The adsorption capacity of an activated carbon ⿿ calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ...ion from aqueous solution. The study was carried out at pH=5, in NaCl medium and in the ionic strength range 0.1⿿0.75molL⿿1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared.
Calcium alginate (AA-Ca) improves the adsorption capacity (qm) of active carbon (AC) in the ACAA-Ca adsorbent material (e.g., qm=15.7 and 10.5mgg⿿1 at I=0.25molL⿿1, for ACAA-Ca and AC, respectively).
SEM-EDX and thermogravimetric (TGA) measurements were carried out in order to characterize the composite material. The results of the speciation study on the Pb(II) solution and of the characterization of the ACAA-Ca and of the pristine AA-Ca and AC were evaluated in order to explain the specific contribution of AC and AA-Ca to the adsorption of the metal ion.
Several different definitions were in the past proposed to describe the term chemical speciation, and some of them were accepted from the scientific community ....
Gel beads of calcium alginate, pectate and polygalacturonate salts have been tested as sorbent materials for mercury(II) removal from aqueous solutions. Physico-chemical properties of gel beads, ...defined by SEM–EDX, TGA and texture and density analysis, were correlated with gel beads sorption capacity towards Hg2+ ion. A speciation study in aqueous solution was carried out to define the strength of interaction of mercury ion with the polymers investigated and to assess the more suitable experimental conditions to achieve the best effectiveness of Hg2+ sorption by gel beads. On the basis of the speciation study, pH values in the 3–5.5 pH range were considered appropriated for mercury(II) sorption by gel beads. Kinetics of mercury(II) sorption and calcium(II) release from the sorbent materials were studied at pH 3, 3.6 and 5.2. The highest sorption rate (K) and amount of mercury(II) adsorbed were obtained at pH 3 and 3.6; therefore, pH 3.3 was chosen for the equilibrium study of Hg2+ sorption at 25°C. The results obtained by using Langmuir and Freundlich isotherm equations show the following sorption capacity trend: Ca–Pect>Ca–PGA>Ca–AA.
Water is essential for humans, animals, and plants; pollutants, usually derived from anthropogenic activities, can have a serious effect on its quality. Heavy metals are significant pollutants and ...are often highly toxic to living organisms, even at very low concentrations. Among the numerous removal techniques proposed, adsorption onto suitable adsorbent materials is considered to be one of the most promising. The objective of the current study was to determine the effectiveness of halloysite nanotubes (HNT) functionalized with organic amino or thiol groups as adsorbent materials to decontaminate polluted waters, using the removal of Hg
2+
ions, one of the most dangerous heavy metals, as the test case. The effects of pH, ionic strength (
I
), and temperature of the metal ion solution on the adsorption ability and affinity of both materials were evaluated. To this end, adsorption experiments were carried out with no ionic medium and in NaNO
3
and NaCl at
I
= 0.1 mol L
−1
, in the pH range 3–5 and in the temperature range 283.15–313.15 K. Kinetic and thermodynamic aspects of adsorption were considered by measuring the metal ion concentrations in aqueous solution. Various equations were used to fit experimental data, and the results obtained were explained on the basis of both the adsorbent’s characterization and the Hg
2+
speciation under the given experimental conditions. Thiol and amino groups enhanced the adsorption capability of halloysite for Hg
2+
ions in the pH range 3–5. The pH, the ionic medium, and the ionic strength of aqueous solution all play an important role in the adsorption process. A physical adsorption mechanism enhanced by ion exchange is proposed for both functionalized materials.
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► Complexes of uranyl in aqueous solution with inorganic and organic ligands. ► Particular attention was paid to ligands of biological and environmental interest. ► Stability of ...complexes with different type of ligands was discussed. ► Sequestering ability of the different classes of ligands was evaluated and compared. ► Ligand classes with the highest sequestering ability are useful for bioremediation.
The interactions of dioxouranium(VI) cation with different organic and inorganic ligands of environmental and biological interest were carefully examined with the aim to draw a chemical speciation picture of this ion in natural aquatic ecosystems and in biological fluids. Since UO
2
2+ ion shows a significant tendency to hydrolyze, particular attention was paid in considering the hydrolysis species formation both in the presence and in absence of ligands. The results reported in the literature show that formation of the hydrolytic species assumes a great importance in the complexation models for all the UO
2
2+-ligand systems considered. In particular, the following ligands have been taken into account: (i) hydroxyl, chloride, fluoride, sulfate, carbonate and phosphate, as inorganic ligands, and (ii) carboxylates (with particular reference to oxalate and citrate), amines, amino acids, poly(amino carboxylates) (complexones), nucleotides, phosphonates, mercapto compounds and sulfonates, as organic ligands. In order to elucidate the speciation of uranyl in the presence of dissolved natural organic matter, the interactions with humic and fulvic acids were also considered. The strength of interaction in all the systems considered was expressed in terms of stability constants of complex species and, if available, of the relative thermodynamic stability parameters. When possible, if data reported in the literature were sufficiently homogeneous, trends of stability were found for the different ligands of the same class and for ligands of different classes. Moreover, relationships were derived for poly-functional ligands, such as poly-carboxylate, poly-amine and poly(amino carboxylate) ones, useful to predict the stability constants as a function of the number of binding sites per molecule, considering also, as in the case of amino acids, the contribution of the single functional groups to the whole stability of uranyl species formed. In addition, using the stability data collected for the uranyl-ligand systems considered, the sequestering capacity of some classes of ligands towards uranyl was calculated in terms of pL
0.5, i.e., the ligand concentration useful to bind at least 50% of the cation. A comparison of pL
0.5 of the most important classes of ligands considered was made to point out the different effectiveness in the UO
2
2+ sequestration by the different ligands which can be present in multi-component solutions as natural waters and biological fluids. Finally, some considerations are reported about the different experimental techniques employed to study the complex formation in solution.
Some composite materials have been prepared, constituted by a cyclodextrin-
-urethane-based nanosponge matrix in which a reduced graphene oxide/silver nanoparticles photocatalyst has been dispersed. ...Different chain extenders were employed for designing the nanosponge supports, in such a way as to decorate their hyper-cross-linked structure with diverse functionalities. Moreover, two different strategies were explored to accomplish the silver loading. The obtained systems were successfully tested as catalysts for the photodegradation of emerging pollutants such as model dyes and drugs. Enhancement of the photoactive species performance (up to nine times), due to the synergistic local concentration effect exerted by the nanosponge, could be assessed. Overall, the best performances were shown by polyamine-decorated materials, which were able to promote the degradation of some particularly resistant drugs. Some methodological issues pertaining to data collection are also addressed.
The interactions of epinephrine ((
)-(-)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol;
) with different toxic cations (methylmercury(II): CH
Hg
; dimethyltin(IV): (CH
)
Sn
; dioxouranium(VI): UO
...) were studied in NaCl
at different ionic strengths and at
= 298.15 K (
= 310.15 K for (CH
)
Sn
). The enthalpy changes for the protonation of epinephrine and its complex formation with UO
were also determined using isoperibolic titration calorimetry:
= -39 ± 1 kJ mol
,
= -67 ± 1 kJ mol
(overall reaction),
= -26 ± 4 kJ mol
, and
= 39 ± 2 kJ mol
. The results were that UO
complexation by
was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye-Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL
parameters. The sequestering ability trend resulted in the following: UO
>> (CH
)
Sn
> CH
Hg
. For example, at
= 0.15 mol dm
and pH = 7.4 (pH = 9.5 for CH
Hg
), pL
= 7.68, 5.64, and 2.40 for UO
, (CH
)
Sn
, and CH
Hg
, respectively. Here, the pH is with respect to ionic strength in terms of sequestration.
The interactions of dopamine 2-(3,4-Dihydroxyphenyl)ethylamine, (Dop−) with cadmium(II), copper(II) and uranyl(VI) were studied in NaCl(aq) at different ionic strengths (0 ≤ I/mol dm−3 ≤ 1.0) and ...temperatures (288.15 ≤ T/K ≤ 318.15). From the elaboration of the experimental data, it was found that the speciation models are featured by species of different stoichiometry and stability. In particular for cadmium, the formation of only MLH, ML and ML2 (M = Cd2+; L = dopamine) species was obtained. For uranyl(VI) (UO22+), the speciation scheme is influenced by the use of UO2(acetate)2 salt as a chemical; in this case, the formation of ML2, MLOH and the ternary MLAc (Ac = acetate) species in a wide pH range was observed. The most complex speciation model was obtained for the interaction of Cu2+ with dopamine; in this case we observed the formation of the following species: ML2, M2L, M2L2, M2L2(OH)2, M2LOH and ML2OH. These speciation models were determined at each ionic strength and temperature investigated. As a further contribution to this kind of investigation, the ternary interactions of dopamine with UO22+/Cd2+ and UO22+/Cu2+ were investigated at I = 0.15 mol dm−3 and T = 298.15K. These systems have different speciation models, with the MM’L and M2M’L2OH M = UO22+; M’ = Cd2+ or Cu2+, L = dopamine common species; the species of the mixed Cd2+ containing system have a higher stability with respect the Cu2+ containing one. The dependence on the ionic strength of complex formation constants was modelled by using both an extended Debye–Hückel equation that included the Van’t Hoff term for the calculation of the formation enthalpy change values and the Specific Ion Interaction Theory (SIT). The results highlighted that, in general, the entropy is the driving force of the process. The quantification of the effective sequestering ability of dopamine towards the studied cations was evaluated by using a Boltzmann-type equation and the calculation of pL0.5 parameter. The sequestering ability was quantified at different ionic strengths, temperatures and pHs, and this resulted, in general, that the pL0.5 trend was always: UO22+ > Cu2+ > Cd2+.
Magnesium has been listed among the 30 critical raw materials by the European Union. In recent years, many green and sustainable alternative Mg2+ sources have been sought to satisfy the EU’s demand ...and to avoid mineral ore consumption. In this context, saltwork bitterns, the by-products of solar sea salt production, have attracted much attention thanks to their high Mg2+ concentrations (up to 80 g/L) and low Ca2+ and bicarbonate contents (<0.5 g/L). Although investigations on Mg2+ extraction from bitterns in the form of Mg(OH)2(s) have already been performed, product purity has never been properly addressed. Mg(OH)2(s) is a chemical compound of great interest and extensive utility in numerous industrial applications only if the powder’s purity is >95% (w/w). This work presents a comprehensive experimental effort of reactive precipitation tests with NaOH solutions at stoichiometric and over-stoichiometric concentrations to: (i) assess the technical feasibility of Mg2+ recovery from real bitterns collected in saltworks of the Trapani district (Italy) and, (ii) for the first time, conduct an extensive purity investigation of the precipitated magnesium hydroxide powders as brucite. This experimental investigation demonstrates the possibility of extracting highly valuable compounds from saltwork bittern waste, embracing the water valorization and resource recovery approach.
•Reduced graphene oxide/Ag composites were embedded into nanosponge architectures.•The composite materials were tested as photocatalysts for dyes degradation.•Synergistic improvement of the catalyst ...efficiency was assessed.•Reusability of the composite photocatalyst material was tested.
Significant activity improvement was achieved by associating graphene oxide-silver composite photocatalysts with cyclodextrin-based nanosponge materials, due to the synergistic effect provided by the supramolecular host abilities of the nanosponge. Three photocatalysts were prepared, fully characterized (FT-IR, ss-NMR, Raman, XRD, SEM, EDX, AFM, ICP, TGA, potentiometric titration), and tested for the oxidative photodegradation of some dyes and phenols, chosen as model organic pollutants. Compared to the unsupported photocatalyst, the nanosponge-based materials showed enhanced performances (being able to carry out the degradation even of dyes which do not react in the presence of the unsupported catalyst), and good recyclability. The activity improvement is attributed to a local concentration effect provided by the nanosponge, able to capture the organic substrate in the proximity of the actual photocatalyst. The results presented herein provide a helpful basis for designing advanced catalytic systems.
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