Recent advances in the source identification and remediation techniques of nitrate contaminated groundwater: A review.

Researchers have long been committed to identify nitrate sources in groundwater and to develop an advanced technique for its remediation because better apply remediation solution and management of water quality is highly dependent on the identification of the NO3- sources contamination in water. In this review, we systematically introduce nitrate source tracking tools used over the past ten years including dual isotope and multi isotope techniques, water chemistry profile, Bayesian mixing model, microbial tracers and land use/cover data. These techniques can be combined and exploited to track the source of NO3- as mineral or organic fertilizer, sewage, or atmospheric deposition. These available data have significant implications for making an appropriate measures and decisions by water managers. A continuous remediation strategy of groundwater was among the main management strategies that need to be applied in the contaminated area. Nitrate removal from groundwater can be accomplished using either separation or reduction based process. The application of these processes to nitrate removal is discussed in this review and some novel methods were presented for the first time. Moreover, the advantages and limitations of each approach are critically summarized and based on our own understanding of the subject some solutions to overcomes their drawbacks are recommended. Advanced techniques are capable to attain significantly higher nitrate and other co-contaminants removal from groundwater. However, the challenges of by-products generation and high energy consumption need to be addressed in implementing these technologies for groundwater remediation for potable use.

Simple and Efficient Detection Approach of Quercetin from Biological Matrix by Novel Surface Imprinted Polymer Based Magnetic Halloysite Nanotubes Prepared by a Sol-Gel Method.

Molecular imprinted polymers coated magnetic halloysite nanotubes (MHNTs-MIPs) were prepared through sol-gel method by using quercetin (Que), APTES and TEOS as template, monomer and cross-linker agent, respectively. The synthesized MHNTs-MIPs were characterized by fourier transform infrared, scanning electron microscope, transmission electron microscope, XRD and vibrating sample magnetometer. Various parameters influencing the binding capacity of the MHNTs-MIPs were investigated with the help of response surface methodology. Selectivity experiments showed that the MHNTs-MIPs exhibited the maximum selective rebinding to Que. Therefore, the MHNTs-MIPs was applied as a solid-phase extraction adsorbent for the extraction and preconcentration of quercetin and luteolin in serum and urine samples. The limits of detection for quercetin and luteolin range from 0.51 to 1.32 ng mL-1 in serum and from 0.23 to 1.05 ng mL-1 in urine, the recoveries are between 95.20 and 103.73% with the RSD less than 5.77%. While the recovery hardly decreased after several cycles. The designed MHNTs-MIP with high affinity, sensitivity and maximum selectivity toward Que in SPE might recommend a novel method for the extraction of flavonoids in other samples like natural products.

Cucurbiturils regulating Fe3O4-Au nanoparticles as a multi-functional platform for Cd2+ sensing and nitrocompound catalysis.

Herein, through the interfacial regulation of cucurbiturils (CBs) on Fe3O4-Au nanoparticles, a novel multifunctional platform is constructed for the sensitive detection of Cd2+ and the selective catalytic reduction (SCR) of nitrocompounds. The reported surface modification strategy provides an efficient approach to prepare a new platform for multiple purposes.

Selective recognition and enrichment of sterigmatocystin in wheat by thermo-responsive imprinted polymer based on magnetic halloysite nanotubes.

Two thermo-responsive molecularly imprinted polymers (MHNTs@MIP and MCNTs@MIP) for the selective extraction of sterigmatocystin have been prepared on the surface of the magnetic halloysite nanotubes (MHNTs) and magnetic carbon nanotubes (MCNTs), respectively. 1, 8-dihydroxyanthraquinone, n-isopropyl acrylamide, methacrylic acid, ethylene dimethacrylate and dimethyl sulfoxide were used as the dummy template, thermo-sensitive functional monomer, co-monomer, cross-linker and porogen, respectively. The magnetic properties, adsorption properties as well as the temperature responsive behaviors of MHNTs@MIP and MCNTs@MIP were systematically studied and compared for the first time. Enough saturation magnetizations of MHNTs@MIP (9.42 emu/g) and MCNTs@MIP (10.54 emu/g) were obtained. MHNTs@MIP and MCNTs@MIP also showed controllable adsorption and release behaviors to sterigmatocystin in response to the temperature change (35 °C and 20 °C). Compared with MCNTs@MIP, MHNTs@MIP had higher adsorption affinity (KL = 0.120 L/mg), higher adsorption kinetic (K2 = 0.0100 g/(mg•min)) and higher imprinting factor (5.22) to sterigmatocystin. These results indicated that MHNTs@MIP was favorable adsorbent for the selective separation of sterigmatocystin. Furthermore, the elution conditions of MHNTs@MIP were optimized by response surface methodology. Under the optimal conditions, MHNTs@MIP coupled with high performance liquid chromatography were successfully applied to the selective recognition, purification, enrichment and detection of sterigmatocystin in wheat samples. The recoveries were calculated from 88.62% to 102.9% with RSDs less than 3.5 % and limit of detection of 1.1 µg/kg. This work provided a suitable carrier for the preparation of imprinted polymers and a practical approach for highly selective recognition and determination of analytes in real samples.

Preparation of novel molecularly imprinted magnetic graphene oxide and their application for quercetin determination.

In this work, quercetin (Que) molecular imprinted polymer (MIP) material decorated on magnetic graphene oxide (MGO) with high performance was prepared for the first time using a surface-imprinting technique. Magnetic graphene oxide was synthesized using the solvothermal route. Methacrylic acid (MAA) was used as functional monomer, ethylene glycol dimethyl acrylate (EGDMA) as cross-linker; Que. was used as template, for the decoration with MIP. The prepared nanocomposite was examined by different characterization methods including fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM). The adsorption performance was investigated. MGO-MIP was found to have high loading (369 mg g-1) and selective capacity making the nanomaterial more performant than previous similar reported nanomaterials. The determination of Que. was carried out by mean of magnetic solid phase extraction method coupled with high-performance liquid chromatography (HPLC) and the extraction conditions studies were also performed out. Under the optimized conditions, MGO-MIP showed great performance for the extraction, separation and determination of Que. in green tea and serum samples, compared to the flavonoid analogs luteolin (Lut) and rutin (Rut) in the same matrix samples.

Selective recognition and enrichment of carbamazepine in biological samples by magnetic imprinted polymer based on reversible addition-fragmentation chain transfer polymerization.

A well-defined molecularly imprinted polymer (Fe3O4@CS@MIP) was synthesized via reversible addition-fragmentation chain transfer polymerization for magnetic solid-phase extraction coupled with high-performance liquid chromatography-diode array detector to detect carbamazepine (CBZ) in biological samples. The composition of Fe3O4@CS@MIP was selected by a two-step screening method. 4-vinyl pyridine, divinylbenzene and dimethylformamide were chosen as the functional monomer, cross-linker and porogen, respectively. The imprinted layer was coated on the surface of the chain transfer agent-modified magnetic chitosan nanoparticles. The prepared Fe3O4@CS@MIP was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller measurement and vibrating sample magnetometer. The results indicated that Fe3O4@CS@MIP had a large surface area (265.8 m2/g), high saturation magnetization (19.88 emu/g) and uniform structure. Besides, the binding property of the Fe3O4@CS@MIP was studied in detail. The Fe3O4@CS@MIP showed high imprinting factor (IF = 4.83) and desirable adsorption capacity (323.10 µmol/g) to CBZ. Under the optimum conditions, the developed method exhibited excellent linearity (R2>0.999) in the range of 0.01-0.5 mg/L and 1.0-30.0 mg/L, and the limits of detection were 1.0 µg/L and 9.6 µg/L for the urine and serum samples, respectively. Good recoveries (88.22%-101.18%) were obtained with relative standard deviations less than 4.83%. This work provided a practical approach for the selective extraction and detection of CBZ in real samples.

Novel mixed hemimicelles based on nonionic surfactant-imidazolium ionic liquid and magnetic halloysite nanotubes as efficient approach for analytical determination.

The co-adsorption of mixed nonionic surfactant and imidazolium-based ionic liquid, Triton X100 (TX100), with 1-cetyl-3-methylimidazolium bromide (C16mimBr) adsorbed onto the surface of magnetic halloysite nanotubes (MHNTs) was used as an efficient adsorbent for simultaneous determination of amlodipine and nimodipine in urine. The designed adsorbent was characterized by TEM, TGA, FTIR, and DLS analysis methods. All the parameters that influence the extraction efficiency are optimized with the aid of response surface methodology (RSM). The effects of nonionic surfactant TX100 with different structures of ionic-liquid-coated MHNTs were investigated. Under optimum conditions, extraction recoveries of amlodipine and nimodipine were in the range of 73.8-81.2 and 94.3-96.1%, with RSDs (n = 3) of 2.6-5.5% in spiked urine samples, respectively. The adsorption mechanism principal of mixed hemimicelles was discussed in this study. The limit of detection obtained for analytes was < 0.002 µg·mL-1. To our knowledge, this was the first attempt using a mixed hemimicelle solid-phase extraction (SPE) based on MHNTs and nonionic surfactant and imidazolium-based ionic liquid for the simultaneous determination of amlodipine and nimodipine in biological samples. Graphical abstract ᅟ.

Folic acid-conjugated chitosan oligosaccharide-magnetic halloysite nanotubes as a delivery system for camptothecin.

In this research, to achieve enhanced intracellular uptake of anticancer drug carriers for efficient chemotherapy, folic acid conjugated chitosan oligosaccharides assembled magnetic halloysite nanotubes (FA-COS/MHNTs) have been tailored as multitask drug delivery system towards camptothecin (CPT). Besides magnetic targeting, the nanocomposites have been reacted with folate complex in order to selectively target cancer cells over expressing the folic acid receptor. HNTs showed to have a high storage capacity of CPT. In vitro, the release results indicated that CPT outflow from the nanocarriers at pH 5 was much greater than that at both pH 6.8 and 7.4. MTT assays showed that the CPT-loaded nanocarriers exhibited stronger cell growth inhibitory against colon cancer cell. Furthermore, nanocarriers gained specificity to target cancer cells because of the enhanced cell uptake mediated by FA moiety and presence of COS. Therefore, the rational designed HNTs nanocarrier for chemotherapy drug showed great potential as tumor-targeted drug delivery carrier.

Halloysite nanotubes in analytical sciences and in drug delivery: A review.

Halloysite (HNT) is a natural inorganic mineral that has many applications in manufacturing. This review (with 192 references) covers (a) the chemical properties of halloysites, (b) the effects of alkali and acid etching on the loading capacity and the release behavior of halloysites, (c) the use of halloysite nanotubes in analytical sciences and drug delivery, and (d) recent trends in the preparation of magnetic HNTs. Synthetic methods such as co-precipitation, thermal decomposition, and solvothermal method are discussed, with emphasis on optimal magnetization. In the analytical field, recent advancements are summarized in terms of applications of HNT-nanocomposites for extraction and detection of heavy metal ions, dyes, organic pollutants, and biomolecules. The review also covers methods for synthesizing molecularly imprinted polymer-modified HNTs and magnetic HNTs. With respect to drug delivery, the toxicity, techniques for drug loading and the various classes of drug-halloysite nanocomposites are discussed. This review gives a general insight on the utilization of HNT in analytical determination and drug delivery systems which may be useful for researchers to generate new ideas. Graphical abstract Schematic presentation of the structure of halloysite nanotubes, selected examples of modifications and functionalization, and represetative field of applications.

Preparation of multifunctional PEG-graft-Halloysite Nanotubes for Controlled Drug Release, Tumor Cell Targeting, and Bio-imaging.

With the intent of enhancing the loading capacity and controlled the release of a low-water soluble drug (quercetin), 6 ar ms (Poly-Ethylene-Glycol)-amine was grafted in the external surface of halloysite nanotubes. The grafted halloysite nanotubes (HNTs-g-PEG) were decorated with carbon quantum dots for additive fluorescents properties. Conjointly, biotin was conjugated to PEG's free amine groups for precise targeting of tumor tissue and higher cellular uptake. The obtained nanoparticles were characterized by the FTIR, TEM, XRD, zeta potential and TGA analysis. The photoluminescence (PL) properties were investigated by firstly, observing under UV-light at 365 nm; then, the fluorescence spectra of modified HNTs at different levels of preparation were obtained and showed a suitable blue fluorescence. Furthermore, the fluorescent properties were demonstrated by the optical image of HNTs-g-PEG-CDs-Biotin obtained from the confocal microscope, which could be interesting for both in vitro and in vivo imaging. Besides, the prepared NPs showed a superior loading capacity of Que (278.36 mg/g) at optimal adsorption conditions comparing to pristine HNTs. The in vitro drug release from these NPs was relatively sustained and pH sensitive. The incubation of the prepared HNTs-g-PEG-CDs-Biotin NPs with HeLa cells showed a low toxicity and a suitable biocompatibility. The MTT assay of the Que-loaded NPs possesses enhanced antitumor activity over the free Que.

Mixed hemimicelle solid-phase extraction based on magnetic halloysite nanotubes and ionic liquids for the determination and extraction of azo dyes in environmental water samples.

An effective and greener mixed hemimicelles magnetic solid phase extraction (MHMSPE) based on magnetic halloysite nanotubes (MHNTs) and ionic liquid (IL) is developed for the simultaneous enrichment and determination of anionic azo dyes in a spiked environmental water sample. In this MHMSPE, the formation of C16mimBr with mixed hemimicelles on the surface of MHNTs leads to the retention of analytes by strong hydrophobic, p-p and electrostatic interactions. This MHMSPE technique combines the advantages of MHNTs and mixed hemimicelles. Zeta potential data demonstrated that mixed hemimicelles were formed in [C16mimBr]/[MHNTs] ratios of the range from 0.15 to 1.33. Different important factors affecting the preconcentration of analytes were investigated and optimized by response surface methodology and one variable at a time. Under the optimum conditions, the limits of detection (LOD) for methyl red and methyl orange (MR and MO) were 0.042 and 0.050 µg L-1 in samples, respectively. The accuracy of the method was assessed by recovery measurements on a spiked sample, and good recoveries 85-87% for MR and 89-93% for MO, with preconcentration factors of 481 and 524, respectively. The low relative standard deviations from 1.6-3.1% for tap water and 2.5-5.4% for lake water was achieved. So far as we know, this is the first development of a mixed hemimicelles SPE based on MHNTs and IL for the extraction of trace anionic azo dyes in environment water samples.

QbD approach by computer aided design and response surface methodology for molecularly imprinted polymer based on magnetic halloysite nanotubes for extraction of norfloxacin from real samples.

This article describes the development, optimization, and evaluation of a novel composite imprinted polymer, on the basis of magnetic halloysite nanotubes (MHNTs-MIPs) using "Quality by Design (QbD)" approach combining computer simulation and response surface methodology. Norfloxacin, methacrylic acid, and ethylene glycol dimethacrylate were used as template, functional monomer and cross-linker, respectively. As a comparison, two MHNTs-MIPs have been prepared with the most suitable functional monomer methacrylic acid (MAA) along with acrylamide (AM). To explain the adsorption behavior, adsorption kinetics and isotherms were studied. Magnetic halloysite nanotubes molecularly imprinted polymers prepared from MAA (MHNTs-MIP1) displayed a high adsorption capacity (349 µg mg-1) toward NOR. A magnetic imprinting solid phase extraction method coupled with high performance liquid chromatography (MHNTs-MISPE-HPLC-UV) was developed for the determination of NOR in serum and water samples, by applying MHNTs-MIP as a sorbent. The recoveries from 83.76% to 103.30% in water and from 90.46% to 99.78% in serum were obtained. Besides remarquable mechanical properties and specific recognition of MHNTs-MIP toward template molecule. It could be also collected and separated fastly by external magnetic field. Moreover, MHNTs-MIPs could be reused for several cycles with the recovery range from 83.25% to 100.96% for water sample and from 85.65% to 100.33% for serum sample. These analytical results of serum and water samples showed that the proposed method based on MHNTs-MIPs is applicable for fast and selective extraction of therapeutic agents from biological fluids and environmental water.

Polymer grafted-magnetic halloysite nanotube for controlled and sustained release of cationic drug.

In this research, novel polymer grafted-magnetic halloysite nanotubes with norfloxacin loaded (NOR-MHNTs) and controlled-release, was achieved by surface-initiated precipitation polymerization. The magnetic halloysite nanotubes exhibited better adsorption of NOR (72.10mgg-1) compared with the pristine HNTs (30.80mgg-1). Various parameters influencing the drug adsorption of the MHNTs for NOR were studied. Polymer grafted NOR-MHNTs has been designed using flexible docking in computer simulation to choose optimal monomers. NOR-MHNTs/poly (methacrylic acid or acrylamide-co-ethylene glycol dimethacrylate) nanocomposite were synthesized using NOR-MHNTs, methacrylic acid (MAA) or acrylamide (AM), ethylene glycol dimethacrylate (EGDMA) and AIBN as nanotemplate, monomers, cross linker and initiator, respectively. The magnetic nanocomposites were characterized by FTIR, TEM, XRD and VSM. The magnetic nanocomposites show superparamagnetic property and fast magnetic response (12.09emug-1). The copolymerization of monomers and cross linker led to a better sustained release of norfloxacin (>60h) due to the strong interaction formed between monomers and this cationic drug. The cumulative release rate of NOR is closely related to the cross linker amount. In conclusion, combining the advantages of the high adsorption capacity and magnetic proprieties of this biocompatible clay nanotube and the advantages of polymer shell in the enhancement of controlled-sustained release of cationic drug, a novel formulation for the sustained-controlled release of bioactive agents is developed and may have considerable potential application in targeting drug delivery system.