Yuantao Chen

The role of graphene oxide and graphene oxide-based nanomaterials in the removal of pharmaceuticals from aqueous media: a review

In this review paper, the ill effects of pharmaceuticals (PhAs) on the environment and their adsorption on graphene oxide (GO) and graphene oxide-based (GO-based) nanomaterials have been summarised and discussed. The adsorption of prominent PhAs discussed herein includes beta-blockers (atenolol and propranolol), antibiotics (tetracycline, ciprofloxacin and sulfamethoxazole), pharmaceutically active compounds (carbamazepine) and analgesics such as diclofenac. The adsorption of PhAs strictly depends upon the experimental conditions such as pH, adsorbent and adsorbate concentrations, temperature, ionic strength, etc. To understand the adsorption mechanism and feasibility of the adsorption process, the adsorption isotherms, thermodynamics and kinetic studies were also considered. Except for some cases, GO and its derivatives show excellent adsorption capacities for PhAs, which is crucial for their applications in the environmental pollution cleanup.

Complexation of radionuclide 152+154 Eu(III) with alumina-bound fulvic acid studied by batch and time-resolved laser fluorescence spectroscopy

To contribute to the understanding of Eu(III) interaction preperties on hydrous alumina particles in the absence and presence of fulvic acid (FA), the complexation properties of Eu(III) with hydrous alumina, FA and FA-alumina hybrids are studied by batch and time-resolved laser fluorescence spectroscopy (TRLFS) techniques. The continuous increase in the fluorescence lifetime of Eu-alumina and Eu-FA with increasing pH indicates that the complexation is accompanied by decreasing number of hydration water in the first coordination sphere of Eu(III). Eu(III) is adsorbed onto alumina particles as outer-sphere surface complexes of ≡(Al−O)−Eu· (OH)· 7H2O and ≡(Al−O)−Eu· 6H2O at low pH values, and as inner-sphere surface complexes as ≡(Al−O)2−Eu+· 4H2O at high pH. In FA solution, Eu(III) forms complexes with FA as (COO)2Eu+(H2O)x and the hydration water number in the first coordination sphere decreases with pH increasing. The formation of ≡COO−Eu−(O−Al≡)· 4H2O is observed on FA-alumina hybrids, suggesting the formation of strong inner-sphere surface complexes in the presence of FA. The surface complexes are also characterized by their emission spectra [the ratio of emission intensities of 5D0→7F1 (λ=594 nm) and 5D0→7F2 (λ=619 nm) transitions] and their fluorescence lifetime. The findings is important to understand the contribution of FA in the complexation properties of Eu(III) on FA-alumina hybrids that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Eu(III), or its analogue trivalent lanthanide and actinide ions in natural environment.

Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe3O4@TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe3O4@TNS nanosheets had high specific areas (114.9 m2 g-1 for core-shell Fe3O4@TNS and 130.1 m2 g-1 for yolk-shell Fe3O4@TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe3O4@TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities (Qmax) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g-1 for core-shell Fe3O4@TNS and 82.85, 173.01 and 283.29 mg g-1 for yolk-shell Fe3O4@TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (ΔH0, ΔS0 and ΔG0) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na+ and UO22+. The yolk-shell Fe3O4@TNS had more extraordinary sorption efficiency than core-shell Fe3O4@TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe3O4@TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications.