Modification of macroporous stainless steel supports with silica nanoparticles for size selective carbon membranes with improved flux

Silica nanoparticles were slip cast into porous stainless steel supports, which were then coated with polyfurfuryl alcohol and pyrolyzed to make nanoporous carbon membranes. The single gas permeances of the membranes formed on modified stainless steel supports were found to be between two and three orders of magnitude larger than the permeances of nanoporous carbon membranes (<10⁻¹¹ mol m⁻² s⁻¹ Pa⁻¹) synthesized on unmodified supports. Importantly, these high permeances (10⁻⁸-10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹) were achieved within the same range of O₂/N₂ selectivities (3-5) that we have observed for single gases permeating at much lower fluxes through the nanoporous carbon membranes on unmodified supports. The nanoporous carbon membranes also were formed by combining the silica nanoparticles with polyfurfuryl alcohol resin and applying the mixture directly onto an unmodified support. This simpler process was as effective in producing selective-high permeance membranes. In both cases the significant increase in permeance without loss of selectivity is attributed to the silica nanoparticles filling the macropores of the stainless steel supports, thereby leading to the formation of very thin but selective carbon layers.     

Landfill gas (LFG) processing via adsorption and alkanolamine absorption

Landfill gas (LFG) was upgraded to pure methane using the adsorption and absorption processes. Different toxic compounds like aromatics and chlorinated compounds were removed using granular activated carbon. The activated carbon adsorbed toxic trace components in the following order: carbon tetrachloride > toluene > chloroform > xylene > ethylbenzene > benzene > trichloroethylene ≈ tetrachloroethylene. After removing all trace components, the gas was fed to absorption apparatus for the removal of carbon dioxide (CO₂). Two alkanolamines, monoethanol amine (MEA) and diethanol amine (DEA) were used for the removal of CO₂ from LFG. The maximum CO₂ loading is obtained for 30 wt.% MEA which is around 2.9 mol L^− 1 of absorbent solution whereas for same concentration of DEA it is around 1.66 mol L ^− 1 of solution. 30 wt% MEA displayed a higher absorption rate of around 6.64 × 10^− 5 mol L^− 1 min^− 1. DEA displayed a higher desorption rate and a better cyclic capacity as compared to MEA. Methane obtained from this process can be further used in the natural gas network for city.     

Evaluation of the photoelectrocatalytic method for oxidizing chloride and simultaneous removal of microcystin toxins in surface waters

The production of chlorine was investigated in the photoelectrocatalytic oxidation of a chloride-containing solution using a TiO₂ thin-film electrode biased at current density from 5 to 50 mA cm⁻² and illuminated by UV light. Such parameters as chloride concentrations from 0.001 to 0.10 mol L⁻¹, pH 2-12, and interfering salts were varied in this study in order to determine their effect on this oxidation process. At an optimum condition this photoelectrocatalytic method can produce active chlorine at levels compatible to water disinfections processes using a chloride concentration higher than 0.010 mol L⁻¹ at a pH of 4 and a current density of 30 mA cm⁻². The method was successfully applied to treat surface water collected from a Brazilian river. After 150 min of photoelectrocatalytic oxidation, we obtained a 90% reduction in total organic carbon removal, a 100% removal of turbidity, a 93% decrease in colour and a chemical oxygen demand (COD) removal of around 96% (N = 3). The proposed technology based on photoelectrocatalytic oxidation was also tested in treating 250 mL of a solution containing 0.05 mol L⁻¹ NaCl and 50 μg L⁻¹ of Microcystin aeruginosa. The bacteria is completely removed after 5 min of photoelectrocatalysis following an initial rate constant removal of −0.260 min⁻¹, suggesting that the present method could be considered as a promising alternative to chlorine-based disinfections.     

Amperometric flow injection analysis as a new approach for studying disperse systems

Fast and simple quantitative determination in dispersed systems (layered double hydroxides - LDHs - suspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min⁻¹) of 0.05 mol L⁻¹ KNO₃ solution and [Cu(H₂O)₆]²⁺, used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (−0.25 V vs Ag/AgCl/NaCl (3 mol L⁻¹)), presents a linear relationship with [Cu(H₂O)₆]²⁺ concentration and the procedure offers high sensitivity (slope = 0.036 μA/(μmol L⁻¹)), a low detection limit (=0.7 μmol L⁻¹) and a wide quantification range (4-200 μmol L⁻¹).The method was applied to [Cu(H₂O)₆]²⁺ determination in two particular LDH-aqueous solution dispersed systems: (1) [Cu(H₂O)₆]²⁺ scavenging by etilendiammintetraacetic acid (EDTA) modified Zn-Al-LDHs, and (2) [Cu(H₂O)₆]²⁺ release from a copper doped Mg-Al-LDHs. The results obtained are comparable to those reported in previous works using different quantification techniques. FI-AM determination is applied without sample pretreatment (solid-supernatant separation) providing a high sampling rate (above 120 samples h⁻¹) that allows a better comprehension of the processes, particularly at the initial stages.     

Polyvinylidene fluoride and polyetherimide hollow fiber membranes for CO2 stripping in membrane contactor

Porous polyvinylidene fluoride (PVDF) and polyetherimide (PEI) hollow fiber membranes incorporating polyethylene glycol (PEG) were prepared via spinning process for CO₂ membrane stripping. CO₂ loaded diethanolamine solution was used as liquid absorbent while N₂ was used as a strip gas. The characterization study of the fibers was carried out in terms of permeation test, contact angle measurement and liquid entry pressure (wetting pressure). Performance study via membrane contactor stripping was carried out at specific operating condition. The experimental results showed that PVDF membrane have high gas permeation, effective surface porosity and contact angle despite having lower liquid entry pressure in comparison with PEI membrane. PVDF-PEG membrane showed the highest stripping flux of 4.0 × 10⁻² mol m⁻² s⁻¹ at 0.7 ms⁻¹ compared to that of PEI membrane. Although the stripping flux for PEI-PEG membranes was slightly lower than PVDF membrane (e.g. 3.5 × 10⁻² mol m⁻² s⁻¹ at liquid velocity of 0.85 ms⁻¹), the membrane wetting pressure of PEI membrane is higher than hydrophobic PVDF membrane. Long term performance of both membranes showed severe flux reduction but started to level-off after 30 h of operation.     

Cr(VI) removal by continuous electrodeionization: Study of its basic technologies

The capabilities of continuous electrodeionization process (CEDI) and its basic technologies (electrodialysis (ED) and ion exchange (IX)) were analyzed in order to remove hexavalent chromium from synthetic solutions at pH 5. A cell with two chambers (dilute and concentrate) was used. Two cation exchange membranes (CM-1) and one anion exchange membrane (AFN) (40 cm² effective area) were employed in the experimental setup. IX technology was single evaluated using an IRA-67 anionic resin to know its independent performance from the other technologies, whereas ED was studied in the cell; I_lim determination was done by I vs. U plots and factors of 0.7 I_lim and 0.85 I_lim were applied to ED process. Finally, EDI process was studied at the same conditions that ED in order to know the resin bed role. During IX the removal reached was 50%; ED 98% after 6.25 h operation with an energy consumption of 1.21 kW h/m³; EDI (anionic bed) accomplishing 97.55% chromium removal (energy consumption of 0.91 kW h/m³). Finally EDI with mixed bed removed 99.8% in 1.3 h and of 0.167 kW h/m³ of energy consumption.     

Electrocatalytic reduction of bromate ion using a polyaniline-modified electrode: An efficient and green technology for the removal of BrO3 in aqueous solutions

The electrocatalytic reduction of bromate ion (BrO₃⁻) was investigated in a three-electrode system using polyaniline (PANI) as the electrode material. Bromate ion reduction and Br⁻ removal were observed during electrochemical treatment because of the catalytic and doping capabilities of the PANI film. BrO₃⁻ removal efficiency in the 0.10 mol L⁻¹ Na₂SO₄ supporting electrolyte achieved 99% at pH 7 in 25 min, with no bromide ion detected in the solution. Optimal removal was found in pH range 6-7, and the pH of the solution had a significant impact on bromate reduction. A reduction mechanism was also discussed by analyzing the cyclic voltammograms of the reduction process and X-ray photoelectron spectra of the main elements (N 1s and Br 3d) on the PANI surface. We propose that during the electrocatalytic reduction process, bromate is reduced to bromide because of the loss of electrons from the nitrogen atoms on the PANI chains. The doping of the resultant Br⁻ ions in the PANI film has an important role in avoiding further oxidation of Br⁻ to BrO₃⁻. The used PANI film can be regenerated by de-doping the Br⁻ ions with a 0.5 mol L⁻¹ H₂SO₄ solution. Thus the process can be considered efficient and green.     

Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H₂SO₄ solutions. The passivity could be overcome in methanolic solutions with 0.1 mol dm−3≤CH₂SO₄≤7 mol dm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H₂SO₄-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH₂SO₄≤0.3 mol dm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm⁻³ a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm⁻³ methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m⁻² at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.     

Direct electrochemistry and electrocatalysis of cytochrome c based on chitosan-room temperature ionic liquid-carbon nanotubes composite

A robust and effective composite film combined the benefits of room temperature ionic liquid (RTIL), chitosan (Chi) and multi-wall carbon nanotubes (MWNTs) was prepared. Cytochrome c (Cyt c) was successfully immobilized on glassy carbon electrode (GCE) surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Cyt c were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Cyt c was obtained in 0.1 mol L⁻¹ pH 7.0 phosphate buffer solution (PBS), indicating the Chi-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0 × 10⁻⁶ to 2.6 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ (S/N = 3). The apparent Michaelis-Menten constant (K_m) was calculated to be 0.45 ± 0.02 mmol L⁻¹. Moreover, the modified electrode displayed a rapid response (5 s) to H₂O₂, and possessed good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Subaquatic oxidation of coal by water-dissolved oxygen

Subaquatic oxidation of two bituminous coals by water-dissolved oxygen was investigated using batch reactor equipped with membrane oxygen sensor. Effects of time, temperature and coal grain size were studied as basic parameters influencing the oxidation process. Obtained results showed the subaquatic coal oxidation can be considered as interaction of the first reaction order with respect to oxygen. From temperature dependence of oxidation rate, activation energies E = 72 ± 4 kJ mol⁻¹ and/or 50 ± 4 kJ mol⁻¹ were calculated. For the samples, oxygen consumption R_O2 was found to be in the range of 2 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹ to 6 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹, such values being quite comparable with R_O2 for aerial oxidation of bituminous coals.     

The treatment of sulfate-rich wastewater using an anaerobic sequencing batch biofilm pilot-scale reactor

This paper presents the results from 92 cycles of an anaerobic sequencing batch biofilm reactor containing biomass immobilized on inert support (mineral coal) applied for the treatment of an industrial wastewater containing high sulfate concentration. The pilot-scale reactor, with a total volume of 1.2 m³, was operated at sulfate loading rates ranging from 0.15 to 1.90 kgSO₄²⁻/cycle (48 h — cycle) corresponding to sulfate concentrations of 0.25 to 3.0 gSO₄²⁻ l^− 1. Domestic sewage and ethanol were utilized as electron donors for sulfate reduction. Influent sulfate concentrations were increased in order to evaluate the minimum COD/sulfate ratio at which high reactor performance could be maintained. The mean sulfate removal efficiency remained between the range of 88 to 92% at several sulfate concentrations. Temporal profiles along the 48 h cycles were carried out under stable operation at sulfate concentrations of 1.0, 2.0 and 3.0 gSO₄²⁻ l^− 1. Sulfate removal reached 99% for cycle times of 15, 25, and 30 h, and the effluents sulfate concentrations were lower than 8 mgSO₄²⁻ l^− 1. The results demonstrate the potential applicability of the anaerobic configuration for the biological treatment of sulfate-rich wastewaters.     

Preparation and characterization of PVDF-montmorillonite mixed matrix hollow fiber membrane for gas–liquid contacting process

Porous PVDF-hydrophobic montmorillonite (MMT) mixed matrix membranes (MMMs) were fabricated via wet spinning method and used in membrane gas absorption process. The effects of hydrophobic MMT nano-clay loadings (1, 3 and 5 wt% of polymer) on the structure and performance were investigated. The fabricated membranes showed both finger-like and sponge-like structure with an increase in the length of finger-like pores in their cross-section, which resulted in higher permeability and lower mass transfer resistance compared to plain PVDF membrane. Also, significant improvements for surface hydrophobicity, critical entry pressure of water and porosity with the addition of filler were observed. The CO₂ absorption test was conducted through the gas–liquid membrane contactor and demonstrated a significant improvement in the CO₂ flux with MMT loading and the membrane with 5 wt% MMT presented highest performance. For example, at the liquid water velocity of 0.5 m s⁻¹, CO₂ flux of the MMM with 5 wt% MMT of 9.73 × 10⁻⁴ mol m⁻² s⁻¹ was approximately 56% higher than the PVDF membrane without nano-filler. In conclusion, MMMs with improved absorption properties can be a promising candidate for CO₂ absorption and separation processes through membrane contactors.     

Effect of pore size distribution of coal-based activated carbons on double layer capacitance

A series of coal-based activated carbons representing a wide range of mesopore content, from 16.7 to 86.9%, were investigated as an electrode in electric double layer capacitors (EDLCs) in 1 mol l⁻¹ H₂SO₄ and 6 mol l⁻¹ KOH electrolytic solutions. The activated carbons (ACs) used in this study were produced from chemically modified lignite, subbituminous and bituminous coals by carbonization and subsequent activation with steam. The BET surface area of ACs studied ranged from 340 to 1270 m² g⁻¹. The performance of ACs as EDLC electrodes was characterized using voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. For the carbons with surface area up to 1000 m² g⁻¹, the higher BET surface area the higher specific capacitance (F g⁻¹) for both electrolytes. The surface capacitance (μF cm⁻²) increases also with the mesopore content. The optimum range of mesopore content in terms of the use of ACs studied for EDLCs was found to be between 20 and 50%. A maximum capacitance exceeding 160 F g⁻¹ and a relatively high surface capacitance about 16 μF cm⁻² measured in H₂SO₄ solution were achieved for the AC prepared from a sulfonated subbituminous coal. This study shows that the ACs produced from coals exhibit a better performance as an electrode material of EDLC in H₂SO₄ than in KOH electrolytic solutions. For KOH, the capacitance per unit mesopore surface is slightly lower than that referred to unit micropore surface (9.1 versus 10.1 μF cm⁻²). However, in the case of H₂SO₄ the former capacitance is double and even higher compared with the latter (23.1 versus 9.8 μF cm⁻²). On the other hand, the capacitance per micropore surface area is the same in both electrolytes used, about 10.0 μF cm⁻².     

Interactions of cobalt chloride with saccharose in aqueous solutions at 298.15 K

Mutual diffusion coefficients (interdiffusion coefficients) and molar electrical conductivities have been measured for cobalt chloride aqueous solutions in the absence and the presence of saccharose at different concentrations (from 0.01 to 0.3 mol dm⁻³) and 298.15 K. The diffusion coefficients were measured by using the conductimetric method. For these aqueous solutions, limiting molar conductivity values have been calculated. The value of λ⁰(Co²⁺) = 105.36 × 10⁻⁴ S m² mol⁻¹, obtained at 298.15 K in pure water solution, agrees well with that reported in the literature. The Nernst diffusion coefficient values derived from diffusion (1.301 × 10⁻⁹ m² s⁻¹) and from conductance (1.295 × 10⁻⁹ m² s⁻¹) are also in good agreement.The dependence of diffusion coefficients and electrical conductivity of CoCl₂ on the concentration of saccharose is discussed by considering the effect of the carbohydrate on the electrolyte dehydration, as well as on the ion-pairs and complexes (CoCl₂-saccharose and ions-saccharose) formation.     

Synthesis, characterization and electroanalytical application of a new SiO2/SnO2 carbon ceramic electrode

A new SiO₂/SnO₂ carbon ceramic composite was prepared by the sol-gel method, and its potential application in electrochemistry as a novel electrode material has been studied. The prepared xerogel was structurally and electrochemically characterized by scanning electron microscopy coupled to energy dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and cyclic voltammetry. The composite was pressed in a rigid disk-shape and used as a conductive substrate to immobilize a water-soluble organic-inorganic hybrid polymer, 3-n-propyl-4-picolinium chloride silsesquioxane. The oxidation of nitrite was studied on this polymer film coated electrode in aqueous solution using cyclic voltammetry and differential pulse voltammetry. This modified electrode exhibited a better defined voltammetric peak shifted negatively about 60 mV. The linear detection limit found for nitrite was from 1.3 × 10⁻⁵ to 1.3 × 10⁻³ mol l⁻¹ and the detection limit was 3.3 × 10⁻⁶ mol l⁻¹.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Effect of limited artificial aeration on constructed wetland treatment of domestic wastewater

To study the effect of limited artificial aeration on domestic wastewater treatment in the constructed wetlands (CWs), four pilot-scale horizontal subsurface flow CWs were operated from October 2006 to September 2007. The types of the four units include aerated and planted CW (APCW), planted CW (PCW), aerated CW (ACW) and CW, and all the units have the identical dimensions of 3 m in length, 0.7 m in width and 1 m in depth. The automated aeration was activated when the oxygen concentrations in the units were lower than 0.2 mg/L and ceased when the oxygen concentrations in the CWs were higher than 0.6 mg/L. More stable alkaline pH values were found in aeration units than that in the non-aeration units. APCW, in which the removal efficiencies of BOD, NH₄⁺-N and TN were 94.4% (16.7 g BOD d^− 1 m^− 2), 89.1% (4.54 g NH₄⁺-N d^− 1 m^− 2), and 86.0%( 4.99 g TN d^− 1 m^− 2) respectively, was more effective at pollutant removal than the other three units. There were no significant differences in TP removal between the aeration units and non-aeration units. Less surface area is needed due to high removal efficiency in APCW and the additional cost of operation is quite little. The results from this experiment indicated that limited artificial aeration in constructed wetlands is a cost-effective method for treating domestic wastewater.     

European inter-laboratory comparison of high pressure CO2 sorption isotherms. I: Activated carbon

In order to assess and improve the quality of high-pressure sorption isotherms of carbon dioxide (CO₂) on coals, an inter-laboratory study (“Round Robin”) has been conducted among four European research laboratories. In a first round of measurements, excess sorption isotherms were determined on Filtrasorb 400 (F400) activated carbon at 318 K using the manometric (TU Delft and RWTH Aachen University) and the gravimetric (FP Mons and INERIS) method up to 16 MPa. The study shows that CO₂ sorption in the supercritical range can be determined accurately with both gravimetric and manometric equipment but requires thorough optimization of instrumentation and measuring as well as proper sample preparation procedures. For the characterization of the activated carbon F400, which we used as benchmark, we have determined a surface area of 1063 m² g⁻¹, and Dubinin-Radushkevich (DR) micropore volume of 0.51 cm³ g⁻¹. Additionally, we analysed the elementary near-surface composition by energy dispersive X-ray spectroscopy (EDX). To characterise the bulk composition of the F400 activated carbon, a proximate and ultimate analysis was performed.The observed excess sorption maxima around 5 MPa have values around 8.0 mol kg⁻¹, which are consistently higher (by upto 0.8 mol kg⁻¹) than literature data.     

Nucleic acid biosensor for DNA hybridization detection using rutin-Cu as an electrochemical indicator

The complex of rutin-Cu (C₈₁H₈₆Cu₂O₄₈, abbreviated by Cu₂R₃, R = rutin) was synthesized and characterized by elemental analysis and IR spectra. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction of Cu₂R₃ with salmon sperm DNA. It was revealed that Cu₂R₃ could interact with double-stranded DNA (dsDNA) by a major intercalation role. Using Cu₂R₃ as a novel electroactive indicator, an electrochemical DNA biosensor for the detection of specific DNA fragment was developed and its selectivity for the recognition with different target DNA was assessed by differential pulse voltammetry (DPV). The target DNA related to coliform virus gene could be quantified ranged from 1.62 × 10⁻⁸ mol L⁻¹ to 8.10 × 10⁻⁷ mol L⁻¹ with a good linearity (r = 0.9989) and a detection limit of 2.3 × 10⁻⁹ mol L⁻¹ (3σ, n = 7) was achieved by the constructed electrochemical DNA biosensor.     

Enhanced performance of a macroporous ceramic support for nanofiltration by using α-Al2O3 with narrow size distribution

Enhanced performance of a macroporous disk alumina support was fabricated through colloidal filtration route, by using α-Al₂O₃ powder with an average particle size of 1.1 μm. The support, sintered at 1250 °C, showed relative high permeances towards water (101 L h⁻¹ m⁻² bar⁻¹) and nitrogen (∼2×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹), with an average surface roughness of ∼175 nm and a high mechanical strength of 61.1 MPa. Titania supported γ-Al₂O₃ mesoporous layers were deposited onto this promising disk α-Al₂O₃ support through dip-coating. The disk membrane A1100/TiO₂/γ-Al₂O₃, with pore size of ca. 4.4 nm, showed a pure water flux as high as 4.5 L m⁻² h⁻¹ bar⁻¹, which is four times higher than that of γ-Al₂O₃ membrane reported in literature. This mesoporous membrane showed relative high retention rate (∼80%) towards di-valent cations like Ca²⁺, Mg²⁺, but not for the mono-valent cation (Na⁺).