Xingeng Ding

Core–shell superparamagnetic monodisperse nanospheres based on amino-functionalized CoFe2O4@SiO2 for removal of heavy metals from aqueous solutions

To remove heavy metals from aqueous solutions, amino-functionalized superparamagnetic CoFe2O4@SiO2 (CoFe2O4@SiO2–NH2) core–shell nanospheres were designed and constructed. In particular, well-defined CoFe2O4 nanoparticles (NPs) were synthesized by reverse co-precipitation. The shell of the CoFe2O4 NPs was composed of amorphous silica (SiO2), which had a thickness of ∼35 nm. Monodisperse CoFe2O4@SiO2 nanospheres grafted with more amino groups had a greater adsorption capacity and higher removal efficiency for heavy metal ions (Cd(II): 199.9 mg g−1, 99.96%; Cu(II): 177.8 mg g−1, 88.05%; Pb(II): 181.6 mg g−1, 90.79%). The effects of the pH, initial concentrations, reaction temperature and time on the adsorption of heavy metal ions by CoFe2O4@SiO2–NH2 were analyzed systematically. The adsorption process on the nanospheres was well described by the Langmuir model. The adsorption kinetics can be best fitted by the pseudo-second-order kinetics model. Analysis of a thermodynamic study of Cu(II) showed that the process of adsorption is spontaneous and endothermic in nature. Owing to the superparamagnetic properties with a high saturation magnetization value (32.92 emu g−1) of CoFe2O4@SiO2–NH2, the metal-loaded nanospheres can be quickly removed from an aqueous solution (30 s) by magnetic separation. Moreover, the nanospheres exhibited good reusability for up to five cycles. The results confirm that the monodisperse amino-functionalized CoFe2O4@SiO2 magnetic nanospheres could be a potential adsorbent for the effective and regenerable removal of heavy metals from aqueous solutions.

Preparation of amino-functionalized CoFe2O4@SiO2 magnetic nanocomposites for potential application in absorbing heavy metal ions

Amino-functionalized nanocomposites with a magnetic CoFe2O4 core and an amorphous SiO2 shell have been designed and synthesized. The core–shell structure was characterized by SEM, EDS, TEM, FTIR and XPS. CoFe2O4@SiO2–NH2 with a high saturated magnetization (28.09 emu g−1) can be easily separated under a moderate external magnetic field within one minute. In addition, the adsorption capacity of the CoFe2O4@SiO2–NH2 for Cu(II), Cd(II) and Mn(II) was 170.829, 144.948 and 110.803 mg g−1, respectively. The removal efficiency was increased from 12 to 85% with an increase in the pH from 4 to 6.5. The adsorbent can be recycled for at least four cycles with a feasible removal efficiency (85.41%). The adsorption process was fitted by pseudo-second-order kinetics and a Langmuir isotherm model. Based on the data of the present investigation, CoFe2O4@SiO2–NH2 could find potential applications in heavy metal ion wastewater treatment.

Preparation of magnetic porous NiFe2O4/SiO2 composite xerogels for potential application in adsorption of Ce(IV) ions from aqueous solution

In this work, a novel magnetic porous adsorbent was prepared via a sol–gel method for the removal of Ce(IV) from aqueous solution. The NiFe2O4/SiO2 composite xerogels were characterized using SEM, BET, FT-IR, XPS, TEM, VSM and XRD. In addition, the effects of initial concentration, amounts of adsorbents, contact time, solution pH and temperature on the adsorption of Ce(IV) were investigated via batch adsorption studies. The results verify the formation of hierarchically porous structures with a specific surface area of 1085.3 m2 g−1. The adsorption capacity for Ce(IV) at 25 °C is 114.56 mg g−1 (91.65%), the adsorption of Ce(IV) onto the composite xerogels was better described by the pseudo-second-order kinetic model, and the data fit well with the Langmuir isotherm model. Thermodynamic parameters such as standard enthalpy (ΔH0), standard entropy (ΔS0) and standard free energy (ΔG0) indicated that the adsorption of Ce(IV) onto composite xerogels was spontaneous and endothermic within the temperature range of 278–338 K. Moreover, the adsorbents showed good performance and recycling ability and could be separated by applying a magnetic field.

PVP-assisted synthesis and photocatalytic properties of magnetic Fe 3 O 4 /SiO 2 /BiOBr composite

In this study, a magnetic Fe3O4/SiO2/BiOBr composite photocatalyst was controllably synthesized a PVP-assisted solvothermal method. The Fe3O4/SiO2/BiOBr composites are composed of many three-dimensional (3D) flower-like BiOBr microspheres loaded with many spherical Fe3O4 particles. The formation mechanism and effect of PVP’s concentration on the products were investigated and proposed. Experimental results showed that PVP might act as a potential crystal plane inhibitor in the system as well as the stabilizer on the surface of BiOBr nanoplates. The Fe3O4/SiO2/BiOBr displayed high photocatalytic activity for the degradation of RhB under visible light irradiation, after which it can be easily recovered by applying an external magnetic field. Moreover, the as-prepared photocatalyst exhibited excellent stability and reusability in the cycled experiments.