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We have investigated the structure and electronic structure of single-and double-walled imogolite nanotubes with Ge and Si as group IV element. While it is known from experiment, and in the case of single-walled tubes confirmed by theory, imogolite nanotubes are monodisperse in diameter. We show that imogolite tubes are also showing a preferred chirality (zigzag), resulting from the hydrogen-bond network on the tube surfaces, and that there is an exceptionally stable form of intertube interaction that supports the formation of monodisperse double-walled imogolite nanotubes. The strongest stabilization of double-walled tubes has been found for tube indexes with nine units of difference around the circumference, and the minimum structure is found for the (12,0)@(21,0) tube in the case of germanium imogolite and (9,0)@(18,0) for imogolite. The electronic structure is only slightly affected by these geometric factors, as are the mechanical properties, which show Young moduli of 320−370 GPa, thus being in the same range as other clay mineral nanotubes.

Chalcopyrite (CuFeS2) is the main source of copper in the world. The development of hydrometallurgical processes to extract copper from chalcopyrite is challenging due to the low leaching kinetics. The main difficulty is in the fact that the kinetics of the leaching process decreases very rapidly, marginally stopping the reaction. A passivation process of the surface has been proposed for explaining the low reaction kinetics. However, the leaching mechanism and the reactants which are involved in the passivation process are still a matter of debate. Therefore, understanding the chalcopyrite surface reactivity and the intricate reaction occurring in the solid/solution interface is of fundamental importance. In the present study, DFT calculations within the plane wave framework were performed to understand the reconstruction of (001), (100), (111), (112), (101), and (110) chalcopyrite surfaces. Metal and sulfur terminated surfaces have been investigated. The structural and electronic properties of the reconstructed surfaces have been discussed in detail. Three different mechanisms of the chalcopyrite surface reconstructions emerged from this study. It is clear that the chalcopyrite surface undergoes important reconstruction in which the sulfide, S2–, ions migrate to the surface which tend to oxidize, forming disulfides, S2 2–, and, concomitantly, reducing the superficial Fe3+ to the Fe2+. It is also observed that the metal atom moves downward to the surface, forming metallic-like bidimensional alloys underneath the surface.

The interaction of water molecule with the reconstructed (001) chalcopyrite surfaces has been investigated by means of density functional calculations. All of the calculations were performed using periodic boundary conditions with SIESTA code. The structural parameters were compared with those obtained through PWscf code in order to evaluate the pseudopotentials and numerical basis set developed for this work. Two different surfaces were studied, namely, sulfur-terminated, (001)-S, and metal-terminated, (001)-M. The (001)-S surface reconstructs, forming disulfide dimers with a bond length of 2.23 Å. The (001)-M surface reconstructs, reordering the metal atoms in order to form planes of metal atoms and interlaced sulfur atoms. Different adsorption sites for the water molecule were investigated. The dissociative mechanism of the water molecule has also been analyzed in detail. For the (001)-S surface, the water adsorption on the iron atom is the preferred mechanism. The dissociative mechanism leads to structures which are, at least, 13 kcal mol À1 higher in energy than the water adsorbed on iron atom. For the (001)-M surface, no minima in the potential energy surface were found, and the water molecule prefers to form a hydrogen bond with the sulfur atoms. The dissociative mechanism for the water adsorption on (001)-M surface is thermodynamically unfavorable. The metal-alloy-like structure underneath of the sulfur atoms and the unfavorable water adsorption indicate that the surface presents some hydrophobic character. The influence of the water molecule in the reconstruction of the (001) chalcopyrite surface and in its reactivity is discussed.

Structural, electronic, and mechanical properties of single-walled chrysotile nanotubes have been investigated using the self-consistent charge density-functional tight-binding method (SCC-DFTB). The naturally occurring chrysotile nanotubes (NTs) are composed of brucite, Mg(OH) 2 , layer in the outer side and tridymite, SiO 2 , in the inner side. The zigzag (17,0)−(45,0) and armchair (9,9)−(29,29) chrysotile nanotubes, which correspond to the radii ranging from 16 to 47 Å, have been calculated. The SCC-DFTB results are in good agreement with available experimental and previously published theoretical results. The chrysotile nanotubes are estimated to be insulator with band gap of 10 eV independently of their chirality and size, and the Young's moduli are estimated to be in the range of 261−323 GPa. In addition, we have shown that the chirality of the NTs does not affect their stability, and the variant with brucite in the inner side and the tridymite in the outer side of the nanotube is indeed less stable with respect to the inverse case.

Herbicide resistance is the evolutionary response of weeds to the selection pressure caused by repeated application of the same active ingredient. It can result from two different mechanisms, known as target site resistance (TSR) and non-target site resistance (NTSR). In addition to single-herbicide resistance, multiple resistance can occur due to herbicides selection or accumulation of resistance genes by cross-pollination. The aim of this research was to investigate the suspect of multiple herbicide resistance of Sumatran Fleabane (Conyza sumatrensis (Retz.) E.Walker) to herbicides frequently used as a burndown application. Dose-responses in a whole-plant assay were carried out to investigate multiple-resistance of Sumatran fleabane to paraquat, saflufenacil, diuron, 2,4-D and glyphosate. Results indicated that the resistance index (ratio R/S) based on herbicide rate to cause 50% mortality (LD 50 ) were 25.51, 1.39, 7.29, 1.84 and 7.55 for paraquat, saflufenacil, diuron, 2,4-D and glyphosate, respectively. Based on herbicide rate required to cause a 50% reduction in plant growth (GR 50 ), the resistant index were 51.83, 14.10, 5.05, 3.96 and 32.90 for the same herbicides, respectively. Our results confirmed multiple resistance of Conyza sumatrensis from Paraná-Brazil to herbicides from five-mode of-action. This was the first report of Conyza sumatrensis resistant to 2,4-D and the first case of Conyza sumatrensis presenting multiple resistant to herbicides from fivemode of-action in the world.

A utilização do lodo de esgoto, como fonte de nutrientes para as plantas, pode ser limitada pela presença de metais, que podem causar contaminação no solo, nos aqüíferos e nas plantas. Lodo de esgoto urbano produzido na Estação de Tratamento da Ilha do Governador (ETIG), Rio de Janeiro (RJ), foi enriquecido com 1.667 mg kg -1 de Cd e 8.000 mg kg -1 de Zn e, após 20 dias de incubação, sob umidade constante (50 % g g -1 ), foi utilizado em doses de 0, 20, 40 e 80 t ha -1 , em amostras de dois solos: Latossolo Vermelho-Amarelo (LV) e Argissolo VermelhoAmarelo (PV). Para avaliar o efeito do Cd e do Zn no crescimento de arroz (IAC-47) foi feito um experimento em casa de vegetação, durante 126 dias, com amostras dos solos LV e PV incubadas com o lodo de esgoto enriquecido. Adotouse um delineamento experimental de blocos ao acaso com quatro repetições. Foram coletados raízes, folhas e grãos e determinados a produção de matéria seca e teores de Cd e Zn. As elevadas doses de Cd e Zn aplicadas no solo, decorrentes da aplicação do lodo de esgoto, não mostraram efeito na produção de matéria seca; nas plantas, os metais concentraram-se nas raízes, com baixa translocação para as folhas. Os níveis de Cd e de Zn encontrados na planta inteira demonstraram a tolerância da variedade de arroz IAC-47 a elevados teores de Cd e Zn.

Changes in the environment, specifically rising temperature and increasing atmospheric carbon dioxide concentration [CO 2 ], can alter the growth and physiology of weedy plants. These changes could alter herbicide efficacy, crop-weed interaction, and weed management. The objectives of this research were to quantify the effects of increased atmospheric [CO 2 ] and temperature on absorption, translocation and efficacy of cyhalofop-butyl on multiple-resistant (MR) and susceptible (S) Echinochloa colona genotypes. E. colona , or junglerice, is a troublesome weed in rice and in agronomic and horticultural crops worldwide. Cyhalofop-butyl is a grass herbicide that selectively controls Echinochloa spp. in rice. Maximum 14 C-cyhalofop-butyl absorption occurred at 120 h after herbicide treatment (HAT) with >97% of cyhalofop-butyl retained in the treated leaf regardless of [CO 2 ], temperature, or genotype. Neither temperature nor [CO 2 ] affected herbicide absorption into the leaf. The translocation of herbicide was slightly reduced in the MR plants vs. S plants either under elevated [CO 2 ] or high temperature. Although plants grown under high [CO 2 ] or high temperature were taller than those in ambient conditions, neither high [CO 2 ] nor high temperature reduced the herbicide efficacy on susceptible plants. However, herbicide efficacy was reduced on MR plants grown under high [CO 2 ] or high temperature about 50% compared to MR plants at ambient conditions. High [CO 2 ] and high temperature increased the resistance level of MR E. colona to cyhalofop-butyl. To mitigate rapid resistance evolution under a changing climate, weed management practitioners must implement measures to reduce the herbicide selection pressure. These measures include reduction of weed population size through reduction of the soil seedbank, ensuring complete control of current infestations with multiple herbicide modes of action in mixture and in sequence, augmenting herbicides with mechanical control where possible, rotation with weed-competitive crops, use of weed-competitive cultivars, use of weed-suppressive cover crops, and other practices recommended for integrated weed management.