Synthesis of Graphene Nanoplatelet-Alginate Composite Beads and Removal of Methylene Blue from Aqueous Solutions

Abstract

The discharge of various types of wastewater into natural streams leads to significant problems by increasing the toxicity of the wastewater. For this reason, methods and materials are being developed by researchers in line with effective, economic, and environmental principles. In this study, the removal of methylene blue, a toxic dyestuff, from aqueous solutions was investigated by synthesizing sodium alginate (SA) and graphene nanoplatelet-sodium alginate composite (SA-GNP) beads. The structural characteristics of the materials were analyzed using FTIR, TGA, optical microscope, and SEM methods. All parameters determining the efficiency of the methylene blue adsorption system were optimized in a batch system. The effects of various factors, such as adsorbent amount, contact time, adsorption temperature, dye concentration, solution pH, pHzpc values of SA and SA-GNP beads, presence of different ions, and beads swelling, on the adsorption process, were investigated. To investigate the mechanism of the adsorption system, the adsorption data were fitted to a non-linear form of the Langmuir, Freundlich, and Temkin equilibrium isotherm models, as well as the Pseudo-first-order (PFO), Pseudo-second-order (PSO), and Bangham kinetic models. High regression coefficients were achieved in the studied kinetic and isotherm models (0.86 ≤ R2 ≤ 0.99), and the experimental data were found to be compatible with the model parameters. Maximum adsorption capacities (qm) of 167.52 mg/g and 290.36 mg/g were obtained for the SA and SA-GNP adsorbents, respectively, at 308 K. The optimum temperature for both adsorption systems was found to be 308 K. The efficiency of methylene blue dyestuff removal was improved with graphene nanoplatelet-based adsorbents.

Removal of toxic Cr(VI) from aqueous medium with effective magnetic carbon-based nanocomposites

“…The TGA curve for Fe 3 O 4 shows that the weight loss is about 5% in the temperature range from 25 °C to 1000 °C. The reason for this may be the amount of physically adsorbed water that pure Fe 3 O 4 contains [ 82 , 83 ]. The TGA results for Fe:GNP (2:1) and Fe:GNP (2:1) show that the presence of higher amounts of Fe 3 O 4 increases the thermal stability of the nanocomposites.…”

“…Equilibrium times of the adsorption systems were determined at room temperature (25 °C) and the adsorption kinetics of the adsorbents on Cr(VI) were investigated. The graphs obtained by applying the nonlinear PFO, PSO, and Bangham kinetic models [ 83 ] to the experimental data with Eq. (2) , Eq.…”

“…In addition, Table 2 shows that the Cr(VI) uptake rate decreases in the following order: Fe:GNP (1:1) > Fe:GNP (2:1) > pure Fe 3 O 4 . The third model examined was the Bangham kinetic model, which is a generalization of the Weber–Morris model and explains the slow diffusion step of the adsorption process in the pores of adsorbent materials [ 83 , 89 ]. The Bangham model, with high regression coefficients, especially for the adsorption of Cr(VI) on the Fe:GNP (2:1) and Fe:GNP (1:1) adsorbents (R 2 ≥ 0.97), shows that the model is compatible with the experimental kinetic data and that the adsorption takes place by diffusion into the pores in the adsorbents [ 83 , 90 ].…”

“…Another model that indirectly describes adsorbent/adsorbate interactions is the Temkin isotherm. According to this model, the adsorption of the Cr(VI) adsorbate with magnetic adsorbents is based on a chemical absorption process [ 83 , 93 ]. Calculated using the Temkin isotherm model, b T (pure Fe 3 O 4 , Fe:GNP (2:1), and Fe:GNP (1:1): 893.6, 525.8, and 397.1 J/mg) is related to the heat of sorption, which indicates the physicochemical nature of the system [ 94 ].…”