Chitosan functionalized activated coke for Au nanoparticles anchoring: Green synthesis and catalytic activities in hydrogenation of nitrophenols and azo dyes

Herein, chitosan (CTS) functionalized activated coke (AC) is proposed as an excellent platform for Au nanoparticles (NPs) anchoring. Due to the surface-rich hydroxyl and amino groups, CTS can act as a three-functional agent such as reductant, linker and stabilizer to improve the stability of catalysts and realize a green synthesis without adding any additional chemicals. The Au NPs/CTS/AC catalysts exhibited a high catalytic activity in hydrogenation of 4-nitrophenol with the rate constant k(app), of 0.6994 min(-1) and turnover frequency (TOF) of 202 h(-1). Several effect parameters: Au loading amount, environmental water samples and common anions were discussed in detail. Besides, the pH and dissolved oxygen (DO) in different environmental water were measured. The results show that although the catalytic performance of Au NPs/CTS/AC was inhibited in some extent, it could maintain a relatively high catalytic activity in real water samples. In addition, the as-prepared catalysts also displayed high catalytic activity in the hydrogenation of various different substituent nitrophenols and azo dyes, indicating the generality of catalysts, and showed good recyclability with the catalytic performance remained 90% within 7 min 40 s over six recycles. The mechanism of green synthetic pathway and catalytic hydrogenation of nitrophenols over Au NPs/CTS/AC was proposed. The results demonstrated that the Au NPs could facilitate Au-H intermediates to form and thus enhance the catalytic activity. This green synthetic Au NPs/CTS/AC has been proved to be a viable and potential material for environmental pollution treatment of nitrophenols and azo dyes hydrogenation.