Carbon quantum dots @ Pd-SnS2 nanocomposite: The role of CQDs @ Pd nanoclusters in enhancing photocatalytic reduction of aromatic nitro compounds

2D layered SnS2 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 NaBH4. 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-SnS2 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 H2O and NaBH4. Under 40 min visible light irradiation, the conversion rate of 4-NP attains 99.7% on CQDs @ Pd-SnS2. The first order reaction rate constant is 0.0332 min-1, 586.5, 202.4 and 31.9 times that on SnS2, CQDs-SnS2 and Pd-SnS2 in the condition of 20 mg·L-1 4-NP and excess NaBH4, respectively. The significant enhancement is ascribed to CQDs @ Pd promoting the charge carrier separation on SnS2 and increasing the adsorption of active hydrogen from the hydrolysis of NaBH4.