Combining hierarchical pores and unsaturated sites into Quasi-MIL-125(Ti) for ultra-fast and efficient adsorption of cationic dyes

Developing new adsorbents with hierarchical pore and unsaturated adsorption sites are highly demanded to achieve rapid adsorption rate and good adsorption selectivity in purifying organic wastewater. We here reported a new Quasi-MIL-125(Ti) synthesized at 340 °C under air atmosphere and considered as a high-efficiency adsorbent for capturing cationic dyes. The morphology of the material is characterized by XRD, SEM, TEM, etc. and the adsorption performance of Quasi-MIL-125(Ti) was systematically studied. Remarkably, it takes only 1 min to rapidly remove 20 mg L-1 MB or NR with 1 g L-1 Quasi-MIL-125(Ti), which is far superior to the previously reported materials. Adsorption isotherm shows that dyes adsorption on Quasi-MIL-125(Ti) follow a Langmuir adsorption isotherm model. The experimental maximum adsorption capacities were 109.3 mg g-1 for MB and 151.1 mg g-1 for NR, respectively. The hierarchical pores facilitate the diffusion and co-adsorption of different dye molecules. Adsorption mechanism reveals that the strong electrostatic attraction originated from the unsaturated Ti sites in Quasi-MIL-125(Ti) contributes to the ultra-fast adsorption behavior during cationic dyes chemisorption process. This study not only provides a promising prospect for the synthetic strategy of super-adsorbents, but also provides reference and theoretical guidance for practical dye wastewater treatment.