Tailoring size and structural distortion of Fe3O4 nanoparticles for the purification of contaminated water

Fe₃O₄ magnetic nanoparticles with different particle sizes were synthesized using two methods, i.e., a co-precipitation process and a polyol process, respectively. The atomic pair distribution analyses from the high-energy X-ray scattering data and TEM observations show that the two kinds of nanoparticles have different sizes and structural distortions. An average particle size of 6–8 nm with a narrow size distribution was observed for the nanoparticles prepared with the co-precipitation method. Magnetic measurements show that those particles are in ferromagnetic state with a saturation magnetization of 74.3 emu g⁻¹. For the particles synthesized with the polyol process, a mean diameter of 18–35 nm was observed with a saturation magnetization of 78.2 emu g⁻¹. Although both kinds of nanoparticles are well crystallized, an obviously higher structural distortion is evidenced for the co-precipitation processed nanoparticles. The synthesized Fe₃O₄ particles with different mean particle size were used for treating the wastewater contaminated with the metal ions, such as Ni(II), Cu(II), Cd(II) and Cr(VI). It is found that the adsorption capacity of Fe₃O₄ particles increased with decreasing the particle size or increasing the surface area. While the particle size was decreased to 8 nm, the Fe₃O₄ particles can absorb almost all of the above-mentioned metal ions in the contaminated water with the adsorption capacity of 34.93 mg/g, which is ∼7 times higher than that using the coarse particles. We attribute the extremely high adsorption capacity to the highly-distorted surface.     

In situ magnetic separation and immobilization of dibenzothiophene-desulfurizing bacteria

In situ cell separation and immobilization of bacterial cells for biodesulfurization were developed by using superparamagnetic Fe₃O₄ nanoparticles (NPs). The Fe₃O₄ NPs were synthesized by coprecipitation followed by modification with ammonium oleate. The surface-modified NPs were monodispersed and the particle size was about 13 nm with 50.8 emu/g saturation magnetization. After adding the magnetic fluids to the culture broth, Rhodococcus erythropolis LSSE8-1 cells were immobilized by adsorption and then separated with an externally magnetic field. The maximum amount of cell mass adsorbed was about 530 g dry cell weight/g particles to LSSE8-1 cells. Analysis showed that the nanoparticles were strongly absorbed to the surface and coated the cells. Compared to free cells, the coated cells not only had the same desulfurizing activity but could also be easily separated from fermentation broth by magnetic force. Based on the adsorption isotherms and Zeta potential analysis, it was believed that oleate-modified Fe₃O₄ NPs adsorbed bacterial cells mainly because of the nano-size effect and hydrophobic interaction.     

Dye adsorption characteristics of magnetite nanoparticles coated with a biopolymer poly(γ-glutamic acid)

Magnetite nanoparticles coated with an anionic biopolymer poly(γ-glutamic acid) (PGA-MNPs) were synthesized and characterized for their methylene blue dye adsorption capability. Both bare- and dye-loaded PGA-MNPs were characterized by FTIR, TEM and VSM measurements, revealing the PGA-MNPs to be superparamagnetic with average particle diameter being 12.4 nm and magnetization value 59.2 emu/g. The synthesized PGA-MNPs were stable in deionized, tap and river waters as well as in acidic and basic media. Redlich-Peterson and Langmuir models precisely described the isotherm and the maximum adsorption capacity was 78.67 mg/g. A pseudo-second-order equation best predicted the kinetics with a maximum adsorption attained within 5 min. Incorporation of sodium or calcium ions reduced the dye adsorption, while a raise in pH enhanced adsorption and a complete desorption occurred at pH 1.0. Dye removal mechanism by PGA-MNPs was probably due to electrostatic interaction through exchange of protons from side-chain α-carboxyl groups on PGA-MNPs surface.     

Immobilization of catalase via adsorption onto metal-chelated affinity cryogels

A poly (acrylamide-allylglycidyl ether) [p(AAm-AGE)] cryogel was prepared by radical polymerization of acrylamide (AAm) and allylglycidyl ether (AGE). Cibacron Blue F3GA (CB) was covalently attached to the p(AAm-AGE) cryogel via the reaction between the chloride groups of the reactive dyes and the epoxide groups of the AGE. The CB-attached p(AAm-AGE) cryogel was chelated with Fe³⁺ ions. This immobilized metal ion affinity chromatography (IMAC) cryogel carrying 25.8 ± 2.0 μmol Fe³⁺ ions was used in adsorption studies to interrogate the effects of pH, protein initial concentration, flow rate, temperature and ionic strength on enzyme activity. Maximum adsorption capacities were found to be 75.7 ± 1.2 mg/g for p(AAm-AGE)-CB-Fe³⁺ cryogels and 60.6 ± 1.0 mg/g for p(AAm-AGE)-CB cryogels, respectively. The adsorbed amounts of catalase per unit mass of cryogel reached a plateau value at about 1.5 mg/mL at pH 6.0. The K_m values were found to be 0.73 ± 0.02 g/L for the free catalase and 0.18 ± 0.02 g/L for the immobilized catalase. The V_max value of free catalase (2.0 × 10³ U/mg enzyme) was found to be lower than that of the immobilized catalase (2.5 × 10³ U/mg enzyme). It was also observed that the enzyme could be repeatedly adsorbed and desorbed onto the p(AAm-AGE)-CB-Fe³⁺ cryogel.     

Adsorption of Cr(VI) and As(V) ions by modified magnetic chitosan chelating resin

Cross-linked magnetic chitosan anthranilic acid glutaraldehyde Schiff's base (CAGS) was prepared for adsorption of both As(V) and Cr(VI) ions and their determination by ICP-OES. Prepared cross-linked magnetic CAGS was investigated by means of SEM, FTIR, wide angle X-ray diffraction (WAXRD) and TGA analysis. The adsorption properties of cross-linked magnetic CAGS resin toward both As(V) and Cr(VI) were evaluated. Various factors affecting the uptake behavior such as pH, temperature, contact time, initial concentration of metal ions, effect of other ions and desorption were studied. The equilibrium was achieved after about 110 min and 120 min for As(V) and Cr(VI), respectively at pH = 2. The adsorption kinetics followed the mechanism of the pseudo-second order equation for all systems studied, evidencing chemical sorption as the rate-limiting step of adsorption mechanism and not involving a mass transfer in solution. The equilibrium data were analyzed using the Langmuir, Freundlich, and Tempkin isotherm models. The best interpretation for the equilibrium data was given by Langmuir isotherm, and the maximum adsorption capacities were 58.48 and 62.42 mg/g for both Cr(VI) and As(V), respectively. Cross-linked magnetic CAGS displayed higher adsorption capacity for Cr(VI). The adsorption capacity of the metal ions increased with increasing temperature under optimum conditions in case of Cr(VI), but decreased in case of As(V). The metal ion-loaded cross-linked magnetic CAGS were regenerated with an efficiency of greater than 88% using 0.2 M sodium hydroxide (NaOH).     

Adsorption of copper and zinc by biochars produced from pyrolysis of hardwood and corn straw in aqueous solution

Biochars produced by pyrolysis of hardwood at 450 °C (HW450) and corn straw at 600 °C (CS600) were characterized and investigated as adsorbents for the removal of Cu(II) and Zn(II) from aqueous solution. The adsorption data were well described by a Langmuir isotherm, with maximum Cu(II) and Zn(II) adsorption capacities of 12.52 and 11.0 mg/g for CS600, 6.79 and 4.54 mg/g for HW450, respectively. Thermodynamic analysis suggested that the adsorption was an endothermic process and did not occur spontaneously. Although Cu(II) adsorption was only marginally affected by Zn(II), Cu(II) competed with Zn(II) for binding sites at Cu(II) and Zn(II) concentrations ?1.0 mM. Results from this study indicated that plant-residue or agricultural waste derived biochar can act as effective surface sorbent, but their ability to treat mixed waste streams needs to be carefully evaluated on an individual basis.     

Congo red adsorption from aqueous solutions by using chitosan hydrogel beads impregnated with nonionic or anionic surfactant

The adsorption performance of CS beads impregnated with triton X-100 (TX-100) as a nonionic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant was investigated for the removal of anionic dye (congo red) from aqueous solution. While the adsorption capacity of CS/TX-100 beads was enhanced at all concentrations of TX-100 (0.005–0.1%), the increase in the concentration of SDS above 0.01% in the CS/SDS beads gradually reduced the adsorption capacity of the beads. Equilibrium adsorption isotherm data indicated a good fit to the Sips isotherm model and a heterogeneous adsorption process. The Sips maximum adsorption capacity in dry weight of the CS/TX-100 beads was 378.79 mg/g and 318.47 mg/g for the CS/SDS beads, higher than the 223.25 mg/g of the CS beads. Modification of CS beads by impregnation with nonionic surfactant, or even anionic surfactant, at low concentrations is a possible way to enhance adsorption of anionic dye.     

Obtaining of new magnetic nanocomposites based on modified polysaccharide

The study presents the preparation of some composite materials with magnetic properties by two different encapsulation methods of magnetite (Fe₃O₄) in a polymer matrix based on carboxymethyl starch-g-polylactic acid (CMS-g-PLA). The copolymer matrix used to obtain the magnetic nanocomposites was synthesized by grafting reaction of carboxymethyl starch (CMS) with d,l-lactic acid (DLLA), in the presence of Sn octanoate [Sn(Oct)₂] as catalyst. Magnetite was obtained by co-precipitation from aqueous salt solutions FeCl₂/FeCl₃ (molar ratio 1/2). The magnetic composites were prepared by precipitation method in acetone (non-solvent) of the DMSO solutions of magnetite and copolymer, and synthesis in situ of the nanocomposites. In the first case, the particle size measured by DLS-technique was 168 nm, and the magnetization was 46.82 emu/g, while after in situ synthesis, the composite materials showed smaller size (141 nm), but the magnetization was reduced (3.04 emu/g). The higher magnetization in the first case is due to the great degree of encapsulation of the magnetite, which was about 43.4 wt.%, compared to 4.37 wt.% for the in situ synthesis (determined by thermogravimetry). The CMS-g-PLA copolymer, magnetite, and the nanocomposites were characterized by infrared spectroscopy (FTIR), near infrared chemical imagistic (NIR-CI), dynamic light scattering (DLS) technique, X-ray diffraction (WAXD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and thermal analyses. Since the polymer matrix and magnetite are biodegradable and biocompatible, the magnetic nanocomposites can be used for conjugation of some drugs. The polymer matrix CMS-g-PLA acts as a shell, and vehicle for the active component, whereas magnetite is the component which makes targeting possible by external magnetic field manipulation.     

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution

A new and simple method has been proposed to prepare magnetic Fe₃O₄-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O₂ in hydrochloric acid aqueous phase containing CS and Fe(OH)₂, and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)₂ were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe₃O₄ nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe₃O₄-CS nanoparticles could reach 35.54 emu/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 μmol min⁻¹ mg⁻¹ (protein), and activity retention was as high as 55.6% at a certain loading amount.     

1株鞘细菌的分离筛选及对铅离子吸附条件的研究

通过单因素试验设计,探讨了不同鞘细菌添加量、初始浓度的铅离子溶液、吸附时溶液的温度和p H对鞘细菌吸附铅离子的影响。在此基础上,采用4因素3水平正交试验设计,进一步探讨鞘细菌对铅离子吸附影响的主要因素及最佳吸附组合。试验结果表明,最佳吸附组合为鞘细菌制备液添加量0.3 g/L、吸附溶液中铅离子初始浓度10 mg/L、摇床振荡吸附温度30℃以及吸附液p H 8。在此条件下,鞘细菌吸附铅离子的吸附量为3.09 mg/g,吸附率达92.74%。     

Investigation of Cr(VI) adsorption onto chemically treated Helianthus annuus: Optimization using Response Surface Methodology

In the present study, chemically treated Helianthus annuus flowers (SHC) were used to optimize the removal efficiency for Cr(VI) by applying Response Surface Methodological approach. The surface structure of SHC was analyzed by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray Analysis (EDX). Batch mode experiments were also carried out to assess the adsorption equilibrium in aqueous solution. The adsorption capacity (q_e) was found to be 7.2 mg/g. The effect of three parameters, that is pH of the solution (2.0-7.0), initial concentration (10-70 mg/L) and adsorbent dose (0.05-0.5 g/100 mL) was studied for the removal of Cr(VI) by SHC. Box-Behnken model was used as an experimental design. The optimum pH, adsorbent dose and initial Cr(VI) concentration were found to be 2.0, 5.0 g/L and 40 mg/L, respectively. Under these conditions, removal efficiency of Cr(VI) was found to be 90.8%.     

Investigation on the removal of Mo(VI) from Mo-Re containing wastewater by chemically modified persimmon residua

Persimmon waste was chemically modified by crosslinking with concentrated sulfuric acid to obtain a novel kind of adsorption gel, which was termed as crosslinked persimmon tannin (CPT), hereinafter. The adsorption behaviors of Mo(VI) with other coexisting metal ions onto the CPT gel were investigated. The gel exhibited selectivity only for Mo(VI) ions evidenced by the high value of separation factor of molybdenum and rhenium (β_Mo/Re = 164.37), and the adsorption mechanism of Mo(VI) as a multispecies was studied. The molybdenum adsorption behavior conforms to the Langmuir model with a remarkably high adsorption capacity of 0.56 mol/kg. A kinetic study for the adsorption of molybdenum at various temperatures confirmed that the endothermic adsorption process followed pseudo-second order kinetics. Moreover, its excellent adsorption properties and applicability for Mo(VI) were demonstrated by the removal and separation of Mo(VI) from different Mo-Re containing industrial wastewaters.     

Use of superparamagnetic particles for isolation of cells

This report describes the preparation and characterization of synthetic ferritin-like particles produced by precipitation of magnetite from a mixture of ferrous and ferric ions in the presence of dextran. The 3-nm diameter particles, containing magnetite cores surrounded by chemisorbed dextran, had a magnetization of 46.7 emu/g of iron with M?ssbauer quadrupole splitting of 2 delta = 0.76 mm/s. The application of these particles as a laboratory reagent for isolation of Legionella from other water bacteria was successfully tested. A 400-fold enrichment for Legionella was obtained.     

Production and characterization of biopolyols and polyurethane foams from crude glycerol based liquefaction of soybean straw

The feasibility of using crude glycerol to liquefy soybean straw for the production of biopolyols and polyurethane (PU) foams was investigated in this study. Liquefaction conditions of 240 °C, >180 min, 3% sulfuric acid loading, and 10-15% biomass loading were preferred for the production of biopolyols with promising material properties. Biopolyols produced under preferential conditions showed hydroxyl numbers from 440 to 540 mg KOH/g, acid numbers below 5 mg KOH/g, and viscosities from 16 to 45 Pa.s. PU foams produced under preferential conditions showed densities from 0.033 to 0.037 g/cm³ and compressive strength from 148 to 227 kPa. These results suggest that crude glycerol can be used as an alternative solvent for the liquefaction of lignocellulosic biomass such as soybean straw for the production of biopolyols and PU foams. The produced biopolyols and PU foams showed material properties comparable to their analogs from petroleum solvent based liquefaction processes.     

Assessment of polyphenolic compounds,in vitro antioxidant and anti-inflammation properties of Securidaca longepedunculata root barks

The present study was carried out to evaluate the antioxidant activities of the root bark extract of Securidaca longepedunculata. This plant material is commonly used in folk medicine in several parts in the world. The bark extracts of S. longepedunculata were evaluated for their total phenols, flavonoids, anthocyanins, tannins content and total antioxidant capacity. The compounds were identified and quantified both by RP-HPLC and UV spectrophotometer; the antioxidant capacity was assessed by ABTS and DPPH tests and expressed as IC₅₀. The total phenolic compounds determinate was 9.86 mg gallic acid equivalents/g dw, the total flavonoid contents was 5.85 mg catechin equivalents/g dw, the total anthocyanin contents was 0.032 mg cyanidin-3-glycosyl equivalents/g dw and the condensed tannins content were 1.03 mg catechin equivalents/g dw. The major compound identified using RP-HPLC was quercetin (0.98 mg/ml). The IC₅₀ value reached 5.5 μg/ml, revealing that the root barks of S. longepedunculata have a very high antioxidant and anti-inflammation properties.     

One-pot synthesis and characterization of cross-linked quaternized chitosan microspheres as protein adsorbent

The one-pot synthesis and characterization of cross-linked quaternized chitosan microspheres (CQCM) as a protein adsorbent are presented. First of all, chitosan particles were prepared by spray drying method, and then they were quaternized and cross-linked in turn with glycidyltrimethylammonium (GTMAC) chloride and glutaraldehyde in isopropanol containing 10% water in one-pot. The effect of the reaction temperature, reaction time and the amounts of added GTMAC and glutaraldehyde on the protein adsorption ability of CQCM was investigated. The adsorption behavior of the CQCM prepared in the optimum synthetic conditions was well described by the Langmuir isotherm with maximum adsorption capacity equal to 1424 mg BSA/g dry weight. The particle size ranged from 7.6 to 48.9 μm. The mechanism of adsorption-desorption of BSA to the CQCM was ion-exchange. Finally, the extraction of soybean peroxidase from crude soybean peroxidase solution using the CQCM was performed.     

Adsorption of chromium (VI) ion from aqueous solution by succinylated mercerized cellulose functionalized with quaternary ammonium groups

Succinylated mercerized cellulose (cell 1) was used to synthesize an anion exchange resin. Cell 1, containing carboxylic acid groups was reacted with triethylenetetramine to introduce amine functionality to this material to obtain cell 2. Cell 2 was reacted with methyl-iodide to quaternize the amine groups from this material to obtain cell 3. Cells 2 and 3 were characterized by mass percent gain, degree of amination and quaternization, FTIR and CHN. Cells 2 and 3 showed degrees of amination and quaternization of 2.8 and 0.9 mmol/g and nitrogen content of 6.07% and 2.13%, respectively. Cell 3 was used for Cr (VI) adsorption studies. Adsorption equilibrium time and optimum pH for Cr (VI) adsorption were found to be 300 min and 3.1, respectively. The Langmuir isotherm was used to model adsorption equilibrium data. The adsorption capacity of cell 3 was found to be 0.829 mmol/g. Kinetic studies showed that the rate of adsorption of Cr (VI) on cell 3 obeyed a pseudo-second-order kinetic model.     

Thermal conversion of alkaline lignin and its structured derivatives to porous carbonized materials

Alkaline lignin was thermally converted to microporous carbon in ca. 50% yield by heating up from room temperature to 900 °C without activation process under flowing of an argon gas. The carbonized material prepared by heating up conditions of 1 °C min⁻¹ showed 530 m²/g of the Brunauer-Emmett-Teller (BET) specific surface area, which increased to 740 m²/g after washing with water. Furthermore, alkaline lignin derivatives were structured as micron scale particles by micelle formation and polymer gelation techniques. Carbonization of the structured lignins could afford high porous materials having BET surface areas above 1000 m²/g without surface activation processes.     

Simultaneous activated carbon adsorption within a membrane bioreactor for an enhanced micropollutant removal

Significant adsorption of sulfamethoxazole and carbamazepine to powdered activated carbon (PAC) was confirmed by a series of adsorption tests. In contrast, adsorption of these micropollutants to the sludge was negligible. The removal of these compounds in membrane bioreactor (MBR) was dependent on their hydrophobicity and loading as well as the PAC dosage. Sulfamethoxazole exhibited better removal rate during operation under no or low (0.1 g/L) PAC dosage. When the PAC concentration in MBR was raised to 1.0 g/L, a sustainable and significantly improved performance in the removal of both compounds was observed - the removal efficiencies of sulfamethoxazole and carbamazepine increased to 82 ± 11% and 92 ± 15% from the levels of 64 ± 7%, and negligible removal, respectively. The higher removal efficiency of carbamazepine at high (1.0 g/L) PAC dosage could be attributed to the fact that carbamazepine is relatively more hydrophobic than sulfmethoxazole, which subsequently resulted in its higher adsorption affinity toward PAC.     

Direct binding and characterization of lipase onto magnetic nanoparticles

Lipase was covalently bound onto Fe(3)O(4) magnetic nanoparticles (12.7 nm) via carbodiimide activation. The Fe(3)O(4) magnetic nanoparticles were prepared by coprecipitating Fe(2+) and Fe(3+) ions in an ammonia solution and treating under hydrothermal conditions. The analyses of transmission electron microscopy (TEM) and X-ray diffraction (XRD) showed that the size and structure of magnetic nanoparticles had no significant changes after enzyme binding. Magnetic measurement revealed the resultant lipase-bound magnetic nanoparticles were superparamagnetic with a saturation magnetization of 61 emu/g (only slightly lower than that of the naked ones (64 emu/g)), a remanent magnetization of 1.0 emu/g, and a coercivity of 7.5 Oe. The analysis of Fourier transform infrared (FTIR) spectroscopy confirmed the binding of lipase onto magnetic nanoparticles. The binding efficiency of lipase was 100% when the weight ratio of lipase bound to Fe(3)O(4) nanoparticles was below 0.033. Compared to the free enzyme, the bound lipase exhibited a 1.41-fold enhanced activity, a 31-fold improved stability, and better tolerance to the variation of solution pH. For the hydrolysis of pNPP by bound lipase at pH 8, the activation energy within 20-35 degrees C was 6.4 kJ/mol, and the maximum specific activity and Michaelis constant at 25 degrees C were 1.07 micromol/min mg and 0.4 mM, respectively. It revealed that the available active sites of lipase and their affinity to substrate increased after being bound onto magnetic nanoparticles.