TiO2 Hollow Microspheres Research Articles

Hierarchical CuO–TiO2 Hollow Microspheres for Highly Efficient Photodriven Reduction of CO2 to CH4

In this study, a scalable one-pot template-free synthesis strategy was employed to fabricate CuO-incorporated TiO2 hollow microspheres in large scale. The as-prepared hollow spherical TiO2 nanoparticles possess unique structural characteristics, namely, large surface area and a hierarchical nanoarchitecture composed of a hollow macroporous core connected with large mesopores in the shell. The large surface area provides a great number of surface active sites for the reactant adsorption and reaction whereas the hierarchical nanoarchitecture enables fast mass transport of reactant and product molecules within the porous framework. In addition, the hollow macroporous core–mesoporous shell nanostructure favors multilight scattering/reflection, resulting in enhanced harvesting of exciting light. Furthermore, the incorporated CuO clusters work efficiently as a cocatalyst to improve the photocatalytic activity. As a result, the CuO-incorporated TiO2 hollow microsphere catalyst demonstrates much higher photocatal...

Experimental study of TiO2 hollow microspheres removal on elemental mercury in simulated flue gas

TiO2 hollow sphere was synthesized by hydrothermal method using trifluoroacetic acid (TFA) and Ti(SO4)2 as raw materials, and it was applied to photocatalytic oxidization of elemental mercury (Hg0) in the simulated flue gas. The prepared samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-vis DRS) and nitrogen adsorption/desorption. The results showed that only anatase phase TiO2 hollow sphere was obtained. The average diameter of TiO2 hollow spheres was about 800nm and the shell thickness was about 200–400nm. When M, the molar ratio of TFA to Ti(SO4)2, was higher than a certain value, the photocatalytic activity of prepared TiO2 hollow spheres began to reduce. When M=2, addition TFA content was the best quantity, which got the best TiO2 hollow spheres and provided the most appropriate F− decomposed from TFA during the sample preparation, which was helpful to its photocatalytic ability. In the experimental temperature range, the photocatalytic oxidation efficiency decreased with the increasing of reaction temperature, and the intensity of UV irradiation had an important effect on the photocatalytic reaction. When UV irradiation intensity was 303.45μWcm−2 and reaction temperature was 55°C, TiO2 hollow sphere sample prepared at M=2 had the highest photocatalytic ability and the mercury removal efficiency reached up to 82.75%.

Controlled preparation of TiO2 hollow microspheres constructed by crosslinked nanochains with high photocatalytic activity

TiO2 hollow microspheres were successfully synthesized via a controlled hydrolysis reaction, which involved the deposition of an inorganic coating of TiO2 on the surface of carbon spheres and subsequent removal of carbon spheres by calcination in air. The as-prepared TiO2 hollow microspheres with an average diameter of 200 nm presented a novel morphology, which was constructed by closely crosslinked TiO2 nanochains. The morphology of the hollow sphere can be controlled by varying the concentration of TiCl3 solution. A possible formation mechanism was also proposed. The photo-degradation of rhodamine B (RhB) aqueous solution showed that TiO2 hollow microspheres exhibited higher photocatalytic activity than that of TiO2 nanoparticles. The enhanced photocatalytic activity of the as-prepared TiO2 microspheres here could result from their hollow structures assembled by TiO2 nanochains and large light-harvesting efficiency.

Highly porous TiO2 hollow microspheres constructed by radially oriented nanorods chains for high capacity, high rate and long cycle capability lithium battery

Hierarchical nanorods chains-constructed TiO2 hollow microspheres (HNC-TiO2-HMSs) have been designed and prepared through a facile one-pot fluorine-free solvothermal alcoholysis route using TiCl4 and isopropanol reaction system. Owing to the assembly of radially oriented nanorods chains leading to the formation of the shell of the hollow spheres, a large series of straight channels along nanorods chains are formed. Such highly porous hollow microspheres with hollow cavity, straight nanorods chains and straight nanochannels are highly desirable for Li ions batteries because such structure can easily store the electrolyte, facilitate the charge diffusion and Li+ insertion and buffer the volume change during the Li+ insertion/extraction process. One of the key innovation of the present work is the fine tuning of water amount released from the esterification of alcohol to induce in a well controlled hydrolysis of TiCl4 and engineer precisely HNC-TiO2-HMSs formation. Most importantly, the released Cl− ions direct the nanorods growing along (001) crystal plane and self-assembling along the radial direction accompanying with nanorods size controlling to form HNC-TiO2-HMSs. The obtained TiO2 anode material with such special structure demonstrates excellent Li+ storage capacity with outstanding cycle performance and superior rate capability at different rates over 700 cycles: a reversible capacity of 216mAhg−1 is obtained after 100 cycles at 1C and a reversible capacity of 112mAhg−1 is retained after 100 cycles at 10C. The SEM, TEM, HRTEM and in-situ XRD techniques have been utilized to shed light on the Li+ insertion process and the phase transformation. Most importantly, a self-improving phenomenon of cycle performance and storage capacity was observed owing to the formation of numerous ~5nm Li2Ti2O4 nanocrystals formed on the surface of the nanorods chains. The results reveal that the high performance of the as-prepared HNC-TiO2-HMSs in terms of storage capacity, cycle performance and rate capability can be attributed to the synergy of the special structure and the self-improving phenomenon. Our simple reaction system may provide a concrete example on the construction of novel hollow spherical porous anode materials for high performance lithium batteries.

Graphene-based hollow TiO2 composites with enhanced photocatalytic activity for removal of pollutants

Catalytically active graphene-based hollow TiO2 composites(TiO2/RGO) were successfully synthesized via the solvothermal method. Hollow TiO2 microspheres are uniformly dispersed on RGO. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) were used for the characterization of prepared photocatalysts. The mass of GO was optimized in the photocatalytic removal of rhodamine B (RhB) as a model dye pollutants. The results showed that graphene-based hollow TiO2 composites exhibit a significantly enhanced photocatalytic activity in degradation of RhB under either UV or visible light irradiation. The formation of the graphene-based hollow TiO2 composites and the photocatalytic mechanisms under UV and visible light were also discussed.

Hollow TiO2 microspheres assembled with rutile mesocrystals: Low-temperature one-pot synthesis and the photocatalytic performance

Hollow TiO2 microspheres assembled with rutile mesocrystal nanorods were precipitated directly from a mixed aqueous solution of K2TiO(C2O4)2, H2O2 and HNO3 at a low temperature of 80°C. The hollow microspheres consisted of rutile mesocrystal nanorods with an average diameter of 200nm and length of 500nm. The morphology evolution upon the reaction duration suggests that the microstructure is formed through a hydrolysis–dissolution–precipitation procedure. The unique nanostructure of the hollow microspheres showed remarkable photocatalytic activity in photodegrading rhodamine B in water under the UV light illumination.

Highly sensitive and selective room-temperature formaldehyde sensors using hollow TiO2 microspheres

Room temperature chemoresistive gas sensors could significantly decrease the demand of power consumption and are thus highly desirable in self-sustained nanosensors. Here we report that chemoresistive sensors fabricated from mesoporous hollow TiO2 microspheres show high sensitivity and selectivity to sub-ppm level of formaldehyde at room temperature with the assistance of low powered UV LED photon energy (2.5mW). The sensor indicated excellent selectivity to other possible interferrents such as methanol, ethanol, acetone, ammonia and methylbenzene at low concentrations. These sensors have a much faster response (∼40s)/recovery (∼50s) characteristic, which significantly surpass the sensing properties shown by other types of nanostructured TiO2 reported in literature.

A hierarchical homogeneous core–shell structure of TiO2 hollow microspheres for high efficiency dye-sensitized solar cells

Core–shell TiO2 (cs-TiO2) hollow microspheres are prepared via a facile hydrothermal method, by using titanium potassium oxalate precursor in dilute sulfuric acid. The characterization shows that the as-prepared TiO2 microspheres have core–shell structure. The diameters of cs-TiO2 microspheres are in the range of 2–5μm. The optical investigation evidences that the cs-TiO2 microsphere film exhibits a prominent light-scattering effect at a wavelength range of 600–800nm. The cs-TiO2 microspheres are applied as a scattering layer on top of a nanocrystalline P25 film, serving as the photoanode of dye-sensitized solar cells (DSSCs). A high efficiency of 7.7% is achieved after introducing the cs-TiO2 hollow microsphere scattering layer, compared with 6.21% for the photoanode with commercial P25. Based on the optical investigation and electrochemical impedance measurement, the improved efficiency can be ascribed to the enhanced light-scattering ability and the reduced interface recombination rate.

Synthesis of uniform hollow TiO2 and SiO2 microspheres via a freezing assisted reverse microemulsion-templated sol–gel method

Uniform titania and silica hollow microspheres of 300–500nm diameter with controlled wall thickness have been successfully synthesized using monodispersed micro-ice as the template generated by freezing water droplets in a reverse microemulsion at −40°C and −80°C and subsequent sol–gel reactions on the surface of the formed micro-ice. Furthermore, the growth mechanism of the hollow spheres by this facile and interesting technique was discussed in detail.

Fabrication of chain-like TiO2 hollow microspheres with enhanced photocatalytic activity

TiO2 hollow microspheres (TiO2-HMSs) have attracted much attention due to their low density, high photoreactivity and easy recovery. However, fabrication of TiO2-HMSs is time-consuming and costly. In this paper, effect of H2O2 on the formation of chain-like TiO2-HMSs was studied using (NH4)2TiF6 as titanium source and urea as neutralizer through a one-pot hydrothermal reaction strategy. The prepared TiO2-HMSs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM). The photocatalytic activity of TiO2-HMSs was evaluated by photocatalytic degradation of an anionic dye X3B under UV irradiation. It was found that the presence of H2O2 not only influences the nucleation, but also enhances the hollowing process of TiO2-HMSs by accelerating the “inside-outside” mass transfer. TiO2-HMSs prepared in the presence of H2O2 showed enhanced photocatalytic activity due to the synergistic effects of well crystallization and hollow structures.

Fabrication of mesoporous titanium dioxide/tin dioxide/carbon hollow microspheres as high performance anode for lithium-ion batteries

Mesoporous titanium dioxide/tin dioxide/carbon (TiO2/SnO2/C) hollow microspheres are fabricated by a facile strategy. In this composite, SnO2 is sandwiched between TiO2 hollow microsphere and carbon coating layer. This intriguing nanostructure effectively buffers volume change and structural stress, and facilitates electron and ion transport throughout the electrode, thus contributing to excellent cycling stability.

Gold nanoclusters based dual-emission hollow TiO2 microsphere for ratiometric optical thermometry

The dual-emitting hollow TiO2 microspheres are prepared and they show dual emission fluorescence with single-excitation, which could be used as nanosensors for accurate measurement of temperature over the wide temperature range (20–80 °C).

Facile template-free preparation of hierarchical TiO2 hollow microspheres assembled by nanocrystals and their superior cycling performance as anode materials for lithium-ion batteries

Uniformly distributed hierarchical anatase TiO2 hollow microspheres assembled by nanocrystals prepared via a facile template-free strategy exhibit an excellent cycling performance as the anode material for lithium-ion batteries.

Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2 hollow microspheres with enhanced visible light photocatalytic activity.

Silver-loaded nitrogen-doped yolk-shell mesoporous TiO2 hollow microspheres (Ag-N-TiO2-YSM) were prepared by employing acetic acid as the hollowing controller and triethanolamine as the N source for the first time. Ag nanoparticles (NPs) were uniformly deposited by a simple in situ photo-reduction method, which can prevent the aggregation of Ag NPs. The efficiency of the as-prepared samples was investigated by monitoring the degradation of rhodamine B and ciprofloxacin under visible light irradiation. The experimental results indicate that N-doped yolk-shell mesoporous TiO2 hollow microspheres show higher photocatalytic activity than P25 TiO2 under visible light irradiation because of N doping and the unique yolk-shell structure. In addition, Ag-N-TiO2-YSM shows enhanced activity compared with N-TiO2-YSM due to the SPR absorption of silver NPs and the fast generation, separation and transportation of the photogenerated carriers. Moreover, the Ag contents can affect the photocatalytic activity of the Ag-N-TiO2-YSM composite. A suitable amount of Ag deposition gives the highest photocatalytic activity. A higher loading does not improve the photocatalytic activity of N-TiO2-YSM further. The active species generated in the photocatalytic system were also investigated. Based on our experimental results, a possible photocatalytic mechanism was proposed. The strategy presented here gives a promising route towards the development of delicate metal@hollow semiconductor composites for many applications in photocatalysis.

Shell-in-Shell TiO2 hollow microspheres and optimized application in light-trapping perovskite solar cells

The shell-in-shell structured TiO2 hollow microspheres with enhanced light scattering ability were synthesized via a facile one step hydrothermal process. The diameter of the microsphere is about 1.5 μm, the core of the unique shell-in-shell structure is composed of TiO2 nanoparticles with a diameter of about 15 nm, while the shell is constructed with ∼50 nm TiO2 nanocubes. The hollow space between the outer shell and the inner shell is about 230 nm. The formation mechanism of the unique shell-in-shell structure is interpreted. The design and the optimized application of shell-in-shell structured TiO2 hollow microspheres in the light-trapping perovskite solar cells are also investigated. Owing to the light scattering properties of the shell-in-shell structure of the hollow microsphere, the optimized photoelectrode exhibits an enhanced photoelectric conversion efficiency of 4.29% using perovskite CH3NH3PbI3 as the sensitizer. The shell-in-shell hollow TiO2 microsphere shows a 21.2% increase in conversion efficiency when compared with P25 nanoparticels photoanode. The conversion efficiency enhancement is mainly attributed to the increase of short-current density induced by the light scattering effect.

Multishelled TiO2 hollow microspheres as anodes with superior reversible capacity for lithium ion batteries.

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

Visible-light responsive carbon–anatase–hematite core–shell microspheres for methylene blue photodegradation

Core shell carbon–anatase–hematite (C@TiO2@α-Fe2O3) microspheres with sandwich-like structures were synthesized by an effective three-step approach. Specifically, using carbonaceous saccharide microspheres as template directs the sequential deposition of TiO2 layer by the modified Stöber method and subsequent α-Fe2O3 layer via the impregnating-calcination process. The samples were characterized by SEM, TEM, XRD, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity towards degradation of methylene blue aqueous solution under visible light irradiation was significantly improved, as compared to that of the TiO2 hollow microspheres and TiO2@α-Fe2O3 hollow microspheres counterparts. This enhancement in photoactivity is mainly attributed to two positive effects of the coupling TiO2 between the C core and α-Fe2O3 shell. Firstly, a matching heterostructure between TiO2 and α-Fe2O3 could dramatically improve the separation of photoinduced electron–hole pairs. Secondly, C-core could enhance the absorption in the visible-light region, serve as good adsorbent towards dye molecules, and provide a network to rapidly transfer the photoexcited electrons from the conduction band of TiO2 during the photocatalytic process. The study also provides a general and effective method in the fabrication of core–shell composites with sound heterojunctions that may show a variety of applications.

Template-free fabrication of rattle-type TiO2hollow microspheres with superior photocatalytic performance

In the paper, an environmentally friendly and template-free route based on a simple hydrothermal process has been developed for preparing rattle-type TiO2 hollow microspheres by using titanium(IV) sulfate (Ti(SO4)2) as the titanium source and glycerol/water as the cosolvent. The SEM and TEM images showed that the obtained TiO2 products were rattle-type hollow nanostructures with a diameter of ca. 1.1 μm. More importantly, the products have a good thermal stability and high crystallinity, which is favorable for their practical applications. According to the experimental results, a possible formation mechanism involving the Ostwald ripening process was proposed combined with various techniques such as SEM, TEM, BET, IR, and UV-vis. The photocatalytic results indicated that the TiO2 microspheres obtained from 750 °C thermal treatment exhibited higher photocatalytic activity for the photodegradation of methyl orange (MO) than those of other calcination temperatures and commercial Degussa P25. To further improve the photocatalytic activity, Ag-doped TiO2 photocatalyst was also prepared by the impregnation method. The results indicated that the photocatalytic activity of the Ag/TiO2 catalysts was greatly enhanced compared with the pure TiO2 catalysts. The possible photodegradation mechanism was also discussed.

Synthesis and characterization of TiO2/C Janus composite particles and its photocatalytic activity for the degradation of rhodamine B

Janus materials with anisotropic chemical structures and physical properties have attracted increasing attention due to their diversified potential applications. In this paper, titanium dioxide/3-(trimethoxysilyl) propylmethacrylate (TiO2/MPS) was obtained by swelling assisted with extrusion of PS@TiO2. Then, the phenolic resin (PF) was coated on the surface of MPS lobe. Finally, TiO2/C Janus composite particles were obtained by sintering at the atmosphere of nitrogen. The middle objects during reactive process and the final product were systematically characterized. Results showed that the Janus porous particles of TiO2/C were snowman-like structure, in which the average diameter of the carbon lobe was 178 nm and that of TiO2 lobe was 226 nm. When used as photocatalysts for Rhodamine B degradation in aqueous solution under UV irradiation, the resulted Janus product exhibited more efficient photocatalytic activity than TiO2 hollow microspheres.

Fabrication of TiO2 hollow microspheres by ammonia-induced self-transformation

TiO2 hollow microspheres (TiO2–HMSs) have attracted great interest in recent years due to their unique physical and chemical properties such as low density, high surface area and effective light-harvesting property. In this paper, anatase TiO2–HMSs were synthesized by hydrothermal treatment of amorphous TiO2 microspheres precursor in the presence of ammonia solution at 180°C. The prepared TiO2–HMSs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM). It was found that the presence of ammonia accelerates the hollowing process of TiO2 microspheres, and the phase transformation from amorphous TiO2 to metastable ammonium titanate occurs firstly and then to anatase TiO2 phase, forming fluffy core/shell and yolk/shell structured microspheres. The photocatalytic activity of the photocatalyst was evaluated both by photocatalytic degradation of cationic dye (Rhodamine B) and anionic dye (Brilliant Red X-3B) under UV irradiation. The calcined fluffy core/shell structured TiO2 microspheres with a hydrothermal reaction time of 18h showed the highest photocatalytic activity. Ammonia-induced self-transformation mechanism was also proposed for the formation of TiO2–HMSs.