Facile fabrication of g‐C3N4/MIL‐53(Al) composite with enhanced photocatalytic activities under visible‐light irradiation

A novel visible‐light‐driven g‐C₃N₄/MIL‐53(Al) composite photocatalyst was successfully prepared using a facile stirring method at room temperature. The g‐C₃N₄/MIL‐53(Al) composites were characterized and their effects on the photocatalytic activities for rhodamine B degradation were investigated. The g‐C₃N₄(20 wt%)/MIL‐53(Al) photocatalyst displayed optimal photocatalytic degradation efficiency, which was about five times higher than the photocatalytic activity of pure g‐C₃N₄. The improved photocatalytic performance of the g‐C₃N₄/MIL‐53(Al) photocatalyst was predominantly attributed to the efficient separation of electron–hole pairs and the low charge‐transfer resistance. g‐C₃N₄/MIL‐53(Al) also exhibited excellent stability and reusability. A proposed mechanism for the enhanced photocatalytic activity is also discussed based on the experimental results. Copyright © 2015 John Wiley & Sons, Ltd.     

Precise regulation of Ultra-thin platinum decorated Gold/Graphite carbon nitride photocatalysts by atomic layer deposition for efficient degradation of Rhodamine B under simulated sunlight

Atomic Layer Deposition (ALD) precise controlling ultra-thin platinum (Pt) modified Graphite carbon nitride (g-C₃N₄) photocatalysts, which had been doped with gold nanoparticles (Au NPs) by photodeposition, were successfully synthesized. The experimental results showed that precise regulation of platinum decorated C₃N₄-Au(C₃N₄-Au/nPt (n is the number of Pt ALD cycles, 1 Å per cycle)) exhibited excellent photocatalytic degradation ability for Rhodamine B (RhB). Under simulated sunlight irradiation, the degradation rate of 10 mg/L RhB(100 mL) by 1.5 mg C₃N₄-Au/10Pt catalysts was 95.8% within 60 min that is much better than other photocatalysts for the degradation of RhB. The efficient degradation mechanism of RhB by C₃N₄-Au/10Pt photocatalysts was studied and the experiments demonstrated the ·O₂^– as main active species played an important role in the photocatalytic process. Local surface plasmon resonance (LSPR) of Au NPs and Schottky barrier between Pt clusters and g-C₃N₄ may be the reasons for enhanced C₃N₄-Au/10Pt photocatalytic performances. Furthermore, the successive catalytic cycles revealed the excellent stability of C₃N₄-Au/10Pt photocatalyst.     

Facile one‐step synthesis of broken case‐like carbon‐doped g‐C3N4 for photocatalytic degradation of benzene

Herein, a novel broken case‐like carbon‐doped g‐C₃N₄ photocatalyst was obtained via a facile one‐pot pyrolysis and cost‐effective method using glyoxal‐modified melamine as a precursor. The obtained carbon/g‐C₃N₄ photocatalyst showed remarkable enhanced photocatalytic activity in the degradation of gaseous benzene compared with that of pristine g‐C₃N₄ under visible light. The pseudo‐first‐order rate constant for gaseous benzene degradation on carbon/g‐C₃N₄ was 0.186 hr^?1, 5.81 times as large as that of pristine g‐C₃N₄. Furthermore, a possible photocatalytic mechanism for the improved photocatalytic performance over carbon/g‐C₃N₄ nanocomposites was proposed.     

Covalent organic frameworks with imine proton acceptors for efficient photocatalytic H2 production

Covalent organic frameworks (COFs) are promising crystalline materials for the light-driven hydrogen evolution reaction (HER) due to their tunable chemical structures and energy band gaps. However, deeply understanding corresponding mechanism is still challenging due to the multiple components and complicated electron transfer and reduction paths involved in photocatalytic HER. Here, the photocatalytic HER investigation has been reported based on three COFs catalysts, 1–3, which are prepared by benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde to react with C₃ symmetric triamines including tris(4-aminophenyl)amine, 1,3,5-tris(4-aminophenyl)benzene, and (1,3,5-tris-(4-aminophenyl)triazine, respectively. As the isostructural hexagonal honeycomb-type COF of 2 and 3 reported previously, the crystal structure of 1 has been carefully correlated through the powder X-ray diffraction study with the help of theoretical simulations. 1 shows highly porous framework with Brunauer-Emmett-Teller surface area of 1249 m²/g. Moreover, the introduction of ascorbic acid into the photocatalytic system of COFs achieves the hydrogen evolution rate of 3.75, 12.16 and 20.2 mmol g^–1 h^–1 for 1–3, respectively. The important role of ascorbic acid in photocatalysis of HER is disclosed to protonate the imine linkages of these COFs, leading to the obvious absorbance red-shift and the improved charge separation efficiency together with reduced resistance in contrast to pristine materials according to the spectroscopic and electronic characterizations. These innovations of chemical and physical properties for these COFs are responsible for their excellent photocatalytic performance. These results elucidate that tiny modifications of COFs structures is able to greatly tune their band structures as well as catalytic properties, therefore providing an available approach for optimizing COFs functionalities.     

Microwave-Assisted Hydrothermal Preparation, Characterization and Photocatalytic Properties of a Chrysanthemum-Shaped ZnWO4 Photocatalyst

A novel chrysanthemum-shaped monocline ZnWO₄ photocatalyst was synthesized by microwave-assisted hydrothermal method with Na₂WO₄·2H₂O and Zn(NO₃)₂·6H₂O as raw materials at different reaction temperatures. The prepared ZnWO₄ photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy, Photoluminescence spectrum (PL) and UV–Vis absorption spectrum (UV–Vis). The photocatalytic property of the prepared chrysanthemum-shaped monocline ZnWO₄ photocatalyst was evaluated by the degradation of Rhodamine B (RhB) in aqueous solution. The effects of reaction temperature on the photocatalytic degradation efficiency of RhB were investigated. The results indicated that the chrysanthemum-shaped monocline ZnWO₄ photocatalyst is prepared by foliated powders with the sizes of about 30 nm and 500 nm respectively at 160 and 220 °C. The PL relative intensity of prepared ZnWO₄ photocatalyst is apparently intensifying with increasing temperature. The photocatalytic property decreases with the increasing recombination probability of the excited electrons and holes. The chrysanthemum-shaped monocline ZnWO₄ photocatalyst prepared at 160 °C possesses the best photocatalytic property, and the degradation efficiency of RhB at 180 min UV-light irradiation is achieved 75 %. The ZnWO₄ has good reusability property on degradation of RhB and the degradation rate is still higher than 65 % after three cycles.     

An Olefin‐Linked Covalent Organic Framework as a Flexible Thin‐Film Electrode for a High‐Performance Micro‐Supercapacitor

Developing effective synthetic strategies as well as enriching functionalities for sp²‐carbon‐linked covalent organic frameworks (COFs) still remains a challenge. Now, taking advantage of a variant of Knoevenagel condensation, a new fully conjugated COF ( g‐C₃₄N₆‐COF ) linked by unsubstituted C=C bonds was synthesized. Integrating 3,5‐dicyano‐2,4,6‐trimethylpyridine and 1,3,5‐triazine units into the molecular framework leads to the enhanced π‐electron communication and electrochemical activity. This COF shows uniform nanofibrous morphology. By assembling it with carbon nanotubes, a flexible thin‐film electrode for a micro‐supercapacitor (MSC) can be easily obtained. The resultant COF‐based MSC shows an areal capacitance of up to 15.2 mF cm^?2, a high energy density of up to 7.3 mWh cm^?3, and remarkable rate capability. These values are among the highest for state‐of‐the‐art MSCs. Moreover, this device exhibits excellent flexibility and integration capability.     

g-C3N4/CaTi2O5复合材料制备及其光催化性能

利用类石墨氮化碳（g-C₃N₄）和亚稳相钙钛氧化物（CaTi₂O₅）固相法制备C₃N₄/CaTi₂O₅复合材料。利用X射线衍射（XRD）、金相显微镜、扫描电子显微镜（SEM）及附带能谱分析仪（EDS）和N₂吸附-脱附对样品的显微结构和比表面积进行检测分析,并用紫外-可见吸收光度计（UV-Vis）测试了样品的光吸收性能,研究C₃N₄与CaTi₂O₅物质的量之比（n_C3N4/nCaTi₂O₅）对C₃N₄/CaTi₂O₅复合样品的物相结构和微观形貌的影响,同时考察C₃N₄/CaTi₂O₅复合样品在可见光照射下光催化降解罗丹明染料效果。实验结果表明：相比纯C₃N₄和CaTi₂O₅样品,C₃N₄/CaTi₂O₅复合样品在可见光下具有较高的光催化性能,随着n_C3N4/nCaTi₂O₅增加,样品的光催化降解率随之增加而后降低,当n_C3N4/nCaTi₂O₅=1：1时,样品的光催化降解率达到最大值99.5%,并且循环重复利用5次后,样品的光催化剂降解率仍几乎保持不变。复合样品光催化性能提高主要归因于复合能级结构有效地抑制了电子和空穴复合所致。     

g-C_3N_4/CaTi_2O_5复合材料制备及其光催化性能

利用类石墨氮化碳(g-C_3N_4)和亚稳相钙钛氧化物(CaTi_2O_5)固相法制备C_3N_4/CaTi_2O_5复合材料。利用X射线衍射(XRD)、金相显微镜、扫描电子显微镜(SEM)及附带能谱分析仪(EDS)和N2吸附-脱附对样品的显微结构和比表面积进行检测分析,并用紫外-可见吸收光度计(UV-Vis)测试了样品的光吸收性能,研究C_3N_4与CaTi_2O_5物质的量之比(nC_3N_4/nCaTi_2O_5)对C_3N_4/CaTi_2O_5复合样品的物相结构和微观形貌的影响,同时考察C_3N_4/CaTi_2O_5复合样品在可见光照射下光催化降解罗丹明染料效果。实验结果表明:相比纯C_3N_4和CaTi_2O_5样品,C_3N_4/CaTi_2O_5复合样品在可见光下具有较高的光催化性能,随着nC_3N_4/nCaTi_2O_5增加,样品的光催化降解率随之增加而后降低,当nC_3N_4/nCaTi_2O_5=1∶1时,样品的光催化降解率达到最大值99.5%,并且循环重复利用5次后,样品的光催化剂降解率仍几乎保持不变。复合样品光催化性能提高主要归因于复合能级结构有效地抑制了电子和空穴复合所致。     

Visible-light-driven Oxygen Vacancy and Carbon Doping of C@TiO2-x Photocatalyst for Enhanced Pollutants Degradation Performance

Oxygen Vacancy (OVs) and carbon doping of the photocatalyst body will significantly enhance the photocatalytic efficiency. However, synchronous regulation of these two aspects is challenging. In this paper, a novel C@TiO_2-x photocatalyst was designed by coupling the surface defect and doping engineering of titania, which can effectively remove rhodamine B (RhB) and has a relatively high performance with wide pH range, high photocatalytic activity and good stability. Within 90 minutes, the photocatalytic degradation rate of RhB by C@TiO_2-x (94.1 % at 20 mg/L) is 28 times higher than that of pure TiO₂. Free radical trapping experiments and electron spin resonance techniques reveal that superoxide radicals (⋅O²⁻) and photogenerated holes (h⁺) play key roles in the photocatalytic degradation of RhB. This study demonstrates the possibility of regulating photocatalysts to degrade pollutants in wastewater based on an integrated strategy.     

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.     

Vinylene‐Linked Covalent Organic Frameworks by Base‐Catalyzed Aldol Condensation

Two 2D covalent organic frameworks (COFs) linked by vinylene (?CH=CH?) groups (V‐COF‐1 and V‐COF‐2) are synthesized by exploiting the electron deficient nature of the aromatic s‐triazine unit of C₃‐symmetric 2,4,6‐trimethyl‐s‐triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensation with multitopic aryl aldehydes to be reticulated into extended crystalline frameworks (V‐COFs). Both V‐COF‐1 (with terepthalaldehyde (TA)) and V‐COF‐2 (with 1,3,5‐tris(p‐formylphenyl)benzene (TFPB)) are polycrystalline and exhibit permanent porosity and BET surface areas of 1341 m² g^?1 and 627 m² g^?1, respectively. Owing to the close proximity (3.52 Å) of the pre‐organized vinylene linkages within adjacent 2D layers stacked in eclipsed fashion, [2+2] photo‐cycloadditon in V‐COF‐1 formed covalent crosslinks between the COF layers.     

Enhancement in the photocatalytic activity of TiO2 nanofibers hybridized with g-C3N4 via electrospinning

TiO₂/g-C₃N₄ nanofibers with diameter of 100–200 nm were prepared by electrospinning method after calcination at high temperature, using polyvinylpyrrolidone (PVP), Melamine (C₃H₆N₆), Ti(OC₄H₉)₄ as raw materials. The composite nanofibers were characterized by XRD, FT-IR, SEM, UV–vis and PL respectively. The effects of different g-C₃N₄ contents on structure and photocatalytic degradation of the composite nanofibers were investigated. The results indicated that with increasing g-C₃N₄ content, the diameter of the composite fibers increased and the morphology changed from uniform structure to a nonuniform one, containing beads. The composite nanofibers displayed the best photocatalytic degradation on RhB, when the g-C₃N₄ content was 0.8 wt%. The degree of degradation was up to 99% at the optimal conditions of 40 min. The degradation activity of the composite nanofibers on RhB, MB and MO was found to be higher than that of the TiO₂ nanofibers.     

Construction of a 2D Graphene‐Like MoS2/C3N4 Heterojunction with Enhanced Visible‐Light Photocatalytic Activity and Photoelectrochemical Activity

A novel graphene‐like MoS₂/C₃N₄ (GL‐MoS₂/C₃N₄) composite photocatalyst has been synthesized by a facile ethylene glycol (EG)‐assisted solvothermal method. The structure and morphology of this GL‐MoS₂/C₃N₄ photocatalyst have been investigated by a wide range of characterization methods. The results showed that GL‐MoS₂ was uniformly distributed on the surface of GL‐C₃N₄ forming a heterostructure. The obtained composite exhibited strong absorbing ability in the ultraviolet (UV) and visible regions. When irradiated with visible light, the composite photocatalyst showed high activity superior to those of the respective individual components GL‐MoS₂ and GL‐C₃N₄ in the degradation of methyl orange. The enhanced photocatalytic activity of the composite may be attributed to the efficient separation of electron–hole pairs as a result of the matching band potentials between GL‐MoS₂ and GL‐C₃N₄. Furthermore, a photocatalytic mechanism for the composite material has been proposed, and the photocatalytic reaction kinetics has been measured. Moreover, GL‐MoS₂/C₃N₄ could serve as a novel sensor for trace amounts of Cu²⁺ since it exhibited good selectivity for Cu²⁺ detection in water.     

Synthesis of ZnTiO3/tourmaline/Ni foam catalyst and enhanced photocatalytic performance

ZnTiO₃/tourmaline loaded on the nickel foam (ZnTiO₃/tourmaline/Ni-foam) is prepared by a facile coating method. Morphology and structure of the photocatalyst were characterized by X-ray diffraction (XRD), scanning electrons microscopy (SEM), raman spectroscopy, UV–vis diffuse reflectance spectrum (UV–vis DRS) and photoluminescence spectroscopy (PL). The photocatalytic properties of the materials were tested by using the Rhodamine B (RhB) solution as the target pollutant. The results indicates that the ZnTiO₃/tourmaline/Ni foam exhibited higher photocatalytic activity than that of ZnTiO₃ and ZnTiO₃/Ni foam under ultraviolet (UV) light irradiation, and its degradation rate was up to 99.2%. Moreover, the degradation rate remained at 91.3% after eight consecutive photocatalytic reaction cycles. The outstanding photocatalytic performances of ZnTiO₃/tourmaline/Ni foam was mainly attributed to the existence of tourmaline, which can help to inhibit the recombination of electron-hole paris, and the proper pore structure of the carrier. Meanwhile, the trapping experiments indicated that ·O₂^– was the main active species in the photocatalytic degradation of RhB.     

Photocatalytic Activity Improvement of g-C3N4 under Visible Light by Optimizing Preparation Conditions

Graphite-like C₃N₄ (g-C₃N₄) is ané cient visible-light-driven photocatalyst which is com-monly used in pollutant degradation. The photoreactivity of g-C₃N₄ depends on the prepa-ration conditions to a large extent. In this work, we linked the preparation conditions of g-C₃N₄ to its stability and photocatalytic activity through dye photodegradation experi-ments and sensitivity mathematical analyses. The sensitivity mathematical analyses show that the effect of calcination temperature is more significant than calcination time on the photoreactivity of g-C₃N₄. The photocatalytic activity of optimized g-C₃N₄ in rhodamine B (RhB) degradation under visible light was 100 times higher than that of non-optimized one. The enhanced performance can be attributed to the increased specific surface area of g-C₃N₄ and the increased migration velocity of photogenerated electron-hole pairs on the surface. This work deepens the understanding of the relation between preparation conditions and the charateristics of g-C₃N₄, and provides an extremely simple method for significantly improving the photoreactivity of g-C₃N₄.     

Copper Phthalocyanine‐Functionalized Graphitic Carbon Nitride: A Hybrid Heterostructure toward Photoelectrochemical and Photocatalytic Degradation Applications

In this work, alcian blue 8GX (AB), a copper(II) phthalocyanine derivative, was employed to functionalize graphitic carbon nitride (g‐C₃N₄) for the preparation of a highly efficient photocatalyst. The approach relies on a facile AB‐assisted ethanol/water mixed‐solvent exfoliation of bulk g‐C₃N₄. The as‐prepared g‐C₃N₄/AB hybrid possesses significantly enhanced solution dispersibility and photoelectrochemical performance resulting from the synergistic effect between g‐C₃N₄ and AB, which involves the optimization of intimate interfacial contact, extension of light absorption range, and enhancement of charge‐transfer efficiency. This synergy contributes enormously to the photocatalytic degradation of rhodamine 6G (R6G) under light irradiation.     

Rational Design of MOF/COF Hybrid Materials for Photocatalytic H2 Evolution in the Presence of Sacrificial Electron Donors

Crystalline and porous covalent organic frameworks (COFs) and metal‐organic frameworks (MOFs) materials have attracted enormous attention in the field of photocatalytic H₂ evolution due to their long‐range order structures, large surface areas, outstanding visible light absorbance, and tunable band gaps. In this work, we successfully integrated two‐dimensional (2D) COF with stable MOF. By covalently anchoring NH₂‐UiO‐66 onto the surface of TpPa‐1‐COF, a new type of MOF/COF hybrid materials with high surface area, porous framework, and high crystallinity was synthesized. The resulting hierarchical porous hybrid materials show efficient photocatalytic H₂ evolution under visible light irradiation. Especially, NH₂‐UiO‐66/TpPa‐1‐COF (4:6) exhibits the maximum photocatalytic H₂ evolution rate of 23.41 mmol g^?1 h^?1 (with the TOF of 402.36 h^?1), which is approximately 20 times higher than that of the parent TpPa‐1‐COF and the best performance photocatalyst for H₂ evolution among various MOF‐ and COF‐based photocatalysts.     

Preparation of porous g‐C3N4/Ag/Cu2O: a new composite with enhanced visible‐light photocatalytic activity

From previous reports, graphitic carbon nitride (g‐C₃N₄) can be used as a photocatalyst, although the low efficiency of solar energy utilization, small specific surface area and high recombination rate of photogenerated electron–hole pairs limit its practical application. For the purpose of increasing photocatalytic activity, especially under irradiation of visible light, we successfully synthesized a new composite, namely porous g‐C₃N₄/Ag/Cu₂O, through chemical adsorption of Ag‐doped Cu₂O on porous g‐C₃N₄, which has not been investigated carefully worldwide. The composition, morphology and optical properties of the composite were investigated through methods including X‐ray diffraction, energy‐dispersive X‐ray, Fourier transform infrared, UV–visible and photoluminescence spectroscopies and transmission electron microscopy. Using rhodamine B as organic pollutant to be degraded under the irradiation of visible light, different mass ratios of Ag/Cu₂O doped on porous g‐C₃N₄ led to enhanced photocatalytic performance of the composite compared to pure porous g‐C₃N₄. When the mass ratio of Ag/Cu₂O is 15%, porous g‐C₃N₄/Ag/Cu₂O exhibits a degradation rate 2.015 times higher than that of pure porous g‐C₃N₄. The reasons for this phenomenon may be attributed to the increased utilization efficiency of visible light, high‐speed separation of photogenerated electron–hole pairs, accelerated interfacial transfer process of electrons and increased surface area of the composite. Copyright © 2016 John Wiley & Sons, Ltd.     

Potassium‐Ion‐Assisted Regeneration of Active Cyano Groups in Carbon Nitride Nanoribbons: Visible‐Light‐Driven Photocatalytic Nitrogen Reduction

As a metal‐free nitrogen reduction reaction (NRR) photocatalyst, g‐C₃N₄ is available from a scalable synthesis at low cost. Importantly, it can be readily functionalized to enhance photocatalytic activities. However, the use of g‐C₃N₄‐based photocatalysts for the NRR has been questioned because of the elusive mechanism and the involvement of N defects. This work reports the synthesis of a g‐C₃N₄ photocatalyst modified with cyano groups and intercalated K⁺ (mCNN), possessing extended visible‐light harvesting capacity and superior photocatalytic NRR activity (NH₃ yield: 3.42 mmol g^?1 h^?1). Experimental and theoretical studies suggest that the ‐C≡N in mCNN can be regenerated through a pathway analogous to Mars van Krevelen process with the aid of the intercalated K⁺. The results confirm that the regeneration of the cyano group not only enhances photocatalytic activity and sustains the catalytic cycle, but also stabilizes the photocatalyst.     

The Role of the Relative Dye/Photocatalyst Concentration in TiO2 Assisted Photodegradation Process

Despite photocatalytic degradation is studied generally focusing the catalyst, its interaction with the contaminant molecule plays a fundamental role in the efficiency of that process. Then, we proposed a comparative study about the photodegradation of two well‐known dyes, with different acidity/basicity – Methylene Blue (MB) and Rhodamine B (RhB), catalyzed by TiO₂ nanoparticles, varying both dye and photocatalyst concentrations. The results showed that the amphoteric character of MB molecules, even in a range of concentration of 5.0–10.0 mg L^?1, did not imply in pH variation in solution. Therefore, it did not affect the colloidal behavior of TiO₂ nanoparticles, independent of the relative dye/catalyst concentration. The acid–base character of RhB influenced the resultant pH of the solution, implicating in different colloidal behavior of the nanoparticles and consequently, in different degradation conditions according to dye concentration. As the isoelectric point of TiO₂ is between the pH range of the RhB solutions used in this study, from 1.0 to 7.5 mg L^?1, the resultant pH was the key factor for degradation conditions, from a well dispersed to an agglomerated suspension.