A new sulfur source for the preparation of efficient Cd(1-x)ZnxS photocatalyst for hydrogen evolution reaction

Cd(1-x)ZnxS hexagonal crystals were for the first time synthesized via thermal sulfurization of Cd(1-x)ZnxO particles by using the elemental sulfur as the sulfur source. A temperature profile in the tube furnace was designed to obtain the proposed particle size, crystal structure, and morphology. Synthesized Cd(1-x)ZnxS particles were characterized with scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance UV-Vis spectroscopy. It was seen that there was a polynomial relationship between the band gap and Cd: Zn ratio in the Cd(1-x)ZnxS. Cd0.58Zn0.23S has shapeless particles between 250 and 500 nm particle size. It was observed that particle size decreased as Zn ratio increased in the Cd(1-x)ZnxS. Cd(1-x)ZnxS hexagonal crystals had nano-step surfaces which were one of the desired factors for achieving high photocatalytic efficiency. Finally, Synthesized Cd(1-x)ZnxS particles were used as photocatalysts for the photocatalytic hydrogen evolution reaction (HER). Cd0.77Zn0.23S structure behaved the most active one among the different compositions of Cd(1-x)ZnxS nanoparticles. Cd0.77Zn0.23S showed almost high photocatalytic activity for HER with 1927 μmol g−1 h−1 hydrogen evolution rate without using noble co-catalyst such as platinum. This good photocatalytic activity was believed to be due to the nanostep surface structure Cd0.77Zn0.23S which led the separation of the reduction and oxidation reaction sites and inhibited the recombination of the generated electrons and holes. Observation of considerably high photocurrent and open circuit potentials and changes in the electrochemical impedance spectroscopy responses supported the photocatalytic activity of the Cd0.77Zn0.23S particles.