An Unlocked Two-Dimensional Conductive Zn-MOF on Polymeric Carbon Nitride for Photocatalytic H2O2 Production

Developing highly efficient catalytic sites for O₂ reduction to H₂O₂, while ensuring the fast injection of energetic electrons into these sites, is crucial for artificial H₂O₂ photosynthesis but remains challenging. Herein, we report a strongly coupled hybrid photocatalyst comprising polymeric carbon nitride (CN) and a two-dimensional conductive Zn-containing metal–organic framework (Zn-MOF) (denoted as CN/Zn-MOF(lc)/400; lc, low crystallinity; 400, annealing temperature in °C), in which the catalytic capability of Zn-MOF(lc) for H₂O₂ production is unlocked by the annealing-induced effects. As revealed by experimental and theoretical calculation results, the Zn sites coordinated to four O (Zn-O₄) in Zn-MOF(lc) are thermally activated to a relatively electron-rich state due to the annealing-induced local structure shrinkage, which favors the formation of a key *OOH intermediate of 2e⁻ O₂ reduction on these sites. Moreover, the annealing treatment facilitates the photoelectron migration from the CN photocatalyst to the Zn-MOF(lc) catalytic unit. As a result, the optimized catalyst exhibits dramatically enhanced H₂O₂ production activity and excellent stability under visible light irradiation.     

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2O2 Production

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn−N₂O₂ moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N₂O₂−S). Systematic analyses demonstrate that the synergetic effects between the N₂O₂ species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O₂ reduction to H₂O₂. Remarkably, the Zn−N₂O₂ moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H₂O₂ generation. Consequently, the Zn−N₂O₂−S SAC exhibits impressive electrochemical H₂O₂ production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm⁻² in the flow cell, it shows a high H₂O₂ production rate of 6.924 mol g_cat⁻¹ h⁻¹ with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.     

Prediction of quantitative calibration factors of some organic compounds in gas chromatography

A quantitative structure-property relationship (QSPR) methodology that involves multilinear (Hansch-type) and nonlinear (radial basis function neural network (RBFNN)) approaches was performed to correlate the quantitative molar calibration factors (f(M)) of 140 organic compounds against structural factors. The statistical characteristics provided by the multiple linear model (R(2) = 0.963; RMS = 0.089; AARD = 3.86% for test set) indicated satisfactory stability and predictive ability, while the predictive ability of the RBFNN model is somewhat superior (R(2) = 0.983; RMS = 0.075; AARD = 3.19% for test set). The multilinear model provided some insight into the main structure factors that modulate the quantitative calibration factor of the investigated compounds.     

The effect of methyl group on the cooperativity between three types of hydrogen bond: O?H···O,C?H···O,and O?H···π

The effect of the methyl group on the cooperativity between three types of hydrogen bond (O H···O, C H···O, and O H···π) in cyclic complex involving an acetylene and two waters has been studied on the basis of high-level ab initio calculations. The total interaction energy of three hydrogen bonds increases as the number of methyl group in the complex increases. The binding distances of O H···π and O H···O hydrogen bonds shorten, while that of C H···O hydrogen bond elongates with increasing methyl group. This indicates that addition of methyl group leads to enhancement of O H···π and O H···O hydrogen bonds, and weakening of C H···O hydrogen bond, as also shown in frequency shift, chemical shifts, charge populations, and stabilization energies of orbital interactions. Although the presence of methyl group has a complicated effect on different type of hydrogen bond, the cooperativity of three hydrogen bonds increases in general with the addition of methyl group. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

反向响应过程抗负载干扰PID控制回路性能评估

反向响应过程广泛存在于化工领域中,但针对反向响应过程的性能评估研究较少。针对一类二阶时滞反向响应过程,通过幂级数展开的方法简化了对象模型,然后研究其抗负载干扰PID控制回路性能评估问题。根据DS-d控制原理获取期望闭环传递函数以及PID控制器参数,推导干扰模型为阶跃情况下的PID控制回路累积绝对误差(IAE)性能基准值,并将其推广到斜坡输入以及一般输入情形,为不同干扰类型情况下的反向响应过程建立通用化的IAE性能评价标准。仿真结果验证了所提性能评估算法的正确性以及通用性。     

Real-time observation of polyelectrolyte-induced binding of charged bilayers

We present real-time observations by confocal microscopy of the dynamic behavior of multilamellar vesicles (MLVs), composed of charged synthetic lipids, when put in contact with oppositely charged polyelectrolyte (PE) molecules. We find that the MLVs exhibit astonishing morphological transitions, which result from the discrete and progressive binding of the charged bilayers induced by a high PE concentration gradient. Our physical picture is confirmed by quantitative measurements of the fluorescence intensity as the bilayers bind to each other. The shape transitions lead eventually to the spontaneous formation of hollow capsules, whose thick walls are composed of lipid multilayers condensed with PE molecules. This class of objects may have some (bio)technological applications.     

Role of the preparation procedure in the formation of spherical and monodisperse surfactant/polyelectrolyte complexes

Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed.     

悬浮液进样—火焰原子吸收光谱法测定玉米中的锌和铁

本文提出了一种悬浮液进样－火焰原子吸收光谱法测定玉米面中锌,铁的新方法。将玉米面悬浮于琼脂胶体中,直接喷入空气－乙炔火焰中,用标准加入法测定,测定结果与灰化法一致。方法简便,快速。     

电感耦合等离子体原子发射光谱法测定粗锑中的As、Bi、Cd、Cu、Fe、Pb和Se元素

通过样品处理、谱线选择、准确度和精密度测定、加标回收实验及与其他测定方法的比对实验,建立了电感耦合等离子体原子发射光谱法(ICP-AES)测定粗锑中As、Bi、Cd 、Cu、Fe、Pb、Se 7种元素的定量分析方法。实验结果表明,该方法准确度高,稳定可靠,相对标准偏差(RSD,n=6)均小于3%,方法的加标回收率在95~105%之间,分析结果与分光光度法、原子吸收光谱法(AAS)及原子荧光光谱法(AFS)分析结果相吻合,能够满足日常对粗锑中杂质元素含量测定的要求。