Fabrication And Catalytic Performance Of The Composite Materials Ag/CA And Ag/CA@GTA

Noble metal nanoparticles are receiving considerable attention because of their unique chemical properties and significant potential applications in sensors, optical devices, electronics, catalysts, and biology. To avoid the aggregation of metal NPs, considerable efforts have been devoted to immobilizing NPs onto different supports, including the use of solid beads, hollow spheres, as well as inorganic mesoporous materials and hydrogels with a three-dimensional(3D) network structure. As a hydrogel, alginate acid is easily to crosslink with the divalent cation and into a stable hydrogel, forming an egg-box-like structure. Alginate hydrogel is stable in most organic solvents and possesses a large amount of functional groups. These properties allow alginate hydrogel to act as a scaffold for loading metal NPs, making it suitable for catalytic applications.We demonstrated a simple and economic route to the synthesis of a stabilized and segregative heterogeneous catalyst using Ag NPs as the active component, alginate as the stabilizer, and GTA as the crosslinking agent. The catalytic activity of the as-prepared Ag/CA hydrogel beads was examined through the catalytic reduction of 4-NP to 4-AP. This material exhibited e?cient heterogeneous catalytic activity in the reduction of 4-nitrophenol(4-NP) to 4-aminophenol(4-AP). However, the circulation usability, which is important for industrial application, is unsatisfactory. Divalent cation-solidified alginate hydrogels are known to able to exchange with Na+ upon addition to a basic solution. The “egg-box” structure is easily damaged and alginate hydrogel redissolves in the solution because of the ion-exchange effect,which lead to the loss of Ag NPs.To solve this problem, glutaraldehyde(GTA) have been chosen as crosslinking agents that could enhance the mechanical strength of alginate hydrogel. In this work, Ag/CA@GTA hydrogel beads with controllable size and dosage of Ag NPs were successfully prepared. Analysis results of the catalytic reduction of 4-NP to 4-AP revealed that Ag/CA@GTA hydrogel beads exhibited remarkable and reproducible activities such that they could be recycled for 10 successive reaction cycles with >97% conversion rate.This article provides a generic method to fabricate catalysts which were used alginate as carrier. In this way different kinds of metallic nanoparticles can be located inside the CA hydrogel beads to catalyze various chemical reactions, which definitely has broad application prospects.