Design and synthesis of biopolymer-derived porous graphitic carbon covered iron-organic frameworks for depollution of arsenic from waters

A series of alginate-derived porous graphitic carbon (PGC) wrapped iron-based organic frameworks (Fe-MIL-88B) composites were synthesized and checked their ability for the removal of arsenite (As(III)) and arsenate (As(V)) from water. Various amounts of PGC (5, 10, 20, and 50 wt/wt %) were utilized as a wrapping material for the development of composites with Fe-MIL-88B@PGCx% and optimized for As(III)/As(V) adsorption. The chemical functionalities, structure, morphology, porous properties and bonding nature of the adsorbents were analyzed using FTIR, PXRD, SEM, BET, and XPS, respectively. Fe-MIL-88B@PGC20% composite was explored to have maximum removal efficiency and fastest adsorption kinetics for As(III)/As(V), of all Fe-MIL-88B@PGCx% composites and pristine Fe-MIL-88B studied here. The developed adsorbents are highly pH dependent and selective in common co-existing anions except for F-, PO43- and humic acid. The Langmuir isotherm studies of As(III) and As(V) adsorption suggest maximum adsorption capacities of 1.6853 and 2.2636 mmol/g, at pH of 3.0 and 9.2, respectively. The XPS analysis of As(III)-sorbed Fe-MIL-88B@PGC20% composite reveals that a portion of As(III) has been oxidized into As(V) during the adsorption process. The continuous flow-bed column study indicates that bed volumes of 249.6 and 452.8 mL of As(III) and As(V) contaminated water was treated, respectively, also reduced the concentration of As(III)/As(V) to less than WHO standards (<10 μg/L).