Ion-imprinted polyvinylimidazole-silica hybrid copolymer for selective extraction of Pb(II): Characterization and metal adsorption kinetic and thermodynamic studies

Smartphone-Based Rapid Quantitative Detection Platform with Imprinted Polymer for Pb (II) Detection in Real Samples

This paper reports the successful development and application of an efficient method for quantifying Pb2+ in aqueous samples using a smartphone-based colorimetric device with an imprinted polymer (IIP). The IIP was synthesized by modifying the previous study; using rhodizonate, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N,N'-methylenebisacrylamide (MBA), and potassium persulfate (KPS). The polymers were then characterized. An absorption study was performed to determine the optimal conditions for the smartphone-based colorimetric device processing. The device consists of a black box (10 × 10 × 10 cm), which was designed to ensure repeatability of the image acquisition. The methodology involved the use of a smartphone camera to capture images of IIP previously exposed at Pb2+ solutions with various concentrations, and color channel values were calculated (RGB, YMK HSVI). PLS multivariate regression was performed, and the optimum working range (0-10 mg L-1) was determined using seven principal components with a detection limit (LOD) of 0.215 mg L-1 and R2 = 0.998. The applicability of a colorimetric sensor in real samples showed a coefficient of variation (% RSD) of less than 9%, and inductively coupled plasma mass spectrometry (ICP-MS) was applied as the reference method. These results confirmed that the quantitation smartphone-based colorimetric sensor is a suitable analytical tool for reliable on-site Pb2+ monitoring.

Mesoporous Silica Nanoparticles for the Uptake of Toxic Antimony from Aqueous Matrices

Contamination of water sources by toxic antimony Sb(III) ions poses a threat to clean water supplies. In this regard, we have prepared a mesoporous silica nanoparticle (MSN)-derived adsorbent by reverse microemulsion polymerization, using cetyltrimethylammonium chloride (CTAC) and triethanolamine (TEA) as co-templates. The physical and chemical properties were characterized using advanced tools. The MSN exhibits a higher surface area of up to 713.72 m2·g-1, a pore volume of 1.02 cm3·g-1, and a well-ordered mesoporous nanostructure with an average pore size of 4.02 nm. The MSN has a high adsorption capacity for toxic Sb(III) of 27.96 mg·g-1 at pH 6.0 and 298 K. The adsorption data followed the Langmuir isotherm, while the kinetics of adsorption followed the pseudo-second-order model. Interestingly, the effect of coexisting iron showed a promoting effect on Sb(III) uptake, while the presence of manganese slightly inhibited the adsorption process. The recyclability of the MSN adsorbent was achieved using a 0.5 M HCl eluent and reused consecutively for three cycles with a more than 50% removal efficiency. Moreover, the characterization data and batch adsorption study indicated physical adsorption of Sb(III) by mesopores and chemical adsorption due to silicon hydroxyl groups.

Molecular Imprints Frozen by Strong Intermolecular Interactions in Place of Cross-Linking

A new way to freeze molecular imprints in a polymer material is reported. So far, molecular imprinted polymers (MIP) involve copolymerization of a functional monomer and large amounts of cross-linking agent, which keeps the template shape memory in rigid molecular imprints. MIP materials are prepared herein without cross-linking agent. Stiff chains of polyaniline grafted on a solid support as a brush-like material achieve the necessary rigidity. Differential adsorption to imprinted and non-imprinted materials provides evidence of molecular imprints. A correct adsorption isotherm for mobile adsorbed layers (Volmer isotherm) is introduced instead of the popular but inadequate Langmuir isotherm. Non-selective adsorption is entropic, whereas adsorption to molecular imprints has an enthalpic contribution coming from specific interactions. Fast adsorption kinetics are a definite benefit with regards to applications such as chromatographic separations and chemical sensors.

Highly efficient and selective removal of trace lead from aqueous solutions by hollow mesoporous silica loaded with molecularly imprinted polymers

A novel type of adsorbent for the selective recognition and adsorption of trace Pb²⁺ from aqueous solutions has been successfully constructed simply by grafting molecularly imprinted polymers (MIPs) onto hollow mesoporous silica (HMS). Attractively, the HMS loaded with MIPs (H-MIPs) exhibits a fast adsorption kinetics, marked adsorption capacity of 40.52mg/g and extremely high selectivity toward Pb²⁺ over Cu²⁺, Zn²⁺, Co²⁺, Mn²⁺ and Ni²⁺, and the selectivity coefficients have been determined to be as high as 50. Moreover, such high adsorptive capability and selectivity were retained for at least 6 runs, indicating the stability and reusability of H-MIPs. Lead ion contaminants in real water samples were successfully concentrated and approximately 100% recovered using H-MIPs. Theoretical analysis shows that the adsorption process of H-MIPs follows the pseudo-second-order kinetic and Langmuir isotherm models. These demonstrate that H-MIPs are greatly potential for the rapid and highly efficient removal of trace Pb²⁺ ions in complicated matrices.

Highly selective monitoring of metals by using ion-imprinted polymers

Ion imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas. Graphical Abstract IIPs for the selective monitoring of metals.

Preparation of new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) using a double-imprinting process for the preconcentration of Pb²⁺ ions

A new ion-selective cross-linked poly(vinylimidazole-co-ethylene glycol dimethacrylate) prepared via a double-imprinting process was developed for the recognition and preconcentration of Pb(2+) from water samples. The sorbent was characterized by FT-IR, SEM, TGA and textural data. The maximum dynamic sorption capacity of Pb(2+) was 42.04 mg Pb(2+) g(-1) of the double-imprinted polymer. The sorption kinetics data were described by a pseudo-second-order model. The double-imprinted polymer exhibited a higher sorption efficiency of Pb(2+) than the blank polymer (non-imprinted polymer). The preconcentration procedure involved the loading of a Pb(2+) solution at pH 7.25 through 40.0 mg of the double-imprinted polymer packed in a mini-column at 5.0 mL min(-1). The selective efficiency of proposed method for the Pb(2+) preconcentration was assured by competitive sorption using different proportions of Pb(2+)/cations and Pb(2+)/anions. An analytical curve was obtained in the range 0.0-300.0 μg L(-1) (r=0.999) and a limit of detection of 2.46 μg L(-1) was obtained. The preconcentration factor was found to be 21, the consumptive index 0.95 mL and the concentration efficiency 5.25 min(-1). The preconcentration method was successfully applied to the Pb(2+) ions determination in different kinds of water samples with high recovery values (91.3-108.9%).

Preparation and properties of ion-imprinted hollow particles for the selective adsorption of silver ions

Four kinds of silver ion-imprinted particles (Ag-IIPs) with different morphologies were prepared by the surface ion-imprinting technology (SIIT) and were used for the selective removal and concentration of silver ions from wastewater. The favorable adsorptivity and selectivity of Ag-IIPs for Ag(+) were confirmed by a series of adsorption experiments at a suitable pH value. The adsorption mechanism was elucidated by analyzing the adsorption isotherms, adsorption thermodynamics, and adsorption kinetics systematically. The Ag(+) adsorption onto the Ag-IIPs was well-described by the Langmuir isotherm model, and it was likely to be a monolayer chemical adsorption. This conclusion was also confirmed by the thermodynamic parameters. Moreover, the adsorption kinetics indicated that the adsorption rate would be controlled jointly by the intraparticle diffusion and the inner surface adsorption process, and the latter process was generally associated with the formation and breaking of chemical bonds. Finally, the effects of different morphologies of the Ag-IIPs for Ag(+) adsorption were also investigated. In aqueous solution, the adsorptivity of the Ag(+) ion-imprinting single-hole hollow particles (Ag-IISHPs) for Ag(+) was highest (80.5 mg g(-1)) because of a specific morphology that features a single hole in the shell. In an oil-water mixture, Ag(+) in the water phase could be adsorbed efficiently by the Ag(+) ion-imprinting Janus hollow particles (Ag-IIJHPs), with emulsifiability originating from the Janus structure.

A Facile Synthesis of Ion Imprinted Mesoporous Silica Adsorbents by a Co-Condensation Pathway and Application in a Fixed-Bed Column Study for Lead Removal

Highly selective lead ion imprinted mesoporous silica adsorbents (PbII-IMS) were prepared through a co-condensation pathway with 3-(γ-aminoethylamino)propyltrimethoxysilane (AAPTS) (PbII-IMS-NN) and 3-aminepropyltriethoxysilyl (APTES) (PbII-IMS-N) as monomers. The prepared adsorbents were characterised by FT-IR spectroscopy, X-ray photoelectron spectroscopy, power X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption–desorption techniques. The results showed that the synthesised adsorbents presented a highly ordered mesoporous structure. In comparison with PbII-IMS-N, PbII-IMS-NN demonstrated a higher adsorption capacity in a series of static and dynamic adsorption experiments, and was further applied to a continuous fixed-bed column study under different conditions. It was found that the breakthrough time of the fixed-bed increased with an increase in bed depth, but decreased with increased flow rate and initial PbII concentration, and the dynamic adsorption data was more consistent with the Thomas model than the Adams–Bohart model. Furthermore, the PbII-IMS-NN showed a greater recognition and binding affinity towards the target lead ions than PbII-IMS-N.

Development of molecularly imprinted poly(methacrylic acid)/silica for clean-up and selective extraction of cholesterol in milk prior to analysis by HPLC-UV

In the present paper the assessment of a novel molecularly imprinted polymer, poly(methacrylic acid)/silica, for clean-up and selective extraction of cholesterol in milk samples is described.