A two-dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir-Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine-linked chemical structure of the obtained monolayer was characterized by tip-enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure-property relationships.

Nanoscale defects in monolayers (MLs) of two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDCs), and 2D polymers (2DPs), can alter their physical, mechanical, optoelectronic, and chemical properties. However, detailed information about nano-defects within 2D covalent monolayers is difficult to obtain because it requires highly selective and sensitive techniques that can provide chemical information at the nanoscale. Here, we report a 2D imine-linked ML prepared from two custom-designed building blocks by dynamic imine chemistry at the air/water interface, in which an acetylenic moiety in one of the blocks was used as a spectroscopic reporter for nano-defects. Combined with density functional theory (DFT) calculations that take into account surface selection rules, tip-enhanced Raman spectroscopy (TERS) imaging provides information of the chemical bonds, molecular orientation, as well as nano-defects in the resulting ML. Additionally, TERS imaging visualizes the topography and integrity of the ML at Au(111) terrace edges, suggesting possible ductility of the ML. Furthermore, edge-induced molecular tilting and a stronger signal enhancement were observed at the terrace edges, from which a spatial resolution around 8 nm could be deduced. The present work can be used to study covalent 2D materials at the nanoscale, which are expected to be of use when engineering their properties for specific device applications.

A two‐dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir–Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine‐linked chemical structure of the obtained monolayer was characterized by tip‐enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure–property relationships.

The behavior of compound 2 [1,3,5-tri(2,2'-bipyridin-5-yl)benzene] with three bipyridine units arranged in a star geometry is investigated in the presence and absence of Ni(ClO). Its properties at the air-water interface as well as after transfer onto a solid substrate are studied by several techniques including Brewster angle microscopy, X-ray reflectivity, neutron reflectivity, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and atomic force microscopy combined with optical microscopy. It is found that compound 2 within the monolayers formed stays almost vertical at the interface and that at high Ni/2 (Ni/2 = 4000, 20'000) ratios two of the three bipyridine units of 2 are complexed, resulting in supramolecular sheets that are likely composed of arrays of linear metal-organic complexation polymers.

A supercritical CO 2 extraction behavior of Eucalyptus oil was investigated under different conditions of pressure, temperature and time with or without cosolvent. The pressure range was from 8 to 25 MPa, temperature from 35 to 55˚C and CO 2 flow rate from 10 to 26 g/min. For 1,8-cineole the appropriate extracting pressure was 15 MPa and temperature was 45˚C. When CO 2 flow rate was 18 g/min, it was benefit to extract the other three substances (limonene, p-cymene and γ-terpinene, respectively) except 1,8-cineole. Prolonging extraction time could not obviously increase the extract concentration, but the extract yield would increase. The results also indicated that ethanol as a modifier could improve extraction velocity and extraction concentration.