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

A comparative study of Cu-based nanoparticles and their spin-coated films: photocatalytic degradation mechanisms and efficiencies towards malachite green and neutral red azo dyes

In this work, a comparison of the photocatalytic activity of free-standing Cu-based nanoparticle mixtures and spin-coated nanoparticle films under visible-light radiation is conducted. Herein, Cu2O, Cu2O-Cu, Cu2O-Cu3N-Cu, and Cu3N-Cu nanoparticle mixtures were successfully synthesized by a non-aqueous sol-gel route and then deposited on a glass substrate by spin-coating. The surface chemistry of the nanoparticles studied by X-ray photoelectron spectroscopy (XPS) allowed elucidating the nanoparticle synthesis mechanism. The UV-Vis absorption spectroscopy illustrates that photocatalytic activity is attributed to the high specific surface of the nanoparticles and their wider absorption range region from 500 to 1100 nm. Unlike the free-standing photocatalysts, the photocatalytic effect of spin-coated nanoparticle films enabled their facile reclamation, which solves a key issue for practical applications of the photocatalysts. The photocatalytic performances on neutral red and malachite green organic dyes were influenced by the type of visible light sources, i.e., solar simulator and natural sunlight. The results indicate that photodegradation efficiency is the highest for Cu2O nanoparticles, reaching values of 82% for neutral red and 94% for malachite green. We also demonstrate that the degradation of cationic neutral red undergoes a photoconversion to its neutral form during the degradation process, which in turn, lowers its degradation efficiency. On the other hand, higher degradation efficiency was observed on malachite green owing to its unique cationic form, soluble in aqueous solutions.

Efficient degradation of emerging pollutant-malachite green in water by pulsed discharge plasma on water surface in cooperation with Fe2+/PMS

The effective and rapid treatment of emerging pollutants in water is an essential solution to the pollution of water environment. The emerging pollutant-malachite green (MG) wastewater was treated using pulsed discharge plasma on water surface system (WSP) combining Fe2+/PMS. Compared with WSP alone, the addition of 125 μM Fe2+ and 0.5 mM peroxymonosulfate (PMS) in WSP could enhance the degradation efficiency and energy efficiency of MG by 32.8% and 9.7% respectively, with the synergistic factor of up to 2.056. UV-Vis absorption spectra and mineralization further demonstrated the synergistic effect. When the peak voltage and air flow rate were 22 kV and 0.7 L/min, the degradation efficiency and kinetic constant of MG could reach 97.9% and 0.259 min-1, respectively. MG degradation with high conductivity (1000 μS/cm) by WSP + Fe2+/PMS not only exhibited the better purification effect, but also could maintain the faster reaction rate. The active species involved in the degradation of MG in WSP + Fe2+/PMS system were mainly ·OH, SO4·-, O2·- and e*-. Furthermore, H2O2 and O3 also have a certain oxidizing effect on MG. Cl-, SO42-, HCO3- and humic acid (HA) could inhibit MG degradation to some extent, but still removed more than 80% of MG in water. The WSP + Fe2+/PMS reaction system was suitable for the treatment of other emerging pollutants in water. The results of LC-MS analysis revealed that the N-demethylation reaction and decomposition of conjugated structure were the important pathways for MG degradation. The H2O2 and acidic liquid environment provided by WSP laid the foundation for the formation of Fenton, and the introduced Fe2+ could fully undergo the Fenton and activation reaction with H2O2 and a small amount of PMS in the liquid phase, which enhanced the generation of active species, especially ·OH.

Coastal aquatic pollutants degradation using ZnCo2O4 nanorods

Water pollution has caused problems in coastal areas, rivers, lakes, and other important water sources around the world as a result of inappropriate waste management. Meanwhile, these pollutants are harmful to humans and aquatic life. Textile dye effluent methyl orange (MO) was used in this work for dye degradation studies employing nanocomposites. As a result, the importance of synthesizing pure ZnO and Co3O4 nanoparticles with composites of ZnCo2O4 (zinc cobaltite) nanorods in three various proportions (90:10, 75:25, and 50:50) is emphasized in this study. Many advanced approaches were used to assess the various features of these materials, including size and shape. Fourier transform infrared (FT-IR) spectroscopy was used to determine the vibrational modes of the materials. The absorption measurements were then carried out using UV-vis spectroscopic techniques, and the photocatalytic breakdown of MO was done under visible light irradiation. The findings revealed that pure materials were inadequate for visible light activity, resulting in decreased degradation efficiencies. Spinel cobaltite structures have potential degradation efficiency under visible light, while ZnCo2O4 (50:50) catalyst has superior degradation efficiency of 59.8% over MO. The crystallite size, morphology, functional group, absorption wavelength, and band gap all play important roles in enhancing the material's photocatalytic activity under visible light. Meanwhile, ZnCo2O4 spinel structures are crucial for increasing charge carriers and reducing electron-hole recombination. As a result, zinc cobaltite minerals are widely used in industrial dye degradation applications.

Ternary tin-doped titanium dioxide/calcium oxide (Sn-TiO2/CaO) composite as a photocatalyst for efficient removal of toxic dyes

In this study, a novel environmentally friendly route was explored for the synthesis of a tin-doped titanium dioxide/calcium oxide (Sn-TiO2/CaO) composite using eggshell as a ternary photocatalyst. The composite was prepared via a simple hydrothermal method, resulting in a unique material with potential applications in photocatalysis. The prepared photocatalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis/diffuse reflectance spectroscopy, scanning electron microscopy, X-ray fluorescence, and the Brunauer-Emmett-Teller techniques. At the same time, the Sn-TiO2/CaO composite shows excellent degradation activity for toxic dyes. The degradation efficiencies for alizarin red, bromophenol blue, methylene blue, malachite green, and methyl red are 68.38%, 62.39%, 76.81%, 86.93%, and 17.52%, respectively, under ultraviolet light irradiation for 35 min at pH = 3. In addition, the best photocatalytic degradation efficiency for zero charge (pH 7) and basic pH is for AR 98.21% and 68.38%, MR 33.01% and 17.52%, BPB 73.17% and 17.52%, MB 72.32% and 76.81%, and MG 85.59% and 86.93%, respectively, under UV light irradiation for 35 min. The increase in photocatalytic activity of the ternary photocatalyst is accredited to the enhancement of electron-hole pair separation. Simultaneous photodegradation and photoreduction of organic dyes show that ternary photocatalysts could be used in real wastewater applications.

Phytosynthesis and characterization of tin-oxide nanoparticles (SnO2-NPs) from Croton macrostachyus leaf extract and its application under visible light photocatalytic activities

Nanotechnology is rapidly becoming more and more important in today's technological world as the need for industry increases with human well-being. In this study, we synthesized SnO2 nanoparticles (NPs) using an environmentally friendly method or green method from Croton macrostachyus leaf extract, leading to the transformation of UV absorbance to visible absorbance by reducing the band gap energy. The products underwent UV, FTIR, XRD, SEM, EDX, XPS, BET, and DLS for characterization. Characterization via UV-Vis spectroscopy confirmed the shift in absorbance towards the visible spectrum, indicating the potential for enhanced photocatalytic activity under visible light irradiation. The energy band gap for as-synthesized nanoparticles was 3.03 eV, 2.71 eV, 2.61 eV, and 2.41 eV for the 1:1, 1:2, 1:3, and 1:4 sample ratios, respectively. The average crystal size of 32.18 nm and very fine flakes with tiny agglomerate structures of nanoparticles was obtained. The photocatalytic activity of the green-synthesized SnO2 nanoparticles was explored under visible light irradiation for the degradation of rhodamine B (RhB) and methylene blue (MB), which were widespread fabric pollutants. It was finally confirmed that the prepared NPs were actively used for photocatalytic degradation. Our results suggest the promising application of these green-synthesized SnO2 NPs as efficient photocatalysts for environmental remediation with low energy consumption compared to other light-driven processes. The radical scavenging experiment proved that hydroxyl radicals (_OH) are the predominant species in the reaction kinetics of both pollutant dyes under visible light degradation.

Enhanced reduction of COD in water associated with natural gas production using iron-based nanoparticles

The natural gas production industry faces the problem of the proper disposal of produced water and its treatment with significantly advanced technologies to meet the minimum quality standard for irrigation activities, commercial purposes, and consumption by living organisms. This study describes an effective method for reducing the COD (chemical oxygen demand) content in formation water using different metal oxide nanoparticles such as iron oxide (FO), iron zinc oxide (FZO), and iron vanadium oxide (FVO) nanoparticles. These nanoparticles were synthesized and fully characterized using powder X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, dynamic light scattering particle size (DLS) analysis and zeta potential analysis. The experimental results revealed that the maximum reduction of COD content was 42.18% using FVO nanoparticles with a dose of 3 g L-1 at 25 °C and pH = 6. Compared to commercial products [Redoxy and Oxy(OXYSORB)], the synthesized FO, FZO, and FVO nanoparticles demonstrated their superiority by achieving excellent results in decreasing the COD content of wastewater associated with natural gas production by more than 86%. This study introduces a promising technique for decreasing the COD content using metal oxide nanoparticles, which are eco-friendly, bio-safe, cheap, and nontoxic materials, and improving the quality of wastewater associated with natural gas production for its safe disposal through sewage and treatment plants.

Enhanced Photocatalytic Degradation of Malachite Green Dye Using Silver-Manganese Oxide Nanoparticles

Efficient and excellent nanoparticles are required for the degradation of organic dyes in photocatalysis. In this study, silver-manganese oxide nanoparticles (Ag-Mn-NPs) were synthesized through a wet chemical precipitation method and characterized as an advanced catalyst that has enhanced photocatalytic activity under sunlight irradiation. The nanoparticles were characterized using scanning electron microscopy (SEM), XRD, UV-vis light spectra, and energy-dispersive X-ray (EDX) spectroscopy, revealing their spherical and agglomerated form. The EDX spectra confirmed the composition of the nanoparticles, indicating their presence in oxide form. These bimetallic oxide nanoparticles were employed as photocatalysts for the degradation of malachite green (MG) dye under sunlight irradiation in an aqueous medium. The study investigated the effects of various parameters, such as irradiation time, catalyst dosage, recovered catalyst dosage, dye concentration, and pH, on the dye's photodegradation. The results showed that Ag-Mn oxide nanoparticles exhibited high photocatalytic activity, degrading 92% of the dye in 100 min. A longer irradiation time led to increased dye degradation. Moreover, a higher catalyst dosage resulted in a higher dye degradation percentage, with 91% degradation achieved using 0.0017 g of the photocatalyst in 60 min. Increasing the pH of the medium also enhanced the dye degradation, with 99% degradation achieved at pH 10 in 60 min. However, the photodegradation rate decreased with increasing dye concentration. The Ag-Mn oxide nanoparticles demonstrate excellent potential as a reliable visible-light-responsive photocatalyst for the efficient degradation of organic pollutants in wastewater treatment.

A State-of-Art Review of the Metal Oxide-Based Nanomaterials Effect on Photocatalytic Degradation of Malachite Green Dyes and a Bibliometric Analysis

A wide range of hard contaminants in wastewater is generated from different industries as byproducts of the organic compound. In this review, various metal oxide-based nanomaterials are employed for the photocatalytic removal of malachite green (MG) dye from wastewater. Some cost-effective and appropriate testing conditions are used for degrading these hard dyes to get higher removal efficiency. The effects of specific parameters are considered such as how the catalyst is made, how much dye is in the solution at first, how much nanocatalyst is needed to break down the dye, the initial pH of the dye solution, the type of light source used, the year of publications, and how long the dye has to be exposed to light to be removed. This study suggests that Scopus-based core collected data employ bibliometric methods to provide an objective analysis of global MG dye from 2011 to 2022 (12 years). The Scopus database collects all the information (articles, authors, keywords, and publications). For bibliometric analysis, 658 publications are retrieved corresponding to MG dye photodegradation, and the number of publications increases annually. A bibliometric study reveals a state-of-art review of metal oxide-based nanomaterials' effects on photocatalytic degradation of MG dyes (12 years).

Photo-Antibacterial Activity of Two-Dimensional (2D)-Based Hybrid Materials: Effective Treatment Strategy for Controlling Bacterial Infection

Bacterial contamination in water bodies is a severe scourge that affects human health and causes mortality and morbidity. Researchers continue to develop next-generation materials for controlling bacterial infections from water. Photo-antibacterial activity continues to gain the interest of researchers due to its adequate, rapid, and antibiotic-free process. Photo-antibacterial materials do not have any side effects and have a minimal chance of developing bacterial resistance due to their rapid efficacy. Photocatalytic two-dimensional nanomaterials (2D-NMs) have great potential for the control of bacterial infection due to their exceptional properties, such as high surface area, tunable band gap, specific structure, and tunable surface functional groups. Moreover, the optical and electric properties of 2D-NMs might be tuned by creating heterojunctions or by the doping of metals/carbon/polymers, subsequently enhancing their photo-antibacterial ability. This review article focuses on the synthesis of 2D-NM-based hybrid materials, the effect of dopants in 2D-NMs, and their photo-antibacterial application. We also discuss how we could improve photo-antibacterials by using different strategies and the role of artificial intelligence (AI) in the photocatalyst and in the degradation of pollutants. Finally, we discuss was of improving the photo-antibacterial activity of 2D-NMs, the toxicity mechanism, and their challenges.

Surface functionalized silver-doped ZnO nanocatalyst: a sustainable cooperative catalytic, photocatalytic and antibacterial platform for waste treatment

The different dyes used and discharged in industrial settings and microbial pathogenic issues have raised serious concerns about the content of bodies of water and the impact that dyes and microbes have on the environment and human health. Efficient treatment of contaminated water is thus a major challenge that is of great interest to researchers around the world. In the present work, we have fabricated functionalized silver-doped ZnO nanoparticles (Ag-doped ZnO NPs) via a hydrothermal method for wastewater treatment. X-ray photoelectron spectroscopy analysis confirmed the doping of Ag with ZnO NPs, and X-ray diffractometry analysis showed a decreasing trend in the crystallite size of the synthesized ZnO NPs with increased Ag concentration. Field emission scanning electron microscopy study of pure ZnO NPs and Ag-doped ZnO NPs revealed nanocrystal aggregates with mixed morphologies, such as hexagonal and rod-shaped structures. Distribution of Ag on the ZnO lattice is confirmed by high-resolution transmission electron microscopy analysis. ZnO NPs with 4 wt% Ag doping showed a maximum degradation of ∼95% in 1.5 h of malachite green dye (80 mg L-1) under visible light and ∼85% in 4 h under dark conditions. Up to five successive treatment cycles using the 4 wt% Ag-doped ZnO NP nanocatalyst confirmed its reusability, as it was still capable of degrading ∼86% and 82% of the dye under visible light and dark conditions, respectively. This limits the risk of nanotoxicity and aids the cost-effectiveness of the overall treatment process. The synthesized NPs showed antibacterial activity in a dose-dependent manner. The zone of inhibition of the Ag-doped ZnO NPs was higher than that of the pure ZnO NPs for all doping content. The studied Ag-doped ZnO NPs thus offer a significant eco-friendly route for the effective treatment of water contaminated with synthetic dyes and fecal bacterial load.