Synthesis of highly-active single-crystalline TiO2 nanorods and its application in environmental photocatalysis

Highly-active anatase TiO₂ nanorods have been successfully synthesized via a simple two-step method, hydrothermal treatment of anatase/rutile titanium dioxide nanoparticle powder in a composite-hydroxide eutectic system of 1:1 M KOH/NaOH, followed by acid post-treatment. The morphology and crystalline structure of the obtained nanorods were characterized using XRD, TEM, SEM/EDX and BET surface area analyzer. The obtained TiO₂ nanorods have a good crystallinity and a size distribution (about 4-16 nm); with the dimensions of 200-300 nm length and of 30-50 nm diameter. Compared with its precursor anatase/rutile TiO₂ nanoparticles and the titanate nanotubes, the pure anatase TiO₂ nanorods have a large specific surface area with a mesoporous structure. The photocatalytic performance of the prepared nanorods was tested in the degradation of the commercial Cibacrown Red (FN-R) textile dye, under UV irradiation. Single-crystalline anatase TiO₂ nanorods are more efficient for the dye removal.     

Hydrothermal synthesis, characterization, photocatalytic activity and dye-sensitized solar cell performance of mesoporous anatase TiO2 nanopowders

Mesoporous anatase TiO₂ nanopowder was synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), HRTEM, and Brunauer-Emmett-Teller (BET) surface area. The as-synthesized sample with narrow pore size distribution had average pore diameter about 3-4 nm. The specific BET surface area of the as-synthesized sample was about 193 m²/g. Mesoporous anatase TiO₂ nanopowders (prepared by this study) showed higher photocatalytic activity than the nanorods TiO₂, nanofibers TiO₂ mesoporous TiO₂, and commercial TiO₂ nanoparticles (P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using the mesoporous anatase TiO₂ was about 6.30% with the short-circuit current density (Jsc) of 13.28 mA/cm², the open-circuit voltage (Voc) of 0.702 V and the fill factor (ff) of 0.676; while η of the cell using P-25 reached 5.82% with Jsc of 12.74 mA/cm², Voc of 0.704 V and ff of 0.649.     

Preparation of highly ordered Fe-SBA-1 and Ti-SBA-1 cubic mesoporous silica via sol-gel processing of silatrane

Silatrane prepared from fumed silica and triethanolamine (TEA) was used as a precursor for the sol-gel synthesis of M-SBA-1 (M = Fe and Ti) at room temperature using cetyltrimethylammonium bromide as a template, and dilute solutions of ferric chloride and titanium glycolate as metal sources. Powder X-ray diffraction (XRD) showed the mesoporous materials to be well-ordered cubic structures, while N₂ adsorption/desorption measurements yielded high surface areas. Diffuse reflectance UV-visible spectroscopy demonstrated that iron (Fe³⁺) and titanium (Ti⁴⁺) were incorporated in the framework of the calcined materials to loadings of 6 wt.% Fe and 10 wt.% Ti without perturbing the ordered mesoporous structure.     

Gel–sol synthesis and aging effect on highly crystalline anatase nanopowder

Highly crystalline TiO₂ anatase nanoparticles were synthesized via gel–sol method by using titanium isopropoxide and triethanolamine. The products were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric/differential thermal analysis and nitrogen gas absorption methods. The particle size ranged from 7 to 24 nm having specific surface area of 64 to 220 m²/g. Selective Ti(OH)₄ gel specifications and hydrothermal test conditions resulted in thermodynamically-stable phase-formation. Aging at 130°C for 4 h resulted in particle size of 7 nm; while at 130 and 160°C for 12 h resulted in 12 and 21 nm, respectively.     

Tunable synthesis of mesoporous titania with different morphologies for dye-sensitized solar cells

Different TiO₂ mesoporous structures, including core-shell spheres (CCSs) and micro-tubes (MTs), are synthesized through adjusting the pH of the solution using TiOSO₄ as titanium source in a hydrothermal route. TiO₂ CSSs with an average diameter of 1.3–3.5 μm exhibit excellent light scattering property and high specific surface area (177.63 m² g^?1). TiO₂ MTs show ultrahigh specific surface area of 276.03 m² g^?1. Dye-sensitized solar cell is fabricated using TiO₂ CSSs as the light scattering layer and TiO₂ nanoparticles (NPs) layer as the bottom layer. The efficiency of Cell-NPs + CSSs is up to 9.24% due to the good light scattering effect and excellent dye loading capacity. Furthermore, TiO₂ MTs are introduced to form the NPs/MTs bottom layer. The Cell-NPs/MTs + CSSs achieves an outstanding efficiency of 9.60% due to the further optimized electron transport path.     

Controlled growth of TiO2 nanorods capped with carboxylate groups by the solvothermal process

A solvothermal method is described for preparing nanomaterials of titanium dioxide (TiO₂) while controlling the growth of rod-shaped nanomaterials. Titanium (IV) isopropoxide (TTIP) and butyl ether were chosen as the precursor and solvent, respectively. Oleic acid and decanoic acid were used as the surfactant. TiO₂ nanospherical particles and nano-rods were synthesized in mass quantities by adjusting the kind of surfactant, the concentration of the precursor, and the solvothermal reaction temperature. The synthesized TiO₂ nanospherical particles and nanorods were uniform and transparent in the toluene. The TiO₂ nanospherical particles were about 3.5 nm in size. The TiO₂ nanospherical particles and nanorods were of a highly crystalline anatase structure. The direction of growth of the TiO₂ nanorods was [001] and the band gap energy of the TiO₂ nanorods, evaluated by optical absorption, was 3.34 eV.     

Anatase nanotubes synthesized by a template method and their application as a green photocatalyst

Anatase nanotubes were synthesized by a template method from four different titanium precursors. Anodized aluminium oxide membranes with a 200-nm pore diameter were used as templates. The resulting nanostructures were characterized by electron microscopies, Raman spectroscopy, X-ray diffraction and nitrogen adsorption. Their photoactivities towards methylene blue dye decomposition were measured and compared with commercial anatase powder (Aldrich, >99%, −325 mesh). Anatase nanotubes obtained from Ti isopropoxide exhibited the longest hollow tubular structures with less amorphous material and the highest surface area, 56 m² g⁻¹. Despite TiO₂ nanotubes showing lower photocatalytic activity than commercial anatase, the possibility of their recovery through several cycles and the feasibility of their utilization in continuous cycling processing make them potential materials of interest in green chemistry     

Surface properties and epoxidation catalytic activity of Ti-SBA15 prepared by direct synthesis

The influence of hydrothermal treatment time on the physicochemical properties and the catalytic activity in cyclohexene epoxidation of titanium-substituted SBA15 silicas prepared by direct one-step synthesis was systematically studied using a combination of N₂ physisorption at −196 °C, X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance UV–Vis, and elemental analysis. The other synthesis parameters were chosen to illustrate the different chemical environments of the titanium species formed before, during, and after the precipitation of anatase TiO₂. At the beginning of hydrothermal treatment, results showed that the titanium species are homogeneously dispersed in the silica framework. When anatase TiO₂ clusters precipitate, they do so mainly on the external surface of the mesoporous material. At higher hydrothermal treatment times, the material showed a decreased catalytic activity even if essentially no variation in their specific surface area was then observed. This lower activity was shown to be due to a partial coverage of active tetrahedral Ti species by extraframework higher coordination TiO₂ deposit.     

Hydrothermal synthesis of 1D TiO2 nanostructures for dye sensitized solar cells

Mono-dimensional titanium oxide nanostructures (multi-walled nanotubes and nanorods) were synthesized by the hydrothermal method and applied to the construction of dye sensitized solar cells (DSCs). First, nanotubes (TiNTs) and nanotubes loaded with titanium oxide nanoparticles (TiNT/NPs) were synthesized with specific surface areas of 253 m²/g and 304 m²/g, respectively. After that, thermal treatment of the nanotubes at 500 °C resulted in their transformation into the corresponding anatase nanorods (TiNT-Δ and TiNT/NPs-Δ samples). X-ray diffraction and Raman spectroscopy data indicated that titanium oxide in the pristine TiNT and TiNT/NP samples was converted into anatase phase TiO₂ during the heating. Additionally, specific surface areas and water adsorption capacities decreased after the heat treatment due to the sample agglomeration and the collapse of the inner nanotube channels. DSCs were fabricated with the nanotube TiNT and TiNT/NP samples and with the anatase nanorod TiNT-Δ and TiNT/NPs-Δ samples as well. The highest power conversion efficiency of η = 3.12% was obtained for the TiNT sample, despite its lower specific surface compared with the corresponding nanoparticle-loaded sample (TiNT/NP).     

PEG-directed hydrothermal synthesis of alumina nanorods with mesoporous structure via AACH nanorod precursors

Al₂O₃ nanorods with mesoporous structures are successfully synthesized from a hydrothermal and thermal decomposition process via the ammonium aluminum carbonate hydroxide (denoted as AACH) precursors. TEM images show that the average diameter of Al₂O₃ nanorods is about 60 nm, and the length is around 1–2 μm. The experimental results show that well-crystallized mesopores with hierarchically distributed pore sizes are embedded in the Al₂O₃ nanorods. The N₂ adsorption–desorption experiment indicates that the as-synthesized alumina nanorods have large surface area (ca. 176 m²/g) and narrow pore-size distributions. At the same time, the as-prepared Al₂O₃ nanorods exhibit strong photoluminescent properties at room temperature. A plausible surfactant-induced nanorod formation mechanism using the poly ethylene glycols as the template agent for the nanorod assembly is also proposed.     

Effect of photoelectrode morphology of single-crystalline anatase nanorods on the performance of dye-sensitized solar cells

TiO₂ terpineol-based pastes with nanorods (NRs) of over 25 μm thickness have been prepared for the photoactive electrodes of the dye-sensitized solar cells (DSSCs). The NRs, with a length of approximately 80 nm and an aspect ratio of about 3, are made by a two-step hydrothermal process. They have the single crystalline anatase structure and can be dispersed well in water and ethanol. With a high thermal stability and larger surface area (47.2 m² g^− 1) than commercial TiO₂ particles (P25, 39.1 m² g^− 1), the well-dispersed anatase NR films with aggregate-free morphology are transparent. For the photocurrent-voltage measurements, the NR cell exhibits high short-circuit photocurrent (J_SC) under 1 Sun AM 1.5 simulated sunlight due to the higher surface area and transmittance. The open-circuit voltage (V_OC) of NR films is not obviously reduced with incremental thickness, which results from the one-dimensional single crystalline structure of NR due to less surface defects. As compared with the P25 cell, DSSCs made with NRs have a higher fill factor (FF) because of the uniform void spaces. An enhancement of conversion efficiency from 4.88% for P25 to 5.67% for NR is achieved. The P25 particles are incorporated in NR films as light-scattering centers, while the R1P1 containing 50 wt.% of P25 has a high V_OC and FF as compared with P25, but the J_SC is still lower than that of the NR.     

Large-scale synthesis and characterization of fan-shaped rutile TiO2 nanostructures

Large-scale fan-shaped rutile TiO₂ nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl₄ as titanium source and chloroform/water as solvents. The physicochemical features of the fan-shaped TiO₂ nanostructures are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), nitrogen absorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy (UV-vis) and Fourier transform infrared spectroscopy (FTIR). Structural characterization indicates that the fan-shaped TiO₂ nanostructures are composed of several TiO₂ nanorods with diameters of about 5 nm and lengths of 300-350 nm. The average pore size and BET surface area of the fan-shaped TiO₂ nanostructures are 6.2 nm and 59 m²/g, respectively. Optical adsorption investigation shows that the fan-shaped TiO₂ nanostructures possess optical band gap energy of 3.11 eV.     

Synthesis of tapered TiO2 tubes by replication of ZnO

Micrometer-long tapered TiO₂ tubes have been successfully prepared by a vapor phase method, using tetrapodlike ZnO as template and tetrabutyl titanate (TBT) as titanium source. A very homogeneous TiO₂ coating layer was first prepared on tetrapodlike ZnO and the ZnO core was removed by hydrochloric acid solution. It was found that the obtained tubes were uniform and composed of anatase TiO₂ nanocrystallites. The wall thickness of the TiO₂ tubes varies from 20 to 60 nm by adjusting the amount of TBT. The BET surface area reaches 95 m² g^− 1. The combination of the tubular structure and special morphology may improve the mass transport and benefit to the recovery of the TiO₂ tubes photocatalyst from treated waste water.     

Synthesis and photocatalytic oxidation properties of titania hollow spheres

The hollow spheres of anatase TiO₂ with higher photocatalytic activity have been fabricated by spherical CaCO₃ nanoparticles as a template, and titanium sulfate (Ti(SO₄)₂) as a precursor, and the CaCO₃ templates were dissolved subsequently in dilute HNO₃ solution. The TiO₂ hollow spheres samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption-desorption isotherms. The characterization results indicate that as prepared TiO₂ hollow spheres sample was transformed to anatase phase in calcined at 400 °C, and the anatase TiO₂ hollow spheres have a higher specific surface area and show much better photocatalytic activity than commercial P25 in the photodegradation of Rhodamine B under the UV irradiation.     

Sol-gel synthesis of alumina,titania and mixed alumina/titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide

In this paper we report on the synthesis of alumina, titania and mixed alumina–titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide [Py_1,4]TFSA via sol-gel methods using aluminium isopropoxide and titanium isopropoxide as precursors. Our results show that the as-synthesized alumina is mainly mesoporous boehmite with an average pore diameter of 3.8 nm. The obtained boehmite is subject to a phase transformation into γ-Al₂O₃ and δ-Al₂O₃ after calcinations at 800 and 1,000 °C, respectively. The as-synthesized TiO₂ shows amorphous behaviour and calcination at 400 °C yields anatase which undergoes a further transformation to rutile at 800 °C. The as-prepared alumina–titania powders are amorphous and transformed to rutile and α-Al₂O₃ after calcination at 1,000 °C TiO₂. The obtained alumina–titania has a higher surface area than those of alumina or titania. The surface area of the as-synthesized alumina–titania was found to exceed 486 m² g⁻¹, whereas the surface areas of the as-synthesized boehmite and titania were around 100 m² g⁻¹, respectively.     

A detailed insight into the preparation of nanocrystalline TiO<Subscript>2</Subscript> powders in supercritical carbon dioxide

This work reports detailed investigations for the preparation of nanostructured titania powders by a solvent-free sol–gel-derived process, operated in supercritical CO₂ (SC-CO₂) at high pressures (10–30 MPa) and large range of temperatures (373–823 K). Depending on the processing temperature, the reaction between Ti(OiPr)₄ and water performed in a single supercritical phase led to the formation of either amorphous (Ti(OH)₄—titanium hydroxide) or crystalline (TiO₂—titanium dioxide) nanostructured particles. Crystalline (anatase) mesoporous powders with high specific surface area were obtained directly in CO₂ solvent under supercritical conditions at temperatures as low as 523 K. The effect of hydrodynamic key process parameters such as stirring and water injection rate on both powder morphology and aggregation degree was also investigated in details. The optimized TiO₂ anatase powders exhibited attractive photocatalytic activity, with high potential for the degradation of water pollutants.     

Preparation and photocatalytic activity of highly ordered mesoporous TiO2–SBA-15

TiO₂–SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO₂₀PO₇₀EO₂₀) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N₂ adsorption–desorption experiments. The resulting TiO₂–SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S_BET of 689 m² g^? 1 and 347 m² g^? 1 at different hydrothermal temperatures (100 °C and 130 °C). The photocatalytic activity of these TiO₂–SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO₂–SBA-15 mesoporous materials prepared at the TiO₂:SiO₂ mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO₂:SiO₂ mass ratio of 75:25.     

Synthesis and characterization of anatase and rutile TiO2 nanorods by template-assisted method

Well-aligned anatase and rutile TiO₂ nanorods and nanotubes with a diameter of about 80–130 nm have successfully been fabricated via sol-gel template method. The prepared samples were characterized by using thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The XRD results indicated that the TiO₂ nanorods were crystallized in the anatase and rutile phases, after annealing at 400–800 °C for different periods of time from 0.2 to 10 h.     

Preparation and characterization of high surface area nanosheet titania with mesoporous structure

High surface area nanosheet TiO₂ with mesoporous structure were synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50–100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO₂ had an average pore diameter about 3–4 nm. The BET surface area and pore volume of the sample are about 642 m²/g and 0.774 cm³/g, respectively.