Green synthesis and synergistic catalytic effect ofAg/reduced graphene oxide nanocomposite

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NANO EXPRESS

Open Access

Green synthesis and synergistic catalytic effect ofAg/reduced graphene oxide nanocomposite Kai-Chih Hsu and Dong-Hwang Chen*

Abstract A nanocomposite of silver nanoparticles and reduced graphene oxide (Ag/rGO) has been developed as a catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride, owing to the larger specific surface area and synergistic effect of rGO. A facile and rapid microwave-assisted green route has been used for the uniform deposition of Ag nanoparticles and the reduction of graphene oxide simultaneously with L-arginine as the reducing agent. The resulting Ag/rGO nanocomposite contained about 51 wt% of Ag, and the Ag nanoparticles deposited on the surface of rGO had a mean diameter of 8.6 ± 3.5 nm. Also, the Ag/rGO nanocomposite exhibited excellent catalytic activity and stability toward the reduction of 4-NP to 4-AP with sodium borohydride. The reduction reaction obeyed the pseudo-first-order kinetics. The rate constants increased not only with the increase of temperature and catalyst amount but also with the increase of initial 4-NP concentration, revealing that the support rGO could enhance the catalytic activity via a synergistic effect. A mechanism for the catalytic reduction of 4-NP with NaBH4 by Ag/rGO nanocomposite via both the liquid-phase and solid-phase routes has been suggested. Keywords: Silver nanoparticles; Reduced graphene oxide; Catalyst; Green synthesis; Synergistic effect

Background The removal of 4-nitrophenol (4-NP) has received continuous attention in the past decades because it is a common organic pollutant in industrial wastewater. Many processes such as adsorption, microbial degradation, photocatalytic degradation, Fenton method, and electrochemical treatment have been developed [1]. Furthermore, 4-NP can be utilized as a precursor of 4-aminophenol (4-AP). 4-AP is not only an intermediate in the syntheses of many analgesic/antipyretic drugs but also can be regarded as a corrosion inhibitor, photographic developer, hair-dyeing agent, and anticorrosion lubricant [2-4]. So, a great deal of efforts have been made on the reduction of 4-NP to 4-AP. Among them, the borohydride reduction of 4-NP to 4-AP by metal nanoparticles such as Au, Ag, Pt, Pd, and Pt-Ni is particularly attractive because this reaction can be performed in aqueous solution under mild condition [5-10]. However, for the sake of energy saving, safe operation, and avoiding the use of organic solvents, the development of more appropriate processes for the reduction of 4-NP to 4* Correspondence: [email protected] Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan

AP in aqueous solutions under mild condition is still in demand. On the other hand, graphene which is a two-dimensional single-layer carbon sheet has attracted great interest recently in various fields of science and engineering because of its unique electrical, optical, thermal, and mechanical properties [11-15]. Although a lot of methods have b