Facile ball-milling synthesis of TiO2 modified ZnO for efficient photocatalytic removal of atmospheric nitric oxide gas under solar light irradiation

Rapid fabrication of MgO@g-C3N4 heterojunctions for photocatalytic nitric oxide removal

Nitric oxide (NO) is an air pollutant impacting the environment, human health, and other biotas. Among the technologies to treat NO pollution, photocatalytic oxidation under visible light is considered an effective means. This study describes photocatalytic oxidation to degrade NO under visible light with the support of a photocatalyst. MgO@g-C₃N₄ heterojunction photocatalysts were synthesized by one-step pyrolysis of MgO and urea at 550 °C for two hours. The photocatalytic NO removal efficiency of the MgO@g-C₃N₄ heterojunctions was significantly improved and reached a maximum value of 75.4% under visible light irradiation. Differential reflectance spectroscopy (DRS) was used to determine the optical properties and bandgap energies of the material. The bandgap of the material decreases with increasing amounts of MgO. The photoluminescence spectra indicate that the recombination of electron-hole pairs is hindered by doping MgO onto g-C₃N₄. Also, NO conversion, DeNOx index, apparent quantum efficiency, trapping tests, and electron spin resonance measurements were carried out to understand the photocatalytic mechanism of the materials. The high reusability of the MgO@g-C₃N₄ heterojunction was shown by a five-cycle recycling test. This study provides a simple way to synthesize photocatalytic heterojunction materials with high reusability and the potential of heterojunction photocatalysts in the field of environmental remediation.

Solar-Energy-Driven Cu-ZnO/TiO2 Nanocomposite Photocatalyst for the Rapid Degradation of Congo Red Azo Dye

This study effectively demonstrates the sonochemical synthesis of visible-light-responsive Cu-ZnO/TiO2 ternary Z-scheme heterojunction nanocomposite photocatalyst. The as-prepared photocatalyst was comprehensively characterized by techniques including high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis (EDX) and elemental dot mapping, X-ray diffraction (XRD), UV-Vis-diffuse reflectance spectroscopy (UV-Vis-DRS), Brunauer–Emmett–Teller (BET) surface area, and Fourier-transform infrared spectroscopy (FTIR). The photocatalytic activity of the Cu-ZnO/TiO2 nanocomposite photocatalyst was assessed for the degradation of Congo red (CR), an azo dye, under direct sunlight. The pseudo-first-order rate constant for CR degradation was found to be 0.09 min−1. The outcome implies that the synthesised nanocomposite photocatalyst demonstrates excellent photocatalytic activity under direct sunlight as 98% degradation of CR dye was achieved in approximately 20 min using the Cu-ZnO/TiO2 nanocomposite photocatalyst. Furthermore, its high recoverability and reusability of five times indicate its excellent catalytic potential.

Enhancing Green Product Generation of Photocatalytic NO Oxidation: A Case of WO3 Nanoplate/g-C3N4 S-Scheme Heterojunction

Nitric oxide (NO) removal by photocatalytic oxidation over g-C₃N₄ has achieved more efficient results. However, there is a concern about the high NO-to-NO₂ conversion yield of products, which is not suitable for the photocatalytic NO reaction. In this study, we modify g-C₃N₄ by WO₃ nanoplates for the first time for photocatalytic NO oxidation over a WO₃/g-C₃N₄ composite to enhance the green product selectivity under atmospheric conditions. The results indicate that the photocatalytic efficiency for NO removal by the WO₃/g-C₃N₄ composite is drastically improved and achieves 52.5%, which is approximately 2.1 times higher than that of pure g-C₃N₄. Significantly, the green product (NO₃^-) selectivity of the WO₃/g-C₃N₄ composite is 8.7 times higher than that of pure g-C₃N₄, and the selectivity remained high even after five cycles of photocatalytic tests. We also conclude that the enhanced green product selectivity of photocatalytic NO oxidation by the WO₃/g-C₃N₄ composite is due to the separation and acceleration of the photogenerated charges of the WO₃/g-C₃N₄ S-scheme heterojunction.