Sensitive simultaneous voltammetric determination of the herbicides diuron and isoproturon at a platinum/chitosan bio-based sensing platform.

Phenylurea herbicides are persistent contaminants, which leads their transport to the surface and ground waters, affecting human and aquatic organisms. Different analytical methods have been reported for the detection of phenylureas; however, several of them are expensive, time-consuming, and require complex pretreatment steps. Here, we show a simple method for the simultaneous electrochemical determination of two phenylurea herbicides by differential pulse adsorptive stripping voltammetry (DPAdSV) using a modified platinum/chitosan electrode. The one-step synthesized platinum/chitosan PtNPs/CS was successfully characterized by TEM, XRPD, and FT-IR, and applied through the sensing platform designated as PtNPs/CS/GCE. This bio-based modified electrode is proposed for the first time for the individual and/or simultaneous electrochemical detection of the phenylurea herbicides diuron and isoproturon compounds extensively used worldwide that present a very similar chemical structure. Electrochemical and interfacial characteristics of the modified electrode were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the oxidation mechanism of diuron and isoproturon occurs in two different pathways, with a peak-to-peak definition of ca. 0.15 V. Under differential pulse adsorptive stripping voltammetry (DPAdSV) optimized conditions, the limit of detection (LOD) was estimated as 7 µg L-1 for isoproturon and 20 µg L-1 for diuron (Ed = +0.8 V; td = 100 s). The proposed method was successfully applied to the determination of both analytes in river water samples, at three different levels, with a recovery range of 90-110%. The employment of the bio-based sensing platform PtNPs/CS/GCE allows a novel and easy analytical method to the multi-component phenylurea herbicides detection.

Adsorption of phenylurea herbicides by tropical soils.

The distribution of pesticides in soils with consequences for their mobility, bioavailability and water contamination is mainly ruled by sorption processes. Such processes are seldom investigated in tropical soils. Thus, specific interactions between tropical soils and most pesticides are widely unknown. Furthermore, the question arises whether the same factors govern adsorption in tropical and temperate soils. Thus, the sorption behaviour of five phenylurea herbicides (PUHs) was studied in eighteen differently composed soils originating from southwestern Nigeria. Sorption data were obtained by equilibrating the soil samples with 0.01 M CaCl2 solutions spiked with increasing concentrations of the target PUHs. The equilibrium data fitted well to the Freundlich isotherm equation (R2 ≥ 0.96), delivering the corresponding parameters (Kf and n). Linear distribution coefficients (Kd) were also calculated. The Pearson correlation was used to identify the specific soil and herbicide properties that have statistically significant correlations with sorption parameters. High correlations were established for various soil properties (pH, cation exchange capacity, organic carbon content, content of amorphous Fe and Mn oxides, clay/silt mass proportions) as well as molecular descriptors (octanol-water partition coefficient (log Kow) and molecular mass (Mw)) of the moderately hydrophobic herbicides. Monuron, chlorotoluron and isoproturon showed higher affinities for soil than previously reported. The gathered knowledge might assist in the assessment and in the precautionary avoidance of potential risks generated by these compounds in tropical soils.

A magnetic covalent aromatic polymer as an efficient and recyclable adsorbent for phenylurea herbicides.

A magnetic covalent aromatic polymer (Fe3O4-NH2-CAP) was synthesized by grinding a covalent aromatic polymer (CAP) and amino-functionalized magnetic nanoparticles (Fe3O4-NH2 NPs). The CAP was prepared by a Friedel-Crafts reaction between biphenyl and 1,3,5-benzenetricarbonyl trichloride. The interaction in the Fe3O4-NH2-CAP is based on hydrogen bond formation between the carbonyl groups in the CAP and the amino groups in the Fe3O4-NH2 NPs. The adsorbent inherits the advantages of the CAP and also has the superior magnetic property of the Fe3O4 NPs. The adsorbent was applied to magnetic solid-phase extraction of six phenylurea herbicides (metoxuron, monuron, chlortoluron, isoproturon, monolinuron, buturon) from soil and water samples. Following elution with 600 µL methanol, the herbicides were quantified by HPLC. The calibration plots are linear in the 1.00-100 ng g-1 herbicide concentration ranges in case of spiked soil samples, and in the 0.10-40 ng mL-1 concentration range for spiked water samples. The limits of detection range from 0.3 to 0.5 ng g-1 (soil) and from 0.01 to 0.03 ng mL-1 (water), with relative standard deviations of <8.0% and < 6.9%, respectively. Graphical abstract Schematic presentation for the preparation of the magnetic covalent aromatic polymer (Fe3O4-NH2-CAP) and of magnetic solid-phase extraction.

Enhanced and Complete Removal of Phenylurea Herbicides by Combinational Transgenic Plant-Microbe Remediation.

The synergistic relationships between plants and their rhizospheric microbes can be used to develop a combinational bioremediation method, overcoming the constraints of individual phytoremediation or a bioaugmentation method. Here, we provide a combinational transgenic plant-microbe remediation system for a more efficient removal of phenylurea herbicides (PHs) from contaminated sites. The transgenic Arabidopsis thaliana plant synthesizing the bacterial N-demethylase PdmAB in the chloroplast was developed. The constructed transgenic Arabidopsis plant exhibited significant tolerance to isoproturon (IPU), a typical PH, and it took up the IPU through the roots and transported it to leaves, where the majority of the IPU was demethylated to 3-(4-isopropylphenyl)-1-methylurea (MDIPU). The produced intermediate was released outside the roots and further metabolized by the combinationally inoculated MDIPU-mineralizing bacterium Sphingobium sp. strain 1017-1 in the rhizosphere, resulting in an enhanced and complete removal of IPU from soil. Mutual benefits were built for both the transgenic Arabidopsis plant and strain 1017-1. The transgenic Arabidopsis plant offered strain 1017-1 a suitable accommodation, and in return, strain 1017-1 protected the plant from the phytotoxicity of MDIPU. The biomass of the transgenic Arabidopsis plant and the residence of the inoculated degrading microbes in the combinational treatment increased significantly compared to those in their respective individual transgenic plant treatment or bioaugmentation treatment. The influence of the structure of bacterial community by combinational treatment was between that of the two individual treatments. Overall, the combination of two approaches, phytoremediation by transgenic plants and bioaugmentation with intermediate-mineralizing microbes in the rhizosphere, represents an innovative strategy for the enhanced and complete remediation of pollutant-contaminated sites.IMPORTANCE Phytoremediation of organic pollutant-contaminated sites using transgenic plants expressing bacterial enzyme has been well described. The major constraint of transgenic plants transferred with a single catabolic gene is that they can also accumulate/release intermediates, still causing phytotoxicity or additional environmental problems. On the other hand, bioaugmentation with degrading strains also has its drawbacks, including the instability of the inoculated strains and low bioavailability of pollutants. In this study, the synergistic relationship between a transgenic Arabidopsis plant expressing the bacterial N-demethylase PdmAB in the chloroplast and the inoculated intermediate-mineralizing bacterium Sphingobium sp. strain 1017-1 in the rhizosphere is used to develop an intriguing bioremediation method. The combinational transgenic plant-microbe remediation system shows a more efficient and complete removal of phenylurea herbicides from contaminated sites and can overcome the constraints of individual phytoremediation or bioaugmentation methods.

A magnetic knitting aromatic polymer as a new sorbent for use in solid-phase extraction of organics.

Magnetic knitting aromatic polymers (Fe3O4/KAPs) are introduced here as a new kind of sorbents. KAPs are hyper-cross-linked-polymers that were prepared via a Friedl-Crafts reaction from triphenylphosphine and benzene as building blocks. The Fe3O4/KAP composite was obtained by coprecipitation of KAP with magnetite nanoparticles. The resulting Fe3O4/KAP is shown to be a viable magnetic sorbent for various organic materials such as the phenylurea herbicides (PUHs), including metoxuron, monuron, chlortoluron, monolinuron and buturon, and also for various phthalates, polycyclic aromatic hydrocarbons and chlorophenols. The Fe3O4/KAP was characterized by means of Brunauer-Emmett-Teller surface area measurements, Fourier-transform infrared spectroscopy, thermogravimetry, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Following desorption with acetonitrile, the analytes were quantified by using HPLC with UV detection. The effects of adsorbent dosage, extraction time, sample pH, ionic strength, desorption solvent and desorption time were optimized for the PUHs. Under optimal conditions, response is linear from 0.5-1.0 up to 50 ng·mL-1 for the five PUHs. Lower limits of detection range between 0.05 and 0.30 ng·mL-1. Other figures of merit include (a) high enrichment factors (60-297), (b) good recoveries (91.8-106.5%), and (c) relative standard deviations of <8.4%. The method was successfully applied to analysis of the PUHs in real samples (bottled mixed juice, milk and soymilk). The results indicate that such Fe3O4/KAPs have a wide application scope as an adsorbent for use in magnetic solid phase extraction. Graphical abstract A magnetic knitting aromatic polymer based nanocomposite (Fe3O4/KAP) was prepared by a one-pot method and explored as an absorbent for magnetic solid-phase extraction (MSPE) of phenylurea herbicides (PUHs) from bottled mixed juice, milk and soymilk samples before quantitation by HPLC with UV detection.

Porphyrin based porous organic polymer modified with Fe3O4 nanoparticles as an efficient adsorbent for the enrichment of benzoylurea insecticides.

Porphyrin-based porous organic polymers (P-POPs) are amorphous polymers linked by strong covalent bonds between the porphyrin subunits that act as building blocks. The authors describe a magnetic P-POP that possesses high surface area, a highly porous structure, and strong magnetism. The MP-POP was employed as a magnetic sorbent for the extraction of benzoylurea insecticides from cucumber and tomato samples prior to their determination by HPLC. The sorbent has a typical sorption capacity of 1.90-2.00 mg∙g-1. The method exhibits a good linear range (0.8-160 ng·g-1), low limits of detection (0.08-0.2 ng·g-1), and high method recoveries (81.8-103.5%) for cucumber and tomato samples. The MP-POP has different adsorption capabilities for the benzoylurea insecticides, phenylurea herbicides and phenols compounds, and the adsorption mechanism is found to be based on π-stacking, hydrogen-bonding, and hydrophobic interactions. Graphical abstract A novel magnetic porphyrin-based porous organic polymer was fabricated and used as the adsorbent for the efficient extraction of benzoylurea insecticides.

Phenylurea herbicide sorption to biochars and agricultural soil.

Biochar is increasingly been used as a soil amendment to improve water-holding capacity, reduce nutrient leaching, increase soil pH, and also as a means to reduce contamination through sorption of heavy metals or organic pollutants. The sorption behavior of three phenylurea herbicides (monuron, diuron and linuron) on five biochars (Enhanced Biochar, Hog Waste, Turkey Litter, Walnut Shell and Wood Feedstock) and an agricultural soil (Yolo silt loam) was investigated using a batch equilibration method. Sorption isotherms of herbicides to biochars were well described by the Freundlich model (R(2) = 0.93-0.97). The adsorption KF values ranged from 6.94 to 1306.95 mg kg(-1) and indicated the sorption of herbicides in the biochars and Yolo soil was in the sequence of linuron > diuron > monuron and walnut shell biochar > wood feedstock biochar > turkey litter biochar > enhanced biochar > hog waste biochar > Yolo soil. These data show that sorption of herbicides to biochar can have both positive (reduced off-site transport) and negative (reduced herbicide efficacy) implications and specific biochar properties, such as H/C ratio and surface area, should be considered together with soil type, agriculture chemical and climate condition in biochar application to agricultural soil to optimize the system for both agricultural and environmental benefits.

In situ formation of solidified supramolecular solvent based dispersive liquid-liquid microextraction for the enrichment of phenylurea herbicides in water, fruit juice, and milk.

A convenient, efficient, and green dispersive liquid-liquid microextraction based on the in situ formation of solidified supramolecular solvents combined with high performance liquid chromatography was developed for the determination of four phenylurea herbicides in liquid samples, including monuron, monolinuron, isoproturon, and chlortoluron. Herein, a novel supramolecular solvent was prepared by the in situ reaction of [P4448]Br and NH4PF6, which had the advantages of low melting point, high density, and good dispersibility. In addition, the microscopic morphology and physical properties of supramolecular solvent were characterized, and the extraction conditions were optimized. The results showed that the analytes had good linearity (R2 > 0.9998) within the linear range. The limits of detection and quantification for the four phenylurea herbicides were in the range of 0.13-0.19 µg L-1 and 0.45-0.65 µg L-1, respectively. The prepared supramolecular solvent is suitable for the efficient extraction of phenylurea herbicides in water, fruit juice, and milk.

Facile synthesis of hydroxylated triazine-based magnetic microporous organic network for ultrahigh adsorption of phenylurea herbicides: An experimental and density-functional theory study.

Microporous organic networks (MONs) are highly porous materials that are particularly useful in analytical chemistry. However, the use of these materials is often limited by the functional groups available on their surface. Here, we described the polymerization of a sea urchin-like structure material at ambient temperature, that was functionalized with hydroxyl, carboxyl, and triazine groups and denoted as OH-COOH-MON-TEPT. A substantial proportion of OH-COOH-MON-TEPT was intricately decorated EDA-Fe3O4, creating a well-designed configuration (EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC) for superior adsorption of the target analytes phenylurea herbicides (PUHs) via magnetic solid-phase extraction (MSPE). The proposed method showed remarkably low limits of detection ranging from 0.03 to 0.22 ng·L-1. Experimental investigations and theoretical analyses unveiled the adsorption mode between EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC and PUHs. These findings establish a robust foundation for potential applications of EDA-Fe3O4 @OH-COOH-MON-TEPT-EDC in the analysis of various polar contaminants.

Photodegradation of phenylurea herbicides sensitized by norfloxacin and the influence of natural organic matter.

The photochemical activity of fluoroquinolone antibiotics (FQs) has gained attention due to the discovery of their phototoxicity and photocarcinogenicity in clinics. This study reveals that norfloxacin (NOR) can sensitize the photodegradation of phenylurea (PU) herbicides. This is attributed to the formation of an excited triplet of norfloxacin (3NOR*) by UV-A irradiation of its quinolone chromophore, which can further react with O2 to form singlet oxygen (1O2). The second-order rate of 3NOR* with PU ranges from 1.54 × 1010 to 2.76 × 1010 M-1s-1. The steady-state concentrations of 3NOR* were calculated as (4.29-31.2)× 10-16 M at 10 µM NOR under UV365nm irradiation. Natural organic matter (NOM) inhibited the degradation of PU induced by 3NOR*. In the presence of 10 mg L-1 NOM, the pseudo-first-order rate constants (kobs,NOM) of the degradation of diuron (DIU), isoproturon (IPU), monuron (MOU), and chlorotoluron (CLU) decreased by 65%, 19%, 36%, and 62%, respectively. NOM mainly acts as a reductant which reacted with the radical intermediates of the PU generated by 3NOR*oxidation, thus reversing the oxidation. The inhibitory effect increases with increasing NOM concentration. Results of this study underscore the role of NOR as a photosensitizer in accelerating the abatement of PU pesticides in sunlit surface waters. This study significantly advances the understandings of the behavior of NOR in aquatic environments.

Preparation of hypercrosslinked porous polymer with manifold functional groups for sensitive determination of phenylurea herbicides in beverages and celtuce samples.

Wide use of phenylurea herbicide has caused serious residue problem and threaten human health. It is important to develop viable method for their sensitive determination. Herein, a multi-functionalized porous polymer was prepared by crosslinking hexafluorobisphenol A with pyromellitic dianhydride. Using the multi-functionalized porous polymer as solid phase extraction sorbent, combined with high performance liquid chromatography, a sensitive method was established for determining phenylurea herbicides in beverages and celtuces. High sensitivity was achieved, with method detection limit (S/N = 3) of 0.01---0.025 ng mL-1 for beverages, 1.70 ng g-1 for celtuce, and quantitation limits of 0.03---0.10 ng mL-1 for beverages, 5.00 ng g-1 for celtuce. The method recoveries were 80.5---120.0 % with relative standard deviations lower than 6.1%. Adsorption mechanism mainly involved F-π, F-O, π-π, polar interactions and hydrogen-bonding interactions. This study offers a simple protocol to develop multi-functional sorbents for extraction of organic pollutants.

New insight into biodegradation mechanism of phenylurea herbicides by cytochrome P450 enzymes: Successive N-demethylation mechanism.

Phenylurea herbicides (PUHs) present one of the most important herbicides, which have cause serious effects on ecological environment and humans. Nowadays enzyme strategy shows great advantages in degradation of PUHs. Here density functional theory (DFT), quantitative structure - activity relationship (QSAR) and quantum mechanics/molecular mechanics (QM/MM) approaches are used to investigate the degradation mechanism of PUHs catalyzed by P450 enzymes. Two successive N-demethylation pathways are identified and two hydrogen abstraction (H-abstraction) reaction pathways are identified as the rate-determining step through high-throughput DFT calculations. The Boltzmann-weighted average energy barrier of the second H-abstraction pathway (19.95 kcal/mol) is higher than that of the first H-abstraction pathway (16.80 kcal/mol). Two QSAR models are established to predict the energy barriers of the two H-abstraction pathways based on the quantum chemical descriptors and mordred molecular descriptors. The determination coefficient (R2) values of QSAR models are > 0.9, which reveal that the established QSAR models have great predictive capability. QM/MM calculations indicate that human P450 enzymes are more efficient in degradation of PUHs than crop and weed P450 enzymes. Correlations between energy barriers and key structural/charge parameters are revealed and key parameters that have influence on degradation efficiency of PUHs are identified. This study provides lateral insights into the biodegradation strategy and removal method of PUHs and valuable information for designing or engineering of highly efficient degradation enzymes and genetically modified crops.

Urea-based magnetic porous organic frameworks as novel adsorbent for the enrichment of phenylurea herbicides in foods.

A novel urea-based magnetic porous organic frameworks Fe3O4@UPOFs (ETTA-PPDI) was synthesized by a simple polymerization reaction under mild conditions. The adsorbent displayed desirable adsorption performance for phenylurea herbicides (PUHs) with optimized adsorption time of only 4 min. The adsorption capacities of the adsorbent for PUHs ranged from 47.30 to 111.93 mg g-1. A magnetic solid-phase extraction based on Fe3O4@UPOFs combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established for the efficient determination of six PUHs in food samples (wheat, edible oil and cucumber), with determination coefficient (R2) ≥ 0.9972. The LODs of the method were in the range of 0.003-0.07 µg kg-1 and recoveries ranged from 82.00 to 112.53%. The relative standard deviations were lower than 6.7%. The newly prepared adsorbent displayed great application prospects for the efficient enrichment of trace phenylurea herbicides in complex food matrices.

Aryl ketones-derived porous organic polymer for enrichment and sensitive detection of phenylurea herbicides in water, tea drink and mushroom samples.

Three aryl ketones-derived porous organic polymers (ATP-POPM, ATP-POPP and ATP-POPO) were fabricated through the aldol condensation reaction of acetylated triphenylsilane precursor (ATP) with different aromatic aldehydes for the first time. The ATP-POPM exhibited superior extraction capacity toward phenylurea herbicides (PUHs). A sensitive method for the simultaneous determination of six PUHs in water, tea drink and mushroom samples was developed with ATP-POPM as solid phase extraction adsorbent prior to high performance liquid chromatography ultraviolet detection. Under the optimized conditions, the linear response of PUHs was 0.09-80.0 ng mL-1 for water, 0.18-100.0 ng mL-1 for tea drinks and 4.50-200.0 ng g -1 for mushroom samples. The detection limits (S/N=3) of the method were 0.03-0.10 ng mL-1, 0.06-0.18 ng mL-1, 1.50-4.50 ng g -1 for water, tea drink and mushroom, respectively. The method recoveries for spiked samples were in the range of 80.7%-116.0%, with relative standard deviations less than 10.3%. The results proved that the established method was sensitive and suitable to detect PUHs with acceptable accuracy and precision. This work provided a powerful tool to synthesize promising adsorbent by aldol condensation reaction for detecting six PUHs simultaneously in real samples.

One-pot fabrication of poly (ionic liquid)s functionalized magnetic adsorbent for efficient enrichment of phenylurea herbicides in environmental waters.

Efficient capture is an essential procedure in the highly sensitive monitoring of phenylurea herbicides (PUHs) in various environmental waters. Herein, a new poly (ionic liquid)s functionalized magnetic adsorbent (PFMA) was conveniently fabricated by means of "one-pot" strategy. The preparation procedure was quite simple by mixing 1-allyl-3-methylimidazoliumbis[(trifluoromethy)sulfonyl]imide, ethylene glycol dimethacrylate, Fe3+, Fe2+, mixed solution of dimethyl sulfoxide/H2O and azobisisobutyronitrile in one pot, and the total reaction time was just 3.0 h which was far shorter than that needed in previous approaches. A series of characterized techniques were employed to observe and inspect the morphology, structure and magnetic properties of prepared PFMA. Results revealed that the adsorbent contained abundant functional groups and superior magnetic property. Combing with magnetic solid-phase extraction (MSPE) format, the resultant PFMA displayed high capture capability towards studied PUHs through multiple interactions, and the enrichment factors were in the range of 126-227. Under the selected extraction parameters, the introduced PFMA/MSPE was combined with HPLC equipped with diode array detector (HPLC/DAD) to measure investigated PUHs at trace levels in various environmental waters. Wide linear range (0.010-200 µg/L), low limit of detection (0.0025-0.015 µg/L) and good precision (RSDs<10%) were achieved. The reliability and practicality of established approach was demonstrated by quantifying trace studied PUHs in various waters. Satisfactory fortified recoveries (80.2-119%) and repeatability were achieved. The results well evidence that the prepared PFMA is a good alternative for capture PUHs, and the introduced approach has wide prospect in the analyzing trace levels of PUHs in water and other complex samples.

Enhanced Biodegradation of Phenylurea Herbicides by Ochrobactrum anthrophi CD3 Assessment of Its Feasibility in Diuron-Contaminated Soils.

The phenylurea herbicides are persistent in soil and water, making necessary the de-velopment of techniques for their removal from the environment. To identify new options in this regard, bacterial strains were isolated from a soil historically managed with pesticides. Ochrobactrum anthropi CD3 showed the ability to remove completely herbicides such as diuron, linuron, chlorotoluron and fluometuron from aqueous solution, and up to 89% of isoproturon. In the case of diuron and linuron, their main metabolite, 3,4-dichloroaniline (3,4-DCA), which has a higher toxicity than the parent compounds, was formed, but remained in solution without further degradation. O. anthropi CD3 was also tested for bioremediation of two different agricultural soils artificially contaminated with diuron, employing bioremediation techniques: (i) biostimulation, using a nutrient solution (NS), (ii) bioaugmentation, using O. anthropi CD3, and iii) bioavailability enhancement using 2-hydroxypropyl-ß-cyclodextrin (HPBCD). When bioaugmentation and HPBCD were jointly applied, 50% of the diuron initially added to the soil was biodegraded in a range from 4.7 to 0.7 d. Also, 3,4-DCA was degraded in soil after the strain was inoculated. At the end of the soil biodegradation assay an ecotoxicity test confirmed that after inoculating O. anthropi CD3 the toxicity was drastically reduced.

Impact of rice straw biochar addition on the sorption and leaching of phenylurea herbicides in saturated sand column.

The application of phenylurea herbicides (PUHs) may lead to the extensive distribution in soils, while the role of straw biochar as a soil amendment on the transport and sorption of PUHs are still unclear. Thus, the transport and sorption behavior of three typical PUHs with rice straw biochar (RSB) was studied in both adsorption simulation experiments of aqueous solution and packed column experiments. The sorption mechanism of RSB to herbicides was investigated through batch sorption studies with three influencing factors including dosage of RSB, pH, and ionic strength (IS) with orthogonal test. The sorption coefficients were improved significantly by increasing the dosage of RSB, while there was no obvious influence by enhancing the pH and IS value. The optimal sorption conditions (pH value at 3, IS at 0.1 M, and RSB dosage at 60 mg) of three herbicides were set and the maximum removal rates of Monuron, Diuron, and Linuron were 41.9%, 25%, and 56.8%, respectively. The co-transport process of RSB and PUHs were investigated under different RSB dosage, pH value, and IS value. The retention effect increased greatly with enhancing the RSB dosage and pH value. However, IS did not have a significant influence on the retention of RSB, and therefore it had little effect on the adsorption capacity, which was consistent with the results of sorption experiments. The breakthrough curves (BTCs) for co-transport were well simulated by the two-site non-equilibrium convection-dispersion equation (CDE). Most of the regression coefficients (R2) were above 0.99, which uncovered the co-transport in packed column were affected by physical absorption and chemical forces. According to the fitting parameters analysis, the RSB particles and PUHs were subjected to a greater resistance and a stronger stability by reducing pH value in porous media. The presence of RSB increased the amount of dynamic sorption sites in the entire co-transport system, which led to a significant promotion of the PUHs' sorption and interception.

A core-shell structured magnetic covalent organic framework as a magnetic solid-phase extraction adsorbent for phenylurea herbicides.

In this work, a core-shell structured magnetic covalent organic framework named as M-TpDAB was constructed with 3,3'-diaminobenzidine (DAB) and 1,3,5-triformylphloroglucinol (Tp) as building units. M-TpDAB was characterized by infrared spectroscopy, nitrogen adsorption-desorption isotherms, powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Using the M-TpDAB as adsorbent, a simple and highly effective method was proposed for preconcentrating phenylurea herbicides before high performance liquid-phase chromatography analysis. In the optimized conditions, a good linearity was achieved within the range of 0.15-100 ng mL-1 for water sample, 1.0-100.0 ng mL-1 for tea drink samples. The limits of detection for the analytes were 0.05-0.15 ng mL-1 for water sample and 0.30-0.50 ng mL-1 for drink samples. Satisfactory recoveries of spiked target compounds were in the range of 84.6%-105% for water sample and 80.3%-102% for tea drink samples. Finally, the M-TpDAB based method was successfully used to determine phenylurea herbicides in tea drinks and water samples, demonstrating a good alternative for analyzing trace level of phenylurea herbicides in water samples.

Fabrication of carboxyl functionalized microporous organic network coated stir bar for efficient extraction and analysis of phenylurea herbicides in food and water samples.

Fabrication of novel coatings continues to be an area of great interest and significance in the development and application of stir bar sorptive extraction (SBSE). In this work, a carboxyl-enriched microporous organic network (MON-2COOH) coated stir bar was designed and fabricated as a novel adsorbent for efficient extraction of four phenylurea herbicides (PUHs) before their determination by high-performance liquid chromatography coupled with photodiode array detector (HPLC-PDA). The MON-2COOH was represented as an effective adsorbent for PUHs due to its large surface area, rigid porous structure, aromatic pore walls and the desired hydrogen bonding sites of introduced carboxyl groups. Variables affecting the SBSE of target analytes were optimized in detail. Under the optimal extraction conditions, favorable correlation coefficients (R2 > 0.996) in the linear range 0.10-250 µg L-1, low limits of detection (LODs, S/N = 3) of 0.025-0.070 µg L-1 and good enrichment factors (46-49) were obtained. Besides, the proposed SBSE-HPLC-PDA method was successfully applied to determine trace PUHs in food and environmental water samples with recoveries in the range of 80.0-104.8% and the precisions (relative standard deviations, RSDs) lower than 9.9% (n = 3). This work revealed the potential of MONs in SBSE of trace contaminants from environmental samples.

Construction of hydroxyl functionalized magnetic porous organic framework for the effective detection of organic micropollutants in water, drink and cucumber samples.

Organic micropollutants have been extensively detected in environmental waters, posing severe hazards to organisms and humans. Effective detection of micropollutants in environmental water and food samples is of significant importance. Herein, a novel magnetic porous organic framework (labeled as M-Qu-POF) was synthesized using natural quercetin as building units via a facile azo-coupling reaction for the first time. Featuring with good magnetism, intrinsic porosity, high surface area and hydrophilic-lipophilic (amphiphilic) structure, the M-Qu-POF displayed high adsorption capacity for phenylurea herbicides (PUHs) pollutants. The adsorption mechanism was investigated by theory calculation, confirming that the hydrogen bonds interaction, π-π interactions and electrostatic interactions play an important role in the adsorption. With the M-Qu-POF as adsorbent, a magnetic solid phase extraction-high performance liquid chromatography method was first established for simultaneous enrichment and detection of six PUHs in environmental water, tea drink and cucumber samples. Under the optimized experimental conditions, good linear range, low detection limits and high enrichment factors were obtained. The method was successfully applied for determination of PUHs in environmental water, tea drink and cucumber samples with satisfactory recoveries (80.0-118%). The result demonstrates that the M-Qu-POF material has a good application prospect in the detection of other organic micropollutants.