Prepare Anatase TiO2 Research Articles

Oxygen defect modulating the charge behavior in titanium dioxide for boosting photocatalytic nitrogen fixation performance

Extremely high-temperature and high-pressure requirement of Haber-Bosch process motivates the search for a sustainable ammonia synthesis approach under mild conditions. Photocatalytic technology is a potential solution to convert N2 to ammonia. However, the poor light absorption and low charge carrier separation efficiency in conventional semiconductors are bottlenecks for the application of this technology. Herein, a facile synthesis of anatase TiO2 nanosheets with an abundance of surface oxygen vacancies (TiO2-OV) via the calcination treatment was reported. Photocatalytic experiments of the prepared anatase TiO2 samples showed that TiO2-OV nanosheets exhibited remarkably increased ammonia yield for solar-driven N2 fixation in pure water, without adding any sacrificial agents. EPR, XPS, XRD, UV-Vis DRS, TEM, Raman, and PL techniques were employed to systematically explore the possible enhanced mechanism. Studies revealed that the introduced surface oxygen vacancies significantly extended the light absorption capability in the visible region, decreased the adsorption and activation barriers of inert N2, and improved the separation and transfer efficiency of the photogenerated electron-hole pairs. Thus, a high rate of ammonia evolution in TiO2-OV was realized. This work offers a promising and sustainable approach for the efficient artificial photosynthesis of ammonia.

Charge reaction kinetics on TiO2 nanotubes under photoelectrochemical water oxidation condition

Artificial photosynthesis relies on the photoreactions between the chemical molecules and photogenerated charges. The oxygen evolution reactions are regarded as the most difficult procedure, because they are multiple-step reactions with multiple charges transfer. Notwithstanding the extensive study on photoelectrochemical and photochemical water oxidation, understanding how the surface charge reacts with the chemical molecules is limited, especially the reaction kinetics of the surface charges. We prepared anatase TiO2 nanotubes array and dense polycrystalline TiO2 films on Ti substrates, where the photocurrent increased about 4–4.5 times on nanotubes compared with the dense films. Moreover, the surface charge reaction rate and the accumulated charge densities were analyzed by transient surface photovoltage and transient photocurrent techniques. It was found a 2nd-order charge reaction behavior could be found when the charge density was high, differently, a 1st-order charge reaction could be observed when the charge density was low. The nanotubes structures would in situ grow from the Ti substrates, which simultaneously enhanced charge separation and transfer kinetics to improve the PEC performance.

Preparation and Photocatalytic Properties of Anatase TiO2 with Hollow Hexagonal Frame Structure

Titanium dioxide (TiO2) has been widely used to solve energy and environmental pollution problems due to its excellent properties. In this study, the precursor (HTiOF3) with a spherical structure composed of hexagonal prisms was prepared via a simple solvothermal method using tetrabutyl titanate, hydrofluoric acid, glacial acetic acid and isopropanol as raw materials. Then, the calcination time and temperature of the precursor were controlled to prepare anatase TiO2 with different morphologies, and the photocatalytic performance of the prepared catalysts was studied. When the precursor was calcined at 600 °C for 7 h, the prepared TiO2 had a unique hexagonal framework structure and exhibited excellent photocatalytic performance. The degradation rate of the RhB solution was 98.58% at 40 min and the rate of hydrogen evolution was 2508.12 μmol g−1 h−1.

A simple route to prepare anatase TiO2 films with dominant (001) facet

TiO2 films were deposited by DC pulsed magnetron sputtering. XRD results showed that all annealed TiO2 films belonged to the single-phase anatase structure. There were different degrees of dominant anatase (001) facet in annealed TiO2 films. Based on various results, it could be found that an auxiliary cooling treatment provided to the substrate during film deposition, would make annealed TiO2 films (that do not have the dominant) have dominant anatase (001) facet. TEM was measured to analyze the structure change of TiO2 films. The formation mechanism of dominant anatase (001) facet was investigated systematically.

Preparation of Anatase Titanium Dioxide Nanoparticle Powders Submitting Reactive Oxygen Species (ROS) under Dark Conditions

Recently, under the circumstances of pandemic of COVID-19 much attention has been paid to titanium dioxide TiO2 as bactericidal agent; however, conventional TiO2 requires ultraviolet radiation or visible light to exercise its photocatalytic properties and its induced antimicrobial activity. In order to expand its applications directed at wide civil life, antibacterial TiO2 being usable under dark conditions has been demanded. The present paper describes the powder characterization of newly developed potassium K and phosphorous P co-doped nanometer-size anatase TiO2 powders using X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM & TEM), Brunauer-Emmett-Teller method (BET), fourier-transform infrared spectroscopy (FT-IR), X-ray absorption fine structure (XAFS), electron spin resonance (ESR) and chemiluminescence (CL). It was found for the first time that thus prepared anatase TiO2 could submit much reactive oxygen species (ROS) even in the dark, which has close relation with bactericidal activity in light interception.

Synthesis and characterization of TiO2-based nanostructures via fluorine-free solvothermal method for enhancing visible light photocatalytic activity: Experimental and theoretical approach

Surface-fluorinated anatase TiO2 nanosheets have been widely prepared using hydrofluoric acid (HF) as morphology controlling agent with several titanium alkoxides. However, hazardous and other scientific problems associated with HF are major obstacles towards its global commercialization. Therefore, this study introduces a facile, green and fluorine-free solvothermal synthetic approach to prepare anatase TiO2 nanosheets (TNSs), involving commercial TiO2 nanoparticles as titanium source and N, N dimethylformamide (DMF) as morphology controlling agent under alkaline environment. A Box-Behnken-Design 3-level experimental design was applied to optimize the major key synthesis parameters for tuneable TNSs performance by manipulating the reaction temperature (120−180 °C), reaction time (3−48 hr) and dose of DMF (5−40 mL). The proposed model was verified through the analysis of variance and performing experiments at predicated optimal conditions (temperature =165.35 °C, time = 25.50 h and DMF dose =22.50 mL). The quadratic model was found to be best-fitted with the maximum correlation coefficients (R2 = 0.989 and adjusted R2 = 0.975) between predicted and actual results. The crystal growth mechanism of TNSs was also proposed. The formation of tetragonal TNSs (10 nm) containing the highest surface area with least bandgap upto 2.62 eV, confirmed through XRD, TEM, BET, DRS, FTIR and XPS measurements. The excellent photocatalytic performance was exhibited by as-developed TNSs for phenol degradation upto 95.33 % under visible-light. The photoactivity of TNSs was found to be strongly associated with synthesis parameters including hydrothermal temperature, reaction time and DMF dose. The phenol degradation data was well explained via pseudo-first-order kinetics and Langmuir isotherm models. Thermodynamic parameters were suggested the nature of phenol degradation process. This enhanced degradation activity of TNSs was attributed to the well-defined morphology, larger surface area, improved energy harvesting aptitude and abated recombination rate of photogenerated electron hole-pairs resulting an enhancement in the photogenerated charge carrier.

A simple and novel synthetic route to prepare anatase TiO2 nanopowders from natural ilmenite via the H3PO4/NH3 process

A simple and novel technique for the preparation of anatase TiO2 nanopowders using natural ilmenite (FeTiO3) as the starting material is reported. Digesting ilmenite with concentrated H3PO4 under refluxing conditions yields a white α-titanium bismonohydrogen orthophosphate monohydrate (TOP), Ti(HPO4)2·H2O, which can be easily isolated via gravity separation from unreacted ilmenite. The addition of ammonia to the separated TOP followed by calcination at 500°C completes the preparation of anatase TiO2. Calcination at temperatures above 800°C converts the anatase form of TiO2 to the stable rutile phase. The removal of iron from ilmenite during the commercial production of synthetic TiO2 is problematic and environmentally unfriendly. In the present study, the removal of iron was found to be markedly simple due to the high solubility of iron phosphate species in concentrated H3PO4 with the precipitation of TOP. The titanium content of the prepared samples on metal basis with silica and phosphorous as major impurities was over 90%. Prepared TiO2 samples were characterized using X-ray fluorescence, Fourier-transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction analyses. The photocatalytic potentials of the commercial and as-prepared TiO2 samples were assessed by the photodegradation of rhodamine B dye.

Preparation and Characterization of Photoactive Anatase TiO2 from Algae Bloomed Surface Water

The purpose of the study was to effectively treat algae bloomed water while using a Ti-based coagulant (TiCl4) and recover photoactive novel anatase TiO2 from the flocculated sludge. Conventional jar tests were conducted in order to evaluate the coagulation efficiency, and TiCl4 was found superior compared to commercially available poly aluminum chloride (PAC). At a dose of 0.3 g Ti/L, the removal rate of turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were measured as 99.8%, 66.7%, and 96.9%, respectively. Besides, TiO2 nanoparticles (NPs) were recovered from the flocculated sludge and scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and X-ray diffraction (XRD) analysis confirmed the presence of only anatase phase. The recovered TiO2 was found to be effective in removing gaseous CH3CHO and NOx under UV-A lamp at a light intensity of 10 W/m2. Additionally, the TiO2 mixed mortar blocks that were prepared in this study successfully removed atmospheric nitrogen oxide (NOx) under UV irradiance. This study is one of the first to prepare anatase TiO2 from flocculated algal sludge and it showed promising results. Further research on this novel TiO2 concerning internal chemical bonds and shift in the absorbance spectrum could explore several practical implications.

A simple route to prepare anatase TiO2 film onto polyimide substrate by DC pulsed magnetron sputtering

TiO2 film was deposited onto polyimide substrate by DC pulsed magnetron sputtering with different sputtering power densities. XRD results showed that with increasing the sputtering power density from 0.83 W/cm2 to 5.00 W/cm2, the crystallinity of as-deposited TiO2 film improved monotonously. And 5.00 W/cm2 was determined as the critical sputtering power density in which the highest temperature the substrate could withstand. Then, XRD and TEM results showed that the as-deposited TiO2 film could have a better anatase structure by providing an auxiliary heating to the substrate at the highest temperature during TiO2 film deposition. Combining the sputtering parameters, as well as DC pulsed voltage waveform, the reason for as-deposited TiO2 film crystallization was investigated systematically.

Template-sacrificial conversion of MnCO3 microspheres to fabricate Mn-doped TiO2 visible light photocatalysts

This study demonstrates a one-step hydrothermal approach to prepare novel spherical microstructures of Mn-doped TiO2 by the in situ template-sacrificial conversion of MnCO3 microspheres grown in a radial direction. After a hydrothermal reaction, MnCO3 microspheres were completely dissolved by HF as a hydrolysis product of [NH4]2TiF6. Furthermore, the hollow and radially porous structures of Mn-doped TiO2 microspheres were obtained without and with stirring during hydrothermal reaction, respectively. The prepared anatase TiO2 microspheres were fully characterized in terms of particle size, morphology, chemical composition, and porosity by X-ray diffraction, scanning and transmission electron microscopies, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller method, respectively. The photocatalytic activity of the prepared TiO2 microspheres was evaluated by the degradation of methylene blue under UV and visible light irradiations. Our versatile approach can be used for different types of metal carbonates to fabricate morphology controllable metal oxide nano- and microstructures.

Comparative study on the pressure-induced phase transformation of anatase TiO2 hollow and solid microspheres

Nanostructured anatase TiO2 undergoes pressure-induced phase transformation, and the transformation sequence is significantly different from the bulk counterpart. The size and the morphology are found both playing a critical role in the phase transformation behavior. In this work, we prepare anatase TiO2 microspheres using a hydrothermal method. By controlling the reaction time, hollow and solid spheres of similar diameters are prepared. TEM and XRD analysis reveals that these microspheres are aggregates of anatase nanocrystalline of size between 15–16 nm. The phase transformation behaviour under high temperature is examined in situ using both Raman spectroscopy and synchrotron x-ray diffraction. We find that although both solid and hollow spheres are micron-sized, they undergo phase transformation sequence similar to nanomaterials with size of several tens of nanometers. Hollow spheres exhibit a higher compressibility than the solid spheres. A detailed analysis based on the formation mechanism of the spheres is performed to explain the unique phase transformation behavior of these materials.

TiO2 Nanotubes Transformation Into 4nm Anatase Nanoparticles

The scope of this work shows novel experimental findings on preparing anatase TiO2 nanoparticles, first anodizing titanium into an organic media for obtaining TiO2 nanotubes, and using these as a photocatalytic active electrode in treating water polluted with organic contaminants. The substrates were grit blasted to obtain mechanical fixation of the generated nanotubular TiO2 structure. This was successfully achieved without diminishment of the nanotubes order and with a self-leveling of the outer surface. A new phenomenon has been investigated consisting of the process of oxidation of the nanotubes in water after anodizing. Along this process, methyl orange added to the aqueous solution was discolored as part of the redox reaction involved. The final state of the modified layer was composed of conglomerates of almost completely crystalline TiO2 nanoparticles, around 4 nm in size, consisting of anatase. SEM and TEM images show the transition of the amorphous nanotubes (atomic disorder/nanometric order) to crystalline disordered particles (atomic order/nanometric disorder).

Controlling Self-Assembly of Cellulose Nanocrystal to Synergistically Regulate (001) Reactive Facets and Hierarchical Pore Structure of Anatase Nano-TiO2 for High Photocatalytic Activity

As one of the most efficient and environmentally benign strategies to treat organic dye pollution, TiO2 photocatalytic technology has attracted increasing and wide interests in environmental governance, for which dominantly exposed (001) facets and high porosity are of great importance for catalytic performance. To date, however, how to synergistically regulate the dominant growth of (001) facets and the formation of hierarchical pore structures still remains challenging. Here, we report a limited growth strategy mediated by the self-assembly of cellulose nanocrystal (CNC) to prepare anatase TiO2 nanocatalyst with dominantly exposed (001) reactive facets. Notably, crystal growth in the confined space of layered CNC structures favors exposing (001) facets, and the easy removal of the soft biotemplate facilitates creating hierarchical pores. Furthermore, the (001) facet percentage, pore size, and porosity can be easily modulated by controlling the CNC concentration. After introducing an up-conversion quantu...

Effect of Lithiation Voltage Limit on the Electrochemical Performance of High Surface Area Anatase TiO2 Nanoparticles and Its Application in Full‐Cell Li–Ion Battery

AbstractTitania based anodes have received considerable interest due to its cycling stability and improved safety. Here, we report the electrochemical performance of high surface area anatase TiO2 nanoparticles synthesized via solvothermal technique. Prepared anatase TiO2 nanoparticles were below 15 nm in average particle size exhibiting high surface area of 251 m2/g and titanium existing in 4+ oxidation state. The electrodes studied by limiting the discharge voltage between 1.0 V and 0.01 V showed significant performance differences. Especially, specific capacity, Coulombic efficiency and storage mechanism of TiO2 depends strongly on lithiation voltage cut‐off limit that is discussed in detail. It was established that discharging to 1.0 V showed better performance hence, subsequent studies the lithiation (discharge) was limited to 1.0 V. High rate capability of the electrodes were tested test up to 60 C and long cycle stability up to 1000 cycles (at 10 C rate). As an energy storage solution, a 2.0 V full‐cell Li‐ion battery was fabricated with the TiO2 nanoparticles as anode against surface modified LiCoO2 as cathode. The full‐cell delivered specific capacities about 165 mAh/g and 105 mAh/g at current densities of 150 mA/g and 3765 mA/g respectively. It also exhibited 126 mAh/g capacity and 85% retention at the end of 100 cycles at a current density of 1000 mA/g. The full‐cell delivered a maximum power density of 5.5 kW/kg and a corresponding energy density of 185 Wh/kg.

Surface plasmon-driven photoelectrochemical water splitting of TiO2 nanowires decorated with Ag nanoparticles under visible light illumination

Here, we demonstrate that TiO2 nanowires (NWs) can be significantly driven by visible light through the decoration with Ag nanoparticles (NPs) (Ag-decorated TiO2 NWs). The Ag-decorated TiO2 NWs show remarkably photoelectrochemical (PEC) water splitting performance under illumination with λ>420 visible light due to surface plasmon resonance (SPR) of Ag NPs. In this work, low power of the used light source (100mW/cm2) was not capable of heating the Ag-decorated TiO2 nanowire photoanode enough to directly split water. In addition, under irradiation with λ>420nm visible light, no photocurrent was produced by TiO2 nanowire photoanode indicates that electron transitions between valence band and conduction band do not take place in prepared anatase TiO2 NWs. Meanwhile, the SPR energy (2.95–2.13eV <3.2eV) is insufficient to excite TiO2 NWs to generate electro-hole pairs through SPR-enhanced electromagnetic fields. Thus the remarkably visible-light-responsive PEC water splitting activity of Ag-decorated TiO2 NWs is not attributed to local heating caused by SPR-mediated photothermal process, large enhancement of electromagnetic fields induced by SPR and scattering of resonant photons. We propose that the visible light PEC water splitting performance of Ag-decorated TiO2 NWs is attributed to electron transfer from Ag NPs to the conduction band of TiO2 NWs mediated by SPR. In addition, a Schottky barrier established at the interface of Ag NPs and TiO2 NWs prevents these transferred electrons from returning to the Ag NPs and significantly retarded the recombination of electron-hole pairs in the Ag NPs, also contributing to visible-light-driven PEC water splitting performance. So the remarkably visible-light-driven PEC water splitting performance of Ag-decorated TiO2 NWs is attributed to the synergistic effects of electron transfer mediated by SPR and the Schottky barrier between Ag NPs and TiO2 NWs. The achieved Ag-decorated TiO2 NWs can be added to these previously prepared TiO2 photocatalysts mainly driven by SPR of Au NPs for the development of new visible light photocatalysts.

Fluoride-assisted synthesis of anatase TiO2 nanocrystals with tunable shape and band gap via a solvothermal approach

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO2 nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5mmol, and the optical band gap decreased from 3.47eV to 3.29eV accordingly. However, when the fluoride was changed to NH4F, the resultant TiO2 nanocrystals possessed an anatase phase but were made up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO2 nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH4F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.

A one-step thermal decomposition method to prepare anatase TiO2 nanosheets with improved adsorption capacities and enhanced photocatalytic activities

Anatase TiO2 nanosheets (NSs) with high surface area have been prepared via a one-step thermal decomposition of titanium tetraisopropoxide (TTIP) in oleylamine (OM), and their adsorption capacities and photocatalytic activities are investigated by using methylene blue (MB) and methyl orange (MO) as model pollutants. During the synthesis procedure, only one type of surfactant, oleylamine (OM), is used as capping agents and no other solvents are added. Structure and properties of the TiO2 NSs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption analysis, UV–vis spectrum, X-ray photoelectron spectroscopy (XPS) and Photoluminescence (PL) methods. The results indicate that the TiO2 NSs possess high surface area up to 378m2g−1. The concentration of capping agents is found to be a key factor controlling the morphology and crystalline structure of the product. Adsorption and photodegradation experiments reveal that the prepared TiO2 NSs possess high adsorption capacities of model pollutants MB and high photocatalytic activity, showing that TiO2 NSs can be used as efficient pollutant adsorbents and photocatalytic degradation catalysts of MB in wastewater treatment.

Hydrofluoric Acid Controlled TiO2 Phase Transformation from Rutile to Anatase at Room Temperature and Their Photocatalytic Performance.

In this study, we first present rutile TiO2 superstructures could be successfully transformed into anatase TiO2 nanoparticles at room temperature by adjusting the amount of hydrofluoric acid (HF) used in aqueous solution. Photocatalytic experiments demonstrated that the as prepared anatase TiO2 exhibited better photocatalytic performance than that of rutile TiO2. We further studied the photocatalytic degradation of RhB on different TiO2 via active species trapping experiments and confirmed that the presence of surface F- on TiO2 was beneficial for the formation of *OH, which was thought to be mainly responsible for the enhancement of photocatalytic performance.

Highly water-dispersible and easily recyclable anatase nanoparticles for photocatalysis

A simple, scalable sol–gel method was developed for preparing anatase TiO2 nanoparticles under mild conditions without the use of surfactants. The synthesized nanocrystals can be easily dispersed in acidic (pH <4) or alkaline (pH >8) aqueous solutions, and form a transparent hydrocolloid which remains stable for more than 1 year. However, the TiO2 nanoparticles could be precipitated from the stable hydrocolloid by adjusting the pH to 5–7, and the nanoparticles harvested by simple filtration. The synergistic effect of the steric hindrance of an ethoxy group on the nanoparticle surface and Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory force were used to explain the ease with which the nanoparticles redisperse in water, the high stability of the suspensions, and the reversible and controllable water dispersibility of TiO2 nanocrystals. Finally, the anatase nanoparticles were used as a recyclable photocatalyst to degrade Rhodamine B (Rh B) under 175W High-Pressure Mercury Lamp illumination. Freshly prepared TiO2 nanoparticles exhibited a high photodegradation efficiency of 99% and the nanocatalyst retained its 99% efficiency even after 10 degradation cycles.

A facile hydrothermal method for the controllable synthesis of TiO2 nanocrystals with tunable shapes

Using OA and OM as the capping surfactants, a facile and harmless hydrothermal method was invented to prepare anatase TiO2 nanocrystals with exposed {101} facets.