Tin sulfides and cadmium sulfide mixture in montmorillonite with enhanced visible-light photocatalytic activity

In situ formation of tin sulfide (SnS) and cadmium sulfide (CdS) mixture in montmorillonite was carried out by the reaction between an aqueous dispersion of Sn ²⁺- and Cd ²⁺-montmorillonite and an aqueous solution of S ²⁻ (from Na ₂S). The effects of Sn ²⁺ / Cd ²⁺ molar ratios were examined. The appearance of two diffraction peaks ( d ₀₀₁ = 1.3 and 1.4 nm) and/or the large mismatch (8%) of SnS and CdS lattices were attributed to the possible formation of SnS and CdS in two different interlayer spaces (segregation) of montmorillonite. The blue shifts of the absorption onset relating to the expansion of band gap energy, and the emission band as well as the increase of emission intensity of the intercalated SnS and CdS mixture were observed with increasing SnS / CdS molar ratio. The photodegradation of rhodamine 6G solution was achieved within 360 min by using the product, which has the molar ratio of Sn / Cd = 3:1. The photocatalytic process followed pseudo-first-order kinetic with a rate constant of 0.011 min ⁻¹ . The scavenger test indicated that superoxide radical (O ₂ ^•- ) was the predominant species involved in the photocatalytic process. This result represented an important role of montmorillonite and the heterostructures of SnS and CdS in tailoring the photocatalytic properties.