光催化与光电催化
压电势构建的内建电场增强光催化和光电催化
Chinese Journal of Catalysis 41 (2020) 534–549催化学报 2020年 第41卷 第4期 | a v a i l ab l e a t w w w.sc i e n c ed i re c t.c o mj o u r n a l h o m e p a g e : w w w.e l s e v i e r.c o m /l o c a t e /c h n j cReview (Special Column for the Youth Innovation Promotion Association, Chinese Academy of Sciences)Piezopotential augmented photo- and photoelectro-catalysis with a built-in electric fieldZhirong Liu a,c,†, Xin Yu b,†, Linlin Li a,c,d,*a Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, ChinabInstitute for Advanced Interdisciplinary Research (iAIR), University of Jinan, Jinan 250022, Shandong, China c School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing 100049, Chinad Center on Nanoenergy Research, School of Physical Science and Technology, Guangxi University, Nanning 530004, Guangxi, ChinaA R T I C L E I N F OA B S T R A C TArticle history:Received 27 September 2019 Accepted 10 November 2019 Published 5 April 2020Rapid technological development and population growth are responsible for a series of imminent environmental problems and an ineluctable energy crisis. The application of semiconductor nano-materials in photocatalysis or photoelectrocatalysis (PEC) for either the degradation of contami-nants in the environment or the generation of hydrogen as clean fuel is an effective approach to alleviate these problems. However, the efficiency of such processes remains suboptimal for real applications. Reasonable construction of a built-in electric field is considered to efficiently enhance carrier separation and reduce carrier recombination to improve catalytic performance. In the past decade, as a new method to enhance the built-in electric field, the piezoelectric effect from piezoe-lectric materials has been extensively studied. In this review, we provide an overview of the proper-ties of piezoelectric materials and the mechanisms of piezoelectricity and ferroelectricity for a built-in electric field. Then, piezoelectric and ferroelectric polarization regulated built-in electric fields that mediate catalysis are discussed. Furthermore, the applications of piezoelectric semicon-ductor materials are also highlighted, including degradation of pollutants, bacteria disinfection, water splitting for H 2 generation, and organic synthesis. We conclude by discussing the challenges in the field and the exciting opportunities to further improve piezo-catalytic efficiency.© 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.Published by Elsevier B.V. All rights reserved.Keywords: PhotocatalysisPhotoelectrocatalysis PiezopotentialBuilt-in electric field Piezo-phototronic effect Reactive oxygen species1. IntroductionWith rapid technological development and population growth, environmental problems and an energy crisis are im-minent [1,2]. Photocatalysis and photoelectrocatalysis (PEC), with the assistance of rationally designed catalysts, provide green and cost-effective ways to alleviate these problems. Theyhave been developed for the degradation of organic contami-nants in the environment, the catalysis of CO 2 reduction, H 2 evolution and biomass conversion for clean fuels, and catalysis of other reactions [3–7].Generally, semiconductors with appropriate energies and band gaps can absorb sunlight and form photogenerated elec-tron-hole pairs, which are then transferred to the photocata-* Corresponding author. Tel: +86-10-82854770; Fax: +86-10-82854800; E-mail: lilinlin@ † Zhirong Liu and Xin Yu contributed equally to this work.The work was supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2015023), National Natural Science Foundation of China (81471784, 51802115), Natural Science Foundation of Beijing (2172058), Natural Science Foundation of Shandong Province (ZR2018BEM010, ZR2019YQ21), Major Program of Shandong Province Natural Science Foundation (ZR2018ZC0843), and Scientific and Technology Project of University of Jinan (XKY1923).DOI: S1872-2067(19)63431-5 | /science/journal/18722067 | Chin. J. Catal., Vol. 41, No. 4, April 2020Zhirong Liu et al. / Chinese Journal of Catalysis 41 (2020) 534–549535lyst’s surface, where they trigger oxidative-reductive reactions [8–10]. Unfortunately, limited solar-light utilization and the high recombination rate of the photoinduced electron-hole pairs still hinder their further industrialization [11–13]. In the last few decades, researchers have fabricated many composite photocatalysts to extend the light absorption range from ultra-violet to visible and near infrared regions, such as graphitic carbon nitride (g-C3N4) [14,15], BiVO4 [16], Fe2O3 [17], Ag3PO4 [18], WO3[19], CdS [20,21], and Sn3O4[22,23]. Furthermore, various modification methods have also been developed to promote the separation of photogenerated electrons and holes, including surface modification [24], metal/nonmetal doping [25,26], and heterojunction construction [27,28]. Moreover, the bias voltage can assist in the directional transmission of elec-trons. Thus, PEC could further enhance carrier separation with the synergy of light illumination and bias voltage [29,30]. However, great challenge still remain for efficient charge sepa-ration to improve the performance of photocatalysis and PEC.Recently, there has been increasing interest in reasonable construction of a built-in electric field by the piezoelectric and piezo-phototronic effects to efficiently enhance carrier separa-tion [31,32]. Piezoelectrics (including ferroelectrics, piezoelec-tric semiconductors, etc.) are a class of materials with noncen-trosymmetric crystal structures [33,34]. Their positive and negative charge centers can be separated under mechanical deformation or an external electric field, which results in the generation of a piezoelectric potential (piezopotential) [35,36]. The piezopotential can modulate the charge carriers at the interface of metal–semiconductor contacts and semiconductor heterojunctions. In the past decade, piezoelectrics have been widely used to regulate the performance of piezoelectric semi-conductor devices, such as transistors [37], solar cells [38], light-emitting diodes (LED) [39,40], and self-powered nanosystems [41]. In photocatalysis and PEC, strained piezoe-lectric semiconductors and ferroelectric materials with per-manent polarization show great promise in enhancing carrier separation and reducing carrier recombination via a built-in electric field [42,43].This review summarizes recent advances in piezocatalysis (including photocatalysis and PEC) enabled and augmented by piezoelectric semiconductors and ferroelectric materials. First, the properties of piezoelectric and ferroelectric materials and the construction mechanism of a built-in electric field for carri-er separation are introduced. Second, the methods used to generate a built-in electric field with a piezopotential are dis-cussed, including ultrasonic waves, mechanical brush-ing/sliding, thermal stress, water flows, and permanent polari-zation of ferroelectricity. Then, potential applications such as the degradation of pollutants, bacterial disinfection, water splitting for H2 evolution, and organic synthesis are elucidated. Finally, the challenges in the field and the scope for future de-velopment of piezo-catalysis are discussed.2. Mechanism of piezopotential assisted catalysisFundamentally, the selected polarized material is the key to proper construction of built-in electric fields. It is therefore essential to understand the properties of piezoelectricity and ferroelectricity, and the mechanism through which they cause interface band bending.2.1. Piezoelectricity and ferroelectricityPiezoelectric materials are a class of dielectric materials with non-centrosymmetric crystal structures, including piezo-electric semiconductors (such as ZnO [41], MoS2 [44], MoSe2 [45]), all ferroelectric materials (such as BaTiO3[46], BiOIO3 [47] polyvinylidene fluoride (PVDF) [48], PbTiO3[49]), and other piezoelectric crystals (such as quartz) (Fig. 1(a)). In this review, we lay emphasis on ferroelectric materials and piezoe-lectric semiconductors that can enhance catalysis.Different from ferroelectric materials, piezoelectric materi-als (green color in Fig. 1(a)) show no polarization without an applied strain (Fig. 1(b)). Taking wurtzite-structured ZnO as an example [50], the positive Zn2+and negative O2‒are tetrahe-drally coordinated, and in the absence of an external force, the centers of the anions and cations overlap. Thus, there is no piezopotential in the crystal. When the crystal is under a tensile or compressive stress, the Zn and O atoms are relatively dis-placed from their original position. As a result, the centers of the positive and negative charges move to the opposite faces of the tetrahedron crystal, generating a piezopotential. As shown in Fig. 1(b), the tensile and compressive stresses produce a polarized electric field with an opposite direction [51]. Driven by the polarized electric field, photo-generated electrons and holes move towards opposite directions and are separated effectively. As a result, a great number of charge carriers that can take part in redox reactions reach the surface of the cata-lysts [52].Different from piezoelectric semiconductors that generate polarized electric field by strain, ferroelectric materials can generate permanent built-in electric fields even without strain (Fig. 1(c)) [53], which is the operational advantage of ferroe-lectric applications. The applied external electric field or me-chanical deformation can induce polarization of the dipole and further adjust the polarized electric field [31,54]. However, the insulating properties of traditional ferroelectric materials make them unsuitable for carrier transport. Nanoscaled ferroelectrics do not have this limitation. The lower limit of ferroelectric ma-terials to show ferroelectricity is about a few nanometers [55]. For example, the currently known critical thickness of barium titanate (BaTiO3) with ferroelectricity is 2.4 nm under ambient conditions. However, the thickness of BaTiO3 film for chargetunneling should be lower than 30 nm [56,57]. Therefore, Ba-Fig. 1.Piezoelectricity and ferroelectricity. (a) Piezoelectric materials contain ferroelectric materials. (b) Piezoelectric semiconductors in the absence of strain (left), under tensile (middle) and compressive (right) stress. (c) Ferroelectric materials without strain.536 Zhirong Liu et al. / Chinese Journal of Catalysis 41 (2020) 534–549TiO 3 with a thickness between 2.4–30 nm is capable of modu-lating charges and is suitable for piezocatalysis. For different piezoelectric nanomaterials, the size/thickness window would be different. From another perspective, the surface oxygen defects and foreign ion doping in nanoscaled BaTiO 3 could transform it from an insulator into a semiconductor with wide-band gap [58]. Thus, when a ferroelectric material with a suitable thickness is appropriately introduced at the interface of heterojunctions, its electrical modulation capability enables redistribution of the free photogenerated electron-hole pairs, improves the separation efficiency of carriers, and subse-quently affects the performance of photocatalysis and PEC. 2.2. Generation of a built-in electric fieldThe photo- and photoelectro-catalytic activity of materials islimited by the recombination of photogenerated electron-hole pairs and the back-reaction of intermediate species [59,60]. A feasible way to enhance photocatalysis is to promote separa-tion and inhibit recombination of the electron-hole pairs. For semiconductor photocatalysts, surface adsorption and foreign atom or surface imperfections (e.g., defects, steps, and impuri-ties) can produce surface states, which are known as extrinsic surface states [61,62]. The presence of these surface states would cause charge transfer between the surface of the semi-conductor catalyst and the bulk phase, thereby forming a space charge layer [63]. After the charge transfer reaches an equilib-rium, the valence band or conduction band of the space charge layer of the semiconductor would bend to form a band bending. The internal electric field generated by ferroelectric polariza-tion, p-n junctions, polar interfaces, and polymorph junctions can change the interface band bending and provide a driving force that promotes the separation of photogenerated carriers [64]. This review focuses on the polarization field built by pie-zoelectric and ferroelectric materials to promote carrier sepa-ration (Fig. 2). Although the built-in electric field could promote carrier separation, it is fixed and easy saturate; therefore, its ability to promote photocatalysis is still limited [65,66]. Regen-erating the built-in electric field in the photocatalytic process and realizing long-term separation of photogenerated carriers is the key to increasing the performance of the built-in electricfield enhanced photocatalysis and realizing photocatalyst recy-cling.3. Built-in electric field mediated catalysisAs discussed above, a built-in electric field can enhance the separation efficiency of photogenerated electron-hole pairs and subsequently improve the performance of photo- and photoe-lectro-catalysis. In this section, the specific methods that could be used to construct a built-in electric field with a piezo poten-tial, including ultrasonic irradiation, mechanical brush-ing/sliding, thermal stress, water flows, and permanent polari-zation of ferroelectricity are discussed. 3.1. Piezopotential mediated catalysis3.1.1. Methods used to exert a mechanical stressDeformation is an essential requirement for the generation of an internal electric field in piezoelectric semiconductors [67]. To control the strain of piezoelectric semiconductors ac-curately, Wang ’s group [68,69] attached a ZnO-based PEC an-ode to a polymethyl methacrylate (PMMA) cantilever. A speed-controlled motor was employed to drive the dynamic and static bending of the PMMA cantilever (Fig. 3(a)). The dis-tance between the shaft of the motor and the cantilever was adjusted to produce a series of strains. Therefore, the strain on ZnO could be regulated precisely and calculated by the tradi-tional cantilever model. Xue et al. [70] vertically grew ZnO NWs on carbon fibers (CFs) and bundled several ZnO/CFs together. When ZnO/CFs were subjected to mechanical brushing/sliding under an external force, ZnO NWs extruded outward and pro-duced a piezopotential across their width (Fig. 3(b)).An ultrasonic wave is a sound wave with a frequency higher than 20,000 Hz. It has good directionality, strong penetration, and long propagation distance in water. Ultrasound waves are commonly used to generate mechanical forces in piezocatalysis [71,72]. Besides the acoustic pressure effect, the ultrasonic cavitation effect is also a major driving force that causes de-formation of piezoelectric semiconductors [73]. When the sound pressure reaches a certain value, the tiny bubble nuclei in the liquid expands rapidly and then suddenly close to gener-ate a shock wave. Ultrasonic cavitation includes a series of dy-namic processes, such as expansion, closure, and oscillation. Pan et al. [74] first captured the cavitation bubble growth and collapse, and generation of microjets with a high-speed camera (Fig. 3(c) and (d)). Furthermore, the frequency of an ultrasonic wave is high and can easily be adjusted by ultrasonic transduc-ers, which could periodically turn on/off the built-in field to prevent it from being weakened or even degraded by photo-generated carriers [31].Interestingly, the internal strain induced by thermal stress was employed to modulate compression of ZnO monocrystal-line nanoplatelets [75]. Owing to the mismatched expansion coefficients of ZnO and TiO 2, anisotropic strain was generated in ZnO/TiO 2 hybrid photocatalysts by sintering and cooling (Fig. 3(e)). Different cooling processes (natural cooling in themuffle furnace and rapid cooling in air, ice, and liquid nitrogen)Fig. 2. Scheme of the photogenerated charge carrier separation en-hanced by the built-in electric field.Zhirong Liu et al. / Chinese Journal of Catalysis 41 (2020) 534–549 537resulted in different magnitudes of compressive strains along the c-axis direction of ZnO and further produced different pie-zoelectric potentials. The ZnO/TiO 2 hybrid photocatalysts cooled at a higher rate had a stronger photocatalytic activity because the residual strain and piezoelectric potential of the sample increased.There are many ways to induce deformation of piezoelectric semiconductors, but most of them need to be deliberately de-signed to generate a deformation force, which can control the strain accurately but limit the practical application of the sem-iconductor. To better utilize the mechanical energy in the nat-ural environment, Chen et al. [76] used water flow to generate stress on ZnO nanorod arrays vertically grown on a three-dimensional Ni foam. When water flowed through the Ni foam, there were some small water turbulences on the inner surface of the foam structure. Meanwhile, the ZnO nanorods on the Ni foam were also subjected to a mechanical force so that deformation could be generated (Fig. 3(f)). As the stirring rate increased, the deformation of the ZnO nanorods increased, resulting in a stronger built-in electric field to promote carrier separation. On the other hand, a 3D foam structure was more effective in reactant diffusion and photocharge migration, thereby enhancing photocatalytic activity. In addition, the heli-cal structure was also used to improve deformation in piezoe-lectric semiconductors [52]. A helical fiber is a typical and in-triguing structure in life and nature. Owing to their extraordi-nary flexibilities, elasticities, and scalabilities, helical microfi-bers can produce a larger deformation than straight microfi-bers in simple harmonic vibration systems. By combining avisible-light responsive photocatalyst, g-C 3N 4, with a main-stream organic piezoelectric PVDF, a self-healing internal elec-tric field was constructed for sustainably enhanced photocatal-ysis (Figs. 3(g) and 3(h)). Reasonable structure design and morphology of a photocatalyst enables it to comprehensively utilize solar energy and mechanical energy in nature, such as wind energy, water flow, tidal energy, etc., which is in line with sustainable development strategies [77].3.1.2. Catalysts with piezoelectric effectsThe most widely used method for constructing a piezoelec-tric catalytic system is using the piezopotential of piezoelectric semiconductors to separate photo-induced carriers generated by photocatalysts [78]. For example, various semiconductor photocatalysts (TiO 2, BiOI, and CdS) were hybridized on a soft porous piezoelectric polymeric film rGO-F/PVDF-HFP (4-azidotetrafluorobenzoic acid-modified gra-phene/polyvinylidene fluoride-co-hexafluoropropylene) (Fig. 4(a)) [79]. TiO 2, BiOI, and CdS are representative of classical UV-active catalysts, visible-light-active photocatalysts, and H 2 evolution catalysts, respectively, which can generate elec-tron-hole pairs under light illumination in a specific wavelength range. Furthermore, a rGO-F/PVDF-HFP piezoelectric film can harvest gentle mechanical disturbances in typical catalytic set-tings to form a piezoelectric field. This electric field enhanced photocatalytic performances of TiO 2, BiOI, and CdS by 300%, 21%, and 400%, respectively (Fig. 4(b)‒(d)). Dai et al. [52] combined visible-light responsive g-C 3N 4 with a helical organicpiezoelectric PVDF to construct a self-healing internal electricFig. 3. Methods used to exert a mechanical stress. (a) Schematic setup of the ZnO-based piezoelectric PEC half-cell for precise control of induced strain [68]. Reproduced with permission [68]. Copyright 2011, American Chemical Society. (b) Schematic images of the woven ZnO NWs/CFs and mechani-cal brushing/sliding under an external force [70]. Reproduced with permission [70]. Copyright 2015, Elsevier. (c) Cavitation clusters consisting of numerous cavitation bubbles in water captured by a high-speed camera. (d) Growth and collapse of cavitation bubbles in the presence of porphy-rin-like metal centers (PMCS) and ultrasonic waves [74]. Reproduced with permission [74]. Copyright 2018, Wiley. (e) Schematic demonstration of a ZnO/TiO 2 hybrid without (top) and with strain (bottom left) and it’s piezopotential distributions under an axial pressure of 10 MPa (bottom right) [75]. Reproduced with permission [75]. Copyright 2016, American Chemical Society. (f) Schematic image of ZnO nanorod deformation under water flow [76]. Reproduced with permission [76]. Copyright 2017, Elsevier. (g) Optical microphotograph of a PVDF/g-C 3N 4 helical microfiber. (h) Digital photograph of a PVDF/g-C 3N 4 helical microfiber before and after being drawn by a paper clip (about 4 mN) [52]. Reproduced with permission [52].Copyright 2019, Wiley.538 Zhirong Liu et al. / Chinese Journal of Catalysis 41 (2020) 534–549field for sustainably enhanced photocatalysis. The photovoltage of PVDF/g-C 3N 4 after deformation was 1.7 mV, fourfold higher than that before the film was deformed (Fig. 4(e)), which im-plied that the deformation of the PVDF/g-C 3N 4 film was condu-cive to the separation and propagation of photogenerated car-riers. The photocatalytic performance was enhanced signifi-cantly when microfibers experienced simple harmonic vibra-tion. Importantly, the piezoelectric field caused by deformation could be saturated within about 10 min under persistent pulse laser irradiation (Fig. 4(f)) and refreshed after the film was deformed again. Therefore, periodic deformation or a self-healing structure is important for continuous generation of built-in electric fields in piezoelectric semiconductors. When a strain was applied on the PVDF fiber, the resulting piezopoten-tial bent the energy band of C 3N 4, and then the generated built-in electric field promoted the separation of photoinduced electron and hole pairs. However, this electric field could be easily saturated by photoinduced carries and outer charged ions, halting the enhancement of photocatalysis. To overcome this problem, in this self-healing piezoelectric catalytic system, an opposite potential was generated via deformation again to repel nearby holes and attract electrons (Fig. 4(g)). The self-healing behavior could sustainably inhibit the recombina-tion of photogenerated carriers and significantly enhance the piezocatalytic effect.Tan et al. [80] constructed a self-biased hybrid piezoelec-tric-photoelectrochemical cell with photocatalytic functionali-ties. ZnO nanorods (NRs) were grown on Ag or Cu nanowires (NWs) via a galvanic displacement deposition method (Fig. 4(h)). Then, Ag-ZnO (AZ) and Cu-ZnO (CZ) were sulfurized to form a core-shell structure Ag/Ag 2S-ZnO/ZnS (ASZS) and Cu/CuS-ZnO/ZnS (CSZS). The lattice spacing of the core and shell was 0.26 and 0.31 nm, matching well with the (002) of ZnO and (111) planes of ZnS, respectively (Fig. 4(i)). By hy-bridizing the wide bandgap materials (ZnO and ZnS) with the narrow bandgap materials (Ag 2S or CuS), a composite withaFig. 4. Catalysts with a piezoelectric effect. (a) Schematic illustration of the design concept of the hybrid piezophotocatalyst. The process includes the mounting of semiconductor catalysts onto a self-powered energy cushion, which was a composite film of rGO-F/PVDF-HFP. (b) Photocatalytic degra-dation of MO catalyzed by TiO 2@rGO-F/PVDF-HFP under UV light. (c) Absorbance of MO catalyzed by BiOI@rGO-F/PVDF-HFP after 24 h under am-bient light. (d) Photocatalytic H 2 evolution rate of CdS@rGO-F/PVDF-HFP under visible light [79]. Reproduced with permission [79]. Copyright 2018,Elsevier. (e) Transient photovoltages of PVDF/g-C 3N 4 composite films on a logarithmic timescale under 355 nm pulse laser irradiation in the absence (A-D) and presence (P-D) of film deformation, respectively. (f) Variation in the transient photovoltages of the PVDF/g-C 3N 4 film with plus laser illu-mination and deformation. P-D&I-4, P-D&I-8, P-D&I-12, and P-D&I-16 stand for the transient photovoltages detected in the presence of film defor-mation and pulse laser irradiation for 4, 8, 12, and 16 min, respectively. S-D presents the transient photovoltage characterized after the film was de-formed again. (g) Diagram showing the process by which the piezoelectric potential in a PVDF/g-C 3N 4 composite helical microfiber is saturated and self-renewed, and the corresponding carrier transfer behavior [52]. Reproduced with permission [52]. Copyright 2019, Wiley. (h) Scanning electron microscope (SEM) image of AZ. (i) High resolution transmission electron microscope (HRTEM) image of ASZS. (j) Schematic illustration of a self-bias hybrid system via a bias link with the corresponding enhanced (k) photocurrent measurement [80]. Reproduced with permission [80]. Copyright 2015, American Chemical Society.Zhirong Liu et al. / Chinese Journal of Catalysis 41 (2020) 534–549 539low bandgap and increased sensitivity to visible light was fab-ricated. Owing to the piezoelectricity of ZnO, a piezoelectric charge would be generated in the hybrid battery under an ul-trasonic wave, and the charge transfer occurred between the Ag NWs electrode and the Pt counter electrode of the PEC bat-tery. This created a voltage bias that improved the photocur-rent density from 8 to 22 mA m −2. When the Ag NWs electrode of the hybrid battery was disconnected from the Pt counter electrode (Fig. 4(j)), the photocurrent decreased (Fig. 4(k)), indicating that the self-bias from the piezopotential had a sig-nificant effect on the photocurrent. This could pave the way for a new generation of self-powered photocatalytic devices for solving environmental and energy crises.3.1.3. Catalysts with a piezophototronic effectWang and co-workers [41] first proposed the concept of the piezophototronic effect in 2010. Piezoelectric semiconductors, such as wurtzite structure ZnO, GaN, InN, and CdS [81], have coupling properties of piezoelectricity, semiconductor charge transport, and light excitation, providing a new fundamental piezo-photocatalytic mechanism to modulate the separation of photogenerated carriers. The piezoelectric optoelectronic effect utilizes the piezopotential to regulate the generation, separa-tion, transport, and recombination processes of interface or junction carriers (Fig. 5), which drive the development of high-performance optoelectronic devices [82]. Wurtzite zinc oxide (ZnO) is a representative piezoelectric semiconductors. The bandgap of ZnO is ~3.37 eV, which is favorable for gener-ating electron-hole pairs under UV light irradiation. In addition, it has high piezoelectric coefficients (10–30 pm V −1 for d 33 and about 5 pm V −1 for d 31) [83]. Through the simple seed-assisted hydrothermal method, single crystal ZnO NWs can grow on substrates of different materials and shapes [70,76], providing significant cost and process advantages for potential industrial applications.Xue et al. [70] synthesized ZnO NWs on carbon fibers (CFs) (Fig. 6(a)) and co-used photonic and mechanical energy for the degradation of organic dyes by coupling the piezoelectric and photocatalytic properties of ZnO NWs. The piezoelectric effect of ZnO NWs/CFs was measured based on the mechanism of a fiber nanogenerator. When the experimental vibration distance was about 1 cm, the open-circuit voltage and short-circuit cur-rent were about 20 mV and 0.5 nA, respectively. When ZnONWs were exposed to UV light, photogenerated electron-hole pairs were generated. At the same time, a periodic force was applied to ZnO NWs/CFs, causing relative sliding between ad-jacent ZnO NWs and bending of the NWs. Therefore, a piezoe-lectric field was formed across their widths, which drove the migration of photo-generated electrons to the positive poten-tial side (stretching side) and holes to the negative potential side (compressed side) (Fig. 6(b)). It increased the separation efficiency of photogenerated electron and holes. More carriers could migrate to the surface, form free radicals, and degrade methylene blue (MB) in an aqueous solution. Moreover, the photodegradation profiles of the MB solution catalyzed by ZnO NWs/CFs increased with increasing frequency of the applied force from 0 to 1 Hz owing to a higher input power (Fig. 6(c)). Similarly, a nanocomposite with ZnO nanorod arrays grown vertically on the 3D Ni foam was synthesized to photocatalyti-cally degrade rhodamine B (RhB) [76]. The photocurrent at a stirring rate of 500 rpm was higher than that obtained under static condition (0 rpm). As the stirring rate was increased to 1000 rpm, the photocurrent density also further increased. This was because the water flow velocity increased as the stir-ring rate increased. Therefore, the ZnO nanorods on the surface of the Ni foam experienced an enhanced deformation degree, inducing an enhanced piezoelectric field. The increased piezo-electric field can promote the separation of photogenerated electron and holes. Therefore, the ZnO nanorod arrays/Ni foam showed an increasing photocurrent as the stirring rate in-creased. Mushtaq et al. [84] fabricated single-crystalline BiFeO 3 NWs (BFO NWs, Fig. 6(d)) that can successfully utilize visible light and mechanical vibrations to degrade organic pollutants. Fig. 6(e) shows that BFO NWs exhibited strong absorption in the UV and visible regions, and the bandgap of BFO NWs was 2.1 eV. The piezoelectricity of a single BFO NW was directly probed using a piezoresponse force microscopy (PFM). From the PFM phase images (Fig. 6(f)), a clear phase contrast be-tween different regions of the NW could be observed, which represented the domains with opposite out-of-plane polariza-tion orientations. The amplitude image shows the presence of distinct and randomly distributed ferroelectric domains. From the phase loop presented, it could be clearly observed that the polarization can be switched to the opposite direction by sweeping the tip bias, and the average phase contrast is close to 180°. The amplitude of the response signal in PFM was directly related to the local strain of the BFO nanostructures. This am-plitude versus bias voltage curve was also hysteretic, and its shape resembled a butterfly loop. These results confirmed the ferroelectric nature of BFO NW. When sunlight and an ultra-sound wave were used simultaneously, 97% of the RhB dye was degraded within 1 h.The piezoelectric semiconductor ZnO was also used to tune PEC water splitting. The PEC anode was a ZnO thin film depos-ited on the ITO electrode [68]. The prepared ZnO thin film had a resistivity of about 107 Ω·cm, which had reasonable charge conductance for water oxidation under illumination and could generate a high piezopotential when deformed. Under a 1.5 V bias and 100 mW cm −2 light intensity, the photocurrent density (J ph) increased by 10.2% or decreased by 8.5% when the ZnOFig. 5. Scheme of the piezophototronic effect. Coupling among piezoe-lectric, optical, and semiconducting properties in piezoelectric semi-conductor materials is the basis of piezo-phototronics.。
有机化学基础知识点有机分子的光电性质与光催化反应
有机化学基础知识点有机分子的光电性质与光催化反应有机化学基础知识点：有机分子的光电性质与光催化反应有机化学是研究碳元素及其化合物的科学，是化学学科的重要分支之一。
在有机化学的学习中，有机分子的光电性质与光催化反应是一个重要的知识点。
本文将在此基础上展开讨论。
一、有机分子的光电性质有机分子的光电性质是指有机分子在受到光照射后发生的电子结构、能级和光谱特性等方面的变化。
主要包括吸光性质、发光性质和光敏性质等。
1. 吸光性质吸光性质是有机分子在可见光或紫外光区域吸收特定波长的光线，使其电子结构发生变化的现象。
有机分子的吸光性质与其分子内所含的共轭结构和取代基有关。
共轭结构能够提高有机分子的吸光性能，而取代基则能调节有机分子的吸光峰位置和吸光强度。
2. 发光性质发光性质是指有机分子在受到激发后能够发出光线的性质。
有机分子的发光性质主要与其电子结构及分子内取代基的影响有关。
通过对有机分子的结构设计和取代基的调控，可以实现发光颜色的调节和发光效率的提高。
3. 光敏性质光敏性质是指有机分子在光照射下发生化学变化的性质。
光敏性有机分子可以通过具有光诱导的化学反应来实现光催化反应。
这种光敏性质可以应用于光控开关、光敏材料等领域。
二、有机分子的光催化反应光催化反应是指在光照作用下，有机分子通过光敏性反应产生激发态，与其他物质发生反应的过程。
光催化反应具有无毒、环保、高效等特点，在有机合成、环境清洁等领域有着广泛的应用。
1. 光催化有机合成光催化有机合成是指利用光照射下有机光敏分子的能级调控，在无需传统强氧化剂和高温条件下，实现有机化合物的合成。
这种方法具有反应选择性高、反应条件温和等优势。
2. 光催化环境净化光催化环境净化是指利用光照射下的光敏分子发生光催化反应，将有害物质转化为无害物质来净化环境。
例如，通过光催化反应可以将有机废水中的有机物降解为CO2和H2O，从而实现废水净化。
3. 光催化能源转化光催化能源转化是指利用光敏分子在光照射下发生光催化反应，将光能转化为化学能或电能。
新型光电催化反应研究进展
新型光电催化反应研究进展随着环境污染问题日益严重，人们开始更加关注环保技术的研究和应用。
在这其中，光电催化反应技术是一种被广泛关注和研究的技术，它具有环保、高效、可持续等特点，被认为是未来环保技术的发展方向之一。
本文将介绍新型光电催化反应研究的进展和应用前景。
一、什么是光电催化反应技术光电催化反应技术是一种将光能转化成电能，并最终催化化学反应的技术。
其基本原理是光照射所激发出的光子，使得半导体表面的电子被激发，产生导电性，这些激发的电子和空穴在光电极表面不断传递，直到达到催化剂表面，从而使得化学反应发生。
光电催化技术可以应用于环境治理、化学合成、能源利用等领域。
二、新型光电催化反应研究进展1.纳米材料在光电催化反应中的应用光电催化反应技术中使用的光电极通常由半导体材料构成，而纳米材料作为半导体材料中的一种，因其具有较大的比表面积、可控性和可重复性等特点而被广泛应用。
目前，不同形状、尺寸的纳米材料如氧化锌纳米棒、二氧化钛纳米管等的光电催化反应能力也被不断研究和改善。
2.新型光催化剂的研究光催化剂是光电催化反应过程中需要的关键物质，目前已经发现许多光催化剂如Pt、Pd、Au等能够促进光电催化反应中一些关键步骤的发生。
近年来，很多科学家也致力于研究新型的光催化剂如红外光响应型催化剂、多金属催化剂等，以提高光电催化反应的效率和选择性。
3.光电催化反应在环境治理中的应用光电催化反应技术在环境治理中有着广泛的应用前景。
如：二氧化碳的催化还原、催化降解有机污染物、除臭、除烟霾和水处理等等。
例如，光电催化反应可以降解污水中的有机物，同时还能将其中的有害物质光解为更稳定的物质，从而避免污染的扩散。
三、新型光电催化反应技术的应用前景目前，光电催化反应技术的研究日渐成熟，其在环境治理、能源利用、化学合成等领域的应用前景非常广阔。
相比传统的环保技术，光电催化反应技术具有不需要使用大量的能量、反应过程中产生的固体废物量少等优点，将为人类未来可持续发展提供新的思路。
半导体光催化
半导体光催化半导体光催化是21世纪初发展起来的一种新型能源技术，它利用太阳能，将有机物、无机物或污染物通过吸收，分解并转化为无害物质的反应过程，实现清洁能源的利用。
半导体光催化的作用原理可以用布朗迁移来理解，即由半导体中的电子-空穴对吸收光子，形成电子-空穴对而引起的电荷转移。
然后，半导体中的电子和空穴可以在光生自由基上进行氧化还原反应，从而分解污染物并将其转化为无害物质，实现污染物消减。
半导体光催化的受体物中含有多种元素，其中，高价金属元素具有强烈的光吸收能力，同时也具有良好的光催化性能，能够有效地催化有机物的氧化和还原反应，从而促进污染物的光降解。
此外，CdSe 材料由其具有低带隙、强烈的吸收带、良好的稳定性和抗氧化性能而被广泛应用于光催化，在提高反应速率和降低光催化反应热量方面有明显的优势。
半导体光催化技术主要有两种，即光电催化和光化学催化。
光电催化是一种利用半导体材料作为催化剂，将紫外光转换成电子，用电子来催化污染物的氧化和还原反应，从而实现污染物的消减。
而光化学催化，则是一种利用半导体材料作为催化剂，将可见光转换成自由基，通过光生自由基来催化污染物的氧化还原反应，从而实现污染物的消减。
半导体光催化技术在污染物的处理中具有显著的效果，它可以大大提高处理效率，并有效降低污染源的处理成本，为污染源的处理提供一种安全、有效、经济的技术手段。
然而，由于半导体催化剂结构的复杂性和原料成本的高昂，以及光催化技术本身存在的局限性，使得半导体光催化技术的应用受到了一定的限制。
因此，为了进一步提高半导体光催化技术的应用效果，我们需要开展多种研究，如开发新型的催化剂，改善半导体光催化剂的反应机理，提高催化性能，探索多种可行的光催化反应工艺，以及研究新型光催化技术。
此外，要加强对半导体光催化技术的实验研究，确保技术的可靠性和可靠性，为解决污染物的处理提供一种安全可行的技术手段。
总之，半导体光催化技术是一种有效的污染物处理技术，可以为污染物的处理提供一种安全有效的技术手段；但是，由于各种技术的局限性，也需要进一步的研究，以进一步提高降解污染物的效率和可靠性。
电催化及光催化
位）是使反应进行的驱动力（自由能降低大, -
△G）, 也称为亲和力（affinity）。这在研究反
应动力学的特性时有重大意义。
•
2. 可利用外部回路（例如, 恒电位）控制超
电压, 使反应条件／反应速度较易控制, 且可实
现剧烈的电解和氧化-还原条件。
•
3. 电流可作为测定反应速度的量。
因此, 测定的灵敏度和精确度都比较高
程。在Helmholz双电荷层中的电位降可使价带
边缘移至受体3能带以上的位置, 这就为电子双
价带转移入受体提供了可能性, 这意味着注入
空穴。
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• 验发现, 未经修飾的半导体的超电位的大小 明显依赖于表面的制法。
• 对修飾过的表面, 就可以接近于活性铂 极的行为。这里, Schottky能垒在有关偏压 情况下, 是相当小的（TiO2,MoSe2）, 对 GaAs, GaP, 超电位则仍为Schottky能垒高 度所控制。
的固有特性。
•
图4-6为经5次电位(1.5V-0.05V)循环的
Pt(111)面的STM像。
• 图11-7 经在1.5V和O.05V(相对于RHE)之间5次电位循环后的 • Pt(111)的[12] STM像 • (100nm X 100nm)
• 图中见到的线是原来存在的单原子的阶梯线 (stepline)。认为大多数是在平台上形成的起伏 的单原子高度的阶梯。因起伏是单原子的, 故 上下高度应当于二个原子, 因而, 见到了直径约 3nm的半球。
• 台和单原子层的阶梯。另外, 具有扭结的 晶面并不能因扭结的增加而观测到新峰, 担和这样的面相对应的峰将会有所变化。 可以说, 扭结也是一种目的晶面。
• 3. 电极表面上的吸附作用
中国光电催化领域发展状况和发展前景
中国光电催化领域发展状况及发展前景一、引言光电催化技术是一种将太阳能转化为化学能的新型技术，具有高效、环保、可持续等优点。
近年来，随着全球对环保和能源问题的关注度不断提高，光电催化技术在中国得到了广泛的应用和发展。
本文将对中国光电催化领域的发展状况及发展前景进行探讨。
二、环保领域应用光电催化技术在环保领域的应用主要包括污水处理、空气净化等方面。
通过光电催化技术，可以将污水中的有机物、重金属等污染物进行光解、电离，从而去除污染物，实现污水处理的目标。
同时，光电催化技术也可以应用于空气净化领域，将空气中的有害物质进行光解、氧化，提高空气质量。
三、能源领域应用光电催化技术在能源领域的应用主要包括太阳能电池、光催化燃料电池等方面。
通过光电催化技术，可以将太阳能转化为电能或化学能，为太阳能电池和光催化燃料电池提供能量来源。
同时，光电催化技术也可以应用于太阳能光热利用领域，提高太阳能的利用率。
四、材料领域应用光电催化技术在材料领域的应用主要包括光催化材料、光电器件等方面。
通过光电催化技术，可以制备出具有优异光催化性能的材料，如TiO2、ZnO等。
同时，光电催化技术也可以应用于光电器件领域，如太阳能电池、光传感器等。
五、人才需求增加随着光电催化技术的不断发展，对人才的需求也在不断增加。
目前，中国在光电催化领域的人才储备相对较少，需要加强人才培养和引进工作。
同时，也需要加强与国际先进技术的交流和合作，提高中国在光电催化领域的整体水平。
六、技术创新推动随着科学技术的不断发展，光电催化技术也在不断创新和进步。
目前，中国在光电催化技术方面的研究已经取得了一定的成果，但仍需要进一步加强技术创新和研发工作。
同时，也需要加强与产业界的合作和交流，推动光电催化技术的产业化发展。
七、结论综上所述，中国在光电催化领域已经取得了一定的成果和发展前景。
未来随着环保和能源问题的不断加剧以及科学技术的不断创新和发展，光电催化技术将会得到更加广泛的应用和发展。
光催化与光电催化
光催化与光电催化
光催化与光电催化都是通过光照下催化剂对化学物质进行反应的方法，但其具体机理和应用有所不同。
光催化是指通过光照下催化剂促进化学反应的方法，此时光的能量被吸收后转化为催化活性位点的能量，使得反应物在较低的温度和压力下发生化学反应。
光催化广泛应用于环境保护、水处理、空气净化、有机合成等领域。
光催化反应的典型例子是可见光下二氧化钛催化氧化有机物。
在此反应中，二氧化钛表面吸收光能后，经历一系列复杂的物理化学过程，生成具有氧化性的电子空穴对，这些电子空穴对可以将水分子氧化为具有氧化性的自由基，从而促进有机物的氧化反应。
相比之下，光电催化则是光电转换和光化学反应相结合的过程。
在此过程中，外加电场和有机化合物的光催化剂共同作用，将光能转换为电能和化学能，实现光电催化反应。
光电催化的应用非常广泛，涵盖了太阳能电池、光电催化分解水为氢气、光电阴极、光电催化二氧化碳还原等多个领域。
光电催化反应时间短、效率高，能够在不需要外界供应的条件下实现化学反应，有望成为一种能源的替代技术。
总之，光催化和光电催化分别是光化学反应和光电转换与光化学反应的两种光化学反应形式，其在环境净化、能源转化和有机合成等领域都有广泛的应用前景。
光催化与光电催化65页PPT文档共67页
35、不要以为自己成功一次就可以了 ，也不 要以为 过去的 光荣可 以被永 远肯定 。
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23、一切节省，归根到底都归结为时间的节省。——马克思 24、意志命运往往背道而驰，决心到最后会全部推倒。——莎士比亚
光催化与光电催化65页PPT 文档
31、别人笑我太疯癫，我笑他人看不 穿。(名 言网) 32、我不想听失意者的哭泣，抱怨者 的牢骚 ，这是 羊群中 的瘟疫 ，我不 能被它 传染。 我要尽 量避免 绝望， 辛勤耕 耘，忍 受苦楚 。我一 试再试 ，争取 每天的 成功， 避免以 失败收 常在别 人停滞 不前时 ，我继 续拼搏 。