Highly hydrophobic and superoleophilic agar/PVA aerogels for selective removal of oily substances from water.

In this study, low-cost, environmentally friendly and porous agar/PVA aerogel sorbent materials with highly hydrophobic property were fabricated for the selective separation of oily substances and organic solvents from water by (i) the cross-linking reaction, (ii) freeze drying process and (iii) surface coating treatment. The characterization of agar/PVA aerogels was performed by water solubility, contact angle, SEM, EDX, mapping and XPS measurements. SEM and porosity results revealed that the increase of PVA amount within aerogel matrix led to a decrease in the pore structure of aerogel material. Agar/PVA (100:0) aerogel had good absorption capacity values (19.0-48.1 g·g-1) for various oily substances and organic solvents. All aerogels had excellent separation efficiency (≥99.3%) for chloroform-water mixture. For chloroform-water mixture and emulsion, the flux value of agar/PVA (100:0) aerogel was found to be 4273 L·m-2·h-1 and 3094 L·m-2·h-1, respectively. New agar/PVA aerogels are promising materials for the effective separation of oil-water or organic solvent-water mixtures and the cleaning of oil-spills from water.

Agar/κ-carrageenan/montmorillonite nanocomposite hydrogels for wound dressing applications.

In this study, agar/κ-carrageenan/montmorillonite (MMT) hydrogels were prepared to examine their usability as wound dressing materials and to see the effect of MMT amount on some properties of agar/κ-carrageenan hydrogel materials. Hydrogels were characterized by SEM-EDX, TEM and DSC analyses. By increasing the MMT content within hydrogel matrix from 0% to 5%, the decomposition temperature of the hydrogel material was increased from 256.6 °C to 262.1 °C. Swelling amount of hydrogels in d-glucose solution (2682%) was found to be much higher compared with other physiological solutions such as physiological saline solution (937%), synthetic urine solution (746%) and simulated wound fluid (563%). The release studies of analgesic lidocaine hydrochloride (LDC) and antibiotic chloramphenicol (CLP) drugs from hydrogel systems demonstrated that the release amount of LDC and CLP from hydrogels could be controlled by MMT amount within hydrogel matrix. The concentrations of drugs within hydrogel sample stored at 4 °C for 6 months did not exhibit a significant change. Hydrogel materials containing CLP exhibited good antibacterial activity against E. coli and S. aureus. Cytotoxicity test results indicated that hydrogels were biocompatible with MG-63 cells. The ultimate compressive stress of agar/κ-carrageenan hydrogel with LDC and CLP and agar/κ-carrageenan/MMT hydrogel including 5% MMT with LDC and CLP was measured as 38.30 kPa and 47.70 kPa, respectively. The experimental results revealed that prepared agar/κ-carrageenan and agar/κ-carrageenan/MMT hydrogels have great potential for wound care applications.

Nanosorbent-based solid phase microextraction techniques for the monitoring of emerging organic contaminants in water and wastewater samples.

This review (including 127 refs) summarizes applications of nanosorbent-based solid phase microextraction (SPME) for the cleanup, extraction, and quantification of Emerging Organic Contaminants (EOCs). SPME is the most widely used technique for the analysis of EOCs from water samples. The selection of sorbent material plays a key role in SPME applications. Here, we have collected information about recent developments in the application of nanosorbents in the SPME technique used for the extraction of EOCs from water and wastewater samples. In this review, the preparation, properties, advantages, and limitations of nanosorbents used in SPME applications are evaluated and discussed. Besides, the applications of these nanosorbents in SPME-based extraction techniques and their analytical characteristics for the determination of EOCs are reviewed. Graphical abstract.

Preparation and characterization of thermosensitive chitosan/carboxymethylcellulose/scleroglucan nanocomposite hydrogels.

The development of thermosensitive smart hydrogels with suitable thermosensitivity is of great importance for various biomedical and pharmaceutical applications. In this study, thermosensitive chitosan/carboxymethylcellulose/scleroglucan/montmorillonite (CHT/CMC/SGL/MMT) nanocomposite hydrogels were prepared for biomedical and pharmaceutical usages and characterized by using rheology, FTIR, SEM, EDX, TEM, XRD, TGA and swelling measurements. Exfoliated distribution of MMT in the network structure of hydrogels proved by XRD and TEM analyses caused a decrease in the pore size of hydrogels. Phase transition temperature of thermosensitive hydrogels was determined precisely by rheological measurements. In the presence of 5% MMT within hydrogel matrix, the gelling temperature of Sample 9 exhibited a decrease from 32.0 °C to 25.3 °C. It was found from TGA that among the CHT/CMC/SGL/MMT hydrogel materials the hydrogel system containing 5% MMT showed the highest decomposition temperature (175 °C). Furthermore, all hydrogel materials exhibited non-Fickian swelling behavior in distilled water and basic medium. The addition of MMT into the hydrogel matrix caused a significant decrease in the swelling amount of thermosensitive hydrogels. The results of this study indicate that thermosensitive CHT/CMC/SGL/MMT hydrogel materials may have potential applications in drug delivery, wound dressing and tissue engineering.

Agar/κ-carrageenan composite hydrogel adsorbent for the removal of Methylene Blue from water.

Water pollution caused by dyes is a significant global problem. Adsorption technique is successfully applied for the removal of dyes from water. In this technique, the use of effective adsorbents is very important. Here, agar/κ-carrageenan composite hydrogel adsorbent prepared through free radical cross-linking reaction in the presence of tri (ethylene glycol) divinyl ether as a cross-linker and characterized by using FTIR, SEM and TGA measurements was used to remove Methylene Blue from water. FTIR results exhibited that electrostatic interaction and hydrogen bonding formation were the main interactions in the adsorptive removal of Methylene Blue by agar/κ-carrageenan hydrogel. Pseudo second order and Langmuir models were found to be the most suitable kinetic and isotherm models, respectively. Maximum dye adsorption capacity of 242.3 mg·g-1 was obtained at 35 °C and pH 7. Thermodynamic parameters were calculated to understand the nature of adsorption process. Different solvents were applied for the regeneration of dye adsorbed-agar/κ-carrageenan hydrogel and the most suitable solvent was determined as ethyl alcohol. The results demonstrated that agar/κ-carrageenan hydrogel is a promising adsorbent for the removal of cationic dyes from water.

Carbon nanotube-based magnetic and non-magnetic adsorbents for the high-efficiency removal of diquat dibromide herbicide from water: OMWCNT, OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites.

In this study, carbon nanotube-based adsorbents, oxidized multi-walled carbon nanotube (OMWCNT) with non-magnetic property and OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites with magnetic property, having different structural and surface properties were prepared and their adsorptive properties for the removal of toxic diquat dibromide (DQ) herbicide from water by adsorption were determined in detail. For each adsorption system, the effects of initial DQ concentration, contact time and temperature on the adsorption processes were determined. Equilibrium time was found to be 300 min for DQ solutions. OMWCNT showed faster adsorption and higher maximum adsorption capacity value than magnetic adsorbents. With increasing initial herbicide concentration from 5.43 mg.L-1 to 16.3 mg.L-1, the values of initial sorption rate exhibited a decrease from 29.1 mg.g-1.min-1 to 4.28 mg.g-1.min-1 for OMWCNT-DQ system, from 1.21 mg.g-1.min-1 to 0.823 mg.g-1.min-1 for OMWCNT-Fe3O4-DQ system and from 0.674 mg.g-1.min-1 to 0.612 mg.g-1.min-1 OMWCNT-κ-carrageenan-Fe3O4 system. Maximum adsorption capacity value of OMWCNT was approximately 2.8-fold higher than magnetic OMWCNT-Fe3O4 and 5.4-fold higher than magnetic OMWCNT-κ-carrageenan-Fe3O4 at 25 °C. Adsorption kinetic and isotherm data obtained for all adsorption systems were well-fitted by pseudo second-order and Langmuir models, respectively. Thermodynamic parameters indicated that the adsorption of DQ onto carbon nanotube-based adsorbents was spontaneous and endothermic process. Furthermore, OMWCNT having the highest herbicide adsorption capacity could be regenerated and reused at least five times. This study showed that carbon nanotube-based adsorbents with magnetic and non-magnetic property were of high adsorption performance for the removal of DQ from water and could be promising adsorbent materials for the efficient removal of herbicides from wastewaters.

Effects of montmorillonite on properties of methyl cellulose/carvacrol based active antimicrobial nanocomposites.

The effect of montmorillonite and carvacrol (as an antimicrobial agent) on the wettability, mechanical, gas barrier, thermal and color properties of methyl cellulose-based nanocomposite films was investigated. To make a comparison among the film samples, methyl cellulose (MC) film and methyl cellulose/montmorillonite (MC/MMT) and methyl cellulose/carvacrol/montmorillonite (MC/CRV/MMT) nanocomposite films with different clay concentration were prepared. The interactions among MMT, CRV and film matrix were characterized by FTIR spectroscopy. The contact angle value of MC film showed an increase of 2.5 fold with the incorporation of 60wt.% MMT into the film matrix. The addition of clay into the film matrix increased the melting point of MC film and improved the mechanical properties of film material. The tensile stress of pure MC film exhibited an increase of 9.2MPa in the presence of 60wt.% MMT. With the addition of MMT into the film matrixes, water vapor permeability values of MC film and MC/CRV film were decreased by 28% and 13%, respectively. The incorporation of 60wt.% MMT into the film matrix caused to a decrease of 47 fold for MC film and 16 fold for MC/CRV film in the oxygen permeability of film sample. The addition of CRV into MC film and MC/MMT nanocomposite films with different clay concentration reduced the mechanical strengths of film materials. Oxygen permeability values of MC film and MC/MMT nanocomposite films decreased with the inclusion of CRV into the film matrix.

Synthesis of magnetic oxidized multiwalled carbon nanotube-κ-carrageenan-Fe3O4 nanocomposite adsorbent and its application in cationic Methylene Blue dye adsorption.

In this study, magnetic oxidized multiwalled carbon nanotube (OMWCNT)-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites were synthesized and used as adsorbent for the removal of Methylene Blue (MB) from aqueous solution. Magnetic nanocomposites were characterized by using of specific surface area, Fourier transform infrared, X-ray diffraction, vibrating sample magnetometry, thermal gravimetric analysis, scanning electron microscope and transmission electron microscope measurements. The results of characterization analyses exhibited that OMWCNT was successfully modified with κ-carrageenan. Furthermore, OMWCNT-Fe3O4 and OMWCNT-κ-carrageenan-Fe3O4 nanocomposites were of a super-paramagnetic property. Adsorption studies revealed that the data of adsorption kinetics and isotherm were well fitted by the pseudo second-order kinetic model and Langmuir isotherm model, respectively. The adsorption amounts of magnetic adsorbents increased with contact time and initial dye concentration. Compared with magnetic OMWCNT-Fe3O4 nanocomposite, magnetic OMWCNT-κ-carrageenan-Fe3O4 nanocomposite showed a better adsorption performance for the removal of MB from aqueous solution. Therefore, OMWCNT-κ-carrageenan-Fe3O4 nanocomposite may be used as a magnetic adsorbent to remove the cationic dyes from wastewaters.

Study on the bindings of dichlorprop and diquat dibromide herbicides to human serum albumin by spectroscopic methods.

The interactions of dichlorprop (DCP) and diquat dibromide (DQ) herbicides with human serum albumin (HSA) protein were studied by UV absorption, fluorescence, synchronous fluorescence and circular dichroism (CD) spectroscopy. Both DCP and DQ quenched the fluorescence emission spectrum of HSA through the static quenching mechanism. The Stern-Volmer quenching constant, binding constant, the number of binding sites and thermodynamic parameters were determined at 288K, 298K, 310K and 318K. In HSA-DCP and HSA-DQ systems, an increase in temperature led to a decrease in the Stern-Volmer quenching constant and binding constant. One binding site was obtained for DCP and DQ on HSA. It was found that DCP can bind to HSA with higher affinity than DQ. Negative ΔH and positive ΔS values were obtained for the binding processes between protein and herbicide molecules. This result displayed that electrostatic interactions play a major role in the formation of HSA-DCP and HSA-DQ complexes. The binding processes were exothermic reactions and spontaneous. In addition, synchronous fluorescence and CD spectra of HSA revealed that the binding of DCP to HSA did not cause a significant conformational change in protein, but the interaction of DQ with HSA led to an alteration in the protein structure.

Characterization of the binding of metoprolol tartrate and guaifenesin drugs to human serum albumin and human hemoglobin proteins by fluorescence and circular dichroism spectroscopy.

The interactions of metoprolol tartrate (MPT) and guaifenesin (GF) drugs with human serum albumin (HSA) and human hemoglobin (HMG) proteins at pH 7.4 were studied by fluorescence and circular dichroism (CD) spectroscopy. Drugs quenched the fluorescence spectra of HSA and HMG proteins through a static quenching mechanism. For each protein-drug system, the values of Stern-Volmer quenching constant, bimolecular quenching constant, binding constant and number of binding site on the protein molecules were determined at 288.15, 298.15, 310.15 and 318.15 K. It was found that the binding constants of HSA-MPT and HSA-GF systems were smaller than those of HMG-MPT and HMG-GF systems. For both drugs, the affinity of HMG was much higher than that of HSA. An increase in temperature caused a negative effect on the binding reactions. The number of binding site on blood proteins for MPT and GF drugs was approximately one. Thermodynamic parameters showed that MPT interacted with HSA through electrostatic attraction forces. However, hydrogen bonds and van der Waals forces were the main interaction forces in the formation of HSA-GF, HMG-MPT and HMG-GF complexes. The binding processes between protein and drug molecules were exothermic and spontaneous owing to negative ∆H and ∆G values, respectively. The values of binding distance between protein and drug molecules were calculated from Förster resonance energy transfer theory. It was found from CD analysis that the bindings of MPT and GF drugs to HSA and HMG proteins altered the secondary structure of HSA and HMG proteins.

Spectroscopic investigations of the interactions of tramadol hydrochloride and 5-azacytidine drugs with human serum albumin and human hemoglobin proteins.

The interactions of tramadol hydrochloride (THC) and 5-azacytidine (AZA) drugs with human serum albumin (HSA) and human hemoglobin (HMG) proteins were investigated by fluorescence, UV absorption and circular dichroism (CD) spectroscopy at pH 7.4 and different temperatures. The UV absorption spectra and the fluorescence quenching of HSA and HMG proteins indicated the formation of HSA-THC and HMG-THC complexes via static quenching mechanism. AZA did not interact with HSA and HMG proteins. It was found that the formation of HMG-THC complex was stronger than that of HSA-THC complex. The stability of HSA-THC and HMG-THC complexes decreased with increasing temperature. The number of binding site was found as one for HSA-THC and HMG-THC systems. Negative enthalpy change (ΔH) and Gibbs free energy change (ΔG) and positive entropy change (ΔS) values were obtained for these systems. The binding of THC-HSA and HMG proteins was spontaneous and exothermic. In addition, electrostatic interactions between protein and drug molecules played an important role in the binding processes. The results of CD analysis revealed that the addition of THC led to a significant conformational change in the secondary structure of HSA protein, on the contrary to HMG protein.

Attachment of benzo-crown ethers onto activated carbon cloth to enhance the removal of chromium, cobalt and nickel ions from aqueous solutions by adsorption.

This work consists of two stages. In the first stage, the adsorption of some monobenzo- and dibenzo-crown ethers onto activated carbon cloth (ACC) was investigated. Adsorption isotherm data were derived at 30 degrees C. Then the ACC surface was modified by saturating it with crown ethers. In the second stage, the adsorption of three metal ions, Cr(III), Co(II) and Ni(II), onto both the ACC and the ACC modified with crown ethers was investigated. The enhancement of adsorption of the ACC upon modification with crown ethers was examined for the three ions. The effects of the type and cavity size of crown ethers, the size and form of the ions on the extent of adsorption were discussed in terms of interactions of adsorbate species with the ACC surface. All the isotherm data were treated according to Langmuir and Freundlich models. Generally, Freundlich model was found to represent the experimental isotherm data better than Langmuir model.

Adsorptive removal of cationic surfactants from aqueous solutions onto high-area activated carbon cloth monitored by in situ UV spectroscopy.

Activated carbon cloth (ACC) was used as adsorbent for the removal of cationic surfactants such as benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl), benzyltributylammonium chloride (BTBACl), benzyldimethyldecylammonium chloride (BDMDACl), benzyldimethyltetradecyl ammonium chloride (BDMTDACl), benzyldimethylhexadecylammonium chloride (BDMHDACl), N-dodecylpyridinium chloride (N-DPCl) and N-cetylpyridinium chloride (CPCl) from aqueous solutions. The adsorption efficiency of the ACC was evaluated for cationic surfactants. Adsorption process was followed by in situ UV spectroscopic technique. The kinetic data, so obtained, were treated according to the pseudo first-order, the pseudo second-order, the Elovich and the intraparticle diffusion models in order to understand the adsorption mechanism of cationic surfactants onto the ACC. The best fit was found with the pseudo second-order model. The experimental isotherm data were obtained at 30 degrees C and analyzed by the Freundlich and the Langmuir models. The parameters of isotherm equations were determined. The Freundlich model was found to represent the experimental data better than the Langmuir model. The observed adsorption behaviors are discussed in terms of the pH of the solution, the nature of cationic surfactants (e.g. functional groups, size, and hydrophobicity) and the nature of the ACC (e.g. surface charge, pore size). A fair linear correlation was found between some adsorption parameters and apparent molar volumes at infinite dilution for benzyltrialkylammonium chlorides.

Removal of anionic surfactants from aqueous solutions by adsorption onto high area activated carbon cloth studied by in situ UV spectroscopy.

The removal of anionic surfactants, benzene sulfonate (BS), p-toluene sulfonate (TS), 4-octylbenzene sulfonate (OBS) and 4-dodecylbenzene sulfonate (DBS) from water and 0.01 M H(2)SO(4) solutions by adsorption onto high area activated carbon cloth (ACC) were studied by in situ UV-spectroscopic technique. The various properties of the ACC were given and the in situ UV-spectroscopic technique was described. Both kinetic and isotherm data were obtained for the adsorption of surfactants. Kinetic data were treated according to intraparticle diffusion, pseudo-first-order, pseudo-second-order and Elovich models. They were found to fit the pseudo-second-order model best. Isotherm data were treated according to well-known Langmuir and Freundlich models. The regression analysis of the data showed that Freundlich model represents the isotherm data of the surfactants better. The rate and extent of adsorption of surfactants were found to increase in the order BS

Adsorption of aromatic organic acids onto high area activated carbon cloth in relation to wastewater purification.

Adsorption of aromatic organic acids: benzoic acid (BA), salicylic acid (SA), p-aminobenzoic acid (pABA) and nicotinic acid (NA), onto high area activated carbon cloth from solutions in 0.4 M H(2)SO(4), in water at natural pH, in 0.1 M NaOH and also from solutions having pH 7.0 were studied by in situ UV-spectroscopic technique. The first-order rate law was found to be applicable for the kinetic data of adsorption. The rates and extents of adsorption of the organic acids were the highest from water or 0.4 M H(2)SO(4) solutions and the lowest from 0.1 M NaOH solution. The order of rates and extents of adsorption of the four organic acids in each of the four solutions (0.4 M H(2)SO(4), water, solution of pH 7.0 and 0.1 M NaOH) was determined as SA>BA>NA approximately pABA. These observed orders were explained in terms of electrostatic, dispersion and hydrogen bonding interactions between the surface and the adsorbate species, taking the charge of the carbon surface and the adsorbate in each solution into account. Adsorption of BA in molecular form or in benzoate form was analyzed by treating the solution as a mixture of two components and applying Lambert-Beer law to two-component system. The adsorption isotherm data of the systems studied were derived at 30 degrees C and fitted to Langmuir and Freundlich equations.

Adsorption behaviors of some phenolic compounds onto high specific area activated carbon cloth.

Adsorption of phenol, hydroquinone, m-cresol, p-cresol and p-nitrophenol from aqueous solutions onto high specific area activated carbon cloth has been studied. The effect of ionization on adsorption of these ionizable phenolic compounds was examined by studying the adsorption from acidic, basic and natural pH solutions. Kinetics of adsorption was followed by in situ UV spectroscopy over a period of 90 min. First-order rate law was found to be valid for the kinetics of adsorption processes and the rate constants were determined. The highest rate constants were obtained for the adsorption from solutions at the natural pH. The lowest rate constants were observed in basic solutions. The rate constants decreased in the order p-nitrophenol approximately m-cresol>p-cresol>hydroquinone approximately phenol. Adsorption isotherms were derived at 30 degrees C and the isotherm data were treated according to Langmuir, Freundlich and Tempkin isotherm equations. The goodness of fit of experimental data to these isotherm equations was tested and the parameters of equations were determined. The possible interactions of compounds with the carbon surface were discussed considering the charge of the surface and the possible ionization of compounds at acidic, basic and natural pH conditions.

Structural and ionization effects on the adsorption behaviors of some anilinic compounds from aqueous solution onto high-area carbon-cloth.

The adsorption of anilinic compounds; aniline, p-toluidine, 1-napthylamine and sodium salt of diphenylamine-4-sulfonic acid from solutions in H2O, in 1 M H2SO4 or in 0.1 M NaOH onto activated carbon-cloth was studied by in situ UV spectroscopy. A specially designed adsorption cell was used for this purpose. The adsorption processes were found to follow first-order kinetics and the rate constants were determined. The pH at the point of zero charge of the carbon-cloth surface was measured as 7.4. The highest rates and extents of adsorption were observed from H2O solutions for aniline, p-toluidine and 1-napthylamine and from solution in 1 M H2SO4 for the sodium salt of diphenylamine-4-sulfonic acid. The adsorption behaviors of these four anilinic compounds in the three solutions (in H2O, in 0.1 M NaOH and in 1 M H2SO4) were explained in terms of electrostatic and dispersion interactions between carbon-cloth surface and the anilinic species. The adsorption isotherm data for the anilinic compounds were derived at 30 degrees C and treated according to Langmuir and Freundlich models. The Freundlich model was found to represent the experimental isotherm data better than Langmuir model.

Binding of lead ion to bovine serum albumin studied by ion selective electrode.

The binding of Pb2+ to bovine serum albumin (BSA) at neutral pH was studied using lead ion selective electrode. The binding data was treated according to Scatchard Equation. The number of binding classes and the number of binding sites, intrinsic dissociation constants and stepwise binding constants for each class were determined. Two binding classes were found. Four binding sites in the first class and five binding sites in the second class were determined. Binding in the first class was stronger than in the second. Similar binding studies were carried out with heat treated BSA. It was found that not only the number of binding sites but also the strength of binding increases upon heat treatment.