Due to unique physicochemical properties, magnesium oxide nanoparticles (MgO NPs) have shown great potential for various applications, including biomedical and environmental remediation. Moreover, the physiochemical properties of MgO NPs can be tailored by metal ion doping that can be utilized in photocatalytic performance and in the biomedical field. There is limited study on the photocatalytic activity and biocompatibility of silver (Ag)-doped MgO NPs. This study was planned for facile synthesis, characterization, and photocatalytic activity of pure and silver (Ag)-doped MgO NPs. In addition, cytotoxicity of pure and Ag-doped MgO NPs was assessed in human normal umbilical vein endothelial cells (HUVECs). Pure MgO NPs and Ag-doped (1, 2, 5, and 7.5 mol%) MgO NPs were prepared via a simple sol-gel procedure. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared samples. XRD results showed the preparation of highly crystalline NPs with no impurity peaks. TEM and SEM studies indicate smooth surfaces with almost spherical morphology of MgO NPs, and Ag-doping did not change the morphology. Elemental composition study suggested that Ag is uniformly distributed in MgO particles. Intensity of the PL spectra of MgO NPs decreased with increasing the concentration of Ag dopants. In comparison to pure MgO NPs, Ag-MgO NPs showed higher degradation of methylene blue (MB) dye under UV irradiation. The improved photocatalytic activity of Ag-MgO NPs was related to the effect of dopant concentration on reducing the recombination between electrons and holes. Cytotoxicity studies showed good biocompatibility of pure and Ag-doped MgO NPs with human normal umbilical vein endothelial cells (HUVECs). These results highlighted the potential of Ag-doped MgO NPs in environmental remediation.

Visible-light-driven photoelectrochemical (PEC) and photocatalytic water splitting systems featuring heterogeneous semiconductor photocatalysts (oxynitrides, oxysulfides, organophotocatalysts) signify an environmentally friendly and promising approach for the manufacturing of renewable hydrogen fuel. Semiconducting electrode materials as the main constituents in the PEC water splitting system have substantial effects on the device’s solar-to-hydrogen (STH) conversion efficiency. Given the complication of the photocatalysis and photoelectrolysis methods, it is indispensable to include the different electrocatalytic materials for advancing visible-light-driven water splitting, considered a difficult challenge. Heterogeneous semiconductor-based materials with narrower bandgaps (2.5 to 1.9 eV), equivalent to the theoretical STH efficiencies ranging from 9.3% to 20.9%, are recognized as new types of photoabsorbents to engage as photoelectrodes for PEC water oxidation and have fascinated much consideration. Herein, we spotlight mainly on heterogenous semiconductor-based photoanode materials for PEC water splitting. Different heterogeneous photocatalysts based materials are emphasized in different groups, such as oxynitrides, oxysulfides, and organic solids. Lastly, the design approach and future developments regarding heterogeneous photocatalysts oxide electrodes for PEC applications and photocatalytic applications are also discussed.

Nanostructured photoanodes are attractive materials for hydrogen production via water photo-electrolysis process. This study focused on the incorporation of carbon quantum dots doped with nitrogen as a photosensitizer into mesoporous tungsten trioxide photoanodes (N-CQD/meso-WO₃) using a surfactant self-assembly template approach. The crystal structure, composition, and morphology of pure and N-CQD- modified mesoporous WO₃ photoanodes were investigated using scanning electron and transmission microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Due to their high surface area, enhanced optical absorption, and charge-carrier separation and transfer, the resulting N-CQD/meso-WO₃ photoanodes exhibited a significantly enhanced photocurrent density of 1.45 mA cm⁻² at 1.23 V vs. RHE under AM 1.5 G illumination in 0.5 M Na₂SO₄ without any co-catalysts or sacrificial reagent, which was about 2.23 times greater than its corresponding pure meso-WO₃. Moreover, the oxygen evolution onset potential of the N-CQD/meso-WO₃ photoanodes exhibited a negative shift of 95 mV, signifying that both the charge-carrier separation and transfer processes were promoted.