Water adsorption performance of UiO-66 modified by MgCl2 for heat transformation applications

UiO-66 is a potential material for adsorption heat transformation (AHT) with high specific surface area, and excellent thermal and chemical stability. However, the low water adsorption capacity of UiO-66 in the low relative pressure range ($0< P/P_0< 0.3$) limits its application in AHT. We prepare the UiO-66 modified by MgCl$_{2 }$ through using the solvothermal method and impregnation method, and study their water vapor adsorption performances and heat storage capacities. Attributed to the extremely high saturated water uptake and excellent hydrophilicity of MgCl$_{2}$, the water adsorption performance of UiO-66 is improved, although the introduction of MgCl$_{2}$ reduces its specific surface area and pore volume. The water adsorption capacity at $P/P_0=0.3$ and the saturated water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 0.57 wt%) modified by the solvothermal method are 0.27 g/g and 0.57 g/g at 298 K, respectively, which are 68.8% and 32.6% higher than the counterparts of pure UiO-66, respectively. Comparing with pure UiO-66, the water adsorption capacity of the UiO-66 (with MgCl$_{2}$ content of 1.02 wt%) modified by the impregnation method is increased by 56.3% and 14.0% at the same pressure, respectively. During 20 water adsorption/desorption cycles, the above two materials show high heat storage densities ($\sim1293 $ J/g and 1378 J/g). Therein, the UiO-66 modified by the solvothermal method exhibits the excellent cyclic stability. These results suggest that the introduction of an appropriate amount of MgCl$_{2}$ makes UiO-66 more suitable for AHT applications.     

静态法和EXAFS技术研究放射性核素63^Ni（Ⅱ）在丝光沸石上的吸附机理

结合静态实验和X射线吸收精细结构光谱（EXAFS）技术研究了接触时问、离子强度、初始浓度以及共存电解质离子等水化学条件对放射性核：63^Ni（Ⅱ）在丝光沸石上的吸附行为和微观机制的影响．宏观实验结果表明：放射性核素。63^Ni（Ⅱ）在丝光沸石上的吸附在pH〈7的范围内受离子强度影响,而在pH〉7的范围内不受离子强度影响．放射性核素63^Ni（Ⅱ）在丝光沸石上的吸附率随着固体浓度的增加而升高,而对应的吸附量却随着固体浓度的增加而降低．溶液中共存的电解质离子对63^Ni（Ⅱ）在丝光沸石上的吸附有一定的促进或抑制作用,具体的影响趋势和程度由共存离子的性质、共存离子与63^Ni（Ⅱ）的络合能力以及与丝光沸石表面的亲和力大小共同决定．EXAFS微观结构分析结果表明：在pH6．5的溶液中,63^Ni（Ⅱ）与丝光沸石结构框架中的Na^＋／Ca。’等阳离子进行离子交换,形成六水合的外层络合物,不同离子强度下63^Ni（Ⅱ）的微观形态没有明显区别．郇Ni（II）在丝光沸石上的吸附随时间的变化呈现两种不同的作用机制：在溶液pH7．2的条件下,吸附初始的快速反应阶段中63^Ni（Ⅱ）的吸附主要以通过形成内层络合物的形式进行;随着接触时间的增长63^Ni（Ⅱ）在丝光沸石上的吸附机理转变为镍页硅酸盐共沉淀或者氢氧化镍沉淀的形成．初始63^Ni（Ⅱ）浓度为100mg／L的EXAFS图谱分析结果表明表面多聚体的形成是此条件下63^Ni（Ⅱ）在丝光沸石上的主要吸附机理．放射性核素63^Ni（Ⅱ）在丝光沸石／水界面的吸附行为和形态分布对于准确预测其在环境介质中的迁移转化和生物有效性等物理化学行为具有重要的意义．     

Different influences of Schottky metal on the strain and relative permittivity of barrier layer between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated.Based on the measured current–voltage and capacitance-voltage curves,the polarization sheet charge density and relative permittivity are analyzed and calculated by self-consistently solving Schrdinger’s and Poisson’s equations.It is found that the values of relative permittivity and polarization sheet charge density of AlN/GaN diode are both much smaller than the ones of AlGaN/GaN diode,and also much lower than the theoretical values.Moreover,by fitting the measured forward I–V curves,the extracted dislocations existing in the barrier layer of the AlN/GaN diode are found to be much more than those of the AlGaN/GaN diode.As a result,the conclusion can be made that compared with AlGaN/GaN diode the Schottky metal has an enhanced influence on the strain of the extremely thinner AlN barrier layer,which is attributed to the more dislocations.     

氨基功能化纳米复合材料对磷酸盐的吸附研究

合成了4种氨基(乙二胺(EDA), 二乙烯三胺(DETA), 三乙烯四胺(TETA)和四乙烯五胺(TEPA))功能化纳米复合材料(NH₂-NCMs, 分别命名为EDA-NCMs, DETA-NCMs, TETA-NCMs和TEPA-NCMs). 采用FTIR(傅立叶变换红外光谱分析), TG/DTG(热重差热分析), XPS(X-射线光电子能谱分析)等手段对其进行了表征, 并考察了其对水中磷酸盐的吸附性能. 结果表明: 溶液pH对其吸附性能影响较大, 在pH为2.5的条件下, 4种吸附剂对磷酸盐的吸附效果最佳; 在5 min内即可达到平衡吸附量的90%; 4种吸附剂对磷酸盐的吸附均符合Langmuir等温吸附模型; 吸附行为均符合准二级速率模型; 吸附反应为自发进行的放热反应和熵减的过程; 推测其吸附机理以静电作用力为主. 4种吸附剂用于磷酸盐含量为50 mg/L的废水处理的吸附率均大于97%, 均达到一级A出水的排放标准(≤1.53 mg/L, 以PO₄^3-计).     

Electric Field Control of Interface Related Spin Splitting in Step Quantum Wells

Spin splitting of the Aly Ga1-y As/GaAs/A1x Ga1-x As/A1-y Ga1-y As （x ≠ y） step quantum wells （ Q Ws） has been theoretically investigated with a model that includes both the interface and the external electric field contribution. The overall spin splitting is mainly determined by the interface contribution, which can be well manipulated by the external electric field. In the absence of the electric field, the Rashba effect exists due to the internal structure inversion asymmetry （SIA）. The electric field can strengthen or suppress the internal SIA, resulting in an increase or decrease of the spin splitting. The step QW, which results in large spin splitting, has advantages in applications to spintronic devices compared with symmetrical and asymmetrical QWs. Due to the special structure design, the spin splitting does not change with the external electric field.     

Cl+CH4反应的含时量子动力学研究

基于新的势能面,运用半刚性振动转子靶(SVRT)模型和含时波包法对Cl+CH4→HCl+CH3反应体系进行了计算,给出了反应过程中体系的振动、转动及空间立体效应对该反应的反应几率和反应阈能的影响,并计算了基态的总散射截面和热速率常数.     

碳掺杂闭口硼氮纳米管场发射第一性原理研究

运用第一性原理研究了闭口硼氮纳米管（BNNT）顶层掺碳体系（C@BNNT）的电子场发射性能.结果表明：随外电场增强,C@BNNT电子结构变化显著,态密度（DOS）向低能方向移动;碳原子的局域态密度（LDOS）在费米能级附近明显增大;赝能隙、最高占据分子轨道（HOMO）/最低未占据分子轨道（LUMO）能隙减小;体系电荷移向帽端.DOS,HOMO/LUMO及Mulliken电荷分析一致表明,与BNNT相比,C@BNNT电子场发射性能显著改善,且C@BN_moreNT性能更优. 关键词： 碳掺杂 硼氮纳米管 电子场发射 第一性原理     

SiO2凝胶玻璃中联吡啶S2→S0辐射跃迁

联吡啶以分子水平掺入SiO2凝胶玻璃中, 显示出独特的光谱性质. 其发射光谱除了正常的S1→S0跃迁产生的中心位于400 nm的发射峰外, 还出现了中心位于454 nm的激基缔合物发射峰. 经200 ℃处理后, 联吡啶分子受Si-O网络刚性约束, 激基缔合发射峰消失, 出现了基于S2→S0辐射跃迁产生的325 nm高能级发射峰. 至550 ℃处理后, 因联吡啶分子基本进入Si-O三维网络的间隙, 发射光谱中只剩下振动结构明显的高能级荧光峰. 上述结果为表征有机/无机复合材料微结构演变提供了荧光探针工具.     

Wendroff的一个不等式的证明

对Wendroff的一个不等式用逐逼近法给出一种证明。     

SHF频段超宽带高温超导滤波器的研制

针对超宽带通信系统的发展趋势,采用1/4波长短截线结构设计了一个工作于超高频(SHF)频段的超宽带高温超导滤波器,滤波器的中心频率为4.2 GHz,相对带宽为50%,讨论了1/4波长短截线结构滤波器的设计原理,给出了所设计超宽带滤波器的理论曲线、模拟仿真结果。实际制作的超宽带高温超导滤波器的测量曲线与模拟仿真曲线基本吻合,得到了满意的结果。