Carboxymethyl cellulose/polyamidoamine hydrogel loaded with nano-Ag particles as recoverable efficient catalyst for reduction of 4-nitrophenol in water

Polyamidoamine (PAMAM) encapsulated nano-Ag is a highly efficient catalyst for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in water. However, PAMAM is easily soluble in water, making the nano-Ag catalyst difficult to recycle. In this work, carboxymethyl cellulose (CMC) was oxidized by sodium periodate to obtain oxidized carboxymethyl cellulose (CMC-CHO) containing aldehyde groups. PAMAM encapsulated nano-Ag (G4.0-PAMAM-Ag) was prepared with G4.0-PAMAM as template. Through the Schiff base reaction between CMC-CHO and G4.0-PAMAM-Ag, the CMC/PAMAM hydrogel loaded with nano-Ag (CMC-PAMAM-Ag) was prepared. The catalytic performance of CMC-PAMAM-Ag in the reduction of 4-NP to 4-AP in water was studied. It was found that its time required for accomplishing the reduction reaction was only 9 min, similar to that of free G4.0-PAMAM-Ag (8 min). Turnover frequency was as high as 169 h(-1), much higher than that of the cellulose/PAMAM composite supported nano-Ag (4.2 h(-1)) and dextrann/PAMAM hydrogel supported nano-Ag (40.2 h(-1)). The recovered hydrogel was characterized by X-ray photoelectron spectroscopy and it was found that the imine bonds in the fresh hydrogel were reduced to the amine bonds in the recovered hydrogel, improving the stability of hydrogel. The recovered hydrogel still had a good catalytic performance.