Synthesis of gold nanoparticles supported at graphene derivatives using green reductants and evaluation of their catalytic activity in 4-nitrophenol reduction

In this study, gold nanoparticles were supported at graphene derivatives (AuNPs@GDs) from chloroauric acid and graphene oxide (GO) by using sodium citrate, L-ascorbic acid, and 4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid (HEPES) as green reductants to evaluate the catalytic activity in the 4-nitrophenol (4-NP) reduction system. Among the three reductants, HEPES which derived AuNP@GD (3) exhibited up to 8.44-fold higher catalytic activity compared with sodium citrate and L-ascorbic acid. To evaluate the influence of mass ratio between Au and GO on the catalytic activity, we controlled adding amounts of chloroauric acid while the other conditions using HEPES were fixed. Notably, decreasing the mass ratio of Au/GO from 0.59 to 0.10 increased the rate constant in the range of 7.6 × 10−3 to 16.1 × 10−3/s. However, when the turnover frequency (TOF) was considered, the maximum value was obtained when Au/GO was 0.39. It can be concluded that AuNPs@GD (4) synthesized using HEPES significantly improved the catalytic activity in both rate constant (10.4 × 10−3/s) and TOF (8.08 × 10−5 mol/g·s) in 4-NP reduction. These results suggest that the type of reductants used to synthesize AuNPs@GDs is a significant factor on the catalytic activity and that GO can help increase the catalytic activity, but has an effective ratio with Au.