Oxidation pathways of malachite green by Fe-catalyzed electro-Fenton process

A very detailed scheme for the Fe³⁺-catalyzed electro-Fenton mineralization of malachite green as a model triarylmethane dye is presented. Bulk electrolyses of 250-mL aqueous solutions of 0.5 mM malachite green with 0.2 mM Fe³⁺ as catalyst have been carried out at room temperature and pH 3.0 under constant current in an undivided cell equipped with a graphite-felt cathode and a Pt anode to assess the performance of the electro-Fenton system. In situ electrogeneration of Fe²⁺ and H₂O₂ from quick cathodic reduction of Fe³⁺ and dissolved O₂ (from bubbled compressed air), respectively, allows the formation of the very oxidizing species hydroxyl radical (OH) in the medium from Fenton's reaction. A pseudo-first-order decay kinetics with an apparent rate constant of k_1,MG = 0.244 min⁻¹ was obtained for total destruction of malachite green by action of OH at 200 mA, requiring 22 min for total decoloration of the solution. In the same experimental conditions, overall mineralization was reached at 540 min. Up to 15 aromatic and short-chain carboxylic acid intermediates were identified along the treatment. The evolution of current efficiency was calculated from the chemical oxygen demand (COD) removal. Based on the time course of most of the by-products and the identification of inorganic ions released, some plausible mineralization pathways are proposed and thoroughly discussed. It has been found that the electro-Fenton degradation of malachite green proceeds via parallel pathways, all of them involving primary splitting of the triaryl structure initiated by attack of OH on the central carbon, thus yielding two different N-dimethylated benzophenones. Successive cleavage of the aromatic intermediates generates oxalic acid as the ultimate short-chain carboxylic acid, whereas N-demethylation of some of them produces formic acid as well. Oxalic acid and its Fe²⁺ complexes, as well as formic acid, can be slowly but totally mineralized by OH.     

Platinum/zinc oxide nanoparticles: Enhanced photocatalysts degrade malachite green dye under visible light conditions

Zinc oxide nanoparticles (ZnO) were prepared via a sol–gel method, and a photo-assisted deposition method was used to prepare platinum on zinc oxide nanoparticles (Pt/ZnO). Several techniques were used to characterize these enhanced photocatalysts: XRD, TEM, UV–vis spectra, PL spectra, XPS, and BET surface area analysis. As-prepared samples’ photocatalytic performances were studied via degradation of malachite green dye under various visible-light-only irradiation scenarios. Results demonstrated the following: platinum (Pt) was well dispersed on and in ZnO's surfaces and pores; as such, Pt/ZnO had less surface area than pure ZnO due to pore blockage; however, advantages gained from enhanced electron-hole separation and decreased band gap width more than made up for this negative effect; moreover, Pt/ZnO prepared with 0.3 wt% Pt exhibited the lowest band gap and the highest photocatalytic activity of the various samples with a solids loading of 0.8 g/l; finally, such samples were recyclable, i.e., photocatalytic performance remained stable even after five uses.     

Application of adaptive neuro-fuzzy interference system on biosorption of malachite green using fir (Abies nordmanniana) cones biomass

Removal of malachite green (MG) onto fir (Abies nordmanniana) cones biomass (FCB) as a lingo-cellulosic-based structure material was investigated in the present study. Characterization of FCB was performed using Fourier transform infra red and scanning electron microscobe analyses. Several parameters (biomass dose and particle size, dye concentration, temperature, and pH) were investigated to determine optimal working conditions. Subsequently, FCB yelded a q_e of 2.2?mg/g for 50?g/L FCB, in an MG solution of 110?mg/L, pH 3.3, at a temperature of 21?°C, on a 0.2-0.4?mm fraction powder after 146?h of contact. Adaptive neuro-fuzzy interference system modeling was applied to experimental data and results showed that predicted model fitted experimental data with R² = 0.994. In a nutshell, it can be concluded that FCB shows good potential for treating MG contaminated waters.     

Adsorption efficiency of poly(malachite green) films towards oxidation of ascorbic acid

Thickness of poly(malachite green) films electropolymerized on a glassy carbon electrode surface, the concentration of ascorbic acid, pH value of the solution, and accumulation time were found to affect the adsorption-controlled anodic peak current of ascorbic acid on this polymer film coated electrode. Adsorption efficiency, defined as the ratio of the active sites in polymer films to the amount of adsorbed ascorbic acid molecules, was then proposed and estimated from the comparison of mathematically simulated cyclic voltammograms with experimental ones. The concentration of ascorbic acid is the greatest parameter affected the adsorption efficiency. Poly(malachite green) film electropolymerized on the glassy carbon electrode was found to be not totally active towards oxidation of ascorbic acid when the concentration of ascorbic acid is too high or when the poly(malachite green) film is too thick. The potential shift of ascorbic acid on the modified electrodes was also discussed.     

Synthesis and Characterization of a Conducting Composite of Polyaniline,Poly(o-Anisidine), and Poly(Aniline-co-o-Anisidine)

A conducting composite of polyaniline, poly(o-anisidine), and poly(aniline-co-o-anisidine) using incorporation of TiO₂ and SiO₂ was prepared by electrochemical polymerization. The films were electropolymerized in a solution containing 0.1 M monomer(s), 1 M sulfuric acid as supporting electrolyte, and 10^?5 M TiO₂ and SiO₂ by applying a sequential linear potential scan rate of 50 mV/s between ? 0.2 and 1.0 V versus an Ag/AgCl electrode. The composites were characterized by cyclic voltametry, UV-visible spectroscopy, electrical conductivity, and thermogravimetric analysis. It was observed that the UV-visible peaks appeared in the region of the conducting emerladine salt phase. In an overall study, the polymers prepared using TiO₂ had a higher conductivity than those prepared with SiO₂; however, higher conductivity was observed for the polyaniline-TiO₂ conducting composite than for the other polymers. The composites did not lose their color at higher temperature and hence can be utilized as the conductive pigments required for antielectrostatic applications.     

Electrosynthesis of poly(aniline-co-o-phenylenediamine) film on steel and its corrosion protection performance

Poly(aniline-co-o-phenylenediamine) (Ani-co-oPD) has been electrosynthesized on steel surface by cyclic voltammetry technique from an aqueous oxalic acid electrolyte. The copolymer film was characterized by FTIR, UV, TGA, and SEM techniques. The corrosion protection performance of poly(Ani-co-oPD) film on steel was found out by impedance and Tafel polarization methods in 1% NaCl. The copolymer film was found to be highly corrosion resistant and a suitable mechanism for corrosion protection is suggested.     

Adsorption of malachite green onto bentonite: Equilibrium and kinetic studies and process design

The adsorption of malachite green onto bentonite in a batch adsorber has been studied. The effects of contact time, initial pH and initial dye concentration on the malachite green adsorption by the bentonite have been studied. Malachite green removal was seen to increase with increasing contact time until equilibrium and initial dye concentration, and the adsorption capacity of bentonite was independent of initial pH in the range 3–11. Four kinetic models, the pseudo first- and second-order equations, the Elovich equation and the intraparticle diffusion equation, were selected to follow the adsorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and correlation coefficients, for each kinetic equation were calculated and discussed. It was shown that the adsorption of malachite green onto bentonite could be described by the pseudo second-order equation. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich equations. Adsorption of malachite green onto bentonite followed the Langmuir isotherm. The thermodynamic parameters, such as ΔH, ΔS and ΔG, were also determined and evaluated. A single stage batch adsorber was designed for different adsorbent mass/treated effluent volume ratios using the Langmuir isotherm.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.     

Protein functionalized Pt nanoparticles-conducting polymer nanocomposite film: Characterization and immunosensor application

We report an electrochemically prepared 3-mercaptopropionic acid (MPA) capped Pt nanoparticles-Polypyrrole (PPy) nanocomposite film based bioelectrode for the detection of human C-reactive protein (αCRP). The electrochemical deposition provides homogeneous distribution of ultrafine Pt(MPA)-NPs within the uniform and adherent PPy film with high degree of geometrical conformity and controllable film thickness. Protein antibody, Ab-αCRP, was covalently immobilized through the site specific carboxyl groups of Pt(MPA)-NPs within the polymer nanocomposite film by carbodiimide coupling reaction. The bioelectrode interfacial surface electron transport study towards protein antigen, Ag-αCRP, was carried out by electrochemical impedance spectroscopy (EIS). The value of ‘n’, a Constant Phase Element exponent used as a gauge of the heterogeneity, for Pt(MPA)-PPy nanocomposite film was found to be 0.88∼1 which is indicative of a homogeneous morphology of the composite film with minimal defects. The EIS of the bioelectrode exhibited significant changes in charge transfer resistance (R_et) component at a low ac frequency of <20 Hz towards Ag-αCRP detection over a linear range of 10 ng mL⁻¹–10 μg mL⁻¹ in PBS with a sensitivity of 109.74 Ωcm² per decade.     

融合多种技术的隐色孔雀石绿印迹传感器的制备及其应用

鉴于隐色孔雀石绿（LMG）对人体健康的危害性,建立灵敏快速检测水产品中LMG残留的方法有着重要意义。本研究将计算机模拟技术、紫外光谱技术、自组装技术及电化学分析等多种技术相融合,成功制备了用于检测LMG的分子印迹电化学传感器（MIECS）。基于纳米材料修饰电极,以LMG为模板分子,运用紫外光谱法结合计算机模拟筛选4-氨基苯硫酚（4-ATP）为最佳功能单体,通过Gaussian 09软件模拟计算LMG和4-ATP预组装体系的构型、作用形式及结合能。利用扫描电镜、红外光谱仪对其进行形貌和化学结构表征,采用循环伏安法和方波伏安法研究其印迹效果和选择性,并将其应用于食品安全快速检测。结果表明,模板分子和功能单体主要形成LMG-2(4-ATP) 型复合物,该传感器具有良好的性能,可特异性识别LMG及其结构类似物;该方法在3.3×10^-11～1.0×10^-6mol/L范围内线性关系良好,检出限为1.0×10^-11mol/L,样品加标回收率为85.5%～101.2%,相对标准偏差为1.28%～2.48%,适用于水产品中LMG残留量的灵敏快速检测。未来MIECS将向更灵敏、准确、快速及小型化和微型化方向发展,并应用于更多领域。     

The study of thermodynamics and kinetics methyl orange and malachite green by SWCNTs,SWCNT-COOH and SWCNT-NH2 as adsorbents from aqueous solution

The effective removal of dyes from aqueous wastes is among the most important issues for many industrialized countries. Removal of methyl orange (MO) and malachite green (MG) from aqueous solutions were studied using single-walled carbon nanotubes (SWCNTs), carboxylate functionalized single-walled carbon nanotubes (SWCNT-COOH) and amide functionalized single-walled carbon nanotubes (SWCNT-NH₂). The adsorption process was found to be controlled by temperature, ionic strength, initial concentration, adsorbent dosage and contact time. The microstructure of carbon nanotubes was characterized using SEM and FTIR. The adsorbents studied exhibits high efficiency for MO and MG adsorption and the equilibrium states could be achieved in 20, 20, 15 (min) for SWCNTs, SWCNT-COOH, SWCNT-NH₂, respectively. Adsorption capacity of each adsorbent increased with increasing active groups on the surface of carbon nanotube, where SWCNT-NH₂ was the most effectively adsorbent.     

Sorption of malachite green on vinyl-modified mesoporous poly(acrylic acid)/SiO2 composite nanofiber membranes

Vinyl-modified mesoporous poly(acrylic acid)/SiO₂ (PAA/SiO₂) composite nanofiber membranes were prepared through a sol-gel electrospinning process. The sorption behavior of malachite green on the membranes was studied. Fourier transform infrared (FTIR) results demonstrated that vinyl groups were grafted onto the silica skeleton. Transmission electron microscopy (TEM) images confirmed the formation of mesopores on the electrospun nanofibers and the pore size was 3.8 nm based on the Barrett-Joyner-Halenda (BJH) model. According to Brunauer-Emmett-Teller (BET) method, the specific surface area of the membranes was 523.84 m²/g. Three widely used isotherms, the Freundlich, Langmuir, and Redlich-Peterson isotherms, were used to model the experimental data of malachite green adsorption on PAA/SiO₂ nanofiber membranes. The best fit was found to be Redlich-Peterson isotherm and the equilibrium adsorption capacity was 220.49 mg/g. The adsorption kinetics followed a pseudo-second-order model. The removal of malachite green from the aqueous phase reached 98.8% in 240 min. The membranes can be regenerated by treated with alcohol solution and reused for multiple cycles, which is beneficial for practical application.     

Removal of malachite green from aqueous solution by zinc oxide nanoparticle loaded on activated carbon: Kinetics and isotherm study

In this research, a novel adsorbent, zinc oxide nanoparticle loaded on activated carbon (ZnO-NP-AC) was synthesized by a simple, low cost and efficient procedure. Subsequently, this novel material was characterizated and identified by different techniques such as Brunauer, Emmett and Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analysis. Unique properties such as high surface area (>603 m²/g) and low pore size (<61 Å) and average particle size lower than 100 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of malachite green (MG). In batch experimental set-up, optimum conditions for quantitative removal of MG by ZnO-NP-AC was attained following searching effect of variables such as adsorbent dosage, initial dye concentration and pH. Optimum values were set as pH of 7.0, 0.015 g of ZnO-NP-AC at removal time of 15 min. Kinetic studies at various adsorbent dosage and initial MG concentration show that maximum MG removal was achieved within 15 min of the start of every experiment at most conditions. The adsorption of MG follows the pseudo-second-order rate equation in addition to interparticle diffusion model (with removal more than 95%) at all conditions. Equilibrium data fitted well with the Langmuir model at all amount of adsorbent, while maximum adsorption capacity was 322.58 mg g⁻¹ for 0.005 g of ZnO-NP-AC.     

Poly(Δ-dicyclopenta[2,1-b:3,4-b′]dithiophene-co-3,4-ethylenedioxythiophene): Electrochemically generated low band gap conducting copolymers

A low HOMO-LUMO gap, alkene bridged bis-bithiophene (Δ^4,4′-dicyclopenta [2,1-b:3,4-b′]dithiophene) has been copolymerized with electron rich 3,4-ethylenedioxythiophene, to produce copolymers with reduced band gaps and enhanced conductivities. Electrochemical band gaps as low as 0.1 eV have been observed, but maximum conductivities were only ca. 0.3 mS cm⁻¹. Poor matching of the HOMO energies of the two components, together with cross-conjugation at the alkene bridge appear to limit charge carrier mobilities. These results provide further evidence that the use of donor and acceptor moieties to decrease band gaps leads to materials with decreased charge carrier mobilities due to charge localization.     

Study of competitive adsorption of malachite green and sunset yellow dyes on cadmium hydroxide nanowires loaded on activated carbon

Cadmium hydroxide nanowires loaded on activated carbon (Cd(OH)₂-NW-AC) was applied for removal of malachite green (MG) and sunset yellow (SY) in single and binary component systems. This novel material was characterized and identified by different techniques such as Brunauer, Emmett and Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis. Unique properties such as high surface area (>1271 m² g⁻¹) and low pore size (<35 Å) and average particle size lower than 50 Å in addition to high reactive atom and presence of various functional groups make it possible for efficient removal of these two dyes. In the single component system in this study, maximum adsorption capacity of 80.6 for SY and 19.0 mg g⁻¹ for MG at 25 °C was reported. The Langmuir model had very well fit with the experimental data (R² > 0.996). A better agreement between the adsorption equilibrium data and mono-component Langmuir isotherm model was found. The kinetics of adsorption for single and binary mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The second-order kinetic model had very well fit with the dynamical adsorption behavior of a single dye for lower and higher initial dye concentrations. SY and MG without spectra overlapping were chosen and analyzed with high accuracy in binary solutions. The effect of multi-solute systems on the adsorption capacity was investigated. The isotherm constants for SY and MG were also calculated in binary component systems at concentrations within moderate ranges, the Langmuir isotherm model satisfactorily predicted multi-component adsorption equilibrium data. The competitive adsorption favored the SY in the A mixture solution (both SY and MG concentration at 10 mg L⁻¹) and B mixture solution (25 mg L⁻¹ of SY and 10 mg L⁻¹ of MG). Also, in both cases, kinetic data was fairly described by two-step diffusion model. An endothermic and spontaneous nature for the adsorption of the dyes studied were shown from thermodynamic parameters in single and binary component systems.     

Gold microspheres with hierarchical structure/conducting polymer composite film: Preparation, characterization and application as catalyst

Monodisperse gold microspheres with novel hierarchical structure and their composite integrated with a conducting film obtained from a new conducting copolymer, poly(acrylonitrile-co-vinyl acetate) -graft- poly(3,4-ethylenedioxythiophene), have been successfully prepared in one step via the in-situ reduction of AuCl₄^- on the conducting film surface. The morphology and structure of the as-prepared composite film are characterized, and its catalytic effect on reduction of p-nitrophenol is investigated. By controlling the concentration of HAuCl₄ and the conductivity (or PEDOT content) of P(AN-co-VA)-g-PEDOT copolymer film, the amount and the size of gold microspheres can be effectively adjusted. It is suggested that the side poly(3,4-ethylenedioxythiophene) chains of the conducting copolymer play both reducing and structure-directing roles during the formation of Au microspheres with hierarchical structure.     

孔雀石绿与蛋白质相互作用的电化学行为的研究

在pH 4.7的NaAc-HAc缓冲液中,孔雀石绿(MG)能与牛血清白蛋白相互作用形成复合物,使孔雀石绿在-0.72 V(vsSCE)处有一极谱还原峰峰电流下降,在最佳条件下,峰电流的下降值同牛血清白蛋白(BSA)的浓度在0.5～20 mg/L范围内呈线性关系,其线性回归方程为Δip(nA)=-4.78+41cBSA(mg/L),相关系数r=0.996(n=10),检出限为0.4 mg/L.可将该方法应用于血清样品的测定,结果满意.     

Poly(indole-6-carboxylic acid) and tetracyanoquinodimethane-modified electrode for selective oxidation of dopamine

Poly(indole-6-carboxylic acid) (PICA) was synthesized electrochemically over glassy carbon electrode (GCE) through potentiodynamic mode of polymerization. The resulting polymer was soluble in Tris-HCl buffer (pH 7.0). The processable polymer was cast over desired electrode surface along with organic redox mediator tetracyanoquinodimethane (TCNQ) as an electron transfer relay using Nafion^®. Nafion^® was used to solubilize TCNQ as well as to introduce permselectivity to the blend of polymer and TCNQ. The above blend was cast over GCE and characterized by cyclic voltammetry followed by its application in electrochemical sensing of dopamine (DA) and ascorbic acid (AA). The modified electrode was found to be selective for DA analysis. The lowest detection limit of DA sensing was found to be 4 μМ with a sensitivity of 18 μA ± 6 nA/mM of DA.     

Extraordinary adsorption of acidic fuchsine and malachite green onto cheap nano-adsorbent derived from eggshell

Removal of dyestuffs such as Acidic Fuchsine(AF) and Malachite Green(MG) being present in many forms in industries is vital to protect water reservoirs from their catastrophic effects on the ecosystem. This study attempts to effectively eliminate these dyes using a low-cost and eco-friendly material. Eggshell, as a biocompatible by-product,was initially characterized, then some modifications were conducted, and its morphology and chemical structure were then examined through(Atomic force microscopy) AFM,(Fourier-Transform Infrared Spectroscopy) FTIR,(Energy-Dispersive X-ray Spectroscopy) EDS and(Brunauer–Emmett–Teller) BET analyses. They revealed that the modifications on raw material gave rise to a natural nano-adsorbent presenting porous medium appropriate for targeted adsorbate molecules with the average particle size and average pore diameter of 54 and ～2 nm, respectively. Functional groups on the adsorbent surface were also of importance to assist the adsorption of AF and MG.The effect of contact time, adsorbent dose, solution p H and initial concentration was evaluated. Pseudo-second order model accurately correlated the experimental kinetic data for both dyes. Moreover, the participation of intra-particle diffusion along with film diffusion in controlling the process was suggested. Langmuir isotherm model fitted very well to the equilibrium data for both dyes and maximum monolayer adsorption capacity of AF and MG was accordingly calculated to be 5000 and 3333.33 mg·g~(-1) respectively. The inherent characteristics of eggshell make it a potential material to remove contaminants from wastewater in future applications.     

Preparation and Characterization of Poly(N-Methylpyrrole)/MoO3 Hybrid Composites

Poly(N-methylpyrrole)/molybdenum trioxide composites have been prepared by in situ anodic polymerization using a 75:25 acetonitrile:water monomer solution, exfoliated molybdenum trioxide particles, and supporting electrolyte as reaction medium. The incorporation of molybdenum trioxide increases the ability of poly(N-methylpyrrole) to exchange charge reversibly (i.e., the electroactivity) by 47%. This has been attributed to the structural changes induced by the molybdenum trioxide, which transforms the uniform and compact surface morphology of poly(N-methylpyrrole) into a more open structure with distinctive topographic features at different levels. These trends facilitate the access and escape of dopant ions during oxidation and reduction processes, respectively, with respect to poly(N-methylpyrrole).