Two-dimensional TiO2 Nanosheets Research Articles

Air-gap-assisted solvothermal process to synthesize unprecedented graphene-like two-dimensional TiO2 nanosheets for Na+ electrosorption/desalination

Designing a high-performance capacitive deionization setup is limited due to the slow salt removal and charge storage capacities. Efforts are being made to replace traditional electrodes with advanced 2D materials. We introduce a simple method for synthesizing two-dimensional titanium dioxide graphene-like nanosheets via a unique air-gap-assisted solvothermal method. Crystalline 2D graphene-like anatase-TiO2 sheets of unprecedented quality were obtained by tuning the air gap in the solvothermal reactor. The 2D TiO2 synthesized by air-gap-assisted solvothermal process has shown an exceptionally high surface area of 934.5 m2/g compared to the pristine TiO2 (249.5 m2/g). The sheets were used as Faradaic electrodes in ion-electrosorption and their capacitive deionization capabilities were evaluated. The electrochemical conductivity was examined via an in situ investigation of Na+-ion migration and storage. The adsorption capacity of 2D TiO2 sheets increased with higher applied potential while keeping the adsorption time constant at 15 min. At adsorption potentials of –0.8 V, –1.0 V, and –1.2 V, desalting rates of 2.09, 2.18, and 2.20 mg g−1 min−1 resulted in adsorption capacities of 31.33, 32.73, and 33.023 mg g–1, respectively. The 2D TiO2 electrode demonstrated high electron-transfer rates, a large desalination capacity, and a rapid average desalting rate. The specific capacity of the 2D-layered TiO2 electrode was found to be about 45.68 F g−1. These results can be attributed to the large specific surface area, short ionic diffusion paths, numerous active adsorption sites, surface defects, and pseudocapacitance. This air-gap-assisted solvothermal method is expected to open new avenues for the synthesis of high-quality 2D materials.

Gold nanoparticles decorated two-dimensional TiO2 nanosheets as effective catalyst for nitroarenes and rhodamine B dye reduction in batch and continuous flow methods

Gold nanoparticles decorated two-dimensional TiO2 nanosheets as effective catalyst for nitroarenes and rhodamine B dye reduction in batch and continuous flow methods

Reaction Pathway of Photocatalytic Water Splitting on Two-Dimensional TiO2 Nanosheets

Using density functional theory and many-body Green’s function theory, we examine the mechanism of the water splitting reaction photocatalyzed by two-dimensional TiO2 nanosheets, which has gained attention recently in the TiO2 community. We reveal the barriers and the hole-transfer pathway in the reaction. Compared with its bulk isomer phases, such as the rutile TiO2, the advantage of the TiO2 nanosheet in this reaction is that the key reaction intermediate Ti-OH has good hole-trapping capacity, which is extremely beneficial for the oxidation half-reaction. However, the poor stability of Ti-OH relative to its precursor is a negative factor for the reaction on the TiO2 nanosheet and might have a huge effect on the photocatalytic efficiency of the nanosheet. We find that introducing Ti vacancies into the nanosheet to convert the TiO2 material into a p-type semiconductor can make bridging oxygen atoms become favorable active sites for water splitting and hence may be an effective way to increase the photocatalytic efficiency.

Engineering stable Pt nanoclusters on defective two-dimensional TiO2 nanosheets by introducing SMSI for efficient ambient formaldehyde oxidation

The strong metal-support interaction (SMSI) has received wide attention in heterogeneous catalysis for the room-temperature oxidation of formaldehyde. An interaction between Pt nanoclusters and oxygen vacancy defects will lead to SMSI over the Pt-based catalysts. In this study, defective two-dimensional (2D) TiO2 nanosheets were synthesized and successfully anchored Pt nanoclusters with a size of 1.3 nm (0.1Pt/TiO2-NS). The 0.1Pt/TiO2-NS catalyst displayed a superior activity of > 95% HCHO conversion at room temperature, which was ∼ 50% higher than that obtained for a counterpart having the commercial TiO2 (Degussa P25) support. The abundant oxygen vacancies and stable Pt nanoclusters on 0.1Pt/TiO2-NS by introducing SMSI boosted the excellent activity and stability of HCHO oxidation. By exploring electron transfer, suppression of small-molecule adsorption and encapsulation, SMSI was well demonstrated. Furthermore, electron transfer from Pt to TiO2-NS led to the electron-deficient Pt surface. The electron-deficient Pt caused by SMSI will enhance the adsorptions of HCHO and H2O/O2, subsequently improving the catalytic performance. SMSI between Pt nanoclusters and oxygen vacancies endowed the 0.1Pt/TiO2-NS catalyst excellent activity and stability to HCHO elimination. In addition, the mechanism for the high HCHO oxidation performance were examined through analysis of in situ HCHO-diffuse reflectance infrared Fourier transform spectra (DRIFTS).

Robust and flexible polymer/MXene-derived two dimensional TiO2 hybrid gel electrolyte for dendrite-free solid-state zinc-ion batteries

Gel electrolytes are key components for flexible energy storage devices. However, disadvantages such as poor ionic conductivity and mechanical behavior limit the practical applications of gel electrolytes. Herein, two-dimensional TiO2 nanosheets are fabricated from Ti3C2Tx MXene by a one-step hydrothermal reaction. The structure and component of Ti3C2Tx MXene can be easily controlled by modulating the synthesis conditions. Influences of TiO2 nanosheets content in PVA-based gel electrolyte are explored, which brings higher ionic conductivity and better mechanical properties with suitable additive amount. As a consequence, with the hybrid gel electrolyte, highly stable Zn plating/stripping is achieved (over 3000 h at 0.5 mA cm−2). Full Zn||PVA-Zn(CF3SO3)2-TiO2||V2O5 cell shows high capacity (216 mAh g−1 after 115 cycles) and excellent cycling performance. This work provides an alternative route to develop high performance hybrid gel electrolyte for flexible energy storage devices such as Li/Na/K/Zn and supercapacitors.

Modification and functional investigation of self-assembled two-dimensional TiO2 nanosheets with abundant hydroxyl groups

Self-assembled two-dimensional (2D) TiO2 nanosheets are only excited under UV light. They suffer from weak visible light absorption and fast recombination of photogenerated electron-holes carriers. In this paper, four kinds of functionalized modifications were realized through complexing self-assembled 2D TiO2 nanosheets with Fe3O4 nanoparticles, Fe2O3 nanoparticles, N doping, and combining with carbon quantum dots due to the large amount of hydroxyl groups present on the surface of the nanosheet, thereby forming the TiO2/Fe3O4, TiO2/Fe2O3, N-doped TiO2, and TiO2/C composites. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the synthesized products, confirming the successful synthesis of self-assembled 2D TiO2-based composites. By modification, the increasingly improved photocatalytic properties of self-assembled 2D TiO2 nanosheets are also presented. These findings may open up a new avenue and stimulate further research to prepare more self-assembled 2D TiO2-based composites.

Tuning optical properties of TiO2 by dimension reduction: from 3D bulk to 2D sheets along {001} and {101} plane

The use of two-dimensional sheets exclusively composed of reactive facets of TiO2 catalyst to explore the possibility of enhanced photocatalytic activity has been an exciting research frontier recently. Using first principles calculations, in this paper we investigate the optical properties of bulk and two-dimensional TiO2 nanosheets, pointing out to what extent the reduced dimensionality and dimension might enhance the photocatalytic reactivity of TiO2.The detailed optical properties of 2D sheets of TiO2 generated along the two distinct facets like (001) and (101) are studied extensively and compared with the bulk counterpart of TiO2 for electronic and optical properties. The TiO2 along (101) sheet is found to retain the semiconducting phase whereas the sheet along (001) direction found to be metallic. We found the anisotropy in TiO2–101 to be in four directions while TiO2–001 to be in two directions. Hence their applications as good optical materials are inevitable. Among the two, TiO2–101 sheet shows better absorption coefficient and extinction coefficient indicating better absorbance but TiO2–001 shows better reflectivity in the visible range of solar spectrum. Thus, we report that (001) and (101) nanosheets of TiO2 differ in their electronic structures and hence in optical properties and so can be used in different photocatalytic and optoelectronic applications well.

Mono-6-thio-β-cyclodextrin-functionalized AuNP/two-dimensional TiO2 nanosheet nanocomposite for the electrochemical determination of trace methyl parathion in water

In this work, two-dimensional TiO2 nanosheets material composited with Au nanoparticles and mono-6-thio-β-cyclodextrin was prepared on electrode surface (SH-β-CD/AuNPs/TiO2NSs/GCE).

Regulation of the Electroanalytical Performance of Ultrathin Titanium Dioxide Nanosheets toward Lead Ions by Non-Metal Doping.

Three non-metallic elements, sulfur, fluorine, and iodine, were used to dope the ultrathin two-dimensional TiO2 nanosheets, which would regulate their electroanalytical properties toward heavy metal ions. Among these doped materials, fluorine-doped TiO2 nanosheets shows the highest electrochemical sensitivity and a superior detection limit toward Pb(II) when the doping concentration is 10%. When compared with the bare TiO2 nanosheets, the sensitivity increased by 102%, and the detection limit decreased by 36.4%. Through combining further electrochemical experiments and density-functional theory calculations, the enhanced electrochemical performance stemming from element doping was then investigated in detail. The theoretical calculation demonstrated that fluorine doping could greatly increase the adsorption energy of Pb(II) on the TiO2 nanosheets and enhance their loading capacity. Both cyclic voltammetric and electrical impedance spectroscopy analysis indicated the enhanced electron transfer rate on the electrode modified by fluorine-doped TiO2 nanosheets. Further measurement on the desorption performance showed the better stripping response of Pb(II) on the electrode with TiO2 nanosheets after fluorine doping, which suggests that fluorine doping is beneficial for Pb(II) diffuse onto the electrode surface for the reduction and stripping reaction. Therefore, the element doping of two-dimensional TiO2 nanosheets provides a facile method to extend the electronic materials toward detection of heavy metal ions in the environment.

Fe2O3 nanothorns sensitized two-dimensional TiO2 nanosheets for highly efficient solar energy conversion

The hybrid structure of Fe2O3 nanothorns/TiO2 nanosheets photoanodes is reported in the work for the first time. Two-dimensional TiO2 nanosheets array films are grown on transparent conductive fluorine-doped tin oxide glass substrate by simple hydrothermal method. The Fe2O3 nanothorns uniformly deposited on the TiO2 backbone are prepared by chemical bath deposition followed by annealing. The phase structure, morphology and optical properties of the heterogeneous composite films are characterized by X-ray diffraction pattern, scanning electron microscopy and UV–visible spectroscopy. Different nanostructured Fe2O3/TiO2 heterostructures are also investigated by controlling the reaction time of the chemical bath deposition. The two-dimensional TiO2 nanosheets provide an extremely porous matrix and high-activity area required for deposition of Fe2O3 sensitizer. The optimal photocurrent density of Fe2O3/TiO2 film reaches 2.50mA/cm2 and the photoconversion efficiency is 1.25%, which is more than six times higher than that of bare TiO2 film (0.2%). The results indicate that the photogenerated carriers can separate and transfer more easily in Fe2O3/TiO2 films due to the type-II band structures formed at the interface between TiO2 and Fe2O3. The Fe2O3/TiO2 heterogeneous films have potential applications in photoelectrochemical solar cells or water splitting.

TiO2 nanosheets synthesized by atomic layer deposition for photocatalysis

Two-dimensional TiO2 nanosheets were synthesized by atomic layer deposition (ALD) on dissolvable sacrificial polymer layer. The photocatalytic performance of free-standing TiO2 nanosheets prepared with different numbers of ALD cycles (100, 300, 500, and 1000) were investigated by evaluating the degradation rates of methyl orange solutions. It is shown that the photocatalytic activity increases due to Ti3+ defect and the locally ordered structures in amorphous TiO2 nanosheets. The difference in the surface areas of nanosheets may also play a crucial role in the photocatalytic activity. The results obtained in this work can have potential applications in fields like water splitting and dye-sensitized solar cells.

Dye-sensitized solar cells based on two-dimensional TiO2 nanosheets as the scattering layers

Two-dimensional (2D) TiO2 nanosheets with high crystallinity and good light scattering properties were synthesized via a simple solvothermal process using reduced graphite oxide as a sacrificing template. X-ray diffraction patterns and electron microscopy images indicated that the prepared 2D TiO2 nanosheets were composed of high-crystalline anatase TiO2 nanoparticles. Then, the 2D anatase TiO2 nanosheets were used as a scattering layer of the photoelectrode, which is expected to produce high-efficiency dye-sensitized solar cells (DSSCs). Compared with ones with pure TiO2 nanoparticle photoelectrodes, DSSCs based on 2D TiO2 nanosheets as middle scattering layer yield the highest photoelectrical conversion efficiency of 7.54 %. This is because the obtained 2D TiO2 nanosheets have excellent light scattering, allowing for fast interfacial charge transfer, the least series resistance, and the best charge collection efficiency. These have been systematically evidenced by the electrochemical impedance spectra, intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy.

Vertical Growth of Two-Dimensional TiO2 Nanosheets Array Films and Enhanced Photoelectrochemical Properties Sensitized by CdS Quantum Dots

In this paper, we report CdS quantum dots (QDs) sensitized vertical growth two-dimensional titanium dioxide (TiO2) nanosheets array films with oriented {001} facets for the first time. The TiO2 nanosheets array films of thickness about 1.2μm exposed 85% high-energy {001} facets were perpendicularly grown on transparent conductive fluorine-doped tin oxide (FTO) glass substrates by a simple one-pot hydrothermal method. The CdS QDs sensitized TiO2 photoelectrode was carried out by successive ionic layer adsorption and reaction (SILAR). CdS QDs with a diameter less than 10nm were uniformly anchored on the surface of the single-crystalline TiO2 nanosheets with active {001} facets. Under AM 1.5 G illumination, the photoelectrode of CdS sensitized TiO2 nanosheets array is found with a photocurrent intensity of 3.24mA/cm2 at a potential of 0V versus Ag/AgCl, which is much higher than that of the bare TiO2 nanosheets array with 0.48mA/cm2. The excellent photoelectrochemical properties of the novel photoanodes suggest that the TiO2 nanosheets array films sensitized by CdS QDs have potential applications in solar cells.