Development of photoactive ZnS-SiO₂ composites on biogenic silica matrix for organic pollutant degradation

Sulfide ZnS-SiO₂ composite photocatalysts with biogenic silica matrix were prepared by sol-gel method based on wet gel and xerogel. FT-IR, SEM, XRD, EDXRF, UV-Vis, and XPS methods were systematically used to characterize the obtained materials. The use of support allowed to obtain stable porous (S_BET = 79-105 m² g^-1; V_pore = 0.25-0.17 cm³·g^-1) ZnS-SiO₂ photocatalysts in aqueous solutions. Zn²⁺ content in methyl orange solution after its degradation was 0.4 MPC. ZnS-SiO₂ composites had 3.68-3.70 eV band gap. The obtained materials were photoactive under different irradiation conditions (sunlight, UV-light, Xenon light, visible light) due to effective separation of charge carriers (e^- and h⁺). Methyl orange degradation degree under UV light excitation was 35-88%, under sunlight - 11-30%. ZnS-SiO₂ composite synthesized using silica xerogel showed a greater photoactivity due to a presence of cone-shaped or cylindrical pores with one open end in its structure and a higher content of ZnS photoactive component. A comparative study of photocatalytic performance of methyl orange degradation by ZnS-SiO₂ under UV irradiation was investigated using radical scavengers. ^•O₂^- was main active species during MO degradation under UV irradiation, and electrons played additional role during the photocatalytic process.