Graphene oxide-chitosan composite aerogel for adsorption of methyl orange and methylene blue: Effect of pH in single and binary systems

A series of composite aerogels with different precursor mass ratios were prepared from graphene oxide (GO) and chitosan (CS) by conducting the crosslinking step after lyophilization, the method of which was recently found beneficial to enhance the adsorptive properties of aerogels. The composite aerogels were then employed for the adsorption of methyl orange (MO) and methylene blue (MB) from water, and the one prepared at GO:CS= 1:2 (w/w) was selected as the optimal compromising the adsorption and mechanical properties. The maximum adsorption amounts of MO and MB were calculated to be 543.4 and 110.9 mg/g at 25 °C. Especially, the effects of pH on adsorption of MO and MB in both single and binary systems were investigated in detail. The aerogel possessed pH-responsive feature for single dye adsorption, tending to adsorb MO at low pH while to adsorb MB at high pH. In the binary system, the pH-responsive feature remained and selective adsorption was observed at low initial dye concentration. In contrast, synergistic adsorption occurred instead at high initial concentration, and MB and MO could be efficiently removed simultaneously in the whole pH range of 3–11.