氮化碳材料的光谱学分析及光催化性能研究

为克服光催化材料可见光利用效率低的缺陷,通过三聚氰胺高温缩聚的方法合成了石墨型氮化碳(g-C₃N₄)材料。采用XRD,SEM,UV-Vis技术对氮化碳材料的微观结构和光学性能进行了表征,并通过降解罗丹明B溶液研究了缩聚温度和不同光源对光催化效率的影响。结果表明,合成的氮化碳层片状结构保存良好,尽管材料表面在高温下断裂形成了不规则的块体颗粒;随着煅烧温度的升高,催化剂在紫外光和可见光部分的吸收都显著增强,这可能是由于材料表面的岩石状块体颗粒提高了材料的比表面积,同时降低了光的反射又提高了对光的吸收。在罗丹明B的光降解测试中,催化剂在可见光和太阳光照射下均表现出了良好的催化效果,缩聚温度为580 ℃时效果最好,分别为94.8%(60 min)和91.1%(90 min)。该方法制备的石墨型氮化碳催化剂对利用清洁能源进行环境净化应用具有极大的潜在价值。     

硝酸辅助合成氮缺陷石墨型氮化碳材料及光谱学分析

通过硝酸辅助高温缩聚三聚氰胺的方法合成了氮缺陷石墨型氮化碳(g-C_3N_4)光催化材料,并利用scanning electron microscope (SEM), brunauer emmett teller (BET), X射线衍射(X-ray diffraction, XRD), ultraviolet-visible spectroscopy (UV-Vis), X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)和Fourier transform infrared spectroscopy (FTIR)等手段对其微观结构和光谱学特征进行了分析, SEM给出了氮化碳和改性材料的表面微观形貌,改性材料表现出了更小的孔径与更加粗糙类似于"矾花"状的表面,说明硝酸的加入显著改变了材料的表面结构。BET图谱可以明显看出硝酸辅助合成材料显示出了较大的比表面积和孔径。XRD图谱显示改性后的材料保持了氮化碳材料的一般结构特征,并且两个特征峰均发生了峰宽以及角度的变化,说明了酸辅助可以改变原材料的结构。从UV-Vis图谱中看出改性材料发生了明显的红移现象,说明材料对可见光的响应较原始氮化碳材料有一定增强。FTIR图谱显示改性后材料在保持原有材料基团的基础上碳氮单键以及氨基基团增多等变化。从XPS图谱中发现改性材料的结合能以及峰面积发生变化,由此得出N元素含量显著提高,推测由于三聚氰胺与硝酸产生部分反应后被高温焙烧引入硝酸中的氮元素。最后测试了材料在可见光和太阳光照射下的催化性能。结果表明,该方法不仅简单易行,硝酸消耗量低,而且合成的g-C_3N_4材料具有很好的多孔结构、更小的粒度和更高的比表面积等微观结构优势,以及增强的光吸收响应特征,更重要的是与由其他方法合成材料的碳氮(C/N)比上升不同,该方法合成的材料C/N比有明显的下降趋势,氨基基团也有增多的表现,这可能因硝酸与三聚氰胺在高温烧结过程中的化学反应所导致。可见光和太阳光照射催化降解罗丹明B(RhB)的试验结果表明,当硝酸用量为2 mL时g-C_3N_4材料的催化效果最佳,降解率均达到99%,分别是无硝酸条件下的2.8倍和2.5倍,并且材料的循环性降解测试表明材料的可回收性强。这种高效易得、方便工业化推广和可回收性强的g-C_3N_4材料为今后的实际应用提供了极好的参考。     

Ag负载WO3/TiO2光催化剂的合成及其催化性能

以钛酸丁酯、无水乙醇、钨酸铵为原料,采用溶胶-凝胶法合成了WO3/TiO2复合光催化剂;采用光还原技术制备了Ag负载WO3/TiO2光催化剂,借助X射线粉末衍射(XRD)和UV-Vis光谱等技术对样品的组成和光吸收性能进行了表征,并以罗丹明B为模型污染物考察样品的光催化活性。XRD分析表明,所得粉体均为锐钛矿型纳米TiO2,且与WO3复合后,纳米TiO2特征衍射峰宽化,强度降低;UV-Vis光谱分析表明,载银使得催化剂在400—700nm的可见光区域对光响应,且在紫外光区吸收显著增强,对光具有更高的利用率;以罗丹明B为降解物的光催化实验表明,WO3复合对纳米TiO2光催化活性有显著的影响,而载Ag后其光催化活性进一步提高,将该光催化剂用于炼油厂废水的处理,效果较好。     

石墨相氮化碳的制备条件优化用以提高其在可见光下的光催化活性

通过染料的光降解实验和敏感性数学分析探讨了石墨相氮化碳(g-C₃N₄)的制备条件与其稳定性和光催化活性之间的联系. 结果表明,相比于焙烧时间,焙烧温度的改变更为显著地影响了g-C₃N₄ 的光催化活性. 制备条件优化之后的g-C₃N₄在可见光照射下催化降解罗丹明B(RhB)的活性比未优化时提高了约100倍,归因于材料比表面积的增大和表面光生电子-空穴迁移速度的增强.     

基于W@WO3纳米薄膜光催化特性增强研究

采用无催化剂高温反应热蒸发和磁控溅射相结合的方法,在碳布上生长了W@WO_3纳米结构薄膜。通过XRD、SEM、XPS测试表明样品结构具有很好的结晶性,且W颗粒吸附在WO_3纳米薄膜上构成了欧姆结,可用于提高半导体材料的电荷分离效率。通过将样品放入罗丹明B溶液进行可见光照射5h,76%的RB可被降解,与降解效率为26%的WO_3纳米结构相比,经过W修饰后的样品光催化性能可得到大幅提升。实验利用碳布作为衬底生长出大比表面积纳米薄膜,可为了提供更多的光催化反应的活性位点。实验无需采用价格昂贵的贵金属修饰,也无需采用催化剂,可为低成本简易制备高质量的光催化材料提供有效制备方法,在污水等有机物的处理降解领域具有广阔的应用前景。     

高压熔渗生长法制备金刚石聚晶中碳的转化机制研究

在6 GPa和1500 ℃的压力和温度范围内, 利用高压熔渗生长法制备了纯金刚石聚晶, 深入研究了高温高压下金刚石聚晶生长过程中碳的转化机制. 利用光学显微镜、X-射线衍射、场发射扫描电子显微镜检测, 发现在熔渗过程中金刚石层出现了石墨化现象, 在烧结过程中金刚石颗粒表面形貌发生了变化. 根据实验现象分析, 在制备过程中存在三种碳的转化机制: 1)金属熔渗阶段金刚石颗粒表面石墨化产生石墨; 2)产生的石墨在烧结阶段很快转变为填充空隙的金刚石碳; 3)金刚石直接溶解在金属溶液中, 以金刚石形式在颗粒间析出, 填充空隙. 本文研究碳的转化机制为在高温高压金属溶剂法合成金刚石的条件下(6 GPa和1500 ℃的压力和温度范围内)工业批量化制备无添加剂、无空隙的纯金刚石聚晶提供了重要的理论指导.     

MoO_(3-x)/PCN的原位合成及其增强光催化产氢性能的研究（英文）

本文通过简单的一步浸渍煅烧法原位合成了氧化钼纳米晶/聚合物氮化碳复合光催化剂,该不含铂基助催化剂的氧化钼修饰聚合物氮化碳光催化剂在可见光照射下表现出增强的光催化产氢性能,最高产氢速率为15.6μmol/h,是普通聚合物氮化碳样品的3倍以上.相应的结构与性能的分析表明,与后浸渍法不同,在原位生长过程中高分散的超小氧化钼纳米晶体与聚合物氮化碳之间形成了紧密的耦合界面结构,可见光产氢活性的提升源自高分散的超小氧化钼纳米晶与聚合物氮化碳之间形成的紧密界面,以及该界面结构形成的肖特基结带来的有效电荷载流子转移.     

MoO3-x/PCN的原位合成及其增强光催化产氢性能的研究

本文通过简单的一步浸渍煅烧法原位合成了氧化钼纳米晶/聚合物氮化碳复合光催化剂，该不含铂基助催化剂的氧化钼修饰聚合物氮化碳光催化剂在可见光照射下表现出增强的光催化产氢性能，最高产氢速率为15.6 μmol/h，是普通聚合物氮化碳样品的3倍以上. 相应的结构与性能的分析表明，与后浸渍法不同，在原位生长过程中高分散的超小氧化钼纳米晶体与聚合物氮化碳之间形成了紧密的耦合界面结构，可见光产氢活性的提升源自高分散的超小氧化钼纳米晶与聚合物氮化碳之间形成的紧密界面，以及该界面结构形成的肖特基结带来的有效电荷载流子转移.     

V型热解火焰合成碳纳米管的催化剂选择与分析

碳纳米管是一种新型碳材料.催化剂是碳纳米管制备中的重要影响因素,而燃烧法合成碳纳米管必须使用催化剂.本文利用V型热解火焰来研究碳纳米管的合成条件,主要在理论和实验两个方面分析研究了催化剂的作用、种类、颗粒大小、失活等方面对碳纳米管生长的影响,从而为V型热解火焰法合成碳纳米管时催化剂的选取提供依据.理论分析和实验结果表明: Fe(CO)5作为一种铁剂催化剂非常适合催化CO合成碳纳米管.利用碳的"溶解-扩散-析出"机理可以用来解释Fe(CO)5催化CO合成碳纳米管的过程.     

初始温度及碳源对碳纳米管气相爆轰法合成的影响

改变初始温度以及分别使用甲烷和乙炔气体作碳源时气相爆轰合成碳纳米管,研究了初始温度与不同碳源对碳纳米管的影响。利用X射线衍射(XRD)、透射电镜(TEM)、拉曼(Raman)光谱等对碳纳米管进行表征。结果表明,随着初始温度的升高,所合成的碳纳米管的产量减少且石墨化程度降低,但管壁会变得光滑且管径有所增加。当使用乙炔时,所合成的产物中没有碳纳米管,而是合成了石墨化程度较高的无定形碳,随着催化剂量的增加,产物中碳包覆颗粒增多且包覆层清晰可见,但存在结构缺陷。当初始温度在110~130 ℃时,使用甲烷气体运用气相爆轰的手段是合成碳纳米管的较佳方案。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

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.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.