Gang Song

l-cysteine intercalated layered double hydroxide for highly efficient capture of U(VI) from aqueous solutions

l-cysteine intercalated Mg/Al layered double hydroxide (Cys-LDH) composites were fabricated and applied for treating the U(VI) contaminated wastewater under various conditions. Interaction mechanisms and adsorption properties were investigated by using batch experiments with spectroscopy analysis. The adsorption isotherms and kinetics were fitted perfectly with the Langmuir isotherm and the pseudo-second-order model, respectively. The significant maximum adsorption capacity of Cys-LDH (211.58u202fmg/g) compared to LDH was attributed to the larger number of functional groups on Cys-LDH. The presence of humic acid (HA) decreased U(VI) elimination on Cys-LDH at high pH but increased U(VI) removal at low pH. Typically, the presence of various anions (such as NO3-, Cl-, ClO4- and SO42-) did not obviously affect U(VI) adsorption on Cys-LDH, while the coexisted CO32- significantly affected U(VI) elimination. The predominate adsorption were determined to be the formation of Cys-U(VI)-Cys complexes with cysteine in the Cys-LDH interlayers. The results demonstrated that the Cys-LDH are promising adsorbents for efficient elimination and extraction of radionuclides in actual environmental contamination management.

Highly efficient Pb(II) and Cu(II) removal using hollow Fe3O4@PDA nanoparticles with excellent application capability and reusability

Potentially toxic metals in sewage and industrial effluents pose a serious threat to human health and the environment. Herein, core–shell hollow magnetic polydopamine nanoparticles (denoted as Fe3O4@PDA) were fabricated via a simple one-pot synthesis method and applied for the elimination of Pb(II) and Cu(II) from wastewater. The versatile polydopamine (PDA) layer with abundant functional groups (amine, imine and catechol groups) provided favourable sites to bind metal ions. The experimental results showed that the adsorption processes were significantly affected by the pH values of the suspension. The ionic strength-independent adsorption processes indicated the existence of inner-sphere surface complexes of Pb(II) and Cu(II) on Fe3O4@PDA. The results showed that Fe3O4@PDA exhibited fast removal kinetics for Pb(II) and Cu(II), which achieved equilibrium within 3 h. The adsorption processes were well fitted by the pseudo-second-order kinetic model and Langmuir isotherm model. Furthermore, the removal capacities of Fe3O4@PDA were calculated to be 57.25 mg g−1 for Pb(II) and 86.35 mg g−1 for Cu(II), which were much higher than those of pure Fe3O4 and other materials. Most importantly, the adsorption efficiencies of Pb(II) and Cu(II) on Fe3O4@PDA were still ∼71% and ∼70% after five cycles, respectively. In summary, the hollow Fe3O4@PDA nanoparticles can be used as outstanding materials for the elimination of Pb(II) and Cu(II), which is beneficial to reduce the toxic effects of heavy metal ion contaminated water.

Influence of carbonate on sequestration of U(VI) on perovskite

Cubic perovskite (CaTiO3) was successfully synthesized by a facile solvothermal method and was utilized to sequestrate U(VI) from aqueous solutions. The batch experiments revealed that carbonate inhibited U(VI) sequestration at pHu2009>u20096.0 due to the formation of uranyl-carbonate complexes. The maximum sequestration capacity of U(VI) on perovskite was 119.3u2009mg/g (pH 5.5). The sequestration mechanism of U(VI) on perovskite were investigated by XPS and EXAFS techniques. According to XPS analysis, the presence of U(IV) and U(VI) oxidation states revealed the photocatalytic reduction of U(VI) by perovskite under UV-vis irradiation. In addition, photocatalytic reduction performance significantly decreased in the presence of carbonate. Based on EXAFS analysis, the occurrence of U-Ti and U-U shells revealed the inner-sphere surface complexation and reductive precipitation of U(VI) on perovskite. These findings herein are crucial for the application of perovskite-based composites in the decontamination of U(VI) in aquatic environmental cleanup.

Impact of water chemistry on surface charge and aggregation of polystyrene microspheres suspensions

The discharge of microplastics into aquatic environment poses the potential threat to the hydrocoles and human health. The fate and transport of microplastics in aqueous solutions are significantly influenced by water chemistry. In this study, the effect of water chemistry (i.e., pH, foreign salts and humic acid) on the surface charge and aggregation of polystyrene microsphere in aqueous solutions was conducted by batch, zeta potentials, hydrodynamic diameters, FT-IR and XPS analysis. Compared to Na+ and K+, the lower negative zeta potentials and larger hydrodynamic diameters of polystyrene microspheres after introduction of Mg2+ were observed within a wide range of pH (2.0-11.0) and ionic strength (IS, 0.01-500mmol/L). No effect of Cl-, HCO3- and SO42- on the zeta potentials and hydrodynamic diameters of polystyrene microspheres was observed at low IS concentrations (<5mmol/L), whereas the zeta potentials and hydrodynamic diameters of polystyrene microspheres after addition of SO42- were higher than that of Cl- and HCO3- at high IS concentrations (>10mmol/L). The zeta potentials of polystyrene microspheres after HA addition were decreased at pH2.0-11.0, whereas the lower hydrodynamic diameters were observed at pH<4.0. According to FT-IR and XPS analysis, the change in surface properties of polystyrene microspheres after addition of hydrated Mg2+ and HA was attributed to surface electrostatic and/or steric repulsions. These investigations are crucial for understanding the effect of water chemistry on colloidal stability of microplastics in aquatic environment.

Macroscopic and microscopic investigation of uranium elimination by Ca–Mg–Al-layered double hydroxide supported nanoscale zero valent iron

In the past few decades, uranium (235, 238U(VI)) has turned into a forefront environmental issue due to its extensive use in the nuclear industry and its toxicity and radioactivity. Herein, nanoscale zero valent iron (nZVI), which was supported on Ca–Mg–Al-layered double hydroxide (Ca–Mg–Al-LDH/nZVI), was fabricated via an in situ growth route and employed for U(VI) decontamination from aqueous solutions. Spectroscopy and microscopy (SEM, TEM, FTIR, XRD, BET, and XPS) technologies were applied for the investigation of the properties of Ca–Mg–Al-LDH/nZVI and the U(VI) elimination mechanism. Ca–Mg–Al-LDH/nZVI had a remarkable BET surface (426.8 m2 g−1), abundant functional groups (i.e., Fe–O, Al–O, –OH, etc.), high efficiency (4 h to achieve equilibrium) and large adsorption capacities (Qmax = 216.1 mg g−1) for U(VI) removal. The decontamination process of U(VI) was observed to be pH-dependent and ionic strength-independent, suggesting that the adsorption was predominated by inner-sphere surface coordination. XPS spectroscopy analyses indicated that the reduction and adsorption of nZVI and the adsorption of Ca–Mg–Al-LDH dominated U(VI) elimination on Ca–Mg–Al-LDH/nZVI. The environmentally friendly synthesis method, excellent physicochemical properties and remarkable removal performance suggested that Ca–Mg–Al-LDH/nZVI was applicable as a potential adsorbent for U(VI) decontamination from wastewater in environmental pollution remediation.