Fly ash-, foundry sand-, clay-, and pumice-based metal oxide nanocomposites as green photocatalysts

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Sunlight active cellulose/g-C3N4/TiO2nano-photocatalyst for simultaneous degradation of methylene blue dye and atenolol drug in real wastewater

The paper critically addresses two contemporary environmental challenges, the water crisis and the unrestricted discharge of organic pollutants in waterways together. An eco-friendly method was used to fabricate a cellulose/g-C3N4/TiO2photocatalytic composite that displayed a remarkable degradation of methylene blue dye and atenolol drug under natural sunlight. Introducing graphitic carbon nitride (g-C3N4) onto pristine TiO2improved hybrid material's photonic efficacy and enhanced interfacial charge separation. Furthermore, immobilizing TiO2/g-C3N4on a semi-interpenetrating cellulose matrix promoted photocatalyst recovery and its reuse, ensuring practical affordability. Under optimized conditions, the nano-photocatalyst exhibited ∼95% degradation of both contaminants within two hours while retaining ∼55% activity after ten cycles demonstrating a promising photostability. The nano-photocatalyst caused 66% and 57% reduction in COD and TOC values in industrial wastewater containing these pollutants. The photocatalysis was fitted to various models to elucidate the degradation kinetics, while LC-MS results suggested the mineralization pathway of dye majorly via ring opening demethylation. >98% disinfection was achieved againstE. coli(104-105CFU·ml-1) contaminated water. This study thus paves multifaceted strategies to treat wastewater contaminants at environmental levels employing nano-photocatalysis.

Modification of the electronic structure of g-C3N4 using urea to enhance the visible light-assisted degradation of organic pollutants

Graphitic carbon nitride has been proven to be a good candidate for using solar energy for photo-induced pollutant degradation. However, the high photo-induced holes-electron recombination rate, unfavorable morphology, and textural properties limited their application. In this study, we present a novel g-C3N4 with a novel electronic structure and physiochemical properties by introducing a single nitrogen in the graphitic network of the g-C3N4 through a novel method involving step-by-step co-polycondensation of melamine and urea. Through extensive characterization using techniques such as XPS, UPS-XPS, Raman, XRD, FE-SEM, TEM, and N2 adsorption-desorption, we analyze the electronic and crystallographic properties, as well as the morphology and textural features of the newly prepared g-C3N4 (N-g-C3N4). This material exhibits a lower C/N ratio of 0.62 compared to conventional g-C3N4 and a reduced band gap of 2.63 eV. The newly prepared g-C3N4 demonstrates a distinct valance band maxima that enhances its photo-induced oxidation potential, improving photocatalytic activity in degrading various organic pollutants. We thoroughly investigate the photocatalytic degradation performance of N-g-C3N4 for Congo red (CR) and sulfamethoxazole (SMX), and removal of up to 90 and 86% was attained after 2 h at solution pH of 5.5 for CR and SMX. The influence of different parameters was examined to understand the degradation mechanism and the influence of reactive oxygenated species. The catalytic performance is also evaluated in the degradation of various organic pollutants, and it showed a good performance.

Incorporation of g-C3N4 nanosheets and CuO nanoparticles on polyester fabric for the dip-catalytic reduction of 4 nitrophenol

In the present work, we present the preparation of a new emerged heterogeneous catalyst (PE/g-C3N4/CuO) by in situ deposition of copper oxide nanoparticles (CuO) over the graphitic carbon nitride (g-C3N4) as the active catalyst and polyester (PE) fabric as the inert support. The synthesized sample (PE/g-C3N4/CuO) "dip catalyst" was studied by using various analytical techniques (Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy and dispersive X-ray spectroscopy (SEM/EDX), and transmission electron microscopy (TEM). The nanocomposite is utilized as heterogeneous catalysts for the 4-nitrophenol reduction in the presence of NaBH4, in aqueous solutions. According to experimental results, PE/g-C3N4/CuO with a surface of 6 cm2 (3 cm × 2 cm) demonstrated the catalyst exhibit excellent catalytic activity with 95% reduction efficiency for only 4 min of reaction and an apparent reaction rate constant (Kapp) of 0.8027 min-1. Further evidence that this catalyst based on prepared PE support can be a good contender for long-lasting chemical catalysis comes from the remarkable stability after 10 repetitions reaction cycles without a noticeably loss in catalytic activity. The novelty of this work consists to fabricate of catalyst based of CuO nanoparticles stabilized with g-C3N4 on the surface of an inert substrate PE, which results in an heterogenous dip-catalyst that can be easily introduced and isolated from the reaction solution with good retention of high catalytic performance in the reduction of 4-nitrophenol.

A Review on Resource Utilization of Spent V-W-Ti Based Selective Catalytic Reduction Catalysts

To address the environmental pollution caused by nitrogen oxides, V₂O₅-WO₃/TiO₂ is widely used as a catalyst based on selective catalytic reduction (SCR) technology. However, spent SCR catalysts pose a potential hazard to the environment due to the presence of heavy metals. This problem continues to plague countries with predominantly thermal power generation, and landfills as the dominant disposal method wastes significant metal resources. Previous research into the recovery of these metal resources has received considerable attention. Here, we summarise the methods of recovery and find that research trends are beginning to move towards improving the added value of recovered products. One very promising application is photocatalysts; however, the atomic efficiency of current methods is not satisfactory. Therefore, this review first focuses on the regeneration of spent SCR catalysts and the processes used for elemental extraction to clarify what forms of V, W and Ti can be obtained from existing processes. This is followed by providing directions for the conversion of spent SCR catalysts into photocatalysts with improvements based on such processes. From a different perspective, this also provides a new resource for photocatalysts and is expected to significantly reduce the cost of photocatalyst production.

Nickel adsorption from waters onto Fe3O4/sugar beet pulp nanocomposite

In this study the magnetic nanocomposite material was synthesized with Fe₃O₄ impregnated to sugar beet pulp using chemical precipitation technique. Ni(II) removal performance of magnetic nanocomposite was investigated under different environmental conditions such as contact time, adsorbent dose, pH, initial heavy metal concentration, etc. The experimental studies have shown that, 81.2% Ni(II) removal efficiency was achieved at optimal conditions (25 mg/L initial Ni(II) concentration at 40 minute contact time, 200 rpm shaking speed, 5 g/L nanocomposite dose and pH 6.6). Freundlich and Langmuir isotherm experiments were performed and correlation coefficients were determined as 94.5% and 99.4%, respectively. The maximum adsorption capacity of material was achieved as 9.36 mg/g. These findings indicate that the adsorption that takes place is a monolayer process. The results of the pseudo-second order kinetic model (R² = 0.9947) indicate the chemisorptions process is used for Ni(II) removal using the electrostatic interaction. Thermodynamic studies illustrated that Ni(II) adsorption onto nanocomposite are exothermic and causes a decrease in the entropy. The adsorption of Ni(II) ions is non-spontaneous except for at low temperature and low initial concentrations. Nanocomposite characterization was illuminated with XRD, FT-IR, BET, TGA, TEM, SEM/EDX analysis.

Natural Volcanic Material as a Sustainable Photocatalytic Material for Pollutant Degradation under Solar Irradiation

Recently, photocatalysis has been demonstrated as a solid approach for efficient wastewater cleaning. Using natural materials as photocatalysts means a promising solution to develop green catalysts for environmental purposes. This work aimed to study the suitability of a natural volcanic material (La Gomera, Canary Islands, Spain) as a photocatalytic material for the degradation of pollutants in wastewater with solar energy. After analysing the properties of the natural material (BET surface 0.188 m²/g and band-gap of 3 eV), the photocatalytic activity was evaluated at laboratory and pilot plant scale for the degradation of methylene blue (MB) in water (50 mg L⁻¹), at 20 °C, during a period of 4 h, under UV/Vis light and solar irradiation. Photolytic and adsorption studies were developed to distinguish the photocatalytic contribution to the wastewater decontamination process by photocatalysis. Our results enable us to determine the viability of black sand as a photocatalytic material activated by solar irradiation (photodegradation of MB up to 100% by using solar energy), developing a natural and green photocatalytic system with significantly high potential for application in a sustainable wastewater cleaning process.