The Salen unit represents one of the most important ligands in coordination chemistry. We report herein the first example of a Salen-based covalent organic framework (COF), in which both the construction of the COF structure and the functionalization with Salen moieties have been realized in a single step. Due to its structural uniqueness, the obtained COF material, Salen-COF, possesses high crystallinity and excellent stability. Based on this, a series of metallo-Salen-based COFs were prepared via metalation for further applications.
A guest-induced reversible crystal-structure transformation is identified in a new 3D covalent organic framework (COF) by comprehensive analyses using powder X-ray diffraction, organic vapor sorption isotherm, and Xe NMR spectroscopy. The revolving imine bond in interpenetrating 3D networks is uncovered as the key to the dynamic behavior, the potential applications of which are illustrated by gas separation and heterogeneous catalysis, thus paving the way to the design of stimuli-responsive and multifunctional COF materials.
To improve the understanding of dynamic impact in 1:9 crossing panel, which is suffering from rapid surface degradation, detailed modelling and experimental studies are performed. A three-dimensional explicit finite element (FE) model of a wheel rolling over a crossing rail, that has an adaptive mesh refinement procedure coupled with twodimensional geometrical contact analyses, is developed. It is demonstrated that this modelling strategy performs much better than the 'conventional' FE modelling approach. Also, the experimental validations show that the FE results agree reasonably well with the field measurements. Using the validated FE model, the tribological behaviour of contact surfaces is studied. The results indicate that the proposed modelling strategy is a promising tool for addressing the problems of wheel-crossing dynamic impact.
Verification of the explicit finite element (FE) model with realistic wheel-rail profiles against the CONTACT model, which has not been sufficiently discussed, is performed by comparing the resulting shear stress, slip-adhesion area, etc., obtained from the two models. The followup studies using the verified FE model on the influence of the varying operational patterns (such as different friction, traction, etc.) on the surface and subsurface tribological responses of wheel-rail interaction are accomplished through a series of simulations. It can be concluded that the results obtained from most of the explicit FE simulations agree reasonably well with the ones from CONTACT. Also, the increase of the friction and traction can bring the stress concentrations from the subsurface upwards to the surface.
Dichromate is a widespread contaminant in wastewater,
threatening
the health of humans and other organisms. Therefore, effective detection
and removal of dichromate from water is of great significance. Herein,
a tetraphenylethylene functionalized cationic organic network (CON-LDU2) was constructed via a facile quaternization reaction. CON-LDU2 was successfully integrated with both detection and
removal functionalities toward dichromate. On the one hand, benefiting
from the strong fluorescence, CON-LDU2 was employed as
a chemosensor, it could efficiently and selectively probe Cr2O7
2– in water with “turn-off”
fluorescent response. On the other hand, the cationic skeleton and
free anions inside framework make CON-LDU2 an excellent
adsorbent for Cr2O7
2–, it
could capture Cr2O7
2– from
water with rapid kinetics and high capacity. The kinetic constant
for adsorption of Cr2O7
2– can
reach up to 1.784 g mg–1 min–1, while the capacity is determined as 325 mg g–1. Furthermore, CON-LDU2 displayed good recyclability
and can be reused for at least 5 cycles. Therefore, CON-LDU2 can serve as an ideal candidate not only in detection but also in
removal of Cr2O7
2– in water
medium.
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