Microstructural analyses of loaded and/or unloaded semisynthetic porous material for understanding of superadsorption and optimization by response surface methodology

Abstract

Physicochemically modified goat collagen fiber (PCMGCF), a porous semisynthetic adsorbent of excellent reusability/recyclability, adsorption capacities (ACs) and waste remediation efficiency, was synthesized from scraps collagen to report individual and synergistic superadsorption of chemically distinct hazardous textile/leather anionic dyes, like mono-azo (Acid Red 131/AR131), bis-azo (Acid Blue 113/AB113) and metal-complex-azo (Acid Brown 369/AB369) and cationic triphenylmethane dyes, like Methyl Violet (MV) and Malachite Green (MG). A new strategy was introduced for comprehensive understanding of the comparative physicochemical changes in microstructures, adsorption mechanism and dye allocations within macro-, meso- and micro-pores of PCMGCF, through extensive analyses of 13C CP MAS NMR, O1s-/N1s-/C1s-/S2p3/2-/Cr2p3/2-XPS, FTIR, TGA, DTG, DSC, XRD, SEM and EDX analyses and by measuring the isotherm, kinetics, diffusion and thermodynamics parameters of adsorption. Appearance of several physicochemical effects in simultaneous adsorption, like metachromasia, H-/J-aggregate, dye–dye complex, cation-anion-PCMGCF adduct, hydrophobic interaction of alkylamino groups, H-bonding and orientation effects of dyes, like side on, tilted and peripheral, were determined through UV–Vis analyses. Individual and interactive effects of input variables on performance potential were measured through response surface methodology (RSM). Diffusion mechanism of thermodynamically favourable chemisorption process was studied by intraparticle diffusion model of Weber-Morris. However, ACs of AR131, AB113 and AB369 were found to be 32.02, 31.52 and 27.70mgg−1, respectively, at optimum conditions (i.e. 200mgL−1, 299K, pHi=4 and 0.25g of PCMGCF).