Metallic nanoparticles decorated chitosan hydrogel wrapped pencil graphite: Effective catalyst for reduction of water pollutants and hydrogen production

Chitosan hydrogel entrapped pencil graphite composite (CH/PG) was prepared with the strategy to confine metal nanoparticles (M0) in hydrogel. CH/PG could robustly anchor and remarkably disperse M0 on the surface and inside hydrogel. M0 like copper (Cu0@CH/PG), silver (Ag0@CH/PG), nickel (Ni0@CH/PG), cobalt (Co0@CH/PG) and iron (Fe0@CH/PG) were anchored in CH/PG hydrogel. All the prepared hydrogels were tested and displayed outstanding performance in reduction of water pollutants and hydrogen (H2) generation. The catalytic reduction of 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), 2,6-dinitrophenol (2,6-DNP), methylene blue (MB), congo red (CR), methyl orange (MO), acridine orange (ArO), and potassium ferricynide (K3[Fe(CN)6]) were investigated using CH/PG and M0@CH/PG in the presence of NaBH4. In addition, CH/PG and M0@CH/PG were examined in hydrogen generation by methanolysis and hydrolysis of NaBH4. Among all the catalysts, CH/PG was more efficient in catalytic H2 generation (HGR = 2050 mLg–1min–1) while Ag0@CH/PG was more efficient in catalytic reduction of water contaminants. The reduction rate of Ag0@CH/PG was fast for 4-NP and reduced completely within 6.0 min with rate constant of 0.845 min–1. The impacts of different parameters like NaBH4 concentration, catalyst dosage, pollutant concentration, and temperature were precisely examined. Moreover, the recyclability of the catalyst was investigated up to three times, where slight decrease in reduction time was noted.