Adsorption of heavy metals with new graphene-based materials

Abstract

This study evaluates the performance of four different graphene-based materials as adsorbents for the removal of heavy metals (Cu2+, Cd2+ and CrO4 2-) from aqueous solutions. The adsorbents were firstly characterized by scanning electron microscopy, thermogravimetric analysis and porosimetry. The effect on the adsorption of different parameters, such as contact time, pH of the aqueous solution, adsorbent concentration and initial metal concentration, is studied here. The maximum removal percentage for Cu2+ and Cd2+ are 98.92% and 94.88% respectively, when an initial concentration of 5 mg/L at pH=6 and 2 g/L of adsorbent were used. In the case of CrO4 2- an adsorbed percentage of 67.93% was obtained with 10 g/L of adsorbent, an initial concentration of was 5 mg/L and pH=2. Competitive experiments for Cu2+ and Cd2+ were performed, the results showed no significant decrease in the adsorption of the metals compared to the single metal experiments. The adsorption processes were characterized by applying different adsorption isotherm models (Langmuir, Freundlich and Temkin) to the experimental data. The Langmuir isotherm model fitted well with the experimental data obtained for Cu2+, Cd2+ and CrO4 2- for most of the four adsorbents, resulting in maximum adsorption values (qmax) of between 2.6 to 5.4 mg/g for Cu2+ and Cd2+. This qmax was a lower (0.5 mg/g) for CrO4 2-. The results showed that these graphene-based adsorbents can be used to effectively remove Cu2+, Cd2+ and CrO4 2- from aqueous solutions, having single metal or multimetal composition as there is not competition for the adsorbent in the experimental conditions tested