Preparation of thiol-modified Fe3O4@SiO2 nanoparticles and their application for gold recovery from dilute solution

Optimization of Au(III) adsorption by the Taguchi method using pyrogallol functionalized silica nanoparticles

Pyrogallol molecules were successfully immobilized onto aminopropyl molecule functionalized MCM41 nanoparticles to obtain a fast and high gold adsorption capacity. The Taguchi statistical method was used to determine the factors affecting the gold(III) adsorption efficiency. The effect of six factors, pH, rate, adsorbent mass, temperature, initial Au(III) concentration and time, each with 5 levels, on the adsorption capacity was investigated by forming an L25 orthogonal. The analysis of variance (ANOVA) of each factor showed that all factors had significant effects on adsorption. pH 5, 250 rpm stirring speed, 0.025 g adsorbent mass, 40 °C temperature, 600 mg L^-1 Au(III) concentration and 15 min time were determined to be the optimum adsorption conditions. The maximum Langmuir monolayer adsorption capacity of APMCM1-Py for Au(III) was calculated to be 168.54 mg g^-1 at 303 K. The adsorption mechanism fits the pseudo-second-order kinetic model assuming the formation of a single chemical adsorption layer on the adsorbent surface. The adsorption isotherms are best represented using the Langmuir isotherm model. It exhibits a spontaneous endothermic behavior. FTIR, SEM, EDX and XRD analyses showed that mostly phenolic -OH functional groups adsorb Au(III) ions on the APMCMC41-Py surface with their reducing character. These results enable the rapid recovery of gold ions from weakly acidic aqueous solutions by reduction of APMCM41-Py NPs.

Mercury(II) and lead(II) ions removal using a novel thiol-rich hydrogel adsorbent; PHPAm/Fe3O4@SiO2-SH polymer nanocomposite

The abundant release of toxic heavy metals into wastewater has been a serious threat to human health, aquatic environments, plants, and animals; thus, it is critical to purify wastewater of these pollutants through a proper treatment process. A novel hydrogel compound was synthesized using partially hydrolyzed polyacrylamide (PHPAm) and functionalized Fe₃O₄-coated magnetic nanoparticles (PHPAm/Fe₃O₄@SiO₂-SH) that is efficient in removal of mercury and lead from wastewater. This new magnetic nanoadsorbent is characterized using scanning electron microscope, Fourier-transform infrared, thermogravimetric analysis, vibrating sample magnetometer, and energy-dispersive X-ray analysis. The central composite design under response surface methodology (CCD-RSM) was applied in designing the experiments to optimize the main parameters affecting the adsorption capacity: initial concentration (77.50 mg L^-1), pH (6.11 and 6.48), adsorbent dosage (25 mg), and contact time (115 and 106 min) for both Hg²⁺ and Pb²⁺ adsorption, respectively. Quadratic models were used for variable predictions and analysis of variance was applied to evaluate the statistical parameters and investigate the interactions of the variables. The high determination coefficient (R² 0.99) for both metals indicates a good correlation between actual and predicted response values. Additionally, thermodynamic modeling showed an endothermic and exothermic for Hg²⁺ and Pb²⁺, respectively, and also the spontaneous nature of both metals' adsorption process within the temperature range of 288-318 K. Mercury and lead kinetic studies were in agreement with pseudo-second-order modeling, and the equilibrium results revealed that the Langmuir isotherm best fit the experimental data with maximum adsorption capacities of 256.41 and 227.27 (mg g^-1) for Hg²⁺ and Pb²⁺, respectively. Overall, PHPAm/Fe₃O₄@SiO₂-SH is thought to have highly promising potential for investigating heavy metals in wastewater treatment, and will make important contributions to similar studies that may be conducted in the future.

Transformation of Waste Toner Powder into Valuable Fe2O3 Nanoparticles for the Preparation of Recyclable Co(II)-NH2-SiO2@Fe2O3 and Its Applications in the Synthesis of Polyhydroquinoline and Quinazoline Derivatives

Ecological recycling of waste materials by converting them into valuable nanomaterials can be considered a great opportunity for management and fortification of the environment. This article deals with the environment-friendly synthesis of Fe₂O₃ nanoparticles (composed of α-Fe₂O₃ and γ-Fe₂O₃) using waste toner powder (WTP) via calcination. Fe₂O₃ nanoparticles were then coated with silica using TEOS, functionalized with silane (APTMS), and immobilized with Co(II) to get the desired biocompatible and cost-effective catalyst, i.e., Co(II)-NH₂-SiO₂@Fe₂O₃. The structural features in terms of evaluation of morphology, particle size, presence of functional groups, polycrystallinity, and metal content over the surface were determined by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (P-XRD), field emission gun-scanning electron microscopy (FEG-SEM), energy-dispersive X-ray analysis (EDX), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET) analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) studies. XPS confirmed the (II) oxidation state of Co, and ICP-AES and EDX supported the loading of Co(II) over the surface of the support. P-XRD proved the polycrystalline nature of the Fe₂O₃ core and even after functionalization. In comparison to previously reported methods, Co(II)-NH₂-SiO₂@Fe₂O₃ provides an eco-friendly procedure for the synthesis of polyhydroquinoline and quinazoline derivatives with several advantages such as a short reaction time and high yield. Polyhydroquinoline and quinazoline derivatives are important scaffolds in pharmacologically active compounds. Moreover, the developed nanocatalyst was recyclable, and HR-TEM and P-XRD confirmed the agglomeration in the recycled catalyst resulted in a decrease in yield after the fifth run. The present protocol provides a new strategy of recycling e-waste into a heterogeneous nanocatalyst for the synthesis of heterocycles via multicomponent reactions. This made the synthesized catalyst convincingly more superior to other previously reported catalysts for organic transformations.

Magnetic Zr-Based Metal-Organic Frameworks: A Highly Efficient Au (III) Trapper for Gold Recycling

In this work, the magnetic Zr-based MOF composites with excellent retrievability were prepared using Fe₃O₄@SiO₂ as the core and UiO-66-NH₂ as the shell. Fe₃O₄@SiO₂ core could introduce mesopores and result in capillary condensation in MOF composites, which aggravated with the dosage of Fe₃O₄@SiO₂. The as-synthesized MOF composites could be rapidly retrieved from aqueous solution via magnetic separation in 10 seconds. pH imposed an important effect on Au (III) adsorption by governing the ion exchange and electrostatic interaction between Au (III) anions and adsorbents, and the optimal adsorption happened at pH 7. The adsorption process fitted well with the pseudo-second order kinetics model and Langmuir adsorption model. The maximum adsorption capacity of Au (III) by FSUN-10 and FSUN-50 at 298 K were determined to be 611.18 mg∙g^-1 and 463.85 mg∙g^-1, respectively. Additionally, Au (III) uptakes increased with temperature. Beyond experiments, the adsorption mechanisms were thoroughly studied through systematic characterization, molecular dynamics simulation (MDS) and density functional theory (DFT) study. It was verified that Au (III) was adsorbed via coordination to hydroxyl and amino groups and was reduced to Au (I) and Au (0) by amino groups. The diffusion coefficient of Au (III) along UiO-66-NH₂ was calculated to be 5.8 × 10^-5 cm²∙s^-1. Moreover, the magnetic Zr-based MOF composites exhibit great industrial value in gold recycling with high adsorption selectivity and good recyclability.

Efficient capture of U(VI) by magnetic Zr(IV)-ethylenediamine tetramethylene phosphonic acid inorganic-organic hybrid

The separation of magnetic adsorbents from aqueous solutions is made simple by using an external magnetic field. Herein, magnetic Zr(IV)-ethylenediamine tetramethylene phosphonic acid (EDTMPA) hybrids (MZrOP-x-T, x, and T were the different quality of Fe₃O₄@C and temperature in the synthesis process, respectively). A study was conducted on the uses of MZrOP-x-T in the capture of U(VI). The influences of pH, adsorption period, initial concentration, and temperature were all investigated. Furthermore, the desorption and reusability of the materials were explored. The optimal values of x and T were 0.2 g and 100 °C, respectively. At 298.15 K, the maximum adsorption capacity of MZrOP-0.2-100 was 330.30 mg·g^-1. The current research demonstrates that MZrOP-0.2-100 is a potentially effective material in removing U(VI) from radioactive solution.

A comprehensive study on the adsorption-photocatalytic processes using CoFe2O4/SiO2/MnO2 magnetic nanocomposite as a novel photo-catalyst for removal of Cr (VI) under simulated sunlight: Isotherm, kinetic and thermodynamic studies

PURPOSE

The present study aimed to investigate the efficiency of CoFe₂O₄/SiO₂/flower-like MnO₂ nanoparticles as a catalyst for Cr (VI) adsorption-photocatalytic processes.

METHODS

The magnetic nanocomposite used was first synthesized and then characterized using TEM, SEM, EDX, XRD, FTIR, XRF and BET advanced techniques. The removal of the Cr (VI) was performed through a batch adsorption approach and the effects of sample pH (A; 2-6), initial chromate concentration (B; 50-100 ppm) and adsorbent weight to sample volume ratio (C; 1-3 mg ml^-1), hole scavenger (0.1 -0.3%w/v) and time (E; 30-60 min), to evaluate the individual and interactive effects under ultraviolet light conditions, were also studied by the central composite design in the photocatalytic process of adsorption.

RESULTS

The adsorption-photocatalytic performance of the CoFe₂O₄/SiO₂/MnO₂ composite was high in which 98.1% of Cr(VI) after 30 min of photocatalytic treatment in optimum conditions (i.e. pH = 3, catalyst concentration = 2 mg L^-1, Cr(VI) concentration = 200 mg L^-1, and hole scavenger concentration = 0.4% (w/ v), At laboratory temperature, speed = 400 rpm, under UV radiation).Under optimum conditions, Cr(VI) reductive followed pseudo-second-order kinetics and followed the Langmuir and Temkin isotherms, also, positive value of ΔH° indicates endothermic nature.

CONCLUSIONS

The results showed that the synthesized CoFe₂O₄/SiO₂/MnO₂ magnetic nanocomposite holds a great potential for use as a photocatalyst to remove Cr (VI) in adsorption reactions. It can be used as an effective catalyst in the eradication of Cr (VI) wastewater.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-021-00763-1.

Magnetic polyphenol nanocomposite of Fe3O4/SiO2/PP for Cd(II) adsorption from aqueous solution

In order to solve the water solubility and difficult re-use of plant polyphenol (PP) in Cd(II) adsorption, PP was immobilized on the surface of magnetic material in this study. A core-shell nanocomposite Fe₃O₄/SiO₂/PP (∼18 nm) was synthesized with 3-8 nm SiO₂ and 2-5 nm PP. TGA analysis revealed the PP coating amount was 2.39%. VSM detection suggested that saturation magnetization of Fe₃O₄/SiO₂/PP was 45.94 emu/g. The adsorption equilibrium was reached in 2 h and the adsorption kinetics followed a pseudo-second-order model. The adsorption data fitted well to a Langmuir isotherm, achieving a 98.6% of Cd(II) removal at 0.6 g, pH 7.0, 298 K and 160 rpm. The adsorption capacity of Cd(II) on Fe₃O₄/SiO₂/PP highly depended on the pH. The adsorption capacity increased as the initial solution pH was increased in the range of 3.0-8.0. The adsorbed Cd(II) on Fe₃O₄/SiO₂/PP could be effectively desorbed by 0.1 mol/L of HNO₃ and the Fe₃O₄/SiO₂/PP still maintained a stable adsorption capacity after five cycles. The adsorption mechanism of Cd(II) on Fe₃O₄/SiO₂/PP is mainly dependent on complexation and electrostatic adsorption from the FTIR and XPS analyses. This study provided a new way for PP to remove Cd(II) from aqueous solution.

Development of Nanocomposite Film Comprising of Polyvinyl Alcohol (PVA) Incorporated with Bacterial Cellulose Nanocrystals and Magnetite Nanoparticles

Nanocomposite film of poly(vinyl alcohol) (PVA) incorporated with bacterial cellulose nanocrystals (BCNCs) and magnetite nanoparticles (Fe₃O₄) is reported in this study. The BCNC-Fe₃O₄ nanoparticles and PVA film was prepared by in situ synthesis technique using chemical co-precipitation. Different concentrations of BCNC-Fe₃O₄ (20%, 40% and 60% w/w) were mechanically dispersed in PVA solution to form the nanocomposite film. Transmission electron microscopy (TEM) analysis of BCNC-Fe₃O₄ nanoparticles showed irregular particle sizes ranging from 4.93 to 30.44 nm with an average size distribution of 22.94 nm. The presence of characteristic functional groups of PVA, BCNC and Fe₃O₄ were confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. Scanning electron microscope (SEM) attached energy dispersive spectroscopy (EDS) and vibrating sample magnetometer (VSM) analysis revealed that, the iron content and magnetic property increased with increasing BCNC-Fe₃O₄ content. The saturation magnetizations (MS) value increased from 5.14 to 11.56 emu/g. The PVA/ BCNC-Fe₃O₄ at 60% showed the highest Young's modulus value of 2.35 ± 0.16 GPa. The prepared film could be a promising polymeric nanomaterial for various magnetic-based applications and for the design of smart electronic devices.

Iron Oxide (Fe3O4)-Supported SiO2 Magnetic Nanocomposites for Efficient Adsorption of Fluoride from Drinking Water: Synthesis, Characterization, and Adsorption Isotherm Analysis

This research work reports the magnetic adsorption of fluoride from drinking water through silica-coated Fe3O4 nanoparticles. Chemical precipitation and wet impregnation methods were employed to synthesize the magnetic nanomaterials. Moreover, the synthesized nanomaterials were characterized for physicochemical properties through scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray powder diffraction. Screening studies were conducted to select the best iron oxide loading (0.0–1.5 wt%) and calcination temperature (300–500 °C). The best selected nanomaterial (0.5Fe-Si-500) showed a homogenous FeO distribution with a 23.79 nm crystallite size. Moreover, the optimized reaction parameters were: 10 min of contact time, 0.03 g L−1 adsorbent dose, and 10 mg L−1 fluoride (F−) concentration. Adsorption data were fitted to the Langmuir and Freundlich isotherm models. The Qm and KF (the maximum adsorption capacities) values were 5.5991 mg g−1 and 1.869 L g−1 respectively. Furthermore, accelerated adsorption with shorter contact times and high adsorption capacity at working pH was among the outcomes of this research work.

Synthesis and Characterization of Triamine modified coated Iron Sand Hybrid Nanomaterials originating from Kendal Coast

Nanomaterials have broad and unique applications in various fields. In this research, synthesis of Iron Sand Magnetic Hybrid nanomaterials coated with propyldiethylenetriammine modified silica (PB@SiO2@TA) originating from the coast of Muara Kencan, Kendal Regency. This study began with iron sand preparation, continued with activation, dispersing iron sand, then coating iron sand with propyldiethylenetriammine modified silica. The resulting product was characterized by X-Ray Fluorescence (XRF), Fourier Transform Infrared (FT-IR) Spectrophotometer, X-Ray Diffractometer (XRD), and Transmission Electron Microscope (TEM). The characterization results show that the iron sand of the coast of Muara Kencan Beach has a high iron oxide content (81.66%) with minerals in the form of magnetite. The characterization results also showed that the nanomaterial hybrid iron sand coated with propyldiethylenetriammine modified silica (PB@SiO2@TA) was successfully synthesized with a crystal size of 36.21 nm, with better particle dispersion than the prepared iron sand.

Fe3O4 nanoparticles functionalized with poly(ethylene glycol) for the selective separation and enrichment of Au(iii)

Mechanism of Fe₃O₄@CPTES@PEG magnetic nanoparticles for selectively adsorbing Au(iii) from aqueous solution at pH = 1.0.

Plasma assisted-synthesis of magnetic TiO2/SiO2/Fe3O4-polyacrylic acid microsphere and its application for lead removal from water

Hybrid microsphere of polyacrylic acid (PAA) grafted TiO₂/SiO₂/Fe₃O₄ (TSF-PAA) was synthesized via coating polyacrylic acid on the core-shell-shell TiO₂/SiO₂/Fe₃O₄ (TSF) structure with the aid of plasma technique. The synthesized microsphere was applied to remove Pb²⁺ from water. The state-of-the techniques including TEM, FTIP, TGA, and XPS were used to characterize the morphology and the surface functionalities of the microsphere and confirmed that PAA was successfully grafted on TSF surfaces and active functional groups were introduced. A combination of the BET, VSM, and XRD results showed that plasma treatment decreased surface area of TSF by 36%, whereas its magnetic property and crystalline structure were not significantly altered. Both the Pb²⁺-sorbed magnetic TSF and TSF-PAA can be separated with a magnet from the aqueous phase. The pH and dosage changes of the microspheres exerted an intense influence on their lead removal efficiency. Compared to TSF, the removal capacity of Pb²⁺ by TSF-PAA was considerably improved from 65% to 95%, attributable to the fact that PAA coating induced by plasma treatment additionally introduced carboxylic and hydroxyl groups to TSF. Their introduction greatly enhanced the interaction between Pb²⁺ and TSF-PAA relative to that with TSF, which had hydroxyl groups only as supported by XPS analysis.

The effect of solvent parameters on properties of iron-based silica binary aerogels as adsorbents

The magnetic Fe₃O₄-SiO₂ binary aerogel and nonmagnetic α-Fe₂O₃-SiO₂ binary aerogels are obtained by adjusting the solvent type during the solvothermal reaction and varying the Fe/Si proportion in the sol-gel process. The microstructure, surface charge and the formation mechanism of iron-based silica binary aerogels are analyzed by SEM, zeta potential and BET. The influence of the Fe/Si proportion on the surface group and morphology of binary aerogels is also investigated by FTIR and TEM analysis. The adsorption behavior of the iron-based silica binary aerogels on the Congo Red (CR) dye is also discussed by adsorption kinetics model and adsorption isotherm model. In addition, the effects of pH and initial concentration of the solutions, adsorption time and the maximum adsorption capacities for CR of iron-based silica binary aerogels adsorbents are also discussed, respectively. Moreover, the maximum adsorption capacity of as-prepared magnetic Fe₃O₄-SiO₂ binary aerogels for dyes achieved 489.13 mg g^-1, the maximum adsorption capacity of nonmagnetic α-Fe₂O₃-SiO₂ reached 454.55 mg g^-1, respectively. Thus, the iron-based silica binary aerogels provides valuable clues for the study of other aerogel materials as adsorbents.

Loading of Cisplatin into Mesoporous Silica Nanoparticles: Effect of Surface Functionalization

Cisplatin ( cis-diaminedichloroplatinum(II), CDDP) plays a crucial role in the treatment of various malignant tumors. However, its clinical efficacy and applicability are restricted by issues of toxicity and resistance. Here, for drug delivery purposes, the outer surface of MCM-41 mesoporous silica nanoparticles (MSNs) was functionalized with poly(ethylene glycol) ( M_w = 10 000 g/mol) or low-molecular-weight ( M_w = 1800 g/mol) branched polyethyleneimine (PEI). Given the strong affinity of sulfur for platinum, thiol-functionalized MSNs were synthesized for comparison by co-condensation with (3-mercaptopropyl)triethoxysilane. CDDP loading was performed either by adsorption or impregnation in aqueous media without the use of dimethyl sulfoxide as a solubilizer. CDDP loading capacities obtained by impregnation were higher than those obtained by adsorption and varied from 3.9 to 16.1 wt %, depending on the functional group. Loaded nanomaterials were characterized by scanning electron microscopy, scanning transmission electron microscopy-high-angle annular dark-field, and Raman spectroscopy. Depending on the functional groups, platinum-based species were either dispersed in the nanomaterials as nanocrystals or uniformly distributed as molecular species. The spectral signature of CDDP was strongly modified when platinum species were homogeneously distributed within the nanomaterials. Preliminary drug release studies performed at 37 °C showed that the behavior of CDDP-loaded MSNs strongly depends on the nature of the present functional groups. Among the functionalization routes investigated in this paper, PEI-based functionalization showed the most promising results for further applications in controlled drug release with the absence of burst release and a sustained release over 72 h.

Facile Synthesis of Polypyrrole-Functionalized CoFe₂O₄@SiO₂ for Removal for Hg(II)

In order to avoid using toxic or harmful operational conditions, shorten synthesis time, enhance adsorption capacity, and reduce operational cost, a novel magnetic nano-adsorbent of CoFe₂O₄@SiO₂ with core–shell structure was successfully functionalized with polypyrrole (Ppy). The physical and chemical properties of CoFe₂O₄@SiO₂-Ppy are examined by various means. The as-prepared CoFe₂O₄@SiO₂-Ppy nanomaterial was used to adsorb Hg²⁺ from water. During the process, some key effect factors were studied. The adsorption process of Hg²⁺ onto CoFe₂O₄@SiO₂-Ppy was consistent with the pseudo-second-order kinetic and Langmuir models. The Langmuir capacity reached 680.2 mg/g, exceeding those of many adsorbents. The as-prepared material had excellent regeneration ability, dispersibility, and stability. The fitting of kinetics, isotherms, and thermodynamics indicated the removal was endothermic and spontaneous, and involved some chemical reactions. The application evaluation of electroplating wastewater also shows that CoFe₂O₄@SiO₂-Ppy is an excellent adsorbent for Hg²⁺ ions from water.

Plant tannin immobilized Fe3O4@SiO2 microspheres: A novel and green magnetic bio-sorbent with superior adsorption capacities for gold and palladium

In this paper, a new core-shell nanostructured magnetic bio-based composite was prepared by immobilizing persimmon tannin (PT) onto Fe₃O₄@SiO₂ microspheres, and the as designed Fe₃O₄@SiO₂@PT was utilized for adsorptive recovery of Au(III) and Pd(II). The preparation, morphology, composition and magnetic property of Fe₃O₄@SiO₂@PT were characterized. Adsorption parameters of Fe₃O₄@SiO₂@PT towards Au(III) and Pd(II) including initial pH, reaction time, initial concentration of metal ions, effect of acidity and interference of coexisting metal ions were investigated. It is sufficiently confirmed that silica was coated on Fe₃O₄ and persimmon tannin was immobilized on aminated Fe₃O₄@SiO₂. The thickness of silica and loaded persimmon tannin are around 18 nm and 14 nm, respectively. With only 1.00 wt% of persimmon tannin, however, the maximum adsorption capacities of Fe₃O₄@SiO₂@PT for Au(III) and Pd(II) were as high as 917.43 and 196.46 mg·g^-1, respectively. In addition, after adsorption of Au(III) and Pd(II), the magnetization saturation values (Ms) of Fe₃O₄@SiO₂@PT were high enough to guarantee efficient magnetic seperation. Metallic gold could be facilely recovered from wastewaters containing Au(III).

Polydopamine functionalized hydrogel beads as magnetically separable antibacterial materials

In the present study, magnetically separable hydrogel beads of ionically cross-linked alginate were functionalized with polydopamine (PDA). The rationale behind this was to enhance the structural stability and antibacterial profile of PDA/Alg/Fe₃O₄ beads (K3). Incorporation of superparamagnetic magnetite (Fe₃O₄) nanoparticles endowed the hydrogel beads with magnetism. X-ray diffraction (XRD) analysis revealed the successful formation of pure Alg/Fe₃O₄ nanoparticles having an inverse spinel structure. Vibrating sample magnetometry (VSM) confirmed their superparamagnetic behaviour with M_s values of 36.18 and 30.46 emu g⁻¹ at 5 and 300 K, respectively. High resolution-transmission electron microscopy (HR-TEM) images showed alginate capping and the size of the Alg/Fe₃O₄ nanoparticles (∼8 nm). The successful deposition of PDA granules on the K3 bead surface was verified by field emission-scanning electron microscopy (FE-SEM). The PDA functionalization was further justified by VSM, XRD and Fourier-transform infrared spectroscopy (FT-IR). During swelling experiments, K3 beads displayed appreciable structural stability compared to bare/non-functionalized beads. Wettability studies revealed K3 beads to be hydrophilic with a contact angle of ∼55°. Rheological parameters including storage modulus (G′) and shear viscosity of K3 increased upon PDA functionalization. During antibacterial tests, K3 strongly inhibited E. coli, S. typhi, S. aureus and L. monocytogenes in a concentration and time dependent manner. Fluorescence staining experiments showed that K3 could greatly alter the bacterial membrane integrity. Reusability experiments with K3 beads substantiated their effective broad-spectrum antibacterial performance for three consecutive cycles.

Surface functionalization with polydopamine augments the structural stability and antibacterial profile of magnetic hydrogel beads.

Highly promoted removal of Hg(ii) with magnetic CoFe2O4@SiO2 core–shell nanoparticles modified by thiol groups

A simple and environmentally friendly material, CoFe₂O₄@SiO₂–SH, was prepared successfully with CoFe₂O₄ nanoparticles coated by SiO₂ which was further functionalized with thiol groups (–SH).

Recycling of iron and silicon from drinking water treatment sludge for synthesis of magnetic iron oxide@SiO₂ composites

More attention has been paid to the deterioration of water bodies polluted by drinking water treatment sludge (DWTS) in recent years. It is important to develop methods to effectively treat DWTS by avoiding secondary pollution. We report herein a novel investigation for recovery of Si and Fe from DWTS, which are used for the synthesis of two iron oxide@SiO2 composites for adsorption of reactive red X-3B (RRX-3B) and NaNO2. The results show that Fe(3+) (acid-leaching) and Si(4+) (basic-leaching) can be successfully recovered from roasted DWTS. Whether to dissolve Fe(OH)3 precipitation is the key point for obtaining Fe3O4 or γ-Fe2O3 particles using the solvothermal method. The magnetic characteristics of Fe3O4@SiO2 (390.0 m(2) g(-1)) or Fe2O3@SiO2 (220.9 m(2) g(-1)) are slightly influenced by the coated porous SiO2 layer. Peaks of Fe-O stretching vibration (580 cm(-1)) and asymmetric Si-O-Si stretching vibrations (1080 cm(-1)) of Fe3O4@SiO2 indicate the successful coating of a thin silica layer (20-150 nm). The adsorption capacity of RRX-3B and NaNO2 by Fe3O4@SiO2 is better than that of Fe2O3@SiO2, and both composites can be recycled through an external magnetic field. This method is an efficient and environmentally friendly method for recycling DWTS.

Coating of magnetite with mercapto modified rice hull ash silica in a one-pot process

In this research, mercapto-silica coated magnetite (Fe3O4-SiO2-SH) has been prepared in aqueous solution through a simple approach so called a one-pot process. The Fe3O4-SiO2-SH was prepared in nitrogen condition by mixing magnetite, 3-mercaptopropyltrimethoxysilane (MPTMS), and sodium silicate (Na2SiO3) solution extracted from rice hull ash, and adjusting the pH of 7.0 using hydrochloric acid. The residue was washed with deionized water, dried at 150°C and separated with an external magnetic field. In that work, the volume of MPTMS and Na2SiO3 was varied and the total amount of Si represented as silica was kept constant. Characters of the material including the functional group presence, the structure, the porosity, the morphology and stability toward various solvents were identified and evaluated. Results of characterization indicated that mercapto-silica has been coated magnetite particle with a simple one-pot process. Coating mercapto-silica on magnetite increases particle size, surface area, and chemical stability. Additionally, Fe3O4-SiO2-SH also shows high stability toward various organic solvents. The magnetic property of magnetite does not change after coating and the addition of nonmagnetic material still gives high value of maximum saturation magnetization. The presence of mercapto groups effective for interaction with heavy metal ions, the high chemical stability without removing the magnetic property promises the prospective application of Fe3O4-SiO2-SH in the future such as for separation and removal of heavy metal ions from aquatic environments.