Magnetic Nitrogen-Doped Porous Carbon Nanocomposite for Pb(II) Adsorption from Aqueous Solution

We report in the present study the in situ formation of magnetic nanoparticles (Fe₃O₄ or Fe) within porous N-doped carbon (Fe₃O₄/N@C) via simple impregnation, polymerization, and calcination sequentially. The synthesized nanocomposite structural properties were investigated using different techniques showing its good construction. The formed nanocomposite showed a saturation magnetization (M_s) of 23.0 emu g⁻¹ due to the implanted magnetic nanoparticles and high surface area from the porous N-doped carbon. The nanocomposite was formed as graphite-type layers. The well-synthesized nanocomposite showed a high adsorption affinity toward Pb²⁺ toxic ions. The nanosorbent showed a maximum adsorption capacity of 250.0 mg/g toward the Pb²⁺ metallic ions at pH of 5.5, initial Pb²⁺ concentration of 180.0 mg/L, and room temperature. Due to its superparamagnetic characteristics, an external magnet was used for the fast separation of the nanocomposite. This enabled the study of the nanocomposite reusability toward Pb²⁺ ions, showing good chemical stability even after six cycles. Subsequently, Fe₃O₄/N@C nanocomposite was shown to have excellent efficiency for the removal of toxic Pb²⁺ ions from water.     

MnO2 nanozyme induced the chromogenic reactions of ABTS and TMB to visual detection of Fe2+ and Pb2+ ions in water

In this study, we used a simple and rapid colourimetric reaction for visual sensing of Fe²⁺ and Pb²⁺ ions in water by employing nano-MnO₂ as a natural oxidase mimic to respectively catalyse ABTS and TMB in citrate-phosphate buffer solution (C-PBS) at 25°C and pH 3.8. It was found that nano-MnO₂ possessed highly oxidase-mimicking activity with the K_m values of 0.030 and 0.027 toward ABTS and TMB, respectively, indicating TMB had a stronger affinity on nano-MnO₂ than ABTS. Interestingly, the presence of 0.01 mmol·L^?1 Fe²⁺/Pb²⁺ ion was able to significantly down-regulate the activity of MnO₂ nanozyme in nano-MnO₂-mediated ABTS reaction processes (P < 0.01), which mainly due to the strong adsorption of metal ion toward nano-MnO₂ surface via the electrostatic attractions, thus leading to the passivation and inactivation of MnO₂ nanozyme catalytic activity. Thereinto, Fe²⁺ reacted with multivalent manganese by oxidation-reduction, while Pb²⁺ was specifically adsorbed onto the surface of MnO₂ nanozyme and formed complexes. Notably, only Fe²⁺ ion inhibited the activity of MnO₂ nanozyme-TMB with a detection limit as low as 1.0 μmol·L^?1. In MnO₂ nanozyme-ABTS sensing systems, Fe²⁺ and Pb²⁺ ions detection limit of 0.5 and 2.0 μmol·L^?1 were, respectively, achieved with a linear response range of 0–0.02 and 0–0.8 mmol·L^?1, implying the developed MnO₂ nanozyme-ABTS sensor was potentially applicable for the visual determination of Fe²⁺ and Pb²⁺ ions in water. In the real water samples, MnO₂ nanozyme-ABTS achieved high accuracy (relative errors: 3.4?10.5%) and recovery (96?110%) for respective detection of Fe²⁺ and Pb²⁺ ions. The simple and rapid MnO₂ nanozyme-ABTS sensing systems might provide a practical assay for visual detection of Fe²⁺ and Pb²⁺ ions in the environmental water samples.     

Thermodynamics Analysis and Removal of P in a P-(M)-H2O System

In order to efficiently remove phosphorus, thermodynamic equilibrium diagrams of the P-H₂O system and P-M-H₂O system (M stands for Fe, Al, Ca, Mg) were analyzed by software from Visual MINTEQ to identify the existence of phosphorus ions and metal ions as pH ranged from 1 to 14. The results showed that the phosphorus ions existed in the form of H₃PO₄, H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻. Among them, H₂PO₄⁻ and HPO₄²⁻ were the main species in the acidic medium (99% at pH = 5) and alkaline medium (97.9% at pH = 10). In the P-Fe-H₂O system ((P) = 0.01 mol/L, (Fe³⁺) = 0.01 mol/L), H₂PO₄⁻ was transformed to FeHPO₄⁺ at pH = 0–7 due to the existence of Fe³⁺ and then transformed to HPO₄²⁻ at pH > 6 as the Fe³⁺ was mostly precipitated. In the P-Ca-H₂O system ((P) = 0.01 mol/L, (Ca²⁺) = 0.015 mol/L), the main species in the acidic medium was CaH₂PO₄⁺ and HPO₄²⁻, and then transformed to CaPO₄⁻ at pH > 7. In the P-Mg-H₂O system ((P) = 0.01 mol/L, (Mg²⁺) = 0.015 mol/L), the main species in the acidic medium was H₂PO₄⁻ and then transformed to MgHPO₄ at pH = 5–10, and finally transformed to MgPO₄⁻ as pH increased. The verification experiments (precipitation experiments) with single metal ions confirmed that the theoretical analysis could be used to guide the actual experiments.     

Effect of Transition Element Ions on the Catalytic Activity of Titanium Dioxide during Chemical Deposition of Metallic Copper

We have established the high catalytic activity of TiO₂, modified by Pd²⁺, Cu²⁺, Fe³⁺, and Co²⁺ ions, in reduction of Cu²⁺ ions by formaldehyde in solution. We propose a likely scheme for the electronic processes that occur, including injection of electrons from the reducing agent into the conduction band and formation of metallic nanoparticles on the surface that effectively catalyze deposition of metallic copper.     

Effect of Physiological Concentrations of Vitamin C on the Inhibitation of Hydroxyl Radical Induced Light Emission from Fe2+-EGTA-H2O2 and Fe3+-EGTA-H2O2 Systems In Vitro

Ascorbic acid (AA) has antioxidant properties. However, in the presence of Fe²⁺/Fe³⁺ ions and H₂O₂, it may behave as a pro-oxidant by accelerating and enhancing the formation of hydroxyl radicals (^•OH). Therefore, in this study we evaluated the effect of AA at concentrations of 1 to 200 µmol/L on ^•OH-induced light emission (at a pH of 7.4 and temperature of 37 °C) from 92.6 µmol/L Fe²⁺—185.2 µmol/L EGTA (ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid)—2.6 mmol/L H₂O₂, and 92.6 µmol/L Fe³⁺—185.2 µmol/L EGTA—2.6 mmol/L H₂O₂ systems. Dehydroascorbic acid (DHAA) at the same range of concentrations served as the reference compound. Light emission was measured with multitube luminometer (AutoLumat Plus LB 953) for 120 s after automatic injection of H₂O₂. AA at concentrations of 1 to 50 µmol/L and of 1 to 75 µmol/L completely inhibited light emission from Fe²⁺-EGTA-H₂O₂ and Fe³⁺-EGTA-H₂O₂, respectively. Concentrations of 100 and 200 µmol/L did not affect chemiluminescence of Fe³⁺-EGTA-H₂O₂ but tended to increase light emission from Fe²⁺-EGTA-H₂O₂. DHAA at concentrations of 1 to 100 µmol/L had no effect on chemiluminescence of both systems. These results indicate that AA at physiological concentrations exhibits strong antioxidant activity in the presence of chelated iron and H₂O₂.     

Highly Sensitive and Selective Fluorescence “Turn-On” Detection of Pb (II) Based on Fe3O4@Au–FITC Nanocomposite

New nanocomposites, Fe₃O₄@Au–FITC, were prepared and explored to develop a fluorescent detection of Pb²⁺. The Fe₃O₄@AuNPs–FITC nanocomposites could be etched by Pb²⁺ in the presence of Na₂S₂O₃, leading to fluorescence recovery of FITC quenched by Fe₃O₄@Au nanocomposites. With the increase of Pb²⁺ concentration, the fluorescence recovery of Fe₃O₄@AuNPs–FITC increased gradually. Under optimized conditions, a detection limit of 5.2 nmol/L of Pb²⁺ with a linear range of 0.02–2.0 µmol/L were obtained. The assay demonstrated negligible response to common metal ions. Recoveries of 98.2–106.4% were obtained when this fluorescent method was applied in detecting Pb²⁺ spiked in a lake-water sample. The above results demonstrated the high potential of ion-induced nanomaterial etching in developing robust fluorescent assays.     

Studies on the adsorption of plutonium (IV) on alumina from phosphoric acid-nitric acid solution

Results of experiments on the adsorption of plutonium (IV) on alumina and their application to the recovery of plutonium from analytical waste solutions containing phosphoric-nitric acid are reported. Distribution ratios of plutonium (IV) between alumina and solutions containing varying concentrations of phosphoric acid and nitric acid are determined. The influence of various ions like UO₂ ²⁺, Fe³⁺, MoO₄ ^2–, VO²⁺ and SO₄ ^2– on the distribution ratio is evaluated. Saturation values of adsorption of plutonium (IV) on alumina and optimum conditions for loading and elution of plutonium on a column packed with alumina are described.     

The effect of metal ions with different valences on the retardation of soil-bentonite barrier materials and its mechanism

In this paper, with K＋, Ca2＋ and Fe3＋ as the objects of study, retardation of soil-bentonite （SB） barrier materials for metal ions with different valences is investigated, and the adsorption mechanism, migration patterns and permeation behavior are explored so as to provide a theoretical basis for their application. The results show that the adsorption process for metal ions with different valences by SB barrier materials is fast, and the higher the valence, the greater the adsorption capacity. The fitting of the adsorption process conforms to pseudo-second-order adsorption kinetics and Langmuir-Freundlich adsorption equation, which explains that chemical adsorption is the dominating state and that the SB surface has certain heterogeneity. The permeability coefficient of K＋, Ca2＋ and Fe3＋ in SB each has a maximum and the higher the valence, the sooner the maximum appears. Also the higher the valence, the more obvious the effect on SB retardation performance; and the sooner the ion breaks through the barrier wall completely, that is, the wall＇s retardation performance for higher valent ions may decline.     

Insertion of Phosphenium Ions into a Bicyclo[1.1.0]Tetraphosphabutane Iron Complex

By reacting [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₄)] (1) with in situ generated phosphenium ions [Ph₂P][A] ([A]⁻ = [OTf]⁻ = [O₃SCF₃]⁻, [PF₆]⁻), a mixture of two main products of the composition [{Cp‴Fe(CO)₂}₂(µ,η^1:1-P₅(C₆H₅)₂)][PF₆] (2a and 3a) could be identified by extensive ³¹P NMR spectroscopic studies at 193 K. Compound 3a was also characterized by X-ray diffraction analysis, showing the rarely observed bicyclo[2.1.0]pentaphosphapentane unit. At room temperature, the novel compound [{Cp‴Fe}(µ,η^4:1-P₅Ph₂){Cp‴(CO)₂Fe}][PF₆] (4) is formed by decarbonylation. Reacting 1 with in situ generated diphenyl arsenium ions gives short-lived intermediates at 193 K which disproportionate at room temperature into tetraphenyldiarsine and [{Cp‴Fe(CO)₂}₄(µ₄,η^1:1:1:1-P₈)][OTf]₂ (5) containing a tetracyclo[3.3.0.0^2,7.0^3,6]octaphosphaoctane ligand.     

Electrochemical properties of <Emphasis Type="Italic">n</Emphasis>-sulfonatothiacalyx[4]arene complexes with Fe<Superscript>3+</Superscript> and [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> ions

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H₄XNa₄) complexes with [Co(dipy)₃]³⁺ and Fe³⁺ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)₃]³⁺ bound extraspherically to the upper rim and Fe³⁺ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)₃]³⁺ · H₃X^5?, H₃X^5? · Fe³⁺, and ternary [Co(dipy)₃]³⁺ · H₃X^5? · Fe³⁺ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)₃]³⁺, ΔΔG ₀ = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe³⁺). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)₃]²⁺ outer ions.     

Facile synthesis of Fe3O4@C hollow nanospheres and their application in polluted water treatment

Nanostructured carbon-based materials, such as carbon nanotube arrays have shown respectable removal ability for heavy metal ions and organic dyes in aqueous solution. Although the carbon-based materials exhibited excellent removal ability, the separation of them from the aqueous solution is difficult and time-consuming. Here we demonstrated a novel and facile route for the large-scale fabrication of Fe₃O₄@C hollow nanospheres, with using ferrocene as a single reagent and SiO₂ as a template. The as-prepared Fe₃O₄@C hollow nanospheres exhibited adsorption ability for heavy metal ions and organic dyes from aqueous solution, and can be easily separated by an external magnet. When the as-prepared Fe₃O₄@C hollow nanospheres were mixed with the aqueous solution of Hg²⁺ within 15 min, the removal efficiency was 90.3%. The as-prepared Fe₃O₄@C hollow nanospheres were also exhibited a high adsorption capacity (100%) as the adsorbent for methylene blue (MB). In addition, the as-prepared Fe₃O₄@C hollow nanospheres can be used as the recyclable sorbent for water treatment via a simple magnetic separation.     

Removal of Cd(II) from Micro-Polluted Water by Magnetic Core-Shell Fe3O4@Prussian Blue

A novel core-shell magnetic Prussian blue-coated Fe₃O₄ composites (Fe₃O₄@PB) were designed and synthesized by in-situ replication and controlled etching of iron oxide (Fe₃O₄) to eliminate Cd (II) from micro-polluted water. The core-shell structure was confirmed by TEM, and the composites were characterized by XRD and FTIR. The pore diameter distribution from BET measurement revealed the micropore-dominated structure of Fe₃O₄@PB. The effects of adsorbents dosage, pH, and co-existing ions were investigated. Batch results revealed that the Cd (II) adsorption was very fast initially and reached equilibrium after 4 h. A pH of 6 was favorable for Cd (II) adsorption on Fe₃O₄@PB. The adsorption rate reached 98.78% at an initial Cd (II) concentration of 100 μg/L. The adsorption kinetics indicated that the pseudo-first-order and Elovich models could best describe the Cd (II) adsorption onto Fe₃O₄@PB, indicating that the sorption of Cd (II) ions on the binding sites of Fe₃O₄@PB was the main rate-limiting step of adsorption. The adsorption isotherm well fitted the Freundlich model with a maximum capacity of 9.25 mg·g⁻¹ of Cd (II). The adsorption of Cd (II) on the Fe₃O₄@PB was affected by co-existing ions, including Cu (II), Ni (II), and Zn (II), due to the competitive effect of the co-adsorption of Cd (II) with other co-existing ions.     

Adsorption of Cl? ions on electrodeposited rhodium black layer (rhodized electrode) at low concentrations

The adsorption of Cl^– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl^– ion concentrations (c10^–5 mol dm^–3) in 1 mol dm^–3 H₂SO₄ supporting electrolyte. The specific adsorption of Cl^– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined.     

Relationship between the basicity, De-SO2 activity and reductivity of sulfate in Mg?Al?Fe?O mixed spinel catalyst

Effects of Al³⁺ ions being partially substituted by Fe³⁺ ions in the magnesium-alumina spinel structure on the activity of SO₂ oxidative adsorption and the reductive decomposition of sulfate have been studied. Both the number of the basic centers and the strength of basicity were altered when Fe³⁺ ion was introduced into the MgAl₂O₄ structure, which resulted in the simultaneous improvement of the activity of SO₂ oxidative adsorption and the reductivity of sulfate.     

Fine Control of the Redox Reactivity of a Nonheme Iron(III)–Peroxo Complex by Binding Redox-Inactive Metal Ions

Redox-inactive metal ions are one of the most important co-factors involved in dioxygen activation and formation reactions by metalloenzymes. In this study, we have shown that the logarithm of the rate constants of electron-transfer and C−H bond activation reactions by nonheme iron(III)–peroxo complexes binding redox-inactive metal ions, [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ (Mⁿ⁺=Sc³⁺, Y³⁺, Lu³⁺, and La³⁺), increases linearly with the increase of the Lewis acidity of the redox-inactive metal ions (ΔE), which is determined from the g_zz values of EPR spectra of O₂^.−-Mⁿ⁺ complexes. In contrast, the logarithm of the rate constants of the [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ complexes in nucleophilic reactions with aldehydes decreases linearly as the ΔE value increases. Thus, the Lewis acidity of the redox-inactive metal ions bound to the mononuclear nonheme iron(III)–peroxo complex modulates the reactivity of the [(TMC)Fe^III(O₂)]⁺-Mⁿ⁺ complexes in electron-transfer, electrophilic, and nucleophilic reactions.     

Photocatalytic Activity of High Aspect Ratio TiO2 Nanorods

In this article, TiO₂ nanorods (aspect ratio >20) were prepared through a polyol process and doped with metal ions (Cu²⁺, Ni²⁺, Fe³⁺, and Cr³⁺). Compared with TiO₂ nanoparticles, the TiO₂ nanorods displayed relatively higher photocatalytic activity for the degradation of copper sulfophthalocyanine. Moreover, the photocatalytic activity was greatly enhanced when the metal ions were doped in the TiO₂ nanorods.     

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).     

Effect of Complexation on Photocatalytic Degradation of Dissolved Organic Nitrogen Compounds

Abstract

The effect of metal ions on TiO₂ mediated photocatalytic oxidation for the determination of dissolved organic nitrogen compounds is investigated. Ethylenediaminetetraaceticacid was chosen as a model molecule for DON compounds. At pH 2, 5, 7, and 10 aqueous EDTA solutions were irradiated at 254 nm in the presence of Fe²⁺, Cu²⁺, Zn²⁺, Ni²⁺ or Co²⁺ ions. The sum of produced nitrate, nitrite, and ammonium ion concentrations gave the total oxidation recovery. At low pH, the photocatalytic oxidation recoveries of Fe‐EDTA, Ni‐EDTA, and Co‐EDTA were significantly lower than the photocatalytic degradation of EDTA. The presence of free Fe²⁺, Ni²⁺, and Co²⁺ ions decreased the photocatalytic oxidation recovery. The [NH₄ ⁺]/[NO₃ ^?] ratio was higher for Cu‐EDTA.     

苯乙烯三嗪衍生物的合成及在重金属离子识别中的应用

合成了2,4-二(2-噻吩乙烯基)-6-(4'-N,N-二甲氨基苯乙烯基)-1,3,5-均三嗪(2)并鉴定了其结构。在乙腈-水混合介质中,化合物2在355和416nm处呈现双吸收峰,加入Cu²⁺,Hg²⁺ 和Fe³⁺ 后,均在520nm附近形成新的吸收峰。化合物2与Cu²⁺、Hg²⁺ 和Fe³⁺ 均形成1:1型配合物,其结合常数分别为1.9×10⁵L·mol^-1,6.6×10³L·mol^-1,2.7×10³L·mol^-1。对照化合物4与金属离子的光谱响应与化合物2相似,仅吸收峰的位置不同。因此,可认为化合物2和4中三嗪环中的N和噻吩环中的S与Cu²⁺、Hg²⁺ 和Fe³⁺ 共同配位形成了稳定的金属配合物。     

Investigations for Modification of Polyacrylamide-Bentonite by Phytic Acid and its Usability in Fe3+, Zn2+ and UO2 2+ Adsorption

Composite of polyacrylamide-bentonite (PAA-B) was prepared by direct polymerisation of PAA in a suspension of bentonite (B). Adsorption and thermodynamic features of phytic acid (Phy) adsorption onto B, PAA and PAA-B, and those of Fe³⁺, Zn²⁺, UO₂ ²⁺ adsorption onto PAA-B and its modification by Phy (PAA-B-Phy) have been investigated. The reusability, storagability, ion selectivity and recoverability of sorbed ions with 1 M HCl have also been considered.The chemical and physical structure of adsorbents has been characterised by means of FT-IR and XRD. All adsorption isotherms for Phy and the ions were L-type of the Giles classification except, the one which is S type for adsorption of Phy onto PAA. The maximum adsorption capacities for the ions adsorbed were in order of UO₂ ²⁺ > Fe³⁺ > Zn²⁺ for PAA-B and Zn²⁺ > Fe³⁺ > UO₂ ²⁺ for PAA-B-Phy. Langmuir equilibrium constants for the adsorption of ions onto PAA-B-Phy were significantly higher than those found for PAA-B; the magnitude of increase for UO₂ ²⁺ was about 100. The thermodynamic parameters indicated that adsorption reactions are spontaneous in terms of adsorption free enthalpy.The chemical structure of PAA-B-Phy was not changed at the end of the studies of reusability and storagability. The composite was selective for UO₂ ²⁺ of the ions of interest.The composite of PAA-B and its modification by Phy have been used for the first time in this investigation. It is proposed that the composites can be practically used in the investigations and applications of adsorption.