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.     

Weakly bound complexes of N2O: an ab initio theoretical analysis toward the design of N2O receptors

Ab initio calculations at MP2/6-311++G(2d,2p) and MP2/6-311++G(3df,3pd) computational levels have been used to analyze the interactions between nitrous oxide and a series of small and large molecules that act simultaneously as hydrogen bond donors and electron donors. The basis set superposition error (BSSE) and zero point energy (ZPE) corrected binding energies of small N2O complexes (H2O, NH3, HOOH, HOO*, HONH2, HCO2H, H2CO, HCONH2, H2CNH, HC(NH)NH2, SH2, H2CS, HCSOH, HCSNH2) vary between -0.93 and -2.90 kcal/mol at MP2/6-311++G(3df,3pd) level, and for eight large complexes of N2O they vary between -2.98 and -3.37 kcal/mol at the MP2/6-311++G(2d,2p) level. The most strongly bound among small N2O complexes (HCSNH2-N2O) contains a NH..N bond, along with S-->N interactions, and the most unstable (H2S-N2O) contains just S-->N interactions. The electron density properties have been analyzed within the atoms in molecules (AIM) methodology. Results of the present study open a window into the nature of the interactions between N2O with other molecular moieties and open the possibility to design N2O abiotic receptors.     

Theoretical Study of Hydrogen Bonding Interaction of 1:1 Dimer of HNO with HArF

The hydrogen bonding interaction of 1:1 dimer formed between HNO and HArF molecule has been completely investigated in the present study using Second-order M?ller-Plesset Perturbation (MP2) method in conjunction with 6-311+G**, 6-311++G** and 6-311++G(2d,2p) basis sets. The standard and CP-corrected calculations have been employed to determine the equilibrium structures, the vibrational frequencies and interaction energies. The interaction energies of the dimers were also calculated at G2MP2 level. Two stable structures are found as the minima. Dimer I(H···F)is a five-membered cyclic hydrogen bonded structure and is more stable than the Dimer II(H···O). The blue-shifted N-H···F hydrogen bond is confirmed with standard and CP-corrected calculations by the MP2 and DFT methods in conjunction with different basis sets. The results obtained at MP2 in conjunction with different basis sets show there is a red-shifted hydrogen bond (Ar-H···O) in the Dimer II(H···O). The topological and electronic properties, the origin of red- and blue-shifted hydrogen bonds were investigated at MP2/6-311++G(2d,2p) with CP corrected calculations. From the NBO analysis, the reasonable explanations for the red- and blue-shifted hydrogen bonds were proposed.     

H2CO与双卤分子间卤键的电子密度分析

运用B3LYP和MP2方法在6-311++G(d,p)基组水平上, 对H2CO-XY(XY=F2、Cl2、Br2、ClF、BrF、BrCl)卤键体系进行构型全优化, 得到了O…X—Y型卤键复合物. 结果表明, MP2/6-311++G(d,p)计算结果与实验值较吻合. 并在MP2水平下计算了分子间的相互作用能, 用完全均衡校正CP(counterpoise procedure)方法对基函数重叠误差(BSSE)进行了校正. 利用电子密度拓扑分析方法对卤键复合物的电子密度拓扑性质进行了分析研究.     

甲醛与乙腈相互作用的理论研究

在HF/6-311G(d,p)、 MP2/6-311G(d,p)和B3LYP/6-311G(d,p)水平上,对H2CO和CH3CN以及设计的4种结构H2CO…CH3CN复合物等进行几何全优化和振动频率计算,排除振动频率为负值的非局域极小点结构,并对稳定的环状构型复合物结合能进行基组重叠误差校正和零点振动能校正.分子间相互作用的能量分解分析显示,静电能在H2CO...CH3CN相互作用能量中占主导地位,电荷转移能居第二位.     

气相中O3与HSO自由基间的氢键复合物

气相中O3与HSO自由基之间的相互作用及其反应在大气化学中非常重要.在DFT-B3LYP/6-311++G**和MP2/6-311++G**水平上求得O3+HSO复合物势能面上的稳定构型,B3LYP方法得到了三种构型(复合物Ⅰ,Ⅱ和Ⅲ),而MP2方法只能得到一种构犁(复合物Ⅱ).在复合物Ⅰ和Ⅲ中,HSO单元中的1H原子作为质子供体.与O3分子中的端基O原子作为质子受体相互作用,形成红移氢键复合物;而在复合物Ⅱ中,虽与复合物Ⅰ和Ⅲ中具有相间的质子供体和质子受体,却形成了蓝移氢键复合物.B3LYP/6-311++G**水平上计算的单体间相互作用能的计算考虑了基组重甍误差(BSSE)和零点振动能(ZPVE)校正,其值在-3.37到-4.55 kJ·mol-1之间.采用自然键轨道理论(NBO)对单体间相互作用的本质进行了考查,并通过分子中原子理论(AIM)分析了三种复合物中氢键的电子密度拓扑性质.     

气相中O3与HSO自由基间的氢键复合物

气相中O3与HSO自由基之间的相互作用及其反应在大气化学中非常重要. 在DFT-B3LYP/6-311++G**和MP2/6-311++G**水平上求得O3+HSO复合物势能面上的稳定构型, B3LYP方法得到了三种构型(复合物I, II和III), 而MP2方法只能得到一种构型(复合物II). 在复合物I和III中, HSO单元中的1H原子作为质子供体, 与O3分子中的端基O原子作为质子受体相互作用, 形成红移氢键复合物; 而在复合物II中, 虽与复合物I和III中具有相同的质子供体和质子受体, 却形成了蓝移氢键复合物. B3LYP/6-311++G**水平上计算的单体间相互作用能的计算考虑了基组重叠误差(BSSE)和零点振动能(ZPVE)校正, 其值在-3.37到-4.55 kJ·mol-1之间. 采用自然键轨道理论(NBO)对单体间相互作用的本质进行了考查, 并通过分子中原子理论(AIM)分析了三种复合物中氢键的电子密度拓扑性质.     

单电子卤键复合体系H3C···Br-Y(Y=H, CN, NC, CCH, C2H3)的作用机制

对单电子溴键复合物H₃C···Br—Y(Y=H, CCH, CN, NC, C2H3)的结构与性质进行了理论研究. 在B3LYP/6-311++G**水平上计算了稳定构型并做了频率分析. BSSE矫正的相互作用能(E^BSSE)和NBO及AIM分析输入的波函数在MP2/6-311++G**水平下完成. 复合物H₃C···Br—Y中, CH₃(供电子体)自由基均提供一未成对电子与Br—Y中Br(受电子体)形成了单电子溴键, 此单电子溴键也具有“三电子”键的特征. 单电子溴键的形成导致甲基H的背向Y弯曲和Br—Y键的拉长及红移单电子溴键复合物的产生. 考察了电子受体中不同取代基, C(spⁿ)-Br杂化及溶剂的存在对复合物作用的影响, 将单电子氢键, 单电子卤键和单电子锂键的作用强度做了对比, 进一步对Popelier提出的氢键体系中的前三个重要拓扑指标在单电子溴键体系中的重现性进行了探讨.     

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

The characteristics and structures of single-electron halogen bond complexes [H₃C?Br-Y (Y = H, CCH, CN, NC, C₂H₃)] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H₃C?Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH₃ (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a “three-electron bond”. Due to the formation of the single-electron Br bond, the C-H bonds of the CH₃ radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.     

CH2Cl与OH自由基反应机理的理论研究

The reaction mechanism of CH2Cl radical with OH radical to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl has been studied by using quantum chemistry ab initio calculations. The optimized geometrical parameters,and vibrational frequencies of all species were obtained at the UMP2（FC）level of theory in conjunction with 6-311++G* basis set. Besides,the zero-point energies（ZPE）,relative energies and total energies of all species were calculated using Gaussian-3（G3）model. The results of theoretical study indicate that the activated intermediate CH2ClOH is first formed through a barrierless process,followed by atoms migration,radical groups rotation and bonds fission to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl,respectively. And all channels are exothermic by 72.81,338.54 and 354.08 kJ/mol. The reaction heat of reactants to H2CO+HCl is 281.27 kJ/mol more than that of reactants to HCCl+H2O. This result accords with that of experiments.     

Theoretical investigation of hydrogen bonds between CO and HNF2, H2NF, and HNO

Ab initio quantum mechanics methods were applied to investigate the hydrogen bonds between CO and HNF2, H2NF, and HNO. We use the Hartree-Fock, MP2, and MP4(SDQ) theories with three basis sets 6-311++G(d,p), 6-311++G(2df,2p), and AUG-cc-pVDZ, and both the standard gradient and counterpoise-corrected gradient techniques to optimize the geometries in order to explore the effects of the theories, basis sets, and different optimization methods on this type of H bond. Eight complexes are obtained, including the two types of C...H-N and O...H-N hydrogen bonds: OC...HNF2(C(s)), OC...H2NF(C(s) and C1), and OC...HNO(C(s)), and CO...HNF2(C(s)), CO...H2NF(C(s) and C1), and CO...HNO(C(s)). The vibrational analysis shows that they have no imaginary frequencies and are minima in potential energy surfaces. The N-H bonds exhibit a small decrease with a concomitant blue shift of the N-H stretch frequency on complexation, except for OC...HNF2 and OC...H2NF(C1), which are red-shifting at high levels of theory and with large basis sets. The O...H-N hydrogen bonds are very weak, with 0 K dissociation energies of only 0.2-2.5 kJ/mol, but the C...H-N hydrogen bonds are stronger with dissociation energies of 2.7-7.0 kJ/mol at the MP2/AUG-cc-pVDZ level. It is notable that the IR intensity of the N-H stretch vibration decreases on complexation for the proton donor HNO but increases for HNF2 and H2NF. A calculation investigation of the dipole moment derivative leads to the conclusion that a negative permanent dipole moment derivative of the proton donor is not a necessary condition for the formation of the blue-shifting hydrogen bond. Natural bond orbital analysis shows that for the C...H-N hydrogen bonds a large electron density is transferred from CO to the donors, but for the O...H-N hydrogen bonds a small electron density transfer exists from the proton donor to the acceptor CO, which is unusual except for CO...H2NF(C(s)). From the fact that the bent hydrogen bonds in OC(CO)...H2NF(C(s)) are quite different from those in the others, we conclude that a greatly bent H-bond configuration shall inhibit both hyperconjugation and rehybridization.