Similarities and differences in adsorption mechanism of dichlorvos and pymetrozine insecticides with coconut fiber biowaste sorbent.

In this study, the similarities and differences of the adsorption mechanisms between dichlorvos and pymetrozine and coconut fiber biowaste sorbent (CF-BWS) were investigated. CF-BWS was produced using the slow pyrolysis process at 600 °C for 4 h. HCl acid modification was used to improve the specific surface area. The properties of CF-BWS were analyzed by SEM, FT-IR, BET, and pHpzc. The adsorption kinetics of dichlorvos and pymetrozine on the CF-BWS were well explained by the pseudo-second-order model. The adsorption isotherms for both insecticides were followed the Langmuir isotherm. The difference in molecular structures and surface chemistry caused the difference in adsorption mechanisms of both insecticides. The pore-filling and the hydrophobic interactions were the key mechanisms for both insecticide adsorptions. However, the π-π electron donor-acceptor interaction played the major role in the pymetrozine adsorption but hardly impacted on the adsorption of dichlorvos. The hydrogen bonding mechanism was pronounced in the pymetrozine adsorption, but it had little influence on the dichlorvos adsorption. The CF-BWS is exhibited as an excellent material for the removal of both pollutants and has high potential to be used further as the adsorbent in water treatment process.

Catalytic Degradation of Dichlorvos Using Biosynthesized Zero Valent Iron Nanoparticles.

The removal of dichlorvos contamination from water is a challenging task because of the presence of direct carbon to phosphorous covalent bond, which makes them resistant to chemical and thermal degradation. Although there have been reports in the literature for degradation of dichlorvos using nanomaterials, those are based on photocatalysis. In this paper, we report a simple and rapid method for catalytic degradation of dichlorvos using protein-capped zero valent iron nanoparticles (FeNPs). We have developed an unprecedented reliable, clean, nontoxic, eco-friendly, and cost-effective biological method for the synthesis of uniformly distributed FeNPs. Yeast extract was used as reducing and capping agent in the synthesis of FeNPs, and synthesized particles were characterized by the UV-visible spectroscopy, X -ray diffraction, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). TEM micrographs reveal that the nanoparticles size is distributed in the range of 2-10 nm. Selected area electron diffraction pattern shows the polycrystalline rings of FeNPs. The mean size was found to be 5.006 nm from ImageJ. FTIR spectra depicted the presence of biomolecules, which participated in the synthesis and stabilization of nanoparticles. As synthesized, FeNPs were used for the catalytic degradation of dichlorvos in aqueous medium. The degradation activity of the FeNPs has been investigated by the means of incubation time effect, oxidant effect, and nanoparticle concentration effect. The ammonium molybdate test was used to confirm the release of phosphate ions during the interaction of dichlorvos with FeNPs.

Paper-based chromatographic chemiluminescence chip for the detection of dichlorvos in vegetables.

Paper chromatography was a big breakthrough in the early of 20th century but it is rarely used due to the long separation time and the diffusion on the sample spots. In this work, for the first time, a paper-based chemiluminescence (CL) analytical device combined with paper chromatography was developed for the determination of dichlorvos (DDV) in vegetables without complicated sample pretreatment. The paper chromatography separation procedure can be accomplished in 12 min on a paper support (0.8 × 7.0 cm(2)) by using 5 µL sample spotted on it. After sample developing, the detection area (0.8 × 1.0 cm(2)) was cut and inserted between two layers of water-impermeable single-sided adhesive tapes. The paper-based chip was made by attaching the middle layer of paper onto the bottom layer. Then it was covered by another tape layer, which was patterned by the cutting method to form a square hole (0.8 × 1.0 cm(2)) in it. 10 µL mixed solution of luminol and H2O2 was dropped on the detection area to produce CL. A linear relationship was obtained between the CL intensity and the concentrations of DDV in the range between 10.0 ng mL(-1) and 1.0 µg mL(-1)and the detection limit was 3.6 ng mL(-1). Water-soluble metal ions and vitamins can be developed at different spatial locations relative to DDV, eliminating interference with DDV during detection. The paper-based chromatographic chip can be successfully used for the determination of DDV without complicated sample preparation in vegetables. This study should, therefore, be suitable for rapid and sensitive detection of trace levels of organophosphate pesticides in environmental and food samples.

Trace determination of dichlorvos in environmental samples by room temperature ionic liquid-based dispersive liquid-phase microextraction combined with HPLC.

Using 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) room temperature ionic liquid (RTIL) as extraction solvent, tetrahydrofuran (THF) as disperser solvent, the organophosphorus pesticide dichlorvos in water was determined by dispersive liquid-liquid microextraction (DLLME) combined with high-performance liquid chromatography. Factors affecting RTIL-DLLME (type of disperser solvent, amount of RTIL, volume of disperser solvent, percentage of NaCl and volume and pH of water sample) were optimized by the single-factor method, obtaining the most favorable results when using 65 µL of [BMIM][PF6] and 260 µL of THF to extract the compound from an 8-mL water sample at pH 5.0 containing 25% (w/v) of NaCl. Under these optimum conditions, an enrichment factor of 215-fold was obtained. The calibration curves were linear in the concentration range of 2-1,000 µg/L. The limit of detection calculated at a signal-to-noise ratio of 3 was 0.2 µg/L. The relative standard deviations (RSD) for six replicate experiments at 20, 100 and 200 µg/L concentration levels were 1.8%, 1.3% and 1.3 %, respectively. Then the proposed method was applied to the analysis of three different water sample sources (tap, farm and rain water) and the relative recoveries and RSD of spiked water samples were 95.6-102.4% and 0.6-3.1%, respectively, at three different concentration levels of 20, 100 and 200 µg/L.

Degradation of dichlorvos using hydrodynamic cavitation based treatment strategies.

The degradation of an aqueous solution of dichlorvos, a commonly used pesticide in India, has been systematically investigated using hydrodynamic cavitation reactor. All the experiments have been carried out using a 20 ppm solution of commercially available dichlorvos. The effect of important operating parameters such as inlet pressure (over a range 3-6 bar), temperature (31 °C, 36 °C and 39 °C) and pH (natural pH = 5.7 and acidic pH = 3) on the extent of degradation has been investigated initially. It has been observed that an optimum value of pressure gives maximum degradation whereas low temperature and pH of 3 are favorable. Intensification studies have been carried out using different additives such as hydrogen peroxide, carbon tetrachloride, and Fenton's reagent. Use of hydrogen peroxide and carbon tetrachloride resulted in the enhancement of the extent of degradation at optimized conditions but significant enhancement was obtained with the combined use of hydrodynamic cavitation and Fenton's chemistry. The maximum extent of degradation as obtained by using a combination of hydrodynamic cavitation and Fenton's chemistry was 91.5% in 1h of treatment time. The present work has conclusively established that hydrodynamic cavitation in combination with Fenton's chemistry can be effectively used for the degradation of dichlorvos.

[Rapid elimination of surface organophosphorous pollutants using hydroxyl radical].

According to the frequency of contamination accident for organic compounds in recent years, two kinds of organophosphorus pesticides dichlorvos and omethoate, as the simulated organic pollutants, were rapidly eliminated using spraying hydroxyl radical produced by strong electric-field ionization discharge method on an aluminium flat plate about 160 cm2. The high concentration aqueous *OH solution was produced from H2O(gas) and O2 with plasma reaction. In a condition, where pH is 6 and the initial densities of dichlorvos and omethoate on the simulation plane are both 60 microg x cm(-2), when the spray density of *OH reaches 3.9 microg x cm-2, removal efficiencies of dichlorvos and omethoate are 90%, and mineralization rates are 64% and 72%, respectively. The effect of pH for removal efficiency was also investigated. The results found that the removal efficiency of organophosphorus pollutants first decreased slowly and then increased fast with the increase of pH from 2 to 12 and the lowest removal rate appeared when pH close to neutral. The degradation rates of dichlorvos and omethoate both ascend by 21% and 26% respectively with pH 12 than that of pH 6. Four factors and three levels orthogonal test indicated that the degradation by *OH played a major role at the surface oxidation removal rapid of organophosphorus pollutants in a short period of time.

[Study on decomposed products of trichlorfon in process of gas chromatographic analysis by mass spectrometry].

The decomposed products of trichlorfon in gas chromatographic analysis were identified by mass spectrometry (MS). After MS interpretation, three decomposed products, trichloroacetaldehyde, dimethyl phosphite and dichlorvos were identified. The effects of gas chromatographic conditions on decomposed products of trichlorfon, e. g. injection temperature, injection mode and oven ramp, were studied. The experiments showed that all of the factors have effects on decomposed products of trichlorfon, however, the injection temperature is the key factor to cause trichlorfon being decomposed. The higher the injection temperature is, the bigger the amount of trichlorfon being decomposed. When the injection temperature was raised from 150 degrees C to 250 degrees C, the remaining trichlorfon fell from 86% to 20%. Therefore, on-cold column injection mode gas chromatography or high performance liquid chromatography was recommended for exact quantification of trace trichlorfon.

Study on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos.

In this paper, dichromate and dichlorvos are selected as the deputies of inorganic and organic pollutants, respectively, and TiO2/beads is used as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, H2O2 concentration, metal ions, anions, pH value, and organic compounds on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos are studied. From the studies, the differences of the parameters effect on the photocatalytic degradation of organic and inorganic pollutants are obtained. The results show that the optimum amount of the photocatalyst used is 6.0 g cm(-3) for the photocatalytic reactions. With the addition of a small amount of H2O2, the photocatalytic reduction of dichromate is inhibited while the photocatalytic oxidation of dichlorvos is accelerated. With the addition of trace amounts of Fe3+ or Cu2+, both the reactions are accelerated, and with the addition of Zn2+ and Na+, no obvious effects on the reactions are observed. Acidic solution is favorable for the photocatalytic reduction of dichromate; and acidic and alkaline solutions are favorable for the photocatalytic oxidation of dichlorvos. Adding SO4(2-), the photocatalytic oxidation is accelerated and adding Cl- the reaction is inhibited; and with the addition of trace amounts of SO4(2-), Cl- and NO3-, no obvious effects on the photocatalytic reduction of dichromate are observed. With the addition of methanol and toluene, the photocatalytic reduction of dichromate is accelerated, and the photocatalytic oxidation of dichlorvos is inhibited. The possible roles of the additives on the reactions are also discussed.

Catalytic ozonation of an organophosphorus pesticide using microporous silicate and its effect on total toxicity reduction.

Catalytic ozonation is promising as one of the advanced oxidation processes because of its effective use of ozone and its improved treatability of organic compounds through radical reactions. In this article, we investigated the feasibility of microporous silicates as a potential catalyst for a catalytic ozonation process. Organophosphorus insecticide, dichlorvos (DDVP), was employed as a model chemical for assessing conventional ozonation and catalytic ozonation, because its oxidative intermediate is toxic and is not degraded by direct ozonation. It was found that ozone was well adsorbed and simultaneously decomposed in microporous silicates, resulting in the production of possible radical species. In the presence of microporous silicates, radical reactions by decomposed ozone were evidenced by phosphate ion release that shows a degradation of a toxic intermediate of DDVP. Accordingly, cytotoxicity was successfully decreased. In a continuous treatment process combining a conventional ozonation vessel and a microporous silicate column for an effective use of residual ozone, enhanced degradation of DDVP was demonstrated by a decrease of DOC, an increase of the PO4(3-) concentration and reduction in the cytotoxicity. This new treatment mechanism is likely to be promising as an advanced water treatment process particularly when we think about better toxicity reduction of wastewaters.

[Solid-phase microextraction of dichlorvos from white spirits].

DDVP was isolated from white spirits using Solid-Phase Microextraction (SPME) technique, and determined by wide-bore capillary gas chromatography (GC) coupling a flame ionization detector. This method had an excellent linearity among 0.5-12 mg/L. Correlation coefficient and minimum detectable concentration were 0.9983 and 0.05 mg/L respectively. This method enables the extraction, the enrichment and the injection to integrate into a single step, and it was free-solvent in whole process. SPME is an advanced technique for the extraction and analysis of the samples.