Synthesis of cadmium sulfide pillared layered compounds and photocatalytic reduction of nitrate under visible light irradiation

Layered compound/CdS nanocomposites incorporating CdS pillars in the interlayer of layered compounds such as hectorite, H2Ti4O9 and H4Nb6O17 were prepared by the stepwise ion exchange reactions of the layered compounds with C3H7NH3+ and Cd2+ followed by the reaction with H2S gas. The pillar height was less than 1 nm and the band gap energy was slightly larger than that of normal crystalline CdS. Although the host layered compounds were insulators or wide band gap semiconductors, CdS pillared layered compounds showed photocatalytic activity under visible light irradiation. Nitrate ion was photochemically reduced to nitrite, nitrogen and ammonia by irradiating visible light (λ>400 m) from a high pressure mercury lamp to nitrate solution containing H2Ti4O9/CdS and H4Nb6O17/CdS nanocomposites in the presence of a sacrificial hole acceptor such as methanol, whereas no photoreduction of nitrate proceeded in the presence of unsupported CdS and hectorite/CdS nanocomposite, indicating that the incorporation of CdS pillars in the interlayer of a semiconducting layered compound such as H2Ti4O9 and H4Nb6O17 was much more efficient in enhancing the nitrate reduction activity than when an insulator such as hectorite was used.