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.     

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.     

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.     

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.     

Three-dimensionalization via control of laser-structuring parameters for high energy and high power lithium-ion battery under various operating conditions

Laser-structuring is an effective method to promote ion diffusion and improve the performance of lithium-ion battery(LIB)electrodes.In this work,the effects of laser structuring parameters(groove pitch and depth)on the fundamental characteristics of LIB electrode,such as interfacial area,internal resistances,material loss and electrochemical performance,are investigated,LiNi_0.5Co_0.2Mn_0.3O₂ cathodes were structured by a femtosecond laser by varying groove depth and pitch,which resulted in a material loss of 5%-14%and an increase of 140%-260%in the in terfacial area between electrode surface and electrolyte.It is shown that the importance of groove depth and pitch on the electrochemical performance(specific capacity and areal discharge capacity)of laser-structured electrode varies with current rates.Groove pitch is more im porta nt at low current rate but groove depth is at high curre nt rate.From the mapping of lithium concentration within the electrodes of varying groove depth and pitch by laser-induced breakdown spectroscopy,it is verified that the groove functions as a diffusion path for lithium ions.The ionic,electronic,and charge transfer resistances measured with symmetric and half cells showed that these internal resistances are differently affected by laser structuring parameters and the changes in porosity,ionic diffusion and electronic pathways.It is demonstrated that the laser structuring parameters for maximum electrode performance and minimum capacity loss should be determined in consideration of the main operating conditions of LIBs.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

绿色化学理念在高分子化学实验教学中的渗透

绿色化学是促进人类与自然和谐发展的化学,培养绿色化学意识是实现社会可持续发展的基本要求。高分子化学实验是高等院校高分子材料专业或材料化学高分子方向本科生开设的一门必修课,对学生进行绿色化学教育具有非常有利的条件。文章分析了在高分子化学实验课程中开展绿色化学教育的必要性与可行性;介绍了高分子化学实验教学中开展绿色化学教育的具体措施。通过绿色化学理念在高分子化学实验教学中渗透,在提高学生动手能力的同时,又增强了学生的绿色化学意识。     

计算化学实验的课程建设

With the fast development of theoretical chemistry methodologies and computer hardware and software technologies, computational chemistry has become more and more imperative in chemical science. Accordingly, we have initiated "Computational Chemistry Experiments" course based on "Introductory Computational Chemistry" course developed in the Department of Chemistry, Tsinghua University since 2013, to provide basic training and computational chemistry practices for undergraduate students. The popular quantum chemistry software Gaussian is used as the major tool in the course. We focus on the exploratory feature of computational chemistry, creating initial structures and optimizing geometries, to provide fundamental training for students to comprehend the difference of traditional experimental chemistry and modern computational chemistry. Systematic research training is offered to develop the creative thinking capacity of students in using computational chemistry methods in chemistry education and research.     

充满生机和科学机遇的磷化学研究所

简要地综述了第十五届国际磷化学会议的报告内容，介绍了目前磷化学的主要 研究领域，包括不对称合成、配合化学，生物碱化学，药物化学，农业化学等相关 领域的研究动态及新进展。     

化学:人类生存和发展的基础——以诺贝尔化学奖为线索

截止2020年诺贝尔化学奖共颁发了112次,其见证了化学学科的发展历程、化学学科与人类生活密不可分的联系,以及化学学科发展的最前沿。以诺贝尔化学奖为主线,联系诺贝尔化学奖趣闻,讲解化学学科将是人类生存的基础,乃至对人类社会和生存发展做出的重要贡献,可以使大家认识到化学学科的重要性,并且更加了解如何进行化学研究,促进化学学科的长足发展。     

Emergences of supramolecular chemistry: from supramolecular chemistry to supramolecular science

We describe the field of supramolecular chemistry as a consequence of the progress of chemistry from its premises to recent achievements. Supramolecular chemistry has been claimed to be an emergent field of research taking its roots in chemistry. According to the definitions of emergences related to hierarchy or more recently to scope, supramolecular chemistry is shown to have bottom-up or top-down emergences. The bottom-up emergence, directly related to hierarchy by definition, opens up the world of nanochemistry and nanomaterials while the top-down one, attributable to scope due to the implication of supramolecular chemistry in other fields of research, open the world of supramolecular biochemistry. Both emergences lead supramolecular chemistry to become a supramolecular science. Combining supramolecular chemistry with biology opens new direction in the study of life and it origin.     

化学教学新课堂：科学抗疫中的化学知识

As the break out of COVID-19 epidemic, the prevention and control work was consequently carried out. Chemistry plays an important role in the white war. The structure of mask contains the knowledge of interfacial chemistry. The material of mask encompasses the knowledge of polymer chemistry. Nucleic acid test and COVID-19 vaccine research need the knowledge of biological chemistry. The sanitizers involve the knowledge of inorganic and organic chemistry. The knowledge of physical chemistry takes effect in daily hand washing with soap. Each drug against COVID-19 virus was a complex organic compound. All the above things can be taken as appropriate examples in chemistry teaching to display the charm of chemistry. Meanwhile, these examples help students to realize that chemistry works as a vital part in our lives and therefore active their motivation to study chemistry well.     

计算化学辅助无机化学课堂教学模式的探索

According to the characteristics of inorganic chemistry and in view of the current problems in classroom teaching of inorganic chemistry, the computational chemistry assisted teaching model has been introduced in this paper. The implementation of this innovative model is not only helpful for students to understand the difficult knowledge of inorganic chemistry, but also popularize the practical application of computational chemistry, which provides an opportunity for the establishment of the big data platform of chemistry in colleges and universities.     

理论化学与下世纪“化学学科重组”前瞻

本文展望了理论化学的发展趋势并预言了下个世纪“化学学科的重组”。作者建议了现代化学的定义：化学是研究从原子,分子片,分子,超分子,生物大分子到分子的各种不同尺度和不同程度的聚集态的合成和反应,分离和分析,结构和形态,物理性能和生物活性及其规律和应用的科学． 根据这个定义,从化学的研究对象不同,在２１ 世纪化学分支学科可能发生重组,因此化学可以划分为如下八个层次：１） 原子层次的化学; ２） 分子片层次的化学; ３） 分子层次的化学; ４） 超分子层次的化学; ５）生物与分子层次的化学; ６） 宏观聚集态化学; ７） 介观聚集态化学和８） 复杂分子体系的化学     

计算化学数据与图形在普通化学教学中的运用

In view of the fact that there are no physical chemistry and structural chemistry courses in most of the non-chemistry department, the knowledge of computational chemistry of the college students is very limited. It is beneficial to quote some simulation research contents of computational chemistry properly in general chemistry teaching process. This will broaden students' vision, promote students' enthusiasm for learning, update the content of general chemistry teaching, cultivate the thinking ability, and finally improve the quality of teaching.     

《高分子化学》教学中有机化学知识的有效利用探索

高分子化学和有机化学紧密相连,后者是学习前者的基础.在高分子化学教学中,有效利用有机化学知识解释聚合物的一些概念,将有助于学生更好的理解和掌握高分子化学知识.本文根据教学实践,介绍了几点利用有机化学知识帮助解释高分子化学中的概念或反应的实例,并对教材中存在的疑点提出了自己的看法.