Disruption of model cell membranes by carbon nanotubes

Carbon nanotubes (CNTs) have one of the highest production volumes among carbonaceous engineered nanoparticles (ENPs) worldwide and are have potential uses in applications including biomedicine, nanocomposites, and energy conversion. However, CNTs possible widespread usage and associated likelihood for biological exposures have driven concerns regarding their nanotoxicity and ecological impact. In this work, we probe the responses of planar suspended lipid bilayer membranes, used as model cell membranes, to functionalized multi-walled carbon nanotubes (MWCNT), CdSe/ZnS quantum dots, and a control organic compound, melittin, using an electrophysiological measurement platform. The electrophysiological measurements show that MWCNTs in a concentration range of 1.6–12 ppm disrupt lipid membranes by inducing significant transmembrane current fluxes, which suggest that MWCNTs insert and traverse the lipid bilayer membrane, forming transmembrane carbon nanotubes channels that allow the transport of ions. This paper demonstrates a direct measurement of ion migration across lipid bilayers induced by CNTs. Electrophysiological measurements can provide unique insights into the lipid bilayer–ENPs interactions and have the potential to serve as a preliminary screening tool for nanotoxicity.     

Improved hydrophilicity of zinc oxide-incorporated layer-by-layer polyelectrolyte film fabricated by dip coating method

ZnO nanoparticles suspended in poly(acrylic acid) (PAA) were deposited onto layer-by-layer (LBL) polyelectrolyte (PET) films fabricated from poly(allylamine hydrochloride) (PAH) and PAA by dip coating method. Effect of etching time and concentration of ZnO suspension on hydrophilicity of the LBL-PET films before and after UV irradiation was examined using water contact angle measurement. 2.0 M PAH/PAA solutions with a dipping speed of 3.0 cm/min provided stable LBL-PET films with thickness sufficient for HCl etching. Glass substrates with the etched LBL-PET film dipped into 0.2 wt.% ZnO suspension exhibited the contact angle of 10° after irradiated by UV for 60 min.     

Direct preparation of silver nanoparticles and thin films in CO2-expanded hexane

Small, uniform and suspended silver nanoparticles were directly prepared in CO₂-expanded hexane by reducing a synthesized metal precursor, silver isostearate, with hydrogen but without introducing additional capping agents. By increasing CO₂ pressure, the suspended silver nanoparticles could be further deposited on a solid substrate to form silver thin film via gas antisolvent and the subsequent supercritical drying processes. The silver thin films prepared by the aforementioned method possessed a uniform thickness of about 150 nm without surface cracking and low electrical resistivity (5.64 × 10⁻⁶ Ω cm) after applying an annealing process. Due to the deposition of nano-sized silver particles, the annealing temperature could be as low as 175 °C that is lower than the softening points of many transparent polymeric substrates used for fabrication of flexible conductive films.     

Encapsulation of nanoparticles using CO2-expanded liquids

A new process for encapsulation based on the principle of precipitation of nanoparticles by pressure reduction of CO₂ gas-expanded liquids (PPRGEL) is presented here. Encapsulation has been studied for two types of core solid nanoparticles, namely suspended and in situ produced particles from solution. Mechanisms for both types of encapsulations have been proposed: for the former type deposition happens because of mass transfer from the bulk solution; for the latter type encapsulation happens if the supersaturation profiles of the core and coating solutes are staggered in time in order that the core solute precipitates first and the coating solute deposits on it by mass transfer. A model for the process that includes nucleation and growth has been developed to select systems and process conditions that favor encapsulation. The mechanisms have been experimentally verified at 52 bar and 303 K for (i) encapsulation of suspended nanoparticles of silica with ascorbylpalmitate (AP) dissolved acetone and (ii) encapsulation of in situ produced tartaric acid (TA) nanoparticles with AP, both initially dissolved in acetone. A uniform coating of about 10–20 nm of AP is formed on the 250 nm silica particles. For the two-solute system it is observed that AP deposits on TA resulting in encapsulated particles of an average size of about 520 nm.     

Spectroscopic and microscopic studies of vesicle rupture by AgNPs attack to screen the cytotoxicity of nanomaterials

It is well-known that silver nanoparticles (AgNPs) with 1–10 nm of diameter attached to the surface of cell membrane were able to penetrate into the cell followed by rupturing of the cell. However, most studies for cytotoxicity used living organisms and were time-consuming. Therefore, in this study, we proposed a model method for fingerprinting of nanotoxicity of AgNPs in mimetic cell membranes using phosphor lipid. The vesicle rupturing mechanism by AgNPs attack was investigated using surface plasmon resonance (SPR) spectroscopy and atomic force microscopy (AFM).     

Recycling of excess sludge using titanium tetrachloride (TiCl4) as a flocculant aid with alkaline-thermal hydrolysis

The highly strengthened treatment and disposal of excess sludge based on economic and environmental regulation factors is one of the important issues to be dealt with in the activated sludge process. In this study, the reduction and recycling technology of excess sludge were investigated for the aim of achieving a zero emission of excess sludge produced from the activated sludge process using titanium tetrachloride (TiCl₄) as a flocculant aid with alkaline-thermal hydrolysis. Alkaline-thermal hydrolysis of excess sludge was obtained 73% and 40% reduction rate at pH 13 (60 8 °C) and pH 11 (60 8 °C), respectively. Flocculation was carried out using a Ti-salt flocculant and the collected sludge was dewatered and incinerated at 600 °C to produce TiO₂ nanoparticles. The amount of total suspended solids and volatile suspended solids was significantly decreased with pH increase. The optimal dose of Ti-salt flocculation aid to improve dewatering ability of sludge breakage was 23.95 Ti-mg l^?1. Also, in the batch culture, the supernatant after flocculation and the organic matter released from the lysed sludge were found to be useful as a source of energy for the growth of microorganisms during the aerobic operations period. TiO₂ produced from Ti-salt flocculation of excess sludge (TES) was characterized by X-ray diffraction, scanning electron microscopy/energy dispersive X-ray and photocatalytic activity.     

Effect of concentration and degree of saturation on co-precipitation of catechin and poly(l-lactide) by the RESOLV process

Rapid expansion of subcritical solutions into liquid solvents (RESOLV) was able to consistently produce catechin (CTC)-loaded poly(l-lactide) (PLLA) nanoparticles. The effects of CTC concentration and processing conditions – pre-expansion temperature and pressure, and degree of saturation – on the size and morphology of CTC-loaded PLLA nanoparticles were investigated, as well as the loading capacity (LC), entrapment efficiency (EE), and release of CTC. RESOLV experiments were carried out with 0.1 wt% CTC + 0.2 wt% PLLA and 0.2 wt% CTC + 0.2 wt% PLLA solutions in mixtures of EtOH and CO₂ (3:2, wt/wt) with pre-expansion temperature and pressure of 60–100 °C and 265–325 bar, respectively. The obtained CTC-loaded PLLA nanoparticles were spherical, with average sizes, LC, and EE ranges of ∼30–40 nm, 2.4–7.3%, and 4.7–22.0%, respectively. CTC concentration, pre-expansion temperature, and degree of saturation had significant effects on LC and EE of CTC, without affecting the size of composite nanoparticles. The LC and EE of CTC increased with increasing pre-expansion temperature and degree of saturation, and with decreasing CTC concentration. The release profiles of CTC from the nanoparticles exhibited an initial stage of burst release (first 8 h) followed by a sustained release (∼1–9 days). Furthermore, the fraction of CTC being released from the nanoparticles decreased with increasing the degree of saturation of subcritical solutions prior to rapid expansion and with increasing the LC of CTC.     

A simple approach for the synthesis of bi-functional Fe3O4@WO3 − x core–shell nanoparticles with magnetic-microwave to heat responsive properties

A facile direct precipitation method has been developed for the synthesis of multi-functional magnetic, microwave to heat responsive properties with Fe₃O₄ nanoparticles as the core and WO_3 − x as the shell. Transmission electron microscopy (TEM) images revealed that the obtained bi-functional nanoparticles had a core-shell structure and a spherical morphology. The average size was ~ 250 nm, and the thickness of the shell was ~ 15 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and the WO_3 − x shell were obtained. The nanoparticles showed both strong magnetic, and unique microwave to heat responsive properties, which may lead to development of nanoparticles with great potential for applications in drug targeting delivery, controlled release drug, photo- and microwave-thermal combination therapy and water treatment.     

Raman Spectroscopy and Kelvin Probe Force Microscopy characteristics of the CVD suspended graphene

In this work we present combined Kelvin probe force microscopy and Raman spectroscopy studies of supported and suspended structures formed out of chemical vapor deposition (CVD) grown graphene. Work function of both suspended and supported graphene was -4.81 ± 0.06eV and -4.92 ± 0.06eV respectively. By G and 2D modes correlation we showed, that CVD graphene was influenced by biaxial strain. Increased contact potential difference (CPD) on the suspended graphene in comparison with the areas of the supported graphene was the sign of increased strain (from 0.05% to ~ 0.12%) rather than decreased doping (p-doping decreased from ~ 5.5 × 10¹²cm^-2 to ~ 4.5 × 10¹²cm^-2).     

Nanoporous anatase ceramic membranes as fast-proton-conducting materials

Nanoporous anatase ceramic membranes were prepared via particulate sol–gel processes. The calcined xerogels were mesoporous, with a BET surface area of 121 m²/g, an average pore diameter of 5.8 nm and a pore volume of 0.236 cm³/g. Proton conductivity of the membranes was measured as a function of temperature and relative humidity, R.H. When anatase membranes are treated at pH 1.5, the proton conductivity increased in the whole range of temperature and R.H. It indicates that the surface site density (number of water molecules per square nanometer) of these materials has a strong effect on conductivity. The proton conductivity of the studied anatase membranes followed an Arrhenius-like dependence on the temperature (from room temperature to 90 °C), in both treated and untreated membranes. A sigmoidal dependence of the conductivity on the R.H. was observed with the greatest increase noted between 58 and 81% R.H. in both treated and untreated anatase membranes. The highest value of proton conductivity was found to be 0.015 S/cm at 90 °C and 81% R.H., for treated anatase ceramic membranes. An increase of the conductivity could be achieved by means of longer times of treatment.According to the activation energy values, proton migration in this kind of materials could be dominated by the Grotthuss mechanism in the whole range of R.H. The similar values of proton conductivity, lower cost and higher hydrophilicity of these membranes make them potential substitutes for perfluorosulfonic polymeric membranes in proton exchange membrane fuel cells (PEMFCs).     

Novel method for synthesis of Fe core and C shell magnetic nanoparticles

Using a newly developed method, carbon-encapsulated iron (Fe) nanoparticles were synthesized by plasma due to ultrasonication in toluene. Fe core with carbon shell nanoparticles were characterized using Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM). Fe nanoparticles of diameter 7–115 nm are encapsulated by 7–8 nm thick carbon layers. There was no iron carbide formation observed between the Fe core and the carbon shell. The Fe nanoparticles have body centered cubic (bcc) crystal structure. Synthesized nanoparticles showed a saturation magnetization of 9 A m²/kg at room temperature. After thermal treatment crystalline order of the nanoparticles improved and saturation magnetization increased to 24 A m²/kg. We foresee that the carbon-encapsulated Fe nanoparticles are biologically friendly and could have potential applications in Magnetic Resonance Imaging (MRI) and photothermal cancer therapy.     

Towards the perfect graphene membrane? – Improvement and limits during formation of high quality graphene grown on Cu-foils

We investigated the structure and crystalline quality of monolayer graphene grown by hydrogen and methane chemical vapor deposition (CVD) on polycrystalline Cu foils. Our data show that the high temperature hydrogen pretreatment of the Cu foil has to be performed at a sufficiently high H₂ pressure in order to avoid graphene (g) formation already during the pretreatment, which limits the achievable domain size during subsequent growth in the CH₄/H₂ mixture. Methane–hydrogen CVD sustains g growth but induces the faceting of the Cu substrate. Characterization by low energy electron microscopy evidenced a staircase Cu substrate morphology of alternating (4 1 0) and (1 0 0) planes interrupted by (n 1 1) type facets. The g flakes cover the staircase shaped support as a coherent layer. The polycrystalline film mostly contains rotational domains that are preferentially, but not strictly, aligned with respect to the stepped support surface. The substrate induced corrugated morphology occurs also underneath large single crystalline flakes and is transferred to suspended membranes, produced by etching the Cu underneath the graphene. Thus, membranes manufactured from g-Cu are non flat. This explains their reported softened elastic response and the formation of so called nanorippled graphene after transfer from the Cu support which deteriorates its electrical conductivity.     

Pt nanoparticles loaded titanium picolinate framework for photocatalytic hydrogen generation

Pt nanoparticles have been embedded into layers of a titanium picolinate framework by a photodeposition method. TEM images show the embedded and adsorbed Pt nanoparticles in the space between the layers with size of c.a 1 nm. The obtained Pt loaded titanium picolinate framework functions as an efficient photocatalyst for hydrogen evolution from methanol/water solution upon irradiation at wavelength longer than 300 nm (159.3 μmol h^− 1/0.1 g TiPF catalyst).     

A novel synthesis method for manganese ferrite nanopowders: The effect of manganese salt as inorganic additive in electrosynthesis cell

Manganese ferrite nanoparticles were electro-crystallized in an electrochemical cell containing two iron electrodes, and an electrolyte solution of sodium sulfate, sodium butanoate, and manganese sulfate hydrate. The samples were characterized by X-ray diffraction, electron microscopy, magnetometry, and Mössbauer spectroscopy methods. The crystal structure of the samples was studied using X-ray diffraction. Based on obtained results we found that the manganese ferrite nanoparticles are formed in the electrochemical cell containing 0.001 M manganese sulfate hydrate. Also, the formation of a paramagnetic secondary phase in the sample without manganese is suppressed by adding manganese salt in the electrochemical cell. The nanoparticle size, shape, and morphology were characterized using electron microscopy. Magnetization curves show that all samples are magnetically soft and their specific magnetization ranges from 15 A m² kg⁻¹ to 75 A m² kg⁻¹, depending on the growth conditions. Room temperature Mössbauer spectra confirm the formation of nonstoichiometric spinel ferrite of magnetite or manganese ferrite, again depending on the growth conditions. Based on Mössbauer analysis, reduction in the population of octahedral sites provides direct evidence for the presence of the manganese ions substitution in the octahedral sites.     

Dispersing WO3 in carbon aerogel makes an outstanding supercapacitor electrode material

Tungsten oxide, originally poor in capacitive performance, was made an excellent electrode material for supercapacitors, by dispersing it to carbon aerogels (CA), a conductive and mesoporous hosting template, that drastically improved the utilization of WO₃ for capacitance generation. The WO₃ was introduced to the CA, in a form of well-dispersed single crystalline nanoparticles of 15–40 nm in size, with a simple immersion-calcination process. A one order of magnitude improvement in specific capacitance was achieved with the present composition, from 54 F/g for WO₃ nanoparticles to 700 F/g for WO₃/CA composites (scaned at 25 mV/s in 0.5 M H₂SO₄ over a potential window of −0.3 to 0.5 V). The WO₃/CA composites exhibited an excellent high rate capability with a 60% retention in specific capacitance at 500 mV/s, almost perfect cycle efficiency of 99%, and outstanding cycling stability of only 5% decay in specific capacitance after 4000 cycles.     

Effect of suspension stability on bonding strength and electrochemical behavior of electrophoretically deposited HA–YSZ nanostructured composite coatings

In the present study, HA–YSZ nanostructured composites were deposited on Ti–6Al–4 V substrates by electrophoretic deposition of suspensions containing 0, 10, 20 and 40 wt% YSZ. The stability of each suspension was determined by applying response surface methodology, DLVO theory and zeta potential measurement for different YSZ contents and dispersant concentrations. The maximum zeta potential and electromobility of suspended particles was obtained for the suspension with 20 wt% YSZ. The electrophoretic deposition of HA–YSZ nanostructured composites was carried out at a constant voltage of 20 V for 120 s. The deposition kinetics was studied based on a mass-charge correlating approach under ranges of voltage (20–60 V), time (30–300 s) and wt% YSZ (0–40). The as–deposited and sintered HA–YSZ coatings were characterized by SEM, XRD, DSC–TG and FT–IR analyses. The micro-scratch behavior of coated samples indicated the highest critical contact pressures of crack initiation, P_c1 = 4.50 GPa, crack delamination, P_c2 = 5.14 GPa and fracture toughness, K_IC = 0.622 MPa m^1/2 for HA-20 wt% YSZ sample. The results of potentiodynamic polarization measurements showed that the implementation of 20 wt% YSZ could efficiently decrease the corrosion current density and corrosion rate of coated samples, while corrosion potential and linear polarization resistance were increased.     

Synthesis,growth mechanism and thermal stability of copper nanoparticles encapsulated by multi-layer graphene

Copper nanoparticles encapsulated by multi-layer graphene have been produced in large quantity (in grams) by metal-organic chemical vapor deposition at 600 °C with copper(II) acetylacetonate powders as precursor. The obtained graphene/copper shell/core nanoparticles were found to be formed by a novel coalescence mechanism that is quite different from the well-known dissolution–precipitation mechanism for some other graphene/metal (such as nickel, iron or cobalt) shell/core nanoparticles. Differential scanning calorimetry and thermogravimetric analyses showed that the copper nanoparticles encapsulated by multi-layer graphene with a thickness of 1–2 nm were thermally stable up to 165 °C in air atmosphere. Moreover, high-resolution transmission electron microscopy showed that the single-crystal copper nanoparticles, after exposure to air for 60 days, did not exhibit any sign of oxidation.     

Preparation and characterization of polyvinyl chloride based nanocomposite nanofiltration-membrane modified by iron oxide nanoparticles for lead removal from water

In this research (polyvinyl chloride-blend-cellulose acetate/iron oxide nanoparticles) nanocomposite membranes were prepared by casting technique to lead removal from wastewaters. The effect of blend ratio of polymer binder (PVC to CA) and Fe₃O₄ nanoparticles concentration on physico-chemical characteristics of membranes were studied. Water permeability and ionic rejection tests, water content and mechanical properties measurements and SEM analysis were carried out in membranes characterizations. Obviously, modified membrane containing 10 wt% CA and 0.1 wt% Fe₃O₄ nanoparticles showed better performance in lead removal compared to other modified membranes and also pristine ones.     

Oxygen permeation properties of BSCF5582 tubular membrane fabricated by the slip casting method

BSCF5582 tubular oxygen separation membranes were prepared using the most cost effective slip casting techniques. The optimum slurry composition was identified and a dense, and crack free 60 mm long BSCF5582 tubular membrane being successfully prepared after the programmed sintering process. The effects of the feed flow rate and the sweeping flow rate on the oxygen permeation flux of the tubular BSCF5582 membrane were investigated. The oxygen permeation flux increased with an increase of the oxygen chemical potential gradient to a maximum of 42.5 cm³/min in an O₂/N₂ condition at 1223 K for the 1.5 mm thick, 60 mm long BSCF tube, a value which corresponds to 1.42 cm³/min cm². The ionic conductivity of the oxygen was successfully calculated in the dominant electron conducting regime. The ionic conductivity was found to increase with an increase of the temperature to 900 °C, indicating that it is a thermally activated process with an activation energy of 0.70 ± 0.1 eV in an air environment.     

Fabrication of polyetherimide microporous membrane using supercritical CO2 technology and its application for affinity membrane matrix

Polyetherimide (PEI) microporous membranes with uniform cellular structure, high porosity, and narrow pore size distribution were formed by supercritical CO₂ (ScCO₂) phase inversion method, and the membrane was modified to be a matrix for the preparation of affinity membrane due to its low solvent residue and appropriate porous structure. The effects of ScCO₂ temperature and pressure on the morphology and pure water flux of the membrane were investigated. The membrane prepared at 24 MPa and 45 °C with a large mean cell diameter of 6.0 μm, high porosity of 73%, narrow pore size distribution and a pure water flux of 56 L/(m² h bar) was coated with chitosan to improve its hydrophilicity and coupled with Cibacron Blue F3GA (CB) as a special ligand to form an affinity membrane (PEI-coated chitosan-CB membrane). The PEI-coated chitosan-CB membrane showed a high adsorption capacity of 33.9 mg/g membrane to bovine serum albumin and was higher than most of affinity membranes. Moreover, the tensile strength of PEI-coated chitosan-CB membrane was 11.58 MPa and was much higher than those of affinity membranes. This work demonstrates that ScCO₂ phase inversion method is a potential method to prepare an affinity matrix.