Influence of Thermal and Photochemical Treatments on Structure and Optical Properties of Single‐Layer Carbon Nitride

Abstract

The temperature of the synthesis of bulk graphitic carbon nitride (GCN) by the polycondensation of melamine, T p , is found to affect the structure and spectral properties of colloidal single layer carbon nitride (SLCN) nanosheets produced from the bulk GCN via the liquid-phase exfoliation. As T p is elevated the SLCN sheets get decorated with hydroxyl groups and become smaller due to a higher degree of destruction of the original bulk GCN. Both the size decrease and the presence of OH groups in the SLCN contribute to an increase in the photoluminescence (PL) quantum yield growing up to 56% for T p ¼ 700 C. The illumination of colloidal SLCN in air-saturated aqueous solutions results in the oxidation of nanosheets with a partial conversion of amino groups into C─OH groups in reactions with oxygen. The oxidation also results in the fragmentation of SLCN particles into smaller moieties and PL quenching. Oppositely, the illumination in argon-saturated solutions results in the reduction of SLCN sheets with the formation of C─C bonds between the components of adducts of SLCN with the products of a partial polyheptazine hydrolysis as well as between separate SLCN particles accompanied by the elimination of amino and hydroxyl groups.

Self-assembly of colloidal single-layer carbon nitride

“…By combining both self-assembly effects we can potentially design new ordered coatings showing a long-range geometrical regularity and a broad tunability of the chemical properties of layered "walls" forming the hexagonal patterns. The colloidal SLCN species stabilized by NEt 4 OH reveal highly intense broad-band photoluminescence, 28 photochemical activity, 63 and the capability of charge transfer when combined with semiconductor 27,64 and metal 27,65 nanocrystals. These functional properties are expected to be preserved in the final intercalates and 2D self-assemblies making such materials promising for light-conversion applications.…”

Tuning the surface plasmon resonance in gold nanocrystals with single layer carbon nitride

“…We showed earlier that colloidal SLCN nanosheets contain primary and secondary amino-groups arising from both the incomplete character of the melamine polycondensation and from the hydrolysis of GCN particles during the exfoliation procedure. 35,36 We reported that the amino-groups of SLCN can bind to ZnO NCs restricting their growth and resulting in a sizeselected series of ZnO/SLCN NCs. 37 In a similar way, the aminogroups of SLCN are expected to bind to the surface of Au NCs restricting their growth in the in situ version of the synthesis or to form bridges between Au NCs in the ex situ version, resulting in the formation of Au NC aggregates.…”

“…The SLCN sheets are composed of conjugated heptazine heterocycles and reveal semiconducting properties with a bandgap of z2.7 eV. 35 The incomplete character of the melamine polycondensation at the stage of the synthesis of bulk GCN as well as a partial hydrolytic decomposition of polyheptazine sheets during the exfoliation procedure result in the fact that the colloidal SLCN particles are decorated with amino-groups 35,36 that can bind to ZnO NCs controlling their growth dynamics and nal NC size. 37 A photoluminescence study of ZnO/SLCN composites showed the unique size-dependent character of the electronic interactions occurring in such a tandem 37 and indicated the feasibility of using SLCN as a functional ligand affecting not only the size of inorganic NCs but also their electronic properties.…”

Exploring Highly Efficient Broadband Self‐Trapped‐Exciton Luminophors: from 0D to 3D Materials

“…[16,64] These studies were focused mainly on GCN samples produced by the polycondensation of melamine and tetraethylammonium hydroxide (TEAH, NEt 4 OH) as an exfoliating agent, which yielded stable and luminescent aqueous colloidal solutions of SLCN and allowed the spectral and photophysical properties of SLCN to be characterized with relation to the properties of the original bulk GCN. [16,[64][65][66] We have also revealed phenomena of selfassembly of NEt 4 OH-stabilized SLCN sheets when the colloidal SLCN solutions were subjected to solvent evaporation. These effects can be used to form new functional nanomaterials with a tailored spatial organization and functional properties (photochemical activity, charge transport properties, PL emission, etc.).…”

“…[16,64,67] These properties, in turn, can be influenced by the conditions of melamine polycondensation, in particular, by the polycondensation temperature T pc and, to some extent, by the polycondensation duration t pc at T pc = const. [16,[64][65][66]…”