An in situ infrared study of magnesium hydroxide dehydroxylation under electric fields

A specially designed IR electrolysis cell is described, which allows samples to be simultaneously heated and electrolysed during the recording of their IR spectra. By means of this cell, changes in the intensity of the hydroxyl stretching band at 3670 cm^?1 were recorded as a function of temperature both in the presence and absence of an applied electric field. The intensity of the ?OH band decreases with temperature in two distinct stages, both of which are influenced by the electric field. The effect of the electric field on the regain of spectral intensity of the hydroxyl band on re-cooling the sample to room temperature was also studied, and the results discussed in terms of the delocalization of the protons from their respective molecules, possibly by a field-dependent tunnelling mechanism. The effect of the field on the shape and frequency of the ?OH stretching band is also discussed.     

Development of a simultaneous extraction and cleanup method for pyrethroid pesticides from indoor house dust samples

An efficient and reliable analytical method was developed for the sensitive and selective quantification of pyrethroid pesticides (PYRs) in house dust samples. The method is based on selective pressurized liquid extraction (SPLE) of the dust-bound PYRs into dichloromethane (DCM) with analysis by gas chromatography/mass spectrometry. Various adsorbents and combinations of extraction solvents and temperatures were evaluated to achieve a high-throughput sample preparation that eliminates the post-extraction cleanup step. The final method used sulfuric acid-impregnated silica (acid silica) and neutral silica together in the extraction cell with the dust sample to provide both extraction and cleanup simultaneously. The optimal ratio of dust/acid silica/silica was 1:0.8:8. The extraction was performed at 2000 psi, at 100 °C with DCM for 5 min in three cycles. Method precision and accuracy were evaluated by the analysis of triplicate aliquots of the dust samples and the samples fortified with the target PYRs. The accuracy measured as the recoveries of the PYRs in the fortified samples ranged from 85% to 120%. The precision measured as the relative standard deviation of replicate samples was within ±25%. The SPLE method was applied to 20 house dust samples collected from households that participated in two field studies regarding exposures to pesticides and other pollutants. Similar concentrations of target PYRs were obtained for the SPLE and a stepwise extraction/cleanup procedure. The SPLE procedure reduces organic solvent consumption and increases the sample throughput when compared with a traditional stepwise extraction and cleanup procedure. This study demonstrates that the SPLE procedure can be applied to complex dust matrices for analysis of PYRs for large scale exposure or environmental monitoring studies.     

Infrared spectroscopic studies of hydrogen-bonded complexes in cryogenic sulutions

We have measured the ν_s(OH) band parameters of the IR absorption spectra for a wide variety of hydrogen-bonded (HB) complexes of CH₃OH(D), CF₃CH₂OH, and (CF₃)₃COH(D) with some simplest representatives of various classes of bases in Xe and Kr in the temperature range 120–270 K. The ν_s(OH) absorption bands of the HB complexes in solution in atomic solvents have been demonstrated to be narrower by a factor of 2 to 4 than in molecular solvents at the same temperature. The fact that the ν_s(OH) bandwidths in Xe and in the gas phase at similar temperatures are practically the same indicates that these bandwidths are in both cases governed mainly by the contribution of “hot transitions” from a sequence of excited levels of the ν_β low-frequency bending mode of the hydrogen bond. The other characteristic features revealed for the complexes under study in liquid Xe and Kr at ν_s(OH) frequency shifts up to 500 cm⁻¹ include: (1) slight temperature dependence of the ν_s(OH) bandwidth (0.1–0.3 cm⁻¹/K), (2) almost “normal” isotope frequency ratio ν_s(OH)/ν_s(OD) (1.34–1.36) and (3) low ν_s(OH) temperature shift values (0.1–0.4 cm⁻¹/K).     

Polarised vibrational spectra of KH2PO3 single crystal

Polarised IR and Raman spectra for KH₂PO₃ single crystal samples were measured at room temperature. Additionally, the IR spectra for the Xb(Z) sample were also measured at low temperatures (300–14 K). The spectra are discussed on the basis of oriented gas model and group theory. The stretching νOH vibrations of the hydrogen bonds with the OO distances of 2.547 and 2.529 Å give characteristic broad ABC-type bands in the IR (polarised parallel to the X and to the b(Z) directions) and Raman (xx, xz and yx) spectra. The Davydov-type (correlation field or factor group) splitting is not observed for the νOH modes. The presence of two independent hydrogen bonds in the crystal is manifested by splitting of the C band into two (C′, C″) components and by the different frequencies of the out-of-plane bending γOH vibrations. The in-plane bending modes δOH are strongly mixed/coupled with the stretching vibrations of the PO₃ groups.

The C bands (C′ and C″) change into quite sharp bands on lowering of the temperature. Various simplified models for internal vibrations of the phosphite anions are applied for finding a correlation between the crystal structure and polarised vibrational spectra. The stretching vibrations of the νPH groups manifest their unequivalence in two symmetry-independent hydrogenphosphite anions.     

在(TPA)2O-Na2O-SiO2-H2O体系中MFI型硅沸石的结晶行为(Ⅱ)──硅沸石微细晶粒的低温合成及其结构和性质表征

以白炭黑和硅溶胶为桂源, 在(TPA)₂O-Na₂O-SiO₂－H₂O体系60℃下合成了高结晶度纯相硅佛石.由SEM测得其晶粒尺寸为0.2μm和0.45μm, 用XRD线宽法测得的为0.02μm.与180℃时合成的硅沸石样品相比, 低温合成的细晶粒硅沸石已具备纳米级材料的若干特性.其正乙烷吸附量反常增大;XRD、FTIR、²⁹SiMASNMR和TG／DTG／DTA的研究证明, 其结构破坏温度和单斜／正交对称性相转变温度明显下降, 桂羟基缺陷明显增加.     

Vibrational spectra of a ferrocenyl phosphine derivative chemisorbed on 3-aminopropylsilyl modified silica gel

Samples of silica gel dried at different temperatures, silica gel modified with 3-aminopropylsilyl (APS) and silica gel modified with APS and further with a ferrocenyl phosphine derivative were investigated by DRIFT, transmission FTIR and MicroRaman spectroscopy. The reaction between 3-aminopropyltrimethoxysilane (APTMS) and silica gel was mainly identified by the diminishing or vanishing intensity of the stretching band of the free OH groups in the silica gel. Further chemical reaction of the APS groups with a ferrocenyl phosphine derivative (suitable as ligand in homogeneous catalysis) was identified in the IR spectra by the appearance of the CN stretching band of the formed Schiff base, and diminishing intensity of the δ(NH₂) modes. According to the IR spectra the reaction of the ferrocenyl phosphine derivative with the APS-modified silica gel is almost quantitative. From the recorded IR and Raman spectra, conclusions concerning the substitution of APTMS methoxy groups during the chemisorption on silica gel were derived. Through deconvolution of the complex Raman band in the siloxy stretching region of the APS-modified silica gel, the newly formed siloxy bond was identified.     

Dielectric Properties of Hyperbranched Polyesteramide with Long Alkyl Chain End Groups

Summary: Hyperbranched polyesteramides were prepared using phethalic anhydride (Ph An) or maleic anhydride (M An) as an A₂ monomer and diethanol amine (DEA) as B′B₂ monomer. Bulk condensation technique was used to synthesize polymers with both OH and modified polymers with long alkyl chain end groups. The prepared polymers were characterized using ¹H-NMR, FTIR and TGA. Solution viscosity for hyperbranched polyester amide with hydroxyl end groups was measured as well. Dielectric and electric properties of the modified samples were investigated over a range of frequency and temperatures. No relaxation peak is noticed in the dielectric spectrum ε(ν) at various temperatures. The illustration of the imaginary part of the electric modulus M″ versus frequency shows a peak which is shifted towards higher frequency in increasing temperature.     

Vibrational analysis of H2 and D2 adsorption on Pt/SiO2

Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)3SiOSi(OH)3. The spectroscopy experiments showed reversible formation of isolated OH and OD groups on the silica surface when the samples were exposed to H2 and D2, respectively. In addition to the absorption peak corresponding to isolated OH and OD groups, an intense broad band was observed around 3270 cm(-1) (2500 cm(-1)) during H2 (D2) exposure. Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. The surface coverage of new OH groups was found to correlate to the platinum loading in the samples, indicating that the new silanol groups were formed in the vicinity of the Pt particles. In the investigated temperature interval, the formation rate of OH groups was not found to be temperature dependent.     

Size resolved infrared spectroscopy of Na(CH3OH)n (n = 4-7) clusters in the OH stretching region: unravelling the interaction of methanol clusters with a sodium atom and the emergence of the solvated electron

Size resolved IR action spectra of neutral sodium doped methanol clusters have been measured using IR excitation modulated photoionisation mass spectroscopy. The Na(CH(3)OH)(n) clusters were generated in a supersonic He seeded expansion of methanol by subsequent Na doping in a pick-up cell. A combined analysis of IR action spectra, IP evolutions and harmonic predictions of IR spectra (using density functional theory) of the most stable structures revealed that for n = 4, 5 structures with an exterior Na atom showing high ionisation potentials (IPs) of ~4 eV dominate, while for n = 6, 7 clusters with lower IPs (~3.2 eV) featuring fully solvated Na atoms and solvated electrons emerge and dominate the IR action spectra. For n = 4 simulations of photoionisation spectra using an ab initio MD approach confirm the dominance of exterior structures and explain the previously reported appearance IP of 3.48 eV by small fractions of clusters with partly solvated Na atoms. Only for this cluster size a shift in the isomer composition with cluster temperature has been observed, which may be related to kinetic stabilisation of less Na solvated clusters at low temperatures. Features of slow fragmentation dynamics of cationic Na(+)(CH(3)OH)(6) clusters have been observed for the photoionisation near the adiabatic limit. This finding points to the relevance of previously proposed non-vertical photoionisation dynamics of this system.     

Low-temperature study of ultradisperse polytetrafluoroethylene

The temperature behavior of the IR and EPR spectra of the industrial polytetrafluoroethylene F-4 sample and ultradisperse polytetrafluoroethylene (UPTFE) sample obtained by the thermogas dynamic method has been studied. It is shown that the spiral-chain conformation is preserved for both structures and that ordering tends to increase at lower temperatures. The IR spectral parameters of UPTFE were found to change irregularly at 273 K and 233 K due to a rearrangement of the crystalline component of the polymer. The observed temperature changes in the EPR spectra of the middle radicals in the samples are caused by gradual freeze-out of the molecular motions in UPTFE to a temperature ～25° lower than in F-4, due to differences in the molecular and supramolecular structures of the samples.     

Iron-substituted Beta molecular sieve: Synthesis and characterization

A synthesis of crystalline ferrisilicate having zeolite BEA topology (Fe-Beta) and containing significant quantities of iron in the framework (22 Fe atoms per unit cell based on 192 T-atoms per unit cell) has been reported. The synthesis of Fe-Beta was carried out using tetraethylammonium hydroxide (TEAOH), 25% methanolic instead of an aqueous solution, as a source of organic template. X-Ray powder diffraction (XRD) and scanning electron micrography (SEM) were used to check the structural identity and phase purity of the Fe-Beta samples. A thermogravimetric analysis (TGA) study showed that the amount of TEAOH ions interacting with Fe-Beta framework increases with increase in the iron content of the sample. The Fe ions in Fe-Beta were in the trivalent oxidation state which was confirmed by an X-ray photoelectron spectroscopy (XPS) study. A comparison of Si/Fe ratios determined by chemical analysis and XPS method allowed us to conclude that Fe³⁺ species are distributed homogeneously from the bulk to the surface of Fe-Beta crystallites. However, the O_1s XP spectra indicated the presence of small amounts of extraframework iron oxidic impurities in as-synthesized as well as calcined samples. The infrared (IR) spectra showed three types of hydroxyl groups in Fe-Beta located at 3740, 3670 and a very broad band at ∼ 3540 cm ⁻¹. The band at 3680 cm⁻¹ was found to be affected by pyridine adsorption and therefore was assigned to structural bridging hydroxyl groups (SiOHFe) formed by substitution of iron in the zeolite framework. The shift in the IR OH stretching frequency towards higher wave number and the desorption of NH₃ at lower temperature for Fe-Beta samples as compared to Al-Beta zeolite allowed us to conclude that the strength of Brönsted acid sites in Fe-Beta materials is lower than those Brönsted acids sites in Al-Beta zeolites.     

Nitrogen as a Probe Molecule for the IR Studies of the Heterogeneity of OH Groups in Zeolites

One of the methods of IR studies of the heterogeneity of Si–OH–Al groups in zeolites is the investigation of the frequency shift of the band of free OH bands restored upon the adsorption of ammonia and subsequent desorption at increasing temperatures. We extended this method by following the shift of the band of the OH group interacting by hydrogen bonding with nitrogen. The advantage of nitrogen, compared with CO, which has been commonly used as a probe molecule in studies on hydrogen bonding, is that for nitrogen the frequency shift is smaller than for CO and therefore there is no overlapping of shifted OH band with the bands of ammonium ions. For zeolites NaHY, HMFI, and HBEA, the frequency shift of IR bands of both free and hydrogen-bonded Si–OH–Al with the increase of ammonia desorption temperature evidences the heterogeneity of these hydroxyls. On the other hand, in zeolite HFAU of Si/Al = 31, Si–OH–Al were found to be homogeneous. Heterogeneity of OH groups may be explained both by the presence of Si–OH–Al of various number of Al near the bridge and of Si–OH–Al of various geometry.     

Quantitative LIBS analysis of vanadium in samples of hexagonal mesoporous silica catalysts

The method for the analysis of vanadium in hexagonal mesoporous silica (V-HMS) catalysts using Laser Induced Breakdown Spectrometry (LIBS) was suggested. Commercially available LIBS spectrometer was calibrated with the aid of authentic V-HMS samples previously analyzed by ICP OES after microwave digestion. Deposition of the sample on the surface of adhesive tape was adopted as a sample preparation method. Strong matrix effect connected with the catalyst preparation technique (1st vanadium added in the process of HMS synthesis, 2nd already synthesised silica matrix was impregnated by vanadium) was observed. The concentration range of V in the set of nine calibration standards was 1.3-4.5% (w/w). Limit of detection was 0.13% (w/w) and it was calculated as a triple standard deviation from five replicated determinations of vanadium in the real sample with a very low vanadium concentration. Comparable results of LIBS and ED XRF were obtained if the same set of standards was used for calibration of both methods and vanadium was measured in the same type of real samples. LIBS calibration constructed using V-HMS-impregnated samples failed for measuring of V-HMS-synthesized samples. LIBS measurements seem to be strongly influenced with different chemical forms of vanadium in impregnated and synthesised samples. The combination of LIBS and ED XRF is able to provide new information about measured samples (in our case for example about procedure of catalyst preparation).     

大气压射频等离子体化学气相沉积TiO2体系的发射光谱诊断

开展了大气压射频(RF)等离子体化学气相沉积(PCVD)TiO₂放电体系的发射光谱诊断研究, 分别考察了氧气分压、钛酸四异丙酯(TTIP)分压和输入功率对氧原子谱线相对强度、氩原子激发温度、OH振动温度以及转动温度的影响. 结果表明: 随着氧气分压的增加, 氧原子谱线相对强度先迅速增加至峰值后缓慢下降, OH振动温度缓慢增加, 而氩原子激发温度和OH转动温度基本不变. 随着TTIP 分压的增加, 氧原子谱线相对强度下降, 氩原子激发温度没有明显变化, 而OH振动温度和转动温度增加. 随着输入功率的增加, 氧原子谱线相对强度下降, 氩原子激发温度、OH振动温度和转动温度升高.     

硅胶自环己烷中吸附环己酮和苯甲酸

用经不同温度处理的亲水硅胶(表面总羟基浓度不同)和甲基化硅胶(只含有缔合羟基或不同表面浓度的自由羟基的硅胶)为吸附剂, 测定了自环己烷中吸附环己酮和苯甲酸的等温线, 以及几种硅胶样品的红外光谱图, 探讨了表面自由羟基和缔合羟基在溶液吸附中的作用.     

H(2)O Outgassing Properties of Fumed and Precipitated Silica Particles by Temperature-Programmed Desorption

Temperature-programmed desorption was performed at temperatures up to 850 K on as-received fumed and precipitated silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 38–61 kJ/mol. However, the activation energies of desorption for chemisorbed water varied from 80 to >247 kJ/mol for fumed silica, Cab-O-Sil-M-7D, and 96 to 155 kJ/mol for precipitated silica, Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>126 kJ/mol) will not escape silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (80–109 kJ/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies <126 kJ/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1–0.4 wt% of water in silica-reinforced polysiloxane formulations containing 21% Cab-O-Sil-M-7D and 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that the adsorbed H₂O and the Si–OH bonds on the silica surfaces are the major contributors to water outgassing from these types of silica-filled polymers.     

Magnetic properties of composite materials based on plant- or mineral-derived amorphous silica

Fe _x (O, OH) _y –SiO₂ composite samples are prepared. The composite matrix is amorphous silica prepared by controlled precipitation from silicate solutions or silica derived from rice husks. The iron is shown to exist in the form of acagenite β-FeO(OH) or hematite α-Fe₂O₃. The magnetic properties of the composites are studied at temperatures in the range 2–300 K and fields in the range ±5 T. The composite samples exhibit superparamagnetic properties.     

Comparison of the long time stability of some SiCxOy: H films and related compounds with respect to postdeposition incorporation of OH groups

Summary Thin films with composition SiC_xO_y: H and SiO_x:H, produced under different industrial conditions (high rates) have been measured by IR spectroscopy in order to examine the incorporation of OH groups of water. These measurements have been repeated for a period of three weeks to investigate the hygroscopic behaviour. The sample produced with PVD is hydrogen free and only a small degree of OH incorporation takes place. The other samples produced by CVD methods show various amounts of hydrogen concentration. In some cases the composition changes drastically which has also been confirmed by XPS measurements.     

稀土Ce掺杂对ZnO结构和光催化性能的影响

采用共沉淀-焙烧法合成了一系列不同含量的稀土Ce掺杂的ZnO光催化剂. 利用傅里叶变换红外(FT-IR)光谱、粉末X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)光谱、光致发光(PL)谱等技术对所制备的光催化剂进行了系列表征. 以酸性橙II脱色降解为模型反应, 考察了掺杂不同含量的铈及不同焙烧温度对ZnO的物理结构和光催化脱色性能的影响. 结果表明: 掺入质量分数(w)为2%的铈可以明显改善氧化锌表面状态, 有利于产生更多的表面羟基; 同时可以抑制光生电子与光生空穴(e^-/h⁺)的复合, 显著提高光催化脱色活性和光催化稳定性; 焙烧温度对光催化剂的晶体结构、表面性能和光催化活性产生较大影响, 500 °C的焙烧处理使样品的结晶度较高, 同时催化剂颗粒粒径较细, 表面具有丰富的羟基. 但过高的焙烧温度(600-800 °C)将导致催化剂的物理结构发生恶化, 降低光催化性能.     

稀土Ce掺杂对ZnO结构和光催化性能的影响

采用共沉淀-焙烧法合成了一系列不同含量的稀土Ce掺杂的ZnO光催化剂. 利用傅里叶变换红外(FT-IR)光谱、粉末X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见(UV-Vis)光谱、光致发光(PL)谱等技术对所制备的光催化剂进行了系列表征. 以酸性橙II脱色降解为模型反应, 考察了掺杂不同含量的铈及不同焙烧温度对ZnO的物理结构和光催化脱色性能的影响. 结果表明: 掺入质量分数(w)为2%的铈可以明显改善氧化锌表面状态, 有利于产生更多的表面羟基; 同时可以抑制光生电子与光生空穴(e^-/h⁺)的复合, 显著提高光催化脱色活性和光催化稳定性; 焙烧温度对光催化剂的晶体结构、表面性能和光催化活性产生较大影响, 500 °C的焙烧处理使样品的结晶度较高, 同时催化剂颗粒粒径较细, 表面具有丰富的羟基. 但过高的焙烧温度(600-800 °C)将导致催化剂的物理结构发生恶化, 降低光催化性能.