3.5 UV-vis DRS analysis
As observed in Fig. 6, the optical properties of pristine ZnCdS nanoparticles, CoP polyhedrons, Co3O4 QDs are investigated by the UV-vis diffuse reflectance spectra (UV-vis DRS). Obviously, UV-vis DRS depict the fact that the three samples manifest strong visible light absorption. And original ZnCdS nanoparticles exhibit a light absorption with an edge of about 560 nm, meaning the significant semiconductor characteristics. However, the CoP polyhedrons and Co3O4 QDs exhibit an intense light absorption from 300 to 800 nm, implying their semi-metallic nature nature [42,43]. In fact, TMPs have been proved to have semi-metallic nature and high electrical conductivity. QDs with narrow emission bandwidth are confined three-dimensionally. Thus, CoP and Co3O4QDs can serve as electron sink to greatly promote the separation efficiency of charges from ZnCdS and fundamentally inhibit the recombination of photo-excited carriers, so as to lead to highly-efficient hydrogen evolution rate.