Photoluminescence spectrum using DFT for double-walled carbon nanotubes with metallic constituents.

A theoretical study of the photoluminescence (PL) of double-walled carbon nanotubes (DWCNTs) using density functional theory (DFT) theory is reported in this work. The DWCNTs are of the armchair/armchair type and the structures studied have the arrangements (3,3)/(2,2), (8,8)/(4,4), (12,12)/(6,6), (16,16)/(8,8), (6,6)/(3,3), (10,10)/(5,5), (14,14)/(7,7), and (18,18)/(9,9). The PL spectra were obtained taking into account different DWCNT axial lengths ranging from 0.49 nm ≤ L ≤ 2.33 nm and their inner nanotube diameters in the range of 0.31 ≤ Dinn ≤ 1.22 nm; variations in their inter-wall separations were also considered, 0.18 ≤ Dinw ≤ 0.61 nm. Although the DWCNTs have metallic SWCNT constituents, such structures give rise to photoluminescence due mainly to both curvature effects and inter-wall interaction of the inner and outer nanotubes; these two factors modify significantly their electronic structure; besides, they also lead to these structures to exhibit the quenching effect. We realized calculations at a DFT level in which we used the generalized gradient approximation (GGA) to establish the molecular geometries and the fundamental state energies. To obtain the results of the PL spectra, the constituent SWCNTs were optimized in their ground state, with the hybrid function CAM-B3LYP, which is a mixed functional exchange and correlation, and the base set that was used is the 6-31G.

Carbofuran degraded by iron-doped anatase: Weakening the cholinesterase inhibitory activity in the photoproducts mixture.

Carbofuran is a toxic carbamate pesticide, and its use has increased in recent years. While marketing information indicates stability in different chemical media, carbofuran exhibits relative photolability. The aim of this research was to decompose carbofuran and to identify the photoproducts achieved when two different doped titania photocatalysts were employed under UV irradiation. The iron-doped TiO2 materials were obtained (a) via a hydrothermal method and (b) by an ultrasound-assisted sol-gel method. The precursors were TiOSO4⋅xH2O and Fe3(NO3)·9H2O. X-ray studies confirmed that the anatase phase of the iron-doped TiO2 resulted from the two preparation methods. The photocatalytic performance of the prepared materials was monitored by LC/ESI-QTOF-MS, enabling the identification of photoproducts: oxo-carbamates, hydroxylated benzofuranes, a carboxamide, and one amine. By using the iron-doped TiO2 materials, 2,2-dimethyl-2,3-dihydrobenzofuran-3,7-diol was the most abundant photoproduct, and N,2,2-trimethyl-2,3-dihydrobenzofuran-7-amine was the only compound that had not been previously reported in the photolysis and photocatalysis of carbofuran. The product 3-hydroxy carbofuran, a cholinesterase inhibitor, was quantified and was found to be transformed into compounds that lack this inhibitive property.