A two-step sol-gel method for synthesis of nanoporous TiO2

This article reports a study of the effects of synthesis parameters on the preparation and formation of mesoporous titania nanopowders by employing a two-step sol-gel method. These materials displayed crystalline domains characteristic of anatase. The first step of the process involved the hydrolysis of titanium isopropoxide in a basic aqueous solution mediated by neutral surfactant. The solid product obtained from step 1 was then treated in an acidified ethanol solution containing the same titanium precursor to thicken the pore walls. Low pH and higher loading of the Ti precursor in step 2 produced better mesoporosity and crystallinity of titanium dioxide polymorphs. The resultant powder exhibited a high surface area (73.8 m2/g) and large pore volume (0.17 cm3/g) with uniform mesopores. These materials are envisaged to be used as precursors for mesoporous titania films as a wide band gap semiconductor in dye-sensitized nanocrystalline TiO2 solar cells.     

TiO(2)/LiCl-based nanostructured thin film for humidity sensor applications

A simple and straightforward method of depositing nanostructured thin films, based on LiCl-doped TiO(2), on glass and LiNbO(3) sensor substrates is demonstrated. A spin-coating technique is employed to transfer a polymer-assisted precursor solution onto substrate surfaces, followed by annealing at 520°C to remove organic components and drive nanostructure formation. The sensor material obtained consists of coin-shaped nanoparticles several hundred nanometers in diameter and less than 50 nm thick. The average thickness of the film was estimated by atomic force microscopy (AFM) to be 140 nm. Humidity sensing properties of the nanostructured material and sensor response times were studied using conductometric and surface acoustic wave (SAW) sensor techniques, revealing reversible signals with good reproducibility and fast response times of about 0.75 s. The applicability of this nanostructured film for construction of rapid humidity sensors was demonstrated. Compared with known complex and expensive methods of synthesizing sophisticated nanostructures for sensor applications, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), this work presents a relatively simple and inexpensive technique to produce SAW humidity sensor devices with competitive performance characteristics.     

One-step synthesis of hierarchically porous hybrid TiO2 hollow spheres with high photocatalytic activity

Hierarchically porous hybrid TiO₂ hollow spheres were solvothermally synthesized successfully by using tetrabutyl titanate as titanium precursor and hydrated metal sulfates as soft templates. The as-prepared TiO₂ spheres with hierarchically pore structures and high specific surface area and pore volume consisted of highly crystallized anatase TiO₂ nanocrystals hybridized with a small amount of metal oxide from the hydrated sulfate. The proposed hydrated-sulfate assisted solvothermal (HAS) synthesis strategy was demonstrated to be widely applicable to various systems. Evaluation of the hybrid TiO₂ hollow spheres for the photo-decomposition of methyl orange (MO) under visible-light irradiation revealed that they exhibited excellent photocatalytic activity and durability.     

浸蚀多孔铝模板制备TiO2亲水薄膜材料

利用浸蚀多孔铝模板,涂覆TiO2溶胶和纳米粉组成的料浆,制得TiO2亲水性阵列薄膜。通过对此薄膜SEM及表面接触角分析,研究了聚乙二醇改性、存放时间、SiO2的添加等对其亲水性的影响。结果表明:浸蚀多孔铝模板制备的TiO2薄膜无需紫外光激发即表现出良好的亲水性,5s内可达到完全铺展;料浆中添加0.02～0.04g/mL聚乙二醇能一定程度上提高薄膜材料亲水性并减缓其亲水性的降低;添加纳米SiO2制备的TiO2/SiO2复合薄膜亲水性优于纯TiO2薄膜,经聚乙二醇改性后为超亲水性,超亲水性能在黑暗中维持5天。     

Resistive and capacitive response of nitrogen-doped TiO2 nanotubes film humidity sensor

Dielectric oxides are traditionally used to fabricate resistive surface humidity-sensing devices, as well as capacitive sandwich-structured sensors. In the present work, relative humidity (RH) sensors were fabricated by employing vertically aligned TiO(2) nanotubes array (TNA) film produced using electro-chemical anodization of Ti foil followed by a nitrogen-doping process, simultaneously showing resistive and capacitive humidity-sensing properties in the range of 11.3-93.6%. For the sample formed at optimized experimental conditions, the capacitance (C(S)) and resistance (R(S)) of the as-fabricated RH sensors made from nitrogen-doped TiO(2) nanotubes film could be simultaneously obtained. Both the resistive and capacitive sensitivity (K(R) and K(C)) of the as-fabricated TiO(2) nanotube RH sensors show distinct dependence on the frequency of alternating current (AC) voltage signal and RH. At higher water coverage, water-water interaction will result in lowering of the water dissociation barrier, leading to an increase of conductance. With the increase of RH, the polarization of as-adsorbed water molecules will also occur, causing a sharp increase of capacitance. For an explanation of the frequency response of both C(S) and R(S), ionic transport, as well as the polarization effect, should be comprehensively considered. The changes of capacitance and resistance at different temperatures are plausibly caused by thermal expansion and surface state modification by adsorption and desorption of oxygen and water.     

The synthesis of nanosized TiO2 powder using a sol-gel method with TiCl4 as a precursor

Nanosized TiO₂ powder with anatase structure was synthesized by a sol-gel method using TiCl₄ ethanol solution as a precursor. The grain size of TiO₂ powder was homogenous and was about 10 nm after the precursor was calcined at 500 °C for 1 hour. Anatase TiO₂ powder formed after the precursor was calcined at a temperature ranging from 300 °C to 550 °C. The gelatinizing mechanism of TiCl₄ in ethanol solution can be described as followings. When mixed with ethanol, TiCl₄ reacted with ethanol to form TiCl _x (OCH₂CH₃)_{4 – x} species and HCl gas. During gelatinizing process, TiCl _x (OCH₂CH₃)_{4 – x} species absorbed water from atmosphere to form Ti(OH)₄ precursor, which was polymerized to be an inorganic polymer. The formation of inorganic polymer of Ti(OH)₄ was intensified with gelatinizing time. In contrast, the organic component was removed from the precursor. The formation of anatase TiO₂ can also be promoted by increasing gelatinizing time. The influence of alcohol on the reacting progress and dispersivity was also studied. The size and activity of alcohol molecule were found to have influence on the polymerization and mineralization degree of the precursor and the dispersivity of TiO₂ powders.     

A hygrometer comprising a porous silicon humidity sensor with phase-detection electronics

A novel hygrometer is presented, comprising a capacitive humidity sensor with a porous silicon (PS) dielectric and electronics. The adsorption of water vapor by the PS layer leading to change of its effective dielectric constant is modeled with an effective medium approximation (EMA). A simple, but precise, phase-sensitive electronic circuit has been developed. This detects any change of phase of a sinusoidal signal transmitted through the PS dielectric and correlates to ambient humidity. It is outlined how the nonlinear response of the sensor is compensated through piecewise linearization. The sensor is tested in combination with the phase detection circuitry. Excellent linearity over the entire range of relative humidity is achieved. Experimental results show a resolution better than 0.1% and an accuracy of 2% (near the transition region) and better than 0.1% (otherwise). The response time is less than 10 s with good stability.     

溶胶-凝胶法制备多孔纳米金属铜膜

为了制备多孔纳米金属膜材料,以醋酸铜为前躯体、聚乙二醇为模板剂、二乙醇胺为络合剂,通过溶胶-凝胶法在玻璃基片上制备了多孔纳米金属铜膜.利用XRD、IR、TG-DTG和SEM对所制备的纳米金属铜膜材料进行了分析及表征,并研究了溶胶浓度、PEG添加量、退火温度对多孔铜膜结构的影响.结果表明,当溶胶浓度为0.6 mol/L时,铜离子与PEG1000的毫克分子比值是42.86∶1,退火温度为500℃时,可以得到较好的多孔结构纳米Cu薄膜.不同的PEG加入量、溶胶浓度以及热处理温度都会对薄膜的形貌有较大的影响.     

Preparation and properties of a humidity sensor based on LiCl-doped porous silica

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Impact of morphology on high-speed humidity sensor performance

Capacitive-based humidity sensors were fabricated using unique nanostructured aluminum-oxide thin films. These sensors exhibited extremely fast desorption response times as short as 42 ms. In this paper, we present the effects of varying the thin-film porosity on sensor performance. Specifically, we look at the capacitive response and the desorption response time of the sensors. It was found that increased porosity tends to decrease the desorption response time and increase the relative humidity where the devices become sensitive.     

Analysis of the d.c. and a.c. properties of K2O-doped porous Ba0.5Sr0.5TiO3 ceramic humidity sensor

A humidity sensor using K₂O-doped porous Ba_0.5Sr_0.5TiO₃ ceramic is investigated. This ceramic humidity sensor exhibits a porous structure. The porous ceramic easily absorbs water vapour throughout the pores. The log-conductance against relative humidity (r.h.) sensitivity of this sensor is greater than 4 orders of magnitude in the range of 15∼95% r.h. at 400 Hz and 25°C. The adsorption process of the sensor is very fast. Its adsorption response time in r.h. variation from 15 to 95% is within a few seconds. Charging-discharging and complex impedance analysis techniques are used to analysis the direct current (d.c.) and alternating current (a.c.) response of this device under 50∼95% r.h. The sample can be polarized like electrolytes on charging process due to electrode space charge and grain surface water molecular polarization effects. The degree of polarization is enhanced with increasing r.h. The conduction carriers of this sensor in a humid atmosphere are ions and electrons, and the dominant conduction carrier is the ion. Using complex impedance analysis techniques, an equivalent circuit model associated with “non-Debye” capacitance is built. This model separates the sample into three regions: crystal grain, grain surface and electrode surface. The grain surface resistance and electrode surface resistance decrease sharply with increasing r.h., but crystal grain resistance is not affected by water vapour.     

溶胶凝胶法制备TiO2薄膜的微观结构和光学性能研究

以乙二醇甲醚为溶剂,羟基纤维素（HPC）为添加剂,用溶胶-凝胶法制备了多孔TiO2薄膜。扫描电镜（SEM）观察发现多孔TiO2薄膜孔径随HPC含量增加而变大。X射线衍射（XRD）表明得到的TiO2薄膜均为锐钛矿相,对XRD点阵参量进行计算,发现随HPC含量的增大,薄膜晶粒尺寸先减小后增大。表面轮廓仪膜厚测试表明随HPC含量的增大,薄膜厚度逐渐减小。UV—vis光谱分析表明随HPC含量增大,薄膜透射性能有所下降。     

溶胶-凝胶法制备聚醚砜/TiO2杂化膜

采用溶胶-凝胶法制备聚醚砜-二氧化钛杂化膜,用TEM对铸膜液中二氧化钛分散程度进行表征,并用SEM及接触角仪对膜材料的表面及断面形态、膜材料的亲水性能进行表征.结果表明,当TiO2凝胶添加量(质量分数)达到4%时,表面明显分布有大量分布均匀的TiO2纳米粒子,其断面结构则表现为皮层变厚,亚孔层消失,只存在指状大孔结构,表现为水通量随之增大,改善了聚醚砜材料的疏水性,提高了膜的抗污染性.随着二氧化钛纳米粒子浓度的提高,由于纳米粒子的团聚现象导致其在聚合物基上不能分散均匀,当膜受到外力作用时引起膜内部应力集中,使膜力学性能下降.     

模板法制备介孔TiO2光催化剂的研究进展

介绍了各样模板及相关介孔制备体系,包含表面活性剂模板制备,非表面活性剂模板制备,其它模板制备及非模板制备。结果显示介孔结构可以很好的提高纳米TiO2的光催化活性,虽然在少数例子中介孔结构对光催化活性产生的影响很小或是没有影响。重点论述了上述研究方法的原理、优缺点和在改变TiO2性能中的应用,以及这些方法相结合所取得的一些研究进展;并指出这些方法在TiO2光催化剂的研究中发挥的重要作用。     

Characterization of a nanosized TiO2 gas sensor

Thin films were obtained by r.f. reactive sputtering from a Ti_.1W_.9 target onto a Si substrate followed by annealing in air at 800 °C. The thermal treatment results in a nanosized TiO₂ thin film with high surface-to-volume ratio. The nanosized structure, its stability, together with the ease of preparation, make this material suitable as a gas sensor. The sensing layer proved capable to detect 20 ppm of NO₂ at a temperature suitable for monitoring of exhaust gases of engines. Its high sensitivity suggests use of this sensor for environmental purposes.     

Porous nanocrystalline TiO2 with high lithium-ion insertion performance

Porous nanocrystalline anatase TiO₂ was prepared by a modified hydrolytic route coupled with an intermediary amorphization/recrystallization process. The phase structure and morphology of the products were analyzed by X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The electrochemical properties were investigated by cyclic voltammetry, constant current discharge–charge tests, and electrochemical impedance techniques. Applied as an anode in a lithium-ion battery, the material exhibited excellent specific capacities of 130 mAh g^?1 (at the rate of 2000 mA g^?1) and 96 mAh g^?1 (at the rate of 4000 mA g^?1) after 100 cycles; the coulombic efficiency was ~99.5 %, indicating excellent rate capability and reversibility. Furthermore, the electrochemical impedance spectra showed improved electrode kinetics after cycling. These results indicate that the porous nanocrystalline TiO₂ synthesized by this improved synthesis route might be a promising anode material for high energy and high power density lithium-ion battery applications.     

碳球模板剂对TiO2光阳极微结构及其光电性能影响研究

以葡萄糖为原料水热合成碳球作为模板剂,将其与TiO2纳米晶共混制备纳米多孔TiO2光阳极。采用场发射电子扫描电镜(SEM)、台阶仪、紫外-可见分光光度计(UV-Vis)等对TiO2薄膜的表面形貌、厚度和散射能力进行表征。研究发现,随着碳球含量的增加,光阳极单位体积内的表面积先增加后减小;薄膜对光的散射能力也呈现同样趋势。采用所制备的光阳极组装染料敏化太阳能电池,性能测试结果表明,随着碳球含量的增加,电池短路电流密度先增加,后减小。当碳球加入量为TiO2纳米晶质量的3%时,电池光电转换效率达到最佳为5.15%。     

复合模板剂下制得介孔TiO2光催化活性的研究

以吐温-80（Tween-80）和司班-80（Span-80）为复合模板剂，采用溶胶-凝胶（sol-gel）工艺制得介孔TiO2。通过对甲基橙溶液进行光催化降解试验表明：模板剂的种类与用量、光照距离和甲基橙溶液的原始浓度等因素对所制得介孔TiO2试样的光催化活性产生明显的影响。实验结果证明，本研究所得介孔TiO2材料具有较高的光催化活性，500℃下煅烧5h制备的样品在2．5h内可使浓度为0．02g／L的甲基橙溶液降解率达到94．7％，明显高于市售纳米TiO2粉体的降解率78．1％；通过X-ray衍射分析获知所制TiO2为锐钛矿型。     

多孔TiO2的制备表征及光催化研究

以钛酸四丁酯为前驱物，在溶胶-凝胶法和硬脂酸法的合成样品的过程中添加正硅酸乙酯，分别合成出纳米TiO2，焙烧成晶后通过HF除去硅，形成了多孔TiO2。通过XRD、SEM、UV-Vis、BET等测试手段，比较正硅酸乙酯对不同合成方法合成的样品的影响。在对甲基橙的紫外光催化试验中，添加正硅酸乙酯再由HF处理后合成的样品表现出较高的催化活性，这与此方法合成的样品的表面积较大有关。