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1.
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. 相似文献
2.
Zhixin Jin Bin-Bin Yu Min Liao Di Liu Jingwei Xiu Zheng Zhang Efrat Lifshitz Jiang Tang Haisheng Song Zhubing He 《Journal of Energy Chemistry》2021,(3)
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. 相似文献
3.
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. 相似文献
4.
Bingshuai Liu Huang Zhou Huihui Jin Jiawei Zhu Zhe Wang Chenxi Hu Lvhan Liang Shichun Mu Daping He 《中国化学快报》2021,32(1):535-538
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(E1/2) 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. 相似文献
5.
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. 相似文献
6.
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. 相似文献
7.
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. 相似文献
8.
Pengqing Bi Shaoqing Zhang Tong Xiao Minghuan Cui Zhihao Chen Junzhen Ren Chaochao Qin Guanghao Lu Xiaotao Hao Jianhui Hou 《中国科学:化学(英文版)》2021,64(4):599-607
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. 相似文献
9.
Junsu Park Hyeongi Song Inseok Jang Jaepil Lee Jeongwook Um Seong-guk Bae Jihun Kim Sungho Jeong Hyeong-Jin Kim 《Journal of Energy Chemistry》2022,(1):93-102
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,LiNi0.5Co0.2Mn0.3O2 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. 相似文献
10.
Yang Zhou Aiping Fang Fazhan Wang Huili Li Quansheng Jin Lingjing Huang Chunmei Fu Jun Zeng Zhaohui Jin Xiangrong Song 《中国化学快报》2020,31(2):494-500
Nowadays,tremendous researches have been focused on the core-shell lipid-polymer nanoparticles(LPNs) due to the advantages of both liposomes and polymer nanoparticles.In this work,LPNs were applied to encapsulate brinzolamide(Brz-LPNs) for achieving sustained drug release,improving drug corneal permeation and enhancing drug topical therapeutic effect.The structure of Brz-LPNs was composed of poly(lactic-co-glycolic) acid(PLGA) nanocore which encapsulated Brz(Brz-NPs) and lipid shell around the core.Brz-LPNs were prepared by a modified thin-film dispersion method.With the parameters optimization of Brz-LPNs,optimal Brz-LPNs showed an average particle size of151.23±1.64 nm with a high encapsulation efficiency(EE) of 86.7%±2.28%.The core-shell structure of Brz-LPNs were confirmed by transmission electronic microscopy(TEM).Fourier transformed infrared spectra(FTIR) analysis proved that Brz was successfully entrapped into Brz-LPNs.Brz-LPNs exhibited obvious sustained release of Brz,compared with AZOPT^■ and Brz-LPs.Furthermore,the corneal accumulative permeability of Brz-LPNs significantly increased compared to the commercial available formulation(AZOPT^■) in vitro.Moreover,Brz-LPNs(1 mg/mL Brz) showed a more sustained and effective intraocular pressure(IOP) reduction than Brz-LPs(1 mg/mL) and AZOPT^■(10 mg/mL Brz) in vivo.In conclusion,Brz-LPNs,as promising ocular drug delivery systems,are well worth developing in the future for glaucoma treatment. 相似文献
11.
Ji-Lai Li Cai-Yun Geng Xu-Ri Huang Chia-Chung Sun 《Theoretical chemistry accounts》2007,117(3):417-429
The reaction of atomic radical F with propyne has been studied theoretically using ab initio quantum chemistry methods and
transition state theory. The potential energy surface was calculated at the CCSD(T)/aug-cc-pVDZ (single-point) level using
the UMP2/6-311++G(d,p) optimized structures. Two reaction mechanisms including the addition–isomerization–elimination reaction
mechanism and the directed hydrogen abstraction reaction mechanism are considered. For the hydrogen abstraction reactions,
i.e., the most probable evolution pathway in the title reaction, the HF formation occurs via direct abstraction mechanism
dominantly and the H atom picked up by the atomic radical F should come mostly from the methyl group of normal propyne. On
the other hand, for the addition–isomerization–elimination mechanism, the most feasible pathway should be the atomic radical
F attacking on the C≡C triple bond in propyne (CH3C≡CH) to form a weakly-bound adduct A1 with no barrier, followed by F addition to the C≡C triple bond to form the low-lying
intermediate isomer 5. Subsequently, isomer 5 directly dissociates to P3 H2CCCHF + H via transition state TS5/P3. The other reaction pathways on the doublet PES are less competitive due to thermodynamical or kinetic factors. Furthermore,
based on the analysis of the kinetics of all channels through which the addition and abstraction reaction proceed, we expect
that the competitive power of reaction channels may vary with experimental conditions for the title reaction. The present
work will provide useful information for understanding the processes of atomic radical F reaction with other unsaturated hydrocarbons.
This material is available from author via E-mail. 相似文献
12.
The known reactions between a neutral radical and a neutral closed-shell sigma-type molecule are generally associated with the atom/group-abstraction (e.g., CN, OH reactions) or the carbenoid insertion processes (e.g., CH reactions). In this article, we describe a new type of neutral radical-molecule reaction that feature the nucleophilic addition and elimination mechanism based on the systematic Gaussian-3//MP2(full)/6-31G(d) investigations on the PH(3)CH+HX model reactions (X = CH(3), NH(2), OH, F, CH(2)F, CHF(2), CF(3), NHCH(3)/CH(2)NH(2), OCH(3)/CH(2)OH). The novel properties are found to benefit both from the radical and ylidic characters of PH(3)CH, and the type of reagent HX determines the nucleophilic addition reactivity. The present work is the first study on the chemical reactivity of the ylidic radicals. 相似文献
13.
14.
May Joy Contado Jeanette Adams Nancy J. Jensen Michael L. Gross 《Journal of the American Society for Mass Spectrometry》1991,2(2):180-183
The collision-induced allylic cleavage reactions of deuterium-labeled [M ? H + 2Li)+ and [M ? H]- ions of monounsaturated fatty acids were investigated. Three concerted mechanistic possibilities were considered for this process: a l,4-elimination of a vinylic H, a retro-ene reaction, and a l,4-conjugate elimination. A fourth mechanistic possibility, a two-step radical version of the retro-ene and l,4-conjugate elimination reactions, was also considered. The radical reactions are in accord with the isotopic labeling results and offer certain mechanistic consistencies for cleavage of both C-C allyl bonds; they are expected, however, to have large activation energies. The lower-energy concerted alternatives, the retro-ene reaction for cleavage of the proximal and the l,4-conjugate elimination for cleavage of the distal C-C allyl bond, are also consistent with experimental results. The alternative of two different concerted mechanisms for cleavage of the two allyl bonds, however, is at odds with the charge-remote concept. 相似文献
15.
The mechanisms for the reaction of allyltributylstannane with a number of fragmentation probes, alpha-substituted acetophenones, were studied. All reactions were shown to proceed through free radical chain sequences since they could be initiated by AIBN and inhibited by m-dinitrobenzene (DNB). alpha-Halo- and alpha-(benzoyloxy)acetophenones (I and II, PhCOCR(1)R(2)X; X = F, Cl, Br, OCOPh; R(1), R(2) = H, Me) yielded the allylation products, PhCOCR(1)R(2)CH(2)CH=CH(2)), through a chain sequence involving as the propagation step: an electron transfer from Bu(3)Sn(*) to I and II, fragmentation of the ketyl anion PhCOCR(1)R(2)X(*)(-), and addition of PhCOCR(1)R(2)(*) to allyltributylstannane. The reactions of alpha-(arylsulfonyl)acetophenones (IIIa-c, PhCOCR(1)R(2)Y, Y = SO(2)Tol-p), however, gave a nearly 1:1 mixture of allyl tosyl sulfone and the corresponding ketone, PhCOCHR(1)R(2). The (1)H and (13)C NMR of the reaction mixture between allyltributylstannane and alpha-(p-methylbenzenesulfonyl)isobutyrophenone substantiated the intermediacy of the tin enolate PhC(OSnBu(3))=CMe(2). These results suggested that a radical addition elimination mechanism was involved in the reactions of IIIa-c with allylstannane. The reaction of alpha-phenylthioacetophenone (IV, PhCOCH(2)SPh) gave both the electron transfer and the addition elimination products (PhCOCH(2)CH(2)CH=CH(2), PhCOCH(3)), indicating that both pathways were involved in the formation of the products. 相似文献
16.
A systematic study of the types of fragmentation undergone by internally excited protonated molecules is presented. Two representative functional groups, ethers and ketones, are selected, and both aliphatic and aromatic substituents are examined. The ions are formed by protonation or alkylation in a chemical ionization source, and caused to fragment by collision at high relative kinetic energy. The prevalence of 1,3-rearrangements and the breakdown of the even electron fragmentation rule highlight the ion chemistry uncovered here. Specific findings include: (i) electron unpairing reactions associated with alkyl radical loss are common. These are probably energetically less favorable simple bond cleavages and are observed in competition with entropically less favorable elimination reactions. (ii) Alkane elimination is a characteristic reaction, which often occurs by a four-centered mechanism. Several variations on this reaction type are encountered. (iii) Alkene elimination is another ubiquitous reaction which occurs by a four-centered mechanism in the systems studied here. Competition between alkene and alkane loss is extremely sensitive to the particular system in hand. 相似文献
17.
1,1,2,2,3,3,4‐Heptafluorocyclopentane (F7A) has considerable potential to be a new halon replacement due to its environmental friendliness and low‐toxicity. However, the reaction processes of F7A with hydroxyl and hydrogen free radicals, which are of great importance for investigating its fire suppression mechanisms, are still unclear. In this paper, ab inito and density functional theory are used to deduce the possible reaction pathways for the reactions of F7A with hydroxyl and hydrogen free radicals at the CCSD/cc‐pVDZ//B3LYP/6‐311++G (d,p) level of theory. Two distinct reaction pathways including ten elementary reaction channels for F7A with hydroxyl free radical, and five distinct reaction pathways including twenty elementary reaction channels for F7A with hydrogen free radical are investigated. The geometries, vibrational frequencies and reaction energy barriers are also determined. Based on the calculated results, the possible reaction mechanisms are proposed and discussed. The most feasible reaction channel for F7A with hydroxyl free radical is that leads to CH(OH)CH2(CF2)3+·F, and the most feasible reaction channel for F7A with hydrogen free radical is that leads to (CF2)3CH2CH·+HF. The study is helpful to further study its fire suppression mechanisms and promote it to be a new generation of halon replacement. 相似文献
18.
The outcomes of radical cyclizations and Heck reactions of N-(cyclohex-2-enyl)-N-(2-iodophenyl)acetamides depend critically on the configurations of the chiral axis and the stereocenter. In substrates without an ortho-methyl group, the diastereomeric precursors interconvert slowly at ambient temperatures. Cyclization of enriched mixtures of diastereomers provided similar yields of acetyl tetrahydrocarbazoles or dihydrocarbazoles, suggesting that interconversion of the radical or organometallic intermediates also occurs. Diastereomers of N-(cyclohex-2-enyl)-N-(2-iodo-4,6-dimethylphenyl)acetamides with an additional ortho-methyl group did not interconvert at ambient temperatures and were readily resolved. In radical cyclizations, syn diastereomers were prone to cyclize, while anti isomers were not. Strikingly, Heck reactions gave the opposite result; anti isomers were prone to cyclization and syn isomers were not. Heck reactions of allylic acetates occur with β-hydride elimination when acetate is trans to palladium and with β-acetoxy elimination when acetate is cis. This is surprising because prior studies have suggested that a trans relationship of palladium and acetoxy is essential for acetate elimination. Analyses of the results provide insights into mechanisms for radical cyclization and for insertion and elimination in the Heck reaction. 相似文献
19.
20.
Sperotto E van Klink GP van Koten G de Vries JG 《Dalton transactions (Cambridge, England : 2003)》2010,39(43):10338-10351
The copper-mediated aromatic nucleophilic substitution reactions developed by Fritz Ullmann and Irma Goldberg required stoichiometric amounts of copper and very high reaction temperatures. Recently, it was found that addition of relatively cheap ligands (diamines, aminoalcohols, diketones, diols) made these reactions truly catalytic, with catalyst amounts as low as 1 mol% or even lower. Since these catalysts are homogeneous, it has opened up the possibility to investigate the mechanism of these modified Ullmann reactions. Most authors agree that Cu(I) is the true catalyst even though Cu(0) and Cu(II) catalysts have also shown to be active. It should be noted however that Cu(I) is capable of reversible disproportionation into Cu(0) and Cu(II). In the first step, the nucleophile displaces the halide in the LnCu(I)X complex forming LnCu(I)ZR (Z = O, NR′, S). Quite a number of mechanisms have been proposed for the actual reaction of this complex with the aryl halide: 1. Oxidative addition of ArX forming a Cu(III) intermediate followed by reductive elimination; 2. Sigma bond metathesis; in this mechanism copper remains in the Cu(II) oxidation state; 3. Single electron transfer (SET) in which a radical anion of the aryl halide is formed (Cu(I)/Cu(II)); 4. Iodine atom transfer (IAT) to give the aryl radical (Cu(I)/Cu(II)); 5. π-complexation of the aryl halide with the Cu(I) complex, which is thought to enable the nucleophilic substitution reaction. Initially, the radical type mechanisms 3 and 4 where discounted based on the fact that radical clock-type experiments with ortho-allyl aryl halides failed to give the cyclised products. However, a recent DFT study by Houk, Buchwald and co-workers shows that the modified Ullmann reaction between aryl iodide and amines or primary alcohols proceeds either via an SET or an IAT mechanism. Van Koten has shown that stalled aminations can be rejuvenated by the addition of Cu(0), which serves to reduce the formed Cu(II) to Cu(I); this also corroborates a Cu(I)/Cu(II) mechanism. Thus the use of radical clock type experiments in these metal catalysed reactions is not reliable. DFT calculations from Hartwig seem to confirm a Cu(I)/Cu(III) type mechanism for the amidation (Goldberg) reaction, although not all possible mechanisms were calculated. 相似文献