Process Optimization by a Response Surface Methodology for Adsorption of Congo Red Dye onto Exfoliated Graphite-Decorated MnFe₂O₄ Nanocomposite: The Pivotal Role of Surface Chemistry

• Main Authors: Van Thinh Pham, Hong-Tham T. Nguyen, Duyen Thi Cam Nguyen, Hanh T. N. Le, Thuong Thi Nguyen, Nhan Thi Hong Le, Kwon Teak Lim, Trinh Duy Nguyen, Thuan Van Tran, Long Giang Bach
• Format: Article
• Language: English
• Published: MDPI AG 2019-05-01
• Series: Processes
• Subjects: surface functional groups; exfoliated graphite; Boehm titration; MnFe₂O₄ nanoparticles; Congo red decontamination; response surface methodology
• Online Access: https://www.mdpi.com/2227-9717/7/5/305

Natural graphite, a locally available, eco-friendly, and low-cost carbonaceous source, can be easily transformed into exfoliated graphite (EG) with many surface functional groups via a chemical oxidation route. Combination between EG and magnetic MnFe₂O₄ is a promising strategy to create a hybrid kind of nanocomposite (EG@MnFe₂O₄) for the efficient adsorptive removal of Congo red (CR) dye from water. Here, we reported the facile synthesis and characterization of chemical bonds of EG@MnFe₂O₄ using several techniques such as Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). In particular, the quantity method by Boehm titration was employed to identify the content of functional groups: Carboxylic acid (0.044 mmol/g), phenol (0.032 mmol/g), lactone (0.020 mmol/g), and total base (0.0156 mmol/g) on the surface of EG@MnFe₂O₄. Through the response surface methodology-optimized models, we found a clear difference in the adsorption capacity between EG-decorated MnFe₂O₄ (62.0 mg/g) and MnFe₂O₄ without EG decoration (11.1 mg/g). This result was also interpreted via a proposed mechanism to elucidate the contribution of surface functional groups of EG@MnFe₂O₄ to adsorption efficiency towards CR dye.