【作者】 蒋海燕；

【导师】 戴洪兴；

【作者基本信息】 北京工业大学 ， 应用化学， 2012， 博士

【摘要】 光催化技术是一项新兴的废水净化技术，催化剂是实现该技术的关键所在。作为一种非钛基可见光响应的半导体光催化剂，BiVO₄因其具有较高的光催化活性而备受关注。BiVO₄具有三种晶相结构，即四方锆石型、单斜白钨矿型和四方白钨矿型。其中，以带隙能为2.4eV单斜相BiVO₄的光催化活性最高。本文采用多种方法合成了具有规整形貌和多孔结构的单斜相BiVO₄和氟掺杂BiVO₄。利用X射线衍射（XRD）、热重与差热（TGA-DSC）、激光拉曼光谱（Laser Raman）、傅立叶变换红外光谱（FT-IR）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、选区电子衍射（SAED）、氮气吸附-脱附（BET）、X射线光电子能谱（XPS）、X射线荧光光谱（XRF）、紫外-可见漫反射光谱（UV-Vis DRS）等技术表征了这些光催化材料的物理性质，并考察了其在可见光照射下光催化降解苯酚、亚甲基蓝和甲基橙的催化活性。研究内容主要包括：（1）采用醇-水热法并以Bi（NO₃）₃H₂O和NH₄VO₃为金属源，NaOH为pH值调节剂，乙醇和乙二醇为溶剂，在十二胺（DA）、油胺（OL）或油酸（OA）存在的条件下，制得了规整形貌和多孔结构的BiVO₄样品。表面活性剂（DA、OL或OA）和pH值对所得BiVO₄样品的晶相结构和粒子形貌有着重要影响。当醇-水热温度为100oC时，以DA、OL或OA为表面活性剂并调节反应前驱液pH值为1.5或3.0时，可制得多孔橄榄球状单斜相BiVO₄；在醇-水热温度仍保持为100oC时，以DA为表面活性剂，当反应前驱液pH值升至7.0和11.0时，可分别制得短棒状单斜相BiVO₄和层状多孔球形正交相Bi₄V₂O₁₁。在这些BiVO₄样品中，比表面积为12.7m2/g的多孔橄榄球状样品在苯酚降解反应中体现出最好的可见光响应光催化活性。橄榄球状多孔单斜相BiVO₄样品之所以具有如此优异的光催化性能，是因为它具有高的比表面积和表面氧空位密度、多孔结构、低的带隙能和独特的粒子形貌。（2）以硝酸铋和偏钒酸铵为无机源，各种碱为pH值调节剂，通过采用三嵌段共聚物P123(HO（CH₂CH₂O）₂₀（CH₂CH（CH₃）O）₇₀（CH₂CH₂O）₂₀H)辅助水热法可制得多分枝状、多孔球状或多孔八角状单斜相BiVO₄单晶。反应前驱液pH值、表面活性剂、水热温度和碱源性质对BiVO₄样品的粒子形貌有着重要影响。P123的引入有助于形成BiVO₄材料的多孔结构。以P123辅助水热法在反应前驱液pH值为3或6时所制得的BiVO₄样品在紫外和可见光区均有较强的光吸收，因而在降解亚甲基蓝和苯酚的反应中体现出优异的光催化活性。多孔八角状单斜相BiVO₄单晶优异的可见光响应光催化活性与其高的比表面积、低的带隙能和独特的粒子形貌紧密相关。（3）采用水热合成法可制得多种形貌和多孔结构的单斜相BiVO₄。表面活性剂和pH值对BiVO₄样品的粒子形貌和孔结构有着重要影响。以聚乙烯吡咯烷酮（PVP）为表面活性剂，以尿素调节反应前驱液pH值为2，经100oC水热处理可制得具有多孔球形BiVO₄；以NaHCO₃调节反应前驱液pH值为7和8，在160oC水热处理可分别制得花簇状和花束状BiVO₄。采用PVP辅助的水热法所制得的BiVO₄具有更高的比表面积（5.0⁸.4m²/g）和更低的带隙能（2.45².49eV）。比表面积为8.4m²/g的球状BiVO₄材料在可见光照射下降解甲基橙（MO）的反应中显示出优异的光催化活性。这一优良光催化性能与其较高的比表面积、较低的带隙能、较高的氧空位密度和独特的孔道结构有关。（4）以硝酸铋和偏钒酸铵为无机源，NaOH为pH值调节剂，P123为表面活性剂，采用醇-水热法制备了多种形貌的单斜BiVO₄。表面活性剂和溶液pH值对所得BiVO₄的粒子形貌具有重要影响。在醇-水热温度为180oC，pH值为2、7或10时，可分别制得多孔球状、花状和片状BiVO₄；而采用P123作表面活性剂，在醇-水热温度为180oC且pH为2时可制得棒状BiVO₄。BiVO₄形貌的不同导致这些样品的比表面积、表面氧空位密度和（040）晶面暴露率存在差异。在四个BiVO₄样品中，棒状BiVO₄样品具有最高的比表面积、氧空位密度和（040）晶面暴露率以及最低的带隙能，使其对甲基橙降解显示出最好的光催化活性。BiVO₄样品对甲基橙降解的光催化活性存在形貌效应，棒状形貌有利于提高BiVO₄的光催化性能。（5）通过用NH4F处理经水热法所制得的BiVO₄的方法制备了不同氟掺杂量的BiVO₄材料。氟掺杂不会改变BiVO₄样品的晶相结构。相比于未掺杂的BiVO₄样品，氟掺杂的BiVO₄样品具有更高的结晶度和表面氧空位密度、更强的吸光性能和更低的带隙能。在可见光照射且反应液中添加少量H₂O₂的条件下光催化降解苯酚溶液的反应中，比表面积和带隙能分别为14.6m²/g和2.42eV的多孔球状氟掺杂BiVO₄样品（实际F/Bi摩尔比为0.29）显示出更好的光催化活性。氟掺杂BiVO₄样品的优异光催化性能与其高结晶度、比表面积和氧空位密度、强光吸收性能、低的带隙能和独特的粒子形貌相关。更多还原

【Abstract】 Phtotocatalysis is an emerging technology for the purification of waste water andphotocatalyst is a key issue in the photocatalytic process. As a non-titania basedvisible-light-driven semiconductor photocatalyst, BiVO₄has recently attracted muchattention due to its excellent photocatalytic performance. BiVO₄has three crystalphases of tetragonal zircon, monoclinic scheelite, and tetragonal scheelite, amongwhich the monoclinic scheelite BiVO₄with a bandgap energy of2.4eV is the mostactive photocatalytically under visible-light irradiation. In the thesis, monoclinicBiVO₄and fluorine-doped BiVO₄with regular morphologies and/or porousstructures were fabricated by adopting various methods. Physicochemical propertiesof the as-prepared materials were characterized by means of techniques, such asX-ray diffraction （XRD）, thermogavimetric analysis （TGA）, differential scanningcalorimetry （DSC）, laser Raman spectroscopy （Raman）, Fourier transform infraredspectroscopy （FT-IR）,, scanning electron microscopy （SEM）, transmission electronmicroscopy （TEM）, selected-area electron diffraction （SAED）, N2adsorption-desorption （BET）, X-ray photoelectron spectroscopy （XPS）, X-rayfluorescence spectroscopy （XRF）, and ultraviolet-visible diffuse reflectancespectroscopy （UV-vis DRS）. Photocatalytic activities of the as-fabricated sampleswere evaluated for the degration of phenol, methylene blue （MB）, and methylorange （MO） under visible-light illumination. The main results obtained in thepresent investigations are as follows:（1） Bismuth vanadates with multiple morphologies and/or porous structures wereprepared using the alcoho-hydrothermal strategy with bismuth nitrate andammonium metavanadate as metal source, NaOH as pH adjustor, ethanol andethylene glycol as solvent, and/or dodecylamine （DA）, oleylamine （OL） or oleicacid （OA） as surfactant. It is found that the surfactant and pH value had asignificant influence on the particle morphology and even the crystalline structureof the product. Porous olive-like monoclinic BiVO₄samples could be preparedwith DA, OL or OA as surfactant at pH=1.5or3.0and alcoho-hydrothermaltemperature=100oC. With DA as surfactant at an alcoho-hydrothermaltemperature of100oC, short-rod-like monoclinic BiVO₄and porous layeredspherical orthorhombic Bi₄V₂O₁₁were obtained when the pH value of theprecursor solution was raised to7.0and11.0, respectively. Among the BiVO₄samples, the porous olive-like one with a surface area of12.7m²/g exhibited thebest visible-light-driven photocatalytic performance for phenol degradation. It isconcluded that the excellent photocatalytic activity of the porous olive-like BiVO₄sample was associated with its higher surface area and surface oxygen vacancydensity, porous structure, lower bandgap energy, and unique morphology. （2） Monoclinic BiVO₄single-crystallites with a polyhedral, porous spherical orporous octapod-like morphology were selectively prepared using the triblockcopolymer P123(HO（CH₂CH₂O）₂₀（CH₂CH（CH₃）O）₇₀（CH₂CH₂O）₂₀H)-assistedhydrothermal method with bismuth nitrate and ammonium metavanadate as metalsource and various bases as pH adjustor. The pH value of the precursor solution,surfactant, and hydrothermal temperature had an important impact on particlearchitecture of the BiVO₄product. The introduction of P123favored thegeneration of BiVO₄with porous structures. The BiVO₄derived hydrothermallywith P123at pH=3or6possessed good optical absorption performance both inUV-and visible-light regions and hence showed excellent photocatalytic activitiesfor the degradation of MB and phenol. It is concluded that the highvisible-light-driven catalytic performance of the porous octapod-like BiVO₄single-crystallites is associated with the higher surface area, porous structure,lower band gap energy, and unique particle morphology.（3） Monoclinic BiVO₄with multiple morphologies and/or porous structures werefabricated using the hydrothermal strategy. It is observed that the pH value andsurfactant exerted a great effect on the morphology and pore structure of theBiVO₄product. Spherical BiVO₄with porous structures, flower-cluster-likeBiVO₄, and flower-bundle-like BiVO₄were generated hydrothermally at100oCwith poly（vinyl pyrrolidone）（PVP） and urea （pH=2） and at160oC with NaHCO₃（pH=7and8）, respectively. The PVP-derived BiVO₄showed much highersurface areas （5.08.4m²/g） and narrower bandgap energies （2.452.49eV）. Thebest photocatalytic performance of the spherical BiVO₄material （surface area=8.4m²/g） in the degradation of MO under visible-light irridiation was associatedwith its higher surface area, narrower bandgap energy, higher surface oxygenvacancy density, and unique porous architecture.（4） Monoclinic BiVO₄with multiple morphologies were fabricated using thealcoho-hydrothermal strategy with bismuth nitrate and ammonium metavanadateas inorganic source, NaOH as pH adjustor, and/or the triblock copolymer P123assurfactant. The surfactant and pH value had a significant influence on the particlemorphology of the BiVO₄product. Porous spherical, flower-like, and sheet-likeBiVO₄were fabricated at alcoho-hydrothermal temperature=180oC and pH=2,7or10, respectively, whereas the rod-like BiVO₄was obtained in the presence ofP123at alcoho-hydrothermal temperature=180oC and pH=2. The difference inparticle morphology of BiVO₄led to the changes in surface area, surface oxygenvacancy density, and （040） crystal plane exposure. Among the four BiVO₄samples,the rod-like one showed the highest surface area, surface oxygen vacancy density,and （040） crystal plane exposure, and the lowest bandgap energy, rendering it to exhibit the best photocatalytic activity for MO photodegradation. We believe thatthere was the presence of a morphological effect on the photocatalyticperformance of the BiVO₄material and the rod-like morphology seems to befavorable for the enhancement in photocatalytic performance.（5） Fluorine-doped BiVO₄materials with different fluorine concentrations werefabricated by adopting the post-treatment of the hydrothermally derived BiVO₄with NH4F. The doping of fluorine did not change the crystal structure of BiVO₄.Compared to the undoped BiVO₄, the fluorine-doped BiVO₄samples showedhigher crystallinity and surface oxygen vacancy density, better optical absorbanceperformance, and lower bandgap energy. The spherical porous BiVO₄sample witha surface area of14.6m²/g and a bandgap energy of2.42eV （the real F/Bi molarratio was0.29） exhibited the excellent photocatalytic activity for the degradationof phenol in the presence of a small amount of H₂O2under visible-light irradiation.Such an excellent photocatalytic performance is attributed to the higher surfacearea and surface oxygen vacancy density, lower band gap energy, stronger opticalabsorbance performance, lower bandgap energy, and unique particle morphology.更多还原