A review on magnetic sensors for monitoring of hazardous pollutants in water resources

Water resources have long been of interest to humans and have become a serious issue in all aspects of human life. The disposal of hazardous pollutants in water resources is one of the biggest global concerns and poses many risks to human health and aquatic life. Therefore, the control of hazardous pollutants in water resources plays an important role, when it comes to evaluating water quality. Due to low toxicity, good electrical conductivity, facile functionalization, and easy preparation, magnetic materials have become a good alternative in recent years to control hazardous pollutants in water resources. In the present study, the idea of using magnetic sensors in controlling and monitoring of pharmaceuticals, pesticides, heavy metals, and organic pollutants have been reviewed. The water pollutants in drinking water, groundwater, surface water, and seawater have been discussed. The toxicology of water hazardous pollutants has also been reviewed. Then, the magnetic materials were discussed as sensors for controlling and monitoring pollutants. Finally, future remarks and perspectives on magnetic nanosensors for controlling hazardous pollutants in water resources and environmental applications were explained.

Review on molecular imprinting technology and its application in pre-treatment and detection of marine organic pollutants

Molecular imprinting technology (MIT) has been considered as an attractive method to produce artificial receptors with the memory of size, shape and functional groups of the templates and has become an emerging technique with the potential in various fields due to recognitive specificity, high efficient selectivity and mechanical stability, which can effectively remove background interference and is suitable for the pre-treatment and analysis of trace level substances in complex matrix samples. Nearly 100 papers about the application of MIT in the detection of marine pollutants were found through Science Citation Index Expanded (SCIE). On this basis, combined with the application of MIT in other fields, the pre-treatment process of marine environmental samples was summarized and the potential of four types of different molecularly imprinted materials in the pre-treatment and detection of marine organic pollutants (including antibiotics, triazines, organic dyes, hormones and shellfish toxins) samples was evaluated, which provides the innovative configurations and progressive applications for the analysis of marine samples, and also highlights future trends and perspectives in the emerging research field.

Layered porous organic frameworks as a novel adsorbent for the solid phase extraction of chlorophenols prior to their determination by HPLC-DAD

A layered porous organic framework (L-POF) with high surface area and porous volume was used as a novel adsorbent for adsorption of chlorophenols (CPs). The L-POF showed much higher adsorption capacity for four CPs (2-CP, 3-CP, 2,3-CP, 2,4-CP) compared with corresponding amorphous POF and some commercial adsorbents. Then, an L-POF-based solid-phase extraction method combined with high-performance liquid chromatography for analyzing CPs at the wavelength of 280 nm in water and honey samples was established. Under the optimum conditions, four CPs exhibited good linearity in the range 0.10-80.0 ng mL^-1 for water and 2-400 ng g^-1 for honey samples with determination coefficient r² > 0.996. The method has low limits of detection of 0.03-0.10 ng mL^-1 for water and 0.5-1.0 ng g^-1 for honey samples. The method presented satisfactory precision and accuracy with relative standard deviations ≤ 7.8% and recoveries of 80-115%. High enrichment factors of 123-190 for water and 63-97 for honey were obtained. The validated method was successfully used to determine CPs in water and honey samples. The L-POF also displayed prominent adsorption performance for many other dyes and organic contaminants. This suggests that it can be an ideal candidate as adsorbent for wide application in separation and analysis. Graphical Abstract.

Enhanced photocatalytic degradation of doxycycline using a magnetic polymer-ZnO composite

A novel magnetic polymer-ZnO composite was prepared by incorporating Fe₃O₄ and ZnO nano-particles in the structure of an adsorbent polymer. Precipitation polymerization was used for synthesizing the adsorbent polymer and its efficiency for extracting doxycycline from aqueous solution was optimized according to several parameters including time, pH and amount of polymer. Results showed the highest extraction efficiency at neutral pH of the doxycycline solution in 20 min, and the capacity of the polymer was about 20 mg/g. The magnetic property of a material is important for fast and facile separation of composite particles after each use. Magnetic polymer-ZnO composite was synthesized by adding Fe₃O₄ and ZnO nano-particles to the polymerization mixture in order to take advantage of both sorption and photocatalytic degradation mechanisms. The obtained composite was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy equipped with wavelength dispersive X-ray spectroscopy and used for enhanced photocatalytic degradation of doxycycline in aqueous solution. Results showed 76.5% degradation of doxycycline in 6 hours which was significantly higher than the degradation observed by an equivalent amount of ZnO nano-particles. Photocatalytic degradation of doxycycline fitted the pseudo first order kinetic model with a rate constant of 4 × 10^-3 μg mL^-1 min^-1.

Solid-phase extraction of chlorophenols in seawater using a magnetic ionic liquid molecularly imprinted polymer with incorporated silicon dioxide as a sorbent

A type of magnetic ionic liquid based molecularly imprinted polymer coated on SiO₂ (Fe₃O₄@SiO₂@IL-MIPs) was prepared with 1-vinyl-3-ethylimidazole ionic liquid as functional monomer, and 1,4-butane-3,3'-bis-1-ethylimidazole ionic liquid as cross linker, 4-Chlorophenol as template was successfully applied as a selective adsorbent for selective extraction of 5 chlorophenols in seawater samples by using the magnetic solid-phase extraction (MSPE) method. 11 types of Fe₃O₄@SiO₂@IL-MIPs were synthesized and investigated for their different compositions of functional monomer (such as [C₂min][Br], [C₂min][BF₄], [C₂min][PF₆], acrylamide, methacrylic acid and 4-vinyl pyridine) and cross-linker (such as [C₄min₂][Br], [C₄min₂][BF₄], [C₄min₂][PF₆], divinylbenzene, and ethylene glycol dimethacrylate), respectively. The [C₂min][BF₄] and [C₄min₂][PF₆] based Fe₃O₄@SiO₂@IL-MIP with the highest extraction efficiencies was applied to the optimization experiment of MSPE process (including extraction time, adsorbent mass and desorption solvents). Good linearity was obtained with correlation coefficients (R²) over 0.9990 and the relative standard deviations for the intra-day and inter-day determination were less than 3.10% with the extraction recoveries ranged from 85.0% to 98.4%. The results indicated that the proposed Fe₃O₄@SiO₂@IL-MIPs possesses great identification and adsorption properties, and could be used as a good sorbent for selective extraction of CPs in environment waters.

Simple and selective detection of quercetin in extracts of plants and food samples by dispersive-micro-solid phase extraction based on core–shell magnetic molecularly imprinted polymers

In the present study, a D-μ-SPE clean-up method was established for the analysis of quercetin in extracts of plants and food samples using a magnetic molecularly imprinted polymer as the sorbent by HPLC-UV detection.

Fabrication of ofloxacin imprinted polymer on the surface of magnetic carboxylated cellulose nanocrystals for highly selective adsorption of fluoroquinolones from water

A novel adsorbent with high selectivity for fluoroquinolone (FQ) compounds was developed, based on the surface functionalization of magnetic carboxylated cellulose nanocrystals (M-CCNs) with molecularly imprinted polymer (MIP) comprising amine moieties. The imprinting was achieved by a radical polymerization technique, which uses glycidyl methacrylate, tetraethylenepentamine, ofloxacin, ethylene glycol dimethacrylate, and azobisisobutyronitrile as the functional monomer, active groups provider, template molecule, crosslinking agent, and initiator, respectively. The developed material (M-CCNs@MIP) was comprehensively characterized and shown to exhibit high adsorption capacity and selectivity with rapid equilibration time. Moreover, the adsorption isotherms could be well-fitted with the Freundlich model, and the adsorption kinetics followed the pseudo-second-order model. The maximum adsorption capacities for M-CCNs@MIP after 2 and 20min were 34.09 and 40.65mgg^-1, respectively, compared to 9.98 and 15.28mgg^-1 observed for the unimprinted polymer (M-CCNs@NIP). By coupling the M-CCNs@MIP adsorbent with high-performance liquid chromatography, an approach was established to enhance the selective adsorption of seven structurally similar FQ compounds in river water samples. The recoveries of the seven FQs ranged from 81.2 to 93.7%, and the limits of detection were between 5.4 and 12.0ngmL^-1. The M-CCNs@MIP adsorbent also retained good performance after seven consecutive cycles of reuse.

Synthesis of core–shell imprinting polymers with uniform thin imprinting layer via iniferter-induced radical polymerization for the selective recognition of thymopentin in aqueous solution

Core–shell imprinting microspheres for the selective and rapid recognition of thymopentin with the aid of a novel polymeric ionic liquid.