Enhancing Cr(vi) removal performance of Ti₃C₂T through structural modification by using a spray freezing method

Structural modification is expected to be a facile way to enhance the adsorption performance of MXene. In this work, the structural modification of Ti₃C₂T was carried out by a spray freezing method, and two kinds of nano-structure (spherical and flaky) of Ti₃C₂T were prepared by adjusting the solution concentration of Ti₃C₂T . Then the Cr(vi) adsorption capacity and removal efficiency of the spherical and flaky Ti₃C₂T was investigated, respectively. It is found that flaky Ti₃C₂T was produced with a Ti₃C₂T concentration of 3 mg mL^-1, while spherical Ti₃C₂T was obtained with a concentration of 6 mg mL^-1. The long diameter of flaky Ti₃C₂T is about 8-10 μm, and the specific surface area is 17.81 m² g^-1. While spherical Ti₃C₂T had a diameter of about 1-4 μm and a specific surface area of 17.07 m² g^-1. The optimized structure of flaky and spherical Ti₃C₂T improves the maximum adsorption capacity by 97% and 33%, respectively, compared with the few-layer Ti₃C₂T . The maximum adsorption capacity of flaky Ti₃C₂T was 928 mg g^-1, while that of spherical Ti₃C₂T was 626 mg g^-1. The adsorption capacity of both Ti₃C₂T structures decreased with the increase of pH, and reached the maximum value at pH = 2; meanwhile, the adsorption capacity of both Ti₃C₂T structures increased with the increase of Cr(vi) concentration. The adsorption of Cr(vi) on flaky Ti₃C₂T was very fast, reaching equilibrium in 3 min, while spherical Ti₃C₂T took 5 min. The adsorption of Cr(vi) on both Ti₃C₂T structures belonged to the monolayers, heat-absorbing chemical adsorption, and the diffusion process of Cr(vi) was regulated by the external diffusion and internal diffusion of particles. Its adsorption mechanism was the combination of reductive adsorption and electrostatic adsorption.