Graphene–Biochar Composite for Effective Congo Red Dye Removal from Water

Abstract

Congo red (CR), a harmful pollutant, is increasingly contaminating aquatic environments. The removal of CR from wastewater is important. This study developed a novel graphene–biochar composite (GR-BC) to enhance CR treatment. The physicochemical properties of GR-BC were studied using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller techniques. The CR adsorption capacities of biochar (BC) and GR-BC were analyzed using batch adsorption experiments. The effect of the initial pH of the CR solution, CR concentration, and adsorption time of CR were determined. The SEM, XRD, and FT-IR results showed that graphene was loaded successfully onto the BC. The BET results showed that GR-BC had a larger surface area than BC. The adsorption experiments showed that the highest CR adsorption efficiency occurred at pH 2, and reached 99.6% and 99.5% for BC and GR-BC, respectively. The GR-BC treatment was better at removing CR dye than was BC. The highest Langmuir adsorptive capacity of GR-BC (414.9 mg·g−1) was double of that of BC (193.8 mg·g−1). The higher R2 values for the Freundlich isotherm than for the Langmuir isotherm indicate that the Freundlich isotherm model best fit the experimental data for both BC and GR-BC. The pseudo-second-order model (R2>0.99) successfully described the adsorption kinetics of CR dye by both BC and GR-BC. In addition, the influence of ionic strength and coexisting ions on CR adsorption by BC was greater than that on CR adsorption by GR-BC, indicating that GR-BC is more stable than BC. Recycling experiments showed that CR removal still 50% after the fifth cycle for GR-BC, which was higher than that for BC (35%), suggesting that GR-BC has better reusability than BC. Thus, the GR-BC composite is a potential adsorbent for CR dye removal.