Carbon quantum dots @ Pd-SnS nanocomposite: The role of CQDs @ Pd nanoclusters in enhancing photocatalytic reduction of aromatic nitro compounds.

2D layered SnS is one of the most popular semiconductor photocatalysts. However, its performance on photocatalytic reduction of aromatic nitro compounds is unsatisfactory, due to charge carrier recombination and weak adsorption of active hydrogen from the hydrolysis of NaBH. Herein, we have prepared CQDs @ Pd nanoclusters with Pd nanoparticles below 5 nm through an in-situ reducing Pd(Ⅱ) with CQDs containing some oxygen-containing groups at first. CQDs @ Pd-SnS is achieved through a strong interaction of sulfur ions bonding on nanometric Pd surface. The composite shows a stable and efficient visible-light-driven catalytic reduction of aromatic nitro compounds in HO and NaBH. Under 40 min visible light irradiation, the conversion rate of 4-NP attains 99.7% on CQDs @ Pd-SnS. The first order reaction rate constant is 0.0332 min, 586.5, 202.4 and 31.9 times that on SnS, CQDs-SnS and Pd-SnS in the condition of 20 mg·L 4-NP and excess NaBH, respectively. The significant enhancement is ascribed to CQDs @ Pd promoting the charge carrier separation on SnS and increasing the adsorption of active hydrogen from the hydrolysis of NaBH.