Scalable Synthesis of Collagenic-Waste and Natural Rubber-Based Biocomposite for Removal of Hg(II) and Dyes: Approach for Cost-Friendly Waste Management.

For initiating a prosperous cost-friendly waste management of small-scale industries, cow buffing dust (CBD), one of the abundantly available semisynthetic collagenic solid wastes, has been used as a nonsulfur cross-linker of natural rubber (NR) for fabricating an NRCBD-biocomposite superadsorbent. The as-prepared reusable biocomposite bearing variegated collagenic and noncollagenic N-donors, along with the O-donors, has been reported for ligand-selective preferential superadsorption from waste water. Thus, a CBD and NR-based scalable biocomposite bearing optimum cross-linking, excellent physicochemical properties, and reusability has been developed via systematic optimization of the torque and reaction time for cost-friendly adsorptive exclusion of dyes, such as 2,8-dimethyl-3,7-diamino-phenazine (i.e., safranine, SF) and (7-amino-8-phenoxazin-3-ylidene)-diethylazanium dichlorozinc dichloride (i.e., brilliant cresyl blue), BCB, and Hg(II). The CBD-aided curing of NR has been achieved through the formation of a cross-linked chromane-ring originated via reaction between the methylol-phenol ring of phenol-formaldehyde resin and isoprene unit of NR. The partial disappearance of unsaturation in cured-NRCBD, relative variation of crystallinity, surface properties, elevated thermal stabilities, and ligand-selective superadsorption have been studied by advanced microstructural analyses of unadsorbed and/or adsorbed NRCBD using Fourier transform infrared (FTIR), C nuclear magnetic resonance, ultraviolet-visible, and O 1s-/N 1s-/C 1s-/Hg 4f-X-ray photoelectron spectroscopies, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, field emission scanning electron microscopy, energy-dispersive spectroscopy, and pH. Response surface methodology-based optimization has been employed to attain the optimum potential of NRCBD, considering the interactive effects between pH, temperature, and concentration of the dye. H-aggregate and time-dependent hypochromic effect has been observed during individual adsorption of dyes. Moreover, the prevalence of chemisorption via ionic interaction between NRCBD and SF, BCB, and Hg(II) has been realized by FTIR, fitting of kinetics data to the pseudosecond-order model, and measurement of activation energies. The Brunauer-Emmett-Teller and Langmuir isotherms fit the best to BCB and SF/Hg(II), respectively. Thermodynamically spontaneous chemisorption have shown the maximum adsorption capacities of 303.61, 46.14, and 166.46 mg g for SF, BCB, and Hg(II), respectively, at low initial concentration of Hg(II)/dyes = 40 ppm, 303 K, and adsorbent dose = 0.01 g.