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.     

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.     

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.     

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.     

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.     

Determination of Phenolic Compounds Based on Co‐Immobilization of Methylene Blue and HRP on Multi‐Wall Carbon Nanotubes

This work evaluated an amperometric biosensor based on multi‐wall carbon nanotubes (MWCNT), chemically modified with methylene blue (Met) and horseradish peroxidase (HRP), for detection of phenolic compounds. The dependences of the biosensor response due to the enzyme immobilization procedure, HRP amounts, pH and working potential were investigated. The amperometric response for catechol using the proposed biosensor showed a very wide linear response range (1 to 150 μmol L^?1), good sensitivity (50 nA cm^?2 μmol^?1 L), excellent operational stability (after 300 determinations the response remained at 97%) and very good storage stability (lifetime>3 months). Based on all these characteristics, it is possible to affirm that the material is promising for phenol detection due to its good electrochemical response and enzyme stabilization. The biosensor response for various phenolic compounds was investigated.     

Urea biosensor based on amperometric pH-sensing with hematein as a pH-sensitive redox mediator

The natural dye hematein in water solution was used as a pH-sensitive redox-active mediator for amperometric pH-sensing. The electrochemical characteristics were studied using cyclic voltammetry and chronoamperometry. Several types of urea biosensors were constructed with urease on the surface of platinum and graphite composite electrodes or in the bulk of the graphite composite. They were used for the amperometric urea determination at a working potential of 0 mV (versus SCE) using 0.5 mM hematein. Detection limits and response linearity was in the micromolar range depending on the biosensor type, concentration and pH of buffers used. An interference study of various cations, anions, and substances, which may be present in real samples demonstrated good selectivity for the determination of urea. The biosensors showed good operational (>3 h) and storage (>3 months) stability. The results of urea determination in blood and urine obtained by biosensor correlated well with those obtained by a spectrophotometric reference method.     

Nonenzymatic Electrochemical Biosensor Based on Novel Hydrophilic Ferrocene‐terminated Hyperbranched Polymer and its Application in Glucose Detection

We designed a novel water soluble topological structure polymer‐ferrocene‐ terminated hyperbranched polyurethane (HPU‐Fc) with good water solubility. The redox behaviors and the electrochemical kinetics parameters of HPU‐Fcs were explored by cyclic voltammetry (CV) according to electrochemical principle. The topological structure polymer was applied for the design and engineering of non‐enzymatic glucose sensor. The designed sensor showed good response to glucose concentration with good stability, favorable accuracy and high selectivity. The electrode was also used to detect glucose in blood samples, and the glucose contents detected by the electrode were in good agreement with those from the hospital where a common automatic biochemical analyzer (HF240–300) was used. This finding makes HPU‐Fc a promising biosensor for directly sensing glucose.     

Platinum nanoparticles functionalized nitrogen doped graphene platform for sensitive electrochemical glucose biosensing

In this work, we reported an efficient platinum nanoparticles functionalized nitrogen doped graphene (PtNPs@NG) nanocomposite for devising novel electrochemical glucose biosensor for the first time. The fabricated PtNPs@NG and biosensor were characterized using transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, static water contact angle, UV–vis spectroscopy, electrochemical impedance spectra and cyclic voltammetry, respectively. PtNPs@NG showed large surface area and excellent biocompatibility, and enhanced the direct electron transfer between enzyme molecules and electrode surface. The glucose oxidase (GOx) immobilized on PtNPs@NG nanocomposite retained its bioactivity, and exhibited a surface controlled, quasi-reversible and fast electron transfer process. The constructed glucose biosensor showed wide linear range from 0.005 to 1.1 mM with high sensitivity of 20.31 mA M⁻¹ cm⁻². The detection limit was calculated to be 0.002 mM at signal-to-noise of 3, which showed 20-fold decrease in comparison with single NG-based electrochemical biosensor for glucose. The proposed glucose biosensor also demonstrated excellent selectivity, good reproducibility, acceptable stability, and could be successfully applied in the detection of glucose in serum samples at the applied potential of −0.33 V. This research provided a promising biosensing platform for the development of excellent electrochemical biosensors.     

Ascorbate oxidase electrochemical biosensor based on the biocompatible poly(3, 4-ethylenedioxythiophene) matrices for agricultural application in crops

The vitamin C(VC) in crops was successfully determined using ascorbate oxidase(AO) electrochemical biosensor based on the biocompatible poly(3,4-ethylenedioxythiophene)(PEDOT) matrices,which was easily prepared by one-step electrodeposition technique in ionic liquid microemulsions.The fabricated biosensor displayed excellent bioelectrocatalytic performance to the oxidation of VC,wide linear range,low detection limit,fast response time,good operational and storage stability,the good results of the determination of VC in vegetable crops indicated that the fabricated biosensor will be a good candidate for the physiological and biochemical studies of crops in near future.     

壳聚糖固定化葡萄糖氧化酶生物传感器测定葡萄糖的含量

应用壳聚糖将葡萄糖氧化酶固定于鸡蛋膜上,结合氧电极制得葡萄糖传感器.实验表明,壳聚糖比戊二醛能更好地固定葡萄糖氧化酶,最佳条件为壳聚糖浓度0.3%、固定化酶量0.8 mg、 pH 7.0、缓冲溶液浓度300 mmol/L和温度25 ℃.本葡萄糖传感器的线性范围为0.016～1.10 mmol/L;检出限为8.0 μmol/L(S/N=3), 响应时间<60 s,有很好的稳定性,寿命>3个月.同一个传感器重复使用以及同方法制作的不同传感器之间都有很好的重现性,RSD分别为2.5%(n=10)和4.7%(n=4).实际样品中可能存在的烟酰胺、 VB6、 VB12、 VE、Ca2+、 Mg2+、 K+和Zn2+等对葡萄糖的测定不产生干扰.本传感器已成功地应用于市售饮料中葡萄糖含量的测定.     

Amperometric Biosensor for Hydrogen Peroxide,Using Supramolecularly Immobilized Horseradish Peroxidase on the β‐Cyclodextrin‐Coated Gold Electrode

Horseradish peroxidase, previously modified with 1‐adamantane moieties, was supramolecularly immobilized on gold electrodes coated with perthiolated β‐cyclodextrin. The functionalized electrode was employed for the construction of an amperometric biosensor device for hydrogen peroxide using 1 mM hydroquinone as electrochemical mediator. The biosensor exhibited a fast amperometric response (6 s) and a good linear response toward H₂O₂ concentration between 12 μM and 450 μM. The biosensor showed a sensitivity of 1.02 mA/M cm², and a very low detection limit of 5 μM. The electrode retained 97% of its initial electrocatalytic activity after 30 days of storage at 4 ⁰C in 50 mM sodium phosphate buffer, pH 7.0.     

An amperometric glucose biosensor based on the immobilization of glucose oxidase on the CuGeO3 nanowire modified electrode

A new amperometric biosensor based on adsorption of glucose oxidase (GOx) at the CuGeO₃ nanowires (NW) modified glassy carbon electrode (GCE) is reported in this article. The properties of the biosensor were characterized by Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and electrochemical techniques. The GCE modified with the CuGeO₃ NW/GOD showed excellent electrocatalytical response to the oxidation of glucose. Different parameters including GOx concentration, working potential and pH of supporting electrolyte that governed the analytical performance of the biosensor have been studied in detail and optimized. The biosensor was applied to detect glucose with a linear range of 0.5 to 7 mM. The biosensor exhibited excellent reproducibility and stability.     

A hydrogen peroxide biosensor based on multiwalled carbon nanotubes-polyvinyl butyral film modified electrode

A novel approach to construct a amperometric biosensor for determination of H₂O₂ is described. Horseradish peroxidase (HRP) as a base enzyme was immobilized into the mixture of multiwalled carbon nanotubes (MWNTs) and polyvinyl butyral (PVB). Taking the classical hydroquinone as mediator, cyclic voltammetry and amperometric measurements were used to study and optimize the performance of the resulting H₂O₂ biosensor. The effect of the concentration of MWNTs, HRP, hydroquinone, solution pH, and the working potential of amperometry on the electrochemical biosensor was systematically studied. The results showed that the fabricated biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with wide linear range from 0.000832 to 0.6 mM, and low detection limit 0.000167 mM (S/N = 3) with fast response time less than 8 s. The apparent Michaelis–Menten constant was determined to be 0.049 mM. Additionally, the biosensor exhibited high sensitivity, rapid response and good long-term stability.     

A Sensitive Biosensor for Determination of Cu2+ by One‐step Electrodeposition

A simple one‐step electrodeposition method is described to fabricate three dimensional ordered macroporous chitosan?prussian blue?single walled carbon nanotubes (3DOM CS?PB?SWCNTs) film onto the gold electrode surface to fabricate a copper ions (Cu²⁺)‐specific DNAzyme biosensor. The new sensing strategy for sensitive and selective detection of Cu²⁺ was based on Au nanorods (AuNRs) as signal amplification labels. The electrochemical signal of glucose increased with the concentration of Cu²⁺ increasing. The morphologies and electrochemistry of the composites were investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and so on. Linear correlations of copper ion concentration were obtained in the range from 10^?18 M to 10^?5 M, achieving with a limit of detection of 10^?19 M (S/N=3). Parameters affecting the biosensor response such as temperature, the cleavage time and the time of hybridization were optimized. This biosensor showed a wide range, low detection limit, good reproducibility and high stability. Additionally, these striking properties endow the biosensor with a great promise for analytical applications.