| In order to reduce the environmental contamination caused by quinclorac and alleviate its effect of phytotoxicity on tobacco, this thesis systematically studied the mechanisms and impacts of modified montomorillonites and biochars on the adsorption and migration of quinclorac as well as the mitigation effect on injured tobacco, by using batch equilibrium methods, incubation and pot experiments. Firstly, the montomorillonites were modified by hexadecyl trimethyl ammonium bromide and chitosan, respectively. The two modified montomorillonites (named as HDT-M and CTS-M, respectively) were characterized by Brunauer-Emmett-Teller (BET) surface area, Fourier transform spectroscopy (FT-IR), x-ray diffraction (XRD) and scanning electron microscope (SEM). And on this basis, the adsorption-desorption of quinclorac in aqueous solution onto the two modified montomorillonites and two biochars (named as BC1 and BC2) with different properties were studied and the interaction mechanisms between the adsorbents and quinclorac were also elucidated. Finally, the mechanisms of the four adsorbents added to soil influencing the sorption-desorption and dissipation of quinclorac, as well as its mitigation effect on injured tobacco were also investigated. Through these researches, some results were obtained as follows.1. The preparation conditions of modified montomorillonites was optimizedThe effect of modifiers’dosage, reaction temperature, reaction time and pH on the preparation of modified montomorillonites was studied by single-factor experiments. The preparation condition of HDT-M was that:the natural montomorillonite was to be treated with 4 M H2SO4 for acidizing before modification, with the dosage of modifier twice the CEC of montomorillonite, the reaction temperature at 60℃, and the reaction time of 4 h. The preparation condition of CTS-M was that:the natural montomorillonite was treated with 1.0 M NaCl before modification, with the mass ratio of chitosan and Na-montomorillonite being 1.2:1, the pH of chitosan solution set at about 5.0, the reation temperature at 50℃, and the reaction time of 5 h.2. The impact mechanisms of the modified montomorillonites and biochars on the adsorption-desorption of quinclorac in aqueous solution were elucidated(1) The adsorption isotherms of quinclorac on HDT-M fitted well with both Frendulich and Linear isotherm models. However, the adsorption isotherms of quinclorac on CTS-M and biochars only suited Frendulich isotherm model.(2) The adsorption kinetics data of quinclorac on the two modified montomorillonites were well described by the pseudo-second-order kinetics models. However, the adsorption kinetics data of quinclorac on the two biochars were well described by the pseudo-first-order kinetics models, indicating that microporous diffusion was the rate-limiting step.(3) The adsorption capacities of HDT-M and biochars for quinclorac decreased with the increase in pH. However, with the increase of pH, the adsorption capacities of CTS-M for quinclorac increased firstly and then decreased. The increase ionic strength was not conducive to the adsorption of quinclorac on CTS-M and HDT-M, but beneficial to the adsorption capacities of biochars for quinclorac. The adsorption capacity of HDT-M for quinclorac decreased with an increase in temperatures from 25℃ to 45℃, but the adsorption capacity of CTS-M and biochars for quinclorac increased with the increase of temperature.(4) The effect of different solvents on the desorption of quinclorac were quite different. Compared with H2O,0.1 M HCl and 0.1 M NaCl,0.1 M NaOH could easily desorb the quinclorac from modified montomorillonites, but all of these four solvents could not effectively desorb quinclorac from biochars.(5) There were interactions between quinclorac and the two modified montomorillonites, probably including hydrophobic interaction, electrostatic attraction, cationic dipole, hydrogen bond and van der waals force, and so on. However, the main interactions between the two biochars and quinclorac were pore filling effect, hydrogen bond and van der waals force.3. Effect of the two modified montomorillonites and the two biochars added to soil on the adsorption, dissipation of quinclorac and its mitigation effect on injured tobacco caused by quinclorac was explicit(1) The quinclorac sorption increased in soils with the supplement of modified montomorillonites and biochars, but the desorption of quinclorac exhibited significant hyteresisi in all amended soils, which reduced the environmental water contamination caused by quinclorac in soil.(2) The effect of modified montomorillonites and biochars added to soil on the dissapation of quinclorac was quite different. After an incubation of 90 days, the dissipation rate of quinclorac, with an initial concentratin of 10.0 mg/kg, was 48.2%, 54.9%,78.5%,90.0%,78.0% in BC1, BC2, CTS-M, HDT-M amended soils and unmended soils, respectively. The corresponding half-life value of quinclorac was 138.63d,99.02d,46.21d,30.14d and 49.51d. respectively. One of the degradation products was determined as 3,7-dichloroquinoline-8-aldehyde by UHPLC-QTOF/MS.(3) The tobacco seedlings were treated with quinclorac of 0.005 mg/L and 0.01 mg/kg in hydroponic and soil cultures, respectively on the basis of biological and physiological indexes by pot experiments. And on this basis, the mitigation effect of four adsorbents on injured tobacco caused by quinclorac in hydroponic and soil cultures was investigated. The results showed that, except for HDT-M, the other three materials BC1, BC2, and CTS-M obviously retarded the impact of quinclorac on tobacco growth, and it would not cause adverse effect on the tobacco growth with the increase of adsorbents’dosage.Experiment results showed that although HDT-M had a good sorption property, it was toxic to tobacco seedlings. Therefore it was not fit for the mitigation of injured tobacco caused by quinclorac. As a comparison, biochars and CTS-M, as environmentally friendly adsorbents, not only had a good adsorption property, but also could alleviate the phytotoxic effect of quinclorac on tobacco. |
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