Herein we report the synthesis of a crystalline graphitic carbon nitride, or g‐C3N4, obtained from the temperature‐induced condensation of dicyandiamide (NH2C(NH)NHCN) by using a salt melt of ...lithium chloride and potassium chloride as the solvent. The proposed crystal structure of this g‐C3N4 species is based on sheets of hexagonally arranged s‐heptazine (C6N7) units that are held together by covalent bonds between C and N atoms which are stacked in a graphitic, staggered fashion, as corroborated by powder X‐ray diffractometry and high‐resolution transmission electron microscopy.
Melting into shape: Crystalline graphitic carbon nitride (see graphic for structure) has been prepared by temperature‐induced condensation in a salt melt of lithium chloride and potassium chloride. The structure was studied by powder X‐ray diffraction and high‐resolution transmission electron spectroscopy.
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Triazine‐based graphitic carbon nitride (TGCN) is the most recent addition to the family of graphene‐type, two‐dimensional, and metal‐free materials. Although hailed as a promising low‐band‐gap ...semiconductor for electronic applications, so far, only its structure and optical properties have been known. Here, we combine direction‐dependent electrical measurements and time‐resolved optical spectroscopy to determine the macroscopic conductivity and microscopic charge‐carrier mobilities in this layered material “beyond graphene”. Electrical conductivity along the basal plane of TGCN is 65 times lower than through the stacked layers, as opposed to graphite. Furthermore, we develop a model for this charge‐transport behavior based on observed carrier dynamics and random‐walk simulations. Our combined methods provide a path towards intrinsic charge transport in a direction‐dependent layered semiconductor for applications in field‐effect transistors (FETs) and sensors.
Beyond graphene, between layers: Triazine‐based carbon nitride, a new member of the graphene family of metal‐free 2D materials, grows as macroscopic thin films on a glass substrate. In this organic narrow‐band‐gap semiconductor, the electrical conductance is favored in out‐of‐plane direction, in contrast to other 2D materials. The hopping mechanism in between layers is supported by transient‐absorption spectroscopy and numerical calculations.
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Metal‐organic frameworks (MOFs) with encapsulated nanoparticles (NPs) enjoy a vastly expanded application potential in catalysis, filtration, and sensing. The selection of particular modified ...core‐NPs has yielded partial successes in overcoming lattice mismatch. However, restrictions on the choice of NPs not only limit the diversity, but also affect the properties of the hybrid materials. Here, we show a versatile synthesis strategy using a representative set of seven MOF‐shells and six NP‐cores that are fine‐tuned to incorporate from single to hundreds of cores in mono‐, bi‐, tri‐ and quaternary composites. This method does not require the presence of any specific surface structures or functionalities on the pre‐formed cores. Our key point is to regulate the diffusion rate of alkaline vapors that deprotonate organic linkers and trigger the controlled MOF‐growth and encapsulation of NPs. This strategy is expected to pave the way for the exploration of more sophisticated MOF‐nanohybrids.
Here, we show a versatile, general synthesis strategy using a representative set of seven MOF‐shells (ZIF‐zni, ZIF‐8, ZIF‐67, FJU‐30, MIL‐88(Fe), HKUST‐1, and MOF‐74(Co)) and six cores (Ag, Au, NaYF4, β‐FeOOH, Fe2O3 and Ni3Fe(CN)62) that are fine‐tuned such that from single to hundreds of cores are incorporated in mono‐, bi‐, tri‐ and quaternary composites.
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In the past decade, research in the field of artificial photosynthesis has shifted from simple, inorganic semiconductors to more abundant, polymeric materials. For example, polymeric carbon nitrides ...have emerged as promising materials for metal-free semiconductors and metal-free photocatalysts. Polymeric carbon nitride (melon) and related carbon nitride materials are desirable alternatives to industrially used catalysts because they are easily synthesized from abundant and inexpensive starting materials. Furthermore, these materials are chemically benign because they do not contain heavy metal ions, thereby facilitating handling and disposal. In this Review, we discuss the building blocks of carbon nitride materials and examine how strategies in synthesis, templating and post-processing translate from the molecular level to macroscopic properties, such as optical and electronic bandgap. Applications of carbon nitride materials in bulk heterojunctions, laser-patterned memory devices and energy storage devices indicate that photocatalytic overall water splitting on an industrial scale may be realized in the near future and reveal a new avenue of ‘post-silicon electronics’.Carbon nitrides are potentially cheap and metal-free alternatives for catalysts, semiconductors, battery materials and memory devices. In this Review, we discuss the synthesis, design and morphology of these materials, and reflect on the ability of methods such as templating, etching, dye sensitization, heteroatom doping and co-polymerization, as well as the assembly of various heterojunctions, to improve device performance.
Fully-aromatic, two-dimensional covalent organic frameworks (2D COFs) are hailed as candidates for electronic and optical devices, yet to-date few applications emerged that make genuine use of their ...rational, predictive design principles and permanent pore structure. Here, we present a 2D COF made up of chemoresistant β-amino enone bridges and Lewis-basic triazine moieties that exhibits a dramatic real-time response in the visible spectrum and an increase in bulk conductivity by two orders of magnitude to a chemical trigger - corrosive HCl vapours. The optical and electronic response is fully reversible using a chemical switch (NH
vapours) or physical triggers (temperature or vacuum). These findings demonstrate a useful application of fully-aromatic 2D COFs as real-time responsive chemosensors and switches.
To this day, the active components of integrated circuits consist mostly of (semi-)metals. Concerns for raw material supply and pricing aside, the overreliance on (semi-)metals in electronics limits ...our abilities (i) to tune the properties and composition of the active components, (ii) to freely process their physical dimensions, and (iii) to expand their deployment to applications that require optical transparency, mechanical flexibility, and permeability. 2D organic semiconductors match these criteria more closely. In this review, we discuss a number of 2D organic materials that can facilitate charge transport across and in-between their π-conjugated layers as well as the challenges that arise from modulation and processing of organic polymer semiconductors in electronic devices such as organic field-effect transistors.
Metal-free 2D covalent organic materials transport charges along and in-between π-conjugated layers. Here, we look at the prospects of graphitic carbon nitrides and covalent organic frameworks as 2D semiconductors "beyond graphene and silicon".
Water splitting using polymer photocatalysts is a key technology to a truly sustainable hydrogen‐based energy economy. Synthetic chemists have intuitively tried to enhance photocatalytic activity by ...tuning the length of π‐conjugated domains of their semiconducting polymers, but the increasing flexibility and hydrophobicity of ever‐larger organic building blocks leads to adverse effects such as structural collapse and inaccessible catalytic sites. To reach the ideal optical band gap of about 2.3 eV, A library of eight sulfur and nitrogen containing porous polymers (SNPs) with similar geometries but with optical band gaps ranging from 2.07 to 2.60 eV was synthesized using Stille coupling. These polymers combine π‐conjugated electron‐withdrawing triazine (C3N3) and electron donating, sulfur‐containing moieties as covalently bonded donor–acceptor frameworks with permanent porosity. The remarkable optical properties of SNPs enable fluorescence on‐off sensing of volatile organic compounds and illustrate intrinsic charge‐transfer effects.
Just right! A library of eight highly modular, photoactive S‐ and N‐containing porous polymers (SNPs) enabled exploration of the ideal conditions for photocatalytic water splitting. Intrinsic push–pull effects lead to enhanced separation of photo‐induced charge‐carriers and to exquisite control of the band gap, yielding materials with the highest hitherto reported hydrogen evolution rate.
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A layered, covalent, triazine‐based framework (CTF) was synthesized via the condensation of 2,6‐naphthalenedicarbonitrile under ionothermal conditions. The polytrimerization of this bi functional ...carbon nitrile in zinc chloride at lower temperatures yields a well‐ordered, close‐packed framework. At elevated temperatures an amorphous, yet porous solid is obtained, which shows remarkable thermal stability (640 °C) and a high surface area (2255 m2 g−1 and 1.51 cm3 g−1).
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Graphitic carbon nitride has been predicted to be structurally analogous to carbon‐only graphite, yet with an inherent bandgap. We have grown, for the first time, macroscopically large crystalline ...thin films of triazine‐based, graphitic carbon nitride (TGCN) using an ionothermal, interfacial reaction starting with the abundant monomer dicyandiamide. The films consist of stacked, two‐dimensional (2D) crystals between a few and several hundreds of atomic layers in thickness. Scanning force and transmission electron microscopy show long‐range, in‐plane order, while optical spectroscopy, X‐ray photoelectron spectroscopy, and density functional theory calculations corroborate a direct bandgap between 1.6 and 2.0 eV. Thus TGCN is of interest for electronic devices, such as field‐effect transistors and light‐emitting diodes.
Only five non‐metallic materials of the graphene family were known up to date: graphene, hBN, BCN, fluorographene, and graphene oxide. For the first time, crystalline thin films of triazine‐based graphitic carbon nitride (TGCN) are now presented. TGCN is structurally similar to graphite but it is a semiconductor. The thin films are a few to several hundreds of atomic layers thick and display a direct bandgap between 1.6 and 2.0 eV.
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