Studies On Pesticides Multi-residue Analysis And Hydrodechlorination Of Contaminants In Groundwater Based On Carbon Materials

Carbon family contains activated carbon, carbon fiber, graphitized carbon black, diamond, fullerence, carbon nanotubes, and graphene. Graphene is one of the fascinating new additions into the carbon family. As a perfect two-dimensional carbon material, graphene has ultra large surface area and comprises large delocalized π-electron system, which means it has high capacity for adsorption of target molecules and can form strong π-π stacking interaction with aromatic rings. It has been widely used in pollutants adsorption and analytical chemistry. Considering the significant interferences of matrix background, this research took continuous and systematic efforts to implement advanced nanomaterials. In our studies, we prepared graphene, amine modified graphene and graphitic carbon nitride, which are used in sample preparation techniques in pesticide multi-residue analysis. The modified analytical method meets the requirement as "time-saving, labor-saving, cheap, solvent-saving, less environmental pollutants". The main research contents are:(1) A multi-residue analytical method is validated on 24 representative pesticides residues in onion, garlic, and leek. This method is based on modified QuEChERS sample preparation with mixture of graphene, PSA, and GCB as reversed-dispersive solid phase extraction (dSPE) material and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Graphene was firstly used as dSPE cleanup sorbent in onion, garlic, and leek. Our results firstly reveal that the mixed sorbent of graphene, PSA, and GCB has remarkable ability to cleanup interfering substances in dSPE procedure when comparing with the mixture of PSA and GCB. Use of matrix-matched standards provides acceptable results for most pesticides with overall average recoveries between 70.1 and 109.7% and consistent RSDs<15.6%. In any case, this method still meets the 1-10μg/kg detection limit needs for tested pesticides and may be used for qualitative screening applications, in which any identified pesticides can be quantified and confirmed by a more intensive method that achieves>70% recovery.(2) Amine modified graphene is successfully synthesized via a one-pot solvothermal reaction between graphene oxide and ammonia water, methylamine or n-butyl amine. The presence of amine groups in graphene is identified by Fourier-transform infrared spectrometry, X-ray photoelectron spectroscopy and an X-ray diffractometer. The ability of amine modified graphene to cleanup fatty acids and other interfering substances from acetonitrile extracts of oil crops has been evaluated. It is found that the resulting CH3NH-G exhibits the best performance in interfering substances removal. Meanwhile, a multi-residue method is validated on 31 representative pesticide residues in four oil crops (rapeseed, peanut, sesame seeds and soybean). This method is based on modified QuEChERS sample preparation with CH3NH-G as dSPE material and liquid chromatography-tandem mass spectrometry. Use of matrix-matched standards provides acceptable results for most pesticides with overall average recoveries between 70.5 and 100% and consistent RSDs<13%, except for pymetrozine, thidiazuron and diuron. In any case, this method still meets the 0.1-8.3μg/kg detection limit needs for most pesticides and may be used for qualitative screening applications, in which any identified pesticides can be quantified and confirmed by a more intensive method that achieves>70% recovery.(3) Unique graphitic carbon nitride (g-C3N4) nanovessels have been prepared and applied as dSPE adsorbent for determining benzoylurea pesticides in different juice samples using high performance liquid chromatography equipped with ultraviolet detection. The g-C3N4 nanovessels were obtained on a large scale by thermally converting low-cost urea without additive assistance, which avoided a complex synthesis process, consumption of organic solvent, and limits of tailoring the reaction pressure and atmosphere. The g-C3N4 nanovessels have been characterized using transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, and elemental analysis. The conditions affecting the extraction efficiency were optimized, including adsorbent amount, extraction time, sample volume, and choice and volume of desorption solvent. Under the optimal conditions, comparable detection limits of 6μg/L and good recoveries of 70.4-96.4% for six BUs have been achieved. Meanwhile, g-C3N4 nanovessels showed excellent reuse potential. The results indicated that g-C3N4 nanovessels repesented a promising SPE adsorbent for the enrichment and trace analysis of pollutants.(4) The adsorption mechanism of five benzoylurea insecticides onto g-C3N4 in water has been studied. The adsorption kinetic data of g-C3N4 exhibited rapid removal of pesticides in less than 3min. The adsorption of BUs represented a very small decrease with increase in the pH of the solution (the decrease of adsorption ranged 0.6-3.8%/unit pH). The adsorption isotherms data fit Langmuir model and Freundlich model well. The adsorption of BUs onto g-C3N4 proved to be dependent on the electron-donating abilities of the S and O atoms and the strong π-bonding network of benzene rings. G-C3N4 is considered to be a promising adsorbent for removing pesticides pollutants from water.Organochlorine pesticides (OCPs) are one group of persistent organic pollutants (POPs) in aqueous systems which are going to be eliminated or reduced on the release into the environment under the Stockholm Convention on Persistent Organic Pollutants adopted by many countries. Because of their persistent in the environment and biological accumulation through the food web, OCPs can cause environmental damage and affect human health. DDT is a common OCR In our studies, we aprepared Pd/Fe-AC aiming to hydrodechlorinate DDT. Before that, we divided DDT into two significant chemical structure-chlorobenzene and chloroform and studied chlorobenzene and chloroform hydrodechlorination with Pd/Fe-AC. Better than DDT, chlorobenzene and chloroform have simple chmical structure, which can help us to study the reaction mechanism of Pd/Fe-AC clearly.Chlorobenzene and chloroform hydrodechlorination with Pd/Fe-AC, Pd/AC and Pd/Fe were conducted to study bimetallic synergistic effect of Pd/Fe in Pd/Fe-AC and the sorption effect of AC. The catalytic hydrodechlorination reactions followed first-order kinetics. The surfaced Pd activity is Pd/Fe-AC> Pd/AC> Pd/Fe. It was observed that electron transfer, caused by Pd/Fe galvanic couple, obviously accelerated contaminant reduction with Pd/Fe-AC as catalyst. Pd components containing Fe0 consumed H2 generated by Fe0 corrosion. Carbon support is highly capable to gather probe compounds as well as transfer spillover atomic hydrogen, which is contributed to enhance hydrodechlorination activity. The study of chlorobenzene and chloroform hydrodechlorination is for the assumption of DDT hydrodechlorination with Pd/Fe-AC. Chlorinated functional groups in DDT cannot be dechlorinated completely.