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.     

Transformation of silver nanospheres into triangular nanoplates through a photoinduced process

Triangular silver nanoplates exhibit excellent optical and catalytic properties in many fields, such as catalysts, sensors and bio-medicine. In this paper, triangular nanoplates were generated just in the presence of sodium citrate through a light-induced ripening process, which were converted from spherical silver nanoparticles by reducing silver nitrate with sodium borohydride. By using UV–Vis spectroscopy, particle size analyzer, transmission electron microscopy (TEM) and Ag⁺ concentration analysis, the effects of precursors during the preparation of triangular nanoplates were systematically investigated and the optimal experimental conditions were determined. Based on density functional theory (DFT), the adsorption energies of citrate ion, malate ion and tartronate ion on Ag (1 1 1), (1 1 0) and (1 0 0) were calculated. In addition, theoretical calculations coupled with experimental observations showed that citrate ion as capping agent could more preferentially bind to Ag (1 1 1) and thus blocked Ag (1 1 1) while only allowing extensive growth along the lateral direction. This well explains sodium citrate is an efficient agent in preparing triangular silver nanoplates.     

Influence of Temperature on the Formation of Silver Nanoparticles by using a Seed‐Free Photochemical Method under Sodium‐Lamp Irradiation

Silver nanoparticles can be prepared by using a seed‐free photo‐assisted citrate reduction method under the irradiation of a sodium lamp. Under the same irradiation intensity, bath temperatures are crucial in influencing the reaction rate, morphologies of final products, and shape evolution of the silver nanostructures. For example, when the bath temperature is 80 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 38±6 %, 35±10 %, and 12±8 %, respectively. However, when the bath temperature is 30 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 6±3 %, 0 %, and 83±16 %, respectively. Time‐dependent UV/Vis spectra and TEM images show that silver nanoplates were formed at the earlier reaction stage and greatly decreased in amount at the later stage when the bath temperatures are less than or equal to 40 °C. This indicates that the silver nanoplates, which can be regarded as intermediates, are kinetically favored products. They are not thermodynamically favored products at these relatively low bath temperatures. The SERS spectra of crystal violet (CV) show that all the silver colloids synthesized at various temperatures exhibit good enhancement factors and that the colloids prepared at lower bath temperatures have a higher enhancement factor.     

Solvent-induced shape evolution of PVP protected spherical silver nanoparticles into triangular nanoplates and nanorods

The reaction between silver nitrate and poly(N-vinyl-2-pyrrolidone) (PVP) in pyridine at ambient conditions could lead to the formation of spherical nanoparticles or quadrilateral and triangular silver nanoplates, depending on the silver-to-PVP ratio used. It is proposed that the spherical Ag nanoparticles, which were formed early in the reaction, were transformed into nanoplates through an Ostwald ripening process driven by the bridging flocculation of small spherical Ag nanoparticles. This unique and hitherto unreported shape evolution process was carefully followed by a combination of techniques, viz., UV-visible spectroscopy, TEM, and powder X-ray diffraction.     

三角形银纳米片的合成及其影响因素

报道了一种在不需光照的条件下制备三角形银纳米片的新方法.在表面活性剂BRIJ35存在下,将硝酸银用硼氢化钠和柠檬酸钠还原,在不同温度范围内反应形成各种尺度的三角形银纳米片,探讨了硼氢化钠浓度、BRIJ35浓度和表面活性剂的种类和溶液pH值等因素对银纳米颗粒形貌和尺寸的影响.     

Dissolution-recrystallization mechanism for the conversion of silver nanospheres to triangular nanoplates

A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH(4) reduction of AgNO(3) in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O(2)/Cl(-) etching of the Ag nanospheres and the reduction of the released Ag(+) by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag(0) atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).     

用双还原法制备三角形银纳米片及其光学性能

在硼氢化钠和柠檬酸三钠共存的体系中还原硝酸银, 以聚乙烯吡咯烷酮(PVP)为表面活性剂和保护剂, 水浴加热制备得到三角形银纳米片, 用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)吸收光谱、表面增强拉曼散射(SERS)光谱对其进行了表征. 结果表明: 三角形银纳米片产物为立方相金属银, 边长为(100±40) nm, 厚度为(10±5) nm; 产物表现出与球形银纳米粒子完全不同的吸收光谱; 柠檬酸根在银晶核不同晶面的选择吸附、PVP的包覆作用及Ag(111)晶面的层错对产物的形成起决定作用; 与球形纳米颗粒相比, 三角形银纳米片膜对吡啶(Py)分子有显著的SERS活性.     

Preparation of novel silver-gold bimetallic nanostructures by seeding with silver nanoplates and application in surface-enhanced Raman scattering

Novel silver-gold bimetallic nanostructures were prepared by seeding with silver nanoplates in the absence of any surfactants. During the synthesis process, it was found that the frameworks of silver nanoplates were normally kept though the basal plane of silver nanoplates became rugged. The real morphology of these nanostructures depended on the molar ratio of gold ions to the seed particles. When the molar ratio of gold ions to silver atoms increased from 0.5 to 4, porous or branched silver-gold bimetallic nanostructures could be made. The growth mechanism was qualitatively discussed based on template-engaged replacement reactions and seed-mediated deposition reactions. Due to the unusual structures, they exhibited interesting optical properties. Moreover, they were shown to be an active substrate for surface-enhanced Raman scattering measurements.     

Silver microflowers and large spherical particles: Controlled preparation and their wetting properties

In this article, we report a simple wet-chemical method to prepare silver microflowers and large spherical particles. The formation of the two different microstructures of silver is based on the reduction of AgNO(3) by para-phenylenediamine in aqueous medium at room temperature. The controlling of the silver microstructures can be achieved only by adjusting the concentration of the reactants. It is found that the two different silver microstructures display opposite wetting properties. Large spherical silver particles exhibit superhydrophilic properties with a contact angle (CA) of close to 0 degrees, microflower-like silver particles exhibit highly hydrophobic properties with CA about 132 degrees. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV-vis spectra are used to characterize the chemical structure of the obtained products.     

Application of a voltammetric method for investigation the formation mechanisms of silver nanoparticles in multicomponent solutions

A voltammetric method has been tested for the investigation of the kinetics of formation of silver nanoparticles in two systems: (a) silver(I) triflourineacetate, methylcellosolve, butyl acetate, toluene and methyl methacrylate with methacrylic acid copolymer; and (b) silver nitrate, sodium citrate, poly-N-vinyl-2-pirrolydone, sodium borohydride. It could be established for the first system that the formation rate of metal nanoparticles from silver triflourineacetate solutions depends on the dielectric constant and complexing ability of the solvent. The formation of silver particles proceeds faster in methylcellosolve than in other solvents. The butyl acetate addition to the solution contributes to the complex stability of methylcellosolve with silver triflourineacetate and decelerates the formation process of particles. It could be shown that nitrogen purging of solutions containing poly-N-vinyl-2-pirrolydone affects the silver-ion concentration in the first stage of synthesis and accelerates the formation process of nanoparticles for the second system. The spherical silver nanoparticles which are formed at the first stage of the synthesis are destroyed after starting the UV–irradiation. Then new silver nanoparticles (triangular prisms) are formed.     

Mechanistic study of photomediated triangular silver nanoprism growth

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.