Single-component Aqueous Solutions Research Articles

Amphoteric chitosan derivatives for the removal of basic and reactive dyes from aqueous solutions

The present study describes the use of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide and 2-acrylamido-2-methyl-1-propanesulfonic acid as grafting agents to chitosan (CS) natural polymer were examined. Two chitosan derivatives were synthesized in this study, and then added in single-component aqueous solutions in order to study the removal of Methylene Blue (MB) and Remazol Brilliant Blue R (RBBR) dyes, by adsorption, in a more innovative way. The characterization of the chitosan derivatives was achieved via X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Adsorption efficiency of the chitosan derivatives was tested at several pH values (2–12) and for adsorbent’s dosage between 10 and 50 mg per 30 mL effluent. The rising of temperature from 25 to 65 °C led to increased adsorption capacity. Equilibrium data were fitted to both the more common Langmuir and Freundlich isotherm models, as well as the Sips isotherm model. Pseudo 1st and 2nd kinetic order equations and a relatively simple phenomenological kinetic model for adsorption kinetics, were studied as well as the thermodynamic parameters were calculated. The adsorption capacity for CS grafted with [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (CS-SBMA) was 238.1 and 244.5 mg/g for MB and RBBR removal, respectively, at 25 °C, while for CS grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid (CS-AMPS) the adsorption capacity was 219.5 and 203.9 mg/g for MB and RBBR removal, respectively, at 25 °C.

Creation of Polymer Hydrogelator/Poly(Vinyl Alcohol) Composite Molecular Hydrogel Materials.

Polymer hydrogels, including molecular hydrogels, are expected to become materials for healthcare and medical applications, but there is a need to create new functional molecular gels that can meet the required performance. In this paper, for creating new molecular hydrogel materials, the gel formation behavior and its rheological properties for the molecular gels composed of a polymer hydrogelator, poly(3-sodium sulfo-p-phenylene-terephthalamide) polymer (NaPPDT), and water-soluble polymer with the polar group, poly(vinyl alcohol) (PVA) in various concentrations were examined. Molecular hydrogel composites formed from simple mixtures of NaPPDT aqueous solutions (0.1 wt.%~1.0 wt.%) and PVA aqueous solutions exhibited thixotropic behavior in the relatively low concentration region (0.1 wt.%~1.0 wt.%) and spinnable gel formation in the dense concentration region (4.0 wt.%~8.0 wt.%) with 1.0 wt.% NaPPDT aq., showing a characteristic concentration dependence of mechanical behavior. In contrast, each single-component aqueous solution showed no such gel formation in the concentration range in the present experiments. No gel formation behavior was also observed when mixed with common anionic polymers other than NaPPDT. This improvement in gel-forming ability due to mixing may be due to the increased density of the gel's network structure composed of hydrogelator and PVA and rigidity owing to NaPPDT.

Photocatalytic Pt/Ag3VO4 micromotors with inherent sensing capabilities for corroding environments

Autonomous self-propelled micromachines based on semiconductors are at the forefront of environmental pollutants degradation research to palliate the effects of the contamination arising from the constant manufacturing of new products. Nonetheless, testing these micromotors with real-life products is almost an unexplored field, limiting the degradation of pollutants to single-component aqueous solutions or suspensions at the laboratory scale, which hinders the translation of these micromachines into useful systems. Herein, Ag3VO4 has been devised as a micromotor by an asymmetric deposition of a thin layer of Pt, giving rise to Pt/Ag3VO4 micromotors (Janus particle). Their motion capabilities have been demonstrated under UV light in fuel-free conditions. Their photocatalytic performance at laboratory scale has been confirmed for the degradation of Rhodamine B while, as a first approximation of a real-life application, the degradation of an energy drink has also been tested. During this latter exploration, the Pt/Ag3VO4 micromotors were corroded by the citric acid present in the pollutant, releasing Ag nanoparticles into the media. As a proof of concept, the position of the generated Ag nanoparticles’ surface plasmon resonance absorption maximum has been demonstrated to show a dependency on the concentration of citric acid.

Strongly Basic Anion Exchange Resin Based on a Cross-Linked Polyacrylate for Simultaneous C.I. Acid Green 16, Zn(II), Cu(II), Ni(II) and Phenol Removal.

The adsorption ability of Lewatit S5528 (S5528) resin for C.I. Acid Green 16 (AG16), heavy metals (Zn(II), Cu(II) and Ni(II)) and phenol removal from single-component aqueous solutions is presented in this study to assess its suitability for wastewater treatment. Kinetic and equilibrium studies were carried out in order to determine adsorption capacities, taking into account phase contact time, adsorbates’ initial concentration, and auxiliary presence (NaCl, Na2SO4, anionic (SDS) and non-ionic (Triton X100) surfactants). The pseudo-second-order kinetic model described experimental data better than pseudo-first-order or intraparticle diffusion models. The adsorption of AG16 (538 mg/g), phenol (14.5 mg/g) and Cu(II) (5.8 mg/g) followed the Langmuir isotherm equation, while the uptake of Zn(II) (0.179 mg1−1/nL1/n/g) and Ni(II) (0.048 mg1−1/nL1/n/g) was better described by the Freundlich model. The auxiliary’s presence significantly reduced AG16 removal efficiency, whereas in the case of heavy metals the changes were negligible. The column studies proved the good adsorption ability of Lewatit S5528 towards AG16 and Zn(II). The desorption was the most effective for AG16 (>90% of dye was eluted using 1 mol/L HCl + 50% v/v MeOH and 1 mol/L NaCl + 50% v/v MeOH solutions).

Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration.

We recently found that rough glass surfaces (RGSs) can in situ mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (CnTABs, n = 12, 14, and 16), a kind of typical cationic STAs. That is, a CnTAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried CnTAB aggregates were then rehydrated in a monomer solution of CnTAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS in situ mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of CnTABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of CnTABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.

Batch and continuous adsorption of Cu(II) and Zn(II) ions from aqueous solution on bi-functionalized sugarcane-based biosorbent.

A new one-pot synthesis method optimized by a 23 experimental design was developed to prepare a biosorbent, sugarcane bagasse cellulose succinate pyromellitate (SBSPy), for the removal of Cu(II) and Zn(II) from single-component aqueous solutions, in batch and continuous modes. The bi-functionalization of the biosorbent with ligands of different chemical structures increased its selectivity, improving its performance for removing pollutants from contaminated water. The succinate moiety favored Cu(II) adsorption, while the pyromellitate moiety favored Zn(II) adsorption. Sugarcane bagasse (SB) and SBSPy were characterized using several techniques. Analysis by 13C Multi-CP SS NMR and FTIR revealed the best order of addition of each anhydride that maximized the chemical modification of SB. The maximum adsorption capacities of SBSPy for Cu(II) and Zn(II), in batch mode, were 1.19 and 0.95mmolg-1, respectively. Homogeneous surface diffusion, intraparticle diffusion, and Boyd models were used to determine the steps involved in the adsorption process. Isothermal titration calorimetry was used to assess changes in enthalpy of adsorption as a function of SBSPy surface coverage. Fixed-bed column adsorption of Cu(II) and Zn(II) was performed in three cycles, showing that SBSPy has potential to be used in water treatment. Breakthrough curves were well fitted by the Thomas and Bohart-Adams models.

Acrylic acid copolymers as adsorbent materials for the removal of anti-inflammatory pharmaceuticals from synthetic biomedical wastewaters

In this experimental study, the use of acrylic acid, and 1-vinylimidazole as monomers for the synthesis of one polymer (PVI) and one copolymer (PVI- co -PAA) was examined using trimethylolpropane trimethacrylate as the cross-linking agent. The synthesized polymeric materials were characterized using Fourier transform infrared spectroscopy (FTIR), BET analysis, Thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) and were evaluated towards their adsorption efficiency for the removal of two non-steroidal anti-inflammatory drugs, ibuprofen (IBU) and diclofenac (DCF), from single-component aqueous solutions. Parameters like pH, contact time, initial concentration of the drug and temperature were examined for their possible effect to the process. Acidic conditions appear to favor the uptake of the studied compounds. Moreover, the adsorption equilibrium data were fitted to Langmuir and Freundlich models calculating the maximum adsorption capacity, while Langmuir model exhibited a better fit indicating monolayer coverage of the pharmaceuticals onto the surface of synthesized derivatives. Furthermore, increase of temperature from 25 to 65 ℃ caused an enhancement of the adsorption ability, for both polymeric materials. while thermodynamic analysis revealed the spontaneous and endothermic nature of the process. • PVI and PVI- co -PAA polymers were synthesized. • Characterization was conducted with FTIR, TGA, BET and SEM analysis. • Acid pH appears to favor the process. • Equilibrium data exhibited better fitting to Langmuir model. • Thermodynamic analysis showed the spontaneous and endothermic nature of the process.

Micro-mixing in flow-type process for supercritical CO2 extraction of ferulic acid and gallic acid from aqueous solution

Micro-mixing technique in a flow-type process was applied for supercritical CO2 extraction of ferulic acid and gallic acid from aqueous solutions. Four principles of micro-mixing techniques such as swirl-mixing, cross-junction, T-junction, and cross-flow T-junction were used for the supercritical extractions. Swirl-mixer provides the best micro-mixing technique in terms of high extraction efficiency and high stability of the length of liquid slug formation. Using swirl-mixing technique, gallic acid was slightly extracted from single-component aqueous solution and its extraction efficiency was lower than ferulic acid. However, extraction of gallic acid from an aqueous solution containing both gallic and ferulic acids was undetectable since it acts as the promoter to facilitate the extraction of ferulic acid into CO2 extracts. At 39.5 °C, 14.3 MPa and using swirl-mixing technique, the extraction efficiency of ferulic acid from the aqueous solution was 10.5 % and it was further increased to 11.6 % with addition of 2.0 mol. % of ethanol as co-solvent. These results show the applicability of micro-mixing for supercritical CO2 extraction of highly polar compounds from aqueous solution.

Synthesis of poly (hydroxamic acid) ligand for removal of Cu (II) and Fe (II) ions in a single component aqueous solution

Biosorbents are the alternatives for the removal of heavy metals because they are cheaper and more effective. This is attributed to the metallic elements interactions with the functional groups on the surface of the adsorbent. Additionally, the surface of biosorbents can further be improved by pretreatment and modification leading to the formation of functional derivatives onto the cellulose backbone. In this study pine cone powder was pretreated using Fenton reagent and modified by grafting with acrylic acid in order to enhance structural characteristics of the material. Grafting of acrylic acid onto Fenton treated pine cone powder was achieved by a free radical procedure in which ceric ammonium nitrate (CAN) was used as an initiator. Furthermore, a new poly (hydroxamic acid) ligand was synthesized from the poly(acrylic acid) grafted pine cone powder for heavy metal ions removal from aqueous media. The observed FTIR bands that shifted from 1727 cm−1 shifted to 1616 cm−1 confirmed that ester functional groups were converted to hydroxamic acid groups, which was further confirmed by elemental analysis results. The poly (hydroxamic acid) ligand was further characterized by TGA/DTA, XRD, SEM-EDS techniques. The TGA/DTA results revealed that the poly(acrylic acid) grafted pine cone powder had better thermal stability. The XRD spectra revealed that the structure of pine cone powder is composed mainly of crystalline cellulose. The SEM results indicated that the grafted pine cone powder showed a smooth surface, which is an indication that the acrylic acid was coated on the surface of the Fenton treated pine cone powder. It further revealed a coarse surface the poly (hydroxamic acid) ligand confirming the conversion of the carboxyl group to hydroxamic acid group. The linear Langmuir isotherm plot gave an R2 values of 0.9997 for Cu (II), 0.9961 Fe (II) biosorption while Freundlich isotherm plot R2 values were 0.9581 for Cu(II) and 0.9671 Fe (II) biosorption. These results demonstrate that the Freundlich isotherm was not a good fit to describe the process of adsorbed metal ions and their equilibrium concentration in solution. The theoretical values qe (mg g−1) of the pseudo second order model compared with those for the pseudo first order kinetic model agree with the experimental value qe (mg g−1). Therefore, these results confirm the chemisorption of Cu (II) and Fe (II) onto poly (hydroxamic acid) ligand.

Approaches to a Mathematical Modeling of the Density of Nitrate Solutions on the Basis of Concepts of Apparent Molar Volume As Applied to Hydrometallurgical Processes of the Nuclear Fuel Cycle

A method is suggested for calculating the density of single-component aqueous solutions of nitric acid and nitrate salts contained in solutions used in hydrometallurgical processes on the nuclear fuel cycle. The method uses apparent molar volumes and the water concentration. The method makes it possible to calculate the density of nitric acid solutions up to 17 M (HNO3 dihydrate) and salts to the point of formation of saturated solutions with an error not exceeding 0.2%. The values of the apparent molar volumes linearly depend on the concentration of water, and the apparent molar values approximated to the infinite dilution correspond to the Pitzer values.

Chitosan Grafted Adsorbents for Diclofenac Pharmaceutical Compound Removal from Single-Component Aqueous Solutions and Mixtures.

The main purpose of this study was to investigate the synthesis of some cross-linked carboxyl-grafted chitosan derivatives to be used as selective adsorbents for diclofenac (DCF) pharmaceutical compounds from aqueous mixtures. Four different materials were synthesized using succinic anhydride (CsSUC), maleic anhydride (CsMAL), itaconic acid (CsITA), and trans-aconitic acid (CsTACON) as grafting agents. After synthesis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were performed before and after DCF adsorption. In addition, a complete adsorption evaluation was carried out for all materials studying some important parameters. The optimum pH was 4; the amino groups of DCF can be protonated at pH = 4 (–NH+), so this groups can easily attract the clear negatively carboxyl moieties (–COO−) of the chitosan adsorbents. The Qm for CsTACON was higher than those of the other materials, at all temperatures studied. By altering the temperature from 25 to 35 °C, an increase (16%) of Qm (from 84.56 to 98.34 mg g−1) was noted, while similar behavior was revealed after a further increase of temperature from 35 to 45 °C, improving by 5% (from 98.34 to 102.75 mg g−1). All isotherms were fitted to Langmuir, Freundlich, and Langmuir-Freundlich (L-F) models). In addition, a kinetic model was proposed taking into account not only the interactions but also the diffusivity of the molecule (DCF) into the polymeric network. The behavior of the prepared chitosan materials in simultaneously removing other compounds (synergetic or antagonistic) was also evaluated by experiments performed in mixtures. DCF presented the highest removal from the mixture in the order: CsTACON (92.8%) > CsITA (89.5%) > CsSUC (80.9%) > CsMAL (66.2%) compared to other pharmaceutical compounds (salicylic acid, ibuprofen and ketoprofen). Desorption was achieved by using different eluants (either water or organic). The highest desorption ability was found for acetone (100% for CsTACON, CsSUC, CsMAL and 77% for CsITA) for all materials.

Spontaneous vesicle formation and vesicle-to-micelle transition of sodium 2-ketooctanate in water

Single-tailed short-chain alkyl keto-acids/salts, a class of fatty acid/salt derivatives, such as sodium 2-ketooctanate (KOCOONa), are a kind of weakly acid/salt type amphiphiles and plausible prebiotic molecules, and the current understanding of their aggregation behavior in aqueous solutions is still limited. Herein, the aggregation behavior of KOCOONa in aqueous solution was studied by changing its concentration (C), using equilibrium surface tension, conductivity, and fluorescence measurements. The aggregates formed were characterized using freeze-fracture and cryogenic transmission electron microscopy, dynamic light scattering, atomic force microscopy, and confocal laser scanning microscopy. A concentration-driven stepwise aggregation was identified in the KOCOONa solution. Vesicles can spontaneously form from the single-component aqueous solution, with a critical vesicle concentration (CVC) of ∼15mM, which is obviously lower than that of octanoic acid/salt (120–200mM). With increasing C, a vesicle-to-micelle transition can occur, showing a critical micelle concentration (CMC) of ∼80mM. In addition, the membrane permeability of the KOCOONa vesicles was examined using small-size Calcein and large-size FITC-BSA as fluorescence probes, showing a size-selective permeability, similar to short-chain (C8-C11) fatty acid vesicles. For the first time, the aggregation behavior of single-tailed keto-acid salt surfactant is reported.

Synthetic strong base anion exchange resins: synthesis and sorption of Mo(VI) and V(V)

The result of synthesizing anion exchangers bearing trimethylammonium functionalities is presented. Ion exchange resins of poly(4-vinylbenzyltrimethylammonium chloride) (PVBTAC) (Resin 1) and poly(3-acrylamidopropyltrimethylammonium chloride) (PAPTAC) (Resin 2) were obtained via the radical polymerization technique and studies on the sorption of molybdenum and vanadium ions were conducted at 20, 30, and 40 °C using the batch method from single-component aqueous solutions. The greatest total sorption capacities were 198 mg Mo(VI) g−1 at 20 °C and 193 mg V(V) g−1 at 40 °C for Resin 1. The calculated thermodynamic parameters demonstrated that the sorption of Mo(VI) was an exothermic process, while the uptake of V(V) was endothermic. The kinetic studies revealed the compliance of the process with a quasi-second-order kinetic model. Simultaneously, equilibrium was achieved within 15 min in two rate-controlled stages. The fitting of the Langmuir and Freundlich mathematical models demonstrated the chemical character of the sorption processes. Elution and reuse studies showed that Mo(VI) may be completely recovered from both resins using a sodium carbonate solution. Moreover, the investigated materials are suitable for repeated sorption/desorption cycles.

The Adsorption of Pb, Zn, Cu, Ni, and Cd by Modified Ligand in a Single Component Aqueous Solution: Equilibrium, Kinetic, Thermodynamic, and Desorption Studies.

In this investigation, an amino functionalized adsorbent was developed by grafting 4-aminobenzoic acid onto the backbone of cross-linked chitosan beads. The 3 sets of beads including chitosan (CX), glutaraldehyde cross-linked chitosan (CCX), and 4-aminobenzoic acid grafted cross-linked chitosan (FGCX) were characterized by FTIR, XRD, SEM, and TGA. The water content and amine concentration of FGCX were determined. The effect of adsorption parameters was studied and the optimum was used for further studies. Equilibrium data was obtained from the adsorption experiment carried out at different initial concentration; the data were applied in isotherm, thermodynamics, and kinetic studies. The Langmuir and Dubinin-Kaganer-Radushkevich (DKR) models were successful in describing the isotherm data for the considered metal ions while the Freundlich and Temkin model fit some of the considered metal ions. Pseudo-second-order and intraparticle model described the kinetic data quite well. Thermodynamic parameters such as Gibb's free energy change (ΔGo), enthalpy change (ΔHo), and entropy change (ΔSo) were calculated and the results showed that the adsorption of Pb, Cu, Ni, Zn, and Cd ions onto FGCX is spontaneous and endothermic in nature. Regeneration of the spent adsorbent was efficient for the considered metal ions.

Application of waste materials as potential biosorbents for Cu(II) and Zn(II) removal

Mining is probably the most common activity that fundamentally impacts the country. The problems connected with the extraction of sulphide ores arise especially during the final stage of mining, closure and abandonment of the extraction area, when the conditions for the generation of strong acid water are most likely to occur. With respect to the diversity of compounds in acid mine drainage (AMD) and its low pH values it is hard to find an effective and inexpensive “active” treatment process. Recently, numerous approaches have been studied for the development of cheaper and more effective technologies, both to decrease the amount of heavy metals and to improve the quality of the treated effluent. Adsorption has become one of the alternative treatments; in the recent years, the search for low-cost adsorbents that have metal-binding capacities has intensified. Adsorption of heavy metals (Cu and Zn) from single-component aqueous solutions onto non-modified poplar sawdust, hemp shives and peat has been studied using the batch-adsorption techniques. For this purpose, solutions with different concentrations ranging from 10 to 150 mg/L have been used. The study was carried out to examine the adsorption capacity of the low-cost waste materials as potential biosorbents for the removal of heavy metals from acid mine drainage. The adsorption isotherms could be better fitted by the Langmuir model (values of the correlation factor range from 0.974 to 0.997). The values of the separation factor (RL) in the present study were found to be within 0.037–0.728, indicating the favorable adsorption process. From the comparison of maximum sorption capacities, it is evident that the best adsorption properties are exhibited by the hemp shives, and copper is overall better adsorbed than zinc (Qmax = 12.84 mg/g and 8.28 mg/g for copper and zinc, respectively). The results indicate that these freely abundant, low-cost waste materials can be treated as economically viable for the removal of metal ions in acidic conditions.DOI: http://dx.doi.org/10.5755/j01.ct.67.1.15003

Determination of effective hydrodynamic diameters of biopolymer molecules in high-viscosity mixtures by photon-correlation spectroscopy

Using model high-viscosity single-component and mixed systems based on biopolymers with different molecular sizes (poly(ethylene glycol), dextran, and polysucrose) as examples, it is shown by photon-correlation spectroscopy combined with monoand polymodal analysis that solvent viscosity should be used, when calculating the hydrodynamic diameter of molecules in single-component aqueous solutions and mixed solutions of dextran and polysucrose, which have close molecule sizes, by the Stokes–Einstein equation. For mixtures of dextran and polysucrose with polyethylene glycol, the viscosity of the medium, the role of which is played by the poly(ethylene glycol) solution, should be used.

On the real performance of cation exchange resins in wastewater treatment under conditions of cation competition: the case of heavy metal pollution

Sorption performance of cation-exchange resins Amberlite® IRN77 and Amberlite™ IRN9652 toward Cs(I) and Sr(II) has been tested in single-component aqueous solutions and simulated waste effluents containing other monovalent (Effluent 1) or divalent (Effluent 2) metal cations, as well as nitrate, borate, or carbonate anions. The individual sorption isotherms of each main component were measured by the solution depletion method. The differential molar enthalpy changes accompanying the ion-exchange between Cs+ or Sr2+ ions and protons at the resin surface from single-component nitrate solutions were measured by isothermal titration calorimetry and they showed a higher specificity of the two resins toward cesium. Compared to the retention limits of both resins under such idealized conditions, an important depression in the maximum adsorption capacity toward each main component was observed in multication systems. The overall effect of ion exchange process appeared to be an unpredictable outcome of the individual sorption capacities of the two resins toward various cations as a function of the cation charge, size, and concentration. The cesium retention capacity of the resins was diminished to about 25% of the "ideal" value in Effluent 1 and 50% in Effluent 2; a further decrease to about 15% was observed upon concomitant strontium addition. The uptake of strontium by the resins was found to be less sensitive to the addition of other metal components: the greatest decrease in the amount adsorbed was 60% of the ideal value in the two effluents for Amberlite® IRN77 and 75% for Amberlite™ IRN9652. It was therefore demonstrated that any performance tests carried out under idealized conditions should be exploited with much caution to predict the real performance of cation exchange resins under conditions of cation competition.

Nanostructured fluids from pluronic® mixtures

Micellization and gelation of binary mixtures of EO99PO69EO99 (pluronic(®) F127) and EO80PO27EO80 (pluronic(®) F68) in aqueous solutions were investigated by means of micro-differential scanning calorimetry and rheology and for a total copolymer concentration fixed at 20 wt%. The aim of this investigation is to determine the interplay between micellization and macroscopic gelation of the mixed solutions. Micro-DSC reveals the formation of two distinct populations in F127/F68 mixtures during heating and subsequent cooling of the solutions. The enthalpies of micellization of each copolymer and the respective onset temperatures remained constant after mixing indicating the predominance of two independent processes of micellization in the mixtures. The F127 exhibits a crystallization transition, at a distinct temperature which persists, but increases in the mixtures with concentrations higher than 10 wt%. Rheological measurements were performed during heating ramps or after maturation periods versus frequency. They showed two types of gelation transitions: either a steep increase of the storage and the loss moduli, which corresponds to the crystallization temperature of the F127 micelles or a progressive jamming transition when no crystal can form. Maturation process has a major effect on the rheological properties of the mixed gels, possibly related to local rearrangements of the two micellar phases. This investigation highlights the unique features of the binary pluronic(®) mixtures, compared to dilution effects of single component aqueous solutions.

Glassy aerosols with a range of compositions nucleate ice heterogeneously at cirrus temperatures

Abstract. Atmospheric secondary organic aerosol (SOA) is likely to exist in a semi-solid or glassy state, particularly at low temperatures and humidities. Previously, it has been shown that glassy aqueous citric acid aerosol is able to nucleate ice heterogeneously under conditions relevant to cirrus in the tropical tropopause layer (TTL). In this study we test if glassy aerosol distributions with a range of chemical compositions heterogeneously nucleate ice under cirrus conditions. Three single component aqueous solution aerosols (raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA) and levoglucosan) and one multi component aqueous solution aerosol (raffinose mixed with five dicarboxylic acids and ammonium sulphate) were studied in both the liquid and glassy states at a large cloud simulation chamber. The investigated organic compounds have similar functionality to oxidised organic material found in atmospheric aerosol and have estimated temperature/humidity induced glass transition thresholds that fall within the range predicted for atmospheric SOA. A small fraction of aerosol particles of all compositions were found to nucleate ice heterogeneously in the deposition mode at temperatures relevant to the TTL (<200 K). Raffinose and HMMA, which form glasses at higher temperatures, nucleated ice heterogeneously at temperatures as high as 214.6 and 218.5 K respectively. We present the calculated ice active surface site density, ns, of the aerosols tested here and also of glassy citric acid aerosol as a function of relative humidity with respect to ice (RHi). We also propose a parameterisation which can be used to estimate heterogeneous ice nucleation by glassy aerosol for use in cirrus cloud models up to ~220 K. Finally, we show that heterogeneous nucleation by glassy aerosol may compete with ice nucleation on mineral dust particles in mid-latitudes cirrus.

Removal of dyes from aqueous solutions with untreated coffee residues as potential low-cost adsorbents: Equilibrium, reuse and thermodynamic approach

Industrial wastes of coffee (untreated coffee residues, UCR) were used as low-cost adsorbents for the removal of dyes (reactive and basic) from single-component aqueous solutions. The cost potential is high given for the non-further treatment of the coffee residues (just only washing with distilled water to remove dirt/color, and drying in oven). The characterization of adsorbents was carried out with SEM micrographs, titrations for point of zero charge (PZC), BET analysis for surface area, titrations (Boehm method) for surface functional groups, and energy dispersive X-ray microanalysis (EDX) for elemental analysis/composition. The optimum pH found after adsorption experiments was pH=2 for reactive and pH=10 for basic dyes. The equilibrium experimental data were fitted to Langmuir, Freundlich, and Langmuir–Freundlich model (best correlation: R2>0.997). The calculated maximum adsorption capacities (Qmax) for the reactive dye at 25°C were 179mg/g (pH=2) and 295mg/g for the basic one (pH=10). Pseudo-first, -second, and -third order kinetic equations were used to fit the kinetic data (pseudo-second order equation presented the most sufficient correlation, R2>0.992). Some other adsorption parameters, as agitation rate, initial dye concentration and temperature (25, 45 and 65°C) were also determined. Also, a full thermodynamic evaluation was realized, calculating the parameters of enthalpy, free energy and entropy (ΔH0, ΔG0, and ΔS0). The desorption was evaluated with experiments for the optimum desorption pH and desorption kinetics, while the ability of reuse was determined with 10 cycles of adsorption–desorption (the reduction in adsorption percentages from the 1st to 10th cycle was approximately 7% for both dyes). Additionally, experiments in dyeing mixtures were realized in dyeing mixtures composed of (i) separately reactive or basic dyes, and (ii) simultaneously reactive and basic dyes. After the dosage of 3g/L of adsorbent, a very slight change was observed in equilibrium for all types of dyeing mixtures studied.