Hydrothermal topotactic epitaxy of SrTiO3 on Bi4Ti3O12 nanoplatelets: understanding the interplay of lattice mismatch and supersaturation

The engineering of epitaxial, two-dimensional (2D) nano-heterostructures has stimulated great interest owing to an expectation of better functional properties (e.g., photocatalytic, piezoelectric). Hydrothermal topotactic epitaxy is one of the promising synthetic approaches for their preparation, particularly the formation of a highly ordered, epitaxial interface and possibilities for the preparation of anisotropic nanostructures of symmetrical materials. The present study highlights the key parameters when steering the alkaline, hydrothermal, topochemical conversion process from Bi₄Ti₃O₁₂ nanoplatelets to the intermediate, epitaxial, SrTiO₃/Bi₄Ti₃O₁₂ nano-heterostructures and the final SrTiO₃ nanoplatelets by balancing the lattice mismatch and the supersaturation. An atomic-scale examination revealed the formation of an ordered epitaxial SrTiO₃/Bi₄Ti₃O₁₂ interface with the presence of dislocations. The SrTiO₃ grows in islands for a stoichiometric amount of Sr (Sr/Ti = 1) and the growth resembles a layer-by-layer mode for surplus Sr content (Sr/Ti ≥ 12). The latter enables SrTiO₃ overgrowth of the Bi₄Ti₃O₁₂ basal surface planes, protecting them against dissolution from the top and consequently ensuring the preservation of the platelet morphology during the entire transformation process, the kinetics of which is controlled by the base concentration. A developed understanding of this particular transformation provides the guiding principles and ideas for designing other defined or complex epitaxial heterostructures and structures under low-temperature hydrothermal conditions.

Experimental Studies on TiO2 NT with Metal Dopants through Co-Precipitation, Sol-Gel, Hydrothermal Scheme and Corresponding Computational Molecular Evaluations

In the last decade, TiO₂ nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO₂ nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO₂ nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO₂ nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO₂ hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO₂ nanotubes with metal doping for ion storage devices such as batteries.

Wet to Dry Controls Lanthanide Scandate Synthesis

The choice of temperature and gas conditions used in a water pressure-controlled reactor is guided by density functional theory (DFT) to synthesize nearly phase-pure lanthanide scandate nanoparticles (LnScO₃, Ln = La, Nd, Sm, Gd). In this synthetic method, low water-vapor partial pressures, well below water's gas liquidus, inhibit particle growth, while an excess of water vapor results in undesired rare-earth hydroxide and oxyhydroxide secondary phases. The optimal humidity for high-purity LnScO₃ particle synthesis is shown to vary with the lanthanide; DFT is used to calculate the thermodynamics of secondary phase formation for each lanthanide tested such that the role of water vapor may be quantified and used to maintain phase purity (greater than 96 mol %) across the series. The combination of thermodynamic calculation and experimental confirmation with this pressure-controlled reactor provides an opportunity to explore analogous syntheses of other inorganic perovskite nanoparticles.

Aerosol-Assisted Chemical Vapor Deposition (AACVD) Technique of SrTiO3: B Thin Films and Study the Structural and Optical Properties and Hall Effect Measurements

Aerosol-assisted chemical vapor deposition (AACVD) technique is very precise implemented to fabrication of structured SrTiO3 and Sr1-xBxTiO3 thin films at doping ratio (x = 2, 4, 6 and 8) % at temperature 400 °C on a glass substrate. The X-Ray Diffraction (XRD) patterns illustrated that the SrTiO3 and Sr1-xBxTiO3 thin films have a polycrystalline nature and cubic structure, the detailed characterization of the films by X-ray diffraction (XRD), the Surface Morphology studied by using (AFM) and (SEM). Have been noticed from AFM measurement the Roughness and RMS were increased with increases doping ratio. The optical properties of SrTiO3 and Sr1-xBxTiO3 thin films have been studied at doping ratio (x = 2, 4, 6 and 8) % at rate (300-900) nm. The transmittance spectrum is characterized by the opposite behavior of the absorbance spectrum. The transmittance generally increases with the increase in the wavelength of radiation, at wavelengths with low energies while the absorbance decreased slowly at spectrum rate (300-900) nm i.e. in the visible region. The band gap (Eg) is decreased at (3.2 - 2.5) eV which indicates that the doping process has led to the emergence of localized levels in the region confined by the valence and conduction bands, led to a reduction in the photon energy required for direct electronic transitions to occur. Found the carriers concentration charge are holes of Sr1-xBxTiO3 thin films at doping ratio (x = 2, 4, 6 and 8) %. Many properties can be improved by adding impurities such as Boron (B) to the SrTiO3, which can be used in solar cells, electronic industries or thermoelectric generators by controlling the optical or structural properties of the material by controlling the materials and percentages of impurity, or through heat treatment of the material, such as annealing, for example or exposure to different temperatures.

Role of SrCO3 on Photocatalytic Performance of SrTiO3-SrCO3 Composites

Perovskites such as SrTiO3 are interesting for photocatalytic applications due to their structure-related and electronic properties. These properties are influenced by the presence of SrCO3 which is often formed simultaneously during the hydrothermal synthesis of SrTiO3. In this study, SrTiO3-SrCO3 composites with different contents of SrCO3 (5–24 wt%) were synthesized. Their morphological, structural, and optical properties were investigated using complementary methods such as scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen sorption, and diffuse reflectance spectroscopy (DRS). Their photocatalytic activity was assessed during the degradation of diclofenac (DCFNa) in aqueous solution and CO2 photoreduction under Xe lamp irradiation. Improved photocatalytic efficiency in DCFNa degradation was observed for all the studied composites in comparison with SrTiO3, and the highest mineralization efficiency was obtained for the sample with 21 wt% SrCO3 content. The presence of SrCO3 led to an increased concentration of active species, such as •OH radicals. Otherwise, its presence inhibits CH4 and C2H6 production during CO2 photoreduction compared with pure SrTiO3.

A review of advances in multifunctional XTiO3 perovskite-type oxides as piezo-photocatalysts for environmental remediation and energy production

Over more than three decades, the field of engineering of photocatalytic materials with unique properties and enhanced performance has received a huge attention. In this regard, different classes of materials were fabricated and used for different photocatalytic applications. Among these materials, recently multifunctional XTiO₃ perovskites have drawn outstanding interest towards environmental remediation and energy conversion thanks to their unique structural, optical, physiochemical, electrical and thermal characteristics. XTiO₃ perovskites are able to initiate different surface catalytic reactions. Under ultrasonic vibration or heating, XTiO₃ perovskites can induce piezo-catalytic reactions due to the titling of their conduction and valence bands, resulting in the formation of separated charge carriers in the medium. In addition, under light irradiation, XTiO₃ perovskites are considered as a new class of photocatalysts for environmental and energy related applications. Herein, we addressed the recent advances on variously synthesized, doped and formulated XTiO₃ perovskite-type oxides showing piezo- and/or photocatalytic exploitation in environmental remediation and energy conversion. The control of structural crystallite size and phase, conductivity, morphology, oxygen vacancy control, doping agents and ratio has a significant role on the photocatalytic and piezocatalytic activities. The different piezo or/and photocatalytic processes mechanistic pathways towards varying applications were discussed. The current challenges facing these materials and future trends were addressed at the end of the review.

Preparation of SrTiO3 nanocubes by CO2 laser vaporization (LAVA) and hydrothermal maturation

SrTiO₃ is of particular interest for numerous applications such as photocatalytic water splitting, as an electrode material for thermoelectrics or as piezoceramics for sensors. Here we report on an advanced CO₂ laser vaporization (LAVA) method for the production of faceted, single-phase SrTiO₃ nanoparticles with an average particle size of 35 nm. Starting from a coarse SrTiO₃ raw powder, spherical SrTiO₃ nanoparticles were obtained by a laser-induced gas-phase condensation process. The composition of the nanoparticles corresponds to that of the starting powder, as XRD and FT-IR measurements show. Further hydrothermal treatment at 275 °C for 4 hours leads to the formation of faceted nanocubes with increasing crystallite size, as demonstrated by TEM, HR-TEM and XRD measurements. During a final washing step in 0.1 M HCl, SrCO₃ impurities were dissolved and thus single-phase SrTiO₃ nanocubes were successfully obtained, as shown by FT-IR, XRD and TEM analyses. The presented process facilitates the production of single-phase, highly crystalline SrTiO₃ nanopowders in sufficient quantities for subsequent use in a variety of applications, in particular for hydrogen production by photocatalytic water splitting.

Scalable Synthesis of Pt/SrTiO3 Hydrogenolysis Catalysts in Pursuit of Manufacturing-Relevant Waste Plastic Solutions

An improved hydrothermal synthesis of shape-controlled, size-controlled 60 nm SrTiO₃ nanocuboid (STO NC) supports, which facilitates the scalable creation of platinum nanoparticle catalysts supported on STO (Pt/STO) for the chemical conversion of waste polyolefins, is reported herein. This synthetic method (1) establishes that STO nucleation prior to the hydrothermal treatment favors nanocuboid formation, (2) produces STO NC supports with average sizes ranging from 25 to 80 nm with narrow size distributions, and (3) demonstrates how SrCO₃ formation and variation in solution pH prevent the formation of STO NCs. The STO synthesis was scaled-up and conducted in a 4 L batch reactor, resulting in STO NCs of comparable size and morphology (m = 22.5 g, d_avg = 58.6 ± 16.2 nm) to those synthesized under standard hydrothermal conditions in a lab-scale 125 mL autoclave reactor. Size-controlled STO NCs, ranging in roughly 10 nm increments from 25 to 80 nm, were used to support Pt deposited through strong electrostatic adsorption (SEA), a practical and scalable solution-based method. Using SEA techniques and an STO support with an average size of 39.3 ± 6.3 nm, a Pt/STO catalyst with 3.6 wt % Pt was produced and used for high-density polyethylene hydrogenolysis under previously reported conditions (170 psi H₂, 300 °C, 96 h; final product: M_w = 2400, Đ = 1.03). As a well-established model system for studying the behavior of heterogeneous catalysts and their supports, the Pt/STO system detailed in this work presents a unique opportunity to simultaneously convert waste plastic into commercially viable products while gaining insight into how scalable inorganic synthesis can support transformative manufacturing.

Hollow Multishelled Structured SrTiO3 with La/Rh Co-Doping for Enhanced Photocatalytic Water Splitting under Visible Light

La- and Rh-co-doped SrTiO₃ (STO:La/Rh) hollow multishelled structures (HoMSs) are fabricated by adding La³⁺ and Rh³⁺ ions during the hydrothermal process of converting TiO₂ HoMSs to STO HoMSs. STO:La/Rh HoMSs have successfully expanded the light absorption edge to 520 nm. Accompanied with the benefits of the unique hierarchical structure and relatively thin shells, STO:La/Rh HoMSs exhibit elevated light-harvesting capacity and charge separation efficiency. Compared with STO:La/Rh nanoparticles (NPs), STO:La/Rh HoMSs demonstrate enhanced photocurrent response, photocatalytic hydrogen evolution activity, and the quantum efficiency. Moreover, overall water splitting is realized by a Z-scheme system combining STO:La/Rh HoMSs with BiVO₄ (BVO) nanosheets with 1 wt% Pt as the co-catalyst. Steady evolution of hydrogen and oxygen is performed under both visible light and simulated sunlight irradiation. The solar-to-hydrogen efficiency of double-shelled STO:La/Rh HoMS-BVO photocatalysts reaches 0.08%, which is twofold higher than STO:La/Rh NP-BVO photocatalysts.

SrTiO3/Bi4Ti3O12 Nanoheterostructural Platelets Synthesized by Topotactic Epitaxy as Effective Noble-Metal-Free Photocatalysts for pH-Neutral Hydrogen Evolution

Low-temperature hydrothermal epitaxial growth and topochemical conversion (TC) reactions offer unexploited possibilities for the morphological engineering of heterostructural and non-equilibrium shape (photo)catalyst particles. The hydrothermal epitaxial growth of SrTiO3 on Bi4Ti3O12 platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO3/Bi4Ti3O12 platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO3 nanoplatelets at the completed stage of the TC reaction. The Bi4Ti3O12 platelets act as a source of Ti(OH)62- species and, at the same time, as a substrate for the epitaxial growth of SrTiO3. The dissolution of the Bi4Ti3O12 platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO3 occurs on both bismuth-oxide-terminated basal surface planes of the Bi4Ti3O12 platelets. In the progress of the TC reaction, the Bi4Ti3O12 platelet is replaced from the lateral ends toward the interior by SrTiO3, while Bi4Ti3O12 is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO3/Bi4Ti3O12 platelets show stable and 15 times higher photocatalytic H2 production (1265 μmol·g-1·h-1; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO3 nanopowders (81 μmol·g-1·h-1; STH = 0.012%) in pH-neutral water/methanol solutions. A plausible Z scheme is proposed to describe the charge-transfer mechanism during the photocatalysis.

A template-free synthesis of mesoporous SrTiO3 single crystals

Well-defined mesoporous SrTiO3 single crystals were fabricated via a template-free method, undergoing a reversed crystal growth, which crystallize from the external and then proceed gradually inwards.

Nitrogen doped graphene quantum dots as a cocatalyst of SrTiO3(Al)/CoOx for photocatalytic overall water splitting

Nitrogen doped graphene quantum dots as a cocatalyst of SrTiO₃(Al)/CoO_x for photocatalytic overall water splitting.

Morphogenesis mechanisms in the hydrothermal growth of lead-free BCZT nanostructured multipods

The nanostructuring approach may offer a new route to tailor lead-free ferroelectrics with superior energy storage performance for ceramic actuators and capacitors.

Peering into the Formation of Template-Free Hierarchical Flowerlike Nanostructures of SrTiO3

The development of efficient advanced functional materials is highly dependent on properties such as morphology, crystallinity, and surface functionality. In this work, hierarchical flowerlike nanostructures of SrTiO3 have been synthesized by a simple template-free solvothermal method involving poly(vinylpyrrolidone) (PVP). Molecular dynamics simulations supported by structural characterization have shown that PVP preferentially adsorbs on {110} facets, thereby promoting the {100} facet growth. This interaction results in the formation of hierarchical flowerlike nanostructures with assembled nanosheets. The petal morphology is strongly dependent on the presence of PVP, and the piling up of nanosheets, leading to nanocubes, is observed when PVP is removed at high temperatures. This work contributes to a better understanding of how to control the morphological properties of SrTiO3, which is fundamental to the synthesis of perovskite-type materials with tailored properties.

Polyethylene Glycol as Shape and Size Controller for the Hydrothermal Synthesis of SrTiO3 Cubes and Polyhedra

Understanding the correlation between the morphological and functional properties of particulate materials is crucial across all fields of physical and natural sciences. This manuscript reports on the investigation of the effect of polyethylene glycol (PEG) employed as a capping agent in the synthesis of SrTiO₃ crystals. The crucial influence of PEG on both the shape and size of the strontium titanate particles is revealed, highlighting the effect on the photocurrents measured under UV–Vis irradiation.

On the formation of superoxide radicals on colloidal ATiO3 (A = Sr and Ba) nanocrystal surfaces

Controlling the surface chemistry of colloidal semiconductor nanocrystals is critical to exploiting their rich electronic structures for various technologies. We recently demonstrated that the hydrothermal synthesis of colloidal nanocrystals of SrTiO₃, a technologically-relevant electronic material, provided a strong negative correlation between the presence of an O₂-related surface defect and hydrazine hydrate [W. L. Harrigan, S. E. Michaud, K. A. Lehuta, and K. R. Kittilstved, Chem. Mater., 2016, 28(2), 430]. When hydrazine hydrate is omitted during the aerobic hydrothermal synthesis, the surface defect is observed. However, it can be removed by either the addition of hydrazine hydrate or by purging the reaction solution with argon gas before the hydrothermal synthesis. We also propose that the formation of the O₂-related defect is mediated by the reduction of dissolved O₂ by lactate anions that are present from the titanium precursor. This work helps elucidate the nature of the O₂-related defect as a superoxide anion and presents a mechanism to explain its formation during the hydrothermal synthesis of SrTiO₃ and related BaTiO₃ nanocrystals.

Unveiling the efficiency of microwave-assisted hydrothermal treatment for the preparation of SrTiO3 mesocrystals

Material processing has become essential for the proper control, tuning and consequent application of the properties of micro/nanoparticles. In this case, we report herein the capability of the microwave-assisted hydrothermal (MAH) method to prepare the SrTiO3 compound, as a case study of inorganic compounds. Analyses conducted by X-ray diffraction, X-ray photoelectron and X-ray absorption spectroscopies confirmed that the MAH route enables the formation of pristine SrTiO3. The results indicated that the combination of thermal and non-thermal effects during the MAH treatment provides ideal conditions for an efficient and rapid synthesis of pristine SrTiO3 mesocrystals. Scanning electron microscopy images revealed a cube-like morphology (of ca. 1 μm) formed via a self-assembly process, influenced by the MAH time. Additionally, photoluminescence measurements revealed a broad blue emission related to intrinsic defects, which decreased with the MAH synthesis time.

K. N, V. P. N. N, M. K. Understanding the role of alcohols in the growth behaviour of ZnO nanostructures prepared by solution based synthesis and their application in solar cells

We report the successful control of the ZnO nanostructures by a simple solution method using alcohols such as methanol, ethanol, butanol, hexanol, octanol and decanol as solvents.

New Insights into Sensitization Mechanism of the Doped Ce (IV) into Strontium Titanate

SrTiO₃ and Ce⁴⁺ doped SrTiO₃ were synthesized by a modified sol–gel process. The optimization synthesis parameters were obtained by a series of single factor experiments. Interesting phenomena are observable in Ce⁴⁺ doped SrTiO₃ systems. Sr²⁺ in SrTiO₃ system was replaced by Ce⁴⁺, which reduced the surface segregation of Ti⁴⁺, ameliorated agglomeration, increased specific surface area more than four times compared with pure SrTiO₃, and enhanced quantum efficiency for SrTiO₃. Results showed that Ce⁴⁺ doping increased the physical adsorption of H₂O and adsorbed oxygen on the surface of SrTiO₃, which produced additional catalytic active centers. Electrons on the 4f energy level for Ce⁴⁺ produced new energy states in the band gap of SrTiO₃, which not only realized the use of visible light but also led to an easier separation between the photogenerated electrons and holes. Ce⁴⁺ repeatedly captured photoelectrons to produce Ce³⁺, which inhibited the recombination between photogenerated electrons and holes as well as prolonged their lifetime; it also enhanced quantum efficiency for SrTiO₃. The methylene blue (MB) degradation efficiency reached 98.7% using 3 mol % Ce⁴⁺ doped SrTiO₃ as a photocatalyst, indicating highly photocatalytic activity.

Topochemical transformation of single crystalline SrTiO3 microplatelets from Bi4Ti3O12 precursors and their orientation-dependent surface piezoelectricity

This work described the synthesis of SrTiO₃ microplatelets with improved characteristics, explored the related topochemical mechanism, and discovered their orientation-dependent surface piezoelectricity.

Emerging La2O2CN2 matrix with controllable 3D morphology for photoluminescence applications

Shape-controlled La₂O₂CN₂ microstructures are synthesized and are used as hosts for doping with various RE³⁺ to realize different colored emissions.