Pore partition in two-dimensional covalent organic frameworks.

Covalent organic frameworks (COFs) have emerged as a kind of crystalline polymeric materials with high compositional and geometric tunability. Most COFs are currently designed and synthesized as mesoporous (2-50 nm) and microporous (1-2 nm) materials, while the development of ultramicroporous (<1 nm) COFs remains a daunting challenge. Here, we develop a pore partition strategy into COF chemistry, which allows for the segmentation of a mesopore into multiple uniform ultramicroporous domains. The pore partition is implemented by inserting an additional rigid building block with suitable symmetries and dimensions into a prebuilt parent framework, leading to the partitioning of one mesopore into six ultramicropores. The resulting framework features a wedge-shaped pore with a diameter down to 6.5 Å, which constitutes the smallest pore among COFs. The wedgy and ultramicroporous one-dimensional channels enable the COF to be highly efficient for the separation of five hexane isomers based on the sieving effect. The obtained average research octane number (RON) values of those isomer blends reach up to 99, which is among the highest records for zeolites and other porous materials. Therefore, this strategy constitutes an important step in the pore functional exploitation of COFs to implement pre-designed compositions, components, and functions.

Synthesis and photovoltaic properties of ester group functionalized polythiophene derivatives.

To increase the open circuit voltage (V(OC)) of polymer solar cells (PSCs) based on polythiophene, two new ester group functionalized polythiophene derivatives, PCTDT and PCTBDT, were designed and synthesized via alternating copolymerization of thiophene-3-carboxylate (CT) with the 2,2'-bithiophene (DT) and benzodithiophene (BDT) units, respectively. The resulting copolymers exhibited broad and strong absorptions in the visible region, which was similar to that of the commonly used poly(3-hexylthiophene) (P3HT). Through cyclic voltammetry measurements, it was found that both copolymers showed lower HOMO energy levels (-5.27 eV for PCTDT and -5.36 eV for PCTBDT) than that of P3HT (-5.03 eV), indicating that the HOMO energy level could be efficiently reduced by introducing the ester group into the polymer side chain. Photovoltaic properties of the copolymers blended with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) as electron acceptor were investigated. The obtained two devices possessed both relatively large short circuit current (I(SC)) and higher V(OC) than that of P3HT:PCBM blend. For PCTBDT:PCBM blend, a power conversion efficiency (PCE) up to 2.32%, an I(SC) of 6.94 mA · cm(-2), and a V(OC) of 0.80 V were observed while PCTDT:PCBM system demonstrated a PCE of 1.75% with a V(OC) of 0.68 V.

Highly efficient ultraviolet photodetectors based on TiO(2) nanocrystal-polymer composites via wet processing.

Solution-processed inorganic/organic hybrid films based on anatase TiO(2) nanocrystals and poly (9,9-dihexylfluorene) (PFH) are fabricated via a simple spin-coating method and characterized by atomic force microscopy, UV-vis absorption and photoluminescence spectra. The photodetector devices are made from hybrid TiO(2)/PFH bulk heterojunction films sandwiched between poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) pre-coated ITO and Al electrodes. The device characteristics, including current-voltage (I-V) curves under UV illumination, spectral response, response time and bias dependence, are studied. The photovoltaic effect is observed and the photocurrent shows an increase with increasing TiO(2) content from 2.5 to 11 wt%. The high UV photo-to-dark current ratio of 10(3), fast response time less than 200 ms and a responsivity of 54.6 mA W( - 1) are obtained for the hybrid photodetector. The fast photoresponse is attributed to the enhanced interfacial dissociation of excitons. The overlap of the spectral response with the UV-A range (320-400 nm) and the low-cost wet fabrication method show their potential for environmental and biological uses.

Solvent-dependent fluorescence property of multi-walled carbon nanotubes noncovalently functionalized by pyrene-derivatized polymer.

Multi-walled carbon nanotubes (MWCNTs) were supramolecularly functionalized by pyrene-derivatized hydrolyzed poly(styrene-co-maleic anhydride) (pyrene-HSMA) in aqueous solution. The MWCNTs/pyrene-HSMA conjugates were found to exhibit a solvent-dependent fluorescence property by photoluminescence measurements. The fluorescence intensity of the MWCNTs/pyrene-HSMA conjugate was used as a probe to estimate the interaction between polymer and MWCNTs in solvents. The polymer conformation around the MWCNTs was demonstrated by atomic force microscopy. We suggested that pyrene-HSMA functionalized MWCNTs in a non-wrapping mode, and that the conformation change of the polymer around the MWCNTs resulted in the solvent-dependent fluorescence property. The dispersion state of the MWCNTs/pyrene-HSMA conjugate in various solvents was also investigated by transmission electron microscopy. The fluorescence responses of the MWCNTs/pyrene-HSMA conjugate to pH value and temperature were studied as well.

Antibacterial activity of two-dimensional MoS2 sheets.

Graphene-like two-dimensional materials (2DMats) show application potential in optoelectronics and biomedicine due to their unique properties. However, environmental and biological influences of these 2DMats remain to be unveiled. Here we reported the antibacterial activity of two-dimensional (2D) chemically exfoliated MoS2 (ce-MoS2) sheets. We found that the antibacterial activity of ce-MoS2 sheets was much more potent than that of the raw MoS2 powders used for the synthesis of ce-MoS2 sheets possibly due to the 2D planar structure (high specific surface area) and higher conductivity of the ce-MoS2. We investigated the antibacterial mechanisms of the ce-MoS2 sheets and proposed their antibacterial pathways. We found that the ce-MoS2 sheets could produce reactive oxygen species (ROS), different from a previous report on graphene-based materials. Particularly, the oxidation capacity of the ce-MoS2 sheets toward glutathione oxidation showed a time and concentration dependent trend, which is fully consistent with the antibacterial behaviour of the ce-MoS2 sheets. The results suggest that antimicrobial behaviors were attributable to both membrane and oxidation stress. The antibacterial pathways include MoS2-bacteria contact induced membrane stress, superoxide anion (O2(˙-) induced ROS production by the ce-MoS2, and the ensuing superoxide anion-independent oxidation. Our study thus indicates that the tailoring of the dimension of nanomaterials and their electronic properties would manipulate antibacterial activity.