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.     

高效发光材料[(C^N)2IrL]+阳离子配合物的结构和光谱特征

从理论上研究了一系列Ir(Ⅲ)[(C^N)2IrL]+[C^N=ppy, L=pzpy(1); C^N=dfppy, L=pzpy(2); C^N=ppy, L=pybi(3); C^N=tpy, L=acac(4); 其中ppy=2-苯基吡啶, dfppy=2-(2,4-双氟苯基)吡啶, pzpy=2-吡唑基吡啶, pybi=1-苯基-2-(吡啶基)-1H-苯并咪唑, tpy=2-(4-甲苯基)-吡啶, acac=乙酰丙酮]配合物的结构和光谱特征. 分别在B3LYP/LanL2DZ和CIS/LanL2DZ计算水平下优化了它们的基态和激发态结构. 计算得到的Ir-N, Ir-C和Ir-O基态键长和相应实验值符合较好. 在激发态下, Ir-N和Ir-C键长增加了约0.0003~0.003 nm, 而Ir-O键长则缩短了约0.0012 nm. 在含时密度泛函理论(TD-DFT)计算水平下, 结合极化连续介质模型(PCM), 得到配合物1~4的最低能的吸收和发射分别出现在398 nm(1), 370 nm(2), 419 nm(3)和437 nm(4)以及511 nm(1), 457 nm(2), 602 nm(3)和479 nm(4). 配合物1, 2, 4的跃迁属于d(Ir)+π(C^N)→π*(C^N)的电荷转移跃迁, 而化合物3的跃迁则归因于d(Ir)+π(C^N)→π*(pybi)的电荷转移跃迁. 这表明此类配合物的吸收和发射主要受前线分子轨道的金属成分控制, 同时也受辅助配体L的影响.     

1-甲基胸腺嘧啶A-带结构动力学

获取了1-甲基胸腺嘧啶(MT)涵盖紫外光谱中A带和B带吸收的共5 个激发波长的共振拉曼光谱, 并结合密度泛函理论方法研究了MT的电子激发和Franck-Condon 区域结构动力学. 在TD-B3LYP/6-311++G(d,p)计算水平下, A带和B带吸收被分别指认为π_H→π_L^*/π_H-2→π_L+2^*和π_H→π_L+2^→/π_H-2→π_L^*跃迁. 甲基参与嘧啶环的共轭使MT的A带最大吸收波长λ_max相对于胸腺嘧啶(T)发生明显红移, 并对Franck-Condon区域的动态结构产生一定影响. A带和B带共振拉曼光谱分别被指认为14 个振动模式和11 个振动模式的基频、泛频和组合频. C5＝C6伸缩+C6H12面内弯曲振动v₉, 环变形振动v₁₆和N3C2N1反对称伸缩+C4C5C10反对称伸缩振动v₁₈占据了A带共振拉曼光谱强度的绝大部分. 这表明¹π_Hπ_L^*激发态结构动力学主要沿这些反应坐标展开. 考察了溶剂对共振拉曼光谱的影响, 结果表明, C4＝O9伸缩+N3H11面内弯曲振动v₈的活性与溶剂性质有关, 其激发态位移量随溶剂性质的变化规律与胸腺嘧啶一致.     

以苯基吡唑为主配体的Ir配合物电子结构和光谱性质的密度泛函理论研究

用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)的B3LYP方法对以苯基吡唑ppz为主配体的4种Ir配合物Ir(ppz)₃, Ir(ppz)₂(acac), Ir(ppz)₂(pic)和Ir(ppz)₂(dbm)的电子结构和光谱性质进行了理论研究. 计算结果表明, 辅助配体的改变对Ir配合物的最高占据轨道(HOMO)的影响不大, 但会显著的降低分子最低空轨道(LUMO)的能级, 从而调节Ir配合物的HOMO和LUMO间的能隙. 4种配合物对应的发射跃迁分别为Ir(ppz)₃:d(Ir)+π(ppz)→π*(ppz); Ir(ppz)₂(pic):d(Ir)+(ppz)→π*(pic); Ir(ppz)₂(acac), Ir(ppz)₂(dbm):d(Ir)+π(acacdbm)→π*(acacdbm). 金属配合物的发光颜色可以通过选择合适的辅助配体调节.     

The polarization dependent differential cross sections of the reactions:H+LiH~+(v=0,j=0)→H_2+Li~+ and H~++ LiH(v=0,j=0)→H_2~++Li

<正>Quasi-classical trajectory(QCT) calculations have been carried out to study the generalized polarization dependent differentialcross sections(PDDCSs) for the reactions H + LiH~+(v = 0,j = 0)→H_2 + Li~+ and H~+ + LiH(v = 0,j = 0)→H_2~+ + Li occurring onthe two lowest-lying electronic states of the LiH_2~+ system,using the ab initio potential energy surfaces(PESs) of Martinazzo et al.[3].Four PDDCSs,i.e.,(2π/σ)(dσ_(00)/dω_t),(2π/σ)(dσ_(20)/dω_t),(2π/σ)(dσ_(22+)/dω_t),(2π/σ)(dσ_(21-)/dω_t) have been discussed in detail.     

A MS-CASPT2 study of the low-lying electronic excited states of CH2BrCl

The low-lying singlet excited states of CH₂BrCl have been calculated using multiconfigurational CASSCF, second-order perturbation theory CASPT2 and its multistate extension MS-CASPT2. The CASSCF method shows spurious valence–Rydberg mixing and a wrong order of states. Inclusion of dynamical correlation by single root CASPT2 lowers dramatically the energy of the valences states but does not lead to a complete separation between valence and Rydberg states. This situation is improved by the MS-CASPT2 calculations, which gives two valence states for both A^′ and A″ symmetries below the lowest Rydberg state, corresponding to n(Br)→σ^*(C–Br) and n(Cl)→σ^*(C–Cl) transitions at 6.1 eV (203 nm) and 7.2 eV (173 nm), and being repulsive along C–Br and C–Cl coordinates.     

尿嘧啶和5-氯尿嘧啶1S0→1S2跃迁动态结构的共振拉曼光谱

采用含时量子波包理论的简单模型对5-氯尿嘧啶和尿嘧啶的共振拉曼光谱开展了强度分析拟合, 获得了1(π, π*)激发态的几何结构变化动态特征. 结果表明, 尿嘧啶1S0→1S2跃迁的动态结构特征因5-位氯原子取代而改变. 5-氯尿嘧啶的动态结构特征主要沿C5=C6伸缩振动+C6H12 弯曲振动和N3H9/N1H7弯曲振动+N1C6伸缩振动反应坐标展开, 而尿嘧啶的动态结构特征主要沿嘧啶环的伸缩振动+C5H11/C6H12/N1H7弯曲振动和C4=O10伸缩振动反应坐标展开. π和π*轨道中氯原子的pz电子参与嘧啶环的p-π共轭作用导致了在1(π, π*)激发态上5-氯尿嘧啶的振动重组能更多地配分给嘧啶环的弯曲振动模式和C5=C6伸缩振动模式. 尿嘧啶在甲醇中的激发态动态结构特征与在水中的基本一致, 但波包沿C5H11/C6H12/N1H7弯曲振动+N1C6伸缩振动(υ12)和环呼吸振动(υ17)反应坐标的运动明显增强.     

CH自由基共振增强多光子电离光谱

ＣＨ自由基在燃烧化学、星际化学、化学发光和化学激光研究中占有重要的地位,并且作为最简单的碳氢化合物,ＣＨ自由基是理想的理论计算模型分子,在理论研究领域中也有着重要的地位．因此 ,多年来人们对ＣＨ自由基进行了大量的研究［１ -９］,但是对于ＣＨ自由基,到目前为止大部分局限于低激发态的研究,对于较高激发态的研究报导则很少见．Ｃｈｕｐｋａ等［２ -６］用(２ １)ＲＥＭＰＩ方法获得了ＣＨＤ态的ｖ＝２振动能级光谱．然而后来Ｔｊｏｓｓｅｍ和Ｓｍｙｔｈ［７］测量了同波段的ＲＥＭＰＩ光谱,发现他们测得的光谱谱峰强度与…     

具有T型基块的新型金属-有机配位聚合物Mn3(BTC)2(H2O)9·(H2O)的合成与结构

近年来,金属-有机配位聚合物作为一种新型的微孔晶体材料越来越引起人们的广泛关注．这种材料不仅在结构上有类似分子筛的孔道结构,而且在去除孔道中的溶剂分子后仍能保持骨架的完整性,BET比表面积远大于相似孔道的分子筛,所以它们在吸附、分离、催化和分子识别方面具有潜在的价值．不同于由硅氧或铝氧四面体为骨架的传统分子筛微孔材料,这类晶体材料主要是由金属离子（或金属氧簇）与有机配体（大多数是芳香多酸和多碱）构成的建筑单元通过共价键或者分子间作用力构成的．     

Ion-pair dissociation dynamics of Cl2: adiabatic state correlation

The ion-pair dissociation dynamics of Cl2 -->(XUV) Cl(-)((1)S0) + Cl(+)((3P(2,1,0)) in the range 12.41-12.74 eV have been studied employing coherent extreme ultraviolet (XUV) radiation and the velocity map imaging) method. The ion-pair yield spectrum has been measured, and 72 velocity map images of Cl(-)((1)S0) have been recorded for the peaks in the spectrum. From the images, the branching ratios among the three spin-orbit components Cl(+)((3)P2), Cl(+)((3)P1) and Cl(+)((3)P0) and their corresponding anisotropic parameters beta have been determined. The ion-pair dissociation mechanism is explained by predissociation of Rydberg states converging to ion-core Cl2(+)(A(2)Pi(u)). The Cl(-)((1)S0) ion-pair yield spectrum has been assigned based on the symmetric properties of Rydberg states determined in the imaging experiments. The parallel and perpendicular transitions correspond to the excitation to two major Rydberg series, [A(2)Pi(u)]3d pi(g), (1)Sigma(u)(+) and [A(2)Pi(u)]5s sigma(g), (1)Pi(u), respectively. For the production of Cl(+)((3)P0), it is found that all of them are from parallel transitions. But for Cl(+)((3)P1), most of them are from perpendicular transitions. The production of Cl(+)((3)P2) is the major channel in this energy region, and they come from both parallel and perpendicular transitions. It is found that for most of the predissociations the projection of the total electronic angular momentum on the molecular axis (Omega) is conserved. The ion-pair dissociation may be regarded as a probe for the symmetric properties of Rydberg states.     

Synthesis,Crystal Structure and Photoluminescence of [Gd(C_6NO_2H_5)_3-(H_2O)_2]_(2n)·(nH_5O_2)(nHgCl_5)(2nHgCl_4)·(2nH_2O)

A heterometallic 4f-5d inorganic-organic metal-isonicotinato hybrid Gd(C6NO2H5)3-(H2O)22n·(nH5O2)(nHgCl5)(2nHgCl4)·(2nH2O) 1 has been synthesized via hydrothermal reaction and structurally characterized.Complex 1 crystallizes in the space group C2/c of monoclinic system with four formula units in a cell:a=24.234(8)=b=20.816(7)=c=15.333(3)=β=128.091(8)°=V=6088(3)3=C36H47Cl13Gd2Hg3N6O20=Mr=2260.92=Dc=2.467 g/cm3=S=0.896=μ(MoKα)=10.331 mm-1=F(000)=4216=R=0.0344 and wR=0.0629.The crystal structure analysis reveals that the title complex is characteristic of a one-dimensional chain-like structure.Photoluminescent investigation reveals that the title complex displays a broad and intense emission in the green region.