Unveiling the role of Mn-Cd-S solid solution and MnS in MnxCd1-xS photocatalysts and decorating with CoP nanoplates for enhanced photocatalytic H2 evolution

Abstract

A series of MnxCd1-xS (0 < x < 1, marked as MCS-x) photocatalysts were synthesized by a facile hydrothermal method. The Mn-Cd-S solid solution and impurity phase of α-MnS would coexist in the as-prepared products once x ≥ 0.3. Among these photocatalysts, the MCS-0.5 sample exhibited the highest photocatalytic H2 evolution rate of 5.540 mmol‧g−1‧h−1 with the lactic acid as sacrificial reagent, which may be due to the joint action of the formation of Mn-Cd-S solid solution promoting conduction band potential to enhance the reduction ability and MnS as the recombination center of photogenerated electron-hole pairs. Moreover, the photocatalytic H2 evolution performance of MCS-0.5 sample was further significantly improved on coupling with CoP nanoplates as the cocatalysts, and the optimal loading content was 5 wt% with a H2 evolution rate of 42.95 mmol‧g−1‧h−1, which was nearly 7.75 times higher than that of bare MCS-0.5 and even exceeded that of 1 wt% Pt/MCS-0.5. It could be found from the results of multiple characterization technologies that the excellent photocatalytic H2 evolution activity of CoP/MCS-0.5 composites might be probably attributed to the more efficient transfer and separation of photogenerated charge carriers at the interface between CoP and MCS-x, and more active sites provided by the CoP nanoplates. This current work would clarify the role of Mn-Cd-S solid solution and impurity phase of MnS in the MCS-x samples during the photocatalytic reaction, and reveal that CoP nanosheets might replace Pt as an effective and non-noble metal cocatalyst for the photocatalytic H2 evolution.