Hollow TiO2 Nanoparticles Research Articles

Hollow TiO2 Nanoparticles Capped with Polarizability-Tunable Conducting Polymers for Improved Electrorheological Activity.

Hollow TiO2 nanoparticles (HNPs) capped with conducting polymers, such as polythiophene (PT), polypyrrole (PPy), and polyaniline (PANI), have been studied to be used as polarizability-tunable electrorheological (ER) fluids. The hollow shape of TiO2 nanoparticles, achieved by the removal of the SiO2 template, offers colloidal dispersion stability in silicone oil owing to the high number density. Conducting polymer shells, introduced on the nanoparticle surface using vapor deposition polymerization method, improve the yield stress of the corresponding ER fluids in the order of PANI < PPy < PT. PT-HNPs exhibited the highest yield stress of ca. 94.2 Pa, which is 5.0-, 1.5-, and 9.6-times higher than that of PANI-, PPy-, and bare HNPs, respectively. The improved ER response upon tuning with polymer shells is attributed to the space charge contribution arising from the movement of the charge carriers trapped by the heterogeneous interface. The ER response of studied ER fluids is consistent with the corresponding polarizability results as indicated by the permittivity and electrophoretic mobility measurements. In conclusion, the synergistic effect of hollow nanostructures and conducting polymer capping effectively enhanced the ER performance.

Preparation, characterization, and application of hollow nano‐TiO2@modified graphene/fluorinated copolymer nanocomposite leather finishing agents

AbstractA novel nanocomposite leather‐finishing agent (denoted as H‐TiO2@SDS‐rGO/F‐PBMA) composed of fluorinated copolymer (denoted as F‐PBMA) matrix using methyl methacrylate (abbreviated as MMA), butyl acrylate (abbreviated as BA) as well as acrylic acid (abbreviated as AA) as monomers and H‐TiO2@SDS‐rGO composite nanoparticles as nano‐additives were successfully fabricated by aqueous emulsion polymerization in this paper. The hollow TiO2 nanoparticles (denoted as H‐TiO2) were firstly prepared with tetrabutyl titanate as titanium source wall and tetraethyl silicate as silicon source core through an alkali etching method, and then they were compounded with reduced graphene oxide (rGO) modified by sodium dodecyl sulfate (denoted as SDS‐rGO) for obtaining H‐TiO2@SDS‐rGO composite nanoparticles. Fourier transform infrared spectra, X‐ray diffraction, Raman spectra, scanning electron microscopy, and nuclear magnetic resonance spectra were used to characterize the structure and morphology of different samples. The experimental results reveal that the nanocomposite leather‐finishing agent not only has excellent transparency, but also endows sheepskin better weather resistance, thermal stability, hydrophobicity and mechanical properties compared with traditional leather finishing agents.

Preparation and electrorheological properties of eggshell-like TiO2 hollow spheres via one step template-free solvothermal method

In this paper, we prepared eggshell-like TiO2 hollow sphere nanoparticles by one-step template-free method, and studied its electrorheological (ER) properties at different electric field strengths. The microstructure, composition, and morphology of eggshell-like TiO2 hollow sphere was characterized by SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (X-ray powder diffractometer), FI-IR (Fourier transform infrared spectroscopy), BET (Brunner Emmett Teller) measurements. XRD and FT-IR confirm the existence of pure anatase-type titanium oxide. BET measurement verifys the hollow structure belonging to eggshell-like TiO2 hollow nanoparticles. With the help of SEM and TEM techniques, by changing the reaction time, we learned about the approximate formation process of eggshell - like TiO2 hollow nanoparticles and observed the hollow structure. After a series of characterization methods, we have a further and deeper understanding of eggshell-like TiO2 hollow ball nanoparticles. Thus, we found that the one-step templateless method we used to prepare eggshell like TiO2 hollow spherical nanoparticles is simple and easy to operate, with a short reaction cycle and non-toxic and harmless. And the electrorheological properties, including the variation of shear stress, shear viscosity, as well as electrorheological efficiency of eggshell-like TiO2 hollow sphere-based electrorheological fluid with shear rate under different electric field were studied by using high-speed rotary rheometer. At the same time, the obtained eggshell-like TiO2 hollow spherical nanoparticles have good electrorheological properties and are a kind of electrorheological materials with promising application prospects.

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.

Fabrication and cavity-size-dependent photocatalytic property of TiO2 hollow nanoparticles with tunable cavity size

TiO2 hollow nanoparticles with tunable cavity size were prepared via a microwave-assisted hydrolysis reaction between TiCl4 and different amounts of HF aqueous solution, followed by calcination at 400 °C for 2 h. The obtained TiO2 hollow nanoparticles with tunable cavity size were characterized with TEM, SEM, XRD, Raman, BET, UV–vis absorption spectra, and photocurrent measurement. It was found that the tunable cavity size of TiO2 hollow nanoparticles was apparently enlarged from 1 to 3 nm to 7–9 nm by increasing the content of HF, and that HF also plays a crucial role in the crystallization of TiO2. The TiO2 hollow nanoparticles exhibit the unique cavity-size-dependent properties of UV absorption and photocatalytic activity for acetone degradation. This study offers a novel approach to fabricating TiO2 hollow nanoparticles with tunable cavity size, and the unique cavity-size-dependent photocatalytic property has potential for wide popularization and application prospects.

Effect of Morphology of Titanium Dioxide Nanoparticles on Photocatalytic Activity

Dispersing nanoparticles into the matrix is a simple but effective method to improve properties of coating layer. Titanium dioxide (TiO2), known for its photocatalytic activity (PCA) to degrade organic substances and to protect microbial infection, is considered to be potential candidate. However, intense light is required to achieve high PCA. Scattering layer composing of hollow TiO2 nanoparticles, known as light harvester in solar cell devices, may be suitable for photocatalysis at lower light intensity. In this work, we studied the effect of hollow morphology to the PCA of TiO2 nanoparticles. Hollow TiO2 nanoparticles were successfully synthesized using hard-template-assisted sol-gel method. Transmission Electron Microscope (TEM) images show hollow TiO2 nanoparticles possessing 125-nm hollow core and 50-nm TiO2 shell. X-ray Diffraction (XRD) results revealed no crystalline peak for both calcined and non-calcined samples, but difference for each sample was reported by Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-DRS). UV-DRS spectrum showed the higher diffuse reflectance for both hollow TiO2 samples than the dense counterpart, suggesting multiple light scattering and high reflection. However, energy bandgaps of amorphous and calcined hollow TiO2 samples are higher than dense counterparts.

Multi-dimensional anatase TiO2 materials: Synthesis and their application as efficient charge transporter in perovskite solar cells

Recently, organo-metal halide perovskite (e.g., CH3NH3PbI3) solar cells have shown a significant surge in progress and efficiency. The photovoltaic performance of perovskite solar cells (PSC) extensively depends on the morphology of the materials at nano-level, because the intrinsic electrical, optical and electrochemical properties also change with a change in morphology. Different TiO2 nanostructures with diverse dimensionalities, 0D hollow TiO2 nanoparticles (HTNPs), 3D hollow TiO2 mesospheres (HTMSs) and 3D hierarchical TiO2 spheres (HTSs) were synthesized hydrothermally. The PSCs based on 3D HTSs or 3D HTMSs as electron transport layers (ETLs) shows better performance than the PSCs fabricated with 0D HTNPs as ETL. The enhanced results can be attributed to the better penetration of the perovskite materials in the porous network of the HTSs or HTMSs and decreased interfacial recombination due to superior charge extraction and electron transport at the HTSs/CH3NH3PbI or HTMSs/CH3NH3Pb interfaces. By using a self-assembled TiO2 compact layer (c-TiO2), followed by a mesoporous layer of HTSs, produces PSCs with an excellent efficiency of 15.08%. Such c-TiO2-ETL films may improve PSCs performance by enhancing electron extraction and block the photogenerated holes.

Template-free scalable synthesis of TiO2 hollow nanoparticles for excellent photoelectrochemical applications

With the energy crisis and resource depletion nowadays, novel, highly performing, and cost-effective semiconductors are in urgent demand for efficiently harvesting solar energy for photoelectrochemical applications. Herein, this study presents low-cost anatase TiO2 hollow nanoparticles as prepared by a critical liquid-phase deposition (LPD) processing combined with a hydrothermal reaction and calcination processing, without involving any templates. The additional LPD processing not only makes the resulting samples more visible light responsive, but also results in hollowing the TiO2 nanoparticles (nanosheets vs. hollow nanoparticles). Importantly, commercial TiO2 powder is employed as the starting material to achieve the final synthesis of TiO2 hollow nanoparticles, making it scalable and cost-effective for production and applications. As a by-product, the fluoride, formed during the preparation process, is assumed to play a significant role in hollowing through chemically induced self-transformation and Ostwald ripening, in addition to enhancing the crystallinity. The beneficial structural evolution to the hollow nanoparticles enables the improvement of the photoelectrochemical performance through impressive inhibition of the recombination of the photoelectrons and holes, which is well evidenced by I ph and EIS (Nyquist plot), as well as by I–V curve and electron lifetime evaluations as for the assembled DSSCs with the prepared TiO2 hollow nanoparticles under simulated sunlight illumination (50 mW/cm2).

Urchin-Inspired TiO2@MIL-101 Double-Shell Hollow Particles: Adsorption and Highly Efficient Photocatalytic Degradation of Hydrogen Sulfide

Titanium dioxide (TiO2) is a commonly used photocatalysis for the oxidation of hydrogen sulfide (H2S). However, the low surface area and adsorption ability of TiO2 limit the photocatalytic decomposition rate. Here, a tunable metal–organic framework (MOF) coating is applied to hollow TiO2 nanoparticles using a versatile step-by-step self-assembly strategy. The hollow structure provides a high surface area, and the selected MIL-101 (Cr) MOF has a high and regenerable adsorption ability for H2S. The TiO2@MIL-101 double-shell hollow particles enable a catalytic cycle involving simultaneous adsorption and degradation of H2S, with considerably enhanced photocatalytic reaction rate. This work provides a method for improving photocatalytic performance through the design of hollow MOF-based materials that rationally combine the power of MOF and TiO2.

Template‐Directed Fabrication of Anatase TiO2 Hollow Nanoparticles and Their Application in Photocatalytic Degradation of Methyl Orange

Polymerization‐induced self‐assembly (PISA) was used to fabricate polymeric nanoparticles via reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) using diblock copolymer poly(glycerol monomethacrylate)‐block‐poly(2‐dimethylaminoethyl methacrylate) (PGMMA‐ PDMAEMA‐CTA) as the macro RAFT agent. The dispersion of polymeric nanoparticles with a final concentration of about 210 mg/g (solid content of 21%) was obtained via this efficient method (PISA). The resultant polymeric nanoparticles consisting of corona‐shell‐core three layers with weak polyelectrolyte PDMAEMA as the shell were used as sacrificial template to fabricate TiO2 hollow nanoparticles. The negatively charged titanium precursor was absorbed into the PDMAEMA shell via the electrostatic interaction, and hydrolyzed to form polymer/TiO2 hybrid nanoparticles. Anatase TiO2 hollow nanoparticles were formed after removing the polymeric templates by calcination at 550 °C. The experiments of photocatalytic degradation of methyl orange showed that the resultant anatase TiO2 hollow nanoparticles had high photocatalytic activity and good reusability.

Graphene Oxide Wrapped SiO2 /TiO2 Hollow Nanoparticles Loaded with Photosensitizer for Photothermal and Photodynamic Combination Therapy.

Graphene oxide (GO) enwrapped SiO2 /TiO2 hollow nanoparticles (GO-HNP) are synthesized by the Stöber method and used as a nanocarrier for loading protoporphyrin IX (PpIX). The synthesized nanoparticle has high dispersibility and high uniformity in diameter (ca. 50 nm). Furthermore, this nanoparticle shows λ=808 nm laser induced PpIX release properties (photoinduced "on-off" drug-release system). GO-HNP-PpIX is employed for inducing both photothermal therapy (PTT) and photodynamic therapy (PDT). The synergic effect of PTT and PDT exhibits powerful anticancer properties. When cancer cells are treated with GO-HNP-PpIX and irradiated with both visible light and a NIR laser, the cell viability drops dramatically to 2.5 %, which is an anticancer effect approximately 13 times higher than that obtained in a previous study. Moreover, no significant cell damage has been observed under λ=808 nm laser irradiation. The GO-HNP-PpIX system suggests an external stimuli-responsive efficient anticancer treatment effect toward human breast cancer cells.

Anatase TiO2single crystal hollow nanoparticles: their facile synthesis and high-performance in dye-sensitized solar cells

In this paper, we successfully synthesized anatase TiO2 hierarchical microspheres (S0), anatase TiO2 sub-micro hollow mesospheres (S50), anatase TiO2 single crystal hollow nanoparticles (S100), nanoparticles (S250) and (S500) by using different amounts of hydrofluoric acid (HF) versus titanium n-tetrabutoxide (TBT) and acetic acid (AcOH). The structure and morphology of the as-prepared materials were confirmed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DSSCs (dye-sensitized solar cells) based on anatase single crystal hollow TiO2 nanoparticles (S100) as a photoanode showed an efficient power conversion efficiency of 8.94% along with a current density of 17.39 mA cm−2 and an open circuit voltage of 778 mV, which is higher than the DSSCs based on S0 (8.10%), S50 (8.57%), S250 (7.25%) and S500 (6.12%). The high performance of S100 as a DSSC is attributed to their hollow structure which might help to harvest more light, higher light scattering and trapping abilities and comparatively higher surface area. Therefore, we can expect that our materials are promising for assembling superior photoelectrodes for future preparation of highly-efficient DSSCs and may lead to applications for energy storage, water splitting, catalysis, and gas sensing.

Synthesis and electrophoretic deposition of hollow-TiO2 nanoparticles for dye sensitized solar cell applications

Hollow TiO2 nanoparticles having ∼200 nm size are successfully prepared via selective etching of Au@TiO2 core shell nanoparticles which were synthesized by microwave hydrothermal growth. Electrophoretic deposition was successfully applied to make hollow TiO2 nanoparticles scattering layer for dye-sensitized solar cells (DSSCs) applications. The surface morphology and roughness features of deposited hollow TiO2 nanoparticles films are studied by field emission scanning electron microscope and atomic force microscope techniques respectively. The light scattering property of H–TiO2 makes it a promising candidate for use as the scattering layer in dye sensitized solar cells. Enhanced JSC values for the H–TiO2 based DSSCs were attributed to larger dye adsorption and stronger light scattering compared to the commercial TiO2 nanoparticle with a crystalline size of 20 nm.

Ag doped hollow TiO2 nanoparticles as an effective green fungicide against Fusarium solani and Venturia inaequalis phytopathogens

Chemical-based pesticides are widely used in agriculture to protect crops from insect infestation and diseases. However, the excessive use of highly toxic pesticides causes several human health (neurological, tumor, cancer) and environmental problems. Therefore nanoparticle-based green pesticides have become of special importance in recent years. The antifungal activities of pure and Ag doped (solid and hollow) TiO2 nanoparticles are studied against two potent phytopathogens, Fusarium solani (which causes Fusarium wilt disease in potato, tomato, etc) and Venturia inaequalis (which causes apple scab disease) and it is found that hollow nanoparticles are more effective than the other two. The antifungal activities of the nanoparticles were further enhanced against these two phytopathogens under visible light exposure. The fungicidal effect of the nanoparticles depends on different parameters, such as particle concentration and the intensity of visible light. The minimum inhibitory dose of the nanoparticles for V. inaequalis and F. solani are 0.75 and 0.43 mg/plate. The presence of Ag as a dopant helps in the formation of stable Ag–S and disulfide bonds (R–S–S–R) in cellular protein, which leads to cell damage. During photocatalysis generated •OH radicals loosen the cell wall structure and this finally leads to cell death. The mechanisms of the fungicidal effect of nanoparticles against these two phytopathogens are supported by biuret and triphenyl tetrazolium chloride analyses and field emission electron microscopy. Apart from the fungicidal effect, at a very low dose (0.015 mg/plate) the nanoparticles are successful in arresting production of toxic napthoquinone pigment for F. solani which is related to the fungal pathogenecity. The nanoparticles are found to be effective in protecting potatoes affected by F. solani or other fungi from spoiling.

Self-development of hollow TiO2 nanoparticles by chemical conversion coupled with Ostwald ripening

In this communication, the TiO2 materials with porous and hollow nanostructures were successfully synthesized through one-pot solvothermal process without any surfactant and template. Our study demonstrated that, the chemical conversion could induce the self-development of hollow TiO2 nanostructures coupled with the physical Oswald ripening process. In particular, the chemical conversion took place progressively from the particle surface to the core of an assembly, generating the converted TiO2 materials. The exterior TiO2 grains were quickly transformed to be a solid and stable surface shell of spheres. Continuous chemical conversion process for inner grains of spheres would lead to the formation of loose package of grains and thus could facilitate would the outward migration and deposition of inner grains onto the stable exterior shell of spheres. The depletion of interior material resulted in generation and development of hollow core structure. This study can be basis for the fabrication of hollow structures of different solid materials by one-pot solvothermal process.

Efficient dye-sensitized solar cells based on carbon-doped TiO2 hollow spheres and nanoparticles

Different structures of TiO2 photoelectrodes are fabricated with various arrangement modes of the layers. TiO2 nanoparticles, synthesized by stabilizing agent free non-hydrolytic sol–gel method, are employed as the under layer, whereas carbon-doped TiO2 hollow spheres, prepared by hydrothermally grown carbon template, are used as the scattering layer of solar cells. The nanoparticles (22 nm) have anatase structure, while 300–700 nm hollow spheres show mixtures of anatase and rutile phases. X-ray photoelectron spectroscopy confirms that carbon is doped into TiO2 hollow spheres, resulting in a decrease in band gap energy in the range 2.96–3.13 eV compared with 3.04 eV band gap energy for the nanoparticles. The diffuse reflectance spectroscopy measurements show that the hollow spheres exhibit higher scattering property than the nanoparticles. The single layer solar cell made of nanoparticles and carbon-doped TiO2 hollow spheres shows the highest efficiency of 7.21 and 7.02 %, respectively. Further enhancement of photovoltaic performance is obtained by light scattering mechanism aided by fabrication of double layer solar cells due to higher incident photon-to-current conversion and less recombination. The double layer solar cell made of nanoparticles as the under layer and hollow spheres (containing 86 % anatase–14 % rutile) as the scattering layer shows the highest efficiency of 8.55 %.

Triblock copolymer-assisted construction of 20 nm-sized ytterbium-doped TiO2 hollow nanostructures for enhanced solar energy utilization efficiency

Rare-earth doped titania single-crystalline hollow nanoparticles of 20 nm are constructed via a simple sol-gel process. Amphiphilic ABA tri-block copolymers played a key role in assisting the formation of hollow structure, for which a hollow nanostructure growth mechanism is proposed. By introducing rare earth into the synthesis process, the as-prepared nanoparticles exhibit near-infrared light absorption properties. Photo-decomposition efficiency of Orange II azo dye can be successfully evaluated when using Yb3+-doped TiO2 hollow nanoparticles as photocatalysts; it is more than two times higher than the pure TiO2 hollow nanoparticles. The hollow nanostructured Yb3+-doped TiO2 samples are exploited as photoanodes in N719-sensitized solar cells and prove able to improve the photoelectric conversion efficiency by measuring the solar cell parameters of dye-sensitized solar cells (DSSCs) under simulative sunlight.

Fabrication of Au@Ag core/shell nanoparticles decorated TiO2 hollow structure for efficient light-harvesting in dye-sensitized solar cells.

Improving the light-harvesting properties of photoanodes is promising way to enhance the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). We synthesized Au@Ag core/shell nanoparticles decorated TiO2 hollow nanoparticles (Au@Ag/TiO2 HNPs) via sol-gel reaction and chemical deposition. The Au@Ag/TiO2 HNPs exhibited multifunctions from Au@Ag core/shell NPs (Au@Ag CSNPs) and TiO2 hollow nanoparticles (TiO2 HNPs). These Au@Ag CSNPs exhibited strong and broadened localized surface plasmon resonance (LSPR), together with a large specific surface area of 129 m(2) g(-1), light scattering effect, and facile oxidation-reduction reaction of electrolyte from TiO2 HNPs, which resulted in enhancement of the light harvesting. The optimum PCE of η = 9.7% was achieved for the DSSCs using photoanode materials based on TiO2 HNPs containing Au@Ag/TiO2 HNPs (0.2 wt % Au@Ag CSNPs with respect to TiO2 HNPs), which outperformed by 24% enhancement that of conventional photoanodes formed using P25 (η = 7.8%).

Multi‐Shell Porous TiO2 Hollow Nanoparticles for Enhanced Light Harvesting in Dye‐sensitized Solar Cells

An optimized configuration for nanomaterials in working electrodes is vital to the high performance of dye‐sensitized solar cells (DSSCs). Here, a fabrication method is introduced for multi‐shell TiO2 hollow nanoparticles (MS‐TiO2‐HNPs) via a sol–gel reaction, calcination, and an etching process. The prepared uniform MS‐HNPs have a high surface area (ca. 171 m2 g−1), multireflection, and facile electrolyte circulation and diffusion. During the MS‐HNP fabrication process, the amount of SiO2 precursor and H2O under reaction has a significant effect on aggregation and side reactions. The etching process to obtain pure TiO2 is influenced by anatase crystallinity. Additionally, single‐shell (SS)‐TiO2‐HNPs and double‐shell (DS)‐TiO2‐HNPs are synthesized as a control. The MS‐TiO2‐HNPs exhibit a high surface area and enhance light reflectance, compared with the SS‐ and DS‐TiO2‐HNPs of the same size. The power conversion efficiency of the optimized MS‐TiO2‐HNP‐based DSSCs is 9.4%, compared with the 8.0% efficiency demonstrated by SS‐TiO2‐HNP‐DSSCs (a 17.5% improvement). These results enable the utilization of multifunctional MS‐HNPs in energy material applications, such as lithium ion batteries, photocatalysts, water‐splitting, and supercapacitors.

Microscale Hierarchical Three-Dimensional Flowerlike TiO2/PANI Composite: Synthesis, Characterization, and Its Remarkable Photocatalytic Activity on Organic Dyes under UV-Light and Sunlight Irradiation

A microscale hierarchical 3D flowerlike TiO2/PANI composite with enhanced photocatalytic activity was synthesized via a sol–gel method, and the as-synthesized samples were characterized by XRD, SEM, TEM, FT-IR, UV–vis adsorption, BJH, and TGA/DSC. The outcome of the photocatalytic experimental demonstrating the TiO2/PANI hybrid with a Ti/ANI (aniline) molar ratio of 1:1 (denoted as T/P) showed high photocatalytic activity upon the degradation of Congo red (CR) and methyl orange (MO) under both UV-light and sunlight irradiation. The unique hierarchical 3D flowerlike structure endows the T/P hybrid with a large surface area of 38.81 m2/g. The intermeshed PANI nanoflakes could make full use of the light resource by multiple reflections between the nanoflakes. Moreover, the intrinsic cavity of the hollow TiO2 nanoparticles can also increase the light-capturing efficiency. The synergistic effect between PANI and TiO2 hollow nanoparticles results in a reduction of the photoinduced electron–hole recombination rate as well as enhanced photocatalytic activity under UV-light and sunlight. Given the unique spatial structure and high photocatalytic characteristics of the T/P composite, there is great potential for applications in water treatment.