Visible light driven hydrogen evolution by photocatalytic reforming of lignin and lactic acid using one-dimensional NiS/CdS nanostructures

Uniform one-dimensional (1D) NiS/CdS nanocomposites have been fabricated using CdS nanowires (NWs) and NiS nanoparticles as building blocks through two-pot solvothermal synthesis. The synergistic interaction between CdS and NiS, stemming from their intimate contact, efficiently enhanced charge carrier separation, with the NiS, as a non-noble metal cocatalyst, enriching the active sites for H2 production from water. Consequently, compared with pristine CdS NWs, the 1D NiS/CdS nanocomposite exhibited improved visible light reactivity in the generation of H2. The activity of NiS/CdS with 20 mol% of NiS loading, under the coexistence of lactic acid and lignin as hole scavengers, is 5041 times that of pristine CdS, with an apparent quantum efficiency (AQE) of 44.9% for H2 generation. To gain deeper insight into the mechanism behind the enhanced performance, ultrafast dynamics studies based on femtosecond transient absorption (TA) techniques have been applied to probe the charge carrier dynamics. The results reveal that presence of 0.2 molar ratio of NiS improved the average charge carrier lifetime of CdS NWs by 97 times, potentially leading to more efficient charge separation and transfer. However, further increasing the NiS loading resulted in shorter lifetime or faster electron-hole recombination, attributed to aggregation of NiS nanoparticles. The dynamics results agree well with the photocatalytic results in that the longer charge carrier lifetime correlates with improved performance in hydrogen evolution. This work demonstrates a simple approach to controlled synthesis of well-shaped 1D nanocomposite photocatalysts for visible-light driven energy conversion, particularly involving the use of biomass.