Search Results (22)

The structure and catalytic activity of Pd monolayers versus single Pd atoms were studied for the reverse water–gas shift reaction (rWGSR) at the anatase (101) and (001) facets for which Pd flat fragments have been observed experimentally. Thermodynamic and partial kinetic analyses of five steps of the rWGSR scheme were considered on the two facets. The projected density of states for the d-orbitals of single Pd atoms of the (101) facet of a-TiO₂ are compared to the ones for Pd atoms in both monolayers at (101) and (001) facets to interpret the different activity of Pd. The low activity of single Pd atoms is probably related to the (001) facet, while a Pd monolayer participates at the (101) facet due to its heterogeneity induced by the support. Full article

Deposited by a reactive atmospheric pressure non-thermal TiCl₄/O₂/Ar plasma, anatase TiO₂ single crystal sheet-connected film exhibits two large exposed {001} facets and a high concentration of oxygen defects. Strong white photoluminescence centered at 542 nm has been observed with naked eyes, whose internal quantum efficiency is 0.62, and whose intensity is comparable to that of commercial fluorescent lamp interior coatings. Based on the simulation results of a hybrid global–analytical model developed on this atmospheric pressure non-equilibrium plasma system, the mechanism of a self-confined growth of single crystal sheets was proposed. A high concentration of oxygen defects is in situ incorporated into the anatase crystal lattice without damaging its crystallographic orientation. This method opens a new way to construct 3D porous metal-oxide single crystal sheet-connected films with two exposing high energy surfaces and a large concentration of oxygen defects. Full article

Semiconductor minerals are widely present on the surface of Earth, but their roles in the process of peptide formation from amino acids are less studied, especially the role of different crystal facets in the origin of life. In this research, High Performance Liquid Chromatography (HPLC), thermogravimetric analysis (TA/DTA), Nuclear Magnetic Resonance (NMR) and simulation calculations were used to study the condensation of glycine on the surface of anatase with (001) crystal facets and ordinary anatase as well as the reaction mechanism. Combined with TA/DTA and heating experiments (80–130 °C), it was found that anatase with (001) crystal facets and ordinary anatase could both catalyze the condensation of glycine to form corresponding oligopeptides (mainly DKP, Gly₂ and Gly₃). Anatase with (001) crystal facets shows better catalytic effect, which can reduce the condensation temperature of glycine to 90 °C. With the increase in temperature, the condensation efficiency of anatase with (001) crystal facets for Gly₂ is relatively higher, and the maximum yield is about 0.20 mg/m². The condensation efficiency of ordinary anatase for Gly₃ is relatively higher, and the maximum yield is about 0.28 mg/m². The results of FTIR and simulation calculation show that the electron density of the carboxyl group changes after glycine is adsorbed on the surface of anatase, which is easily subject to the nucleophilic attack of amino groups to promote the condensation reaction. These results can provide reference for the research of condensation of small biomolecules on semiconductor mineral surfaces in the origin of life. Full article

TiO₂-supported catalysts have been widely used for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about the effect of their different crystalline surfaces on their activity during the hydrodeoxygenation process. In this work, Au supported on anatase TiO₂, mainly exposing 101 or 001 facets, was investigated for the hydrodeoxygenation (HDO) of guaiacol. At 300 °C, the strong interaction between the Au and TiO₂-101 surface resulted in the facile reduction of the TiO₂-101 surface with concomitant formation of oxygen vacancies, as shown by the H₂-TPR and H₂-TPD profiles. Meanwhile, the formation of Au^δ−, as determined by CO-DRIFT spectra and in situ XPS, was found to promote the demethylation of guaiacol producing methane. However, this strong interaction was absent on the Au/TiO₂-001 catalyst since TiO₂-001 was relatively difficult to be reduced compared with TiO₂-101. The Au on TiO₂-001 just served as the active site for the dissociation of hydrogen without the formation of Au^δ−. The hydrogen atoms spilled over to the surface of TiO₂-001 to form a small amount of oxygen vacancies, which resulted in lower activity than that over Au/TiO₂-101. The catalytic activity of the Au/TiO₂ catalyst for hydrodeoxygenation will be controlled by tuning the crystal plane of the TiO₂ support. Full article

The growth of nanocrystals (NCs) from metal oxide-based substrates with exposed high-energy facets is of particular importance for many important applications, such as solar cells as photoanodes due to the high reactivity of these facets. The hydrothermal method remains a current trend for the synthesis of metal oxide nanostructures in general and titanium dioxide (TiO₂) in particular since the calcination of the resulting powder after the completion of the hydrothermal method no longer requires a high temperature. This work aims to use a rapid hydrothermal method to synthesize numerous TiO₂-NCs, namely, TiO₂ nanosheets (TiO₂-NSs), TiO₂ nanorods (TiO₂-NRs), and nanoparticles (TiO₂-NPs). In these ideas, a simple non-aqueous one-pot solvothermal method was employed to prepare TiO₂-NSs using tetrabutyl titanate Ti(OBu)₄ as a precursor and hydrofluoric acid (HF) as a morphology control agent. Ti(OBu)₄ alone was subjected to alcoholysis in ethanol, yielding only pure nanoparticles (TiO₂-NPs). Subsequently, in this work, the hazardous chemical HF was replaced by sodium fluoride (NaF) as a means of controlling morphology to produce TiO₂-NRs. The latter method was required for the growth of high purity brookite TiO₂ NRs structure, the most difficult TiO₂ polymorph to synthesize. The fabricated components are then morphologically evaluated using equipment, such as transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and X-ray diffraction (XRD). In the results, the TEM image of the developed NCs shows the presence of TiO₂-NSs with an average side length of about 20–30 nm and a thickness of 5–7 nm. In addition, the image TEM shows TiO₂-NRs with diameters between 10 and 20 nm and lengths between 80 and 100 nm, together with crystals of smaller size. The phase of the crystals is good, confirmed by XRD. The anatase structure, typical of TiO₂-NS and TiO₂-NPs, and the high-purity brookite-TiO₂-NRs structure, were evident in the produced nanocrystals, according to XRD. SAED patterns confirm that the synthesis of high quality single crystalline TiO₂-NSs and TiO₂-NRs with the exposed {001} facets are the exposed facets, which have the upper and lower dominant facets, high reactivity, high surface energy, and high surface area. TiO₂-NSs and TiO₂-NRs could be grown, corresponding to about 80% and 85% of the {001} outer surface area in the nanocrystal, respectively. Full article

In this work, brookite TiO₂ nanocrystals with co-exposed {001} and {120} facets (pH0.5-T500-TiO₂ and pH11.5-T500-TiO₂), rutile TiO₂ nanorod with exposed {110} facets and anatase TiO₂ nanocrystals with exposed {101} facets (pH3.5-T500-TiO₂) and {101}/{010} facets (pH5.5-T500-TiO₂, pH7.5-T500-TiO₂ and pH9.5-T500-TiO₂) were successfully synthesized through a one-pot solvothermal method by using titanium (V) iso-propoxide (TTIP) colloidal solution as the precursor. The crystal structure, morphology, specific surface area, surface chemical states and photoelectric properties of the pHx-T500-TiO₂ (x = 0.5, 1.5, 3.5, 5.5, 7.5, 9.5, 11.5) were characterized by powder X-ray diffraction (XRD), field scanning transmission electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), nitrogen adsorption instrument, X-ray photoelectron spectroscopy (XPS), UV-Visible diffuse reflectance spectra and electrochemical impedance spectroscopy (EIS). The photocatalytic activity performance of the pHx-T500-TiO₂ samples was also investigated. The results showed that as-prepared pH3.5-T500-TiO₂ nanocrystal with exposed {101} facets exhibited the highest photocatalytic activity (95.75%) in the process of photocatalytic degradation of methyl orange (MO), which was 1.1, 1.2, 1.2, 1.3, 1.4, 1.6, 10.7, 15.1 and 27.8 fold higher than that of pH5.5-T500-TiO₂ (89.47%), P25-TiO₂ (81.16%), pH9.5-T500-TiO₂ (79.41%), pH7.5-T500-TiO₂ (73.53%), pH0.5-T500-TiO₂ (69.10%), CM-TiO₂ (61.09%), pH11.5-T500-TiO₂ (8.99%), pH1.5-T500-TiO₂ (6.33%) and the Blank (3.44%) sample, respectively. The highest photocatalytic activity of pH3.5-T500-TiO₂ could be attributed to the synergistic effects of its anatase phase structure, the smallest particle size, the largest specific surface area and exposed {101} facets. Full article

MoS₂/TiO₂-based nanostructures have attracted extensive attention due to their high performance in many fields, including photocatalysis. In this contribution, MoS₂ nanostructures were prepared via an in situ bottom-up approach at the surface of shape-controlled TiO₂ nanoparticles (TiO₂ nanosheets and bipyramids). Furthermore, a multi-technique approach by combining electron microscopy and spectroscopic methods was employed. More in detail, the morphology/structure and vibrational/optical properties of MoS₂ slabs on TiO₂ anatase bipyramidal nanoparticles, mainly exposing {101} facets, and on TiO₂ anatase nanosheets exposing both {001} and {101} facets, still covered by MoS₂, were compared. It was shown that unlike other widely used methods, the bottom-up approach enabled the atomic-level growth of well-defined MoS₂ slabs on TiO₂ nanostructures, thus aiming to achieve the most effective chemical interactions. In this regard, two kinds of synergistic heterojunctions, namely, crystal face heterojunctions between anatase TiO₂ coexposed {101} and {001} facets and semiconductor heterojunctions between MoS₂ and anatase TiO₂ nanostructures, were considered to play a role in enhancing the photocatalytic activity, together with a proper ratio of (101), (001) coexposed surfaces. Full article

As a widely existing mineral types on Earth, semiconductor minerals play an important role in the origin of life and the material geochemical cycle. The first step of peptide formation is amino acid adsorption on the mineral surface, but the role and mechanism of different crystal facets of semiconductor minerals are not well understood. Anatase (TiO₂) with exposed (001) facets was synthesized by a hydrothermal method, and then analyzed and compared with the purchased ordinary anatase (TiO₂) for the adsorption of glycine, the simplest amino acid. XRD, SEM and TEM results show that the hydrothermally synthesized anatase (TiO₂) has a good anatase crystal form, which is micro-nano-scale flake particles and mainly composed of (001) facets. The results of HPLC used in the adsorption experiment showed that under optimal conditions (pH 5 to 6, an adsorption time of 24 h, and an initial concentration of 0.09 mol/L), the adsorption quantity of glycine on anatase (TiO₂) with exposed (001) facets may reach 10 mg/m², which is larger than that for ordinary anatase (TiO₂) with exposed (101) facets. Based on a combination of various characterizations and simulation calculations, the results proved that anatase can activate thermodynamically stable γ-glycine to β-glycine. The adsorption of glycine on anatase (TiO₂) has two forms, one is the zwitterionic form in which the carboxyl group forms a bridge structure with two Ti atoms connected by surface bridging oxygen, and the dissociated form is in which the amino group forms a bond with the surface Ti atom. Among these, glycine is mainly adsorbed to anatase by dissociative molecules on the anatase (TiO₂) with exposed (001) facets and by zwitterion adsorption on the anatase (TiO₂) with exposed (101) facets. This research elucidates the conditions and mechanism of amino acid adsorption by semiconductor minerals in weak acidic environment, which is similar to the environmental pH that was beneficial to the formation of life on the early Earth. Therefore, these can provide a reference for the further study of the role of semiconductor minerals in the adsorption and polymerization of small biomolecules in the origin of life. Full article

Mesoporous monodisperse microballs of amorphous titania were prepared from solution of absolute ethanol, tetrabutyl titanate (TBOT) and potassium chloride via a sub-zero sol–gel route. The as-obtained microballs were used as the precursor in an alcohothermal (ethanol with a small amount of water) process to synthesize monodisperse mesoporous microballs built of decahedral anatase nanocrystals. FE-SEM observation and XRD analysis have confirmed that the formed decahedral anatase-rich powder retained the original spherical morphology of the precursor. Importantly, a hierarchical structure composed of faceted anatase has been achieved under “green” conditions, i.e., fluorine-free. Additionally, the hysteresis loops (BET results) have confirmed the existence of mesopores. Interestingly, faceted microballs show noticeable photocatalytic activity under UV/vis irradiation for hydrogen generation without any co-catalyst use, reaching almost forty times higher activity than that by famous commercial titania photocatalyst—P25. It has been proposed that enhanced photocatalytic performance is caused by mesoporous structure and co-existence of two kinds of facets, i.e., {001} and {101}, and thus hindered charge carriers’ recombination. Full article

Water pollution can be treated through the photocatalytic reaction of TiO₂ or TiO₂ compounds. A solvothermal method was used to prepare Fe₃O₄ and Fe₃O₄@TiO₂ composite photocatalyst with (001) high-energy facets exposed in the anatase phase. TiO₂ and Fe₃O₄@TiO₂ were characterized by field emission scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy, X-ray diffraction spectroscopy and Raman spectroscopy. It was found that the composite Fe₃O₄@TiO₂ can reduce the band gap and maintain a certain proportion of (001) high-energy facet exposure. The band gaps of Fe₃O₄@TiO₂ and TiO₂ are 2.5 eV and 2.9 eV, respectively. The exposure percentages of (001) facets of Fe₃O₄@TiO₂ and TiO₂ are about 25.2% and 12.1%, respectively. Fe₃O₄@TiO₂ was used for photocatalytic degradation of Acid Red 73, and it was found that Fe₃O₄@TiO₂ could improve the efficiency of photocatalytic degradation of Acid Red 73. The photocatalytic degradation rates of Fe₃O₄@TiO₂ and TiO₂ at 24 min were 93.56% and 74.47%, respectively. The cycle experiment of photocatalytic degradation of Acid Red 73 by Fe₃O₄@TiO₂ showed that at the fifth cycle, the rate of dye degradation decreased to 77.05%, but the rate of dye degradation can reach more than 90% after self-cleaning treatment. The photocatalytic degradation mechanism is explained by the energy band theory and the first-order kinetic equation model. Full article

Anatase TiO₂ are the most widely used photocatalysts because of their unique electronic, optical and catalytic properties. Surface chemistry plays a very important role in the various applications of anatase TiO₂ especially in the catalysis, photocatalysis, energy conversion and energy storage. Control of the surface structure by crystal facet engineering has become an important strategy for tuning and optimizing the physicochemical properties of TiO₂. For anatase TiO₂, the {001} crystal facets are the most reactive because they exhibit unique surface characteristics such as visible light responsiveness, dissociative adsorption, efficient charge separation capabilities and photocatalytic selectivity. In this review, a concise survey of the literature in the field of {001} dominated anatase TiO₂ crystals and their composites is presented. To begin, the existing strategies for the synthesis of {001} dominated anatase TiO₂ and their composites are discussed. These synthesis strategies include both fluorine-mediated and fluorine-free synthesis routes. Then, a detailed account of the effect of {001} facets on the physicochemical properties of TiO₂ and their composites are reviewed, with a particular focus on photocatalysis and Li-ion batteries applications. Finally, an outlook is given on future strategies discussing the remaining challenges for the development of {001} dominated TiO₂ nanomaterials and their potential applications. Full article

In this paper, we report a novel and simple method for synthesizing the microspheres self-assembled from ultrathin anatase TiO₂ nanosheets with a high percentage of (001) facets via the hydrolysis process of the single-reagent (potassium fluorotitanate). We then used optical microscopy, scanning electron microscopy, and high-resolution confocal laser Raman spectroscopy to characterize the microspheres generated under different conditions. The study found that the size of the anatase TiO₂ microspheres synthesized was 0.5–3 μm. As the synthesis time increased, the corroded surface of the microspheres gradually increased, resulting in the gradual disappearance of the edges and corners of the anatase nanosheets. The exposure percentage of the (001) facets of ultrathin anatase nanosheets synthesized for 2 h at 180–200 °C are close to 100%. The microsphere whose surface is completely covered by these anatase nanosheets also has nearly 100% exposed (001) facets. This new anatase nanosheet-based self-assembled microsphere will have great application potential in pollution prevention, environmental protection, and energy fields. Full article

Characterization of functional nanocrystalline materials in terms of quantitative determination of size, size dispersion, type, and extension of exposed facets still remains a challenging task. This is particularly the case of anisotropically shaped nanocrystals (NCs) like the TiO₂ photocatalysts. Here, commercially available P25 and P90 titania nanopowders have been characterized by wide-angle X-ray total scattering techniques. Synchrotron data were modelled by the reciprocal space-based Debye scattering equation (DSE) method using atomistic models of NC populations (simultaneously carrying atomic and nanoscale structural features) for both anatase and rutile phases. Statistically robust descriptors are provided of size, morphology, and {101} vs. {001} facet area of truncated tetragonal bipyramids for anatase, jointly to polymorph quantification. The effects of using the proper NC shape on the X-ray diffraction pattern are analyzed in depth through DSE simulations by considering variable bipyramid aspect ratios (resulting in different {101} vs. {001} surface) and relative dispersion in a bivariate manner. We demonstrate that using prismatic NCs having equal volume and aspect ratio as bipyramids provides reasonably accurate sizes and {101} and {001} surface areas of the parent morphology. Full article

Herein, high-energy {001} facets and Sn⁴⁺ doping have been demonstrated to be effective strategies to improve the surface characteristics, photon absorption, and charge transport of TiO₂ hierarchical nanospheres, thereby improving their photocatalytic performance. The TiO₂ hierarchical nanospheres under different reaction times were prepared by solvothermal method. The TiO₂ hierarchical nanospheres (24 h) expose the largest area of {001} facets, which is conducive to increase the density of surface active sites to degrade the adsorbed methylene blue (MB), enhance light scattering ability to absorb more incident photons, and finally, improve photocatalytic activity. Furthermore, the Sn_xTi_1−xO₂ (STO) hierarchical nanospheres are fabricated by Sn⁴⁺ doping, in which the Sn⁴⁺ doping energy level and surface hydroxyl group are beneficial to broaden the light absorption range, promote the generation of charge carriers, and retard the recombination of electron–hole pairs, thereby increasing the probability of charge carriers participating in photocatalytic reactions. Compared with TiO₂ hierarchical nanospheres (24 h), the STO hierarchical nanospheres with 5% n_Sn/n_Ti molar ratio exhibit a 1.84-fold improvement in photodegradation of MB arising from the enhanced light absorption ability, increased number of photogenerated electron–hole pairs, and prolonged charge carrier lifetime. In addition, the detailed mechanisms are also discussed in the present paper. Full article

The photocatalytic activity of a series of anatase TiO₂ materials with different amounts of exposed (001) facets (i.e., 12% (TiO₂-1), 38% (TiO₂-3), and 63% (TiO₂-3)) was tested in a batch slurry reactor towards liquid-phase bisphenol A (BPA, c₀(BPA) = 10 mg/L, c_cat. = 125 mg/L) degradation. Photo-electrochemical and photo-luminescence measurements revealed that with the increasing amount of exposed anatase (001) facets, the catalysts generate more electron-hole pairs and OH∙ radicals that participate in the photocatalytic mineralization of pollutants dissolved in water. In the initial stages of BPA degradation, a correlation between % exposure of (001) facets and catalytic activity was developed, which was in good agreement with the findings of the photo-electrochemical and photo-luminescence measurements. TiO₂-1 and TiO₂-3 solids achieved 100% BPA removal after 80 min in comparison to the TiO₂-2 sample. Adsorption of BPA degradation products onto the TiO₂-2 catalyst surface was found to have a detrimental effect on the photocatalytic performance in the last stage of the reaction course. Consequently, the global extent of BPA mineralization decreased with the increasing exposure of anatase (001) facets. The major contribution to the enhanced reactivity of TiO₂ anatase (001) surface is the Brønsted acidity resulting from dissociative chemisorption of water on a surface as indicated by FTIR, TPD, and MAS NMR analyses. Full article