TiO2–carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

TiO₂–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO₂ layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO₂ layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO₂ layer proved to be best for efficient charge separation among the tested samples. The optimized TiO₂–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO₂ nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO₂–CNT heterojunctions and TiO₂ nanotubes were 0.75 h⁻¹ (R² = 0.983) and 0.39 h⁻¹ (R² = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO₂–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO₂ nanotubes. These results demonstrate the super capability of the TiO₂–CNT heterojunction arrays in photocatalysis with comparison to TiO₂-only nanomaterial.     

Photoelectrochemical oxidation behavior of methanol on highly ordered TiO2 nanotube array electrodes

The highly ordered titanium dioxide nanotube array (HOTDNA) electrodes were prepared in hydrofluoric acid solution by electrochemical anodic oxidation technique on a pure titanium sheet. The HOTDNA electrodes were characterized by X-ray diffraction, SEM microscopy, and UV–vis spectra. It has shown high density, well ordered and uniform titanium dioxide nanotube array film covered on these electrodes and the TiO₂ structure depending on the heating condition, the anatase phase of TiO₂ appeared when heating to 500 °C. The photoelectrochemical characteristics of methanol in 0.5 M Na₂SO₄ on the HOTDNA electrodes were investigated. The cyclic voltammetry, photocurrent-time and open-circuit photopotential response of methanol on the HOTDNA electrode were represented and significant photogenerated current was observed upon illumination in the UV regions with the light of 253.7 nm central wavelength. The effect of variables such as light intensity, applied potential, and methanol concentration on the photoelectrochemical response was investigated. It was found that the photocurrent was greatly influenced by these factors.     

氮掺杂TiO2光催化剂的制备及可见光催化性能研究

在溶胶-凝胶法基础之上,以尿素为氮源,通过较温和的反应条件来制备氮掺杂TiO₂光催化剂。以亚甲基蓝为模型化合物、日光色镝灯为光源,探索了其可见光光催化性能;并用XRD、低温氮气吸附-脱附技术、UV-Vis等表征了其结构特征;同时以对苯二甲酸为探针分子,结合化学荧光技术研究了光催化体系中·OH自由基的变化规律,进一步验证了其光催化活性规律。结果表明：氮掺杂能引起TiO₂光催化剂的激发吸收光谱明显红移并具较好的可见光响应性;在不同煅烧温度和尿素/钛酸丁酯物质的量的比     

脉冲沉积制备Cu2O/TiO2纳米管异质结的可见光光催化性能

在用阳极氧化法制备有序排列TiO₂纳米管阵列薄膜的基础上,引入脉冲沉积工艺,成功实现了均匀、弥散分布的Cu₂O纳米颗粒修饰改性TiO₂纳米管阵列,形成Cu₂O/TiO₂ 纳米管异质结复合材料. 利用场发射扫描电镜（FESEM）、场发射透射电镜（FETEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）和紫外-可见漫反射光谱（UV-Vis DRS）对样品进行表征,重点研究了Cu₂O/TiO₂ 纳米管异质结的光电化学特性和对甲基橙（MO）的可见光催化降解性能. 结果表明,Cu₂O纳米颗粒均匀附着在TiO₂纳米管阵列的管口和中部位置,所制备的Cu₂O/TiO₂ 纳米管异质结具有高效的可见光光催化性能;在浓度为0.01 mol·L^-1的CuSO₄溶液中制得的Cu₂O/TiO₂纳米管异质结表现出最好的电化学特性和光催化性能;另外,对Cu₂O纳米颗粒影响光催化活性的机理进行了讨论.     

氮掺杂TiO2/HTi2NbO7纳米片复合材料的制备及其可见光催化性能

首先采用高温固相法制备层状前驱体CsTi_2NbO_7,通过与硝酸进行质子交换反应可得到层状HTi_2NbO_7,然后将HTi_2NbO_7分散在四丁基氢氧化铵(TBAOH)溶液中进行剥离反应,得到HTi_2NbO_7纳米片悬浮液,并进行冷冻干燥处理。以尿素为N源,将冷冻干燥的HTi_2NbO_7纳米片与TiO_2前驱体(钛酸异丙酯)混合物进行高温焙烧处理,成功地合成了新型氮掺杂Ti O_2/HTi_2NbO_7纳米片(N-TTN)复合材料。采用扫描电子显微镜(SEM)、高倍透射电子显微镜(HRTEM)、X射线衍射(XRD)、N_2吸附-脱附测试、X射线光电子能谱(XPS)、紫外可见吸收光谱(UV-Vis)及电化学测试等对材料的形貌、晶体结构、比表面积、孔分布和光吸收性能等进行表征与分析。研究发现锐钛矿型TiO_2纳米颗粒均匀地分散在HTi_2NbO_7纳米片表面,在两组分间形成异质结结构。通过在可见光下降解有机污染物罗丹明B(RhB)来评价不同样品的光催化活性。结果表明,N-TTN复合材料具有最优的光催化降解活性,活性的增强主要归功于N元素的掺杂、异质结的构筑、增大的比表面积和丰富的介孔结构。     

CNTs/TiO2多孔复合膜的组装及光催化性能

提出了一种在掺氟的SnO2(FTO)导电玻璃上组装碳纳米管(CNTs)/Fe-Ni/TiO2多孔复合膜光催化剂的新方法.采用喷涂热解法(SPD)将掺杂镍和铁的含有嵌段聚合物P123的二氧化钛前驱体溶胶涂覆在FTO导电玻璃上,制备Fe-Ni/TiO2多孔膜,再采用化学气相沉积法(CVD)在Fe-Ni/TiO2膜上原位生长CNTs,得到CNTs/Fe-Ni/TiO2多孔复合膜光催化剂.CNTs/Fe-Ni/TiO2复合膜具有多级孔结构特征,在TiO2表面原位生长的CNTs不但具有较好的石墨化结构,且CNTs较均匀地分布在整个膜层的孔中.考察了CNTs/Fe-Ni/TiO2复合膜光催化剂的结构和性能,并通过降解甲基橙溶液评价了复合膜的光催化活性.结果表明,CNTs的复合及铁和镍的掺杂等改性显著提高了TiO2膜材料的光催化活性.     

Synthesis of molecular imprinted polymer modified TiO2 nanotube array electrode and their photoelectrocatalytic activity

A tetracycline hydrochloride (TC) molecularly imprinted polymer (MIP) modified TiO₂ nanotube array electrode was prepared via surface molecular imprinting. Its surface was structured with surface voids and the nanotubes were open at top end with an average diameter of approximately 50 nm. The MIP-modified TiO₂ nanotube array with anatase phase was identified by XRD and a distinguishable red shift in the absorption spectrum was observed. The MIP-modified electrode also exhibited a high adsorption capacity for TC due to its high surface area providing imprinted sites. Photocurrent was generated on the MIP-modified photoanode using the simulated solar spectrum and increased with the increase of positive bias potential. Under simulated solar light irradiation, the MIP-modified TiO₂ nanotube array electrode exhibited enhanced photoelectrocatalytic (PEC) activity with the apparent first-order rate constant being 1.2-fold of that with TiO₂ nanotube array electrode. The effect of the thickness of the MIP layer on the PEC activity was also evaluated.     

Effect of electrolysis conditions on photocatalytic activities of the anodized TiO2 films

Photocatalytic activities of anodized TiO₂ films for decomposition of gaseous acetaldehyde were investigated. The anodized TiO₂ films were fabricated by galvanostatic anodization in a mixed electrolyte composed of H₂SO₄, H₃PO₄, and H₂O₂. Pre-nitridation treatment effectively enhanced the photocatalytic activity of the anodized TiO₂ films. The electrolysis parameters such as anodization time, current density, electrolyte temperature, and electrolyte composition significantly affected the photocatalytic activity of the anodized TiO₂ films. The improvement of photocatalytic activity of the anodized films is attributed to increase in surface areas of the anodized specimens.     

Fabrication and photocatalytic activity of high-efficiency visible-light-responsive photocatalyst ZnTe/TiO2 nanotube arrays

A new ZnTe modified TiO₂ nanotube (NT) array catalyst was prepared by pulse potential electrodeposition of ZnTe nanoparticles (NPs) onto TiO₂ NT arrays, and its application for photocatalytic degradation of anthracene-9-carboxylic acid (9-AnCOOH) was investigated. The even distribution of ZnTe NPs was well-proportionately grown on the top surface of the TiO₂ NT while without clogging the tube entrances. Compared with the unmodified TiO₂ NT, the ZnTe modified TiO₂ NT (ZnTe/TiO₂ NT) showed significantly enhanced photocatalytic activity towards 9-AnCOOH under simulated solar light. After 70 min of irradiation, 9-AnCOOH was degraded with the removal ratio of 45% on the bare TiO₂ NT, much lower than 80%, 90%, and 100% on the ZnTe/TiO₂ NT with the ZnTe NPs prepared under the pulsed “on” potentials of −0.8, −1.0, and −2.0 V, respectively. The increased photodegradation efficiency mainly results from the improved photocurrent density as results of enhanced visible-light absorption and decreased hole-electron recombination due to the presence of narrow-band-gap p-type semiconductor ZnTe.     

TiO2纳米纤维无纺布的制备及光催化性能研究

以聚乙烯吡咯烷酮(PVP)作为配位剂与钛酸正丁酯(Ti(C₄H₉O)₄)反应制得前驱体，再以乙醇为溶剂，CH3COOH作为催化剂，采用静电纺丝法制得PVP/TiO₂复合纳米纤维，经550 ℃、700 ℃和900 ℃焙烧后分别得到以锐钛矿型的TiO₂为主、以金红石型TiO₂为主和完全金红石晶型的TiO₂纳米纤维。对所制得的纳米纤维的结晶度、纯度和形貌，分别采用差热-热重分析(TG-DTA)、红外光谱(IR)、X射线粉末衍射(XRD)、扫描电镜(SEM)等进行了表征。光降解苯酚水溶液的实验结果表明，550 ℃下煅烧得到的以锐钛矿占主体的TiO₂纳米纤维，2 h使浓度为50 mg·L^-1苯酚水溶液的降解率超过85%，这充分说明这种TiO₂电纺纳米纤维具有良好的光催化性能。     

Enhancement of ethanol electrooxidation on plasmonic Au/TiO2 nanotube arrays

Novel electrocatalysts Au/TiO₂ nanotube arrays (Au/TiO₂NTs) were prepared by loading low-content(1.9 at.%) of Au nanoparticles (AuNPs) onto highly ordered TiO₂ nanotube arrays (TiO₂NTs). Ethanol electrooxidation indicates that visible-light (λ > 400 nm) irradiation can significantly enhance the activity as well as resistpoisoning of Au/TiO₂NTs electrocatalysts that are activated by plasmon resonance. Au/TiO₂NTs catalysts calcinated at 300 °C display the highest performance due to the strong synergistic interactions between TiO₂ and Au NPs. The combination of visible-light irradiation with a controllable potential offers a new strategyfor enhancing the performance of anodes in direct ethanol fuel cell (DEFC).     

Photocatalytic activity of N-doped TiO2: photocatalytic synthesis of o-aminophenol at room temperature

The photocatalytic synthesis of o-aminophenol in methanol was investigated with N-doped TiO₂ nanoparticles under UV-light irradiation. The catalytic quantities of N-doped TiO₂ prepared by a simple modified sol–gel process with urea as nitrogen source rapidly reduced o-nitrophenol to the corresponding amine at room temperature.     

载有C60的TiO2纳米粒子光催化活性

以水溶性C₆₀和TiO₂粒子为前驱体,采用水热法制备了载有C₆₀的锐钛矿型TiO₂纳米粒子。应用X射线衍射、透射电子显微镜、红外光谱、紫外-可见漫反射光谱、荧光光谱对产物进行了表征。以对-硝基苯酚为模型污染物研究了产物的光催化活性,结果表明适量负载C₆₀可以提高TiO₂纳米粒子的光催化活性,C₆₀起着传输电子、促进TiO₂光生载流子分离的作用,且经7次循环使用后对-硝基苯酚的降解效率仍能达到74%。讨论了载有C₆₀的TiO₂纳米粒子光催化降解对-硝基苯酚的机理。     

Cu掺杂TiO2及其纳米管的制备、表征与光催化性能

通过溶胶-凝胶法和水热法制备了Cu掺杂TiO₂纳米粉末及其纳米管,并通过XRD、TEM、FE-SEM、EDS、UV-Vis/DRS等手段分析了样品的结构。发现以Cu掺杂TiO₂纳米粉末为水热反应原料制备的纳米管中不含Cu,对其原因进行了分析讨论并通过Zn掺杂TiO₂纳米粉末证实：以金属掺杂TiO₂纳米粉末为原料,通过水热法制备TiO₂纳米管中不含有相应金属离子,这是由于金属离子在强碱水热条件下形成金属配离子,使金属离子溶解于水中而不能形成金属掺杂TiO₂纳米管。对所得样品进行了光催化性能测试,发现：Cu掺杂TiO₂粉末的光催化产氢效率为0.75 μmol·(g·h)^-1,高于由其本身及P25通过水热法制备的TiO₂纳米管(分别为：0.42 μmol·(g·h)^-1,0.25 μmol·(g·h)^-1)的光催化产氢效率。     

TiO_2表面NiO光催化活性中心的构建及其光催化析氢性能研究

本文采用离子快速注入法,在低温条件下利用微量NiO物种对TiO_2光催化剂表面微结构进行了修饰和改性,构建了NiO光催化反应活性中心。研究结果表明,Ni物种是以TiO_2-NiO-H形式存在于TiO_2表面;相对于未修饰的TiO_2光催化剂,NiO的修饰很大程度上提高了其光催化析氢性能,在最佳条件下,放氢速率由1.1μmol·h~(-1)提高到241.4μmol·h~(-1)。另外,Ni物种含量,热处理温度,乙醇电子给体浓度,催化剂悬浮浓度对光催化析氢性能也有明显的影响。光电化学实验结果表明,NiO的表面修饰能够产生有效的光催化反应活性中心,增强了光生电子-空穴电子对的分离效果。所制备的光催化剂采用X射线粉末衍射(XRD),光电子能谱(XPS)等技术进行表征。     

Photocatalytic hydrogen evolution over mesoporous TiO2/metal nanocomposites

Na⁺ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m²/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO₂ samples prepared were found to have photocatalytic activity in Cu^II, Ni^II and Ag^I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO₂ Degussa P25.The effects of the thermal treatment of mesoporous TiO₂ upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO₂/Ag⁰ to TiO₂/Ni⁰ to TiO₂/Cu⁰ was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites.