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Synthesis, characterization, and application of TiO2-SnS2/GO-RGO-based material for photocatalytic H2 production under Solar light irradiation

With the increased growth of the world economy and the instability of energy supply using non- renewable raw materials, it is necessary to enhance the use of renewable energy sources. Among alternative fuels, hydrogen (H2) is often called the „fuel of the future“. Since most of the commercially available H2 is produced through the CO2-intensive process, the European Commission has published in July 2020 „Hydrogen strategy for a climate-neutral Europe“, where hydrogen is labelled as “green“ if it is produced through processes that as input energy use the one generated from renewable sources. Among the scientific community, a very ambitious way to produce “green“ hydrogen is photocatalytically from water under solar light irradiation. In such processes, one of the most efficient and studied materials is titanium dioxide (TiO2), which photoactivity can be improved through material engineering solutions based on composites formation. In this work, separately synthesized TiO2 and tin dichalcogenide (SnS2) were coupled together with graphene oxide (GO) obtained by the modified Hummers method and subjected to solvothermal synthesis to get TiO2-SnS2/GO-RGO ternary photoactive material. Through the synthesis, GO was considerably reduced (RGO). Materials with an SnS2 content of 5 and 10% wt. and 0.1% wt. of GO- RGO were prepared and subjected to the following characterization techniques: FTIR, TGA, UV-Vis diffuse reflectance spectroscopy (DRS), XRD and photoelectrochemical characterization (OCP, EIS, Mott-Schottky measurements), as well as H2 production experiment in a sealed quartz-covered photoreactor with 20% vol. TEOA solution under 300W Xe lamp irradiation for 5 hours. Based on UV-Vis analysis and Mott Schottky measurements, investigated materials have appropriate conduction band (CB) positions – more negative than 0V vs. standard H2 electrode (SHE) that is required for H2 generation. The band gap (Eg) values of tested TiO2-based composites were calculated from DRS measurements with the use of Kubelka-Munk transformations. Results have shown that all investigated ternary composites (TiO2- SnS2/GO-RGO) show visible light absorption, while the good sensitivity of photocatalyst to visible light was also confirmed by monitoring OCP in chopped LED light. The n-type conductivity of the photocatalysts was proved with the Mott-Schottky plot, which indicated that electrons represent major charge carriers. GO-RGO inside TiO2/SnS2 composites (0.1% wt.) increases photoresponse and reduces the charge recombination rate that is calculated from normalized OCP decay curves after turning off LED irradiation. The presence of the GO-RGO in the photocatalytic materials affected the increase in H2 production, compared to composites without GO-RGO - TiO2-SnS2 (5% wt.) and TiO2-SnS2 (10% wt.). The highest H2 production amount of 95 μmol/hLgphotocatalyst was recorded for TiO2-SnS2 (5% wt.)/0.1% wt. GO-RGO. Proven H2 production from 20% vol. TEOA solution opens the possibility of testing the production of H2 form an aqueous solution containing organic pollutants, thus enabling simultaneous energy recovery, as well as the decomposition of organic pollutants.

Synthesis, characterization, TiO2-SnS2/GO-RGO, hydrogen production

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