Showing papers on "Photocatalysis published in 2014"
TL;DR: Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,†
Abstract: Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,† †State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China ‡Department of Chemistry, College of Arts and Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, Missouri 64110, United States
1,990 citations
TL;DR: A variety of reaction types have now been shown to be amenable to visible light photocatalysis via photoinduced electron transfer to or from the transition metal chromophore, as well as energy-transfer processes.
Abstract: Background Interest in photochemical synthesis has been motivated in part by the realization that sunlight is effectively an inexhaustible energy source.Chemists have also long recognized distinctive patterns of reactivity that are uniquely accessible via photochemical activation. However, most simple organic molecules absorb only ultraviolet (UV) light and cannot be activated by the visible wavelengths that comprise most of the solar energy that reaches Earth’s surface. Consequently, organic photochemistry has generally required the use of UV light sources. Visible light photocatalysis. ( A ) Transition metal photocatalysts, such as Ru(bpy) 3 2+ , readily absorb visible light to access reactive excited states. ( B ) Photoexcited Ru*(bpy) 3 2+ can act as an electron shuttle, interacting with sacrificial electron donors D (path i) or acceptors A (path ii) to yield either a strongly reducing or oxidizing catalyst toward organic substrates S. Ru*(bpy) 3 2+ can also directly transfer energy to an organic substrate to yield electronically excited species (path iii). bpy, 2,29-bipyridine; MLCT, metal-to-ligand charge transfer. Advances Over the past several years, there has been a resurgence of interest in synthetic photochemistry, based on the recognition that the transition metal chromophores that have been so productively exploited in the design of technologies for solar energy conversion can also convert visible light energy into useful chemical potential for synthetic purposes. Visible light enables productive photoreactions of compounds possessing weak bonds that are sensitive toward UV photodegradation. Furthermore, visible light photoreactions can be conducted by using essentially any source of white light, including sunlight, which obviates the need for specialized UV photoreactors. This feature has expanded the accessibility of photochemical reactions to a broader range of synthetic organic chemists. A variety of reaction types have now been shown to be amenable to visible light photocatalysis via photoinduced electron transfer to or from the transition metal chromophore, as well as energy-transfer processes. The predictable reactivity of the intermediates generated and the tolerance of the reaction conditions to a wide range of functional groups have enabled the application of these reactions to the synthesis of increasingly complex target molecules. Outlook This general strategy for the use of visible light in organic synthesis is already being adopted by a growing community of synthetic chemists. Much of the current research in this emerging area is geared toward the discovery of photochemical solutions for increasingly ambitious synthetic goals. Visible light photocatalysis is also attracting the attention of researchers in chemical biology, materials science, and drug discovery, who recognize that these reactions offer opportunities for innovation in areas beyond traditional organic synthesis. The long-term goals of this emerging area are to continue to improve efficiency and synthetic utility and to realize the long-standing goal of performing chemical synthesis using the sun.
1,859 citations
TL;DR: This review covers state-of-the-art accomplishments in visible-light-induced selective organic transformations by heterogeneous photocatalysis and discusses three sections based on the photocatalyst type: metal oxides such as TiO2, Nb2O5 and ZnO; plasmonic photocatalysts like nanostructured Au, Ag or Cu supported on metal oxide; and polymeric graphitic carbon nitride.
Abstract: The future development of chemistry entails environmentally friendly and energy sustainable alternatives for organic transformations. Visible light photocatalysis can address these challenges, as reflected by recent intensive scientific endeavours to this end. This review covers state-of-the-art accomplishments in visible-light-induced selective organic transformations by heterogeneous photocatalysis. The discussion comprises three sections based on the photocatalyst type: metal oxides such as TiO2, Nb2O5 and ZnO; plasmonic photocatalysts like nanostructured Au, Ag or Cu supported on metal oxides; and polymeric graphitic carbon nitride. Finally, recent strides in bridging the gap between photocatalysis and other areas of catalysis will be highlighted with the aim of overcoming the existing limitations of photocatalysis by developing more creative synthetic methodologies.
1,177 citations
1,049 citations
TL;DR: An effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported, and it was found that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.
Abstract: The major challenge of photocatalytic water splitting, the prototypical reaction for the direct production of hydrogen by using solar energy, is to develop low-cost yet highly efficient and stable semiconductor photocatalysts. Herein, an effective strategy for synthesizing extremely active graphitic carbon nitride (g-C3N4) from a low-cost precursor, urea, is reported. The g-C3N4 exhibits an extraordinary hydrogen-evolution rate (ca. 20 000 μmol h−1 g−1 under full arc), which leads to a high turnover number (TON) of over 641 after 6 h. The reaction proceeds for more than 30 h without activity loss and results in an internal quantum yield of 26.5 % under visible light, which is nearly an order of magnitude higher than that observed for any other existing g-C3N4 photocatalysts. Furthermore, it was found by experimental analysis and DFT calculations that as the degree of polymerization increases and the proton concentration decreases, the hydrogen-evolution rate is significantly enhanced.
978 citations
TL;DR: This paper aims to inspire readers to search for further new applications for this material in catalysis and in other fields by describing the methods used for synthesizing this material with different textural structures and surface morphologies.
Abstract: Graphitic carbon nitride, g-C3N4, is a polymeric material consisting of C, N, and some impurity H, connected via tris-triazine-based patterns. Compared with the majority of carbon materials, it has electron-rich properties, basic surface functionalities and H-bonding motifs due to the presence of N and H atoms. It is thus regarded as a potential candidate to complement carbon in material applications. In this review, a brief introduction to g-C3N4 is given, the methods used for synthesizing this material with different textural structures and surface morphologies are described, and its physicochemical properties are referred. In addition, four aspects of the applications of g-C3N4 in catalysis are discussed: (1) as a base metal-free catalyst for NO decomposition, (2) as a reference material in differentiating oxygen activation sites for oxidation reactions over supported catalysts, (3) as a functional material to synthesize nanosized metal particles, and (4) as a metal-free catalyst for photocatalysis. Th...
919 citations
TL;DR: A composite material consisting of CdS nanocrystals grown on the suface of a nanosized MoS2/graphene hybrid as a high-performance noble-metal-free photocatalyst for H2 evolution under visible light irradiation is reported.
Abstract: Exploiting noble-metal-free cocatalysts is of huge interest for photocatalytic water splitting using solar energy. Here we report a composite material consisting of CdS nanocrystals grown on the suface of a nanosized MoS2/graphene hybrid as a high-performance noble-metal-free photocatalyst for H2 evolution under visible light irradiation. Through the optimizing of each component proportion, the MoS2/G-CdS composite showed the highest photocatalytic H2 production activity when the content of the MoS2/graphene cocatalyst is 2.0 wt % and the molar ratio of MoS2 to graphene is 1:2. The photocatalytic H2 evolution activity of the proposed MoS2/G-CdS composite was tested and compared in Na2S–Na2SO3 solution and lactic acid solution. A 1.8 mmol/h H2 evolution rate in lactic acid solution corresponding to an AQE of 28.1% at 420 nm is not only higher than the case in Na2S–Na2SO3 solution of 1.2 mmol/h but also much higher than that of Pt/CdS in lactic acid solution. The relative mechanism has been investigated. It...
856 citations
TL;DR: A simple one-step hydrothermal method toward in situ growth of ultradispersed mesoporous TiO2 nanocrystals with (001) facets on GAs results in highly active photocatalysis, a high rate capability, and stable cycling.
Abstract: TiO2/graphene composites have been well studied as a solar light photocatalysts and electrode materials for lithium-ion batteries (LIBs). Recent reports have shown that ultralight 3D-graphene aerogels (GAs) can better adsorb organic pollutants and can provide multidimensional electron transport pathways, implying a significant potential application for photocatalysis and LIBs. Here, we report a simple one-step hydrothermal method toward in situ growth of ultradispersed mesoporous TiO2 nanocrystals with (001) facets on GAs. This method uses glucose as the dispersant and linker owing to its hierarchically porous structure and a high surface area. The TiO2/GAs reported here exhibit a highly recyclable photocatalytic activity for methyl orange pollutant and a high specific capacity in LIBs. The strong interaction between TiO2 and GAs, the facet characteristics, the high electrical conductivity, and the three-dimensional hierarchically porous structure of these composites results in highly active photocatalysi...
746 citations
TL;DR: In this paper, the fundamental photophysics of localized surface plasmon resonance (LSPR) excitation in the context of driving chemical transformations are discussed, and various demonstrated chemical conversions executed using direct plasmoric photocatalysis is reviewed.
Abstract: Recent reports have shown that plasmonic nanostructures can be used to drive direct photocatalysis with visible photons, where nanostructures act as the light absorber and the catalytic active site. These reports have showcased direct plasmon driven photocatalysis as a route to concentrate and channel the energy of low intensity visible light into adsorbed molecules, enhancing the rates of chemical transformations, and offering pathways to control reaction selectivity. In this perspective, we will discuss the fundamental photophysics of localized surface plasmon resonance (LSPR) excitation in the context of driving chemical transformations. The various demonstrated chemical conversions executed using direct plasmonic photocatalysis will be reviewed. Experimental observations, such as the dependence of photocatalytic rate on illumination intensity and photon energy, will be related to microscopic mechanisms of photocatalysis. In addition, theoretical treatments of various mechanisms within the process of d...
743 citations
TL;DR: It is shown that a particular dye molecule can channel the combined energy from two absorbed photons to the reduction and subsequent coupling reactions of aryl halide molecules, expanding the reach of photocatalysis to a broader range of compounds, such as chlorides, which are too stable to breach with a single photon.
Abstract: Biological photosynthesis uses the energy of several visible light photons for the challenging oxidation of water, whereas chemical photocatalysis typically involves only single-photon excitation. Perylene bisimide is reduced by visible light photoinduced electron transfer (PET) to its stable and colored radical anion. We report here that subsequent excitation of the radical anion accumulates sufficient energy for the reduction of stable aryl chlorides giving aryl radicals, which were trapped by hydrogen atom donors or used in carbon-carbon bond formation. This consecutive PET (conPET) overcomes the current energetic limitation of visible light photoredox catalysis and allows the photocatalytic conversion of less reactive chemical bonds in organic synthesis.
722 citations
TL;DR: It is shown that cobalt(II) oxide (CoO) nanoparticles can carry out overall water splitting with a solar-to-hydrogen efficiency of around 5% and that the high photocatalytic activity of the nanoparticles arises from a significant shift in the position of the band edge of the material.
Abstract: Cobalt oxide nanoparticles can carry out overall water splitting with a solar-to-hydrogen efficiency of around 5%.
TL;DR: It is proposed that employing a hydroxyl anion/radical redox couple to efficiently relay the hole from the semiconductor to the scavenger leads to a marked increase in the H2 generation rate without using expensive noble metal co-catalysts.
Abstract: Photocatalytic efficiency can be limited by slow transfer of photoexcited holes and high charge recombination rates. Using a hydroxyl anion–radical redox couple leads to enhanced photocatalytic H2 generation on Ni-decorated CdS nanorods. Photocatalytic conversion of solar energy to fuels, such as hydrogen, is attracting enormous interest, driven by the promise of addressing both energy supply and storage1. Colloidal semiconductor nanocrystals have been at the forefront of these efforts owing to their favourable and tunable optical and electronic properties2,3,4 as well as advances in their synthesis5,6. The efficiency of the photocatalysts is often limited by the slow transfer and subsequent reactions of the photoexcited holes and the ensuing high charge recombination rates. Here we propose that employing a hydroxyl anion/radical redox couple to efficiently relay the hole from the semiconductor to the scavenger leads to a marked increase in the H2 generation rate without using expensive noble metal co-catalysts. The apparent quantum yield and the formation rate under 447 nm laser illumination exceeded 53% and 63 mmol g−1 h−1, respectively. The fast hole transfer confers long-term photostability on the system and opens new pathways to improve the oxidation side of full water splitting.
TL;DR: The successful deposition of Au NPs, having sizes smaller than 3 nm, onto ZnO NPs is demonstrated and these materials have great potential for use in water purification and antibacterial products.
Abstract: Semiconductor nanostructures with photocatalytic activity have the potential for many applications including remediation of environmental pollutants and use in antibacterial products. An effective way for promoting photocatalytic activity is depositing noble metal nanoparticles (NPs) on a semiconductor. In this paper, we demonstrated the successful deposition of Au NPs, having sizes smaller than 3 nm, onto ZnO NPs. ZnO/Au hybrid nanostructures having different molar ratios of Au to ZnO were synthesized. It was found that Au nanocomponents even at a very low Au/ZnO molar ratio of 0.2% can greatly enhance the photocatalytic and antibacterial activity of ZnO. Electron spin resonance spectroscopy with spin trapping and spin labeling was used to investigate the enhancing effect of Au NPs on the generation of reactive oxygen species and photoinduced charge carriers. Deposition of Au NPs onto ZnO resulted in a dramatic increase in light-induced generation of hydroxyl radical, superoxide and singlet oxygen, and production of holes and electrons. The enhancing effect of Au was dependent on the molar ratio of Au present in the ZnO/Au nanostructures. Consistent with these results from ESR measurements, ZnO/Au nanostructures also exhibited enhanced photocatalytic and antibacterial activity. These results unveiled the enhanced mechanism of Au on ZnO and these materials have great potential for use in water purification and antibacterial products.
TL;DR: Using time-resolved Fourier-transform infrared spectroscopy and under reaction conditions, intermediates of water oxidation catalysed by an abundant metal-oxide catalyst, cobalt oxide (Co3O4), are identified.
Abstract: In any artificial photosynthetic system, the oxidation of water to molecular oxygen provides the electrons needed for the reduction of protons or carbon dioxide to a fuel. Understanding how this four-electron reaction works in detail is important for the development of improved robust catalysts made of Earth-abundant materials, like first-row transition-metal oxides. Here, using time-resolved Fourier-transform infrared spectroscopy and under reaction conditions, we identify intermediates of water oxidation catalysed by an abundant metal-oxide catalyst, cobalt oxide (Co3O4). One intermediate is a surface superoxide (three-electron oxidation intermediate absorbing at 1,013 cm(-1)), whereas a second observed intermediate is attributed to an oxo Co(IV) site (one-electron oxidation intermediate absorbing at 840 cm(-1)). The temporal behaviour of the intermediates reveals that they belong to different catalytic sites. Knowledge of the structure and kinetics of surface intermediates will enable the design of improved metal-oxide materials for more efficient water oxidation catalysis.
TL;DR: This review concentrates on the use of electric fields within catalyst particles to mitigate the effects of recombination and back-reaction and to increase photochemical reactivity.
Abstract: The photocatalytic activity of materials for water splitting is limited by the recombination of photogenerated electron–hole pairs as well as the back-reaction of intermediate species. This review concentrates on the use of electric fields within catalyst particles to mitigate the effects of recombination and back-reaction and to increase photochemical reactivity. Internal electric fields in photocatalysts can arise from ferroelectric phenomena, p–n junctions, polar surface terminations, and polymorph junctions. The manipulation of internal fields through the creation of charged interfaces in hierarchically structured materials is a promising strategy for the design of improved photocatalysts.
TL;DR: In this article, carbon quantum dots modified P25 TiO2 composites (CQDs/P25) with a "dyade"-like structure were prepared via a facile one-step hydrothermal reaction.
Abstract: Carbon quantum dots modified P25 TiO2 composites (CQDs/P25) with a “dyade”-like structure were prepared via a facile one-step hydrothermal reaction. CQDs/P25 exhibited improved photocatalytic H2 evolution under UV-Vis and visible light (λ > 450 nm) irradiation without loading any noble metal cocatalyst, compared to pure P25. A possible mechanism of the photocatalytic H2 production activity over CQDs/P25 was proposed based on detailed measurements of the transient photocurrent response, surface photovoltage and hydroxyl radicals. CQDs play dual roles on the improved photocatalytic activity of CQDs/P25. Under UV-Vis light irradiation CQDs act as an electron reservoir to improve the efficient separation of the photoinduced electron–hole pairs of P25. However, under visible light irradiation CQDs act as a photosensitizer to sensitize P25 into a visible light response “dyade” structure for H2 evolution.
TL;DR: It is indicated that the heterostructured combination of g-C3N4, Ag and TiO2 microspheres provides synergistic photocatalytic activity through an efficient electron transfer process.
Abstract: The visible-light photocatalytic performance of the heterostructured g-C3N4/Ag/TiO2 microspheres was investigated. As an electron-conduction bridge, Ag nanoparticles were photodeposited as the interlayer between g-C3N4 and the surface of TiO2 microspheres to increase visible-light absorption via the surface plasmon resonance. The interface between Ag/TiO2 and g-C3N4 facilitates the direct migration of photoinduced electrons from g-C3N4 to Ag/TiO2, which is conductive to retarding the recombination of electron–holes. The g-C3N4 (4%)/Ag/TiO2 microsphere sample shows significant photocatalytic activity, higher than the sum of g-C3N4 (1.2 mg) and Ag/TiO2 samples, or the sum of TiO2 and Ag/g-C3N4 (1.8 mg) samples. It indicates that the heterostructured combination of g-C3N4, Ag and TiO2 microspheres provides synergistic photocatalytic activity through an efficient electron transfer process.
TL;DR: In this article, the authors focus on the research efforts that have been made so far for H2 generation from water splitting by UV and visible light-driven photocatalysis and discuss a number of synthetic modification methods for adapting the electronic structure to enhance the charge separation in the photocatalyst materials.
TL;DR: In this paper, the separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been investigated by ball milling and heat treatment methods, and the performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination.
Abstract: The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C 3 N 4 -WO 3 photocatalysts with different main parts of C 3 N 4 or WO 3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C 3 N 4 -WO 3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C 3 N 4 -WO 3 photocatalyst is WO 3 (namely g-C 3 N 4 /WO 3 ), the transport process of the photogenerated electrons and holes adopts the generic band–band transfer. Meanwhile, g-C 3 N 4 is covered by WO 3 powder, and the role of g-C 3 N 4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO 3 -g-C 3 N 4 photocatalyst is g-C 3 N 4 (namely WO 3 /g-C 3 N 4 ), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly.
TL;DR: In this article, the microscopic mechanisms of interface interaction, charge transfer and separation, as well as the influence on the photocatalytic activity of g-C3N4/NaNbO3 composite were systematic investigated.
Abstract: Visible-light-responsive g-C3N4/NaNbO3 nanowires photocatalysts were fabricated by introducing polymeric g-C3N4 on NaNbO3 nanowires. The microscopic mechanisms of interface interaction, charge transfer and separation, as well as the influence on the photocatalytic activity of g-C3N4/NaNbO3 composite were systematic investigated. The high-resolution transmission electron microscopy (HR-TEM) revealed that an intimate interface between C3N4 and NaNbO3 nanowires formed in the g-C3N4/NaNbO3 heterojunctions. The photocatalytic performance of photocatalysts was evaluated for CO2 reduction under visible-light illumination. Significantly, the activity of g-C3N4/NaNbO3 composite photocatalyst for photoreduction of CO2 was higher than that of either single-phase g-C3N4 or NaNbO3. Such a remarkable enhancement of photocatalytic activity was mainly ascribed to the improved separation and transfer of photogenerated electron–hole pairs at the intimate interface of g-C3N4/NaNbO3 heterojunctions, which originated from the...
TL;DR: Various examples of advanced TiO2 composites have been discussed in relation to their visible light induced photoconversion efficiency, dynamics of electron-hole separation, and decomposition of organic and inorganic pollutants, which suggest the critical need for further development of these types of materials for energy conversion and environmental remediation purposes.
Abstract: In recent years, the area of developing visible-light-active photocatalysts based on titanium dioxide has been enormously investigated due to its wide range of applications in energy and environment related fields. Various strategies have been designed to efficiently utilize the solar radiation and to enhance the efficiency of photocatalytic processes. Building on the fundamental strategies to improve the visible light activity of TiO2-based photocatalysts, this Perspective aims to give an insight into many contemporary developments in the field of visible-light-active photocatalysis. Various examples of advanced TiO2 composites have been discussed in relation to their visible light induced photoconversion efficiency, dynamics of electron–hole separation, and decomposition of organic and inorganic pollutants, which suggest the critical need for further development of these types of materials for energy conversion and environmental remediation purposes.
TL;DR: In this paper, the g-C3N4/Ag3VO4 hybrid photocatalysts were prepared by Ag3VO 4 anchoring on the surface of g-c3n4/c3v4.
Abstract: The g-C3N4/Ag3VO4 hybrid photocatalysts were prepared by Ag3VO4 anchoring on the surface of g-C3N4. The transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photo-electron spectroscopy analyses demonstrated that Ag3VO4 nanoparticles well distributed on the surface of g-C3N4 and the g-C3N4/Ag3VO4 hetero-junctions were formed. Compared with pure g-C3N4 and Ag3VO4, the g-C3N4/Ag3VO4 hybrid materials displayed much higher photocatalytic activity for basic fuchsin degradation (20 mg/L, 50 mL) under visible-light irradiation. The 40 wt% g-C3N4/Ag3VO4 photocatalyst exhibited optimal removal rate constant of 0.92 h−1, which was 11.5 and 6.6 times higher than that of pure g-C3N4 and Ag3VO4, respectively. Density functional theory calculations indicated that complementary conduction and valence band-edge hybridization between g-C3N4 and Ag3VO4 could apparently increase separation efficiency of electron-hole pairs of g-C3N4/Ag3VO4 composites, which was confirmed by photoluminescence spectra. In addition, it was found that h+ and •O2−1generated in the photocatalytic process played a key role in basic fuchsin degradation.
TL;DR: In this article, the authors showed that visible light irradiation of graphitic carbon nitride (g-C3N4), a polymeric semiconductor, in an alcohol/water mixture with O2 efficiently produces H2O2 with very high selectivity (∼90%).
Abstract: Photocatalytic production of hydrogen peroxide (H2O2) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O2) as an oxygen source is a potential method for safe H2O2 synthesis because the reaction can be carried out without the use of explosive H2/O2 mixed gases. Early reported photocatalytic systems, however, produce H2O2 with significantly low selectivity (∼1%). We found that visible light irradiation (λ > 420 nm) of graphitic carbon nitride (g-C3N4), a polymeric semiconductor, in an alcohol/water mixture with O2 efficiently produces H2O2 with very high selectivity (∼90%). Raman spectroscopy and electron spin resonance analysis revealed that the high H2O2 selectivity is due to the efficient formation of 1,4-endoperoxide species on the g-C3N4 surface. This suppresses one-electron reduction of O2 (superoxide radical formation), resulting in selective promotion of two-electron reduction of O2 (H2O2 formation).
TL;DR: A mechanism in which the role of Au is to respond under visible light and Cu binds to CO and directs the reduction pathway is proposed.
Abstract: Commercial P25 modified by Au–Cu alloy nanoparticles as thin film exhibits, for CO2 reduction by water under sun simulated light, a rate of methane production above 2000 μmol (g of photocatalyst)−1 h–1. Although evolution of hydrogen is observed and O2 and ethane detected, the selectivity of conduction band electrons for methane formation is almost complete, about 97%. This photocatalytic behavior is completely different from that measured for Au/P25 (hydrogen evolution) and Cu/P25 (lower activity, but similar methane selectivity). Characterization by TEM, XPS, and UV–vis spectroscopy shows that Au and Cu are alloyed in the nanoparticles. FT-IR spectroscopy and chemical analysis have allowed one to detect on the photocatalyst surface the presence of CO2•–, Cu–CO, and elemental C. Accordingly, a mechanism in which the role of Au is to respond under visible light and Cu binds to CO and directs the reduction pathway is proposed.
TL;DR: In this article, the authors demonstrate the synthesis of highly efficient Fe-doped graphitic carbon nitride (g-C3N4) nanosheets via a facile and cost effective method.
Abstract: Herein, we demonstrate the synthesis of highly efficient Fe-doped graphitic carbon nitride (g-C3N4) nanosheets via a facile and cost effective method. The synthesized Fe-doped g-C3N4 nanosheets were well characterized by various analytical techniques. The results revealed that the Fe exists mainly in the +3 oxidation state in the Fe-doped g-C3N4 nanosheets. Fe doping of g-C3N4 nanosheets has a great influence on the electronic and optical properties. The diffuse reflectance spectra of Fe-doped g-C3N4 nanosheets exhibit red shift and increased absorption in the visible light range, which is highly beneficial for absorbing the visible light in the solar spectrum. More significantly, the Fe-doped g-C3N4 nanosheets exhibit greatly enhanced photocatalytic activity for the degradation of Rhodamine B under sunlight irradiation. The photocatalytic activity of 2 mol% Fe-doped g-C3N4 nanosheets is almost 7 times higher than that of bulk g-C3N4 and 4.5 times higher than that of pure g-C3N4 nanosheets. A proposed mechanism for the enhanced photocatalytic activity of Fe-doped g-C3N4 nanosheets was investigated by trapping experiments. The synthesized photocatalysts are highly stable even after five successive experimental runs. The enhanced photocatalytic performance of Fe-doped g-C3N4 nanosheets is due to high visible light response, large surface area, high charge separation and charge transfer. Therefore, the Fe-doped g-C3N4 photocatalyst is a promising candidate for energy conversion and environmental remediation.
TL;DR: In this article, the photocatalytic degradation activity of graphitic carbon nitride (g-C3N4) and Bi2MoO6 composites for Rhodamine B was examined under visible light irradiation.
Abstract: Heterojunctions of graphitic carbon nitride (g-C3N4) and Bi2MoO6 were solvothermally synthesized and characterized by X-ray diffraction, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. The photocatalytic degradation activity of the g-C3N4/Bi2MoO6 composites for Rhodamine B was examined under visible light irradiation. The heterojunction composites exhibited higher photocatalytic activity than pure g-C3N4 or Bi2MoO6. The photocatalytic activity of the composites increased then decreased with increasing Bi2MoO6 content. The g-C3N4/Bi2MoO6 heterojunction with a Bi2MoO6 content of 16.1 wt.% exhibited the highest photocatalytic activity, and its photocatalytic efficiency was more than three times those of pure g-C3N4 or Bi2MoO6. The enhanced photocatalytic activity of the g-C3N4/Bi2MoO6 heterostructure photocatalyst was attributed predominantly to the efficient separation of photoinduced electrons and holes. The g-C3N4/Bi2MoO6 heterojunction photocatalyst exhibited excellent stability and reusability. A detailed mechanism for the enhanced photocatalytic activity is discussed. Superoxide radicals were the major active species. This study provides a visible light responsive photocatalyst with potential in environmental remediation applications.
TL;DR: In this paper, reduced graphene oxide (RGO)-CdS nanorod composites were successfully prepared by a one-step microwave-hydrothermal method in an ethanolamine-water solution.
Abstract: Solar-fuel production has attracted considerable attention because of the current demand to find alternative transportation fuels with particular emphasis on those fuels obtained photocatalytically from water and CO2. In this work, reduced graphene oxide (RGO)–CdS nanorod composites were successfully prepared by a one-step microwave-hydrothermal method in an ethanolamine–water solution. These composite samples exhibited a high activity for the photocatalytic reduction of CO2 to CH4, even without a noble metal Pt co-catalyst. The optimized RGO–CdS nanorod composite photocatalyst exhibited a high CH4-production rate of 2.51 μmol h−1 g−1 at an RGO content of 0.5 wt%. This rate exceeded that observed for the pure CdS nanorods by more than 10 times and was better than that observed for an optimized Pt–CdS nanorod composite photocatalyst under the same reaction conditions. This high photocatalytic activity was ascribed to the deposition of CdS nanorods onto the RGO sheets, which act as an electron acceptor and transporter, thus efficiently separating the photogenerated charge carriers. Furthermore, the introduction of RGO can enhance the adsorption and activation of CO2 molecules, which speeds up the photocatalytic reduction of CO2 to CH4. The proposed mechanism for the observed photocatalytic reaction with the RGO–CdS nanorod composite was further confirmed using transient photocurrent response and electrochemical impedance spectra. This work not only demonstrates a facile microwave-assisted hydrothermal method for fabricating highly active RGO–CdS nanorod composite photocatalysts, but also demonstrates the possibility of utilizing of an inexpensive carbon material as a substitute for noble metals in the photocatalytic reduction of CO2.
TL;DR: In this article, two types of photocatalysts (M/MnOx/BiVO4 and M/Co3O4/BVO4) with reduction and oxidation cocatalyst were successfully prepared on the different facets of BiVO4 by photo-deposition method.
Abstract: Cocatalysts play important roles in promoting the catalytic reactions of semiconductor photocatalysts. Especially, deposition of dual cocatalysts, i.e., oxidation and reduction cocatalysts, onto a semiconductor photocatalyst can significantly improve its photocatalytic activity due to the synergetic effect of rapid consumption of photogenerated electrons and holes. However, in most cases, the cocatalysts are randomly deposited onto the semiconductor photocatalysts, where the cocatalysts cannot function fully. Herein, based on the findings that photogenerated electrons and holes can be spatially separated onto the different facets of BiVO4, we have successfully prepared two types of photocatalysts (M/MnOx/BiVO4 and M/Co3O4/BiVO4, where M stands for noble metals) with reduction and oxidation cocatalysts selectively deposited onto the {010} and {110} facets of BiVO4 by a photo-deposition method. Remarkably enhanced photocatalytic activities were observed for such assembled photocatalysts in control experiments of photocatalytic water oxidation and photocatalytic degradation of methyl orange and rhodamine B. In-depth investigations show that the enhanced photocatalytic performances are due to not only the intrinsic nature of charge separation between the {010} and {110} facets of BiVO4, but also the synergetic effect of dual-cocatalysts deposited onto the different facets of BiVO4. This work further proves the feasibility of the general concepts for approaching efficient artificial photosynthesis systems, namely, engineering of crystal-based photocatalysts by selective deposition of suitable reduction and oxidation cocatalysts onto the different facets of light absorbing semiconductor crystals.
TL;DR: In this article, a review of the key mechanisms of photocatalysis, highlights the recent developments pertaining to pure TiO2 nanotube arrays and modified by non-metals, metals and semiconductors, and their applications in the photocatalytic degradation of organic dyes.
Abstract: Semiconductor photocatalysis is a promising physicochemical process for the photodegradation of organic contaminants and bacterial detoxification. Among various oxide semiconductor photocatalysts, TiO2 has garnered considerable attention because of its outstanding properties including strong oxidizing activity, chemical and mechanical stability, corrosion resistance, and nontoxicity. This Review briefly introduces the key mechanisms of photocatalysis, highlights the recent developments pertaining to pure TiO2 nanotube arrays and TiO2 nanotube arrays modified by non-metals, metals and semiconductors, and their applications in the photocatalytic degradation of organic dyes. The improved photocatalytic efficiencies of modified TiO2 nanotube arrays are compared with unmodified counterparts. Current challenges and prospective areas of interest in this rich field are also presented.
TL;DR: In this article, a novel and simple synthetic approach toward core-shell Ag@C3N4 nanocomposites was developed, which showed dramatic photoinduced electron-hole separation efficiency and photocatalytic activity under visible light irradiation.
Abstract: A novel and simple synthetic approach toward core–shell Ag@C3N4 nanocomposites is developed. Ag@C3N4 core–shell nanostructures were formed via reflux treatment of Ag nanoparticles with graphitic C3N4 nanosheets in methanol. The core–shell hybrid photocatalysts showed dramatic photoinduced electron–hole separation efficiency and photocatalytic activity under visible light irradiation. The photocurrent intensity, photocatalytic activity for the photodegradation of methylene blue (MB) and hydrogen evolution reaction of Ag@C3N4 were about 4, 1.8 and 30 times as that of pure C3N4 sample, respectively. The enhanced photocatalytic activity for core–shell Ag@C3N4 originated from a combined result of the localized surface plasmon resonance (LSPR) effect for Ag and hybrid effect from C3N4, resulting in the coupling interaction of the enhanced light absorption intensity, high separation efficiency of photogenerated electrons–holes, longer lifetime of charge carriers and its favorable adsorptivity.