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This study presents the use of the modified coffee husk and coffee lignin as sorbents in the heavy metal ions sorption of Pb(II), Cd(II), Cr(III), and Cu(II) in an aqueous solution. The modification of sorbents was carried out by the impregnation method, using silver nitrate (AgNO3) and sodium borohydride (NaBH4) as a nanoparticles’ (NPs) precursor, and reducing agent, respectively. The obtained nanocomposite material was morphologically characterized by electron microscopy. In addition, an evaluation of metal ions’ sorption, pseudo-first-order, and pseudo-second-order kinetics modeling was performed. Finally, antifungal activity was evaluated on different Candida species. Coffee and lignin modified with AgNPs increased the extraction capacity with the highest sorption for Pb ions with 2.56 mg/g and 1.44 mg/g, respectively.

Water pollution is a global problem threatening the entire biosphere and affecting the life of many millions of people [...]

Water pollution is an environmental problem that affects the ecosystem and living beings. Adsorption is one of the best technologies for the removal of heavy metals. Since waste recovery is the basis of the Circular Economy, agro-industrial waste is emerging as low-cost adsorbents for these pollutants from wastewater. Residues of pine sawdust, sunflower seed hulls and corn residues mix were evaluated as adsorbents of synthetic aqueous solutions of Ni(II), Zn(II) and Cd(II). These residues were characterized to determine their structure and composition, and to understand the adsorption mechanism. Adsorption efficiencies and capacities for the adsorbents and adsorbates were determined and compared. From the obtained results, it is possible to affirm that all biomasses used are good alternatives to the synthetic materials, with adsorption efficiencies greater than 50%. The order of adsorption was Cd > Zn > Ni. At the concentration range checked, adsorption efficiencies decreased in sawdust when a mixture of all metals together was considered (as present in real sewage). Finally, the heavy metals were immobilized, with efficiencies over 88.5%, in clay ceramics (as brick’s precursors). This procedure would help to minimize the contamination that could be generated by the disposal of spent adsorbents, rarely explored in the literature.

Human hair is considered a ubiquitous waste product and its accumulation can cause environmental problems. Hence, the search for alternatives that take advantage of this waste as a new raw material is of interest, and contributes to the idea of the circular economy. In this study, chemically modified human hair was used as a low cost biosorbent for the removal of heavy metal ions from aqueous solutions. The effect of the contact time, the pH, and the biosorbent concentration on the biosorption process were investigated. Kinetic modeling indicated that the pseudo-second order kinetic equation fitted well with R2 &gt, 0.999. Furthermore, the equilibrium data fitted the Langmuir adsorption isotherm at 295 K resulting in saturation concentrations of 9.47 &times, 10&minus, 5, 5.57 &times, 5, 3.77 &times, 5, and 3.61 &times, 5 mol/g for the sorption of Cr(III), Cu(II), Cd(II), and Pb(II), respectively. The biosorption process did not change the chemical structure and morphology of the hair, which was shown by FTIR and SEM. In addition, desorption experiments prove that 0.1 mol/L EDTA solution is an efficient eluent for the recovery of Pb(II) from the treated human hair. To summarize, treated human hair showed satisfactory biosorption capacity and can be considered as an effective biosorbent for the treatment of water with a low concentration of heavy metal ions.

This paper describes a comparative study of activated composite (ACM) and hybrid membranes (HM), both incorporating the commercial anion exchanger Aliquat 336 as a carrier, for the transport of Pt(IV) ions in chloride media. The incorporation of the carrier molecules in the polymeric network of both types of membranes is one of the approaches to overcome supported liquid membrane (SLM) instability. ACM are membranes with a bilayer structure: a porous lower polymeric support prepared by phase inversion (polysulfone) and a dense upper layer made by interfacial polymerisation (polyamide). HM are plasticized membranes consisting of a polymeric matrix of cellulose triacetate with a plasticizer and modified by the incorporation of an inorganic material (silanes) prepared by a sol–gel route. The efficiency of both types of membrane for the transport of Pt(IV) ions has been investigated, and several parameters affecting metal transport have been evaluated, such as the composition of the stripping phase and the selectivity of the membranes in the presence of Pd(II) ions. Moreover, comparative studies for both ACM and HM systems have been made by contacting the same feed solution in a triple-compartment cell. Finally, the results of these membrane systems are compared with those previously reported using polymer inclusion membranes (PIM) and SLM for the transport of Pt(IV) under similar experimental conditions.

The industrial manufacture of membranes is well established at the present time. More than any other process, the production of ultrafiltration membranes by immersion or evaporation (phase inversion) precipitation techniques is one of the most common. In many cases, the macroscopic properties of the membranes are similar from one membrane to another and it is impossible to distinguish them, while they differ notably from the microscopic point of view. The aim of this work is to develop a method for the classification of polysulfone ultrafiltration membranes prepared either by immersion or evaporation. It also presents a classification of those membranes by thickness. For these purposes, near infrared spectroscopy (NIR) combined with chemometric techniques are attempted here for the first time in the area of membrane research. The NIR technique permits fast analytical measurement of membrane samples, together with the possibility of characterization in on-line mode, without destruction or invasion of the samples. This appears to be an excellent routine analysis for purposes of membrane classification. The membranes were prepared in our Universitat Autonoma de Barcelona (UAB) laboratory and, after obtaining the NIR spectra, principal component analysis (PCA) was used to describe the system. The second stage involved the application of a pattern recognition method: supervised independent modeling of class analogy (SIMCA) in order to classify unknown samples. Finally, the ultrafiltration membranes were classified in terms of the membrane preparation technique (immersion or evaporation). In addition, membranes prepared by immersion were classified by thickness.

The target of agricultural biomass waste recovery from hydrolysis treatment is presented by comparing the performance of two different types of enzymatic polymeric membranes that were previously developed and characterized, based on a polysulfone derivative or monolithic polymers. Our aim was to achieve in one single step both enzymatic catalyzed hydrolysis of the xylan polysaccharide and the separation of the released products for the recovery of the short chain xylooligosaccharides. We present the behaviour of two different membrane modules operating in different procedure settings. The possible reuse of the membranes has also been evaluated. Xylooligosaccharides products have been characterized using Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS). The application of such enzymatic membranes enables the recovery of short chain xylooligosaccharides from biomass waste treatment, which has many potential applications in the food and pharmaceutical industries as well in the production of renewable energy.

A macrovoid structure is formed in polysulfone (PSf) polymeric membranes prepared by the immersion technique using N-dimethylformamide (DMF)/water as a solvent/non-solvent pair. It is actually important controlling the macrovoid formation process, because macrovoids can cause unwanted mechanical failure during high-pressure applications. In order to control the formation of these structures, the influence of different parameters like membrane thickness, solvent additives (isopropyl myristate, IPM or N-hexadecyl- l -hydroxypriline, HHP), temperature of the coagulation bath, and solvent/non-solvent pair has been studied for chiral activated membranes. With the same purpose, corresponding membranes where physically characterized by scanning electron microscopy (SEM) measurements of their cross-section images. Those SEM images have been treated by the software IFME®, which provides the parameters of asymmetry and irregularity of the membranes. The surface of the membranes has been analyzed by atomic force microscopy (AFM) and brightness analysis in order to calculate their roughness. A comparison of the same PSf membranes, but prepared by evaporation precipitation, or by using chloroform/methanol as solvent/non-solvent pair during the immersion precipitation step, has been also checked. That paper helps us to understand and predict which will be the best conditions to prepare the optimum membranes.

We report on a new enzyme/support system to immobilize proteins such as enzymes through a covalent bond on polysulfone membranes. In the present case the enzyme endo-1,4-β-xylanase (E.C.3.2.1.8) is attached to polysulfone previously derivatized by introducing an acrylate group. Membranes are properly prepared from this polysulfone acrylate. Afterwards the enzyme is immobilized though the amino groups of side chains of the amino acids of the enzyme and the acrylate group of the derivatized polysulfone. Such immobilization of the enzyme is confirmed by microelemental analysis as well as by amino acid analysis by HPLC. Moreover, the enzymatic activity of the membranes was evaluated and compared with that corresponding to the free enzyme. Certain physical parameters (asymmetry, irregularity, pore size and surface roughness) of the corresponding enzymatic membranes were obtained from SEM and AFM image interpretation.

Activated composite membranes (ACM) containing bis-(2-ethyl-hexyl) phosphoric acid (DEHPA) have been found to facilitate the transport and separation of aromatic amino acids. The ACM, prepared according to a previously established procedure, were used to experimentally determine their behavior for the transport of phenylalanine (Phe), that was used as target amino acid. A general characterization of the Phe transport through DEHPA-ACM membranes including: the existence of facilitated counter transport, reproducibility and the effect of buffering the feed solution has been performed prior to a systematic study of the influence of some chemical transport parameters. In this concern, the initial Phe concentration, the nature and concentration of the stripping agent and the pH of the feed solution have been optimized (the feed phase was 0.5 mM of Phe in a 2 M NaCl solution at pH 3 and a 2 M HCl solution was used as stripping phase). Also, the influence of the DEHPA concentration in the casting solution used to prepare the membrane is established. It is found that the membrane phase controls the rate transport up to a DEHPA concentration of 1200 mM. Finally, although the affinity of the aromatic amino acids phenylalanine, tryptophan (Trp) and tyrosine (Tyr) for DEHPA is in the order Phe>Trp>Tyr, the selectivity of the DEHPA-ACM was found to be Trp>Phe>Tyr.

A new supported liquid membrane system based on a palladium carrier (trans-benzylchloride bis-triphenylfosfine palladium(II) (BPP-Pd (II))) for the transport and pre-concentration of amino acids has been characterised. The amino acid tryptophan (Trp) has been used as a target for the membrane transport. The affinity of the anionic form of Trp for the metallic centre (Pd(II)) is the power that maintains the extraction of the amino acids. The lower pH in the receiving phase changes the speciation of the amino acid leading to its release in the receiving phase. Various parameters that characterise the Trp transport by this liquid membrane have been studied, i.e. carrier concentration, stripping agent, concentration of the stripping agent, pH in the donor phase and pre-concentration time. A valuable pre-concentration factor of 45 was achieved with an initial Trp concentration of 0.1 mM at pH 9 of the donor solution and after 40 h of running the transport experiment.

This paper describes an approach to the chemical characterisation of the facilitated transport of lead(II) and cadmium(II) by an activated composite membrane (ACM) containing immobilised di-(2-ethyl-hexyl)phosphoric acid (DEHPA). Such membranes were prepared, by interfacial polymerisation and characterised physically and chemically. The ACMs were used to experimentally determine their transport behaviour for Pb(II) and Cd(II). So, the influence of some chemical parameters (i.e. DEHPA concentration on the ACM, the feed solution composition, the concentration of nitric acid in the stripping solution, and the ionic strength of the feed and stripping aqueous solutions) was assayed for each metal ion. A correlation of the chemical behaviour of those ACM systems with the physical characterisation of those membranes, prior to and after their use, is reported. The optimum chemical conditions for Pb(II) and Cd(II) transport enhance the lifetime of the ACMs, giving higher DEHPA immobilisation on the polymeric phase of the composite membrane.

The immobilized metal affinity chromatography (IMAC) technique principles applied to the facilitated transport of anions across liquid membranes (LM) is shown. Two approaches have been developed for preparing the LM carrier: either the formation of a metallic complex, by the appropriate metal extraction, or the use of a commercial water insoluble organometallic complex. The characteristics of such a metallic complex to transport anions, being stable enough to avoid the leaching of the metal, are established. Once the metallic complex was prepared, it was used as carrier for anions in the corresponding LM (by the interactions of the anions with this specific metal properly immobilised). Pd(II) metal complexes in organic diluent have been studied for the transport of NO2− as specific target system for LM. For this purpose, different types of reagents were used as Pd(II) extractants to get the proper immobilisation of this metal and thus, to accomplish for the best transport of NO2−. Among them, tri-isobutylfosfine sulphide (Cyanex 471) was found to provide best characteristics as anion carrier for the organic Pd(II)–Cyanex 471 complex. On the other hand, the organometallic complex trans-benzylchloride bis-triphenylfosfine palladium(II) (BPP–Pd(II)) has been studied as nitrite carrier, providing a higher rate of transport than the Pd(II) extracted complex. Different parameters have been investigated to contribute to NO2− transport, including the nature of stripping solutions, pH of feed solution and membrane modifiers. Selectivity of the liquid membrane transport has been also determined as well as the influence of membrane modifiers in the selectivity of anion transport. The results have been compared to the behaviour of the BPP–Pd(II) complex as ISE carrier for anions.

A solvent impregnated hollow fibre (SIHF) module has been developed for the preconcentration of lead by using bis(2-ethylhexyl) phosphoric acid (DEHPA) dissolved in kerosene as extractant. The module has been designed for an on-line determination of trace amounts of lead(II) at mg l −1 (ppm) level by flame atomic absorption spectrometry (FAAS). The SIHF system is based on the metal liquid–liquid distribution between aqueous solutions of different acidity and the mentioned organic solution. The highest enrichment factor of Pb(II) was determined at pH=4.0 using a formic acid/formiate buffer solution. Preconcentration experiments were carried out at low lead(II) concentration (mg l −1 level) by using the SIHF module. This study includes the influence of hydrodynamic and chemical conditions on the loading and elution of Pb(II) on the SIHF, i.e., flow rate through the fibres, acidity of the eluent (as nitric acid concentration) and the chemical nature of the acid used in the elution. Breakthrough curves were determined for different sampling flow rates, 0.54 ml min −1 was selected to minimise the loading volume of Pb(II) sample. 0.1 M nitric acid was chosen as eluent solution, and perchloric acid also shows appropriate elution characteristics. The degree of concentration obtained for Pb(II) are of 10 fold the original concentration. The quantification limit for Pb(II) achieved with this preconcentration system is 0.17 mg l −1 . The results obtained indicate that the SIHF system can be applied for on-line determination of trace amounts of lead(II) by FAAS.

A method for the determination of the total metal ion concentration in samples of unknown composition after separation on a chelating resin was applied to the determination of aluminium(III) concentration in real freshwater samples, using Chelex 100 as a sorbing resin. The method, called chelating resin titration, was previously tested on synthetic samples, and allows also the evaluation of the side reaction coefficient [αM(I)] of the metal ion in the presence of the resin, which is useful for the study of metal speciation. To obtain this information, the sorption equilibria of aluminium(III) on Chelex 100 under the experimental conditions must be exactly known. These equilibria were investigated according to a previously reported method, based on the determination of the sorption curves of aluminium on Chelex 100 from solutions of known composition, sometimes containing chelating substances. It was found that the sorption of aluminium on Chelex 100 takes place by formation of three species, AlL, AlL(OH) and Al(OH)3. The corresponding exchange coefficients were determined. Despite the fact that Chelex 100 sorbs aluminium(III) strongly, it was found that the sorption from fresh waters was not quantitative, which was ascribed to the strong complexation of aluminium in the samples considered. The values of αM(I) of aluminium in some freshwater samples at natural pH and acidified up to pH 3 were determined. They were found to be much higher than those ascribable to hydrolysis or to inorganic and organic ligands present in natural waters, being for instance 1012.1 at pH 7.48 and 107.5 at pH 4.88. A similar determination carried out in a 10–3 mol kg–1 sodium chloride solution containing a known amount of aluminium at pH ≈ 8 gave log αM(I) = 14, completely ascribable to hydrolysis, showing that an accurate evaluation can be obtained by the proposed method.

The complex formation between Se(IV) and Na(DDTC) has been exploited to carry out the transport of selenite through an SSLM. The differences of solubilities of the related complex in aqueous and in organic kerosene solution along with the additional effect of H 2 O 2 have provided the conditions for such transport. In this case, the study reveals that transport of selenite is effectively facilitated by DDTC. It has been determined that the concentration of HCl in the stripping solution has an optimum value around 2.0 M. The presence of H 2 O 2 in the stripping solution is necessary to accomplish the mass transfer of selenite. The role of this reagent has been investigated. The transport has shown to be selective for Se(IV) and Cu 2+ in the presence of Mg 2+ , Fe 3+ and Ca 2+

A hollow fiber supported liquid membrane (HFSLM) system for the separation and concentration of vanadium (V) has been developed and characterized by using tricaprylylmethylammonium chloride (Aliquat 336®) dissolved in dodecane as carrier. The transport of vanadium through the liquid membrane is based on a pH gradient between feed and stripping solutions to provide an appropriate change on the chemical species of aqueous vanadate, i.e., aqueous metavanadate, VO2(OH)2−1 (4.0 8.0) is not extracted. Selective separation and concentration experiments were carried out at low vanadium(V) concentration (mg 1−1 level). The study of the HFSLM includes the influence of hydrodynamic, physical and chemical conditions, i.e., flow rate of feed solution through the fibers, number and length of fibers, lifetime of the system, initial vanadium concentration in the feed solution, and pH of aqueous phases. Transport of V(V) increases with the flow rate of the feed solution through the fibers until a ‘plateau’ is reached (> 0.2 ml min−1 in a single fiber). It has been shown that in a HFSLM module, the membrane area increases with the number of fibers but also there is an increase of the sterical hindrance between the fibers which reduces the expected increase of vanadium transport. On the other hand, the length of the fibers has a scarce influence on the transport process. The effect of the acidity of the feed solution on the vanadium transport shows a similar behavior to that obtained previously for liquid-liquid distribution and laminar SLM studies. The results obtained indicate that vanadium(V) can be effectively concentrated and selectively separated by hollow fiber SLM containing Aliquat 336® as carrier.

A synthetic receptor that can discriminate dicarboxylic acids based on host-guest principles has been prepared. This compound incorporates two amidopyridine units as hydrogen-bonding centers that are capable of binding the carboxylic acid functional group. The receptor was dissolved in a kerosene/dodecanol mixture and used as a carrier in supported liquid membranes. Facilitated transport based on the liquid-liquid distribution of dicarboxylic acids between aqueous feed and stripping solutions and an organic phase containing the carrier was accomplished. This transport was driven by a pH gradient that assures the predominance of the protonated neutral form of the carboxylic acids in the feed solution and the corresponding deprotonated form in the stripping solution. Selective transport of dicarboxylic acids was observed allowing for an efficient separation of different carboxylic acids.

A liquid membrane system for vanadium transport has been designed by using tricaprylylmethylammonium chloride (Aliquat 336®) dissolved in isopropylbenzene (cumene) or dodecane as carrier. The work has been undertaken by first determining the liquid-liquid distribution of vanadium(V) between aqueous solutions of different acidity and an organic solution containing the carrier. Optimum conditions for both extraction (4 Transport experiments were carried out at low vanadium(V) concentration (ppm level). The study of the liquid membrane included the influence of hydrodynamic and chemical conditions, i.e., stirring speed, organic solvent, carrier concentration, ionic strength and pH of the aqueous phases. Dodecane membranes provided higher transport of vanadium(V) than cumene membranes. Dodecanol, ranging from 0 to 10% (v/v), was added to the dodecane solution of Aliquat 336® to enhance its solubility. The effect of acidity of the feed solution on vanadium transport showed a similar behaviour to that obtained for the liquid-liquid distribution studies. On the contrary, selectivity properties of the liquid membrane showed clear differences with the corresponding data of solvent extraction, i.e., molybdate extracted by Aliquat 336® was not transported through the liquid membrane. The results obtained in both batch distribution experiments and dynamic membrane transport indicated that vanadium(V) was extracted by means of metavanadate chemical species.

The present work studies the mass transfer and separation of Ag+ through a liquid membrane immobilized in a micro porous laminar membrane from some base metals, e. g. Cu, Zn, Pb. Fe. The transport of silver from aqueous nitrate colutions to ammonia aqueous solutions have been studied. The active liquid membrane consist of a solution of triisobutyl phosphine sulphide, Cyanex 471, dissolved in isopropylbenzene absorbed in a micro porous film of polyvinildene fluoride. The results have been analyzed by a linear diffusion model which interprets closely the experimental transport data. Diffusion coefficient of the permeating species and the thickness of the aqueous diffusion layer were determined. The selectivity of silver transport through the liquid membrane provides an effective silver separation from solutions containing the base metals Cu, Fe, Pb and Zn. Such results have been applied to a treatment of the sulfide mineral spharelite.

Chiral activated membranes were prepared and tested for the enantioseparation of the racemic drug SR-propranolol. Polysulfone (PS) based membranes were investigated for this purpose, and N-Hexadecyl-l-hydroxyproline (HHP) was tested as a chiral carrier. The prepared membranes were characterized using two different membrane modules. In both cases, the concentration profile of both enantiomers of propranolol in the aqueous solutions over time is measured using the technique of capillary electrophoresis (CE). The influence of the simultaneous variation of both the concentration of the carrier in the membrane and the pH of the stripping solution, on the propranolol transport rate and the enantioselectivity across the chiral activated membranes, was studied. The propranolol transport rate through the membranes was investigated and established by response surface modelling. Clear enantioselective transport was encountered under the working conditions corresponding to the lower propranolol transport rate. In that case an alpha value of 1.7 was attained. © 2005 Elsevier B.V. All rights reserved.