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.     

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.     

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.     

酵母对抑制剂耐受的系统分析

纤维素生产乙醇的关键问题之一是水解产生的抑制性物质对乙醇发酵具有明显的抑制效应,因而引起了国内外研究者的广泛关注.研究发现,在抑制剂存在下,酵母在基因表达水平,蛋白水平和代谢物水平都有相应的耐受响应,且这些响应错综复杂.从系统角度运用组学的方法研究这一体系将有助于全面深入了解酵母的耐受机制.本文综述了系统研究的思路和方法在酵母对抑制剂耐受方面的研究状况;对主要研究手段和成果进行了回顾;并对酵母发酵乙醇系统分析的前景进行了展望.     

Miniaturized electrochemical sensors and their point-of-care applications

Most of the current analytical methods depend largely on laboratory-based analytical techniques that require expensive and bullky equipment,potentially incur costly testing,and involve lengthy detection processes.With increasing requirements for point-of-care testing(POCT),more attention has been paid to miniaturized analytical devices.Miniaturized electrochemical(MEC)sensors,including different material-based MEC sensors(such as DNA-,paper-,and screen electrode-based),have been in strong demand in analytical science due to their easy operation,portability,high sensitivity,as well as their short analysis time.They have been applied for the detection of trace amounts of target through measuring changes in electrochemical signal,such as current,voltage,potential,or impedance,due to the oxidation/reduction of chemical/biological molecules with the help of electrodes and electrochemical units.MEC sensors present great potential for the detection of targets including small organic molecules,metal ions,and biomolecules.In recent years,MEC sensors have been broadly applied to POCT in various fields,including health care,food safety,and environmental monitoring,owing to the excellent advantages of electrochemical(EC)technologies.This review summarized the state-of-the-art advancements on various types of MEC sensors and their applications in POCT.Furthermore,the future perspectives,opportunities,and challenges in this field are also discussed.     

Stabilizing High-voltage Cathode Materials for Next-generation Li-ion Batteries

The pressing demand for high-energy/power lithium-ion batteries requires the deployment of cathode materials with higher capacity and output voltage.Despite more than ten years of research,high-voltage cathode mate-rials,such as high-voltage layered oxides,spinel LiNi0.5Mn1.5O4,and high-voltage polyanionic compounds still cannot be commercially viable due to the instabilities of standard electrolytes,cathode materials,and cathode electrolyte interphases under high-voltage operation.This paper summarizes the recent advances in addressing the surface and interface issues haunting the application of high-voltage cathode materials.The understanding of the limitations and advantages of different modification protocols will direct the future endeavours on advancing high-energy/power lithium-ion batteries.     

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.     

Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.     

GPC-LALLS研究各类顺丁橡胶的分子量分布

凝胶色谱与激光小角光散射(GPC-LALLS)联用是高聚物表征的有效手段,但将它用来研究橡胶的报导还很少见,这是由于实践中存在着一定的团难。对顺丁橡胶的表征国外曾有一些报导^[1-3]。GPC-LALLS法不仅可以测定试样的几种平均分子量,更有意义的是可以直接测得谱图各区间的分子量,而且溶质的分子量越大,散射光强越高,因此光散射法对大分子特别敏感,本工作利用这方法的特点,克服了技术上的困难,对国内外不同催化体系合成的顺丁胶进行了对比表征,得到了满意的结果。     

聚丙烯酸丁酯-四氢呋喃稀溶液性质

<正> 聚丙烯酸酯是一类具有优良性能和广泛用途的高分子材料。为了探讨材料性能与分子结构的关系,我们用小角激光光散射法、膜渗透压法、稀溶液粘度法及高效体积排斥色谱法研究了聚丙烯酸丁酯的(PBA)稀溶液性质。订定了聚丙烯酸丁酯在四氢呋喃中的极限粘数-分子量关系式。估算了分子的无扰尺寸与热力学参数。证明该聚合物与聚苯乙烯在所用的色谱条件下符合流体力学体积普适标定关系。     

PREPARATION OF MICROPOROUS ULTRA HIGH MOLECULAR WEIGHT POLYETHYLENE (UHMWPE) BY THERMALLY INDUCED PHASE SEPARATION OF A UHMWPE/LIQUID PARAFFIN MIXTURE

Ultra-high molecular weight polyethylene (UHMWPE) with a microporous structure was prepared via thermally induced phase separation (TIPS).Liquid paraffin (LP) was used as a diluent in the preparation of microporous UHMWPE. Small angle laser light scattering (SALLS) and differential scanning calorimetry (DSC) were used to determine the phase separation temperatures,i.e.the cloud points and the dynamic crystallization temperatures,respectively.It was found that the cloudI points were coincident with the cr...     

激光小角光散射测定高聚物的分子量

本工作建议了一种比较方便可行的、用已知瑞利因子的溶剂标定激光小角散射光度计的方法。纯溶剂的瑞利值R_θ与其散射强度比(G_θ/G_0)有如下关系:R_θ/n=φ[(G_θ/G_0)-δ],式中n为溶剂折光指数;φ为仪器常数;δ为与背景有关的参数。以已知瑞利值的甲苯、苯、环己烷、氯仿及四氯化碳的R_θ/n对测定的(G_θ/G_0)值作图,得到了较好的线性关系,从直线斜率可定φ值。以此方法标定的仪器测定了十个聚苯乙烯窄分布试样均得到了满意的结果。     

环形聚苯乙烯的稀溶液性质——Ⅱ. 第二维利系数

第二维利系数(A_2)是表征高分子链段间和高分子溶剂分子间相互作用的参数。对于环形高分子的第二维利系数,最早Casassa曾做过计算。利用“双接触”模型,Casassa计算了环形高分子的第二维利系数(A_(2r))为A_(2r)=(N_αβN~2/2M~2)[1-C_z O(z~2)]式中M为聚合物的分子量,N_α为Avogadro常数,N为高分子链段数,β为表征链段对排斥体积的二元集团积分,Z为排斥体积参数。式中系数C对环形或线形分子数值不同。     

Studies on molecular weight distribution of carbon fiber polymer precursors synthesized using mixed solvents

The molecular weight distributions were estimated for carbon fiber polymer precursors such as poly（acrylonitrile-co -itaconic acid） synthesized by semi batch solution polymerization in mixed solvents media with the azonitrile compounds as initiator under the different ratios of solvent and non solvent from 0.75 to 2.5 in weight.The copolymer was characterized by using Fourier transform infrared spectroscopy（FTIR） and nuclear magnetic resonance（¹H-NMR） analyses.The molecular weight distributions were evaluated by M_v/M_n ratios estimated from viscosity and osmotic measurements,and M_w/M_n estimated from size exclusion chromatography.The molecular weight distributions of these polymers as determined from M_v/M_n and M_w/M_n are 2.9 to 3.2 and 2.0 to 2.5 respectively.The molecular distributions were close to a narrow distribution of 2.0 when the solvent/non-solvent ratio was varied between 1.4 and 2.0.Intrinsic viscosity[?]as a function of molecular weight of poly（acrylonitrile-co-itaconic acid） was evaluated by means of low angle laser light scattering with size exclusion chromatography（SEC-LALLS） and viscometry with SEC（SEC-VISCO）.The relationship between[?]and M_w for poly（acrylonitrile-co-itaconic acid） in DMF at 50℃was[?]= 1.1×10^-5M_w^0.79,where[?]is obtained in dL/g.     

Laser light scattering as GPC detector

The use of low angle laser light scattering (LALLS) as a detector in gel permeation chromatography (GPC) is discussed. The advantage of this technique is primarily based on the ability of LALLS to continously measure the absolute molecular weight and also to detect minute concentrations of high molecular weight species such as microgel. The weakness of the system is in the low sensitivity for low molecular weight material. In this paper, our experience of the KMX-6 from Chromatix illustrates the possibilities for the characterization of polymers by the combination of LALLS and GPC. The applications discussed are mainly from our work with polyethylene and poly(vinyl chloride). Special emphasis is given to the determination of long chain branching and microgel.     

小角激光光散射法测定聚甲基丙烯酸-6-磺己基钠特性粘数-分子量关系

<正> 聚甲基丙烯酸己磺酸钠(PSSHMA)是我们最近合成的,具有较好的抗凝血性能。对于带磺酸基聚合物抗凝血性能的研究,文献报道还不多。我们用羟基己磺酸钠与甲基丙烯酸反应制备了甲基丙烯酸己磺酸钠(SSHMA)新单体,在此异相酯化反应中,使用了四丁基硫酸氢铵(TBAB)作为催化剂,使反应较顺利的进行,得纯单体。经复钙时     

建筑用梳形共聚物分散剂溶液行为的光散射研究

采用激光光散射研究了一种主链为聚丙烯酸侧链为聚乙二醇的梳形共聚物分散剂的一些溶液行为.从静态光散射得出了较为合理的表观重均分子量、均方旋转半径等参数.动态光散射给出了流体力学半径分布及其角度和浓度依赖性.结合静态和动态光散射,上述梳形共聚物分散剂在溶液中的构象也得到初步的表征.通过与描述梳形聚合物的Gay-Raphae模型进行比较表明,这类梳形共聚物溶液在低盐离子和低pH值条件下存在聚集行为,形成以PAA主链为核PEG为壳层的类胶束聚集.     

Size Exclusion Chromatography with Low Angle Laser Light Scattering Detection

Abstract

A review is given of the use of low angle laser light scattering (LALLS) detection in conjunction with size exclusion chromatography (SEC) to measure polymer molecular weight distributions without conventional SEC column calibration methods. A summary of light scattering theory is presented, and instrument configurations and principles of operation are described for two LALLS photometers. Also discussed are the overall performance of the SEC/LALLS technique and data from selected applications.