Several clay-organic complexes were synthesized by placing quaternary ammonium cations on smectite by cation exchange. They were then examined for their ability to adsorb phenol and several of its chlorinated congeners. The organic cations used were: hexadecylpyridinium (HDPY+), hexadecyltri-methyl ammonium (HDTMA+), trimethylphenyl ammonium (TMPA), and tetramethylammonium (TMA+). The complexes containing long-chain alkyl (hexadecyl) groups were the most hydrophobic and adsorbed the phenols from water in proportion to their hydrophobicities, which increase with chlorine addition (phenol < chlorophenol < dichloropohenol < trichlorophenol). With n-hexane as the solvent, different adsorption was found which depended on the type and degree of solvent interactions with the compound and the clay-organic complex. Thus, the amount of adsorption of these phenols on clay-organic complexes was dependent on the relative energies of adsorbent-adsorbate and adsorbate-solvent interactions.

A montmorillonite exchanged with large hydroxy-Al cations was thermally treated to convert the hydroxy cations to oxide pillars and to generate permanent microporosity in the interlayers. The pillared clay products were characterized by X-ray powder diffraction (XRD) and water-sorption measurements to delineate the effect of aging of the pillaring solutions, the methods of drying and concentration of clay-water suspensions, and the temperatures of calcination on micropore volumes. Although samples prepared at different conditions gave d(001) reflections of 17–17.5 Å, at least to 500°C, the concentrations of clay-water suspensions and the temperatures of calcination significantly changed the pore-size distribution and the volume of micropores present in the sample, as calculated from the water-sorption isotherms. A narrow pore-size distribution having little or no macroporosity or external surface condensation was observed in samples prepared by the addition of the pillaring solution directly to the clay (solid) without first making a clay-water suspension and calcining the sample at ≥400°C. About 87% of the total volume was found to be micropores of ≤14–17 Å in the sample calcined at 600°C. Aging the pillaring solution, however, did not influence either the water-sorption isotherms or the XRD patterns significantly under the conditions specified. Essentially the same results were obtained for samples prepared from both hydroxy-Al polymer (OH/Al = 2) and aluminum chlorohydrol (ACH) solutions.

Although alumina-pillared clays exhibited an extreme type-I isotherm (Langmuir type) for nitrogen adsorption, the sorption of water vapor gave an isotherm of unusual shape that fit neither a BET nor a Langmuir equation. This latter behavior has previously been attributed to a unique pore size and hydrophobicity and is apparently common to all pillared montmorillonite materials. The hydrophobicity of the pillared clay apparently developed on calcination by the migration of protons from the interlayers to the octahedral sheets, in which sites of cationic substitution (negative charge) were located. Protons migrated back to the interlayers by treatment with NH3, which subsequently converted to NH4+ in the interlayers. The exchange of the NH4+ by Ca2+ introduced hydrophilicity to the alumina-pillared clay, which was reflected both in the shape of the water isotherm (close to moderate Brunauer type I), the heat of sorption, and the total sorption capacity.

Several clay organic complexes were prepared by placing organic cations on the exchange sites of smectite clays and studied as sorbents for pentachlorophenol (PCP). The organic cations used ranged from very hydrophobic in nature (e.g., dioctadecyldimethyl+ (DODMA+)- and hexadecyltrimethyl+ (HDTMA+)-ammonium) to those having minimal hydrophobic properties, such as tetramethylammonium+ (TMA+). In general, the more hydrophobic the cation on the smectite the greater the uptake of PCP from water. For the very hydrophobic clays (DODMA+- and HDTMA+-smectite) the uptake of PCP was via non-polar interactions between the alkyl (e.g., -C18) groups on the organic cation and PCP. In a mechanistic sense, this interaction appeared to be similar to a partitioning process between water and the organic phase of the clay-organic complex. The organic phases of DODMA+-smectite were about 10 times more effective than the organic matter of natural sediments for removing PCP from water. For those organo-clays containing small organic cations (e.g., TMA+), the organic phase consisted of separate small organic moieties, such as the methyl group. This phase did not act as an effective partitioning medium despite a significant carbon content, and very little PCP was taken up. Results from this study suggest the possibility of treating soils and subsurface materials with large hydrophobic organic cations to enhance the sorptive properties of these natural materials.

Contact angles of glycerol and diiodomethane drops were measured on the surface of kaolin pellets covered with different amounts of dodecylamine chloride (DDACl) to as much as one monolayer. For a glycerol drop, the contact angle changed from 25.7° (bare surface) to 45.4° for the surface precoated with 0.125 monolayer of DDACl, but remained nearly constant above this level up to one monolayer. For a diiodomethane drop, the contact angle changed from 28.6° (bare surface) to 58.1° for one DDACl monolayer precoating. Using these contact angles and a modified Young equation, the dispersive and nondispersive components of the surface free energy of DDACl-covered kaolin were calculated. These data showed that in the extreme case (one monolayer) the dispersive component was reduced by the DDACl from ∼36 mJ/m2 (bare surface) to 25.4 mJ/m2, i.e., the value characteristic for paraffin (25.5 mJ/m2); however, the nondispersive component was not reduced to zero. A minimum value (15.83 mJ/m2) was determined for the sample covered with 0.125 DDACl monolayer (calculated), and a slight increase in the nondispersive component was observed for greater coverages. Such a change of the nondispersive component suggests that, at higher coverages, some adsorbed DDACl molecules were oriented with their polar ends off the surface. Based on the values of the γsfd and γsfn, the work of water spreading was calculated. This work was positive for the bare surface (32.8 mJ/m2) and methanol-treated (36.5 mJ/m2) kaolin surface, but negative for 0.125 DDACl monolayer precoating (-31.1 mJ/m2). It remained essentially unchanged for higher coverages. These data mean that bare and methanol-treated kaolinite surfaces were hydrophilic and that DDACl-treated surfaces were hydrophobic.

Landfill leachate is one of the most difficult effluents with which to deal from an environmental perspective because of its concentration and complex composition, including refractory and toxic components such as heavy metals or xenobiotic organic compounds. The objective of the present study was to use organically modified bentonite (OMB) to dispose of landfill leachate >10 y old. The OMB was synthesized using a new method, which removed four steps (filtering, washing, drying, and grinding) from the traditional process. After treatment using OMB, the chemical oxygen demand concentration (COD concentration, an index of the organic pollutants in the landfill leachate, was determined using the potassium dichromate method) of the landfill leachate sample decreased from 2400 to 245 mg/L in 5 h, i.e. the organic pollutants reduction efficiency was as high as 90%. Gas chromatography-mass spectrometry results indicated that most of the organic compounds were removed during the process. The modified and unmodified bentonite contained in the OMB deal with the hydrophobic and hydrophilic organic pollutants, respectively, resulting in significant degradation of the leachate. The study results have provided a new cost-effective method for treatment of landfill leachate.

Organo-montmorillonite (OMnt) has wide applications in paints, clay-polymer nanocomposites, biomaterials, etc. In most cases, the dispersibility and swellability of OMnt dictate the performance of OMnt in the target products. Previous studies have revealed that the properties can be improved when multiple organic species are co-introduced into the interlayer space of montmorillonite (Mnt). In the present study, single surfactant erucylamide (EA), dual-surfactants cetyltrimethyl ammonium bromide (CTAB) and octadecyltrimethyl ammonium chloride (OTAC), and ternary-surfactants EA, CTAB, and OTAC were co-introduced into Mnt by solution intercalation. The resulting OMnts were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry-differential thermogravimetry (TG-DTG), water contact-angle tests, scanning electronic microscopy (SEM), laser particle-size analysis, and swelling indices. Mnt co-modified by ternary CTAB, OTAC, and EA led to a large d001 value (4.20 nm), surface hydrophobicity with a contact angle of 95.6°, swellability (50 mL/g) with small average particle sizes (2.1−2.8 μm) in xylene, and >99% of the OMnt particles were kept as <5 μm in deionized water. The formation of EA-modified-Mnt was proposed according to hydrophobic affinity, hydrogen bonding, and van der Waals forces. The nanoplatelets of the CTA+, OTA+, and EA co-modified OMnts in xylene were assembled into a house-of-cards structure by face-to-edge and edge-to-edge associations. The electrostatic attractions, electrostatic and steric repulsions, and hydrophobic interactions were responsible for the good dispersibility of OMnt in xylene. The ternary surfactant co-modified OMnt with high dispersion and swellability will make OMnt better suited for real-world applications.

Modification of the surfaces of montmorillonite (Mnt) by organic molecules is an effective method for improving their affinity toward non-aqueous substances, and has resulted in extensive industrial applications as rheological control agents, drilling fluids, and other functional materials used in applications ranging from environmental remediation to coatings. The present study reviewed recent progress in organo-modification of Mnt, and provides state-of-the-art insights into proposed modification mechanisms and the peculiar functionalities of the resulting organo-montmorillonite (OMnt). Several routes have been employed to modify Mnt, including ion exchange with organic ions, surface adsorption, and grafting of organics. Commonly used organic modifiers include cationic, anionic, zwitterionic, non-ionic, and polymeric species. Organo-modification is driven by multiple interactions: van der Waals forces, cation exchange, electrostatic interaction, hydrogen bonds, and ion–dipole interaction. OMnt, in general, exhibits synergistic and/or antagonistic effects when used in oil-based drilling fluids, environmental remediation, or layered silicate/polymer nanocomposites. The detailed mechanisms of non-ionic and zwitterionic modification of Mnt remain unclear. This literature survey suggests that future work should emphasize deeper understanding of interactions between the Mnt and the organic modifiers, and meanwhile expand the applications of OMnt into catalysis, drug carriers, and the biomedical field.

Herein, we report an efficient method to produce silver (Ag) nanoparticle-decorated silicon (Si) nanowire (NW) arrays on a pyramidal Si (P-Si) substrate by using a pure chemical method and rapid thermal annealing in different atmospheres. A metal-assisted chemical etching technique was used to produce vertical Si NW arrays on pyramidal Si. The etching was observed to be heavily dependent on the substrate type. On planar Si (100), the etching was observed to occur in a uniform manner. However, the etching rate was observed to increase from the top to the base of the Si pyramid. The Si NWs produced from P-Si have zig-zag sidewalls as observed from high-resolution transmission electron microscopy images. However, for the same oxidant concentration, Si NWs produced from planar Si (100) consist of straight and amorphous sidewalls. Local variation of oxidant concentration is responsible for the formation of different sidewalls. The substrates are both surface-enhanced Raman scattering (SERS) active and hydrophobic. The hydrophobicity is due to the dual scale of roughness contributed to by both pyramidal and NW structures. Finite-difference time-domain simulation shows that the gap between two Ag spheres and also the gap between Si NWs and Ag spheres contributed to SERS enhancement.

The changes of adsorption properties of uncalcined Al-pillared montmorillonite were studied. A soda-activated bentonite from Slovakia was reacted with polymeric hydroxoaluminium salt solutions. During storagein air at room temperature for three years, the basal spacing decreased by 0.15–0.2 nm; the specific surface area was reduced by 80% and the total pore volume by 40–60%. Adsorption experiments from ethanol-cyclohexane mixtures revealed the decreasing adsorption capacity and the increasing hydrophobicity. The changing surface character was also evident in the decrease in enthalpy of immersion in ethanol from 65.3 J/g to 8.3 J/g (sample B) and from 37.8 J/g to 5.2 J/g (sample C). The alteration probably arises from gradual formation of gibbsite-like interlayers and the redistribution of charges.

Relationships between soil sorption normalized to organic carbon (Koc) and molecular properties of 71 herbicides were examined. The Koc values were obtained from the literature. Various molecular properties were calculated by quantum mechanical methods using molecular modeling software. The quantitative structure activity relationship (QSAR) models based on four molecular properties, van der Waals volume (VDWv), molecular polarizability (α), dipole moment (μ), and energy of highest occupied molecular orbital (eHOMO), together accounted for 70% of the variation in Koc. Herbicides were broadly divided into six families based on structural similarities, and separate equations were established for each group. The three descriptors, VDWv, α, and μ, along with either energy of lowest unoccupied molecular orbital (eLUMO), or electrophilic superdelocalizability (SE), or eHOMO appeared to be determinants and accounted for 82 to 99% of the variation in Koc. Applicability of these models was tested for one herbicide analogue and 10 metabolites. The QSAR models appear to be specific to structurally similar chemicals. The QSAR models could be developed to predict Koc of structurally similar compounds even before they are synthesized or for some of the metabolites of existing herbicides. Models of this type can also be developed to create priority lists for testing, so that time, money, and efforts can be focused on the potentially most hazardous chemicals.

The relationship between hydrophobicity and the protective effect of whey protein hydrolysates (WPHs) against oxidative stress was studied. Whey protein was first hydrolysed by pepsin and trypsin to obtain WPHs. After absorbed by macroporous adsorption resin DA201-C, three fractions named as M20, M40, and M60 were eluted by various concentrations of ethanol. The hydrophobicity showed a trend of increase from M20 to M60. Antioxidant ability test in vitro indicated that all the three components of WPHs displayed reasonably good antioxidant ability. Moreover, with the increase of hydrophobicity, antioxidant ability of WPHs improved significantly. Then rat pheochromocytoma line 12 (PC12) cells oxidative model was built to evaluate the suppression of oxidative stress of three components on PC12 cells induced by H2O2. Morphological alterations, cell viability, apoptosis rate, and intracellular antioxidase system tests all indicated that WPHs exert significant protection on PC cells against H2O2-induced damage. Among them, M60 had the highest protective effect by increasing 19·3% cell survival and reducing 28·6% cell apoptosis. These results suggested hydrophobicity of WPHs was contributing to the antioxidant ability and the protective effect against oxidative damage.

Aspergillus fumigatus has become a leading cause of fungal morbidity and mortality, especially in immunocompromised patients. This fungus is able to grow as a multicellular community and produce a hydrophobic extracellular matrix (ECM), mainly composed of galactomannan and α-1,3 glucans, to protect itself from host defenses and antimicrobial drugs. This matrix envelops the fungus hyphae, binding them into a contiguous sheath on the colony surface, forming a biofilm and increasing the fungal resistance to adverse environmental factors. Adherence to host cells and resistance to physical removal play a key role in fungal colonization and invasion of the host and in a wide range of infections. Here we show that, by using atomic force spectroscopy, it is possible to exploit the peculiar hydrophobicity of the biofilm components (i.e., cell walls, ECM) to detect the biofilm spread, its growth, and lysis on rough surfaces. By means of this approach, we demonstrate that alginate lyase, an enzyme known to reduce negatively charged alginate levels in microbial biofilms, reduces the biofilm adhesion forces suggesting a loss of ECM from the biofilm, which could be used to enhance pharmacological treatments.

Whey protein hydrolysates were generated at different total solids (TS) levels (50–300 g/l) using the commercially available proteolytic preparation Debitrase™ HYW20, while enzyme to substrate ratio, pH and temperature were maintained constant. Hydrolysis proceeded at a faster rate at lower TS reaching a degree of hydrolysis (DH) of 16·6% at 300 g TS/l, compared with a DH of 22·7% at 50 g TS/l after 6 h hydrolysis. The slower breakdown of intact whey proteins at high TS was quantified by gel-permeation HPLC. Reversed-phase (RP) HPLC of hydrolysate samples of equivalent DH (~15%) generated at different TS levels indicated that certain hydrophobic peptide peaks were present at higher levels in hydrolysates generated at low TS. Sensory evaluation showed that hydrolysates with equivalent DH values were significantly (P<0·0005) less bitter when generated at 300 g TS/l (mean bitterness score=25·4%) than hydrolysates generated at 50 g TS/l (mean bitterness score=39·9%). A specific hydrophobic peptide peak present at higher concentrations in hydrolysates generated at low TS was isolated and identified as β-lactoglobulin f(43–57), a fragment having the physical and chemical characteristics of a bitter peptide.

The spatial organisation of soils is crucially important in affecting belowground function, and the associated delivery of ecosystem services. Fungi constitute an important part of the soil biomass. As well as playing key roles in nutrient cycling and biotic interactions, they are also intimately involved in soil structural dynamics. Fungi mediate the formation of soil structure at a variety of spatial scales via charge, adhesive and enmeshment mechanisms. They also produce large quantities of hydrophobic compounds that affect water infiltration properties of soils. Fungi can also destroy soil structure via decomposition of organic matter that affects soil aggregation. In turn, soil structure affects fungi. The filamentous growth-form of fungi is a very efficient spacefilling structure well adapted for life in a spatially heterogeneous environment such as soil, but the labyrinthine pore network ultimately regulates how fungal mycelia grow through and function within the soil. The distribution of water within soils plays a crucial role in governing fungal development and activity, as does the spatial distribution of nutrient resources. This article reviews the continual interplay that occurs between soil structure and fungi, and discusses how self-organisation mechanisms may operate in the soil system.