Oxidized cellulose nanofibers (CNF), embedded in an electrospun polyacrylonitrile (PAN) nanofibrous scaffold, were grafted with cysteine to increase the adsorption capability for chromium (VI) and lead (II). Thiol-modified cellulose nanofibers (m-CNF) were characterized by titration, FT-IR, energy dispersive spectroscopy (EDS) and SEM techniques. Static and dynamic Cr(VI) and Pb(II) adsorption studies of m-CNF nanofibrous composite membranes were carried out as a function of pH and of contact time. The results indicated these membranes exhibited high adsorption capacities for both Cr(VI) (87.5 mg/g) and Pb(II) (137.7 mg/g) due to the large surface area and high concentration of thiol groups (0.9 mmol of –SH/gram m-CNF). The morphology and property of m-CNF nanofibrous composite membranes was found to be stable, and they could be used and regenerated multiple times with high recovery efficiency.
Thiol-functionalized chitin nanofibers for As (III) adsorption
Natural polysaccharide chitin nanofibers, prepared with a series of chemical and mechanical treatments, were used as an absorbent material for arsenic (As(III)) removal. The dimensions of chitin nanofibers, determined by small-angle X-ray scattering (SAXS), were about 6 nm in thickness, 24 nm in width and a few hundred nanometers in length. The chemical/mechanical treatment enabled the chitin nanofiber surface to be charged, thus facilitating the dispersion of nanofibers in aqueous suspension at neutral pH. The large amount of amine groups (1.7 mmol/g) on the nanofiber surface provided opportunities for further modifications, such as formation of amide bonds. In this study, grafting of cysteine was carried out to create adsorption sites for arsenic metal ion (AsO2−) removal. The thiol-functionalized chitin nanofibers ([-SH] = 1.1 mmol/g) were characterized by titration, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The arsenic adsorption performance of thiol-modified chitin nanofibers was evaluated under different pH conditions and at different metal ion concentrations, where the maximum adsorption capacity was found to be 149 mg/g at pH = 7.0 using the Langmuir Model. This adsorption capacity was higher than any existing chitin/chitosan-based hydrogel or bead absorbent systems.
Telluric rings: The tellurophene-containing low-bandgap polymer PDPPTe2T, prepared by microwave-assisted ipso-arylative polymerization, exhibited red-shifted absorption spectra compared to the thiophene analogue. Bulk heterojunction solar-cell devices from PDPPTe2T and PC71BM reach a power conversion efficiency of 4.4 % and produce photocurrent at wavelengths up to 1 μm.
We report the synthesis of a tellurophene-containing low-bandgap polymer, PDPPTe2T, by microwave-assisted palladium-catalyzed ipso-arylative polymerization of 2,5-bis[(α-hydroxy-α,α-diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC71BM show PCE values of up to 4.4 %. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 µm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon–carbon bonds between the tellurophene and thiophene rings, which results in the red-shift in absorption upon substitution of tellurium for sulfur.
(Received 12 Mar 2014, Accepted 30 Apr 2014; First published online 01 May 2014)
We report a general strategy for fine-tuning the bandgap of donor–acceptor–donor based organic molecules by modulating the electron-donating ability of the donor moiety by changing the benzochalcogenophene donor groups from benzothiophenes to benzoselenophenes to benzotellurophenes. These molecules show red-shifts in absorption and external quantum efficiency maxima from sulfur to selenium to tellurium. In bulk heterojunction solar cell devices, the benzoselenophene derivative shows a power conversion efficiency as high as 5.8% with PC61BM as the electron acceptor.