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1.
Synthesis of inorganic single crystals with exposed high‐reactivity facets is a desirable target in the catalytic chemistry field. Polyhedral AgBr microcrystals with an increased percentage of exposed high‐reactivity {111} facets have been successfully prepared for the first time, and the photocatalytic performance of these microcrystals when used as an AgBr/Ag plasmonic photocatalyst was investigated. The results indicate that the as‐prepared sample has high photocatalytic activity and, under the same measurement conditions, the photodegradation rate of methyl orange dye over these microcrystals is at least four times faster than with other shapes of AgBr/Ag microstructure, as well as 20 times faster than with the highly efficient Ag3PO4 photocatalyst. DFT calculations suggest that the AgBr (111) surface is mainly composed of unsaturated Ag atoms and has a relatively high surface energy, both of which are favorable for enhancing the photocatalytic activity of the AgBr/Ag polyhedron photocatalyst. This work not only provides a highly efficient plasmonic photocatalyst of polyhedral AgBr/Ag microcrystals with an increased percentage of exposed high‐reactivity AgBr {111} facets, but also demonstrates that the shape and crystalline quality of the exposed facets have an important influence on the photocatalytic activities.  相似文献   

2.
AgBr nanoplates with exposed {111} facets have been synthesized in high yield by a facile precipitation reaction, and the as-prepared nanoplates exhibited greatly enhanced photocatalytic properties for the degradation of organic pollutants, which may be primarily ascribed to the relatively higher surface energy of {111} facets.  相似文献   

3.
光催化反应发生在半导体材料的表面,材料表面的原子/电子结构直接影响光催化剂的活性或选择性。因此,发展具有特定晶面的半导体光催化剂受到各国学者的普遍关注,被认为是调控光催化材料性能的有效途径之一。自2008年yang等首次合成高表面能{001}晶面占优的锐钛矿TiO2单晶以来,控制合成暴露不同晶面TiO2晶体的研究得到了迅猛的发展,已发展了多种方法合成了具有不同晶面的TiO2晶体。研究表明,选择性地暴露特定的活性晶面能够显著地提高光催化剂的活性或者改变光催化反应的选择性。但是,含有完整晶面构型的TiO2单晶样品的颗粒尺寸一般都较大,通常为几微米,因而显著增加了光生载流子传输与分离的难度,并且导致材料较小的比表面积,限制了对光催化活性的进一步提高。能否在合成含特定晶面单晶的同时增加多孔结构成为有效解决这一问题的关键。最近, Crossland等采用晶种模板法成功合成了介孔的锐钛矿TiO2单晶,并且通过光电器件研究证实了采用该思路可进一步提高材料的光电性能。金红石TiO2在光催化全分解水方面具有独特的优势,然而关于多孔单晶金红石TiO2的研究相对较少,尤其是合成热力学不稳定的高表面能{111}晶面完全暴露的多孔金红石单晶面临较大的技术挑战因而一直未见文献报道。本文利用晶种模板法,以TiCl4溶液为含Ti前驱体、NaF为形貌控制剂、采用水热处理制备出不同比例{111}晶面的介孔金红石单晶。我们前期工作表明, NaF可作为形貌控制剂合成低表面能{110)晶面占优的介孔金红石单晶。本文发现,通过改变NaF的添加量,可有效调变{111}/{110}晶面比例,最终合成完全暴露{111}高表面能的介孔金红石TiO2单晶。扫描电镜结果显示,当添加20 mg NaF时,合成{110}占优的具有高长径比的介孔晶体;当NaF用量增加到40 mg时{110}晶面进一步缩短;至80 mg时则制备出{111})高能面完全暴露的金红石TiO2晶体。值得注意的是,对比研究表明,不采用模板合成了与多孔晶体完全相对应的不同{111}/(110}晶面比例的实心金红石晶体。透射电镜及选区电子衍射以及结合X射线衍射进一步证实,多孔的金红石TiO2晶体与实心金红石单晶均都为单晶结构,孔结构贯穿于样品内部且具有较高的晶面结晶性。氮气吸附实验发现,虽然三个不同晶面比例介孔金红石单晶样品间的形貌具有显著的差异,但比表面积非常相近(分别为24,25,28 m2/g),孔径也都为50 nm左右,该值与所用SiO2模板球的直径以及TEM观察结果相一致。光催化产氢性能结果表明,选择性的暴露活性晶面显著提高了光催化活性,仅含高能面{111}的介孔金红石单晶样品具有最高的产氢速率(约800μmol h–1 g–1),比常规{110}晶面占优的介孔单晶样品速率提高了约一倍。尤其比实心单晶样品的产氢速率提高了至少一个数量级,这应归结于介孔结构特性所导致的表面反应活性位增加、电子传输距离缩短以及光吸收增强协同作用的结果。  相似文献   

4.
In the work presented here, well‐dispersed ferric giniite microcrystals with controlled sizes and shapes are solvothermally synthesized from ionic‐liquid precursors by using 1‐n‐butyl‐3‐methylimidazolium dihydrogenphosphate ([Bmim][H2PO4]) as phosphate source. The success of this synthesis relies on the concentration and composition of the ionic‐liquid precursors. By adjusting the molar ratios of Fe(NO3)3 ? 9H2O to [Bmim][H2PO4] as well as the composition of ionic‐liquid precursors, we obtained uniform microstructures such as bipyramids exposing {111} facets, plates exposing {001} facets, hollow spheres, tetragonal hexadecahedron exposing {441} and {111} facets, and truncated bipyamids with carved {001} facets. The crystalline structure of the ferric giniite microcrystals is disclosed by various characterization techniques. It was revealed that [Bmim][H2PO4] played an important role in stabilizing the {111} facets of ferric giniite crystals, leading to the different morphologies in the presence of ionic‐liquid precursors with different compositions. Furthermore, since these ferric giniite crystals were characterized by different facets, they could serve as model Fenton‐like catalysts to uncover the correlation between the surface and the catalytic performance for the photodegradation of organic dyes under visible‐light irradiation. Our measurements indicate that the photocatalytic activity of as‐prepared Fenton‐like catalysts is highly dependent on the exposed facets, and the surface area has essentially no obvious effect on the photocatalytic degradation of organic dyes in the present study. It is highly expected that these findings are useful in understanding the photocatalytic activity of Fenton‐like catalysts with different morphologies, and suggest a promising new strategy for crystal‐facet engineering of photocatalysts for wastewater treatment based on heterogeneous Fenton‐like process.  相似文献   

5.
In this paper, we successfully fabricate a stable and highly efficient direct sunlight plasmonic photocatalyst Ag-AgBr through a facile hydrothermal and subsequently sunlight-induced route. The diffuse reflectance spectra of Ag-AgBr indicate strong absorption in both UV and visible light region. The obtained photocatalyst shows excellent sunlight-driven photocatalytic performance. It can decompose organic dye within several minutes under direct sunlight irradiation and maintain a high level even though used five times. In addition, both the scanning electron microscopy images and X-ray photoelectron spectroscopy dates reveal the as-prepared photocatalyst to be very stable. Moreover, the mechanism suggests that the high photocatalytic activity and excellent stability result from the super sensitivity of AgBr to light, the surface plasmon resonance of Ag nanoparticles in the region of visible light, and the complexation between Ag(+) and nitrogen atom. Thus, the facile preparation and super performance of Ag-AgBr will make it available to utilize sunlight efficiently to remove organic pollutants, destroy bacteria, and so forth.  相似文献   

6.
Photocatalytic oxidation is a promising technology for governing emission of environmental pollutants and managing energy crisis. Typically, the photocatalytic performance of photocatalysts is highly dependent on the type of exposed crystal surfaces. As a semiconductor oxide photocatalyst, the different exposed crystal surfaces of bismuth oxyiodide (BiOI) exhibit different photocatalytic oxidation performances. In this study, we chose BiOI as the model material and provided a novel method to improve the photocatalytic oxidation performance by regulating the main exposed crystal facets. Using boron nitride (BN) nanosheets as the templates, two-dimensional/two-dimensional (2D/2D) BiOI/BN nanocompounds were fabricated via an in situ growth method. Owing to the electrostatic interaction, the positively charged BiOI {001} facets prefer to contact the negatively charged BN {001} facet, thus inducing the exposure of BiOI {110} facets. This was identified via X-ray diffraction and transmission electron microscopy analyses. Compared with BiOI {001} facets, there were more lattice oxygen atoms in the BiOI {110} facets. Thus, the exposure of BiOI {110} facets would promote more surface lattice oxygen atoms exposed on the surface of BiOI, which was confirmed by X-ray photoelectron spectroscopy and density functional theory calculations. To evaluate the photocatalytic oxidation performance of BiOI/BN, the photocatalytic NO oxidation reaction was tested under visible light irradiation (λ > 420 nm). Among all the nanocompounds, the BiOI/BN-1.0:1.4 nanocompound exhibited the best NO oxidation ratio of 44.2%, which was almost 30 times higher than that of pristine BiOI (1.4%). The enhanced photocatalytic activity could be attributed to the following two aspects. One, the successful combination of BN effectively promoted the separation of photogenerated carriers, which was identified by steady-state and time-resolved fluorescence spectra, transient photocurrent responses, and electrochemical impedance spectra. Two, benefiting from the introduction of BN nanosheets, BiOI tends to mainly expose the oxygen-rich {110} facets. As a result, the content of O on the BiOI surface increased from 38.3% to 46.6%. Thus, NO preferred to adsorb on the {110} facets of BiOI nanosheets, which was confirmed by theoretical and experimental results. More importantly, the adsorbed NO spontaneously combined with the lattice oxygen atom of the BiOI (110) surface to form nitrogen dioxide (NO2). These findings can provide a novel strategy to tune exposed oxygen-rich facets by constructing 2D/2D photocatalysts for ensuring efficient photocatalytic oxidation performance.   相似文献   

7.
In this article, we report that Ag/AgBr nanostructures and the corresponding graphene oxide (GO) hybridized nanocomposite, Ag/AgBr/GO, could be facilely synthesized by means of a surfactant-assisted assembly protocol, where an oil/water microemulsion is used as the synthesis medium. We show that thus-produced nanomaterials could be used as highly efficient and stable plasmonic photocatalysts for the photodegradation of methyl orange (MO) pollutant under sunlight irradiation. Compared with the bare Ag/AgBr nanospecies, Ag/AgBr/GO displays distinctly enhanced photocatalytic activity. More importantly, the as-prepared nanostructures exhibit higher photocatalytic activity than that of the corresponding Ag/AgBr-based nanomaterials synthesized viaa water/oil microemulsion and than that of the corresponding Ag/AgCl-based nanospecies synthesized by an oil/water microemulsion. An explanation has been proposed for these interesting findings. Our results suggest that thus-manufactured Ag/AgBr/GO plasmonic photocatalysts are promising alternatives to the traditional UV light or visible-light driven photocatalysts.  相似文献   

8.
采用水热法和光致还原法制备了具有等离子体共振效应的Ag@AgBr可见光催化剂,利用XRD,SEM,EDX,DRS和XPS等手段对产物的结构和性能进行表征,并研究了催化剂在可见光下对罗丹明B(RhB)的光催化降解性能,考察了催化剂的循环使用及捕获剂对Ag@AgBr光催化性能的影响.结果表明:贵金属Ag纳米粒子的表面等离子体共振效应可显著增强Ag@AgBr对可见光的吸收;催化剂对罗丹明B具有较高的可见光降解活性和稳定性,在可见光下照射90 min,对罗丹明B的降解率达95%以上,光催化剂循环使用5次仍具有良好的光催化降解活性;淬灭实验表明在Ag@AgBr降解罗丹明B过程中,吸附在催化剂表面的h+、·OH、O2·-是主要的活性物种.  相似文献   

9.
We recently reported that Ag(3)PO(4) exhibits excellent photooxidative capabilities for O(2) evolution from water and organic dye decomposition under visible-light irradiation. However, very little is known about the shape and facet effects of Ag(3)PO(4) crystals on their photocatalytic properties. Herein we have developed a facile and general route for high-yield fabrication of single-crystalline Ag(3)PO(4) rhombic dodecahedrons with only {110} facets exposed and cubes bounded entirely by {100} facets. Moreover, studies of their photocatalytic performance have indicated that rhombic dodecahedrons exhibit much higher activities than cubes for the degradation of organic contaminants, which may be primarily ascribed to the higher surface energy of {110} facets (1.31 J/m(2)) than of {100} facets (1.12 J/m(2)).  相似文献   

10.
Cuprous oxide microcrystals with {111}, {111}/{100}, and {100} exposed facets were synthesized. 31P MAS NMR using trimethylphosphine as the probe molecule was employed to study the acidic properties of samples. It was found that the total acidic density of samples increases evidently after sulfation compared with the pristine cuprous oxide microcrystals. During sulfation, new {100} facets are formed at the expense of {111} facets and lead to the generation of two Lewis acid sites due to the different binding states of SO42− on {111} and {100} facets. Moreover, DFT calculation was used to illustrate the binding models of SO42− on {111} and {100} facets. Also, a Pechmann condensation reaction was applied to study the acidic catalytic activity of these samples. It was found that the sulfated {111} facet has better activity due to its higher Lewis acid density compared with the sulfated {100} facet.  相似文献   

11.
Spatially resolved surface photovoltage spectroscopy (SRSPS) was employed to obtain direct evidence for highly anisotropic photogenerated charge separation on different facets of a single BiVO4 photocatalyst. Through the controlled synthesis of a single crystal with preferentially exposed {010} facets, highly anisotropic photogenerated hole transfer to the {011} facet of single BiVO4 crystals was observed. The surface photovoltage signal intensity on the {011} facet was 70 times stronger than that on the {010} facets. The influence of the built‐in electric field in the space charge region of different facets on the anisotropic photoinduced charge transfer in a single semiconductor crystal is revealed.  相似文献   

12.
Anatase TiO(2) microspheres with controlled surface morphologies and exposed crystal facets were directly synthesized on metal titanium foil substrates by means of a facile, one-pot hydrothermal method without use of any templating reagent. The obtained products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelecron spectroscopy (XPS), and the focused ion beam (FIB) technique. The sizes of the resultant microspheres ranged from 1.1 to 2.1 μm. The transformation of anatase TiO(2) microspheres with exposed {001} facets surface to nanosheets surface with {101} facets was achieved by simply controlling the hydrothermal reaction time. The anatase TiO(2) microspheres with exposed square-shaped plane {001} facets were obtained by controlling the reaction time at 1 h. The prolonged reaction time transforms the anatase TiO(2) microspheres with exposed square-shaped plane {001} facets to eroded {001} facets then to a nanosheet surface with exposed {101} facets. With hydrothermal synthesis, the surface morphological structure and crystal facets formation are highly dependent on dissolution/deposition processes, which can be strongly influenced by attributes, such as pH of the reaction media, the total concentration of dissolved and suspended titanium species, and the concentration of fluoride in the reaction solution. The changes of these attributes during the hydrothermal process were therefore measured and used to illustrate the morphology and crystal-facet transformation processes of anatase TiO(2) microspheres. The surface morphologies and crystal-facet transformations during hydrothermal processes were found to be governed by the compositional changes of the reaction media, driven by dynamically shifted dissolution/deposition equilibria. The photocatalytic activities of the photoanodes made of anatase TiO(2) microspheres were evaluated. The experimental results demonstrated that the photocatalytic activity of anatase TiO(2) microspheres with exposed {001} facets was found to be 1.5 times higher than that of the anatase TiO(2) microspheres with exposed {101} facets.  相似文献   

13.
A plasmonic Ag/AgBr nanohybrid has been synthesized by in situ thermal reduction of AgBr nanoparticles in polyols. This directly converted Ag/AgBr shows significant absorption over the full visible spectrum. The enhanced light absorption in the spectral region of 450 nm to 800 nm was due to the plasmonic nanosized Ag grown on the surface of AgBr nanoparticles with mixed morphologies and increased sizes. Under visible light irradiation, the plasmonic Ag/AgBr exhibits high activity and stability for the photodegradation of organic pollutants, e.g. methylene blue. The contribution of the SPR and its synergistic effect with the photosensitive AgBr in the photocatalytic activity were verified. Based on the plasmon-mediated charge injection and the band structure of the metal-semiconductor heterojunction, a mechanism of the plasmon synergistically enhanced photocatalytic process was proposed.  相似文献   

14.
One-dimensional (1D) Ag/AgBr/TiO2 nanofibres (NFs) have been successfully fabricated by the one-pot electrospinning method. In comparison with bare TiO2 NFs and Ag/AgBr/PVP (polyvinylpyrrolidone) NFs, the 1D Ag/AgBr/TiO2 NFs photocatalyst exhibits much higher photocatalytic activity in the degradation of a commonly used dye, methylene blue (MB), under visible light. The photocatalytic removal efficiency of MB over Ag/AgBr/TiO2 NFs achieves almost 100 % in 20 min. The photocatalytic reaction follows the first-order kinetics and the rate constant (k) for the degradation of MB by Ag/AgBr/TiO2 NFs is 5.2 times and 6.6 times that of Ag/AgBr/PVP NFs and TiO2 NFs, respectively. The enhanced photocatalytic activity is ascribed to the stronger visible light absorption, more effective separation of photogenerated electron-hole pairs, and faster charge transfer in the long nanofibrous structure. The Ag/AgBr/TiO2 NFs maintain a highly stable photocatalytic activity due to its good structural stability and the self-stability system of Ag/AgBr. The mechanisms for photocatalysis associated with Ag/AgBr/TiO2 NFs are proposed. The degradation of MB in the presence of scavengers reveals that h+ and ?O 2 ? significantly contribute to the degradation of MB.  相似文献   

15.
Gold-silver alloy nanocages with controllable pores on the surface have been synthesized via galvanic replacement reaction between truncated Ag nanocubes and aqueous HAuCl4. Unlike in the previous studies, the initiation of replacement reaction started in a controllable way, simultaneously from eight corners of the truncated Ag nanocubes where {111} facets were exposed. The formation of cubic nanocages with pores at all the corners was determined by the capping agent, poly(vinyl pyrrolidone) (PVP), which preferentially covered the {100} facets of a truncated Ag nanocube.  相似文献   

16.
This article presents a quantitative analysis of the role played by poly(vinylpyrrolidone) (PVP) in seed-mediated growth of Ag nanocrystals. Starting from Ag nanocubes encased by {100} facets as the seeds, the resultant nanocrystals could take different shapes depending on the concentration of PVP in the solution. If the concentration was above a critical value, the seeds simply grew into larger cubes still enclosed by {100} facets. When the concentration fell below a critical value, the seeds would evolve into cuboctahedrons enclosed by a mix of {100} and {111} facets and eventually octahedrons completely covered by {111} facets. We derived the coverage density of PVP on Ag(100) surface by combining the results from two measurements: (i) cubic seeds were followed to grow at a fixed initial concentration of PVP to find out when {111} facets started to appear on the surface, and (ii) cubic seeds were allowed to grow at reduced initial concentrations of PVP to see at which concentration {111} facets started to appear from the very beginning. We could calculate the coverage density of PVP from the differences in PVP concentration and the total surface area of Ag nanocubes between these two samples. The coverage density was found to be 140 and 30 repeating units per nm(2) for PVP of 55,000 and 10,000 g/mol in molecular weight, respectively, for cubic seeds of 40 nm in edge length. These values dropped slightly to 100 and 20 repeating units per nm(2), respectively, when 100 nm Ag cubes were used as the seeds.  相似文献   

17.
Hierarchical TiO(2) nanospheres with controlled surface morphologies and dominant {001} facets were directly synthesized from Ti powder by a facile, one-pot, hydrothermal method. The obtained hierarchical TiO(2) nanospheres have a uniform size of 400-500?nm and remarkable 78?% fraction of {001} facets. The influence of the reaction temperature, amount of HF, and reaction time on the morphology and the exposed facets was systematically studied. A possible growth mechanism speculates that Ti powder first dissolves in HF solution, and then flowerlike TiO(2) nanostructures are formed by assembly of TiO(2) nanocrystals. Because of the high concentration of HF in the early stage, these TiO(2) nanostructures were etched, and hollow structures formed on the surface. After the F(-) ions were effectively absorbed on the crystal surfaces, {001} facets appear and grow steadily. At the same time, the {101} facets also grow and meet the {101} facets from adjacent truncated tetragonal pyramids, causing coalescence of these facets and formation of nanospheres with dominant {001} facets. With further extension of the reaction time, single-crystal {001} facets of hierarchical TiO(2) nanospheres are dissolved and TiO(2) nanospheres with dominant {101} facets are obtained. The photocatalytic activities of the hierarchical TiO(2) nanospheres were evaluated and found to be closely related to the exposed {001} facets. Owing to the special hierarchical architecture and high percentage of exposed {001} facets, the TiO(2) nanospheres exhibit much enhanced photocatalytic efficiency (almost fourfold) compared to P25 TiO(2) as a benchmark material. This study provides new insight into crystal-facet engineering of anatase TiO(2) nanostructures with high percentage of {001} facets as well as opportunities for controllable synthesis of 3D hierarchical nanostructures.  相似文献   

18.
According to the concept of active sites, the activity of heterogeneous catalysts correlates with the number of available catalytic sites and the binding affinity of the substrates. Herein, we report a single-molecule, single-particle fluorescence approach to elucidate the inherent photocatalytic activity of exposed surfaces of anatase TiO(2), a promising photocatalyst, using redox-responsive fluorogenic dyes. A single-molecule imaging and kinetic analysis of the fluorescence from the products shows that reaction sites for the effective reduction of the probe molecules are preferentially located on the {101} facets of the crystal rather than the {001} facets with a higher surface energy. This surprising discrepancy can be explained in terms of face-specific electron-trapping probability. In situ observation of the catalytic events occurring at the solid/solution interfaces reveals the hidden role of the crystal facets in chemical reactions and their impact on the efficiency and selectivity of heterogeneous (photo)catalysts.  相似文献   

19.
以Ag2WO4为载体,采用离子交换法合成了新型的AgBr/Ag2WO4复合光催化剂.利用XRD、SEM和UV-Vis对AgBr/Ag2WO4催化剂进行了表征,在可见光条件下(500 W、λ>420 nm)、以甲基橙(MO)为染料模型研究了AgBr/Ag2WO4的光催化活性.结果表明,AgBr/Ag2WO4具有比单独的AgBr和Ag2WO4更佳的催化活性,其中30%-AgBr/Ag2WO4复合催化剂具有最大光催化活性.机理研究表明,在MO的降解过程中,·O2-起主要作用,h+次之而·OH可以忽略.AgBr和Ag2WO4之间构成的异质结有效分离了光生电子和空穴,提高了催化剂的活性.  相似文献   

20.
Porous metal‐organic frameworks (MOFs) loading metal nanoparticles to form a composite photocatalyst demonstrated unique advantages. Modification of the electron donating group on the aromatic linkers of MOFs could increase the absorption range of light, thereby increasing the photocatalytic activity. In this study, we prepared a composite photocatalyst using a stable NH2‐functionalized MOF (UiO‐66‐NH2) to load semiconductor Ag/AgBr nanoparticles, and the resultant composites have intense optical absorption throughout visible light range. The greatly enhanced optical absorption and the unique hetero‐junction between Ag/AgBr and UiO‐66‐NH2 render efficient separation and utilization of photogenerated electron‐hole pairs. Therefore, Ag/AgBr@UiO‐66‐NH2 showed much more excellent photocatalytic activity, compared with unmodified UiO‐66 loading Ag/AgBr (Ag/AgBr@UiO‐66) and reported AgX@MOF catalysts. Moreover, the composite photocatalysts showed excellent stability during cycling experiment.  相似文献   

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