Photocatalytic activity of TiO2-ZnO/g-C3N4 nanocomposites for methylene orange and Rhodamine B dyes removal from water and photocatalytic hydrogen generation

Efficient visible-light-active ZnO/Cs0.33WO3/g-C3N4 double Z-type heterojunction photocatalyst for rhodamine B photodegradation

Developing highly efficient photocatalyst systems for the removal of cancer-causing organic dye substances from polluted water and wastewater is now in high demand because of the growing problem of contaminated water. An affordable technique was employed to create a ternary ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite with highly efficient and rapid photodegradation capabilities for degrading rhodamine B (RhB) dye. Using visible-light irradiation, the photocatalytic tests revealed that the proposed ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite is efficiently able to degrade more than 91 % of RhB dye within 15 min, 97.5 % within 20 min, and 99.9 % within 30 min, which is significantly efficient compared to sole ZnO and Cs0.33WO3. The kinetic rate constant of RhB photodegradation catalyzed by the ternary ZnO/Cs0.33WO3/g-C3N4 nanocomposite is assessed to be about 31 times faster than that of Cs0.33WO3 and about 3.5 times faster than that of ZnO. The investigation of the photodegradation mechanism suggested that the ternary ZnO/Cs0.33WO3/g-C3N4 nanocomposite follows a direct Z-scheme mechanism for charge transfer. The creation of a ternary ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite is valuable for increasing the surface area, strengthening the contact between its components, enhancing absorption capacity of visible light, increasing the generation rate of the photoexcited charge carriers, improving the separation efficiency of photogenerated charge carriers, and reducing their undesired recombination rate. As a consequence, the visible-light-mediated degradation of organic dye contaminants is significantly improved.

Photocatalytic degradation and upcycling of nitrate-rich textile wastewater to ammonia over a tandem reactor

Textile is one of the industrial sectors producing multiple types of polluting substances, including dyes and nitrate. Lately, the realization of pollutant degradation through electrochemical treatment has been applied more commonly. However, in textile wastewater a high level of organic dyes can inhibit the electrocatalytic reduction of nitrate. Hence, we construct a tandem reactor to synchronously remove the organic dyes and nitrate contaminants as well as yield the value-added ammonia product from the simulated textile wastewater. The tandem reactor shows impressive efficiency towards photocatalytic decomposing methylene blue (MB), methyl orange (MO) and methyl violet (MV) (~ 100%) coupled with NO3--to-NH3 conversion (maximum NH3 evolution value of 44.3 μg cm-2) under different bias potentials. Liquid chromatography mass spectroscopy (LC-MS) has been applied to understand the dyes degradation pathways. The dyes are oxidized by active species hydroxyl radicals ·OH and h+ under irradiation. The electrons are transferred to the cathode for nitrate reduction. In addition, the tandem reactor displays favorable energy consumption for the simulated textile wastewater treatment. Moreover, mung bean germination experiments were complemented for toxicity assessment of the system. This study presents a conceptual tandem reactor for the synergistic regulation of complex pollutants removal processes, highlighting the potential of photoelectrochemical (PEC) and electrochemical catalysis coupled to advance sustainable wastewater management technologies.

Contribution of Copper Slag to Water Treatment and Hydrogen Production by Photocatalytic Mechanisms in Aqueous Solutions: A Mini Review

Hydrogen has emerged as a promising energy carrier, offering a viable solution to meet our current global energy demands. Solar energy is recognised as a primary source of renewable power, capable of producing hydrogen using solar cells. The pursuit of efficient, durable, and cost-effective photocatalysts is essential for the advancement of solar-driven hydrogen generation. Copper slag, a by-product of copper smelting and refining processes, primarily consists of metal oxides such as hematite, silica, and alumina. This composition makes it an attractive secondary resource for use as a photocatalyst, thereby diverting copper slag from landfills and generating 0.113 μmol/g h of hydrogen, as noted by Montoya. This review aims to thoroughly examine copper slag as a photocatalytic material, exploring its chemical, physical, photocatalytic, and electrochemical properties. Additionally, it evaluates its suitability for water treatment and its potential as an emerging material for large-scale solar hydrogen production.

Plant-mediated Z-scheme ZnO/TiO2-NCs for antibacterial potential and dye degradation: experimental and DFT study

Efficient separation of electron-hole pairs remains pivotal in optimizing photogenerated carrier functionality across diverse catalytic and optoelectronic systems. This study presents the fabrication of a novel hollow direct Z-scheme photocatalyst, ZnO/TiO2. A thorough analysis encompassing various techniques such as Ultraviolet-Visible Spectroscopy (UV-Vis), X-ray Diffraction (XRD), Transmission electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), and Energy-Dispersive X-ray Spectroscopy (EDX) provided detailed insights into the complex material characteristics of the ZnO/TiO2 heterojunction catalyst. The findings revealed coexisting anatase TiO2 and wurtzite ZnO phases, each retaining distinct attributes within the nanocomposites (NCs) structure. The study showcased the photocatalytic efficacy of ZnO/TiO2-NCs in decomposing Methylene Blue and Acridine Orange under UV irradiation, correlated with their underlying structures. Enhanced degradation of these dyes resulted from the establishment of a direct Z-scheme heterojunction between ZnO and TiO2. Employing Density Functional Theory (DFT) using Quantum ESPRESSO, this research analyzed phase diagrams and band structures, elucidating electronic properties and structural correlations. The study characterized a ZnO/TiO2 composite, revealing a band gap of 3.1-3.3 eV through UV-Visible spectroscopy and confirming its formation without impurity phases via XRD analysis. TEM and EDX showed uniform element dispersion (Zn: 27%, Ti: 29.62%, C: 5.03%, O: 38.35%). Computational analysis using DFT indicated a reduction in stable phases with increasing temperature. Enhanced dye degradation was observed (MB: 88.9%, AO: 84%), alongside significant antibacterial activity. In the future we predict that research will focus on development of scaled up production and photocatalytic activity through surface modification, while unveiling mechanistic insights and environmental applicability for multifunctional use in water treatment and antibacterial applications, leading to further advancement of the field.