Heterogeneous photocatalytic degradation of recalcitrant pollutants over CdS–TiO2 nanotubes: Boosting effect of TiO2 nanoparticles at nanotube–CdS interface

The heterogeneous photocatalytic degradation of a textile dye, over TiO2 nanotubes (T_NT) containing nanocrystals of cadmium sulfide (CdS) and an interfacial layer of TiO2 nanoparticles (T_NP) is presented. T_NT is prepared by anodization of Ti mesh. A TiCl4 treatment is implemented to deposit T_NP on T_NT when applicable. CdS nanocrystals are prepared using a successive ionic layer adsorption and reaction approach. Methyl orange (MO) and phenol conversion on the different photocatalysts follows the trend: T_NT/T_NP/CdS > T_NT/CdS > T_NT with the actual values of fractional conversion of MO being 0.94, 0.64, and 0.04 respectively. The role of Na2S in MO photodegradation and CdS stabilization is examined in detail. The addition of a limited amount of Na2S (up to a concentration of 0.02 M) with MO has multiple benefits including (i) improvement in electron separation and transport, (ii) stabilization of the CdS, and (iii) enhancement of the photocatalytic degradation of MO by 35%.

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► CdS deposits on TiO2 nanotubes enhance photodegradation of methyl orange and phenol.
► Interfacial TiO2 nanoparticulate film (T_NP) boosts photocatalysis in both cases.
► Optimal Na2S + toxin stabilize CdS and promotes charge separation and photocatalysis.
► Charge transfer mechanism examined with photoelectrochemical and Mott–Schottky tests.