Chemical activation and magnetization of onion waste derived carbon for arsenic removal

Arsenic is a known human carcinogen and its contamination of drinking water has been a global challenge. In this study, magnetic activated carbon (MAC) as an efficient adsorbent material was synthesized by hydrothermal method. Three adsorbent materials MCH, MCH3 and MCNa were synthesized using different chemical activators like HNO3, H3PO4 and NaOH respectively. Structural and morphological features of the adsorbents before and after magnetization were determined by XRD, FTIR, FESEM, EDX and TGA. BJH nitrogen adsorption–desorption isotherm was used to find the surface area and pore size of adsorbents while the surface charge was determined by measuring zeta potential. FESEM images clearly showed the incorporation of magnetite nanoparticles into a porous network. The XRD further confirmed the formation of magnetite nanoparticles within the network of porous carbon with average crystallite sizes of 6.3, 5.8, 5.5 nm for MCH, MCH3 and MCNa respectively. To examine the adsorption behaviour of As(III) onto the MAC, batch adsorption experiments were conducted with the effect of different parameters like initial concentration, temperature, time, amount of adsorbent and pH. The results showed that MCNa is a potential adsorbent for As(III) with removal efficiency of 99%. Overall adsorption process follows pseudo 2nd order kinetics while the Langmuir model was found well applicable to the experimental data. Thermodynamics of adsorption and desorption studies suggest that chemisorption is a predominant adsorption mechanism. Cost-effectiveness, novelty and magnetic recovery are the key features making onion-based MAC a potential adsorbent for the removal of As(III) from contaminated water