Benzoic Acid Modulation of MIL-88B(Fe) Nanocrystals toward Tunable Synthesis of MOF-Based Fenton-like Degradation Catalysts

Rational control of metal–organic framework (MOF) morphology into desired shapes and sizes has brought properties, such as accelerated adsorption/desorption kinetics, increased specific surface area, and improved bioavailability. An efficient strategy to control MOF morphology is through the coordination modulation method (CMM), where molecules known as modulators inhibit growth at specific crystal facets. The use of a modulator compound, benzoic acid (BA), produced MIL-88B(Fe) particles of varying shapes and sizes in certain concentration ratios relative to the ligand, terephthalic acid (TA). Low BA concentrations (∼0.25 to 0.5 times relative to the ligand concentration) resulted in rod- and spindle-like nanocrystals, while high concentrations of BA up to ∼10 times relative to the TA concentration form typical octahedral and spherical microcrystals. The different shapes and sizes directly influence both adsorption and catalytic performances. The smaller crystals (spindle and rod) exhibited a higher methylene blue (MB) adsorption capacity at a faster adsorption rate relative to large crystals. Meanwhile, larger crystals (octahedral and spherical) resulted in superior catalytic activities with ∼97% MB degradation in less than 30 min, ascribed to higher accessibility of active sites due to the presence of microstructural defects. This work provides critical insights for future rational designs of catalytic MOFs toward a wider plethora of applications.