Hierarchical TiO2 Microspheres Research Articles

N-doped carbon/TiO2 composites with enhanced photocatalytic performance for the removal of organic pollutants

A nitrogen doped carbon (NC) material, obtained via the camphor combustion technique, was used to develop a TiO2 based visible light photocatalyst. Various physical and analytical techniques were used to characterize the structural, morphological and photocatalytic study of the obtained catalyst. The results illustrate that N-doped carbon/TiO2 composites (NCT) exhibit NC spheroids embedded on the surface of 3D flower-like hierarchical TiO2 microspheres composed of 1D nanorods. The presence of C-N, C-C, N-Ti-O and Ti-O-C was successfully confirmed by the FTIR study. The UV–vis absorption spectra revealed the energy bandgap between 2.4 and 2.8 eV, confirming the enhanced visible light absorption ability for the NCT samples with increased wt% of N-doped carbon. The NCT sample has achieved 86% photodegradation of methyl orange in an aqueous solution within 25 min under mercury light irradiation and 85% within 10 min under natural sunlight irradiation. In addition, NCT3 composite degrades 30% of BPA (20 ppm) within 210 min under mercury light irradiation. The enhanced catalytic activity of the composite material was ascribed due to the high surface area, large pore size and high pore. Also, the high absorption in the visible range and efficient charge transfer of the charge carriers were credited for the enhanced photocatalytic activity of the NCT3 sample.

Constructing 3D hierarchical TiO2 microspheres with enhanced mass diffusion for efficient glucose photoreforming under modulated reaction conditions

Three-dimensional (3D) TiO2 hierarchical microspheres (THMs) were successfully prepared via a facial template-free hydrothermal approach. The possible growth mechanism of THM was also investigated by TiCl4 concentration-, time-, and temperature-dependent experiments. The results indicate that the formation of an urchin-like hierarchical structure may follow a “nucleation-dissolution and recrystallization-assembly” process. THM was employed for photoreforming under various catalyst and glucose concentrations, solvent compositions, and pH values. The H2 production rate, glucose conversion, arabinose and formic acid selectivity reached 9.44 mmol gcat.−1h−1, 86.35%, 11.32%, and 46.87%, respectively, under the modulated condition with Pt as cocatalyst; this is attributed to the enhanced mass diffusion caused by the 3D hierarchical morphology as well as the interaction between unsaturated Ti atoms (or oxygen vacancies) in THM and the hydroxyl oxygen atoms on glucose. In addition, the enhanced light absorption induced by defects also exerts a positive effect. In this work, we present an emerging sustainable strategy for the coproduction of H2 and value-added chemicals from biomass-based glucose with economic photocatalysts under mild conditions.

Dual co-catalysts Ag/Ti3C2/TiO2 hierarchical flower-like microspheres with enhanced photocatalytic H2-production activity

Solar-powered semiconductor photocatalysis is considered a powerful strategy for addressing environmental pollution and energy crisis. Nevertheless, the separation and transfer abilities of photogenerated photocatalysts remain unsatisfactory. Herein, dual Ti3C2 nanosheets/Ag co-catalysts synergistically decorated hierarchical flower-like TiO2 microspheres for boosting photocatalytic H2 production were fabricated by electrostatic self-assembly and subsequent photoreduction procedures. The optimal Ag/Ti3C2/TiO2 composite demonstrated an excellent photocatalytic H2-production rate of 1024.72 μmol g−1 h−1 under simulated solar irradiation, achieving nearly 40, 2.3, and 1.8 folds with respect to that obtained on pristine TiO2, optimized Ti3C2/TiO2 composite, and Ag/TiO2 composite, respectively. The considerably improved photocatalytic H2-production activity is associated with the synergistic effect of the hierarchical flower-like structure of TiO2, excellent electrical conductivity of Ti3C2, and surface plasmon resonance effect of Ag, which enhances the light absorption capacity and promotes the separation and transfer of photogenerated carriers. This study provides insight into the design of high-efficiency photocatalysts with dual co-catalysts for solar H2 production.

The facile synthesis of 3D hierarchical flower-like TiO2 microspheres with enhanced photocatalytic activity

A 3D hierarchical flower-like rutile TiO2 microspheres assembled by well-aligned 1D nanorods were efficiently synthesized using the solvothermal method at a temperature of 140 °C for 5 h. The synthesized TiO2 microspheres have an average crystallite size of about 6.9–8.4 nm. According to SEM, FESEM and TEM analysis, flower-like TiO2 microspheres are made up of nanorods that grow radially from the center and are several nm thick on average. The XRD, EDS and XPS analysis revealed that titanium and oxygen peaks were present with no other impurity peaks. The volume ratio of water and toluene plays a vital role that was significantly affecting the chemical properties of synthesized TiO2 materials. Compared to other samples, the hierarchical 3D TiO2 microspheres Ti(1:1) had a small crystallite size, a lower bandgap, a comparatively large BET surface area of about 130 m2/g and a pore volume of 0.179 cm3/g, which revealed more favorable for photocatalytic activity. Ti(1:1) photocatalyst degraded MO by almost 96 and 94% within 50 and 40 min, respectively, when exposed to mercury light and sunlight. Also, it showed that within 60 min of mercury light irradiation, RhB degraded up to 65%. Additionally, an LC-MS study was performed for the degradation of MO dye solution and a possible degradation path was proposed.

Microwave-assisted hydrothermal solution process for accelerated formation of 3D hierarchical flowery anatase-TiO2 microspheres with excellent photocatalytic activity

A microwave-assisted hydrothermal solution synthesis methodology is used to prepare 3D hierarchical flowery TiO2 microspheres quickly and without calcination.

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.

Hierarchical TiO2 microspheres supported ultrasmall palladium Nanocrystals: A highly efficient catalyst for Suzuki reaction

A hierarchical titanium dioxide microspheres-supported palladium catalyst (Pd/TiO2-350) was prepared and characterized using BET, XRD, XPS, SEM, EDX, and TEM analyses. An ICP-OES analysis of Pd/TiO2-350 further confirmed the successful Pd immobilization on TiO2 with a palladium loading of 0.1 mmol g−1. Pd/TiO2-350 efficiently catalyzed the Suzuki-Miyaura reaction of aryl iodides with arylboronic acids to give the corresponding biaryl derivatives in good to excellent yields. After the reaction, the catalyst was recovered by centrifugation and reused three times without significant loss of its catalytic activity. Moreover, the loading of palladium species further decreased to 0.001 mol%, and the total turnover number and turnover frequency of the catalyst reached as high as 99 000 and 0.57 s−1, respectively.

Low-temperature NH3-SCR reaction over 3D Cu/Fe-TiO2-rGO composite catalyst synthesized by photoreduction method

Nitrogen oxides is a typical atmospheric pollutant and selective catalytic reduction with NH3 is an efficient and commonly used solution to remove NO from power plants and factories. In this paper, the Cu/Fe-TiO2-rGO catalysts with 3D hierarchical dandelion-like TiO2 microspheres and reduced graphene oxide as carrier were prepared by photocatalytic reduction method. The catalyst possessed the improved NO removal rate due to the following advantages: firstly, graphene oxide improved the specific surface area of Cu/Fe-TiO2-rGO catalyst. In addition, the Fe species promoted NH3 desorption and increased the oxidation of Cu species leading to the improvement of the low temperature activity of the catalyst. In another aspect, the amount of graphene oxide used to prepare MOx/GO by common hydrothermal method is large. The catalyst synthesized by photoreduction method with less amount and higher dispersion degree of reduced graphene oxide possessed the best NO conversion rate over 97 % at 250 °C, and Cu and Fe species were simultaneously distributed on the surface of rGO and 3D TiO2 microspheres. What was more, a large number of Lewis acid sites and a small amount of Brönsted acid sites in the catalysts were detected, and Fe element improved the NO conversion of Cu0.4Fe0.6-TiO2-rGO sample by Langmuir–Hinshelwood mechanism.

Au thorn-decorated TiO2 hierarchical microspheres with superior photocatalytic bactericidal activity under red and NIR light irradiation

Herein, we fabricated a novel surface plasmon resonance (SPR) photocatalyst Au(T)-TiO2(MS) by anchoring Au thorns on TiO2 hierarchical microspheres (MS). It was found that the flower-like TiO2 microspheres with a size of ~800 nm consist of many lamellar petals and the Au thorns with length of dozens of nanometers were anchored on TiO2(MS). By analyzing the DRS, PL spectra, transient photocurrents and electrochemical impedance spectra, it was disclosed that Au thorns not only respond to visible and NIR light but also effectively promote the separation of photogenerated charge carriers in TiO2(MS). The photocatalytic inactivation of E. coli K12 indicated that Au(T)-TiO2(MS) displayed excellent bactericidal activity and stability under red and NIR light irradiation. Due to the special structure of Au(T)-TiO2(MS), it can produce reactive species outside and within bacteria, both of which work together responsible for the inactivation of E. coli K12. The EPR spin-trap measurements with DMPO and reactive species trapping experiments revealed that all of h+, •OH and •O2− are produced over Au(T)-TiO2(MS), while •O2− and h+ are the main reactive species for bacterium inactivation.

Hierarchical flower-like 0D/3D g-C3N4/TiO2 S-scheme heterojunction with enhanced photocatalytic activity

The wide band gap and high recombination rate of photogenerated electron-hole pairs greatly limit the photocatalytic efficiency of TiO2 under sunlight irradiation. We constructed a novel photocatalyst (TiO2/CNQDs-3) with the heterojunction of non-toxic, metal-free zero-dimensional carbon nitride quantum dots (CNQDs) and three-dimensional hierarchical flower-like TiO2 microspheres, which not only enhanced the visible-light absorption capability, but also inhibited the recombination of photogenerated electron-hole pairs. The TiO2/CNQDs-3 showed a high light absorption intensity, transient photocurrent density and photodegradation efficiency of methyl orange. And the reaction rate constant of the TiO2/CNQDs-3 for the first-order reaction kinetics was 5.4 times and 2.2 times that of the pure TiO2 and P25, respectively. With the increase of pH, the photodegradation efficiency of methyl orange by the TiO2/CNQDs-3 decreased due to electrostatic repulsion. Moreover, the main active species were ∙OH, h+ and ∙O2-, and the Step-scheme (S-scheme) heterojunction enhanced the photodegradation of methyl orange. The TiO2/CNQDs composites are environmentally friendly, inexpensive, fast in the separation of electron-hole pairs, strong in redox capacity, large in specific surface area and pore volume, and have good application prospects in photodegradation of pollutants.

All-solid-state Z-scheme heterostructures of 1T/2H-MoS2 nanosheets coupled V-doped hierarchical TiO2 spheres for enhanced photocatalytic activity

Highly efficient all-solid-state Z-scheme semiconductors are of great significance to the photocatalytic performance. Herein, we design and construct edge-rich bicrystalline 1T/2H-MoS2 nanosheet cocatalyst modified V-doped hierarchical TiO2 microspheres for the photocatalytic removal of oxytetracycline hydrochloride. In this catalyst system, the conductive 1T phase of MoS2 accelerates the charge transfer kinetics and works as an electron mediator in a Z-scheme, while 2H phase of MoS2 and V-TiO2 is the photosensitizer and reactant adsorbed sites, respectively. The optimized VTM-5% heterojunction possesses superior degradation efficiency than that of bare components, which is ascribed to the enhanced light-harvesting capacity, populated exposed active sites, rapid photogenerated charge transfer, and excellent affinity to reactant molecules. Moreover, a built-in electric field forms via an intensive electronic interaction of positively charged V-TiO2 and negatively charged 1T/2H-MoS2, as confirmed by density functional theory calculation. This study provides new insights into the rational design of noble metal-free cocatalyst-based Z-scheme photocatalysts toward environmental remediation.

Photocatalytically recovering hydrogen energy from wastewater treatment using MoS2 @TiO2 with sulfur/oxygen dual-defect

Photocatalysis is a promising technology for energy and environment applications. Herein, a dual-defect heterojunction system of TiO2 hierarchical microspheres with oxygen vacancies modified with ultrathin MoS2−x nanosheets (MoS2−x @TiO2-OV) is designed for simultaneously degrading pollutants and evolving hydrogen. MoS2−x @TiO2-OV exhibits a dramatically enhanced photocatalytic activity with a H2 evolution rate of 2985.16 μmol g−1h−1. In treating the simulated pharmaceutical wastewater, MoS2−x @TiO2-OV is capable of purifying various refractory contaminants, with the highest H2 evolution rate of 41.59 μmol g−1h−1 during enrofloxacin degradation. While treating the simulated coking wastewater, the catalyst achieves a H2 evolution rate of 102.72 μmol g−1h−1 and a mineralization rate of 50%. Computational studies suggest that the dual-defect is superior for the adsorption of H* and producing·OH (‘dual-defect boosted dual-function’). Also, the dual-defect sites significantly boosted the charge-carrier separation and transfer efficiencies. This work highlights the crucial role of defect engineering to develop the energy-recovering wastewater treatment approaches.

Synergistic Catalytic Effect of the Combination of Deep Eutectic Solvents and Hierarchical H-TiO2 Nanoparticles toward the Synthesis of Benzimidazole-Linked Pyrrolidin-2-One Heterocycles: Boosting Reaction Yield

Synthesis of bioactive heterocyclic compounds comprising pyrrolidinone linked to a benzimidazole moiety by an eco-friendly and efficient route was investigated. The targeted scaffolds were synthesized from substituted arylamines and available o-phenylenediamine under ultrasonic irradiation in the presence of a mixture of a deep eutectic solvent (DES) and hierarchical TiO2 (H-TiO2) microspheres as a green catalytic system. Two DESs were synthesized by separately mixing FeCl2 and CuCl2 with urea. On the other hand, hierarchical TiO2 (H-TiO2) was synthesized by a solvothermal route and characterized by XRD, SEM, Raman spectroscopy, and XPS. The results demonstrate that the best reaction yields are obtained by using H-TiO2 microspheres in the DES. Besides, the synthesized compounds were screened for their antibacterial activity against different bacteria. Overall, eight derivatives were confirmed to exhibit antibacterial activity.

Application of Bunchy TiO2 Hierarchical Microspheres as a Scattering Layer for Dye-Sensitized Solar Cells

A novel bunchy TiO2 hierarchical microspheres composite nanostructure with strings of anatase TiO2 hierarchical micro-spheres and rutile nanobelts framework (HSN) was synthesized via an one-pot hydrothermal process. This new structure presents great specific surface area, large pore size distribution, homogeneous three-dimensional (3D) structure, high crystallinity and excellent light scattering performance simultaneously. The bi-layer photoanode film was successfully prepared which TiO2 P25 as absorption layer and HSN as an efficient scattering layer on the top of TiO2 P25 film in dye sensitized solar cells (DSSC). The bi-layer DSSC taken on a great progress in the power conversion efficiency (PCE) achieved 8.08%. However, the PCE of single and double layer TiO2 film DSSCs just showed 6.72% and 3.67% respectively. Such improvement was mainly because of the efficient scattering centers (HSN) which can bring the enhanced dye loading, fast charge transfer and excellent light harvesting efficiency.

Hierarchical flower-like TiO2 microspheres for high-selective NH3 detection: A density functional theory study

TiO2 is proved to be a promising material in the detection of various hazardous gases at the high temperature. However, gas adsorption-diffusion capacity at the room temperature is limited by their insufficient specific surface area and surface active sites. Herein, we report a strategy to synthesis of flower-like TiO2 microspheres assembled by nanosheets and characterize the selective adsorption of NH3 by using density functional theory (DFT). The as fabricated flower-like TiO2 microspheres show an outstanding gas sensitivities (∼122 to 50 ppm NH3) and high selectivity for NH3 detection at room temperature. The higher adsorption energy and smaller adsorption distance of NH3 on TiO2 (001) indicate the much stronger interaction NH3-TiO2 system. The present studies provide useful gas sensing materials with fine morphologies for the development of high-performance room temperature NH3 sensors.

N-doped TiO2 hierarchical microspheres as electrode for high-performance supercapacitors

In this work, N-doped TiO2 hierarchical microspheres were prepared by a hydrothermal process for high performance supercapacitor. This structured microsphere can provide a large specific surface area and a suitable pore size, which is conducive to electrolyte infiltration, and the nitrogen doping can improve the electrical properties of intrinsic TiO2. Combining these two strategies, the specific capacitance of N-doped TiO2 microspheres increases from 2.26 to 11.89 mF/cm2 at current density of 1 mA/cm2 and the capacitance remains 90.5% of the original capacity after 10,000 cycles.

Hierarchical TiO2 microspheres with enlarged lattice spacing for rapid and ultrastable sodium storage

Intercalation-type TiO2 anode materials have garnered extensive interest for use in Na-ion batteries owing to their low cost and excellent stability. However, such materials are limited by their unsatisfactory specific capacity, particularly at high rates. Herein, we demonstrated the synthesis of hierarchical anatase TiO2 microspheres with enlarged lattice spacings using a simple salt template-assisted spray pyrolysis technique. The broad lattice distance can not only promote ionic transfer but also reduce the band gap with locally enhanced differential charge density, according to density functional theory calculations. Consequently, the resultant sample exhibited reversible specific capacities as high as 362 and 141.8 mA h g−1 at 50 and 5 A g−1, respectively. Impressively, the sample retained specific capacities of 154 mA h g−1 at 1.0 A g−1 after 1600 cycles and of 93.4 mA h g−1 at 5 A g−1 after 7700 cycles. To the best of our knowledge, the Na storage performance of the prepared sample is one of the best among that of TiO2-dominated anode materials. These findings provide new insight into the preparation of novel anode materials for Na-ion batteries with high ionic and electronic conductivities.

Macroporous-mesoporous C-, S-, N-doped titania microspheres via the polyHIPE microspheres templates

Doping and increasing specific surface area by forming highly porous structures are two effective ways to enhance the photocatalytic performances of TiO2 particles. Here for the first time, we report a new facile method to prepare the macroporous-mesoporous C-, S-, N-doped TiO2 (C/S/N-TiO2) microspheres via polyHIPE microspheres as templates. The chemical and crystalline structures of these hierarchical porous TiO2 microspheres are analyzed with FTIR, XPS, EDS, and XRD. The macroporous-mesoporous structures are confirmed with SEM observation and BET analysis. UV–vis DRS spectra analysis shows that the band gaps of C doped TiO2, C/N doped TiO2, C/S doped TiO2 and C/S/N doped TiO2 are estimated to be 3.07, 3.01, 2.94 and 2.81 eV, respectively, which are significantly narrower than that of TiO2 nanoparticles (3.23 eV). Photoluminescence spectra demonstrate that the recombination of electrons and holes in these macroporous-mesoporous TiO2 microspheres is also suppressed. The hierarchical porous C/S/N-TiO2 microspheres show high visible-light catalytic efficiency and excellent cycling stability to degrade RhB dye.

Hierarchical flower-like TiO2 microspheres with improved dye-sensitized solar cell performance

Hierarchical flower-like TiO2 microspheres (FMS) and TiO2 nanorice (NR) were obtained, respectively, by controlling the dosage of Ti precursor via a simple hydrothermal process. Flower-like TiO2 microspheres consist of nanopetals grown from the center radially, the nanopetals are about several nm in average thickness, and each nanopetal has a thinned tip with an average size of 15 nm. The unique hierarchical TiO2 microspheres with large surface area (118.6 m2 g−1) suggested its potential application in dye-sensitized solar cells (DSSCs). The power conversion efficiency of FMS-based DSSCs (9.58%) is much higher than that of NR-based DSSCs (7.13%), which could be ascribed to its excellent light-scattering and dye absorption ability, shorter electron transport pathway and longer electron recombination time derived from the thin thickness and large specific surface area of nanopetals.

Mixed-Surfactant-Assisted Synthesis of Dual-Phase Li4 Ti5 O12 -TiO2 Hierarchical Microspheres as High-Performance Anode Materials for Li-Ion Batteries.

A mixed-surfactant-assisted method was developed to synthesize dual-phase Li4 Ti5 O12 -TiO2 hierarchical microspheres. The ratio of anionic/cationic surfactant could regulate the primary structure morphology and the dual-phase ratio of the final product, in which the primary structure morphology could be stacked nanosheets, small nanoparticles, or large nanoparticles. The sample with a primary structure morphology of small nanoparticles had the highest specific surface area of 79.38 m2 g-1 and the best electrochemical performance because of its high Li+ migration rate, low polarization, and appropriate TiO2 content. Its capacity reached 153.5 mA h g-1 at a current rate of 40 C, and it retained nearly 100 % of its capacity after 100 cycles. A self-assembly mechanism of the mixed surfactant was highlighted to explain the formation of hierarchical microspheres. The physical and electrochemical properties of obtained material were correlated effectively.