N-doped bismuth molybdate decorated with Pt nanoparticles removal azo dyes efficiently via the synergistic effect of adsorption and photocatalysis

Highlights: • The separation of photogenerated electron-hole pairs is promoted under the synergistic effect of Pt NPs and N-Bi₂MoO₆. • Outstanding degradation rate of 90.13% was acquired through synergy of adsorption and photocatalysis. • The degradation rate of 0.5%Pt/N-Bi₂MoO₆ was 4 times and 1.8 times higher than that of pure Bi₂MoO₆ and N-Bi₂MoO₆. • The 0.5% Pt/N-Bi₂MoO₆ composite has excellent stability (more than 5 cycles). -- Abstract: A promising and highly efficient 0.5%Pt/N-Bi₂MoO₆ photocatalyst was synthesized by two-step hydrothermal route and NaBH₄ reduction method to obtain outstanding adsorption performance and photocatalytic efficiency. The degradation yield obtained by 0.5%Pt/N-Bi₂MoO₆ composite catalyst for orange II was 90.13%, which was 4 times and 1.8 times higher than that of pure Bi₂MoO₆ and N-Bi₂MoO₆, respectively. Such prominent photodegradation efficiency was primarily ascribed to the introduction of Pt and N narrowed the band gap of the bulk Bi₂MoO₆ material and surface plasmon resonance (SPR) effect triggered by Pt nanoparticles (NPs), which significantly broadened the optical absorption range and improved separation efficiency of electron-hole pairs. Furthermore, the effects of the initial pH of the solution, the initial concentration of the catalyst, the optical properties and the loading of Pt were discussed. Notably, the adsorption process could be described by the Freundlich model, where 1/n = 0.536, indicating that the concentration had a weak influence on the adsorption capacity. Finally, it had been determined that superoxide anion radicals (• O₂^-) and photogenerated holes (h⁺) were the main active species for the degradation of orange II.