Suppressing Strong Exciton–Phonon Coupling in Blue Perovskite Nanoplatelet Solids by Binary Systems

Quasi-two-dimensional (2D) perovskites are promising candidates for light generation owing to their high radiative rates. However, strong exciton–phonon interactions caused by mechanical softening of the surface act as a bottleneck in improving their suitability for a wide range of lighting and display applications. Moreover, it is not easily available to tune the phonon interactions in bulk films. Here, we adopt bottom-up fabricated blue emissive perovskite nanoplatelets (NPLs) as model systems to elucidate and as well as tune the phonon interactions via engineering of binary NPL solids. By optimizing component domains, the phonon coupling strength can be reduced by a factor of 2 driven by the delocalization of 2D excitons in out-of-plane orientations. It shows the picosecond energy transfer originated from the Förster resonance energy transfer (FRET) efficiently competes with the exciton–phonon interactions in the binary system.     

基于三维荧光光谱法和PARAFAC对多环芳烃定性定量分析

三维荧光光谱法在研究多环芳烃(PAHs)类物质的荧光信息时起到了重要作用。多环芳烃类物质具有致癌性,难降解性,多由尾气排放,垃圾焚烧产生,危害着人类健康及环境,因此人们不断探索对多环芳烃检测的方法。实验选取多环芳烃中的苊和萘作为检测物质,利用FLS920荧光光谱仪,为避免荧光光谱仪本身产生的瑞利散射影响,设置起始的发射波长滞后激发波长40 nm,设置扫描的激发波长(λex)范围为:200~370 nm,发射波长(λem)范围为:240~390 nm,对多环芳烃进行荧光扫描获取荧光数据,采用三维荧光光谱技术结合平行因子算法对混合溶液中的苊和萘进行定性定量分析。实验选用的苊和萘均购于阿拉丁试剂官网,配制浓度为10 mg·L-1的一级储备液,再将一级储备液稀释,得到苊和萘浓度为0.5,1,1.5,2,2.5,3,3.5,4和4.5 mg·L-1的二级储备液,并将苊和萘进行混合。在进行光谱分析前需要对苊和萘的光谱进行预处理,采用空白扣除法扣除拉曼散射的影响,并采用集合经验模态分解(EEMD)消除干扰噪声。实验测得苊存在两个波峰,位于λex=298 nm,λem=324/338 nm处,萘存在一个波峰,位于λex=280 nm,λem=322 nm处。选用的PARAFAC算法对组分数的的选择很敏感,因此采用核一致诊断法预估组分数,估计值2和3的核一致值都在60%以上,分别对混合样品进行了2因子和3因子的PARAFAC分解,将分解后得到的激发发射光谱数据和各组分浓度数据进行归一化处理,并绘制光谱图,与归一化处理后的真实的激发发射光谱图和各组分浓度图进行对比。同时将PARAFAC得到的混合样本的预测浓度,通过计算回收率(R)和均方根误差(RMSEP)来判定定量分析的准确度。选择2因子时,各混合样品中苊和萘拟合度为95.7%和96.7%,平均回收率分别为101.8%和98.9%,均方根误差分别为0.0187和0.0316;选择3因子时,各混合样品中苊和萘拟合度为95.3%和95.8%,平均回收率分别为97%和102.5%,均方根误差分别为0.033和0.116,由三项指标可得选用2因子进行定性定量分析的效果明显好于选用3因子。分析实验结果表明,基于三维荧光光谱法和PARAFAC算法对混合样品进行定性定量分析,能够有效的判定混合样品的类别,同时能够成功的预测出混合样品的浓度。     

A giant enhancement of magnetic moment in a ternary three-shell icosahedral cluster: Fe@Mn12@Au20

ABSTRACT

The average magnetic moment per atom of Mn₁₃ cluster is expected to be enhanced by doping or coating with a shell. Several ternary core–shell icosahedral clusters TM@Mn₁₂@Au₂₀ were constructed by combining substituting the central Mn with VIII elements (Fe, Co, Ni, Ru, Rh, Pd and Pt) and coating with a icosahedral Au₂₀ shell, and systematically studied by using the first-principles density functional method. Compared to Mn₁₃, Fe@Mn₁₂@Au₂₀ cluster shows a giant enhancement on total magnetic moment (52?µ_B) which can be greatly attributed to the ferromagnetic coupling between spin moments of atoms. Coating with Au₂₀ shell enlarged the average distances of TM-Mn and Mn-Mn and is a useful way to change the magnetic coupling style. By analysis of density of states and electron localisation functional, we can conclude that the weak hybridisation between Fe and Mn in Fe@Mn₁₂@Au₂₀ is propitious to maintain their original direction of spin moments of atoms and then form ferromagnetic coupling.     

Nanostructured BiVO4 Derived from Bi-MOF for Enhanced Visible-light Photodegradation

BiVO4,a promising visible-light responding photocatalyst,has aroused extensive research interest because of inexpensiveness and excellent chemical stability.However,its main drawback is the poor photoinduced charge-transfer dynamics.Building nanostructures is an effective way to tackle this problem.Herein,we put forward a new method to prepare nanostructured BiVO4 from Bi-based metal-organic frameworks[Bi-MOF(CAU-17)]precursor.The as-prepared material has a rod-like morphology inherited from the Bi-MOF sacrificial template and consists of small nanoparticle as building blocks.Compared with its counterparts prepared by conventional methods,MOF-derived nanostructured BiVO4 shows better light absorption ability,narrower bandgap,and improved electrical conductivity as well as reduced recombination.Consequently,BiVO4 nanostructure demonstrates high photocatalytic activity under visible light towards the degradation of methylene blue.Methylene blue can be degraded up to 90%within 30 min with a reaction rate constant of 0.058 min-1.Moreover,the cycling stability of the catalyst is excellent to withstand unchanged degradation efficiency for at least 5 cycles.     

Gas-Sensing Activity of Amorphous Copper Oxide Porous Nanosheets

In this paper, the gas-sensing properties of copper oxide porous nanosheets in amorphous and highly crystalline states were comparatively investigated on the premise of almost the same specific surface area, morphology and size. Unexpectedly, the results show that amorphous copper oxide porous nanosheets have much better gas sensing properties than highly crystalline copper oxide to a serious of volatile organic compounds, and the lowest detection limit (LOD) of the amorphous copper oxide porous nanosheets to methanal is even up to 10 ppb. By contrast, the LOD of the highly crystalline copper oxide porous nanosheets to methanal is 95 ppb. Experiments prove that the oxygen vacancies contained in the amorphous copper oxide porous nanosheets play a key role in improving gas sensitivity, which greatly improve the chemical activity of the materials, especially for the adsorption of molecules containing oxygen-groups such as methanal and oxygen.     

An improved LC–MS/MS method for determination of docetaxel and its application to population pharmacokinetic study in Chinese cancer patients

Because of its unpredictable side effects and efficacy, the anticancer drug docetaxel (DTX) requires improved characterisation of its pharmacokinetic profiles through population pharmacokinetic studies. A sensitive and rugged LC–MS/MS method for the detection of DTX in human plasma was developed and optimised using paclitaxel as an internal standard (IS). The plasma samples underwent rapid extraction using hybrid solid-phase extraction-protein precipitation. The analyte and IS were separated with an isocratic system on a Zorbax Eclipse Plus C₁₈ column using water containing 0.05% acetic acid along with 20 μM of sodium acetate and methanol (30/70, v/v) as the mobile phase. Quantification was performed using a triple quadrupole mass spectrometer through multiple reaction monitoring in positive mode, using the m/z 830.3 → 548.8 and m/z 876.3 → 307.7 transitions for DTX and paclitaxel, respectively. The range of the calibration curve was 1–500 ng/mL for DTX, and the linear correlation coefficient was >0.99. The accuracies ranged from −4.6 to 4.2%, and the precision was no higher than 7.0% for the analytes. No significant matrix effect was observed. Both DTX and the IS showed considerable recovery. This method was finally applied to the establishment of a population pharmacokinetic model to optimise the clinical use of DTX.     

A simple sol–gel hydrothermal method for the synthesis of defective TiO2 nanocrystals with excellent visible-light photocatalytic activity

Research on Chemical Intermediates - Defective TiO2 nanocrystals (D-TiO2) were synthesized by a simple, mild and green sol–gel hydrothermal method. The as-prepared sample possesses a high...     

Water-induced formation of an alkali-ion dimer in cryptomelane nanorods

Tunneled metal oxides such as α-Mn₈O₁₆ (hollandite) have proven to be compelling candidates for charge-storage materials in high-density batteries. In particular, the tunnels can support one-dimensional chains of K⁺ ions (which act as structure-stabilizing dopants) and H₂O molecules, as these chains are favored by strong H-bonds and electrostatic interactions. In this work, we examine the role of water molecules in enhancing the stability of K⁺-doped α-Mn₈O₁₆ (cryptomelane). The combined experimental and theoretical analyses show that for high enough concentrations of water and tunnel-ions, H₂O displaces K⁺ ions from their natural binding sites. This displacement becomes energetically favorable due to the formation of K²⁺ dimers, thereby modifying the stoichiometric charge of the system. These findings have potentially significant technological implications for the consideration of cryptomelane as a Li⁺/Na⁺ battery electrode. Our work establishes the functional role of water in altering the energetics and structural properties of cryptomelane, an observation that has frequently been overlooked in previous studies.

Water displaces potassium ions and initiates the formation of a homonuclear dimer ion (K²⁺) in the tunnels of hollandite.     

Interplay of Hole Transfer and Host–Guest Interaction in a Molecular Dyad and Triad: Ensemble and Single‐Molecule Spectroscopy and Sensing Applications

A new molecular dyad consisting of a Cy5 chromophore and ferrocene (Fc) and a triad consisting of Cy5, Fc, and β‐cyclodextrin (CD) are synthesized and their photophysical properties investigated at both the ensemble and single‐molecule levels. Hole transfer efficiency from Cy5 to Fc in the dyad is reduced upon addition of CD. This is due to an increase in the Cy5‐Fc separation (r) when the Fc is encapsulated in the macrocyclic host. On the other hand, the triad adopts either a Fc‐CD inclusion complex conformation in which hole transfer quenching of the Cy5 by Fc is minimal or a quasi‐static conformation with short r and rapid charge transfer. Single‐molecule fluorescence measurements reveal that r is lengthened when the triad molecules are deposited on a glass substrate. By combining intramolecular charge transfer and competitive supramolecular interaction, the triad acts as an efficient chemical sensor to detect different bioactive analytes such as amantadine hydrochloride and sodium lithocholate in aqueous solution and synthetic urine.