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951.
The photolysis of 16 polychlorinated biphenyls (PCBs) (including mono- through deca-chlorinated) in n-hexane was investigated under ultraviolet irradiation using a 500-W high-pressure mercury lamp. Photolysis of PCBs follows pseudo-first-order reaction kinetics, with photolysis rate constants ranging between 0.0011 s^-1 for PCB-52 and 0.0574 s^-1 for PCB-118. The degradation rates of PCBs by high-pressure mercury lamp irradiation were remarkably independent with respect to the degree of chlorination. Furthermore, partial least squares (PLS) models were developed to provide insight into which aspect of the molecular structure influenced PCB photolysis rate constants. It was found that the photolysis rates of PCBs increased with an increase in the net charge on the carbon atom (qc), (ELUMO-EHOMO)^2, and the Y-axis dipole moment (μy) values, or the decrease in the energy of the second highest occupied molecular orbital (EHOMO-1), energy of the lowest unoccupied molecular orbital (ELUMO), ELUMO + EHOMO, ELUMO - EHOMO, most positive atomic charge (q^+), and the twist angle of the chlorine atom (TA) values. 相似文献
952.
953.
为了提高对地表水中苯系物的检测能力,参加了某国际机构组织的地表水中苯系物检测比对活动。能力验证的样品采用吹扫、捕集和解析等前处理后,通过气相色谱-质谱法检测地表水中苯、甲苯、间/对二甲苯和邻二甲苯的浓度;并通过建立数学模型来分析和计算测试过程中的不确定度分量,以对其不确定度进行评定。结果表明:苯、甲苯、间/对二甲苯、邻二甲苯的检测结果满意率均为100%;从标准溶液、内标溶液、多功能自动进样器取样、样品测量的重复性和回收率等方面引入的不确定度进行评定,并将不确定度进行合成,得到苯、甲苯、间/对二甲苯和邻二甲苯的扩展不确定度(k=2)依次为0.077、0.095、0.250和0.140。 相似文献
954.
Perfluorooctanoic acid(PFOA)is recalcitrant to degrade and mineralize.Here,the effect of temperature on the photolytic decomposition of PFOA was investigated.The decomposition of PFOA was enhanced from 34% to 99% in 60 min of exposure when the temperature was increased from 25 to 85°C under UV light(201–600 nm).The limited degree of decomposition at 25°C was due to low quantum yield,which was increased by a factor of 12 at 85°C.Under the imposed conditions,the defluorination ratio increased from 8% at 25°C to 50% at85°C in 60 min.Production of perfluorinated carboxylic acids(PFCAs,C7–C5),PFCAs(C4–C3)and TFA(trifluoroacetic acid,C2)accelerated and attained a maximum within 30 to 90 min at 85°C.However,these reactions did not occur at 25°C despite extended irradiation to180 min.PFOA was decomposed in a step-wise process by surrendering one CF2unit.In each cyclical process,increased temperature enhanced the quantum yields of irradiation and reactions between water molecules and intermediates radicals.The energy consumption for removing eachμmol of PFOA was reduced from 82.5 k J at 25°C to 10.9 k J at 85°C using photolysis.Photolysis coupled with heat achieved high rates of PFOA degradation and defluorination. 相似文献
955.
956.
Yuancheng Li Gang Yu Jun Huang Bin Wang Shubo Deng Yujue Wang 《Environmental science and pollution research international》2018,25(32):31799-31804
Unintentionally produced persistent organic pollutants (UPOPs) include polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz). With the booming of municipal waste incinerators (MWIs) in China, the emission of UPOPs has generated great concern. As an alternative technology of dioxin control, catalytic decomposition has not been used in China, mainly due to the absence of national demonstration projects. Also, the simultaneous removal of various UPOPs has not been well investigated.In this study, a pilot-scale selective catalytic oxidative (SCO) system using a self-developed honeycomb catalyst was built and tested in a typical municipal waste incinerator (MWI) of China. The original concentration of PCDD/Fs in flue gas after the treatment of activated carbon injection (ACI) still exceeded the national emission standard (0.1 ng I-TEQ/Nm3), while the concentrations of PeCBz and HxCBz were one order of magnitude higher than that of PCDD/Fs. For the testing temperature varying from 300 to 200 °C, the removal efficiency of PCDD/Fs range from 39 to 95 %, followed by dl-PCBs with the range of 56–89 %. PeCBz and HxCBz were also removed, though their removal efficiencies were lower than those of PCDD/Fs and dl-PCBs. Both temperature and degree of chlorination influence the removal efficiencies. 相似文献
957.
以壳聚糖(CTS)和巯基乙酸为主要原料,通过酰胺化反应将巯基引入到CTS高分子链上,制备出高分子重金属絮凝剂巯基乙酰化壳聚糖(MACTS)。以含Cd(II)水样为考察目标,采用响应曲面法中的BBD和CCD实验对MACTS的制备条件进行优化,从残差分析、方差分析、响应面分析和优化条件等方面对BBD法和CCD法进行比较。结果表明,BBD法和CCD法建立的二次多项式模型回归性分别为显著和非常显著,模型选择均合理;BBD法和CCD法拟合模型的决定系数R2分别为0.871 0、0.919 7,模型相关性均较好;通过BBD法和CCD法优化制备条件后的MACTS处理含Cd(II)水样,Cd(II)的最低剩余浓度分别为0.83、0.76 mg·L-1。在优化MACTS的制备条件上采用CCD法更优于BBD法。 相似文献
958.
甲醛作为一种常见的挥发有机化合物(VOC),对人体健康构成长期危害。为提高活性炭纤维(ACF)对甲醛等有害气体的吸附去除能力,采用不同浓度的碱处理和不同温度的氮修饰对ACF进行耦合改性,对共同改性后的ACF进行SEM、BET和XPS等分析测试,获得相关物理化学参数,并评价其吸附去除甲醛气体的性能。研究结果表明:碱处理后的ACF获得了发达的微孔结构和较高的比表面积。氮修饰后,ACF表面含氮官能团数量明显提高。改性后的ACF去除甲醛的性能得到了明显的提升,对初始浓度为4 mg·m-3的甲醛去除率高达98%。吸附去除甲醛性能的提高应该归因于比表面积的大幅度提升和表面含氮官能团数量增加的共同作用。 相似文献
959.
Daily average concentrations of fine and coarse particulates, and TSP samples have been measured simultaneously at daytime and night-time periods by using Universal and PS-1 sampler in a suburban area of central Taiwan from June to August 1998. The samples were analyzed by atomic absorption spectrometry to determine the fine and coarse particulate concentrations of metallic elements (Ca, Fe, Mn, Pb, Cu, Zn and Cr). The concentration of PM2.5 and TSP showed a decreased trend for the daytime period. The fine particle concentrations were about two times as that of coarse particulate concentrations. The averaged fine particulate concentrations at daytime are higher than at night-time. Ca and Fe were mostly in the coarse particulate mode. The correlation coefficients were 0.63 and 0.69 for elements Ca and Fe in the coarse particle mode for day and night periods. Pb showed a similar distribution ratio with Mn for the fine to coarse particle ratios at both day and night period. Pb and Mn are highly correlated for the day (R = 0.78) and night period (R = 0.61) at particle size <2.5 microm. Cu and Zn were mainly in fine particles at both day and night period. Fe and Ca consist of the major parts of all the elements. Elemental Mn is the lowest among the rest of the heavy metals. 相似文献
960.