Xiaoliang Zhang

Facile hydrothermal preparation of recyclable S-doped graphene sponge for Cu2+ adsorption

Graphene sponge (GS) has been widely employed for water purification, but adsorption capacity loss frequently occurs during the formation of spongy structure. In this study, we reported the hydrothermal preparation of S-doped GS for the removal of Cu(2+) with a huge adsorption capacity of 228 mg/g, 40 times higher than that of active carbon. The adsorption isotherm could be well fitted into the Freundlich model with a KF value of 36.309(L/mg)(1/n). The equilibrium adsorption could be fully achieved in the first 5 min. In the thermodynamics study, the negative ΔG indicated that the adsorption was spontaneous and physisorption in nature. The positive ΔH implied that the adsorption was endothermic. The changes of both pH and ionic strength had no apparent influence on the adsorption. S-doped GS could be easily regenerated by washing with acidic thiourea. Moreover, S-doped GS could be used for the adsorption of other heavy metal ions, too. The implication to the applications of S-doped GS in water treatment is discussed.

Fe3O4@SiO2 nanoparticles as a high-performance Fenton-like catalyst in a neutral environment

Advanced oxidation processes (AOP) have been widely applied in water treatment. However, traditional Fenton reactions based on a Fe2+–H2O2 system requires an acidic environment and generates a large amount of Fe3+ ions. Herein, we reported that magnetic Fe3O4 core–SiO2 shell nanoparticles (Fe3O4@SiO2 NPs) could be used as a Fenton-like catalyst for the decomposition of H2O2, resulting in the decoloration of methylene blue (MB). Fe3O4@SiO2 NPs had much higher activity than bare Fe3O4 cores, suggesting the coating of SiO2 enhanced the catalytic activity. Most importantly, the best performance of Fe3O4@SiO2 NPs was observed at neutral pH values. A higher temperature facilitated the diffusion of MB in solution, and thus, promoted the decoloration efficiency. The radical reaction nature was reflected by the electron spin resonance spectrum and the significant inhibition of the decoloration in the presence of the radical scavenger tertiary butanol. Fe3O4@SiO2 NPs could be magnetically separated and partially regenerated after the decoloration. The implication for the applications of Fe3O4@SiO2 NPs in water treatment is discussed.

Fe3O4/SiO2/C nanocomposite as a high-performance Fenton-like catalyst in a neutral environment

The traditional Fenton system (Fe2+–H2O2) only works in an acidic environment and produces a large quantity of sludge. In this study, we reported that a Fe3O4/SiO2/C nanocomposite (FSCNC) could be used as a high-performance Fenton-like catalyst for the decoloration of methylene blue (MB). To prepare FSCNC, SiO2 was precipitated on Fe3O4 cores by the hydrolysis of tetraethyl orthosilicate, and the deposition of carbon was via the hydrothermal dehydrogenation of glucose. FSCNC showed much higher catalytic activity than naked Fe3O4 at a neutral pH of 7.5. Efficient decoloration of MB was achieved within 15 min in the FSCNC–H2O2 system. The FSCNC–H2O2 system worked well in the pH range of 3.5–9.5 and showed good resistance to radical scavengers tertiary butanol and ethanol. Higher H2O2 concentration and temperature were preferred to achieve faster kinetics. The regeneration of FSCNC was easily achieved by washing the catalyst and about 70% of the initial activity was retained after 8 cycles. The implication to the future applications of FSCNC as a Fenton-like catalyst is discussed.