Phenoxyacetic Acid Herbicides Research Articles

Transport of herbicides by PIN-FORMED auxin transporters.

Auxins are a group of phytohormones that control plant growth and development 1. Their crucial role in plant physiology has inspired development of potent synthetic auxins that can be used as herbicides 2. Phenoxyacetic acid derivatives are a widely used group of auxin herbicides in agriculture and research. Despite their prevalence, the identity of the transporters required for distribution of these herbicides in plants is both poorly understood and the subject of controversial debate 3,4. Here we show that PIN-FORMED auxin transporters transport a range of phenoxyacetic acid herbicides across the membrane and we characterize the molecular determinants of this process using a variety of different substrates as well as protein mutagenesis to control substrate specificity. Finally, we present Cryo-EM structures of Arabidopsis thaliana PIN8 with 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-chlorophenoxyacetic acid (4-CPA) bound. These structures represent five key states from the transport cycle, allowing us to describe conformational changes associated with substrate binding and transport across the membrane. Overall, our results reveal that phenoxyacetic acid herbicides use the same export machinery as endogenous auxins and exemplify how transporter binding sites undergo transformations that dictate substrate specificity. These results enable development of novel synthetic auxins and for guiding precision breeding of herbicide resistant crop plants.

Biomonitoring urinary pesticide metabolites in preschool children by supported liquid extraction and ultra-high performance liquid chromatography-tandem mass spectrometry and their association with oxidative stress

Investigating pesticide exposure and oxidative stress in preschool children is essential for elucidating the determinants of environmental health in early life, with human biomonitoring of urinary pesticide metabolites serving as a critical strategy for achieving this objective. This study demonstrated biomonitoring of 2 phenoxyacetic acid herbicides, 2 organophosphorus pesticide metabolites, and 4 pyrethroid pesticide metabolites in 159 preschool children and evaluated their association with oxidative stress biomarker 8-hydroxydeoxyguanosine. An enzymatic deconjugation process was used to release urinary pesticide metabolites, which were then extracted and enriched by supported liquid extraction, and quantified by ultra-high performance liquid chromatography-tandem mass spectrometry with internal standard calibration. Dichloromethane: methyl tert‑butyl ether (1:1, v/v) was optimized as the solvent for supported liquid extraction, and we validated the method for linear range, recovery, matrix effect and method detection limit. Method detection limit of the pesticide metabolites ranged from 0.01 μg/L to 0.04 μg/L, with satisfactory recoveries ranging from 70.5 % to 95.5 %. 2,4,5-Trichlorophenoxyacetic acid was not detected, whereas the other seven pesticide metabolites were detected with frequencies ranging from 10.1 % to 100 %. The concentration of urinary pesticide metabolites did not significantly differ between boys and girls, with the median concentrations being 9.39 μg/L for boys and 4.90 μg/L for girls, respectively. Spearman correlation analysis indicated that significant positive correlations among urinary metabolites. Bayesian kernel machine regression revealed a significant positive association between urinary pesticide metabolites and 8-hydroxydeoxyguanosine. Para-nitrophenol was the pesticide metabolite that contributed significantly to the elevated level of oxidative stress.

Computational investigation of HO•-induced atmospheric transformation and ecological risk assessment of 2-methyl-4-chlorophenoxyacetic acid

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a pervasive phenoxyacetic acid herbicide, frequently identified in environmental matrices. This study undertakes a systematic investigation of the atmospheric environmental transformation behavior and potential ecological risks of hydroxyl radical (HO•) induced MCPA for the first time, employing computational chemistry and computational toxicology methodologies. Our findings indicate that the initial degradation of MCPA can be triggered by both HO•-addition and hydrogen-abstraction reactions, with the latter being more likely to occur. The primary reaction pathways were identified as R2, R3, R8, and R13. The total rate constant for the gas-phase reaction of MCPA with HO• was calculated as 8.59 × 10−12 cm3 molecule −1 s−1 at 298 K. This total rate constant displayed a distinct positive temperature dependence within the temperature range of 250–375 K. Structures of 25 transformation products, which include 7 experimentally observed compounds, were determined from further reactions of crucial intermediates. The toxicity assessment of MCPA and its transformation products indicated that most of the hydroxyl oxidation products exhibit toxicity to aquatic organisms and possess mutagenic, developmental toxic, non-genotoxic carcinogenic, and skin irritating or corrosive properties. This research contributes to a comprehensive understanding of the transformation mechanisms, kinetics, and environmental repercussions of gas-phase MCPA, enhancing our ability to predict and mitigate its ecological impact.

Switchable deep eutectic solvent as green and efficient media for liquid-phase microextraction of phenoxyacetic acid herbicides in water and food matrices

In this work, a switchable deep eutectic solvent (SDES) based on fatty acid and polyetheramine ion pair was prepared for liquid-phase microextraction (LPME) of phenoxyacetic acid herbicides in drinking water, beverage and honey matrices. The as-synthesized SDES equipped with an interesting characteristic of fast and reversible polarity switching, achieving homogeneous extraction and rapid bi-phase separation simultaneously. Several key parameters affecting the extraction performance were investigated comprehensively by Box-Behnken design. Under the optimal conditions, the method exhibited excellent linearity (15–4000 μg L−1), low detection limits (3–5 μg L−1), desirable precision (RSD < 8.1 %), and satisfactory recovery (72.6–98.7 %). More importantly, the introduction of SDES can simplify the pre-treatment procedure, shorten extraction time (4 min), and avoid the usage of traditional organic solvent during the whole extraction process. In addition, the switching mechanism of SDES was characterized by FT-IR and 1H NMR, and the forming mechanism of SDES was investigated using density-functional theory. The green of the method was estimated using the analytical ecological scale, the analytical green calculator, and the green analytical procedure index. The cytotoxicity of SDES was investigated and the result displayed that toxicity of the SDES was very low with the EC50 > 500 mg/L. Therefore, the proposed method was green and efficient and revealed considerable application prospects for the extraction of trace analytes from complex materials.

Bioinspired Herbicides-Ionic Liquids or Liquid Cocrystals?

This research provides information about combinations of several amino acids, including l-proline (Pro), l-arginine (Arg), and l-histidine (His), with phenoxyacetic acid herbicides (MCPA and 2,4-D). Five amino acid ionic liquids (AAILs), one amino acid higher-melting salt (AAHMS), and two amino acid liquid cocrystals (AALCs) were obtained in high yields (>90%). The ionization of the six new structures was confirmed by NMR, IR, and molecular modeling. X-ray crystallography was used to definitively confirm the binding location of the mobile hydrogen. Furthermore, we propose a computational method for estimating the energy of specific hydrogen bond(s) in AAIL crystals based on the NBO and QTAIM hydrogen bond parameters obtained by model calculations. An in-depth analysis of the structures allowed to answer the question posed in the title, ionic liquids or liquid cocrystals? AAILs based on arginine and histidine were obtained. In contrast, combining proline with MCPA and 2,4-D led to AALCs. Finally, the compounds were analyzed to measure their herbicidal activity. These studies proved that the novel form of MCPA or 2,4-D improved its ability to control weeds compared to commercial formulations containing the same active ingredients.

The potential of self-activated carbon for adsorptive removal of toxic phenoxyacetic acid herbicide from water

Phenoxyacetic acid herbicides are widely used in agriculture for controlling weeds. These organic compounds are persistent and recalcitrant, often contaminating water and soil. Therefore, we studied five pristine biochars (BCs), and southern yellow pine (SYP) based self-activated carbon (SAC) for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide. Among the tested adsorbents, SYP-SAC-15 demonstrated higher (>90%) 2,4-D removal from water. The SYP-SAC-15 was produced using a facile and green route where the biomass pyrolysis gases worked as activating agents creating a highly porous structure with a surface area of 1499.79 m2/g. Different adsorption kinetics and isotherm models were assessed for 2,4-D adsorption on SYP-SAC-15, where the data fitted best to pseudo-second order (R2 > 0.999) and Langmuir (R2 > 0.991) models, respectively. Consequently, the adsorption process was mainly dominated by the chemisorption mechanism with monolayer coverage of SYP-SAC-15 surface with 2,4-D molecules. At the optimum pH of 2, the maximum 2,4-D adsorption capacity of SYP-SAC-15 reached 471.70 mg/g. Furthermore, an increase in the water salinity demonstrated a positive influence on 2,4-D adsorption, whereas humic acid (HA) showed a negative impact on 2,4-D adsorption. The regeneration ability of SYP-SAC-15 showed excellent performance by retaining 71.09% adsorption capability at the seventh adsorption-desorption cycle. Based on the operating pH, surface area, spectroscopic data, kinetics, and isotherm modeling, the adsorption mechanism was speculated. The 2,4-D adsorption on SYP-SAC-15 was mainly governed by pore filling, electrostatic interactions, hydrogen bonding, hydrophobic and π-π interactions.

DABCOnium Ionic Liquid‐Immobilized Silica Gel for Solid Phase Extraction of Phenoxyacetic Acid Herbicides in Water Samples**

AbstractA novel sorbent (SiO2‐(CH2)3‐DABCO) for solid‐phase extraction (SPE) was successfully prepared by chemical‐bonding formation of diazabicyclo[2.2.2]octane ionic liquid onto silica gel. The structure of SiO2‐(CH2)3‐DABCO sorbent was characterized by FT‐IR, TGA, SEM, EDX, and BET methods. Cartridges packed with the synthetic SiO2‐(CH2)3‐DABCO were used for the preconcentration of trace‐level of phenoxyacetic acid herbicides in water samples for the first time. The factors influencing on the recovery were investigated, such as type of ion liquids, loading volume, eluents, elution volume, loading rate, and capacity. After the enrichment, the phenoxyacetic acid herbicides were analyzed by high‐performance liquid chromatography with an ultraviolet detector. Four model phenoxyacetic acid herbicides, including 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA), 2,4,5‐trichlorophenoxyacetic acid (2,4,5‐T), fenoprop (2,4,5‐TP) and haloxyfop were well retained and separated by this material with a recovery efficiency from 77 to 103 %. The SiO2‐(CH2)3‐DABCO demonstrated a good capacity corresponding to 0.56 mg of the analyte adsorbed per 100 mg of the material. The mixture of phosphate buffer (pH 7) : MeOH (50 : 50, v/v) was used to elute the analytes and provided the highest recovery with the standard deviations from 2.4 to 6.5. The high sensitivity with detection limits of 1.070–9.587 μg/L can be achieved.

"One-pot" preparation of aminated carbon nanotube-modified magnetic nanoparticles and their application to the quantification of phenoxyacetic acid herbicides in cereal and vegetable samples

有效萃取是分析复杂样品中苯氧羧酸类除草剂(PAs)残留的关键步骤。为此,该文利用“一锅法”水热技术快速、简便地制备了氨基碳纳米管功能化磁性纳米粒子(NH2-CNTs@M)并作为磁固相萃取(MSPE)的萃取介质,用于萃取谷物和蔬菜样品中痕量PAs。研究利用多种手段对NH2-CNTs@M的形貌、尺寸、磁性性质等进行了表征,结果表明Fe3O4的粒径、氨基化碳纳米管的直径以及NH2-CNTs@M的磁饱和值分别为30 nm、40 nm和44.2 emu/g。详细考察了制备条件和萃取参数对NH2-CNTs@M/MSPE萃取性能的影响,结果表明,NH2-CNTs@M/MSPE可通过π-π、疏水和氢键作用有效富集目标化合物,最佳萃取条件如下:吸附剂用量为30 mg,解吸溶剂为含2.0%(v/v)甲酸的乙腈溶液,吸附时间和解吸时间分别为8.0 min和3.0 min,基底pH值为6.0,不调节基底的离子强度。将NH2-CNTs@M/MSPE与高效液相色谱-二极管阵列检测技术(HPLC-DAD)联用,建立了谷物和蔬菜中PAs的灵敏检测方法。谷物和蔬菜基质中苯氧羧酸类除草剂的检出限(LOD, S/N=3)分别为0.32~1.6 μg/kg和0.53~1.6 μg/kg,定量限(LOQ, S/N=10)分别为0.94~4.8 μg/kg和1.6~4.8 μg/kg。在两种实际样品中不同浓度下的加标回收率分别为73.1%~112%和72.3%~113%。与现有方法相比,所建方法具有萃取速度快、灵敏度高和环境友好等特点。

Enhanced photocatalytic oxidation of a phenoxyacetic acid herbicide using TiO2–FeOOH/Fe2O3 assisted with sulfate radicals

Enhanced photocatalytic oxidation of a phenoxyacetic acid herbicide using TiO2–FeOOH/Fe2O3 assisted with sulfate radicals

Structure, thermal stability and magnetic behavior of Mn(II) complexes with phenoxyacetic acid herbicides

The reaction of manganese(II) chloride with ammonium salt of 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-bromophenoxyacetic acid (4-Br) gave rise to the formation of hydrated complexes with formulas: Mn(MCPA)2·2H2O, Mn(2,4-D)2·2H2O and Mn(4-Br)2·3H2O. The compounds were characterized by elemental and thermal analyses, spectroscopic methods, as well as, by magnetic measurements. The complexes crystallize in monoclinic system. The Mn(II) ion is surrounded by oxygen atoms (from carboxylate groups and water molecules) in the octahedral arrangement. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed that compounds obey the Curie-Weiss law and have the paramagnetic properties. Being heated up to 1173 K the complexes decompose in three steps - first to anhydrous compounds: Mn(MCPA)2/Mn(2,4-D)2/Mn(4-Br)2 through intermediate products: MnO/Mn2OCl2/Mn2OBr2 to the following oxides: Mn2O3/Mn3O4/Mn3O4. The X-ray single crystal structure analysis was performed for Mn(II) complex with 4-bromophenoxyacetic acid after its recrystallization from N,N-dimethylformamide. The formation of hexanuclear cluster of manganese(II) carboxylate with a hydrophobic exterior was observed.

Batch and packed bed techniques for adsorptive aqueous phase removal of selected phenoxyacetic acid herbicide using sugar industry waste ash

Abstract Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Detection of 2,4-dichlorophenoxyacetic acid herbicide using a FGE-sulfatase based whole-cell Agrobacterium biosensor

2,4-Dichlorophenoxyacetic acid (2,4-D) has been widely used as a herbicide for agricultural purposes. Currently, the available methods for detecting 2,4-D require multi-step sample preparations and expensive instruments. The use of a whole cell biosensor is an interesting approach that is straightforward and simple to use. In this study, we constructed a genetic-based Agrobacterium tumefaciens biosensor based on a cadA promoter and cadR regulator from Bradyrhizobium sp. strain HW13 (2,4-D degrader) with a formylglycine generating enzyme (FGE)-sulfatase as the reporter gene. The performance of the biosensor was further improved through direct evolution of the cadR activator. The detection limit of cadR mutants for phenoxyacetic acid herbicides including 2,4-D and 4-Chlorophenoxyacetic acid (4-CPAA) were 1.56 μM (an eight-fold improvement compared to wild-type CadR). The biosensor could detect 2,4-D contamination in environmental samples without encountering interference from other complex compounds. The Agrobacterium biosensor was also stable after storing in a simple Luria-Bertani (LB) medium at 4 °C for 30 days where the activity remained at 82% when exposed to 100 μM of 2,4-D. This novel biosensor, with its high stability under simple storage conditions, exhibits promising potential to be used as an inexpensive and easy-to-use tool to screen for 2,4-D contamination in environmental sources.

Use of aloin-based and rosin-based electrospun nanofibers as natural nanosorbents for the extraction of polycyclic aromatic hydrocarbons and phenoxyacetic acid herbicides by microextraction in packed syringe method prior toGC-FID detection.

Thesynthesis of three kinds of sorbentsis described. The first kind was a hydrophobic nanofiber as a specific sorbent for non-polar compounds. The second one was a hydrophilic nanofiber as a specific sorbent for polar compounds and the third one was a generic sorbent synthesized from hydrophilic and hydrophobic compounds. The functional groups were natural compounds extracted from aloin plant and gum of pine tree. The aloin/polyacrylonitrile (PAN), rosin/PAN, and aloin/rosin/PAN electrospun nanofibers were synthesized through electrospinning strategy and then characterized using field emission scanning electron microscopy and Fourier transform infrared spectroscopy. Thereafter, the synthesized sorbents were used in microextraction using thepacked syringe (MEPS) method. The determination was conducted using gas chromatographywithflame ionization detection (GC-FID). Under the optimum condition, the method using aloin/rosin/PAN nanofibers as a sorbent showed a good linearity in the range 1.0-250ngmL-1 for polycyclic aromatic hydrocarbons (PAHs) (as a model for non-polar compounds) and 1.0-200ngmL-1 for phenoxyacetic acid herbicides (CAPs) (as a model for polar compounds) with correlation coefficient (R2) higher than 0.997. Limits of detections (LODs) for PAHs and CAPs were in the range 0.1-0.3ngmL-1 and 0.3-0.5ngmL-1, respectively. The intra-day (n = 3) and inter-day (between 3days) relative standard deviations (RDSs%) were in the range 6.3-12.3% for a single syringe. Finally, the MEPS-GC-FID method was applied as a simple, facile, and time and cost-effective method to analyze environmental, farm, and industrial water samples. Graphical abstract Herein, aloin/rosin/polyacrylonitrile (PAN) electrospun nanofiber was successfully synthesized and applied as a sorbent for extraction of polycyclic aromatic hydrocarbons (PAHs) as non-polar compounds and phenoxyacetic acid herbicides (CPAs) as polar compounds from aqueous solutions before GC-FID analysis.

Automated Mixed Matrix Membrane Microextraction Prior to Liquid Chromatography for the Determination of Chlorophenoxy Acid Herbicides in Sewage Water Samples

A new automated flow-through adsorption/desorption procedure using a multiwalled carbon nanotube immobilised mixed matrix membrane is described. The membrane consisted of 25% (w/w) multiwall carbon nanotube loading in a cellulose triacetate polymer matrix as support and was cast and embedded in a flow-through cell with a channel of an approximate length of 20 mm, a width of 2 mm, and a depth of 1.5 mm. The membrane immobilised with nanoparticles was activated using 1-octanol as a conditioning solvent. For the analyte adsorption process, 6 mL of the sample was passed through the cell at a flow rate of 0.2 mL min−1. The entrapped target analytes were then desorbed dynamically with 60 µL of 2-propanal at a flow rate of 5 µL min−1 prior to HPLC/UV analysis. The performance of the system was demonstrated for the determination of chlorinated phenoxyacetic acid herbicides in sewage water samples. Under the optimum conditions, the linearity of this method ranged from 50 to 1000 ng mL−1, with a correlation coefficient (r) ≥ 0.993 and a detection limit varying from 15 to 20 ng mL−1. Enrichment factors of up to 55 were achieved with relative recoveries of 95–99% and precision values of 6.1–7.5%.

Preferential removal of 2,4-dichlorophenoxyacetic acid from contaminated waters using an electrocatalytic ceramic membrane filtration system: Mechanisms and implications

A selective electrocatalytic ceramic membrane filtration (ECMF) system was developed using molecular imprinting (MI) TiO2@SnO2-Sb (MI-TiO2@SnO2-Sb) anode for selectively eliminating 2,4-dichlorophenoxyacetic acid (2,4-D). The introduction of MI sites enhanced the removal of 2,4-D compared to the control. At a charging voltage of 3 V under flow-by mode, the 2,4-D removal rate of MI-TiO2@SnO2-Sb ECMF system was 1.91 times that of the control (without MI), attributed to the specific recognition sites (leading to selectivity) and the enhanced reactive oxygen species production in the presence of MI sites. In the coexistence of interferent phenoxyacetic acid herbicides, MI-TiO2@SnO2-Sb ECMF system also showed higher selective coefficient than the control (without MI). More importantly, flow-through mode could enhance the selectivity since the membrane filtration enhanced the mass transfer of target micropollutant towards MI sites. The imparted selectivity was mainly attributed to the size matching and special interaction between the target molecules and imprinted cavities.

Solid-phase extraction of phenoxyacetic acid herbicides in complex samples with a zirconium(IV)-based metal-organic framework.

A zirconium(IV)-based metal-organic framework material (MOF-808) has been synthesized in a simple way and used for the extraction of phenoxyacetic acids in complex samples. The material has good thermal and chemical stability, large specific surface area (905.36m²/g), and high pore size (22.18Å). Besides, it contains a large amount of Zr-O groups, easy-to-form Zr-O-H bond with carboxyl groups of phenoxyacetic acids, and possesses biphenyl skeleton structure, easy to interact with compounds through π-π and hydrophobic interactions. These characteristics make the material very suitable for the extraction of certain compounds with a high extraction efficiency and excellent selectivity. The extraction conditions were optimized, and then an analytical method was successfully established and applied for analysis of actual samples. The solid-phase extraction method based on prepared material had a wide linear range of 0.2-250μg/L and a low detection limit of 0.1-0.5μg/L for four phenoxyacetic acid compounds including 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy) propionic acid, 4-chlorophenoxyacetic acid, and dicamba. The relative standard deviations of intra- and interday precision were 1.8-3.8 and 4.3-6.9%, and the recoveries after spiking were between 77.1 and 109.3%. The results showed that the material is a desired substituent for the extraction of compounds with benzene ring structure containing carboxyl groups.

Zirconium(IV)-based metal-organic frameworks (UiO-67) as solid-phase extraction adsorbents for extraction of phenoxyacetic acid herbicides from vegetables.

A zirconium(IV)-based metal organic framework, composed of 4,4'-biphenyldicarboxylic acid ligands and Zr6 O4 (OH)4 clusters, was successfully fabricated. Characterizations were performed on fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller, and thermogravimetric analysis, which confirmed that it possessed large specific surface area, high pore volume, and strong acid resistant stability. Furthermore, the prepared material containing biphenyl skeleton and a large number of Zr-O bonds, can grasp acid herbicides especially phenoxyacetic acid herbicides with aromatic structures through π-π interaction, hydrophobic interaction and Zr-O-H+ bonds. Based on these advantages, a method was developed for the determination of four phenoxyacetic acid herbicides from vegetable samples. Under the optimal conditions, wide linearities from 0.3 to 250 μg/L and low limits of detection from 0.1 to 0.5 μg/L were obtained. The intra- and interday relative standard deviations were 1.56-3.92 and 5.01-7.65%, respectively. The proposed method was applied to analyze phenoxyacetic acid herbicides residues in the tomato, cucumber, and white gourd samples. The satisfactory recoveries (86.12-103.44%) for the spiked samples in vegetable samples were achieved which demonstrated the method was an efficient pretreatment procedure and has a potential application for the trace determination of phenoxyacetic acids from a complex matrix.

Graphene reinforced multiple monolithic fiber solid-phase microextraction of phenoxyacetic acid herbicides in complex samples

To increase the specific surface area (SSA) of monolith-based adsorbent for the extraction of phenoxyacetic acid herbicides (PAAs) in complex samples, graphene was embedded in an adsorbent based on poly (4-vinylpyridine-co-ethylene glycol dimethacrylate) monolith (GEM). The new adsorbent was employed as extraction phase of multiple monolithic fiber solid-phase microextraction (MMF-SPME). The influences of preparation conditions and extraction parameters on the enrichment performance of GEM/MMF-SPME for PAAs were investigated in detail. Results well indicated that the embedded graphene could obviously enhance the SSA of the adsorbent and introduce π-π electrostatic stacking groups. The prepared GEM/MMF-SPME could extract PAAs effectively by means of π-π electrostatic stacking, hydrophobic, ion-exchange and hydrogen bonding interactions. Under the most favorable conditions, a convenient, sensitive, cost-effective and environmentally friendly method for the determination of trace PAAs in water and rice samples was developed by the combination of GEM/MMF-SPME and high performance liquid chromatography-diode array detection (HPLC-DAD). Results showed that for water sample, the limits of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) values were in the range of 0.093–0.12 μg/L and 0.31–0.41 μg/L, respectively. The corresponding values in rice sample were 0.36–0.66 μg/kg and 1.18–2.27 μg/kg, respectively. The proposed method was successfully applied to quantify trace PAAs in water and rice samples. Recoveries achieved for water and rice samples at different spiked concentrations were in the ranges of 70.0–118% and 70.0–117%, respectively. The RSDs varied from 0.3% to 10% for all analytes. The results well revealed the potential application of GEM/MMF-SPME as an effective sample preparation processes for the monitoring of PAAs in water, rice and other complex samples.

Effects of Post-Pyrolysis Air Oxidation of Biomass Chars on Adsorption of Neutral and Ionizable Compounds.

This study was conducted to understand the effects of thermal air oxidation of biomass chars experienced during formation or production on their adsorptive properties toward various compounds, including five neutral nonpolar and polar compounds and seven weak acids and bases (pKa = 3-5.2) selected from among industrial chemicals and the triazine and phenoxyacetic acid herbicide classes. Post-pyrolysis air oxidation (PPAO) at 400 °C of anoxically prepared wood and pecan shell chars for up to 40 min enhanced the mass-normalized adsorption at pH ∼ 7.4 of all test compounds, especially the weak acids and bases, by up to 100-fold. Both general and specific effects were identified. The general effect results from "reaming" of pores by the oxidative removal of pore wall matter and/or tarry deposits generated during the pyrolysis step. Reaming creates new surface area and enlarges nanopores, which helps relieve steric hindrance to adsorption. The specific effect results from creation of new acidic functionality that provides sites for the formation of very strong, charge-assisted hydrogen bonds (CAHB) with solutes having comparable pKa. The CAHB hypothesis was supported by competition experiments and the finding that weak acid anion adsorption increased with surface carboxyl content, despite electrostatic repulsion from the growing negative charge. The results provide insight into the effects of air oxidation on pollutant retention.

Sunlight responsive WO3/ZnO nanorods for photocatalytic degradation and mineralization of chlorinated phenoxyacetic acid herbicides in water

Highly effective WO3/ZnO nanorods (NRs) were synthesized via a hydrothermal–deposition method for degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under natural sunlight. The structural properties of WO3/ZnO NRs such as morphology, crystal structure, porous properties and light absorption characteristics were investigated in detail. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the prepared samples were two-phase photocatalysts consisted of WO3 and ZnO NRs. The UV–vis diffuse reflectance spectroscopy result showed that the addition of WO3 altered the optical properties of the photocatalysts. In contrast with the pure ZnO NRs, commercial anatase TiO2 and commercial WO3, the WO3/ZnO NRs showed excellent sunlight photocatalytic activities in degrading 2,4-D. The optimal WO3 loading and calcination temperature were also determined. Based on the band position, the synergetic effect of WO3 and ZnO NRs was the source of the enhanced photocatalytic activity as validated by PL and terephthalic acid-photoluminescence measurements. The reaction intermediates and degradation pathways of 2,4-D were elucidated by a HPLC method. In addition, the extent of mineralization during the 2,4-D degradation was also estimated using total organic carbon (TOC) and ion chromatography (IC) analyses.