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In this paper, a 5-aminoisophthalic acid (APTA) functionalized magnetic composite nanoparticles (Fe3O4@SiO2-APTA) are reported for adsorbing methylene blue (MB) from wastewater. The nanoparticles were analyzed by high resolution transmission electron microscopy, scanning electron microscopy, fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, N2 adsorption/desorption, and vibrating sample magnetometer. The factors affecting the adsorption of methylene blue, initial concentration, adsorption time and pH of the solution were studied in detail. It was found that the adsorption capacity of magnetic composite nanoparticles depended on the pH of the solution. The results show that Fe3O4@SiO2-APTA exhibits an excellent adsorption performance with the maximum adsorption capacity (46.24 mg/g) for MB at pH 11. In addition, experimental results show that the adsorption of MB on Fe3O4@SiO2-APTA nanoparticles conforms to the pseudo-second-order kinetic model the Freundlich isotherm model, and reaches the adsorption equilibrium within 30 min. After consecutive use five times, adsorption percentages of MB were retained 70%, showing a good reusability of the adsorbent. The superior adsorption performances of Fe3O4@SiO2-APTA are attributed to electrostatic interaction, hydrogen bonding, and chemical sorption compared with recent adsorbents. Therefore, this work provides a promising approach for removal of MB with high efficiency, low cost.

In this paper, novel ferrocene functionalized sandwich-type core–shell structure magnetic nanocomposites (Fe3O4@SiO2–FC/COOH) are synthesized using the Fe3O4 as the core and the ferrocene and 5-Aminoisophthalic acid as the functional dendrimers. Taking advantage of high redox activity benefit of ferrocene, Fe3O4@SiO2–FC/COOH is fabricated to adsorb Cr(VI) and reduce it to nontoxic Cr(III) in aqueous solution. The structure and morphology of prepared magnetic adsorbent are characterized by FTIR, XRD, SEM, XPS, TEM, EDS, and TGA. Moreover, the effects of different factors (such as solution pH, adsorption time, adsorption temperature, adsorbent dosage etc.) on adsorption are evaluated. XPS analysis indicates that Cr(VI) is successfully reduced to nontoxic Cr(III) after adsorption by Fe3O4@SiO2–FC/COOH. The Fe3O4@SiO2–FC/COOH exhibits excellent removal efficiency with a maximum Cr(VI) adsorption of 228.395 mg g−1 at pH 2.0. In addition, the adsorption experimental results fit well with the Freundlich isotherm model and the pseudo-second-order kinetic model. Desorption experiment results demonstrate that the regenerated adsorption capacity can exceed more than 95% after five times adsorption–desorption cycles. Therefore, this work provides a promising approach for Cr(VI) removal from water solution.

In this paper, carboxylated ethylenediamine functionalization Fe3O4@SiO2 nanoparticles (Fe3O4@SiO2-EDA-COOH NPs) have been developed in order to remove methylene blue (MB) from aqueous solution. The chemical structure, morphology and magnetic characteristics of the magnetic composite nanoparticles were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), High resolution transmission electron microscopy (HR-TEM), Scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). To explore the truth, some methylene blue adsorption influenced factors of initial concentration, contact time and solution pH were at length investigated. The results showed that the absorption capacity depended strongly on pH, and the maximum adsorption value for MB (43.15 mg/g) was obtained at pH 10. In addition, the equilibrium was attained within 60 min, and the adsorption kinetics and adsorption isotherms data can be well accorded with pseudo-second-order kinetic model and Freundlich isotherm model, respectively. Most importantly, remarkable enhancement in adsorption capacity for MB is achieved than other reported adsorbents. It is worth noting that adsorbents can be quickly recovered from aqueous solution by external magnet. Finally, the plausible adsorption mechanism was briefly discussed. Our results suggest that novel nanoparticle Fe3O4@SiO2-EDA-COOH is a promising adsorbent in improving adsorption performance of MB from aqueous solution.

In this paper, using amidoxime as a functional monomer, different generations of polyamidoxime dendrimer magnetic microspheres (Fe3O4@SiO2-g-PAMAM-AO) were fabricated to adsorb Pb2+ and Ni2+ in aqueous solution. The magnetic adsorbents were characterized by FTIR, XRD, SEM, XPS, TEM, EDS, TGA and BET. The effects of different factors (such as solution pH, adsorption time, adsorption temperature, adsorbent dosage etc.) on adsorption were evaluated. Fe3O4@SiO2-g-PAMAM-AO has a maximum Pb(II) adsorption of 157.25 mg g−1 (100 mg L−1) at pH 5.5. Furthermore, Fe3O4@SiO2-g-PAMAM-AO showed an excellent adsorption performance for the removal of Ni(II) with a maximum adsorption capacity of 191.78 mg g−1 (100 mg L−1) at pH 8.0. The sorption isotherm data fitted the Freundlich isotherm model well. Adsorption kinetics analysis showed that it was best described by the pseudo-second-order rate model. Desorption experiment results showed that the adsorbent can be reused in the adsorption–desorption cycles.

Poly(amidoamine) dendrimer-based dithiocarbamate magnetic composites (Fe3O4@SiO2–PAMAM–DTC) were synthesized for the adsorption of Co2+ from aqueous solution. The adsorbents were characterized by X-ray diffraction (XRD), fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), vibrating sample magnetometer (VSM) and N2 adsorption/desorption. The effects of different factors (such as solution pH, adsorption time, adsorption temperature, adsorbent dosage and competitive ions etc.) on adsorption were investigated. The experimental results showed that, the kinetic data was fitted to the pseudo-second-order model, and the adsorption data was consistent with the Frenudlich isotherm model. The adsorption process was spontaneous and endothermic. The magnetic composite is easy to synthetise, and the most important thing is that it can be quickly separated from aqueous solution by a magnet. The Fe3O4@SiO2–PAMAM–DTC composite can be a potential adsorbent for the removal of Co2+ from aqueous solution.

A novel core-shell structure congo red composite nanoparticle (Fe3O4@SiO2-CR) was synthesized under mild conditions, aiming to remove methylene blue (MB) from aqueous solution. The structure, morphology and magnetic characteristics of the adsorbent Fe3O4@SiO2-CR were investigated by X-ray diffraction (XRD), fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). Fe3O4@SiO2-CR exhibited a typical superparamagnetic with a saturation magnetization value of 55.8 emu/g, which can be rapidly separated from aqueous solution under external magnetic field. The influencing factors such as contact time, initial pH, and MB concentration on final removal efficiency were evaluated. When the initial concentration of MB was 27 mg/L, the maximum adsorption capacity of methylene blue at room temperature was 31.44 mg/g within 30 s at pH 11. In addition, the adsorption behavior of this new adsorbent follows the Freundlich isotherm and the pseudo-second-order kinetic model. The regeneration study proved that the Fe3O4@SiO2-CR can be repeatedly utilized. The adsorption mechanism studies indicate that the adsorption of MB onto Fe3O4@SiO2-CR may be related to electrostatic attraction, aromatic-aromatic attraction, and hydrogen bonding attraction. All the results suggest that Fe3O4@SiO2-CR composites can be a promising material for the removal of MB from wastewater.

Using chemical co-precipitation method to make a magnetic magnetite, dithiocarbamate-multifunctional embedded in the carboxyl group to synthesize a novel nanocomposite Fe3O4@SiO2-DTPA-DTC for adsorption the Co2+ from aqueous solution. The Fe3O4@SiO2-DTPA-DTC composites were characterized by XRD, SEM, TEM, FT-IR, XPS, TGA and VSM in this study. From the adsorption study, removal efficiency of Co2+ on Fe3O4@SiO2-DTPA-DTC is up to 98%. The adsorption reached equilibrium within 5 min. The optimum pH was recorded to be 6.0. The adsorption process fitted with Freundlich isotherm model and adsorption mechanism is chemical adsorption. After five-cycle adsorption test, the nanocomposites maintain high removal efficiency. The results showed that the Fe3O4@SiO2-DTPA-DTC can be considered as a promising adsorbent to adsorption the Co2+ from aqueous solution.