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.     

Second harmonic generation at the interface of copper tetra-tert-butyl phthalocyanine Langmuir-Blodgett film/metal

As one of the most primitive nonlinear optical phenomena, optical second harmonic genera-tion (SHG) has been investigated for half a century and it has become a very useful spectroscopic tool in the study of surface and interface[1—3]. It was theoretically shown that the SH signal cannot be generated in a centrosymmetric system. However, the generation of SH signal from the centro-symmetric molecules such as fullerene (C60) and CuPc has been detected[4—7]. In our recent ex-periments, an …     

Spectroscopic consideration of the surface potential built across phthalocyanine thin films on a metal electrode

The nonlinear optical properties of tert-butyl phthalocyanine copper Langmuir-Blodgett (CuttbPc LB) films and vacuum-evaporated phthalocyanine copper (CuPc) films deposited on a metal surface were investigated by second-harmonic generation (SHG) spectroscopy. At the organic/metal interface, a space charge field is formed due to the presence of excess charge injected from a metal electrode to the organic layer. Since the Pc molecule has D4h symmetry, an inversion center is present and the optical SH process is not allowed under the electric-dipole approximation. However, the space charge field at the interface directly influences the symmetric structure of the electrons in the Pc molecule. We investigated the contributions of the surface potential to the SHG using Pc LB and vacuum-evaporated films deposited on aluminum (Al) and gold (Au) metal electrodes, where a distinctive difference in the spectrum for the Pc films on the Al and Au surfaces was observed. The contribution of the surface potential was revealed based on the resonant conditions of the SH process, taking into account the electric-quadrupole transition and dc-field-induced electric-dipole transition.     

用激光第二谐振光研究阴离子在多晶铜电极表面上的吸附

首次用激光产生的第二谐振光(SHG)检测到金属/水溶液界面上阴离子在多晶铜电极表面上的吸附,阴离子吸附特性对SHG强度影响明显,由多晶铜电极在(0.5-x)mol/L NaClO_4+xmol/L NaBr溶液中的SHG强度-电位曲线表明铜电极表面对ClO_4~-的吸附非常弱,对Br~-有特定的吸附,SHG强度随Br~-浓度增加而增强,结果表明SHG是定量研究电化学界面区吸附特性的灵敏有效的探针,可揭示金属与吸附质间相互作用的本质。     

Magnetic dipolar interactions in solid gold nanosphere dimers

We report the first observation of a magnetic dipolar contribution to the nonlinear optical (NLO) response of colloidal metal nanostructures. Second-order NLO responses from several individual solid gold nanosphere (SGN) dimers, which we prepared by a bottom-up approach, were examined using polarization-resolved second harmonic generation (SHG) spectroscopy at the single-particle level. Unambiguous circular dichroism in the SH signal was observed for most of the dimeric colloids, indicating that the plasmon field located within the interparticle gap was chiral. Detailed analysis of the polarization line shapes of the SH intensities obtained by continuous polarization variation suggested that the effect resulted from strong magnetic-dipole contributions to the nanostructure's optical properties.     

Pure surface plasmon resonance enhancement of the first hyperpolarizability of gold core-silver shell nanoparticles

We report the optical second harmonic (SH) response from gold core-silver shell nanoparticles supported at a liquid-liquid interface in the spectral region where the second harmonic generation (SHG) frequency is resonant with the surface plasmon (SP) resonance excitation of the nanoparticles. We compare these results with that obtained by classical linear optical absorption spectroscopy and show that the nonlinear optical response is dominated by the SP resonance enhancement with negligible contributions from the interband transitions. As a result, the SH spectrum exhibits two clear SP resonance bands attributed to the two SP resonances of the composite nanostructure formed by the gold core-silver shell nanoparticles. Absolute values of the hyperpolarizabilities are measured by hyper Rayleigh scattering (HRS) and compared that of pure gold nanoparticles. The hyperpolarizability measured at a harmonic energy of 3.0 eV, enhanced through excitation of the high energy SP resonance of the nanoparticle, increases with the silver content whereas the hyperpolarizability measured at a harmonic energy of 2.4 eV, enhanced through the excitation of the low energy SP resonance of the nanoparticle, decreases because of the shift of this resonance away from the harmonic frequency. The hyperpolarizability determined by HRS and the square root of the SHG intensities, scaling with the nanoparticle hyperpolarizability, have similar trends with respect to the silver content indicative of closely related adsorption properties yielding similar surface concentrations at the liquid-liquid interface.     

Second-harmonic generation for studying structural motion of biological molecules in real time and space

SHG and sum-frequency generation (SFG) are surface-selective, nonlinear optical techniques whose ability to measure the average tilt angle of molecules on surfaces is well known in non-biological systems. By labeling molecules with a second-harmonic-active dye probe, SHG detection is extended to any biological molecule. The method has been used in previous work to detect biomolecules at an interface and their ligand-induced conformational changes. Here I demonstrate that SHG can be used to study structural motion quantitatively using a probe placed at a specific site (Cys-77) in adenylate kinase, a protein. The protein is also labeled non-site-specifically via amines. Labeled protein is absorbed to a surface and a baseline SH signal is measured. Upon introducing ATP, AMP or a specific inhibitor, AP(5)A, the baseline signal changes depending on the ligand and the labeling site. In particular, a substantial change in SH intensity is produced upon binding ATP to the amine-labeled protein, consistent with the X-ray crystal structures. In contrast, SHG polarization measurements are used to quantitatively determine that no rotation occurs at site Cys-77, in agreement with the lack of motion observed at this site in the X-ray crystal structures. A method for building a global map of conformational change in real time and space is proposed using a set of probes placed at different sites in a biomolecule. For this purpose, SH-active unnatural amino acids are attractive complements to exogenous labels.     

Structure and growth of thin films of aniline on silver: nucleation and premelting of nanocrystallites, porosity, and crystallization

The structure and growth of thin films of aniline vapor deposited on Ag(111) and Ag(110) surfaces have been examined using optical second harmonic generation (SHG) and linear optical differential reflectivity (DR). Aniline thin films deposited at 90 K give a detectable SH signal that arises from small polycrystallites with orientation anisotropy in the film. Upon annealing, the SH signal decreases, first due to premelting (at approximately 145 K) of the polycrystallites and then sublimation (at approximately 180 K) of the film. Quantitative analysis of the SH intensity change by a premelting model [J. Phys. Chem. 1988, 92, 7241] allows the determination of the average size of the crystallites as 1.1 nm in diameter and containing approximately 45 aniline molecules. The existence of the nanocrystalline structure and its premelting are confirmed by DR experiments. The DR signal around 145 K exhibits change corresponding to an order-disorder transition. Quantitative analysis of the DR data results in the same nanocrystallite size. Experimental observations indicate that films deposited at 90 K contain not only nanocrystallites but also approximately 30% porosity, which can be reduced by annealing. At temperatures above 195 K, micron-size crystallites start to form within the amorphous film, causing a large amount of light scattering while the film sublimates. It appears that, for molecules such as aniline with stronger intermolecular interactions, more enthalpy is released, upon adsorption to the local surrounding molecules, causing them to reorient into crystalline form. The low deposition temperature, on the other hand, prevents diffusion for further crystallization beyond nanocrystallites. The refractive index of the amorphous aniline solid can be determined as 1.68 +/- 0.03.     

Increased interfacial thickness of the NaF, NaCl and NaBr salt aqueous solutions probed with non-resonant surface second harmonic generation (SHG)

Specific ion effects on the nonlinear optical response from the water molecules at the air/sodium halide solution interfaces are measured using non-resonant surface second harmonic generation (SHG). Procedures have been developed to monitor and remove the impurities in the salt solution samples to ensure measurement of small changes in the SHG signal. Quantitative polarization analysis of the measured SHG data indicated that the average orientation of the interfacial water molecules changed only slightly around 40 degrees with the increase of the bulk concentration of the three sodium halides, namely NaF, NaCl and NaBr, from that of the neat air/water interface. The observed significant SHG signal increase with the bulk salt concentration is attributed to the overall increase of the thickness of the interfacial water molecular layer, following the order of NaBr > NaCl approximately NaF. The absence of the electric-field-induced SHG (EFISHG) effect indicated that the electric double layer at the salt aqueous solution interface is much weaker than that predicted from the molecular dynamics (MD) simulations. These results provided quantitative data to the specific anion effects on the interfacial water molecules of the electrolyte aqueous solution, not only for the larger and more polarizable Br(-) anion, but also for the smaller and less polarizable F(-) and Cl(-) anions.     

Layer-by-layer deposited organic/inorganic hybrid multilayer films containing noncentrosymmetrically orientated azobenzene chromophores

Organic/inorganic hybrid multilayer films with noncentrosymmetrically orientated azobenzene chromophores were fabricated by the sequential deposition of ZrO2 layers by a surface sol-gel process and subsequent layer-by-layer (LbL) adsorption of the nonlinear optical (NLO)-active azobenzene-containing polyanion PAC-azoBNS and poly(diallyldimethylammonium chloride) (PDDA). Noncentrosymmetric orientation of the NLO-active azobenzene chromophores was achieved because of the strong repulsion between the negatively charged ZrO(2) and the sulfonate groups of the azobenzene chromophore in PAC-azoBNS. Regular deposition of ZrO(2)/PAC-azoBNS/PDDA multilayer films was verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. Both UV-vis absorption spectroscopy and transmission second harmonic generation (SHG) measurements confirmed the noncentrosymmetric orientation of the azobenzene chromophores in the as-prepared ZrO2/PAC-azoBNS/PDDA multilayer films. The square root of the SHG signal (I(2omega)(1/2)) increases with the increase of the azobenzene graft ratio in PAC-azoBNS as the number of deposition cycles of the ZrO(2)/PAC-azoBNS/PDDA films remains the same, while the second-order susceptibility chi(zzz)(2) of the film decreases with the increase of the azobenzene graft ratio. Furthermore, the present method was successfully extended to realize the noncentrosymmetric orientation of azobenzene chromophores in multilayer films when small organic azobenzene compounds with carboxylic acid and/or hydroxyl groups at one end and sulfonate groups at the other end were used. The present method was characterized by its simplicity and flexibility in film preparation, and it is anticipated to be a facile way to fabricate second-order nonlinear optical film materials.     

Electrodeposition of flattened Cu nanoclusters on a p-GaAs(001) electrode monitored by in situ optical second harmonic generation

In situ optical second harmonic generation (SHG) technique was employed to investigate the shape and density of Cu nanoclusters, which were electrochemically formed on p-GaAs(001) electrode surfaces. Since GaAs is not a centrosymmetric medium, a significant portion of SHG signal arises from the bulk dipole susceptibility, but it was possible to separate a surface-induced signal from a bulk-induced signal by choosing an appropriate experimental geometry and appropriate data processing. The rotational anisotropy (RA) pattern of the SHG signal from a p-GaAs(001) electrode changed in both shape and magnitude during potential cycling in an electrolyte solution containing Cu2+. The surface plasmon-induced SHG signal from Cu nanoclusters deposited on GaAs was attributed to the modulation source for the RA-SHG pattern. More detailed study was carried out with both in situ SHG and ex situ AFM measurements for Cu nanoclusters deposited by potential step. The results showed that the SHG signal at the present optical geometry was sensitive to the number of oblate or flattened Cu nanoclusters with lateral diameter larger than 30 nm and that the SHG enhancement occurred because of resonant coupling between the surface plasmon induced in the flattened Cu nanoclusters and the near-infrared fundamental light.