Novel synthesis and electrochemical investigations of ZnO/C composites for lithium-ion batteries

For the first time, ZnO/C composites were synthesized using zinc glycerolate as a precursor through one-step calcination under a nitrogen atmosphere. The effect of the heat treatment conditions on the structure, composition, morphology as well as on the electrochemical properties regarding application in lithium-ion batteries are investigated. The products obtained by calcination of the precursor in nitrogen at 400—800 °C consist of zinc oxide nanoparticles and amorphous carbon that is in-situ generated from organic components of the glycerolate precursor. When used as anode material for lithium-ion batteries, the as-prepared ZnO/C composite synthesized at a calcination temperature of 700 °C delivers initial discharge and charge capacities of 1061 and 671 mAh g^?1 at a current rate of 100 mA g^?1 and hence 1.5 times more than bare ZnO, which reaches only 749/439 mAh g^?1. The native carbon improves the conductivity, allowing efficient electronic conductivity and Li-ion diffusion. By means of ex-situ XRD studies a two-step storage mechanism is proven.

     

Core–shell nanostructure supported Pt catalyst with improved electrocatalytic stability in oxygen reduction reaction

Core–shell nanostructure electrode (TiO₂@C) for oxygen reduction reaction is prepared with TiO₂ nanoparticles at 900 °C in a methane atmosphere. The TiO₂@C supported Pt catalyst (Pt/TiO₂@C) contains Pt nanoparticles on TiO₂@C nanostructure electrodes consisting of TiO₂ as a core and carbon as a shell. In the accelerated stability test, the Pt/TiO₂@C exhibits a superior ORR stability to conventional carbon supported Pt catalyst. It is likely that the enhanced catalytic properties of the nanostructure supported Pt catalyst may be due to graphite-like carbon and an improved electronic conductivity of the core–shell nanostructure.     

Phase transformation in semi-transparent TiO2 films irradiated with CO2 laser

Anatase (TiO₂) thin films were obtained by immersion of glass plates into a titanium sol-gel precursor followed by calcination at 450 °C for 3 h. The Raman results for the CO₂ laser irradiated TiO₂ films show that laser radiation is able to promote favorable changes of anatase phase in anatase/rutile mixtures. Nevertheless, the transformation process level depends on laser characteristics and scan speed of the radiation treatment.     

Synthesis and electrophoretic deposition of hydrothermally synthesized multilayer TiO2 nanotubes on conductive filters

TiO₂ nanotubes were synthesized by the decomposition of titanium isopropoxide in water and the calcination at 450 °C for 2 h to form TiO₂ nanoparticles. The synthesized TiO₂ in anatase form nanoparticles were processed hydrothermally in 10 M NaOH solution at 130 °C for 24 h to obtain multilayer TiO₂ nanotubes. TEM analysis revealed that the diameters of the tubes were around 10 nm and they are in the length of 100 nm. Subsequently, colloidal suspensions containing 1% wt. Of TiO2 nanotubes were prepared with TEA and butanol and electrophoretic deposition (EPD) experiments were conducted in order to obtain coatings on Ni and carbon filters using a deposition time of 10 min. and an applied voltage of 65 V. It is also shown that multilayer TiO₂ nanotubes having outer diameter around 10 nm and inner diameters of 4.3 nm can be produced using the described technique. EPD is also shown to be an effective technique to coat three dimensional components, such as Ni and C filters for various applications including water and air purification systems.     

Thermal Conductivity and Viscosity Measurements of Water-Based TiO<Subscript>2</Subscript> Nanofluids

In this study, the thermal conductivity and viscosity of TiO₂ nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO₂ nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO₂ nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3ω method for measuring the thermal conductivity. The 3ω method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO₂ nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO₂ nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.     

Formation of TiO<Subscript>2</Subscript> nanotubes by thermal decomposition of poly(vinyl alcohol)-titanium alkoxide hybrid nanofibers

Anatase type TiO₂ nanotubes were formed by calcination of poly(vinyl alcohol)-Ti alkoxide hybrid precursor nanofibers in air. The outer and inner diameters of the TiO₂ nanotubes calcined at 500 °C for 5 h were ca. 440 nm and ca. 270 nm, respectively. The specific surface area of the TiO₂ nanotubes was 38.8 m²/g, and the existence of mesopores (average pore diameter, 14.8 nm) on the nanotube wall was indicated by the nitrogen adsorption isotherm (−196 °C). The photocatalysis of the TiO₂ nanotubes was superior to that of commercially available anatase type TiO₂ nanoparticles.     

Titanium glycolate-derived TiO2 nanomaterials: Synthesis and applications

Titanium oxide (TiO₂) is one of the most widely studied materials due to its fascinating properties and versatile applications in environmental and energy fields ranging from photocatalysis to solar cells and lithium ion batteries. The significance and variety of these applications have attracted great attention and spurred substantial progress in the synthesis and fundamental understanding of TiO₂-based nanomaterials, nanocomposites, and nanoderivatives. This review summarizes the recent advances in the design and preparation of TiO₂-based nanomaterials, nanocomposites, and nanoderivatives obtained from titanium glycolate precursor. Utilizing different fabrication strategies, titanium glycolate precursor with controllable morphology and size has been successfully produced, and it can be directly transformed into crystalline TiO₂ nanomaterials through diverse post-treatments, including calcination thermal-decomposition, and refluxing, hydrothermal, and microwave treatment-assisted hydrolysis. Furthermore, doped TiO₂, TiO₂-composites, and other derivatives could be simply achieved by adding additional chemicals during transformation. The favorable properties of the resulting TiO₂-based materials are also discussed, which are relevant to energy and environmental applications in the areas of dye-sensitized solar cells, lithium ion batteries, photocatalytic hydrogen evolution, photocatalytic CO₂ reduction, photocatalytic degradation, and adsorption removal of pollutants.     

Effect of rapid cooling time on optical absorption and band gap energy of TiO2 nanoparticles

In this paper, TiO₂ nanoparticles were synthesized via sol–gel method by using of TiCl₄ as a precursor in the ethanol solution. The structure and the morphology of TiO₂ nanoparticles were characterized by X-ray diffraction and scanning electron microscopy. We have studied the optical properties by using of UV–Vis spectroscopy. The results show that the calcination temperature is an important factor in size of nanoparticles, the morphology of powders and the band gap energy of TiO₂ nanoparticles. Also, rapid cooling time of samples is an important factor to decrease band gap energies, considerably. The calculated band gap of the TiO₂ nanoparticles is in range of 2.39–3.50 eV.     

Low temperature preparation of nanocrystalline solid solution of strontium barium niobate by chemical process

Sr_xBa_1-xNb₂O₆ (with x = 0.4, 0.5 and 0.6) powders have been prepared by thermolysis of aqueous precursor solutions consisting of triethanolamine (TEA), niobium tartarate and, EDTA complexes of strontium and barium ions. Complete evaporation of the precursor solution by heating at ∼ 200°C, yields in a fluffy, mesoporous carbon rich precursor material, which on calcination at 750°C/2 h has resulted in the pure SBN powders. The crystallite and average particle sizes are found to be around 15 nm and 20 nm, respectively.     

Influence of silver doping on the phase transformation and crystallite growth of electrospun TiO2 nanofibers

Ag doped TiO₂ nanofibers were fabricated by electrospinning technique using polyvinyl pyrrolidone (PVP) and titanium isopropoxide (TiP) as precursor. The effects of silver and calcination temperature on the preparation of electrospun TiO₂ nanofibers were investigated. The calcination temperature determines the TiO₂ phases as ether anatase or rutile. When the calcination temperature increased, crystallite size of TiO₂ nanofiber increased. The crystallite size of Ag doped TiO₂ nanofiber is smaller than that of the pure TiO₂ nanofiber because silver is retrained in this phase transformation. Silver controlled the phase transformation as well as had an inhibition effect on the growth of anatase crystallite.     

Photocatalytic properties of porous TiO2/Ag thin films

In this study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol-gel spin-coating technique. By introducing polystyrene (PS) spheres into the precursor solution, porous TiO₂/Ag thin films were prepared after calcination at a temperature of 500 °C for 4 h. Three different sizes (50, 200, and 400 nm) of PS spheres were used to prepare porous TiO₂ films. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry (XRD) and by scanning electron microscopy to reveal structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.When PS spheres of different sizes were introduced after calcination, the as-prepared TiO₂ films exhibited different porous structures. XRD results showed that all TiO₂/Ag films exhibited a major anatase phase. The photodegradation of porous TiO₂ thin films prepared with 200 nm PS spheres and doped with 1 mol% Ag exhibited the best photocatalytic efficiency where ∼ 100% methylene blue was decomposed within 8 h under UV exposure.     

Preparation and characterization of titania powders obtained via hydrolysis of titanium tetraisopropoxide

TiO₂ powders were prepared through the hydrolysis of titanium isopropoxide followed by calcination at temperatures of 200 °C to 600 °C. The obtained powders were characterized by N₂ adsorption-desorption and X-ray powder diffraction. The results confirmed strong dependence between specific surface area of the TiO₂ powders and both the conditions of the hydrolysis process and the calcination temperature. While calcination temperature strongly affected crystallinity of the product, no significant influence of the hydrolysis conditions on this parameter was observed. TiO₂ powders prepared at various conditions were examined as catalysts for photodegradation of Acid Red 18 in water. Photoactivities of the prepared powders were influenced by both the amount of water used to hydrolyze the TiO₂ precursor and the temperature of calcination process. TiO₂ samples calcined at 500 °C appeared to be the most active and the photocatalytic activities of the prepared materials increased along with the amount of water used for the hydrolysis process.     

Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system

By the magnetically modulated microwave absorption method (MAMMA) we observed the modifications induced by different calcination temperatures (between 830°C and 870°C) on the 2223 phase formed in a system sintered at (855±5)°C with the starting composition Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y . The presence of the 2223 phase in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850°C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other lower-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at, 800°C for 5 min in a flowing nitrogen atmosphere. We labeled as metastable the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.     

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.     

TiO2 and Co Nanoparticle‐Decorated Carbon Polyhedra as Efficient Sulfur Host for High‐Performance Lithium–Sulfur Batteries

Metal organic frameworks (MOFs)‐derived porous carbon is proposed as a promising candidate to develop novel, tailorable structures as polysulfides immobilizers for lithium–sulfur batteries because of their high‐efficiency electron conductive networks, open ion channels, and abundant central ions that can store a large amount of sulfur and trap the easily soluble polysulfides. However, most central ions in MOFs‐derived carbon framework are encapsulated in the carbon matrix so that their exposures as active sites to adsorb polysulfides are limited. To resolve this issue, highly dispersed TiO₂ nanoparticles are anchored into the cobalt‐containing carbon polyhedras that are converted from ZIF‐67. Such a type of TiO₂ and Co nanoparticles‐decorated carbon polyhedras (C? Co/TiO₂) provide more exposed active sites and much stronger chemical trapping for polysulfides, hence improving the sulfur utilization and enhancing reaction kinetics of sulfur‐containing cathode simultaneously. The sulfur‐containing carbon polyhedras decorated with TiO₂ nanoparticles (S@C? Co/TiO₂) show a significantly improved cycling stability and rate capability, and deliver a discharge capacity of 32.9% higher than that of TiO₂‐free S@C? Co cathode at 837.5 mA g^?1 after 200 cycles.     

Substitutional Carbon‐Modified Anatase TiO2 Decahedral Plates Directly Derived from Titanium Oxalate Crystals via Topotactic Transition

Changing the composition and/or structure of some metal oxides at the atomic level can significantly improve their performance in different applications. Although many strategies have been developed, the introduction of heteroatoms, particularly anions to the internal part of metal oxide particles, is still not adequate. Here, an effective strategy is demonstrated for directly preparing polycrystalline decahedral plates of substitutional carbon‐doped anatase TiO₂ from titanium (IV) oxalate by a thermally induced topotactic transition in an inert atmosphere. Because of the carbon concentration gradient introduced in side of the plates, the carbon‐doped TiO₂ (TiO_2–xC_x) shows an increased visible light absorption and a two orders of magnitude higher electrical conductivity than pure TiO₂. Consequently, it can be used as a photocatalyst and an active material for lithium storage and shows much superior activity in generating hydroxyl radicals under visible light and greatly increased electrical‐specific capacity at high charge–discharge rates. The strategy developed could also be applicable to the atomic‐scale modification of other metal oxides.     

Dispersible SnO2:Sb and TiO2 Nanocrystals After Calcination at High Temperature

High-temperature treatment of functional nanomaterials, through postsynthesis calcination, often represents an important step to unlock their full potential. However, such calcination steps usually severely limit the preparation of colloidal solutions of the nanoparticles due to the formation of sintered agglomerates. Herein, a simple route is reported to obtain colloidal solutions of calcined n-conductive antimony doped tin oxide (ATO) as well as titanium dioxide (TiO₂) nanoparticles without the need for additional sacrificial materials. This is achieved by making use of the reduced contact between individual nanoparticles when they are assembled into aerogels. Following the calcination of the aerogels at 500 °C, redispersion of the nanoparticles into stable colloidal solutions with various solvents can be achieved. Although a slight degree of sintering is inevitable, the size of the resulting aggregates in solution is still remarkably small with values below 30 nm.     

The synthesis of nanosized TiO2 powder using a sol-gel method with TiCl4 as a precursor

Nanosized TiO₂ powder with anatase structure was synthesized by a sol-gel method using TiCl₄ ethanol solution as a precursor. The grain size of TiO₂ powder was homogenous and was about 10 nm after the precursor was calcined at 500 °C for 1 hour. Anatase TiO₂ powder formed after the precursor was calcined at a temperature ranging from 300 °C to 550 °C. The gelatinizing mechanism of TiCl₄ in ethanol solution can be described as followings. When mixed with ethanol, TiCl₄ reacted with ethanol to form TiCl _x (OCH₂CH₃)_{4 – x} species and HCl gas. During gelatinizing process, TiCl _x (OCH₂CH₃)_{4 – x} species absorbed water from atmosphere to form Ti(OH)₄ precursor, which was polymerized to be an inorganic polymer. The formation of inorganic polymer of Ti(OH)₄ was intensified with gelatinizing time. In contrast, the organic component was removed from the precursor. The formation of anatase TiO₂ can also be promoted by increasing gelatinizing time. The influence of alcohol on the reacting progress and dispersivity was also studied. The size and activity of alcohol molecule were found to have influence on the polymerization and mineralization degree of the precursor and the dispersivity of TiO₂ powders.     

An efficient photo-catalytic VOC removal process by one-pot synthesized N-F/TiO2 nanoparticles in fluidized-spouted bed reactor

Photocatalytic degradation under visible light irradiation is an important task of using solar energy for the removal of environmental pollutants. N-F/TiO₂ nanoparticles were synthesized in one-pot sol–gel condition using tetra-isopropyl-orthotitanate as the TiO₂ precursor and NH₄F as the N-F doping source. Diffuse reflectance spectroscopy (DRS) analysis of the material has shown a reduction of band gap energy and shifting absorption edge to the visible wavelengths. A fluidized-spouted bed reactor equipped with the light source was designed and constructed for the oxidation process of VOC from the high airflow rate under Hg lamp irradiation using synthesized N-F/TiO₂ nanoparticles. Acetaldehyde was used as the air pollutant model molecule of VOC in this process. The effluent acetaldehyde concentration was analyzed continuously along the time by an online Gas Chromatography (GC) from the start up to reaching steady conditions. The results have revealed significant enhancement of acetaldehyde removal by the N-F/TiO₂ sample fabricated with an equal weight ratio of NH₄F/Ti. After steady conditions, almost 100% removal of acetaldehyde was observed in the spouted bed reactor from a high airflow stream of 5?L/min polluted with 1000?ppm acetaldehyde at room-temperature conditions, under 80?W Hg with 500 Lux intensity.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.