A green process for efficient lignin (biomass) degradation and hydrogen production via water splitting using nanostructured C, N, S-doped ZnO under solar light

Herein, we have reported the simultaneous water splitting and lignin (biomass) degradation using C, N and S-doped ZnO nanostructured materials. The synthesis of C, N and S-doped ZnO was achieved via calcination of bis-thiourea zinc acetate (BTZA) complex. Calcination of the complex at 500 °C results in the formation of C, N, and S doping in a mixed phase of ZnO/ZnS, whereas calcination at 600 °C gives a single phase of ZnO with N and S-doping, which is confirmed by XRD, XPS and Raman spectroscopy. The band gap of the calcined samples was observed to be in the range of 2.83-3.08 eV. Simultaneous lignin (waste of paper and pulp mills) degradation and hydrogen (H₂) production via water splitting under solar light has been investigated, which is hitherto unattempted. The highest degradation of lignin was observed with the sample calcined at 500 °C, i.e., C, N, S-doped ZnO/ZnS when compared to the sample calcined at 600 °C, i.e., N and S doped ZnO. The degradation of lignin confers the formation of a useful fine chemical as a by-product, i.e., 1-phenyl-3-buten-1-ol. However, excellent H₂ production, i.e., 580, 584 and 643 μmol h^-1 per 0.1 g, was obtained for the sample calcined at 500, 550 and 600 °C, respectively. The photocatalytic activity obtained is considerably higher as compared to earlier reported visible light active oxide and sulfide photocatalysts. The reusability study shows a good stability of the photocatalyst. The prima facie observations show that lignin degradation and water splitting is possible with the same multifunctional photocatalyst without any scarifying agent.