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51.
52.
In a chemical sense, the positive muon is a light proton. It is obtained at the ports of accelerators in beams with a spin
polarization of 100%, which makes it a highly sensitive probe of matter. The muonium atom is a light hydrogen isotope, nine
times lighter than H, with a muon as its nucleus. It reacts the same way as H, and by addition to double bonds it is implemented
in free radicals in which the muon serves as a fully polarized spin label. It is reviewed here how the muon can be used to
obtain information about muonium and radical reaction rates, radical structure, dynamics, and local environments. It can even
tell us what a fragrance molecule does in a shampoo. 相似文献
53.
Modeling the effects of concentration history on the slow desorption of trichloroethene from a soil at 100% relative humidity 总被引:1,自引:0,他引:1
To determine the effects of concentration history on slow sorption processes, desorption kinetic profiles for trichloroethene (TCE) were measured for a soil at 100% relative humidity subject to different exposure concentrations and exposure times. Exposure concentrations ranged from 1% to 80% of the saturation vapor pressure (Ps) for TCE, and exposure times (i.e., time allowed for sorption before desorption begins) ranged from 1 to 96 days. A spherical diffusion model based on a gamma distribution of sorption rates and a gamma distribution of desorption rates was developed and applied to the data. At 80% P/Ps, the entire gamma distributions of sorption and desorption rates were available for TCE. In accordance with a micropore filling mechanism, the fraction of these distributions available for TCE sorption decreased with decreasing P/Ps. Experimental results are consistent with a micropore-filling mechanism, where the amount of slow desorbing mass decreased with decreasing exposure time, and the fraction of slow desorbing sites filled decreased with decreasing exposure concentration. Simulation results suggest that diffusion limits the rates that micropores fill, and that rates of sorption and desorption for soil contaminated at smaller values of P/Ps are, on average, less than those at larger values of P/Ps (i.e., slow desorption rates are a function of exposure concentration). Simulation results also suggest that the model adequately describes the effects of exposure concentration and exposure time on the rates of sorption and desorption, but not on the capacity of the slow sites for TCE. This work is important because contaminant concentrations in the subsurface vary in space and time, and the proposed model represents a new and mechanistically based approach to capture the effects of this heterogeneity on slow desorption. 相似文献
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Xiaoxiao Yin Junyu Tao Guanyi Chen Xilei Yao Pengpeng Luan Zhanjun Cheng Ning Li Zhongyue Zhou Beibei Yan 《Frontiers of Environmental Science & Engineering》2023,17(1):6
56.
In this study, we examined the experimental catalytic oxidation of gaseous monochlorobenzene (MCBz) with O3 over Fe2O3 in a packed bed reactor to investigate the feasibility of economical low temperature decomposition at a high space velocity (SV). We investigated the effects of several reaction parameters (temperature, O3 concentration, and SV) on the MCBz oxidation. At 150 °C, the conversion of MCBz over Fe2O3 in the absence of O3 was only 3%; it increased to 91% over Fe2O3 in the presence of 1200 ppm of O3 at a high SV of 83 s−1. A long-term operation study revealed that the conversion of MCBz was stable for more than 96 h. In the steady state, the carbon and chlorine balances were 88% and 86%, respectively. Applying a Langmuir-Hinshelwood kinetic model, we estimated an activation energy of 16.7 kJ mol−1 for MCBz oxidation over Fe2O3 in the presence of O3. 相似文献
57.
This work addresses the effect that plants (Typha latifolia and Carex lurida) have on the reduction of Cr(VI) in wetland sediments. Experiments were carried out using tubular microcosms, where chemical species were monitored along the longitudinal flow axis. Cr(VI) removal was enhanced by the presence of plants. This is explained by a decrease in the redox potential promoted by organic root exudates released by plants. Under these conditions sulfate reduction is enhanced, increasing the concentration of sulfide species in the sediment pore water, which reduce Cr(VI). Evapotranspiration induced by plants also contributed to enhance the reduction of Cr(VI) by concentrating all chemical species in the sediment pore water. Both exudates release and evapotranspiration have a diurnal component that affects Cr(VI) reduction. Concentration profiles were fitted to a kinetic model linking sulfide and Cr(VI) concentrations corrected for evapotranspiration. This expression captures both the longitudinal as well as the diurnal Cr(VI) concentration profiles. 相似文献
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锌在石灰性土壤中的吸附动力学初步研究 总被引:10,自引:1,他引:10
采用恒流淋洗法研究了外加锌在石灰性土壤中的吸附动力学特性.通过对石灰性土壤样品,人工模拟样品和纯CaCO_3物质吸附锌的动力学实验,结果衰明,石灰性土壤中的CaCO_3组分是外加锌的主要载体,且被CaCO_3组分所保持的锌不易被0.01mol/LCaCl_2溶液解吸下来。还拟用了几种动力学方程(一级动力学方程,Elovich方程和抛物线扩散方程)对本实验得到的动力学曲线进行描述和数据处理,结果表明石灰性土壤吸附锌的动力学特征主要由土壤中CaCO_3组分决定的。 相似文献