Influence Of Solution Chemistry Research Articles

Recovery of volatile fatty acids using forward osmosis: Influence of solution chemistry, temperature, and membrane orientation.

This study investigates the suitability of forward osmosis (FO) for recovery of volatile fatty acids (VFAs) from anaerobic digesters (ADs) and identifies the conditions favorable for commercially viable maximum recovery of VFAs. The recovery efficiency of VFAs is evaluated using a polyamide (PA)-based thin-film composite (TFC) membrane. The pH (3, 5, 7, and 9), temperature (20°C and 40°C), and membrane orientation (active-layer [AL]-facing FS and AL facingDS) were changed, and water flux, reverse salt flux (RSF), rejection rate, and concentration factor (CF) were evaluated for five VFAs. The water flux and RSF were higher at a higher pH, temperature and in AL-DS mode. A low rejection rate of 23-36% and a CF of 0.20-1.90 were observed at a pH below the pKa due to the solubility of molecular VFAs, while rejection rates was 80-97% and concentration increase by 1 to 4.8-fold at a pH above the pKa values were achieved due to deprotonation of VFAs and changes in membrane surface charges. With an equal increase in temperature of FS and DS from 20 to 40°C, the rejection rate decreased by almost 20%. While with a transmembrane temperature change, a decrease in rejection rate of 20% was observed compared with baseline experiments due to decreases in viscosity and high diffusivity. In AL-DS mode, VFAs were rejected at a rate of almost 20% lower than that in AL-FS mode due to internal concentration polarization and membrane properties. These findings provide useful information on the factors that can influence optimal recovery rates of VFAs.

Recovery of Volatile Fatty Acids Using Forward Osmosis: Influence of Solution Chemistry, Temperature, and Membrane Orientation

Recovery of Volatile Fatty Acids Using Forward Osmosis: Influence of Solution Chemistry, Temperature, and Membrane Orientation

Effect of solution chemistry on aqueous As(III) removal by titanium salts coagulation.

Solution chemistry is of great importance to the removal of arsenic by coagulation through influencing the speciation of arsenic, the in situ precipitation of metal salts coupled with the adsorption and coprecipitation behavior of arsenic during coagulation. While the researches on the influence of solution chemistry in As(III) removal by titanium salts, a promising candidate for drinking water treatment was still deficient. Batch tests were performed to evaluate the removal of As(III) by titanium salts coagulation under solution chemistry influences. The results indicated that As(III) removal by Ti(SO4)2 and TiCl4 increased first and then decreased with the rising of solution pH from 4 to 10. TiCl4 preformed better in As(III) removal than Ti(SO4)2 at pH4-8, but the opposite trends were observed at pH9-10. XPS analysis indicated that the involvement of surface hydroxyl groups was primarily responsible for As(III) adsorption on Ti(IV) precipitates. As(III) removal was inhibited in the presence of SO42- mainly by competitive adsorption, especially at elevated SO42- concentration under acidic and alkaline conditions. F- exerted a greater suppressive effect than SO42- via indirectly hindering Ti(IV) precipitate formation, and through direct competitive adsorption with H3AsO3, the inhibitive effect increased as F- concentration increased and depended highly on solution pH. As(III) removal was promoted by co-existing Fe(II) primarily through the facilitation of Ti(IV) precipitation, especially under neutral and alkaline conditions, while it was inhibited to a different extent by the presence of high-concentration Mn(II) possibly via competitive adsorption. The presence of Ca2+ and Mg2+ enhanced the removal of As(III), but the positive effect did not increase as ionic concentration elevated.

Influence of solution chemistry on the solubility, crystallisability and nucleation behaviour of eicosane in toluene : acetone mixed-solvents

Compositionally dependent solution structure is found to influence the solubility, crystallisability and nucleation mechanism of eicosane when crystallising from toluene : acetone mixed-solvent solutions.

Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: effects of pH and organic ligands

Advancing the understanding of stability behavior and aggregation mechanisms of quantum dot (QD) nanoparticles in natural systems is fundamental to elucidate their fate and transport, bioavailability, environmental toxicity, and subsequent risks to environmental and public health. This study investigates the aggregation kinetics and colloidal stability of QDs as a function of pH and organic ligands—acetate, oxalate, and citrate. Results indicated an influence of solution chemistry upon both the aggregation kinetics and colloidal stability of QDs. The zeta potential of QDs, with a point of zero charge (pHPZC) between pH 1.5 and 3.5, decreased (from positive to negative) with increasing solution pH. The diameter of QD aggregates was ~500 nm in the region of pHPZC and decreased with pH when pH > pHPZC to 40–50 nm. Organic ligands enhanced the negative zeta potentials of QDs at pH = 1.5 and pH = 3.5. The impact of ligands on the levels and rates of aggregation was pH dependent; furthermore, the presence of ligands increased the diameters of all QD nanoaggregates at pH 3.5 (e.g., 817 nm for 0.001 M citrate). QDs and organic ligand-QD nanoparticle complexes remained stable across pH values 5–9. In terms of environmental and toxicological risk assessments, results revealed that QDs and organic ligand-QD nanoparticle complexes remain stable across a significant range of pH values (5–9), indicating that this stability behavior could enhance the mobility, transport, and residence time of QDs in terrestrial and aqueous environments, and facilitate the bioavailability of QDs, therefore augmenting the adverse effects of QDs in the environment.

Adsorption of Human Serum Albumin on Graphene Oxide: Implications for Protein Corona Formation and Conformation.

The influence of solution chemistry on the adsorption of human serum albumin (HSA) proteins on graphene oxide (GO) was investigated through batch adsorption experiments and the use of a quartz crystal microbalance with dissipation (QCM-D). The conformation of HSA layers on GO was also examined with the QCM-D. Our results show that an increase in ionic strength under neutral pH conditions resulted in stronger binding between HSA and GO, as well as more compact HSA layers on GO, emphasizing the key role of electrostatic interactions in controlling HSA-GO interactions. Calcium ions also facilitated HSA adsorption likely through charge neutralization and bridging effect. At physiological ionic strength conditions (150 mM), maximum HSA adsorption was observed at the isoelectric point of HSA (4.7). Under acidic conditions, the adsorption of HSA on GO led to the formation of protein layers with a high degree of fluidity due to the extended conformation of HSA. Finally, the attachment of GO to a supported lipid bilayer that was composed of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine, a model for cell membranes, was reduced in the presence of protein coronas. This reduction in GO attachment was influenced by the conformation of the protein coronas on GO.

Influence of solution chemistry on the boron content in inorganic calcite grown in artificial seawater

The ratio of boron to calcium (B/Ca) in marine biogenic carbonates has been proposed as a proxy for properties of seawater carbonate chemistry. Applying this proxy to planktic foraminifera residing in the surface seawater largely in equilibrium with the atmosphere may provide a valuable handle on past atmospheric CO2 concentrations. However, precise controls on B/Ca in planktic foraminifera remain enigmatic because it has been shown to depend on multiple physicochemical seawater properties. To help establish a firm inorganic basis for interpreting the B/Ca records, we examined the effect of a suite of chemical parameters ([Ca2+], pH, [DIC], salinity and [PO43−]) on B/Ca in inorganic calcite precipitated in artificial seawater. These parameters were primarily varied individually while keeping all others constant, but we also tested the influence of pH and [DIC] at a constant calcite precipitation rate (R) by concurrent [Ca2+] adjustments. In the simple [Ca2+], pH and [DIC] experiments, both R and B/Ca increased with these parameters. In the pH–[Ca2+] and [DIC]–[Ca2+] experiments at constant R, on the other hand, B/Ca was invariant at different pH and decreased with [DIC], respectively. These patterns agree with the behavior of solution [BTotal/DIC] ratio such that, at a fixed [BTotal], it is independent of pH but decreases with [DIC]. Based on these results, R and [BTotal/DIC] ratio appear to be the primary controls on B/Ca in inorganic calcite, suggesting that both B(OH)4− and B(OH)3 are possibly involved in B incorporation. Moreover, B/Ca modestly increased with salinity and [PO43−]. Inorganic calcite precipitated at higher R and in the presence of oxyanions such as SO42− and PO43− in growth solutions often undergoes surface roughening due to formation of crystallographic defects, vacancies and, occasionally, amorphous/hydrous CaCO3. These non-lattice sites may provide additional space for B, particularly B(OH)3. Consequently, besides the macroscopic influence of R and bulk solution chemistry, molecular-scale processes associated with calcite nucleation can be an important consideration for B incorporation, especially in complex ionic solutions. Lastly, the covariance of B/Ca with [DIC] and salinity observed here qualitatively agrees with those in planktic foraminifers. It follows that their impact on foraminiferal B/Ca is partly inorganically driven, which may explain why the effect is evident across different species.

Influence of solution chemistry on the inactivation of particle-associated viruses by UV irradiation

MS2 inactivation by UV irradiance was investigated with the focus on how the disinfection efficacy is influenced by bacteriophage MS2 aggregation and adsorption to particles in solutions with different compositions. Kaolinite and Microcystis aeruginosa were used as model inorganic and organic particles, respectively. In the absence of model particles, MS2 aggregates formed in either 1mM NaCl at pH=3 or 50–200mM ionic strength CaCl2 solutions at pH=7 led to a decrease in the MS2 inactivation efficacy because the virions located inside the aggregate were protected from the UV irradiation. In the presence of kaolinite and Microcystis aeruginosa, MS2 adsorbed onto the particles in either 1mM NaCl at pH=3 or 50–200mM CaCl2 solutions at pH=7. In contrast to MS2 aggregates formed without the presence of particles, more MS2 virions adsorbed on these particles were exposed to UV irradiation to allow an increase in MS2 inactivation. In either 1mM NaCl at pH from 4 to 8 or 2–200mM NaCl solutions at pH=7, the absence of MS2 aggregation and adsorption onto the model particles explained why MS2 inactivation was not influenced by pH, ionic strength, and the presence of model particles in these conditions. The influence of virus adsorption and aggregation on the UV disinfection efficiency found in this research suggests the necessity of accounting for particles and cation composition in virus inactivation for drinking water.

Effect of hydrodynamic conditions of electrodeposition process on microstructure and functional properties of Ni-W/ZrO2 nanocomposites

Ni-W/ZrO2 nanocomposite coatings were electrodeposited in a system with a rotating disk electrode (RDE), which ensures constant and controlled hydrodynamic conditions. The influence of solution chemistry on the co-discharge kinetics of W(VI) and Ni(II) species from citrate solution have been studied. It was found that in the range of less negative cathode potentials both partial processes (deposition of tungsten and nickel) are controlled by charge transfer reaction, whereas with further increase of the cathodic polarisation the W(VI) electroreduction process becomes diffusion controlled. The addition of ceramic particles to the alloy plating bath changes cathodic polarisation, and thus chemical composition of the deposited Ni-W matrix. The effect of rotating rate of the steel RDE on the chemical composition and homogeneity of embedded zirconia nanoparticles in the Ni-W alloy matrix was investigated. The optimal hydrodynamic conditions for electrodeposition of homogeneous Ni-W/ZrO2 nanocomposites with enhanced functional properties were determined based on microstructural (morphology, phase composition, crystallite size), micromechanical (microhardness, Young's modulus), and tribological (wear resistant, friction coefficient) properties. The maximum incorporation of ZrO2 nanoparticles (about 4.5wt%) was achieved at the disk cathode rotation speed of 300rpm. Ni-W/ZrO2 coatings obtained in such hydrodynamic conditions were characterized by the highest hardness (9.1GPa) and Young's modulus (205GPa), but due to the significant brittleness revealed the lowest wear resistance.

Influence of Solution Chemistry and Soft Protein Coronas on the Interactions of Silver Nanoparticles with Model Biological Membranes.

The influence of solution chemistry and soft protein coronas on the interactions between citrate-coated silver nanoparticles (AgNPs) and model biological membranes was investigated by assembling supported lipid bilayers (SLBs) composed of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) on silica crystal sensors in a quartz crystal microbalance with dissipation monitoring (QCM-D). Our results show that the deposition rates of AgNPs on unmodified silica surfaces increased with increasing electrolyte concentrations under neutral pH conditions. Similar trends were observed when AgNPs were deposited on SLBs, hence indicating that the deposition of AgNPs on model cell membranes was controlled by electrostatic interactions. In the presence of human serum albumin (HSA) proteins at both pH 7 and pH 2, the colloidal stability of AgNPs was considerably enhanced due to the formation of HSA soft coronas surrounding the nanoparticles. At pH 7, the deposition of AgNPs on SLBs was suppressed in the presence of HSA due to steric repulsion between HSA-modified AgNPs and SLBs. In contrast, pronounced deposition of HSA-modified AgNPs on SLBs was observed at pH 2. This observation was attributed to the reduction of electrostatic repulsion as well as conformation changes of adsorbed HSA under low pH conditions, resulting in the decrease of steric repulsion between AgNPs and SLBs.

Sorption of Phenanthrene onto Diatomite under the Influences of Solution Chemistry: A Study of Linear Sorption based on Maximal Information Coefficient

The effectiveness of diatomite as the low-cost sorbent in the removal of polycyclic aromatic hydrocarbons (PAHs) from water was investigated. The effects of ionic strength, pH, dissolved organic matter, and temperature on sorption of phenanthrene (PHE) to two types of diatomite clay (DM 545 and DM 577) were systematically studied. The maximal information coefficient (MIC) was calculated to reveal the linearity/nonlinearity in the sorption process under the influences of aqueous chemistry parameters. Results indicated that the solution parameters played an essential role in the PHE sorption behavior at the aqueous/diatomite interface. The sorption isotherms of PHE on diatomite at different temperatures could well fit the Freundlich equation. Thermodynamic studies confirmed that the sorption behavior of PHE on diatomite was spontaneous and exothermic from 283 to 303 K. The calculation of MIC revealed the linear relationship between the aqueous PAHs and sorbed PAHs at the water/diatomite interface. The results can be used to support the potential application of diatomite for the treatment of PAH-contaminated effluents.

Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

“Clumped-isotope” thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13C and 18O isotopes bound to each other within carbonate minerals in 13C18O16O22− groups (heavy isotope “clumps”). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals.We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13C–18O bond ordering (Δ47) and δ18O of CO32− and HCO3− molecules at a 25°C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13C–18O bond abundances and δ18O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ47 and δ18O compositions of CO32− and HCO3− ions are significantly different from each other. Experiments constrain the Δ47–δ18O slope for a pH effect (0.011±0.001; 12⩾pH⩾7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ47–δ18O slope of 0.011±0.003, consistent with a pH effect.Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ47 and δ18O are intermediate between HCO3− and CO32−. We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50°C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many natural systems. The two types of experiments yielded statistically indistinguishable results, and these measurements yield a calibration that overlaps with our theoretical predictions for calcite at equilibrium. The slow-growing Devils Hole calcite exhibits Δ47 and δ18O values consistent with lattice equilibrium.Factors influencing DIC speciation (pH, salinity) and the timescale for DIC equilibration, as well as reactions at the mineral–solution interface, have the potential to influence clumped-isotope signatures and the δ18O of carbonate minerals. In fast-growing carbonate minerals, solution chemistry may be an important factor, particularly over extremes of pH and salinity. If a crystal grows too rapidly to reach an internal equilibrium (i.e., achieve the value for the temperature-dependent mineral lattice equilibrium), it may record the clumped-isotope signature of a DIC species (e.g., the temperature-dependent equilibrium of HCO3−) or a mixture of DIC species, and hence record a disequilibrium mineral composition. For extremely slow-growing crystals, and for rapidly-grown samples grown at a pH where HCO3− dominates the DIC pool at equilibrium, effects of solution chemistry are likely to be relatively small or negligible. In summary, growth environment, solution chemistry, surface equilibria, and precipitation rate may all play a role in dictating whether a crystal achieves equilibrium or disequilibrium clumped-isotope signatures.

Ciprofloxacin adsorption on graphene and granular activated carbon: kinetics, isotherms, and effects of solution chemistry

Ciprofloxacin (CIP) is a commonly used antibiotic and widely detected in wastewaters and farmlands nowadays. This study evaluated the efficacy of next-generation adsorbent (graphene) and conventional adsorbent (granular activated carbon, GAC) for CIP removal. Batch experiments and characterization tests were conducted to investigate the adsorption kinetics, equilibrium isotherms, thermodynamic properties, and the influences of solution chemistry (pH, ionic strength, natural organic matter (NOM), and water sources). Compared to GAC, graphene showed significantly faster adsorption and reached equilibrium within 3 min, confirming the rapid access of CIP into the macroporous network of high surface area of graphene as revealed by the Brunner–Emmet–Teller measurements analysis. The kinetics was better described by a pseudo-second-order model, suggesting the importance of the initial CIP concentration related to surface site availability of graphene. The adsorption isotherm on graphene followed Langmuir model with a maximum adsorption capacity of 323 mg/g, which was higher than other reported carbonaceous adsorbents. The CIP adsorption was thermodynamically favourable on graphene and primarily occurred through π − π interaction, according to the FTIR spectroscopy. While the adsorption capacity of graphene decreased with increasing solution pH due to the speciation change of CIP, the adverse effects of ionic strength (0.01–0.5 mol L−1), presence of NOM (5 mg L−1), and different water sources (river water or drinking water) were less significant on graphene than GAC. These results indicated that graphene can serve as an alternative adsorbent for CIP removal in commonly encountered field conditions, if proper separation and recovery is available in place.

Bactericidal mechanism of BiOI–AgI under visible light irradiation

The BiOI–AgI nanocomposites were synthesized by a solvothermal process, followed by an in-situ ion exchange reaction. The disinfection activities of BiOI–AgI on model cell type, Gram-negative Escherichia coli (E. coli), were examined under visible light irradiation conditions. BiOI–AgI could completely inactivate 5×107CFUmL−1E. coli cells in 18min under visible light irradiation (λ⩾400nm). The bactericidal mechanisms involved in this photocatalytic disinfection process were systematically investigated. Ag+ ions released from the nanocomposites did not contribute to the bactericidal activity of BiOI–AgI. Active species including h+, O2−, e−, and H2O2 generated by BiOI–AgI played important roles in the inactivation of bacteria. Direct contact of bacterial cells and nanoparticles was found to be essential for the disinfection processes. The destruction of cell membrane and emission of cytoplasm directly inactivated the cells. The influence of solution chemistry (pH and ionic strength) on disinfection process was also estimated. Low pH condition was found to be favorable for the inactivation process. High disinfection efficiencies were achieved at a wide range of solution ionic strength (0–1000mM). The reusability of BiOI–AgI were also determined. BiOI–AgI exhibited strong antibacterial activity toward E. coli even in five consecutively reused cycles. This study indicated that the fabricated BiOI–AgI could be potentially utilized to disinfect bacteria in water (even with high salinity).

The influence of solution chemistry on the morphology of ammonium dinitramide crystals

The influence of solutions on ammonium dinitramide (ADN) crystal morphology was investigated using a combined experimental and molecular dynamics simulation approach. Scanning electron microscopy showed that ADN recrystallized from acetone, propanol, dimethyl sulfoxide (DMSO), and ethanol exhibited a lamellar structure, in contrast to the polyhedron structure obtained with isopropanol/NaF. X-ray diffraction analysis revealed that ADN crystals are mainly composed of six crystal faces (010, 011, 110, 100, 121, 031), and acetone, propanol, DMSO, and ethanol result in crystals in which growth at face (100) dominated. Molecular dynamics simulations indicated that the accessible surfaces and lattice energy (Elatt) vary with the crystal faces. The interaction energy between solutions and crystal faces (Eint) was dependent on both crystal faces and solution components, as was the attachment energy (Eatt). The relative standard deviation Rdev′ of the growth rate of the crystal faces was ordered as follows: acetone (0.117) > propanol (0.098) > DMSO (0.094) > ethanol (0.087) > isopropanol (0.078) > isopropanol/NaF (0.073). A larger Rdev′ resulted in a lamellar structure, while a smaller Rdev′ gave more homogeneous growth rates that resulted in polyhedron crystals.

Retention and transport of an anaerobic trichloroethene dechlorinating microbial culture in anaerobic porous media

The influence of solution chemistry on microbial transport was examined using the strictly anaerobic trichloroethene (TCE) bioaugmentation culture KB-1®. A column was employed to determine transport behaviors and deposition kinetics of three distinct functional species in KB-1®, Dehalococcoides, Geobacter, and Methanomethylovorans, over a range of ionic strengths under a well-controlled anaerobic condition. A quantitative polymerase chain reaction (qPCR) was utilized to enumerate cell concentration and complementary techniques were implemented to evaluate cell surface electrokinetic potentials. Solution chemistry was found to positively affect the deposition rates, which was consistent with calculated Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energies. Retained microbial profiles showed spatially constant colloid deposition rate coefficients, in agreement with classical colloid filtration theory (CFT). It was interesting to note that the three KB-1® species displayed similar transport and retention behaviors under the defined experimental conditions despite their different cell electrokinetic properties. A deeper analysis of cell characteristics showed that factors, such as cell size and shape, concentration, and motility were involved in determining adhesion behavior.

Influence of Solution Chemistry on the Selective Adsorption of Uranium and Thorium onto Activated Carbon

Radioactive element separation is of particular interest in nuclear technology. For this purpose, batch experiments were carried out in order to find the best separation conditions of uranium [U(VI)] and thorium [Th(IV)] from aqueous solution using rice straw activated carbon. The influence of pH and contact time on selective adsorption of U(VI) and Th(IV) was investigated. The results indicate that the velocity of these species from liquid phase to the surface of carbon is rapid enough. The reaction rate was fast, requiring only a short contact time of 40 min for U(VI) and 100 min for Th(IV). Sorption reaches maximum at pH 4 for Th(IV) and at pH 5.5 for U(VI). U(VI) and Th(IV) can be separated by the judicious controlling of pH and contact time. They can be separated from each other at pH 4 with different contact time [Th(IV) at lower time and U(VI) at 200 min]. Studies were conducted to examine the change in the adsorption behavior of U(VI) and Th(IV) on adsorbent as a function of employing different complexing agents of mineral and organic acids that are important in industrial and environmental processes, including hydrochloric, nitric, acetic, sulfuric, and phosphoric acids at 0.1M concentration. Acetic acid enhances U(VI) and Th(IV) uptake compared to mineral acids. These procedures may be useful in the separation of U(VI) and Th(IV) from natural or industrial samples containing these elements.

Influence of solution chemistry on heavy metals removal by bioadsorbent tea waste modified by poly (vinyl alcohol)

AbstractIn this study, the macroporous spherical composite biomaterials, Poly(vinyl alcohol)/teawaste (PVA/TW), were prepared and investigated for their potential to remove Pb2+, Hg2+, and Cu2+ from aqueous solution. Investigations showed that adsorption capacity of Hg2+ by PVA/TW bead was much higher than that of Pb2+ and Cu2+, while adsorption rate of Pb2+ was fastest. The experimental data obtained for Pb2+-PVA/TW, Hg2+-PVA/TW, and Cu2+-PVA/TW at different solution temperatures indicate a monolayer type biosorption, which explains why the Langmuir isotherm accurately represents the experimental data obtained in this study. The Langmuir maximum biosorption capacities of Pb2+, Hg2+, and Cu2+ onto PVA/TW were 81.56, 175.68, and 49.08 mg/g at 298 K, respectively, which is comparatively superior to most other low-cost biomaterials. Fourier transform infrared spectroscopic analysis of the metal-loaded biosorbents confirmed the participation of –COOH, –NH2, and O–CH3 groups in the complexation of Pb2+, Hg2+, ...

Influence of Solution Chemistry on the Release of Multiwalled Carbon Nanotubes from Silica Surfaces

The release of multiwalled carbon nanotubes (MWNTs) that were deposited on silica surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). MWNTs were deposited on silica surfaces at elevated NaCl and CaCl2 concentrations before being rinsed with eluents of different solution chemistries to induce their remobilization. Energetically speaking, the MWNTs were released from the primary energy minimum when the background NaCl or CaCl2 concentrations were decreased at pH 7.1. The increase in electrostatic repulsion between MWNTs and silica likely caused a reduction in the energy barrier, which enabled the release of MWNTs. The degree of release increased in a stepwise fashion when the nanotubes were sequentially exposed to eluents of decreasing electrolyte concentrations, possibly due to the heterogeneity in nanotube surface charge densities. The degree of release via a successive reduction in NaCl concentration was lower at pH 4.0 than at 7.1 due to MWNTs and silica surfaces exhibiting a less negative surface charge at pH 4.0. Most of the deposited MWNTs were released when the pH was decreased from 7.1 to 4.0 at 1.5 mM CaCl2. This was attributed to the elimination of calcium bridging between the carboxyl groups on MWNTs and silanol groups on silica surfaces.

Interaction of Multiwalled Carbon Nanotubes with Supported Lipid Bilayers and Vesicles as Model Biological Membranes

The influence of solution chemistry on the kinetics and reversibility of the deposition of multiwalled carbon nanotubes (MWNTs) on model biological membranes was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Supported lipid bilayers (SLBs) comprised of zwitterionic 1,2-dioleoyl-sn-glyero-3-phosphocholine (DOPC), as well as DOPC vesicles, were used as model cell membranes. Under neutral pH conditions, the deposition kinetics of MWNTs on SLBs increased with increasing electrolyte (NaCl and CaCl2) concentrations. In the presence of NaCl, favorable deposition was not achieved even at a concentration of 1 M, which is attributed to the presence of strong repulsive hydration forces due to the highly hydrophilic headgroups of SLBs. Conversely, favorable deposition was observed at CaCl2 concentrations above 0.5 mM when the charge of SLBs was reversed from negative to positive through the binding of Ca(2+) cations to the exposed phosphate headgroups. Favorable nanotube deposition was also observed at pH 2, at which the DOPC SLBs exhibited positive surface charge, since the isoelectric point of DOPC is ca. 4. When MWNTs on SLBs were rinsed with low ionic strength solutions at pH 7.3, only ca. 20% of deposited nanotubes were released, indicating that nanotube deposition was mostly irreversible. The deposition of MWNTs on DOPC vesicles under favorable deposition conditions did not result in any detectable leakage of solution from the vesicles, indicating that MWNTs did not severely disrupt the DOPC bilayers upon attachment.