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.     

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.     

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.     

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.     

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.     

闯关式与翻转式结合的课堂教学方法——以化工原理课程为例

Flipped classroom and open classroom are both new teaching modes to improve the efficiency of teaching. Based on the combination of these two teaching strategies and the principles of chemical engineering course, this article uses the distillation section as an example to illustrate the implement process of this teaching mode. In light of the characteristics of the principles of chemical engineering course, we design and introduce the combination of the flipped and open classroom into teaching, and results of this strategy, mainly including teaching analysis, teaching strategy, teaching process and effectiveness. We come up with teaching methods and modes that are well suited to the learning characteristics of undergraduates, aiming to provide references.     

“SPOC+翻转课堂+传统课堂+全过程考核”混合教学模式——以近代化学基础(有机化学)课程教学实践为例

In this paper, we summarized the problems of traditional teaching mode in the course of fundamentals of modern chemistry (organic chemistry) and explored a mixed teaching mode that combines SPOC, flipped classroom, traditional classroom and whole process examination. The practical results show that this model is helpful for the improvement of teaching quality and worth popularizing.     

现代教育技术构建氧化还原反应线上实验教学的策略探索与实践

In the era of "Internet +", with the help of national excellent MOOC course of Chinese university and Mlabs-virtual experimental software, Tencent classroom is built to provide a diversified and efficient online inorganic chemistry basic laboratory classroom by combining a variety of modern education technologies with the concept of flipped classroom. Taking the redox reaction experiment as an example, we designed a multi-link teaching process and carried out a multi-faceted assessment. The online teaching can not only strengthen the cultivation of students' comprehensive and innovating ability, but also help teachers to update the teaching mode and create the new experimental content in line with the development of the times, so as to realize the mutual learning between teachers and students in the exploration of experimental teaching reform.     

分析化学在线课堂引入实验视频教学模式改革

The current situation of analytical chemistry teaching and reform, as well as some problems in micro-videos of online classroom was analyzed. In order to solve these problems, short experimental videos were introduced to the online classroom to demonstrate experimental methods. The new teaching mode achieves mutual integration and promotion of the classroom teaching and laboratory teaching, providing opportunities and challenges for the teaching reform of chemistry online course. The results of the teaching reform were investigated and analyzed by questionnaire.     

基于雨课堂的任务导向式化学专业英语教学模式探索与实践

针对传统化学专业英语教学中存在的问题,提出将任务导向与雨课堂相结合的教学模式运用到专业英语课程的教学中。分析了任务导向与雨课堂相融合的特点,阐述了在专业英语教学中实施以雨课堂为基础的任务导向式教学环节与方法,利用问卷调查和定性对比方式考查了教学效果。结果发现,该教学模式能够显著地提高课堂气氛、师生互动度和学生参与度;融合雨课堂能显著提高任务教学的效果;雨课堂能一定程度地改善日常教学管理;该教学模式对学生兴趣和学业成绩的提高具有促进作用。     

"课程思政"背景下有机化学教学模式探索

有机化学是化学化工及相关专业的重要基础课程,复杂的反应与深奥的理论使其成为理工科院校中较难掌握的课程之一。在当今高校青年学生成长的时代特征与大的社会背景下,只重视专业讲授、轻思想教育的课堂模式,已经跟不上时代的要求。理工科专业课程教师在教授专业内容的同时,把思想引领与价值观塑造融入专业教学中,将教学与育才有机地融合,能极大提升课堂教学效果与质量,有利于培养素质过硬的专业人才。本文从化学史与化学热点问题分析两个角度,阐述了开展有机化学课程思政的具体方法举措,并对实际效果进行了研究分析。     

利用无机化学在线课程资源，开展翻转课堂的教学实践

During the years of 2015 to 2018, the inorganic chemistry course in Tianjin University has gradually transited from small private on-line course (SPOC) to flipped classroom. Flipped classroom teaching practices were carried out at more than 30 classes at our university by the sufficient use of on-line course resources. These practices effectively improve the quality of teaching, and greatly solve the problem of poor learning initiative and low participation of the students existing in current traditional teaching model. This article in detail introduces and summarizes the following four aspects, including transition of teaching modes, construction of online resources, online and offline supervising, test scores analysis and teaching thought. The effective ways for flipped classroom mode are discussed to improve students' knowledge and learning ability. And it also provides references for teachers to carry out their classroom teaching reform.     

基于中国大学MOOC、慕课堂和QQ群三结合的分析化学课程在线教学实践

中国地质大学(武汉)分析化学课程团队采用国家精品在线开放课程作为课程资源、慕课堂作为智慧教学工具、QQ群作为在线讲授和辅导答疑的平台,成功地开展了分析化学课程在线教学实践。实践表明,基于MOOC、慕课堂和QQ群三结合的在线教学形式受到了学生的欢迎和喜爱,学生普遍易于接受,参与积极性高,初显教学效果较好。     

在线课程与翻转课堂相结合的大学化学混合式教学实践

介绍了自2017年以来天津大学大学化学课程使用在线课程和翻转课堂相结合的混合式教学实践,包括课程的组织模式、翻转课堂内容的选择、翻转课堂课时与课程总课时的比例、期末成绩分析和教学反思等。教学实践结果显示,选取学生在中学化学有一定基础的知识点作为教学内容,课时占课程总课时的30%–50%时进行翻转课堂教学,教学效果明显好于完全传统教学的平行对照班。     

利用有机波谱教学网站iSpec进行游戏化课堂教学的实践*

针对学生在有机化学波谱学学习过程中枯燥、难以形象化的具体情况,介绍一个利用有机波谱在线学习的网站进行游戏化课堂教学的学习活动,以期提升学生在该课程学习中的积极性及学习效果。该教学活动的实施分为课堂和课后进行,主要依托iSpec网站游戏竞赛的答题模式,结合教师课堂教学及学生自主学习,进行相关知识技能的教授,最终提升学生的学习效率与效果。