超声波酸性体系下MCM-41的合成及表征

以十六烷基三甲基溴化铵(CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,以超声波为辅助手段于酸性介质中制备出了MCM-41介孔分子筛,采用XRD、TEM、FTIR等手段对样品进行了分析表征.结果表明,所合成样品具备MCM-41所特有的六方排列的一维孔道结构和较高的有序度,所合成的MCM-41平均粒径为11nm,孔径约为2.7nm.     

超声波对合成介孔材料Al-MCM-41的有序度的影响

在超声频率为20 kHz,电功率为500 W的超声波作用下,分别以Al（NO₃）₃和Al₂ （SO₄）₃做铝源合成了具有不同Si/Al比的Al-MCM-41。XRD结果显示,尽管超声波作用下,掺杂杂原子Al也要降低介孔材料的有序度,但其有序度降低的程度比普通水热法要小,超声波的辅助可以在同样反应时间内得到比普通水热法具有更高有序度的Al-MCM-41,即在掺杂过程中,超声波要比普通搅拌有利于介孔材料保持其骨架稳定性。此外考察了超声波作用时间对产品有序度和粒度的影响。     

镧掺杂的介孔分子筛的合成及其光学性能研究

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,正硅酸乙酯(TEOS)为硅源,采用水热晶化法,合成了镧掺杂的MCM-41介孔分子筛。通过X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、透射电镜(TEM)、紫外-可见(UV-Vis)光谱等测试手段对其孔结构和镧原子的存在状态进行了表征。XRD和TEM结果表明,合成样品具有典型的二维六方有序介孔结构,样品的傅里叶变换红外光谱和紫外-可见光谱表明镧被成功的引入到介孔骨架中。     

ZnO/MCM-41复合材料的制备及其光谱性质

以硅酸钠(NaSiO3·9H2O)为硅源,三甲基十六烷基溴化铵(CTAB)为模板剂在碱性条件下水热合成介孔分子筛MCM-41,然后以其为主体,采用锌盐浸渍-灼烧的方法.在介孔分子筛MCM-41上负载了氧化锌(ZnO)纳米微粒,并通过扫描电子显微镜,红外光谱(1R).紫外可见吸收光谱(UV-Vis),N2-吸附脱附和荧光光谱等手段对产品进行了系列表征.结果表明,分子筛平均直径约为1.7μm,对不同温度下灼烧后得到的ZnO/MCM-41组装体的光谱性质进行研究表明介孔分子筛MCM-41的尺寸所限,制备出的ZnO粒子粒径小于2 nm.量子尺寸效应使得ZnO/MCM-41组装体中的ZnO纳米粒子的紫外可见吸收光谱及荧光光谱均发生蓝移.通过红外光谱分析得知ZnO负载到MCM-41上并没有改变介孔分子筛原有的骨架结构.     

MCM-41负载磷钨酸的制备与表征

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,以正硅酸乙酯(TEOS)为硅源,采用水热合成法制备了介孔分子筛MCM-41,并利用浸渍法将磷钨酸(HPW)负载在MCM-41分子筛上,得到HPW/MCM-41催化剂f采用X射线衍射、傅里叶变换红外光谱、透射电镜等手段对负载型催化剂进行了表征.结果表明,磷钨酸负载到MCM-...     

多酸-介孔分子筛复合材料的制备、表征及光催化活性

采用浸渍法将具有光催化活性的多金属氧酸盐(polyoxometalate,POM)磷钨酸和硅钨酸负载到介孔分子筛MCM-41,制备了H3PW12O40/MCM-41和H4SiW12O40/MCM-41两种复合材料,以红外光谱(FT-IR)、X射线衍射(XRD)、N2吸附、高分辨透射电镜(HRTEM)等分析手段对所合成的多酸-分子筛复合材料进行了表征,并以农药百草枯的光催化降解考察了复合材料的光催化活性。所合成的复合材料同时保留了母体多酸的Keggin特征结构和载体MCM-41分子筛均匀的六方孔道结构,比表面积超过200m2.g-1。用于农药百草枯的光催化降解实验表明,两种复合材料均具有较高的光催化活性。在365nm紫外光辐照下,以H3PW12O40/MCM-41和H4SiW12O40/MCM-41为催化剂催化反应14h后,百草枯(10mg.L-1)的降解转化率分别达到92.0%和87.6%,反应符合一级化学动力学模型,半衰期分别为3.7和4.6h。     

纳米级介孔分子筛及其超分子发光功能材料的制备与表征

本文在超声波条件下以三甲基十六烷基溴化铵为模板剂,正硅酸乙酯为硅源合成了纳米级（10－40nm)的介孔分子筛（MCM－41）,其筛孔直径在2．7nm左右,选择Eu(Phen)4为客体,纳米级介孔分子筛为主体,在无水乙醇中进行分子组装,制备具有强发光性能的超分子纳米材料MCM－41－Eu(Phen),采用HRTEM,TEM,XRD,TG,IR和荧光光谱检测手段对产物进行了表征。     

MCM-41水分吸附特性的调控研究

本文以介孔分子筛MCM-41为研究对象,通过合成与后改性法,调控其孔径、表面性质以及平衡阳离子种类。通过X射线衍射、液氮吸附对介孔材料结构进行结构分析,采用动态水分吸附仪研究其水分吸附特性,并结合吸附等温线热力学模型进行分析。研究结果表明:铝嫁接有效提高MCM-41在低湿度下吸附量,并且随着嫁接浓度的增大而增加;通过阳离子置换强化了低湿度环境下MCM-41的吸附量,不同阳离子置换后的强化效果:Mg~(2+)+Li~+Na~+。热力学模型分析表明阳离子置换后的吸附剂表面均一,且具有较好的亲水性。     

咪唑离子液体中离子热合成磷铝分子筛及其表征

用一系列咪唑类离子液体做溶剂和结构导向剂,通过离子热方法,合成了磷铝分子筛及过渡金属(Co,Fe)掺杂的磷铝分子筛.XRD和FT-IR表明所有产物均为方钠石(SOD)结构.元素分析表明Co和Fe进入了分子筛骨架中.系统考察了磷铝比、晶化温度和离子液体种类对产物性能的影响.结果表明较低的磷酸浓度和较高的反应温度(170-190℃)有利于分子筛的晶化过程.     

Ni_2P/介孔分子筛催化剂的原位漫反射红外光谱研究

以介孔分子筛MCM-41,MCM-48,SBA-15,SBA-16为载体,硝酸镍为镍源,磷酸氢二铵为磷源,通过浸渍法制备了含有磷化镍前体的介孔分子筛样品,然后在氢气气氛中进行程序升温还原,得到了磷化镍/介孔分子筛催化剂.采用原位漫反射红外光谱法,用CO作为探针分子,对样品的吸附特征进行了研究.结果表明,在介孔分子筛表面CO存在着较弱的物理吸附.在Ni2P/MCM-41催化剂样品表面有四种CO的吸附态:(1)在2055cm-1处形成的Ni(CO)4物种的吸附,(2)在2 091cm-1处的配位不饱和Niδ(0<δ<1)物种上的吸附,(3)在2 127 cm-1处的Ni+物种上的吸附,(4)在2 198～2 202 cm-1范围内的P物种上的吸附.在Ni2P/MCM-48,Ni2P/SBA-15,Ni2P/SBAZ-16催化剂样品表面有二种CO的吸附态:在2 051～2 055cm-1处的Ni(CO)4吸附和在2 093～2 096 cm-1处的配位不饱和Niδ+(0<δ<1)物种上的吸附.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.