Mechanistic study of iodinated trihalomethanes adsorption onto MOF-derived carbons: Effect of porous structures and adsorption mechanisms

Abstract

The pyrolysis modification at 700 and 900 ºC of the flexible 1D-channel and 3D-hexagonal frameworks of MIL-53(Al) and MIL-88B(Fe), respectively, were conducted to evaluate their adsorption efficiency on five iodinated trihalomethanes (I-THMs) in single- and mixed-solute solutions. MIL-88B(Fe)-derived carbon at 900 ºC (CMIL88–900) exhibited great increases in surface area, porosity, and hydrophobicity, resulting in the excellent adsorption rates and capacities of five I-THMs (4–44 times calculated by linear isotherm) compared to powdered activated carbon (PAC). The primary adsorptive mechanisms onto CMIL88–900 consists of hydrophobic partitioning and an ion-dipole interaction at the acidic surface functional groups (ASGs), which is supported by the diffusibility of the small molecular structure of I-THMs. Bromodiiodomethane demonstrated the highest competitive adsorption capacity on CMIL88–900 in single- and mixed-solute solutions due to it having the highest hydrophobicity and smallest molecular structure. MIL-53(Al)-derived carbon at 900 ºC (CMIL53–900) showed comparable I-THMs adsorption capacities with PAC, approximately 10 times lower than those detected from CMIL88–900. The ion-dipole interaction between the I-THMs and ASGs of CMIL53–900 served as the dominant adsorptive mechanism. Chlorinated haloform showed higher adsorption capacity on CMIL88–900 than brominated and iodinated haloforms. Among the three dominant I-DBPs, dichloroiodomethane had the highest adsorption capacity on CMIL88–900 compared to iodoacetic acid and iodoacetamide, respectively, due to its hydrophobicity and having the lowest molecular weight.