两类不同阳极电氧化过程中的失活现象及氧化机制

利用电化学测试技术分析了两类不同阳极在电氧化降解对氯苯酚过程中的失活现象及氧化机制. 结果表明, 对氯苯酚在“I”类阳极Pt和“II”类阳极含氟树酯(polytetrafluoroethylene, PTFE)的β-PbO2 (PTFE-β-PbO2)上可发生直接氧化反应, 且两者的电催化活性均会在短时间内失活. 高电位电解能使失活的PTFE-β-PbO2和Pt得到再生, 但Pt电极需要更高的电解电位. 常见有机溶剂(如丙酮、四氢呋喃、二甲基亚砜)的浸洗可以再生失活的Pt电极, 但不能再生PTFE-β-PbO2电极. 对于“I”类阳极Pt, 当阳极电位大于2.0 V时, 除对氯苯酚的直接氧化反应外, 晶格氧的氧化作用成为整个降解过程的主导因素; 而对“II”类阳极PTFE-β-PbO2, 当阳极电位大于1.8 V时, 除直接氧化反应外, 羟基自由基的降解反应成为对氯苯酚去除的主要原因.     

Light-responsive nanocomposites combining graphene oxide with POSS based on host-guest chemistry

A facile methodology has been proposed to construct lightresponsive nanocomposites composed of GO and POSS based on host-guest inclusion of CD/Azo. Through manipulating photo-irradiation conditions, GO and POSS moieties in GO-POSS exhibited impressive and reversible supramolecular assembly/disassembly behaviors and had remarkable effect on oxygen barrier property of PVA-coated films, which would have potential application for smart gas barrier materials in packaging.     

Enhanced cycle ability of spinel LiMn2O4 by controlling the phase purity and structural strain

By applying the annealing step during the solid-state synthesis, well-crystallized spinel LiMn₂O₄ with high phase purity was fabricated. The sensitive effect of heating procedure on the structural and electrochemical properties of LiMn₂O₄ product was investigated. It was found that preheat-treatment-calcinations-annealing process can effectively eliminate the impurity phase. The post-annealing process also leads to a better crystalline and suitable strain for the LiMn₂O₄ product, which contributes to the enhanced cycling performance.     

Pyrrolidine–pyridinium based organocatalysts for highly enantioselective Michael addition of cyclohexanone to nitroalkenes

A novel class of pyrrolidine–pyridinium based organocatalysts has been developed and demonstrated to efficiently catalyze the asymmetric Michael addition reactions of unmodified cyclohexanone to nitroalkenes in the ionic liquid BMImBF₄ with up to 95% yield and nearly 100% ee. The catalytic system could be reused for four times and still retained high enantioselectivity. X-ray crystallographic analysis results suggested that a sterically hindered pyridinium moiety on the catalyst played an important role in the chiral induction.     

Sub-10 nm V2O5 Crystals on Carbon Nanosheets for Advanced All-Solid-State Lithium Metal Batteries

V₂O₅, as a lithium-free cathode material, has inherent defects such as sluggish kinetics and volume change and, at the same time, requires a lithium metal anode that tends to form dendrites in liquid electrolytes. Both the lithium dendrite and the flammable electrolyte solvent bring longtime safety issues. This work introduces nonflammable inorganic–organic composite solid electrolyte to inhibit the growth of the lithium dendrite and suppress the instability caused by V₂O₅ nanometerization. However, the long-term cycling and rate performances are still insufficient even when reducing V₂O₅ size to about 50 nm. As an improvement, sub-10 nm V₂O₅/C nanosheets are designed and prepared using corn stalks as precursors through simple impregnation and calcination process. The V₂O₅/C offers a much better electrode/electrolyte contact and interface stability than bulk V₂O₅ and commercial V₂O₅ in the inorganic–organic composite solid electrolyte. The discharge capacity is 228 mAh g⁻¹ at 0.1 C after 50 cycles and ≈110 mAh g⁻¹ at 2.0 C.     

9,9’-螺双芴的光电性能

采用密度泛函理论(DFT)-B3LYP/6-31G(d)方法对9,9'-螺双芴低聚物[(SBF)n(n=1-4)]体系进行全优化, 得到各分子的最高占据轨道(HOMO)和最低空轨道(LUMO)能量及HOMO-LUMO能隙, 结果表明各分子整体表现出很好的共轭性质. 并在分子的阳离子和阴离子状态的优化结构基础上, 计算得到电离势(IP)、电子亲和势(EA)、空穴抽取能(HEP)、电子抽取能(EEP)和重组能等相关能量. 利用单激发组态相互作用(CIS)/3-21G方法优化得到9,9'-螺双芴单体的S1激发态的几何构型. 用含时密度泛函理论(TD-DFT)方法计算得到了分子吸收光谱和荧光光谱的相关数据. 随着聚合长度的增加, 能隙变窄, 空穴注入和电子转移的能力都相应提高, 吸收光所需能量减小, 吸收强度(f)增大, 光谱红移. 采用线性外推法, 利用低聚物分子的各种性质与聚合度n之间的关系, 得到高聚物的相应性质.为考察9位螺芴化的影响, 将(SBF)n的相关性质与母体芴的低聚物[(FL)n(n=1-4)]进行比较, 由两者的计算结果对比显示, 在芴的9位螺芴化可以提高电子和空穴的传输能力, 并同时保留芴优良的发光性质.     

三氟甲磺酸盐催化甲苯硝化反应的研究

利用三氟甲磺酸盐作为新型的Lewis酸催化剂, 用于甲苯与等物质的量的硝酸的硝化反应. 通过对不同催化剂进行考察发现Zr(OTf)₄和Sm(OTf)₃的催化性能最好, 甲苯转化率分别达77.1%和67.4%. 使用98%硝酸能使转化率达100%, 而用甲苯作溶剂时转化率达95.4%. 对硅胶负载催化剂的考察发现硅胶负载催化剂Sm(OTf)₃能使甲苯转化率升至89.9%, 且异构体分布有所改变, 其o∶m∶p为44.6∶5.7∶49.7.     

A solution to the stereochemical problems posed by amaryllidaceae constituents using a highly syn-selective arylcuprate conjugate addition to γ-amino and γ-carbamato-α,β-enoates

Various substituted arylcuprates undergo stereocontrolled additions to l-serine-derived γ-amino- and γ-carbamato-α,β-enoates with high syn-selectivities. The stereochemical outcome of these reactions is fully consistent with the reductive elimination-based model proposed previously. This method is well suited for the preparation of a broad range of biologically active amaryllidaceae constituents and their aromatic analogues.     

Steady rise of a small spherical gas bubble along the axis of a cylindrical pipe at high Reynolds number

Steady irrotational flow of inviscid liquid of density ρ_l around a spherical gas bubble which lies on the axis of a cylindrical pipe is investigated using the analysis of Smythe (Phys. Fluids 4 (1961) 756). The bubble radius b=qa is assumed small compared to the pipe radius a, and the interfacial tension between gas and liquid is γ. Far from the bubble, in the frame in which the bubble is at rest, the liquid velocity along the pipe is v₀, whereas the liquid velocity at points on the wall closest to the bubble is U_zw=v₀(1+1.776q³+⋯). The decrease in wall pressure as the bubble passes is therefore Δp=1.776ρ_lv₀²q³. When the Weber number W=2bv₀²ρ_l/γ is small, the bubble deforms into an oblate spheroid with aspect ratio χ=1+9W(1+1.59q³)/64. If the fluid viscosity μ is non-zero, and the Reynolds number Re=2v₀ρ_lb/μ is large, a viscous boundary layer develops on the walls of the pipe. This decays algebraically with distance downstream of the bubble, and an exponentially decaying similarity solution is found upstream. The drag D on the bubble is D=12πμv₀b(1−2.21Re^−1/2)(1+1.59q³)+7.66μv₀bRe^1/2q^9/2, larger than that given by Moore (J. Fluid Mech. 16 (1963) 161) for motion in unbounded fluid. At high Reynolds numbers the dissipation within the viscous boundary layers might dominate dissipation in the potential flow away from the pipe walls, but such high Reynolds numbers would not be achieved by a spherical air bubble rising in clean water under terrestrial gravity.     

激光光源条件对谷氨酸钠拉曼光谱的影响

采用多种激光和不同功率等,对谷氨酸钠晶体进行了激光拉曼光谱的影响研究。结果表明不同波长和功率的光源,对测定存在一定的影响,谱峰位移在6 cm-1以内。紫外激光由于光能量较大对样品有一定的破坏作用,造成拉曼光谱的减弱和泯灭,需采用光路衰减。拉曼谱峰的响应与光源的功率有着很好的线性关系,其相关系数r　0.999。首次提出单位光功率所产生的拉曼光强与所用的波长有关,与所用的光功率无关。