Shadows of ordered graphs

Isoperimetric inequalities have been studied since antiquity, and in recent decades they have been studied extensively on discrete objects, such as the hypercube. An important special case of this problem involves bounding the size of the shadow of a set system, and the basic question was solved by Kruskal (in 1963) and Katona (in 1968). In this paper we introduce the concept of the shadow ∂G of a collection G of ordered graphs, and prove the following, simple-sounding statement: if n∈N is sufficiently large, |V(G)|=n for each G∈G, and |G|<n, then |∂G|?|G|. As a consequence, we substantially strengthen a result of Balogh, Bollobás and Morris on hereditary properties of ordered graphs: we show that if P is such a property, and |Pk|<k for some sufficiently large k∈N, then |Pn| is decreasing for k?n<∞.     

Preparation of Magnetic Ordered Mesoporous Carbon Composite and Its Application in Direct Electrochemistry of Horseradish Peroxidase

A novel magnetic ordered mesoporous carbon composite was prepared. Electrochemical measurements showed that the ordered mesoporous carbon composite provided an excellent matrix for the co‐adsorption of horseradish peroxidase (HRP). HRP could be separated and collected by the application of a magnetic field and its direct electron‐transfer could be achieved in the solution, not on the electrode thereby preventing the degradation of the enzyme. The cyclic voltammetric experimental results of HRP indicated that HRP displayed a pair of stable peaks with a formal potential of ?0.306 V in PBS. The resulting biosensor exhibited fast amperometric response to hydrogen peroxide.     

可调有序介孔炭在有机和硫酸电解液中的电容性质

采用硬模板法, 掺杂硼酸制备了一系列有序介孔炭材料, 并研究了其在有机和硫酸电解液中的电容性质. 结构分析表明, 该类炭材料具有平行排列的有序介孔孔道, 随硼酸摩尔分数从0增大至50%, 炭材料孔径尺寸从3.3 nm增大至5.7 nm, 表面含氧量从2.0%增大至5.2%(摩尔分数). 电化学测试表明, 在有机电解液中, 炭材料的电容性能主要是双电层电容, 含氧官能团没有引入明显的赝电容. 在硫酸电解液中, 掺杂5%硼酸制备的有序介孔炭材料BOMC-5的质量比电容值最大, 为140.9 F·g^-1; 随含氧量增大, 炭材料单位面积比电容值增大, 掺杂50%硼酸制备的炭材料BOMC-50的单位面积比电容值达到0.17 F·m^-2, 说明含氧官能团在硫酸电解液中引入明显的赝电容. 炭材料的表面化学性质决定了材料表面与电解液的浸润性, 是影响炭材料比电容保持率的主要因素.     

基于气息图案法有序多孔薄膜的制备改性及应用进展

有序多孔薄膜在过滤分离、催化、生物医学等领域有重要的应用前景。在众多制膜方法中,气息图案法以其简便易行、制膜效果好、环保等特点得到了广泛关注。科学家们一直致力于采用不同的材料和手段来进一步提高气息图案法多孔薄膜的性能。本文结合了最新的研究状况,探讨了基于气息图案法有序多孔薄膜的制备、改性及应用进展,并对未来的发展方向作...     

Co/AAO纳米有序阵列复合结构的光致发光和光吸收特性

以草酸电解液制备的高度有序的纳米级多孔阳极氧化铝(AAO)为模板,采用交流电化学沉积工艺合成了Co/AAO纳米有序阵列复合结构。分别研究了AAO模板和Co/AAO结构的光致发光和光吸收特性。结果表明,AAO模板在350～550nm范围内存在较强的光致发光带,其峰位在395nm处;Co/AAO纳米有序阵列复合结构的光致发射峰位亦在395nm处,且发光峰强度随Co沉积量的增加而迅速减弱。实验发现,Co/AAO纳米有序阵列复合结构的光吸收边从近紫外至近红外的波段范围内发生大幅度红移,最大红移量甚至超过380nm。文章定性分析并解释了Co/AAO纳米有序阵列复合结构吸收边大幅度红移及其光发射峰位不变、而峰强减弱的主要原因。     

Tuning Mass Transport in Electrocatalysis Down to Sub-5 nm through Nanoscale Grade Separation

Nano and single-atom catalysis open new possibilities of producing green hydrogen (H₂) by water electrolysis. However, for the hydrogen evolution reaction (HER) which occurs at a characteristic reaction rate proportional to the potential, the fast generation of H₂ nanobubbles at atomic-scale interfaces often leads to the blockage of active sites. Herein, a nanoscale grade-separation strategy is proposed to tackle mass-transport problem by utilizing ordered three-dimensional (3d) interconnected sub-5 nm pores. The results reveal that 3d criss-crossing mesopores with grade separation allow efficient diffusion of H₂ bubbles along the interconnected channels. After the support of ultrafine ruthenium (Ru), the 3d mesopores are on a superior level to two-dimensional system at maximizing the catalyst performance and the obtained Ru catalyst outperforms most of the other HER catalysts. This work provides a potential route to fine-tuning few-nanometer mass transport during water electrolysis.