Dual regulation by calcium ions and MXene: Enhanced methylene blue adsorption performance of reduced graphene oxide composite hydrogels

Abstract

The 3D porous structure of graphene functional materials possessed characteristics such as high porosity and large specific surface area, enabling dye molecules to easily enter and diffuse within the 3D network, thereby emerging as a promising solution for treating dye wastewater pollution. In this study, reduced graphene oxide@MXene (RGO@MXene) composite hydrogels with a 3D porous structure were prepared using the hydrothermal reduction method with MXene and graphene oxide as raw materials, and their adsorption performance toward methylene blue (MB) was investigated. The RGO@MXene composite hydrogels doped with 20 wt% MXene exhibited the best removal efficiency for MB, showcasing excellent adsorption performance following the introduction of MXene. During the preparation of the composite hydrogels, the introduction of Ca²⁺ as a cross-linking agent not only reduced the preparation time but also adjusted the specific surface area and pore size distribution of the hydrogel. Therefore, the RGO@MXene-CaCl₂ composite hydrogels achieved an MB removal rate of 86.25% within a shorter timeframe. The results indicated that the adsorption process conformed to the pseudo-second-order kinetic and Langmuir isotherm models and was heat-absorbing and spontaneous, and the RGO@MXene-CaCl₂ composite hydrogels had an adsorption capacity of up to 1568.6 mg·g⁻¹ for MB. This observation suggested that the adsorption process was influenced by various mechanisms such as external diffusion, surface adsorption, and internal diffusion. In addition, our study showed that the RGO@MXene-CaCl₂ composite hydrogels not only had better reusability, but also exhibited better adsorption for wastewater containing large amounts of inorganic salts.Our study further revealed that the microwave irradiation spectra of 3D RGO@MXene composite aerogels changed before and after MB adsorption, exhibiting characteristic features of RGO or MXene. This finding confirms the adsorption of MB, suggesting a potential new method for its detection. This research demonstrates promising applications in both dye wastewater treatment and the detection of MB.