TiO2 Microspheres Research Articles

Visible Light-Driven Micromotors in Fuel-Free Environment with Promoted Ion Tolerance.

Light-driven electrophoretic micromotors have gained significant attention recently for applications in drug delivery, targeted therapy, biosensing, and environmental remediation. Micromotors that possess good biocompatibility and the ability to adapt to complex external environments are particularly attractive. In this study, we have fabricated visible light-driven micromotors that could swim in an environment with relatively high salinity. To achieve this, we first tuned the energy bandgap of rutile TiO2 that was hydrothermally synthesized, enabling it to generate photogenerated electron-hole pairs under visible light rather than solely under UV. Next, platinum nanoparticles and polyaniline were decorated onto the surface of TiO2 microspheres to facilitate the micromotors swimming in ion-rich environments. Our micromotors exhibited electrophoretic swimming in NaCl solutions with concentrations as high as 0.1 M, achieving a velocity of 0.47 μm/s without the need for additional chemical fuels. The micromotors' propulsion was generated solely by splitting water under visible light illumination, therefore offering several advantages over traditional micromotors, such as biocompatibility and the ability to operate in environments with high ionic strength. These results demonstrated high biocompatibility of photophoretic micromotors and high potential for practical applications in various fields.

A two-electron migration mechanism co-constructed by K+ passivation and defect engineering for efficient TiO2 photocatalytic hydrogen evolution

As a promising candidate for photocatalytic hydrogen evolution reaction, Pt/TiO2 photocatalysts with low cost and high activity are considered to be one of the most ingenious strategies for obtaining both high-purity hydrogen and high-value products using inexhaustible sunlight as the sole driving force. In this work, a TiO2 microsphere with internal defect engineering co-constructed by oxygen vacancies (Ov) and B-doping was prepared by using a one-step solvent volatilization method, whose surface was cleverly modified by the K+ passivation layer. Compared with the hydrogen evolution activity of pure TiO2 (2.7 μmol/g/h), that of HB-TiO2 was improved by 460% (124 μmol/g/h), while that of KHB-TiO2 was improved by 1300% (352 μmol/g/h). The prominent performance is attributed to the accelerated carrier separation induced by the internal defect-engineering and the efficient two-electron migration mechanism assisted by the K+ passivation layer. On the premise of not destroying the internal defect engineering that facilitates carrier separation, the fascinating surface K+ passivation mechanism inhibits carrier recombination and improves visible light utilization by healing the electronic structure of the TiO2 surface and then using Pt-Ti metal bonds to directly migrate two-electron to Pt for the hydrogen evolution reaction. Our work demonstrates the promising strategy for the modification of defective TiO2 microspheres with K+ passivation layer, opening a new avenue for the construction of a two-electron migration mechanism for efficient hydrogen evolution reaction.

High-performance visible-light photocatalysis induced by dye-sensitized Ti3+-TiO2 microspheres

Strong visible-light absorption and high surface areas contribute to high-perform semiconductor photocatalysis. This work aims to fabricate self-doped Ti3+-TiO2 microspheres and dye sensitized self-doped Ti3+-TiO2 composites with high surface areas and visible-light absorption via one-pot solvothermal strategy for highly enhanced photocatalytic tetracycline degradation under visible-light irradiation. The experimental results showed that the obtained Ti3+-TiO2 microspheres showed enhanced visible-light capture capacity and a larger surface area of 204.9 m2 g−1. Besides, the obtained Eosin Y/Ti3+-TiO2 composites showed efficient visible-light absorption and highly boosted photocatalytic performance towards tetracycline degradation. The highest rate constant for Eosin Y/Ti3+-TiO2-9% composite reached as high as 0.06657 min−1, approximately 8.09 times that of commercial TiO2, strongly demonstrating the significant roles of dye sensitization. Finally, a reasonable dye-sensitization visible-light photocatalytic mechanism was suggested.

NH2-MIL-125(Ti)/amorphous TiO2 microspheres for enhanced visible light photocatalytic selective oxidation of amines

Metal–organic frameworks (MOFs) have received increasing attention for conducting miscellaneous photocatalytic reactions. Amorphous TiO2, despite the lack of visible light activity, can be a platform for integrating with a Ti-based MOF NH2-MIL-125(Ti) during hydrothermal process. Herein, amorphous TiO2 microspheres are synthesized to enhance the activity of NH2-MIL-125(Ti) by integration. The morphology, porosity, and activity of NH2-MIL-125(Ti)/amorphous TiO2 microspheres are systematically investigated by various methods. The photocatalyst NH2-MIL-125(Ti)/amorphous TiO2 exhibits enhanced conversions, more than five times that of pristine NH2-MIL-125(Ti), for the selective oxidation of benzylamine. A series of optical and electrochemical characterizations are performed to clarify the mechanism for the photocatalytic selective oxidation of benzyl amines. Specifically, for NH2-MIL-125(Ti)/amorphous TiO2, visible light absorption is from NH2-MIL-125(Ti); and faster electron transfer to molecular oxygen is due to amorphous TiO2. This work shows that integrating MOFs with metal oxides can be crucial in enhancing visible light photocatalysis.

Calcium-doped TiO2 microspheres and near-infrared carbazole-based sensitizer for efficient co-sensitized dye-sensitized solar cell

Here, we synthesized metal-free organic dye (CCPICPB) with two carbazole donor groups and two anchoring groups that exhibit a panchromatic absorption in the near-infrared range of up to 750 nm. To study the photophysical properties of synthesized CCPICPB dye, the UV–Vis and cyclic voltammetric experiments were studied and the obtained results were validated with theoretical simulation studies. After that, the solvothermal approach is used to synthesize pristine anatase and calcium (Ca)-doped TiO2 microspheres with a smooth morphology. These microstructures are examined in depth using XRD, electron microscopy and electrochemical analysis methods. On TiO2 and Ca-doped TiO2 photoanode materials, we first evaluated the performance of CCPICPB dye. Upon our optimized experimental condition, the 3% Ca-TiO2 photoanode-based device exhibits an efficiency of 4.04%, which is greater than that of the pristine TiO2 photoanode-based device (2.93%). Because of the quicker electron transport in the Ca-TiO2 film, the short-circuit current density and efficiency of DSSCs were improved. Moreover, when the CCPICPB dye was used as a co-sensitizer with the common Ru(II) dye (Z907), interestingly it showed the highest efficiency (6.11%) when compared with Z907 alone (5.12%). This improved efficiency of the co-sensitized device resulted from greater VOC conjugated with improved JSC. The JSC was improved because CCPICB dye could compensate for the photocurrent loss caused by redox electrolyte while the VOC was improved because electron recombination was inhibited under the co-sensitization conditions.Graphical abstract

A Novel Strategy for Liposomal Drug Separation in Plasma by TiO2 Microspheres and Application in Pharmacokinetics.

Liposomes are nano-scale materials with a biofilm-like structure. They have excellent biocompatibility and are increasingly useful in drug delivery systems. However, the in vivo fate of liposomal drugs is still unclear because existing bioanalytical methods for quantitation of total and liposomal-encapsulated drugs have limits. A novel strategy for liposomal-encapsulated drug separation from plasma was developed via the specific coordinate binding interaction of TiO2 microspheres with the phosphate groups of liposomes. Liposomal-encapsulated docetaxel was separated from plasma by TiO2 microspheres and analyzed by the UPLC-MS/MS method. The amount of TiO2, pH of the dilutions, plasma dilution factors and incubation time were optimized to improve extraction recovery. The characterization of the adsorption of liposome-encapsulated drugs by TiO2 microspheres was observed by electron microscopy. For understanding the mechanism, pseudo-first and the pseudo-second order equations were proposed for the adsorption process. The study fully validated the method for quantitation of liposomal-encapsulated in plasma and the method was applied to the pharmacokinetic study of docetaxel liposomes. The encapsulated docetaxel had a concentration range of 15-4000 ng/mL from the plasma sample using a TiO2 extraction method. Successful method validation proved the method was sensitive, selective and stable, and was suitable for quantitation of docetaxel liposomes in plasma samples. Extraction recovery of this method was higher than that of SPE method. As shown in electron microscopy, the liposomes adsorbed on TiO2 microspheres were intact and there was no drug leakage. The study proposed pseudo-first and the pseudo-second order equations to facilitate the adsorption of liposomal drugs with TiO2 microspheres. The proposed strategy supports the pharmacokinetic study of docetaxel liposomes in rats. TiO2 extraction method was stable, reproducible, and reliable for quantitation of encapsulated docetaxel. Because of versatility of lipids, it is expected to a universal bioanalysis method for the pharmacokinetic study of liposomes.

Lychee-like TiO2@Fe2O3 Core-Shell Nanostructures with Improved Lithium Storage Properties as Anode Materials for Lithium-Ion Batteries.

In this study, lychee-like TiO2@Fe2O3 microspheres with a core-shell structure have been prepared by coating Fe2O3 on the surface of TiO2 mesoporous microspheres using the homogeneous precipitation method. The structural and micromorphological characterization of TiO2@Fe2O3 microspheres has been carried out using XRD, FE-SEM, and Raman, and the results show that hematite Fe2O3 particles (7.05% of the total mass) are uniformly coated on the surface of anatase TiO2 microspheres, and the specific surface area of this material is 14.72 m2 g-1. The electrochemical performance test results show that after 200 cycles at 0.2 C current density, the specific capacity of TiO2@Fe2O3 anode material increases by 219.3% compared with anatase TiO2, reaching 591.5 mAh g-1; after 500 cycles at 2 C current density, the discharge specific capacity of TiO2@Fe2O3 reaches 273.1 mAh g-1, and its discharge specific capacity, cycle stability, and multiplicity performance are superior to those of commercial graphite. In comparison with anatase TiO2 and hematite Fe2O3, TiO2@Fe2O3 has higher conductivity and lithium-ion diffusion rate, thereby enhancing its rate performance. The electron density of states (DOS) of TiO2@Fe2O3 shows its metallic nature by DFT calculations, revealing the essential reason for the high electronic conductivity of TiO2@Fe2O3. This study presents a novel strategy for identifying suitable anode materials for commercial lithium-ion batteries.

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.

Red anatase TiO2 microspheres with exposed major {0 0 1} facets and boron-stabilized hydrogen-occupied oxygen vacancies for visible-light-responsive water oxidation

In pursuit of efficient solar energy to chemical energy conversion through band engineering of wide-bandgap photocatalysts such as TiO2, a compromise occurs between a narrow bandgap and high-redox-capacity photo-induced charge carriers, which impairs the potential advantages associated with the widened absorption range. The key to this compromise is an integrative modifier that can simultaneously modulate both the bandgap and band edge positions. Herein, we theoretically and experimentally demonstrate that oxygen vacancies occupied by boron-stabilized hydrogen pairs (OVBH) serve as an integrative band modifier. Compared to hydrogen-occupied oxygen vacancies (OVH), which require the aggregation of nanosized anatase TiO2 particles, oxygen vacancies coupled with boron (OVBH) can be easily introduced into large and highly crystalline TiO2 particles, as shown by density functional theory (DFT) calculations. The coupling with interstitial boron facilitates the introduction of paired hydrogen atoms. The red-colored {001} faceted anatase TiO2 microspheres with OVBH benefit from the narrowed bandgap of 1.84 eV and the down-shifted band position. These microspheres not only absorb long-wavelength visible light up to 674 nm but also enhance visible-light-driven photocatalytic oxygen evolution.

Self-templating synthesis and photocatalytic activity of hollow TiO2 microspheres prepared by the sol–gel + solvothermal method

The microstructure of TiO2 hollow microspheres has a significant impact on the photocatalytic activity, especially the diameter, thickness, specific surface area and crystallinity, which are key factors for structure regulation. In this study, a self-template synthesis strategy for preparing hollow TiO2 hydrate microspheres by the sol–gel+ (methanol) solvothermal method was proposed. With the increase of the H2O/TBOT molar ratio (Rw) in the range of 0.75 ∼ 3.75, amorphous TiO2 colloidal microspheres with flower-like, hollow and solid structures of different sizes were prepared, and the control of TiO2 hydrate hollow microsphere diameters in the range of 1000 nm ∼ 1800 nm was realized. After calcination at 600 °C for 2 h, the structure was not damaged and had good crystallinity. TiO2 hollow spheres of Rw = 1.5 were used for ultraviolet photocatalytic degradation of 20 mg·L-1 phenol for 120 min, and the mineralization rate was >99%, which was better than P25. A series of analyses shows that under the experimental conditions, the hydrolysis rate can be controlled by regulating the H2O/TBOT molar ratio, which is the key factor in the synthesis of different structural sizes.

Mesoporous single-crystal-based TiO2 microspheres decorated by carbon nitride for obviously improved photocatalytic performance and recyclability

A novel porous TiO2 (PT) with mesoporous single-crystal-based microsphere morphology has been synthesized by a hard-template method and then decorated by graphitic carbon nitride (g-C3N4, CN) nanosheets. The prepared composites (CN/PT) exhibit improved photocatalytic activity in degradation of methylene blue (MB) compared to nonporous bulk TiO2 (BT), PT and g-C3N4, and much better recyclability than commercial P25 TiO2. The enhancement of photocatalytic activity of composites can be attributed to the increased active sites on PT surfaces, and the Z-scheme heterojunction promoting charge separation of photogenerated carriers.

In situ synthesis of the mesoporous C–TiO2 microspheres derived from partial hydrolysis tetrabutyl titanate for enhanced photocatalytic degradation under visible light

C–TiO2 microspheres were prepared in situ through microwave-assisted solvothermal method followed by low-temperature heat treatment in this study. Different carbon content doping samples were obtained through different temperatures of heat treatment. The characterization results indicate that C–TiO2 samples are exclusively composed of anatase crystallites, and also the interstitial carbon and the surface carbonate species are confirmed existed in the samples, which could significantly enhance the photocatalytic activity under visible light. When irradiated for 60 min under 5 W visible-light, the degradation efficiency of 40 mg/l methylene blue (200 mg catalyst) and 10 mg/l methyl orange (100 mg catalyst) can reach 92.59% and 98.42%, respectively, which is significantly higher than that of commercial titania P25 (5.74% and 24.53%, respectively). In addition, the sample exhibits excellent recyclability and stability, which might be considered as a novel and facil scheme for modification of titania photodegradation driven by visible light.

Fabrication and Photocatalytic Activity of Single Crystalline TiO2 Hierarchically Structured Microspheres

Single crystalline anatase TiO2 microspheres with co-exposed {001}/{101} facets were prepared by a facile one-pot hydrothermal method using NaF as a morphology controlling agent. The influences of the NaF amount on the morphology and also on the photocatalytic activity were investigated systematically. The obtained microspheres possessed better morphology when the concentration of NaF was chosen at 0.1 mol/L, and the experimental results indicated that the crystal structure and morphology played important roles on the photocatalytic activity, based on the experimental results it was found that the photocatalytic degradation efficiency of TiO2 microspheres on Tetracycline hydrochloride could reach 76.4% in 2 h. Finally, a growth mechanism was proposed by investigating the growth process, i.e., a synergistic effect of F ions modified Ostwald ripening and oriented attachment.

A conversion strategy on photo-response bifunctional motor enriched with oxygen vacancies enable lignin depolymerization

Overconsumption of fossil energy is mitigated by conversion of lignin to higher value products in the pulp and paper industry, where the breakage of the β-O-4 linkages plays a prominent role as the core technology. Herein, a photo-response motor (Au–H–TiO2) using water as fuel was prepared by using the one-step solvent volatilization method to break the β-O-4 linkages in lignin models under visible light irradiation. The Au–H–TiO2 with microscopic morphology of H-doped surface oxygen-deficient TiO2 microspheres semi-encapsulated by Au layers exploits the liquid flow difference formed by the proton elimination reaction occurring on the TiO2 hemispherical surface encapsulated by Au layers (Au hemispherical surface) as the power source of driving photocatalysis. Structural and spectroscopic analyses confirm that the abundant oxygen vacancies possess the ability to prolong the separation time of photogenerated carriers on the TiO2 hemispherical surface not encapsulated by Au layers (TiO2 hemispherical surface) and achieve an efficient visible light response by building a new band gap within the forbidden band. Simultaneously, the oxygen vacancies on the Au hemispherical surface act as photoelectron trapping sites to accelerate the movement rate of Au–H–TiO2 by promoting the elimination of protons. Notably, Au–H–TiO2 fueled by visible light and water can drive the synergistic vibration of the lignin models to ensure its uniform dispersion in water and complete the breakage of the β-O-4 linkages of the lignin models within 240 min without external mechanical assistance. Herein, it is predicted that high-value utilization of lignin using solar radiation as a single influencing factor has a promising research value.

Integrating surface functional modification and energy-level adapted coupling of photocatalyst with ultrafast carrier separation for uranium extraction

Photo-assisted uranium extraction is recognized as a promising U-extraction method by turning soluble hexavalent uranium (U(VI)) into insoluble tetravalent uranium (U(IV)). However, efficient charge separation and abundant uranium confinement sites are two key factors for efficient uranium extraction. Herein, a facile and universal parallel strategy is reported to fabricate confinement-site-rich photocatalysts with ultrafast carrier separation by energy band-tailored coupled surface functional modification for photo-assisted extraction of uranium. As a proof-of-concept demonstration, Mn-doped mesoporous TiO2 microspheres with phosphoric acid modification (Mn-TiO2@PO4) are successfully synthesized, which enables accelerated carrier separation efficiency and enhances the U(VI) selectivity. By virtue of the theoretical simulation, in conjunction with other spectral analyses, we demonstrate that Mn doping efficiently modifies the band structure with improved electron-hole separation, and surface phosphoric acid modification can enhance the affinity for uranyl ions. Accordingly, the removal rate of Mn-TiO2@PO4 for U(VI) is up to 94%, which was 6.6 times as powerful as the pristine TiO2 microspheres. This study offers a valuable paradigm for the rational design of advanced photocatalysts with band-tailored coupled and surface functional modification for photo-assisted extraction of uranium.

Novel BiVO4/TiO2 composites with Z-scheme heterojunction for photocatalytic degradation

Snowflake-like BiVO4 and TiO2 microspheres were fabricated using a hydrothermal method, and BiVO4/TiO2 composites with Z-scheme heterojunction were synthesized via physical mixing. The photocatalytic activity of as-prepared photocatalysts was evaluated by degradation of Rhodamine B (RhB) under simulated solar illumination. The highest photodegradation efficiency of 96.7 % was achieved for the BiVO4/TiO2 composites with a BiVO4 loading of 30 wt%. The remarkable photocatalytic performance of the BiVO4/TiO2 composite photocatalysts was primarily attributed to the formation of Z-scheme heterojunction between BiVO4 and TiO2, which expanded light response range and accelerated separation of photogenerated carriers. This work provides an effective approach for fabricating Z-scheme photocatalysts and demonstrates the potential of BiVO4/TiO2 composites for the degradation of pollutants in wastewater.

Thiol-functionalized TiO2 microspheres and Fe(0) nanoparticle-loaded polymeric hydrogel for the selective recovery of Cr(iii) and Cr(vi) from the aquatic medium

Synthesis and characterization of novel nanohybrid thiol-functionalized TiO2 microspheres and Fe(0) NP-loaded polymeric hydrogel for the benchmark recovery of Cr(iii) and Cr(vi).

Boosted charge transfer in Pt cluster anchored TiO2 microspheres with rich oxygen vacancies for solar driven H2 production from lignocellulosic biomass

Pt nanoclusters anchored porous TiO2 microspheres with abundant oxygen vacancy was developed as a highly-efficient photocatalyst for solar driven photocatalytic lignocellulosic biomass-to-H2 conversion.

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.

β-O-4 linkage breakage of lignin enabled by TiO2 with off/on switchable defect sites for photocatalysis

Hydrogenated titanium dioxide (H–TiO2) was synthesized by using a one-step solvent volatilization method. The Ti–H bonds were formed by hydrogen doping and subsequently oxidized to Ti–O bonds in air atmosphere. In comparison to air atmosphere, using the N2 annealing environment as a switch to promote the formation of oxygen vacancies improved visible light absorption and prolonged carrier recombination time. Furthermore, compared with conventional TiO2 microspheres, the catalytic activity was doubled by breaking the β-O-4 linkage in lignin models. The transformation of lignin into high-value compounds was enabled by TiO2-based photocatalyst under visible light. TiO2 microspheres enriched in oxygen vacancies which make full use of the annealing atmosphere as a switch to control defect engineering were synthesized by using a mild, facile, and efficient process. This work provides a new approach to significantly improve the photocatalytic efficiency for practical applications.