TiO2 Hollow Particles Research Articles

A thorough investigation of the utilization of metal-organic framework (MOF) coated titanium dioxide in photocatalytic applications: A review

Overall, this review provides accessible information about Metal-organic frameworks (MOFs) coated on TiO2 surfaces that can advance the photocatalytic activity of designing and creating more efficient materials as well as promoting application. TiO2 photocatalyst has been extensively studied for the unraveling of various environmental issues. Despite its potential, the high rate of recombination of photogenerated charge carriers and its broad band-gap energy pose obstacles to its application in photocatalysis. In order to overcome these hurdles, our research has concentrated on the incorporation of MOF coatings. The production of photoactive MOF coatings is a key issue because they have excellent photocatalytic performance and offer many industrial opportunities for photocatalysis. Different methods have been applied to produce MOF shell or layer on TiO2 NRs, NTs, NWs, and hollow particles. The object of this review is to supply an overview of the research on applying the MOF coating to the titania surface.

Dual-asymmetrically selective interfaces-enhanced poly(lactic acid)-based nanofabric with sweat management and switchable radiative cooling and thermal insulation

All-weather personal thermal regulation has far been challenged by variable environments especially the regulatory failure caused by highly-dense solar radiation, low environmental radiation and the fluctuated epidermal moisture in different seasons. Herein, from the design of interface selectivity, dual-asymmetrically optical and wetting selective polylactic acid-based (PLA) Janus-type nanofabric is proposed to achieve on-demand radiative cooling and heating as well as sweat transportation. Hollow TiO2 particles are introduced in PLA nanofabric causing high interface scattering (∼99%) and infrared emission (∼91.2%) as well as surface hydrophobicity (CA > 140°). The strictly optical and wetting selectivity help achieve ∼12.8℃ of net cooling effect under > 1500 W/m2 of solar power and ∼5℃ of cooling advantage higher than cotton fabric and sweat resistance simultaneously. Contrarily, the semi-embedded Ag nanowires (AgNWs) with high conductivity (0.245 Ω/sq) endows the nanofabric with visible water permeability and excellent interface reflection for thermal radiation from body (>65%) thus causing ∼7℃ of thermal shielding. Through simple interface flipping, synergistical cooling-sweat reducing and warming-sweat resisting can be achieved to satisfy the thermal regulation in all weather. Compared with conventional fabrics, multi-functional Janus-type passive personal thermal management nanofabrics would be of great significance to achieve the personal health maintenance and energy sustainability.

The Fig-Like hierarchical Double-Shelled hollow TiN particles as sulfur host for Lithium-Sulfur batteries

Lithium-sulfur battery(LSB)’s commercial manufacturing has been mainly retarded by the “shuttle effect” and low electrical conductivity of polysulfides (LiPSs). Designing a cathode with hollow and hierarchically porous structures was expected to solve the above problems. Herein, a kind of TiN particles with the hierarchical hollow double-shelled structures was synthesized and applied to cathodes of LSB. The Fig-like hollow TiO2 particles (FHTiO2s) were firstly synthesized by the hard-template method. Subsequently, the Fig-like hierarchical hollow double-shelled TiN particles (FHTiNs) were synthesized by the template-free sequential transformation and separation approach (STSA). It was verified that the heating temperature and time were key parameters. Special Fig-like double-shell hollow structures could greatly increase the loading of S, and the excellent initial capacity of FHTiNs cathodes was up to 1159 mAh/g. On the one hand, the Fig-like framework in internal cavity and double-shell structures could promote the ultrahigh specific surface area, and the adsorption to LiPSs was improved by increasing active sites; On the other hand, the shuttle effect of LiPSs was weakened by the fig-like framework and double-shell structures, which slowed down the massive dissolution of sulfur in the electrolyte. As a result, the pleasant rate performance of FHTiNs cathodes was up to 400 mAh/g at 5C. This novel structures and synthesis method provided a new strategy for the designing of LSB cathodes.

Synthesis of TiO2 hollow nanoparticles with different shell thickness and effect of structure on photocatalytic activity

Over the past decades, the accumulation of organic pollutants in surface water, groundwater, and even drinking water have raised as a serious issue. A photocatalytic process using a semiconductor like TiO2 is one solution for the degradation of organic pollutants in water, however, the low efficiency of the photocatalytic reaction is still a problem. In recent years, increasing the efficiency of semiconductors by controlling the structure and morphology has been in the spotlight, and hollow structures have gathered specific attention thanks to their unique structure. In this study, hollow TiO2 particles with different shell thicknesses are synthesized and the effect of particle size and shell thickness on photocatalytic activity of TiO2 has been investigated.

Diffusion mechanism and release profile of a multivitamin from TiO2 hollow particles

The present study aimed to control the release rate profile of a multivitamin that has hydrophilic and hydrophobic properties and to investigate its diffusion rate from titanium dioxide (TiO2) hollow particles. The TiO2 hollow particles encapsulating the vitamins C and E were prepared via a sol-gel process using an inkjet nozzle. The obtained particles were evaluated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The sustained release rate was estimated by the dialysis bag method. Additionally, a diffusion mechanism for the multivitamin from the TiO2 hollow particles was proposed.TiO2 particles prepared by this method exhibited spherical porous structures. The TiO2 hollow particles were successful in encapsulating both the hydrophilic vitamin C and the hydrophobic vitamin E, resulting in a sustained release profile for these two components from the TiO2 hollow particles. The release behavior of the multivitamin was quite different from that of each single vitamin. This is related to the adsorption state of each vitamin on the TiO2 particle surface. The effective diffusion coefficient of VC derivative (8.403 × 10−13 cm2/s) was faster than that of VE derivative (1.671 × 10−13 cm2/s). This tendency may be attributed to the difference between hydrophilic and hydrophobic properties. Additionally, the value of effective diffusion coefficient in multi-component was always larger than that in single component. The value of Knudsen diffusion coefficient in VC and VE derivative was 2.684 × 10−3 and 2.264 × 10−3 cm2/s, respectively. In all samples, Knudsen diffusion coefficient was larger than molecular diffusion coefficient. The diffusion mechanism of the active ingredients likely depends on the pore size of TiO2 and the molecular size of the active ingredients.

A facile method for the fabrication of SiO2 and SiO2/TiO2 hollow particles using Na2SO4 particles as templates

We present an effective and environmental-friendly pathway to prepare SiO2 hollow particles using Na2SO4 particles as templates, which involved sol-gel silica coating on surface of the templates and subsequent removal of the Na2SO4 templates by water-dissolution. Further, SiO2/TiO2 double-shell hollow particles were prepared by coating TiO2 on the surface of the hollow SiO2 particles. The morphologies and structures of the synthesized hollow particles were characterized using SEM, TEM, XRD, FTIR, BET, and UV. The sizes and shapes of the hollow particles can be controlled by using Na2SO4 templates with different sizes and shapes. The sizes of hollow particles were in the range from 500 nm to 15 μm. By changing the concentration of silicon precursor, the shell thickness of hollow SiO2 particles can be controlled in the range of 25–200 nm. In addition, SiO2/TiO2 double-shell hollow particles showed better photocatalytic degradation of Rhodamine B than that of hollow TiO2 particles and solid TiO2 particles. The important characters of the water-soluble Na2SO4 template method is as follows:

Radiation stability of TiO2 hollow particles pigments and coatings synthesis by hydrothermal methods from TTIP

The effect of protons (E = 100 keV and F = 5 × 1015 cm−2) exposure on the diffuse reflectance spectra of the TiO2 hollow particles powders and coatings based on them in wavelength range from 250 to 2500 nm have been investigated. The synthesis of the hollow particles was carried out by the hydrothermal method using chemicals TTIP and TBAH. The coatings were prepared from a mixture of hollow particles and organosilicon binder (polydimethylsiloxane). Evaluating the changes of the solar absorptance it was found that the radiation stability of the TiO2 hollow particles and coatings based on them is higher than the radiation stability of the powder and coatings based on microparticles. The low radiation stability of the hollow particles is due to a decrease in the concentration of radiation-induced defects.

Fabrication of Efficient Visible-light-responsive TiO2-WO3 Hollow Particle Photocatalyst by Electrospray Method

A visible-light-responsive TiO2-WO3 hollow particle photocatalyst was successfully fabricated by an electrospray method, followed by hydrothermal treatment and calcination at 873 K. The photocatalytic decomposition of acetaldehyde with pristine TiO2 and TiO2-WO3 hollow particles was evaluated under visible light irradiation (λ > 400 nm). The decomposition of acetaldehyde did not proceed readily with hollow TiO2 particles under visible light irradiation, whereas the hollow TiO2-WO3 particles showed high photocatalytic activity for the decomposition of acetaldehyde.

Synthesis of TiO2 hollow particles with highly dispersed CaCO3 template particulates and their photoactivity toward a VOC pollutant

This brief article reports a suitable preparation of TiO2 hollow particles using titanium tetra-isopropoxide (TTIP) as a precursor and highly dispersed calcium carbonate (CaCO3) particle templates prepared from CaCl2 and dimethylcarbonate in the presence of the dispersing agent polyvinylpyrrolidone. The synthesis of TiO2 hollow particles was optimized considering certain experimental conditions: (a) the amount of TTIP, (b) the hydrolysis rate of TTIP in water/ethanol solvent, and (c) the mass of CaCO3 template particulates. The morphology and particle sizes of the resulting hollow particles (CaCO3 templates removed on addition of acid) were assessed by scanning electron microscopy (SEM and SEM-EDX); their crystalline phase (anatase) was determined by X-ray diffraction techniques and the specific surface area by the BET method. A formation mechanism of the TiO2 particles is described in terms of the TiO2 particulates generated under each experimental condition. The photoactivity of the TiO2 hollow particles was subsequently examined through the transformation of a volatile organic pollutant (iso-propanol) in air whose faster rate of photodegradation relative to TiO2 particles (synthesized without CaCO3) correlates with the greater specific surface area of these hollow particles (19.0 vs. 65.1 m2 g−1).

Synthesis and Characterization of Hollow TiO2 Particles Coated with Polyimide Brushes by Click Chemistry

In order to improve the compatibility between nanoparticles and polymer matrix, a feasible processing way for grafting polyimides (PI) on the surface of hollow TiO2 particles was developed. Hollow TiO2 spheres were prepared by using polystyrene-methyl acrylic acid latex as a template starting from tetrabutyl titanate. Surface graft of azide-decorated hollow TiO2 spheres with well-defined alkyne-terminated PI were achieved by "click" chemistry in three steps: (1) choloromethylation and azidization of hollow TiO2, (2) preparation of alkyne-terminated PI by polycondensation, (3) click coupling between the azidized hollow TiO2 and the alkyne-terminated PI under the catalysis of CuSO4/sodium ascorbate. Fourier transform infrared (FTIR) and Nuclear Magnetic Resonance (1HNMR) spectra were used to illustrate quantitative transformation of the PI brushes on hollow TiO2 particles into the desired functional group. The morphology of hollow TiO2-PI composite particles was characterized by transmission electron microscopy (TEM) which showed the irregular hollow structure. The results indicate that the grafting of polymer chains with thermostability and flame retardance on the surface of hollow TiO2 sphere is successful.

Geometrical implication of ion transporters employing an ellipsoidal hollow structure in pseudo-solid electrolytes.

We demonstrate facilitated ion transport in oligomer electrolytes by introducing TiO2 hollow particles of ellipsoidal and spherical shapes. It was found that the TiO2 hollow particles of ellipsoidal shape are much more effective in constructing ionic diffusion paths for the Grotthuss mechanism, resulting in highly enhanced diffusion coefficients of ions such as I(-) and I3(-) in oligomer electrolytes. Compared to the hollow spheres of the TiO2 component, the ellipsoidal hollow particles of the TiO2 component provide 11% larger ionic diffusion coefficients, because of their geometry with a relatively small diffusion resistance. Since the facilitated ion transport can render fast redox reactions at both photo and counter electrodes, the solid state dye-sensitized solar cells employing oligomer electrolytes based on the TiO2 hollow ellipsoids exhibit highly improved photovoltaic performances including highly improved energy-conversion efficiency without destabilizing the cell.

Preparation of hollow TiO2 nanoparticles through TiO2 deposition on polystyrene latex particles and characterizations of their structure and photocatalytic activity

In a mixed solvent of water and ethanol, polystyrene/titanium dioxide (PSt/TiO2) composite particles of core-shell structure were prepared by hydrolysis of tetrabutyl titanate in the presence of cationic PSt particles or anionic PSt particles surface-treated using γ-aminopropyl triethoxysilane. Hollow TiO2 particles were obtained through calcination of the PSt/TiO2 core-shell particles to burn off the PSt core or through dissolution of the core by tetrahydrofuran (THF). An alternative process constituted of preheating the PSt/TiO2 particles at 200°C to allow partial crystallization followed by calcination or PSt dissolution by THF. The outcome TiO2 particles thus prepared were examined by TEM, and hollow TiO2 particles were observed. The crystalline phase structure and phase transformation were characterized, which revealed that preheating before the removal of the PSt core was useful to achieve the desired hollow TiO2 particles, and the calcination process was beneficial to the formation of anatase and rutile structures. The tests of TiO2 particles as catalyst in the photodegradation of Rhodamine B demonstrated that a much higher catalytic activity was observed with the TiO2 hollow particles prepared through calcination combined with preheating.

Au-TiO 2 Yolk-Shell Particles for Photocatalysis Application

Abstract Au-TiO2 yolk-shell particles with gold as core and mesoporous TiO2 as shell have been synthesized by deposition of TiO2 nanoparticles onto Au-silica core-shell particles via modified sol-gel method at room temperature followed by the removal of silica midlayer by NaOH treatment. The Au-TiO2 yolk-shell particles exhibit a high colloidal stability, which can be applied as excellent heterogeneous photocatalysts for the photodegradation of the dye Rhodamine B under UV irradiation. The Au-TiO2 yolk-shell particles have shown much higher photocatalytic activity than that of the hollow TiO2 particles without gold.

Fine control of titania deposition to prepare C@TiO2 composites and TiO2 hollow particles for photocatalysis and lithium-ion battery applications

In this study, an effective method of slow hydrolization of metal alkoxide (e.g., Ti(C4H9O)4) in an ethanol–water system was systematically investigated and used to finely control the deposition of titania on carbon colloids. A model of adsorption–hydrolization of precursors during the coating process was rationally built for the first time to interpret the usability of the method and facilitate its further extension. Using this strategy, titania in the form of supported nanocrystals or layers on carbon colloids (TiO2/C, C@TiO2) was successfully tailored. Meanwhile, finely dispersed hollow TiO2 nanoparticles with shells consisting of different crystalline structures were also prepared by varying the calcination conditions after removing the carbon cores. More importantly, the effects of the crystalline and nano/macrostructures of the as-prepared TiO2 samples in photocatalysis and lithium-ion battery applications were analyzed in detail. The preliminary results show that anatase–rutile TiO2 hollow particles demonstrate a higher catalytic activity in the photo-degradation of rhodamine B than anatase TiO2 hollow particles, powders, and P25. However, in the case of Li-ion battery applications, the anatase TiO2 hollow particles exhibited better performance as anode materials with high capacities of around 190 mA h g−1, 140 mA h g−1, and 120 mA h g−1 at current densities of 60 mA g−1, 120 mA g−1, and 300 mA g−1, respectively, accompanied by stable cyclability.

General Synthesis and Optical Properties of Monodisperse Multifunctional Metal-Ion-Doped TiO2 Hollow Particles

Various, monodisperse, multifunctional metal-ion-doped TiO2 hollow particles are prepared by a general metal-ion-doped method. They show brilliant colors in the visible region and low reflectance in the ultraviolet range. For example, the reflectances of green Co-doped TiO2, red Fe-doped TiO2, green Co/Zn-doped TiO2, and sky blue Co/Al-doped TiO2 particles are 5.9, 4.8, 5.9, and 4.8%, respectively, and the infrared emissivities in the region of 8−14 μm are very high, 97.5, 93.7, 95.2, and 96.9%, respectively. These results show that the monodisperse hollow particles could be potential candidates as good pigments, ultraviolet prevention materials, and thermal conservation materials. In addition, Al-doped TiO2 and Al/Fe-doped TiO2 particles are also prepared by this strategy.

Preparation of platinum-doped hollow spheres and their electrocatalytic activity in water electrolysis

Pure TiO2 hollow spheres were prepared by using poly(styrene-methacrylic acid) latex particles as template; thereafter, titania hollow spheres were coated by platinum with an appropriate amount of choloroplatinic acid solution to obtain Pt/TiO2 catalysts. The morphology and structure of nonstructural Pt/TiO2 hollow spheres were characterized by BET, XRD, TGA, SEM and TEM analysis. In the samples, a remarkably uniform layer of Pt consisting of particles from 5 to 70 nm in size was formed over TiO2 hollow spheres. We found the electrocatalytic nature of the samples by cyclic voltammetric experiment in acidic solution. The anodic peak current density of 20 wt% Pt-loaded TiO2 hollow particles was observed 2.5 times higher than that of 5 wt% Pt/TiO2 in the same experimental condition. Also, the anodic current density of 20 wt% Pt/TiO2 hollow spheres calcined at various temperatures followed the order: 400 °C≈500 °C>600 °C. The electrocatalytic activity of the Pt-loaded TiO2 hollow spheres depends on the amount of atomic platinum present in the sample; a higher concentration of platinum results in a larger current density value in anodic sweep, resulting in more oxygen production during electrolysis. Pt/TiO2 hollow sphere catalysts have also shown long term electrocatalytic stability in acidic media.