In this paper, transition metal phosphide (TMP) was used as cocatalyst to enhance the photocatalytic activity of Cd0.5Zn0.5S solid solution for nitrogen fixation under visible light irradiation. The Ni2P/Cd0.5Zn0.5S photocatalyst was characterized by X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic data showed that Ni2P/Cd0.5Zn0.5S had higher activity than pure Cd0.5Zn0.5S for photocatalytic dinitrogen (N-2) fixation in the absence of any scavengers. After 1 h visible light irradiation (lambda > 400 nm), the concentration of NH3 reached to 101.5 mu mol L-1. And the quantum efficiency at 420 nm monochromatic light reached 4.32%, which much higher than other semiconductors. Time -resolved PL spectra, photocurrent and electrochemical impedance (EIS) spectroscopy revealed that higher photo -induced carrier separation efficiency of Ni2P/Cd0.5Zn0.5S. This work introduced Cd0.5Zn0.5S solid solution photocatalyst to reduce nitrogen, and offered a greenly, economically and efficiently way for nitrogen fixation. (C) 2016 Elsevier B.V. All rights reserved.