Synthesis of freestanding silica and titania-silica aerogels with ordered and disordered mesopores

Freestanding blocks of silica and titania-silica aerogels were prepared by the sol-gel method. It is possible to prepare crack-free, titania-silica aerogels with high titanium content by a careful control of the synthesis conditions. Prehydrolysis, complexation and polymer addition were used to adjust the hydrolysis and condensation rates of the silicon and titanium alkoxide precursors. Photoactive anatase TiO₂ nanocrystals with a large surface area (i.e., up to 300m²g⁻¹) were crystallized from the gel network by the high-temperature ethanol supercritical drying, and the resulting aerogel blocks were gas permeable and display a transition-regime diffusion behavior. Pore and volume shrinkages were observed in samples prepared by ethanol supercritical drying when the titanium content was increased resulting in a lower flux. Adding Pluronic P123 creates ordered mesopore domains and produces large pore aerogels even at high titanium contents. The photocatalytic oxidation reaction of trichloroethylene was performed by flowing the reactant gas mixture through the UV-irradiated aerogel blocks with excellent results.     

Study on the active sites of Cu-ZSM-5 in trichloroethylene catalytic combustion with air

The catalytic activity of Cu-ZSM-5 in trichloroethylene （TCE） combustion increases with the increasing skeletal Cu amount and however decreases with the increase of surface amorphous CuO, which is detected by infrared spectroscopy （IR） and diffuse reflectance ultraviolet-visible spectroscopy （DRS-UV-vis）, therefore the skeletal Cu species are concluded to be the active sites for the TCE combustion.     

同位素稀释超高效液相色谱串联质谱测定尿液中苯系物和三氯乙烯代谢产物

建立同位素内标稀释,超高效液相色谱串联质谱(Uhra performance liquid chromatography-tandem mass sepctrometry,UPLC-MS/MS)同时测定尿中苯系物和三氯乙烯代谢产物的方法,并用于孕妇尿样的分析.尿样过经含同位素内标的醋酸铵缓冲液稀释10倍后,过滤,取滤液进样分析.采用C18色谱柱,梯度洗脱进行UPLC分离,电喷雾负离子扫描多反应监测(Multiple reaction monitoring,MRM)模式检测.方法检出限在0.0350～ 1.75 μg/L之间,方法的日内和日间精密度分别为1.2％～9.1％和2.0％～9.7％;用所建立的方法测定了650个孕妇尿液样品,并统计分析了其地区差异,加标回收率为85.0％～104％.所建立的方法快速灵敏,适合尿液样品的批量分析.     

乙醇/水体系负载型纳米Cu/Fe二元合金的合成、改性及其还原三氯乙烯的性能

在乙醇/水体系中采用KBH4液相还原法, 以石墨微粉为载体, Cu为复合金属, 通过两步法合成了具有球状团簇结构的负载型纳米Cu/Fe二元合金. 与单纯负载型纳米Fe0相比, 该复合材料对三氯乙烯(TCE)具有更高的还原脱氯性能, 纳米Fe0的质量浓度为10 g/L时, 5 h内能将10 mg/L的TCE完全去除. 将十六烷基三甲基溴化铵(CTAB)用于负载型纳米二元合金的表面改性, 改性后的材料对TCE的还原脱氯性能提高. 改性材料连续降解TCE 36 d, 10.2 mg/L TCE在7 h内即完全去除, 材料改性后不易氧化失活, 还原性能保持长期稳定.     

ADSORPTION OF CHLOROFORM AND TRICHLOROETHYLENE IN WATER WITH A NEW KIND OF HYPERCROSSLINKED RESINS

In this paper two newly developed hypercrosslinked resins were used to treat micropolluted drinking water and their static and kinetic adsorption were investigated at 293 K. The results show that these two adsorbents are superior to Amberlite XAD-4 for removing chloroform and trichloroethylene in aqueous solutions. The breakthrough capacity and the total capacities from mini-column adsorption studies for chloroform and trichloroethylene on XAD-4, ZH-01 and ZH-00 are calculated respectively under experimental conditions     

A Validated GC-MS Assay for the Quantitation of Trichloroethylene (TCE) from Drinking Water

Trichloroethylene (TCE) is a common ground and surface water contaminant found in the United States. A validated GC-MS assay for the quantitation of TCE in drinking water is presented here. The limit of quantitation, 5 µg/L, is lower than current validated methods for the analysis of TCE from water. This assay requires a small sample volume, has simple sample preparation, fast run time, high recovery, and reproducible and accurate results.     

Microwave-assisted extraction of trichloroethylene from clay samples

A new method for volatile organic compounds (VOCs) extraction from low-permeability media, such as clay, has been developed and tested using trichloroethylene (TCE) as a model compound. The method is based on microwave-assisted extraction (MAE), which uses microwave energy to heat the extracting solvent and the sample. MAE allows the extraction process to be carried out at elevated temperatures and pressures, which dramatically reduces the time required to complete the process. A custom-made PTFE vessel was used for extraction investigations. TCE analysis was performed using gas chromatography with electron capture detection (GC-ECD). Three different solvents were tested: methanol, 1?:?1 hexane?:?acetone mixture, and 10?:?1 hexane?:?acetone mixture. A comparison of TCE recoveries from clay samples using the new method and the standard methanol extraction method was carried out. The newly developed method and the method currently in use were found to recover similar amounts of TCE. The major advantage of the MAE technique is the very short time needed to obtain complete analyte recovery (6–10?min), which makes it possible to analyse a large number of samples without the need for sample preservation or prolonged storage. Thus, the new method is much more efficient than the existing methods. The technique has a good potential for field application.     

Adsorption behavior of organic halides on zeolites

The adsorption behavior and the differential heat of adsorption of chloroform were measured on various types of zeolite (faujasite, ZSM-5 and mordenite) with different Si/Al ratios. The results reveal that saturated adsorption is almost proportional to the micropore volume and is independent of the micropore structure or the Si/Al ratio. However, initial heat of adsorption was the highest (90 kJ mol⁻¹) on the mordenite with low Si/Al ratio, while low on the faujasite with high Si/Al ratio or ZSM-5 (50 kJ mol⁻¹). Change in initial heat of adsorption with Si/Al ratio is small for faujasite or mordenite and large for ZSM-5. For the comparison, trichloroethylene adsorption behavior of zeolite was also investigated. Saturated adsorption of trichloroethylene was almost constant for all types of zeolite, while the faujasite with high Si/Al ratio exhibited an adsorption isotherm of type V in BDDT (Brunauer, Deming, Deming and Teller) classification. The tendencies of heat of immersion are similar to the results of the initial heat of adsorption.