TiO2 Aerogel Research Articles

Microwave assisted synthesis of high surface area TiO2 aerogels: A competent photoanode material for quasi-solid dye-sensitized solar cells

TiO2 aerogels are 3-dimensional interconnected network structures offer high surface area, large pores and low density. In the present work, we synthesized TiO2 aerogels by a microwave assisted sol-gel method and employed it as a photo-anode material in quasi-solid dye-sensitized solar cells (QSDSSCs). This work mainly focuses on the effect of microwave irradiation on primary TiO2 nanoparticles, the building blocks of the aerogel network. The crystallite size determined from X-ray diffraction indicates that the crystal growth was controlled, as the particle-particle attraction prevailed by the thermal effect instigated during microwave irradiation. The smaller crystals enhanced the surface area of TiO2 aerogels and the amount of dye adsorption. The porous morphology and the interconnected network structure of aerogels were ascertained by Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopic (TEM) analysis. A maximum power conversion efficiency of 5.2% with a short-circuit current density of 15.18 mA/cm2 and an open circuit voltage of 0.62 V was realized by utilizing TiO2 aerogel as photoanode in QSDSSCs.

Sol–gel synthesis of highly TiO2 aerogel photocatalyst via high temperature supercritical drying

Nanocrystalline powders of TiO2 xerogel and aerogel were prepared by using acid-modified sol–gel approach. For TiO2 aerogel material (TA), the solvent was high temperature supercritically extracted at 300°C and 100bars. However, the TiO2 xerogel material (TX) was dried at 200°C and ambient pressure. The effects of the drying processes on the crystalline structure, phase transformation and grain growth were determined by Raman spectroscopy, SAED and X-ray diffraction (XRD) analyses using Rietveld refinement method. The TiO2 aerogel was composed of anatase crystalline structure. The TiO2 xerogel material was composed of anatase, brookite and small amount of amorphous phase with anatase as dominant phase. The TX sample still contains a relatively high concentration of carbon than that of TA, indicating the amorphous character of TiO2 xerogel. These materials were applied as catalyst for the degradation of indigo carmine in aqueous medium. Photo-degradation ability of TA and TX was compared to the TiO2 commercial Degussa P25. The photo-catalytic results showed that the degradation efficiency was in the order TA>P25>TX. The photo-degradation of indigo carmine followed pseudo first order reaction kinetics.

TiO2 aerogel–Cu-BTC metal-organic framework composites for enhanced photon absorption

Novel composites containing titania aerogel and Cu-BTC metal-organic framework (MOF) were synthesized via sol-gel route and characterized by various techniques. The concentration of MOF in composites was varied between 5 and 20weight% with respect to titania precursor. The presence of prominent peaks of Cu-BTC in the small-angle X-ray diffraction (SAXD) analysis confirmed the incorporation of MOF in the composite. This is further confirmed by Fourier Transform Infrared Spectral analysis (FTIR), energy-dispersive X-ray spectroscopy (EDS) analysis and elemental mapping studies. The Brunauer-Emmett-Teller(BET) surface area was found to vary between 204 and 240m2g−1 depending upon MOF concentration in the composites. It was noted that the pore distribution was found to be narrowed on increasing MOF concentration in the composite. Transmission Electron Microscope (TEM) and Field Emission Scanning Electron Microscope (FE-SEM) images revealed the nanoporous morphology of the composites. The incorporation of MOF to TiO2 aerogel showed a significant increase of absorption in the visible region. These properties suggest that TiO2 aerogel-Cu-BTC composites are promising materials for photovoltaic and photocatalytic applications.

Oxidation-stable plasmonic copper nanoparticles in photocatalytic TiO2 nanoarchitectures.

Ultraporous copper/titanium dioxide (Cu/TiO2) aerogels supporting <5 nm diameter copper nanoparticles are active for surface plasmon resonance (SPR)-driven photocatalysis. The extended nanoscale Cu‖TiO2 junctions in Cu/TiO2 composite aerogels-which arise as a result of photodepositing copper at the surface of the nanoparticulate-bonded TiO2 aerogel architecture-stabilize Cu against oxidation to an extent that preserves the plasmonic behavior of the nanoparticles, even after exposure to oxidizing conditions. The metallicity of the Cu nanoparticles within the TiO2 aerogel is verified by aberration-corrected scanning transmission electron microscopy, electron energy-loss spectroscopy, and infrared spectroscopy using CO binding as a probe to distinguish Cu(0) from Cu(i). In contrast, photoreduction of Cu(ii) at a commercial nanoscale anatase TiO2 powder with primary particle sizes significantly larger than those in the aerogel results in a copper oxide/TiO2 composite that exhibits none of the plasmonic character of Cu nanoparticles. We attribute the persistence of plasmonic Cu nanoparticles without the use of ligand stabilizers to the arrangement of Cu and TiO2 within the aerogel architecture where each Cu nanoparticle is in contact with multiple nanoparticles of the reducing oxide. The wavelength dependence of the photoaction spectra for Cu/TiO2 aerogel films reveals visible-light photocatalytic oxidation activity initiated by an SPR-driven process-as opposed to photo-oxidation initiated by excitation of narrow-bandgap copper oxides.

Heat-insulating aerogel composites for a hydrothermal reactor

The SiO2–TiO2 aerogel composites used in the heat insulation of a hydrothermal reactor and the method of their fabrication using a liquid glass technology are analyzed. The process of fabrication of the composite material includes the following stages: the ion exchange of sodium liquid glass with the formation of silica hydrosol; the concentration of hydrosol; the formation of hydrogel and its maturing; the formation of alcogel of an SiO2–TiO2 composite material; surface modification; subcritical drying of alcogel with the formation of SiO2–TiO2 composite ambigel; and its heat treatment, granulation, and classification. The influence of infrared absorber (titanium dioxide) and the temperature of heat treatment of an SiO2–TiO2 aerogel composite material on its structural and thermal characteristics is studied.

Plasma treated TiO2 aerogel nanostructures as photoanode material and its influence on the performance of quasi-solid dye-sensitized solar cells

The present study demonstrates the effect of oxygen plasma treatment on the structural, optical and electrical properties of TiO2 aerogel nanostructure and the usefulness of these materials as photoanode in DSSC. X-ray diffraction pattern indicates that long exposure of plasma on TiO2 aerogel nanostructure initiates amorphous nature due to the generation of oxygen vacancies. High-Resolution Transmission Electron Microscope (HRTEM) and Selected Area Electron Diffraction (SAED) pattern also supports the change in crystallinity after plasma treatment. The Intensity Modulated Photocurrent spectroscopy (IMPS) and Intensity Modulated Photovoltage Spectroscopic (IMVS) study shows that the electron life time is increased after plasma treatment even in the presence of oxygen vacancies. The power conversion efficiency of 10min plasma treated TiO2 aerogel is enhanced to 3.94% due to low concentration of oxygen vacancies which is beneficial for better electron transport through these surface vacant sites.

Thermal stability of anatase TiO2 aerogels

Titanium dioxide (TiO2) aerogels were prepared with sol–gel ambient pressure drying method by using titanium tetrachloride (TiCl4) as precursor and tetraethoxysilane as modifier, calcinated at different temperature and characterized by X‐ray diffraction, transmission electron microscopy and small angle X‐ray scattering. The results showed that the TiO2 aerogels remained amorphous under 500 °C, changed to anatase from 600 °C and further changed to rutile from 900 °C. Between 60 °C and 500 °C, the primary particles within the samples concentrated mainly upon small sizes, enlarged and diverged remarkably above 600 °C. The crystalline grains grew and agglomerated with the rise of the calcination temperature. The TiO2 aerogels at a temperature higher than 800 °C have better stability than anatase because of the formation of partial Ti―O―Si bonds. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Doped TiO2 aerogels as alternative catalyst supports for proton exchange membrane fuel cells: A comparative study of Nb, V and Ta dopants

Nb, Ta and V-doped TiO2 aerogels and xerogels have been synthesized as possible new alternatives to carbon blacks for Proton Exchange Membrane Fuel Cells catalyst supports. A comparative study of different dopants was realized in a single study. Nb, Ta and V showed different behaviors with respect to the final material structure and morphology, composition and electronic conductivity. They are all prone to surface segregation, to different extents. V-doped TiO2 apart, the rutile structure could only be obtained after calcination in a reducing atmosphere at 800 °C for Nb or Ta-doped TiO2. The electronic conductivity exhibited a maximum at 10 at.% for Nb and Ta, 5 at.% for V. Nb revealed to be the most appropriate dopant to increase the electronic conductivity of TiO2, followed by Ta and V. 4–5 orders of magnitude were gained after Nb doping for xerogels conductivity to reach almost 0.1 S cm−1. The role of point defects was discussed to account for phase transition and evolution of conductivity.

Freestanding titanium metallic aerogel

Nanoporous titanium was prepared by an in-situ template confined synthetic strategy involving the magnesiothermic reduction on TiO2 aerogel template at relative low temperature and hydrochloric acid etching process. The resulting self-supporting monolith with α titanium as the major phase retained the similar morphology of initial template and exhibited a high specific surface area about 99.1m2/g. In addition, as the ideal laser-irradiated target material for production of multi-keV X-rays, the titanium aerogel has successfully realized the voluminal heating when irradiated by the high-energy laser pulse on the Shenguang-II facility, and the Ti K-shell emitted X-ray spectrum ranging from 3 to 9keV was detected using X-ray elliptical crystal spectrometer. More importantly, the result could provide significant reference for further research about the application of metal aerogel target in the field of the multi-keV X-ray sources, which was essential for radiography of inertial-confinement-fusion (ICF) experiments.

Methyl tert-butyl ether as a new solvent for the preparation of SiO2–TiO2 binary aerogels

SiO2–TiO2 binary aerogels have been synthesized for the first time using methyl tert-butyl ether as supercritical fluid. It has been shown that the aerogels prepared in methyl tert-butyl ether and isopropanol contain nanocrystalline anatase and that amorphous SiO2–TiO2 aerogels with a homogeneous distribution of their components can be obtained in CO2. A considerable contribution to the large specific surface area of the aerogels is made by micropores, especially when supercritical drying is carried out in CO2 and isopropanol.

Correlating Changes in Electron Lifetime and Mobility on Photocatalytic Activity at Network-Modified TiO2 Aerogels

We use intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS) to characterize carrier dynamics in titania (TiO2) aerogels under photocatalytic conditions. By systematically increasing the weight fraction of the sol–gel precursor during TiO2 sol–gel synthesis, we are able to impart drastic changes in carrier transport/trapping and improve the photocatalytic activity of TiO2 aerogels for two mechanistically divergent photochemical reactions: reductive water splitting (H2 generation) and oxidative degradation of dichloroacetate (DCA). The lifetimes of photogenerated electrons increase in going from lowest-to-highest precursor concentrations, as measured by IMVS, indicating increasing site density for electron traps—a trend that correlates with an 8× improvement for photocatalytic H2 generation. Electron mobility in the aerogel films, as measured by IMPS, decreases with increasing trap density, further implicating the trapping sites as reactive sites. In ...

Molecular dynamics simulation study of meso-confined propane in TiO2

We report the structural and dynamical properties of propane confined in mesoporous TiO2, studied using MD simulations. Results indicate that the propane molecules have a tendency to be adsorbed at the pore walls forming sequential layers. Three different regimes of translational motion can be identified which correspond to motion at different time scales accessible to different experimental probes. The variation of the dynamical behavior with loading differs for different regimes and the trend for one of these is consistent with that obtained in recent neutron scattering experiments on propane in mesoporous TiO2 and silica aerogel. The rotational motion of propane molecules confined in the pore exhibits a very fast free rotation at short times which is followed by isotropic rotational diffusion. This work provides an explanation to the counterintuitive observations of an enhancement in the diffusivity with an increased loading of confined propane in recent neutron scattering experiments.

Nanostructure Developments of TiO2 Nanocrystals and Aerogels and Their Dye-Sensitized Solar Cell Application.

We synthesized TiO2 nanoparticles (TPs) as a reference via hydrothermal method and also TiO2 aerogels (TAs) via CO2 supercritical drying method. We investigated crystal phase transformation behavior of TPs and TAs with temperature. As-prepared TPs are anatase and rutile phase transformation from anatase starts at 600 °C and was complete at 700 °C. However, TAs are amorphous phase until 300 °C and the crystallization to anatase occurs at 400 °C, and remains anantase phase until 700 °C. At the results of nitrogen adsorption and desorption analyses, TPs with specific surface area of 209 m2/g at 100 °C showed the decrease of the specific surface area and pore volume with increasing temperature and 95% of decrease at 700 °C. TAs showed higher specific surface area, 498 m2/g at 100 °C, and the decreasing trend according to temperature is similar with those of TPs. We prepared three types of photoelectrodes, TPs, TAs, and TATPs (1:1 TAs and TPs composite photoelectrode). After results of DSC photocurrent conversion efficiency measurements of the three type cells, we found that TATPs showed the improved cell efficiency by 1% point, compared with a reference TPs below 15 micrometer thickness. In conclusion, the introduction of nanoporous TAs can improve the photocurrent conversion efficiency due to their high specific surface area for high dye adsorption without degrading of electron transfer.

The Optimum of Preparation and Characterization of Aerogels like Hydrophobic Titania by Ambient Pressure Drying

The influence of different factors in the alcogel preparation process and ambient pressure drying process on packing density of hydrophobic TiO2 aerogel synthesized by ambient pressure drying (APD) and the optimum preparation conditions were investigated by the orthogonal test with four-factor and three-level L9(34), respectively. The morphology and structural properties of hydrophobic TiO2 aerogels with different density were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetry (TG), N2 adsorption-desorption measurement and Scanning Electron Microscope (SEM). The results showed that the most important factors in the preparation process for TiO2 aerogels with low-density under ambient pressure are aging time, the volume ratio of C2H5OH to TBT, ethanol immersion time and hydrophobic modification time. The optimized preparation conditions are that aging time is 24 h, the volume ratio of C2H5OH to TBT is (7+7) : 5, the volume ratio of H2O to TBT is 1.7 : 5, the volume ratio of HAc to TBT is 1.7 : 5, ethanol immersion time is 24 h, hydrophobic modification time is 48 h, hexane solvent replacement time is 24 h and the drying temperature is 393 K. TiO2 aerogels with density of 460 kg/m3 was obtained at the optimized conditions. TiO2 aerogel with lower density displays higher specific surface area, porosity and pore volume as well as the larger pore size.

Robust, Highly Thermally Stable, Core–Shell Nanostructured Metal Oxide Aerogels as High-Temperature Thermal Superinsulators, Adsorbents, and Catalysts

Robust, highly thermally stable, MOx/(MOx–SiO2)/SiO2 core–shell nanostructured metal oxide aerogels with a MOx core and (MOx–SiO2)/SiO2 shell are produced via novel alkoxide chemical liquid deposition techniques. The core–shell nanostructure not only significantly reinforces the nanoparticles but also effectively inhibits the crystal growth and phase transition of metal oxide upon heat treatment, which enhances the heat resistance from approximate 400–800 °C up to 1000–1300 °C. The resultant core–shell nanostructured Al2O3, ZrO2, and TiO2 aerogels can support at least 5800 times their weight and exhibit high surface areas of 139, 186, and 154 m2/g after fired at 1300, 1000, and 1000 °C, respectively, which are the highest surface areas for metal oxide aerogels ever reported. We demonstrate that the core–shell ZrO2 and TiO2 aerogels show enhanced adsorption and photocatalytic performances, respectively, for dye after fired at 1000 °C. The core–shell Al2O3 aerogel/mullite fiber/TiO2 composite possesses ultralow thermal conductivities of 0.058, 0.080, and 0.11 W/mK at 800, 1000, and 1200 °C, respectively, which are the lowest values for inorganic aerogels ever reported. The resulting materials are promising candidates as high-temperature (400–1300 °C) thermal superinsulators, adsorbents, and catalysts.

Design of multicomponent aerogels and their performance in photocatalytic hydrogen production

Multicomponent aerogels were prepared from the preformed components (i) crystalline TiO2 nanoparticles, (ii) Pt nanoparticles as well as (iii) multilayer reduced graphene oxide (m-rGO) and were subsequently tested for photocatalytic H2 evolution. The multicomponent photocatalysts showed a 3D architecture consisting of crosslinked TiO2 nanoparticles which are decorated with (1–2nm) platinum nanoparticles with embedded m-rGO. The three-component materials retained the mesoporosity and high surface area of pure TiO2 aerogels, as illustrated by transmission electron microscopy and nitrogen sorption experiments. This architecture is responsible for the enhancement of the photocatalytic activity, which reached a maximum hydrogen production rate of 11.61mmolH2g−1h−1 for the TiO2 aerogel with a cocatalyst content of 0.4wt% Pt. In comparison, a Pt/TiO2 reference powder produced only about 3.28mmolH2g−1h−1. In this way, the aerogel architecture enables the design of compositions other than Pt/TiO2 or even the co-assembly of further active materials such as conducting components into the aerogel matrix as shown by the addition of m-rGO to the Pt/TiO2 aerogels.

Pt/N–TiO2 Aerogel Composites Used for Hydrogen Production Via Photocatalysis Process

Pt/N–TiO2 aerogel photocatalysts were obtained by means of sol–gel process followed by low temperature supercritical drying. Urea and guanidine-HCl were used as nitrogen sources. Pt clusters were loaded on photocatalysts surface by photoreduction process. Enhanced photocatalytic activities and H2 evolution rates were obtained on photocatalysts containing nitrogen impurities.

Preparation and Characterization of TiO2/Coconut-Activated Carbon Photocatalytic Materials

Using Ti (OC4H9)4 as the precursor,and GAC as carrier, making use of technology of hydrolyzation and natural assembling,TiO2/GAC composite material was preparated at the lower temperature.The characterization of obtained TiO2 /Coconut-Activated Carbon’scrystal structure and appearance by XRD and SEM.The adsorption capacity and photocatalytic performance on phenol were measured.Results show that TiO2/GAC surface was well-distributed and remains a little interspace.A nanocrystal TiO2 aerogel size is without 30nm.The sample shows lower adsorption compared to GAC.But photocatalytic efficiency was higher than GAC under the exposure of the sunlight or the violet.

Towards TiO2[sbnd]Ag porous nanocomposites based SERS sensors for chemical pollutant detection

Since the TiO2 environmental friendly character and the affinity of a large variety of molecules to bind to the silver surfaces are well-known, novel porous nanoarchitectures based on TiO2 aerogel and Ag colloidal particles deposited on a poly(methyl methacrylate) (PMMA) substrate were obtained. The ability of the deposited porous structures to detect by surface-enhanced Raman spectroscopy (SERS) contaminant species adsorbed from aqueous media was tested. The morphological particularities of the bulk samples during the deposition on the PMMA substrates were preserved. The SERS detection efficiency was assessed by using congo red as a test molecule. No matter the average size of the Ag nanoparticles, the lowest detectable concentrations were found be of around 5×10−6M for all samples. The morphological parameters such as median pore diameter and cumulative pore volume were also taken into consideration when discussing the detection performances. Moreover, calibration curves have been obtained in order to estimate an unknown concentration of the analyte. The obtained results show the real potential of the prepared porous composites for further use in the development of new SERS-based sensors for monitoring of water quality, especially when the contaminants are dye molecules.

Antimony-Doped Tin Oxide Aerogels as Porous Electron Collectors for Dye-Sensitized Solar Cells

Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for TiO2 in dye-sensitized solar cells (DSCs). The high surface area, porosity and particle interconnectivity inherent to aerogels, and the conductivity and transparency of ATO make these structures attractive as porous electron collectors. Aerogels were prepared by sol–gel processing and supercritical drying of ATO containing varying amounts of Sb. These were coated with varying TiO2 layer thicknesses by atomic layer deposition, sensitized with an organic dye (D149), and made into DSC devices using iodide/triiodide (I–/I3–) and ferrocene/ferrocenium (Fc/Fc+) electrolytes. Scanning electron microscopy was used to study the morphological characteristics of the aerogel materials. The effect of ALD cycles on the dye adsorption was measured. Current–voltage characteristics were used to study device performance. We found that ATO aerogels with 15% Sb have improved performance over TiO2 and undoped tin oxide aerogel devices. DSC ...