Catalytic efficiency of copper nanoparticles modified silica-alginate hydrogel nanocomposite towards reduction of water pollutants and H2 generation

Abstract

In the present study, a viscous solution of sodium alginate polymer (Alg) containing dispersed silica (Si) was prepared for the fabrication of hydrogel beads. It was added dropwise into a divalent calcium (Ca+2) ions solution which convert each drop into a hydrogel bead i.e, Si@AlgBD. In the next step, the outer surface of the Si@AlgBDs were modified with five different types of metal. As a result, it gives five types of metal coated M+n/Si@AlgBDs catalyst. These coated M+n [M+n = Ag+, Ni+2, Fe+3, Co+2, and Cu+2] were converted into zero-valent metal nanoparticles (MNPs) [M0 = Ag0, Ni0, Fe0, Co0, and Cu0] by NaBH4, which act as a strong reducing agent. Firstly, all catalysts were analyzed for the reduction of 4-NP to 4-AP to check out the efficiency of catalysts. Among which the reduction rate was higher for Cu0/Si@AlgBDs catalyst and was chosen for further study. Secondly, the Cu0/Si@AlgBDs catalyst was examined for the decolorization of 2-nitrophenol (2-NP), 2,6-dinitrophenol (2,6-DNP), methyl orange (MO), congo red (CR), and acridine orange (ArO). Additionally, its catalytic reduction was analyzed for the reduction of 4-NP to 4-AP in different quality of water sources. The highest reduction rate of 6.207 × 10−1 and 8.619 × 10−1 min−1 was calculated for CR and 4-NP, respectively. Beside its catalytic reduction, the same catalyst was evaluated for the generation of H2 gas from NaBH4 through methanolysis. Where, the lowest Ea energy of 25.9 kJ/mol was calculated at room temperature. In both experimental procedures i.e, catalytic reduction and H2 production, different parameters, such as, catalyst dosage, different amount of the NaBH4, initial concentration of the 4-NP, and temperature effect for the H2 production were studied in detail. Similarly, the hydrogel beads were characterized by SEM, EDX, and ICP-OES to identify and find out the successful incorporation of MNPs on Si@AlgBDs. Finally, the recyclability of the catalyst was also investigated.