Crystal Phase Research Articles

Fabrication of a coral-like barium titanate nano-piezoelectric coating and its effect on promoting osteogenic differentiation of rat bone marrow mesenchymal stem cells in vitro

Objective: To investigate the biocompatibility of coral-like barium titanate nano-piezoelectric coatings and the influence of ultrasound-excited piezoelectric effect on the early osteogenic differentiation. Methods: The barium titanate nano-piezoelectric coating (the coating group) was prepared on the surface of titanium metal by anodic oxidation, hydrothermal reaction and high-temperature annealing, and polished titanium specimens were used as control group. The surface morphology, composition, and crystal phase and hydrophilicity of the two groups of titanium specimens were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and contact angle meter. The piezoelectric properties of the materials were characterized by piezoresponse force microscopy. Rat bone marrow mesenchymal stem cells (BMSC) were cultured and identified and seeded the surface of titanium specimens in two groups. The cells seeded on blank culture plates were used as blank group. After low intensity pulsed ultrasound intervention, cell proliferation and live/dead staining were detected to evaluate cytocompatibility of the coatings. Alkaline phosphatase (ALP) activity of each group was detected by ALP staining kit, and the expression of osteogenesis-related genes [integrin, bone morphogenetic protein 2 (BMP-2), Runt-related transcription factor 2 (RUNX2)] was detected by real-time fluorescent quantitative PCR (RT-qPCR) to evaluate the effect of the coating on promoting the early osteogenic differentiation of BMSC. Results: The surface of titanium specimens in the coating group showed a uniform coral-like morphology, and the diameter of the coral tentacles was 70-100 nm. The main component was tetragonal barium titanate. The surface hydrophilicity of the coating group (water contact angle 10.12°± 0.93°) was significantly better than that of the control group (water contact angle 78.32°±0.71°) (F= 10 165.91, P<0.001). The coating has a stable piezoelectric property with a piezoelectric constant of about 5 pC/N. Cell experiments showed that, with or without ultrasound, the cell proliferation activity of the coating group was significantly lower than that of the blank group and the control group on the third day (P<0.05). On the fifth day, with or without ultrasound, there was no significant difference in cell proliferation activity between the three groups (P>0.05). After 7 days of culture, the ALP activity of the coating group was significantly higher than that of the blank group and the control group (P<0.05). The results of RT-qPCR showed that the mRNA expression of integrin and BMP-2 in the coating group with ultrasound was significantly higher than that in the other groups with ultrasound, and was higher than that of the coating group without ultrasound (P<0.05). The expression of integrin mRNA in the control group with ultrasound was significantly higher than that in the control group without ultrasound (P<0.05). The expression of RUNX2 mRNA in the coating group with ultrasound was significantly higher than that in the coating group without ultrasound (P<0.05). Conclusions: The coral-like barium titanate nano-piezoelectric coating exhibits favorable biocompatibility and stable piezoelectric property, and facilitates the early osteogenic differentiation of BMSC under the excitation of low-intensity pulsed ultrasound.

Controlling vertical phase separation and crystallization via solvent synergy strategy to empower layer-by-layer processed organic solar cells

The novel sequential layer-by-layer (LbL) processed organic solar cells (OSCs) have attracted continuous attention due to their advantages of ideal vertical phase separation, efficient charge transport and collection, and potentiality for large-scale production from laboratory to factory. Herein, a solvent synergy strategy is put forward to control morphology, crystallization and vertical phase distribution of blend films, which means the donor PM6 and acceptor Y6 treated by high/low boiling point solvents are fabricated using LbL solution process, respectively. Based on device with a configuration of ITO/ZnO/PM6:Y6/MoO3/Ag, OSCs derived from the solvent synergy strategy can obtain a remarkable power conversion efficiency (PCE) up to 15.03%, which is comparable to that of the bulk heterojunction devices prepared by conventional one-step solution method. This impressive result provides an insightful understanding of phase segregation and crystalllization in LbL processed OSCs assisted by the solvent synergy strategy. It lays the foundation for fabrication and optimization of high-performance, large-area OSCs in industrial production.

Visualizing Phase Evolution of Co2C for Efficient Fischer-Tropsch to Olefins.

Cobalt carbide (Co2C) possesses high catalytic efficiency Fischer-Tropsch synthesis (FTS), while the products selectivity appears sensitive to crystallography geometry. Since the Anderson-Schulz-Flory (ASF) distribution in FTS is broken through fabricating facetted Co2C nanocrystals, yet the underlying mechanism of Co2C crystallization remains unclarified suffering from sophisticated catalyst composition involving promoter agents. Herein, the synthesis of high-purity single-crystal nanoprisms (Co2C-p) for highly efficient FTS is reported to lower olefins. Through comprehensive microstructure analysis, e.g., high-resolution TEM, in situ TEM and electron diffraction, as well as finite element simulation of gas flow field, for the first time the full roadmap of forming catalytic active cobalt carbides is disclosed, starting from reduction of Co3O4 precursor to CoO intermediate, then carburization into Co2C-s and subsequent ripening growth into Co2C-p. This gas-induced engineering of crystal phase provides a new synthesis strategy, with many new possibilities for precise design of metal-based catalyst for diverse catalytic applications.

Theoretical studies and temperature-dependent Raman spectroscopy of Schiff's bases 5O.12 liquid crystalline compound

Comparative Raman spectra and different physical properties of 5O.12 liquid crystal compound using density functional theory is studied in this article. The molecular structure of 5O.12 liquid crystal has been optimized by using density functional theory (DFT). The Raman spectroscopy examination is critical for observing the properties and behavior of liquid crystals. 5O.12 is a Schiff-based with several liquid crystalline phases, including Nematic, Smectic A, and Smectic B. The phases of the liquid crystal vary as the temperature changes, providing essential information about the liquid crystal's molecular arrangement. The density functional theory with standard basis set 6–31 G (d, p) paired with B3LYP functional is used to study the theoretical Raman spectra and various physical properties. Theoretical details of Raman spectra give excellent agreement with experimental results. Experimental Raman spectra were examined with temperature in all of the observed phases in this article. Comparative Raman studies at different temperatures help in understanding thermodynamic and structural behavior of molecular systems. Peak positions and line width are investigated further as temperature varies, yielding precise and significant information about the molecule's ordering and behaviour. DFT is used to do research on different physical properties like HOMO LUMO, relative energy gaps and various thermochemical properties such as entropy, heat capacity, thermal energy. These characteristics give an understanding of the stability of molecules, as well as the optical properties and structure of liquid crystalline compounds.

An Equalized Flow Velocity Strategy for Perovskite Colloidal Particles in Flexible Perovskite Solar Cells.

The non-uniform distribution of colloidal particles in perovskite precursor results in an imbalanced response to the shear force during flexible printing process. Herein, it is observed that the continuous disordered migration occurring in perovskite inks significantly contributes to the enlargement of colloidal particles size and diminishes the crystallization activity of the inks. Therefore, a molecular encapsulation architecture by glycerol monostearate to mitigate colloidal particles collisions in the precursor ink, while simultaneously homogenizing the size distribution of perovskite colloids to minimize their diffusion disparities, is devised. The utilization of colloidal particles with a molecular encapsulation structure enables the achievement of uniform deposition during the printing process, thereby effectively balancing the crystallization rate and phase transition in the film and facilitating homogeneous crystallization of perovskite films. The large-area flexible perovskite device (1.01 cm2 and 100 cm2) fabricated through printing processes, achieves an efficiency of 24.45% and 15.87%, respectively, and manifests superior environmental stability, maintaining an initial efficiency of 91% after being stored in atmospheric ambiences for 150 days (unencapsulated). This work demonstrates that the dynamic evolution process of colloidal particles in both the precursor ink and printing process represents a crucial stride toward achieving uniform crystallization of perovskite films.

Nano-cutting mechanism of ion implantation-modified SiC: reducing subsurface damage expansion and abrasive wear

This study utilized ion implantation to modify the material properties of silicon carbide (SiC) to mitigate subsurface damage during SiC machining. The paper analyzed the mechanism of hydrogen ion implantation on the machining performance of SiC at the atomic scale. A molecular dynamics model of nanoscale cutting of an ion-implanted SiC workpiece using a non-rigid regular tetrakaidecahedral diamond abrasive grain was established. The study investigated the effects of ion implantation on crystal structure phase transformation, dislocation nucleation, and defect structure evolution. Results showed ion implantation modification decreased the extension depth of amorphous structures in the subsurface layer, thereby enhancing the surface and subsurface integrity of the SiC workpiece. Additionally, dislocation extension length and volume within the lattice structure were lower in the ion-implanted workpiece compared to non-implanted ones. Phase transformation, compressive pressure, and cutting stress of the lattice in the shear region per unit volume were lower in the ion-implanted workpiece than the non-implanted one. Taking the diamond abrasive grain as the research subject, the mechanism of grain wear under ion implantation was explored. Grain expansion, compression, and atomic volumetric strain wear rate were higher in the non-implanted workpiece versus implanted ones. Under shear extrusion of the SiC workpiece, dangling bonds of atoms in the diamond grain were unstable, resulting in graphitization of the diamond structure at elevated temperatures. This study established a solid theoretical and practical foundation for realizing non-destructive machining at the atomic scale, encompassing both theoretical principles and practical applications.

Calcium phosphate controls nucleation and growth of calcium oxalate crystal phases in kidney stones.

Kidney stone disease is a serious disease due to the severe pain it causes, high morbidity, and high recurrence rate. Notably, calcium oxalate stones are the most common type of kidney stone. Calcium oxalate appears in two forms in kidney stones: the stable phase, monohydrate (COM), and the metastable phase, dihydrate (COD). Particularly, COM stones with concentric structures are hard and difficult to treat. However, the factor determining the growth of either COM or COD crystals in the urine, which is supersaturated for both phases, remains unclear. This study shows that calcium phosphate ingredients preferentially induce COM crystal nucleation and growth, by observing and analyzing kidney stones containing both COM and COD crystals. The forms of calcium phosphate are not limited to Randall's plaques (1-2 mm size aggregates, which contain calcium phosphate nanoparticles and proteins, and form in the renal papilla). For example, aggregates of strip-shaped calcium phosphate crystals and fields of dispersed calcium phosphate microcrystals (nano to micrometer order) also promote the growth of concentric COM structures. This suggests that patients who excrete urine with a higher quantity of calcium phosphate crystals may be more prone to forming hard and troublesome COM stones.

Simulating the Lyotropic Phase Behavior of a Partially Self-Complementary DNA Tetramer.

DNA oligomers in solution have been found to develop liquid crystal phases via a hierarchical process that involves Watson-Crick base pairing, supramolecular assembly into columns of duplexes, and long-range ordering. The multiscale nature of this phenomenon makes it difficult to quantitatively describe and assess the importance of the various contributions, particularly for very short strands. We performed molecular dynamics simulations based on the coarse-grained oxDNA model, aiming to depict all of the assembly processes involved and the phase behavior of solutions of the DNA GCCG tetramers. We find good quantitative matching to experimental data at both levels of molecular association (thermal melting) and collective ordering (phase diagram). We characterize the isotropic state and the low-density nematic and high-density columnar liquid crystal phases in terms of molecular order, size of aggregates, and structure, together with their effects on diffusivity processes. We observe a cooperative aggregation mechanism in which the formation of dimers is less thermodynamically favored than the formation of longer aggregates.

Enriched Surface Oxygen Vacancies of CeO2 Nanosheets: Surfactant Free Synthesis at Room Temperature and its Enhanced Anti‐bacterial Property

AbstractIn this work, flower shape cerium oxide (CeO2) nanosheets were synthesized at room temperature through a facile precipitation method without adding any surfactant. The synthesized nanosheets were characterized by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffractometry (XRD) and X‐ray photoelectron spectroscopy (XPS). Results showed that the CeO2 nanosheets form a petal‐like morphology and have fluorite crystal structure with no crystal phase impurity while the average crystallite size of nanosheets i. e. ~10 nm. The CeO2 nanosheets are applied as an antimicrobial agent and the antibacterial property against G+ and G− bacteria i. e. (E. coli and S. Aureus) were studied. The obtained results showed that the synthesized CeO2 nanosheets had good antibacterial performance at different concentrations, which should be attributed to the reversible Ce3+/Ce4+ valence states and greater oxygen vacancies. XPS study of CeO2 nanosheets after antibacterial test confirmed the existence of Ce3+ ions and oxygen vacancies. CeO2 nanosheets have showed the greater potential as antibacterial nanomaterials against both the bactericides.

Phosphate/Silicate Ratio Allows for Fine-Tuning of Bioactive Glass Crystallisation and Glass-Ceramic Microstructure

A combination of XRD, solid-state NMR and state-of-the-art imaging techniques were used to investigate how the calcium orthophosphate/calcium silicate ratio affects the crystallisation of bioactive glasses in the system SiO2-P2O5-CaO-CaF2. In the phosphate-free glass, xonotlite, wollastonite and cuspidine crystallised. From 2.4 mol% P2O5, fluorapatite also formed, while the amount of wollastonite decreased. Crystallisation tendency was low for low phosphate contents, while above 3 mol% P2O5 it increased. The phosphate-free glass showed a volume crystallisation mechanism with constant activation energy. By contrast, the glass with the largest phosphate to silicate ratio showed both volume and surface crystallisation, causing a pronounced decrease in activation energy with crystallisation degree. This work shows that by changing the phosphate/silicate ratio we can determine which crystal phases form, obtaining for example fluorapatite-free or wollastonite-free glass-ceramics, depending on the desired application and properties such as mechanical strength or activity in contact with physiological solutions.

The Role of Oxygen Vacancies in Phase Transition and the Optical Absorption Properties within Nanocrystalline ZrO2.

Zirconia (ZrO2) nanoparticles were synthesized using a solvothermal method under varying synthesis conditions, namely acidic, neutral, and alkaline. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were leveraged to investigate the phase evolution and topographical features in detail. The resulting crystal phase structures and grain sizes exhibited substantial variation based on these conditions. Notably, the acidic condition fostered a monoclinic phase in ZrO2, while the alkaline condition yielded a combination of tetragonal and monoclinic phases. In contrast, ZrO2 obtained under neutral conditions demonstrated a refinement in grain sizes, constrained within a 1 nm scale upon an 800 °C thermal treatment. This was accompanied by an important transformation from a monoclinic phase to tetragonal phase in the ZrO2. Furthermore, a rigorous examination of XPS data and a UV-visible spectrometer (UV-vis) analysis revealed the significant role of oxygen vacancies in phase stabilization. The notable emergence of new energy bands in ZrO2, in stark contrast to the intrinsic bands observed in a pure monoclinic sample, are attributed to these oxygen vacancies. This research offers valuable insights into the novel energy bands, phase stability, and optical absorption properties influenced by oxygen vacancies in ZrO2. Moreover, it proposes an innovative energy level model for zirconia, underpinning its applicability in diverse technological areas.

Formation Mechanism and Morphology Evolution of β-NaYF4 Single Microcrystals in Hydrothermal Process

Lanthanide-doped upconversion (Ln-doped UC) materials with predicable phase and geometry are attractive for their promising application in optics and biological. Herein, we report a facile strategy for deterministic synthesis of β-NaYF4 microcrystals by an ethylenediaminetetraacetic acid (EDTA) assisted hydrothermal process. The nucleation and growth process of the β-NaYF4 microcrystals have been experimentally revealed with different hydrothermal times. The phase and geometry of as-obtained crystals can be well manipulated by the experimental parameters such as pH values, precursors’ ratio, and reactant concentrations. The formation and morphology evolution mechanism of β-NaYF4 single microcrystals can be qualitatively analyzed using energy minimization principles under the thermodynamic and kinetic control. In addition, we presented the colour-changing up-conversion of Tm3+ and Yb3+ doped single β-NaYF4 microrod. Our work could help the understanding on crystal growth and design of rare earth fluoride mateirals at micro and nanoscale.

Electron–phonon coupling and a resonant-like optical observation of a band inversion in topological crystal insulator Pb1−x Sn x Se

The optical reflectivity of n-type Pb0.865Sn0.135Se and Pb0.75Sn0.25Se solid solutions was measured in the THz spectral region energetically corresponding to optical phonon excitations and in the temperature range from 40 K to 280 K. The first solid solution exhibits an open energy gap with trivial band ordering at all temperatures, while for the second one the transition from trivial insulator to topological crystal insulator phase is expected. The analysis of Pb0.75Sn0.25Se data performed within the dynamic dielectric function formalism revealed an anomaly of resonance-like character in the temperature dependence of LO phonon frequency. The formula for LO phonon energy renormalization reproduced observed anomaly for energy gap equal to zero, the phase transition occurred at T 0 = (172 ± 2) K. This effect was absent for Pb0.865Sn0.135Se. Present results show that reflectivity measurements in the THz range in the vicinity of LO phonon frequency can be valuable experimental method for precise determining of band inversion temperature in narrow-gap topological materials.

Synergistic electrochemical and optical properties of a UVC class quaternary nanocomposite incorporating graphene oxide and samarium chromium oxide perovskite

This research presents a comprehensive investigation into a novel quaternary nanocomposite comprising graphene oxide (GO), samarium chromium oxide perovskite (SmCrO3), silicon dioxide (SiO2), and tin dioxide (SnO2). The nanocomposite was synthesized using a modified Stöber method. In order to assess its potential applications in supercapacitors and UVC devices, an extensive analysis of its electrochemical and optical properties was conducted. The crystal structure and phase identification were analyzed using X-ray diffraction (XRD) and Rietveld refinement with X'pert HighScore Plus software, confirming the successful formation of the nanocomposite. Scanning electron microscopy (SEM) provided valuable insights into the structural morphology, while energy dispersive X-ray spectroscopy (EDS) confirmed the presence of constituent elements. Fourier transform infrared (FTIR) analysis and Raman Spectroscopy elucidated the functional groups and chemical bonds, confirming the successful synthesis of the nanocomposite. UV–Vis spectroscopy and photoluminescence (PL) spectroscopy revealed its strong UV radiation absorption and intensified fluorescence properties and confirming the band gap of SmCrO3 and GO/SmCrO3/SiO2/SnO2 quaternary nanocomposite as ∼5.4 eV and 4.84 eV respectively. The potential of nanocomposite potential as a supercapacitor material was evaluated through cyclic voltammetry (CV) measurements and electrochemical impedance spectroscopy (EIS) analyses. Remarkably, the specific capacitance of the nanocomposite reached 253.75 Fg−1 at a scan rate of 10 mVs−1, and electrochemical surface area of 507 cm2, highlighting its exceptional charge storage capability and promising prospects for high-performance energy storage devices. This comprehensive study addresses a significant knowledge gap, providing a profound understanding of the electrochemical and optical behavior of the quaternary nanocomposite. The observed exceptional results underscore its suitability for supercapacitor applications and expected favorable material for UVC device technologies.

Dissolvable photovoltaic cells on hydrogel

Solar energy is potentially the largest source of renewable energy for providing electrical power for human society. However, significant advances are required to make photovoltaic technologies have a low-carbon footprint in manufacture, be environmentally friendly at the end of their lives through recyclability, and be biodegradable. Here we report dissolvable organic photovoltaic devices based on poly(2-hydroxyethyl methacrylate), which show equal power conversion efficiency to their glass substrate-based counterparts. We use a novel method of including smectic liquid crystal (7-dioctyl[1]benzothieno[3,2- b][1]benzothiophene, C8-BTBT) as a crystal phase regulator in the heterojunction donor:acceptor polymer system to maintain the disposable organic solar cell efficiency without pre- or post-thermal annealing. The results show strong promise not only for more sustainable solar-cell fabrication but also as disposable and biocompatible solar cells for self-powered (energy harvesting) wearable and biomedical devices.

Nb2O5 film optical properties and laser-induced damage by phase-change-driven tuning

Niobium oxide (Nb2O5) is widely used in optical and electrical fields because of its high refractive index, wide band gap, high laser-induced damage threshold (LIDT) and high transparency in the ultraviolet to middle-infrared-wavelength range (0.35–7 μm). In this study, Nb2O5 films with different crystalline phases were successfully prepared on BK7 and Si substrates through electron beam evaporation (EB) and post-annealing. Based on the results of X-ray diffraction (XRD) and Raman spectroscopy analysis, the impact of the post-annealing technique on the structure, and optical and physical properties of Nb2O5 films was thoroughly discussed at the molecular level. The crystal phase of an Nb2O5 film and its molecular bonds considerably affect its properties. The Nb2O5(-12 1 2) film prepared in this study exhibited a higher LIDT (17.72 J/cm2) and a higher RMS (0.447 nm) than the corresponding films prepared in previous studies. Following the post-annealing process, the band gap and refractive index of the prepared films were significantly higher than those of the as-deposited film. Thus, this study has significant guiding implications for Nb2O5 film applications and the development costs of the films.

InP Crystal Phase Heterojunction Transistor with a Vertical Gate-All-Around Structure.

Crystal phase transitions can form a new type of heterojunction with different atomic arrangements in the same material: crystal phase heterojunction (CPHJ). The CPHJ has an inherently strong impact on band engineering without concerns over critical thicknesses with misfit dislocations and a semiconductor-metal transition. In-plane CPHJ was recently demonstrated in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials and utilized for conventional planar field-effect transistor applications. However, scalability such as gate electrostatic control, miniaturization, and multigate structure have been limited because of the geometrical issue. Here, we demonstrated a transistor using the CPHJ with a vertical gate-all-around structure by forming a CPHJ in conventional III-V semiconductors. The CPHJ, composed of wurtzite InP nanowires with zincblende InP substrates, showed an atomically flat heterojunction without dislocations and indicated a Type-II band discontinuity across the junction. The CPHJ transistor had moderate to good gate electrostatic controllability with high on-state currents and transconductance. The CPHJ offer will provide a new switching mechanism and add a new junction and device design choice to the long history of transistors.

Unveiling dual crystallization peaks in Zn2P2O7 glass: Insights into stability, nucleation, and growth kinetics

This study reports on the successful synthesis of Zn2P2O7 glass using the conventional melt-quenching method. The state of the material has been investigated using X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC), to verify its amorphous and glassy state with the onset of two distinct crystallization peaks. These peaks were indicative of the transition to α-Zn2P2O7 and γ-Zn2P2O7 phases during the annealing process, a finding that was supported by Fourier-transform infrared spectroscopy (FTIR) analysis. This marked the inaugural occasion where the stabilization of both Zn2P2O7 phases from their respective annealed glassy state was achieved. The crystallization kinetics and associated parameters of Zn2P2O7 glass were deeply delved into, with various models including Kissinger, Ozawa, and the Matusita-Sakka approach. The applied models elucidate the mechanisms of growth and nucleation within the glass matrix. This kinetic study provided valuable insights into the crystallization process, revealing that α-Zn2P2O7 is both kinetically and thermally more stable than the γ-phase. However, it is less thermodynamically stable compared to the γ-phase. Besides, the study of phase transformations and crystallization kinetics was enhanced by the analysis of the Avrami index.

Synthesis of transparent tin-doped indium oxide (ITO)-containing glass-ceramic coating by the sol-gel route for UV/NIR-shielding

Transparent glass-ceramic containing tin-doped indium oxide nano-crystalline phase was synthesized using the sol-gel method. The prepared sol, which was based on sodium aluminoborosilicate glass composition, was applied on soda-lime-silicate glass substrate through the dip-coating technique. Developing such glass-ceramics can offer several advantages, including reducing the total cost of production, enhanced chemical durability and a low-temperature synthesis process. The thermal behavior of the dried gels was investigated using simultaneous thermal analysis (STA), to determine the decomposition temperature of the nitrate salts in the gel, its glass crystallization temperature, and finally to optimize the heat treatment regime and optical properties as well. UV–Vis–NIR spectroscopy of the coated samples after heat treatment at 500 °C for 10 h revealed high visible transparency (T>70%) while indicating significant UV/NIR shielding, i.e. near zero and 10 % transmission, respectively. Phase analysis and crystallization behavior studies were conducted using XRD and FE-SEM to evaluate the morphology and size of the precipitated crystallites. According to the results, the optimum heating program for ITO crystallization was heating temperature and soaking time of 500 °C and 10 h, respectively. The undesirable crystalline phase of InBO3 was precipitated as the main crystalline phase by increasing the heat treating temperature to 550 °C. Furthermore, the glass structure was studied using FTIR spectroscopy demonstrating a highly polymerized glassy network for the coating. The effect of the precursors-to-solvent ratio during the synthesis process on the final optical properties was also investigated.

Metal–Organic Framework‐Based Hetero‐Phase Nanostructure Photocatalysts with Molecular‐Scale Tunable Energy Levels

AbstractAs an effective method to modulate the physicochemical properties of materials, crystal phase engineering, especially hetero‐phase, plays an important role in developing high‐performance photocatalysts. However, it is still a huge challenge but significant to construct porous hetero‐phase nanostructures with adjustable band structures. As a kind of unique porous crystalline materials, metal–organic frameworks (MOFs) might be the appropriate candidate, but the MOF‐based hetero‐phase is rarely reported. Herein, we developed a secondary building unit (SBU) regulating strategy to prepare two crystal phases of Ti‐MOFs constructed by titanium and 1,4‐dicarboxybenzene, i.e., COK and MIL‐125. Besides, COK/MIL‐125 hetero‐phase was further constructed. In the photocatalytic hydrogen evolution reaction, COK/MIL‐125 possessed the highest H2 yield compared to COK and MIL‐125, ascribing to the Z‐Scheme homojunction at hetero‐phase interface. Furthermore, by decorating with amino groups (i.e., NH2‐COK/NH2‐MIL‐125), the light absorbing capacity was broadened to visible‐light region, and the visible‐light‐driven H2 yield was greatly improved. Briefly, the MOF‐based hetero‐phase possesses periodic channel structures and molecularly adjustable band structures, which is scarce in traditional organic or inorganic materials. As a proof of concept, our work not only highlights the development of MOF‐based hetero‐phase nanostructures, but also paves a novel avenue for designing high‐performance photocatalysts.