【作者】 叶立群；

【导师】 昝菱；

【作者基本信息】 武汉大学 ， 无机化学， 2013， 博士

【摘要】 半导体光催化技术在解决环境和能源两个世界性课题方面有着举足轻重的地位,提高光催化剂的光催化活性是该领域的终极目标。由于半导体光催化剂的不同晶面具有不同的表面原子和电子结构,因而晶面暴露严重影响了其光催化活性。为此,本论文开展了二氧化钛和卤氧化铋的晶面光催化活性研究。获得的主要研究内容和结论归纳如下：1.以六氟氧钛为钛源和氟源,成功合成了｛001｝-｛101｝和｛001｝-｛010｝锐钛矿TiO2双晶面共存样品。比较二者的光催化活性发现,｛010｝晶面取代｛101｝晶面后抑制了TiO2的光催化活性。机理研究表明,｛101｝-｛001｝晶面共存样品的光生载流子能够有效的分离,而｛010｝晶面取代｛101｝晶面后,光生载流子却不能够有效的分离,因而光催化活性下降。2.以钛酸盐为前驱体,通过无氟的方法成功合成了90%暴露｛101｝、｛001｝和｛010｝晶面的锐钛矿TiO2单晶面样品。首次研究了反应介质对低指数晶面光催化活性顺序的影响,发现在液体介质中,光催化生成羟基自由基顺序为：｛001｝>｛101｝>｛010｝；但是在气体介质中,光催化还原CO2活性却为：｛010｝>｛101｝>｛001｝。机理研究表明,气相介质中光还原CO2的活性顺序主要由CO2分子在不同晶面的吸附能力决定,液体介质中光催化产羟基自由基由不同晶面在液体介质中光生载流子分离效率和H2O分子在不同晶面的吸附能力决定。3.以K2Ti6013为前驱体,合成了TiO2纳米双锥(TiO2-NP)和TiO2纳米带(TiO2-NB),二者暴露的晶面都为｛101｝晶面,可以用于研究相同晶面暴露但不同型貌锐钛矿TiO2(101)样品的光催化活性。ROS产量检测、瞬态PL光谱、XPS光谱和ATR-IR光谱显示三维的TiO2-NP比一维的TiO2-NB含更多的｛101｝晶面间的棱,吸附了更多的解离水,且光生载流子寿命比TiO2-NB更长。4.以Bin(Tu)xCl3n为前躯体,成功合成了BiOCl内米片,其暴露的｛001｝晶面百分比(从71%到87%)可以由BiCl3:Tu的投料比调控。光催化活性结果显示,｛001｝晶面暴露的越多,BiOCl纳米片的紫外光光催化活性就越高。机理研究表明,BiOCl｛001｝晶面上的高氧原子浓度和低的Bi-O键能导致其紫外诱导氧空穴浓度随着｛001｝晶面的比例增加而增加,最后使得BiOCl的紫外光催化活性与其｛001｝晶面暴露比例成正比。5.发现Bin(Tu)xCl3n可以作为光敏剂,并通过部分水解Bin(Tu)xCl3n,首次制备了Bin(Tu)xCl3n内部敏化的BiOCl (001)纳米片可见光光催化剂。在可见光下(λ≥420nm),其光催化降解活性RhB分别为P25和纯BiOCl勺112倍和13倍。光催化机理证实Bin(Tu)xCl3n的敏化作用增强了BiOCl的可见光催化活性,超氧自由基为该催化过程中的主要活性物种,而且可以无色的分子探针NBT来量化之。6.在氩气气氛下,通过简单的紫外光诱导BiOCl产生氧空位,成功制备了黑色BiOCl.其可见光催化降解RhB活性是白色BiOCl的20倍。活性物种捕获实验表明,在可见光照射下,光生空穴是黑色BiOCl光催化过程中的主要活性物种,同时也有少量的超氧自由基起生成。7.通过直接煅烧BiI3前驱体,成功合成了高度对称的BiOI单晶纳米片(BiOI SCNs),其{001}晶面暴露比例可以高达95%。BiOI纳米片的厚度和{001｝晶面暴露比例可以通过改变煅烧温度和时间来调整。光催化实验结果显示｛001｝晶面为BiOI SCNs的活性晶面,其可见光催化降解RhB活性为不规则BiOI的7倍。该｛001}晶面依赖的光催化活性原于｛001｝晶面的暴露可以提高BiOI光生载流子的分离效率。8.通过化学气相转化方法合成了BiOI纳米结构薄膜。该BiOI薄膜中的BiOI为高度对称的、暴露｛001｝晶面的纳米片。BiOI的层状结构、化学气相转化固定和｛001｝晶面100%的O终止原子分别导致BiOI薄膜表现出了比P25TiO2薄膜更高的光催化活性、稳定性和光催化选择性。最后,我们提出了BiOI光催化产生O2·-可能机理。9.通过低温液相沉积法制备出Ag/AgX/BiOX (X=Cl, Br)三元可见光催化剂,其可见光催化降解RhB活性比Ag/AgX和BiOX都要高很多。光催化活性物种捕获实验和超氧自由基量化实验表明纳米Ag粒子在Ag/AgCl/BiOCl和Ag/AgBr/BiOBr中作用是不同的。在Ag/AgCl/BiOCl中,纳米Ag粒子作用为SPR效应：在Ag/AgBr/BiOBr中,纳米Ag粒子作用为Z-机制桥。10.通过低温液相沉积法制备出BiOBr-g-C3N4复合光催化剂,其可见光催化降解RhB活性比BiOBr和g-C3N4都要高很多。光催化活性物种捕获实验和超氧自由基量化实验表明g-C3N4导带电子能够迁移到比BiOBr的导带底更高的位置,与O2反应生成O2·-。更多还原

【Abstract】 Semiconductor photocatalytic technology plays a very important role in solving the energy crisis and environmental protection which are the world problems. And the enhanced photocatalytic activity of photocatalys is the ultimate goal of the field. In this case, we carried out the photocatalytic activity of TiO2and BiOX (X=Cl, Br and I) with active facts exposure. The main contents and conclusion are as follows:1. Anatase TiO2crystals with{101}-{001} and{010}-{001} two facets coexistence were synthesized by (NH4)2TiF6acting as titanium and fluorine sources and the photocatalytic activity of the samples were investigated. The replacement of{101} by{010} facets inhibits the photocatalytic activity of anatase TiO2. The mechanism study demonstrated that photoinduced charge transfer properties between{101} facets and{001} facets resulted in the efficient charge separation. Replacing{101} by{010}, the charge transfer mechanism was altered and the photoinduced electron-hole pairs cannot be separated well. The photocatalytic activity of it has thus been inhibited.2. Anatase TiO2nanocrystals with{101},{001} or{010} single facets90%exposing were controllable synthesized from potassium titanate without fluorine. The liquid phase photocatalytic activity order of anatase TiO2facets for·OH production is{001}>{101}>{010}. But the gaseous phase photocatalytic activity order for of anatase TiO2facets for photoreduction of CO2to CH4is{010}>{101}>{001}. DRS, PL and ATR-IR spectra analysis showed that the photoactivity order of the gas phase for the photoreduction of CO2to CH4mainly depends on the CO2molecule adsorption property on the different exposed facet, and the separation efficiency of photo-generated carriers determines the photoactivity order for the·OH production in liquid phase.3.3D TiO2nanobipyramids (TiO2-NP) and1D TiO2nanoblets (TiO2-NB) were synthesized potassium titanate K2Ti6O13. The as-synthesized3D TiO2nanobipyramids and1D TiO2nanoblets all show high{101} facet exposed percentages and were used to investigate the shape effect of TiO2with the same facets exposure.3D TiO2nanobipyramids (101) showed higher photocatalytic activity than1D TiO2nanoblets (101). The reasons were discussed using ROS (reactive oxygen species) production, time-resolved photoluminescence spectra, XPS (X-ray photoelectron spectroscopy) spectra and ATR-IR (attenuated total reflectance infrared spectroscopy) spectra. The postulated mechanism suggests that3D TiO2 nanobipyramids has more step edges which results in more-OH/H2O molecules adsorption and longer life times of photoinduced carriers than1D TiO2nanoblets.4. BiOCl nanosheets (BiOCl NSs) were synthesized by hydrolyzing a hierarchical flowerlike molecular precursor (Bin(Tu)xCl3n,Tu=thiourea). The{001} facets percentage was controlled from71%to87%, by adjusting the feed ratios of BiCl3:Tu in molecular precursors. The relationship between the percentage of{001} facets and the photoactivity of BiOCl was investigated and a positive correlation was found. The mechanism study showed that the high oxygen atom density in{001} facets is considered the fundamental cause for the increase of the UV-induced oxygen vacancies in the crystal lattice, that enhances, consequently, the photoactivity of BiOCl.5. Bismuth complexes, Bin(Tu)xCl3n, were found to be photosensitizers for the first time. BiOCl nanosheets with inner Bin(Tu)xCl3n were synthesized The as-synthesized BiOCl displayed high visible light (λ≥420nm) photocatalytic activity which was112and13times higher than P25and BiOCl without Bin(Tu)xCl3n, for degrading RhB, respectively. The investigation of the photocatalytic mechanism demonstrated that Bin(Tu)xCl3n sensitized the BiOCl and resulted in unusually high visible light photocatalytic activity. The superoxide radical was the main active species in the photodegradation process. Furthermore, the concentration of the superoxide radical was quantized by the molecular probe nitroblue tetrazolium.6. Black BiOCl with oxygen vacancies was prepared by UV light irradiation with Ar blowing. The as-prepared black BiOCl sample showed20times higher visible light photocatalytic activity than white BiOCl for RhB degradation. The trapping experiment showed that the superoxide radical (O2·-) and holes (h+) were the main active species in aqueous solution under visible light irradiation.7. Highly symmetrical BiOI single-crystal nanosheets (BiOI SCNs) with dominant exposed{001} facets (up to95%) have been synthesized by annealing Bil3. The thickness and the{001} facets percentage of BiOI SCNs can be tuned by changing the annealing temperature. BiOI SCNs exhibit higher photoactivity (about7times) than irregular BiOI for degradation of Rhodamine B (RhB) dye under visible light irradiation. The{001} facets are the reactive facets of BiOI. The origin of{001} facets-dependent photoactivity is due to an improvement of the separation efficiency of photo-induced electrons and holes.8. BiOI thin film (BiOI TF) was prepared via a low temperature chemical vapor transport (CVT) route for the first time. As-synthesized BiOI thin film was composed of high symmetrical BiOI nanosheets with dominant exposed{001} facets. It displayed better photocatalytic activity, durability and selectivity than benchmark P25TiO2thin film and the origin come from the layered structure and good photoelectrochemical performance, CVT immobilization, the100%terminal oxygen atoms of{001} facets, respectively. At end, the photocatalytic mechanism with O2·-production was studied.9. Ag/AgX/BiOX (X=Cl, Br) three-component visible-light-driven (VLD) photocatalysts were synthesized by a low-temperature chemical bath method. The Ag/AgX/BiOX composites showed enhanced VLD photocatalytic activity for the degradation of rhodamine B, which was much higher than Ag/AgX and BiOX. The photocatalytic mechanisms were analyzed by active species trapping and superoxide radical quantification experiments. It revealed that metallic Ag played a different role for Ag/AgX/BiOX VLD photocatalysts, surface plasmon resonance for Ag/AgCl/BiOCl, and the Z-scheme bridge for Ag/AgBr/BiOBr.10. BiOBr-g-C3N4inorganic-organic composite photocatalysts were synthesized by a one-step chemical bath method at low temperature The BiOBr-g-C3N4composite showed much higher visible-light-driven (VLD) photocatalytic activity than pure g-C3N4and BiOBr for rhodamine B (RhB) degradation. The active species trapping and quantification experiments indicated that the photoinduced charges transfer between g-C3N4and BiOBr resulted in the O2·-generation at a higher conduction band of BiOBr.更多还原