Adsorption Of Organic Molecules Research Articles

Theoretical study of the interaction of surfactants and drugs with natural zeolite

The presence of surfactant in a solid surface can modify its properties and improve the adsorption of certain organic molecules. In the present work, different combined systems formed by surfactants, drugs, water and a clinoptilolite channel model have been studied using semiempirical calculations. We modeled the interaction of each organic molecule with the external surface of clinoptilolite model. The results indicate that the cationic surfactant is well adsorbed on the clinoptilolite model unlike the anionic surfactant. The most polar drug, metronidazole, is the best adsorbed on the zeolite model, followed by aspirin and sulfamethoxazole. Taking into account this fact, we also model another system formed by surfactant–drug–water (S–D–W) in order to reproduce the interaction of the different drugs with a cationic surfactant in solution and to evaluate the role of the surfactant in the drug adsorption process. In this system the order of the drug adsorption is opposite to that obtained for the zeolite alone: the adsorption of an hydrophobic molecule like sulfamethoxazole is favored. Moreover, for aspirin and sulfamethoxazole the adsorption enthalpies are higher in the S–D–W system. This fact suggests that the presence of surfactant on the external surface of clinoptilolite could improve the adsorption of some drugs on this zeolite.

Adsorption structures of benzene on a Si(5512)-2×1 surface: A combined scanning tunneling microscopy and theoretical study

In the first ever attempt to study the adsorption of organic molecules on high-index Si surfaces, we investigated the adsorption of benzene on Si(5 5 12)-(2x1) by using variable-low-temperature scanning tunneling microscopy and density-functional theory (DFT) calculations. Several distinct adsorption structures of the benzene molecule were found. In one structure, the benzene molecule binds to two adatoms between the dimers of D3 and D2 units in a tilted butterfly configuration. This structure is produced by the formation of di-sigma bonds with the substrate and of two C[Double Bond]C double bonds in the benzene molecule. In another structure, the molecule adsorbs on honeycomb chains with a low adsorption energy because of strain effects. Our DFT calculations predict that the adsorption energies of benzene are 1.03-1.20 eV on the adatoms and 0.22 eV on the honeycomb chains.

Effect of ZnO loading to activated carbon on Pb(II) adsorption from aqueous solution

The effect of zinc oxide loading to granular activated carbon on Pb(II) adsorption from aqueous solution was studied in comparison with zinc oxide particles and oxidized activated carbon. Cu(II), Cd(II) and nitrobenzene were used as reference adsorbates to investigate the adsorption. The BET surface area and point of zero charge (pH PZC) in the aqueous solution were measured for the adsorbents. The adsorption isotherms were examined to characterize the adsorption of heavy metals and organic molecules. The heavy metal adsorption was improved by both the zinc oxide loading and the oxidation of activated carbon. In contrast, the adsorption of nitrobenzene was considerably reduced by the oxidation, and slightly decreased by the zinc oxide loading. The zinc oxide loading to the activated carbon was found to be effectively used for the Pb(II) adsorption whereas only a part of surface functional groups was used for the zinc oxide particles and the oxidized activated carbon. From the experimental results, the surface functional groups responsible for the Pb(II) adsorption on the zinc oxide loaded activated carbon were considered to be hydroxyl groups that formed on the oxide, while those on the oxidized activated carbon were considered to be carboxylic groups.

NH3on Si(001): Self-organized patterns of adsorbates investigated by a combination of scanning tunneling microscopy experiments and density functional theory calculations

The adsorption and dissociation of NH3 on Si(001) has been investigated by a combination of scanning tunneling microscopy experiments and density functional theory calculations. We have identified the NH2 adsorbed group and used this to analyze the arrangement of adsorbed molecular fragments on this surface. We find that there is a statistically significant ordering to these fragments, which changes with adsorption temperature. We propose that a hydrogen-bonding interaction between adsorbed fragments and impinging molecules is responsible for the observed ordering at room temperature, which has general implications for the adsorption of organic molecules on this surface. © 2005 The American Physical Society.

Binding of chemicals to melanins re-examined: Adsorption of some drugs to the surface of melanin particles

This work presents a first attempt to study the interaction of some drugs with melanins, realistically considered as solid aggregates of primary particles. This situation appears similar to the adsorption of organic molecules onto the surface of colloidal absorbers, as active carbon, zeolites or titanium dioxide. We have applied some of the most popular theoretical models used in technological applications with the aim to give a more realistic picture of the melanin–drug interaction responsible for some observed side effects in vivo. Moreover, this approach can simplify the problem of the search of the physical parameters dominating the binding processes, by reducing the phenomenon to a simple physisorption/chemisorption, at least in a first approximation. We have studied the binding to melanin of gentamicin, methotrexate and chlorpromazine, molecules with different physico-chemical and structural characteristics. Our study demonstrates the possibility to fit experimental adsorption data with Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich equations. In such a way we obtain binding parameters useful to characterize the drug–surface interaction in terms of energy and of mean affinity.

X-ray-diffraction characterization of Pt(111) surface nanopatterning induced by C60 adsorption

Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C(60) with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C(60) molecules and the clean Pt(111) surface results in the formation of an ordered sqrt[13] x sqrt[13]R13.9 degrees reconstruction based on the creation of a surface vacancy lattice. The C(60) molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.

Zeolite-Fiber Integrated Optical Chemical Sensors for Detection of Dissolved Organics in Water

MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules, i.e., 2-propanol or pentanoic acid in this study, from aqueous solutions in the zeolitic pores. Reversible and monotonic sensor signals were observed in response to the variation of 2-propanol concentration in water with fast response. However, the sensor exhibited a much slower response to pentanoic acid than to 2-propanol. It was also found that substitution of Si by Al in the MFI framework increased the adsorption of pentanoic acid that resulted in enhanced sensor responses.

Piezoelectric Crystal Liquid Flow Detection Systems Based on Alkyl (C18)-Benzo-15-Crown 5 for Organic Compounds and Metal Ions

A water in soluble long-chain crown ether alkyl (C18)-benzo-15-crown-5 was synthesized and applied as a coating material on quartz crystal membranes of a liquid flow piezo electric crystal sensor. The oscillating crown ether-coated piezo electric (PZ) crystal with a home-made computer inter face was prepared as a liquid chromato graphic (LC) detector for organic species and metal ions in aqueous solutions. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules or metal ions on crown ether molecules. Effects of functional group, molar mass, steric hindrance, and polarity of organic molecules on frequency responses of the crown ether coated PZ crystal detector were investigated. The frequency responses of the crown ether coated PZ crystal detector for various molecules were in the order: amines > carboxylic acids > alcohols > ketones. The crown ether PZ detector also exhibited good sensitivity for some heavy metal ions and the frequency shifts were in the order: Cr3+ » Pb2+ > Co2+ > Cd2+ > Ni2+ > Cu2+. The crown ether coated piezo electric crystal LC detector demonstrated low detection limits for various polar organic molecules, e.g., 6.0 × 10−5 M for propylamine, and metal ions, e.g., 2.9 × 10−5 M (1.8 ppm) for Cu2+; the crown ether PZ detector also gave good reproducibility when re used. A quite sensitive electrochemical quartz crystal microbalance (EQCM) detection system was also set-up for detecting trace heavy metal ions in solutions. The variation in frequency of the PZ crystal and the diffusion current were observed simultaneously after the reduction in heavy metal ions such as Cu2+ and Ni2+. The EQCM detection system exhibited fairly good sensitivity, e.g., 112 Hz/ppm for Cu2+ and a good detection limit, e.g., 0.13 ppm for Cu2+ ions. Comparison between EQCM and PZ detection systems was made and discussed.

Geochemical Influences on Life's Origins and Evolution

The early Earth was hot and chaotic, bombarded intensely from 4.5 to 3.8 billion years ago. In ponds near the flanks of volcanoes, feldspars and zeolites from volcanic flows and ash were alternately washed by fluids and dried, fostering adsorption and catalytic processes. Some silica-rich surfaces favored adsorption of organic molecules, including amino acids, which were produced by lightning in volcanic clouds. Catalysis then promoted polymerization to generate more complex molecules. Dissolution of alkali feldspars created a honeycomb of cavities, which may have acted as temporary cell walls, while phosphorus released from the weathering feldspar framework was available for energy molecules. Following the emergence of the first cells, geochemical processes continued to influence biological evolution. Alkali-rich volcanoes introduced metallic elements, which served as nutrients in the food supply and may also have accelerated the rate of primate evolution prior to the appearance of hominids.

γ-Fe 2O 3 oriented growth by surfactant molecules in microemulsion

γ-Fe 2O 3 nanoparticles, nanorods and multi-pod nanostructure were prepared via a surfactant-assisted process using sodium dodecyl sulfate (SDS) as oriented template. The most influential factors on γ-Fe 2O 3 shape control including the ratio of surfactant injection quantity in microemulsion and reaction time were both studied. The hysteresis loop was operated to show that magnetic properties of γ-Fe 2O 3 were strongly influenced by the morphology of the crystal. The routine entails the executable synthesis of the desired nanostructures with novel physical properties for applications in nanotechniques based on the matching adsorption of organic molecules on the special facet of anisotropic crystalline nuclei.

Molecular Adsorption‐Mediated Control over the Electrical Characteristics of Polycrystalline CdTe/CdS Solar Cells

The effect of surface treatments on p-CdTe/n-CdS solar cell performance was examined. Adsorption of organic molecules with various magnitudes and directions of the dipole moment on p-CdTe resulted in controlled changes in electron affinity and surface bond bending. Similar adsorption on CdTe in state-of-the-art p-CdTe/n-CdS solar cells changes the cell performance, and we explain this by a combination of increased series resistance and changes in light absorption and in cell photovoltage. While at this stage no improvement in performance has been found with these cell structures, which are the result of years of empirical optimization, the molecular effect on the photovoltage shows that it is possible in this way to control the photovoltaic effect at this junction. Separate optimization may well lead to improvement by inserting a dipole layer near the photovoltaic interface. Our results also show that this is even possible when dipole adsorption is performed on the complete polycrystalline thin-film cell.

Theoretical investigation of adsorption of organic molecules onto Fe(110) surface

The adsorption of typical organic molecules onto a clean Fe(110) surface was investigated using density functional theory (DFT). DFT calculations were carried out with the BOP exchange-correlation functional in the DMol 3 program. The Fe(110) surface was modeled by using dilayer Fe 18 and Fe 32 slabs under the periodic boundary condition. The surface relaxation effect was taken into account in calculations using an Fe 32 slab. The results show that the order of the molecular adsorption energies is methylamine>methylacetamide>methylacetate, while no bound molecular adsorption structure was obtained for acetic acid, dimethyl ether, or methanol. Accordingly, we conclude that the adhesiveness of organic molecules onto an iron surface may be closely related to the charge transferability of the molecules. The experimental results of X-ray photoelectron spectroscopy in vacuo (methanol on Fe(110) easily dissociates into methoxy and hydrogen fragments even at 100 K and sublimes at 140 K following the adsorption) may correspond to the result of the present calculation, where the adsorbed state of methanol was found to be unstable, in contrast to a previous DFT study, where the adsorption energy of methanol was estimated to be 21.03 kcal/mol.

Self-assembling behavior and optical properties of triangular silver nanoplates

Triangular silver nanoplates with its border size of 100±10nm and thickness of 30nm were synthesized by a chemical method. These triangular silver nanoplates were characterized by TEM, UVVis spectroscopy and xrays diffraction analysis. Results obtained showed that these triangular silver nanoplates are perfect with sharp corners and selfassembled into twodimensional ordered monolayer on the carboncovered copper grid due to the adsorption of organic molecules in between these silver nanoplates. The wellaligned silver film on Si (100) substrate showed strong surfaceenhanced Raman scattering for pyridine molecules.

Molecular molds

A problem in nanometer-scale applications that combine silicon technology with organic molecules, is the selective adsorption of organic molecules on the silicon surface. Reducing the active device size down to a single molecule requires a very precise geometry of the molecule–surface connection. Here, we report the room temperature adsorption of biphenyl or Trima molecules in artificially created individual molecular molds on a passivated silicon surface. These molecular molds are areas of clean silicon atoms with well defined geometries, fabricated by sequential removal of single hydrogen atoms from the hydrogenated silicon surface using the scanning tunneling microscope (STM) tip. The mold geometry can be controlled to adsorb the molecules at a selected place and in a desired orientation. The potential selection of molecules according to physical size or chemical properties is a step towards combined molecular and semiconductor chip technology.

Chiral metal surfaces from the adsorption of chiral and achiral molecules

Chiral surfaces, capable of existing in two distinguishable mirror forms that cannot be superimposed, are attracting worldwide attention. The adsorption of complex organic molecules provides a means of introducing the ultimate discrimination function of chirality to a metal surface. Here, a comparison of the chiral tartaric acid (HOOC–CHOH–CHOH–COOH) molecule and the achiral succinic acid (HOOC–CH 2–CH 2–COOH) molecule on a Cu(110) surface is presented. For both molecules, two-dimensional assembly is found to depend strongly on molecule–metal bonding interactions, whereas the presence/absence of the OH groups causes subtler, second-order effects on the self-assembled structure. The driving force for creating chiral organisations is shown to arise from adsorption-induced asymmetrisation, via molecular distortion and/or metal reconstruction of the local adsorption unit. The macroscopic chirality of the surface is then determined by whether nucleation points of both chirality can be equally created, or whether non-degeneracy can be introduced to favour one chirality.

STM study of large organic molecules adsorption on Si(100)-2 × 1

The adsorption of large organic molecules, including tetracene and perylene, on clean Si(100) is followed by scanning tunnelling microscopy (STM) in an ultra high vacuum environment. Different adsorption sites have been observed for these organic molecules. Two types of tetracene adsorption are indicated by filled state images but three types can be distinguished in empty state images. Molecules aligned both along and perpendicular to the silicon dimer rows can be observed. Measurements of the length of this molecule in all configurations indicate that the molecule stays intact during the adsorption process. High resolution of STM images reveal that the perylene molecules bond to the substrate in a vertical orientation and forming packs of perylene aligned perpendicular to the silicon dimmer rows. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Determination of biodegradable dissolved organic carbon in waters: comparison of batch methods

An effect of different types of bacterial inocula upon the final biodegradable dissolved organic carbon (BDOC) result was investigated in samples of both low and high BDOC concentrations. Stream water and leaf leachate samples were incubated either with free, suspended bacteria or with bacteria attached to the stream sediment particles or attached to artificial substrata. The time course of dissolved organic carbon (DOC) decomposition was observed using absorbance analysis of DOC. BDOC determination by means of commonly used suspended bacteria as the inoculum made for an underestimation of BDOC between 5% and 25%, compared with attached bacterial community (biofilm). The reason for these findings could be the higher microbial diversity, higher metabolic activity of attached bacteria and abiotic adsorption of organic molecules to inorganic support and biofilm matrix surfaces. Adsorbed DOC is easily hydrolyzed and utilized by biofilm bacteria.

Surface-science approach to the study of mercaptobenzoxazole on Cu(1 0 0)

We present a combined approach, based on photoemission experiments and DFT calculations, to the study of the adsorption of aromatic organic molecules on metal substrates. Our main purpose was to characterize the interface electronic properties and to search for electron states delocalized between the substrate and the molecular overlayer. We demonstrate how the interplay between theory and experiment, within a surface-science framework, is a powerful tool to gain insight into these issues. In particular, the computational results allow us to give a microscopic characterization, in terms of relative molecule–substrate coupling, of the photoemission peaks.

High-Concentration Dispersion of Single-Wall Carbon Nanotubes

We report a novel method to exfoliate and disperse single-wall carbon nanotubes (SWNT) into organic and aqueous solutions. The method is based on treatment of single-wall carbon nanotubes with a solution of hydroxylamine hydrochloric acid salt [(NH2OH)(HCl)] and does not require truncation of the tubes or surface adsorption of organic molecules. The solution dispersed tubes can easily be incorporated into an organic matrix in order to obtain a nanocomposite. We illustrate the method by forming PMMA−SWNT and PS−SWNT nanocomposites. 1% SWNT PMMA nanocomposite having a draw ratio of ∼6 showed a dramatic 7× increase in the strain to fracture compared to fibers of similar draw ratio made from pure PMMA.

Atomic Force Microscopy of Self-Assembled Nanostructures of TPPS<sub>4</sub> on SAM Substrates

The adsorption of organic molecules on solid surfaces is one of the fundamental processes for the development of molecular-based nanodevices. Here we focus on the adsorption and ordering of the TPPS4-based J-aggregates on silicon and gold as well as on self-assembled monolayer (SAM) surfaces. The SAMs used for the experiments were based on the chemisorption of thiol containing compounds onto gold. Long ω-substituted alkanethiols are spontaneously assembled on gold to form highly ordered and densely packed layers with controllable chemical and physical properties. TPPS4 J-aggregates were dispersed on SAM surfaces, and on plain gold and silicon substrates for comparison. The dimensions of aggregates, measured by means of atomic force microscopy, varied depending on the type of substrate. Long stripe-like aggregates were flattened on the substrate surface, and the height and width of aggregates highly correlated with the polarity of surface groups. For example, the J-aggregates were narrower on hydrophobic substrates (with non-polar groups) and wider on hydrophilic substrates (with polar groups). These observations support the hypothesis, that TPPS4 forms .soft. cylindrical aggregates, that appear flattened on the substrate.