Near monodisperse TiO2 nanoparticles and nanorods

Highly crystalline, near monodisperse TiO2 nanoparticles, nanorods and their metal-ion-doped (Sn4+, Fe3+, Co2+, and Ni2+, etc.) derivatives have been prepared by well-controlled solvothermal reactions. Through adjusting the reaction parameters, such as reaction temperature, duration, and concentration of the reactants, the size, shape, and dispersibility of the products can be controlled. A possible reaction mechanism can be proposed based on experimental evidence.     

Facile synthesis and characterization of functionalized, monocrystalline rutile TiO2 nanorods

Functionalized, monocrystalline rutile TiO2 nanorods were prepared from TiCl4 in aqueous solution under acidic conditions in the presence of dopamine, followed by aging and hydrothermal treatment at 150 degrees C. The surface-bound organic ligand controls the morphology as well as the crystallinity and the phase selection of TiO2. The presence of monocrystalline rutile TiO2 was confirmed by X-ray powder diffraction and HRTEM investigations. The as-prepared nanorods are soluble in water at pH <3. The surface functionalization was analyzed by IR and 1H NMR, confirming the presence of dopamine on the surface. The surface amine groups can be tailored further with functional molecules such as dyes. Confocal laser scanning microscopy (CLSM) was used to characterize the binding of the fluorescent dye 4-chloro-7-nitrobenzofurazan (NBD) to the functionalized surface of the TiO2 nanorods.     

N-halamine biocidal coatings via a layer-by-layer assembly technique

Two N-halamine copolymer precursors, poly(2,2,6,6-tetramethyl-4-piperidyl methacrylate-co-acrylic acid potassium salt) and poly(2,2,6,6-tetramethyl-4-piperidyl methacrylate-co-trimethyl-2-methacryloxyethylammonium chloride) have been synthesized and successfully coated onto cotton fabric via a layer-by-layer (LbL) assembly technique. A multilayer thin film was deposited onto the fiber surfaces by alternative exposure to polyelectrolyte solutions. The coating was rendered biocidal by a dilute household bleach treatment. The biocidal efficacies of tested swatches composed of treated fibers were evaluated against Staphylococcus aureus and Escherichia coli. It was determined that chlorinated samples inactivated both S. aureus and E. coli O157:H7 within 15 min of contact time, whereas the unchlorinated control samples did not exhibit significant biocidal activities. Stabilities of the coatings toward washing and ultraviolet light exposure have also been studied. It was found that the stability toward washing was superior, whereas the UVA light stability was moderate compared to previously studied N-halamine moieties. The layer-by-layer assembly technique can be used to attach N-halamine precursor polymers onto cellulose surfaces without using covalently bonding tethering groups which limit the structure designs. In addition, ionic precursors are very soluble in water, thus promising for biocidal coatings without the use of organic solvents.     

Perpendicular rutile nanosheets on anatase nanofibers: Heterostructured TiO2 nanocomposites via a mild solvothermal method

A novel hierarchically heterostructured TiO₂ nanocomposite, which consists of rutile nanosheets perpendicular standing on anatase nanofibers, is successfully created through a two-step approach. Firstly, the fibrous anatase TiO₂ framework is fabricated by a facile electrospinning method, then a layer of relative uniform rutile nanosheets grow on the fibers after a mild solvothermal reaction process. This work provides a convenient and effective route for fabricating desired three-dimensional nanocomposite and should be easily extended through to many other materials system.     

Green synthesis and dye-sensitized solar cell application of rutile and anatase TiO2 nanorods

Journal of Solid State Electrochemistry - Nanorods (NRs) of TiO2 have biogenically been&nbsp;prepared, i.e., from the extract of Phellinus linteus mushroom. The presence of mixed anatase and...     

硝酸根接枝诱导组装金红石相TiO2纳米束以增强光催化产氢（英文）

化石燃料的快速消耗加速了全球能源危机和环境污染等问题.光催化产氢直接利用清洁和可持续的太阳能实现向化学燃料的转化,因而成为一种有前景的技术.众多半导体光催化剂中,二氧化钛因其高光催化活性、稳定的化学性质、低成本和无毒等优势而被广泛用作分解水产氢的光催化剂.最近,金红石相TiO2纳米晶体在某些情况下被证明具有光催化的潜力,然而其光生电子-空穴对的快速复合显著抑制了光催化效率.表面修饰、构建异质结和负载助催化剂等策略被用来提高光生载流子的分离效率以减少复合损失,从而提升光催化活性.由于光催化反应通常发生在光催化剂的表面活性位点上,因此通过改善表面性质改变电荷转移途径对光催化活性具有重要影响.磷酸、硫酸、硼酸和盐酸等无机酸的修饰可以改变光催化剂的表面基团,分别通过促进表面羟基的形成和氧气的吸附以及改变表面电荷性质更有效地捕获空穴,实现光生电子和空穴的分离,有助于光催化降解有机污染物.然而,这种影响机制显然不适用于光催化产氢体系,目前对无机酸修饰用于分解水产氢的研究鲜有报道.因此,通过酸改性策略制备高效产氢的光催化剂仍然是一个相当大的挑战.本文利用硝酸诱导策略合成纺锤状金红石相二氧化钛纳米束(R-TiO2).首先,制备层状质子化钛酸盐(LPT)作为TiO2的前体,随后,加入浓硝酸以诱导向金红石相TiO2的转变,并组装形成纺锤状纳米束.对照实验显示,硝酸的酸化可以诱导LPT向金红石相TiO2的转变,而相同条件下浓硝酸后处理不会引起晶相的转变.纺锤形纳米束的形成源于,硝酸诱导R-TiO2沿(110)方向生长并彼此粘附,硝酸诱导组装过程成功在TiO2表面修饰上硝酸根,同时扩大了光吸收范围,有效减少了电荷复合损失.光催化产氢测试证明了R-TiO2光催化剂具有高效的产氢性能,产氢速率为402.4μmol h-1,是Degussa P25的3.1倍,并且显著高于未经浓硝酸处理的锐钛矿(52.0μmol h^-1)或金红石相(110.8μmol h^-1)光催化剂.为了说明表面硝酸根的影响,分别从晶体和化学结构、形态以及表面电荷性质方面比较了光催化反应前后的变化,结果表明,R-TiO2增强的光催化效率可归因于硝酸根基团的负场效应,有利于在表面上捕获带正电的质子以促进载流子分离,提高光催化产氢的效率.总之,本工作不仅对于发展表面修饰策略制备高效产氢光催化剂的研究具有重要意义,而且提出了一种不同于文献报道的无机酸影响机制.     

Chemical assembly of TiO2 and TiO2@Ag nanoparticles on silk fiber to produce multifunctional fabrics

Activated carbon fibers (ACFs) were prepared by chemical activation of poly(p-phenylene terephthalamide (PPTA) with phosphoric acid, with a particular focus on the effects of impregnation ratio and carbonization temperature on both surface chemistry and porous texture. Thermogravimetric studies of the pyrolysis of PPTA impregnated with different amounts of phosphoric acid indicated that this reagent has a strong influence on the thermal degradation of the polymer, lowering the decomposition temperature and increasing the carbon yield. As concerns surface chemistry, TPD and chemical analysis results indicated that the addition of phosphoric acid increases the concentration of oxygenated surface groups, with a maximum at an impregnation ratio of 100 wt.%. The resulting materials present uncommon properties, namely a large amount of oxygen- and phosphorus-containing surface groups and a high nitrogen content. Porosity development following H(3)PO(4) activation was very significant, with values close to 1700 m(2)/g and 0.80 cm(3)/g being reached for the BET surface area and total pore volume, respectively. The pore size distributions remained confined to the micropore and narrow mesopore (<10 nm) range.     

Fabrication of fluorescent nanotubes based on layer-by-layer assembly via covalent bond

A pressure-filter-template approach was employed to prepare fluorescent nanotubes of polyethyleneimine (PEI) and 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) through covalent combination in the porous of alumina template based on the layer-by-layer (LbL) assembly technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images exhibited a tubular structure of the obtained samples. The wall thickness of the nanotubes is well controlled by varying the assembled cycle number, which is detected by UV-visible spectroscopy. Fourier transform infrared (FT-IR) spectroscopy confirmed the formation of covalent bonds between PEI and PTCDA in nanotubes.     

Dual-stimuli responsive PNiPAM microgel achieved via layer-by-layer assembly: magnetic and thermoresponsive

We describe the synthesis, characterisation and surface-modification of magnetic nanoparticles and a poly(N-isopropylacrylamide) microgel, followed by the assembly and characterisation of magnetic nanoparticles on the microgel. To facilitate this deposition, the surface of the microgel is first modified via the layer-by-layer assembly of polyelectrolytes. One advantage of this concept is that it allows an independent optimization and fine tuning of the magnetic and thermoresponsive properties of individual components (nanoparticles and microgels) before assembling them so that the hybrid core-shell structure retains all the individual properties. The decisive parameter when exploiting the thermoresponsive and magnetic properties in such hybrid core-shell structures is the amount of heat transfer from the magnetic core onto the thermosensitive (loaded) microgel (for the subsequent heat-triggered release of drugs). Inductive heat study reveals that the heat generated by the magnetic nanoparticles is sufficient to cause the collapse of the microgel above its volume phase transition temperature. Successful confinement of positively and negatively charged magnetic nanoparticles between polyelectrolyte layers is achieved using the layer-by-layer deposition onto the microgel. Dynamic light scattering measurements show (i) the presence of each layer successfully deposited, (ii) the preservation of thermoresponsivity in the coated microgel, and (iii) that the magnetic nanoparticles do not get detached during the phase transition of the microgel. Electrophoresis measurements confirm charge reversal at every stage of layering of polycations, polyanions and magnetic nanoparticles. This unique combination of thermoresponsivity and magnetism opens up novel perspectives towards remotely controlled drug carriers.     

Versatile electrostatic assembly of nanoparticles and polyelectrolytes: Coating,clustering and layer-by-layer processes

Engineered nanoparticles made from noble metals, rare-earth oxides or semiconductors are emerging as the central constituents of future nanotech developments. In this review, a survey of the complexing strategies between nanoparticles and oppositely charged polyelectrolytes developed during the last three years and based on electrostatic interactions is presented. These strategies include the one-step synthesis of stable and functionalized nanoparticles, the one- and multilayer coating of individual nano-objects, the controlled clustering of particles and the generation of capsules and thin films with superior functionalities. Among the formulation processes reported, three main classes are identified: the direct mixing route, the desalting transition pathway and the well-known layer by layer method. Finally, some latter developments, trends and applications of electrostatic assemblies in materials science and nanomedicine are highlighted.     

Chemical reactions on rutile TiO2(110)

Understanding the surface chemistry of TiO2 is key to the development and optimisation of many technologies, such as solar power, catalysis, gas sensing, medical implantation, and corrosion protection. In order to address this, considerable research effort has been directed at model single crystal surfaces of TiO2. Particular attention has been given to the rutile TiO2(110) surface because it is the most stable face of TiO2. In this critical review, we discuss the chemical reactivity of TiO2(110), focusing in detail on four molecules/classes of molecules. The selected molecules are water, oxygen, carboxylic acids, and alcohols-all of which have importance not only to industry but also in nature (173 references).     

Microfaceting explains complicated structures on rutile TiO2 surfaces

Surface structures on rutile TiO2 (001) have been studied by using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional calculations. Prior investigations have observed many kinds of complicated surface structures; however, detailed atomic structures and the mechanism of the reconstructions are still unknown. We evaluate the energetical stability of the surface structures. The calculational results suggest that a [111] microfaceting model is energetically stable compared with the unreconstructed (1 x 1) model. We propose microfaceting structural models that are in good agreement with atomically resolved STM images. This structural concept can be extended to other rutile TiO2 surfaces in general.     

Synthesis of oriented arrays of TiO2 nanorods via a high temperature conversion of carbon nanotubes

Oriented arrays of both rutile and anatase nanorods have been synthesised in a two-stage process, employing multi-walled carbon nanotubes as the initial structural template.     

Photocatalytic synthesis of silver nanoparticles stabilized by TiO2 nanorods: a semiconductor/metal nanocomposite in homogeneous nonpolar solution

A novel colloidal approach toward semiconductor/metal nanocomposites is presented. Organic-soluble anatase TiO(2) nanorods are used for the first time to stabilize Ag nanoparticles in optically clear nonpolar solutions in the absence of specific ligands for silver. Metallic silver is generated upon UV illumination of deaerated TiO(2) solutions containing AgNO(3). The Ag nanoparticles can be obtained in different size-morphological regimes as a function of the irradiation time, due to light-induced photofragmentation and ripening processes. A mechanism for the colloidal stabilization of the silver nanoparticles is tentatively suggested, which regards the TiO(2) nanorods as inorganic stabilizers, thus acting in the same manner as conventional surfactant molecules. The proposed photocatalytic approach offers a convenient method for producing TiO(2)/Ag nanocomposite systems with a certain control over the metal particle size without the use of surfactants and/or additives. Stable colloidal TiO(2)-nanorod-stabilized Ag nanoparticles can be potentially available for a number of applications that require "clean" metal surfaces, such as homogeneous organic catalysis, photocatalysis, and sensing devices.     

Drying and nondrying layer-by-layer assembly for the fabrication of sodium silicate/TiO2 nanoparticle composite films

Influences of drying and nondrying steps on structures of layer-by-layer (LbL) assembled sodium silicate/TiO(2) nanoparticles films (donated as silicate/TiO(2) films) have been systematically investigated. The nondrying LbL assembly produces highly porous silicate/TiO(2) films with large thickness. In contrast, the silicate/TiO(2) films fabricated with a drying step after each layer deposition are flat and thin without porous structures. In situ atomic force microscopy (AFM) measurements confirm that the sodium silicate and TiO(2) nanoparticles are deposited in their aggregated forms. A N(2) drying step can disintegrate the aggregated silicate and TiO(2) nanoparticles to produce thin silicate/TiO(2) films with compact structures. Without the drying steps, the aggregated silicate and TiO(2) nanoparticles are well retained, and their LbL assembly produces highly porous silicate/TiO(2) films of large thickness. The highly porous silicate/TiO(2) films are demonstrated to be useful as reusable film adsorbents for dye removal from wastewater because they can adsorb a large amount of cationic organic dyes and decompose them under UV irradiation. The present study is meaningful for exploring drying/nondrying steps for tailoring structure and functions of LbL assembled films.     

Adsorption of organic molecules on rutile TiO2 and anatase TiO2 single crystal surfaces

The interaction of organic molecules with titanium dioxide surfaces has been the subject of many studies over the last few decades. Numerous surface science techniques have been utilised to understand the often complex nature of these systems. The reasons for studying these systems are hugely diverse given that titanium dioxide has many technological and medical applications. Although surface science experiments investigating the adsorption of organic molecules on titanium dioxide surfaces is not a new area of research, the field continues to change and evolve as new potential applications are discovered and new techniques to study the systems are developed. This tutorial review aims to update previous reviews on the subject. It describes experimental and theoretical work on the adsorption of carboxylic acids, dye molecules, amino acids, alcohols, catechols and nitrogen containing compounds on single crystal TiO(2) surfaces.     

Ethanol photo-oxidation on a rutile TiO2(110) single crystal surface

The reaction of ethanol has been studied on the surface of rutile TiO(2)(110) by Temperature Programmed Desorption (TPD), online mass spectrometry under UV excitation and photoelectron spectroscopy while the adsorption energies of the molecular and dissociative modes of ethanol were computed using the DFT/GGA method. The most stable configuration is the dissociative adsorption in line with experimental results at room temperature. At 0.5 ML coverage the adsorption energy was found equal to 80 kJ mol(-1) for the dissociative mode (ethoxide, CH(3)CH(2)O(a) + H(a)) followed by the molecular mode (67 kJ mol(-1)). The orientation of the ethoxides along the [001] or [110] direction had minor effect on the adsorption energy although affected differently the Ti and O surface atomic positions. TPD after ethanol adsorption at 300 K indicated two main reactions: dehydration to ethylene and dehydrogenation to acetaldehyde. Pre-dosing the surface with ethanol at 300 K followed by exposure to UV resulted in the formation of acetaldehyde and hydrogen. The amount of acetaldehyde could be directly linked to the presence of gas phase O(2) in the vacuum chamber. The order of this photo-catalytic reaction with respect to O(2) was found to be 0.5. Part of acetaldehyde further reacted with O(2) under UV excitation to give surface acetate species. Because the rate of photo-oxidation of acetates (acetic acid) was slower than that of ethoxides (ethanol), the surface ended up by being covered with large amounts of acetates. A reaction mechanism for acetaldehyde, hydrogen and acetate formation under UV excitation is proposed.     

Transport and retention of TiO2 rutile nanoparticles in saturated porous media under low-ionic-strength conditions: measurements and mechanisms

The mechanisms governing the transport and retention kinetics of titanium dioxide (TiO(2), rutile) nanoparticle (NP) aggregates were investigated in saturated porous media. Experiments were carried out under a range of well-controlled ionic strength (from DI water up to 1 mM) and ion valence (NaCl vs CaCl(2)) comparable to the low end of environmentally relevant solution chemistry conditions. Solution chemistry was found to have a marked effect on the electrokinetic properties of NP aggregates and the sand and on the resulting extent of NP aggregate transport and retention in the porous media. Comparable transport and retention patterns were observed for NP aggregates in both NaCl and CaCl(2) solutions but at much lower ionic strength with CaCl(2). Transport experimental results showed temporal and spatial variations of NP aggregate deposition in the column. Specifically, the breakthrough curves displayed a transition from blocking to ripening shapes, and the NP retention profiles exhibited a shift of the maximum NP retention segment from the end toward the entrance of the column gradually with increasing ionic strength. Additionally, the deposition rates of the NP aggregates in both KCl and CaCl(2) solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Upon close examination of the results, it was found that the characteristics of the obtained transport breakthrough curves closely followed the general trends predicted by the DLVO interaction-energy calculations. However, the obtained NP retention profiles were found to deviate severely from the theory. We propose that a NP aggregate reconformation through collision between NP aggregates and sand grains reduced the repulsive interaction energies of NP-NP and NP-sand surfaces, consequently accelerating NP deposition with transport distance and facilitating approaching NP deposition onto NPs that had already been deposited. It is further suggested that TiO(2) NP transport and retention are determined by the combined influence of NP aggregate reconformation associated with solution chemistry, travel distance, and DLVO interactions of the system.     

Dispersion and Structure Studies of Molybdenum Oxide on Anatase TiO2

X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) were used to characterize the structure of the mixture of molybdenum oxide and anatase calcined at 723 K. The resuits indicate that molybdenum oxide can disperse onto the surface of anatase (TiO2) and the dispersion threshold is 11.2 mg in per gram of MoO3 or 4.8 Mo atoms/nm^2 TiO2. When the coment of MoO3 is below the dispersion threshold, MoO3 species is in highly dispersed state interacting strongly with TiO2 support and in discrete tetrahedral coordination. [MoO4], on the surface of TiO2. When the MoO3 loading is above this value, MoO3 exists in both dispersed phase and crystalline phase. MoO3 in dispersed phase is still a discrete [MoO4] tetrahedron; MoO3 in crystal phase is in octahedral coordination.