TiO2 Hollow Research Articles

Electrospinning spinneret: A bridge between the visible world and the invisible nanostructures

Electrospinning spinneret: A bridge between the visible world and the invisible nanostructures

Well-designed MOF-derived hollow octahedral structure TiO2 coupled with ultra-thin porous g-C3N4 to enhance the degradation of real liquor brewing wastewater

The poor visible light utilization and the quick recombination of photogenerated charge of photocatalysts are major issues dominating the application of photocatalysts in the treatment of industrial wastewater. Herein, a novel TiO2/g-C3N4 S-scheme heterojunction photocatalyst was constructed by homogeneously embedding hollow octahedral TiO2 nanoparticles (HOT) in ultra-thin porous g-C3N4 nanosheets (UPCN). SEM and TEM demonstrate that the HOT possesses hollow octahedron structure. The results of XRD, XPS and FT-IR imply that the HOT/UPCNx composites have been prepared successfully. The HOT/UPCN0.4 (mass ratio of TiO2 to g-C3N4 = 1:2) exhibits the highest chemical oxygen demand (COD) removal rate for real liquor brewing wastewater (LBW) 50.4% which is 2.2 times that of Degussa P25. After 5 cycles of performance test (25 h), the COD removal rate of HOT/UPCN0.4 was reduced by 7.1%. The excellent photocatalytic performance in the degradation of real LBW can be ascribed to the construction of S-scheme heterojunction which extending the light absorption range and providing effective channels for the separation and transfer of charge as well as hollow octahedron and porous structure which enhancing the light utilization. Moreover, the tight interface junction and large contact interface between HOT and UPCN provide more “highways” for the transfer of photogenerated charge.

Single Atom-Doped Nanosonosensitizers for Mutually Optimized Sono/Chemo-Nanodynamic Therapy of Triple Negative Breast Cancer.

Sonodynamic therapy (SDT) represents a promising therapeutic modality for treating breast cancer, which relies on the generation of abundant reactive oxygen species (ROS) to induce oxidative stress damage. However, mutant breast cancers, especially triple-negative breast cancer (TNBC), have evolved to acquire specific antioxidant defense functions, significantly limiting the killing efficiency of SDT. Herein, the authors have engineered a distinct single copper atom-doped titanium dioxide (Cu/TiO2 ) nanosonosensitizer with highly catalytic and sonosensitive activities for synergistic chemodynamic and sonodynamic treatment of TNBC. The single-atom Cu is anchored on the most stable Ti vacancies of hollow TiO2 sonosensitizers, which not only substantially improved the catalytic activity of Cu-mediated Fenton-like reaction, but also considerably augmented the sonodynamic efficiency of TiO2 by facilitating the separation of electrons (e- ) and holes (h+ ). Both the in vitro and in vivo studies demonstrate that the engineered single atom-doped nanosonosensitizers effectively achieved the significantly inhibitory effect of TNBC, providing a therapeutic paradigm for non-invasive and safe tumor elimination through the mutual process of sono/chemo-nanodynamic therapy based on multifunctional single-atom nanosonosensitizers.

Hollow hemispherical Si-doped anatase for efficient carbamazepine degradation via photocatalytic activation of peroxymonosulfate

Photocatalytic persulfate activation on semiconductor (such as TiO2) supported transition metal catalysts exhibits great potential in removing refractory organic pollutants, but it often encounters the issues of unsatisfactory activity and undesirable metal leaching. Herein, novel three-dimensional (3D) Si-doped TiO2 materials without transition metal doping are proposed for efficient photocatalytic activation of peroxymonosulfate (PMS). Unlike creating an inverse opal structure using polymer sphere templates in prior research, the SiO2 opal template enables the creation of hollow hemispherical structured Si-doped TiO2 (denoted as HHS-Si/TiO2) with hierarchical macro-mesopores. The SiO2 template also endows the HHS-Si/TiO2 materials excellent sintering-resistant properties and completely inhibits the crystalline phase transition from anatase to rutile at high temperatures, benefiting from the confinement effect and formation of Si-O-Ti bonds. The HHS-Si/TiO2 materials calcined at 400–900 °C show similar and excellent activities and stability in PMS activation under solar light irradiation to fast degrade carbamazepine (CBZ) and various other pollutants. The influences of PMS dosage, pH value and water matrix on CBZ degradation are illustrated. The HHS-Si/TiO2 materials are advantageous (especially at high calcination temperatures) over the commercial, the template-free synthesized and the inverse opal structured TiO2 materials for photocatalytic activation of PMS, because of their 3D hollow hemispherical structure, interconnected small anatase nanocrystals and Si-doping. PMS is mainly activated by the photo-generated electrons. HO• (dominant), SO4•− and holes are the reactive species responsible for CBZ degradation. This work provides enhanced understanding on the synthesis of 3D Si-doped TiO2 materials and it would provide useful information on developing efficient catalysts for photocatalytic PMS activation.

Light trapping by porous TiO2 hollow hemispheres for high efficiency photoelectrochemical water splitting.

Photocatalytic water splitting has recently received increasing attention as a green fuel source. The controlled nano-geometry of the photocatalytic material can improve light harvesting. In this study, as a proof of concept, hollow hemisphere (HHS)-based films of TiO2 material were created by a conventional electrospray method and subsequently applied for photoelectrochemical (PEC) water splitting. To preserve the morphology of the HHS structure, a hydrolysis precipitation phase separation method (HPPS) was developed. As a result, the TiO2 HHS-based thin films presented a maximum PEC water splitting efficiency of ca. 0.31%, almost two times that of the photoanode formed by TiO2 nanoparticle-based films (P25). The unique morphology and porous structure of the TiO2 HHSs with reduced charge recombination and improved light absorption are responsible for the enhanced PEC performance. Light scattering by the HHS was demonstrated with total reflection internal fluorescence microscopy (TRIFM), revealing the unique light trapping phenomenon within the HHS cavity. This work paves the way for the rational design of nanostructures for photocatalysis in fields including energy, environment, and organosynthesis.

Hierarchical hollow TiO2/In2S3 heterojunction photocatalyst decorated with spatially separated dual co-catalysts for enhanced photocatalytic H2 evolution

The Pt/TO/IS/PdS photocatalytic system was delicately designed, which exhibited enhanced visible-light-driven photocatalytic H2 production because of the heterojunciton structures and the decoration of spatially separated dual co-catalysts.

Entrapment of polysulfides by a BiFeO3/TiO2 heterogeneous structure on separator for high-performance Li–S batteries

Owing to the environmental friendliness, high specific energy, high theoretical capacity, and low cost, lithium-sulfur (Li–S) battery has drawn great attention as the next-generation device. However, the poor conductivity of the sulfur and lithium sulfides, large volumetric expansion of S to Li2S after lithiation, and the dissolution of lithium polysulfides in electrolyte, lead to low specific capacity, high cyclic capacity loss, and bad cycle performance. Here, we propose a heterojunction structure of multiferroic BiFeO3 anchored on hollow spheric TiO2 coated on Celgard separator to overcome the “shuttle effect” of dissolved intermediate polysulfides, improving poor conductivity of S and its discharge products Li2S2/Li2S, and inhibiting lithium dendrites. The multiferroic BiFeO3 provides a spontaneous polarization to trap polysulfides, and hollow spheric TiO2 divides a large surface area for sulfur expansion and improves the poor conductivity of S and BiFeO3 simultaneously. As a result, the discharge capacity remained at 754 mAh g−1 with coulombic efficiency over 99.2% and 83.7% retention of the initial specific capacity after 800 cycles at 1.0C.

Hollow and porous TiO2 in PVA matrix nanocomposite green synthesis using ionic liquid micelle for Congo red removal from contaminated water

A new green procedure has been applied to prepare TiO2 nanocomposite in polyvinyl alcohol (PVA) matrix using an aqueous micelle solution of ionic liquid 1-methyl-3-octylimidazolium bromide by determining critical micelle concentration (CMC). The COSMO-SAC model has been used to calculate the activity coefficient of water and understand the water molecules’ behavior in the synthesis mixture. The prepared nanocomposite was porous and layered that has been characterized using FT-IR, XRD, DSC, TGA, SEM, EDX, and elemental mapping. The prepared nanocomposite has been used to remove Congo red dye from contaminated water with the adsorption process. The Langmuir, Freundlich, and Temkin isotherms have been used for modeling equilibrium adsorption of dye removal. Also, the optimized process factors have been evaluated that could achieve 97% dye removal in the following conditions: pH = 12, T = 25 ℃, and t = 45 min using 0.2 g TiO2@PVA (Mesh 100)/L of 10 ppm Congo red aqueous solution. Also, the efficiency of the nanocomposite was 88% after 5 recovery cycles from the optimized condition.

Molecularly Imprinted Methyl-Modified Hollow TiO2 Microspheres

The possibility of generating organically modified hollow TiO2 microspheres via a simple sol-gel synthesis was demonstrated for the first time in this work. A mixture of titania precursors, including an organically modified precursor, was used to obtain methyl-modified hollow TiO2 microspheres selective for bilirubin by the molecular imprinting technique (Methyl-HTM-MIM). Methyl-HTM-MIM were prepared by a sol-gel method using titanium (IV) isopropoxide (TTIP), and methyltitanium triisopropoxide (MTTIP) as precursors. Two ratios of titania precursors were tested (1/6 and 1/30 molMTTIP/molTTIP). With the characterization results obtained by the SEM and ATR-FTIR techniques, it was possible to establish that only the 1/30 molMTTIP/molTTIP ratio allowed for the preparation of hollow spheres with a reasonably homogeneous methylated-TiO2 shell. It was possible to obtain a certain degree of organization of the hybrid network, which increased with calcination temperatures. By adjusting isothermal adsorption models, imprinting parameters were determined, indicating that the new methylated microspheres presented greater selectivity for bilirubin than the totally inorganic hollow TiO2 microspheres. The effectiveness of the molecular imprinting technique was proven for the first time in an organically modified titania material, with imprinting factor values greater than 1.4, corresponding to a significant increase in the maximum adsorption capacity of the template represented by the molecularly imprinted microspheres. In summary, the results obtained with the new methyl-HTM-MIM open the possibility of exploring the application of these microspheres for selective sorption (separation or sensing, for example) or perhaps even for selective photocatalysis, particularly for the degradation of organic compounds.

Controllable preparation and photocatalytic performance of hollow hierarchical porous TiO2/Ag composite microspheres

Mesoporous titania-based composites have attracted much attention in the world due to their large specific surface area, high material transport efficiency, and photocatalytic efficiency. The hollow and hierarchical porous structure is rarely involved in a binary photocatalytic material. In the present work, a novel type of hollow hierarchical porous TiO2/Ag composite microsphere with tunable microstructure was successfully prepared by simple solution methods, including sol-gel method, template method and impregnation method. Hollow hierarchical porous TiO2 microspheres were prepared by a sol-gel process with P123 as a hierarchical pore structure guide agent and template method with polystyrene microspheres as a hollow hard template. Further, hollow hierarchical porous TiO2/Ag composite microspheres were obtained by modifying Ag in the hollow hierarchical porous TiO2 microspheres by the impregnation method. The different hollow hierarchical porous TiO2/Ag composite microspheres are obtained by changing the molar ratio R of Ti/Ag. The optimal addition amount of Ti and Ag in sample HHPA6 (10:0.5) is the molar ratio of 10:0.5, and the experimental value of XPS is the molar ratio of 10:0. 91. Compared with the hollow hierarchical porous TiO2 microspheres, the excitation wavelength of composite microspheres is shifted to the visible light direction by 24 nm, and their response range and their light utilization rate were improved. When the molar ratio R of Ti/Ag is 10:0.5, hollow hierarchical porous TiO2/Ag composite microspheres have a specific surface area of 177 m2/g, the pore volume of 0.37 cm3/g, and the primary and secondary pore size of 4.04 nm and 7.74 nm, respectively. It shows the highest photocatalytic activity in the ultraviolet band of 365 nm and 395 nm, and the degradation rate of methyl orange solution is 96.84% and 98.65%, respectively. Their excellent photocatalytic performance is attributed to their special structure combining hierarchical pores and hollow structures as well as the synergistic effect of Ag and TiO2.

Hollow TiO2/Poly (Vinyl Pyrrolidone) Fibers Obtained via Coaxial Electrospinning as Easy-to-Handle Photocatalysts for Effective Nitrogen Oxide Removal.

Herein, we present a method for fabricating hollow TiO2 microfibers from Ti (OBu)4/poly (vinyl pyrrolidone) sol-gel precursors and their effects on denitrification as a photocatalyst for air purification. Various sizes of hollow TiO2 fibers were developed using coaxial electrospinning by controlling the core flow rate from 0 to 3 mL h-1. At higher flow rates, the wall layer was thinner, and outer and core diameters were larger. These features are correlated with physical properties, including specific surface area, average pore diameter, and crystalline structure. The increase in the core flow rate from 0 to 3 mL h-1 leads to a corresponding increase in the specific surface area from 1.81 to 3.95 µm and a decrease in the average pore diameter from 28.9 to 11.1 nm. Furthermore, the increased core flow rate results in a high anatase and rutile phase content in the structure. Herein, hollow TiO2 was produced with an approximately equal content of anatase/rutile phases with few impurities. A flow rate of 3 mL h-1 resulted in the highest specific surface area of 51.28 m2 g-1 and smallest pore diameter size of ~11 nm, offering more active sites at the fiber surface for nitrogen oxide removal of up to 66.2% from the atmosphere.

Core-shell hollow nanostructures as highly efficient polysulfide conversion and adsorption cathode for shuttle-free lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are disclosed as prospective alternatives for next-generation energy storage technologies, due to their high theoretical energy density and cost-effectiveness. However, the shuttle effect and sluggish conversion reaction of polysulfide (LiPS) inhibit them from commercial application. To overcome these challenges, we anticipated a novel strategy to rational design a hollow titanium oxide nanosphere that is decorated with vanadium phosphide nanosheets (h-TiO2@VP) as an efficient sulfur host. The combination of strong chemical adsorption ability of hollow TiO2 nanospheres and excellent LiPS conversion catalyst of VP nanosheets which help to suppress the shuttling effect. The theoretical calculation showed that the h-TiO2@VP-50 (ratio of 5:5) could deliver higher conductivity and better adsorption ability toward LiPS. In particular, the composite of h-TiO2@VP and sulfur (h-TiO2@VP/S) cathode reveals a high specific capacity of ∼1430 mAh g−1 at 0.1C, and an excellent rate capacity of ∼521 mAh g−1 at 5C. Even at a high sulfur loading of ∼ 7.5 mg cm−2, the h-TiO2@VP/S cathode-based Li-S battery delivers an exceptional areal capacity of ∼ 7.13 mAh cm−2. This study opens a new door for designing the highly efficient Li-S battery cathode which can be a promising alternation for the state-of-the-art Li-ion cell.

Mechanistic study for enhanced photocatalytic degradation of acetaminophen by Fe(III) doped TiO2 hollow submicrospheres

The Fe (III) ions incorporated into TiO2 hollow submicrospheres are an excellent photocatalyst that could improve the catalyst activity by varying experimental parameters like controlling the flow rate, rotation speed, and contaminant concentration. Fe-TiO2 hollow submicrospheres with different Fe wt% in TiO2 were prepared. Our studies revealed that 2.5 wt% Fe-TiO2 has the best photocatalyst activity to generate strong oxidizing hydroxyl radicals during the photocatalytic degradation reaction. Ex-situ L and K-edge of Ti and Fe X-ray absorption near edge structure (XANES) spectra showed that Fe3+ ions in the 2.5 wt% sample produced more structural distortions in the TiO6 octahedral symmetry. Further, in-situ XANES Ti and Fe 3d spectral changes above the Fermi level (EF) revealed an increased electron charge transfer attributed to the Fe 3dz2- O 2pz orbital hybridization. Fe(III) doping not only increases the interaction between transition metal (Fe and Ti) 3d orbitals in TiO2, but also promotes the Fe(III)/Fe(II) redox kinetics and the associated photo-Fenton degradation of acetaminophen. Taking advantage of the magnetic property of the catalyst, the samples can be effectively recycled by applying a magnetic field.

Boosting solar-driven water splitting via spatially separated noble-metal-free-based dual reaction sites in cactus-like hollow TiO2

Noble-metal-free sulfides have certain photocatalytic activities and can be used as cocatalysts in reduction reactions. Metal sulfides have a catalytic mechanism similar to that of noble metals, and S ions can exert a force on H+ in water, improving the adsorption capacity of the catalyst for water molecules; this is beneficial to the hydrogen evolution reaction. Moreover, metal oxides can accelerate the consumption of holes and improve the efficiency of electron-hole separation. Herein, a novel TiO2 nanomaterial with a cactus-like hollow structure and with spatially separated MoS2 and NiO dual cocatalysts (denoted as NiO/TiO2/MoS2) is reported for use in catalytic hydrogen evolution under solar light irradiation. Space-separated dual reaction sites (MoS2 and NiO) with redox capability can efficiently promote the separation of photogenerated carriers of the catalyst. Furthermore, the special hollow structure enhances the solar light absorption efficiency by reducing the penetration loss to narrow the band gap. The density functional theory (DFT) calculation results show that, compared to Pt, the MoS2 cocatalyst loaded on the TiO2 surface is more conducive to efficient proton/electron transfer and easier molecular hydrogen release. As a result, the supported MoS2 cocatalyst on TiO2 has comparable photocatalytic hydrogen evolution performance to the noble metal Pt.

Crystallization of hollow TiO2 into anatase at mild conditions, for improved surface recognition in selective photocatalysis

The objective of this work was the exploration of low calcination temperature ranges (< 350 ºC) to obtain molecularly imprinted microspheres (MIM) with a high crystallinity as anatase, in cooperation of an acidic pretreatment aiming at the preservation of the hollow shape and also of the selective binding sites. It was confirmed the possibility of obtaining bilirubin-imprinted crystalline TiO2 microspheres (highly crystalline anatase, as confirmed by XRD) exhibiting higher photocatalytic efficiency associated especially with the hollow shape and calcination at lower temperatures (200 ºC or 250 ºC). It was with the calcination temperature of 250 ºC that the highest photocatalytic efficiency was obtained, under UV irradiation, associated with the highest adsorption selectivity (α(K) = 19) and degradation selectivity (α(k) = 2.7) observed for the degradation of the template against a closely related analogue compound.

Self-Healing Coating with a Controllable Release of Corrosion Inhibitors by Using Multifunctional Zinc Oxide Quantum Dots as Valves.

As an intelligent response system, self-healing anticorrosion materials containing nanocontainers have aroused increasing demands. It is highly expected that the nanocontainers can rapidly respond on corrosion signals to efficiently release corrosion inhibitors, meanwhile to avoid an undesirable leakage before the local corrosion happening. Herein, zinc oxide quantum dot (ZnO-QD)-sealed hollow mesoporous TiO2 nanocontainers loading with 14.2% benzotriazole (BTA) inhibitor have been successfully prepared [hollow mesoporous titanium dioxide nanospheres (HMTNs)-BTA@ZnO-QDs]. ZnO-QDs play the multifunctional roles on anticorrosion of the self-healing coating. The corrosion tests of coatings on the carbon steel well demonstrate that ZnO-QDs can not only act as a valve to seal and release BTA on the time but also act as a precursor to produce the protective film of Zn(OH)2 by the reaction of Zn2+ ions with OH- around the cathode region to inhibit the corrosion of carbon steel. After being soaked in 3.5% NaCl solution for 30 days, the |Z|0.01Hz value of the coating with HMTNs-BTA@ZnO-QDs still maintains at 2.87 × 107 Ω cm2. Once the defects are formed in the coating, the acid-responsive ZnO-QD valves are rapidly decomposed to release BTA inhibitor; meanwhile, the resulted Zn(OH)2 layer prevent the carbon steel substrate from corrosion in the cathode area. Therefore, it could be promising that the present design of the nanocontainers matching with the multifunctional ZnO-QDs can offer a valuable strategy to construct the self-healing and anticorrosion coatings with a multiresponse to the corrosion environment.

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.

Periodic mesoporous organosilica functionalized hollow TiO2 sphere for selective aerobic oxidation

A promising synthetic method of functionalized titanium dioxide (TiO2) has been proposed in this work which combined photoactive porphyrin-periodic mesoporous organosilica (PMO) with hollow TiO2 nanospheres to achieve a multi-component synergistic system. The prepared composite TiO2@Pro showed photocatalytic activity in aerobic oxidation of sulfide in the aqueous phase under visible light. The high reactivity was attributed to the increased adsorption and diffusion of substrates due to the catalyst’s large specific surface area (337 m2/g), amphiphilicity, wide visible light absorption, and high electron-hole pair separation rate. This strategy provides a new way of designing TiO2-based photocatalysts for heterogeneous catalysis under visible light.

Visible-light photocatalytic degradation of dyes by TiO[formula omitted]–Au inverse opal films synthesized by Atomic Layer Deposition

TiO2–Au composite planar films and inverse opals were synthesized by Atomic Layer Deposition (ALD) using Direct Liquid Injection for TiO2 deposition and for the injection of preformed Au nanoparticles (NPs). A few nanometers thick layer of TiO2 was deposited after the Au NPs. Thermal annealing at 380 °C allowed to remove the polystyrene beads template and to form anatase TiO2.The obtained inverse opals have a layered structure of hollow TiO2 spheres interconnected by channels formed at the template beads contacts. Au NPs are homogeneously distributed on the surface. Their localized surface plasmon resonance (SPR) at 587 nm confirm that they are embedded in TiO2. These photocatalysts were tested for the degradation of methylene blue solutions under visible-light illumination. A significant photocatalytic effect is reported with a 95% degradation after 7 h of exposure only for the composite inverse opal. This results from the transfer of hot electrons from the NPs excited at their SPR to the conduction band of TiO2. They generate reactive oxygen species at the surface of TiO2 which are involved in the initial stage of MB degradation. These results highlight the potential of ALD for the fabrication of complex composite structures for application in photocatalysis.

Plasmonic Au functionalized 3D SrTiO3/TiO2 hollow nanosphere enables efficient solar water splitting

Semiconductor-based photocatalyst serves as an attractive candidate for harnessing solar energy to generate renewable hydrogen via water splitting. Here, a novel Au/SrTiO3/TiO2 (T3) photocatalyst of 3D SrTiO3/TiO2 hollow nanosphere decorated by plasmonic Au nanoparticle (NP) is precisely constructed via an in-situ growth of cubic SrTiO3 on anatase TiO2 hollow nanospheres. By carefully regulating the SrTiO3/TiO2 interface structure, the optimized Au/SrTiO3/TiO2 (T3) photocatalyst achieves a remarkable photocatalytic H2 evolution rate of 327.8 μmol g−1 h−1 without Pt as cocatalyst. Specifically, spectroscopic analyses and characterization results comprehensively prove that the favorable plasma electric field (Au) and the internal electric field (SrTiO3/TiO2 heterojunction) coupled with the 3D electron transfer channel in 3D Au-SrTiO3/TiO2 hollow nanospheres synergistically promote the interfacial charge separation and accelerate the interfacial transfer of charge carriers for efficient solar-driven photocatalytic H2 evolution. This work presents a new strategy for the rational design of plasmonic metal functionalized 3D heterojunction photocatalysts for highly efficient solar-to-chemical energy conversion.