Heterovalent State and Oxygen Vacancy Defect Structure-Associated V/S Co-Doped SnO2 for Catalytic Reduction of Organic and Cr6+ Pollutants in the Dark

V/S co-doped SnO₂ bimetal sulfur-oxides catalysts labeled as (Sn,V)_1-x(S,O)_2-y or (SnVSO) with heterovalent state and oxygen vacancy defect are prepared via a green and facile method. The presence of SnVSO in the heterovalent states of Sn⁴⁺/Sn²⁺ and V⁵⁺/V⁴⁺ facilitates the rapid transfer of the electrons. It improves the electronic charge lifetime, accelerating the efficiency of the catalytic reduction of pollutants. The V/S co-doped SnO₂ regulates the bandgap energy structure. The hydrazine adjusts the heterovalent metal states to reduce Sn⁴⁺ to Sn²⁺ and V⁵⁺ to V⁴⁺. Also, it introduces oxygen vacancies to SnVSO to maintain the charge equilibrium and increase the active surface reactive sites, which enhance the catalytic activity. The SnVSO-3 prepared with 0.4 mL hydrazine exhibits excellent catalytic activity, which wholly reduces 20 ppm of 100 mL methyl orange (MO), rhodamine B (RhB), methylene blue (MB), hexavalent chromium (Cr⁶⁺), and 4-nitrophenol (4-NP) within 6 min. In addition, the SnVSO-3 also has good stability after repeated 6 runs with a reduction efficiency of 96.8%. Therefore, the V/S co-doped SnO₂ sulfur oxide catalysts have a promising potential for reducing Cr⁶⁺ and organic pollutants.