Adsorption of two pesticides on a clay surface: a theoretical study

The contamination of water resources with many organic xenobiotic compounds poses a challenge to environmental sciences and technologies [1]. Although in many cases these contaminants are present only in small concentrations, the large variety of such compounds (some of which are classified as priority pollutants) is a matter of concern. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many of these pollutants [2]. In this regard, the choice of adsorbent materials is crucial, which requires an understanding of the details involved in the adsorption of more or less complex organic molecules by a variety of surfaces of different types. In addition to laboratory studies, computational studies may be valuable in this study [3]. MCPA (2-methyl-4-chlorophenoxyacetic acid, a herbicide) and Clofibric acid (2-(4-chlorophenoxy)-2-methylpropanoic, the metabolite of a pharmaceutical, clofibrate, and also a herbicide) are two phenoxy acids that differ only slightly in their structures. However, a quite distinct behavior in adsorption phenomena on clay materials has been observed in past studies [4]. By relating those differences with the molecules' structural features through atomistic computational studies, some insight may be gained into the respective adsorption processes of this type of compounds. In the present work quantum chemical calculations at density functional theory level have been performed to study the adsorption of MCPA and Clofibric acid by a clay surface model. Since hydration plays an important role for the adsorption process of these species, solvent effects were considered by inclusion of water molecules explicitly into the quantum chemical calculations. The deprotonated negatively charged species were found to strongly interact with the surface and the distinct behavior of both species upon adsorption was compared with experimental evidences

Validation of Satellite Rainfall Products for Western Uganda.

Central equatorial Africa is deficient in long-term, ground-based measurements of rainfall; therefore, the aim of this study is to assess the accuracy of three high-resolution, satellite-based rainfall products in western Uganda for the 2001–10 period. The three products are African Rainfall Climatology, version 2 (ARC2); African Rainfall Estimation Algorithm, version 2 (RFE2); and 3B42 from the Tropical Rainfall Measuring Mission, version 7 (i.e., 3B42v7). Daily rainfall totals from six gauges were used to assess the accuracy of satellite-based rainfall estimates of rainfall days, daily rainfall totals, 10-day rainfall totals, monthly rainfall totals, and seasonal rainfall totals. The northern stations had a mean annual rainfall total of 1390 mm, while the southern stations had a mean annual rainfall total of 900 mm. 3B42v7 was the only product that did not underestimate boreal-summer rainfall at the northern stations, which had ~3 times as much rainfall during boreal summer than did the southern stations. The three products tended to overestimate rainfall days at all stations and were borderline satisfactory at identifying rainfall days at the northern stations; the products did not perform satisfactorily at the southern stations. At the northern stations, 3B42v7 performed satisfactorily at estimating monthly and seasonal rainfall totals, ARC2 was only satisfactory at estimating seasonal rainfall totals, and RFE2 did not perform satisfactorily at any time step. The satellite products performed worst at the two stations located in rain shadows, and 3B42v7 had substantial overestimates at those stations

Structure-SONLO Property Relationship On Nickel Complexes: A TD-DFT Study

The search on organometallic compounds for the development of novel nonlinear optical (NLO) materials with large second-order nonlinearities (SONLO) is currently the subject of significant interest in view of their potential application in the area of integrated optics [1]. Experimental and computational systematic studies were made on half-sandwich organometallic complexes presenting the typical push-pull feature in which the metal centre, bound to a highly polarizable conjugated backbone, acts as an electron-releasing or withdrawing group. With this feature, large quadratic hyperpolarizabilities arise from small energy gaps between excited and ground states, large changes in dipole moment upon molecular excitation and large transition dipole moments. The results revealed that h5-monocyclopentadienylmetal organometallic moieties can be very efficient electron-donor groups in complexes presenting thiophene-based ligands with a nitro group as an electron acceptor [2-4]. Nevertheless, the understanding of the relationship between the structure and experimental molecular NLO phenomena is not completely clear, namely the effect of the conjugation length of the chromophores. The time-dependent density functional theory (TD-DFT) method within the DFT frame provides the satisfactory molecular orbital explanation for the electronic excitation, which is usually recommended for calculating the excited-state behaviours. In the case of organometallic complexes, the TD-DFT method is one of the most suitable choices to calculate accurately the excited energy and first hyperpolarizabilities. In order to contribute to a clarification on the molecular organometallic structure-SONLO properties relationship and to enhance the SONLO performance of half-sandwich complexes with substituted thienyl chromophores, we report herein a DFT and TD-DFT study on the nickel complexes [Ni(η5-C5Y5)(PR3)(XC{SC4H2}nNO2)] and [Ni(η5-C5H5)(PH3)(CC{SC4H}(NO2)2] (Y=H, Me; R=H, Ph; X= N, C; n=1,2) using the Gaussian03W program package. The effect of different monocyclopentadienyl and phosphine co-ligands, the conjugated length of the chromophore and its coordination mode to the metal centre and the number of nitro substitutents on the first hyperpolarizability will be evaluated

First hyperpolarizabilities of half-sandwich iron (II) complexes with thiophene acetylide ligands: a DFT study

Organometallic complexes have been studied as potential building blocks for second-order nonlinear optical (SONLO) materials in view of their potential application in the area of integrated optics.1 Experimental work on 5-monocyclopentadienyliron(II) complexes with acetylide and nitrile benzene-based chromophores showed that acetylides have higher first hyperpolarizabilities (β) than the corresponding nitriles.2 Also, studies on a series of similar complexes with substituted oligo-thiophene nitrile ligands showed that these complexes have better NLO properties than the corresponding benzenoid structures.3 These results suggest that combination of acetylide thiophene ligands with 5-monocyclopentadienyliron moiety would maximize the NLO response. In order to predict the first hyperpolarizabilities and for a better understanding on the electronic factors that may be responsible for the second-order nonlinear optical behavior of 5-monocyclopentadienyliron(II) complexes with substituted thienyl-acetylide ligands, density functional theory (DFT) based calculations as well as time dependent DFT (for the prediction of UV/Vis absorption spectra) were performed for the model complexes [FeCp(H2PCH2CH2PH2)(CC{SC4H2}Y)] (Y=NMe2, NH2, OMe, H, Br, CHO, CN, NO2). Spatial localization of electron charge by means of topological analysis of the electron localization functions (ELF) has been performed to gain insight into the nature of bonding between the acetylide ligands and the organometallic moiety. Calculations were also made in the free acetylide ligands in order to study the role played by the organometallic fragment in the second-order NLO properties of the studied complexes

Population pressure and global markets drive a decade of forest cover change in Africa\u27s Albertine Rift

Africa\u27s Albertine Rift region faces a juxtaposition of rapid human population growth and protected areas, making it one of the world\u27s most vulnerable biodiversity hotspots. Using satellite-derived estimates of forest cover change, we examined national socioeconomic, demographic, agricultural production, and local demographic and geographic variables, to assess multilevel forces driving local forest cover loss and gain outside protected areas during the first decade of this century. Because the processes that drive forest cover loss and gain are expected to be different, and both are of interest, we constructed models of significant change in each direction. Although rates of forest cover change varied by country, national population change was the strongest driver of forest loss for all countries – with a population doubling predicted to cause 2.06% annual cover loss, while doubling tea production predicted to cause 1.90%. The rate of forest cover gain was associated positively with increased production of the local staple crop cassava, but negatively with local population density and meat production, suggesting production drivers at multiple levels affect reforestation. We found a small but significant decrease in loss rate as distance from protected areas increased, supporting studies suggesting higher rates of landscape change near protected areas. While local population density mitigated the rate of forest cover gain, loss was also correlated with lower local population density, an apparent paradox, but consistent with findings that larger scale forces outweigh local drivers of deforestation. This implicates demographic and market forces at national and international scales as critical drivers of change, calling into question the necessary scales of forest protection policy in this biodiversity hotspot. Using a satellite derived estimate of forest cover change for both loss and gain added a dynamic component to more traditionally static and unidirectional studies, significantly improving our understanding of landscape processes and drivers at work

First Hyperpolarizability Of Some Nickel-Acetylide Complexes: A DFT Study

The search for new organometallic materials with second-order nonlinear optical (SONLO) properties is currently the subject of considerable interest due to their potential technologic applications in photonic devices for telecommunications and optical computing. Experimental systematic studies were made on half-sandwich complexes presenting nitrile and acetylide benzene and thiophene-based chromophores [1-3]. The results revealed that the combination of acetylide thiophene ligands with appropriate organometallic fragments would maximize the SONLO response. Also, recent TD-DFT studies on h5-monocyclopentadienyliron(II) complexes with substituted thienyl-acetylide ligands revealed the fundamental role played by the organometallic fragment on the corresponding SONLO properties [4]. In our continuous effort to get a better understanding on the electronic factors that may dictate the SONLO properties of η5-monocyclopentadienylmetal complexes with substituted thienyl-acetylide chromophores, we report herein the preliminary density functional theory (DFT) and time-dependent DFT (TD-DFT) results on the complexes [NiCp(PR3)(CC{SC4H2}nY)] (R=H, Ph; Y= CHO, CN, NO2; n=1,2) using the Gaussian03W program package. For instance, Figure 1 shows the optimized structure for NiCp(PH3)(CC{SC4H2}NO2. The effect of the phosphine, the Y-substituent and the conjugated length of the chromophore on the first hyperpolarizability will be evaluated. Some experimental spectroscopic data will be also explained on the basis of the TD-DFT calculations

Studies On SONLO Properties Of Half-Sandwich Complexes Using TD-DFT Calculations

During the last decades there´s been a growing interest in the use of organometallic complexes as potential building blocks for second-order nonlinear optical (SONLO) materials, namely for photonics and integrated optics applications [1]. h5-Monocyclopentadienylmetal complexes are known to be good candidates for SONLO purposes. Systematic studies in these systems give the basis to predict that the combination of substituted acetylide thiophene chromophores with ruthenium and iron metal centers can enhance the first hyperpolarizabilitiy [2,3]. Also, it is well known that the first hyperpolarizability of purely organic push-pull molecules increases strongly with the length of the conjugated chain. Nevertheless, the exploitation of this effect in several h5-monocyclopentadienylmetal complexes showed contradictory results. The time-dependent density functional theory (TD-DFT) method within the DFT frame provides the satisfactory molecular orbital explanation for the electronic excitation, which is usually recommended for calculating the excited-state behaviours. In the case of organometallic complexes, the TDDFT method is one of the most suitable choices to calculate accurately the excited energy and first hyperpolarizabilities. In this work we used the TD-DFT method to study the first hyperpolarizabilities of [MCp(P_P)(CC{SC4H2}nY)] complexes (M=Ru, Fe; P_P= H2PCH2CH2PH2, DPPE; Y= CHO, NO2; n= 1,2) (Figure 1). The effect of the bidentate phosphine, different electron-withdrawing groups and the conjugated length of the chromophore will be evaluated. Our interest is not only to predict the β values but also to investigate the microscopic SONLO mechanism in these complexes

Phytoremediation: An Option for Removal of Organic Xenobiotics from Water

Pollution by persistent organic pollutants (pesticides, pharmaceuticals, petroleum hydrocarbons, PAHs, PCBs, etc.) is an environmental problem that is recognized worldwide. In order to address this problem, cost effective technologies have been developed and evaluated for the decontamination of soil and water resources. Phytoremediation is a promising technology that uses plants and the associated rhizosphere microorganisms to remove, transform/detoxify, or accumulate organic and inorganic pollutants present in soils, sediments, surface or ground water, wastewater, and even the atmosphere. In fact, as a result of their sedentary nature, plants have evolved diverse abilities for dealing with toxic compounds in their environment. They, therefore, possess a variety of pollutant attenuation mechanisms that makes their use in remediating contaminated land and water more feasible than physical and chemical remediation. Currently, phytoremediation is used for treating many classes of organic xenobiotics including petroleum hydrocarbons, chlorinated solvents, polycyclic aromatic hydrocarbons, pesticides, explosives, pharmaceutical compounds and their metabolites, and it involves several decontamination mechanisms. There are several different types of phytotechnologies such as, for instance, treatment constructed wetlands. The aim of this work is to present a review on the application of phytoremediation technologies for water decontamination from persistent organic pollutants, with special emphasis focused on the removal of a class of emergent pollutants that has recently been receiving a lot of attention, the pharmaceutically active compounds. Within the realm of phytotechnologies, constructed wetlands for wastewater treatment are dedicated a special focus as these systems have been used with success for the removal of several different types of organic xenobiotics

"Wetlands: Water Living Filters?",

Human societies have indirectly used natural wetlands as wastewater discharge sites for many centuries. Observations of the wastewater depuration capacity of natural wetlands have led to a greater understanding of the potential of these ecosystems for pollutant assimilation and have stimulated the development of artificial wetlands systems for treatment of wastewaters from a variety of sources. Constructed wetlands, in contrast to natural wetlands, are human-made systems that are designed, built and operated to emulate wetlands or functions of natural wetlands for human desires or needs. Constructed wetlands have recently received considerable attention as low cost, efficient means to clean-up not only municipal wastewaters but also point and non-point wastewaters, such as acid mine drainage, agricultural effluents, landfill leachates, petrochemicals, as well as industrial effluents. Currently, untreated wastewater discharge in the natural wetlands sites is becoming an increasingly abandoned practice whereas the use of constructed wetlands for treatment of wastewater is an emerging technology worldwide. However, natural wetlands still play an important role in the improvement of water quality as they act as buffer zones surrounding water bodies and as a polishing stage for the effluents from conventional wastewater treatment plants, before they reach the receiving water streams. In fact, one of the emerging issues in environmental science has been the inefficiency of wastewater treatment plants to remove several xenobiotic organic compounds such as pesticides and pharmaceutical residues and consequent contamination of the receiving water bodies. Recent studies have shown that wetlands systems were able to efficiently remove many of these compounds, thus reaffirming the importance of the role which can be played by wetlands in water quality preservation. The aim of this work is to present a review on the application of wetlands as “living” filters for water purification, with special emphasis focused in the removal of micropollutants, especially xenobiotic organic compounds such as pharmaceuticals and pesticides residues, which are not efficiently removed by conventional wastewater treatment plants. Furthermore, the role of wetlands as protection zones which contribute to the improvement of the aquatic ecosystems’ quality will be discussed

Removal of Antibiotics by “Green” Clay Sorbents

Contamination of water resources with pharmaceuticals has been one of the top concerns of environmental sciences in the latest years [1], the matter having received very significant media coverage recently [2]. Antibiotics in particular have been gathering considerable attention and are amongst the most serious worries due to the development of antibiotic resistant bacteria as result of prolonged exposure [1, 2]. Because most wastewater treatment plants were only designed for removing bulk pollutants, many other more specific pollutant types that are present in low concentrations in the wastewaters are often inefficiently treated and end up being released into receiving water bodies. Although in many cases these contaminants are detected only at small concentrations in environmental samples, the large variety of such compounds and the high potential for adverse interactions with living organisms (due to the nature of their action) is a matter of serious concern. Several advanced technologies have been evaluated as options to treat these contaminants, e.g. advanced oxidative processes or membrane filtration, but despite the sometimes high removal efficiencies attained, these technologies are too expensive to be considered as viable solutions on a large scale. Adsorption, alone or as part of a more complex water or wastewater treatment process, has been seen as playing a very important role in the removal of many organic xenobiotic pollutants [3]. In this regard, the choice of adsorbent materials is crucial. However, pollutants removal efficiency is not the sole selection criterion, as the cost of the materials may provide or preclude economic viability of the water/wastewater treatment system. Therefore, the quest for efficient adsorbents that are widely available, and do not require expensive processing in order to be used (thereby allowing lower production costs) is a very important aspect of research aimed to manage this environmental problem. In this work we present the study of sorption properties of clay materials (LECA and vermiculite) for the removal of some pharmaceuticals two antibiotics (sulfametoxanol and oxytetracycline) from water. The dependence of removal efficiencies on pollutants initial concentrations, contact time with the adsorbents and other system/environment conditions was assessed. The two clay materials were compared in terms of their more balanced performance towards the removal of the pharmaceuticals tested and the materials are suggested as a useful component of a water or wastewater treatment system designed for the removal of pharmaceutical contaminants