The Role of Micromorphology of SnS2 on the Adsorption Process of Methylene Blue

In this study, three SnS2 samples with different morphologies were synthesized using a one-step hydrothermal method, and the effect and mechanism of morphology on their adsorption ability toward methylene blue (MB) were studied. XRD and SEM revealed effective preparations of SnS2 with flake, flower-like, and granular morphologies, as well as their size variations. The BET results indicate that the specific surface areas follow the order flower-like > granular > flake. Adsorption experiments demonstrated that the morphology of SnS2 considerably impacts their MB adsorption ability. Kinetic investigations implied that the adsorption of MB on flower-like and granular SnS2 followed a pseudo-second-order kinetic model, with adsorption rates in the order of flower-like > granular. MB adsorption on flake SnS2 followed the Weber–Morris model. The adsorption of MB on all three SnS2 structures followed the Langmuir isotherm model, with the flower-like SnS2 exhibiting the highest maximum adsorption capacity of 33.1 mg/g, which is 28.8% and 27.8% higher than that of the flake structure (25.7 mg/g) and the granular structure (25.9 mg/g), respectively. Adsorption thermodynamics indicated that the ΔGθ for MB adsorption on all morphologies was negative, suggesting their spontaneous adsorption process. Furthermore, ΔGθ decreased with increasing temperature, indicating that higher temperatures promote MB adsorption. In addition, both the values of ΔHθ and the ΔSθ for the MB adsorption on SnS2 were in the order of flower-like > granular > flake SnS2, suggesting that MB is more easily adsorbed on the flower-like SnS2 than granular SnS2 and final flake SnS2. DFT simulations confirmed that the distinct exposed facets of the flower-like morphology yielded the strongest adsorption energies, revealing the essential structure–property relationship for designing highly efficient 2D adsorbents. This work reveals the important effect of SnS2 morphology on its adsorption behavior and gives essential insights for the design and development of adsorbents.