Copper-Based Metallogel of Bovine Serum Albumin and Its Derived Hybrid Biomaterials as Aerogel and Sheet: Comparative Study of the Adsorption and Reduction of Dyes and Nitroaromatics

Abstract

This paper deals with the synthesis of a protein-inorganic hybrid hydrogel and its derived materials, including aerogel and sheet, and the demonstration of their application potentials. For this, a common and abundant protein, bovine serum albumin (BSA), and a copper salt were used in order to prepare a hydrogel by cross-linking the protein molecules using epichlorohydrin and embedding Cu2+ ions to give BSA_Cuhydrogel (1). When this material was lyophilized, it resulted in the product powder BSA_Cuaerogel (2); however, when dried under vacuum, it yielded a blue sheet material, BSA_Cusheet (3). All three of these biomaterials were characterized by spectroscopy and microscopy and further studied for three different applications, and the data were compared in order to establish the material vs property/activity relationship. The applications include (i) adsorption of organic dyes, (ii) reductive degradation of these dyes, and (iii) the reductive transformation of nitroaromatic compounds. The study revealed the efficient adsorption of the anionic and neutral dyes, while the adsorption of the cationic dye was much lower. The adsorption capacities (in mg/g) of Congo red followed the trend BSA_Cuaerogel (367 ± 6) > BSA_Cuhydrogel (274 ± 4) > BSA_Cusheet (204 ± 3). The comparison of the rate of reductive degradation of Congo red and methylene blue follows the same trend as that of the adsorption of the dyes. The reductive degradation was demonstrated for six cycles by reusing the recovered catalyst after every cycle. More than half a dozen nitroaromatics were studied for their reduction using BSA_Cuaerogel. In the case of p-nitrophenol, the rate of reduction follows the trend 2 > 1 > 3. Thus, this paper deals with a methodology to synthesize both a robust hydrogel incorporating metal ions and other derived protein-based biomaterials, viz., an aerogel and sheet, and a comparison of their activity toward the adsorption and degradation of dyes and nitroaromatics.