Ion-Imprinted Polymeric Materials for Selective Adsorption of Heavy Metal Ions from Aqueous Solution

The introduction of selective recognition sites toward certain heavy metal ions (HMIs) is a great challenge, which has a major role when the separation of species with similar physicochemical features is considered. In this context, ion-imprinted polymers (IIPs) developed based on the principle of molecular imprinting methodology, have emerged as an innovative solution. Recent advances in IIPs have shown that they exhibit higher selectivity coefficients than non-imprinted ones, which could support a large range of environmental applications starting from extraction and monitoring of HMIs to their detection and quantification. This review will emphasize the application of IIPs for selective removal of transition metal ions (including HMIs, precious metal ions, radionuclides, and rare earth metal ions) from aqueous solution by critically analyzing the most relevant literature studies from the last decade. In the first part of this review, the chemical components of IIPs, the main ion-imprinting technologies as well as the characterization methods used to evaluate the binding properties are briefly presented. In the second part, synthesis parameters, adsorption performance, and a descriptive analysis of solid phase extraction of heavy metal ions by various IIPs are provided.

Sustainable Synthesis of Iron-Zinc Nanocomposites by Azadirachta indica Leaves Extract for RSM-Optimized Sono-Adsorptive Removal of Crystal Violet Dye

Environmental pollution has exacerbated the availability of clean water to mankind. In this study, Azadirachta indica leaf extract was used for sustainable synthesis of Fe-Zn nanocomposites (IZNC). The instrumental techniques of Fourier transformed infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) were used to determine the structural and chemical composition. The overall surface was mildly acidic in nature, as the pH_PZC was observed to be 6.00. The ultrasonicated adsorption experiments were designed by central composite design (CCD). The best responses, which proposed a contaminants removal of 80.39%, were assessed using the response surface methodology (RSM). By repeating experimental runs at the expected optimum operating parameters (OOP), the method was experimentally affirmed with the %mean error and %RSD₉ being 2.695% and 1.648%, respectively. The interaction of CV dye and the nanocomposite showed tremendous adsorption efficiency towards crystal violet (CV) dye, as revealed by isotherm studies. Fitting kinetics and isotherm models were affirmed by root mean square error (RMSE), χ2, and a Pearson regression coefficient. Thermodynamic studies proved spontaneity of the CV dye adsorption over the nanocomposites. The values for ΔG^o, ΔH^o, and ΔS^o were observed to be -1.089 kJ/mol, 28.59 kJ/mol, and -3.546 kJ/mol, respectively. Recovery of CV dye was carried out in a variety of media, including NaOH, NaCl, and CH₃COOH. The maximum CV recovery was achieved in an acidic media. The robustness of adsorption was affirmed by the interference of various matrix ions, including KCl, LiCl, NaCl, and MgCl₂, which did not significantly affect the adsorption process. The maximum adsorption capacity was obtained at a low concentration of LiCl. The results show that a green synthesis approach for nanocomposite synthesis might be an effective and economical way to remove organic contaminants from wastewater. Moreover, it is also effective for effluent treatment plants (ETP) for waste management purposes, in which it may be coupled with chlorine as a disinfectant to purify water that can be used for domestic and irrigation purposes.

Recent advances of ordered mesoporous silica materials for solid-phase extraction

This review mainly focuses on the development and application of ordered mesoporous silica materials for solid-phase extraction in recent years. It overviews not only bare mesoporous silica but also the functionalized mesoporous silica with organic groups, molecularly imprinted polymers, and magnetic materials. These mesoporous silica materials were used as the extraction adsorbents in cartridge solid-phase extraction, dispersive solid-phase extraction, magnetic solid-phase extraction, micro-solid-phase extraction and matrix solid phase dispersion. Coupled with atomic emission spectrometry, chromatography or other detection methods, these techniques efficiently extracted and sensitively determined various targets, such as metal ions, perfluorocarboxylic acids, pesticides, drugs, endocrine disruptors, phenols, flavanones, polycyclic aromatic hydrocarbons, parabens and so on. Based on unique advantages of mesoporous silica materials, the developed analytical method successfully analyzed different matrix samples, like environmental water samples, soil samples, food samples, biological samples and cosmetics. In addition, the prospects of these materials in solid-phase extraction are presented, which can offer an outlook for the further development and applications.

Development of Solid Phase Extraction Method Based on Ion Imprinted Polymer for Determination of Cr(III) Ions by ETAAS in Waters

In this work, a new solid phase extraction method for the determination of chromium species in water samples by electrothermal atomic absorption spectrometry was developed. For selective separation of Cr(III) ions under dynamic conditions, two ion imprinted polymers containing Cr(III)-1,10-phenanthroline complex (Cr(III)-phen) were prepared with the use of one (styrene, ST) or two (styrene and 4-vinylpyridine, ST-4VP) functional monomers. The physicochemical properties of those solid sorbents towards Cr(III) ions were studied and compared. It was found that Cr(III) ions were retained on the Cr(III)-phen-ST and Cr(III)-phen-ST-4VP polymers with high efficiency and repeatability (91.6% and 92.9%, RSD < 2%) from solutions at pH 4.5. The quantitative recovery of the analyte (91.7% and 93.9%, RSD < 4%) was obtained with 0.1 mol/L EDTA solution. The introduction of 4VP, an additional functional monomer, improved selectivity of the Cr(III)-phen-ST-4VP polymer towards Cr(III) ions in the presence of Cu(II), Mn(II) and Fe(III) ions, and slightly decreased the sorption capacity and stability of that polymer. The accuracy of procedures based on both polymeric sorbents was proved by analyzing the standard reference material of surface water SRM 1643e. The method using the Cr(III)-phen-ST polymer was applied for determining of Cr(III) ions in tap water and infusion of a green tea.

Eco-friendly synthesis of self-regenerative low-cost biosorbent by the incorporation of CuO: a photocatalyst sensitive to visible light irradiation for azo dye removal

Acid pretreated biomass Lemna minor (BM-H3PO4) was used as support for CuO nanoparticles loading, to investigate the dye biosorption capacity and the photocatalytic performance under artificial visible light. The surface morphology, crystal structure, elemental composition, and the bandgap of modified biomass have been determined using FE-SEM, XRD, EDX, XPS, FTIR, and UV-DR analysis. The results showed that NH2 and P-O functional groups of (BM-H3PO4) can attract the copper ions (Cu2+), which can facilitate the loading of CuO nanoparticles hence, smaller nanoparticles with an average diameter of 21 nm was obtained. It was also found that when the CuO was incorporated in BM-H3PO4 in a proper mass ratio of 0.4, the biosorption efficiency was enhanced to 3 times compared with BM-H3PO4 and reached a maximum of 91%, at a dye concentration of 20 mg/L, solution pH equal to 5, and an ambient temperature of 25 °C. Furthermore, CuO-modified BM-H3PO4 exhibits a better photocatalytic activity than pure CuO in the presence of H2O2 and visible light irradiation, where the dye was completely removed and mineralized after 240 min, evidenced by COD measurement. The photocatalytic regeneration also shows that the biosorption efficiency was maintained at 91% over 3 cycles, indicating the significant self-regenerative capacity of the biosorbent.

ZnCl2-activated carbon from soybean dregs as a high efficiency adsorbent for cationic dye removal: isotherm, kinetic, and thermodynamic studies

Activated carbon was prepared from soybean dregs using chemical activation by zinc chloride. The influence of activation parameters such as impregnation ratio, activation temperature and carbonization time was investigated. The physicochemical properties of activated carbon were characterized using SEM, FTIR, BET and TGA, respectively. The effect factors including pH, contact time, temperature and dose on the adsorption properties of methylene blue onto activated carbon were studied. The adsorption equilibrium data of methylene blue onto activated carbon were well fitted to the Langmuir model, giving a maximum adsorption capacity of 255.10 mg/g. It indicates that activated carbon is a promising adsorbent for removing methylene blue from aqueous solution. The kinetic data were well described by the pseudo-second-order model. Thermodynamic parameters indicate that adsorption process is spontaneous and endothermic.The effect of temperature on MB adsorbed by AC shows that the equilibrium adsorption capacity increases with increasing temperature from 303 to 323 K. Increasing adsorption capacities with temperature indicate that the adsorption of MB onto AC is controlled by an endothermic reaction.

An environmental friendly enrichment method for microextraction of cadmium and lead in groundwater samples: Impact on biological sample of children

A novel ionic liquid-based vortex assisted dispersive liquid-liquid micro extraction procedure(IL-VADLLμE) was proposed for the enrichment of toxic metals, cadmium (Cd) and lead (Pb) in different types of water samples, domestic treated and groundwater (tube well and hand pump). Whereas, the concentration of both toxic metals was also determined in the scalp hair of children (age ranged 1-3 years), drinking contaminated groundwater termed as exposed group, whereas for comparative purposes scalp hair of age matched children consumed domestically treated water, named as non-exposed group. To preconcentrate the trace levels of Cd and Pb, a green chelating agent, l-cysteine (2-amino-3-sulfhydrylpropanoic acid) was used for complexation, an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM] [PF₆] utilized as extractant and hexafluorophosphate ion (PF₆^-) as anion pairing agent, which facilitate the enrichment of hydrophobic complexes of analytes into the acceptor phase. Various operative features for the IL-VADLLμE method like pH of standards/samples, volume of ionic liquid and sample solution, concentration of ligand, ion pair reagent and ionic liquid, vortex and electrical shaking time (for comparative purpose), were thoroughly optimized. The projected method was effectively applicable to assess the Cd and Pb in trace level in real water sample (surface and groundwater) and scalp hair samples of children belongs to exposed and non-exposed areas. The high contents of both toxic metals in scalp hair samples of children consuming groundwater indicate that the adverse impacts of both toxic metals especially Pb on the general health as well as neuron and skeletal problem, from child hood.

Synthesis and application of magnetic-surfaced pseudo molecularly imprinted polymers for zearalenone pretreatment in cereal samples

Zearalenone (ZEA) is a fungal contaminant widely found in grains. In cereal samples, trace zearalenone was extracted and enriched using magnetic-surfaced pseudo molecularly imprinted polymers (SPMIPs) and detected. SPMIPs were prepared with Fe₃O₄ as the magnetic core, modified halloysites nanotubes as supporting materials, and selective imprinted polymers as shells. Vinyl was modified on the surface of halloysites nanotube. SPMIPs were synthesized with pseudo templates. SPMIPs as the adsorbent of dispersed-solid phase extraction (μ-SPE) were used to purify and enrich ZEA from maize samples. After optimized, the pretreatment method was evaluated. The linearity of the method was ranged within 10-200 ng mL^-1. LOD and LOQ were 2.5 ng mL^-1 and 8 ng mL^-1 respectively. The ZEA spiking recoveries in maize samples ranged within 74.95-88.41% were with good RSDs lower than 4.25%. The developed method was successful applied in maize, oat, and wheat sample treatments and compared.

Synthesis of N-doped TiO2/SiO2/Fe3O4 magnetic nanocomposites as a novel purple LED illumination-driven photocatalyst for photocatalytic and photoelectrocatalytic degradation of naproxen: optimization and different scavenger agents study

N-doped TiO₂/SiO₂/Fe₃O₄ as a new magnetic photocatalyst that is active in visible light has been prepared by simple sol-gel method. The prepared samples were characterized by XRD, FESEM, EDX, TEM, BET, BJH, VSM, XPS, FT-IR, and DRS-UV/Vis analysis. The photocatalytic effect of synthesized samples on naproxen degradation was studied. The operational parameters were optimized through central composite design to achieve maximum efficiency. The optimum values for maximum efficiency were obtained at pH of 4.29, catalyst mass of 0.06 g, naproxen concentration of 9.33 mg L^-1, and irradiation time of 217.06 min. At these optimum conditions, the maximum photocatalytic degradation percentages of naproxen were found to be 96.32% at desirability function value of 1.0. Coupling the electrical current with the photocatalytic process proved that the electrical current was considerably efficient in decreasing the degradation time of removing the naproxen from aqueous solutions. The photocatalytic activity of the nanoparticles was also studied under sunlight. Considering the results provided by UV-Vis spectrophotometry and total organic carbon, it was found that the prepared samples are extraordinarily efficient to degrade naproxen under both purple LED and solar lights. Furthermore, the effect of different scavenger agents on naproxen degradation has been studied.

Ultrasonic assisted synthesis of magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide for sonochemical simultaneous removal of sunset yellow and tartrazine dyes by response surface optimization: Application of derivative spectrophotometry

The magnetic Ni-Ag bimetallic nanoparticles supported on reduced graphene oxide (Ni-Ag NPs/rGO) was synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), field emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM). Subsequently, this magnetic hybrid material as a novel adsorbent was applied for the sonochemical simultaneous removal of sunset yellow and tartrazine dyes in combination with first-order derivative spectrophotometric method to resolve the overlap between the spectra of these dyes. With magnetic properties, the adsorbent could easily be collected from aqueous solution using an external magnetic field. The parameters including initial concentration of each dye, adsorbent dosage and sonication time were studied by Box-Behnken design (BBD) and response surface methodology (RSM), while pH was studied by one-at-a-time approach. According to Box-Behnken design based on desirability function (DF), the best experimental conditions was set as initial sunset yellow concentration 10 mgL^-1, initial tartrazine concentration 8.5 mgL^-1, adsorbent dosage 0.045 g and sonication time of 15 min. The equilibrium data was fitted to different isotherm models and the results revealed the suitability of the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 28.57 and 26.31 mg g^-1 for sunset yellow and tartrazine, respectively. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. The reusability of the magnetite nanoparticles revealed about 8% decrease in the removal efficiency within four consecutive runs.

Application of ultrasonically modified cloud point extraction method for simultaneous enrichment of cadmium and lead in sera of different types of gallstone patients

A novel and greener ultrasonically assisted/modified cloud point extraction procedure for the simultaneous preconcentration of lead and cadmium in serum samples of different types of gallstone patients was developed. The chelates of the under study metals, formerly formed with 8-hydroxyquinoline, were extracted in the micelles of a nonionic surfactant prior to analysis by flame atomic absorption spectrometer (FAAS). After the arrival of the cloud point, the critical micellar mass produced was homogenously dispersed in the aqueous phase with the help of ultrasound energy. The reliability of the developed procedure was tested by relative standard deviation (% RSD), which was found to be <5%. The performance of the proposed procedure was checked by applying to certified reference material and spiking standard in real samples. All the experimental parameters were optimized. The developed procedure of Um-CPE was applied successfully for the analysis of the target heavy metals in serum samples of different types of gallstone patients and referents. The higher levels of the understudy metals were observed in the patients as compared to the referents but the levels of the both metal were found to be considerably higher in patients with pigmented gallstones.

Design of a new technique based on combination of ultrasound waves via magnetite solid phase and cloud point microextraction for determination of Cr(III) ions

In this work, we focused on development of a new techniques by coupling of ultrasound irradiation, cloud point method and magnetite solid phase microextraction for the extraction and preconcentration of Cr(III) ions from aqueous solutions. In order to reduce cost and improve practicability of proposed process a new efficient and regenerable magnetite sorbent (functionalized chitosan grafted-amino graphene oxide (GO) decorated by zinc ferrite nanoparticles (CS-GO-Zn: Fe₂O₄)) was synthesized through hydrothermal method and then characterized by FT-IR, FE-SEM, EDS and XRD analysis. Effect of initial sample volume and type, volume and concentration of eluent on the ER%_Cr(III) were investigated and optimized using one at a time method. Correlation between the main and interaction effects of other operational parameters such as Cr(III) ion concentration, CS-GO-Zn: Fe₂O₄ mass, sonication time, pH and solution temperature on the ER%_Cr(III) were investigated and optimized by central composite design coupled with desirability function approach. The results revealed that there were significant effects for most investigated terms on the ER%_Cr(III) and maximum ER% of 88.09% was obtained in desirability value of 1.0. This maximum efficiency was obtained at 0.035µg/mL Cr(III) ion concentration, 40.16°C temperature, 0.016g of CS-GO-Zn: Fe₂O₄, pH 6.36 and 9.20min sonication time. In addition, under the optimal conditions the linear range, limit of detection, enrichment factor and relative standard deviation were found to be 0.02-4.4µg/mL, 0.002µg/mL, 23.23 and 1.68% respectively. Finally, the method was successfully applied to the separation and preconcentration of Cr(III) ion from tap, river and mineral waters.

Rapid and high-capacity ultrasonic assisted adsorption of ternary toxic anionic dyes onto MOF-5-activated carbon: Artificial neural networks, partial least squares, desirability function and isotherm and kinetic study

The present paper focused on the ultrasonic assisted simultaneous removal of fast green (FG), eosin Y (EY) and quinine yellow (QY) from aqueous media following using MOF-5 as a metal organic framework and activated carbon hybrid (AC-MOF-5). The structure and morphology of AC-MOF-5 was identified by SEM, FTIR and XRD analysis. The interactive and main effects of variables such as pH, initial dyes concentration (mgL^-1), adsorbent dosage (mg) and sonication time (min) on removal percentage were studied by central composite design (CCD), subsequent desirability function (DF) permit to achieved real variable experimental condition. Optimized values were found 7.06, 5.68, 7.59 and 5.04mgL^-1, 0.02g and 2.55min for pH, FG, EY and QY concentration, adsorbent dosage and sonication time, respectively. Under this conditions removal percentage were obtained 98.1%, 98.1% and 91.91% for FG, EY and QY, respectively. Two models, namely partial least squares (PLS) and multi-layer artificial neural network (ANN) model were used for building up to construct an empirical model to predict the dyes under study removal behavior. The obtained results show that ANN and PLS model is a powerful tool for prediction of under-study dyes adsorption by AC-MOF-5. The evaluation and estimation of equilibrium data from traditional isotherm models display that the Langmuir model indicated the best fit to the equilibrium data with maximum adsorption capacity of 21.230, 20.242 and 18.621mgg^-1, for FG, EY and QY, respectively, while the adsorption rate efficiently follows the pseudo-second-order model.

Simultaneous removing of Pb2+ ions and alizarin red S dye after their complexation by ultrasonic waves coupled adsorption process: Spectrophotometry detection and optimization study

Funthenalized chitosan (CS) was composited with mesoprous SBA-15 and characterized via. different techniques such as FT-IR and FE-SEM. Subsequently, this new material was applied for simulations ultrasound-assisted adsorption of Pb²⁺ ion and alizarin red S (ARS) dye after their complexation. Efficient conventional variables in adsorption process such as initial ARS and Pb²⁺ concentration, adsorbent mass and sonication time were studied by small central composite design (CCD) and optimized with desirability function approach. Lack of fit testes and model summary statistics for linear, 2FI, quadratic and cubic models were investigated and according to the insignificant lack of fit and maximizing the R-squared (R²), adjusted R-squared and the predicted R-squared quadratic model was selected for other step analysis for removal of ARS dye, while, for Pb²⁺ ions 2FI model was selected as best model. Quadratic model ANOVA for ARS dye removal shows the F-value parameter (683.91), very low p-value model (<0.0001) and p-value lack of fit (0.0568) that implied this model was highly significant. Also, 2FI model ANOVA for Pb²⁺ ions removal shows the F-value parameter (282.51), very low p-value model (<0.0001) and p-value lack of fit (2.05). According to desirability function approach maximum removal percentage of ARS (87.61%) and Pb²⁺ ions (83.54%) was shown at optimum of condition that were set as at: 25 and 25mgL^-1, 0.028g and 11.8min for initial ARS and Pb²⁺ ions concentration, adsorbent mass and sonication time, respectively. Finally, it was found that the equilibrium and kinetic of adsorption process follow the Langmuir isotherm and pseudo-second-order kinetic model, respectively. From the Langmuir isotherm, maximum monolayer capacity (q_max) was obtained 50.25 and 57.14mgg^-1 for ARS and Pb²⁺ ions removal, respectively.

Preparation of an ion imprinted functionalized mesoporous silica for rapid and specific absorption Cr(iii) ions in effluents

We developed an effective and selective method to remove Cr(iii) ions in acidic effluents.