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The NiAl layered double hydroxides (NiAl-LDHs) as well as NiAl layered double oxides (NiAl-LDOT, T: 300, 400, 500, 600 °C) were successfully synthesized by hydrothermal process and calcination treatment, and served as adsorbents for the efficient uptake of arsenate (As(V)) from aqueous solutions. Batch experiments were carried out at various solution pH, original As(V) concentration, contact time and calcination temperature. It was found that As(V) adsorption capacity on these composites can be changed by controlling the calcination temperature, and followed the order NiAl-LDO500 (198.1 mg/g) > NiAl-LDO400 (180.9 mg/g) > NiAl-LDO300 (160.2 mg/g) > NiAl-LDO600 (121.4 mg/g) > NiAl-LDH (60.7 mg/g), which could be ascribed to abundant surface adsorption sites and a “memory effect” provided by “Ni-O or Al-O” bonds. The thermodynamic experiments revealed that the elimination of As(V) was spontaneous and endothermic. In addition, multiple characterizations and batch experiments have been carried out to prove the surface adsorption and intercalation by rebuilding of primary layered structure contributed to As(V) adsorption. This discovery can provide a new insight into the elimination of As(V) from wastewater for environmental remediation.

Sandwich-like structure of graphene oxide (GO) @SiO2@C-Ni nanosheets were prepared by combining an extended stober method with subsequent carbonization treatment, in which polydopamine was used as reducing agent and carbon source. Firstly, the GO nanosheets were covered with SiO2 interlayer and finally coated with a outer shell of nickel ion doped polydopamine (PDA-Ni2+) with an extended stober method. Followed by a carbonization to produce the GO@SiO2@C-Ni sheets with metallic nickel nanoparticles embedded in PDA-derived thin graphic carbon layer. Notably, silica interlayer played a vital role in the formation of such GO@SiO2@C-Ni sheets. Without the protection of SiO2, the hydrophobic graphene@C-Ni composites were obtained instead. While with silica layer as the spacer, the obtained hydrophilic GO@SiO2@C-Ni composites were not only well dispersed in the solution, but also can be adjusted in terms of the size and density of Ni nanoparticles (NPs) on surface by changing the calcination temperature or the molar ratio between dopamine and nickel salt. Furthermore, nickel nanoparticles decorated on GO@SiO2 sheets were employed to enrich His-rich proteins (BHb and BSA) via specific metal affinity force between polyhistidine groups and nickel nanoparticles.

A novel magnetic flower-shaped yolk-shell like structure composite Fe3O4@NC@MnO2 (Fe3O4 nanostructures coupled with N-doped carbon and MnO2, denoted as FNCM) was successfully fabricated through a facile and scalable tactic. By batch experiments, the maximal removal capacites of FNCM towards Re(VII) and As(V) can reach 110.9 and 236.3 mg/g at 293 K, respectively. Besides, the formed FNCM had excel dispersion, moderate specific surface area (46.23 m2/g) and saturation magnetization (∼20 emu/g). Next, the adsorption performance of FNCM towards Re(VII) and As(V) was investigated as function of contact time, pH, interfering ions and solution temperature. It was indicated that FNCM possessed wonderful adsorption performance towards Re(VII) and As(V) elimination under the acidic condition, rarely affected by other co-existing ions under the same concentration, and exhibited higher removal capacity. Furthermore, On the base of zeta potential and microscopic spectra analysis, the adsorption mechanism of FNCM towards Re(VII) and As(V) can be drown to three aspects: complexation between Re(VII)/As(V) and oxygen-containing functional groups (oxide–metal bonds (O–M bonds)), electrostatic interaction, and protonated N adsorption. In all, these results imply that the FNCM could be as a potential candidate for remediating water contaminated with practical applications.