Structure-directed synthesis of Cr₂O₃/WO₃·0.33H₂O adsorbents for rapid removal of cationic pollutants

Structural modulation is essential to advance adsorption performance. Herein, amorphous Cr₂O₃-modified crystalline WO₃·0.33H₂O composites were fabricated via a hydrothermal-heating route using chromium acetate as a structure-directing agent. Adjusting the Cr/W precursor molar ratio tailors the material microstructure, which evolves from nanorod microspheres to nanofibrous networks and granular particles. The incorporated Cr³⁺ modulates lattice growth and surface roughness owing to its ionic compatibility with W, yielding an optimized hierarchical mesoporous network with a high specific surface area of 192.61 m² g^-1. The optimized composite exhibits efficient methylene blue adsorption, achieving 87.2% removal within 10 min and 99.9% removal within 1 h, with a maximum adsorption capacity of 92.54 mg g^-1. It also exhibits excellent selectivity toward various cationic dyes and rapidly separates anionic methyl orange from binary and quaternary mixed dye solutions within 1 min. The adsorption behavior follows pseudo-second-order kinetics and the Langmuir isotherm and is primarily governed by physical adsorption. The material's selective adsorption originates from surface electrostatic interactions, while abundant surface hydrogen bonding further enhances adsorption capacity. This work provides a feasible strategy for microstructure and interfacial engineering of WO₃-based composites toward rapid and selective removal of cationic pollutants.