Dual cocatalysts decorated three dimensionally ordered mesoporous g-C3N4 with homogeneous wall thickness for enhanced photocatalytic performance

Making several components be more intimate interfacial contacts in the photocatalyst is an efficient strategy to improve the separation and transfer of photogenerated charge carries and enhance the photocatalytic performance in the visible light region. In this work, a promising photocatalyst was fabricated by loading of Au nanoparticles and Cd_(0.58)Zn_(0.42)S nanoparticles onto the three dimensionally ordered mesoporous g-C₃N₄ material (Au/3DOM CN/Cd_(0.58)Zn_(0.42)S) via two-step synthesis method to significantly intensify the transfer capability of charge. The results of characterization demonstrate that Au/3DOM CN/Cd_(0.58)Zn_(0.42)S photocatalyst possesses the intimate interfacial contacts of three components and homogeneous wall thickness of 3DOM g-C₃N₄ framework, and these properties give Au/3DOM CN/Cd_(0.58)Zn_(0.42)S photocatalyst an ability that it can harvest a wider range of visible light and endow it superior photocatalytic activities for hydrogen evolution from water splitting and RhB degradation. Finally, a possible mechanism was proposed based on the photoelectrochemical measurement. This work would provide a new strategy to design and fabricate g-C₃N₄-based with 3DOM architecture materials with superior photocatalytic activity.     

Enhancing the Photocatalytic Activity of Anatase TiO2 by Improving the Specific Facet‐Induced Spontaneous Separation of Photogenerated Electrons and Holes

Recently, it has been proven that directional flow of photogenerated charge carriers occurs on specific facets of TiO₂ nanocrystals. Herein, we demonstrate that the photocatalytic activity of anatase TiO₂ nanocrystals in both photoreduction and photooxidation processes can be enhanced by selectively depositing Pt nanoparticles on the {101} facets, which strengthens spontaneously surface‐induced separation between photogenerated electrons and holes in the photocatalysis process. An optimal ratio of the oxidative {001} facets to the reductive {101} facets exists with regard to the photocatalysis of the faceted TiO₂ nanocrystals, and this is crucial for balancing the recombination and redox reaction rates of photogenerated electrons and holes. The present work might help us gain deeper insight into the relation between the specific surface of semiconductor photocatalysts and their photocatalytic activities and provides us with a new route to design photocatalysts with high photocatalytic activity.     

Enhanced photocatalytic H2 production over dual-cocatalyst-modified g-C3N4 heterojunctions

Ag nanoparticles (NPs) were deposited on the surface of g-C₃N₄ (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H₂ generation performance under solar-light irradiation. An H₂ production rate of 9.728 mmol·g^?1·h^?1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C₃N₄, 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H₂ generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C₃N₄, which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H₂ production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C₃N₄-related composite photocatalysts for H₂ production by using different co-catalysts.     

Semi-chemical interaction between graphitic carbon nitride and Pt for boosting photocatalytic hydrogen evolution

Owing to the exorbitant overpotential and serious carrier recombination of graphitic carbon nitride （gC₃N₄）,noble metal （NM） is usually served as the H₂evolution co-catalyst.Although the NM （such as Pt）nanoparticles can reduce the H₂evolution overpotential,the weak van der Waals interaction between Pt and g-C₃N₄makes against the charge transfer.Herein,the solvothermal method is developed to achieve semi-chemical interaction betwee...     

Curious behaviors of photogenerated electrons and holes at the defects on anatase,rutile, and brookite TiO2 powders: A review

Photocatalytic reactions are governed by photogenerated charge carriers upon band gap excitation. Therefore, for better understanding of the mechanism, the dynamics of photocarriers should be studied. One of the attractive materials is TiO₂, which has been extensively investigated in the field of photocatalysis. This review article summarizes our recent works of time-resolved visible to mid-IR absorption measurements to elucidate the difference of anatase, rutile, and brookite TiO₂ powders. The distinctive photocatalytic activities of these polymorphs are determined by the electron-trapping processes at the defects on powders. Powders are rich in defects and these defects capture photogenerated electrons. The depth of the trap is crystal phase dependent, and they are estimated to be < 0.1 eV, ∼0.4 eV and ∼0.9 eV for anatase, brookite, and rutile, respectively. Electron trapping reduces probability to meet with holes and then elongate the lifetime of holes. Therefore, it works negatively for the reaction of electrons but positively works for the reaction of holes. In the steady-state reactions, both electrons and holes should be consumed. Hence, the balance between the positive and negative effects of defects determines the distinctive photocatalytic activities of anatase, rutile, and brookite TiO₂ powders.     

Facile Synthesis of Porous g-C3N4 with Enhanced Visible-Light Photoactivity

Porous graphitic carbon nitride (g-C₃N₄) was prepared by dicyandiamide and urea via the pyrolysis method, which possessed enhanced visible-light-driven photocatalytic performance. Its surface area was increased from 17.12 to 48.00 m²/g. The porous structure not only enhanced the light capture capacity, but also accelerated the mass transfer ability. The Di (Dicyandiamide)/Ur (Urea) composite possessed better photocatalytic activity for Rhodamine B in visible light than that of g-C₃N₄. Moreover, the Di/Ur-4:5 composite showed the best photoactivity, which was almost 5.8 times that of g-C₃N₄. The enhanced photocatalytic activity showed that holes and superoxide radical played a key role in the process of photodegradation, which was ascribed to the enhanced separation of photogenerated carriers. The efficient separation of photogenerated electron-hole pairs may be owing to the higher surface area, O dopant, and pore volumes, which can not only improve the trapping opportunities of charge carriers but also the retarded charge carrier recombination. Therefore, it is expected that the composite would be a promising candidate material for organic pollutant degradation.     

Prussian Blue Type Cocatalysts for Enhancing the Photocatalytic Water Oxidation Performance of BiVO4

The efficiency of photocatalytic overall water splitting reactions is usually limited by the high energy barrier and complex multiple electron-transfer processes of the oxygen evolution reaction (OER). Although bismuth vanadate (BiVO₄) as the photocatalyst has been developed for enhancing the kinetics of the water oxidation reaction, it still suffers from challenges of fast recombination of photogenerated electron-hole pairs and poor photocatalytic activity. Herein, six M^II-Co^III Prussian blue analogues (PBAs) (M=Mn, Fe, Co, Ni, Cu and Zn) cocatalysts are synthesized and deposited on the surface of BiVO₄ for boosting the surface catalytic efficiency and enhancing photogenerated carries separation efficiency of BiVO₄. Six M^II-Co^III PBAs@BiVO₄ photocatalysts all demonstrate increased photocatalytic water oxidation performance compared to that of BiVO₄ alone. Among them, the Co−Co PBA@BiVO₄ photocatalyst is employed as a representative research object and is thoroughly characterized by electrochemistry, electronic microscope as well as multiple spectroscopic analyses. Notably, BiVO₄ coupling with Co−Co PBA cocatalyst could capture more photons than that of pure BiVO₄, facilitating the transfer of photogenerated charge carriers between BiVO₄ and Co−Co PBA as well as the surface catalytic efficiency of BiVO₄. Overall, this work would promote the synthesis strategy development for exploring new types of composite photocatalysts for water oxidation.     

光诱导双助催化剂在半导体表面的自发形成（英文）

半导体光催化体系的助催化剂在光生电荷分离和表面催化反应过程中扮演着重要的角色.然而,在反应条件下助催化剂的化学态是否发生改变尚不清楚.本文以钽酸钠为模型光催化剂,系统地研究了镍基助催化剂在光催化分解水反应中的化学态.结果发现,在光诱导条件下半导体钽酸钠单晶表面自发形成了金属镍和氧化镍双助催化剂.首先用传统的水热法合成只暴露单一晶面的六面体钽酸钠半导体单晶光催化剂和暴露不等同晶面的二十六面体钽酸钠半导体单晶光催化剂.原位光沉积结果显示,暴露不同晶面的二十六面体钽酸钠半导体单晶光催化剂存在晶面间的电荷分离现象,进一步利用该现象可以确定不同催化活性位上镍基助催化剂的作用.XPS结果显示,半导体钽酸钠单晶表面的镍基助催化剂存在的不同价态.高分辨透射电镜结果表明,不同晶面上的镍基助催化剂具有不同的形貌,并且通过晶格衍射条纹的对比确认了不同镍基助催化剂物种的归属和作用.将表面浸渍氧化镍的二十六面体钽酸钠半导体光催化剂用于全分解水测试发现,反应开始阶段H_2:O_2比值小于2:1,说明部分光生电子被消耗掉,用于还原氧化镍,生成了金属镍.将表面还原的金属镍光催化剂进行全分解水测试发现,反应开始阶段H_2:O_2比值大于2:1,说明部分光生空穴被消耗掉,用于氧化金属镍,生成了氧化镍,金属镍和氧化镍最终在反应的过程中达到了平衡.金属镍担载在{001}晶面上,起着还原助催化剂的作用,参与质子还原,释放出H_2;氧化镍担载在其他晶面上,扮演着氧化助催化剂,参与水的氧化,释放出O_2;金属镍和氧化镍共同促进了光催化全分解水反应,使反应活性达到了最高.这种双助催化剂的自发形成现象不仅存在于二十六面体钽酸钠单晶半导体表面,在六面体钽酸钠单晶半导体表面也同样存在,是一个普适性的现象.在六面体钽酸钠半导体单晶光催化剂表面同样可以发现不同形貌的镍基助催化剂,分别归属于金属镍和氧化镍.本文说明了助催化剂的化学态在光催化反应的条件下是可以发生改变的,并且光生电荷可以在半导体表面诱导双助催化剂的自发形成.     

Gold/monolayer graphitic carbon nitride plasmonic photocatalyst for ultrafast electron transfer in solar-to-hydrogen energy conversion

Gold (Au) plasmonic nanoparticles were grown evenly on monolayer graphitic carbon nitride (g-C₃N₄) nanosheets via a facile oil-bath method. The photocatalytic activity of the Au/monolayer g-C₃N₄ composites under visible light was evaluated by photocatalytic hydrogen evolution and environmental treatment. All of the Au/monolayer g-C₃N₄ composites showed better photocatalytic performance than that of monolayer g-C₃N₄ and the 1% Au/monolayer g-C₃N₄ composite displayed the highest photocatalytic hydrogen evolution rate of the samples. The remarkable photocatalytic activity was attributed largely to the successful introduction of Au plasmonic nanoparticles, which led to the surface plasmon resonance (SPR) effect. The SPR effect enhanced the efficiency of light harvesting and induced an efficient hot electron transfer process. The hot electrons were injected from the Au plasmonic nanoparticles into the conduction band of monolayer g-C₃N₄. Thus, the Au/monolayer g-C₃N₄ composites possessed higher migration and separation efficiencies and lower recombination probability of photogenerated electron-hole pairs than those of monolayer g-C₃N₄. A photocatalytic mechanism for the composites was also proposed.     

Heteroatom-Doped Ag25 Nanoclusters Encapsulated in Metal–Organic Frameworks for Photocatalytic Hydrogen Production

Atomically precise metal nanoclusters (NCs) with unique optical properties and abundant catalytic sites are promising in photocatalysis. However, their light-induced instability and the difficulty of utilizing the photogenerated carriers for photocatalysis pose significant challenges. Here, MAg₂₄ (M=Ag, Pd, Pt, and Au) NCs doped with diverse single heteroatoms have been encapsulated in a metal–organic framework (MOF), UiO-66-NH₂, affording MAg₂₄@UiO-66-NH₂. Strikingly, compared with Ag₂₅@UiO-66-NH₂, the MAg₂₄@UiO-66-NH₂ doped with heteroatom exhibits much enhanced activity in photocatalytic hydrogen production, among which AuAg₂₄@UiO-66-NH₂ presents the best activity up to 3.6 mmol g⁻¹ h⁻¹, far superior to all other counterparts. Moreover, they display excellent photocatalytic recyclability and stability. X-ray photoelectron spectroscopy and ultrafast transient absorption spectroscopy demonstrate that MAg₂₄ NCs encapsulated into the MOF create a favorable charge transfer pathway, similar to a Z-scheme heterojunction, when exposed to visible light. This promotes charge separation, along with optimized Ag electronic state, which are responsible for the superior activity in photocatalytic hydrogen production.     

Highly efficient photocatalytic degradation for antibiotics and mechanism insight for Bi2S3/g-C3N4 with fast interfacial charges transfer and excellent stability

Bi₂S₃/g-C₃N₄ (BSCN) samples with different mass ratios of CN to BS were prepared by a facile and practicable hydrothermal method with 2D g-C₃N₄ nanosheets (CN). The microscopic morphology and structure of pure CN, BS and BSCN were measured by multiple testing methods. Analysis results show that the BSCN was prepared successfully, and the Bi₂S₃ nanoparticles closely and uniformly adhered to the surface of CN with sheet-like structure. The introduction of Bi₂S₃ did not change the structure of the CN. The results of the ultraviolet–visible spectroscopic analysis, photoluminescence spectra and electrochemical performance indicated that BSCN showed superior visible-light response compared with CN, and the separation and transfer efficiency of photogenerated carriers was significantly improved. With the decrease of mass ratio of CN/BS, the photocatalytic activity of BSCN initially increased and then decreased for 20 ppm of Rhodamine B solution (RhB), and the Bi₂S₃/g-C₃N₄-B with a mass ratio of 8:1 for CN to BS showed optimal photocatalytic performance (98.98%). Furthermore, the Bi₂S₃/g-C₃N₄-B exhibited apparent degradation effects (1.021 x10^-2, 0.879 x10^-2 and 0.793 x10^-2 min^?1) to three kinds of antibiotics (tetracycline, ciprofloxacin, and oxytetracycline). The BSCN samples still maintained higher degradation efficiency after five cycles of degradation to tetracycline. The capture experiments and the electron spin resonance (ESR) spectra analysis indicated that the h⁺ and ·O₂^? played a major role, and ·OH played secondary role during the photocatalytic reaction.     

Advantaging Synergy Photocatalysis with Graphene‐Related Carbon as a Counterpart Player of Titania

The enhancement of photocatalytic activity of TiO₂ can be made either by promoting absorption efficiency of photon energy or by reducing recombination losses of photogenerated charge carriers, for which fabrication of nanocomposite structure with carbon materials is an optional selection. Among various nanocarbons, graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) are more favorable as the counterpart materials because they can provide availability of both obverse and reverse surface, thus doubling effective sites for adsorption, loading of nanoparticles, and interfacial interaction with the loaded nanoparticles. Composition of G/GO with titania, therefore, is a hopeful strategy for achieving synergy or cooperative effect in photocatalysis. In this personal account, we focus on the background and methodology of several soft chemical approaches that we have utilized up to date to fabricate nanocomposites of G/GO and titania, aiming to shed light on the importance of designing of nanocomposite structure for enhancing photocatalysis. In addition, we emphasize the role of interfacial interaction between carbon and titania by exemplifying a hybridized photocatalyst based on inexpensive biomass‐derived carbon sphere (CS), and demonstrate that it is a crucial influential factor underlying an enhanced visible light photocatalysis. CS can be a better selection as a counterpart component than G/GO, whose core‐shell composing structure with titania (TiO₂@CS) can efficiently induce charge transfer so as to achieve a much higher photocatalytic performance under visible light illumination as compared to the composite of rGO and titania.     

Influence of carbon source on the anatase and brookite mixed phase of the C-doped TiO2 nanoparticles and their photocatalytic activity

Choosing resorcinol, phloroglucinol, ethylene glycol and glycerol as carbon sources, respectively, C-doped TiO₂ nanoparticles are prepared via hydrothermal method. Here glucose is first used to determine the optimal C-doping amount and reaction environment. The experimental results reveal that adding small amount of carbon in TiO₂ can change the phase structure of the TiO₂, the self-characteristic of carbon source influences the ratio of anatase to brookite in the mixed phase structures, and the carbon source with no benzene ring can lead to a high content of brookite phase. The mixed crystal phases show lower band gap energy and less photogenerated electronic-hole recombination. Furthermore, a high content of hydroxyls in carbon source and a high ratio of brookite phase in the mixed crystal phases are beneficial to the photocatalytic performance.     

Synergic effect of Type II ZnO/BiVO4 magnetic heterostructures for visible light-driven degradation of bisphenol A and methyl violet

Construction of an effective heterojunction for unimpeded flow of photogenerated charges and their prolonged separation is imperative for environmental photocatalysis. Herein, we have designed an efficient magnetic ZnO/BiVO₄ type-II heterostructure, which was employed for proficient degradation of persistent methyl violet dye with an efficiency of 97.6% in 90 min and a hazardous organic pollutant, namely, bisphenol A. UV-DRS and photoluminescence studies demonstrated that the fabricated nanocomposite exhibited effective light absorption and prolonged charge separation, thereby resulting in high photocatalytic efficacy under visible light irradiation. The efficacy of developed magnetic ZnO/BiVO₄ was also compared with pristine BiVO₄ and undoped magnetic ZnO, which indicated that the constructed heterostructure displayed approximately threefold and sixfold activity in contrast with bare BiVO₄ and undoped magnetic ZnO nanoparticles, respectively. Radical trapping studies, ESR analysis along with GC-MS analysis were conducted to elucidate the mechanistic pathway during the photodegradation process. This work provides a rational technical approach and research ideas for photocatalytic degradation of harmful organic pollutants in an environment-friendly manner by employing energy-efficient LEDs. Besides, good recyclability of catalyst makes it a promising candidate for large-scale applications.     

废生物质衍生碳修饰多孔石墨氮化碳异质结用于海水中氧四环素的高效光降解

以香蕉皮(BP)和尿素为原料,采用单步热处理工艺合成了一种无金属光催化剂。生物质衍生碳(BC)与多孔石墨相氮化碳(pg-C₃N₄)间的紧密界面效应显著增加了复合材料(pg-C₃N₄/BC)的比表面积,扩大了光响应范围,并提升了光诱导电子的迁移速率及光催化剂的稳定性。在可见光照射70 min后,pg-C₃N₄/BC降解人工海水中氧四环素(OTC)的反应速率常数为pg-C₃N₄的9.4倍。另外,由于光生电荷分离和转移的促进作用,pg-C₃N₄/BC在连续流反应过程中对OTC也具有更优异的光催化降解效果。此外,提出了一种潜在的光催化机制,以解释pg-C₃N₄/BC复合材料性能增强的原因。     

Dual MOF-Derived MoS2/CdS Photocatalysts with Rich Sulfur Vacancies for Efficient Hydrogen Evolution Reaction

Cocatalyst plays an important role in efficient charge transfer and separation for photocatalysis. Herein, a MoS₂/CdS photocatalyst with MoS₂ as cocatalyst was designed by using Mo-MOF and Cd-MOF as precursors. Due to the existence of rich sulfur vacancies and 1T phase, MoS₂ shows strong charge capture and transport ability. The photo-generated electrons on conduction band (CB) can be bound by the sulfur vacancy of CdS and effectively transported to MoS₂ through the compact interface between the CdS nanoparticles and 2D large-scale MoS₂. The optimal photocatalyst 1 %MoS₂/CdS exhibited dramatically improved photocatalytic hydrogen production activity, which is 28 times that of pristine CdS and even about 2 times that of 1 %Pt/CdS with same loading amount of noble metal Pt. This work highlights the role of Mo-MOF derived MoS₂ with 1T-2H phases as a sustainable and prospective candidate of cocatalyst for improving charge separation and photocatalytic stability of MoS₂/CdS composites.     

CeTiO4/g-C3N4复合材料的制备及其高效的光催化染料降解性能

采用简单固相法成功制备了CeTiO₄/g?C₃N₄?x(CTO/CN?x,x g为g?C₃N₄的添加量)复合材料,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、N₂吸附-脱附测试、紫外可见吸收光谱(UV?Vis)及电化学测试对材料进行表征。研究发现:CeTiO₄与g?C₃N₄层状纳米片紧密复合,并成功构建了界面异质结结构;形成CTO/CN?x复合相的光催化材料具有良好的可见光光响应性能,且光生空穴-电子对的分离和迁移率明显提高;通过太阳光模拟不同样品光催化降解有机污染物罗丹明B,降解140 min后复合材料CTO/CN?6表现出最高的光催化活性,反应速率常数为0.0202 min^-1。其活性增强的主要原因是异质结结构的构筑降低了CTO光生载流子的复合几率,提高了光生载流子的迁移速率。     

废生物质衍生碳修饰多孔石墨氮化碳异质结用于海水中氧四环素的高效光降解

以香蕉皮(BP)和尿素为原料,采用单步热处理工艺合成了一种无金属光催化剂。生物质衍生碳(BC)与多孔石墨相氮化碳(pg-C₃N₄)间的紧密界面效应显著增加了复合材料(pg-C₃N₄/BC)的比表面积,扩大了光响应范围,并提升了光诱导电子的迁移速率及光催化剂的稳定性。在可见光照射70 min后,pg-C₃N₄/BC降解人工海水中氧四环素(OTC)的反应速率常数为pg-C₃N₄的9.4 倍。另外,由于光生电荷分离和转移的促进作用,pg-C₃N₄/BC 在连续流反应过程中对 OTC 也具有更优异的光催化降解效果。此外,提出了一种潜在的光催化机制,以解释pg-C₃N₄/BC复合材料性能增强的原因。     

Band Structure Engineering of Single Pt Atoms on Fe−TiO2 for Enhanced Photocatalytic Performance

Single atomic site catalysts display the maximal atom-utilization efficiency, unique structural properties, and remarkable enhancements on catalytic activity. Herein, single Pt atoms loaded Fe−TiO₂ catalysts were prepared. Fe³⁺ doping leads to the formation of oxygen vacancies and improve the interaction between TiO₂ and Pt. Single Pt atoms are thus anchored and effectively modify the local energy band structure of TiO₂. The optimized local band structures improve the intrinsic photoexcitation of Pt/Fe−TiO₂, promote the separation of photogenerated carriers, and extend the lifetime of photogenerated carriers. Meanwhile, the electrons transfer from the excited dyes to the conduction band edge of Pt/Fe−TiO₂ is also facilitated due to the shift-down of the conduction band edge. Therefore, with the increase of the Pt content (till up to 0.6 wt%), the photocatalytic performance of Pt/ Fe−TiO₂ with the confined single Pt atoms is significantly boosted in either the intrinsic or the sensitized photocatalytic process.     

Heterojunction architecture of Nb2O5/g-C3N4 for enhancing photocatalytic activity to degrade organic pollutants and deactivate bacteria in water

Water pollution has become a serious problem owing to the development of society. Photocatalysis is a promising approach to remove various pollutants in water, such as organic pollutants and antibiotic resistance bacteria. Meanwhile, the design of heterojunction between two semiconductors is an effective path to improve photocatalytic properties due to its potential in improving separation and transfer of photoinduced carriers. In this study, Nb₂O₅/g-C₃N₄ (NO/CN) composite materials were prepared through a one-step heating method. Characterizations confirmed successful preparation of NO/CN heterojunction structure and better optical properties than pure g-C₃N₄ and Nb₂O₅. NO/CN composite materials showed excellent photocatalytic efficiency for Escherichia coli (E. coli) inactivation (95%) compared with the pure Nb₂O₅ (10%) and g-C₃N₄ (77%). Meanwhile, NO/CN exhibited better organic pollutants removal (RhB for 94%, methyl orange (MO) for 15% and methylene blue (MB) for 87%) under visible light, which is likely owing to the heterojunction structure between g-C₃N₄ and Nb₂O₅ that leads to the good separation of photogenerated electron-hole pair. Free radical scavenging and electron spin resonance (ESR) experiments demonstrated that superoxide radicals (^?O₂^?) and holes (h⁺) were the dominant radicals. Therefore, the NO/CN was proposed to be a promising material for effective disinfection and removal of organic contaminants in water treatment.