Due to the increasing industrialization and population growth, energy crises and environmental pollution have become major challenging problems to the human society in the 21st century. Photocatalysis gain immense interest in the field of green energy as a photoconversion technology of converting solar fuel to chemical fuel. The rapid recombination of photogenerated charge carriers, poor light absorption and lack of satisfactory visible light active materials are the major hurdles for single component system to achieve descent photocatalytic activity under solar light.
This presentation will address our investigations of how the heterojunction based photocatalysts (metal/semiconductor-semiconductor) has constructive effect on the photocatalytic activity and overcomes drawbacks of single component photocatalysts. The main part of the work is to enhance the separation and transfer efficiency of photogenarated charge carriers and improve visible light absorption. In order to do this we have synthesized different heterojunction based photocatalysts Pd-SrIn2O4-TiO2, Pd-CdS@CdO-TiO2, In2S3-gC3N4 and ZnCo2O4 marigold flowers and investigated their photocatalytic activity for hydrogen evolution reaction and dye degradation applications. We found that heterojunction based photocatalysts exhibit the enhanced photocatalytic activity as compared to its individual parts. This enhancement may be due to the combined effect of increased visible light absorption, separation and transfer efficiency of photogenerated charge carriers, effective surface area and co-catalytic effect of Pd NPs through the formation of Schottky junction. The structural, morphological and optical properties were studied using XRD, RAMAN, XPS, SEM, TEM and UV-Vis spectroscopy. Time resolved PL spectroscopy, photocurrent and electrochemical measurements were used to study the photoinduced charge-transfer in the composite samples. The band potentials were calculated from Mott-Schottky plot and UV-Vis spectroscopy. Based on the band potentials, probable charge transfer schemes in binary and ternary heterojunction photocatalysts were also proposed. The photocatalytic activity of these heterojunction photocatalysts were also investigated for dye degradation application. To investigate the degradation reaction mechanism in depth, the active species formed during the reaction process and pH dependence were studied.