纳米催化剂在CO_(2)加氢制甲醇中的研究进展北大核心CSCD

为减缓温室效应,将CO_(2)转换成高附加值的甲醇是减少CO_(2)排放的有效途径,而高效催化剂是CO_(2)加氢制甲醇反应规模化的关键.可调控合成的具有量子尺寸效应的纳米催化剂在该反应上具有独特的优势.因此我们深入探讨了反应机理,综述了纳米材料在CO_(2)加氢制甲醇中的研究进展,最后给出了高效催化剂可能的发展方向.     

FTIR监测北京地区CO2和CH4及其变化分析

近几十年来,温室效应导致地表温度明显上升,其所引起的全球气候变迁问题越来越受到人们的关注.CO2和CH4是大气中主要的两种人为温室气体,对它们进行连续的测量,获取它们长时间变化情况对大气环境科学具有重要的意义.目前国内监测这两种气体的主要手段是气相色谱方法.鉴于傅里叶变换红外光谱技术的优点,使用开放式长光程FTIR系统在北京地区对这两种气体进行了监测.该系统直接测量开放光路中的环境气体的大气吸收光谱,并使用非线性最小二乘方法进行光谱分析,获取待测组分的浓度信息.在实验部分给出了2005年9月4日到2005年9月10日6天中的北京地区CO2及CH4的测量结果,并对两者的变化趋势和相关性进行了分析.     

Excitation and relative differential oscillator strengths for trifluoromethyl sulphur pentafluoride, SF5CF3, in the UV–VUV region by electron energy loss spectroscopy

Electron energy loss spectroscopy (EELS) has been used to study the photo-absorption spectrum of trifluoromethyl sulphur pentafluoride (SF₅CF₃) for the first time. Comparison is made with the EELS spectrum of sulphur hexafluoride (SF₆). The photolysis of the compound is discussed with relevance to estimated lifetimes in the atmosphere. It is estimated that the lifetime of SF₅CF₃ is of the order of 1000 years.     

Spectroscopic requirements for ACCURATE, a microwave and infrared-laser occultation satellite mission

The proposed satellite mission ACCURATE consists of a small constellation of satellites in low Earth orbit, combining microwave occultation for thermodynamic state profiling with infrared-laser occultation for greenhouse gas and line-of-sight wind profiling. The mission aims to detect six greenhouse gas molecules with four additional isotopologues (H₂O, CO₂, CH₄, N₂O, O₃, CO, ¹³CO₂, OC¹⁸O, HDO, and H₂¹⁸O) in the upper troposphere and lower stratosphere in the 4000-5000 cm⁻¹ spectral region. Greenhouse gas profiles will be retrieved to within 1-2% accuracy using a ‘differential’ method, requiring two spectral points for each species - one to sample the spectral line and the other nearby to sample the baseline.An estimation of retrieval errors for the ACCURATE mission reveals that errors in spectroscopic line parameters dominate all other error sources. Poor knowledge of the spectroscopy introduces systematic errors into the retrieved greenhouse gas profiles. Using a simple approach, it was shown that the best line parameters currently available are too large to allow retrievals of greenhouse gases to within the stated ACCURATE mission goals of 1% accuracy for CO₂ and 2% for all other species. Therefore, spectroscopic line parameters for targeted lines need to be improved before the ACCURATE mission can be launched. Requirements have been formulated in this direction, and laboratory experiments outlined that could meet these requirements.     

Determination of Imidacloprid in Tomato Grown in Greenhouse Based on Copper(II) Phthalocyanine Modified Carbon Ceramic Electrode by Differential Pulse Voltammetry

A new sol‐gel derived electrocatalytic carbon ceramic electrode was prepared by incorporating copper(II) phthalocyanine (CuPc) in a carbon ceramic network. This electrode was used as a sensitive electrochemical sensor for determination of the insecticide Imidacloprid (1‐(6‐chloro‐3‐pyridylmethyl)‐N‐nitro‐imidazolidin‐2‐ylideneamine) by differential pulse voltammetry (DPV). The resulting modified electrode exhibits a cathodic peak potential shifted positively and an increasing in cathodic peak current in comparison with unmodified electrode. The redox properties of this modified electrode at various pH values and CuPc percentage were investigated. The catalytic current obtained from differential pulse voltammetry is linearly dependent on Imidacloprid concentration over the two linear ranges of 0.67‐17 μM and 17‐93 μM with correlation coefficient of R² = 0.9999 and R² = 0.990, respectively. The detection limit for Imidacloprid was found to be 0.28 μM according to lower linear range. Possible interferences from several common pesticides were also evaluated. The inherent stability, high sensitivity, low detection limit and low cost for each preparation are advantages of this sensor. Determination of Imidacloprid in commercial formulation and residual Imidacloprid in tomato grown in greenhouse (protected cultivation) was also conducted. The results obtained from commercial formulation were completely consistent with those obtained through the standard high‐performance liquid chromatography (HPLC) method.     

低功耗无线传感器网络节点温室大棚监控系统的设计

本文介绍基于ZigBee技术采用CC2530为核心处理器,利用了TI公司Z-stack协议栈和OSAL操作系统,构成了无线传感器网络的温室大棚监控系统。通过在温室大棚内布置多个监测点和调节设备,完成对各区域的温度、湿度和光照度进行采集。本监控系统具有低功耗、体积小、易于扩展、工作可靠等优点,目前己在淮安某镇大棚蔬菜基地投入使用,运行情况良好,提高了经济效益。     

官能团修饰对MOF-5的气体分子吸附影响

采用紧束缚近似计算方法,研究了金属有机骨架(MOF-5)和不同官能团(―NO2,―NH2,―CH3,―OZn)修饰后的MOF-5不同吸附位点的CO2等温室气体和部分工业废气吸附性能以及对不同气体的选择性吸附能力.结果表明,对于未修饰的MOF-5,位点I和II是主要的吸附位点,最大吸附能可达-0.25eV.官能团修饰提高了MOF-5对CO2的吸附能力,其与官能团活性和局部位型密切相关.其中―NO2修饰使各位点的CO2吸附能力都有一定提高.同时,―NO2修饰后MOF-5对空气环境(O2,N2,H2O,CO2),工业废气环境(CO2,CO,NO,NO2,SO2,SO3)中不同气体有明显的选择性吸附能力.     

基于反射光谱的温室黄瓜叶片磷素含量分析与预测

以温室栽培黄瓜作物为对象,分析了叶片反射光谱与叶片磷素含量之间的相关关系,并建立了预测模型。首先利用便携式光谱辐射仪测量了自然光照条件下温室黄瓜叶片的光谱反射率,并计算了反射率光谱的一次微分光谱。相关分析表明反射率光谱与叶片含P量之间具有一定的相关性,但线性相关不显著。利用微分光谱可以部分消除系统误差、背景噪声等的影响,明显提高了相关系数,但预测模型精度仍然达不到实用程度。在理论分析的基础上,选取978,920,737和458 nm等4个波长作为特征波长,分别利用人工神经网络和支持向量机建立了黄瓜叶片P素含量对应于微分光谱特性的非线性预测模型,结果表明两种算法都获得了较好的预测效果,支持向量机模型的预测能力(R_v=0.754)优于人工神经网络模型(R_v=0.712)。     

The green synthesis of exceptional braided,helical carbon nanotubes and nanospiral platelets made directly from CO2

Helical carbon nanotubes currently cost ~15,000–19,000 USD/kg commercially and are ~10–15 times the price of straight carbon nanotubes of similar dimensions. They have not previously been made from the greenhouse gas CO₂ nor had new variants of the helical morphology been demonstrated. In this study, a novel, inexpensive electrosynthesis of these helical nanocarbon materials from CO₂ is presented. This material may be produced by molten carbon growth conditions that (1) maximize torsional stresses, such as those that may occur during rapid, nucleated carbon reduction, (2) enhance defects that cause formation of heptagonal, rather than the conventional hexagonal building blocks of graphene cylindrical walls, and (3) uniformly control those enhanced defects to repeatedly induce a uniform spiral conformation. These conditions are achieved with at least two of the following experimental conditions: (i) high electrolysis current density, (ii) sp³ defect-inducing agents, such as added oxide, and (iii) controlled concentration of iron added to the electrolyte or cathode. Here, it is shown with SEM, TEM, EDX, XRF, and Raman spectroscopy that a molten controlled electrolyte carbonate synthesis to induce defect formation, and a high rate of electrolysis (0.6 A/cm²) leads to a high yield of helical nanotubes, helical nanofibers, or helical nanoplatelet carbon morphologies.     

Multiresidue method using SPME for the determination of various pesticides with different volatility in confined atmospheres

An analytical method is described for assessing the vapour concentration of 11 pesticides (bioallethrin, chlorpyriphos methyl, folpet, malathion, procymidone, quintozene, chlorothalonil, fonofos, penconazole and trimethacarb) in confined atmospheres (e.g. a greenhouse after pesticide application). This study is a successful extension of a method previously developed by the authors for dichlorvos to much less volatile pesticides. Sampling was performed by using polydimethylsiloxane–solid phase micro-extraction (PDMS–SPME) fibres immersed in a 250-mL sampling flask through which air samples were dynamically pumped from the analysed atmosphere. After a 40-min sampling duration, samples were analysed by GC/MS.Calibration was performed from a vapour-saturated air sample. The linearity of the observed signal versus pesticide concentration in the vapour phase was proved from spiked liquid samples whose headspace concentrations were measured by using the proposed method. This procedure gave calibration curves with regression coefficients (R²) greater than 0.98, and the repeatability of these measurements was found with RSDs of 1.9–7.6%. As a field application test, this analysis procedure was used for the determination of gaseous procymidone concentrations as a function of time in the atmosphere of an experimental 8-m² and 20-m³ greenhouse. The pesticide was sprayed according to real cultivation conditions, and measurements were made for 80 h after application (8 measurements). The observed concentrations found ranged from 200 to 500 µg m^–3, thus indicating the level of contamination of the air breathed by people in such working conditions.Abbreviations GC/MS gas chromatography/mass spectrometry - SIM selective ion monitoring - FC43 perfluorotributylamine - RSD relative standard deviation - LOD limit of detection - LOQ limit of quantification