High Yield Exfoliation of WS2 Crystals into 1-2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS2/CdS Nanorod Composites

Monolayer WS2 has interesting properties as a direct bandgap semiconductor, photo catalyst, and electrocatalyst, but it is still a significant challenge to prepare this material in colloidal form by liquid phase exfoliation (LPE). Here, we report the preparation of 1-2 layer semiconducting WS2 nanosheets in a yield of 18-22 wt % by a modified LPE method that involves preintercalation with substoichometric quantities of n-butyllithium. The exfoliated WS2 nanosheeets are n-type, have a bandgap of similar to 1.78 eV, and act as a cocatalyst with CdS nanorods in photocatalytic hydrogen evolution using lactate as a sacrificial electron donor. Up to a 26-fold increase in H-2 evolution rate was observed with WS2/CdS hybrids compared with their pure CdS counterpart, and an absorbed photon quantum yield (AQE) of >60% was measured with the optimized photocatalyst.