Heterolayered TiO2@layered double hydroxide-MoS2 nanostructure for simultaneous adsorption-photocatalysis of co-existing water contaminants

Abstract

The highly ordered heterolayered-nanostructure TiO2@Layered double hydroxide/Molybdenum disulfide (TiO2@LDH/MoS2; T@L/M) is formed by electrostatically-driven self-assembly of positively charged TiO2-dispersed-LDH layers (T@L) and negatively charged MoS2 nanosheets. TiO2 are incorporated in-situ across the LDH during synthesis yielding exfoliated TiO2-dispersed-LDH layers (T@L). Prior to MoS2 assembly, its interlayer spacing is enlarged and defects are created in basal-plane exposing sulfur-rich sites. Visible-light-active MoS2 and TiO2 synthesized heterostructure extending the T@L/M photoactivity in visible spectrum (2.92 eV) for enhanced degradation capacity. This enables a strong adsorptive-photocatalytic dual modality removal of both cationic and anionic organic dyes (97–99%) that usually cannot be achieved using one material facilitating visible-light-driven self-regeneration of exhausted adsorption sites. While dye removal efficiency varies within (4–7) % of the first cycle over 5 repeated uses, it simultaneously enables excellent affinity and selectivity for heavy metal ions (distribution coefficient ~107 mL/g for Ag+, Pb2+) with enormous adsorption capacity for single metal ion 421.8 mg/g (Ag+) which is at the top of materials known for such removal. It rapidly lowers toxic Pb2+ (from 10 mg/L to ≤0.8 µg/L) well below the standard drinking water limit. The self-regenerating heterostructure for targeting and removing multiple water pollutants of diverse physicochemical properties has not been reported until now.