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.     

High Power Density Electric Double Layer Capacitor with Improved Activated Carbon

Introduction　　Recently ,therehasbeenanincreasinginterestinthedevelopmentofelectricdoublelayercapacitors (EDLCs)us inghighlyporouscarbonsastheelectrodematerialsduetotheirpossibletechnologicalapplicationsasenergystoragede vicespossessinghighpowerdensitycapability .1,2 Themainadvantagesofsuchdevicesaretheirpossiblehighratecapa bilityandlongcyclelifeascomparedtorechargeablebatter ies,butitsenergydensityislowerthanthatofrechargeablebatteries.Inordertoobtaintherequiredenergyandpowerdensity,EDLC…     

具特定晶面且大比表面积贵金属纳米晶催化基元的构筑

贵金属纳米晶在电催化等领域具有广泛应用. 其催化活性往往与纳米晶体的表面结构直接相关,而催化剂的贵金属原子利用率与比表面积密切相关. 因小尺寸纳米晶难以保留特定的晶面,而具有特定表面的纳米晶通常结晶成尺寸较大、比表面积比较小的晶体,调控纳米晶的尺寸和表面结构两种策略似乎相互矛盾. 如何可控合成同时具有特定表面结构和大比表面积的贵金属纳米晶具有重要的意义. 本综述从形貌调控角度详细介绍提高贵金属纳米晶原子利用率的方法策略;总结调控单贵金属及其合金同时具有特定晶面和大比表面积的研究现状;最后,对纳米晶的形貌调控领域未来的发展趋势提出展望.     

介孔α-Fe2O3表面配合反应平衡常数测定

采用十二胺为模板剂、氨水做沉淀剂成功制备了介孔α-Fe2O3,通过粉末X射线衍射(XRD)、透射电镜(TEM)、N2吸附/脱附技术对样品晶相、形貌和比表面积进行了表征.根据介孔α-Fe2O3悬浮液的酸碱滴定数据,使用FITEQL软件,采用双电层恒电容模型计算得出了介孔α-Fe2O3的表面酸碱反应平衡常数.在此基础上研究了Cu2+,Pb2+,Zn2+在介孔氧化铁表面的吸附行为,使用WinSGW软件模拟得出了相应的表面配合反应平衡常数并讨论了其吸附机理.     

制备方法对钒磷氧复合氧化物晶相和比表面积的影响

采用水相、有机相及球磨法等不同方法制备了VPO催化剂,使用BET、XRD等测试手段对VPO催化剂的比表面积、晶相结构进行了表征,研究发现水相法制备时,比表面积较小,晶相较复杂,焙烧温度升高,结晶度增加,有机相和球磨法制备时,催化剂的比表面积较大,晶相几乎为(VO)2P2O7,在超临界条件下干燥,可使所有催化剂比表面积显著增大，晶相更完善。     

几种尖晶石型复合氧化物纳米粉体的制备及气敏性

采用化学共沉淀法合成了4种尖晶石型复合氧化物MFe₂O₄(M=Cu²⁺,Zn²⁺,Cd²⁺,Mg²⁺).X射线粉末衍射分析、透射电镜及比表面测定等表征结果表明它们均为具有较大比表面积的纳米粉体,平均粒径<50nm.将样品做成厚膜型气敏元件,测定了其对乙炔、液化石油气、一氧化碳、氢气和乙醇等还原(可燃)性气体的气敏特性。     

纳米氢化钠的热稳定性和化学反应活性

Nanometric sodium hydride (NaH*) possesses a large specific surface area. Its chemical reactivity is in orders of magnitude higher than that of the conmercial one. After heat treatment at 2ll℃, the specific surface area of NaH* becomes smaller whereas its chemical reactivity is even higher. This fact indicates that the specific surface area of NaH* particles is an important but not the only factor for its high reactivity. NaH treated at (400℃, 6h) still retains a specific surface area of 30m2 g-1 and gives fairly high chemical reactivity.     

Verification of gamma-spectroscopy programs: Accuracy and detectability

The newly revised ANSI N42.14^1.2 has provided analysis software developers with a set of well defined, consistent and unbiased procedures designed to evaluate the accuracy and limitations of peak search and peak area analysis programs. This work uses two of the procedures outlined in this standard to evaluate five peak analysis algorithms currently in use in Canberra and Nuclear Data software packages. The first procedure examines a program's behavior as the centroid separation and peak height ratio of a doublet are varied. A previous review of these data³ demonstrated significant peak area inaccuracies at peak separations at or below 1.5 FWHM. We will discuss improvements made to some of these programs and the impact on the doublet results. The second procedure examines a program's behavior as the Compton continuum beneath a fixed peak area is increased. For the same five algorithms we will discuss the dependence of peak area on Compton continuum and also explore the limits of peak detectability.     

石油焦水蒸气气化过程孔隙结构和气化速率的变化

以氮气为吸附质，测定了部分气化石油焦的比表面积、孔容及其随孔径的分布，研究了石油焦的孔隙结构在气化过程中的变化及其对气化反应的影响。结果表明，石油焦的孔主要由微孔组成；水蒸气条件下气化时石油焦的比表面积、孔容随碳转化率增加而不断增大；不同孔隙率和比表面积的石油焦，其气化反应速率曲线变化趋势不同；石油焦的比气化反应速率与孔隙结构有着紧密的关系，比气化反应速率和有效比表面积之间有着较好的线性关系。     

非晶态超微粒子镍合金催化剂的研究 Ⅰ．Ni－B合金的制备及表征

非晶态超微粒子，镍基合金，硼合金，合金催化剂，表征