Highly Ordered Nitrogen‐Rich Mesoporous Carbon Nitrides and Their Superior Performance for Sensing and Photocatalytic Hydrogen Generation

Abstract

Mesoporous carbon nitrides (MCN) are fascinating materials with unique semiconducting and basic properties that are useful in many applications including photocatalysis and sensing. Most syntheses of MCN focus on creating theoretically predicted C 3 N 4 stoichiometry with ab and gap of 2.7 eV using an ano-hardt emplating approach with triazine-based precursors.However,the performance of the MCN in semiconducting applications is limited to the MCN framework with as mall band gap,whichwould be linked with the addition of more N in the CN framework, but this remains ahuge challenge.Here, we report ap recursor with high nitrogen content, 3-amino-1,2,4-triazole,t hat enables the formation of new and wellordered 3D MCN with C 3 N 5 stoichiometry (MCN-8), which has not been predicted so far,a nd al ow-band-gape nergy (2.2 eV). This novel class of material without addition of any dopants shows not only as uperior photocatalytic watersplitting performance with at otal of 801 mmol of H 2 under visible-light irradiation for 3h but also excellent sensing properties for toxic acids.Carbon nitrides (CN) are of particular importance because of their unique properties such as high bulk moduli, low density,high thermal conductivity,semiconductivity,biocompatibility,a nd tunability of band gaps.[1] These properties make them special and help to advance their performance in various applications including adsorption, gas storage,photocatalysis,e nergy storage,a nd sensing.[2-4] However,t he efficiency of these materials in the above applications is related to their crystal structure,p orosity,a nd most importantly the nitrogen content in the CN framework. The porosity in CN was first realized by Vinu et al. who used the hard templating approach for creating CN with ahigh specific surface area and remarkable pore structures. [5,6] These materials suffer from poor nitrogen content due to al ow thermodynamic stability of Ni nt he carbon framework at ahigh temperature,which limits their performance in various applications.T his triggers various research groups to develop different preparation routes for porous CN by annealing the precursors with high nitrogen content at ahigh temperature. Forexample,non-porous graphitic C 3 N 4 has been prepared by using different Nrich precursors such as cyanamide,thiourea, ammonium thiocyanate,m elamine,u rea, and cyanuric chloride.[4] On the other hand, mesoporous carbon nitrides (MCN) can be prepared by anano-hard templating approach using nitrogen-containing precursors such as triazine or cyanamide or guanidine. [7][8][9][10] Then itrogen content of these materials are limited to the C/N ratio higher than 0.75 (C 3 N 4 ), which generally provides CN walls with triazine network. [11,12] In contrast to MCN with the stoichiometry of C 3 N 4 ,MCN with C 3 N 5 framework has not been synthesized as it is challenging and requires modification of the CN framework structure in order to introduce more nitrogen into the triazine network. MCN with C 3 N 5 and well-ordered porous structure could sign...

Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction Reaction

“…The X‐ray diffraction analysis (XRD) was carried out to examine ordered morphology and crystal structure of the synthesized C 3 N 7 and C 3 N 6 . The XRD patterns in low angle region show an intense peak at 0.99° and 0.98° for the C 3 N 7 and C 3 N 6 , respectively, which is corresponding to (211) reflection of geometry of KIT‐6 template, confirming formation of carbon nitrides with 3D‐connected porous structure ( Figure a) . Both samples exhibit a layered structure like g‐C 3 N 4 , showing (002) reflection at 2θ = 27.2° in the wide angle‐XRD patterns as represented in Figure b.…”

“…Because of its semiconducting property and diverse functionalities, the g‐C 3 N 4 attracts intense research interest for water splitting, redox catalysis, sensing and gas adsorption . Besides the g‐C 3 N 4 , nonstoichiometric and N‐rich carbon nitrides such as C 3 N 5 and C 3 N 6 have been explored by many researchers . Our group was successful in preparing mesoporous s‐heptazine‐based C 3 N 5 with terminal groups of triazole using a precursor of 3‐amino‐1,2,4‐triazole which showed excellent photocatalytic and sensing properties .…”

“…Besides the g‐C 3 N 4 , nonstoichiometric and N‐rich carbon nitrides such as C 3 N 5 and C 3 N 6 have been explored by many researchers . Our group was successful in preparing mesoporous s‐heptazine‐based C 3 N 5 with terminal groups of triazole using a precursor of 3‐amino‐1,2,4‐triazole which showed excellent photocatalytic and sensing properties . Very recently, Kumar et al used azide precursor of 2,5,8‐trihydrazino‐s‐heptazine to demonstrate azo‐linked but nonporous C 3 N 5 composed of s‐heptazine core structure .…”

“…By varying the nature of the carbon nitride precursors, new family of carbon nitride with a high nitrogen content and unique chemical structure could be prepared. However, it is challenging to increase N/C atomic ratio over 2 in carbon nitrides since many parts of CN frameworks in the carbon nitride should be replaced with thermodynamically less stable NN frameworks as the nitrogen content increases . Formation of pentagonal CNN framework such as the triazole could be one of ways to stabilize NN bond in the carbon nitride with the N/C ratio over 2.…”

Nonsiliceous Mesoporous Materials: Design and Applications in Energy Conversion and Storage

“…N‐doped carbon can be obtained through the polymerization of different aromatic and/or aliphatic carbons and high nitrogen‐containing molecular precursors via hard‐ and/or soft‐templating approaches. Mane developed a precursor with high nitrogen content, 3‐amino‐1,2,4‐triazole, that enabled the formation of new and well‐ordered 3D mesoporous graphite‐like C 3 N 4 with C 3 N 5 stoichiometry (MCN‐8), presenting a low bandgap energy of 2.2 eV . Highly nitrogen‐doped mesoporous carbon spheres can be prepared with large mesopores (≈16 nm) and small particle sizes (≈200 nm), which contribute to the mass transport by reducing and smoothing the diffusion pathways, leading to high electrocatalytic activity .…”