How can the Functioning of Treatment Wetlands be Enhanced?

Wetlands have already been recognized to hold the capacity for efficiently reducing or removing large amounts of pollutants from point sources (e.g. municipal and certain industrial effluents) as well as non-point sources (e.g. mining, agricultural and urban runoff) including organic matter, suspended solids, excess of nutrients, pathogens, metals and other micropollutants. This pollutants removal is accomplished by the interdependent action of several physical, chemical and biological processes which include sedimentation, filtration, chemical precipitation, sorption, biodegradation, and plants uptake among others. The mechanisms and the interdependences among the wetlands’ components (water, substrate and biota) are complex and not yet entirely understood, although some progresses have been achieved in the latest years as the awareness to the water depurative functions of wetlands becomes more widespread. In fact, studies have led to both a greater understanding of the potential of natural wetland ecosystems for pollutants assimilation and the design of new natural water treatment systems inspired in these natural systems, the constructed wetlands systems (CWS). These CWS can be defined as man-made systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and their associated microbial populations to assist in treating wastewater. They are designed to take advantage of many of the same processes that occur in natural wetlands, but do so within a more controlled environment. However, until now these systems have been approached primarily as a “black-box”, without a thorough understanding of the processes involved. Ultimately, the optimization of CWS for the removal of more specific target compounds requires a basic knowledge of the processes involved in the removal of the pollutants and the interactions between those and the CWS components. New trends in CWS research are moving towards the study of such processes and interactions and focus on the selection and optimization of the CWS components for more specific applications. The aim of this work is to present a review on the main pollutant removal and transformation mechanisms in wetlands, the pollutants fate in the system and the roles played by the most important components of CWS (water, substrate and biota) in the processes and how they affect the overall treatment system performance. Some focus will be given to the most recent studies published on this subject especially those involving the treatment of micropollutants by CWS and the mechanisms that may be involved in the removal of these particular substances. Some of the questions remaining to be addressed about the removal mechanisms in CWS and the aspects of CWS operation that still require optimization will also be highlighted in this review

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

Recent Developments in the Study of the Behavior of Fluorescent Membrane Probes in Lipid Bilayers: Molecular Dynamics Approach

We present a review of recent developments in the study of the behavior of fluorescent membrane probes in lipid bilayers by molecular dynamics simlations

Mono and Binuclear Complexes for Nonlinear Optical Switching: A DFT Study

The search for materials exhibiting switchable second-order nonlinear optical (SONLO) properties has attracted a great deal of attention owing to their potential application as key nanoscale components for digital processing and data storage. Our research in organometallic complexes with SONLO properties resulted in the development of some new promising thienyl-acetylide 5-monocyclopentadieniliron(II) and ruthenium(II) complexes [1,2]. These compounds present typical push-pull architecture (crucial for maximizing the molecular quadratic hyperpolarizability, β), were an electron donor is linked to an electron acceptor group by a conjugated system. Changing the donor/acceptor abilities of any of these end-groups, by redox means for example, gives the chance to control the magnitude of β value, and hence obtain a SONLO switch. In this presentation, we show the application of Density Functional Theory (DFT) in the prediction of SONLO switching properties of mono and bimetallic complexes bearing two organometallic fragments, 5-monocyclopentadienyliron(II) and 5-monocyclopentadienylnickel(II) moieties, in different formal oxidation states. The obtained hyperpolarizabilities will be correlated with structural and electronic data. Results show that redox changes provide a feasible way to obtain good SONLO switches

Molecular simulation of C60 adsorption onto a TiO2 rutile (110) surface

Monte Carlo molecular simulation study is presented on the adsorption and growth of C60 films on the surface of the (1 1 0) face of rutile. Simulations are performed for a temperature of 600 K using atomistic models both for the fullerene molecules and the TiO2 surface. It is found in this work that C60 is adsorbed preferably in an ordered arrangement along the surface depressions over the exposed undercoordinated Ti cations. At low densities adsorption occurs preferably at alternate rows, with locations in consecutive rows being occupied appreciably only at higher C60 densities. At low densities, the fullerene molecules tend to aggregate into islands in the surface plane. Additional layers of C60 form only as the density increases, and do so before a monolayer is completed in all consecutive rows. Full monolayer capacity obtained at the highest densities is about 0.9 C60 molecules per nm2, but this is only achieved by completing the packing of molecules in interstices at a slightly upper level. The fraction of the molecules that lie closest to the surface only amounts to 0.6 molecules per nm2

Ruthenium Complexes For SONLO: DFT Calculations Of The Molecular Hyperpolarizability

Nonlinear optical (NLO) materials are of considerable interest because of their possible applications in the emerging technologies of optoelectronic and photonic devices. Fundamental research in this area has been focused in the establishment of detailed structure–activity correlations for first hyperpolarizability (β), which govern SONLO effects, in view to obtain large intrinsic optical nonlinearities. A combination of fast response time, low-lying intense metal-to-ligand or ligand-to-metal charge transfer (MLCT or LMCT) transitions, and the potential of variable oxidation state, d-electron count, and ligand environment in tuning NLO performance make organometallics very promising systems for nonlinear optics. Organometallic fragments have been demonstrated to be able to act as potential electron donors or electron acceptors in second-order nonlinear optical chromophores. Among organometallic electron donors, CpM(L)2 (M=Fe, Ru; L=phosphines) moieties seem to be promising candidates. Coplanarity of the metals and the π-electrons of the thiophene-based ligands was suggested to be valuable for second-order optical nonlinearity [1-2]. Theoretical studies using time-dependent density functional theory (TD-DFT) method within the DFT frame has been used to calculate accurately the excited energy and first hyperpolarizabilities of organometallic complexes. These theoretical studies are very useful for a better understanding on the electronic factors that may be responsible for the SONLO properties in order to fine tuning the electronic properties of new compounds. Also, they can be used as a guideline to the molecular design and the time consuming synthetic work. Recently, TD-DFT studies on h5-monocyclopentadienyliron(II) and nickel (II) complexes with substituted thienyl-acetylide ligands has shown a linear dependence of the first hyperpolarizability with the wavelength of the lowest energy electronic transition. Also, it was possible to confirm the better ability of the iron moiety to induce large hyperpolarizabilities [3-4]. We report therein the results of DFT and TD-DFT calculations on the model complexes [RuCp(H2PCH2CH2PH2)(CC{SC4H2}Y)] (Y=NMe2, NH2, OMe, H, CHO, CN, NO2) in view to predict the corresponding first static hyperpolarizabilities and to study the role played by the ruthenium organometallic fragment on the SONLO properties of these complexes. A quantitative correlation with optical data is used in order to compare the results with those found in parent iron and nickel derivatives studies

Experimental and Simulation Study of n-Heptane Adsorption on Rutile

The adsorption of n-heptane on microcrystalline rutile has been studied experimentally by thermodynamic techniques (adsorption isotherms and microcalorimetry) over a wide range of coverage at 303 K and complemented by Grand Canonical Monte Carlo simulations. The differential heat of adsorption exhibited three descending segments corresponding to the adsorption of n-heptane on three types of surfaces. The mean molar adsorption entropy of n-heptane in the monolayer was less than the entropy of the bulk liquid by ca. −23 J/(mol K), thus revealing a hindered state of motion for the n-heptane molecules on the surface of rutile. Simulations of the adsorption of n-heptane were performed on the three most abundant crystallographic faces of rutile. The adsorption isotherm obtained from the combination of the isotherm for each face weighted by the respective abundance was found to be in good agreement with experimental data. A structural characterization of n-heptane near the surface was also conducted which indicated that the substrate strongly perturbed the distribution of the n-heptane conformations relative to the situation found for the gaseous phase. Adsorbed molecules are predominantly orientated with their long axes, with the zig-zag planes of their backbones parallel to the surface and preferentially aligned along the five-fold cus Ti 4+ ions of the faces. Fewer gauche conformations were observed for molecules near the surface than was characteristic of the bulk phase

Second Order Hyperpolarizabilities Dependence on the Benzenic Ring position of Organic and Organometallic Benzo[c]thiophene species: an assessment by DFT methods

Nonlinear optical (NLO) active organic chromophores find application in a wide range of technological applications, from molecular electronics to optical sensors and switches. Thus, the establishment of methods that can predict a priori the optical properties of organic or organometallic chromophores is indeed a crucial topic of current research. Density Functional Theory (DFT) methods are by far the most used computational methods for estimation of optical properties of molecules due to their low computational effort and accurate results. [1] Furthermore, they allow the study of structure/activity correlations in molecules without the need to synthesize all of them. DFT calculations can be used for a screening of NLO chromophores prior to the synthetic labor. Among all the available DFT functionals, B3LYP is by far the most common. Others, like CAM-B3LYP are now being evaluated and they show similar or improved results concerning the prediction of optical properties. [2] In the present work a combination of DFT with the Finite Field (FF) method was used to investigate the influence on the benzenic ring position on the magnitude of the static first hyperpolarizibility of several nitro acetylene organic fragments based on benzo[c]thiophenes. Time Dependent – DFT methods (TD-DFT) were employed to determine the spectral data of all the compounds. After the screening of the organic chromophores was complete, coordination to an iron (II) and ruthenium (II) monocyclopentadienyl fragment was investigated. The chromophores for coordination were chosen according to available procedures in literature to further synthetic achievement. Results show that better NLO responses should be obtained when the benzene ring is close to the electron donor group, whilst the presence of such aromatic ring close to the acceptor group should lead to a decreasing on the NLO response. This behavior is justified, among other possibilities, in terms of HOMO-LUMO band gaps by correlation of the DFT and TD-DFT methodologies