甲醛光催化氧化的反应机理

采用程序升温脱附（TPD）, 电子自旋共振（ESR）及自旋捕获 电子自旋共振(ST ESR)等物理方法对甲醛光催化氧化过程中,反应物的吸附状态、自由基中间物种及反应机理 进行了研究.结果表明,在光催化氧化空气中微量甲醛的反应条件下,吸附在催化剂表面的空 气中的氧气被光生电子还原为•O－2,微量水被空穴氧化为•OH.二者为甲醛的深度氧化提供了高活性的氧化剂.甲醛是通过中间产物甲酸而氧化为终点 产物二氧化碳的.     

以Co2＋掺杂纳米TiO2为光催化氧化剂的原位光致化学发光分析方法 研究及其应用

研究了Co2＋掺杂TiO2纳米粒子在光信号诱导下产生的超氧阴离子自由基在纳米粒子表面的吸附和解吸特性. 当以该纳米粒子为光催化氧化剂进行原位光致化学发光反应时, 光诱导产生的超氧阴离子自由基通过扩散穿过纳米粒子表面的双电层到达本体溶液, 与溶液中的化学发光试剂进行化学发光反应. 由于超氧阴离子自由基在纳米粒子表面的吸附、解吸和双电层效应, 使得光化学反应和其后的光生氧化剂的化学发光反应具有时间和空间的分辨特性. 将 Co2＋掺杂TiO2纳米粒子光致化学发光反应的特点与鲁米诺化学发光体系结合, 建立了一种原位光致化学发光反应的新方法, 并提出了一种基于纳米技术调控化学发光反应的新思路. 在最佳反应条件下, 该方法对格列本脲响应的线性范围为2.0×10－8～1.0×10－6 g•mL－1, 检出限为6×10－9 g•mL－1.     

C2H3＋NO2反应速率常数的研究

利用激光光解C2H3Br产生C2H3自由基,在气相298 K, 总压2.66×103 Pa的条件下,研究C2H3与NO2的反应,用激光光解-激光诱导荧光（LP-LIF）检测中间产物OH自由基的相对浓度随着反应时间的变化关系,报导了双分子反应C2H3＋NO2的速率常数k(C2H3＋NO2)=(1.8±0.05)×10－11cm3•molec.－1•s－1,同时也得到OH＋NO2反应的速率常数k(OH＋NO2)=(2.1±0.15)×10－12 cm3•molec.－1•s－1.     

肾上腺素电氧化过程的快速扫描循环伏安研究

以快速循环伏安法为主要手段,研究了肾上腺素电化学氧化反应机理.肾上腺素在1 m ol•dm－3 H2SO4中的电化学氧化反应,具有扩散控制的基本特征,并伴随着电活性质粒的 弱吸附现象.在快速电势扫描条件下,肾上腺素电氧化过程遵从EC反应机理.当肾上腺素浓度低于1.00×10－3 mol•dm－3时,吸附现象的特征趋于显现出来;在快速电势扫描速率下,电活性质粒吸附的特征更加明显.结合表面伏安法分析,估算了肾上腺素电氧化过程的传递系数α=0.264.电化学反应速率常数ks=31.81 s－1.     

次亚磷酸根在镍电极上的电氧化机理与动力学

用电化学质谱(EMS)和动力学模型分析等方法研究了次亚磷酸根在镍电极上的电化学氧化机理和动力学.研究表明，次亚磷酸根的电化学氧化是通过从P－H键脱离一个原子H，形成磷中心自由基(PHO2－•)，而磷中心自由基(PHO2－•)进一步进行电化学反应形成最终产物亚磷酸。利用该模型，推导出相关动力学方程并通过与实验数据拟合获得动力学参数.结果表明，该模型能很好地模拟次亚磷酸根在镍电极上的电化学氧化过程.     

TiO2和ZnO表面CO光催化氧化活性研究

在TiO2和ZnO表面CO光催化氧化研究中发现,365 nm紫外光照下TiO2表面无活性,而ZnO表面却有明显的CO光催化氧化活性.研究表明,主要是由于紫外光照下,ZnO光分解而TiO2没有光分解,从而在表面产生不同吸附形态的氧所致.而且,ZnO表面CO光催化氧化反应活性可在27 h内保持稳定,暗示气相光催化反应中,ZnO不会因为光腐蚀而使其催化活性降低.     

MMI作为铜的盐酸酸洗缓蚀剂作用机理的研究

用失重法研究了N-甲基-2-巯基咪唑（MMI）在5％盐酸中对铜的酸洗缓蚀性能.探讨了温度和MMI浓度对缓蚀效果的影响，从中得出了MMI在铜表面的吸附等温式，计算了吸附热及MMI的加入对铜在盐酸中腐蚀反应活化能的影响，进而探讨了MMI对铜缓蚀作用的机理.结果表明， 30 ℃下，在5％盐酸中，当MMI的浓度在3 mmol•L－1和8 mmol•L－1之间时,缓蚀率随MMI浓度的增加而迅速增加，当浓度达到8 mmol•L－1时，缓蚀率趋于定值，而当浓度小于3 mmol•L－1时， MMI的加入会加速铜的腐蚀；吸附在铜表面的MMI分子间的作用力整体表现为引力； MMI在铜表面的吸附是吸热反应； MMI的加入降低了铜的腐蚀反应活化能.     

二氧化钛薄膜上三氯乙烯光催化氧化反应机理

 研究了二氧化钛薄膜上三氯乙烯(TCE)气相光催化氧化的反应机理. 结果表明,TCE气相光催化氧化反应生成的氯气可引发TCE的连锁反应. 当添加氯气的浓度相同时TCE表面光催化反应的初速率约为光化学反应初速率的2倍,说明连锁反应主要发生在催化剂表面. 氯可吸附在催化剂表面,作为电子的接受体抑制空穴与电子复合,提高TiO2光催化剂的活性. 除了TCE与吸附在催化剂表面的·OH的相互作用及反应产物/中间产物二氯乙酰氯的光催化分解可生成氯气以外,光气在与氯气共存时的光分解也有利于氯的生成.     

瞬态吸收光谱研究苯与H2O2水溶液的反应机理

利用瞬态吸收光谱技术研究了不同条件下苯与H2O2水溶液复相体系的激光闪光光解情况,考察了其瞬态物种的生长和衰减等行为.研究表明, •OH自由基和苯反应生成C6H6-OH加合物,其反应速率常数在近中性和酸性条件下分别为(8.0～8.1)×109 L•mol－1•s－1和7.7×109 L•mol－1•s－1, 而在碱性时则为(6.7～6.9)×109 L•mol－1•s－1,在有氧条件下C6H6-OH加合物被氧化为C6H6-OHO2后,进一步分解成对苯醌;C6H6-OH加合物和激发态的苯也可直接与H2O2反应生成对苯醌,三种反应途径同时存在.     

肾上腺素氧化反应的研究——氧化反应动力学和机理以及自由及中间体

用紫外吸收光谱法结合计算机模拟研究了肾上腺素(Adjn)在Cu(Ⅱ)离子催化下, 用H_2O_2氧化产生肾上腺素红(Adom)的反应动力学, 考查了反应的速率随体系中肾上腺素的初始浓度, Cu(Ⅱ)离子浓度和H_2O_2浓度的变化情况。在流动法或添加自由基稳定剂的条件下, 利用顺磁共振法检测丁肾上腺素自氧化, 光氧化和Cu(Ⅱ)离子催化H_2O_2氧化产生的半醌自由基。考查了Cu(Ⅱ)离子催化下自由基的相对浓度随反应条件的变化情况。在反应动力学和顺磁共振实验的基础上所提出的可能的反应机理, 半定量地解释此反应动力学实验结果和顺磁共振实验中的自由基行为。     

Synthesis of uniform anatase TiO2 nanoparticles by the gel-sol method 2. Adsorption of OH- Ions to Ti(OH)4 gel and TiO2 particles

The pH value in the gel-sol system for the preparation of uniform anatase TiO2 nanoparticles, as a decisive factor for controlling the size and shape of the final product, was found to be significantly changed during the formation process of the anatase TiO2 particles from a condensed Ti(OH)4 gel. The dramatic evolution of pH with the progress of the synthetic process has clearly been explained in terms of the adsorption and desorption of a hydroxide ion (OH-) ora proton (H+) on the solids transforming with time. The adsorption and desorption of OH- or H+ were enhanced by the presence of an inert electrolyte such as NaClO4, as explained by its shielding effect on the electrical interactions between the electrically charged precipitates and free OH- and H+ ions. The electrolyte also hampered the phase transformation of Ti(OH)4 precipitate to anatase TiO2. This effect of electrolytes was explained in terms of the inhibited nucleation of anatase TiO2 by enhanced adsorption of OH- ions toTiO2 embryos. The points of zero charge (PZC) of the amorphous Ti(OH)4 precipitate and the anatase TiO2 particles at 25 degrees C were obtained from the change in pH associated with the adsorption and desorption of OH- or H+, i.e., 4.6 for Ti(OH)4 precipitate and 6.0 for anatase TiO2 in the presence of 0.1 mol dm(-3) NaClO4. The PZCof the Ti(OH)4 precipitate measured at 25 degrees C after additional aging at 100 degrees C for 30 min was shifted to 4.1, owing to the promoted adsorption of OH-.     

Effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of nanoporous titanium dioxide electrodes

Titanium dioxide is a widely used photocatalyst whose properties can be modified by fluoride adsorption. This work is focused on the effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of TiO(2) nanoporous thin films. Surface fluorination was achieved by simple addition of HF to the working solution (pH 3.5). Open circuit potential as well as ex situ XPS measurements verify that surface modification takes place. Fluorination triggers a significant capacitance increase in the accumulation potential region, as revealed by dark voltammetric measurements for all the TiO(2) samples studied. The photoelectrocatalytic properties (measured as photocurrents under white light illumination) depend on the substrate being oxidized and, in some cases, on the nature of the TiO(2) sample. In particular, the results obtained for electrodes prepared with a mixed phase (rutile + anatase) commercial nanopowder (PI-KEM) indicate that the processes mediated by surface trapped holes, such as the photooxidation of water or methanol, are accelerated while those occurring by direct hole capture from the adsorbed state (formic acid) are retarded. The photooxidation of catechol and phenol is also enhanced upon fluorination. In such a case, the effect can be rationalized on the basis of a diminished recombination and a surface displacement of both the oxidizable organic substrates and the poisoning species formed as a result of the organics oxidation. Photoelectrochemical and in situ infrared spectroscopic measurements support these ideas. In a more general vein, the results pave the way toward a better understanding of the photocatalysis phenomena, unravelling the importance of the reactant adsorption processes.     

Effects of polyoxometalate and fluoride on adsorption and photocatalytic degradation of organic dye X3B on TiO2: the difference in the production of reactive species

It has been reported that addition of polyoxometalates (POM) or fluoride anions into the TiO(2) dispersions can significantly enhance the photocatalytic degradation (PCD) of weakly adsorptive organic pollutants in water such as chlorophenol. In this work, however, contradictory effects of POM and fluoride were observed on the PCD of highly adsorptive substrate X3B, an anionic organic dye, under similar conditions. The total rate of X3B PCD, determined by total loss of X3B both in solution and on the catalyst surface, was increased in the presence of fluoride, but the rate was decreased in the presence of POM. In both cases, the dark adsorption of X3B on TiO(2) was greatly decreased, ascribed to competitive adsorption of POM or fluoride that reduces the positive charges on the catalyst surface. The spectral analysis and the kinetic study using tert-butyl alcohol as hydroxyl radical scavenger revealed that the PCD of X3B on naked TiO(2) was predominately initiated by direct hole transfer, whereas addition of POM or fluoride into the TiO(2) dispersions enhanced the degradation of X3B via hydroxyl radical pathway. It is proposed that the surface occupation of POM on TiO(2) accelerates the production of surface-bound hydroxyl radicals, due to enhanced charge separation, whereas the fluoride replacement of surface hydroxyl groups of TiO(2) increases the production of free hydroxyl radicals in solution, due to enhanced hole availability for water oxidation. Assume that the relative reactivity among various active follows the order of free hydroxyl radicals > subsurface holes > surface-bound hydroxyl radicals, the proposal could account for the observed effects of POM and fluoride on the PCD of both weakly and highly adsorptive organic substrates over TiO(2) such as chlorophenol and X3B.     

Mechanistic evaluation of arsenite oxidation in TiO2 assisted photocatalysis

We report herein a detailed assessment of the roles of O2, H2O2, *OH, and O2-* in the TiO2 assisted photocatalytic oxidation (PCO) of arsenite. Although both arsenite, As(III), and arsenate, As(V), adsorb extensively onto the surface of TiO2, past studies relied primarily on the analysis of the arsenic species in solution, neglecting those adsorbed onto the surface of TiO2. We used extraction and analyses of the arsenic species adsorbed onto the surface of the TiO2 to illustrate that the oxidation of As(III) to As(V) occurs in an adsorbed state during TiO2 PCO. The TiO2 photocatalytic oxidation (PCO) of surface adsorbed As(III) in deoxygenated solutions with electron scavengers, Cu2+, and polyoxometalates (POM) yields oxidation rates that are comparable to those observed under oxygen saturation, implying the primary role of oxygen is as a scavenger of the conduction band electron. Pulse radiolysis and competition kinetics were employed to determine a rate constant of 3.6 x 10(6) M(-1) s(-1) for the reaction of As(III) with O2-*. Transient absorption studies of adsorbed hydroxyl radicals, generated by subjecting colloidal TiO2 to radiolytic conditions, provide convincing evidence that the adsorbed hydroxyl radical (TiO2+*OH) plays the central role in the oxidation with As(III) during TiO2 assisted photocatalysis. Our results suggest the reaction of superoxide anion radical does not contribute in the conversion of As(III) when compared to the reaction of As(III) with *OH radical during TiO2 PCO.     

偶氮染料吸附和光催化氧化动力学

以甲基橙和酸性大红两种偶氮染料为模拟污染有机物,对它们的暗吸附和光催化氧化行为进行研究.实验结果表明,两种偶氮染料的吸附受溶液酸碱度影响很大,酸性（pH=3）条件下,两种染料吸附量都很大,酸性大红吸附量更大；近中性（pH≈6）时两种染料的吸附显著减少；碱性（pH=9）条件下两种染料不发生吸附.光催化反应结果显示,碱性条件或酸性条件下两种染料降解速度都很快.说明在不同酸碱度条件下,光催化反应按不同机理进行.酸性条件下,反应在催化剂表面进行,在碱性介质中,光催化氧化在溶液中进行.提出了一个碱性条件下的动力学方程,经过进一步简化,可以得到表观一级方程,形式上和准一级L-H方程十分相似,但其含义不同.     

Experimental study of dimethyl methylphosphonate decomposition over anatase TiO2

Removal from air and decomposition of dimethyl methylphosphonate (DMMP) over high surface area anatase TiO(2) at ambient temperature have been quantitatively studied by employing Fourier transform infrared (FTIR) technique under static conditions. In the first scenario of air purification, DMMP underwent reactive adsorption that upon completion was followed by photocatalytic oxidation. DMMP was captured over the TiO(2) surface at the speed of external diffusion. Hydrolysis of adsorbed DMMP led to methanol and methyl methylphosphonate (MMP). At low DMMP coverage quantity, it hydrolyzed completely with the formation of completely surface-bound methanol at 1% relative humidity (RH) and mostly gaseous methanol at 50% RH. Photocatalytic oxidation generated CO(2) as the only carbonaceous gaseous product and bidentate formates as the intermediate surface product. At high DMMP coverage quantity, it was captured incompletely and hydrolyzed partially with CH(3)OH in the gas phase only, 50% RH enhancing both processes. Photocatalytic oxidation generated gaseous HCOOH, CO, and CO(2) and was incomplete due to catalyst deactivation by nonvolatile products. In the second scenario of air purification, DMMP underwent adsorption, hydrolysis, and photooxidation at the same time. It resulted in the quickest removal of DMMP from the gas phase and completion of oxidation in 30 min, suggesting this process for practical air decontamination. At least 0.8 nm(2) of TiO(2) surface per each DMMP molecule should be available for complete purification of air.     

Photoelectrochemical behavior of nanostructured TiO(2) thin-film electrodes in contact with aqueous electrolytes containing dissolved pollutants: a model for distinguishing between direct and indirect interfacial hole transfer from photocurrent measurements

A model for describing the photoelectrochemical behavior of nanostructured TiO(2) thin-film electrodes in contact with aqueous electrolytes containing dissolved pollutant species is presented. The model correlates the steady-state photocurrent, the illumination intensity, and the specific photooxidation mechanism for dissolved pollutant species in competition with water molecules. For physical events, the model considers the existence of hole trapping at surface states and the specific hole-transfer mechanisms taking place at the semiconductor-electrolyte interface (direct, via photogenerated valence-band free holes or indirect, via photogenerated surface-bound OH radicals or both). The model has been applied to the study of the photooxidation of aqueous solutions of formic acid and methanol. In agreement with previous results concerning massive polycrystalline electrodes, methanol is found to be photooxidized via indirect hole transfer, whereas formic acid is photooxidized mainly with the participation of valence-band free holes.     

Loading effects of silver oxides upon generation of reactive oxygen species in semiconductor photocatalysis

Superoxide anion radical (O(2)(-*)) and OH radical generations in suspensions of Ag metal-, Ag(2)O-, or AgO-loaded TiO(2) and BiVO(4) photocatalysts in alkaline conditions (pH 12.0) were examined by means of a luminol chemiluminescence (CL) technique and a spin-trapping fluorescence one in which terephthalic acid reacts with an OH radical to afford the highly fluorescent 2-hydroxyterephthalic acid (TAOH), respectively. The observed luminol CL intensity was remarkably enhanced by the AgO loading on TiO(2) as well as BiVO(4). This can be explained by enhancement of O(2)(-*) production on the AgO-loaded photocatalysts caused by the synergetic effects on the thermocatalytic activity upon the AgO surface and the efficient electron-hole separation at the photocatalyst/AgO interface. On the other hand, loading effects of AgO on the TAOH formation were not so significant compared to those on the CL observation, though the TAOH formation rates for the TiO(2) samples were much larger than those for the BiVO(4) ones by about three orders of magnitude. The properties of O(2)(-*) and OH radical generations on these photocatalysts are discussed on the basis of the luminol CL kinetics and approximate band edge positions of TiO(2), BiVO(4), and silver oxides.     

几种低碳醇在Pt／TiO2上的光催化产氢速率的研究

主要考察了无氧条件下低碳醇（甲、乙、丙醇）在Pt/TiO2表面光催化重整反应制氢。深入探讨了几种低碳醇与其放氢速率的构-效关系,提出了低碳醇在Pt/TiO2光催化剂表面吸附态的模型。     

In situ IR study of surface hydroxyl species of dehydrated TiO2: towards understanding pivotal surface processes of TiO2 photocatalytic oxidation of toluene

The surface species on P25-TiO(2) were characterized by FTIR after evacuation at 50-550 °C. The functions of OH groups on P25-TiO(2) catalysts have been tested by the adsorption and photooxidation of toluene in an in situ IR cell. FTIR studies show that the hydroxyl species on P25-TiO(2) are clearly temperature-dependent and P25-TiO(2) has six isolated hydroxyls with bands at 3734, 3715, 3688, 3671, 3658 and 3640 cm(-1). The OH groups on P25 play different roles in the photo-oxidation process: surface hydroxyls with bands at 3688, 3671, 3658 and 3640 cm(-1) act as adsorption sites while surface hydroxyls with bands at 3734 and 3715 cm(-1) act as sources of the ˙OH radical.