等浓度的氯化铵和硫酸铵溶液哪个pH高

有中学化学参考资料题:0.10 mol/L的NH4Cl和(NH4)2SO4溶液哪个pH值高?这似乎是个中学生可做的简单题目,仔细考虑不是如此.如果简单地认为盐酸和硫酸都是强酸,而硫酸是二元酸,硫酸铵溶液中铵盐浓度为0.20 mol/L,那么NH4Cl溶液pH高,那是不妥的.硫酸是二元酸,第一个氢离子能完全电离,第二个氢离子部分电离,如此考虑情况怎么样呢?是不是答案发生变化?这要通过计算来说明.     

Vanadium-based polyanionic compounds as cathode materials for sodium-ion batteries:Toward high-energy and high-power applications

Sodium ion batteries(SIBs)have been regarded as one of the alternatives to lithium ion batteries owing to their wide availability and significantly low cost of sodium sources.However,they face serious challenges of low energy&power density and short cycling lifespan owing to the heavy mass and large radius of Na⁺.Vanadium-based polyanionic compounds have advantageous characteristic of high operating voltage,high ionic conductivity and robust structural framework,which is conducive to their high energy&power density and long lifespan for SIBs.In this review,we will overview the latest V-based polyanionic compounds,along with the respective characteristic from the intrinsic crystal structure to performance presentation and improvement for SIBs.One of the most important aspect is to discover the essential problems existed in the present V-based polyanionic compounds for high-energy&power applications,and point out most suitable solutions from the crystal structure modulation,interface tailoring and electrode configuration design.Moreover,some scientific issues of V-based polyanionic compounds shall be also proposed and related future direction shall be provided.We believe that this review can serve as a motivation for further development of novel V-based polyanionic compounds and drive them toward high energy&power applications in the near future.     

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin(Sn)halide-based perovskite solar cells(PSCs)fall a large gap behind those of lead halide-based PSCs,mainly because of poor film quality of the former.Here we report an efficient strategy based on a simple secondary crystallization growth(SCG)technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface.They were discovered to enhance the film crystallinity and suppress the oxidation of Sn²⁺remarkably,hence reduce trap state density and non-irradiative recombination in the absorber films.Furthermore,the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces.Consequently,a champion device efficiency of 8.07% was achieved alo ng with significant enhancements in VOC and JSC,in contrast to 5.35% of the control device value.Moreover,the SCG film-based devices also exhibit superior stability comparing with the control one.This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.     

Total synthesis of TRADD death domain with arginine N-GlcNAcylation by hydrazide-based native chemical ligation

TNFR1-associated death domain protein(TRADD)with arginine N-GlcNAcylation is a novel and structurally unique posttranslational modification(PTM)glycoprotein that blocks the formation of death-inducing signaling complex(DISC),orchestrating host nuclear factorκB(NF-κB)signaling in entero-pathogenic Escherichia coli(EPEC)-infected cells.This particular glycosylated modification plays an extremely vital role for the effective colonization and pathogenesis of pathogens in the gut.Herein we describe the total synthesis of TRADD death domain(residues 195-312)with arginine235 NGlcNAcylation(Arg-GIcNAc TRADD(195-312)).Two longish peptidyl fragments of the wild-type primary sequence were obtained by robust,microwave-assisted,highly efficient,solid-phase peptide synthesis(SPPS),the N-GlcNAcylated sector was built by total synthesis and attached specifically to resinbound peptide with an unprotected ornithine residue via silver-promoted on-resin guanidinylation,ArgGlcNAc TRADD(195-312)was constructed by hydrazide-based native chemical ligation(NCL).The facile synthetic strategy is expected to be generally applicable for the rapid synthesis of other proteins with Arg-GIcNAc modification and to pave the way for the related chemically biological study.     

Steam activation of Fe-N-C catalyst for advanced power performance of alkaline hydrazine fuel cells

Alkaline hydrazine liquid fuel cells(AHFC) have been highlighted in terms of high power performance with non-precious metal catalysts.Although Fe-N-C is a promising non-Pt electrocatalyst for oxygen reduction reaction(ORR),the surface density of the active site is very low and the catalyst layer should be thick to acquire the necessary number of catalytic active sites.With this thick catalyst layer,it is important to have an optimum pore structure for effective reactant conveyance to active sites and an interface structure for faster charge transfer.Herein,we prepare a Fe-N-C catalyst with magnetite particles and hierarchical pore structure by steam activation.The steam activation process significantly improves the power performance of the AHFC as indicated by the lower IR and activation voltage losses.Based on a systematic characterization,we found that hierarchical pore structures improve the catalyst utilization efficiency of the AHFCs,and magnetite nanoparticles act as surface modifiers to reduce the interracial resistance between the electrode and the ion-exchange membrane.     

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO₂ and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm² and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.     

A new strategy to access Co/N co-doped carbon nanotubes as oxygen reduction reaction catalysts

Carbon nanotubes(CNTs),as one-dimensional nanomaterials,show great potential in energy conversion and storage due to their efficient electrical conductivity and mass transfer.However,the security risks,time-consuming and high cost of the preparation process hinder its further application.Here,we develop that a negative pressure rather than a following gas environment can promote the generation of cobalt and nitrogen co-doped CNTs(Co/N-CNTs) by using cobalt zeolitic imidazolate framework(ZIF-67) as a precursor,in which the negative pressure plays a key role in adjusting the size of cobalt nanoparticles and stimulating the rearragement of carbon atoms for forming CNTs.Importantly,the obtained Co/N-CNTs,with high content of pyridinic nitrogen and abundant graphitized structure,exhibit superior catalytic activity for oxygen reduction reaction(ORR) with half-wave potential(E_1/2) of 0.85 V and durability in terms of the minimum current loss(2%) after the 30,000 s test.Our development provides a new pathway for large-scale and cost-effective preparation of metal-doped CNTs for various applications.     

Recent Advances of Pure Organic Room Temperature Phosphorescence Materials for Bioimaging Applications

Bioimaging,as a powerful and helpful tool,which allows people to investigate deeply within living organisms,has contributed a lot for both clinical theranostics and scientific research.Pure organic room temperature phosphorescence(RTP)materials with the unique features of ultralong luminescence lifetime and large Stokes shift,can efficiently avoid biological autofluorescence and scattered light through a time-resolved imaging modality,and thus are attracting increasing attention.This review classifies pure organic RTP materials into three categories,including small molecule RTP materials,polymer RTP materials and supramolecular RTP materials,and summarizes the recent advances of pure organic RTP materials for bioimaging applications.     

Combined QSAR/QSPR,Molecular Docking,and Molecular Dynamics Study of Environmentally Friendly PBDEs with Improved Insulating Properties

To improve the insulating properties of polybrominated diphenyl ethers(PBDEs), we studied the molecular structures and energy gap(Eg) values of 209 PBDEs using a three-dimensional quantitative structure-activity relationship(3D-QSAR) model, molecular docking, and molecular dynamics. We also analyzed the interaction mechanisms of PBDEs using a 2D-QSAR model, molecular substitution characteristics, and molecular docking. The 3D-QSAR model showed that the 2-, 4-, 5-, and 6-positions significantly influenced the PBDE insulating properties. Using BDE-34 as a template molecule, we designed six derivatives with 0.47%-28.44% higher insulation tlian BDE-34. Compared with BDE-34, the stability and flame retardancy of the above six derivatives were not adversely affected. These derivatives, except for 2,6-cyanomethyl-BDE, 2-cyanomethyl-BDE, and 2-aniinomethyl-BDE, were more toxic and biodegradable than BDE-34, but showed weaker bioaccumulation and migration abilities than BDE-34. Mechanism analysis showed that the highest occupied orbital energy, the most negative charge, and the dipole moment were the main quantitative parameters that aflected the PBDE insulating properties. PBDE insulation gradually decreased as the number of Br atoms increased. The level of similarity between the substitution patterns on the two benzene rings was significantly correlated with PBDE insulation, with hydrophobic groups having a more significant efiect on PBDE insulation.     

Novel fusiform core-shell-MOF derived in tact metal@carb on composite:An efficient cathode catalyst for aqueous and solid-state Zn-air batteries

Owing to the varied mechanisms of ORR/OER,exploiting cost-effective bifunctional catalysts with robust ORR/OER activities and excellent performances in Zn-air batteries is still a challenge.In this work,the Co/CoO@NSC bifunctional catalyst is obtained by using Zn-MOF@Co-MOF as self-template.The Co/CoO@NSC composite has interconnected porous architecture with in tact metal@carb on structure,exhibiting superior electrocatalytic activities toward ORR and OER that can be comparable with the Pt/C and RuO₂ catalysts,respectively.The Co/CoO@NSC-based aqueous Zn-air battery achieves a high specific capacity(759.7 mAh/g)and energy density(990.5 Wh/kg),and ultra-long rechargeable property(more than 400 h/1200 cycles).The Co/CoO@NSC-based solid-state Zn-air battery also delivers an excellent performance with a long cycle life(more than 143 h/858 cycles).Most importantly,the newly synthesized and recharged Co/CoO@NSC-based solid-state Zn-air battery can be used to light up a 2 V LED lamp for more than 28 h,demonstrating the superior practicability as rechargeable power source.     

基于吉布斯弯曲界面相平衡判据的开尔文方程推导

对两种界面热力学处理方法(古根海姆法与吉布斯法)进行了介绍。采用吉布斯界面热力学方法建立了存在界面相时两相平衡的热力学判据,并以此为基础提出了一种新的开尔文方程推导方法。     

对球状液滴拉普拉斯公式热力学推导方法的讨论

本文针对球状液滴拉普拉斯公式热力学推导方法进行了讨论分析。首先从界面热力学基本方程的建立方法和界面热力学基本方程中作为偏微分的压强的数学定义两个角度进行分析,得出了液滴界面热力学基本方程中,压强为与之平衡的外界气体压强。另外,从实际发生的物理过程来看,本文所质疑的球状液滴拉普拉斯公式的热力学推导方法采用无外力做功时液滴体积增大d V的过程是明显违反热力学第一定律的。     

平衡时溶液的表面吸附

溶液的表面吸附仍是表面热力学当中的一个具有挑战性的问题.在本文中我们定义了一个新的热力学态函数,表面吸附的平衡条件是这个态函数的微分为零.基于这个条件,我们推导了描述平衡时表面吸附的新方程.在推导过程中没有采用假想分界面.新的表面吸附方程和Gibbs表面吸附方程完全不一样.还通过分子动力学方法模拟了氯化钠溶液,模拟结果和我们的理论预测符合较好.     

Theoretical temperature dependency of gas hydrate former solubility under hydrate-liquid water equilibrium

Available experimental data and current semi-empirical models suggest a positive trend for the gas hydrate former solubility in the bulk liquid phase as a function of temperature under hydrate-liquid water equilibrium. Such a trend has been widely reported without theoretical explanation. This work proposes a comprehensive derivation, based on fundamental thermodynamics, of the gas hydrate former solubility dependency on temperature for any binary system under two-phase equilibrium.     

Some remarks to the derivation of the “generalized Lippmann equation”

In the present communication, an attempt is made to demonstrate (once again) some of the problems with the derivation of the “generalized Lippmann equation” considered to be valid by many researchers for solid electrodes and to address the problems in the framework of the Gibbs model of the interface by using only the basic principles of thermodynamics. By surveying the relevant literature, it has been shown that during the derivation of the equation, it was completely ignored that the Gibbs-Duhem equation (i.e., the electrocapillary equation) is a mathematical consequence which follows directly from the homogeneous degree one property of the corresponding thermodynamic potential function; consequently, the resulting expression cannot be correct. Some alternative approaches have also been considered. The adequacy of the open system and the partly closed system approach has been critically discussed, together with the possibility of introducing new thermodynamic potential functions.

     

Surface Tension: Mechanics,Thermodynamics, and Relaxation Times

A microscopic analysis is presented of the existing definitions of equilibrium surface tension, which can be divided into two types: mechanical and thermodynamic. Each type of definition can be studied from the presentation below according to thermodynamic hypotheses or molecular calculations. An analysis of the planar interface is given and its generalization for curved (spherical) interfaces is considered. The distinction between approaches describing the surface tension of metastable and equilibrium droplets is discussed. Based on nonequilibrium thermodynamics, it is shown that the introduction of metastable droplets is due to a violation of the relationship between the times of impulse and chemical potential relaxation in condensed phases. Problems of calculating the surface tension in nonequilibrium situations are created.     

在非平衡态热力学的基础上探索建立催化理的新途径

平衡态热力学一直被认作多相催化理论的基石之一。但是,它并不能概括工作中的催化剂的状态和行为,这主要是这里还发生一些非平衡过程。催化体系常常处于非平衡状态之下,而非平衡态条件下体系状态和行为,同时取决于体系的动力学和热力学。联系动力学和热力学最一般的关系式并非原来的De Donder不等式：Ar≥0,而是新的De Donde方程ln r^-/r^-=A/RT。同时发生的总反应之间的热力学耦合对总反应的作用只是形式上的,远不及催化反应链中各基元步骤之间在动力学上的耦合那么重要。通过在动力学方程中引入反应亲和力（热力学位）得到的动力学-热力学结合近似分析,可以用来分析非平衡态的催化反应和催化剂状态。非平衡态热力学在建立多相催化理论中,较之原来的平衡态热力学将能提供更能采纳的和更有意义的物理化学背景。     

Thermodynamics of mechanical transduction of surface confined receptor/ligand reactions

Chemomechanics of surface stress is discussed in terms of interfacial thermodynamics. In the first section the paper shows how to quantitatively describe the chemical equilibrium of a receptor/ligand binding reaction confined at a solid-liquid interface and how the overall work of the reaction splits into chemical and surface work, that appears as a surface pressure. In the second section this thermodynamic model is applied to describe the experimental results of microcantilever bending induced by DNA hybridization occurring onto one of its faces.     

Equivalent Potential Functions to Calculate Thermodynamic Equilibria*

The present paper contains an analysis of alternative functions to describe chemical equilibrium. In particular we show the equivalence of equilibrium criteria based on pressure, volume and temperature, and corresponding constraints, with respect to those popularly used in thermodynamics, i.e. those based on the minimization of internal energy, enthalpy, Helmholtz and Gibbs potentials. The analysis emphasizes the role of mathematical virtual procedures in determining the equilibrium conditions and the irrelevance of physico-chemical transformations that bring the system into the equilibrium state. Different examples, including a new derivation of Saha’s equation, are dealt with to validate this conceptual approach. This paper is dedicated to the memory of one of the authors, Giuseppe Petrella, who unfortunately is not with us any more.     

稀溶液中化学势的计算以及渗透压公式的推导

将溶液中某组分化学势的计算方式归纳为两种:(1)利用气液平衡时,溶液中某组分的化学势和气相中该组分的化学势相等这一关系来计算;(2)利用溶液中某组分化学势的全微分表达式直接积分来计算。在此基础上,给出了渗透压公式的一种新推导方式,并指出部分物理化学教材关于渗透压定义(Π=p2-p1)的不合理性以及推导渗透压时存在的不妥之处。