Acacia auriculiformis leaf extract mediated green synthesis of goethite and boehmite embedded activated sawdust for Cr(VI) adsorption
Priyanka Priyadarsini Samal, Md. Atif Qaiyum, Adrija Ghosh, Roshni Kumari, Jhilirani Mohanta, Saismruti Das, Jashminirani Swain, Banashree Dey, Soumen Dey
Abstract
A well-decorated bimetallic Fe/Al-O(OH)@plywood dust composite hereinafter FAAS has been prepared by a green technique comprised of mild phosphoric acid activation of commercial sawdust, followed by the co-precipitation of Fe/Al salt in the presence of Acacia auriculiformis leaf extract. FAAS has been demonstrated as an efficient Cr(VI) scavenger from simulated and real wastewater by both batch and fixed bed columns. The material has been characterized by SEM-EDX, HRTEM-SAED, XRD, FTIR, TGA-DTG, BET surface area, zeta potential, and pHzpc. Irregular bumps were seen in the FESEM image of FAAS which became smooth after Cr(VI) adsorption. Successful bimetallic loading on the sawdust matrix was confirmed from the FTIR spectra. The material was found to be thermally stable and the surface area was found to be 94.23 m2.g−1. The pHzpc of FAAS was 5.91. The surface charge of FAAS was found to be 36.3 mV which helps in Cr(VI) adsorption. Uptake capacity increased with temperature, and the Langmuir uptake capacity was 170.648 mg.g−1 for linear model and 193. 913 mg. g−1 for non-linear model at 328K. The uptake process followed both Langmuir and Freundlich isotherm models in both linear and non-linear models and concurrent to pseudo-second-order kinetics with R2=0.999. The material was well regenerated using a dilute base in up to 68% and could be reused for up to three cycles with minimal loss in activity. Fixed bed column run with varying concentration, input pH, and flow rate strongly advocates its field applicability. The column uptake capacity was achieved to be 218.500 mg.g−1 at 7 mg. L–1 and neutral pH. The Cr(VI)-exhausted material was pyrolyzed to decline the toxic effect of chromium and reused with 55% efficiency. The reliability and test validity were checked by the standard deviation (range: 0.007-0.246) and the relative standard deviation (range: 1.086-2.137%). Excellent adsorption capacity over other contemporary adsorbents, easy preparation, good regeneration capacity, and production of secondary adsorbent advocate the reason for a choice for sustainable water treatment.