Effectiveness of novel xerogels adsorbents for cadmium uptake from aqueous solution in batch and column modes: Synthesis, characterization, equilibrium, and mechanism analysis

Abstract

In the present study, new organic–inorganic mesoporous materials are prepared. The FTIR, SEM, 29Si CP MAS NMR and nitrogen adsorption–desorption experiments are utilized to portray the novel xerogels. Application for the cadmium(II) uptake from aqueous solution using the as-synthesized hybrid materials as adsorbent is explored. Operating parameters influencing the adsorption procedure, for instance, solution pH, contact time and temperature are contemplated. The adsorption kinetic analysis abides by pseudo-second-order model and the intra-particle diffusion model display that the rate-controlled step is directed by film-diffusion before all else and afterward is taken by intra-particle diffusion. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models are assigned to portray the adsorption isotherms. Experimental data seem to be adequate with Langmuir model showing high monolayer adsorption capacities of Cd(II) onto both novel adsorbents (507–493 mg g−1). Mean free energy values assessed from d–R isotherm prescribe that cadmium sequestration by the two hybrid materials eventuated by chemisorption. Besides, the dynamic process exposed relatively high breakthrough capacity for both xerogels and the column data are well validated by Thomas model. Computed thermodynamic parameters depict that the adsorption of Cd(II) ions onto the two adsorbents is favorable and exothermic in nature. FTIR and XPS analysis, uncover that the fundamental mechanism of the cadmium removal is the chelation of metal ions with the ligating nitrogen atoms (N) of amino functionalized xerogel (M1). Though, onto sulfhydryl-functionalized xerogel (M2) it is presumably through the ion-exchange reaction between Cd2+ ions and (SH) groups. The desorption investigation show that the synthesized hybrid materials possess a remarkable reusability. Prior tests produced on electroplating effluents reveal that the as-prepared xerogel could be strongly used for the cadmium uptake from real wastewater.