微波辅助制备TiO2光催化剂及应用的研究进展

微波作为一种新型高效的加热制备技术,在材料化学领域中表现出清洁、高效、耗能少、收率高以及选择性好等优点,使其在材料制备等领域得到了广泛的应用。TiO₂由于具有高催化活性、无毒、化学物理性质稳定等优点,在降解环境中的污染物方面受到了极大的关注。将微波加热技术应用在制备TiO₂光催化剂中,可减少热处理时间,降低成本,并有效减少TiO₂材料的团聚现象,得到了更加均一的产品。综述了近几年来微波辅助制备TiO₂光催化剂的5种制备方法：微波水热法、微波溶胶-凝胶法、微波液相沉积法、微波干燥法、微波微乳液法,及其光降解有机污染物中的应用,旨在为促进微波加热技术在TiO₂光催化剂领域中的应用发展提供参考。     

球状ZnS纳米结构的制备及其气敏特性研究

采用两步水热法合成了球状硫化锌(ZnS)纳米结构。利用X射线衍射仪(XRD)、X射线能谱分析仪(EDS)和扫描电子显微镜(SEM)对制得的ZnS纳米结构的晶相、化学组分及微观形貌进行了表征与分析,分析结果表明:制得的ZnS为立方闪锌矿纳米球,平均粒径150nm。同时,对基于ZnS纳米结构的气体传感器进行了甲烷气敏性能测试,实验结果表明:在最佳工作温度(175℃)条件下,该传感器对100×10-6甲烷的响应灵敏度为2.25。     

低温水热法制备ZnS:Co+Cr纳米晶及其光学性能研究

采用低温水热法制备出3-巯基丙酸(MPA)修饰的ZnS:Co+Cr纳米晶. 利用X射线衍射仪、粒度分析仪、透射电镜、紫外-可见分光光度计、荧光分光光度计和XPS能谱仪等对ZnS:Co+Cr纳米晶的结构、形貌、粒径分布和发光性能进行了表征. 结果表明: 合成的ZnS:Co+Cr纳米晶有较好的单分散性, 平均粒径为9.3 nm, 均为立方闪锌矿结构; ZnS:Co+Cr纳米晶的吸收边位于320 nm处, 并在728 nm处出现Co²⁺的特征吸收峰; 当Cr²⁺浓度为0.75at%, 水热反应温度为160℃时, ZnS:Co+Cr纳米晶PL峰最强; XPS能谱表明Cr²⁺部分被氧化成Cr³⁺。     

纳米晶钛酸锶钡(Ba0.5Sr0.5TiO3)粉体的微波水热合成

采用微波水热法合成了纳米晶钛酸锶钡(Ba0.5Sr0.5TiO3)粉体,通过XRD、TEM、SEM等分析手段表征粉体,研究了微波水热合成反应温度、时间和前驱物浓度对反应产物形貌、粒度的影响,获得了制备纳米晶钛酸锶钡粉体的最优工艺参数.实验结果表明:在微波水热反应温度为195℃、反应时间20～30min、前驱物浓度为0.16mol/L时获得的粉体粒径小而且均匀,粉体平均粒度为60nm.     

活性炭负载TiO2复合光催化剂的光催化活性研究

采用水热法将TiO2负载在不同活性炭上形成复合光催化剂,通过SEM和XRD对所得复合催化剂进行表征,并对亚甲基蓝(MB)进行光催化降解。结果表明:复合光催化剂具有很高的光催化降解率,其中椰壳活性炭载体优于煤质活性炭载体。负载的TiO2均为锐钛矿晶型,晶粒发育较完善、粒径小、分布均匀。TiO2负载量的提高未能改变光催化活性,反而降低了复合光催化剂的吸附能力。煅烧处理可以进一步提高光催化活性。     

ZnS:Cu纳米颗粒的制备及发光性质

采用水热法制备了Cu离子掺杂的ZnS(ZnS:Cu)纳米颗粒,研究了锌硫比和反应时间对ZnS:Cu纳米颗粒光致发光性质的影响.通过X射线衍射(XRD)和透射电子显微镜(TEM)对样品的物相和形貌进行分析表征,发现该方法得到立方闪锌矿结构的球形ZnS: Cu纳米晶,粒径在1～6nm之间.室温下,用350nm波长的紫外光激发ZnS:Cu纳米粒子,可以得到归属于浅施主能级与铜￡z能级之间的跃迁产生的绿色发光,发光强度随锌硫比的增大和反应时间的延长先增强后减弱,发射峰位随锌硫比和反应时间的变化有一定移动.认为浅施主能级为与硫空位有关的能级,锌硫比和反应时间对硫空往的数量和能级位置有一定影响.     

HY沸石层接层法负载ZnS及光催化性能研究

为得到高效廉价的光催化剂,利用层接层技术,以HY沸石为载体在其表面通过Zn2+与聚乙烯亚胺(PEI)分子链上的NH2(或-NH-)络合作用,经硫化、退火处理制备出HY/(ZnS)n光催化剂,并通过UV-Vis测试和催化制氢实验进行光催化性能研究.研究表明:HY/(ZnS)n催化剂对紫外光有响应,且光催化产氢总量和产氢平均速率均随着负载层数n的增大而增大.进一步通过XRD、XPS、SEM-EDS分析手段对制得的光催化剂结构和物化性质进行了表征,分析表明,在HY沸石表面负载,形成了纤维棒状立方闪锌矿结构的ZnS.     

ZnS微球的水热法合成与光催化活性

以硝酸锌为锌源、硫脲和硫代乙酰胺为硫源、表面活性剂十六烷基三甲基溴化铵(CTAB)为软模板,采用水热法成功合成了ZnS微球,借助XRD,XPS,SEM和UV-vis等多种测试手段对其进行了表征,并以罗丹明B为模型污染物研究了样品的光催化性能.物相结构分析表明,所得样品为纯度较高的立方闪锌矿型ZnS;SEM分析表明,样品为纳米级的ZnS粒子层层堆积组装而成的微球体,以硫代乙酰胺为硫源时,微球直径在500～1000nm之间,而以硫脲为硫源时微球直径约为1.5μm;UV-vis吸收光谱分析表明样品在200～320nm波长范围内对光有较强的吸收,作为光催化剂具有一定应用潜力.     

磁载核壳型TiO_2复合光催化剂的研究进展

TiO2是一种高效的光催化剂,为解决TiO2纳米颗粒从悬浮体系中分离回收难的问题,可将其包覆于磁性微球之外,借助于磁场的作用实现快速有效分离。简要介绍了磁载核壳型TiO2复合光催化剂的基本概念、分类及制备方法。根据磁载复合光催化剂的核壳之间是否包覆结合层,将其分为直接包覆磁载TiO2光催化剂和非直接包覆磁载TiO2光催化剂。磁载TiO2复合光催化剂的制备方法有溶胶-凝胶法、均匀沉淀法、微乳液法、原位生长法以及微波水热法等。还介绍了磁载核壳型TiO2复合光催化剂在水处理方面的应用,并且对其未来的发展前景进行了展望。     

微波辅助合成ZnS∶Ce纳米晶

以乙酸锌为锌源、硫酸高铈为铈源、硫代乙酰胺为硫源、淀粉为分散剂,微波辅助合成了ZnS∶Ce纳米晶。通过X射线衍射仪、红外光谱仪、荧光分光光度计和激光粒度分析仪对其物相结构、原子键价结构、光学性能和颗粒粒径大小进行了表征分析。研究了不同Ce离子掺杂量对产品结构和光学性能的影响。结果表明:所制备的ZnS∶Ce纳米晶体具有闪锌矿立方相结构,其晶粒大小分布范围为3.5~4.5nm;颗粒大小范围为100~600nm,D50=290nm。激发波长为230nm时,其荧光发射峰在408nm处;掺杂Ce离子浓度增加,ZnS∶Ce纳米晶材料的荧光强度降低,其原因是发生了浓度淬灭现象。     

水溶性ZnS量子点的共沉淀法制备、 表征及其光学性能

以硫化钠和乙酸锌为反应物,3-巯基丙酸为表面包覆剂,利用共沉淀法制备了水溶性ZnS量子点。并采用X射线衍射仪、透射电子显微镜和荧光分光光度计等对样品的结构、形貌、粒径和光学性能进行了表征。结果表明:所得样品为ZnS立方型闪锌矿结构,量子点的形状呈不规则球形,粒径主要集中在4.8nm左右;样品在585～590nm之间出现了黄色荧光发射波峰。同时,利用红外光谱对ZnS量子点的合成机理进行了初步分析。     

Continuous white luminescence of ZnS:Pb2+ and core/shell ZnS:Pb2+/ZnS nanocrystals

High-quality water-soluble ZnS:Pb2+ nanocrystals were synthesized via a simple chemical codepositing method. The as-synthesized ZnS:Pb2+ nanocrystals show high monodispersity and crystallinity with a narrow size distribution (3.2 +/- 0.4 nm). ZnS:Pb2+/ZnS core/shell structures were also obtained by coating a ZnS shell displaying significantly enhanced photoluminescence (PL) intensity and photostability. For the ZnS:Pb2+/ZnS samples the position of emission spectrum shows a red-shift of approximately 10 nm, which produces a fairly pure white emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.31, 0.33). These phenomena are explained by a model of multiple Pb2+ luminescent centers.     

Chemical vapor deposition synthesis and photoluminescence properties of ZnS hollow microspheres

ZnS hollow microspheres were prepared via a facile template-free chemical vapor deposition (CVD) route using metallic zinc powders and sulphur sublimed as reactants. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometer (EDX). The results showed that the as-prepared ZnS hollow spheres had uniform size about 4–8 μm in diameter. The growth mechanism of such interesting was discussed. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.     

Mechanochemical Synthesis and Characterization of Group II-VI Semiconductor Nanoparticles

Synthesis of metal sulfide semiconductor nanoparticles of group II-VI; namely ZnS, PbS, CdS, and CuS; by mechanochemical method was carried out in a high energy ball mill from corresponding metal acetates and sodium sulfide. The samples were continuously milled for 10 h with sample withdrawal at 2 h time interval. Structural properties of nanoparticles were studied by x-ray diffraction (XRD), transmission electron microscope (TEM), and ultraviolet-visible spectra. Particle size distribution and stability of 10 h milled samples were examined using particle size analyzer and Turbiscan. It was found that nanoparticles synthesized by mechanochemical method had mean particle sizes as small as 2–25 nm, low agglomeration, narrow size distribution, and uniformity of particle structure and morphology.     

Effect of activator distribution on photo- and X-ray excited luminescence properties of ZnS:Cu,Cl phosphors

ZnS:Cu,Cl phosphors were prepared by conventional solid state reaction with the aid of NaCl-MgCl₂ flux. The copper activator was introduced into the phosphor precursors by three different methods: co-precipitated with ZnS (CP), wet-coated onto ZnS powders (WC), and simply mixed with ZnS in a mortar (SM). The samples were characterized by X-ray powder diffraction, photoluminescence spectra and X-ray excited luminescence spectra. The results show that both photo- and X-ray excited luminescence intensities of the as-prepared ZnS:Cu,Cl phosphors are in the decreasing order of CP > WC > SM. The different copper activator distribution in the phosphors resulting from the different methods was the main reason responsible for the different luminescence intensity, and uniform distribution is beneficial to the luminescence of the phosphors.     

ZnS/ SiO2 介孔组装体系的发光性质

通过Sol-gel 法得到SiO₂ 介孔固体, 浸泡热分解后获得ZnS/ SiO₂ 介孔组装体。吸收光谱和荧光光谱表明: 随复合量增大, 蓝移量减小; 在氮气中退火后, 吸收边位置和荧光谱中的峰位随退火温度升高向长波方向移动且发光增强, 450 ℃以后减缓。经计算, 颗粒尺寸的理论值与其自由激子半径相当, 说明吸收边的移动起因于量子尺寸效应。      

Photocatalytic mineralization of carboxylic acids over Fe-loaded ZnS nanoparticles

Zinc sulfide (ZnS) nanoparticles prepared by hydrothermal synthesis were subsequentially impregnated with different iron amounts (0.5−5.0 at%) to obtain Fe-loaded ZnS nanoparticles. Phase composition, crystallinity, crystal size, and morphology of 0.5–5.0 at% Fe-loaded ZnS nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). Specific surface area determined by the Brunauer, Emmett and Teller (BET) method was found to be in the range of 85–197 m²/g. The average particle size obtained from TEM analysis of pure ZnS and 2.0 at% Fe-loaded ZnS nanoparticles was 5–20 nm. The optical absorption properties of the samples measured by UV–vis diffuse reflectance spectroscopy (UV–vis DRS) clearly indicated the bathochromic shift upon loading ZnS with Fe. Photocatalytic activities of pure ZnS and Fe-loaded ZnS nanoparticles were examined by studying the mineralization of oxalic acid and formic acid under UVA illumination. It was found that 2.0 at% Fe-loaded ZnS sample exhibited the highest degradation activity possibly due to the presence of Fe in an optimum amount and the increases of surface area and light absorption in UVA region.     

Multicolor luminescence from transition metal ion (Mn2+ and Cu2+) doped ZnS nanoparticles

Mn and Cu doped ZnS nanoparticles in powder form were prepared by a simple solvothermal route. Particle size and crystal structure of the products were investigated through X-ray diffraction study revealing the formation of cubic ZnS nanoparticles of average diameter 2.5 nm. Particle size was also verified by the high resolution transmission electron microscopic images. Blue emission at approximately 445 nm was observed from the undoped sample, which was attributed to the presence of large surface defects. With increasing doping concentration the defect related emission gradually quenches and subsequently the impurity related emissions appeared. Mn doped samples exhibited orange emission at approximately 580 nm which may be attributed to the transition between (4)T1 and (6)A1 energy levels of the Mn2+ 3d states. Whereas, the Cu doped ZnS nanoparticles exhibited a red shifted strong blue emission at approximately 466 nm which is attributed to the transition of the electrons from the surface states to the 't2' levels of Cu impurities.     

High yield growth of uniform ZnS nanospheres with strong photoluminescence properties

High yield ZnS nanospheres were generated conveniently in aqueous solution with the assistance of surfactant polyvinyl pyrrolidone (PVP). The products were characterized by XRD, EDX, XPS, FESEM, TEM and HRTEM. The as-prepared ZnS nanospheres were uniform with an average diameter of 80 nm. The role of PVP in the forming of ZnS nanospheres was investigated. The results indicated that surfactant PVP plays a crucial role on the morphology and size of the products. Moreover, a tentative explanation for the growth mechanism of ZnS nanospheres was proposed. UV–vis and PL absorption spectrum were used to investigate the optical properties of ZnS nanospheres. The UV–vis spectrum indicated that the sample exhibits a dramatic blue-shift. PL spectrum reveals that ZnS nanospheres have a strong visible emission peak centered at 516 nm with excitation light of 400 nm.