Rationalizing the SER spectra of bacteria

The SER spectra of riboflavin and FAD are identical and are resonance enhanced at 514 or 532 nm. Signals from FAD/ riboflavin dominated SER spectra whenever these compounds were present with proteins or bacteria. SER spectra of very different bacteria such as Pseudomonas. aeruginosa, Bacillu. subtilis and Geobacillus. stearothermophilus were dominated by signals from FAD, even when these bacteria were added to a preformed colloid. The SERS signal of FAD is greatly reduced at 785 nm, and SER spectra of bacteria excited at 785 nm are quite different than those collected at 514 or 532 nm. This supports the assignment of the peaks in the 514 nm SER spectra of bacteria to FAD rather to amino acids or N-acetylglucosamine. The SER spectra of certain mixes of adenine and FAD showed similar changes to those of bacteria when the excitation was changed from 514/532 nm to 785 nm. The ratio of colloid: bacteria was of critical important for obtaining good SER spectra, and the addition of sodium sulfate was also beneficial. Removal of EPS from bacteria before analysis facilitated interaction with the silver surface, and may be a useful step to include in identification protocols.

Influencing factors on kaolinite-potassium acetate intercalation complexes

This paper presents an immersion method for preparing the kaolinite-potassium acetate intercalation complexes. The effectiveness of intercalation and influencing factors were analysed and evaluated. The results show that the intercalation of kaolinite by potassium acetate is strongly related to crystallinity of kaolinite, concentration of intercalating agent solution, aging time and pH. The well-crystallized kaolinite is conducive to intercalation by potassium acetate. A higher concentration of intercalating agent (≥30%) can complete the intercalation in a short time (<12h), but at lower concentrations intercalation took significantly longer (≥144h). The weak alkaline condition of pH=10 proved to be the most suitable environment for the formation of intercalation complex. A good intercalated complex can be obtained at room temperature.

Sodium niobate adsorbents doped with tantalum (TaV) for the removal of bivalence radioactive ions in waste waters

Sodium niobates doped with different amount of tantalum (TaV) were prepared via thermal reaction process. It was found pure nanofibril and bar-like solids can be obtained when tantalum was introduced into the reaction system. For the well-crystallized fibril solids, the Na+ ions are difficult to be exchanged, and the radioactive ions such as Sr2+ and Ra2+ ions just deposit on the surface of the fibers during the sorption process, resulting in lower sorption capacity and distribution coefficients (Kd)`. However, the bar-like solids are poorly-crystallized and have lots of exchangeable Na+ ions. They are able to remove highly hazardous bivalent radioactive isotopes such as Sr2+ and Ra2+ ions. Even in the presence of lots of Na+ ions, they also have higher Kd. More importantly, such sorption finally intelligently triggers considerable collapse of the structure, resulting in the entrapment of the toxic bivalent cations permanently in the solids so that they can be safely disposed. This study highlights new opportunities for the preparation of Nb-based adsorbents to efficiently remove the toxic radioactive ions from contaminated water.

Influence of hydrocarbon contamination on clay soil microstructure

Microstructural (fabric, forces and composition) changes due to hydrocarbon contamination in a clay soil were studied using Scanning Electron Microscope (micro-fabric analysis), Atomic Force Microscope (forces measurement) and sedimentation bench test (particle size measurements). The non-polluted and polluted glacial till from north-eastern Poland (area of a fuel terminal) were used for the study. Electrostatic repelling forces for the polluted sample were much lower than for the non-polluted sample. In comparison to non-polluted sample, the polluted sample exhibited lower electric charge, attractive forces on approach and strong adhesion on retrieve. The results of the sedimentation tests indicate that clay particles form larger aggregates and settle out of the suspension rapidly in diesel oil. In non-polluted soil, the fabric is strongly aggregated – densely packed, dominate the face-to-face and edge-to-edge types of contacts, clay film tightly adheres to the surface of larger grains and interparticle pores are more common. In polluted soil, the clay matrix is less aggregated – loosely packed, dominate the edge-to-face types of contacts and inter-micro-aggregate pores are more frequent. Substantial differences were observed in the morphometric and geometrical parameters of pore space. The polluted soil micro-fabric proved to be more isotropic and less oriented than in non-polluted soil. The polluted soil, in which electrostatic forces were suppressed by hydrocarbon interaction, displays more open porosity and larger voids than non-polluted soil, which is characterized by occurrence of the strong electrostatic interaction between clay particles.

Formation of one-dimensional capped ZnO nanoparticle assemblies at the air/water interface

The self-assembling behavior and microscopic structure of zinc oxide nanoparticle Langmuir-Blodgett monolayer films were investigated for the case of zinc oxide nanoparticles coated with a hydrophobic layer of dodecanethiol. Evolution of nanoparticle film structure as a function of surface pressure (π) at the air-water interface was monitored in situ using Brewster’s angle microscopy, where it was determined that π=16 mN/m produced near-defect-free monolayer films. Transmission electron micrographs of drop-cast and Langmuir-Schaefer deposited films of the dodecanethiol-coated zinc oxide nanoparticles revealed that the nanoparticle preparation method yielded a microscopic structure that consisted of one-dimensional rodlike assemblies of nanoparticles with typical dimensions of 25 x 400 nm, encased in the organic dodecanethiol layer. These nanoparticle-containing rodlike micelles were aligned into ordered arrangements of parallel rods using the Langmuir-Blodgett technique.

Surface modification of alumina nanofibres for the selective adsorption of alachlor and imazaquin herbicides

The effective removal of pollutants using a thermally and chemically stable substrate that has controllable absorption properties is a goal of water treatment. In this study, the surfaces of thin alumina (γ-Al2O3) nanofibres were modified by the grafting either of two organosilane agents, 3-chloro-propyl-triethoxysilane (CPTES) and octyl-triethoxysilane (OTES). These modified materials were then trialed as absorbents for the removal of two herbicides, alachlor and imazaquin from water. The formation of organic groups during the functionalisation process established super hydrophobic sites on the surfaces of the nanofibres. This super hydrophobic group is a kind of protruding adsorption site which facilitates the intimate contact with the pollutants. OTES grafted substrate were shown to be more selective for alachlor while imazaquin selectivity is shown by the CPTES grafted substrate. Kinetics studies revealed that imazaquin was rapidly adsorbed on CPTES-modified surfaces. However, the adsorption of alachlor by OTES grafted surface was achieved more slowly.

Characterisation of organoclays and adsorption of p-nitrophenol : environmental application

Organoclays were synthesised through ion exchange of a single surfactant for sodium ions, and characterised by a range of method including X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The change in surface properties of montmorillonite and organoclays intercalated with the surfactant, tetradecyltrimethylammonium bromide (TDTMA) were determined using XRD through the change in basal spacing and the expansion occurred by the adsorbed p-nitrophenol. The changes of interlayer spacing were observed in TEM. In addition, the surface measurement such as specific surface area and pore volume was measured and calculated using BET method, this suggested the loaded surfactant is highly important to determine the sorption mechanism onto organoclays. The collected results of XPS provided the chemical composition of montmorillonite and organoclays, and the high-resolution XPS spectra offered the chemical states of prepared organoclays with binding energy. Using TGA and FT-IR, the confirmation of intercalated surfactant was investigated. The collected data from various techniques enable an understanding of the changes in structure and surface properties. This study is of importance to provide mechanisms for the adsorption of organic molecules, especially in contaminated environmental sites and polluted waters.