Structure, Photoluminescence Emissions, and Photocatalytic Activity of Ag2SeO3: A Joint Experimental and Theoretical Investigation

Novel organically linked ZnII hydrogenselenite coordination polymers: synthesis, characterization, and efficient TiO2 photosensitization for enhanced photocatalytic hydrogen production

This study focused on the solvothermal synthesis, characterization, and photocatalytic activities of two novel coordination polymers, namely [Zn(μ-HSeO3)2(bipy)]n (1) and [Zn(μ-HSeO3)2(phen)]n (2). These compounds represent the first organically linked ZnII hydrogenselenite coordination polymers. The synthesis of compounds 1 and 2 involved the addition of 2,2'-bipyridine and 1,10-phenanthroline, respectively, to SeO2 and ZnO in methanol as the solvent. The novel hydrogenselenite compounds were thoroughly characterized using spectroscopic and crystallographic methods. The photocatalytic solids (TiO2-1A and TiO2-2A) were prepared by immobilizing compounds 1-2 onto TiO2 through the sol-gel approach. These photocatalysts were then evaluated for hydrogen evolution via water splitting using a 300 W Hg/Xe lamp as the irradiation source. Among the newly synthesized photocatalytic materials, TiO2-1A demonstrated auspicious photocatalytic performance for hydrogen gas production. Its catalytic activity overcame the observed for the pure solid support TiO2 and Degussa P25 (commercial titania), making compound 1 a particularly attractive TiO2 photosensitizer. Additionally, TiO2-1A exhibited superior photocatalytic activity compared to TiO2-2A. The latter performed better than freshly prepared TiO2, approaching that of Degussa P25. These findings highlight the potential of compound 1 as an effective photosensitizer for TiO2-based photocatalysis, making it a promising candidate for applications in clean energy generation, specifically in hydrogen production by water splitting.

Towards a relationship between photoluminescence emissions and photocatalytic activity of Ag2SeO4: combining experimental data and theoretical insights

A systematic theoretical and experimental study was carried out to find a relationship between photoluminescence emissions and photocatalytic activity of Ag₂SeO₄ obtained by different synthesis methods (sonochemistry, ultrasonic probe, coprecipitation and microwave assisted hydrothermal synthesis). Experimental characterization techniques (XRD with Rietveld refinement, Raman, FTIR, UV-vis, XPS and photoluminescence spectroscopy) were used to elucidate its structural order at short, medium, and long ranges. Morphological analysis performed by FE-SEM showed distinct morphologies due to the different methods of synthesis. Based on density functional theory (DFT) calculations, it was possible to study in detail the Ag₂SeO₄ surface properties, including its surface energy, geometry, and electronic structure for the (100), (010), (001), (101), (011), (110), (111), (021), (012) and (121) surfaces. The equilibrium morphology of Ag₂SeO₄ was predicted as a truncated octahedron with exposed (111), (001), (010) and (011) surfaces. Photoluminescence emissions showed a band covering the visible spectrum, and the Ag₂SeO₄ obtained by the coprecipitation method presented the most intense band with a maximum in the red region. Photocatalytic results confirmed that Ag₂SeO₄ synthesized by the sonochemistry method is the best photocatalyst for rhodamine B degradation under UV light irradiation.

Magnetically Recyclable Fe3O4@TMU-32 Metal-Organic Framework Photocatalyst for Tetracycline Degradation Under Visible Light

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials being used as photocatalysts for efficient pollutant removal and environmental remediation. In this study, the TMU-32 MOF was synthesized as an effective photocatalyst for the photodegradation of tetracycline (TC) with 96% efficiency in 60 min under visible light. The high photocatalytic activity of the TMU-32 MOF is mainly due to its large specific surface area, which is beneficial for promoting both the adsorption of TC and the separation of the photoinduced charges. Moreover, its desired crystallinity makes it a semiconductor with an appropriate band gap energy. Next, a composite of the TMU-32 MOF with Fe₃O₄ nanoparticles (as Fe₃O₄@TMU-32) was prepared as a magnetically recyclable photocatalyst. The results showed that the photocatalytic activity of the Fe₃O₄@TMU-32 nanocomposite is slightly lower (68% degradation of TC within 60 min) than that of TMU-32 toward TC degradation since Fe₃O₄ nanoparticles are not acting as a photocatalyst and are used only to make the host photocatalyst (here, TMU-32) magnetically separable. The effects of the photocatalyst concentration and recyclability on the photodegradation of TC were studied under similar conditions. We found that the Fe₃O₄@TMU-32 composite is easily recycled without a significant loss of photocatalytic activity after being used several times, indicating the stability of the photocatalyst. Finally, a density functional theory study was also conducted to investigate the structural and electronic properties such as the band gap energy and density of states of the TMU-32 MOF and the Fe₃O₄@TMU-32 composite. Our computational results are in good agreement with the experimental ones. A photocatalytic degradation mechanism was finally proposed under visible-light photoirradiation.