Size and stability modulation of ionic liquid functionalized gold nanoparticles synthesized using Elaeis guineensis (oil palm) kernel extract

Bio-synthesis approach for gold nanoparticles (AuNPs) has received tremendous attention as an efficient and eco-friendly process. However, kinetic growth and colloidal stability of AuNPs synthesized by this process remained challenging. In this study, Elaeis guineensis (oil palm) kernel (OPK) extract prepared in an ionic liquid (IL)[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate) was employed to control and tune the size and morphology of AuNPs. Synthesized AuNPs were characterized using UV-vis spectrophotometer, dynamic light scattering (DLS) and transmission electron microscopy (TEM) to observe any changes in absorbance, surface charge and particle size, respectively. IL mediated AuNPs were examined for 120 days and found well dispersed and stable at room temperature. UV-vis analysis demonstrated that volume of extract played an important role to control the stability of AuNPs. After 120 days, only 8.86% reduction from maximum absorbance was observed using 2 mL of volume of extract, which was elevated to 47.64% in case of 0.3 mL. TEM analysis was performed periodically after day 1, day 30, day 60, day 90 and day 120 and minor increase in the size was observed. Insignificant change in zeta potential value after 120 days supported enhanced stability of IL mediated AuNPs. Crystalline nature of AuNPs was confirmed by X-ray diffraction (XRD) pattern. The particles size and zeta potential of AuNPs was measured as 8.72 nm and −18.7 mV, respectively. However, the absence of [EMIM][OAc] from OPK extract resulted into larger particles size (9.64 nm), low zeta potential value (−13.9 mV) and enhanced aggregation of particles. Finally, experimental data were used to predict the theoretical and the experimental settling time for AuNPs to evaluate colloidal stability.     

Deposition of oriented zeolite A films: in situ and secondary growth

Zeolite A suspensions with a monomodal, narrow particle size distribution have been prepared. The suspended particles in a TMAOH water solution at pH 9 are negatively charged with a zeta potential of −43 mV. Modification of the external surface of the zeolite particles by a silylation reaction produces particles that, when they are suspended in water, are positively charged and have a zeta potential of +40 mV.The suspensions of the negatively or positively charged particles can be used for the preparation of adsorbed layers of particles on oppositely charged substrates by electrostatic attraction. This deposition process leads to a high coverage of the substrate with well-adhered particles. The cubic morphology of the zeolite particles results in preferential orientation after deposition. The particles are oriented with their {h 0 0} planes (cube faces) parallel and perpendicular to the substrate (out-of-plane orientation). The particles are randomly oriented with respect to the direction perpendicular to the substrate (in-plane orientation). Although, under optimized conditions, the coverage is high and only one adsorption cycle is necessary, the particles are not closely packed.Alternately, the zeolite particle suspensions can be used to deposit close-packed arrays of particles by convective particle transport during dip coating on substrates bearing the same charge as the zeolite particles. Using monodispersed zeolite A suspensions and slow speed dip coating close-packed hexagonal colloidal crystals were prepared. The type of colloidal crystal deposits formed range from continuous sublayers, monolayers, or multilayers to isolated discoidal clusters consisting of few zeolite particles. Factors affecting the deposited layer(s) structure are particle concentration of the suspension and withdrawal speed. In addition to close packing, the layers prepared by dip coating exhibit preferred orientation with the particle faces lying parallel and perpendicular to the substrate surface. Moreover, this second route of precursor film formation by colloidal crystallization leads to domains of well-aligned zeolite particles in three dimensions, i.e. with their faces parallel to each other. The oriented domains span the length of several particles; however, low angle boundaries and other defects during colloidal crystallization prevent the formation of macroscopically three-dimensionally ordered zeolite particles.The precursor layers were subjected to secondary growth in order to prepare continuous intergrown films. Secondary growth proceeds initially by local epitaxy on the deposited particles. Later in the process, deposition proceeds by incorporation of particles from solution along with re-nucleation on the growing film. The intergrown films have predominately [h 0 0] out-of-plane orientation; however, after extended secondary growth treatment a population of [h h h] grains appears on the surface of the regrown films.     

Preparation of nano-sized LiCoO2 powder by the combination of sonication and modified Pechini process

A sonication (ultrasonic processing) and modified Pechini process were combined to fabricate nano-sized LiCoO₂ powder. A composition of precursor solution for fabricating LiCoO₂ was modulated by controlling the molar ratios of lithium acetate to cobalt acetate and ethylene glycol to citric acid, respectively. The sonication was applied on the precursor solution to get highly dispersed transition-metal oxide powder. The sonicated precursor gels pre-dried were calcined in the range of 400 to 800 °C for 10 h. Effect of sonication on the particle size and the morphology of LiCoO₂ prepared by the modified Pechini process was elucidated. After calcination, the unsonicated LiCoO₂ powder had an aggregated-like morphology, as combined loosely and/or firmly, while the sonicated LiCoO₂ was more ultra-finely particulated and presented more mono-dispersed morphology without severe aggregation. The nano-sized LiCoO₂ with high crystallinity and homogeneity could be prepared by the combination of sonication and modified Pechini process.     

Measurements of differential capacitance in room temperature ionic liquid at mercury,glassy carbon and gold electrode interfaces

Differential capacitances were measured in 1-propyl-3-methylimidazolium tetrafluoroborate (PMIBF₄) ionic liquid at three different electrode substrates (Hg, GC (glassy carbon) and Au) as a function of potential. Essentially different capacitance–potential curves were obtained at different electrodes. From the parabolic electrocapillary curve measured at dropping Hg electrode in PMIBF_4, the potential of zero charge (PZC) was found to be −0.31 V vs. Ag/AgCl (wire). However, the capacitance–potential curve at Hg electrode was found not to show any valley related to the PZC, whereas at GC and Au electrodes a minimum was observed at 0.29 and −0.51 V, respectively. The results are in disagreement with the recent theoretical study which implies that the capacitance–potential curve should be of bell shape with the maximum value of capacitance at PZC. The parabolic capacitance–potential curve similar to those obtained in inorganic molten salts was also observed for the first time at GC electrode. Probable causes of the difference in their capacitance–potential curves were also discussed.     

Combination of microspheres and sol-gel electrophoresis for the formation of large-area ordered macroporous SiO2

A simple and effective fabrication scheme involving sequential electrophoretic depositions of polystyrene (PS) microspheres (500 nm and 1 μm in diameter) and SiO₂ sols (~ 5 nm in diameter) to produce large-area ordered macroporous SiO₂ inverse opals (2 × 2 cm²) on ITO substrates is demonstrated. The zeta potentials for PS microsphere suspension and SiO₂ sols are measured to determine an optimized processing window in which both samples carry negative surface charges and sol-gel transformation can be properly implemented. Our approach entails the electrophoresis of PS microspheres to render a colloidal crystal with negligible defects. Afterward, SiO₂ sols are infiltrated to the interstitial voids among the closely-packed PS microspheres via another electrophoresis process, followed by an oxidation treatment to remove the PS colloidal template and complete the densification of SiO₂ gels. The resulting SiO₂ inverse opals reveal impressive surface uniformity and structural integrity. Fourier transform infrared spectroscopy confirms the complete removal of PS microspheres, leaving an intact SiO₂ skeleton, whereas X-ray diffraction pattern indicates its amorphous nature.     

Development of a stability-indicating high performance liquid chromatography method for assay of erythromycin ethylsuccinate in powder for oral suspension dosage form

In this study an effective method was developed to assay erythromycin ethylsuccinate for an oral suspension dosage form. The chromatographic separation was achieved on an X-Terra™ C₁₈ analytical column. A mixture of acetonitrile–ammonium dihydrogen phosphate buffer (0.025 mol L^-1) (60:40, V/V) (pH 7.0) was used as the mobile phase, effluent flow rate monitored at 1.0 mL min⁻¹, and UV detection at 205 nm. In forced degradation studies, the effects of acid, base, oxidation, UV light and temperature were investigated showing no interference in the peak of drug. The proposed method was validated in terms of specificity, linearity, robustness, precision and accuracy. The method was linear at concentrations ranging from 400 to 600 μg mL⁻¹, precise (intra- and inter-day relative standard deviations <0.65), accurate (mean recovery; 99.5%). The impurities and degradation products of erythromycin ethylsuccinate were selectively determined with good resolution in both the raw material and the final suspension forms. The method could be useful for both routine analytical and quality control assays of erythromycin ethylsuccinate in commercial powder for an oral suspension dosage form and it could be a very powerful tool to investigate the chemical stability of erythromycin ethylsuccinate.     

Effect of gamma irradiation on Burkholderia thailandensis (Burkholderia pseudomallei surrogate) survival under combinations of pH and NaCl

This study evaluated the effect of gamma irradiation on Burkholderia thailandensis (Burkholderia pseudomallei surrogate; potential bioterrorism agent) survival under different levels of NaCl and pH. B. thailandensis in Luria Bertani broth supplemented with NaCl (0–3%), and pH-adjusted to 4–7 was treated with gamma irradiation (0–0.5 kGy). Surviving cell counts of bacteria were then enumerated on tryptic soy agar. Data for the cell counts were also used to calculate D₁₀ values (the dose required to reduce 1 log CFU/mL of B. thailandensis). Cell counts of B. thailandensis were decreased (P<0.05) as irradiation dose increased, and no differences (P≥0.05) in cell counts of the bacteria were observed among different levels of NaCl and pH. D₁₀ values ranged from 0.04 to 0.07 kGy, regardless of NaCl and pH level. These results indicate that low doses of gamma irradiation should be a useful treatment in decreasing the potential bioterrorism bacteria, which may possibly infect humans through foods.     

Preparation of clear colloidal solutions of detonation nanodiamond in organic solvents

Highly transparent colloidal solutions of detonation nanodiamonds in organic solvents such as tetrahydrofuran (THF), methyl ethyl ketone (MEK) and acetone were attained in this investigation through an easy process, in which the detonation nanodiamond powder was oxidized at 420 °C for 1.5 h and then dispersed into solvents by beads-milling with the addition of the surfactant, oleylamine (OLA). The results of both Fourier transform infrared spectroscopy and zeta potential measurements confirm that a readily apparent number of Lewis acid sites composed of mainly carboxylic acid and cyclic acid anhydrides were derived on the surface of thermally oxidized nanodiamond (T-ND). This acid sites-derived T-ND is chemically active, favoring the formation of charge-transfer complexes with the amino-containing surfactants such as OLA and octadecylamine (ODA). After being dispersed with one of the surfactants, OLA or ODA, the T-ND shows good dispersion stability in organic solvents; however, the dispersion efficiency of the saturated ODA is not as good as that of the unsaturated OLA. By using the dispersant OLA, accompanied with de-agglomeration by beads-milling, a clear colloidal solution of T-ND in solvents of THF, MEK or acetone can be easily attained and stabilized for at least 3 months.     

Preparation of a poly(methyl methacrylate)-reduced graphene oxide composite with enhanced properties by a solution blending method

Poly(methyl methacrylate) (PMMA)/graphene nanocomposites were prepared by a simple solution blending method. The glass transition temperature of the produced PMMA/graphene composite was increased by 37 °C with 1.0 wt.% RGO content, which is approximately 40% of improvement compared to that of pure PMMA. The thermal expansion coefficient (TEC) decreased by 68% with as low as 0.1 wt.% RGO loading. The electrical conductivity of the nanocomposites reached up to 0.037 S/m even with only 2.0 wt.% RGO, which increased by more than twelve orders of magnitude. The resulting nanocomposites showed that a stable colloidal suspension of graphene dispersion in organic solvent before blending with PMMA is necessary to fabricate the nanocomposites with enhanced properties.     

Surface-enhanced Raman studies of bradykinin using colloidal gold

In this paper, bradykinin (BK), an endogenous peptide hormone, which is involved in a number of physiological and pathophysiological processes was deposited onto the colloidal Au nanoparticles. The surface-enhanced Raman spectroscopy (SERS) was used to determine the adsorption mode of BK under different environmental conditions, including: excitation wavelengths (514.5 nm and 785.0 nm), pH of aqueous sol solutions (from pH = 3 to pH = 11), and size of the colloidal nanoparticles (10, 20, and 50 nm). The metal surface plasmon of the colloidal suspended Au nanoparticles was examined by ultraviolet-visible (UV–vis) spectroscopy. The results showed that the C-terminal part of BK plays a crucial role in the adsorption process onto the colloidal suspended Au particles. The Phe^5/8 and Arg⁹ residues of BK mainly participate in the interactions with the colloidal Au nanoparticles. At acidic pH of the solution (pH = 3), the BK COO⁻ terminal group through the both oxygen atoms strongly binds to the Au nanoparticles. The Phe⁵/Phe⁸ rings adopt tilted orientation with respect to the colloidal Au nanoparticles with diameters of 10 and 20 nm. As the particle size increases to 50 nm, the flat orientation of the Phe ring(s) with respect to the Au nanoparticles is observed.     

Direct determination of arsenate based on its electrocatalytic reduction at the poly(aniline-co-o-aminophenol) electrode

It was found that the copolymer poly(aniline-co-o-aminophenol) (PANOA) can strongly catalyze the reduction of arsenate in a NaCl solution, which was proved by cyclic voltammetry and the determination of activation energy. On the basis of the electrocatalytic reduction of arsenate, the PANOA copolymer was used as a probe to determine directly arsenate. The electrocatalytic activity of the PANOA electrode toward As(V) reduction strongly depended on the pH and the applied potential. Under the optimal conditions, the PANOA electrode can be used to determine directly As(V) concentration in a wide linear range (n = 19) of 0.949 and 495 μM with a correlation coefficient of 0.995 and a limit of detection of 0.495 μM. The sensitivity of the electrode was 0.192 μA μM^?1 cm^?2. The PANOA electrode had the good storage stability and a less negative operation potential of ?0.15 V (vs. SCE).     

Effect of iron (III) hydroxide sol as a support for oligomerization of l-phenylalanine in aqueous solution

An oligomerization of l-phenylalanine in aqueous solution was studied in the presence of iron (III) hydroxide sols. To an aqueous solution of the iron hydroxide sols prepared from iron (III) chloride,l-phenylalanine with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride was added. After stirring for 48 h at 0 °C, 3 M HCl solution was added to the reaction mixture to decompose the colloidal iron hydroxide. Oligo (l-phenylalanine) was isolated by centrifugation and washed with acidic water. The maximum yield of 15% was obtained at around pH 6.3. This value was 2.5 times higher than that obtained without the iron hydroxide sols at the same pH. Adsorption study of l-phenylalanine indicated that assemblies of l-phenylalanine onto the iron hydroxide sols were predominant factor to improve the yield of the oligomerization product. The presence of nitrate anions changes the pattern of the yield of oligo (l-phenylalanine) against pH values. The maximum yield of 20% was obtained at around pH 3. This value was four times higher than that obtained without the iron hydroxide sols at the same pH. Effect of NaCl for the oligomerization of l-phenylalanine in an aqueous solution was also studied.     

Utilization of anion exchange resin Spectra/Gel for separation of arsenic from water

Arsenic in drinking water is one of the most challenging health hazards facing mankind today. Arsenic is a naturally occurring carcinogen and creates epidemiological problems through chronic ingestion from drinking water. Arsenic is present in water primarily as As(III) or As(V). Removal of both As(III) and As(V) from water by adsorption on strong base anion-chloride has been studied. Arsenic concentration was measured by Inductively Coupled Argon Plasma (ICP) analysis. The resin was regenerated and the adsorbed arsenic fractions were eluted by using 2 M NaCl. The effect of different parameters that influence adsorption process, such as relative arsenic and resin concentrations, retention time, and pH, were investigated. Results obtained revealed that As(III) was poorly adsorbed, whereas As(V) was successfully retained on the resin. The adsorption process was optimized by using 1 g resin for 16 ppm As(V) at pH 9 for 30 min. The removal efficiency of As(V) was 99.2%.     

Stability and tribological performances of fluid phospholipid bilayers: Effect of buffer and ions

We have investigated the mechanical and tribological properties of supported Dioleoyl phosphatidylcholine (DOPC) bilayers in different solutions: ultrapure water (pH 5.5), saline solution (150 mM NaCl, pH 5.8), Tris buffer (pH 7.2) and Tris saline buffer (150 mM NaCl, pH 7.2). Friction forces are measured using a homemade biotribometer. Lipid bilayer degradation is controlled in situ during friction tests using fluorescence microscopy. Mechanical resistance to indentation is measured by force spectroscopy with an atomic force microscope. This study confirms that mechanical stability under shear or normal load is essential to obtain low and constant friction coefficients. In ultrapure water, bilayers are not resistant and have poor lubricant properties. On the other hand, in Tris saline buffer, they fully resist to indentation and exhibit low (μ = 0.035) and stable friction coefficient with no visible wear during the 50 min of the friction test. The unbuffered saline solution improves the mechanical resistance to indentation but not the lubrication. These results suggest that the adsorption of ions to the zwiterrionic bilayers has different effects on the mechanical and tribological properties of bilayers: higher resistance to normal indentation due to an increase in bilayer cohesion, higher lubrication due to an increase in bilayer–bilayer repulsion.     

New insights into the mechanism of flow-electrode capacitive deionization

We report on Faradaic reactions producing H⁺ (anode) and OH^– (cathode) in flow-electrode capacitive deionization (FCDI) operated at 1.2 V. These reactions underline an additional electrodialytical desalination mechanism within capacitive deionization, which proceeds in parallel to the known electrosorption mechanism. Examination of flow-electrodes (100 ml each, 5% (wt) activated carbon) during FCDI (121 cm² effective membrane area) of 150 ml, 4 g/l NaCl solution revealed that significant amounts of Na⁺ and Cl⁻ ions (up to 50% and 30% of Cl⁻ and Na⁺, respectively) were not adsorbed in the activated carbon particles but were rather dissolved in the aqueous phase of the flow-electrodes. Production of acid (resulting in pH ≈ 1.5) and base (pH ≈ 12.5) in the flow-anode and -cathode solutions was observed during the operation. Reverse pH behaviors were obtained during the regeneration of the flow-electrodes by potential reversal. pH neutralization of the flow-electrode solutions resulted in a sharp increase in both the desalination rate and the electric current of the FCDI cell. Reacting NaOH and HCl in a short-circuited FCDI cell resulted in NaCl production in the water compartment and pH neutralization of both flow-electrodes.Apparently reversible Faradaic reactions that occur on the flow electrodes in the FCDI can be dependent on the properties of the carbon material, electrolyte composition and applied operational parameters (e.g. cell potential) and need to be studied in further detailed investigations.     

Capacitive deionization concept based on suspension electrodes without ion exchange membranes

A new type of capacitive deionization (CDI) system, based on capacitive suspension electrodes (CSEs), was developed for the purpose of desalting brackish and seawater through the use of flowable carbon suspensions. CSEs derived from activated carbon and acetylene black demonstrated a specific capacitance of 92 F g^− 1 in a static mode in a 0.6 M NaCl solution. The novel system introduced here is a proof of concept that capacitive suspension electrodes can be envisioned to desalt water without the aid of ion exchange membranes (IEMs).     

Surface charge tuning of ceria particles by titanium doping: Towards significantly improved polishing performance

Titanium-doped ceria Ce_1 ? x Ti_xO₂ (x = 0–0.3) powders were prepared and their material removal rate (MRR) values for polishing the ZF₇ optical glass were evaluated with respect to their particle sizes, surface charges, crystallinity as well as the suspension stability. Significantly increased MRR values with a particle zeta potential dependence were observed for all the Ti-doped ceria powders, indicating that ceria abrasives with high MRR can be designed and synthesized by tuning particle surface charge using the titanium doping method. The XRD and Raman spectroscopic analyses revealed that the large increase in MRR and the surface negative zeta potentials were attributed to lattice defects due to the formation of CeO₂–TiO₂ solid solutions and the CeTi₂O₆ phase. A maximum MRR value of 544 nm min^?1 was obtained using Ce_0.9Ti_0.1O₂ solid solution as a polishing powder for the ZF7 glass. This value is ca. 2.2 times of that obtained from using pure ceria. With the x value further increasing to 0.2 and 0.3, the MRR value decreased slightly with the CeTi₂O₆ phase content increasing. This fact reveals that the contribution of CeTi₂O₆ to the MRR increase is less than that of CeO₂–TiO₂ solid solution.     

Biosorption of copper ions from aqueous solutions by Spirulina platensis biomass

In this study, the economically important micro-alga (cyanobacterium) Spirulina platensis was used as biosorbent for the removal of copper from aqueous solutions. The cyanobacterium was exposed to various concentrations of copper and adsorption of copper by the biomass was evaluated under different conditions that included pH, contact time, temperature, concentration of adsorbate and the concentration of dry biomass. Increased adsorption of copper by the non-living biomass was recorded with gradually increasing pH, and a maximal uptake by the biomass was observed at pH 7. The adsorption of copper was found to increase gradually along with decrease in biomass concentration. Biosorption was found to be at a maximum (90.6%), in a solution containing 100 mg copper/L, at pH 7, with 0.050 g dry biomass and at 37 °C with 90 min of contact time. Analysis of the spectrum obtained with atomic absorption spectrophotometer (AAS), indicated that the adsorbent has a great potential to remove copper from aqueous media contributing to an eco-friendly technology for efficient bioremediation in the natural environment.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Melamine modified carbon felts anode with enhanced electrogenesis capacity toward microbial fuel cells

Surface electropositivity and low internal resistance are important factors to improve the anode performance in microbial fuel cells(MFCs). Nitrogen doping is an effective way for the modification of traditional carbon materials. In this work, heat treatment and melamine were used to modify carbon felts to enhance electrogenesis capacity of MFCs. The modified carbon felts were characterized using X-ray photoelectron spectroscopy(XPS), scanning electron microscope(SEM), atomic force microscopy(AFM)and malvern zeta potentiometer. Results show that the maximum power densities under heat treatment increase from 276.1 to 423.4 m W/m~2(700 °C) and 461.5 m W/m~2(1200 °C) and further increase to472.5 m W/m~2(700 °C) and 515.4 m W/m~2(1200 °C) with the co-carbonization modification of melamine.The heat treatment reduces the material resistivity, improves the zeta potential which is beneficial to microbial adsorption and electron transfer. The addition of melamine leads to the higher content of surface pyridinic and quaternary nitrogen and higher zeta potential. It is related to higher MFCs performance. Generally, the melamine modification at high temperature increases the feasibility of carbon felt as MFCs' s anode materials.