Adsorption of light green and brilliant yellow anionic dyes using amino functionalized magnetic silica (Fe3O4@SiO2@NH2) nanocomposite

Abstract

Fe₃O₄@SiO₂@NH₂ nanocomposite was prepared for highly effective adsorption of two anionic dyes one of which is triarylmethane dye (light green, LG) and the other is azo dye (brilliant yellow, BY). The characterization results demonstrated that superparamagnetic Fe₃O₄ nanoparticles were covered with silica and functionalized with amino groups successfully without losing magnetic character. The effects of adsorbent dosage, contact time, pH, temperature, and dye molecular structure on the adsorption were investigated. Acidic pH was better for both LG and BY, on the other hand, alkaline pH was favorable to some extent for LG in comparison with BY due to the contribution of stacking effect in addition to electrostatic attraction. Kinetic data demonstrated that the driving force for adsorption process could be explained by pseudo-second order mechanism in both systems. The equilibrium data were more compatible with Langmuir isotherm than those of Freundlich isotherm and the maximum adsorption capacities of Fe₃O₄@SiO₂@NH₂ calculated from Langmuir isotherm model for LG and BY at 30?°C and natural pH of the solution were 40.2 and 35.5?mg g^?1. Thermodynamic calculations related to temperature dependence demonstrated that the adsorption process was spontaneous and exothermic.     

Adsorption of acid red 114 and reactive black 5 in aqueous solutions on dendrimer‐conjugated magnetic nanoparticles

The adsorption of the dyes Acid Red 114 and Reactive Black 5 in aqueous solutions on polyhydroxyl dendrimer magnetic nanoparticles (Fe₃O₄@SiO₂‐TRIS) was studied in a batch system. The Fe₃O₄@SiO₂‐TRIS NPs were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscopy. Experiments were performed under different conditions such as the initial dye concentration, adsorbent dose, and pH. The pseudo‐second‐order model provided a very good fit for the two anionic dyes. The Langmuir and Freundlich adsorption models were used to describe the equilibrium isotherms at different temperatures, and the former agreed very well with the experimental data. However, the adsorption capacity of Fe₃O₄@SiO₂‐TRIS NPs was reduced during surface modification, which could be due to the dye occupying the binding sites of the dendrimer. Thermodynamic parameters, namely the change in free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰), were also determined.     

Preparation of magnetic surface molecularly imprinted polymers for the selective extraction of triazines in environmental water samples

ABSTRACT

In this work, a magnetic molecularly imprinted polymer (Fe₃O₄@SiO₂@MIPs) was prepared via a surface-imprinted method for the determination of the triazines in environmental water samples combined with high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer showed that the Fe₃O₄@SiO₂@MIPs was successfully synthesised and exhibited superparamagnetism. The isotherm adsorption, selectivity and adsorption kinetics experiments showed that the Fe₃O₄@SiO₂@MIPs exhibited excellent specific recognition and fast adsorption equilibrium for triazines. The adsorption process is spontaneous and endothermic. The isotherm adsorption was consistent with Scatchard model and adsorption kinetic fit pseudo-second-order kinetic model. Under the optimised adsorption conditions, the Fe₃O₄@SiO₂@MIPs was directly used to selectively enrich six triazines in environmental water samples. The enrichment volume was up to 500 mL, and the matrix effects were down to 0.7–12.4%. The built method has excellent linearities in the range of 0.25–500 ng L^?1 with R² in the range of 0.998–0.999, lower limit of detections (0.02–0.08 ng L^?1) and higher precision (2.4–7.2%). The Fe₃O₄@SiO₂@MIPs is expected to be widely applied to the direct enrichment of triazines in bulk environmental water samples.     

Synthesis of nano‐sized magnetite mesoporous carbon for removal of Reactive Yellow dye from aqueous solutions

In this study, core‐shell structures of magnetite nanoparticles coated with CMK‐8 ordered mesoporous carbon (Fe₃O₄@SiO₂‐CMK‐8 NPs) have been successfully synthesized for the first time by carbonizing sucrose inside the pores of the Kit‐6 mesoporous silica. The nano‐sized mesoporous particles were characterized by X‐ray diffraction, Fourier transform‐infrared spectroscopy, scanning electron microscope, dynamic light scattering, vibrating‐sample magnetometer, Brunauer–Emmett–Teller (BET) and transmission electron microscopy instruments. The obtained nanocomposite was used for removal of Reactive Yellow 160 (RY 160) dye from aqueous samples. The N₂ adsorption–desorption method (at 77 K) confirmed the mesoporous structure of synthesized Fe₃O₄@SiO₂‐CMK‐8 NPs. Also, the surface area was calculated by the BET method and Langmuir plot as 276.84 m²/g and 352.32 m²/g, respectively. The surface area, volume and pore diameter of synthesized nanoparticles (NPs) were calculated from the pore size distribution curves using the Barrett–Joyner–Halenda formula (BJH). To obtain the optimum experimental variables, the effect of various experimental parameters on the dye removal efficiency was studied using Taguchi orthogonal array experimental design method. According to the experimental results, about 90.0% of RY 160 was removed from aqueous solutions at the adsorbent amount of 0.06 g, pH 3 and ionic strength = 0.05 m during 10 min. The pseudo‐second order kinetic model provided a very good fit for the RY 160 dye removal (R² = 0.999). The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models were applied to describe the equilibrium isotherms, and the Langmuir isotherm showed the best fit to data with the maximum adsorption capacity of 62.893 mg/g. Furthermore, the Fe₃O₄@SiO₂‐CMK‐8 NPs could be simply recovered by external magnet, and exhibited recyclability and reusability for a subsequent six runs.     

Selective adsorption and separation of Cs(I) from salt lake brine by a novel surface magnetic ion-imprinted polymer

A new Cs(I) magnetic ion-imprinted polymer (Cs(I)-MIIP) aimed at the selective adsorption and separation of Cs(I) from salt lake brine was prepared. The Fe₃O₄@SiO₂ was used as supporter, Cs(I) as template ion, and carboxymethyl chitosan as functional monomer. The product was characterized by Fourier transform infrared spectra, XRD, energy-dispersive spectrometry, scanning electron microcopy, thermogravimetric analysis, and vibrating sample magnetometer. The adsorption of the Cs(I)-MIIP in solution was investigated, which indicated the maximum adsorption capacity was 36.15?mg·g^?1 under the optimum conditions. The pseudo-first-order kinetic model and the Freundlich isotherm model were applied to predict the adsorption process of Cs(I) onto Cs(I)-MIIP. Selectivity experiments showed that the relative selectivity coefficient (k′) were 24.995, 1.73, 1.43, 4.83, and 1.63 to Cs(I)/Li(I), Cs(I)/Na(I), Cs(I)/K(I), Cs(I)/Rb(I), and Cs(I)/Sr(II) binary solutions, higher than those of NIP, respectively. Furthermore, the Cs(I)-MIIP was successfully applied to the enrichment and separation of Cs(I) from the salt lake brine of Qinghai, with satisfactory Cs(I) recovery rates.     

Comparison of Cadmium Cd2+ and Lead Pb2+ Binding by Fe2O3@SiO2‐EDTA Nanoparticles – Binding Stability and Kinetic Studies

This study describes the synthesis and characterization of ethylenediaminetetraacetic acid (EDTA) functionalized magnetic nanoparticles of 20 nm in size – Fe₃O₄@SiO₂‐EDTA – which were used as a novel magnetic adsorbent for Cd(II) and Pb(II) binding in aqueous medium. These nanoparticles were obtained in two‐stage synthesis: covering by tetraethyl orthosilicate and functionalization with EDTA derivatives. Nanoparticles were characterized using TEM, FT‐IR, and XPS methods. Metal ions were detected under optimized experimental conditions using Differential Pulse Anodic Stripping Voltammetry (DPASV) and Hanging Mercury Drop Electrode (HDME) techniques. We compared the ability of Fe₃O₄@SiO₂‐EDTA to bind cadmium and lead in concentration of 553.9 μg L^?1 and 647.5 μg L^?1, respectively. Obtained results show that the adsorption rate of cadmium binding was very high. The equilibrium for Fe₃O₄@SiO₂‐EDTA‐Cd(II) was reached within 19 min while for the Fe₃O₄@SiO₂‐EDTA‐Pb(II) was reached within 25 minutes. About 2 mg of nanoparticles was enough to bind 87.5 % Cd(II) and 54.1 % Pb(II) content. In the next step the binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles was determined. Only 1.265 mg of Fe₃O₄@SiO₂‐EDTA was enough to bind 96.14 % cadmium ions while 5.080 mg of nanoparticles bound 40.83 % lead ions. This phenomenon proves that the studied nanoparticles bind Cd(II) much better than Pb(II). The cadmium ions binding capacity of Fe₃O₄@SiO₂‐EDTA nanoparticles decreased during storage in 0.5 M KCl solution. Two days of Fe₃O₄@SiO₂‐EDTA storage in KCl solution caused the 32 % increase in the amount of nanoparticles required to bind 60 % of cadmium while eight‐days storage caused further increase to 328 %. The performed experiment confirmed that the storage of nanoparticles in solution without any surfactants reduced their binding capacity. The best binding capacity was observed for the nanoparticles prepared directly before the electrochemical measurements.     

Improvement on physical properties of polyethersulfone membranes modified by poly(1‐vinylpyrrolidone) grafted magnetic Fe3O4@SiO2 nanoparticles

Polyethersulfone (PES) and poly(1‐vinylpyrrolidone) (PVP) were used to prepare ultrafiltration membranes with grafted Fe₃O₄ magnetic nanoparticles (PVP‐g‐Fe₃O₄@SiO₂). The structure of synthesized PVP‐g‐Fe₃O₄@SiO₂ was confirmed by FT‐IR and SEM analysis. Physical properties of blend membranes such as thermal resistance, Tensile strength, water uptake, and hydrophilicity were also investigated. Blended membranes of PES/PVP‐g‐Fe₃O₄@SiO₂ have exhibited higher thermal resistance due to increasing the modified nanoparticle content. The hydrophilicity of the synthesized PES/PVP‐g‐Fe₃O₄@SiO₂ membranes also improved by increasing the PVP‐g‐Fe₃O₄@SiO₂ content. As expected, increasing the hydrophilicity of blended membrane, caused enhancement of fouling resistance in membranes. Results showed that the content of PVP‐g‐Fe₃O₄@SiO₂ has different effects on the properties of synthesized composite membranes. Despite increasing the content of PVP‐g‐Fe₃O₄@SiO₂ has a negative effect on elongation, positive effects on maximum stress was observed. Moreover, the water uptake of synthesized membranes was significantly enhanced in comparison to other similar studies.     

Monomer Protonation‐Dependent Surface Polymerization to Achieve One‐Step Grafting Cross‐Linked Poly(4‐Vinylpyridine) Onto Core–Shell Fe3O4@SiO2 Nanoparticles

Functional polymer‐grafting silica nanoparticles hold great promise in diverse applications such as molecule recognition, drug delivery, and heterogeneous catalysis due to high density and uniform distribution of functional groups and their tunable spatial distance. However, conventional grafting methods from monomers mainly consist of one or more extra surface modification steps and a subsequent surface polymerization step. A monomer protonation‐dependent surface polymerization strategy is proposed to achieve one‐step uniform surface grafting of cross‐linked poly(4‐vinylpyridine) (P4VP) onto core–shell Fe₃O₄@SiO₂ nanostructures. At an approximate pH, partially protonated 4VP sites in aqueous solution can be strongly adsorbed onto deprotonated silanol groups ( Si O⁻) onto Fe₃O₄@SiO₂ nanospheres to ensure prior polymerization of these protonated 4VP sites exclusively onto Fe₃O₄@SiO₂ nanoparticles and subsequent polymerization of other 4VP and divinylbenzene monomers harvested by these protonated 4VP monomers onto Fe₃O₄@SiO₂ nanoparticles, thereby achieving direct grafting of cross‐linked P4VP macromolecules onto Fe₃O₄@SiO₂ nanoparticles.     

Thiol-functionalized Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> microspheres with superparamagnetism and their adsorption properties for Au(III) ion separation

Thiol-functionalized Fe₃O₄/SiO₂ microspheres (Fe₃O₄/SiO₂-SH) with high saturation magnetization (69.3 emu g^–1), superparamagnetism, and good dispersibility have been prepared by an ethylene glycol reduction method in combination with a modified Stöber method. The as-prepared composite magnetic spheres are characterized with fourier transform infrared spectroscopy (FT-IR), zeta potential, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference magnetometer, and tested in separation of Au(III) ions from aqueous solutions. The data for Au(III) adsorption on Fe₃O₄/SiO₂-SH are analyzed with the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models, and the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. The adsorption behaviors of Au(III) on Fe₃O₄/SiO₂-SH follow the Langmuir isotherm model, and the adsorption process conforms to the pseudo-second-order kinetic model. The maximum adsorption capacity of Au(III) on Fe₃O₄/SiO₂-SH is 43.7 mg g^–1. Acetate anions play an important role yet Cu(II) ions have little interference in the adsorption of Au(III) on the adsorbent. A satisfactory recovery percentage of 89.5% is acquired by using an eluent with 1 M thiourea and 5% HCl, although thiols have a high affinity to Au(III) ions based on the hard-soft acid-base (HSAB) theory by Pearson.     

Preparation of 4-sulfonylcalix[6]arene modified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as adsorbent for adsorption of U(VI) from aqueous solution

The 4-sulfonylcalix[6]arene modified Fe₃O₄ (MFS) was characterized by FT-IR, SEM, VSM, TGA, etc., which showed that its saturation magnetization was 64.99 emu g^?1 with the particle size 10–40 nm. The maximum adsorption efficiency by MFS for 2.5 mg L^?1 U(VI) solution amounted to 94.39%, which was higher than that by Fe₃O₄ (65.22%) under its optimum adsorption conditions. The adsorption of MFS and Fe₃O₄ were both followed the pseudo-second order model and the Langmuir isotherm model. The Gibbs free energy change and enthalpy change revealed that the adsorption of U(VI) by MFS was a spontaneous and endothermic process.     

Equilibrium and kinetic study of novel methyltrimethoxysilane magnetic titanium dioxide nanocomposite for methylene blue adsorption from aqueous media

Novel magnetic titanium dioxide nanoparticles decorated with methyltrimethoxysilane (Fe₃O₄@TiO₂‐MTMOS) were successfully fabricated via a sol–gel method at room temperature. The synthesized material was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis and vibrating sample magnetometry. The removal efficiency of the adsorbent was evaluated through the adsorption of methylene blue (MB) dye from water samples. The adsorption isotherm and kinetics were evaluated using various models. The Langmuir model indicated a high adsorption capacity (11.5 mg g^?1) of Fe₃O₄@TiO₂‐MTMOS. The nanocomposite exhibited high removal efficiency (96%) and good regeneration (10 times) compared to Fe₃O₄ and Fe₃O₄@TiO₂ at pH = 9.0. Based on the adsorption mechanism, electrostatic interaction plays a main role in adsorption since MB dye is cationic in nature at pH = 9, whereas the adsorbent acquired an anionic nature. The newly synthesized Fe₃O₄@TiO₂‐MTMOS can be used as a promising material for efficient removal of MB dye from aqueous media.     

Synthesis of a highly active amino‐functionalized Fe3O4@SiO2/APTS/Ru magnetic nanocomposite catalyst for hydrogenation reactions

An amino‐functionalized silica‐coated Fe₃O₄ nanocomposite (Fe₃O₄@SiO₂/APTS) was synthesized. The Fe₃O₄@SiO₂ microspheres possessed a well‐defined core–shell structure, uniform sizes and high magnetization. An immobilized ruthenium nanoparticle catalyst (Fe₃O₄@SiO₂/APTS/Ru) was obtained after coordination and reduction of Ru³⁺ on the Fe₃O₄@SiO₂/APTS nanocomposite. The Ru nanoparticles were not only ultra‐small with nearly monodisperse sizes but also had strong affinity with the surface of Fe₃O₄@SiO₂/APTS. The obtained catalyst exhibited excellent catalytic performance for the hydrogenation of a variety of aromatic nitro compounds, even at room temperature. Moreover, Fe₃O₄@SiO₂/APTS/Ru was easily recovered using a magnetic field and directly reused for at least five cycles without significant loss of its activity.     

Carbazole‐based conjugated polymer covalently coated Fe3O4 nanoparticle as efficient and reversible Hg2+ optical probe

A type of fluorescent–magnetic dual‐function nanocomposite, Fe₃O₄@SiO₂@P‐2, was successfully obtained by Cu⁺‐catalyzed click reaction between acetylene (C?C? H)‐substituted carbazole‐based conjugated polymer ( P‐2) and azide‐terminated silica‐coated magnetic iron oxide nanoparticles (Fe₃O₄@SiO₂–N₃). Optical and magnetization analyses indicate that Fe₃O₄@SiO₂@P‐2 exhibits stable fluorescence and rapid magnetic response. The fluorescence of Fe₃O₄@SiO₂@P‐2 was quenched significantly in the presence of I^? and gave a detection limit (DL) of ～8.85 × 10^?7 M. Given the high binding constant and matching ratio between Hg²⁺ and I^?, the fluorescence of Fe₃O₄@SiO₂@P‐2/I^? complex recovered efficiently with the addition of Hg²⁺. A DL of ～4.17 × 10^?7 M was obtained by this probing system. Recycling of Fe₃O₄@SiO₂@P‐2 probe was readily achieved by simple magnetic separation. Results indicate that Fe₃O₄@SiO₂@P‐2 can be used as an “on–off–on” fluorescent switchable and recyclable Hg²⁺ probe. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3636–3645     

Preparation of Fe3O4/chitosan/poly(acrylic acid) composite particles and its application in adsorbing copper ion (II)

Fe₃O₄/chitosan/poly(acrylic acid) (Fe₃O₄/CS/PAA) composite particles, which are reusable, biodegradable and of high adsorption capacity, have been prepared through polymerizing acrylic acid in chitosan and Fe₃O₄ nanoparticles aqueous solution. By varying in-feed mole ratio of carboxyl to amino group (n^c/n^a) and reactant concentration, the average diameter of Fe₃O₄/CS/PAA composite particles can be controlled to vary from 100 to 300 nm. FT-IR, XRD and TEM were used to characterize Fe₃O₄/CS/PAA composite particles. Results showed that Fe₃O₄ was indeed incorporated into CS/PAA particles. The composite particles showed high efficient to remove copper ions (II) in aqueous solution. Adsorption kinetic studies showed that the adsorption process followed a pseudo-second-order kinetic model and the equilibrium data agreed well with the Langmuir model. The saturated adsorption capacity obtained from the experimental was 193 mg/g in close to proximity to the data 200 mg/g calculated from Langmuir model. The saturated adsorption capacity still retained 100 mg/g after three cycles of adsorption–desorption of copper ions (II).     

Direct Electrochemistry of Hemoglobin Based on Fe3O4@SiO2 Nanoparticles Modified Electrode

A biosensor based on hemoglobin‐Fe₃O₄@SiO₂ nanoparticle bioconjunctions modified indium‐tin‐oxide (Hb/Fe₃O₄@SiO₂/ITO) electrode was fabricated to determine the concentration of H₂O₂. UV‐vis absorption spectra, fourier transform infrared (FT‐IR) spectroscopy, cyclic voltammetry (CV) and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the bioconjunction of Fe₃O₄@SiO₂ with Hb. Experimental results demonstrate that the immobilized Hb on the Fe₃O₄@SiO₂ matrix retained its native structure well. In addition, Fe₃O₄@SiO₂ nanoparticles (NPs) are very effective in facilitating electron transfer of the immobilized enzyme, which can be attributed to the unique nanostructure and larger surface area of the Fe₃O₄@SiO₂ NPs. The biosensor displayed good performance for the detection of H₂O₂ with a wide linear range from 2.03×10^?6 to 4.05×10^?3 mol/L and a detection limit of 0.32 µmol/L. The resulting biosensor exhibited fast amperometric response, good stability, reproducibility, and selectivity to H₂O₂.     

Highly stable magnetically separable copper nanocatalyst as an efficient catalyst for C(sp2)–C(sp) and C(sp2)–C(sp2) cross‐coupling reactions

A copper catalyst has been explored as an efficient and recyclable catalyst to effect Sonogashira and Suzuki cross‐coupling reactions. After modification of 2‐(((piperazin‐1‐ylmethyl)imino)methyl)phenol (PP) on the surface of amorphous silica‐coated iron oxide (Fe₃O₄@SiO₂@Cl) magnetic core–shell nanocomposite, copper(II) chloride was employed to synthesize the Fe₃O₄@SiO₂@PP‐Cu catalyst, affording a copper loading of 1.52 mmol g⁻¹. High yield, low reaction times, non‐toxicity and recyclability of the catalyst are the main merits of this protocol. The catalyst was characterized using Fourier transform infrared, X‐ray photoelectron, energy‐dispersive X‐ray and inductively coupled plasma optical emission spectroscopies, X‐ray diffraction, scanning and transmission electron microscopies, and vibrating sample magnetometry.     

Preparation of novel palladium nanoparticles supported on magnetic iron oxide and their catalytic application in the synthesis of 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols

Novel Pd nanoparticles were prepared in five successive stages: 1) preparation of the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs), 2) coating of Fe₃O₄ MNPs with SiO₂ (Fe₃O₄@SiO₂), 3) functionalization of Fe₃O₄@SiO₂ with 3‐chloropropyltrimethoxy‐ silane (CPTMS) ligand (Fe₃O₄@SiO₂@CPTMS), 4) further functionalization with 3,5‐diamino‐1,2,4‐triazole (DAT) ligand (Fe₃O₄@SiO₂@CPTMS @DAT), and 5) the complexation of Fe₃O₄@SiO₂@CPTMS@DAT with PdCl₂ (Fe₃O₄@SiO₂@CPTMS@ DAT@Pd). Then, the obtained Pd nano‐catalyst characterized by different methods such as the elemental analysis (CHN), FT‐IR, XRD, EDX, SEM, TEM, TG‐DTA and VSM. Finally, the Pd catalyst was applied for the synthesis of various 2‐imino‐3‐phenyl‐2,3‐dihydrobenzo[d]oxazol‐5‐ols.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

Preparation of core-shell magnetic Fe3O4@SiO2-dithiocarbamate nanoparticle and its application for the Ni2+, Cu2+ removal

A typical superparamagnetic nanoparticles-based dithiocarbamate absorbent (Fe₃O₄@SiO₂-DTC) with core-shell structure was applied for aqueous solution heavy metal ions Ni²⁺, Cu²⁺ removal.     

Mesoporous hollow silicon spheres modified with manganese ion sieve: Preparation and its application for adsorption of lithium and rubidium ions

In this work, mesoporous hollow silicon spheres modified with 3‐aminopropyl‐ triethoxysilane (APTES) of loaded hydrogen manganese oxide lithium ion sieve (APTES/HMO‐ HS) was prepared. The structure and morphology of as‐prepared APTES/HMO‐HS were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy and nitrogen adsorption‐desorption measurements. The Brunner‐Emmet‐Teller (BET) surface areas, pore diameters and pore volumes of APTES/HMO‐HS decreased gradually, while the Li:Mn:Si molar ratios range from 1:1:50 to 1:1:10. The obtained hierarchical porous APTES/50HMO‐HS has a high specific surface area (557.1694 m² g^‐1). The lithium and rubidium ions solutions were used to measure the adsorption performance of the APTES/HMO‐HS adsorbent. The pseudo‐first‐order and pseudo‐second‐order kinetics, Langmuir and Freundlich isotherms of APTES/HMO‐HS were investigated; suggesting that the adsorption kinetics can be described by the pseudo‐second‐order kinetic model and the adsorption isotherms well fits the Langmuir isotherm equation. The obtained results show that the prepared APTES/HMO‐HS exhibits excellent abilities to simultaneously and selectively recover Li⁺ and Rb⁺ (11.22 mg·g^‐1 and 8.31 mg·g^‐1) and have a promising application in the simultaneous adsorption of lithium and rubidium ions.