Statistical evaluation of liquid phase sequestration of acridine orange and Cr6+ by novel mesoporous glutamic acid-g-polyacrylamide/plaster of paris/riboflavin hydrogel nanocomposite

Abstract

The adsorption of acridine orange and Cr6+ ion onto plaster of paris reinforced glutamic acid-grafted-polyacrylamide hydrogel nanocomposite modified with riboflavin, Glu-g-PAM/POP/Rb HNC was studied. The Glu-g-PAM/POP/Rb HNC was physico-chemically characterized by Fourier transform infrared spectroscopy, X-ray diffraction analysis, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller analysis. The specific surface area, pore volume and pore diameter were 15.48 m2/g, 0.015 cm3/g and 4.23 nm, respectively. Adsorption process was strategized by response surface methodology (RSM) based on a 3-level 5-factor (initial solution pH, contact time, adsorbent dose, initial adsorbate concentration and temperature) central composite design (CCD), and validity of the estimated parameters was statistically evaluated using analysis of variance (ANOVA). The optimized operating variables were: pH (AO = 10; Cr6+ = 4.15), contact time (AO = 60 min; Cr6+ = 59 min), adsorbent dose (0.8 g/L), initial adsorbate concentration (60 mg/L) and temperature (298 K). Isotherm results were coincident with Langmuir isotherm model. The experimental kinetic adsorption data was congruous with pseudo-second order model, with the uptake rate controlled by both intraparticle and liquid film diffusions. The relatively high Langmuir saturation capacity of 202.63 mg AO/g and 143.68 mg Cr6+/g, supported by the decent recyclability up to four times affirmed the promising performance of the adsorbent. The efficacy of the adsorbent for simultaneous removal of AO and Cr6+ from bi-component system was assessed. The possible adsorption mechanism mainly involved hydrogen bonding, van der Waals forces, electrostatic and π-π interactions. Adsorption of AO and Cr6+ onto Glu-g-PAM/POP/Rb HNC was feasible and exothermic as revealed by the thermodynamic parameters. The findings demonstrated superior adsorbent efficacy for the seizure of pollutants, particularly AO and Cr6+ from aqueous solution.