Effect of preparation on opto-electrical properties of CdS /N, S-rGO photocatalyst for splitting of water by visible light

CdS supported on N, S-rGO photocatalysts were prepared successfully by a hydrothermal and a gas-solid reaction method. Catalysts made by the gas-solid reaction method was found to be more active. XRD, Raman spectroscopy, XPS, UV-DRS, PL and Electrical impedance spectroscopy were used to characterize the prepared catalyst. Present study reveals that catalysts synthesized by the gas-solid reaction at higher temperature had a close-packed hexagonal structure of CdS and also a chemical interaction between CdS and N, S-rGO. The interaction results into development of heterojunction between CdS and NS-rGO. Such interaction was absent in those catalysts which were prepared by the hydrothermal technique. Heterojunction prevents the recombination of photogenerated electrons and holes resulting in the higher rate of hydrogen production. XPS studies show the atomic % N is higher in the catalyst which was prepared by the gas-solid reaction. Electrochemical impedance studies reveal that interfacial charge transfer resistance of CdS/NS-rGO (prepared by the gas-solid reaction) is 6 times lower compared to a catalyst prepared by the hydrothermal method. Flat band potentials, calculated by analysis of Mott. Schottky data reflect that catalysts synthesized by the gas-solid reaction have higher negative values of flat band potential compared to those of hydrothermal synthesis. More negative conduction band edge potential has been observed for CdS supported on the surface of N, S-rGO prepared by the gas-solid reaction which results in an increase in the rate of reduction of H2O/H-2. Defects density, as measured by the Raman spectroscopy, is observed to correlate with activity.