Chitosan-coated polyurethane sponge supported metal nanoparticles for catalytic reduction of organic pollutants

In this research work, polyurethane sponge (PUS) is used as a readily removable substrate for the synthesis of different nanoparticles on the surface and its use in reducing toxic dyes. An aqueous solution of 0.5 wt% chitosan (CH) was coated on PUS to prepare an ionophilic CH-PUS material. The CH-PUS pieces were then kept in 0.05 M concentration of four different salt solutions. After absorbing the metal ions for a 4 h time period, the CH-PUS pieces were treated with 0.2 M NaBH₄ solution to convert the adsorbed ions to the analogous metal nanoparticles. The bare PUS, CH-PUS and M/CH-PUS were analyzed by various spectroscopic techniques. After catalytic testing of different M/CH-PUS under similar conditions using a model reaction of 4-nitrophenol (4-NP) reduction by NaBH₄, we found that Cu/CH-PUS outperformed among the other M/CH-PUS. The Cu/CH-PUS catalyzed the 4-NP reduction with the fastest reaction rate constant of 0.7923 min^-1. We also tested with different factors affecting the reaction rate constant such as different weights of catalyst, various concentrations of 4-NP and NaBH₄. Lastly, after testing Cu/CH-PUS catalyst for the reduction of different dyes, its high performance was observed for the congo red dye.