Synthesis, column packing and liquid chromatography of molecularly imprinted polymers for the acid black 1, acid black 210, and acid Brown 703 dyes

Abstract

Molecularly imprinted polymers have been synthesized for the acid black 1, acid black 210, and acid brown 703 dyes using methacrylic acid, ethylene glycol, and azobisisobutyronitrile as the monomer, cross-linker, and initiator, respectively, in the ratio of 1 : 10 : 44 (template:monomer:cross-linker). The MIPs were used for the selective removal of their corresponding dyes. The selective nature of the MIPs towards their respective dyes was confirmed by a homemade liquid chromatography system. The resultant polymer materials were packed in a stainless steel column and checked for the separation of mixtures of dyes in liquid chromatography. The dyes complementary in structure to the imprinted cavities in the MIPs had long retention times, showing the highly selective nature of the MIPs. The pH, quantity of the MIPs, time, and concentration of the dyes were optimized for the highly efficient removal of the newly synthesized MIP adsorbents in batch adsorption studies. First-order, second-order, and intra-particle diffusion models were applied to all the three MIP-based adsorbents for their kinetic investigations towards the dyes. All the three MIPs selectively absorbed their target template molecule in the presence of four other template dyes having closely related structures with % RSD < 4% for the three batch experiments. The synthesized MIPs were characterized by FTIR, SEM imaging and liquid chromatography. FTIR results strongly confirmed the presence of hydrogen bonding interactions (600-900) between the template and the individual monomers present in the unwashed MIPs. Liquid chromatography revealed the highly selective nature of the MIPs towards their template molecules. The synthesized polymeric substances possess excellent thermal, chemical, and mechanical stability and can be reused several hundred times. The MIPs were applied in the removal of dyes from spiked water samples (river water, tap water and distilled water) where the % removal of the dyes by their corresponding MIPs was greater than 90%.

Fig. 1. Structures of the dyes: acid black 1 (Mw. 616.49 g mol⁻¹λ_max. 618 nm), acid black 210 (Mw. 938.02 g mol⁻¹λ_max. 604 nm), acid brown 703 (Mw. 794.63 g mol⁻¹λ_max. 471 nm), acid black 234 (Mw. 860.8 g mol⁻¹λ_max. 642 nm), basic blue 3 (Mw. 359.89 g mol⁻¹λ_max. 654 nm), acid orange 7 (Mw. 350.32 g mol⁻¹λ_max. 485 nm), acid blue 25 (Mw. 416.38 g mol⁻¹λ_max. 600 nm). Mw = molecular weight.

Fig. 2. FTIR spectra of the template-bound MIP-1 (A), MIP-2 (B) and MIP-3 (C) and template-removed MIP-1 (D), MIP-2 (E) and MIP-3 (F).

Fig. 3. SEM micrographs of MIP-1, MIP-2, and MIP-3. Expanded view of a single MIP particle of MIP-3 after the removal of the template molecule.

Fig. 4. Optimization curves of pH (A), time (B), adsorbent dosage (C) and initial adsorbate concentration (D) for MIP-1, MIP-2 and MIP-3. The pH optimization curve for the NIP is given in (A).

Fig. 5. The pseudo-1st-order kinetic (A), pseudo-2nd-order kinetic (B), and Morris–Weber models (C) for the MIPs (1, 2, and 3) and NIPs.

Fig. 6. Left: Langmuir adsorption isotherms and right: Freundlich adsorption isotherms for MIP-1, MIP-2, and MIP-3. The corresponding isotherm plots for the NIPs are also given.

Fig. 7. Chromatograms obtained using the columns packed with MIP-1 (A), MIP-2 (B), and MIP-3 (C), and column dimensions: 150 mm long, 1 mm ID. Mobile phase: methanol/water 80/20 (v/v%), 0.1% trifluoroacetic acid. The detection wavelength was 624 nm. Eluent flow rate: 40 μL min⁻¹. Each peak has been labelled with the name of its corresponding dye and retention time (t_R) in min.