Covalent triazine
frameworks are an emerging material class that
have shown promising performance for a range of applications. In this
work, we report on a metal-assisted and solvent-mediated reaction
between calcium carbide and cyanuric chloride, as cheap and commercially
available precursors, to synthesize two-dimensional triazine structures
(2DTSs). The reaction between the solvent, dimethylformamide, and
cyanuric chloride was promoted by calcium carbide and resulted in
dimethylamino-s-triazine intermediates, which in
turn undergo nucleophilic substitutions. This reaction was directed
into two dimensions by calcium ions derived from calcium carbide and
induced the formation of 2DTSs. The role of calcium ions to direct
the two-dimensionality of the final structure was simulated using
DFT and further proven by synthesizing molecular intermediates. The
water content of the reaction medium was found to be a crucial factor
that affected the structure of the products dramatically. While 2DTSs
were obtained under anhydrous conditions, a mixture of graphitic material/2DTSs
or only graphitic material (GM) was obtained in aqueous solutions.
Due to the straightforward and gram-scale synthesis of 2DTSs, as well
as their photothermal and photodynamic properties, they are promising
materials for a wide range of future applications, including bacteria
and virus incapacitation.
In this contribution, we aim at supporting theoretical transistor material design using a combination of electronic structure theory, transport simulations, and local current analysis. Our effort focuses on defective zigzag graphene nanoribbons (ZGNRs) to design molecular junctions with an atomically precisely controlled degree of defect dilution. Electronic structure calculations within a periodic density functional theory (DFT) framework yield information about the band structures. These serve as a guide for constructing a transport model of the nanojunctions composed of a defective ZGNR scattering region connected to pristine ZGNR leads. Performing nonequilibrium Green's function simulations on selected systems of interest, their transport properties in the quasi-stationary limit are revealed. Following a recent procedure, associated current densities are mapped on a real-space representation. The presence of defects leads to concentrated current flow in the middle region, which is close to the defect edges. The degree of defect dilution as well as the width of the nanojunction have strong influences on the local current densities.
Lignin represents the most abundant and sustainable aromatic
resource
to produce value-added aromatics. However, an efficient and selective
cleavage of recalcitrant C–C bonds in lignin under mild conditions
remains challenging. Photocatalysis has emerged as a promising strategy
for such a C–C bond cleavage under ambient conditions, although
the activity and selectivity need to be further improved. Herein,
using polyimide as a photocatalyst, we report an efficient and selective
C–C bond cleavage in a β-O-4 lignin model under visible
light at room temperature. The lignin model was converted into aromatic
products with >99% substrate conversion and >99% C–C
bond cleavage
selectivity, which are superior to previously reported photocatalytic
systems. Experimental investigations together with theoretical calculations
indicated that the superior performance of the polyimide photocatalyst
was attributed to its strong photooxidation capability and efficient
charge carrier separation efficiency. Mechanistic studies revealed
that the dehydrogenation of the lignin model driven by photogenerated
holes was the rate-determining step. This work provides useful guidance
for the design of high-performance photocatalysts for selective C–C
bond cleavage of lignin.
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