One-pot synthesis of ultrathin 1T-MoS2 nanosheets as efficient catalyst for reduction of 4-nitrophenol

•Ultrathin 1T-MoS2 nanosheets were synthesized by a one-pot hydrothermal method.•Excess n(S)/n(Mo) and moderate hydrothermal temperature are the key synthetic parameters.•The intercalated NH3 molecules induced phase transformation from 2H-MoS2 to 1T-MoS2.•The activity of 1T-MoS2 is 2.6 times larger than 2H-MoS2 in the reduction of 4-nitrophenol.