TiO2 Hollow Microspheres Research Articles

Photocatalytic oxidation of gas-phase Hg0 by Fe-doped TiO2 hollow microspheres

Fe-doped TiO2 hollow microspheres were prepared by the hydrothermal method and characterized by the X-ray diffraction (XRD), the Scanning Electronic Microscopy (SEM), the Energy Dispersive X-Ray (EDX), the Brunauer-Emmett-Teller (BET), and the UV–visible diffuse-reflectance spectrum (UV–Vis). The as-prepared samples were evaluated for photocatalytic removal of Hg0 under ultraviolet light irradiation. The results showed that the sample had a good photocatalytic performance. When M* (the molar ratio of Fe/Ti) was 0.05, the mercury removal efficiency reached up to 100%. It was found that the incorporation of iron narrowed the energy band gap of TiO2 (from 3.11 eV to 2.58 eV) and the absorbing boundary increased from 398 nm to 480 nm. While too much Fe3+ may occupy the capture sites of electrons and holes, which leads to a decrease of photocatalytic efficiency.

Preparation and application of carbon and hollow TiO2 microspheres by microwave heating at a low temperature

Abstract A fast, simple, and energy-saving microwave-assisted approach was successfully developed to prepare carbon microspheres. The carbon microspheres with a uniform particle size and good dispersity were prepared using glucose as the raw material and HCl as the dehydrating agent at low temperature (90°C) in an open system with the assistance of microwave heating. The carbon microspheres were characterized by elemental analysis, XRD, SEM, FTIR, TG, and Raman. The results showed that the carbon microspheres prepared under the condition of 18.5% (v/v) HCl and heating for 30 min by microwave had a narrow size distribution. The core–shell structure of the carbon core and TiO2 shell was prepared with (NH4)2TiF6, H3BO3 using the microwave-assisted method. The hollow TiO2 microspheres with good crystallinity and high photocatalytic properties were successfully prepared by sacrificing the carbon microspheres.

Construction of TiO2@Bi2WO6 hollow microspheres by template method for enhanced degradation of ethylene under visible light

Abstract A series of TiO2@Bi2WO6 hollow microspheres were constructed by using the solvothermal method with carbon microspheres as a template. The morphology and structure of the TiO2@Bi2WO6 hollow microspheres were characterized, and their activities were evaluated for the photocatalytic degradation of ethylene under visible-light irradiation. The results show that the solvothermal reaction conditions applied for the synthesis of the hollow microspheres played a role on their photocatalytic activity. When 20 wt% Bi2WO6 was added in the mixture and synthesis reaction temperature and time were 90 °C and 3 h, respectively, the TiO2@Bi2WO6hollow microspheres exhibited the highest photocatalytic activity with degradation of ethylene reaching 16.82%, which increased by 387% and 95% compared with those of TiO2 hollow microspheres and Bi2WO6 powder, respectively. The improvement in photocatalytic efficiency is attributed mainly to the high-specific-surface-area hollow structure which contains a large number of tiny pores on the microsphere surface and increases the contact probability between ethylene molecule and photocatalyst. The increase in the number of oxygen vacancies and surface defects improves the separation efficiency of photogenerated electron-hole pairs. In addition, TiO2 and Bi2WO6 create a heterojunction, which narrows the band gap of TiO2@Bi2WO6 and enhances the absorption of visible light.

Study on the catalytic activities of g-C3N4@TiO2 hollow microspheres under UV–visible light

TiO2 and g-C3N4 samples were successfully prepared by simple one-step hydrothermal method and calcination method, respectively. Then, g-C3N4@TiO2 hollow microspheres were prepared by simple water bath evaporation method. This work mainly studies the photocatalytic performance of a series of g-C3N4 composite TiO2 hollow microspheres with different contents. In the experiment, the amount of g-C3N4 was adjusted to obtain the highest photocatalytic activity. Therefore, finding the most suitable amount of g-C3N4 has become the main task of this work. By degrading the catalytic effect of Rhodamine B (RhB) solution, the photocatalytic performance of a series of samples was compared. Finally, it was discovered that when the weight ratio of g-C3N4 to TiO2 was 15%, the photocatalytic effect of the sample prepared in this way was the best and the sample was recorded as 15% g-C3N4@TiO2 composite. The heterostructure of TiO2 and g-C3N4 was constructed through the synergistic effect, achieving excellent photocatalytic performance to a certain extent. Therefore, the degradation rate of 15% g-C3N4@TiO2 composite material is 90.8% within 90 min of UV–visible light irradiation. We further used SEM, TEM, XRD, FT-IR spectroscopy, DRS, XPS and other test methods to characterize the composition, morphology and chemical properties of the composite material.

Preparation of molecularly imprinted hollow TiO2 microspheres for selective photocatalysis

Molecularly imprinted materials have been used in selective photocatalysis, essentially due to surface properties, possibility of reuse and low cost, that enhance their industrial and economic interest. The molecular imprinting technique allows the development of photocatalysts with selective recognition for a template molecule, used during synthesis, by increasing the surface area caused by selective recognition sites for the template used. In this work the preparation of hollow titania microspheres was merged with the process of generating selectivity for bilirubin in the shell structure by molecular imprinting. Three major synthesis parameters (solvent, temperature and TiO2 precursor) were studied by performing a set of experiments based in a full factorial design. The selected synthesis conditions were mainly dictated by the maximization of the surface area normalized by the thickness of the TiO2 shell and its controllability. The microspheres kept the integrity of the spherical shape while dispersed in the synthesis solvent. The observed imprinting features for the hollow microspheres prepared in the final synthesis conditions included imprinting factors of 3.1 for the binding strength and 1.3 for the capacity, and bilirubin/protoporphirin selectivity factors of 4.0 in terms of binding strength and 9.6 in terms of binding capacity. These features are very promising, especially the high selectivity factors, given the high resemblance between bilirubin and protoporphirin, and also due to the threat that the somewhat aggressive treatment for the silica core removal, might eventually pose to the templated microstructure of the shell. In fact, the photocatalytic selectivity of the imprinted microspheres was confirmed, with the observation of up to two-fold faster rates of bilirubin consumption vs. protoporphyrin consumption.

Template-free construction of hollow TiO2 microspheres for long-life and high-capacity lithium storage

Hollow spherical structures with abundant mesoporous are of great interest for electrode materials in lithium-ion batteries (LIBs). Although there are many synthetic strategies, using template-free methods to construct the hollow spherical structures still faces great challenges. Herein, we designed a simple template-free method to successfully obtain uniform hollow TiO2 microspheres (TiO2–H) with a well-defined hollow interior and abundant mesoporous. Owing to the structural superiority, the as-prepared TiO2–H as an electrode material for LIBs delivers a high specific capacity of ∼132 mAh g−1 at a current density of 2.0 C after 200 cycles. Besides, it also exhibits satisfying long-term cycling performances with a high specific capacity of ∼100 mAh g−1 at a large current density of 5.0 C after 800 cycles. These superior cycling performances and strong structure stability of TiO2–H electrodes are attributed to the hollow spherical structures with large specific surface areas and rich mesoporous, which can ensure Li ion diffusion and provide sufficient electrochemical reaction sites, as well as remit the large volume changes.

Fabrication of MoS2-deposited TiO2 hollow microspheres and their enhanced photocatalytic application in the generation of hydrogen

MoS2-deposited TiO2 hollow spheres were synthesized successfully under mild temperature and autogenous pressure. The hydrothermal technique was adopted for the synthesis of the TiO2 hollow microsphere, followed by a photodeposition technique for the deposition of MoS2. The physical and chemical nature of the samples was characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, photoluminescence spectroscopy, XPS and UV–vis spectroscopy. In an aqueous medium under the influence of light, the characterized samples were used in the production of hydrogen via photocatalysis. The increase in the formation of hydrogen content during photocatalysis confirms the successful generation and the benefits of the photogenerated carriers. With an increase in the MoS2 content, there is an incredible change in the photocatalytic performance. The resultant is due to the free moment of the holes and electrons and lessening in charge recombination centres formed as a result of the nano-heterojunction linking between MoS2 and TiO2. A more significant photocatalytic production of hydrogen was achieved using 50 MST sample i.e. 106 μmol−1 g−1 beyond which it tends to decrease with an increase in MoS2 content.Graphic abstract

Fe1 /TiO2 Hollow Microspheres: Fe and Ti Dual Active Sites Boosting the Photocatalytic Oxidation of NO.

Recently, single-atom catalysts have aroused extensive attention in fields of clean energy and environmental protection due to their unique activity and efficient utilization of the active atoms. It is of great importance but still remains a great challenge to unveil the effect of single atoms on precise catalysis. Herein, it is reported that doping TiO2 hollow microspheres (TiO2 -HMSs) with single atomic Fe can boost the photoreactivity of TiO2 -HMSs towards NO oxidation due to the synergistic effects of atomically dispersed Fe and bonded Ti atom which act as dual active sites. The atomically dispersed Fe atoms occupy the subsurface Ti vacancies, and the interaction between Ti 3d and Fe 3d orbitals result in the formation of FeTi bond. Single atomic Fe modulates the electronic structure of the bonded Ti atoms by electron transfer, which facilitates the adsorption and activation of NO and O2 at Fe and bonded Ti sites, respectively. In addition, the introduction of single atomic Fe sharply suppresses the production of toxic NO2 byproduct. The synergistic effects of the dual active sites then cause a drastic promotion in photocatalytic oxidation of NO.

The effect of different morphology of fluoride-mediated TiO2 based on Ostwald ripening on photocatalytic activity

The morphology of the catalyst is one of the important factors affecting the photocatalytic activity. In this work, fluoride-mediated TiO2 with different morphologies was successfully prepared based on Ostwald ripening. In particular, the morphology and structure of the TiO2 sample can be adjusted according to different ionic environments. Combining experiments and characterization, the regulation mechanism of different fluorides on the morphology and structure of TiO2 was proposed, and the transport behavior of photogenerated carriers was evaluated. The results show that the morphology and structure have a greater impact on the photocatalytic activity of TiO2. The hollow structure can promote the separation and transfer of carrier and enhance the light collection ability. The surface fluoride as an electron trap can reduce the carrier recombination rate, which is beneficial to the photocatalytic activity of the as-prepared sample. The hollow structure sample shows a good photocatalytic efficiency in the photocatalytic removal of Hg0 in the gas phase, reaching about twice the commercial P25. Finally, the photocatalytic mechanism of the catalyst and the electron-hole migration path are proposed. This research provides new ideas for the design of hollow TiO2 microspheres, which can be widely used in the field of catalysis.

Mesoporous TiO2 hollow microsphere constructed with TiO2 nanospheres: high light scattering ability and enhanced photovoltaic performance for dye-sensitized solar cells

Mesoporous TiO2 hollow microspheres (HTM) composed of irregularly arranged nanospheres were prepared through a one-pot template-free solvothermal way based on the aldol condensation reaction of acetylacetone. The synthesized hollow TiO2 microspheres were investigated by a series of characterizations. Images of FE-SEM and TEM demonstrate that the surface of TiO2 hollow microsphere with a diameter of 1.5 µm are mesoporous and constructed with 150 nm TiO2 nanospheres. The mesoporous shell of the hollow microspheres is about 110 nm in thickness. XRD pattern shows the prepared samples are anatase phase. UV–Vis spectrum indicates that excellent light scattering ability of the prepared sample. The DSSCs using mesoporous TiO2 hollow microspheres as the top scattering layer exhibits the improvement of short-circuit current density (Jsc) and conversion efficiency (η) of 6.63%, while the benchmarked P25 photoanode is only 5.09%, showing 30% increase in the energy conversion efficiency.

Fabrication and analysis of palmitic acid–decanoic acid@Ce–Eu/TiO2 composite as a building material for regulating indoor environment

AbstractNovel palmitic acid–decanoic acid@Ce–Eu/TiO2 (PA–DA@Ce–Eu/TiO2) microspheres with high photocatalysis–thermal–humidity collaborative performance were prepared via a two‐step method. Ce and Eu were used for codoping to modify the TiO2 hollow microspheres to enhance the photocatalytic properties. Furthermore, a eutectic phase change material (PA–DA) was combined with Ce–Eu/TiO2 hollow microspheres to prepare PA–DA@Ce–Eu/TiO2 microspheres. X‐ray diffraction and UV–VIS spectral analyses proved that Ce–Eu codoping enhanced the photocatalytic properties of the PA–DA@Ce–Eu/TiO2 microspheres under solar light; the degradation rate to gaseous formaldehyde at low concentrations reached 54.98% after 5 h. The pore structure, particle size distribution, microstructure, and thermostability of the PA–DA@Ce–Eu/TiO2 microspheres were determined using N2 adsorption isotherms, laser scattering particle size distribution analysis, scanning electron microscopy, and thermogravimetric analysis, respectively. The results showed that the Ce–Eu/TiO2 microspheres had a typical mesoporous structure, concentrated particle size distribution, and rough surface. The porous structure of the PA–DA@Ce–Eu/TiO2 microspheres was conducive to adsorb/desorb moisture, which was recorded to be 0.0575 g/g at 43.16–75.29% relative humidity. The differential scanning calorimeter analysis showed that the phase transition temperature of the PA–DA@Ce–Eu/TiO2 microspheres was 20–22°C and that the PA–DA@Ce–Eu/TiO2 microspheres were stable at 35°C. After 300 thermal cycles, the heat storage capacity of the PA–DA@Ce–Eu/TiO2 microspheres decreased by only 5%. Thus, we concluded that the PA–DA@Ce–Eu/TiO2 microspheres can purify air and control indoor thermal and humidity environments simultaneously and hence can be used as functional building materials to adjust the indoor environment.

Construction of Double-Shell Hollow TiO2 toward Solvent-Free Polyurethane Films

Solvent-free polyurethane (SFPU) has a fast curing film-forming speed, making the foam and coating layer very dense. Therefore, this film structure has poor hygienic properties. Here, we propose a strategy for introducing double-shell hollow TiO2 microspheres (S@S-TiO2) having a large specific surface area and a special inner and outer cavity structure in the SFPU film, so that the film would develop excellent hygienic properties. First, novel S@S-TiO2 were successfully prepared by a one-step hydrothermal method, which is very rare. Then, the obtained S@S-TiO2 were introduced into SFPU to prepare an S@S-TiO2/SFPU composite film. Then, the morphology and dispersibility of S@S-TiO2 and the composite film were studied by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results show that S@S-TiO2 have an important effect on the hygienic properties of the composite film. Finally, the synergistic effect of TiO2 on the properties of the polyurethane film was further proved by molecular dynamics simulation.

Ag2O/TiO2 hollow microsphere heterostructures with exposed high-energy {001} crystal facets and high photocatalytic activities

In this paper, one-step hydrothermal method was used to prepare the graded titanium dioxide hollow microspheres, and the {001} crystal plane was exposed. The silver oxide nanoparticles were deposited on the exposed crystal face of titanium dioxide by wet chemical coprecipitation to form Ag2O/TiO2 composite material. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption (BET), and so on. The degradation abilities of Ag2O/TiO2 composite materials with different molar ratios to rhodamine B were studied under UV–Vis irradiation. And then the mechanism of photocatalytic degradation was analyzed. The experimental results showed that when the molar ratio of titanium dioxide to silver nitrate was 4:1, the degradation effect was best, and the degradation rate reached 95.4% in 80 min. This outstanding photochemical catalysis performance was mainly due to good cooperation, including exposure of specific crystal planes of TiO2 hollow microspheres and highly scattered Ag2O nanoparticles, and the p–n heterostructure between Ag2O and TiO2 will induce efficient charge separation efficiency.

Single atomic Au induced dramatic promotion of the photocatalytic activity of TiO2 hollow microspheres.

Single atomic Au (Au-SA) is firmly anchored on the surfaces of defective TiO2 (DT) hollow microspheres with oxygen vacancies (Ov), which sharply improves their light-harvesting ability, stimulates charge separation, and facilitates the adsorption and activation of acetone, thus dramatically enhancing their photoreactivity towards acetone oxidation.

Non-aqueous preparation of anatase TiO2 hollow microspheres for efficient dye-sensitized solar cells

TiO2 hollow spheres are fabricated by a facile and template-free approach, which is efficient, cost-saving and favorable for large scale production. The as-prepared TiO2 hollow spheres with diameters ranging from 1 to 1.5 μm and a shell thickness of 150 nm are formed by the self-assembly of nanoparticles with a size of about 12 nm. The mesoporous TiO2 hollow spheres possess a high specific surface area up to 166.2 m2 g−1. TiO2 hollow spheres show superior light trapping characteristics and significantly improve the light scattering ability. The formation of hollow structure is interpreted by the Ostwald ripening mechanism. By employing a double-layered photoanode made of the as-prepared TiO2 hollow spheres as the overlayer and P25 as the bottom layer, the dye-sensitized solar cell achieved a power conversion efficiency of 7.90%, which is ascribed to the enhanced dye loading and light scattering ability of TiO2 hollow spheres.

Comparative study on the pressure-induced phase transformation of anatase TiO2 hollow and solid microspheres

Nanostructured anatase TiO2 undergoes pressure-induced phase transformation, and the transformation sequence is significantly different from the bulk counterpart. The size and the morphology are found both playing a critical role in the phase transformation behavior. In this work, we prepare anatase TiO2 microspheres using a hydrothermal method. By controlling the reaction time, hollow and solid spheres of similar diameters are prepared. TEM and XRD analysis reveals that these microspheres are aggregates of anatase nanocrystalline of size between 15–16 nm. The phase transformation behaviour under high temperature is examined in situ using both Raman spectroscopy and synchrotron x-ray diffraction. We find that although both solid and hollow spheres are micron-sized, they undergo phase transformation sequence similar to nanomaterials with size of several tens of nanometers. Hollow spheres exhibit a higher compressibility than the solid spheres. A detailed analysis based on the formation mechanism of the spheres is performed to explain the unique phase transformation behavior of these materials.

Application of TiO2 hollow microspheres incorporated with up-conversion NaYF4:Yb3+, Er3+ nanoparticles and commercial available carbon counter electrodes in dye-sensitized solar cells

In this work, the up-conversion phosphor NaYF4:Yb3+, Er3+ nanocrystalline mixed with P25 and TiO2 hollow microspheres with high light scattering ability were fabricated as electrode for dye-sensitized solar cells (DSSCs). Meanwhile, we take advantage of the low cost feature of the carbon counter electrode to replace the precious metal Platinum (Pt) of DSSCs. SEM results show that the well-dispersed TiO2 hollow microspheres size is 1.5 μm with surface consisting of a large number of rice-like nanorods. The particle size of the as-prepared NaYF4:Yb3+, Er3+ nanoparticles is about 80 nm. The Photocurrent-Voltage curve of P25/NaYF4:Yb3+, Er3+ cell under 980 nm infrared light has an obvious infrared photoresponse. The fabricated DSSCs using NaYF4:Yb3+, Er3+ achieves power conversion efficiency (PCE) of 5.27% under one sun illumination, which shows an increase of 16% when compared with the benchmark P25 cell (4.55%). In addition, the optimized DSSC using TiO2 hollow microspheres as the top scattering layers with NaYF4:Yb3+, Er3+/P25 exhibits a prominent PCE of 6.23%, which shows a 37% increase in conversion efficiency when compared with the commercial P25 cell (4.55%). The increase in conversion efficiency should be contributed to the dual effects of the enhanced light harvesting of up-conversion NaYF4:Yb3+, Er3+ and light utilization of the top light scattering TiO2 hollow microsphere.

Dramatic promotion of visible-light photoreactivity of TiO2 hollow microspheres towards NO oxidation by introduction of oxygen vacancy

Hollow-structured TiO2 has attracted much attention owing to its low density, good light-reflecting ability, and excellent permeability. However, the wide bandgap (about 3.2 eV for anatase TiO2) and fast recombination of photo-generated carriers hamper its practical application. Herein, oxygen vacancy (OV) was introduced onto the surface of TiO2 hollow microspheres (TiO2-HMSs) by a facile method through calcination of the mixture of hydrogen titanate hollow microspheres (H2TiO3-HMSs) and urea. Using this strategy, both the aims of extending the light-response range and promoting the separation of photo-generated carriers were satisfactorily achieved. The introduction of Ov facilitates the adsorption and activation of NO and O2 on the surface of TiO2-HMSs. This stimulates the production of reactive oxygen species, such as superoxide radicals (O2−) and hydroxyl radicals (OH), resulting in the dramatic promotion of visible-light photocatalytic oxidation of NO.

Steering charge kinetics in W2C@C/TiO2 heterojunction architecture: Efficient solar-light-driven hydrogen generation

The constructing of functional materials with well-defined nanostructure, showing efficient charge separation and transportation properties, has been intensively and in depth investigated to fabricate catalysts for H2 generation from solar-driven water reduction. Here we demonstrate that loading W2C@C structure in which each W2C nanoparticle (NP) is wrapped by carbon shell on surface of hollow TiO2 microspheres (HTMs) can enhance the separation of photogenerated electron-hole pairs by building an internal electric field in W2C@C/HTMs composite structure and act as the reaction active sites for water reduction. As expected, the optimized W2C@C/HTMs construction exhibits the highest photocatalytic H2 generation rate of 6.91 mmol h−1 g−1 under simulated solar light illumination, over 20 times larger than that of bare HTMs. The underlying mechanism has been investigated from the perspective of photochemistry and photophysics based on a series of characterization techniques, which suggests that W2C@C can effectively steer the charge kinetics, maximizing the charge carriers’ separation.

The Size Effect of TiO2 Hollow Microspheres on Photovoltaic Performance of ZnS/CdS Quantum Dots Sensitized Solar Cell.

Size controllable TiO2 hollow microspheres (HMS) were synthesized by a carbonaceous spheres (CS) template method. Based on TiO2 HMS, the ZnS/CdS quantum dots (QDs) were loaded to form a ZnS/CdS@TiO2 HMS photoanode for quantum dots sensitized solar cell (QDSSC). The size effects of TiO2 HMS on photovoltaic performance were investigated, and showed that TiO2 HMS with sizes ~560 nm produced the best short-circuit current density (Jsc) of 8.02 mA cm−2 and highest power conversion efficiency (PCE) of 1.83%, showing a better photovoltaic performance than any other QDSSCs based on TiO2 HMS with size ~330 nm, ~400 nm, and ~700 nm. The improvement of photovoltaic performance based on ~560 nm TiO2 HMS which can be ascribed to the enhanced light harvesting efficiency caused by multiple light reflection and strong light scattering of TiO2 HMS. The ultraviolet-visible (UV-vis) spectra and incident photo to the current conversion efficiency (IPCE) test results confirmed that the size of TiO2 HMS has an obvious effect on light harvesting efficiency. A further application of ~560 nm TiO2 HMS in ZnS/PbS/CdS QDSSC can improve the PCE to 2.73%, showing that TiO2 HMS has wide applicability in the design of QDSSCs.