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.     

原子吸收光谱法测定皇冠草地上部分的7种微量元素

采用原子吸收光谱法测定了皇冠草地上部分所含微量元素铜、锰、锌、铁、镉、铅、铬.结果表明,皇冠草地上部分含有较丰富的铜、锰、锌、铁,RSD≤4.23％(n=4),加标回收率99.20％～103.00％.     

火焰原子吸收法测定藿香中的微量元素

采用火焰原子吸收法测定了广藿香与土藿香中Ca、Mn、Fe、K、Cu、Mg、Zn七种微量元素的含量.方法的回收率在95.6%～110.0%之间,RSD在0.9%～2.5%之间,具有良好的准确度和精密度.结果表明,广藿香中Mn、Fe、K、Cu、Zn等五种元素的含量较为丰富,特别是Mn、K两种元素的含量远高于土藿香.此测定结果可作为探讨藿香中微量元素的含量与药效相关性的科学依据.     

血清六种微量元素与胃癌的相关性

为研究胃癌患者血清微量元素与胃癌的相关性 ,探讨其在胃癌诊断中的应用 ,取甘肃省武威市 2 0例胃癌患者血清作为胃癌组 (C组 ) ,3 0例当地健康志愿者血清作为对照组 (N组 ) ,用电感耦合等离子体原子发射光谱仪 (ICP -AES)进行了 6种微量元素的测定 ,并将结果用SPSS软件作统计分析。结果表明 ,胃癌组血清微量元素值高于对照组的元素有Cu、Cu/Zn、Fe (P <0 0 1 ) :低于对照组的元素有Zn、Mn (P <0 0 5 )。经Logistic回归分析 ,进入方程的为Zn元素 (P<0 0 5 )。多种微量元素联合诊断胃癌的准确率为 87% ,误诊率为 8%。提示 ,甘肃省武威市胃癌患者血清中Cu、Cu/Zn、Fe的升高以及Zn、Mn的降低与胃癌的发生具有相关性。其中Zn与胃癌的发生关系最为密切 ,且Zn降低可能为胃癌发生的癌前因素。测定血清微量元素值可以作为早期诊断胃癌的一种工具。     

火焰原子吸收光谱法测定黄花菜根中微量元素含量

采用火焰原子吸收光谱法测定了黄花菜根中Ca、Fe、Zn、Cu、Mn、K和Mg 7种金属元素含量.结果表明,在常量元素中K、Ca含量较高,微量元素中Fe、Cu含量较高,7种金属元素含量由高到低顺序分别为:K、Ca、Mg、Fe、Cu、Zn、Mn.加样回收率为98.75％～106.25％,该法操作简单、结果准确,是黄花菜根中...     

8味补阴药补阳药中微量元素Fe、Mg、Zn、Ca、Mn、Cu的测定

采用火焰原子吸收光谱法对补阴药石斛、玉竹、北沙参、女贞子和补阳药肉苁蓉、杜仲、菟丝子、补骨脂8味中药进行Fe、Mg、Zn、Ca、Mn、Cu含量测定。结果表明,以平均值而论Mg、Cu含量补阴药与补阳药相当,Fe、Ca含量补阴药低于补阳药,Zn、Mn含量补阴药高于补阳药。以每味中药而论,补阳药菟丝子Fe含量最高,是其他几味中药的近10倍,补阴药石斛Zn、Mn含量最高,是其他几味中药的3~10倍。补阴药、补阳药药效是相对的,但本实验测定各微量元素含量并没有呈现相对性,因此,补阴药、补阳药的药效与Fe、Mg、Zn、Ca、Mn、Cu微量元素的相关性有待于进一步研究。     

传统藏药材高原香薷的矿质元素分析

对传统藏药材香薷中高原香薷种的17种微量元素进行了分析。结果表明,在高原香薷中人体必需微量元素Cu、Zn、Fe、Mn、Co、Ni、Se等含量较高,尤其以Cu、Fe、Mn元素的含量为高。Na、Ca等宏量元素含量亦较高。     

18种中药中微量元素铁锌锰铜的含量研究

为研究治疗黄褐斑常用中药中Fe、Zn、Cu、Mn的含量与药效的关系,测定了18种中药材中Fe、Zn、Cu、Mn含量,并用主成分分析法进行分析.结果表明,Fe含量最高,Zn、Mn次之,Cu最少;Zn和Cu的相关系数最大,且Zn与Cu比均大于1.说明补充Zn可以抑制Cu与酶结合,防治色斑.     

信宜市教育城幼儿园幼儿微量元素营养评估及分析

为了对信宜市教育城幼儿园幼儿微量元素营养进行评估,共采集了教育城幼儿园幼儿239例头发,其中男165例,女74例,用电感耦合等离子体发射光谱法测定头发中的钙、锌、铁、铜、锰和铅的含量,其结果分别为：钙584．844-178．76μg/g,锌178．10±83．38μg/g,铁61．67±17．49μg／g,铜14．03±8．92μg／g,锰2．86±1．73μg／g,铅7．13±2．83μg／g。按照世界卫生组织的四级评估标准进行评估,钙、锌和锰等元素没有发现中度以上的营养缺乏现象,其中铁只有0．4％重度营养缺乏,铜只有8．0％中度营养缺乏,有害元素铅没有发现中度以上超标现象。比对结果,信宜市教育城幼儿园幼儿微量元素营养水平,远优于当地及周边城市的幼儿园幼儿。幼儿园幼儿微量元素营养是否均衡,应作为幼儿园总体评估指标之一。     

青海枸杞子中微量元素含量的测定

测定了青海枸杞子中锌、铜、锰、铅、砷、铁、硒等微量元素的含量。结果表明,青海枸杞子中含锌18.65μg/g,铜15.62μg/g,锰6.24μg/g,铅1.03μg/g,砷0.24μg/g,铁19.68μg/g,硒2.15μg/g,人体必需微量元素含量丰富,是枸杞具有极为重要的保健、防病、治病功能的重要原因之一。     

青海高原道地药材羌活和铁棒锤微量元素含量比较研究

为研究青海高原道地药材羌活和铁棒锤的特性,采用电热板消解法处理样品,原子吸收分光光度法测定了两种药材中Ca、Mg、Cu、Zn、Fe、Mn 6种金属元素的含量。结果表明,Ca、Mg、Cu、Zn、Fe、Mn 6种微量元素含量在两种道地药材中,含量最高的是Ca,平均值分别为(55.78±12.10)mg/g和(26.48±5.79)mg/g;含量最低的元素为Cu,其值分别为(0.28±0.28)mg/g和(0.09±0.06)mg/g;其它元素含量从高到低依次为Mg,Fe,Zn,Mn。可见不同地区的羌活其微量元素的含量有明显的差异,且羌活微量元素含量也存在种间差异,细叶羌活的Ca、Mg元素含量比宽叶羌活的要低,相反,Fe,Cu,Zn 3种元素含量细叶羌活的比宽叶的要高。