Removal of fluoride from aqueous solution by polypyrrole/Fe3O4 magnetic nanocomposite

Highly efficient visible light TiO₂ photocatalyst was prepared by the sol-gel method at lower temperature (≤300 °C), and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). The effects of the heat treatment temperature and time of the as-prepared TiO₂ on its visible light photocatalytic activity were investigated by monitoring the degradation of methyl orange solution under visible light irradiation (wavelength ≥ 400 nm). Results show that the as-prepared TiO₂ nanoparticles possess an anatase phase and mesoporous structure with carbon self-doping and visible photosensitive organic groups. The visible light photocatalytic activity of the as-prepared TiO₂ is greatly higher than those of the commercial TiO₂ (P-25) and other visible photocatalysts reported in literature (such as PPy/TiO₂, P3HT/TiO₂, PANI/TiO₂, N-TiO₂ and Fe³⁺-TiO₂) and its photocatalytic stability is excellent. The reasons for improving the visible light photocatalytic activity of the as-prepared TiO₂ can be explained by carbon self-doping and a large amount of visible photosensitive groups existing in the as-prepared TiO₂. The apparent optical thickness (τ_app), local volumetric rate of photo absorption (LVRPA) and kinetic constant (k_T) of the photodegradation system were calculated.     

Three-dimensional magnetic graphene oxide foam/Fe3O4 nanocomposite as an efficient absorbent for Cr(VI) removal

We developed a novel three-dimensional (3D) graphene oxide foam/Fe₃O₄ nanocomposite (GOF/Fe₃O₄) and evaluated its adsorption performance for Cr(IV) removal. The 3D free-standing graphene foam was firstly synthesized on nickel foam and then oxidized and magnetically functionalized with Fe₃O₄ nanoparticles to form GOF/Fe₃O₄. The GOF/Fe₃O₄ exhibited a very large surface area of 574.2 m²/g, a high saturation magnetization of 40.2 emu/g, and a maximum absorption capacity of 258.6 mg/g for Cr(IV) removal, which significantly outperformed the reported 2D graphene-based adsorbents and other conventional adsorbents. The present work may offer a way to prepare a range of 3D magnetic graphene-based adsorbents for application in effective removal of heavy metal ions.     

Enhanced removal of trace Cr(VI) ions from aqueous solution by titanium oxide-Ag composite adsorbents

Titanium oxide-Ag composite (TOAC) adsorbents were prepared by a facile solution route with Ag nanoparticles being homogeneously dispersed on layered titanium oxide materials. The as-synthesized TOAC exhibited a remarkable capability for trace Cr(VI) removal from an aqueous solution, where the concentration of Cr(VI) could be decreased to a level below 0.05 mg/L within 1h. We have systematically investigated the factors that influenced the adsorption of Cr(VI), for example, the pH value of the solution, and the contact time of TOAC with Cr(VI). We found that the adsorption of Cr(VI) was strongly pH-dependent. The adsorption behavior of Cr(VI) onto TOAC fitted well the Langmuir isotherm and a maximum adsorption capacity of Cr(VI) as 25.7 mg/g was achieved. The adsorption process followed the pseudo-second-order kinetic model, which implied that the adsorption was composed of two steps: the adsorption of Cr(VI) ions onto TOAC followed by the reduction of Cr(VI) to Cr(III) by Ag nanoparticles. Our results revealed that TOAC with high capacity of Cr(VI) removal had promising potential for wastewater treatment.     

Cr(VI) removal from aqueous solution using chemically reduced and functionalized graphene oxide

Chemically reduced and functionalized graphene oxide (GO) was prepared by refluxing of GO with ethylenediamine (ED) using dimethyl formamide (DMF) as solvent. It was confirmed that both ED and DMF contributed to the reduction and functionalization of GO. The resulting adsorbent (ED–DMF–RGO) with amine groups was highly efficient in removing Cr(VI) from its aqueous solution and could be easily separated by filtration. The optimum pH for total Cr removal was observed at pH 2.0 and the Cr(VI) removal capacity of ED–DMF–RGO at this pH was 92.15 mg g^?1, which was about 27 times higher than that of activated carbon, even nearly 4–8 times higher than that of various modified activated carbons. The presence of other ions such as Na⁺, K⁺, Ca²⁺, Cl^?, and Br^? had little effect on the removal of Cr(VI). Interestingly, Cr(VI) was reduced to low-toxic Cr(III) during the adsorption process, which followed an indirect reduction mechanism. Both the Cr(VI) adsorption and subsequent reduction of adsorbed Cr(VI) to Cr(III) contributed to the Cr(VI) removal. The obtained ED–DMF–RGO may be applicable in Cr(VI) removal if they are produced on a large scale and at low price in near future.     

Removal of fluoride from aqueous solution by polypyrrole/Fe3O4 magnetic nanocomposite

Polypyrrole (PPy)/Fe₃O₄ magnetic nanocomposite as a novel adsorbent was prepared via in-situ polymerization of pyrrole (Py) monomer using FeCl₃ oxidant in aqueous medium in which Fe₃O₄ nanoparticles were suspended. The adsorbent was characterized by Attenuated Total Reflectance Fourier transform infrared spectroscope (ATR-FTIR), Brunauer–Emmet–Teller (BET) method, field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscope (XPS) and X-ray diffraction (XRD). Magnetic property of the adsorbent was measured by electron spin resonance (ESR). Subsequently, the ability of the adsorbent to remove fluoride ions from aqueous solution was demonstrated in a batch sorption mode. Results reveal that the adsorption is rapid and that the adsorbent has high affinity for fluoride, which depends on temperature, solution pH and adsorbent dose. From equilibrium modelling, the equilibrium data is well described by Freundlich and Langmuir–Freundlich isotherms while the adsorption kinetics is described by the pseudo-second-order model. Thermodynamic parameters confirm the spontaneity and endothermic nature of the fluoride adsorption. Meanwhile, the fluoride adsorption proceeds by an ion exchange mechanism.     

Magnetic chitosan nanoparticles for removal of Cr(VI) from aqueous solution

A simple method was introduced to prepare magnetic chitosan nanoparticles by co-precipitation via epichlorohydrin cross-linking reaction. The average size of magnetic chitosan nanoparticles is estimated at ca. 30 nm. It was found that the adsorption of Cr(VI) was highly pH-dependent and its kinetics follows the pseudo-second-order model. Maximum adsorption capacity (at pH 3, room temperature) was calculated as 55.80 mg·g^? 1, according to Langmuir isotherm model. The nanoparticles were thoroughly characterized before and after Cr(VI) adsorption. From this result, it can be suggested that magnetic chitosan nanoparticles could serve as a promising adsorbent for Cr(VI) in wastewater treatment technology.     

Effective removal and fixation of Cr(VI) from aqueous solution with Friedel's salt

Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O or Ca₄Al₂(OH)₁₂Cl₂(H₂O)₄) is a calcium aluminate hydrate formed by hydrating cement or concrete in seawater at a low cost. In the current study, we carefully examined the adsorption behaviors of Friedel's salt for Cr(VI) from aqueous solution at different concentrations and various initial pHs. The adsorption kinetic data are well fitted with the pseudo-first-order Lageren equation at the initial Cr(VI) concentration from 0.10 to 8.00 mM. Both the experimental and modeled data indicate that Friedel's salt can adsorb a large amount of Cr(VI) (up to 1.4 mmol Cr(VI)/g) very quickly (t_1/2 = 2–3 min) with a very high efficiency (>99% Cr(VI) removal at [Cr] < 4.00 mM with 4.00 g/L of adsorbent) in the pH range of 4–10. In particular, the competitive adsorption tests show that the Cr(VI) removal efficiency is only slightly affected by the co-existence of Cl⁻ and HCO₃⁻. The Cr(VI)-fixation stability tests show that only less than 0.2% adsorbed Cr(VI) is leaching out in water at pH 4–10 for 24 h because the adsorption/exchange of Cr(VI) with Friedel's salt leads to the formation of a new stable phase (3CaO·Al₂O₃·CaCrO₄·10H₂O). This research thus suggests that Friedel's salt is a potential cost-effective adsorbent for Cr(VI) removal in wastewater treatment.     

Application of oak powder/Fe3O4 magnetic composite in toxic metals removal from aqueous solutions

In this study, the capability of a magnetic composite of oak powder/Fe₃O₄ (OP/Fe₃O₄) for the adsorption of lead, cobalt, and nickel ions from aqueous solutions was examined. Characteristics and structure of oak powder (OP) and OP/Fe₃O₄ magnetic composite were explored by FTIR, SEM, TGA-DTG, VSM, and XRD analysis. The XRD results showed that OP/Fe₃O₄ magnetic composite and OP were in crystalline form. Kinetic behavior of adsorption process was studied using pseudo-first-order, pseudo-second-order, and Elovich models. Results indicated that the pseudo-second-order model (R²?>?0.999) can better describe the kinetic behavior of the metal adsorption process. Equilibrium behavior of the adsorption process was also tested using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Scatchard isotherm models. The results revealed that the adsorption equilibrium data for three metals match with the Freundlich isotherm model (R²?>?0.99). This indicates the effectiveness of heterogeneous surfaces in comparison with homogeneous ones in the adsorption process of metal ions. Moreover, the results showed that the adsorption process of metal ions with the OP/Fe₃O₄ magnetic composite is physical. Finally, negative values of enthalpy and entropy indicated that the process of the metal ion adsorption is spontaneous and exothermic.     

Magnetic nanoparticle (Fe3O4) impregnated onto tea waste for the removal of nickel(II) from aqueous solution

The removal of Ni(II) from aqueous solution by magnetic nanoparticles prepared and impregnated onto tea waste (Fe(3)O(4)-TW) from agriculture biomass was investigated. Magnetic nanoparticles (Fe(3)O(4)) were prepared by chemical precipitation of a Fe(2+) and Fe(3+) salts from aqueous solution by ammonia solution. These magnetic nanoparticles of the adsorbent Fe(3)O(4) were characterized by surface area (BET), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Fourier Transform-Infrared Spectroscopy (FT-IR). The effects of various parameters, such as contact time, pH, concentration, adsorbent dosage and temperature were studied. The kinetics followed is first order in nature, and the value of rate constant was found to be 1.90×10(-2) min(-1) at 100 mg L(-1) and 303 K. Removal efficiency decreases from 99 to 87% by increasing the concentration of Ni(II) in solution from 50 to 100 mg L(-1). It was found that the adsorption of Ni(II) increases by increasing temperature from 303 to 323 K and the process is endothermic in nature. The adsorption isotherm data were fitted to Langmuir and Freundlich equation, and the Langmuir adsorption capacity, Q°, was found to be (38.3)mgg(-1). The results also revealed that nanoparticle impregnated onto tea waste from agriculture biomass, can be an attractive option for metal removal from industrial effluent.     

Fe3O4/BSA纳米磁性复合颗粒的磁响应性能

利用化学液相共沉淀法制备出不同尺寸、具有超顺磁性的纳米磁性Fe3O4/BSA颗粒,经分散后包覆蛋白使其具备良好的生物兼容性,该颗粒可长期、稳定地分散在溶液中。在外加交变磁场(414kA/m,50Hz)下纪录不同颗粒的浊度变化率,并利用光透射性可即时测得介质中浑浊程度与时间的关系,结合浊度-浓度拟合曲线,计算出在外加磁场作用下,磁性纳米复合颗粒对外加磁场的响应程度,半定量计算出相同时间下不同尺寸的微粒吸附在管壁上的质量百分比。结果显示,稳定在介质中的纳米磁性颗粒在外加磁场后,磁响应性随颗粒尺寸增大而增大,颗粒大小分别为10、108和210nm,所对应的磁响应性分别为6%、10%和12%;在外加磁场30s后,该磁性纳米复合颗粒在管壁附着的质量百分比分别为39.9%、70.4%及86.7%。     

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe₃O₄ nanoparticle (Fe₃O₄@Al(OH)₃ NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g^?1 at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (ΔH⁰) and entropy change (ΔS⁰) was 6.836 kJ mol^?1 and 41.65 J mol^?1 K^?1, which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe₃O₄@Al(OH)₃ NPs as adsorbent could reach 0.3 mg L^?1 with an initial concentration of 20 mg L^?1, which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe₃O₄@Al(OH)₃ NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.     

Reduction and removal of Cr(VI) from aqueous solutions using modified byproducts of beer production

Biosorption, as an effective and low-cost technology treating industrial wastewaters containing Cr(VI), has become a significant concern worldwide. In this work, acid-modified byproducts of beer production (BBP) were used to remove Cr(VI) from aqueous solutions. Removal of Cr(VI) increases as the pH is decreased from 4.0 to 1.5, but the maximum of total Cr removal is obtained in a pH range from 2.0 to 2.5. Nearly 60% of the initial Cr(VI) (100 mg L(-1)) was adsorbed or reduced to Cr(III) within the first 10 min at pH 2.0. The Cr(VI) removal capability of acid-modified BBP materials was almost completely retained after regenerating with acid. FT-IR and XPS spectra revealed that carboxylate and carboxyl groups on the surface of modified BBP materials play a major role in Cr(VI) binding and reduction, whereas amide and other groups play a minor role in the Cr(VI) removal process.     

Magnetic removal of dyes from aqueous solution using multi-walled carbon nanotubes filled with Fe2O3 particles

The Fe₂O₃ nanoparticles have been introduced into the multi-walled carbon nanotubes (MWCNTs) via wet chemical method. The resulting products are characterized by TEM, EDX, XRD and VSM. The magnetic MWCNTs have been employed as adsorbent for the magnetic separation of dye contaminants from water. The adsorption test of dyes (Methylene Blue and Neutral Red) demonstrates that it only takes 60 min to attain equilibrium and the adsorption capacities for Methylene Blue and Neutral Red in the concentration range studied are 42.3 and 77.5 mg/g, respectively. The magnetic MWCNTs can be easily manipulated in magnetic field for desired separation, leading to the removal of dyes from polluted water. The integration of MWCNTs with Fe₂O₃ nanoparticles has great potential application to remove organic dyes from polluted water.     

Adsorption of Cr(VI) from aqueous solution by hydrous zirconium oxide

A type of ZrO₂·nH₂O was synthesized and its Cr(VI) removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The Cr(VI) adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model. The adsorption capacity increased from 61 to 66 mg g^?1 when the temperature was increased from 298 to 338 K. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid–liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. The effective desorption of Cr(VI) on ZrO₂·nH₂O could be achieved using distilled water at pH 12.     

Preparation and application of attapulgite/iron oxide magnetic composites for the removal of U(VI) from aqueous solution

Recently, magnetic sorbents have received considerable attention because of their excellent segregative features and sorption capacities. Herein, attapulgite/iron oxide magnetic (ATP/IOM) composites were prepared and characterized. The sorption results indicated that ATP/IOM composites were superior to ATP and iron oxides individually for the removal of U(VI) from aqueous solution. Based on X-ray photoelectron spectroscopy (XPS) analysis and surface complexation model, the main sorption species of U(VI) on ATP were==X(2)UO(2)(0) below pH 4.0 and==S(s)OUO(2)(+), ==S(w)OUO(2)CO(3)(-), and==S(w)OUO(2)(CO(3))(2)(3-) above pH 5.0. However the prevalent species on ATP/IOM composites were==S(s)OUO(2)(+) and==S(w)OUO(2)(CO(3))(2)(3-) over the observed pH range. ATP/IOM composites are a promising candidate for pre-concentration and immobilization of radionuclides from large volumes of aqueous solutions, as required for remediation purposes.     

Enhancing the electrochemical Cr(VI) reduction in aqueous solution

In this study we present the cathodic Cr(VI) reduction using electrodissolution of iron anode. In batch experiments we tested four different cathodic materials; the best conditions were found when copper was used. It is observed that when more current is applied into the electrochemical cell faster reduction rates are achieved. Continuous experiments also reveal that Cr(VI) reduction could be done in a very efficient way. To confirm the experimental data, cyclic voltammetry was used and it was found that the cathodic Cr(VI) reduction is taking place.     

Efficient removal of Cr(VI) from aqueous solution by natural pyrite/rhodochrosite derived materials: Performance,kinetic and mechanism

In this work, pyrite/rhodochrosite (Py_xRh_y) composite synthesized from natural pyrite and rhodochrosite to remediate Cr(VI) containing wastewater was systematically investigated and evaluated. Results show that pyrite/rhodochrosite (1:1) showed the best Cr(VI) removal performance. XRD showed that emergence of MnS and pyrrhotite contributed to a significant increasing Cr(VI) reduction rate. The estimated maximum adsorption capacity was 95.58 mg/g at pH value of 6, temperature of 303.15 k, which was larger than other iron and manganese-based materials. Additionally, thermodynamic study illuminated that Cr(VI) removal by Py₁Rh₁ was a spontaneous and endothermic process. Taffel curve and EIS result presented higher corrosion current and lower electrical resistance for Py₁Rh₁, respectively, which was more favorable for the electron transfer. The surface cyclic regeneration of Fe(II) and Mn(II) provided long-term electron transfer to the Cr(VI) reduction. Our results demonstrated the great potentials of natural pyrite and rhodochrosite synthetic materials in the remediation of Cr(VI) polluted water.