何丽雯
HE Liwen
中图分类号: O611.5, O613.51
文章编号: 1005-3093(2016)04-0285-07
通讯作者:
收稿日期: 2015-09-24
网络出版日期: 2016-04-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
基金资助:
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摘要
采用剥离-重堆积的方法将聚合羟基锆离子和Co2+混合溶液嵌入到钛酸盐板层间, 制得了钴掺杂锆柱撑材料(CZPT), 考察了Co对锆柱撑复合材料(简写为ZPT)的形成及其催化活性的影响。利用X-射线衍射(XRD)、扫描/透射电子显微镜(SEM/HR-TEM)、紫外-可见吸收光谱(UV-Vis)和N2吸附等方法对复合材料进行了表征。结果表明, 掺入质量分数为5%(1∶20)的Co可以使ZPT样品的介孔和比表面积明显增大。同时, 可以抑制体系光生电子与空穴的复合, 吸收光波长有明显的红移。CZPT系列柱撑材料在紫外和可见光辐照下催化降解罗丹明(RhB)的脱色率明显高于ZPT。其中, 复合材料CZPT-5的催化活性最好, 表明材料的光催化活性还与掺杂后柱撑材料中含Co客体与主体间的电子耦合作用有关。
关键词：
Abstract
Mesoporous nanocomposite of Co-doped hydroxyl-Zr -pillared titanate (CZPT) was prepared via an exfoliation-restacking route, and the pre-exfoliated layered titanate was reassembled in an aqueous solution containing hydroxyl-Zr oligocations and Co ions. The influence of the doping Co cations on the preparation and catalytic activity of Zr-pillared titanate (abbreviated as ZPT) composites was investigated. The prepared CZPT was characterized by powder X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV-Vis spectra and porosity measurements. XRD and N2 absorption results suggested that the ZPT doped with 5% Co (mass fraction) had bigger pore diameter and specific area. The presence of 5% Co could effectively suppress the annihilation of the photogenerated hole-electron pairs, and correspondingly the absorption wavelength exhibits obviously red-shift. The degradation of rhodamine B (RhB) under ultraviolet and visible radiation shows that the as-prepared nanocomposite exhibits higher photocatalytic activities than that of layered titanate alone. The enhanced photocatalytic activity of the as-prepared nanocomposite CZPT-5 for the degradation of RhB under visible irradiation may be attributed to the coupling interaction between cations of the host and the Co containing guest.
Keywords：
大气雾霾和废水中具有较大毒性的污染物主要是有机物分子, 它们直接危害人类的身体健康。通常采用化学方法将有机污染物分子逐步分解为CO2和H2O来治污[1-9]。近年来, 二氧化钛与钛酸盐等材料可以利用光催化途径来分解污染物 [8-13]。由于污染物分子通常较大, 光催化反应只能在催化剂的表面发生, 污染物分解效率较低。通过剥离-重堆积的方法, 将大尺寸客体羟基锆离子[Zr4(OH)16-n(H2O)8+n]n+(简写为Zr4)引入到粘土[14]、蒙脱土[15]及钛酸盐[16]等层状物质的层间, 可制备出满足污染物吸附-脱附的介孔纳米插层催化/光催化材料。
目前针对上述材料的研究重点集中于提高光催化剂的光响应范围和光电转化效率, 掺杂改性是能有效改善光催化性能的常用方法[17-20]。N[17]、S[18]、Fe[19]、Ag[11]等金属和非金属的掺杂可有效提高二氧化钛的吸收光响应范围以及催化活性。钴离子用于半导体光催化剂的掺杂时, 具有捕获光生载流子作用。同时, 大多数含Co化合物通常显示鲜艳的颜色, 具有较宽的光响应范围[8, 20]。本文在前期研究的基础上[23, 24], 结合钴的可见光响应活性和锆柱撑钛酸盐材料的结构可调控性, 构筑了掺Co羟基锆柱撑钛酸盐介孔复合材料, 对其结构和光吸收等性能进行表征, 并以罗丹明(RhB)染料废水为光催化降解对象, 评价掺Co复合材料的光催化性能。
实验所用试剂包括: 碳酸铯(分析纯), 八水合氯氧化锆(分析纯), 六水合氯化钴(分析纯), 钛酸四正丁酯(分析纯), 盐酸(质量分数为36%-38%)(分析纯), 硝酸(质量分数为65%-68%)(分析纯), 硝酸银(分析纯), 罗丹明B(分析纯), 四丁基氢氧化铵(25%) (分析纯)。试验用水均为二次去离子水。
复合材料的制备流程如图1所示。参照文献[23, 24]方法, 将TiO2与Cs2CO3按摩尔比5∶1混合并加水研磨, 在800℃下处理20 h制得CsxTi2-x/4□x/4O4 (x=0.7, □=空位)。称取5 g产物CsxTi2-x/4□x/4O4加入到500 mL的HCl(1 molL-1)中搅拌。将悬浊液离心洗涤, 沉淀物于60℃恒温干燥, 得到酸化物HxTi2-x/4□x/4O4H2O (x=0.7)。将0.25 g上述酸化物粉末加入到250 mL 四丁基氢氧化铵(TBAOH)水溶液中。室温下超声振荡60 min后, 将悬浮液离心。所得悬浮液即为钛酸盐单分子层(pH=10-11)。
图1 剥离-重堆积法制备钛酸盐复合材料流程图
Fig.1 Schematic illustration of the exfoliation-restacking route to prepare titanate composites
称取ZrOCl28(H2O)与CoCl26(H2O)粉末分别配制成0.1 molL-1的溶液, 按n(Ti)∶n(Zr+Co) = 5∶1且n(Zr)/n(Co) = 5∶1、10∶1和20∶1分别配制3份锆和钴的混合柱撑液。在60℃恒温搅拌下, 以10 mLmin-1的速率分别将柱撑液滴加到钛酸盐单分子层悬浮液中, 冷却至室温并调节体系pH至5.0-6.0, 静置陈化得到白色沉淀物。用蒸馏水多次洗涤至无Cl- (AgNO3检验), 再将沉淀物置于80℃的真空干燥箱中烘干, 得到掺钴羟基锆柱撑钛酸盐复合材料, 分别记为CZPT-5、CZPT-10和CZPT-20。
用D8 Advance X-射线粉末衍射仪(CuKα靶)测试材料的晶体结构, 工作电压40 kV, 电流40 mA。用JEOL-JEM 2100场发射透射电子显微镜(HR-TEM)和ZEISS EVO18型扫描电镜(SEM)观察微观形貌。用Autosorb-iQ型全自动物理/化学吸附分析仪对比表面积和孔径进行分析, 用BET公式计算材料的比表面积和孔大小。比表面积的测试采用多点法, 且p /p0<0.35, SBET的相关系数R为0.9999; 总孔容取自在N2约p/p0=0.97吸附量计算; 平均孔径(直径)由Barrett-Joyner-Halenda公式计算。用UV-2550型紫外-可见漫反射光谱仪测量样品的吸收光谱, BaSO4作参比样。
本文以光催化降解有机染料罗丹明B(简写为RhB)的反应为探针来评价样品光催化活性。反应在自制的间歇式反应装置中进行[8]。紫外光源为主波长254 nm荧光紫外灯, 可见光光源为Changtuo 500 W氙弧灯(主要为波长大于400 nm, 并用滤光片滤去红外和波长小于400 nm的紫外光)。RhB初始浓度为10 mgL-1。实验时, 将催化剂分散在RhB溶液中, 将形成的悬浮液避光预搅拌30 min, 使之达到吸附-脱附平衡后的RhB浓度为C0。分别打开装置紫外光和可见光辐照, 每间隔一段时间移取3.0 mL悬浮液溶液, 用UV-2550 型紫外-可见分光光度计测试RhB溶液在lmax = 554 nm处的吸光度, 并计算该时间处RhB溶液的浓度Ct。在光催化反应中, 用溶液中RhB的降解率α来反映催化剂的光催化性能: α = [(C0–Ct) / C0]×100%。试验完成后溶液过滤出催化剂进行2次重复性实验。
图2为钛酸铯、氢化钛酸盐和柱撑材料ZPT-5、CZPT-5、CZPT-10和CZPT-20 的XRD谱。可以看出, 钛酸铯(曲线a)和钛酸HxTi2-x/4□x/4O4H2O(曲线b)XRD谱线的衍射峰(020) 2θ 由10.5°向低角度9.6°移动, 形成了0.92 nm的层间距增量, 这是由于水分子和质子H进入到钛酸铯层板间[8]。单分子层纳米片层与客体离子发生静电相互作用后重堆积, 形成柱撑复合材料ZPT-5(曲线c-f), 层间距增大。掺钴羟基锆柱撑材料CZPT-20、CZPT-10和CZPT-5的层间距较之未掺杂前ZPT-5, 由2.01 nm增至2.20 nm, 扣除钛酸盐板层厚度0.75 nm[24], 层间距增量由1.25 nm增至1.45 nm。 这一方面说明锆柱撑液中加入Co2+后, Co2+可取代四核羟基锆离子Zr4中Zr4+形成含钴新团簇[25], 体系电荷密度分布失衡, 直接造成Zr4离子与纳米片层之间的相互作用力变小, 层间距增加。另一方面, 由于ZrOCl2复杂的水解平衡[23-26], 随着Co含量的增加, 柱撑液中会不断有粒度大于或者小于Zr4离子的水解产物出现, 它们与主体板层由于静电作用堆积时, 主客体间作用力不平衡导致柱撑材料的结构畸变, 层间距变化。同时, 也不排除体积较小的钴离子嵌入层间的可能。从图2曲线d-f可以看出, 掺杂后柱撑材料的XRD谱出现明显弥散现象, 这进一步说明钴的掺入导致了进入板层间客体离子的种类及其大小和取向趋于多样化。
图2 钛酸铯、氢化钛酸盐和柱撑材料的XRD谱
Fig.2 Powder XRD spectra of layered cesium titanate (a), layered protonic titanate (b), ZPT-5 (c), CZPT-20 (d), CZPT-10 (e) and CZPT-5 (f)
结合表1和2数据可知, 从ZPT到CZPT-10, 柱撑材料中实际Co的含量也随之增加, 材料孔容和比表面积均有所增大, 孔径则有所减小, 说明钴的掺入有利于形成掺钴Zr4离子, 形成较好的柱撑结构, 有效增大了材料的比表面积; 从CZPT-10到CZPT-5, 钴的实际增加量很小, 说明层间电荷密度趋于饱和。另外, Co的掺入可能会使内部孔道被小尺寸的钴与锆的水解产物离子部分填充, 平均孔径和比表面积也会发生上述变化。
表1 样品的N2等温吸附-脱附曲线测量所得的数据
Table 1 Parameters obtained from N2 adsorption-desorption measurements
| Sample | Surface area/m2g-1 | Pore volume /mLg -1 | Average pore size /nm |
|---|---|---|---|
| SBET | |||
| CsxTi2-x/4□x/4O4 | ~1 | – | – |
| CZPT-20 | 121 | 0.35 | 3.71 |
| CZPT-10 | 122 | 0.36 | 3.66 |
| CZPT-5 | 145 | 0.40 | 3.61 |
| ZPT-5 | 108 | 0.34 | 3.81 |
表2 柱撑材料的元素组成
Table 2 Compositions of pillared composites (%, atomic fraction)
| Sample | Composition | |||
|---|---|---|---|---|
| Co | Zr | Ti | O | |
| CZPT-20 | 0.05 | 16.27 | 19.02 | 64.66 |
| CZPT-10 | 0.12 | 15.04 | 17.92 | 66.93 |
| CZPT-5 | 0.14 | 14.45 | 16.99 | 68.43 |
图3为柱撑材料ZPT-5和CZPT-5的N2吸附-脱附曲线。可以看出, ZPT-5及掺杂后ZPT-5的吸附-脱附曲线变化趋势相似, 均为具有滞留环的Ⅳ型等温线, 表明这两种材料中具有介孔结构。介孔的存在使得有机物分子可以迅速扩散到光催化剂的活性部位, 发生降解反应, 并使产物分子能较快地扩散出去。
图3 柱撑材料的N2等温吸脱附曲线
Fig.3 Nitrogen adsorption (closed symbols)-desorption (opened symbols) isotherms of ZPT-5 (a) and CZPT-5 (b)
图4是CZPT-5的SEM和HRTEM像, 从图4a中可以看出, 柱撑材料呈层状材料的碎片堆积形貌。颗粒表面少量的低衬度物, 可能是部分客体离子直接吸附在材料表面上。图4b表明, 柱撑材料颗粒中存在不同排列方向的晶粒, 同一晶粒中的钛酸盐单分子层平行堆积, 层间填充的是客体离子。值得注意的是, 从图还可以观察到部分略为弯曲的钛酸盐单分子层轮廓, 这种二维纳米片层的变形性为柱撑结构的主客体组装提供了有利条件, 由此导致的晶格畸变表现为XRD衍射峰的宽化。由于掺入后层间域离子的种类多样化, 主客体间的作用力导致结构畸变, 形成大量的板层破裂。不同方向交错的片层无序堆积会形成内部介孔孔洞, 这有利于催化材料对有机污染物的吸附与扩散。
2.3紫外-可见漫散射谱分析
图5a和b分别为样品的紫外-可见漫散射吸收谱(UV-Vis DRS)和(F(R)×hν)0.5对能量(hν)变化关系曲线。如图5a所示, 从300 nm开始, 各样品的吸收值均迅速增大, 到390 nm左右吸收值达到最大; 柱撑钛酸盐的紫外吸收边界在320 nm左右[23], 经Co2+掺杂后, 掺钴锆柱撑钛酸盐复合材料的吸收带边向长波方向红移了60-100 nm, 这进一步收窄了禁带宽度, 将主体材料的吸收光谱带拓展到可见光的范围(图5b)。图5a中350 nm左右的吸收峰归属为Co2+→Zr4+的电荷跃迁, 即Co2+掺杂能级上的电子跃迁到ZrO2的导带; 而600 nm的吸收峰应为Co2+的d-d跃迁。根据文献[27]的处理方法, 测得CZPT-5、CZPT-10和CZPT-20的禁带宽度分别约为2.5 eV、3.1 eV和2.9 eV。柱撑材料随着Co掺杂量的增大, 带隙有减小的趋势, 禁带宽度的收窄能有效增加光致载流子的生成效率, 增强材料的光催化性能。同时, 图5b中在1.7 eV左右出现能隙说明可能有钴的水合离子的掺入。
图5 样品的UV-Vis漫散射吸收光谱(a)和相应的(F(R)hv)0.5-hv关系曲线(b)
Fig.5 UV-Vis diffuse reflectance spectra (a) and (F(R)hv)0.5-hv curves (b) of CZPT samples
不同钴掺杂量下锆柱撑催化剂在紫外-可见光辐照下RhB的脱色率如图6柱状图所示。在催化反应发生前, 通过将催化剂分散在RhB溶液中并在暗室中预先搅拌30 min, 让体系达到吸附-脱附平衡。从UV-Vis谱分析可知, 柱撑材料的吸收光波长大多处于紫外光范围, 故全紫外光辐照下的脱色率高于在可见光辐照下的。
图6 样品光催化降解罗丹明B的降解率
Fig.6 Photodegradation of rhodamine B by layered titanate, ZPT-5, CZPT-20, CZPT-10 and CZPT-5
从图6可以看出, 在紫外光激发下, 120 min后的最终催化降解率排序为CZPT-5 > CZPT-10 > CZPT-20 > ZPT-5 > 层状钛酸盐, 这一变化规律与表1中所列样品比表面积的变化规律相同。与其他纳米片层基复合材料的组装类似, 锆及其掺杂柱撑材料高的比表面积结构是光催化活性远大于主体材料的主要原因[10, 14, 23-26]。同时, Co2+掺杂后复合柱撑材料的催化活性高于掺杂前, 且随着Co2+掺杂量的增加, RhB脱色率逐渐增大, 这表明Co2+掺入后, 柱撑体系层间域中客体趋于多样化, 主客体间的作用力趋于复杂, 致使柱撑材料的XRD谱出现弥散现象, 抑制了柱撑材料晶粒的生长, 比表面积进一步增大。增大的比表面积必然会增加活性位点, 活性点的增多提升了催化剂激发出的光生载流子的效率。
催化剂材料孔结构孔大小和分布特性会直接影响到污染物及产物分子的扩散, 从而影响催化降解反应的动力学进程。钛酸盐柱撑材料形成了较多介孔能有效满足污染物反应和扩散, 因而催化性能远高于未柱撑主体钛酸盐板层。而钴的掺杂可能会导致材料形成了孔容更大的介孔(表1), 有利于进一步提高吸-脱附效率。CZPT-5、CZPT-10和CZPT-20对RhB的脱色率分别为91.71%、87.14%和79.91%, 均为未柱撑钛酸盐(12.91%)的6倍多, 为掺杂前ZPT-5(52.13%)的1.5倍多。除以上原因外, 可能还与Co元素助催化作用有关[23, 26]。
用波长λ > 420 nm的可见光来考察催化剂降解RhB的情况, 结果如图6所示。研究表明, 柱撑材料ZPT-5将主体钛酸盐的能隙从3.7 eV减小到3.1 eV以下[25]。结合材料的UV-Vis DRS分析（图5）可以看出, 随着钴掺杂量的增大, 掺杂钴离子后的CZPT-5将其禁带宽度减小至2.5 eV左右(图5b), 材料在可见光区的吸收增强, 可见光催化活性随之增大, 说明基于主体-客体间的电子耦合可能会提高催化剂的光催化活性。由XRD和UV-Vis分析可知, Co2+的引入除了取代Zr4离子形成新的Zr4团簇, 窄化了聚合Zr4的带隙, 同时可能引入的钴的氧化物具有较小的带隙, 有利于提高可见光利用率。它们可与主体板层依靠静电力作用形成欧姆接触的异质结, 这种耦合效应有利于阻止电子-空穴对的复合[28]。禁带宽度的收窄意味着吸收波长的范围的拓展, 当可见光照射到催化剂表面时, 吸收并参与到光电转化有效能量越多, 单位时间内激发出的光生电子-空穴对增大, 有利于将更多的RhB分子转化为碳水化合物。
表3是催化剂的重复催化实验数据。由表可知, 所有柱撑材料光催化活性的可重复性均不好, CZPT略好于ZPT, 且CZPT中实际钴含量越高, 其重复性越差。主要原因如下: 一方面, CZPT由于主体片层存在较多的小粒径离子的直接吸附, 经过催化反应后, 这部分离子较容易流失, 减少了材料的活性部位; 另一方面, 光催化过程中不可避免有RhB分子吸附于材料的孔内, 再次使用时不能发挥作用, 这也会影响重复性试验时的光催化效率。
表3 柱撑材料的重复催化实验
Table 3 The repeatability of pillared composites (%)
| Sample | 1st | 2nd | 3rd |
|---|---|---|---|
| ZPT-5 | 52.13 | 46.18 | 39.96 |
| CZPT-20 | 79.91 | 61.25 | 49.68 |
| CZPT-10 | 87.14 | 58.59 | 41.01 |
| CZPT-5 | 91.71 | 55.32 | 39.23 |
将掺杂钴的羟基锆离子与剥离后的钛酸盐单分子溶液混合, 通过重堆积反应制得CZPT复合材料。UV-Vis DRS谱表明, 复合材料的吸收边发生了红移, 材料带隙变窄。ZPT的带隙Eg为3.3 eV, 而CZPT-5、CZPT-10和CZPT-20的带隙分别约为2.5 eV、3.1 eV和2.9 eV。在紫外-可见光下催化降解罗丹明B的反应中, 复合材料CZPT呈现出比ZPT更强的光催化活性, 而且随着钴掺杂量的增加, 光催化降解率逐渐提高。研究表明, 钴的掺杂有利于提高柱撑体系的比表面积, 提高材料的可见光利用率。
The authors have declared that no competing interests exist.
| [1] |
Nano-photocatalytic materials: possibilities and challenges ,
Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.
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| [2] |
Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst ,
The photocatalytic splitting of water into hydrogen and oxygen using solar energy is a potentially clean and renewable source for hydrogen fuel. The first photocatalysts suitable for water splitting, or for activating hydrogen production from carbohydrate compounds made by plants from water and carbon dioxide, were developed several decades ago. But these catalysts operate with ultraviolet light, which accounts for only 4% of the incoming solar energy and thus renders the overall process impractical. For this reason, considerable efforts have been invested in developing photocatalysts capable of using the less energetic but more abundant visible light, which accounts for about 43% of the incoming solar energy. However, systems that are sufficiently stable and efficient for practical use have not yet been realized. Here we show that doping of indium-tantalum-oxide with nickel yields a series of photocatalysts, InNiTaO(x = 0-0.2), which induces direct splitting of water into stoichiometric amounts of oxygen and hydrogen under visible light irradiation with a quantum yield of about 0.66%. Our findings suggest that the use of solar energy for photocatalytic water splitting might provide a viable source for `clean' hydrogen fuel, once the catalytic efficiency of the semiconductor system has been improved by increasing its surface area and suitable modifications of the surface sites.
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| [3] |
Preparation and visible light photocatalytic activties of hollow nanospheres of Ag+/Ag-TiO2 ,Ag+/Ag-TiO2纳米空心球制备及其可见光催化性能 ,Magsci 摘要
<p>在TiO<sub>2</sub>/聚苯乙烯复合材料表面沉积硫化银, 空气中煅烧制备了Ag<sup>+</sup>/Ag修饰的二氧化钛纳米空心球(Ag<sup>+</sup>/Ag-TiO<sub>2</sub>纳米空心球, 即Ag<sup>+</sup>/Ag-HTS)。结果表明, 所制备的Ag<sup>+</sup>/Ag-HTS具有可见光催化降解甲基橙的活性, 随着甲基橙的初始浓度降低其催化降解效率提高。肖特基势垒的形成有助于更多的空穴转移到材料的表面, 增强其光催化效率; 表面的Ag<sup>+</sup>有助于电子的清除, 防止光激电子与光激空穴复合。随着硫化银沉积数量的提高, Ag<sup>+</sup>/Ag-HTS的可见光催化活性提高, 其光催化降解甲基橙的反应具有假一级反应的动力学特征。使用25% Ag<sup>+</sup>/Ag-HTS光催化剂, 在可见光下照射2 h甲基橙降解率高达70.6%。</p>
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| [4] |
Heterogeneous fenton oxidation of refractory dye rhodamine B in aqueous solution with mesoporous Fe/SBA-15 ,
介孔Fe/SBA-15非均相芬顿氧化水中难降解染料罗丹明B ,
以介孔二氧化硅SBA-15为 载体,采用等体积浸渍法制备了Fe/SBA-15.通过X射线衍射(XRD)、N2吸附-脱附、扫描电镜(SEM)、透射电镜(TEM)和X射线光电子能 谱(XPS)等技术对其进行了表征,并用于对水溶液中罗丹明B(Rh B)的芬顿氧化.表征结果表明了Fe/SBA-15维持了长程有序的介孔结构,孔径和比表面积都有所下降,并呈现棒状体的聚集态,平均直径为 0.6μm.Fe以α-Fe2O3的形态同时存在于介孔孔道内外.在Fe/SBA-15和H2O2同时存在条件下Rh B的去除是吸附和催化氧化降解的协同作用所致,并且与Fe/SBA-15投加量密切相关,但与初始溶液p H几乎无关.当Fe/SBA-15投加量为0.15 gL-1,Rh B初始浓度为10.0 mgL-1,H2O2/Fe3+摩尔比为2000:1,初始溶液p H为5.4和反应温度为21°C时,Rh B去除率达到了93%.Fe/SBA-15的Langmiur单分子层饱和吸附量为99.11 mgg-1.此外,采用H2O2浸泡方式对使用过的Fe/SBA-15可进行再生,连续6次循环使用后仍可维持80%的Rh B去除率,且每次使用后Fe浸出浓度都在0.1 mgL-1(或者0.6%(质量分数))以下.基于淬灭实验、UV-Vis光谱和气相色谱-质谱(GC-MS)联用仪分析的结果,提出了Rh B的去除机理.非均相芬顿催化剂Fe/SBA-15可用于去除像Rh B这样的生物难降解有机物.
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| [5] |
Enhanced visible-light photocatalytic activity and stability over g-C3N4/Ag2CO3 composites ,
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| [6] |
Visible light driven photocatalytic degradation of Rhodamine B and Direct Red using cobalt oxide nanoparticles ,
Cobalt oxide (Co 3 O 4 ) nanoparticles were prepared by simple, facile and cost effective sol–gel route. Triethanol amine (TEA) was used as surfactant to reduce the size of the particles. The XRD patterns reveal that the crystallite size of the sample prepared without surfactant yields 6902nm and with different surfactant concentrations (502ml, 1002ml, and 1502ml), the estimated crystallite sizes were reduced to 6402nm, 5202nm, and 3202nm respectively. The morphological and elemental composition of the samples was investigated by SEM and EDS. The optical studies revealed the possible electronic transitions which are responsible for an occurrence of two energy band gap in cobalt oxide. The photoluminescence probe for the presence of defects and the results obtained specified that the defects get reduced with the addition of surfactant TEA. Photocatalytic degradation of dyes (Rhodamine B and Direct Red 80) was investigated under visible light using cobalt oxide nanoparticles as catalyst. The effect of catalyst amount and pH of the dye solution was analyzed with the help of UV–visible absorption spectra.
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| [7] |
ZnO and cobalt phthalocyanine hybridized graphene: Efficient photocatalysts for degradation of rhodamine B ,
A novel method has been developed to synthesize graphene–ZnO composite as a highly efficient catalyst by reduction of graphite oxide and in situ deposition of ZnO nanoparticles by chemical reduction reaction. The graphene–ZnO catalyst is capable of complete degradation of rhodamine B under exposure to natural sunlight. Further, the catalytic efficiency of graphene–ZnO catalyst was enhanced by sensitizing with cobalt phthalocyanine. The formation of graphene–ZnO photocatalyst and its further sensitization with cobalt phthalocyanine was characterized using UV–vis, ATR-IR and Raman spectroscopy, powder XRD and thermogravimetric analysis. The morphology of both graphene–ZnO and graphene–ZnO–CoPC catalysts was analyzed using scanning and transmission electron microscopes.
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| [8] |
Mesoporous cobalt-intercalated layered tantalotungstate with high visible-light photocatalytic activity ,
Cobalt-intercalated layered tantalotungstates as high visible-light active photocatalysts have been assembled by tantalotungstatete nanosheets with cobalt ions via an exfoliation–restacking route. It was revealed that the as-prepared nanohybrids are mesoporous with specific surface areas more than 3502m 2 /g and that the cobalt element in the materials is bivalent. The mesopores with average pore diameters of about 4.002nm are originated from the house-of-cards-type stacking of the intercalated crystallites. Introducing cobalt ions into the interlayered region endowed the nanohybrids with distinct spectral responses in visible-light region, resulted from the hybridization of metal d and f orbits in conduction band to narrow the band gap. The intercalated nanohybrids exhibit high photocatalytic activities in the degradation of methylene blue under visible-light irradiation.
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| [9] |
Preparation and characterization of mesoporous TiO2-pillared titanate photocatalyst ,
Mesoporous anatase TiO2-pillared titanate has been successfully prepared by the exfoliation-restacking route. The resulting nanocomposite was characterized by powder X-ray diffraction, scanning electron microscope, thermogravimetric analysis, IR and UV-Vis spectroscopy, specific surface area and porosity measurements. It was revealed that the present nanocomposite exhibits greatly expanded specific surface area (similar to 200 m(2) g(-1)) with 2.8- and 6.6-nm-in-diameter mesopore structure, and that there exists an electronic coupling between the host titanate sheets and the guest anatase TiO2 nanoparticles in the pillared system. The results of degradation of methylene blue under ultraviolet and visible radiation show that the present nanocomposite exhibits much higher photocatalytic activities than that of TiO2 nanoparticles or layered titanate alone, which are based on the bandgap excitation and the dye sensitization.
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| [10] |
Photocatalytic activity of cobalt doped titania for H2 evolution ,钴掺杂二氧化钛的光催化制氢性能 ,
采用聚合络合法(PCM)制备出钴掺杂二氧化钛(Co/TiO<sub>2</sub>)光催化剂. 以热重-差示扫描量热同步热分析(TGA-DSC), 傅里叶变换红外(FT-IR)光谱, X 射线粉末衍射(XRD), 氮气吸附-脱附, 紫外-可见漫反射光谱(UV-Vis DRS), X射线光电子能谱(XPS)等手段对材料进行了表征. 采用光催化制氢作为探针反应, 以氢气的产量评价材料的光催化性能. 结果表明: 采用聚合络合法制备的样品主体成分为锐钛矿晶型的二氧化钛, 钴元素呈高度分散, 钴的掺杂能够明显提升二氧化钛光催化材料的光催化制氢活性, 当钴钛物质的量之比为0.3%时,催化剂具有最佳的光催化制氢活性, 达到2499 μmol, 是同等条件下制备的无掺杂二氧化钛的近六倍. 还对钴离子掺杂增强机理进行了探讨.
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| [11] |
Sonophotocatalytic degradation of methyl orange by nano-sized Ag/TiO2 particles in aqueous solutions ,
<h2 class="secHeading" id="section_abstract">Abstract</h2><p id="">Sonophotocatalytic behaviour of methyl orange (MeO) in aqueous solution illuminated by light generated by a xenon lamp was investigated. For all three kinds of photocatalysts: Degussa P25 (75% anatase, 25% rutile, with a surface area of 55.07 m<sup>2</sup>/g), Yili TiO<sub>2</sub> (mainly anatase, with a surface area of 10.45 m<sup>2</sup>/g) and Ag/TiO<sub>2</sub> (silver loaded on Yili TiO<sub>2</sub>), the degradation followed pseudo-first order kinetics. The results showed a synergistic effect between sonolysis and photocatalysis. Some parameters affecting the sonophotocatalytic degradation of MeO with nanoparticles Ag/TiO<sub>2</sub> were determined. The results indicated that the degradation ratio of MeO increased with the increase of ultrasonic power. An optimum 60 mg/L of Ag/TiO<sub>2</sub> added to relatively low concentrations of MeO was proved to have the most effective degradation efficiency. The study on the effects of hydroxyl radical (<sup><img border="0" alt="radical dot" src="http://cdn.els-cdn.com/sd/entities/rad" class="glyphImg"></sup>OH) scavengers (i.e. mannitol and dimethyl sulfoxide) on the MeO degradation indicated that <sup><img border="0" alt="radical dot" src="http://cdn.els-cdn.com/sd/entities/rad" class="glyphImg"></sup>OH radicals played an important role during MeO degradation, which enhanced MeO to be completely decomposed.</p>
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| [12] |
Facile ion-exchanged synthesis of Sn2+ incorporated potassium titanate nanoribbons and their visible-light-responded photocatalytic activity ,
Sn2+-incorporated potassium titanate (K2Ti6O13) nanoribbons were prepared by a facile acid-free ion-exchanged method in a dehydrated methanol solution at room temperature. XRD patterns suggested that K2Ti6O13 (KTO) and Sn2+-incorporated KTO (SKTO) are well crystallized with monoclinic phase structures. The mole ratio of incorporated Sn2+ to K+ in SKTO was estimated to be 2. X-ray photoelectron spectrum showed that the Sn species of SKTO consisted of 90% of Sn2+ and 10% of Sn4+, suggesting that part of Sn2+ was oxidized to Sn4+ in the incorporation process. The band gap of SKTO was 0.7 eV narrower than that of KTO, which was derived from lift of the top of the valence band due to the hybridization of Sn5s and O2p orbitals. The SKTO nanoribbons showed remarkable photocatalytic activities for H-2 evolution and rhodamine B degradation under visible light irradiation (lambda >= 420 nm). The photocatalytic mechanism and durability were studied in detail. The advantage of this acid-free ion-exchange method is ease of ion-exchange of K+ with H+ and maintenance of the integrity of the 1D nanoribbon structures. This method can be applied to preparation of other Sn2+-incorporated compounds with special nanostructures. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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| [13] |
Preparation and photocatalytic performance of SiO2-pillared layered titanate ,SiO2柱层状钛酸的制备及光催化性能 ,
采用分步反应法制备SiO2柱层状钛酸(SiO<SUB>2</SUB>-H<SUB>2</SUB>Ti<SUB>4</SUB>O<SUB>9</SUB>)光催化材料, 研究了制备过程中烷基胺的链长、胺预撑后的洗涤方式以及与正硅酸乙酯(TEOS)水热反应时间等因素对SiO<SUB>2</SUB>-H<SUB>2</SUB>Ti<SUB>4</SUB>O<SUB>9</SUB>结构的影响. 以亚甲基蓝(Methylene Bule, MB)为探针反应物, 考察了SiO<SUB>2</SUB>柱层状钛酸的光催化性能. 结果表明, 随着烷基胺链长增加, 层间距增大, 有利于在层间引入TEOS; 用1:1的乙醇水溶液洗涤正十二胺撑后的产物的结晶度显著高于用无水乙醇洗涤的产物; 胺撑后的产物与TEOS在130℃条件下水热反应两次可得到层间距为1.45nm、比表面积为148.4m<SUP>2</SUP>/g、结构较规整的SiO<SUB>2</SUB>-H<SUB>2</SUB>Ti<SUB>4</SUB>O<SUB>9</SUB>柱层状材料. 该柱层状材料对亚甲基蓝具有较高的光催化活性. <BR>
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| [14] |
A comparison of Al-Fe and Zr-Fe pillared clays for catalytic wet peroxide oxidation ,
ABSTRACT Catalysts based on pillared clays with Al, Zr and Al-Fe and Zr-Fe have been synthesized from a commercial bentonite and tested for catalytic wet peroxide oxidation (CWPO) using phenol as target compound at 298 K. The Al-Fe pillared clay showed a higher activity than the Zr-Fe one for phenol oxidation, although the second was more active for H2O2 decomposition. Fairly different values of apparent activation energy were obtained for this last reaction with these two types of catalysts, suggesting that the prevailing pathway in H2O2 decomposition is different. The higher activity of the Al-Fe pillared clay for CWPO suggests that this catalyst favours the generation of OH radicals, whereas with the Zr-Fe one H2O2 decomposes predominantly to O2 which has a low oxidation capacity at the mild operating conditions commonly used in Fenton oxidation.
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| [15] |
Physicochemical and catalytic properties of Zr-pillared montmorillonite with varying pillar density ,
Preparation, characterization and catalytic activity of Zr-pillared clays with different pillar density, starting from Niexchanged clay, are described. The physicochemical characteristics of the pillared clays have been evaluated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared (IR), UV–visible diffuse reflectance spectroscopy (UV–VIS-DRS) and sorptometric studies. The decrease in the cation exchange capacity (CEC) of the Niexchanged clay depends upon the pretreatment temperature. The migration of the Niions into vacant octahedral sites was observed in IR spectroscopy. The acidity of the pillared clays was calculated from TG analysis of the adsorbed -butyl amine. Alkylation of phenol with methanol was carried out over these catalysts. Good correlation was observed between the alkylation activity and acidity of the pillared materials. Both O and C-alkylation was observed during the reaction. The pillared materials with lesser pillar density were found to be more selective towards anisole which can be attributed to the control in acidic properties of the materials.
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| [16] |
Pillared titanates: titanium oxide of high surface area and porosity ,
Pillaring layered titanates with robust polyoxometallic oligomers is a route to prepare microporous titanium oxide. In addition to using the organic intercalated compounds as precursors, the pillaring reaction on this layered metal oxide with a high charge density was facilitated by using layered titanate of low crystallinity and small particle size, which was achieved by hydrolyzing TiCl 4 in strong alkaline solution. The resultant compound had a formula close to that of layered trititanate, NaHTi 3 O 7 ·2H 2 O. Both aluminium Keggin ions, formulated as [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ , and hydroxyzirconium tetramer cations, formulated as [Zr 4 (OH) 8 (H 2 O) 16 ] 8+ , were introduced into the interlayers of this layered titanate. The layered structure was retained up to 600°C for the alumina-pillared derivative, but only to 500°C for the zirconia-pillared derivative. The pillared samples had BET surface areas 82 150 m 2 /g and contained both micro- and mesopores. Many of the physicochemical properties of the compounds before and after pillaring were compared. Most of the characteristic properties of TiO 2 were retained on the pillared derivatives.
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| [17] |
Visible light photoelectrochemical response of nitrogen-doped TiO2 thin films prepared by anodic oxidation of titanium nitride films ,阳极氧化TiN薄膜制备N掺杂纳米TiO2薄膜及其可见光活性 ,
室温下通过电泳沉积(EPD)的方法在Ti片表面制备TiN薄膜, 然后对TiN薄膜进行阳极氧化得到N掺杂多孔纳米结构的TiO2薄膜. 利用X射线衍射(XRD), X射线光电子能谱(XPS), 扫描电子显微镜(SEM)及光电化学方法对得到的薄膜进行表征. XRD测试结果表明, 经过阳极氧化并在350 ℃空气气氛中退火1 h的薄膜中存在锐钛矿晶型的TiO2. XPS的结果表明, 样品中的N元素取代部分O, 且N的摩尔分数为0.95%. SEM显示, 经阳极氧化后薄膜表面出现多孔纳米结构. 光电化学测试结果显示, 阳极氧化提高了N掺杂TiO2薄膜在可见光下的光电响应. 经阳极氧化并热处理的薄膜在0 V电位及可见光照射下光电流密度为2.325 μA·cm-2, 而单纯热处理的薄膜在相同条件下光电流密度仅为0.475 μA·cm-2. 阳极氧化得到纳米多孔结构提高了N掺杂纳米TiO2薄膜的表面积, 从而对可见光的响应增大.
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| [18] |
Band gap narrowing of titanium dioxide by sulfur doping ,
Titanium dioxide ( TiO 2 ) doped with sulfur (S) was synthesized by oxidationannealing of titanium disulfide ( TiS 2 ). According to the x-ray diffraction patterns, TiS 2 turned into anatase TiO 2 when annealed at 60066° C . The residual S atoms occupied O-atom sites in TiO 2 to form Ti – S bonds. The S doping caused the absorption edge of TiO 2 to be shifted into the lower-energy region. Based on the theoretical analyses using ab initio band calculations, mixing of the S 663p states with the valence band was found to contribute to the band gap narrowing.
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| [19] |
Efficient hydrogen production by a composite CdS/Mesoporous zirconium titanium phosphate photocatalyst under visible light ,
A novel composite CdS/meoporous zirconium titanium phosphate (ZTP) photocatalyst working under visible light was successfully prepared by a two-step thermal sulfidation procedure. The composite photocatalyst prepared by this method was found to show an activity superior to that of catalysts prepared by direct sulfidation either at room or high temperature. By choosing different Zr/Ti ratios, the conduction band of ZTP could be continuously adjusted. The optimal Zr/Ti ratio was found to be 1:3, where the energy difference between the conduction bands of CdS and ZTP can ensure a large driving force for fluent electron transfer from CdS to ZTP and the conduction band of ZTP substrate is still high enough for efficient hydrogen production. The quantum yield of this composite photocatalyst at 420 nm as measured in experiments reached 27.2%.
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| [20] |
A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production , |
| [21] |
BiVO4/Cobalt phthalocyanine (CoPc) nanofiber heterostructures: synthesis, characterization and application in photodegradation of methylene blue , |
| [22] |
Immobilization of various cobalt (Ⅱ) phthalocyanine sulphonates on nanocrystalline TiO2 thin films and their effect on degradation of methylene blue ,
酞菁钴磺酸盐在纳米TiO2薄膜上的固载化及对亚甲基蓝的降解作用 ,
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| [23] |
Preparation, characterization and photocatalytic activity of mesoporous Zr-pillared titanate ,介孔锆柱撑钛酸盐材料的制备、表征及光催化性能 ,
采用单分子层剥离-重堆积技术将聚合羟基锆离子嵌入到钛酸盐板层间,制得层间距为1.92~2.01 nm的介孔钛酸盐柱撑复合材料。X-射线衍射(XRD)、热重-示差扫描热分析(TG-DSC)、扫描/透射电镜(SEM/HR-TEM)和N<sub>2</sub>吸附等手段对材料物化性质进行了分析。结果表明,客体锆离子主要以[Zr<sub>4</sub>(OH)<sub>16-<i>n</i></sub>(H<sub>2</sub>O)<sub>8+<i>n</i></sub>]<sup><i>n</i>+</sup>(记为Zr<sub>4</sub>)的形式存在于主体层间域中,且柱撑体系中<i>n</i><sub>Zr</sub>/<i>n</i><sub>Ti</sub>比越小,越有利于获得层间距和比表面积较大的柱撑材料。紫外光降解亚甲基蓝实验表明,柱撑材料对亚甲基蓝降解率为钛酸盐主体的3.5倍,这与柱撑形成的介孔结构以及主客体间的电子耦合有关;350 ℃热处理后材料对亚甲基蓝的降解率进一步提高,说明主客体间形成了更有效的欧姆接触。
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| [24] |
Mesoporous cobalt-intercalated layered tetratitanate for efficient visible-light photocatalysis , |
| [25] |
Preparation and catalytic properties of cobalt dopped Zr-intercalated molybdenum disulfide ,含钴羟基锆柱撑MoS2复合材料的制备及催化性能 , |
| [26] |
Zr-exchanged and pillared beidellite: preparation and characterization by chemical analysis, XRD and Zr K EXAFS ,
Zirconia-pillared clays (with synthetic beidellite as host material) were prepared by replacing the sodium interlayer cations by zirconium hydroxy polycations, and then heating to stabilize the structure. The pillaring solution was an aqueous zirconyl chloride solution. The process was first optimized in order to decrease the volume of solution and the reaction time. From the XRD results, the interlayer spacing was found to be near 903 in Zr-exchanged beidellite and slightly lower (703) after calcination. The B.E.T. surface area equals 174m 2 g 611 . In order to follow the pillaring process, an EXAFS study at the Zr K edge was carried out on crystalline zirconyl oxychloride, the pillaring solution, ion-exchanged and pillared beidellite. There is no difference between the nearest and next-nearest-neighbour environments of Zr in solid zirconyl oxychloride and the pillaring solution. Furthermore, it is found that the Zr environment of the zirconyl polycation is preserved in the pillaring process. Although the mean Zr–O and Zr–Zr distances are shortened from 2.21 and 3.5903, respectively, in exchanged beidellite to 2.17 and 3.3803, respectively, in the calcined material, the nearly square frame of the Zr 4 zirconyl units is also preserved after the calcination process. The results are consistent with the intercalation of zirconyl pillars made of isolated zirconyl polycations normal to the (001) planes of the beidellite layers. From the charge deduced from chemical analysis, one polycation cancels the charge of four unit cells of the beidellite.
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| [27] |
Quantitative determination of titanium lattice defects and solid-State reaction mechanism in iron-doped TiO2 photocatalysts , |
| [28] |
Dye-effect in TiO2 catalyzed contaminant photo-degradation: Sensitization vs. charge-transfer formalism , |
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