Mechanistic insight into the adsorption of diclofenac by MIL-100: Experiments and theoretical calculations.

The development of high-efficiency adsorbents and the exploration of their adsorption mechanisms are major challenges in environmental remediation. Herein, MIL-100 was prepared, characterized, and utilized for the adsorptive removal of diclofenac sodium (DCF) from aqueous solutions. A high monolayer adsorption capacity of 773 mg g-1 was recorded. The adsorption mechanism was proposed based on different contributions of two types of pore structure of MIL-100 to the adsorption of DCF from aqueous solutions according to the experimental results and theoretical calculation. During adsorption process, DCF (5.2 × 7.4 × 10.3 Å) diffused through the free area of hexagonal pores (8.6 × 8.6 Å) into the cages of MIL-100, whilst it was adsorbed by the pentagonal pores (4.8 × 5.8 Å) preferentially. Internal mass transfer resistance, which was identified as one of the dominant rate-limiting steps by the mass transfer resistance kinetic models based on the Sips model, will be derived from the diffusion process, which was affected by the size-sieving effect of the pore structure of MIL-100. The successful diffusion of DCF into the interior of MIL-100 and the stable configuration between MIL-100 and DCF accounted for the high adsorption capacity. The capture of DCF into MIL-100 also resulted in the pore size distribution variation of adsorbent, which provided vital experimental evidence for the proposed mechanism. This study may offer deeper insights into other pollutants removal by metal-organic frameworks type adsorbents.