Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature.     

Ti-MWW分子筛吸附H2O和NH3的结构和振动光谱的密度泛函理论计算

Ti-MWW分子筛具有10元环(10MR)孔道体系和12MR超笼以及外表面杯状空穴,在以H2O2水溶液为氧化剂的催化氧化反应中表现出不同于其他钛硅分子筛的特殊溶剂效应和立体选择性.已有的实验和密度泛函理论(DFT)计算研究表明,骨架Ti(IV)可能分布在10MR孔道和12MR超笼中.最近,我们采用DFT计算研究了Ti-MWW分子筛中骨架钛落位,通过比较Ti/Si替代能和红外振动光谱,提出Ti(IV)最可能落位在T1和T3位,并以[Ti(OSi)4]形态存在,显示960 cm–1钛特征振动峰.[Ti(OSi)4]物种水解时Ti–O键发生选择性断裂,生成具有翻转Ti–OH的[Ti(OSi)3OH]物种.由于Ti中心具有Lewis酸性,与配体分子络合后使Ti(IV)的配位状态改变. Ti-MWW分子筛中不同的骨架Ti(IV)落位和形态可能呈现不同的催化选择性.本文应用DFT研究了Ti-MWW分子筛中T1和T3位上不同钛物种与H2O和NH3的吸附作用,考察了其几何结构、吸附能以及红外振动光谱性质,为深入理解骨架Ti(IV)的微观结构及实验红外光谱表征提供参考数据.计算采用36T簇模型,从MWW分子筛晶体结构中分别以T1和T3为中心截取七层骨架原子,末端设为Si–H键并固定为1.46?.结构优化时松弛内部四层骨架原子并固定最外三层骨架原子.所有计算在B3LYP/6-31G(d,p)理论水平完成,计算的吸附能都经过BSSE校正,计算的频率以约化因子0.961校正.所有计算在Gaussian 09软件包完成.计算结果表明,四配位的[Ti(OSi)4]和[Ti(OSi)3OH]物种都能与H2O或NH3分子作用生成三角双锥的五配位络合物. H2O或NH3分子有选择性地进攻Ti–O键的Ti端,形成近乎直线的L–Ti–O键, L–Ti距离可达2.2–2.4?. T1位钛物种的Lewis酸性比T3位的略高.对于[Ti(OSi)3OH]物种, Ti–OH的存在使得Ti(IV)的酸性大大增强,表现出很强的吸附作用.此外,[Ti(OSi)3OH]物种也能通过Ti–OH基团与H2O和NH3形成氢键络合物,但是其吸附能比形成配位络合物的能量更小,说明配体分子更趋向于吸附在Ti中心形成配位络合物.自然键轨道分析表明, Ti(IV)中心的Lewis酸性归因于Ti的空4p轨道接受配体提供的孤对电子,并且属于LUMO+3.所有吸附络合物的特征振动频率分布在两个区域,即钛特征振动区域和羟基振动区域. T1和T3位的[Ti(OSi)4]物种的钛特征振动频率都在960 cm–1,与H2O形成五配位的吸附络合物之后,钛特征振动频率位移到970 cm–1.[Ti(OSi)3OH]物种的钛特征振动频率分别为990 cm–1(T1位)和970 cm–1(T3位),吸附H2O分子后都位移到980 cm–1.相应的NH3吸附络合物的钛特征振动峰频率都高出5 cm–1.分析表明,钛特征振动模式归属于Ti–O–Si键的不对称伸缩振动的协同振动.在羟基伸缩振动区域,气相H2O、末端Si–OH基团以及Ti–OH基团的羟基伸缩振动在3600–3760 cm–1.吸附H2O后,羟基伸缩振动移到3460–3150 cm–1区域.[Ti(OSi)3OH]物种与NH3和H2O形成氢键络合物后,钛羟基的伸缩振动频率分别红移500和1100 cm–1,出现在2700和3200 cm–1区域.吸附分子的O–H和N–H的伸缩振动频率略微蓝移,这反映了Ti物种具有Lewis酸性.     

Combining linear polarization spectroscopy and the Representative Layer Theory to measure the Beer–Lambert law absorbance of highly scattering materials

Visible and Near Infrared (Vis–NIR) Spectroscopy is a powerful non destructive analytical method used to analyze major compounds in bulk materials and products and requiring no sample preparation. It is widely used in routine analysis and also in-line in industries, in-vivo with biomedical applications or in-field for agricultural and environmental applications. However, highly scattering samples subvert Beer–Lambert law's linear relationship between spectral absorbance and the concentrations. Instead of spectral pre-processing, which is commonly used by Vis–NIR spectroscopists to mitigate the scattering effect, we put forward an optical method, based on Polarized Light Spectroscopy to improve the absorbance signal measurement on highly scattering samples. This method selects part of the signal which is less impacted by scattering. The resulted signal is combined in the Absorption/Remission function defined in Dahm's Representative Layer Theory to compute an absorbance signal fulfilling Beer–Lambert's law, i.e. being linearly related to concentration of the chemicals composing the sample. The underpinning theories have been experimentally evaluated on scattering samples in liquid form and in powdered form. The method produced more accurate spectra and the Pearson's coefficient assessing the linearity between the absorbance spectra and the concentration of the added dye improved from 0.94 to 0.99 for liquid samples and 0.84–0.97 for powdered samples.     

Simple and Sensitive Voltammetric Determination of Esculetin Using Electrochemically Reduced Graphene Oxide Modified Electrode

A simple and sensitive voltammetric sensor for esculetin, based on electrochemically reduced graphene oxide film modified glassy carbon electrode, was reported for the quantitative determination of esculetin in the Chinese traditional herbal drug Viola yedoensis Makino. Electrochemical impedance spectroscopy and scanning electron microscopy were employed to study the characteristic of the graphene oxide film. The electrochemical behavior of esculetin on this sensor was investigated in pH 3.0 phosphate buffer solution by cyclic voltammetry. Significant advantages were achieved by the excellent conductivity and the high surface‐to‐volume ratio of electrochemically reduced graphene oxide. A calibration plot of oxidation peak currents versus esculetin concentrations was linear in the range of 4.0 ξ 10^‐8 mol L^‐1 to 5.0 ξ 10^‐6 mol L^‐1 with a detection limit of 2.0 ξ 10^‐8 mol L^‐1. The practical application of the present sensor was demonstrated by determining the concentration of esculetin in real sample with no interference.     

A statistical approach to characterize the viscoelastic creep compliances of a vinyl ester polymer

The objective of this study was to develop a model to predict the viscoelastic material functions of a vinyl ester (VE) polymer with variations in its experimentally obtained material properties under combined isothermal and mechanical loading. Short-term tensile creep experiments were conducted at three temperatures below the glass transition temperature of the VE polymer, with 10 replicates for each test configuration. The measured creep strain versus time responses were used to determine the creep compliances using the generalized viscoelastic constitutive equation with a Prony series representation. The variation in the creep compliances of a VE polymer was described by formulating the probability density functions (PDFs) and the corresponding cumulative distribution functions (CDFs) of the creep compliances using a two-parameter Weibull distribution. Both Weibull scale and shape parameters of the creep compliance distributions were shown to be time and temperature dependent. Two-dimensional quadratic Lagrange interpolation functions were used to characterize the Weibull parameters to obtain the PDFs and, subsequently, the CDFs of the creep compliances for the complete design temperature range during steady state creep. At each test temperature, creep compliance curves were obtained for constant CDF values and compared with the experimental data. The predicted creep compliances of the selected VE polymer in the design space are in good agreement with the experimental data for all three test temperatures.     

Robustness quantification method for network intrusion detection models

Deep learning techniques have been successfully applied to network intrusion detection tasks, but as in the case of autonomous driving and face recognition, the reliability of the system itself has become a pressing issue. Robustness is a key attribute to determine whether a deep learning system is secure and reliable, and we also choose to explore the security of intrusion detection models from a new perspective of robustness quantification. In this paper, we focus on the intrusion detection model based on long and short-term memory, and use a fine-grained linear approximation method to derive a more accurate robustness bound on the nonlinear activation function with tighter linear constraints. We can use this bound to quantitatively measure the robustness of the detection model and determine whether the model is susceptible to the influence of adversarial samples. In our experiments, we test networks with various structures on the MNIST dataset, and the results show that our proposed method can effectively deduce the robustness bounds of output elements, and has good scalability and applicability.     

Intelligent resource allocation for transmission security on IRS-assisted spectrum sharing systems with OFDM

In this paper, intelligent reflecting surface (IRS) technology is employed to enhance physical layer security (PLS) for spectrum sharing communication systems with orthogonal frequency division multiplexing (OFDM). Aiming to improve the secondary users’ secrecy rates, a design problem for jointly optimizing the transmission beamforming of secondary base station (SBS), the IRS’s reflecting coefficient and the channel allocation is formulated under the constraints of the requirements of minimum data rates of primary users and the interference between users. As the scenario is highly complex, it is quite challenging to address the non-convexity of the optimization problem. Thus, a deep reinforcement learning (DRL) based approach is taken into consideration. Specifically, we use dueling double deep Q networks (D3QN) and soft Actor–Critic (SAC) to solve the discrete and continuous action space optimization problems, respectively, taking full advantage of the maximum entropy RL algorithm to explore all possible optimal paths. Finally, simulation results show that our proposed approach has a great improvement in security transmission rate compared with the scheme without IRS and OFDM, and our proposed D3QN-SAC approach is more effective than other approaches in terms of maximum security transmission rate.     

Recent advances in BiOBr-based photocatalysts for environmental remediation

The efficient utilization of solar energy through photocatalysis is ideal for solving environmental issues and the development sustainable future. BiOBr-based semiconductors possess unique narrowed bandgaps and layered structures, thereby widely studied as photocatalysts for environmental remediation. However, a little has been focused on the comprehensive reviewing of BiOBr despite its extensive and promising applications. In this review, the state-of-the-art developments of BiOBr-based photocatalysts for environmental remediation are summarized. Particular focus is paid to the synthetic strategies for the control of the resulting morphologies, as well as efficient modification strategies for improving the photocatalytic activities. These include boosting the bulk phase by charge separation, enhancing the spatial charge separation, and engineering the surface states. The environmental uses of BiOBr-based photocatalysts are also reviewed in terms of purification of pollutants and CO₂ reduction. Finally, future challenges and opportunities of BiOBr-based materials in photocatalysis are discussed. Overall, this review provides a good basis for future exploration of high-efficiency solar-driven photocatalysts for environmental sustainability.