The preparation and characterization of photo-responsive sol–gel materials for 2,4-dichlorophenoxyacetic acid by surface imprinting

The primary objective of this work is to develop a photo-responsive surface molecularly imprinted polymer (SMIP) for 2,4-dichlorophenoxyacetic acid (2,4-D) to overcome the shortcomings of conventional molecularly imprinted polymers. A photo-responsive functional monomer was firstly prepared by covalent connecting azobenzene and 2,4-D. The photo-responsive SMIP was then prepared on SiO₂ nanoparticles via sol–gel process, and 2,4-D was removed via hydrolysis in acid. The SMIP shows specific affinity to 2,4-D and reversible uptake and release of 2,4-D upon alternate irradiation at 365 and 440 nm, respectively. The favorable binding strength of the imprinted receptor sites in the SMIP for 2,4-D is found to be 2.51 × 10⁴ M⁻¹. Density of receptor sites in the SMIP material is 10.59 μmol/g SMIP. The SMIP requires a shorter time to reach equilibrium than does the conventional molecularly imprinted polymer. The well-defined core-shell structure was clearly visualized by high resolution transmission electron microscopy.