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.     

新时代背景下省属高校本科生毕业实习-毕业论文-就业一体化教学模式探索与实践

Based on the questionnaire surveys from 306 undergraduates in 11 classes of chemistry major in the last three years, and the exploration and experience of practical teaching for chemistry major at Qingdao University of Science and Technology, a new integrating teaching model of graduation practice, graduation thesis and employment for chemistry major was constructed. The undergraduates can finish the graduation practice and thesis work in the enterprise, and those who perform well can be employed in the enterprise. The elective courses related to the enterprise are set up in the programme of talent cultivation. The double-position teachers in the construction of the teaching staff and the double supervisor in the practical teaching are explored. Through the deep enterprise-university cooperation, the highly skilled and innovative talents needed by society are cultivated, and the employment rate and the stability of employment are increased.     

化学专业师范生实践性知识水平及影响因素调查研究*

基于自主建构的化学师范生实践性知识水平研究模型,采用自编调查问卷,对河北某高校化学专业271名师范生进行问卷调查,运用SPSS 13.0数据统计分析软件进行数据处理,研究结论如下:(1)化学专业师范生在经过系统的理论学习之后,在实习之前,其实践性知识整体和各维度均处于本研究的中等水平;(2)化学专业师范生实践性知识的5个维度之间具有较强的相关性,各维度在一定程度上相互影响、相互制约;(3)教学经验的积累、大学之前的学习经历、自己敬重和喜欢的老师、优质课的观摩、教学案例分析、微格教学技能训练是影响化学专业师范生实践性知识的主要因素。     

普通化学教学改革与探索

结合近几年的普通化学教学实践,我们分析了普通化学教学实践过程中存在的一些问题,并提出了培养学生的创新能力,不断更新教学内容,将理论教学与实验教学相结合等几方面建议。     

药学专业留学生分析化学实验全英文教学的体会

留学生教育已成为我国高等教育的重要组成部分,而全英文教学是无中文基础的留学生的最佳选择。分析化学实验为药学专业本科生的必修课,本文针对药学专业留学生分析化学实验课的全英文教学过程,从课程的教学安排、教材选用、教学师资、授课方式和考评方式等方面讲述了教学实践中的体会,希望为开设同类课程的全英文教学提供借鉴和参考。     

提高非高分子专业高分子化学教学效果的探讨

《高分子化学》是研究高分子化合物合成和化学反应的一门科学,是高分子材料专业的一门重要专业基础课,是应用化学和化学工程与工艺专业等非高分子专业的选修课。本文针对应用化学和化学工程与工艺专业等非高分子专业在高分子化学教学中存在的问题与对策进行了积极的探索与实践。结合多年的教学体会,从如何上第一节课、教学内容的取舍、课外活动的开展以及教学方法和手段的改进等方面总结出了一些行之有效的提高非高分子专业高分子化学教学效果的具体措施。     

非化学专业无机及分析化学理论与实验教学的一致性

在"讲一练二考三"新型教学理念的指导下,结合多年非化学专业无机及分析化学课程理论教学和实验教学的经验,针对无机及分析化学理论课和实验课教学的特点和存在的一些问题,阐述了在无机及分析化学课程教学中理论课教学内容和实验课教学内容相结合的实践探索和体会,以及取得的效果。     

“互联网+教育”助力分析化学课程群建设

在"互联网+教育"和传统课堂教育交融时期,将微课融入传统课堂,逐步向慕课、翻转课程过渡,将专业基础课程和方向课程组建成分析化学课程群新体系,优化教学内容,传授学科思想,提升学生的专业学习兴趣和教学质量。     

新工科背景下湖南大学应用化学专业教学改革研究与实践

新工科背景下我国高校强调宽口径、跨学科和复合型的应用化学学科人才培养。结合我校近年来应用化学专业教学改革研究的实际情况,从专业综合改革、实践教学、创新创业及海外课程等几个方面,总结了应用化学专业本科教学的改革成果。     

面向化学专业的生物化学教学加减法改进

Biochemistry is one of the basic courses involving interdisciplinary content. For chemistry major students, we put forward specific suggestions on improving teaching, namely addition and reduction teaching. This includes streamlining and integrating the teaching content, incorporating the work of the Nobel Prize in chemistry, and adding cutting-edge interdisciplinary works. A teaching feature by combining the classical biochemistry theory and the advanced interdisciplinary research was developed.     

高分子化学课程教学改革与实践初探

高分子化学是高分子材料专业最重要的专业技术基础课之一,既包含了理论基础知识,又注重实验教学。《高分子化学》作为贵州大学高分子材料与工程专业的主干课之一,作者针对高分子化学课程教学内容多、概念多、推导多、关联多等问题,对高分子化学教学现状进行了分析,从教学体系、教学内容、教学方法、考核方式、教材编写等多个方面提出了课程教学改革的一些见解。实践表明,高分子化学课程教学改革与实践探索在激发学生兴趣,提高学生的综合能力上已经初见成效。