High Surface Area TiO2 Research Articles

Polyol thermolysis synthesis of TiO2 nanoparticles and its paste formulation to fabricate photoanode for dye-sensitized solar cells

Titanium dioxide (TiO2) nanoparticles (NPs) were prepared by a simple polyol thermolysis process using various mole ratios of titanium tetrachloride (TiCl4) and polyvinylpyrrolidone (PVP). The prepared TiO2 NPs were characterized by TG/DTA, XRD, SEM, and BET analysis. The TiO2 NPs obtained using 0.1 M of TiCl4 and 0.02 M of PVP have high surface area with lesser particles size than the same obtained using 0.1 M of TiCl4 with other mole ratios of PVP. The high surface area TiO2 NPs were used to formulate TiO2 paste. The impact of ethyl cellulose, terpineol, and dibutyl phthalate in the formulation of TiO2 paste was optimized with respect to standard TiO2 paste (Dyesol Ltd.) on the adsorption of dye was studied by UV–Vis spectroscopy. The photovoltaic performance of DSSCs fabricated using the formulated TiO2 paste has achieved 97.83 % of power conversion efficiency (PCE) (η = 4.5 %) with respect to the standard TiO2 paste (Dyesol Ltd.) and its PCE were found to be 4.6 % (η). This PCE value was nearly closer to that of the same DSSC fabricated using the standard TiO2 paste (Dyesol Ltd.) and higher than the P25 TiO2 (Degussa) paste and its achieved PCE were found to be 86.04 %.

Nanocrystalline TiO2(B) as Anode Material for Sodium-Ion Batteries

High surface area, nanostructured, and phase-pure TiO2(B) noodles-like secondary particles were successfully synthesized by a facile one-pot synthesis, based on the hydrolysis of TiCl3 using a mixture of ethylene glycol and water at moderate temperature. The primary nanoparticles have a uniform size and are about 15 nm in diameter as determined by TEM analysis and exhibit an increased exposure of the (010) facet as indicated by XRD analysis. Unlike the electrochemical reaction with lithium, the application as sodium-ion electrode material reveals substantial differences, including the initial amorphization of the TiO2(B) particles, accompanied by a partial irreversibility of the sodium storage, presumably related to sodium trapping inside the active material particles and the absence of a stable solid electrolyte interphase, as indicated by galvanostatic cycling and electrochemical impedance spectroscopy, respectively. Besides, TiO2(B)-based electrodes show a stabilized reversible capacity of about 100 mAh g−1 and a very good C rate capability.

As-grown vertically aligned amorphous TiO2 nanotube arrays as high-rate Li-based micro-battery anodes with improved long-term performance

Vertically oriented arrays of high surface area TiO2 nanotubes (NTs) are fabricated by the fast and facile anodic oxidation of a titanium foil. The formation of well-defined one-dimensional nanotubular carpets is assessed by means of morphological Field Emission Scanning Electron Microscopy characterisation, while X-ray diffraction analysis and Transmission Electron Microscopy imaging confirm the amorphous nature of the samples. The electrochemical response evaluated in lab-scale lithium cells is highly satisfying with near-theoretical initial specific capacity and remarkable rate capability, noteworthy in the absence of binders and conductive agents, which would affect the overall energy density. A specific capacity exceeding 200 mAh g−1 is observed at very high 24C and approx. 80 mAh g−1 are retained even at very high 96C rate, thus accounting for the promising prospects in storage devices conceived for high power applications. Moreover, the NTs can perform with good cycling stability and capacity retention approaching 50% of the initial value after very long-term operation along with improved durability (> 2000 cycles).

Photovoltage Effects of Sintered IrO2 Nanoparticle Catalysts in Water-Splitting Dye-Sensitized Photoelectrochemical Cells

Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) utilize high surface area TiO2 electrodes functionalized with light absorbing sensitizers and water oxidation catalysts. Because water splitting requires vectorial electron transfer from the catalyst to the sensitizer to the TiO2 surface, attaching both sensitizer and catalyst to TiO2 in the correct sequence and stabilizing them under photoelectrochemical conditions has been a challenging problem. Rutile-phase IrO2 nanoparticles can be deposited directly on the TiO2 electrode by adsorbing citrate-capped amorphous IrOx and then sintering at 450 °C. Electrodes functionalized with these nanocrystalline particles show higher activity than those made from ligand-capped amorphous IrOx without sintering. In the WS-DSPEC, the Coulombic efficiency for oxygen evolution from the sintered nanoparticle photoelectrodes was near unity. The loading of colloidal IrOx and IrO2 particles onto the porous TiO2 electrodes was quantified by neutron activation analysis. Photovoltage measurements suggest that at high catalyst loading the dominant charge recombination pathway is from photoinjected electrons to IrO2.

Hydrothermally stable regenerable catalytic supports for aqueous-phase conversion of biomass

The hydrothermal stability of TiO2- and ZrO2-based materials was studied by exposing the samples to liquid water at 523K for 60h in a batch reactor. No phase transformation or loss in BET surface area was observed for TiO2-based materials that had initial BET surface area of less than 52m2/g. In contrast, the BET surface area decreased and the primary crystallite size increased for all ZrO2-based materials tested. The BET surface area decreased and the primary crystallite size increased for high BET surface area TiO2 (156m2/g) and ZrO2 (246m2/g). Silica-containing TiO2 only lost 30% of its high BET surface area (from 128 to 90m2/g). In contrast a material composed of silica–phosphate–ZrO2 lost 56–72% of its BET surface area. Using the crystalline TiO2 as a support, we prepared and tested a Pt–ReOx/TiO2 catalyst for hydrodeoxygenation of sorbitol. Pt–ReOx/TiO2 was almost 2 times more active on a total Pt basis than Pt–ReOx/C catalyst. Between 0.1 and 0.9wt% of coke formed on the catalyst surface after reaction depending on the reaction conditions. The coke could be removed and the catalyst activity completely regenerated by an oxidation-reduction treatment. The catalyst showed only minimal change in BET surface area, TiO2 phase and TiO2 crystallite size after more than 163h of time on stream. The CO chemisorption of Pt–ReOx/TiO2 increased after reaction which was probably due to migration of ReOx species away from the Pt during the reaction.

Halogen- and acid-free syntheses of TiO2 nanocrystal coatings and high surface area TiO2 nanocrystal-assembled particles.

Halogen- and acid-free aqueous solutions were developed to synthesize TiO2 nanocrystal coatings and high surface area TiO2 nanocrystal-assembled particles. Fluorine doped tin oxide substrates were covered with TiO2 nanocrystal coatings in the solutions containing titanium(IV) potassium oxalate, 2-hydrate (K2[TiO(C2O4)2] x 2H2O) at 90 degrees C for 3 days. The substrates changed color by the coatings. The nanocrystals were about 10-50 nm in size. They connected with the substrates strongly due to direct nucleation and crystallization on the substrates. Furthemore, TiO2 particles were synthesized from the solutions at 90 degrees C for 3 days. They were assemblies of TiO2 nanocrystals. Brunauer-Emmett-Teller surface area reached to 275 m2/g. Nanospaces were formed by assembly of the nanocrysrtals. They contributed high surface area. Halogen- and acid-free aqueous solution processes had advantages of low environmental load and safety manufacturing environment. Harmless TiO2 coatings and particles can be applied to medical applications, medicines, cosmetics, food additives, etc.

Synthesis of high surface area TiO2 nanoparticles by mild acid treatment with HCl or HI for photocatalytic propene oxidation

Nanostructured TiO2 photocatalysts with small crystalline sizes have been synthesized by sol–gel using the amphiphilic triblock copolymer Pluronic P123 as template. A new synthesis route, based on the treatment of TiO2 xerogels with acid–ethanol mixtures in two different steps, synthesis and extraction–crystallization, has been investigated, analyzing two acids, hydrochloric and hydriodic acid. As reference, samples have also been prepared by extraction–crystallization in ethanol, being these TiO2 materials amorphous and presenting higher porosities. The prepared materials present different degrees of crystallinity depending on the experimental conditions used. In general, these materials exhibit high surface areas, with an important contribution of microporosity and mesoporosity, and with very small size anatase crystals, ranging from 5 to 7nm.The activity of the obtained photocatalysts has been assessed in the oxidation of propene in gas phase at low concentration (100ppmv) using a UVA lamp with a wavelength of 365nm. Under the conditions studied, these photocatalysts show different activities in the oxidation of propene which do not depend on their surface areas, but on their crystallinity and band gap energies. Sample prepared with HCl both during synthesis and in extraction–crystallization steps is the most active one, with superior performance than Evonik P25.

Efficient and exceptionally selective semireduction of alkynes using a supported gold catalyst under a CO atmosphere.

A new efficient method for chemo- and regio-selective semireduction of alkynes using CO/H2O as the hydrogen source catalyzed by gold supported on high surface area TiO2 was developed. A facile and practical synthesis of 1,2-dideuterioalkenes was also realized by using CO/D2O as the reducing agent.

High surface area TiO2nanoparticles by a freeze-drying approach for dye-sensitized solar cells

Titanium dioxide (TiO2) synthesized by freeze drying of a TiO2precursor–polyester composite followed by sintering and its performance when employed in dye-sensitized solar cells.

Synthesis of high surface area TiO2 coatings on stainless steel by electrophoretic deposition

Abstract

TiO2 nanotubes supported NiW hydrodesulphurization catalysts: Characterization and activity

High surface area TiO2 nanotubes (Ti-NT) synthesized by alkali hydrothermal method were used as a support for NiW hydrodesulphurization catalyst. Nickel salt of 12-tungstophosphoric acid – Ni3/2PW12O40 was applied as oxide precursor of the active components. The catalyst was characterized by SBET, XRD, UV–vis DRS, Raman spectroscopy, XPS, TPR and HRTEM. The results obtained were compared with those for the NiW catalysts prepared over high surface area titania and alumina supports. A polytungstate phase evidenced by Raman spectroscopy was observed indicating the destruction of the initial heteropolyanion. The catalytic experiments revealed two times higher thiophene conversion on NiW catalyst supported on Ti-NT than those of catalysts supported on alumina and titania. Increased HDS activity of the NiW catalyst supported on Ti-NT could be related to a higher amount of W oxysulfide entities interacting with Ni sulfide particles as consequence of the electronic effects of the Ti-NT observed with XPS analysis.

Size Control of Particles with Changing Concentration of TIP used as a Precursor for Synthesis of TiO2 by Ultra-Sonic Spray and Pyrolysis Method

The nano sized titanium dioxide was synthesized by the ultra-sonic spray method and pyrolysis of TIP (titanium iso-propoxide), which was employed as the precursor solution. The fine liquid drop of the TIP sprayed by the ultra-sonic spray nozzle was conversed into TiO2 nano particles by pyrolysis through the hot tubular reactor. The concentration of TIP solution was controlled in the range of 0.1∼1.0 M and the morphology, the particle size, the crystal structure, and the surface area of synthesized TiO2 were investigated by SEM, TEM, XRD and N2-adsorption method, respectively. DSSC (dye sensitized solar cells) was also prepared by employing the synthesized TiO2 nano powder as the electrode and the photo-electrical property of TiO2 was compared in terms of efficiency of solar cells. It was further confirmed that the particle size of TiO2 was controlled with changing concentration of TIP solution. When 0.1 M TIP was used as the precursor solution, the size, the surface area and the crystal structure of synthesized TiO2 were approximately 10 nm (by TEM), 56 m2/g and the anatase structure, respectively. The particle size of TiO2 decreased with decreasing concentration of TIP solution. Therefore, it was concluded that the efficiency of DSSC's can be improved by employing high surface area and nano-sized TiO2 as the electrode.

Enhanced Efficiency in Dye-Sensitized Solar Cells Based on TiO2 Nanotube Scattering Layer

The essential goal for the production of dye-sensitized solar cells (DSSCs) is to improve the light-scattering ability of these films. Therefore, transparent high surface area TiO2 layers and an additional scattering layer consisting of TiO2 nanotubes (TNTs) with relatively larger particles are attractive. The light-scattering abilities of these scattering layers also depend on the relative sizes and the phase of the particles in the layers. TNTs were fabricated by a sol-gel method, and the TiO2 powders were produced through an alkali hydrothermal transformation. The size and structure of the TNTs were adjusted by the hydrothermal temperatures. It was observed that the TiO2 films transformed into the rutile phase, which has a more stable structure, as the temperature increases. This study examined the scattering efficiency in terms of the size, crystal phase, and morphology of the scattering particle. With a 6 μm-thin titanium dioxide semiconductor layer as a photoelectrode and an additional light-scattering layer (consisting of TNTs-rutile large-size particle), efficiencies of 4.4% were achieved.

광산란층을 이용한 염료감응형 태양전지의 특성

As an alternative energy, Dye-sensitized solar cells (DSSCs) have received much attention due to low cost manufacturing procedure and high energy consumption rate. Incorporating scattering centers in the nanocrystalline photoanode or additional scattering layers on the nanocrystalline photoanode is an effective way to enhance the light harvest efficiency of the photoanode and the performance of dye-sensitized solar cells (DSSCs). The light scattering abilities of these scattering layers also depend on the relative sizes and phase of the particles in the layers. A higher surface area is normally obtained using large particle sizes. Therefore, transparent high surface area TiO2 layers and an additional scattering layer consisting of TiO2 -Rutile 500 ㎚ paste with relatively larger particles are attractive. In this work, we investigates the applicability of a hybrid TiO2 electrode (or a working electrode with a light scattering layer) in a DSSCs. We fabrication various thin film using TiO2 paste 20 ㎚ and TiO2 paste 500 ㎚. As a result, the efficiency of the a single structure thin film was 3.35% and the efficiency as scattering layer of hybrid structure thin film was 4.36%, 4.73%.

Growing TiO2 nanowires on the surface of graphene sheets in supercritical CO2: characterization and photoefficiency

Tremendous interest exists towards synthesizing nanoassemblies for dye-sensitized solar cells (DSSCs) using earth-abundant and -friendly materials with green synthetic approaches. In this work, high surface area TiO2 nanowire arrays were grown on the surface of functionalized graphene sheets (FGSs) containing −COOH functionalities acting as a template by using a sol–gel method in the green solvent, supercritical carbon dioxide (scCO2). The effect of scCO2 pressure (1500, 3000 and 5000 psi), temperature (40, 60 and 80 °C), acetic acid/titanium isopropoxide monomer ratios (HAc/TIP = 2, 4 and 6), functionalized graphene sheets (FGSs)/TIP weight ratios (1:20, 1:40 and 1:60 w/w) and solvents (EtOH, hexane) were investigated. Increasing the HAc/TIPweight ratio from 4 to 6 in scCO2 resulted in increasing the TiO2 nanowire diameter from 10 to 40 nm. Raman and high resolution XPS showed the interaction of TiO2 with the −COOH groups on the surface of the graphene sheets, indicating that graphene acted as a template for polycondensation growth. UV–vis diffuse reflectance and photoluminescence spectroscopy showed a reduction in titania’s bandgap and also a significant reduction in electron–hole recombination compared to bare TiO2 nanowires. Photocurrent measurements showed that the TiO2nanowire/graphene composites prepared in scCO2 gave a 5× enhancement in photoefficiency compared to bare TiO2 nanowires.

Nanoscale titania ceramic composite supports for PEM fuel cells

Abstract

High surface area TiO2–ZrO2prepared by caustic solution treatment, and its catalytic efficiency in the oxidehydrogenation of para-ethyltoluene by CO2

High surface area TiO2–ZrO2 (1 : 1) has been synthesized by co-precipitation—digestion method using KOH solution as a hydrolyzing agent as well as a digestion medium. The quenching of the mother liquor solution at elevated temperatures resulted in the amorphization of the TiO2–ZrO2 mixed oxide. The highest surface area obtained for TiO2–ZrO2 by the co-precipitation–digestion method is 256 m2 g−1 calcined at 600 °C with complete amorphous nature and having a particle size of less than 5 nm. Herein, we discuss the concept of amorphization of metal oxides based on the digestion times, supported by the characterization of the catalysts and its application in dehydrogenation of substituted benzene, mainly para-ethyltoluene to para-methylstyrene by CO2 as soft oxidant which showed high conversion and selectivities of 69% and 96%, respectively.

Highly sensitive hydrogen peroxide biosensors based on TiO2 nanodots/ITO electrodes

Uniformly dispersed and size-controllable TiO2 nanodots (TN) were directly synthesized on indium-tin-oxide (ITO) electrodes and were further utilized to immobilize horseradish peroxidase (HRP) enzyme and facilitate direct electron transfer for construction of a hydrogen peroxide (H2O2) biosensor. The enzyme adsorption ability of TN/ITO electrodes were investigated using a UV–vis spectrometer, and the results indicated that TiO2 nanodots possess better enzyme adsorption ability than TiO2 film, and this ability could be further improved by varying the mean diameter of the nanodots from 30 nm to 79 nm. The sensitivity of the H2O2 biosensors based on Nafion/HRP/TN/ITO electrodes was significantly increased by adjusting the dimension of TiO2 nanodots on the modified electrode and the sensitivity differences among these electrodes are in accord with their enzyme adsorption ability. TiO2 nanodots with the largest diameter (79 nm) on a ITO electrode had the best enzyme adsorption ability and biosensor performance with a high sensitivity of 1176 μA mM−1 cm−2 as well as a wide linear range of 1–780 μM. These results show that well-dispersed, high surface area and high curvature TiO2 nanodots could be a promising material for protein adsorption and fabrication of electrochemical biosensors.

Photo catalytic oxidation of TNT using TiO2-SiO2 nano-composite aerogel catalyst prepared using sol–gel process

The degradation of nitro aromatics like trinitrotoluene (TNT) released in the waste water from explosive process plants is the serious problem due to toxic and explosive nature of TNT. The poor response of TNT to biodegradation enhanced the gravity of the problem. We have demonstrated that high specific surface area TiO2–SiO2 nano-composite aerogel is promising photo catalyst in successful treating of TNT contaminated aqueous solution. The TiO2–SiO2 composite aerogel with nominal content of 20 and 50% TiO2, used as catalyst, were prepared by co-precursor sol–gel method using titanium isopropaxide and tetramethylorthosilicate as source of titania and silica, respectively. The XRD studies confirmed formation of anatase phase of crystalline TiO2 with nano sized crystallites. The TiO2–SiO2 aerogel showed specific surface area of 1,107 and 485 m2/g for the aerogels containing 20 and 50% TiO2, respectively. The 100 ppm TNT solution was treated, in 700 ml capacity reaction vessel, using H2O2 oxidizer and TiO2–SiO2 aerogel catalyst in presence of UV light (8 W UV lamp). Using TiO2–SiO2 (50/50) aerogel with surface area of 485 m2/g, we succeeded to reduce the TOC to 1 ppm within 3.5 h where as using TiO2/SiO2 (20/80) aerogel with surface area of 1,107 m2/g, the TOC was reduced to about only 7 ppm in the same time. It revealed that the combination of high TiO2 content and high specific surface area is an important factor to achieve effective and faster degradation of TNT for complete mineralization.

Toward high surface area TiO2 brookite with morphology control

TiO2 materials have many practical applications due to their intrinsic physico-chemical properties. Research activities on the properties of TiO2 brookite have been restrained by the difficulty of preparing such a phase. Here, we report on the synthesis of TiO2 brookite prepared by thermal decomposition of a titanium oxalate hydrate compound. Since the characteristics of the prepared TiO2 brookite are dictated by those of the precursor, the present work aims to understand the aqueous precipitation process of the oxalate hydrate phase. It was shown that the formation of the phase occurred via different steps that are affected by the synthesis conditions, i.e. the oxalate source and the duration time. At first, in agreement with the Ostwald's rule of stages, the formation of the oxalate phase implied a metastable intermediate that is a poorly crystallized TiO2 phase. The pH of the solution was shown to impact on the kinetic of transformation of this intermediate toward the final compound. In the presence of alkali ions, the oxalate phase was shown to undergo a dissolution/etching phenomenon that is dependent on the nature of the alkali ion used. The apparent difference in adsorption ability of the alkali ions on the different crystal planes of the titanium oxalate hydrate phase accounted for the variety of the obtained morphologies. Finally, it was suggested that the reaction was promoted by a coordination-assisted mechanism involving the complexing properties of the oxalate anions toward Ti4+ ions. The obtained TiO2 brookite materials exhibit unreached high specific surface area lying between 150 and 400 m2 g−1 while displaying high packing density around 1–1.2 g cm−3. The lithium insertion ability of the prepared material depends on the calcination temperature. Increasing the temperature led to a decrease of the lithium uptake properties but was shown to improve the kinetics of lithium insertion. This was due to an increase of the pore radius size that enabled a faster lithium diffusion transport to be achieved under high current density conditions.