Colloidal TiO2 Research Articles

Self-Assembled Superlattices from Colloidal TiO2 Nanorods

The self-assembly of anatase TiO2 nanorods into 1D (ribbon), 2D (smectic, domino, honeycomb) and 3D (lamellar) liquidcrystalline ordered superlattices is a process that depends on the collaboration between evaporation dynamics and directional interactions. Herein, the roles of entropic depletion attractions and energetic dipole-dipole couplings between TiO2 nanorods in self-assembly process are particularly emphasized. Excess oleic acid surfactants act as depletion agents to induce the inter-rod depletion effect, and the origin of electric dipole moment along the longitudinal axes of TiO2 rods is theoretically authenticated by applying the Accelrys Materials Studio as a new strategy combined with Taskers theory. These nanorod superlattices provided here may have great importance for tailoring new promising structures for photovoltaic application or exploring new inorganic liquid crystal materials. Keywords: Titanium oxide, self-assembly, nanorod superlattice, liquid-crystal order, depletion attraction, dipole-dipole coupling

Electron transfer dynamics from the singlet and triplet excited states of meso-tetrakis( p-carboxyphenyl)porphyrin into colloidal TiO 2 and AuTiO 2 nanoparticles

Electron transfer dynamics of meso-tetrakis( p-carboxyphenyl)porphyrin [TCPP] adsorbed on colloidal TiO 2 and AuTiO 2 nanoparticles have been investigated by time resolved absorption and fluorescence spectroscopy. Optical absorption studies reveal that the TCPP form complex with TiO 2 and AuTiO 2 nanoparticles. Excitation of TCPP adsorbed on the TiO 2 nanoparticle surface leads to electron injection on the conduction band of TiO 2. Electron injection has been confirmed by direct detection of cation radical of the adsorbed dye (TCPP +). The rate constant for the electron injection process is determined from both the singlet and triplet state respectively. The rate of electron injection for TCPP–AuTiO 2 is much faster than TCPP–TiO 2. The injected electrons are quickly transferred to Au and it escorts to ignore the back electron transfer (recombination) process.

Effect of the agglomeration of TiO 2 nanoparticles on their photocatalytic performance in the aqueous phase

TiO 2 nanoparticles have been widely explored as photocatalysts in the degradation of organic matters present in water. However, spontaneous agglomeration of TiO 2 nanoparticles in a suspension is a crucial issue that must be addressed before the photocatalyst can be used for water treatment. In the present work, the nature of the agglomeration of TiO 2 nanoparticles in aqueous suspension was investigated. Two approaches to minimize the agglomeration of colloidal TiO 2 particles were investigated. A careful control over the pH of the system was found to be an effective method for stabilizing colloidal TiO 2 particles and to significantly enhance the adsorption of orange II. As a result, the overall photocatalytic degradation rate was greatly accelerated. In addition to pH control, modification of TiO 2 particles using polyelectrolyte poly allylamine hydrochloride (PAH) was observed to be an effective approach for preventing colloidal TiO 2 particles from agglomeration.

Preparation, characterisation and sensing application of inkjet-printed nanostructured TiO 2 photoanode

Inkjet printing technique is proposed for the fabrication of titanium dioxide (TiO 2) photoanodes with a synthetic colloidal TiO 2 ink. The resultant electrodes were characterised using materials characterisation methods (such as scanning electron microscope, X-ray diffraction and UV–vis spectrophotometer) as well as photoelectrochemical means. The preliminary results indicate that the nanostructure of the original TiO 2 particles is well maintained in the printing process, and the thickness and uniformity of the TiO 2 thin film can be well controlled by the simple printing technique. Combined with photoelectrochemical means, the inkjet-printed TiO 2 photoanode is capable of oxidising organic compounds in aqueous solution, including weak organic adsorbates (e.g., glucose, phenol) and strong organic adsorbates (e.g., potassium hydrogen phthalate (KHP), glutaric acid, malonic acid) indiscriminately in bulk cell. This characteristic is utilized to determine chemical oxygen demand (COD) in aqueous samples. A linear range of 0–120 mg/L of O 2 and a detection limit of 1 mg/L of O 2 were achieved. The photoelectrochemical activity of the printed electrodes was found to be highly reproducible. Inkjet-printing technique can be a versatile method for mass production of TiO 2 photoanodes as sensors.

An analysis of current transients during electrophoretic deposition (EPD) from colloidal TiO 2 suspensions

This is a simple quantitative analysis of the electrical current transients recorded during the electrophoretic deposition (EPD) of TiO 2 particles from ethanol-based suspensions in which the linear correlation between the mass deposited and the charge passed was verified experimentally. Using this experimental knowledge as our starting point, we were able to test a simple electrical model of a deposition cell for its consistency with electrical current density data measured during EPD. Assuming that the background electrochemistry was controlled resistively rather than diffusively, we then tentatively exploited the electrochemical data to gain information on the structure of the deposit during its growth.

Directional enhancement of refractive index and tunable wettability of polymeric coatings due to preferential dispersion of colloidal TiO 2 nanorods towards their surface

We demonstrate the fabrication of nanocomposite coatings, of organic-capped colloidal TiO 2 nanorods dispersed into a poly(methyl methacrylate) matrix, with rising value of refractive index from the bottom to the top layers, and UV-induced surface wettability alteration, in a reversible manner. This behaviour is attributable to preferential dispersion of the TiO 2 nanoparticles towards the superficial layers of the coatings. Above a critical TiO 2 loading, the nanorods at the surface form aggregates deteriorating the optical and the surface properties of the nanocomposites. The optimal conditions for nanocomposite films preparation in terms of optimized nanorods dispersion, optical clarity, and surface smoothness are determined.

Preparation and performance of dye-sensitized solar cells based on ZnO-modified TiO2 electrodes

The ZnO-modified TiO2 electrode was prepared by adding Zn(CH3COO)2·2H2O to the TiO2 colloid during the sol-gel production process, and was used in dye-sensitized solar cells (DSCs). The open circuit voltage (V OC) and fill factor (ff) of the cells were improved significantly. The performances of the ZnO-modified TiO2 electrode such as dark current, transient photocurrent, impedance, absorption spectra, and flat band potential (V fb) were investigated. It is found that the interface charge recombination impedance increases and V fb shifts about 200 mV toward the cathodic potential. The effect mechanism of ZnO modification on the performance of DSCs may be that ZnO occupies the surface states of the TiO2 film.

Electrochemical immunoassay for human chorionic gonadotrophin based on Pt hollow nanospheres and silver/titanium dioxide nanocomposite matrix

AbstractBACKGROUND:A new electrochemical immunosensor for human chorionic gonadotropin (HCG) assay was developed based on Pt hollow nanospheres and silver/titanium dioxide nanocomposites. Silver nanoparticles were initially doped into TiO2and chitosan (Cs) colloids to form silver/titanium dioxide nanocomposites (AgTiO2Cs), which had good redox electrochemical activity and excellent film‐forming ability. Then, the free amino groups of chitosan were used to attach Pt hollow nanospheres for immobilization of human chorionic gonadotropin antibody (anti‐HCG) to construct an immunosensor.RESULTS:Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) confirmed consecutive growth of the multilayer films, and transmission electron microscopy (TEM) was used to describe the microstructure of nanoparticles. Optimal response of the immunosensor was obtained at pH 6.5 and 25 °C with an incubation time of 40 min. The immunosensor exhibited a linear range from 0.5 to 250 mIU mL−1HCG with a detection limit of 0.26 mIU mL−1at three times background noise. The selectivity, stability and repeatability of the immunosensor were satisfactory.CONCLUSION:The strategy showed low‐cost, high sensitivity, broad linear range and fast analytical time. It is expected that the immobilized technique and the detection methodology could be further developed for other proteins. Copyright © 2010 Society of Chemical Industry

Studies on the Photoinduced Interaction between Zn(II) Porphyrin and Colloidal TiO2

The interaction of Zn(II) porphyrin (ZnPP) with colloidal TiO2was studied by absorption and fluorescence spectroscopy. The fluorescence emission of ZnPP was quenched by colloidal TiO2upon excitation of its absorption band. The quenching rate constant (kq) is1.24×1011 M−1 s−1. These data indicate that there is an interaction between ZnPP and colloidal TiO2nanoparticle surface. The quenching mechanism is discussed on the basis of the quenching rate constant as well as the reduction potential of the colloidal TiO2. And the mechanism of electron transfer has been confirmed by the calculation of free energy change(ΔGet)by applying Rehm-Weller equation as well as energy level diagram.

Preconcentration of ultra-trace arsenic with nanometre-sized TiO2 colloid and determination by AFS with slurry sampling

This study describes a united method for the analysis of ultra-trace arsenic in environmental water samples by preconcentration of TiO2 colloid and determination of Atomic Fluorescence Spectrometry (AFS). When the pH values of solution are between 6.0 and 7.0, the adsorption for arsenic is above 98.0% with the dosage of nanometre-sized TiO2 colloid (0.2%) being 6.0 mL. Without desorbing the concentrated arsenic, the precipitated TiO2 is directly inverted to colloid after centrifugation. Arsenic is then determined by AFS with slurry sampling. This united method is simple, fast and sensitive. The detection limit (3σ) and the relative standard deviation (R.S.D) of this method are 10.6 ng L−1 and 7.04% (n = 6), respectively. When the method is applied to the determination of ultra-trace arsenic in environmental standard samples, the results are in good agreement with the standard values. And when it comes to environmental samples, satisfactory results are obtained.

Reversible wettability of hybrid organic/inorganic surfaces of systems upon light irradiation/storage cycles

In this work we present hybrid organic/inorganic structures that can exhibit reversible surface wettability, altered in a controllable manner. In particular, we use the method of photo-patterning to produce polymeric SU-8 pillars of specific geometries, onto which we subsequently deposit colloidal TiO2 nanorods. In this way, we combine the microroughness of the polymeric pillars with the nanoroughness of the nanorod-coating to create highly hydrophobic surfaces. The hydrophobicity of these systems can be changed reversibly into hydrophilicity upon irradiation of the hybrid structures with pulsed UV laser light. This behaviour is due to the well-known property of TiO2, that becomes superhydrophilic upon UV light irradiation. This

Synthesis of Cu-Doped TiO2 Nanorods with Various Aspect Ratios and Dopant Concentrations

Colloidal TiO2 nanorods were synthesized with different aspect ratios and successfully doped with copper via a controlled hydrolysis method. Inductively coupled plasma (ICP) atomic emission spectroscopy analyses showed that the as-prepared TiO2 nanorods contained ∼1.7−3.2 at% Cu. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analyses revealed that the doped nanorods are in a highly crystalline anatase structure and their crystal growth orientation is preferably [001]. The real doping of Ti lattices with Cu ions was evidenced by the analyses of surface compositions and chemical states of the nanorods using X-ray photoelectron spectroscopy (XPS). Through magnetic investigation using vibration sample magnetometry (VSM), it was verified that the Ti1−xCuxO2 nanorods maintain apparent ferromagnetic ordering at room temperature (300 K). The origin of the ferromagnetic property was explained based on the concentration of oxygen vacancies increased by Cu doping, which was also identified by the XPS analyses. The saturation magnetization showed strong dependency on the aspect ratio of nanorods as well as the Cu content in TiO2 nanorods.

Preparation of nano‐TiO2/polystyrene hybride microspheres and their antibacterial properties

AbstractThis study provided a facile method to prepare nano‐TiO2/polystyrene hybride microspheres in ethanol solution. The formation of titanium dioxide (TiO2) nanoparticles and hybrid microspheres were verified by FTIR, SEM, transmission electron microscopy, thermogravimetric analysis, and X‐ray powder diffraction. Monodispersed colloid TiO2 nanoparticles with small particle sizes were obtained, and the average particle size could be effectively controlled from about 10 nm. The antibacterial activity of the organic microspheres and hybride microspheres was also investigated against Escherichia coli. They were able to efficiently inhibit the growth and the multiplication of E. coli under the UV. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The synthesis of aqueous-dispersible anataseTiO2 nanoplatelets

Aqueous well-dispersed and phase-pure anataseTiO2 truncatedoctahedron nanoplatelets (NPLs) were prepared via controlled hydrolysis of titanium tetrachloride (TiCl4) in ethyleneglycol at 240 °C. Two shapes, square and hexagon, were observed by microscopy, exactly corresponding to thetruncated octahedron NPLs. Ethylene glycol was found to produce water in situ that reacts withTiCl4 to produceTiO2 and HCl—thelatter promoting TiO2 colloid peptization. TiO2 truncated octahedron NPLs are formed under the stabilizing action of ethyleneglycol thermolysis derivatives, such as aldehydes. Crystal growth of theTiO2 NPLs was affected by the reaction temperature that determines the waterproduction rate and HCl-assisted peptization. TGA and FT-IR results showed∼1.2% ethylene glycol thermolysis derivatives are attached to the surface of theTiO2 NPLs, which prevents their agglomeration, hence making them easilydispersible in aqueous media. HR-TEM and SAED results showed that theTiO2 NPLs are well crystallized and that the SAED patterns of the singleTiO2 NPL changes with its size and shape. XRD patterns showed that theTiO2 NPLs are phase-pure anatase and the percentage of the{101} planein the TiO2 NPLs to be only 18%—a structural feature that renders theTiO2 NPLs with enhanced UV absorption and reactivity properties.

A General Strategy to Prepare TiO(2)-core Gold-shell Nanoparticles as SERS-tags.

The synthesis and characterization of TiO(2)-based core-shell nanoparticles as surface-enhanced Raman Scattering (SERS) tags are reported. A hydrolysis approach is first used to generate colloidal TiO(2) nanoparticles, which are subsequently tagged with Raman probe molecules and encapsulated within a gold nanoshell. The resulting core-shell nanoparticles are characterized by using a number of techniques including UV-visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX) to confirm the successful coating of the Au shells. These core-shell nanoparticles exhibit very strong and reproducible SERS signals of the Raman probe molecules. Three different types of Raman probe molecules are used to prepare different SERS-active nanoparticles (SERS-tags), which demonstrates the versatility of the design. Such TiO(2)-based metal-coated core-shell nanoparticles will be useful as SERS-tags in biological assay and imaging applications. They may also provide a platform for fundamental studies in the ongoing investigations on the mechanisms of SERS.

Influence of TiO2/Perylene Interface Modifications on Electron Injection and Recombination Dynamics

It is well-known that the efficiency of dye sensitized solar cells can be improved by controlling the interface energetics using molecular interface modifiers. Whereas this leads to a beneficial band level shifting, it also affects the interfacial electron injection and recombination dynamics. Here we demonstrate a significant retardation of the injection process and a loss of ultrafast recombination components by coadsorbing inert gases and solvents with increasing dipole moments on a TiO2/perylene interface. Model perylene dyes with different electronic couplings to the colloidal TiO2 films were subject to precisely defined chemical environments, and the electron transfer dynamics was investigated with femtosecond transient absorption spectroscopy. The coadsorption of N2 and Ar doubled the injection times compared to the ultrafast sub-60 fs electron injection in vacuum. The introduction of solvents led to injection retardations by up to 2 orders of magnitude. This slow-down correlates well with the degr...

Functionalization of polyester fabrics with alginates and TiO 2 nanoparticles

This study was aimed to investigate the possibility of engineering the multifunctional textile nanocomposite material based on the polyester fabric modified with natural polysaccharide alginate and colloidal TiO 2 nanoparticles. The multifunctionality of such nanocomposite material was evaluated by analyzing its UV protection efficiency, antibacterial and photocatalytic activity. The level of UV protection was verified by the UV protection factor (UPF) of polyester fabrics. Antibacterial activity of modified polyester fabrics was tested against Gram-negative bacterium Escherichia coli. The photocatalytic activity of TiO 2 nanoparticles deposited on the polyester fabrics was followed by degradation of methylene blue as a model compound in aqueous solution. Modified polyester fabrics exhibited outstanding antibacterial activity and UV protection efficiency even after five washing cycles, indicating the excellent laundering durability. The total photodegradation of methylene blue was reached after 24 h of UV illumination and this ability was preserved and even enhanced after two consecutive cycles.

Preconcentration of ultra-trace copper in water samples with nanometer-size TiO2 colloid and determination by GFAAS with slurry sampling

A method is presented for the preconcentration of Cu(II) ions using a nanometer-sized TiO2 colloid, and for their determination in environmental water using graphite furnace atomic adsorption spectrometry (GFAAS) with slurry sampling. The adsorption efficiency is above 97% and is reached within short time at pH values between 5.5 and 6.0. Cu(II) was determined by GFAAS without elution. Conditions such as colloid dosage and effects of other ions were studied. The detection limit (3 σ) and the relative standard deviation are 290 ng L-1 and 9.8% (n = 6), respectively. This simple and rapid method was successfully applied to spiked environmental samples with recoveries ranging from 97% – 104%.

Kinetics of lead dioxide electrodeposition from nitrate solutions containing colloidal TiO 2

The influence of particles of colloidal titanium dioxide on lead dioxide electrodeposition from nitrate electrolytes was studied in the work. Addition of the nanostructured ТiO 2 particles to the electrolyte increases the rate of lead dioxide formation. This enhancement is ascribed to extra nucleation sites contributed by Ti–O radicals generated at the TiO 2 surface by OH species, in turn formed by discharge of water. A four stages kinetics scheme is proposed for description of the process of lead dioxide electrodeposition in presence of oxides of the valve metal in colloidal solutions. It is suggested that the presence of TiO 2 nanoparticles influences crystallization, charge transfer and diffusion stages.

Reversibly Light‐Switchable Wettability of Hybrid Organic/Inorganic Surfaces With Dual Micro‐/Nanoscale Roughness

AbstractHere, an approach to realize “smart” solid substrates that can convert their wetting behavior between extreme states under selective light irradiation conditions is described. Hybrid organic/inorganic surfaces are engineered by exploiting photolithographically tailored SU‐8 polymer patterns as templates for accommodating closely packed arrays of colloidal anatase TiO2 nanorods, which are able to respond to UV light by reversibly changing their surface chemistry. The TiO2‐covered SU‐8 substrates are characterized by a dual micro‐/nanoscale roughness, arising from the overlapping of surfactant‐capped inorganic nanorods onto micrometer‐sized polymer pillars. Such combined architectural and chemical surface design enables the achievement of UV‐driven reversible transitions from a highly hydrophobic to a highly hydrophilic condition, with excursions in water contact angle values larger than 100°. The influence of the geometric and compositional parameters of the hybrid surfaces on their wettability behavior is examined and discussed within the frame of the available theoretical models.