Hollow-fiber-type pore-filling membranes made by plasma-graft polymerization for the removal of chlorinated organics from water

Hollow-fiber-type pore-filling membranes were prepared to reduce the emission of toxic chlorinated organics into the environment. These membranes can remove 1,1,2-trichloroethane (TCE) or dichloromethane (DM) from water, and concentrate them in the permeate. The pore-filling membrane can efficiently remove organics from water because of the suppression of the membrane swelling by the porous substrate matrix, and the fact that it can maintain a high solute diffusivity, because of the linear graft chains that fill the substrate pores. Laurylacrylate (LA) or n-butylacrylate (BA) grafted layers were formed inside the porous hollow-fiber substrate, and the pores were filled with the grafted chains formed from plasma-initiated graft polymerization. The hollow-fiber-type LA-grafted membranes showed extremely high separation properties: a 0.09 wt.% TCE aqueous solution was condensed to 99 wt.% TCE in the permeate. The membrane can remove TCE from a water stream, and at the same time, the membrane can purify the TCE for re-use. The membrane also showed high separation performance for an aqueous DM solution. The mass transfer resistance outside the membrane was estimated by using a concentration polarization model. When the mass transfer coefficient at the membrane and feed stream boundary layer was below 10⁻⁴ m/s, the boundary layer resistance affected the membrane performance. This needs to be taken into account when designing the membrane module and operating conditions.     

Hollow fiber supported liquid membrane: a novel technique for separation and recovery of plutonium from aqueous acidic wastes

Low plutonium content acidic waste is generated in nuclear chemical facilities. Study was initiated to develop hollow fiber supported liquid membrane (HFSLM) technique for quantitative separation and recovery of plutonium (Pu) from such wastes using tri-n-butyle phosphate (TBP) in dodecane as carrier. Hollow fiber test module was fabricated using 20 lumens of 33.91 cm² surface area and 9 cm length. After satisfactory testing of the hydrodynamic condition of the module, it was operated at a flow rate of 3 ml min⁻¹ on recycling mode with acidic waste solution containing Pu=8 mg dm⁻³, uranium=15 dm⁻³, gross β⁻=49.33 mCi dm⁻³, gross γ=15.73 mCi dm⁻³ and acidity 3 M HNO₃. In presence of various fission products, selective permeation of Pu(IV) through the bundle of hollow fiber test module was observed to be more than 90% into a stripping phase consisting 0.1 M NH₂OH·HCl in 0.3 M HNO₃. A model is presented to describe the transport mechanism and to evaluate the mass transfer coefficient. The radiation stability was also tested by exposing the membrane upto irradiation level of 1 M rad. Potentiality of the method for the selective separation of plutonium from acidic waste is, thus, clearly seen.     

Performance of a mixed-conducting ceramic membrane reactor with high oxygen permeability for methane conversion

A mixed-conducting perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) ceramic membrane reactor with high oxygen permeability was applied for the activation of methane. The membrane reactor has intrinsic catalytic activities for methane conversion to ethane and ethylene. C₂ selectivity up to 40–70% was achieved, albeit that conversion rate were low, typically 0.5–3.5% at 800–900°C with a 50% helium diluted methane inlet stream at a flow rate of 34 ml/min. Large amount of unreacted molecular oxygen was detected in the eluted gas and the oxygen permeation flux improved only slightly compared with that under non-reactive air/He experiments. The partial oxidation of methane to syngas in a BSCFO membrane reactor was also performed by packing LiLaNiO/γ-Al₂O₃ with 10% Ni loading as the catalyst. At the initial stage, oxygen permeation flux, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation flux to reach its steady state. 98.5% CH₄ conversion, 93.0% CO selectivity and 10.45 ml/cm² min oxygen permeation flux were achieved under steady state at 850°C. Methane conversion and oxygen permeation flux increased with increasing temperature. No fracture of the membrane reactor was observed during syngas production. However, H₂-TPR investigation demonstrated that the BSCFO was unstable under reducing atmosphere, yet the material was found to have excellent phase reversibility. A membrane reactor made from BSCFO was successfully operated for the POM reaction at 875°C for more than 500 h without failure, with a stable oxygen permeation flux of about 11.5 ml/cm² min.     

High-energy ionising radiation initiated decomposition of acetovanillone

Hydroxyl radical, hydrated electron and hydrogen atom intermediates of water radiolysis react with acetovanillone with rate coefficients of (1.05±0.1)×10¹⁰, (3.5±0.5)×10⁹ and (1.7±0.2)×10¹⁰mol^?1 dm³ s^?1. Hydroxyl radical and hydrogen atom attach to the ring forming cyclohexadienyl type radicals. The hydroxyl–cyclohexadienyl radical formed in hydroxyl radical reaction in dissolved oxygen free solution partly transforms to phenoxyl radical. In the presence of O₂ phenoxyl radical formation and ring destruction are observed. Hydrated electron in O₂ free solution attaches to the carbonyl oxygen and undergoes protonation yielding benzyl type radical. In air saturated 0.5 mmol dm^?3 solution using 15 kGy dose most part of acetovanillone is degraded, for complete mineralisation five times higher dose is required. The experiments clearly show that acetovanillone can be efficiently removed from water by applying irradiation technology.     

Facilitated kinetic transport of Cu(II) through a supported liquid membrane with calix[4]arene as a carrrier

In the present investigation, p-morpholinomethylcalix[4]arene (1) has been examined as a carrier in supported liquid membrane (SLM) for Cu(II) transport. The influence of different parameters, such as solvent, membrane dipping time, support membrane, co-anions, donor and acceptor pH, and carrier concentration on Cu(II) transport, was checked. The permeability values were calculated by using Danesi mass transfer model. Higher Cu(II) permeability was observed in diphenyl ether, with 1 h dipping time, Celgard 2500 and Cl^? as co-anion. The optimum pH for donor phase was 2 and that for acceptor phase was neutral at 10^?3 M carrier concentration. Diffusion coefficients were calculated using Reinhoudt's model, lag time measurements as well as by Wilke–Chang relation and compared. The transport was found to be diffusion-controlled in the membrane phase and the diffusion coefficient was calculated to be 1.54 × 10^?10 m/s whereas the extraction constant was calculated to be 1.19 × 10^?5 m/s.     

Electro-electrodialysis of hydriodic acid using the cation exchange membrane cross-linked by accelerated electron radiation

Electro-electrodialysis (EED) of hydriodic acid with HI molality of ca. 9.5 mol/kg was examined in the presence of iodine using a commercial cation exchange membrane (CMB) as a separator. For the increase of the selectivity of proton permeation, the membrane was cross-linked by accelerated electron radiation. The membrane properties (area resistance, ion exchange capacity (IEC), water content) of the cross-linked membranes were measured. The area resistance in 2 mol/dm³ KCl solution of the cross-linked membranes decreased as compared with that of the non-cross-linked membrane (original of CMB membrane). The IEC and water content of cross-linked membranes at each dose rate had almost the same value as that of non-cross-linked membrane. Electro-electrodialysis of hydriodic acid with HI molality of ca. 9.5 mol/kg was examined at 75 °C with 9.6 A/dm². The cross-linked cation exchange membrane by accelerated electron radiation had higher selectivity of the proton permeation by cross-linking structure of polymer than that of the non-cross-linked membrane.     

Phage Langmuir monolayers and Langmuir–Blodgett films

Stable, insoluble Langmuir monolayer films composed of Staphylococcus aureus-specific lytic bacteriophage were formed at an air–water interface and characterized. The phage monolayer was very strong, withstanding a surface pressure of ～40 mN/m at 20 °C. The surface pressure–area (Π–A) isotherm possessed a shoulder at ～7 × 10⁴ nm²/phage particle, attributed to a change in phage orientation at the air–water interface from horizontal to vertical capsid-down/tail-up orientation as surface pressure was increased. The Π–A-dependence was accurately described using the Volmer equation of state, assuming horizontal orientation to an air–water interface at low surface pressures with an excluded area per phage particle of 4.6 × 10⁴ nm². At high pressures phage particles followed the space-filling densely packed disks model with a specific area of 8.5 × 10³ nm²/phage particle. Lytic phage monolayers were transferred onto gold-coated silica substrates from the air–water interface at a constant surface pressure of 18 mN/m by Langmuir–Blodgett method, then dried and analyzed by scanning electron microscopy (SEM) and ellipsometry. Phage specific adsorption (Γ) in Langmuir–Blodgett (LB) films measured by SEM was consistent with that calculated independently from Π–A isotherms at the transfer surface pressure of 18 mN/m (Γ = 23 phage particles/μm²). The 50 nm-thickness of phage monolayer measured by ellipsometer agreed well with the horizontal phage average size estimated by SEM. Surface properties of phage Langmuir monolayer compare well with other monolayers formed from nano- and micro-particles at the air–water interface and similar to that of classic amphiphiles 1,2-diphytanoyl-sn-glycero-3-phosphocholine (phospholipid) and stearic acid.     

Transition metal-nitrogen-carbon catalysts for oxygen reduction reaction in neutral electrolyte

Platinum group metal-free (PGM-free) catalysts based on M-N-C types of materials with M as Mn, Fe, Co and Ni and aminoantipyrine (AAPyr) as N-C precursors were synthesized using sacrificial support method. Catalysts kinetics of oxygen reduction reaction (ORR) was studied using rotating ring disk electrode (RRDE) in neutral pH. Results showed that performances were distributed among the catalysts as: Fe-AAPyr > Co-AAPyr > Mn-AAPyr > Ni-AAPyr. Fe-AAPyr had the highest onset potential and half-wave potential. All the materials showed similar limiting current. Fe-AAPyr had an electron transfer involving 4e⁻ with peroxide formed lower than 5%. Considering H₂O₂ produced, it seems that Co-AAPyr, Mn-AAPyr and Ni-AAPyr follow a 2 × 2e⁻ mechanism with peroxide formed during the intermediate step. Durability test was done on Fe-AAPyr for 10,000 cycles. Decrease of activity was observed only after 10,000 cycles.     

Studies on polypyrrole modified nafion membrane for vanadium redox flow battery

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm⁻² and 0 ^°C for 60 min reduced more than 5 times from 2.87 × 10⁻⁶ cm² min⁻¹ to 5.0 × 10⁻⁷cm² min⁻¹, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm² to 0.22 ml/72 h cm². All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Effect of top layer swelling on the oxygen/nitrogen separation by surface modified polyurethane membranes

Cobalt(II) was chelated on the surface of a hydroxyl terminated polybutadiene (HTPB) based polyurethane (PU) membrane. The surface of a HTPB based PU membrane was first modified by ethylenediamine (EA) plasma. The cobalt chelated membrane was prepared by immersing the plasma treated membrane into a cobalt(II)/formamide solution for various length of time. For a fair comparison, the untreated and plasma treated membranes were also immersed in formamide solution. The gas transport properties of all three membranes were compared. Without solvent immersion, the O₂/N₂ selectivity increased from 2.6 to 3.1 after EA plasma treatment. But the permeability decreased from 0.88 GPU to 0.35 GPU. The selectivity was further improved to 4.4 by immersing the plasma treated membrane in a solution of CoCl₂·6H₂O/formamide for 1 h, but the permeability decreased to 0.23 GPU. The solvent immersion had little effect on the transport properties of the untreated membrane. But the transport properties of the plasma treated and cobalt chelated membranes were greatly affected by the formamide immersion. The oxygen and nitrogen permeabilities of the modified top layers could be calculated from a series model for composite membranes. It was found that both the permeability and selectivity of the top layer of the plasma treated membrane increased with the solvent immersing time. For the top layer of the cobalt chelated membrane, the gas permeability first decreased after 1 h immersion and then increased after further immersion in CoCl₂·6H₂O/formamide solution. The selectivity of cobalt chelated membrane increased as the gas permeability decreased and vice versa. These results implied that the EA grafting enhanced the O₂/N₂ selectivity by increasing its oxygen affinity but the cobalt chelating increased the O₂/N₂ selectivity by enhancing the size sieving effect.     

High-speed recovery of antimony using chelating porous hollow-fiber membrane

A porous hollow-fiber membrane containing an iminodiethanol (IDE) group as the chelate-forming group was applied to the recovery of antimony in the permeation mode. An antimony solution was forced to permeate through the pores of the chelating porous hollow-fiber membrane, driven by a transmembrane pressure. The membrane with a thickness of 0.7 mm and a porosity of 70% had an iminodiethanol group of 1.6 mol/kg of the membrane and a water flux of 0.95 m/h at 0.1 MPa and 298 K. The breakthrough curves of antimony overlapped irrespective of the permeation rate of the antimony solution ranging from 2 to 20 ml/min, i.e. the residence time across the membrane thickness ranging from 3.4 to 0.34 s, because of negligible diffusional mass-transfer resistance of the ionic species of antimony to the iminodiethanol group. At antimony concentrations below 10 mg/l (pH 4.0), a linear adsorption isotherm was obtained. The adsorbed antimony was quantitatively eluted by permeation of 2 M hydrochloric acid through the pores of the membrane.     

An electrolyte partially-wetted cathode improving oxygen diffusion in cathodes of non-aqueous Li–air batteries

An electrolyte partially-wetted cathode for Li–air batteries has been studied in this work. By evaporation of diethyl ether from the organic electrolyte, the cathode is partially filled with electrolyte. Compared to conventional flooded cathodes, a partially wetted cathode allows the gaseous oxygen to penetrate fast into the interior part of the porous cathode for the electrochemical reaction. The effective electrode area for oxygen reduction is increased which enhances the cathode kinetics. Using typical cathode materials, the partially wetted cathodes present a 60% higher discharge capacity at 0.1 mA cm^− 2 and one magnitude higher rate capability than the flooded cathode.     

Application of thin film composite membranes to the membrane aromatic recovery system

The membrane aromatic recovery system (MARS) is a new membrane technology which recovers aromatic acids and bases. The first industrial installation has been operating at a Degussa site in the UK recovering cresols since 2002. The state of the art MARS technology employs a tubular silicone rubber membrane. However, this places some limitations on the process due to relatively low mass transfer rates and limited chemical resistance.In this paper, flat sheet composite membranes were investigated for application to the MARS process. In particular for recovery of compounds, such as 1,2-benzisothiazolin-3-one (BIT) which show low mass transfer rates through the current membrane. These composite membranes are comprised of a thin nonporous PDMS selective layer coated on a microporous support layer cast from polyacrylonitrile, polyvinylidene fluoride, polyetherimide or polyphenylenesulphone. The membranes have been characterised using SEM and gas permeation. The mass transfer of BIT through the composite membranes with no chemical reaction enhancement was an order of magnitude higher than through tubular silicone rubber membranes (10⁻⁷ m s⁻¹ versus 10⁻⁸ m s⁻¹). With chemical reaction enhancement, the mass transfer increased by another order of magnitude to 1.6 × 10⁻⁶ m s⁻¹ for BIT through a PVDF supported composite membrane. Mass transfer through the composite membrane was described well using analysis based on the resistance in series theory with chemical reaction. However, when a high osmotic pressure was applied across the membrane (molarity ∼ 3 M), significant water transport occurred across the membrane.     

Chiral separation of trans-stilbene oxide through cellulose acetate butyrate membrane

An enantioselective membrane was prepared using cellulose acetate butyrate as a membrane material. The flux and permselective properties of membrane using 50% ethanol solution of (R,S)-trans-stilbene oxide as feed solution were studied. The top surface and cross-section morphology of the resulting membrane were examined by scanning electron microscopy. The resolution of over 92% enantiomeric excess was achieved when the enantioselective membrane was prepared with 15 wt % cellulose acetate butyrate and 30 wt % N,N-dimethylformamide in the casting solution of acetone, 10 °C temperature of water bath for the gelation of the membrane, and the operating pressure and the feed concentration of the trans-stilbene oxide were 3 kgf/cm² and 5.2 mmol/L, respectively. Since the cellulose acetate butyrate contained a large amount of asymmetric carbons on the backbone structure, it was possible to form helical structure, this was considered to be the reason for the enantioselectivity of the membrane.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

Quantum effects in photosynthesis

In photosynthesis light is absorbed by the light-harvesting antenna and within several tens of picoseconds transferred to the photosynthetic reaction center (RC) where an ultrafast charge separation is initiated. Photosynthetic purple bacteria employ a single reaction center. In contrast, in photosynthesis of plants, algae and cyanobacteria, two reaction centers, Photosystem II (PSII) and Photosystem I (PSI), operate in series. PSII uses light to extract electrons from water (to produce oxygen); PSI uses light to reduce NADP + to NADPH. The electron transfer from PSII to PSI is coupled to the build-up of a proton motive force (pmf) that is used to form ATP. NADPH and ATP are required in the Calvin-Benson cycle to produce a reduced sugar. In the following we will discuss photosynthetic charge separation and photosynthetic light-harvesting with an emphasis on the role of quantum mechanics.     

Cyclic voltammetry of ion transfer across a room temperature ionic liquid membrane supported by a microporous filter

Cyclic voltammetry is used to study the transfer of a series of cations and anions across a room-temperature ionic liquid (RTIL) membrane composed of tridodecylmethylammonium cation (TDMA⁺) and tetrakis(pentafluorophenyl)borate anion (TPFPB⁻), and supported by a thin (∼112 μm) microporous filter. Essential advantage of the thin membrane system is the substantial reduction of the ohmic potential drop, which is compensated in voltammetric measurements. Reversible partition of TPFPB⁻ allows fixing the potential difference at one membrane interface and polarizing the other membrane interface in a defined way. It is shown that the polarized potential window for the interface between an aqueous electrolyte solution and RTIL attains the value of ca. 0.7 V at the ambient temperature of 25 ± 2 °C. Tetraphenylarsonium tetraphenylborate hypothesis is used for the first time to estimate the standard Gibbs energies of ion transfer from water to RTIL and to establish the scale of the absolute potential differences. A linear Gibbs energy relationship is found for the ion transfer from water to RTIL and o-dichlorobenzene.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

Pyrohydrolysis of carbon nanotubes for Br and I determination by ICP-MS

Bromine and iodine determination was performed in carbon nanotubes (CNTs) by inductively coupled plasma mass spectrometry (ICP-MS) after sample preparation using pyrohydrolysis. Samples of CNTs (up to 500 mg) were mixed with 750 mg of V₂O₅ and heated at 950 °C during 12.5 min in a quartz tube under water vapor and air. The main operational conditions of pyrohydrolysis (carrier gas, absorbing solution, heating time, sample mass and use of V₂O₅) were evaluated. Accuracy was evaluated using certified reference materials (CRM) with similar matrix and also by comparison of results obtained after digestion of samples by microwave-induced combustion (MIC) and determination by ICP-MS. Agreement with CRM values was higher than 97% for Br and better than 96% in comparison with reference values (MIC/ICP-MS) of Br and I in CNTs samples. The limit of detection of the method for Br and I determination by ICP-MS was 0.05 and 0.004 μg g^? 1, respectively. Using a relatively simple and low cost pyrohydrolysis apparatus up to four samples can be processed per hour. The pyrohydrolysis sample preparation procedure is easy to be performed and provide a clean solution for analysis by ICP-MS, which is very attractive for Br and I control in CNTs.