A conformal titanyl phosphate amorphous overlayer for enhancing photoelectrochemical hydrogen peroxide production

Photoelectrochemical(PEC) H₂O₂ production through water oxidation reaction(WOR) is a promising strategy,however,designing highly efficient and selective photoanode materials remains challenging due to competitive reaction pathways.Here,for highly enhanced PEC H₂O₂ production,we present a conformal amorphous titanyl phosphate(a-TP) overlayer on nanoparticulate TiO₂ surfaces,achieved via lysozyme-molded in-situ surface reforming.The a-TP overl...     

Thermodynamics properties of pyridoxal 5 phosphate

The ionization constants and heats of ionization of pyridoxal 5 phosphate groups in the pH range 2–10 have been determined by potentiometric and calorimetric techniques at 20, 25, 30, and 37°C in 0.1M KCl.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

Thermodynamics of micellization of multiheaded single-chain cationic surfactants

The energetics of micelle formation of three single-chain cationic surfactants bearing single (h = 1), double (h = 2), and triple (h = 3) trimethylammonium [(+)N(CH(3))(3)] headgroups have been investigated by microcalorimetry. The results were compared with the microcalorimetric data obtained from well-known cationic surfactant, cetyl trimethylammonium bromide (CTAB), bearing a single chain and single headgroup. The critical micellar concentrations (cmc's) and the degrees of counterion dissociation (alpha) of micelles of these surfactants were also determined by conductometry. The cmc and the alpha values increased with the increase in the number of headgroups of the surfactant. The relationship between the cmc of the surfactant in solution and its free energy of micellization (DeltaG(m)) was derived for each surfactant. Exothermic enthalpies of micellization (DeltaH(m)) and positive entropies of micellization (DeltaS(m)) were observed for all the surfactants. Negative DeltaH(m) values increased from CTAB to h = 1 to h = 2 and decreased for h = 3 whereas DeltaS(m) values decreased with increase in the number of headgroups. The DeltaG(m) values progressively became less negative with the increase in the number of headgroups. This implies that micelle formation becomes progressively less favorable as more headgroups are incorporated in the surfactant. From the steady-state fluorescence measurements using pyrene as a probe, the micropolarities sensed by the probe inside various micelles were determined. These studies suggest that the micelles are more hydrated with multiheaded surfactants and the micropolarity of micelles increases with the increase in the number of headgroups.     

Thermodynamics study of hydrogen storage materials

The growing use of conventional energy such as fossil fuels results in problems degrading our environment. Hydrogen is frequently discussed as a clean energy in the future without pollution. However, efficient and safe storage of hydrogen constitute a key challenge and unresolved problem. One of the main options is solid-state storage technology. A successful solid-state reversible storage material should meet the requirements of high storage capacity, suitable thermodynamic properties, reversibility and fast adsorption and desorption kinetics. This feature article focuses mainly on the development of thermodynamic improvement of hydrogen storage materials in the past few years including the complex hydride, ammonia borane, and metal-organic frameworks.     

Thermodynamics of binding cationic detergents to bovine serum albumin

Molar ratio (Γ_a) for binding cetyl trimethyl ammonium bromide (CTAB), myristyl trimethyl ammonium bromide (MTAB), dodecyl trimethyl ammonium bromide (DTAB) and cetyl pyridinium chloride (CPCL) to globular protein bovine serum albumin have been measured by equilibrium dialysis technique under various conditions of pH, ionic strength and temperatures. In all cases binding isotherms are S-shaped and at high concentrations of an amine, Γ_a appears to reach a constant value Γ^m_a, Γ^m_a may vary from 1 to 836 depending upon temperature, nature of amines and other solution parameters. The standard free energy changes (ΔG°) for BSA-amine binding have been calculated using appropriate reference states. The order of ΔG° for various systems is found to be in agreement with the order of the maximum extent of binding Γ^m_a. The effects of chain length of the surfactants on ΔG° and Γ^m_a are found to be irregular. ΔS° and ΔH° for binding reactions are also found to be significant in magnitude. Binding interactions at various pH and ionic strengths do not exhibit regularities in terms of electrostatic effects. All these observations lead to the conclusion that the binding sites of BSA are highly heterogeneous so that binding interactions become irregular in nature. All types of interactions are involved in the binding process so that the mechanism of binding in an individual system is complex in nature. The thermal stability and intrinsic viscosity of bovine serum albumin in the presence of amines have been examined in the light of the binding process.     

Thermodynamics of hydrogen adsorption on the zeolite Li-ZSM-5

Thermodynamic characterisation of the adsorption process (at a low temperature) of dihydrogen on the zeolite Li-ZSM-5 was carried out by means of variable-temperature infrared spectroscopy, with the simultaneous measurement of temperature and equilibrium pressure. Adsorption renders the H–H stretching mode infrared active, at 4092 cm⁻¹. The standard adsorption enthalpy and entropy resulted to be ΔH⁰=−6.5(±0.5) kJmol⁻¹ and ΔS⁰=−90(±5) Jmol⁻¹ K⁻¹, respectively. The adsorption enthalpy is significantly larger than the liquefaction heat, and this fact renders Li-ZSM-5 a potential cryoadsorbent for hydrogen storage.     

Potassium titanyl phosphate membranes: surface properties and application to ionic solution filtration

The relationship between the surface charge of potassium titanyl phosphate (KTP), studied on powder suspensions, and filtration properties of KTP nanofiltration membranes was studied. An experimental investigation of KTP powder characterization in different electrolytic solutions is presented: electrophoretic measurements show that the colloid particles are negatively charged whatever the solution pH, although they present a point of zero charge about 7.8. The selectivity of the membrane depends on the charge and size of ions. The interactions between the membrane and charged species have to be taken into account to explain the transfer through the membrane. With salts having the same cation, the rejection is higher for divalent anions than for monovalent anions. The best rejection rate is observed for applied pressure lower than 7 bar.     

39K NMR spectra of the powder and single crystal of potassium titanyl phosphate

The powder and single crystal of potassium titanyl phosphate KTiO(PO₄) have been studied by ³⁹K NMR. The quadrupole coupling and ³⁹K isotropic chemical shift parameters have been calculated. The number of formula units in the unit cell of potassium titanyl phosphate is suggested to be equal to the number of magnetically nonequivalent positions of potassium atoms in the lattice.     

新型储氢材料及其热力学与动力学问题

氢能作为一种理想的二次能源受到了国内外科研工作者的广泛关注,研制可以在室温和较低压力下方便、安全、高效地储存氢能的材料是氢能发展的瓶颈.到目前为止,固态储氢材料以能量密度高及安全性好等优势被认为极具应用前景,其中以轻质元素构成的氢化物(包括硼氢化物/铝氢化物(可用通式A(MH4)n表示,其中A是碱金属(Li,Na,K)或碱土金属(Be,Mg,Ca);M是硼或铝;n=1～4)、氨基氢化物(如LiNH2等))、氨硼烷(NH3BH3)、金属有机骨架材料(MOFs)是新型储氢材料研究领域的热点,本文将着重就目前这几类储氢材料的研究当中所涉及到的一些热力学及动力学问题进行总结探讨.     

Thermodynamics of the solution of hydrogen in LaNi5 at small hydrogen contents

Partial thermodynamic parameters for the solution of hydrogen in LaNi₅ have been determined by p-c-T methods on unactivated bulk samples of LaNi₅. The relative partial molar enthalpy of solution of hydrogen, at infinite dilution of hydrogen, is −33,9 kJ (g atom H)⁻¹ (~425 K). This is more exothermic than the heat of absorption corresponding to the formation of the hydride phase from the hydrogen-saturated intermetallic compound. The partial molar enthalpy of solution becomes more endothermic with hydrogen content in the region of solubility in the pure intermetallic compound. The partial thermodynamic quantities at infinite dilution have been found to vary with the stoichiometry of the LaNi_5+x where x varies from −0.2 to + 0.5. The partial molar enthalpy of absorption is most exothermic for the stoichiometric compound.     

Synthesis and crystal structure of new titanyl phosphate Sr2TiO(PO4)2

New strontium titanyl phosphate Sr₂TiO(PO₄)₂ (1) was synthesized and characterized by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and band structure calculations. Titanyl phosphate 1 is isostructural with vanadyl phosphate Sr₂VO(PO₄)₂ and has a layered structure. The titanium atoms are shifted from the centers of the TiO₆ octahedra and form short (1.74 Å) titanyl bonds. The structure of 1 is an unusual example of the disordered orientation of the chains formed by TiO₆ octahedra in complex titanium phosphates.     

Thermal decomposition of titanyl oxalates IV. Strontium and calcium titanyl oxalates

Thermal decomposition of strontium titanyl oxalate tetrahydrate and calcium titanyl oxalate hexahydrate have been studied employing TG, DTA, gas and chemical analysis. The decompositions proceed through three major steps: dehydration, decomposition of the oxalate to a carbonate and the decomposition of the carbonate to yield the final products, the metatitanates. The intermediates of the oxalate decomposition are found to be Sr₂Ti₂O_4+x(CO₃)₂-x(CO₂)_x and Ca₂Ti₂O₄(CO₃)₂, respectively. The entrapment of carbon dioxide in the former and the presence of non-equivalent carbonate groups in the latter are substantiated by their i.r. spectra. The penultimate solid residues are poorly crystalline Sr₂Ti₂O₅CO₃ and amorphous Ca₂Ti₂O₅CO₃. Decompositions of these carbonates are accompanied by growth in particle size of the products, SrTiO₃ and CaTiO₃, respectively.     

Influence of simultaneous heterovalent substitutions in both cationic sites on the ferroelectric properties of PZT type ceramics

Phenomena of conduction in an electric field and of ageing in PZT ceramics set severe limitations on the development of some industrial applications. Whereas it is well known how to suppress conduction with appropriate heterovalent substitutions, the ageing mechanism remains obscure. The purpose of the present study is to look experimentally for an ageing proof structure, and to document the privileged role of the couple (M⁺, Nb⁵⁺) (M⁺ = K⁺ and Na⁺) in resistance to ageing. A structure model is proposed to interpret the possible mechanism of space charge compensation in polar material by imposition of a polarizable superstructure.     

Thermodynamics of hydrogen bonding in hydrophilic and hydrophobic media

The thermodynamics of hydrogen bond breaking and formation was studied in solutions of alcohol (methanol, ethanol, 1-propanol) molecules. An extensive series of over 400 molecular dynamics simulations with an aggregate length of over 900 ns was analyzed using an analysis technique in which hydrogen bond (HB) breaking is interpreted as an Eyring process, for which the Gibbs energy of activation DeltaG can be determined from the HB lifetime. By performing simulations at different temperatures, we were able to determine the enthalpy of activation DeltaH and the entropy of activation TDeltaS for this process from the Van't Hoff relation. The equilibrium thermodynamics was determined separately, based on the number of donor hydrogens that are involved in hydrogen bonds. Results (DeltaH) are compared to experimental data from Raman spectroscopy and found to be in good agreement for pure water and methanol. The DeltaG as well as the DeltaG are smooth functions of the composition of the mixtures. The main result of the calculations is that DeltaG is essentially independent of the environment (around 5 kJ/mol), suggesting that buried hydrogen bonds (e.g., in proteins) do not contribute significantly to protein stability. Enthalpically HB formation is a downhill process in all substances; however, for the alcohols there is an entropic barrier of 6-7 kJ/mol, at 298.15 K, which cannot be detected in pure water.