Adsorption of nitrate onto anionic bio-graphene nanosheet from aqueous solutions: Isotherm and kinetic study

Abstract

In this article, bio-graphene nanosheet was prepared using an agricultural waste and converted to a weak base anionic exchanger. Anionic bio-graphene nanosheet structural characteristics and exchanger capacity for nitrate removal from aqueous solution and optimizations of various experimental parameters were evaluated. Nitrate adsorption was done with developing prediction model using the response surface methodology. In addition, regeneration rate was evaluated with eluting HCl (0.1mol/L) solution. The results of the removal model disclosed that initial concentration of nitrate had reverse effects on the nitrate removal and the effects of other variables (adsorbent dose, contact time and pH) at the pH of zero-point charge was direct. The adsorption data obtained from experiments were in line with the pseudo-second-order kinetic (R2=0.998) and Langmuir isotherm (R2=0.943). Based on the Langmuir model, the maximum adsorption capacity (Qmax) for nitrate removal by anionic bio-graphene nanosheet was 182.506mg/g at 150mgNO3−/L. The results of thermodynamic study showed that the enthalpy change (ΔH°) and entropy change (ΔS°) were 867.97 (kJ/mol) and 3.1432 (J/mol·K), respectively. Also, according to the results, the main mechanism of nitrate adsorption onto the anionic bio-graphene was ion exchange. In addition, regeneration process with 4 repetitions of consecutive adsorptions–regeneration cycles showed high desorption efficiencies and slight losses in its initial adsorption capacity.