In this work,the nature of physisorbed water and its impacts on the structure,surface chemistry,and proton conduction properties of TiO2 nanocrystals were investigated by a combinational spectral technique.All TiO2 nanocrystals were directly prepared by a hydrothermal method,which showed highly hydrated and sulfated surfaces.The surface water molecules were indicated to exist in a wide set of energetically nonequivalent surface hydration groups,leading to the removal of physisorbed and chemisorbed water in sequence with increasing temperature.After heating treatment at 100 ℃ in air,physisorbed water layers were recovered with no significant impacts on the TiO2 nanostructure.On the other hand,when treated at the same temperature in vacuum,the recovery of physisorbed water layers was partially reversible,while a new hydration state appeared due to the filling of the high-energy adsorption sites by water molecules,which led to a significant increase in the amount of water molecules for surface hydration and an accelerated dehydration process toward lower temperature.As a result,an abnormal increase was observed in proton conductivity.These observations were explained in terms of thermally induced changes of surface chemistry and the amount of hydrated water.The results reported in this work are important,which may help understand the roles that the physisorbed water plays in stabilizing the nanostructures and therefore could have a broad class of implications.
Zn1-xMgxO （x = 0, 0.18） thin films were fabricated on the copper substrates by radiofrequency magnetron sputtering using the high pure argon as a sputtering gas. The Zn1-xMgxO films were characterized by X-ray powder diffraction （XRD）, scanning electron microscope （SEM） and galvanostatic tests. The electrochemical test showed an improved electrochemical performance of Zn0.82EMg0.18O thin film as an anode material for lithium ion batteries.
Nanocrystals of Ce1-xMnxO2-δ（x=0.00,0.05,0.10,0.15,and 0.20） were synthesized by a hydrothermal reaction route.The solid solutions crystallized in a cubic fluorite structure with a particle size in the range of 11～15 nm.The incorporation of Mn ions in CeO2 resulted in a lattice volume reduction.Mn ions showed a mixed valence state of ＋2,＋3 and ＋4 in CeO2 lattice.An obvious red-shift of the absorption threshold edge was observed from the UV-visible spectrum.Compared with the bulk CeO2,Ce1-xMnxO2-δ nanocrystals exhibited a lower releasing oxygen temperature as indicated by TPR technique.
A series of Li4Ti5O12 materials were prepared by three different methods： solvothermal, sol-gel, and solid-state reaction methods. Phase composition, morphology, and particle sizes of the samples were studied by powder X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Electrochemical properties of the samples were investigated by charge-discharge tests. It is demonstrated that both sol-gel and solid-state reaction methods provided good control over the chemical composition and microstructure of the active material, in which sol-gel method yielded a fine Li4Ti5O12 spinel having an initial specific capacity of 146 mAh g-1 and low capacity fade during cycling. Comparatively, the solid-state method is simple and promising to prepare Li4Ti5O12 for commercial applications.
A series of Bi2O3 were prepared by a facile hydrothermal method using NaOH and ammonia as the mineralizers. The products were characterized by XRD, IR, UV-vis diffuse reflectance spectra, and photodegradation of Rhodamine B dye. Simply using NaOH to supply a strong base condition, single phase α-Bi2O3 was formed. When changing the amount of NaOH and ammonia, mixed phases of α-Bi2O3, （BiO）4CO3（OH）2 and Bi2O2CO3 were obtained. All samples were found to show photocatalytic activities towards the degradation of Rhodamine B dye under UV light irradiation, in which mixed phase samples showed higher activities than single phase α-Bi2O3 possibly owing to the synergistic effect of the mixed phases.
