ZnO Meso-Mechano-Thermo Physical Chemistry

Cooperative coupling of anisotropic phonon modes intensifies visible thermochromism in layered α-MoO3

Applications that provide versatile, high temperature warnings require the development of thermochromic materials based on solid-state oxides. To boost the visible thermochromic properties, a fundamental approach to reveal the unclear roles of local structure on band structure modulation should be considered by scrutinizing the thermal motion of phonon modes. Herein, we demonstrate that selective coupling of intra-layer phonon modes intensifies the visible thermochromism of layered oxides α-MoO₃. As a result of thermally induced band gap reduction in α-MoO₃, the observed color reversibly changes from white at 25 °C to yellow at 300 °C owing to a red shift of the absorption edge with an increase of temperature. This high-temperature thermochromism is attributed to the anisotropic change of layered α-MoO₃ crystal structures characterized by synchrotron X-ray diffraction. Notably, quantitative characterizations combined with theoretical calculations reveal that the cooperative coupling of active Raman modes in intra-layer [MoO₆] octahedra are responsible for the band gap reduction at high temperature; this defies the general belief regarding the origin of visible thermochromism in layered oxides as the modulation of a van der Waals inter-layer distance. These original results can aid the development of a new strategy to further intensify high-temperature thermochromism by anion doping for highly sensitive temperature-indicating applications.

The magnetism of titanium-defected undoped rutile TiO2: first-principles calculations

The physicochemical properties of TiO2 are largely dependent on the defects. Here, using first-principles calculations, we report a systematic investigation of the magnetic properties of Ti-defected rutile TiO2 systems. The results of our calculations show that the VTi concentration can significantly affect the size of the magnetism, and that the magnetism weakens with decreasing VTi concentration. Studies of phonon dispersion curves show that systems with lower VTi concentrations of 8.33% and 6.25% are kinetically stable. Further detailed calculations on the Ti11O24 system indicate that the magnetism mainly originates from four of the six nearest-neighbor O atoms to the Ti vacancy, but much less from the other two. The magnetic ground states are discussed, and the results show that for the Ti11O24 system, the ferromagnetic (FM) state of the four nearest-neighbor O atoms to the Ti vacancy is the magnetic ground state, and for the Ti22O48 system, the FM state of the two vacancies is the magnetic ground state. In addition, our calculations also indicate that the magnetic properties of Ti-defected TiO2 can be tuned via strain engineering. In general, this metal-defected TiO2 represents a novel kind of semiconductor. Research into the magnetic properties reported in this paper can enrich theoretical knowledge in this area and provide more potential candidates for TiO2-based materials.

Urea-assisted cooperative assembly of phosphorus dendrimer–zinc oxide hybrid nanostructures

The interplay of phosphorus dendrimer–urea during sol–gel mineralization of soluble zinc precursors provides porous lamellar nanostructures.

Preparation of a Highly Conductive Seed Layer for Calcium Sensor Fabrication with Enhanced Sensing Performance

The seed layer plays a crucial role in achieving high electrical conductivity and ensuring higher performance of devices. In this study, we report fabrication of a solution-gated field-effect transistor (FET) sensor based on zinc oxide nanorods (ZnO NRs) modified iron oxide nanoparticles (α-Fe₂O₃ NPs) grown on a highly conductive sandwich-like seed layer (ZnO seed layer/Ag nanowires/ZnO seed layer). The sandwich-like seed layer and ZnO NRs modification with α-Fe₂O₃ NPs provide excellent conductivity and prevent possible ZnO NRs surface damage from low pH enzyme immobilization, respectively. The highly conductive solution-gated FET sensor employed the calmodulin (CaM) immobilization on the surface of α-Fe₂O₃-ZnO NRs for selective detection of calcium ions (Ca²⁺). The solution-gated FET sensor exhibited a substantial change in conductance upon introduction of different concentrations of Ca²⁺ and showed high sensitivity (416.8 μA cm^-2 mM^-1) and wide linear range (0.01-3.0 mM). In addition, the total Ca²⁺ concentration in water and serum samples was also measured. Compared to the analytically obtained data, our sensor was found to measure Ca²⁺ in the water and serum samples accurately, suggesting a potential alternative for Ca²⁺ determination in water and serum samples, specifically used for drinking/irrigation and clinical analysis.

Mechanochemically induced sulfur doping in ZnO via oxygen vacancy formation

Mechanochemically induced oxygen vacancy of ZnO is indispensable in order to control the level of sulfur doping quantitatively.

Facile fabrication and application of SnO2–ZnO nanocomposites: insight into chain-like frameworks, heterojunctions and quantum dots

We report that a novel SnO₂–ZnO chain-like heterojunction framework embedded with SnO₂ and ZnO quantum-dots shows highly efficient photocatalytic performance.

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Surface-bulk modification of zinc oxide for efficient photocatalysis.

Tunnel-dependent supercapacitance of MnO2: effects of crystal structure

A proportional relationship between the specific capacitance of MnO2 and the percentage of effective Mn centers that act as active sites in the Faradaic charge storage has been established on the basis of a tunnel structure–crystallization behavior correlation. A quantitative relationship between the effective Mn centers at the surfaces and in the tunnels can distinguish the specific capacitance values that arise from the adsorption/desorption and insertion/extraction processes, respectively, of different MnO2 crystallographic forms in the Faradaic charge storage. The different specific capacitance values between the MnO2 crystallographic forms are mainly attributed to the different effective utilizations of Mn centers in the size-limited tunnels. The present model demonstrates that increasing the percentage of effective Mn centers via decreasing the crystal size can facilitate obtaining MnO2-based electrode materials with higher specific capacitance values.

Bond order resolved 3d5/2 and valence band chemical shifts of ag surfaces and nanoclusters

Incorporating the tight-binding theory and the bond order-length-strength (BOLS) correlation into the X-ray photoelectron spectra of Ag(111) and (100) surfaces and the Auger electron spectra of Ag nanoparticles deposited on Al2O3 and CeO2 substrates has led to quantitative information of the 3d5/2 and the valence binding energies of an isolated Ag atom and their shifts upon bulk, defect, surface, and nanocrystal formation. It is clarified that the globally positive energy shifts originate from the undercoordination-induced Goldschmidt-Pauling bond contraction and the associated local quantum entrapment and the heterocoordination-induced bond nature alteration at the particle-substrate interfaces. Perturbation to the Hamiltonian by atomic ill-coordination dictates the energy shift that is proportional to the bond energy at equilibrium. Theoretical reproduction of the measured spectroscopic data derived that the 3d5/2 energy of an isolated Ag atom shifts from 363.02 to 367.65 eV and the valence band center from 0.36 to 8.32 eV upon bulk formation. The extended Wagner plots revealed the coefficients of valence recharging and potential screening to be 1.21 and 1.56 for Ag interacting with Al2O3 substrate and 1.15 and 1.50 for Ag with CeO2, respectively. Exercises exemplify the enhanced capabilities of XPS and AES in determining quantitative information regarding the evolution of the local bond length, bond energy, binding energy density, and atomic cohesive energy, with the coordination and chemical environment.

Solution-phase electronegativity scale: insight into the chemical behaviors of metal ions in solution

By incorporating the solvent effect into the Born effective radius, we have proposed an electronegativity scale of metal ions in aqueous solution with the most common oxidation states and hydration coordination numbers in terms of the effective ionic electrostatic potential. It is found that the metal ions in aqueous solution are poorer electron acceptors compared to those in the gas phase. This solution-phase electronegativity scale shows its efficiency in predicting some important properties of metal ions in aqueous solution such as the aqueous acidities of the metal ions, the stability constants of metal complexes, and the solubility product constants of the metal hydroxides. We have elaborated that the standard reduction potential and the solution-phase electronegativity are two different quantities for describing the processes of metal ions in aqueous solution to soak up electrons with different final states. This work provides a new insight into the chemical behaviors of the metal ions in aqueous solution, indicating a potential application of this electronegativity scale to the design of solution reactions.