Preparation And Properties Of Iron Nanoparticles Supported On Sintered Active Carbon

Iron nanoparticles(NPs), a promising adsorbent with large surface areas and prominent interfacical properties, play a siganificant role on the removal of heavy metals and organic pollutants in wastewater. However, their widespread application in water treatment is greatly limited due to the serious aggregation caused by the high surface energy and intrinsic magnetic properties. Therefore, it is of great significance to prevent the iron NPs from aggregation and subsequently enhance the reactivity.This study firstly investigated the preparation, characterization and application of iron NPs for the removal of Pb(II) ions in aquoues solutions. Using polyethylene glycol(PEG-4000 and PEG-20000) and polyvinyl pyrrolidone(PVP) as surfactants, iron NPs were prepared via a Na BH4-reduced method. The properties of the iron NPs were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR) and UV-visible spectrophotometer(UV). The concentration of Pb ions was studied by atomic absorption spectrophotometer(AAS). The SEM tests showed that all the three surfactants improved the dispersion of iron NPs. It is worth noting that fibrous iron NPs were obtained using PEG-4000 and PEG-20000 as a stabilizer, and that fluffy particulated NPs were obtained using PVP as a surfactant. FT-IR tests indicated that three surfactants adsorbed on the surface of iron NPs through the physical force. XRD analyses demonstrated that the surfactants did not change the crystal structures of the iron NPs. UV analysis showed that the dispersion of iron NPs synthesized using PEG-20000 and PVP as surfactants was better than those synthesized using PEG-4000. AAS results manifested that the maximum adsorption capacity of Pb(II) could reach 229 mg/g when iron NPs were prepared by adding 3% PEG-20000.Subsequently, the adsorption of Pb(II) by iron NPs obtained by using PEG-20000 was investigated in detail.The effects of initial Pb concentrations, contact time, solution p Hs and adsorbent dosages in the adsorption capacity were studied. The kinetics and thermodynamic properties of the adsorption process were also investigated to well understand the mechanism. The studies showed that the adsorption process was highly dependent on the initial Pb(II) concentrations, contact time, solution p Hs and adsorbent dosages.The optimum p H value was 5.5~6.1, which could promote metal adsorption.The Pb(II) removal rate was well correlated with the adsorbent dosages and inversely proportional to the initial concentration. The adsorption data were analyzed using Langmuirand Freundlich models. It was found that the former isotherm was better to describe the adsorption process than the latter. The pseudo-first-order kinetic model, pseudo-second-order kinetic model and Elovich model were used to analyze the kinetic data. It was found that, among the three kinetic models, the pseudo-second-order model was the best to describe the adsorption behavior of Pb(II) onto iron NPs. Furthermore, the thermodynamic analyes showed that the adsorption of Pb(II) was endothermic under the experimental conditions. The intra-particle diffusion model demonstrated that the adsorption process was controlled by both liquid diffusion and particle dispersion, the result of the combination between physical and chemical adsorption. The maximum adsorption capacity of as-prepared adsorbent was up to 774.4 mg/g Pb(II).Finally, the preparation and properties of iron NPs supported on sintered active carbon were studied. To increase the removal rate of Pb(II), the iron loading and soaking time were opimized. The surface morphology and crystal structures of as-prepared adsorbents were characterized by SEM, EDS and XRD. The resistance of water corrosion was also investigated. It was found that at the optimized iron loading of 1.8 mmol/g and the soaking time of 60 min, the removal rate and adsorption capacity of Pb(II) can reach 49.65% and 14.33 mg/g respectively, when the initial concentration of Pb(II) was 50 mg/L. SEM and EDS analyses indicated that the iron NPs were mainly distributed in the surface of the active carbon. Moreover, the prepared conditions did not cause sintered active carbon any significant change of original structure. In addition, the supported iron NPs showed better resistance of water corrosion. A very limited amount of iron ions were detected at the presence of shaking. The leaching rate firstly increased and then reached an equilibrium state. The higher iron loadings lead to the greater iron leaching. The maximum concentration of iron in water was much lower than 0.3 mg/L, indicating the long-term performance of free second contamination.