Cigarette soot activated carbon modified with Fe₃O₄ nanoparticles as an effective adsorbent for As(III) and As(V): Material preparation, characterization and adsorption mechanism study

The presence of high concentration of As(III) (arsenite) and As(V) (arsenate) in water system creates severe health problems to the human being and other aquatic animals. In this research, a novel Fe₃O₄/CSAC adsorbent was prepared by the thermal method using cigarette soot activated carbon (CSAC) as a template. Different instrumental techniques like XRD, SEM, EDX, TEM, VSM, BET, Zeta potential and FTIR study were used to confirm the formation of Fe₃O₄/CSAC. This material showed high surface area (575.604 m²/g), low pore size (6.8 nm), small particle size (less than 10 nm) and good magnetic properties (10.77 emu/g), which made the material highly effective for arsenic removal. The adsorption of arsenic was highly pH dependent and 91% and 93% of As(III) and As(V) were removed by this adsorbent at pH 7 and 3. The adsorption process followed the Langmuir isotherm model with the uptake capacities of 80.99 and 107.96 mg/g for As(III) and As(V), respectively. The adsorption data were best fitted to the pseudo second order kinetics model with the rapid adsorption in just 90 min. In presence of Cl⁻, NO₃⁻, SO₄^{2 −}, CO₃^2– and PO₄^{3 −} anions also, the Fe₃O₄/CSAC showed the significant removal of As(III) and As(V). About 89% and 91% of As(III) and As(V) were desorbed with 0.5 M NaOH solution from Fe₃O₄/CSAC surface and the regenerated adsorbent can be used up to four consecutive cycles without any major decrease in removal efficiency. The hydroxyl groups on the Fe₃O₄/CSAC played a key role for the adsorption of As(III) and As(V). The Fe₃O₄/CSAC was found to be a good novel adsorbent for arsenic removal from the water system.