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题名: 非金属掺杂光/电催化材料合成及转化水中污染物机制研究
作者: 张弓
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 刘会娟
其他题名: Preparation of non-metal doped photo- and electro- catalysts for aqueous transformation of contaminants
学位专业: 环境工程
中文摘要:        能源和环境问题是人类活动的两大基本主题,而高效的非均相催化剂是实现将太阳能以及电能等清洁能源向化学能转化、解决能源问题与环境修复的有效手段之一。在光催化领域中,二氧化钛常被用作光催化剂催化裂解水和催化氧化还原水中有机污染物。鉴于二氧化钛禁带宽度较宽,通过对二氧化钛结构的改性以获取全光谱下较高的催化活性,是当前国内外研究热点之一。此外,研发高效廉价的新型光催化材料也是获取高效太阳光利用效率的有效途径。在电催化处理水技术中,原位产生的氢既是一种可再生清洁能源又是电催化还原的重要因素。然而,昂贵的高效析氢、析氧电催化材料制约了电催化技术的广泛应用。本学位论文针对上述问题,开展了高效非金属掺杂光 /电催化材料的合成,及其降解污染物的效能与去除机理研究,具体研究成果如下。
    1)基于静电纺丝技术,制备了一种氮掺杂二氧化钛(N-TiO2)纳米纤维,并将其应用于可见光催化氧化三价砷(As(III))。对二氧化钛生长过程研究发现,聚乙烯吡咯烷酮(PVP)不仅是纺丝过程中必备的模板剂,它还是掺杂氮元素的有效氮源。另外,通过静电纺丝制备的二氧化钛前驱可很大程度上降低二氧化钛金红石晶相转变温度,在相对较低温条件下,可实现有高能面暴露的N掺杂混晶相二氧化钛的制备。N-TiO2在保障其紫外区催化活性的同时,还可以有效提高可见光催化活性。可见光照射 60min,水相中约90%的 As(III)(初始浓度为10 mg L-1)被氧化为五价砷,有利于后续吸附处理。
    2)以溴氧铋为母体,利用醇热法实现碘原子对两个溴原子的取代,制备出BiOBr0.75I0.25光催化材料。 在紫外区,该光催化材料拥有6倍于二氧化钛的光电转化效率;同时,它还展现出 10倍于未发生取代的纯相溴氧铋以及碘氧铋的可见光电转化效率。研究发现,碘的取代有效的缩短了溴氧铋的禁带宽度、降低导带中电子有效质量、增强光生电子与空穴的分离效率,而且还直接影响卤氧铋[Bi2O2]2+层中的电子结构,形成缺陷态的催化材料。计算发现,缺陷的存在不仅进一步缩短光催化材料的禁带宽度,还加强催化剂内部电场,降低光生载流子复合几率。可见光照射下,BiOBr0.75I0.25的投加量为 250 mg L-1时,双酚A(BPA)-1的光催化氧化以及六价铬(CrVI )的催化还原速率可达0.19 min-1,0.056 min-1。
     3 )利用湿式化学法制备了一种具有高比例活性晶面的双锥形钨酸铋纳米颗粒。基于正电子湮灭技术(PAS),确认了具有高比例的活性面的双锥形钨酸铋晶体的成长伴随着面缺陷的形成,并通过 X射线光电子能谱(XPS)分析确定了该缺陷的类型(Bi-O)。另外,基于时间分辨红外光谱的分析结果证实了缺陷的形成有利于光生电子-空穴对的有效分离,同时利用第一原理计算分析认为缺陷的存在会缩短钨酸铋的禁带宽度、提高其对太阳光的利用效率。模拟太阳光照射下,催化剂投加浓度为 250 mg L-1时,双氯芬酸的的降解速率可达到 3.12 min-1.
       4)以植酸为磷源,通过一步法合成了电催化阳极与阴极材料(MoP,CoP)。在酸性以及碱性条件下,为达到 20 mA cm-2极化电流,阴极 MoP@RGO过电位仅为118与93 mV。另外,以 CoP@RGO作为阳极,过电位为310 mV时便可实现10mA cm-2极化电流。研究发现,以植酸为磷源制备的金属磷化物可以实现氧元素有效掺入,不仅增强电催化材料导电性的同时,还会使金属元素与磷之间键长增长,实现电催化性能的提升。随后,通过灼烧植酸形成的碳层作为桥联,将纳米颗粒状电催化材料均匀负载于碳布上,实现柔性电催化阳极和阴极的制备。碱性条件下,外加直流电源 1.6 V偏压可以达到40 mA cm-2 的电流密度。
英文摘要:     Both energy and environment are vital topics for  human survival. Heterogeneous catalysts offer great potential for  converting solar and electronic energy into chemical energy and  for the  environmental remediation.  In the case  of photocatalysis,  typical examples are  TiO2-based photocatalytic  decomposition of  organic contaminants  and water-splitting. Plenty attempts have been made on  modifying of physical structure of TiO2 crystals to enhancing its  activity in the UV and visible regions. Additionally, the development of novel visible light-photoactive catalysts might be the alternative paths for harvesting  solar  energy effectively.  In the  case  of lectrocatalysis  for  the water treatment, the electrochemical  production of hydrogen is  still hampered by following limitations: lack  of effective replacements  for noble-metal-based  materials to  reduce the overpotentials of  the two half-reactions  (hydrogen evolution reaction and  oxygen evolution reaction) during the reactions.
     1) The electrospun method was employed to fabricate N-doped mixed-crystalline TiO2  with  exposed  high  energy  facets.  The  Ti-oxide   transformation  process  was thoroughly studied. During  the mixture crystals  structure formation process, the  high energy  facets  could   be  reserved  due  to   the  lower  calcline  temperature   and  the protective role of polyvinylpyrrolidone (PVP) in the  electrospinning process. Besides,after  calcination, the  N doping  generated  by the  derivate of  the  PVP, extended  the absorption spectrum  of TiO2  to  visible region.  These TiO2  fibers exhibited  superior photo-oxidation  of  As(III)  to  As(V)  both  in  UV  and visible  light  region,  mainly attributed to  the exposure  of high-energy  facets, robust separation  of photo  -excited charge carriers between anatase/rutile  phases, and narrow band-gap induced  by the in situ N doping.
    2) We have  substituted iodine for two bromine  atoms in BiOBr to  overcome the restriction and  provided some deep-seated  insights into how  the substitution boosted the   photocatalytic  property.   The  substituted   BiOBr0.75I0.25exhibited  exceptional photo-activity with the photon-to-current conversion efficiency  approximate six times greater than TiO2  in UV region, and  more than ten times  higher than those of  BiOBr or BiOI in  visible-light region. We found that  the substitution narrowed the  bandgap,facilitated the  diffusion of electron with  small effective mass,  as well as  induced the oxygen vacancies  on [Bi2O2]2+ enhanced intrinsic  electric fields between  [Bi2O2]2+ achieved  in BiOBr0.75I0.25,  thereby distance  the  photogenerated electron  can  diffuse layers. By  virtue of the  stronger dipole moments,  the and negative  halogen atoms was enough to inhibit the recombination.
     3) Bi2WO6 nanostructured bipyramids  with a large fraction of {100}  facets were fabricated by solvothermal method.  The formation of ‘Bi-O’ dimer vacancy pairs due to the presence of  W7+ on {100} high-energy facets was  responsible for the reduction in band  gap and  the decrease  in the recombination  of photo-excited  charge carriers, which  was  unambiguously  confirmed  by  the  positron  annihilation  spectra  (PAS), X-Ray  Photoelectron  Spectrum  (XPS)   and  theoretical  calculations.  The  effective separation of  electron-hole  pairs and  the narrowing  bandgap significantly  improved the photoactivity of Bi2WO6 nanobipyramids, especially under solar light irradiation.
     4) We reported  a universal fabrication  of transition metal phosphides  (TMPs) to HER or OER by the application of naturally biological phytic acid (PA) as phosphorus source and the introduction of GO for high exposing the active  sites. The MoP@RGO hybrid exhibited  low HER  overpotentials  of 118  mV and  93 mV to  drive a  current density of 20 mA cm-2 applied the  CoP@RGO as  catalyst for  OER, 310  mV overpotential  was required  to approach current  density of  10 mA cm-2  . We then  uncovered that  the good  catalytic in 0.5 M H2SO4 and 1 M KOH electrolytes, respectively. When performance of  the hybrids  were due  to the elongation  M-P bond  and the  enhanced electroconductivity. In addition, the PA-based precursor can easily bonded and formed evenly gel on  surface of commercial carbon  cloth (CC), thereby the MoP@RGO  and CoP@RGO  anchored firmly  on  the  flexible substrate.  Remarkably,  an electrolyzer that achieved to current density of 40 mA cm-2   at  voltage 1.6 V, and this demonstrated the possibilities for the practical utilization of the electronic energy in water treatment.

内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/37045
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
张弓. 非金属掺杂光/电催化材料合成及转化水中污染物机制研究[D]. 北京. 中国科学院研究生院. 2016.
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