In situ growth of different numbers of gold nanoparticles on MoS_2 with enhanced electrocatalytic activity for hydrogen evolution reaction

Producing hydrogen through a hydrogen evolution reaction(HER) by splitting water at the suitable overpotential is a great alternative to solving the problems of environmental pollution and the energy crisis. Molybdenum sulfide(MoS_2)has attracted extensive attention as one of the most promising catalytic materials for HER. In this work, we design a facile method to in situ grow gold nanoparticles(Au NPs) on MoS_2. Different numbers of Au NPs with MoS_2 are used to find the best catalytic activity. Due to the larger active surface area and higher conductivity of the Au–MoS_2 composites, all the Au–MoS_2 composites exhibit more enhanced HER electroactivity than pure MoS_2. In brief, the new material architecture exhibits optimized HER activity with a low onset overpotential of 0.12 V, low Tafel slope of 0.163 V·dec~(-1), and an excellent stability in acidic solution.     

巧用二次函数，突破数列最值问题

数列是高中数学的重点与难点.数列最值问题是各类测试的常考点.求数列最值的方法因题而异,其中二次函数法是求解数列最值问题的常用方法.为提高数列最值问题求解效率,应提高二次函数应用意识,借助二次函数性质、图象特点,顺利寻找到解题切入点.     

An optimized,sensitive and stable reduced graphene oxide–gold nanoparticle-luminol-H2O2 chemiluminescence system and its potential analytical application

The chemiluminescence （CL） performance of luminol is improved using reduced graphene oxide/gold nanoparticle （rGO-AuNP） nano-composites as catalyst. To prepare this catalyst, we propose a linker free, one-step method to in- situ synthesize rGO-AuNP nano-composites. Various measurements are utilized to characterize the resulting rGO-AuNP samples, and it is revealed that rGO could improve the stability and conductivity. Furthermore, we investigate the CL signals of luminal catalyzed by rGO-AuNP. Afterwards, the size effect of particle and the assisted enhancement effect of rGO are studied and discussed in detail. Based on the discussion, an optimal, sensitive and stable rGO-AuNP-luminon- H202 CL system is proposed. Finally, we utilize the system as a sensor to detect hydrogen peroxide and organic compounds containing amino, hydroxyl, or thiol groups. The CL system might provide a more attractive platform for various analytical devices with CL detection in the field of biosensors, bioassays, and immunosensors.     

An approach to controlling the fluorescence of graphene quantum dots: From surface oxidation to fluorescent mechanism

We report a facile method of synthesizing graphene quantum dots（GQDs） with tunable emission. The as-prepared GQDs each with a uniform lateral dimension of ca. 6 nm have fine solubility and high stability. The photoluminescence mechanism is further investigated based on the surfacestructure and the photoluminescence behaviors. Based on our discussion, the green fluorescence emission can be attributed to the oxygen functional groups, which could possess broad emission bands within the π –π ＊ gap. This work is helpful to explain the vague fluorescent mechanism of GQDs, and the reported synthetic method is useful to prepare GQDs with controllable fluorescent colors.     

超疏水二氧化钛薄膜的制备及其经紫外光照射引发的超亲水性研究

通过水热反应,在玻璃基底上沉积生成TiO₂薄膜,TiO₂薄膜呈花朵状,具有微纳米级的复合结构,在其表面有大量的乳状突起,经辛基三甲氧基硅烷表面修饰后表现出良好的超疏水性,静态接触角为164°,滚动角为4°。经紫外光照射4~6 h后,其表面变为超亲水性,接触角接近0°。用红外光谱,X射线光电子能谱(XPS)对其表面物质及元素进行表征,最后用Cassie理论对膜的润湿性进行了分析。     

Polymer solar cells based on a PEDOT:PSS layer spin-coated under the action of an electric field

In the process of fabrication of polymer photovoltaic(PV) devices,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) thin film,acting as an anode buffer layer,is spin-coated under the action of an electric field.The PV devices with a PEDOT:PSS layer spin-coated under the action of a static electric field exhibit improved short-circuit current density(J sc) and power conversion efficiency(PCE).The investigation of morphology shows that the appropriate intensity of the electric field can increase the roughness of the surface of the PEDOT:PSS layer,which results in improved contact between the anode and hole transport layer and thus enhances the J sc of the devices.Chemical analysis is also provided by x-ray photoelectron spectroscopy(XPS) spectra.     

Si基CeO_2薄膜的发光特性

利用电子束蒸发技术在p型硅衬底上沉积了200 nm厚的CeO2薄膜样品,将样品置于弱还原气氛中高温退火后,观察到薄膜在385,418 nm以及445 nm左右出现三个明显的发光峰。结合激发光谱、吸收光谱以及XRD分析表明:CeO2薄膜在高温下容易发生失氧反应,出现Ce4+→Ce3+离子转变,Ce3+离子在紫外光的激发下,电子由O2p跃迁到5d能级,再由5d能级向4f能级跃迁,从而产生强烈的蓝紫外发射,而445 nm左右的发光峰则来自于SiO2薄膜的缺陷发光。样品选择900~1 200℃不同温度退火,并且在1 200℃下进行了不同时间的退火。研究结果显示:在1 200℃下进行2 h的退火,薄膜发光强度达到最大。     

The concentration quenching and crystallographic sites of Eu2+ in Ca2BO3Cl

A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.     

The concentration quenching and crystallographic sites of Eu²⁺ in Ca₂BO₃Cl

A yellow phosphor, Ca2BO3 Cl:Eu2+ , is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f 6 5d 1 →4f 7 transition of Eu2+ . Eu2+ ions occupy two types of Ca2+ sites in the Ca2BO3 Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2+ in Ca2 BO 3 Cl. The emission intensity of Eu2+ in Ca2BO3 Cl is influenced by the Eu2+ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.