure g-C₃N₄ exhibits limited photocatalytic activity due to insufficient sunlight usage, small surface area, and a high rate of recombination of electron and hole ([Formula: see text] & [Formula: see text]) pairs created in photocatalytic activity. Doping of g-C₃N₄ is a very effective method for improving the activity as element doped g-C₃N₄ shows excellent bandgap and electronic structure. Doping significantly broadens the light-responsive range and reduces recombination of e^- & h⁺ pairs. Under above context, this review provides a systematic and comprehensive outlook of designing doped g-C₃N₄ as well as efficiency for TCs degradation in aquatic environment.

Noble metal-free doped graphitic carbon nitride (g-C3N4) for efficient photodegradation of antibiotics: progress, limitations, and future directions

Graphitic carbon nitride (g-C₃N₄) is well recognised as one of the most promising materials for photocatalytic activities such as environmental remediation via organic pollution elimination. New methods of nanoscale structure design introduce tunable electrical characteristics and broaden their use as visible light-induced photocatalysts. This paper summarises the most recent developments in the design of g-C₃N₄ with element doping. Various methods of introducing metal and nonmetal elements into g-C₃N₄ have been investigated in order to simultaneously tune the material's textural and electronic properties to improve its response to the entire visible light range, facilitate charge separation, and extend charge carrier lifetime. The degradation of antibiotics is one of the application domains of such doped g-C₃N₄. We expect that this research will provide fresh insights into clear design methods for efficient photocatalysts that will solve environmental challenges in a sustainable manner. Finally, the problems and potential associated with g-C₃N₄-based nanomaterials are discussed. This review is expected to encourage the ongoing development of g-C₃N₄-based materials for greater efficiency in photocatalytic antibiotic degradation.

Ag-Modified ZnO for Degradation of Oxytetracycline Antibiotic and Reactive Red Azo Dye

It is known that low electron-hole separation efficiency is the major disadvantage influencing low photoactivity of the UV-active ZnO photocatalyst. To solve this drawback, the excellent fabrication technique has been used to disperse silver metal on ZnO surface. In this study, an addition of silver content up to 15 wt% was carried out. The 5Ag-ZnO sample, comprising 5 wt% of silver metal, displayed a hexagonal wurtzite structure, and a band gap of 3.00 eV, with high sunlight-active photocatalytic performance of 99-100% and low photo-corrosion problem. The complete degradation of oxytetracycline (OTC) antibiotic and reactive red dye 141 (RR141) dye under natural sunlight was achieved. The highest rate constant of 0.061 min-1 was detected. The enhancement of the performance is mainly due to lowering of the electron-hole recombination rate. Dispersion of silver on ZnO causes the generation of the Schottky barrier at the interface between Ag and ZnO, so that improvement of quantum efficiency and enhancement of the resultant photoactivity could be expected. Furthermore, good distribution of metallic silver also causes a red shift in absorption of light toward the visible spectrum. This is strongly attributed to the surface plasmon resonance effect, which occurred after successful decoration of the noble metal on ZnO. The photocatalyst, with great structural stability, still maintains high photocatalytic efficiency even after five times of use, implying its excellent cycling ability. The present finding offers a new road to generate a silver decorated ZnO photocatalyst for the complete removal of dye and antibiotics contaminated in the environment.

Enhanced photocatalytic degradation of malachite green dye by highly stable visible-light-responsive Fe-based tri-composite photocatalysts

A novel visible-light-sensitive ZnVFeO₄ photocatalyst has been fabricated by the precipitation method at different pH values for the enhanced photocatalytic degradation of malachite green (MG) dye as a representative pollutant under visible light irradiation at neutral pH conditions. The structure and optical characteristics of the prepared photocatalysts were investigated by XRD, FTIR, N2 adsorption-desorption, TEM, diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) analyses. In addition, the photocatalytic activity of ZnVFeO₄ photocatalysts superior the efficiency to be more than that of the mono and bi-metal oxides of iron and iron zinc oxides, respectively. The best sample, ZnVFeO₄ at pH 3, significantly enhances the degradation rate under visible light to be 12.7 × 10^-3 min^-1 and can retain a stable photodegradation efficiency of 90.1% after five cycles. The effect of the catalyst dose and the initial dye concentration on the photodegradation process were studied. This promising behavior under visible light may be attributed to the low bandgap and the decreased electron-hole recombination rate of the ZnVFeO₄ heterostructures. The scavenger experiment confirmed that the hydroxyl radicals induced the MG photodegradation process effectively. Hence, the ZnVFeO₄ is a reliable visible-light-responsive heterostructure photocatalyst with excellent potential for the photodegradation of organic pollutants in wastewater treatment.