Sorption of food dyes on polyurethane foam and aluminum oxide

The sorption of food dyes Sunset Yellow (E-110), Tartrazine (E 102), Ponceau 4R (E-124), Fast Green FCF (E-143) on polyether-based polyurethane foam, and α-Al₂O₃ from water solutions has been studied. It has been found that the maximum sorption is observed in the range of 0.2 M HCl-pH 2 on polyurethane foam and at pH 2–4 on aluminum oxide. Under the optimal conditions the recoveries on polyurethane foam and α-Al₂O₃ are 20–30% and 70–80%, respectively. It has been shown by diffuse reflectance spectroscopy that, for all dyes except for Fast Green FCF, only one form of the dye that dominates under these conditions in the aqueous solution is extracted on the sorbents in the range of 0.5 M HCl, pH 8.0. Possible models of the interaction between the dyes and the sorbent surface are proposed.     

Mechanism of extraction of the palladium(ii) thiocyanate complex by polyether foam

The mechanism of sorption of the palladium(II) thiocyanate complex by polyether-type Polyurethane foam has been investigated. At low thiocyanate concentration, palladium is most likely extracted as Pd(SCN)(2). The results obtained in the presence of enough thiocyanate for formation of the Pd(SCN)(4)(2-) complex are in disagreement with several possible mechanisms for sorption of the anionic metal complex by the foam, such as adsorption, solvent extraction, ligand addition or exchange, and weak or strong base anion-exchange. The extraction of Pd(SCN)(4)(2-) at high pH increased in the order Li(+)< Na(+) < Cs(+)< Rb(+) < K(+)< NH(4)(+) which is in good relation with the "cation-chelation" mechanism. This mechanism was also found predominant in the extraction of Pd(SCN)(4)(2-) complex from hydrochloric acid solutions.     

Facile fabrication of hydrophobic octadecylamine-functionalized polyurethane foam for oil spill cleanup

To improve the hydrophobic property of polyurethane foam for oil spill cleanup, the polyurethane foam with nitrile groups is modified by grafting with oleophilic octadecylamine. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical contact angle measuring device are used to characterize the modified polyurethane foam. The results show that the octadecylamine has been successfully grafted onto the polyurethane foam and improved the foam hydrophobicity. The modified foam exhibits higher contact angle (146.3 ± 2.8°) compared to the unmodified foam (121.4 ± 3.2°). Moreover, the water sorption of the modified foam is 0.11g/g, which is much lower than that of the unmodified foam (0.84g/g). On the other hand, the sorption capacity of the modified foam for toluene, gasoline and diesel sorption is increased by 20?40%. Therefore, the polyurethane foam prepared by us can be effectively used in oil/solvent spill cleanup.     

Kinetics and retention characteristics of some nitrophenols onto polyurethane foams

The kinetics of sorption of the nitrophenols by the unloaded polyurethane foams (PUFs) were found fast, reached equilibrium in few minutes and followed a first-order rate equation with an overall rate constant k in the range (0.16-0.21)±0.01 min⁻¹. The retention of the tested nitrophenols by the unloaded foams is consistent with the “solvent extraction” mechanism. However, the sorption also followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The mean free sorption energy of the nitrophenols onto the PUF was found equal to 7.5±0.4 kJ/mol, which reflects physical sorption. Thus, a dual-mode involves both absorption related to solvent extraction and an added component for surface adsorption seems a more likely sorption mechanism model. While a dual-mode sorption model explains the observed retention behavior, the data suggest that, solvent extraction plays a much larger role than the added component for surface adsorption. The sorption and recovery percentages of the nitrophenols from fresh, natural and industrial wastewater by the proposed unloaded foam columns were quantitatively achieved. The height equivalent to theoretical plates (HETP), N, the breakthrough capacity and the critical capacity for the unloaded foam columns were found in the range of (0.8-1.1)±0.6 mm, (94-132)±3, 3.2-4.02 and 1.5-2.67 mg/g, respectively. The method was successfully applied for the retention and recovery of the tested nitrophenols spiked to fresh and industrial wastewaters.     

Extraction of azo dyes by polyurethane foam

The extraction of 12 closely related mono-azo dyes by polyester and polyether-type polyurethane foams was studied to gain more information regarding the mechanism of the extraction of organic compounds. The effects on extraction of solution pH, dye concentration and salt concentration were investigated. It was found that the extraction of the dyes involved a neutral zwitterionic species and is highly dependent on the parameters studied. The dependency of the extraction on these parameters can be explained in a manner consistent with solvent extraction; however, the dual-mode sorption mechanism seems a more likely model. This mechanism involves both absorption related to solvent extraction, and an added component for surface adsorption. While the dual-mode sorption model explains the observed extraction behaviour, the data suggest that surface adsorption plays a much larger role than previously considered.     

Sorption of iron(III) and iron(II) from acidic chloride solutions by polyether and polyester type polyurethane foams

Summary Iron(III) is sorbed by polyether type open-cell polyurethane foams from HCl solutions of 4 mol/l or higher. The capacity of the foams is around 50 mg·l^–1. The iron (III) sorbed can be eluted from the foam with 0.01 mol/l HCl or distilled water. An optimization of the sorption conditions showed that the process can be used for analytical applications. The polyurethane foam sorbents examined did not sorb iron(II). The mechanism of sorption by polyether foams seems to follow a mechanism similar to that of the extraction of iron(III) by etheric solvents.     

Evaluation of a beta-diketone-imbedded polyurethane foam

A beta-diketone-imbedded polyurethane foam was made for the sorption of uranium from aqueous solutions. The incorporation of the beta-diketone functional group into the polyurethane foam was simple, and relatively inexpensive. The beta-diketone foam was ground to facilitate the evaluation of its ability to extract uranium from aqueous solutions with a wide range of temperature and pH values. The beta-diketone material showed superior extractability of uranium from solutions with pH 7 +/- 3. In general, the beta-diketone material showed greater extractability of uranium at all temperatures and pH values tested when compared to a blank polyurethane foam without the beta-diketone functional group.     

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.     

Sorption of Ion Associates on Polyurethane Foams and Its Application to Sorption–Spectroscopic and Test Methods of Analysis

The results of studying the sorption of various ion associates on polyurethane foams were generalized. The main sorption-affecting factors were found to be the nature, hydrophobicity, and charge of the associate ion; the nature and concentration of the counter ion; the composition of the polymer unit of the polyurethane foam; and the pH and salt composition of the aqueous phase. Correlation equations were proposed to relate the partition coefficients with the hydration energy of counter ions in the ion associates of cationic dyes and metal complexes of 1,10-phenanthroline and with the number of carbon atoms in the alkyl fragment of cationic alkyltrimethylammonium surfactants. A sorption scheme was proposed and substantiated. Examples were given of the practical use of sorption for determining anionic and cationic surfactants, phenols, 1-naphthol, Fe(III), and Ru(IV).     

Continuous sorption of synthetic dyes on dried biomass of microalga Chlorella pyrenoidosa

The sorption of thioflavine T (TT) and malachite green (MG) cationic synthetic dyes on dried biomass of green microalga (Chlorella pyrenoidosa) immobilised in polyurethane foam under continuous column systems conditions using spectrophotometric methods of detection was investigated. Data characterising the sorption of TT and MG on microalgal biomass immobilised in polyurethane foam in a column system from single (C ₀ = 25 μmol dm^?3) or binary equimolar (C ₀ = 25 μmol dm^?3) dye solutions in the form of breakthrough curves were well described by the Thomas (R ² = 0.994–0.912), Yoon-Nelson (R ² = 0.994–0.911), and Clark (R ² = 0.993–0.911) models. Useful parameters characterising the sorption column system were obtained from these mathematical models. The Thomas model, in particular, provided the Q _max (maximal sorption capacity in μmol g^?1) parameter for characterisation of biosorbent and also for evaluation of competitive effects in the TT and MG dyes sorption. For the purposes of biomass regeneration, a one-step desorption of the dyes studied from the microalgal biomass in batch and continuous column systems was performed. Efficiency of TT desorption from microalgal biomass increased in the order: deionised H₂O (50.7 %), 99.5 vol. % 1,4-dioxane (67 %), 20 mmol dm^?3 NiCl₂ (83 %), 96 vol. % ethanol (85 %), 0.1 mol dm^?3 HCl (89 %), 1 mol dm^?3 acetic acid (89 %). In the case of MG, the desorption efficiency increased in the order: deionised H₂O (13 %), 20 mmol dm^?3 NiCl₂ (50 %), 0.1 mol dm^?3 HCl (91 %), 99.5 vol. % 1,4-dioxane (94 %), 1 mol dm^?3 acetic acid (99 %), 96 vol. % ethanol (> 99 %). The presence of carboxyl, phosphoryl, amino, and hydroxyl groups, the important functional groups for sorption of cationic xenobiotics, was also confirmed on the algae biomass surface by potentiometric titration and ProtoFit modelling software. The data obtained showed that the dried immobilised algae biomass could be used as a sorbent for removing toxic xenobiotics from liquid wastewaters or contaminated waters and also presenting the possibilities of mathematical modelling of sorption processes in continuous column systems in order to obtain important parameters for use in practice.     

The sorption properties of rutile and its catalytic activity in the destruction of dyes

The photocatalytic destruction of cationic and anionic dyes on dispersed spectrally pure rutile in the presence of oxygen was studied. The rate constant for these reactions does not correlate with the rate constant for the photobleaching of these dyes in homogeneous solutions in the absence of a catalyst, the rate constants for adsorption, and the rate of establishment of sorption equilibrium in rutile-dye systems, but increases as the sorption value grows. The photocatalytic process substantially disturbs sorption equilibrium in most of the systems studied. The conclusion is drawn that both weakly and strongly sorbed substrate molecules can participate in the photocatalytic process.     

The retention behaviour and separation of some water-soluble organophosphorus insecticides on polyester-based polyurethane foams

This paper reports the concentration of some dissolved organic phosphorus insecticides in water by open-cell polyurethane foam. The results of preliminary screening tests on the retention of the tested insecticides (Diazinon, Malathion and Chloropyrifos) by polyester foams indicated that a very high percent removal of the insecticides was obtained. The retention rate was fast and reaches equilibrium in a few minutes. The various parameters affecting the preconcentration of the tested insecticides by unloaded foam, e.g. pH, extraction media, shaking time, salt effect, flow rate, temperature and sample volumes have been optimized via the static mode of separation. The unloaded foams were employed in columns for the retention and recovery of the tested species. The sorption efficiency and the recovery of the tested compounds by the unloaded foam column were found to be up to 95.5%. The equivalent to a theoretical plate by the unloaded foam was found in the range 1.12 - 1.32 +/- 0.2 mm. The sorption mechanism of the tested species by the foam is discussed. The separation of some of the tested species in a mixture was achieved. The foam membrane offers unique advantages over conventional bulk-type granular sorbents and solvent extraction in offering high flow rates, rapid, versatile, effective separation and preconcentration of different species from aqueous samples. The foam provides the advantages of being, insoluble, easily separable and non-polluting, as well as inexpensive.     

Rotational-diffusion anomalies in dye solutions from transient-dichroism experiments

Subnanosecond transient-dichroism experiments have been performed to investigate the rotational diffusion of dyes in solution. Dyes and solvents were chosen in a way to obtain information on the influence of size, shape and hydrogen-bonding abilities either of the solute or the solvent molecules. One finds slow orientational relaxation of di-anionic xanthene dyes in alcohols, while oblate cationic dyes rotate faster in spite of their comparable size. The rotational diffusion times for alcohol solutions exceed the theoretical values predicted by the Debye-Einstein model except for prolate molecules. For a solute molecule with internal mobility the rotational diffusion exhibits a partial slip behaviour. It is shown that the deviations from the Debye-Einstein model are restricted to alcohols since for other solvents either with or without strong hydrogen-bonding abilities the experimental values agree with the hydrodynamic model including the stick-boundary condition. Experiments on erythrosine B reveal the influence of size and shape of the attached solvent molecules.     

Separation and determination of some trivalent metal ions using rhodamine B grafted polyurethane foam

The incorporation of rhodamine B into polyurethane foam matrix was prepared by mixing the rhodamine B with polyol (polyether) prior to the addition of diisocyanate reagent to form the polyurethane foam material. Rhodamine B grafted polyurethane foam (Rod.B-PUF) was found to be very suitable for the separation and preconcentration of trivalent metal ions e.g. bismuth (III), antimony (III) and iron (III) from thiocyanate solutions. Bismuth and antimony were separated from concentrated acid medium (1–6 M H₂SO₄). Iron (III) was separated from pH 1 to 3. The kinetics of sorption of the Bi (III), Sb (III) and Fe (III) onto the Rod.B-PUF was found to be fast, the extraction is accomplished from 5 to 10 min with average values of half-life of sorption (t_1/2) of 2.9 min. The average values of the Gibbs free energy (ΔG) for the sorption of metal ions onto Rod.B-PUF are ?6.6 kJ mol^?1, which reflect the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Rod.B-PUF was also discussed.     

Recovery of uranium by polyurethane foam impregnated with 5,8-diethyl-7-hydroxy-6-dodecanone oxime

Sorption of uranium(VI) has been inbestigated using an open-cell plyurethane foam impregnated with 5,8-diethyl-7-hydroxy-6-dodecanone oxime (LIX 63). Above pH 4.5 more than 99% of uranium is sorbed onto the LIX 63 impregnated foam, and uranium can be desorbed with a dilute acid from the foam. The sorption capacity for uranium increases linearly with increasing concentration of impregnated LIX 63. Quantitative removal of uranium from salt solutions was accomplished.     

Effect of quaternary ammonium cations on dye sorption to fly ash from aqueous media

The efficacy of the surface modification of fly ash by quarternary ammonium cations in the removal of dyes from aqueous solution is demonstrated. A series of organo-fly ash materials were synthesized by treating fly ash with quarternary ammonium cations such as tetraethylammonium, hexadecyltrimethylammonium, and benzyldimethyltetradecylammonium (TEA, HDTMA, and BDTDA). Two types of dyes were used for the investigation, disperse and anionic dyes. The effects of initial dye concentration, contact time, temperature, and the mechanism of dye sorption were investigated. The sorption was found to be affected by the structure and size of the quaternary ammonium cations as well as that of the dyes. Sorption of dyes was considerably enhanced by the surface modification. Thermodynamic parameters such as free energy (DeltaG0), enthalpy (DeltaH0), and entropy (DeltaS0) for the sorption process were also calculated.     

A Theoretical Study of the UV/Visible Absorption and Emission Solvatochromic Properties of Solvent‐Sensitive Dyes

Using the density‐functional vertical self‐consistent reaction field (VSCRF) solvation model, incorporated with the conductor‐like screening model (COSMO) and the self‐consistent reaction field (SCRF) methods, we have studied the solvatochromic shifts of both the absorption and emission bands of four solvent‐sensitive dyes in different solutions. The dye molecules studied here are: S‐TBA merocyanine, Abdel‐Halim's merocyanine, the rigidified aminocoumarin C153, and Nile red. These dyes were selected because they exemplify different structural features likely to impact the solvent‐sensitive fluorescence of “push‐pull”, or merocyanine, fluorophores. All trends of the blue or red shifts were correctly predicted, comparing with the experimental observations. Explicit H‐bonding interactions were also considered in several protic solutions like H₂O, methanol and ethanol, showing that including explicit H‐bonding solvent molecule(s) in the calculations is important to obtain the correct order of the excitation and emission energies. The geometries, electronic structures, dipole moments, and intra‐ and intermolecular charge transfers of the dyes in different solvents are also discussed.     

Kinetics study of oil sorption with open‐cell polypropylene/polyolefin elastomer blend foams prepared via continuous extrusion foaming

The objective of the present work was to study the sorption kinetics of open‐cell polypropylene/polyolefin elastomer (PP/POE) blend foams. First, open‐cell PP/POE foams of different cell structures were prepared by controlling the foaming temperature via a continuous extrusion foaming process. Second, the effect of the cell structures on the sorption process, rate, and capacity was studied. Pseudo‐first order and pseudo‐second order models were applied to study the sorption kinetics of the PP/POE foams for cyclohexane. Third, the sorption rate and sorption capacity by both volume and weight of the PP/POE foam for different oils and solvents were studied to show how the intrinsic properties of the testing oils and solvents affected the sorption performance. The results showed that the sorption with the PP/POE foams followed the pseudo‐second order kinetics model. Both the cell structures of the foams and the intrinsic properties of the testing oils and solvents affected the sorption performance. For the same testing oil, a higher open‐cell content in the foam was favorable for a higher sorption rate, and a higher void fraction was favorable for a higher sorption capacity. For the same foam, a lower viscosity of the testing oil was favorable for a higher sorption rate. The sorption capacity by volume was closely related to the viscosity of the testing oil, while both the viscosity and the density of the testing oil determined the sorption capacity by weight.     

酚醛型吸附树脂对水体系中吡啶和N,N-二甲基苯胺的吸附性能研究

研究了酚醛型吸附树脂在水体系中对吡啶和N，N-二甲基苯胺的静态和动态吸附行为．结果表明，在水中树脂对吡啶和N，N-二甲基苯胺的吸附主要以疏水吸附机理进行；吸附吡啶和N．N-二甲基苯胺的初始阶段，即达到38．3～48．9％平衡吸附时，吸附速率数据和半经验速率方程很吻合：酚醛型吸附树脂等温吸附吡啶和N，N-二甲基苯胺的平衡吸附数据符合Langmuir方程，相关系数在0．99以上，酚醛型吸附树脂吸附吡啶和N，N-二甲基苯胺属单分子层吸附：用80％的乙醇溶液作洗脱剂来洗脱吸附吡啶已达饱和的JDW-2树脂，效果是很理想的．在3．6个床体积内洗脱率达91．52％，4．8个床体积内洗脱率达到94．85％。表明酚醛型吸附树脂具有优良的洗脱性能．     

Sorption of organic dyes of various molecular weights on mineral sorbents and on sea and lake bottom sediments

The sorption of organic dyes of various molecular weights (from 100 to 700 amu) from aqueous solutions on minerals and on sea and lake bottom sediments was studied.