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.     

三氟乙酸对无金属卟啉-苝酰亚胺分子阵列激发态衰变过程的影响

用紫外-可见吸收光谱和荧光光谱研究了CF₃COOH浓度变化对CHCl₃溶液中N-[p-5′-(m^-10′,15′,20′-三苯基卟啉)基]-N′-正十二烷基-3,4:9,10-四羧基二酰亚胺分子阵列(TrPP-MDPTCDI)的光致激发态衰变机理的影响,发现无论激发无金属卟啉还是酰亚胺基元,分子阵列均表现出质子化无金属卟啉生色团的特征荧光发射.对电子结构的分析说明质子化使[H₂²⁺TrPP^*-MDPTCDI]成为各种激发态中相对稳定的物种,因此,未质子化前占主导的从卟啉到酰亚胺基元的光致电子转移衰变途径在质子化后受到有效抑制,激发卟啉生色团(λ=439nm)直接得到[H₂²⁺TrPP-MDPTCDI^*],并以辐射衰变方式回到基态;激发酰亚胺生色团(λ=491nm)得到的[H₂²⁺TrPP^*-MDPTCDI]通过电荷分离态迅速弛豫到[H₂²⁺TrPP^*-MDPTCDI],并辐射荧光,同时伴随少量的从酰亚胺到质子化无金属卟啉生色团的能量转移.     

EXCITED STATE pKa BEHAVIOUR OF DAPI. A RATIONALIZATION OF THE FLUORESCENCE ENHANCEMENT OF DAPI IN DAPI-NUCLEIC ACID COMPLEXES*

Abstract— The steady state and time resolved fluorescence of the drug and chromosomal staining agent, 4′,6-diamidino-2-phenylindole dihydrochloride, DAPI, was examined under different solvent conditions. In solutions between pH 3 and pH 9 the fluorescence spectral maximum of DAPI was found at 460 nm. The fluorescence decayed with double exponential kinetics, with decay times of 2.86 and 0.144 ns, at all wavelengths below 550 nm. At 550 nm single exponential decay kinetics with a lifetime of 0.153 ns was observed. The fluorescence spectrum could be resolved into two components, the 2.86 ns component having a spectral maximum near 450 nm and the 0.144 ns component having a spectral maximum near 490 nm. The results are rationalized in terms of there being two different configurations of DAPI, one of which undergoes a rapid protonation of the indole ring by proton transfer from the 6-amidinium group in the excited singlet state. The 0.144 ns component is assigned as the fluorescence from the excited state of the protonated indole ring. The results provide an explanation of the fluorescence enhancement in DAPI-nucleic acid complexes.     

酸碱控制的卟啉-苝酰亚胺分子阵列荧光开关

研究了氯仿溶液中分子阵列N,N-二[对-5′-(间-10′,15′,20′-三苯基卟啉)基-苯基]-3,4:9,10-四羧基二酰亚胺(TrPP-PTCDI-TrPP)在不同浓度的三氟乙酸作用下荧光光谱的变化,质子化无金属卟啉的光致激发态成为各种激发态中相对稳定的物种,因此无论激发无金属卟啉基元(λ=439nm)还是酰亚胺基元(λ=491nm),分子阵列都表现出质子化无金属卟啉生色团的特征荧光发射,酸的引入使激发态下高效率的电荷转移衰变途径被关闭,辐射衰变途径被打开.在溶液中引入三乙胺去质子化使电荷转移衰变途径被打开而辐射衰变途径被关闭,因此分子阵列构成了一个通过酸碱控制的荧光开关.考虑到酸碱中和反应的方便性及分子阵列对不同波段光激发同时敏感的广谱性,该分子阵列开关具有特殊优势.     

Intracellular localization of meso-tetraphenylporphine tetrasulphonate probed by time-resolved and microscopic fluorescence spectroscopy.

The effects of solvent pH on spectral properties and fluorescence decay kinetics were investigated in order to characterize the microenvironment of meso-tetraphenylporphine tetrasulphonate (TPPS4) taken up by cells. Steady-state absorption and fluorescence spectra of TPPS4 in buffer solutions of different pH were used to identify a ring protonated species at pH less than or equal to 4. This dictation could also be distinguished from the unprotonated form by its altered fluorescence decay time (3.5 vs. 11.4 ns). In addition, time-resolved spectroscopy gave some evidence of a monocationic species existing at pH 6-9. This was concluded from the occurrence of another component with a decay time of 5 ns. Measurements of the spectral and kinetic properties of the fluorescence emission of single epithelial cells (RR1022) incubated with TPPS4 indicated that the sensitizer was mainly localized in a microenvironment with a pH of 5, a value which occurs intracellularly only within lysosomes. Cells kept in the dark exhibited the characteristic spectra of both the dication and the neutral form. The fluorescence decay showed two components with decay times of 2.6 ns and 10.6 ns. Irradiation of the cells changed the decay times to 4.6 ns and 13.4 ns and the dication fluorescence emission peak vanished, which is in accordance with the results obtained from buffer solutions at pH greater than or equal to 6. Therefore, we deduce that the photodynamic action leads to a rupture of the lysosomes and that the sensitizer is released into the surrounding cytoplasm.     

NANOSECOND LASER PHOTOLYSIS OF RHODOPSIN AND ISORHODOPSIN

Kinetic and spectral measurements have been carried out on the primary intermediate in the photolysis of rhodopsin and isorhodopsin, initiated by a 457 nm, 6 ns (FWHM) laser pulse. In rhodopsin the kinetic decay of bathorhodopsin was found to be 140 ± 15 ns at 20°C. The decay of bathorhodopsin to lumirhodopsin has an activation energy of 51 ± 4 kJ/mol (12.2 ± 1 kcal/mol). The decay kinetics of bathorhodopsin were found to be the same for rhodopsin in membrane and detergent solubilized suspensions. The kinetic decay of the batho product in the photolysis of isorhodopsin was found to be the same as rhodopsin.
The corrected transient spectrum 50 ns following excitation in rhodopsin has two peaks near 560 and 440 nm. A peak was also observed in isorhodopsin near 550 nm at 50 ns following excitation but no transient was observed in the blue. The 550 nm peak in isorhodopsin has an intensity similar to that in rhodopsin indicating that the quantum yields for the formation of batho products of rhodopsin and isorhodopsin are similar under the irradiation conditions used here. Transient spectra for rhodopsin and isorhodopsin 1 μs following excitation are also different. In isorhodopsin the corrected transient spectrum has a peak at 500 nm, similar to low temperature steady state irradiation spectra. The 1 μs transient spectrum in rhodopsin is more intense than in isorhodopsin and shows a peak at 475 nm.     

Pulse radiolysis studies of 4,7-phenanthroline(II)

The one-electron reduction of 4,7-phenanthroline (P) in aqueous solutions at neutral pH has been further studied by pulse radiolysis. The spectral and kinetic properties of the transient formed due to the reaction of 4,7-phenanthroline with hydrated electron were investigated. The transient absorption spectrum obtained 5μs after the pulse exhibits a broad band with a λ_max at 420 nm. The λ_max is 10 nm blue shift compared with the absorption spectrum obtained at pH 2.9 where the reactant was the protonated form. The bimolecular'rate constant of the reaction of 4,7-phenanthroline with hydrated electron was 0etermined to be (2.2±0.1)×10¹⁰ dm³ mol⁻¹ s⁻¹. It was found that the decay of the transient was mainly following a first-order kinetics. The first-order decay rate constant was determined to be (1.25±0.1)×10⁴s⁻¹.     

Pulse radiolysis of butyl acrylate in aqueous solution

The pulse radiolysis of n-butyl acrylate (nBA) in aqueous solution was studied. The rate constant of the reaction of nBA with hydroxyl radicals was calculated as 1.5×10¹⁰ dm³ mol⁻¹ s⁻¹. The absorption spectrum of the OH^·–nBA adduct appeared to have a broad maximum at 300 nm. This spectrum was attributed to the α-carbon centred radicals. It decayed with the first-order rate constant k=1.5×10⁴ s⁻¹ (pH 10.8). The rate constant of the nBA reaction with hydrated electrons was determined as k=1.6×10¹⁰ dm³ mol⁻¹ s⁻¹. The spectrum of H^·–nBA adduct was similar to that recorded for OH^· adduct. It decayed with first-order kinetics at k=1.0×10⁴ s⁻¹. Spectra of the electron adduct were characterised by the band with a maximum at 285 nm (pH 10.0) or at 280 nm (pH 4.0) with ϵ=10 500 dm³ mol⁻¹ cm⁻¹. In acidic solution, radical anion formed upon addition of hydrated electrons to the nBA molecule, undergoes fast, reversible protonation. The decay of the reversibly protonated electron adduct was a second-order process at k=2.5×10⁹ dm³ mol⁻¹ s⁻¹. This reaction took place at the carbonyl oxygen. Slow, irreversible protonation of the electron adduct at high pH takes place at the β-carbon atom at k=2.9×10⁴ s⁻¹.     

水相中四氯化碳的激光闪光光解研究

利用激光闪光光解技术研究了水相中四氯化碳光分解和光氧化的微观机制,并且指证了水相中四氯化碳受光激发所产生的瞬态光谱中的一些瞬态物种的特征吸收峰。并对这些瞬态物种的行为和归宿进行了研究。研究表明在248nm激光作用下,四氯化碳受光激发将分解为CCl~3^.自由基和Cl^.自由基。CCl~3^.自由基在无氧/有氧条件下的反应途径是不同的:在无氧条件下CCl~3^.自由基将进行偶合反应生成更难于降解的C~2Cl~6;而在有氧条件下CCl~3^.自由基则与O~2反应生成CCl~3O~2^.自由基,而CCl~3O~2^.自由基最终转变为COCl~2,这意味着光氧化能够有效地降解CCl~4。Cl^.自由基基本上不受氧气存在的影响,其归宿是与水分子发生电荷转移反应。     

Kinetics of proton release after flash photolysis of 1-(2-nitrophenyl)ethyl sulfate (caged sulfate) in aqueous solution

The kinetics of proton release after laser photolysis of 1-(2-nitrophenyl)ethyl sulfate (caged sulfate) have been characterized by time-resolved absorbance and photoacoustic methods. The absorbance at approximately 400 nm is observed to rise with a biphasic behavior in which a prompt component (formation of the nitronic acid) is followed by a slower (tau approximately 63 +/- 6 ns) phase (deprotonation of the nitronic acid). The decay of this intermediate occurs with a lifetime which is affected by the pH of the solution and the laser pulse energy. In buffered aqueous solution at pH 7, 20 degrees C the aci-nitro decay rate is 18 +/- 4 s(-1). Protons are released to the solution with rate (1.58 +/- 0.09) x 10(7) s(-1) at neutral pH from the nitronic acid intermediate. From the numerical analysis of the protonation kinetics of suitable pH indicators, we could estimate the pK(a) of the nitronic acid as 3.69 +/- 0.05. At acidic pH, a substantial fraction of the aci-nitro intermediate is in the protonated form and this leads to a biphasic release of protons, with the slower phase being characterized by an apparent rate constant strongly dependent on the pH. The strongly acidic character of the final photoproduct (sulfate ion) means that there is negligible buffering of photoreleased protons.     

FLASH PHOTOLYSIS OF 3-IODOTYROSINE IN AQUEOUS SOLUTION AT pH 5

Abstract— The 3-tyrosinyl free radicals (3-Tyr) and iodine atom are formed by flash photolysis of 3-iodotyrosine (3-Tyr-I) in aqueous solutions at pH 5. The presence of iodine atoms in the medium is characterized by the absorption spectrum and the decay kinetics of I formed when KI is added to the system. In the absence of radical scavengers, the 3-Tyr adds to or reacts with the parent molecule to produce a transient species, probably a radical dimer, which has an absorption maximum at 405 nm. The decay of this transient follows second order kinetics whose rate constant increases with decreasing 3-iodotyrosine concentration. Measurements of the dependence of the transient yield on the concentration of added ethanol indicate that the 3-Tyr radical reacts with ethanol by hydrogen abstraction. The rate constants of reaction of the 3-Tyr radical with 3-iodotyrosine and ethanol are deduced from results.