<![CDATA[Sn2+ self-doping of Sn-based photocatalysts is a promising route to visible-light-active photocatalysts, since Sn2+ incorporation narrows the band gap and generates oxygen vacancies that extend light absorption beyond the UV region. However, the Sn2+:Sn4+ molar ratio, which directly controls defect formation, has not been systematically varied in this heterostructure system, so its effect on defect density, band structure, and photocatalytic performance remains unclear. This study investigates that effect. SnO2-x/TiO2 with Sn2+:Sn4+ ratios of 2:1 (ST-2:1) and 1:1 (ST-1:1) were synthesized via a sol-hydrothermal method, characterized by XRD, Raman, XPS, and UV-Vis, and tested for methyl orange (MO) photodegradation under UV-A and visible light. XRD confirmed cassiterite SnO2 as the dominant phase; Raman detected short-range TiO2 ordering. XPS detected Sn2+, Sn4+, Ti3+, Ti4+ in both samples, with oxygen vacancies rising from 12.71% to 17.64% and the valence band maximum shifting upward by 0.54 eV as the Sn2+:Sn4+ ratio increased. Tauc plots gave Eg = 2.21 eV (ST-2:1) and 2.41 eV (ST-1:1), both narrower than pristine SnO2 (3.29 eV) and TiO2 (3.14 eV). ST-2:1 achieved near-complete MO degradation in 10 min under UV-A and 65% in 60 min under visible light, versus only 39% and 10% for ST-1:1, with rate constants 138 and 28 times higher, attributed to its higher defect density and narrower band gap. This study demonstrates that the Sn2+:Sn4+ ratio is an effective, tunable defect-engineering parameter for SnO2-x/TiO2 heterostructures.]]>
Copyrights © 2026
