The resourcefulness of p(4-VP) cryogels as template for in situ nanoparticle preparation of various metals and their use in H2 production, nitro compound reduction and dye degradation

•Modifiable super porous p(4-VP) cryogels.•Versatile cryogels reactor in metal nanoparticle preparation.•Environmentally benign cryogel composites for catalytic use.•Cryogel-M (M: Co, Ni, Cu, and Fe) in H2 production, dye and nitro compound reduction.

Poly(4-vinylpyridine) (p(4-VP)) cryogels were synthesized under cryogenic conditions (T = −18 °C) and were converted to positively charged forms by modifying with different alkyl dihalides of variable chain lengths such as 1,2-dibromoethane (1,2 BE), 1,4-dibromobutane (1,4 BB), 1,6-dibromohexane (1,6 BH), and 1,8-dibromooctane (1,8 BO). The chemical structure of synthesized supermacroporous 1,4 BB-p(4-VP) cryogels were confirmed by FT-IR spectroscopy. The 1,4 BB modified-poly(4-vinylpyridine) (1,4 BB-p(4-VP)) cryogels were used as template for in situ metal nanoparticle preparation as 1,4 BB-p(4-VP)-M (M: Co, Ni, Cu, and Fe) using chloride salts of Co, Ni, Cu, and Fe in ethanol. These metal-nanoparticle macroporous cryogel composites were employed in H2 generation from hydrolysis of sodium borohydride (NaBH4). Metal nanoparticles embedded 1,4 BB-p(4-VP)-M were visualized by TEM, and thermal behavior of 1,4 BB-p(4-VP) cryogels were done by thermogravimetric analyzer (TGA). The metal content of 1,4 BB-p(4-VP)-M was estimated via atomic absorption spectroscopy (AAS). Multiple metal salt loading and reduction cycles were performed for 1,4 BB-p(4-VP) cryogels to increase the amount of contained Co. The activation energies, enthalpy, and entropy for NaBH4 hydrolysis catalyzed by 1,4 BB-p(4-VP)-Co cryogel composites were determined as 47.6 kJ (mol)−1, 46.2 kJ (mol K)−1, and −146.9 J (mol K)−1, respectively. The cryogel network embedded with Co, Ni, Cu, and Fe nanoparticles was also used as a catalyst in the reduction of 4-nitrophenol (4-NP) in an aqueous solution in excess amount of NaBH4. Furthermore, the Cu metal nanoparticle-containing 1,4 BB-p(4-VP) cryogel was utilized in the degradation of methylene blue (MB).

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