Adsorption of UO2 2+ on poly(N,N-diethylacrylamide-co-acrylic acid): effects of pH, ionic strength, initial uranyl concentration, and temperature

The removal of Cu(II) and Pb(II) ions from aqueous solutions by temperature-sensitive hydrogels based on N-isopropylacrylamide and itaconic acid

This study deals with the potential use of poly(N-isopropylacrylamide-co-itaconic acid) temperature-sensitive hydrogels as an adsorbent for the removal of Cu(II) and Pb(II) ions from aqueous solutions. For this aim, the adsorption properties of hydrogels were examined by adsorption capacities, adsorption isotherm, and adsorption kinetics experiments. To describe the adsorption characteristics of hydrogels, the obtained experimental data were evaluated by Langmuir, Freundlich, Redlich-Peterson, and Dubinin-Radushkevich isotherm models. Adsorption kinetics experiments were carried out not only in single systems but also in binary systems where both ions were at equal initial concentrations for competitive adsorption studies. To predict the behaviors of the competitive and non-competitive adsorption process of ions onto hydrogels, the experimental adsorption data were analyzed by the pseudo-first-order model and the pseudo-second-order model. According to non-competitive ion removal findings, the adsorption capacities followed order Cu(II) > Pb(II) for all hydrogels, and the pseudo-second-order kinetic model explained the adsorption properties of the hydrogels. Competitive ion removal studies showed that all hydrogels were selective to Cu(II) ion. Furthermore, in the case of comparative investigations both of competitive Cu(II) and competitive Pb(II) removal by hydrogels, the metal ion removal capacity of N10 hydrogel was found as a bit higher than that of N7.5 and N5 in 48 h. That is, as the acidic group content increased in the hydrogel network, the adsorption capacity values also increased. In addition, the reusability of temperature-sensitive hydrogels seems possible without regeneration or after regenerating with acid, in case the temperature is increased above the LCST. Furthermore, even if it cannot be reused, these hydrogels that retain metal ions reach very small volumes by shrinking when the LSCT is exceeded, and thus they can be eliminated more easily than other conventional gels due to their small size. As a result, this temperature-sensitive hydrogel may propose as an alternative environmentally friendly adsorbent candidate for can be used for water purification and wastewater treatment.

Mussel-inspired anti-biofouling and robust hybrid nanocomposite hydrogel for uranium extraction from seawater

A major challenge of uranium extraction from seawater (UES) is to effectively block the biofouling without destroying the ecological balance, especially prevent the attachment of macroalgae on the surface of the adsorbent. Herein, a robust montmorillonite-polydopamine/polyacrylamide nanocomposite hydrogel is reported by a two-step method, including PDA intercalation MMT and further free radical polymerization with AM monomers. The interpenetrating structure of hydrogel lead to high water permeability with the swelling ratio of 51, which could fully facilitate the internal accessible sites exposure and increase the uranium diffusion. As a result, a high adsorption capacity of 44 mg g^-1 was achieved in lab-scale dynamic adsorption. Most importantly, the prepared anti-biofouling hydrogel adsorbents display excellent anti-adhesion ability towards Nitzschia after 8 days contact. The adsorption capacity of uranium can reach 2130 μg g^-1 in algae-contained simulated seawater. This hydrogel also exhibited a long service life of acceptable mechanical strength and adsorption capacity after at least 6 adsorption-desorption cycles. This new anti-biofouling nanocomposite hydrogel shows great potential as a new generation adsorbent for UES.

Adsorption of Uranium over NH2-Functionalized Ordered Silica in Aqueous Solutions

The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N₂ physisorption, Fourier transform infrared spectroscopy, and elemental C-H-N-S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mg_U·g_ads^-1 for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption-desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption-desorption cycles without any noticeable capacity decrease.

Self-assembly and the hemolysis effect of monodisperse N,N-diethylacrylamide/acrylic acid nanogels with high contents of acrylic acid

Monodisperse temperature/pH sensitive poly(N,N-diethylacrylamide/acrylic acid) (P(DEA/AAc)) nanogels with high contents of AAc up to 40 wt% have been prepared. In this study, it was unexpectedly found that the polydispersity of the nanogels with 40 wt% AAc strongly depended on the initiator concentration. Monodisperse P(DEA/AA) nanogels were synthesized only at a very low concentration of initiator. The phase transition behavior of the nanogels in water can be tuned by pH and temperature. Due to low polydispersity, the nanogels self-assembled into colloidal crystals at different temperatures below the volume phase transition temperature (VPTT). The sharp Bragg peaks of the crystals were significantly blue-shifted as the concentration of the nanogels was increased. In contrast, the condensed suspensions without crystals still exhibited clear colours resulting from a short-range order structure. The reflection spectra of the coloured suspensions showed that the peak wavelength became a bit longer and much broader. And the reflection intensity of the coloured suspensions was much weaker. Elastic and coloured crosslinked nanogel networks prepared by a one-pot and rapid light-initiated crosslinking method showed responses to pH and temperature. Furthermore, the interaction between the nanogels and peptide melittin was investigated. The results showed that an increasing AAc composition led to more efficient inhibition of the hemolytic activity of melittin. The nanogels with 40 wt% AAc composition completely inhibited hemolytic activity at a nanogel concentration of 400 µg ml(-1). Thus, monodisperse P(DEA/AAc) nanogels of high AAc composition may be developed as efficient substitutes for antibody-based antidotes. Owing to the combined influence of the periodic structure of the crystals of the nanogels and an efficient neutralization effect, the P(DEA/AAc) nanogels show promise to become an integral step for preparing valuable naked-eye biosensors as simple, cheap and stable substitutes for antibody-based antidotes.