Search Results (90)

Layered sodium trititanate (Na₂Ti₃O₇) is a promising anode material for sodium-ion batteries due to its suitable charge/discharge plateaus, cost-effectiveness, and eco-friendliness. However, its slow Na⁺ diffusion kinetics, poor electron conductivity, and instability during cycling pose significant challenges for practical applications. To address these issues, we developed a template-free method to synthesize Na₂Ti₃O₇-C hollow microspheres. The synthesis began with polymerization-induced colloid aggregation to form a TiO₂–urea–formaldehyde (TiO₂-UF) precursor, which was then subjected to heat treatment to induce inward crystallization, creating hollow cavities within the microspheres. The hollow structure, combined with a conductive carbon matrix, significantly enhanced the cycling performance and rate capability of the material. When used as an anode, the Na₂Ti₃O₇-C hollow microspheres exhibited a high reversible capacity of 188 mAh g⁻¹ at 0.2C and retained 169 mAh g⁻¹ after 500 cycles. Additionally, the material demonstrated excellent rate performance with capacities of 157, 133, 105, 77, 62, and 45 mAh g⁻¹ at current densities of 0.5, 1, 2, 5, 10, and 20C, respectively. This innovative approach provides a new strategy for developing high-performance sodium-ion battery anodes and has the potential to significantly advance the field of energy storage. Full article

Solar-driven catalytic oxidation processes for the removal of toxic gaseous pollutants have attracted considerable scientific attention, and there is a strong desire to improve the mass transfer, photogenerated charge separation, and O₂ activation by regulating the structure of the photocatalyst. Initially, functionalized graphene–TiO₂ mesoporous hollow nanofibers have been controllably fabricated by a coaxial electrospinning technique, in which functionalized graphene is controllably prepared through a sequential diazonium functionalization and silane modification and ensures its uniform distribution among TiO₂ nanoparticles (NPs). Subsequently, the ultrafine Ag NPs are primarily anchored onto the surface of graphene by an in situ frozen photodeposition strategy, producing Ag/functionalized graphene–TiO₂ mesoporous hollow nanofibers (Ag/SiG-TO MPHNFs). The optimal Ag/SiG-TO MPHNFs exhibit 3.9-fold and 4.6-fold enhancements in CO photooxidation compared with TO MPHNFs and P25 TiO₂, respectively. The enhanced photoactivity can be attributed to three factors: the creation of the mesoporous hollow structure accelerates mass transfer, the incorporation of graphene facilitates the transfer of photogenerated electrons from TiO₂ to graphene, and the anchoring of Ag NPs improves O₂ activation. Full article

Converting carbon dioxide (CO₂) into solar fuels through photocatalysis represents an appealing approach to tackling the escalating energy crisis and mitigating the greenhouse effect. In this study, using melamine–formaldehyde (MF) nanospheres as a nitrogen source, a N element was simultaneously doped into the TiO₂ nanoparticle structure supported by carbon hollow spheres using a one-step carbonization method to form a heterojunction N-CHS@N-TiO₂ (marked as (N-(CHS@TiO₂)). The composite showed superior photocatalytic activity in reducing CO₂ compared with TiO₂ and N-CHS: after 6 h of visible light irradiation, the CO yield was 4.3 times that of N-CHS and TiO₂; 6 h of UV irradiation later, the CO yield reached 2.6 times that of TiO₂ and 7 times that of N-CHS. The substantial enhancement in photocatalytic activity was attributed to the nitrogen simultaneously doped carbon hollow spheres and TiO₂, mesoporous structure, small average TiO₂ crystal size, large surface areas, and the heterostructure formed by N-CHS and N-TiO₂. The UV-vis diffuse reflectance spectra (DRS) exhibit a significant improvement in light absorption, attributed to the visible-light-active carbon hollow sphere and the N element doping, thereby enhancing solar energy utilization. Full article

Fabricating photoanodes with a strong light-scattering effect can improve the photoconversion efficiency of dye-sensitized solar cells (DSSCs). In this work, a facile microwave hydrothermal process was developed to prepare Au@TiO₂ core–shell nanostructures, and then the Au core was removed by etching, resulting in hollow TiO₂. Morphological characterizations such as field emission scanning and transmission electron microscopy measurements have been used for the successful formation of core–shell and hollow TiO₂ nanostructures. Next, we attempted to deposit the different-sized hollow TiO₂-based microspheres simultaneously on the surface of small-sized TiO₂ nanoparticles-based compact film as light-scattering layers via electrophoretic deposition. The deposited hollow TiO₂ microspheres constitute bi- and tri-layers that not only improve the light-harvesting properties but also speed up the photogenerated charge transfer. Compared to commercial TiO₂ compact film (4.75%), the resulting bi-layer and tri-layered films-based DSSCs displayed power conversion efficiencies of 6.33% and 8.08%, respectively. It is revealed that the deposited bi- and tri-layered films can enhance the light absorption ability via multiple photon reflection. This work validates a novel and controllable strategy to develop light-scattering layers with increased light-harvesting properties for highly efficient dye-sensitized solar cells. Full article

Research on how to efficiently utilize solar energy can effectively address the current situation where excessive carbon emissions threaten the natural environment. The solar capture device, as the core component of the solar thermal photovoltaic system, can significantly enhance the absorption properties of the solar thermal photovoltaic system, which is of high research value in the solar energy application area. In this paper, a metamaterial broadband solar capture device based on the top microstructure of semiconductor InAs material is proposed. The model is fabricated from top to bottom with the semiconductor InAs material at the top with Ti material to make hollow cylindrical microstructures, and a combination of SiO₂ material film, Ti material film, and Cu material film as the substrate. In addition to incorporating the properties of metamaterials, the model is also inspired by the quantum-limited domain effect of nano-semiconductors by using the incorporation of InAs top microstructures at the top to further improve the model’s absorption properties. The model was calculated to have an average absorption in the 280–2500 nm waveband of 96.15% and a weighted average absorption in the 280–4000 nm waveband of 97.71% at AM1.5. Results of calculating the model’s reflectivity in the 280–20,000 nm bands show that the reflectivity of the model is higher than 80% in all the bands after the wavelength of 7940 nm, so the model has a certain spectral selectivity. In addition, the thermal radiation efficiency of the model in the 280–2500 nm waveband, when it is used as a thermal emitter, is calculated to reach 94.40% in this paper. Meanwhile, the capture device has good angular insensitivity, which has high potential for practical applications. Full article

Zinc oxide and titanium dioxide are materials with strong photocatalytic and antimicrobial activity. This activity is greater when the material is in nanocrystalline form. It has been seen that these properties are also present in the ZnO-TiO₂ nanocomposite material, and the extent depends on multiple factors, such as crystallinity, structural composition, crystallite size, and morphology. These structural properties can be varied by acting on the synthesis of the material, obtaining a wide variety of composites: random nanoparticles, nanorods, nanowires, nanotubes, nanofibers, tetrapods, core–shell, hollow spheres, inverse opal structures (IOSs), hierarchical structures, and films. When an interface between nanocrystallites of the two oxides is created, the composite system manages to have photocatalytic activity greater than that of the two separate oxides, and in certain circumstances, even greater than P25. The antimicrobial activity results also improved for the composite system compared to the two separate oxides. These two aspects make these materials interesting in various fields, such as wastewater and air treatment, energy devices, solar filters, and pharmaceutical products and in the context of the restoration of monumental cultural assets, in which their use has a preventive purpose in the formation of biofilms. In this review we analyse the synthesis techniques of ZnO-TiO₂ nanocomposites, correlating them to the shape obtained, as well as the photocatalytic and antimicrobial activity. It is also illustrated how ZnO-TiO₂ nanocomposites can have a less negative impact on toxicity for humans and the environment compared to the more toxic ZnO nanoparticles or ZnO. Full article

This comprehensive study explores the kinetics of adsorption and its photocatalytic degradation of methyl orange (MO) using an advanced copper-decorated photocatalyst in the form of hollow fibers (HFs). Designed to boost both adsorption capacity and photocatalytic activity, the photocatalyst was tested in batch experiments to efficiently remove MO from aqueous solutions. Various isotherm models, including Langmuir, Freundlich, Sips, Temkin, and Dubinin–Radushkevich, along with kinetic models like pseudo-first and pseudo-second order, Elovich, Bangham, and Weber–Morris, were utilized to assess adsorption capacity and kinetics at varying initial concentrations. The results indicated a favorable MO physisorption on the nanocomposite photocatalyst under specific conditions. Further analysis of photocatalytic degradation under UV exposure revealed that the material maintained high degradation efficiency and stability across different MO concentrations. Through the facilitation of reactive oxygen species generation, oxygen played a crucial role in enhancing photocatalytic performance, while the degradation process following the Langmuir–Hinshelwood model. The study also confirmed the robustness and sustained activity of the nanocomposite photocatalyst, which could be regenerated and reused over five successive cycles, maintaining 92% of their initial performance at concentrations up to 15 mg/L. Overall, this effective nanocomposite photocatalyst structured in the form of HF shows great promise for effectively removing organic pollutants through combined adsorption and photocatalysis, offering valuable potential in wastewater treatment and environmental remediation. Full article

In this study, an ultra-wideband absorber spanning from UV-B to middle-IR was designed and analyzed using a novel structure. The multilayer metamaterial, arranged from bottom to top, consisted of an Al metal layer, a lower SiO₂ layer, a graphite layer, another SiO₂ layer, a thin Ti layer, and a top SiO₂ layer. The top layer of SiO₂ had a 200 nm square cavity etched out, and then a square Ti nanopillar and a square Ti hollow outside a Ti nanopillar were embedded. This specific arrangement was chosen to maximize the absorption properties across a broad spectrum. The absorption spectrum of the designed absorber was thoroughly analyzed using the commercial finite element analysis software COMSOL Multiphysics^® (version 6.0). This analysis confirmed that the combination of these various components achieved perfect absorption and an ultra-wideband response. The synergistic interaction between the layers and the nanopillars structure contributed significantly to the absorber’s efficiency, making it a promising candidate for applications requiring broad-spectrum absorption. The comprehensive analyses of the parameters for different structures demonstrated that the effects of guided-mode resonance, coupling resonance, optical impedance matching, and propagating surface plasmon resonance existed in the investigated structure. The optimal model, determined through analyses using COMSOL Multiphysics^®, showed that the broadband absorption in the range of 270 to 3600 nm, spanning from UV-B to middle-IR, exceeded 90.0%. The average absorption rate within this range was 0.967, with the highest reaching a near-perfect absorptivity of 99.9%. We also compared three absorption spectra in this study: the t1–t6 flat structure, the t1–t5 flat structure with t6 featuring a square cavity, and the structure proposed in this study. This demonstrates that a square nanopillar and a square hollow embedded in a square cavity can enhance the absorptive properties of the absorber. Full article

Hollow mesoporous hydroxyapatite (HM-HAP) composites coated with titania are prepared to increase the stability and catalytic performance of titania for azo dyes present in the wastewater system. In this work, HM-HAP particles were first synthesized by a hydrothermal method utilizing the CaCO₃ core as a template and then coated with titania to form TiO₂/HM-HAP composites. Utilizing SEM, XRD, XPS, BET, FTIR, EDS, UV–vis DRS spectroscopy, and point of zero charge (PZC) analysis, the coating morphological and physicochemical parameters of the produced samples were analyzed. The photocatalytic efficiency of the synthesized coated composites was assessed by the degradation of methyl red (MR) dye in water. The results indicated that TiO₂/HM-HAP particles could efficiently photodegrade MR dye in water under UV irradiation. The 20% TiO₂/HM-HAP coating exhibited high catalytic performance, and the degradation process was followed by the pseudo-first-order (PFO) kinetic model with a rate constant of 0.033. The effect of pH on the degradation process was also evaluated, and the maximum degradation was observed at pH 6. The analysis of degraded MR dye products was investigated using LC-MS and FTIR analysis. Finally, a good support material, HM-HAP for TiO₂ coatings, which provides a large number of active adsorption sites and has catalytic degradation performance for MR dye, was revealed. Full article

The removal of persistent organic micropollutants (OMPs) from secondary effluent in wastewater treatment plants is critical for meeting water reuse standards. Traditional treatment methods often fail to adequately degrade these contaminants. This study explored the efficacy of a hybrid ozonation membrane filtration (HOMF) process using CeO₂ and CeTiO_x-doped ceramic crossflow ultrafiltration ceramic membranes for the degradation of OMPs. Hollow ceramic membranes (CM) with a 300 kDa molecular weight cut-off (MWCO) were modified to serve as substrates for catalytic nanosized metal oxides in a crossflow and inside-out operational configuration. Three types of depositions were tested: a single layer of CeO₂, a single layer of CeTiO_x, and a combined layer of CeO₂ + CeTiO_x. These catalytic nanoparticles were distributed uniformly using a solution-based method supported by vacuum infiltration to ensure high-throughput deposition. The results demonstrated successful infiltration of the metal oxides, although the yield permeability and transmembrane flow varied, following this order: pristine > CeTiO_x > CeO₂ > CeO₂ + CeTiO_x. Four OMPs were examined: two easily degraded by ozone (carbamazepine and diclofenac) and two recalcitrant (ibuprofen and pCBA). The highest OMP degradation was observed in demineralized water, particularly with the CeO₂ + CeTiO_x modification, suggesting O₃ decomposition to hydroxyl radicals. The increased resistance in the modified membranes contributed to the adsorption phenomena. The degradation efficiency decreased in secondary effluent due to competition with the organic and inorganic load, highlighting the challenges in complex water matrices. Full article

Manganese oxide-cerium oxide supported on titanate nanotubes (i.e., MnCe/TiNTs) were prepared and their catalytic activities towards NH₃-SCR of NO were tested. The results indicated that the MnCe/TiNT catalyst can achieve a high NO removal efficiency above 95% within the temperature range of 150–350 °C. Even after exposure to a HCl-containing atmosphere for 2 h, the NO removal efficiency of the MnCe/TiNT catalyst maintains at approximately 90% at 150 °C. This is attributed to the large specific surface area as well as the unique hollow tubular structure of TiNTs that exposes more Ce atoms, which preferentially react with HCl and thus protect the active Mn atoms. Moreover, the abundant OH groups on TiNTs serve as Brønsted acid sites and provide H protons to expel Cl atom from the catalyst surface. The irreversible deactivation caused by HCl can be alleviated by H₂O. That is because the dissociated adsorption of H₂O on TiNTs forms additional OH groups and relieves HCl poisoning. Full article

The Hollow Cathode Gas Flow Sputtering (GFS) provides special plasma conditions and is of extensive interest as a more affordable alternative to the high vacuum sputtering techniques. In the case of the tubular cathode a circular outlet symmetry stipulates homogeneity issues for both metallic and reactive deposition regimes. Using the results of Direct Simulation Monte Carlo (DSMC), we propose an external coaxial attachment which is manufactured and examined in a nozzle and a diffuser positioning. The impact on the homogeneity of Ti and ${\mathrm{TiO}}_2$ films is examined using profilometry and spectral ellipsometry. Our results demonstrate that the use of the nozzle attachment significantly enhances film homogeneity from about 3 ${\mathrm{cm}}^2$ to more than 12 ${\mathrm{cm}}^2$. It also secures better process control in terms of oxygen stoichiometry and film thickness. Some crucial general issues of the reactive GFS process are discussed. Full article

The fluorinated titanium dioxide (F-TiO₂) hollow spheres with varying F to Ti molar ratios were prepared by a simple one-step hydrothermal method followed by thermal processing. The diameter of the F-TiO₂-0.3 hollow spheres with a nominal ratio of F:Ti = 0.3:1 was about 200–400 nm. Compared with the sensor based on pristine TiO₂ sensing materials, the F-TiO₂-0.3 sensor displayed an enhanced sensing performance toward gaseous formaldehyde (HCHO) vapor at room temperature under ultraviolet (UV) light irradiation. The F-TiO₂-0.3 sensor demonstrated an approximately 18-fold enhanced response (1.56) compared to the pristine TiO₂ sensor (0.085). The response and recovery times of the F-TiO₂-0.3 sensor to 10 ppm HCHO were about 56 s and 64 s, respectively, and a limit-of-detection value of 0.5 ppm HCHO was estimated. The F-TiO₂-0.3 sensor also demonstrated good repeatability and selectivity to HCHO gas under UV light irradiation. The outstanding HCHO gas-sensing properties of the F-TiO₂-0.3 sensor were related to the following factors: the excitation effect caused by the UV light facilitated surface chemical reactions with analyte gas species; the hollow sphere structure provided sufficient active sites; and the surface fluoride (≡Ti−F) created additional chemisorption sites on the surface of the TiO₂ material. Full article

In this numerical study, the performance of ceramic-based mullite hollow fiber (HF) membranes in a direct contact membrane distillation (DCMD) process was evaluated. Three types of membranes were tested: (i) hydrophobic membrane C8-HFM, (ii) rod-like omniphobic membrane (C8-RL/TiO₂), and (iii) flower-like omniphobic membrane (C8-FL/TiO₂). The CFD model was developed and validated with experimental results, which were performed over a 500 min period. The initial mass flux of C8-HFM was 30% and 9% higher than that of C8-FL/TiO₂ and C8-RL/TiO₂, respectively. However, the flower-like omniphobic membrane C8-FL/TiO₂ had the lowest drop in flux, around 11%, while the rod-like omniphobic membrane C8-RL/TiO₂ had a 15% reduction, both better than the 23% reduction in the hydrophobic membrane C8-HFM over the 500 min. The study also analyzed the impact of fouling by examining the variation in mass transfer coefficient (MTC) over time. The results indicated that the ceramic-based mullite HF membranes with TiO₂ flowers and rods demonstrated a high resistance to fouling compared to C8-HFM. The modified membranes could find applications in the desalination and handling of seawater samples containing organic contaminants. The CFD model’s versatility can be utilized beyond the current investigation’s scope, offering a valuable tool for efficient membrane development solutions, particularly for challenges such as the presence of organic contaminants in seawater. Full article

We synthesized hollow spherical titanium oxide particles, which are one of the structural features of fabricating a thin-film photoelectrode, using the particles and evaluated their properties. The XRD diffraction results confirmed the main phase peaks of the target rutile-type hollow spherical titanium oxide (HSTR) and bronze-type hollow spherical titanium oxide (TiO₂(B)). The calcium carbonate used in the core material was also removed. The photocatalytic reaction measurement result showed that the activity of TiO₂(B) in ultraviolet light of 365 nm was higher than that of TiO₂(B). As shown in the visible spectrum, the photo adsorption wavelength of HSTR was approxim ately 700 nm, whereas TiO₂(B) was generally absorbed around 400 nm. A relationship between an electric current peak and the square root of a scan potential speed suggested a reversible reaction system in light irradiation. Full article