SO_2在TiO_2颗粒物表面的非均相反应

使用漫反射红外傅里叶变换光谱(DRIFTS)原位反应器研究了SO2在TiO2颗粒物表面的非均相反应.研究了氧气浓度、相对湿度(RH)及紫外光光照对反应的影响.结果表明,SO2在TiO2颗粒物上可转化为亚硫酸盐或被氧化为硫酸盐.水汽或者紫外光照可促进SO2在TiO2颗粒物表面的非均相氧化反应,在两者都存在的情况下,对促进硫酸盐的生成有协同效应.在干态无光照条件下和一定湿度(RH=40%)紫外光照条件下,以硫酸盐的生成来计算,SO2在TiO2颗粒物表面的反应级数分别为二级和一级;反应摄取系数γBET分别为1.94×10-6和1.35×10-5.TiO2颗粒物表面的羟基参与了反应,在紫外光照下表面生成的活性氧物种在反应中起重要作用.     

Heterogeneous reaction of formaldehyde on the surface of TiO2 particles

The heterogeneous reaction of formaldehyde (HCHO) on the surface of titanium dioxide (TiO₂) was investigated in situ using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with ion chromatography (IC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Formate, dioxymethylene, methoxy, and polyoxymethylene were observed in the infrared spectra of TiO₂ particles during the reaction. On the surface of TiO₂, the adsorbed HCHO was first oxidized to dioxymethylene and further oxidized to formate. The effects of temperature and ultraviolet radiation (UV) on the reaction products and reactive uptake coefficients were studied, and the results indicate that the reaction rate can be accelerated at increasing temperatures as well as under UV. The heterogeneous reaction mechanisms of HCHO on the surface of TiO₂ in the dark and under UV irradiation are proposed. Kinetic measurements show that formate formation on TiO₂ is second order in HCHO concentration and the initial reactive uptake coefficients at room temperature calculated with the Brunauer-Emmett- Teller specific surface area are (0.5–5) × 10^?8 ([HCHO]: 1 × 10¹³?2 × 10¹⁴ molecules/cm³). A linear function relationship exists between the uptake coefficient and the concentration. The apparent activation energy of the reaction was also determined.     

Isoprene Heterogeneous Uptake and Reactivity on TiO2: A Kinetic and Product Study

The heterogeneous interaction of isoprene with TiO₂ surfaces was studied under dark and UV light irradiation conditions. The experiments were conducted at room temperature, using zero air as bath gas, in a flow reactor coupled with a SIFT‐MS (selected‐ion flow‐tube mass spectrometer) and a FTIR spectrometer for the gas‐phase monitoring of reactants and products. The steady‐state uptake coefficient and the yields of the products formed were measured as a function of TiO₂ mass (9–120 mg), light intensity (37–112 W m⁻²), isoprene concentration (36–12000 ppb), and relative humidity (0.01–90% of RH). Under dark and dry conditions, isoprene was efficiently and reversibly adsorbed on TiO₂. In contrast, under humid conditions, isoprene uptake was diminished, pointing to competitive adsorption with water molecules. In the presence of UV light irradiation, isoprene reacted on the surface of TiO₂. The reactive steady‐state uptake coefficient, γ_ss, was independent of RH under most ambient relative humidity conditions (>50%). However, γ_ss was strongly dependent on isoprene initial concentration according to the empirical expression: γ_ss = (2.0 × 10⁻⁴) × [isoprene] with n = 0.35 and 0.28 for 37 and 112 W m⁻² irradiation conditions, respectively. In addition to the kinetics, a detailed product study was performed. The gas‐phase oxidation products were mostly CO₂ (ca. 90% of the carbon mass balance) and a large variety of carbonyl compounds (methyl vinyl ketone, acetone, methacrolein, formaldehyde, acetaldehyde, propanal, traces of butanal, and pentanal), the distribution of which was investigated as a function of mineral oxide mass, isoprene concentration, and RH. Furthermore, the surface‐adsorbed products were determined employing off‐line HPLC chromatography; their concentrations were inversely dependent on RH and decreased to background levels at RH greater than 30%. Finally, the reaction mechanism and possible implications of isoprene reaction on TiO₂ are briefly discussed.     

SO_2在ZnO颗粒物表面的非均相反应

使用原位漫反射红外傅里叶变换光谱(DRIFTS)研究了SO2在ZnO颗粒物表面的非均相反应,考察了相对湿度(RH)及紫外光光照对反应的影响.结果表明:无紫外光光照条件下,SO2在ZnO颗粒物表面反应的主要产物为亚硫酸盐,RH与生成的亚硫酸盐量呈负相关关系;有紫外光光照条件下,SO2在ZnO颗粒物表面反应的主要产物为亚硫酸盐和硫酸盐,随着相对湿度和紫外光照强度的增加,亚硫酸盐向硫酸盐转化.光照和水汽对SO2在ZnO颗粒物上的氧化反应起到协同促进作用.以亚硫酸盐生成量计算,干态无光条件下反应对SO2的级数为1.6,接近二级反应;在RH为40%且紫外光光照条件下,反应对SO2的级数为0.91,接近一级反应;使用BET比表面积作为反应有效面积,反应初始摄取系数在干态无光照条件和RH=40%且紫外光照条件下分别为4.87×10-6和2.29×10-5.     

Impact of greenhouse gas CO2 on the heterogeneous reaction of SO2 on alpha-Al2O3

The heterogeneous reaction of SO₂ on mineral dust surfaces is generally considered as an important chemical pathway for secondary sulfate formation in the troposphere. To this day, there are no reported studies that assess the impact of atmospheric CO₂ in sulfate production on mineral dust surfaces. In this work, we investigate the impact of CO₂ on SO₂ uptake on dust proxy aluminum oxide particles using a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). CO₂ is demonstrated to suppress the heterogeneous oxidation of SO₂ on alpha-Al₂O₃. Compared to that measured in the CO₂-free case, the uptake coefficient is decreased by nearly 57% when Al₂O₃ particles are exposed to the gas flow with atmospheric CO₂ at a relative humidity (RH) of 25%. It is also found that there is a balance between the yield of active moiety −OH provided by Al(OH)₃(CO)(OH)₂ clusters and the loss of basic hydroxyl group on aluminum oxide surfaces blocked by CO₂-derived (bi)carbonate species. This work, for the first time, reveals a negative effect of atmospheric CO₂ on the sulfate formation, which potentially decreases solar-radiation scattering and further exacerbates global warming.     

Heterogeneous reaction of NO2 with sea salt particles

To understand how NO₂ reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones, the heterogeneous reaction of NO₂ on the surface of wet sea salt was investigated with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). Kinetic measurements indicated that nitrate formation on sea salt was second order in NO₂ concentration and reactive uptake coefficients were (5.51 ± 0.19) × 10^?7 and 1.26 ± 10^?6 respectively under 0% and 20% relative humidity (RH) at NO₂ molecular concentration of 1.96 × 10¹⁵ mol/cm³. The results showed that liquid water was formed at the site of MgCl₂·6H₂O, CaCl₂·2H₂O on the surface of sea salt and made the reaction more sustainable by releasing hydrated water and absorbing water from air even under a low RH (? 30%). Therefore, pure NaCl particles should not be used to represent sea salt in studies of the heterogeneous reaction with NO₂.     

Heterogeneous reactions of gaseous methanesulfonic acid with NaCl and sea salt particles

Methanesulfonic acid (MSA) has been identified as one of the most important intermediate products of DMS reactions in the atmosphere. Although considerable amounts of MSA have been found in the marine boundary layer, little is known about the interaction of gaseous MSA with sea salt particles. To understand the fate of MSA in the atmosphere and its potential importance in atmospheric chemistry, the heterogeneous reactions of gaseous MSA with micron-scale NaCl and sea salt particles were studied using diffuse reflectance infrared Fourier transform spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The CH₃SO₃Na and CH₃SO₃ ⁻ were the major products of the condensed phase of the reaction of gaseous MSA with NaCl and with sea salt particles. The steady-state uptake coefficient was determined to be (5.94±2.32)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with NaCl particles and (2.23±1.25)×10⁻⁷ (1 σ) for the reaction of gaseous MSA with sea salt particles. The heterogeneous reaction of MSA with NaCl particles was found to be first-order for MSA. The reaction mechanisms were discussed. Supported by the National Natural Science Foundation of China (Grant No. 40490265) and the National Basic Research Priorities Program (Grant No. 2002CB410802)     

Photocatalytic reduction of dichromate by titanium dioxide supported on hollow glass microbeads

The photocatalytic reduction of dichromate using TiO2/beads as a photocatalyst was studied. The results showed that 3.8 × 10-4 mol/dm3 of dichromate can be completely reduced into Cr3 after illumination for 35 min with a 375 W medium pressure mercury lamp. The effects of factors such as the amount of TiO2/beads , initial concentration of dichromate, initial pH, nitrogen and oxygen atmosphere, and concentration of Fe3 on the photocatalytic reduction of dichromate were investigated. A possible mechamism of the photocatalytic reaction was proposed. After illumination for 200 h, no significant loss of photocatalytic activity of TiO2/beads was observed.     

The Influence of Sulfate‐Doping on the Nature of V Sites in VOx/TiO2 Catalysts

EPR, UV/Vis and FTIR spectroscopy as well as thermal analysis (TA/MS) were applied to study the influence of sulfate species present in the anatase support on the specific nature of VO_x species in supported VO_x/TiO₂ catalysts. Those sulfate species modify the local structure of the supported vanadyl species and lead to the formation of two types of VO²⁺ sites instead of only one type being formed on sulfate‐free anatase. EPR and FTIR spectroscopic measurements revealed that a part of the VO²⁺ species are directly bound to the surface sulfate species. By TA/MS it was found that SO₂ is released at lower temperature from VO_x/TiO₂ in comparison to the vanadium‐free support. The direct bonding between sulfate and VO_x species stabilizes the latter on the surface of VO_x/TiO₂ resulting in three effects: 1) a higher V site dispersion in comparison to sulfate‐free TiO₂, 2) a better resistance of surface vanadyls against diffusion into the bulk of the support and 3) a much faster reoxidation of reduced V sites than observed on sulfate‐free TiO₂.     

Heterogeneous reaction of NO2 on the surface of NaCl particles

The heterogeneous reaction of NO₂ on NaCl particles has been investigated with the new sample preparation and the mode of gas-solid free diffusion. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) is used to characterize the adsorbed products in situ, combined with Ion Chromatographic (IC), X-ray Photoelectron Spectroscopy (XPS) and Scan Electron Microscopy (SEM). Our results indicate that the reaction is not limited to the surface of the NaCl particles, but penetrated into the upper layers. Surface reactive sites determine the reaction. Kinetic measurements show that nitrate formation on sodium chloride is second order in NO₂ concentration and reactive uptake coefficient is (1.54 ± 0.70) × 10⁻⁵.     

Cyclic Voltammetric and Ac Impedance Behavior of TiO2 Electrodes under UV Illumination

Electrochemical behavior of an ITO/TiO₂ electrode both under ultraviolet (UV) illumination and in the dark was investigated using the methods of cyclic voltammetry and ac impedance spectroscopy. A new oxidative peak is observed at 0.15 V when the TiO₂ electrode was illuminated by UV light for a certain time. The peak current and the anodic photocurrent increased with the increase of UV light intensity. It is assumed that the new peak belonging to the oxidation of Ti³⁺, which was formed on the electrode surface during the UV illumination. It is also found that the apparent resistance was decreased but the capacitance was increased when the TiO₂ electrode was illuminated by UV light according to the measurement results of ac impedance. Based on the results in this paper, it was directly proved that Ti³⁺ was actually formed when the electrode was irradiated by UV light.     

Photocatalytic Oxidation of Aniline in the Gas Phase Using Porous TiO2 Thin Films

The gas-phase photocatalytic oxidation of aniline on a new kind of porous nano-TiO₂ composite films is investigated. The composite film was prepared on glass fiber with the water glass as binders and dilute H₂SO₄ solution as solidifying reagent. The surface characters were observed by scanning electron microscope. The photocatalytic degradation of aniline on the composite films was carried out in a TiO₂/UV system. Some important factors affecting the photodegradation, such as the concentration of TiO₂, the initial concentration of aniline, and the existing water vapor, are also studied. The product of photocatalytic oxidation was detected by Fourier transform-Infrared. The partial intermediate products were absorbed on TiO₂ surface, which resulted in catalyst deactivation. But when it was irradiated under UV illumination or solar irradiation for some time, the catalyst could be reused without loss of catalytic activity. Translated from the Journal of Wuhan University (Natural Science Edition), 2005, 51(2) (in Chinese)     

Synthesis of anatase TiO2 in a vinyl-containing ionic liquid and its enhanced photocatalytic activity

TiO₂ microspheres were synthesized by the sol–gel method using the ionic liquid (IL) 1-vinyl-3-propylimidazolium iodide (VPIM⁺I^?) as a reaction medium, then calcined at 500 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, and ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy. The phase of TiO₂ microspheres is anatase, and VPIM⁺I^? is able to favor the growth of anatase phase and prevents the collapse of small pores. The photocatalytic activity of TiO₂-IL was tested by degradation of 2-nitrophenol under UV light illumination. The photocatalytic activity of TiO₂-IL was higher than that of samples prepared in the reaction medium without VPIM⁺I^?.     

Using microwave along with TiO<Subscript>2</Subscript> for degradation of 4-chloro-2-nitrophenol in aqueous environment

In this project, microwave (MW) irradiation, photolysis, and photo catalyst were used for degradation of 4-chloro-2-nitro phenol (4-C2NP) in aqueous environment. The influence of main operating parameters such as initial pH, initial concentration of 4C2NP, power dissipation and the dosage of TiO2 on the degradation efficiency has been investigated. The optimum conditions was obtained such as initial concentration of 4C2NP at 30 mg L^?1, initial pH at 6, power dissipation at 16 W for UV irradiation, and the amount of TiO₂ at 0.2 g L^?1. The removal of 4C2NP and chemical oxygen demand (COD) after 100 min of reaction in the combined method (MW/UV/TiO₂) was obtained as 80.5% and 47.3%, respectively. Almost all processes are followed from the pseudo first order kinetics and the degradation rate of 4C2NP obeyed the following order: UV/TiO₂/MW > UV/TiO₂ > MW/UV > UV>MW.     

Ag-single atoms modified S1.66-N1.91/TiO2-x for photocatalytic activation of peroxymonosulfate for bisphenol A degradation

In this study,Ag_0.23/(S_1.66-N_1.91/TiO_2-x) single-atom photocatalyst was synthesized by in-situ photoreducing of silver on S,N-TiO_2-x nanocomposite and used to degrade bisphenol A（BPA） through heterogeneous activation of potassium peroxymonosulfate（PMS） under visible-light illumination.The structure,physicochemical property,morphology,and electronic property were evalutated by X-ray diffraction（XRD）,Raman spectrum,X-ray photoelectron spectra（...     

Photo Catalytic Degradation of Azo Dyes over Mn2+ Doped TiO2 Catalyst under UV/Solar Light:An Insight to the Route of Electron Transfer in the Mixed Phase of Anatase and Rutile

Mn²⁺ ion was doped into the TiO₂ matrix and its photocatalytic activity was evaluated for the degradation of a mono azo dye methyl orange (MO) and a di‐azo dye brilliant yellow (BY) under UV/solar light. X‐ray diffraction results revealed the phase transformation from anatase to rutile due to the inclusion of Mn²⁺ ion into the TiO₂ matrix. All the doped catalysts showed a red shift in the band gap to the visible region. The degradation reaction of the dyes was found to be dependent on its structure. It was found that mono azo dye degrades faster than di azo dye under UV/solar light. The rate constant under identical conditions calculated for the degradation of MO is 2.4 times (under UV light) and 4.5 times (under solar light) higher compared to BY. Among the photocatalysts studied, Mn²⁺(0.06 at.%)‐TiO₂ showed higher activity under both UV and solar light illumination. The synergestic effect in the bicrystalline framework of anatase and rutile effectively suppresses the charge carrier recombination and enhances the photocatalytic activity. The degradation reaction was followed by UV‐visible spectroscopy and the photoproducts formed were analyzed by GC‐MS techniques.     

Photocatalytic characteristics of TiO2 supported on SiO2

The photocatalytic decomposition of acetaldehyde was carried out on TiO₂/SiO₂. The presence of a support (SiO₂) in TiO₂/SiO₂ helped to promote the efficiency of the photocatalyst. The silica support enhanced the effective surface area of TiO₂ and adsorption of acetaldehyde on TiO₂/SiO₂. TiO₂/SiO₂ synthesized from Ti(SO₄)₂ showed promoting effect on acetaldehyde decomposition. The XPS results revealed that TiO₂/SiO₂ prepared with Ti(SO₄)₂ generated SO ₄ ^2? sites on the TiO₂ surface. The increased acidity could promote the adsorption of acetaldehyde and photocatalytic degradation of acetaldehyde. The sulfate ion seemed to generate the bifunctional sites (acid sites and photoactive sites) and promoted the acetaldehyde decomposition on TiO₂/SiO₂.     

Comparison of CO2 Reduction Performance with NH3 and H2O between Cu/TiO2 and Pd/TiO2

The aim of this study is to clarify the effect of doped metal type on CO₂ reduction characteristics of TiO₂ with NH₃ and H₂O. Cu and Pd have been selected as dopants for TiO₂. In addition, the impact of molar ratio of CO₂ to reductants NH₃ and H₂O has been investigated. A TiO₂ photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO₂ film and Pd/TiO₂ film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO₂ reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO₂ reduction performance with Cu/TiO₂ under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:1:1 while that without UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:0.5:0.5. It is revealed that the CO₂ reduction performance of Pd/TiO₂ is the highest for the molar ratio of CO₂/NH₃/H₂O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO₂ was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO₂ was 3.5 μmol/g. This study has concluded that Cu/TiO₂ is superior to Pd/TiO₂ from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency.     

Double layered, one-pot hydrothermal synthesis of M-TiO2 (M = Fe3+, Ni2+, Cu2+ and Co2+) and their application in photocatalysis

A double layered,one-pot hydrothermal method was adopted in this work to prepare transition metal ions(Fe3+,Ni2+,Cu2+and Co2+)doped TiO2.The morphology and chemical properties of TiO2and the status of metal ions were characterized with XRD,TEM,BET,UV-Vis and XPS analysis.TEM images show that the obtained TiO2was very uniform with an average particle size of 10.4 nm.XPS,TEM and XRD results show that transitional metals were doped onto TiO2in the form of ions.Photocatalytic decomposition of oxalic acid under UV illumination and methylene blue degradation under visible light on these materials were conducted,respectively.The results reveal that Cu2+-TiO2and Co2+-TiO2showed a highest activity under UV and visible light illumination,respectively,and they were both more active than commercial P25 TiO2.With this special design of double layers,the hydrolysis of titanium precursor in the system with water can be easily controlled and metal ions are simply doped.This strategy can be further applied to synthesize metal ion doped TiO2using various metal precursors with controllable amounts,and thus lead to better optimization of highly active photocatalyst.     

The effects of some electrolytes on flocculation with a cationic polyacrylamide

The effects of sodium chloride, sodium sulfate, and alum (aluminum sulfate) on the performance of a cationic polyacrylamide flocculant in a papermaking suspension consisting of bleached (hardwood: softwood, 50∶50) kraft wood-pulp fibres and anatase (TiO₂) were investigated. Sodium chloride and sodium sulfate, 1×10^?5 to 1×10^?2 M, in the presence of polymer, caused negligible changes in the electrophoretic mobility of the TiO₂ and in the first-pass retention of TiO₂ (heteroflocculation of TiO₂ and fibres). Alum at concentrations from 1×10^?5 to 1×10^?4 M at pH 4.0 and 4.5 increased retention with polymer; higher alum concentrations resulted in lower retentions. At pH 4.0 the electrophoretic mobility of the TiO₂ was positive over the entire range of alum concentrations investigated (1×10^?5?3.2×10^?3 M) whereas at pH 4.5 the mobility was negative at 1×10^?5 M alum and charge reversal was observed at about 4×10^?5 M alum. The intrinsic viscosity of the cationic polyacrylamide was decreased by the addition of alum, sodium chloride or sodium sulfate. The effect of alum on the polymer conformation appeared to be that of the non-specific interaction of sulfate ions with a cationic polyelectrolyte. Retention results are discussed in terms of the colloidal stability of TiO₂, the adsorption of polyacrylamide on TiO₂ and the conformation of adsorbed polymer.