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.     

Photophysical properties of a novel Ni(II)-diporphyrin in presence of fullerenes: insights from experimental and theoretical studies

The present paper highlights the photophysical aspects of the topologically new Ni(II)-diporphyrin (Ni(2)-1)/fullerene host-guest ensembles. Both absorption and fluorescence studies reveal that Ni(2)-1 undergoes efficient complexation with both C(60) and C(70) in toluene medium. In the fluorescence study, remarkable enhancement of the fluorescence intensity of Ni(2)-1 was observed by the addition of C(60), while normal quenching of fluorescence occurred in case of C(70). From the fluorescence and UV-vis studies, the binding constants of Ni(2)-1 with C(60) and C(70) were determined to be approximately 1.7 x 10(4) and approximately 2.7 x 10(4) dm(3) mol(-1), respectively. Ab initio theoretical calculations reveal that C(70)/Ni(2)-1 complex favor end-on orientation of C(70) rather than side-on approach.     

Calix[4]arene-linked bisporphyrin hosts for fullerenes: binding strength, solvation effects, and porphyrin-fullerene charge transfer bands

A calix[4]arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26,000 M(-1) for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane < cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of DelatH and DeltaS and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer.     

Nonlinear optical transmission properties of C60 dyads consisting of a light-harvesting diphenylaminofluorene antenna

Highly enhanced nonlinear absorption cross section values of C60(>DPAF-C2M), C60(>DPAF-C9), and C60(>DPAF-C10) dyads were detected up to 5400, 9700, and 14000 GM, respectively, in the 2.0 ps region in toluene at the concentration of 1.5 x 10(-3) M. They were correlated to a trend showing higher efficiency in light transmittance attenuation down to 39-46% for the dyads C60(>DPAF-C10) and C60(>DPAF-C9) with the increase of irradiance intensity up only to 140 GW/cm(2). The phenomena were attributed to additional enhancement on the excited-state absorption of (1)C60*(>DPAF-Cn ) in the subpicosecond to picosecond region over the two-photon absorption of C60(>DPAF-Cn ) in the femtosecond region. Its accumulative 2.0 ps absorption cross sections were estimated to be 8900 GM for (1)C60*(>DPAF-C9), roughly one order of magnitude higher than its intrinsic femtosecond 2PA cross sections.     

Effect of tetraalkylammonium salts on the tacticity of poly(methyl methacrylate), 1. Initiation by ethyl α-lithioisobutyrate

The anionic polymerization of methyl methacrylate (MMA) was carried out in the presence of ethyl α-lithioisobutyrate (α-LiEtIB)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran/toluene (vol. ratio 75/25) at −60°C. It was found that the tacticity of PMMA strongly depends on size and shape of QAS. A highly isotactic polymerization in toluene was observed, when using the system α-LiEtIB/trimethylhexadecylammonium bromide. The initiator system α-LiEtIB/tetrahexylammonium chloride produces polymers with a high (>50%) syndiotactic content and relatively low polydispersity. The influence of QAS on the mode of polymerization is due to specific salt effect resulting from the cation exchange reaction, from the participation of the bulky substituent in the primary solvation shell, and ionic aggregation between the growing anion, Q⁺ and LiX.     

Photoinduced intramolecular electron-transfer processes in [60]fullerene-(Spacer)-N,N-bis(biphenylyl)aniline dyad in solutions

Intramolecular photoinduced charge-separation and charge-recombination processes in a covalently connected C60-(spacer)-N,N-bis(biphenylyl)aniline (C60-spacer-BBA) dyad, in which the center-to-center distance of the electron acceptor and electron donor is 15 A, have been studied by time-resolved fluorescence and transient absorption methods. The observed low fluorescence intensity and the short fluorescence lifetime of the C60 moiety of the dyad in PhCN and THF indicate that charge separation takes place via the excited singlet state of the C60 moiety at a quite fast rate and a high efficiency. The nanosecond transient absorption spectra in PhCN and THF showed the broad absorption bands at 880 and 1100 nm, which were attributed to C60(*-)-spacer-BBA(*+). The charge-separated state decays with a lifetime of 330-360 ns in PhCN and THF at room temperature. From temperature dependence of the charge-recombination rate constants, the reorganization energy was evaluated to be 0.77-0.87 eV, which indicates that the charge-recombination process is in the inverted region of the Marcus parabola. With lowering temperature, the contribution of charge separation via the excited triplet state of the C60 moiety increases due to an increase in solvation of C60(*-)-spacer-BBA(*+).     

Determination of binding strength for the supramolecular complexation of a designed bisporphyrin with C60, C70 and their derivatives employing absorption spectrophotometric, fluorescence and quantum chemical calculations

The present paper reports the synthesis of a designed bisporphyrin (1), and its supramolecular complexes with C60, C70 and their derivatives, namely, tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl C70 butyric acid methyl ester (3) in toluene medium. C60, C70 and their derivatives undergo ground state non-covalent interaction with 1 is evidenced from absorption spectrophotometric study in which it is observed that the intensity of the Soret absorption band of 1 decreases considerably in presence of C60, C70 and their derivatives. Steady state fluorescence studies reveal efficient quenching of fluorescence of 1 in presence of fullerenes. The binding constant (K) values of the fullerene/1 complexes follows the trend: 2/1相似文献   

Conformational behaviour of poly(2,6-dimethyl-1,4-phenylene oxide) in solution—II. Sedimentation coefficients and permeabilities in the semi-dilute region as a function of temperature

Sedimentation and flotation coefficients of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) solutions have been measured as a function of temperature between 60 and 25°. The solvents were toluene and trichloroethane (TCE). Solvent permeabilities have been calculated from the sedimentation or flotation coefficients. PPO is less permeable to the solvents used than polystyrene of comparable molecular weight is to toluene and cyclohexane. Strong solvation of toluene and TCE by PPO molecules is proposed as an explanation for this finding. The measured permeabilities were used to check an earlier calculation of the change of radius of gyration with temperature from intrinsic viscosity data. A larger decrease in radius of gyration with increasing temperature has been calculated in this way than with the earlier assumption of essentially impermeable polymer coils, i.e. with the assumption of the value 2.5 × 10²³ for the universal viscosity parameter Φ₀.     

C60-多吡啶Ru(II)配合物电子光谱的密度泛函理论研究

应用密度泛函理论(DFT)方法对两种C60-多吡啶Ru(II)衍生物进行理论研究. 在TZP全电子基组优化构型基础上, 通过分析前线轨道组成, 探讨金属及配体对C60母体影响; 以LB及SAOP校正局域密度近似, 用含时密度泛函(TDDFT)方法, 考虑溶剂化效应, 计算化合物1和2的电子吸收光谱. 结果表明, 化合物1和2在气相与丙酮溶液中所对应的光谱值差异较为明显, 溶剂化效应使吸收光谱蓝移. 计算得到化合物1和2在丙酮溶液中电子光谱与实验值吻合较好, 低能跃迁多为金属参与的混合跃迁, 高能跃迁主要由C60与配体部分贡献.     

Absorption of toluene in poly(aryl-ether-ether-ketone)

The absorption and swelling of poly(aryl-ether-ether-ketone) (PEEK) in toluene as a function of resin morphology and temperature in the range 35–95°C was investigated. In all cases the weight gain curves exhibit three characteristics: (1) an induction period, which is a strong function of both temperature and initial crystallinity, (2) a main absorption region, which is linear with square-root time, and (3) a final equilibrium value, namely, solubility. The solubility of amorphous PEEK decreases with temperature and the heat of solution is ?0.93 kcal/mol. The induction period varies with the fourth power of the crystallinity and decreases with temperature with an apparent activation energy of 50 kcal/mol. The strength of the interaction between the crystalline regions is markedly reduced at temperatures greater than 80°C. Swelling accompanying the absorption of the toluene is highly anisotropic with most of the dimensional changes occurring in the thickness direction. The deswelling process, however, is essentially isotropic. The concentration of toluene in solution has a strong effect on the transport process; the equilibrium solubility of toluene in amorphous PEEK immersed in a toluene/iso-octane mixture is a linear function of toluene concentration; but the pseudo-diffusion coefficient for the absorption of toluene varies approximately with the fourth power of its concentration.     

First study on the thermo-solvatochromism in aqueous 1-(1-Butyl)-3-methylimidazolium tetrafluoroborate: a comparison between the solvation by an ionic liquid and by aqueous alcohols

The thermo-solvatochromic behaviors of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, RB; 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl) phenolate, WB; 2,6-dibromo-4-[( E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr 2; 2,6-dibromo-4-[( E)-2-(1-n-octylpyridinium-4-yl)ethenyl] phenolate, OcPMBr 2, have been investigated in binary mixtures of the ionic liquid, IL, 1-(1-butyl)-3-methylimidazolium tetrafluorborate, [BuMeIm][BF 4], and water (W), in the temperature range from 10 to 60 degrees C. Plots of the empirical solvent polarities, E T (probe) in kcal mol (-1), versus the mole fraction of water in the binary mixture, chi w, showed nonlinear, i.e., nonideal behavior. Solvation by these IL-W mixtures shows the following similarities to that by aqueous aliphatic alcohols: The same solvation model can be conveniently employed to treat the data obtained; it is based on the presence in the system-bulk medium and probe solvation shell of IL, W, and the "complex" solvent 1:1 IL-W. The origin of the nonideal solvation behavior appears to be the same, preferential solvation of the probe, in particular by the complex solvent. The strength of association of the IL-W complex, and the polarity of the IL are situated between the corresponding values of aqueous methanol and aqueous ethanol. Temperature increase causes a gradual desolvation of all probes employed. A difference between solvation by IL-W and aqueous alcohols is that probe-solvent hydrophobic interactions appear to play a minor role in case of the former mixture, probably because solvation is dominated by hydrogen-bonding and Coulombic interactions between the ions of the IL and the zwitterionic probes.