Sonochemical synthesis of microscale Zn(ii)-MOF with dual Lewis basic sites for fluorescent turn-on detection of Al³⁺...

The effects of synthetic methods, modulator types, the content of the modulator, and reaction time on the size and morphology of a microscale Zn-MOF containing dual Lewis basic amino and carbonyl groups, namely [Zn(NH₂-bdc)(4,4'-bpy)] {NH₂-H₂bdc = 2-amino-1,4-benzenedicarboxylic acid and 4,4'-bpy = 4,4'-bipyridine}, were systemically investigated. Uniform octahedral microparticles of Zn-MOF with an average size of 1.7 μm were obtained within an hour at ambient temperature under ultrasound irradiation using sodium acetate as a modulating agent. Interestingly, Zn-MOF has been demonstrated for the dual-functional fluorescent detection of Al³⁺ and methanol based on a fluorescent turn-on strategy. Very low detection limits (LODs) for Al³⁺ and methanol were achieved using microcrystalline Zn-MOF and reached 30 nM and 0.7% (v/v), respectively. In comparison to the larger size of the polycrystalline Zn-MOF, the microparticles obtained from the ultrasonic route exhibited an improvement in the detection sensitivity. The dual uncoordinated Lewis basic sites play an important role in the sensitivity and selectivity of the detection. Additionally, the fluorogenic change in the sensing process can be observed by the naked eye under UV-light, allowing preliminary on-field screening.