Electrodeposition and characterization of Pd nanoparticles doped amorphous hydrogenated carbon films

Palladium (0) nanoparticles incorporated hydrogenated amorphous carbon (Pd/a-C:H) films were synthesized on single crystal silicon (100) substrates by electrochemical deposition route using methanol and camphor as carbon source, and Pd nanoparticles as dopant. The characterization results indicate that Pd nanocrystalline particles with diameter in the range of 1–5 nm dispersed in the amorphous carbon matrix. Compared with pure a-C:H films, the introduction of Pd nanoparticles didn't change the structure of carbon films. At the end, the growth mechanism of the Pd/a-C:H composite films was discussed.     

Doped titanium dioxide nanocrystalline powders with high photocatalytic activity

Doped titanium dioxide nanopowders (M:TiO₂; M=Fe, Co, Nb, Sb) with anatase structure were successfully synthesized through an hydrothermal route preceded by a precipitation doping step. Structural and morphological characterizations were performed by powder XRD and TEM. Thermodynamic stability studies allowed to conclude that the anatase structure is highly stable for all doped TiO₂ prepared compounds. The photocatalytic efficiency of the synthesized nanopowders was tested and the results showed an appreciable enhancement in the photoactivity of the Sb:TiO₂ and Nb:TiO₂, whereas no photocatalytic activity was detected for the Fe:TiO₂ and Co:TiO₂ nanopowders. These results were correlated to the doping ions oxidation states, determined by Mössbauer spectroscopy and magnetization data.     

膨润土负载掺铁氧化钛光降解苯酚

以钛酸四丁酯为原料,用溶胶-凝胶法制备了以膨润土为载体的负载型TiO2光催化剂;采用分光光度法测试其光降解性能;讨论了影响苯酚降解的主要因素。结果表明,在pH=8.0时,光催化剂的用量为15mg/L,苯酚溶液的浓度为5mg/L时,光照时间为120min,苯酚的降解率可达98.2%。     

Emission Spectra of Tb3+:PVA Polymer Films

This paper reports on the development and optical analysis of Tb³⁺‐doped polyvinyl alcohol (PVA) films. A reference PVA film has also been prepared for which X‐ray diffraction (XRD) spectral profile has been carried out; it was found that this polymer possesses a semi crystalline nature. Spectral analysis of the Tb³⁺:PVA polymer film has been made based on the measurement of the excitation, emission, and decay curves of the emission transitions (⁵D₄→⁷F₆,_5,4&3). Under a UV source (254 nm), a bright green emission was noticed from the surface of Tb³⁺:PVA film. The current study reveals that this terbium polymer film could be suggested as a novel green luminescent material.     

Critical behavior in Co-doped manganites La0.67Pb0.33Mn1−xCoxO3 (0≤x≤0.08)

The critical properties of perovskite manganite La_0.67Pb_0.33Mn_1−xCo_xO₃ (0≤x≤0.08) around the paramagnetic-ferromagnetic phase transition are investigated through various techniques such as the modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis. Though the nature of this transition was found to be in second order, the estimated critical exponents β (0.233≤β≤0.368), γ (1.03≤γ≤1.40) and δ (4.32≤δ≤5.54) are in between the theoretically predicted values for three-dimensional Heisenberg and tricritical mean-field model. This model suggests the coexistence of the short-range and long-range ferromagnetic orders around the critical temperature. The values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system.     

Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75): A first-principles study

The structural, elastic, electronic and optical (x=0) properties of doped Sn_1−xBi_xO₂ and Sn_1−xTa_xO₂ (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants C_ij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO₂ in two polarization directions are compared with both previous calculations and measurements.     

Influence of P2O5 content on the structure of SiO2-Na2O-CaO-P2O5 bioglasses by Si and P MAS-NMR

²⁹Si and ³¹P MAS-NMR has been used in order to study the influence of P₂O₅ content on the structure of SiO₂-Na₂O-CaO-P₂O₅ bioglasses. The ²⁹Si NMR spectra show many Q_Siⁿ entities co-existing in the same glass. For all the glasses, the Q_Siⁿ species are associated with Ca²⁺ and Na⁺. The glass network becomes more and more polymerized when the P₂O₅ content increases. The ³¹P NMR spectra show that the phosphorus is present as monophosphate with or without diphosphate complexes associated with both Ca²⁺ and Na⁺. The increase in phosphorus content modifies the relative abundance of phosphate complexes and leads to changes in the chemical environment around phosphate indicating that the distribution of cations is not homogeneous. Indeed most phosphate complexes attract calcium. The percentage of diphosphate complexes increases with the P₂O₅ content as the silicate network repolymerizes.     

m线法研究掺杂LiNbO3晶体波导基片的光损伤

采用m线法研究了掺杂LiNbO₃晶体波导基片的光损伤,发现抗光损伤能力依次为Mg:LiNbO₃、LiNbO₃、Fe:LiNbO₃(氧化),Fe:LiNbO₃(还原).对于同样材料,质子交换光波导的抗光损伤能力高于钛扩散光波导。     

金属掺杂磷铝分子筛的制备及其光催化性能研究

采用水热合成法,以正磷酸为磷源、硝酸铝为铝源,四丙基溴化铵(TPAB r)为模板剂,原位掺入Fe(NO3)3.9H2O或Zn(NO3)2.6H2O作为金属源,在180℃下晶化3天,以制得金属掺杂的磷铝分子筛.用XRD、XRF、FT-IR、UV-V is-DRS等方法对所合成的分子筛进行表征,以甲基橙溶液为目标降解物在紫外光下评价其光催化性能.初步研究表明,所合成的产品具有A lPO4-5分子筛结构,该系列金属掺杂磷铝分子筛在紫外光下有着较好的光催化性能.     

Vanadium(V)-doped MCM-41 synthesised by a novel one-step procedure

 A novel procedure to synthesise V-doped surfactant–templated mesoporous materials in one step using a V(V) complex is described. The resulting V(V)–MCM-41 material had a bimodal pore size distribution. Received: 25 April 2001 Accepted: 20 June 2001