Improved charge transfer by size-dependent plasmonic Au on C3N4 for efficient photocatalytic oxidation of RhB and CO2 reduction

Abstract

A series of Au/g-C3N4 (Au/CN) nanocomposites were successfully prepared, where g-C3N4 nanosheets (CN NSs) served as a substrate for the growth of different sized Au nanoparticles (Au NPs) using the constant temperature bath-reduction method. The effect of Au NP size on electron transfer efficiency between the interfaces of the nanocomposite was studied. The three-dimensional finite-difference time-domain results revealed that larger Au NPs showed increased strength of the localized surface plasmon resonance effect. An increased number of high-energy electrons were available for transfer from Au NPs to CN under the visible light irradiation, inhibiting electron transfer from CN to Au NPs. Photoelectrochemical performance analysis showed that smaller Au NPs exhibited higher separation efficiency of the electron-hole pairs photo-generated with reasonable distribution density. These results are favorable for the improvement of photocatalytic performance. Compared to other nanocomposites, the 3-Au/CN sample (prepared using 3 mL HAuCl4 solution) with reasonable distribution density and small Au NPs exhibited the best photodegradation activity (92.66%) of RhB in 30 min under the visible light irradiation and photoreduction performance of CO2 to CO and CH4 with yields of 77.5 and 38.5 μmol/g, respectively, in 8 h under UV light irradiation. Considering the experimental results in the context of the literature, a corresponding size-dependent photocatalytic mechanism was proposed.