Electrochemical degradation of a real textile effluent using boron-doped diamond or β-PbO2 as anode

Constant current electrolyses are carried out in a filter-press reactor using a boron-doped diamond (Nb/BDD) or a Ti-Pt/β-PbO₂ anode, varying current density (j) and temperature. The degradation of the real textile effluent is followed by its decolorization and chemical oxygen demand (COD) abatement. The effect of adding NaCl (1.5 g L⁻¹) on the degradation of the effluent is also investigated. The Nb/BDD anode yields much higher decolorization (attaining the DFZ limit) and COD-abatement rates than the Ti-Pt/β-PbO₂ anode, at any experimental condition. The best conditions are j = 5 mA cm⁻² and 55 °C, for the system's optimized hydrodynamic conditions. The addition of chloride ions significantly increases the decolorization rate; thus a decrease of more than 90% of the effluent relative absorbance is attained using an applied electric charge per unit volume of the electrolyzed effluent (Q_ap) of only about 2 kA h m⁻³. Practically total abatement of the effluent COD is attained with the Nb/BDD anode using a Q_ap value of only 7 kA h m⁻³, with an energy consumption of about 30 kW h m⁻³. This result allows to conclude that the Nb/BDD electrode might be an excellent option for the remediation of textile effluents.     

Montmorillonite surface properties and sorption characteristics for heavy metal removal from aqueous solutions

Surface properties of montmorillonite (MMT) and its adsorption characteristics for heavy metals have been investigated with nickel and copper as sorbate from aqueous solutions. Employing the potentiometric and mass titration techniques in batch experimental methods, the point of zero charge (PZC) and point of zero net proton charge (PZNPC) of MMT edges at different ionic strengths present pH_PZC and pH_PZNPC to be 3.4 ± 0.2. A crossing point was observed for the proton adsorption vs. pH curves at different ionic strengths of KCl electrolyte and in investigating MMT remediation potentialities as sorbent for heavy metals polluted waters, the effects of heavy metal concentration, pH, MMT dosage, reaction time and temperature for Cu²⁺ and Ni²⁺ uptake were studied. The sorption of metal ions by MMT was pH dependent and the adsorption kinetics revealed sorption rate could be well fitted by the pseudo-second-order rate model. The data according to mass transfer and intraparticle diffusion models confirmed diffusion of solutes inside the clay particles as the rate-controlling step and more important for the adsorption rate than the external mass transfer. Adsorption isotherms showed that the uptake of Cu²⁺ and Ni²⁺ could be described by the Langmuir model and from calculations on thermodynamic parameters, the positive ΔG° values at different temperatures suggest that the sorption of both metal ions were non-spontaneous. Change in enthalpy (ΔH°) for Ni²⁺ and Cu²⁺ were 28.9 and 13.27 kJ/mol K respectively, hence an endothermic diffusion process, as ion uptake increased with increase in temperature. Values of ΔS° indicate low randomness at the solid/solution interface during the uptake of both Cu²⁺ and Ni²⁺ by MMT. Montmorillonite has a considerable potential for the removal of heavy metal cationic species from aqueous solution and wastewater.     

Adsorption of single Ag and Cu atoms on regular and defective MgO(0 0 1) substrates: an ab initio study

The DFT slab calculations were performed for Ag and Cu atoms adsorbed on both regular and defective MgO(0 0 1) substrates. Both metal atoms and surface O vacancies (F_s centers) were distributed uniformly with a concentration of one Ag, Cu or F_s per 2×2 surface supercell. Surface O²⁻ ions are energetically more preferable for metal-atom adsorption on a regular substrate as compared to Mg²⁺ ions. The nature of the interaction between Ag or Cu adatoms and a defectless MgO substrate is physisorption (despite the difference in the adsorption energies: 0.62 vs. 0.39 eV per Cu and Ag adatom, respectively). Above the F_s centers, metal atoms are bounded much stronger when compared with regular O²⁻ sites (2.4  vs. 2.1 eV per Cu and Ag adatoms, respectively). This is accompanied by a substantial charge transfer towards each adatom (Δq_Cu=0.41e and Δq_Ag=0.32e) as well as a formation of partly covalent Me-F_s bonds across the interface (Mulliken bond populations p_Cu-Fs=0.25e and p_Ag-Fs=0.33e).     

Multifunctional Zn0.99−xMn0.01CuxS nanowires: Structure, luminescence and magnetism

The wurtzite-type Zn_0.99−xMn_0.01Cu_xS (x = 0, 0.003, 0.01) nanowires were prepared by a simple hydrothermal method at 180 °C. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron micrograph (FESEM) and X-ray photoelectron spectrum (XPS). The results showed that both the Mn²⁺ and Cu²⁺ ions substituted for the Zn²⁺ sites in the host ZnS. The ethylenediamine-mediated template was observed, which was used to explain the growth mechanism of the nanowires. The color-tunable emission can be obtained by adjusting the concentrations of Mn²⁺ and Cu²⁺ ions. The ferromagnetism was observed around room temperature.     

Single and binary chromium(VI) and Remazol Black B biosorption properties of Phormidium sp.

Wastewaters of textile and leather dying industries may contain significant quantities of chromium(VI) ions besides anionic and water-soluble dyes. Moreover the temperature of these wastewaters may be a controlling parameter affecting the biosorption efficiency. In this study biosorption of chromium(VI) and Remazol Black B reactive dye by dried Phormidium sp., a thermophilic cyanobacterium, was studied as a function of initial chromium(VI) concentration and temperature in no dye and 100 mg l⁻¹ dye-containing media at an initial pH value of 2.0 at which the biomass exhibited the maximum chromium(VI) and dye uptakes. The decrease of both metal and dye uptakes with temperature indicated that the uptakes were exothermic in nature. Equilibrium uptake of chromium(VI) enhanced considerably with both chromium(VI) and 100 mg l⁻¹ dye concentrations. Moreover the presence of chromium(VI) also increased the uptake of dye. At 25 °C, 22.8 mg g⁻¹ chromium(VI) and 91.3 mg g⁻¹ dye were sorbed by the biomass in binary 100 mg l⁻¹ chromium(VI) and 100 mg l⁻¹ dye-containing medium. The Langmuir was the best suitable adsorption model for describing the biosorption of chromium(VI) individually and in dye-containing medium. The pseudo-second-order kinetic model described both the chromium(VI) and dye biosorptions kinetics accurately.     

Decolorization of different dyes by a newly isolated white-rot fungi strain Ganoderma sp.En3 and cloning and functional analysis of its laccase gene

A laccase-producing white-rot fungi strain Ganoderma sp.En3 was newly isolated from the forest of Tzu-chin Mountain in China. Ganoderma sp.En3 had a strong ability of decolorizing four synthetic dyes, two simulated dye bath effluents and the real textile dye effluent. Induction in the activity of laccase during the decolorization process indicated that laccase played an important role in the efficient decolorization of different dyes by this fungus. Phytotoxicity study with respect to Triticum aestivum and Oryza sativa demonstrated that Ganoderma sp.En3 was able to detoxify four synthetic dyes, two simulated dye effluents and the real textile dye effluent. The laccase gene lac-En3-1 and its corresponding full-length cDNA were then cloned and characterized from Ganoderma sp.En3. The deduced protein sequence of LAC-En3-1 contained four copper-binding conserved domains of typical laccase protein. The functionality of lac-En3-1 gene encoding active laccase was verified by expressing this gene in the yeast Pichia pastoris successfully. The recombinant laccase produced by the yeast transformant could decolorize the synthetic dyes, simulated dye effluents and the real textile dye effluent. The ability of decolorizing different dyes was positively related to the laccase activity. In addition, the 5′-flanking sequence upstream of the start codon ATG in lac-En3-1 gene was obtained. Many putative cis-acting responsive elements were predicted in the promoter region of lac-En3-1.     

Efficient removal of heavy metal ions from aqueous solution using salicylic acid type chelate adsorbent

In this study, 5-aminosalicylic acid was successfully grafted onto the poly(glycidyl methacrylate) (PGMA) macromolecular chains of PGMA/SiO₂ to obtain a novel adsorbent designated as ASA-PGMA/SiO₂. The adsorption properties of ASA-PGMA/SiO₂ for heavy metal ions were studied through batch and column methods. The experimental results showed that ASA-PGMA/SiO₂ possesses strong chelating adsorption ability for heavy metal ions, and its adsorption capacity for Cu²⁺, Cd²⁺, Zn²⁺, and Pb²⁺ reaches 0.42, 0.40, 0.35, and 0.31 mmol g⁻¹, respectively. In addition, pH has a great influence on the adsorption capacity in the studied pH range. The adsorption isotherm data greatly obey the Langmuir and Freundlich model. The desorption of metal ions from ASA-PGMA/SiO₂ is effective using 0.1 mol l⁻¹ of hydrochloric acid solution as eluent. Consecutive adsorption-desorption experiments showed that ASA-PGMA/SiO₂ could be reused almost without any loss in the adsorption capacity.     

Decolorization of reactive textile dyes using water falling film dielectric barrier discharge

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0 mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H₂O₂, Fe²⁺ and Cu²⁺) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315 kJ/L) were studied. Influence of residence time was investigated over a period of 24 h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10 mM H₂O₂ in a system of 80.0 mg/L Reactive Black 5 with applied energy density of 45 kJ/L, after residence time of 24 h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism.     

Magnetic properties of Cu substituted Co-ferrite

Copper substituted Co-Cu ferrites Co_1 − xCu_xFe₂O₄ (0 ≤ x≤0.5) have been studied with Mössbauer spectroscopy, x-ray diffraction, and vibrating sample magnetometer (VSM). The Co-Cu ferrite toroidal core samples were sintered at 860-940 °C for 2 h and the initial permeability, quality factor, density and shrinkage were also measured. The crystal structure was found to be an inverse cubic spinel with the lattice constant a₀ = 8.390 Å and a₀ = 8.386 Å for Co-ferrite and Cu²⁺ substituted Co-ferrite, respectively, by Rietveld profile analysis using the FULLPROF program. Hyperfine field was decreased with increasing Cu²⁺ concentration. The saturation magnetization (Ms) of the Co-Cu ferrite annealed at 900 °C decreased drastically and the coercivity, Hc, dropped dramatically from about 1419 to 455 Oe as copper concentration x decreased from 0.0 to 0.5. This shows that Ms, Hc can be controlled using Cu content, and initial permeability and quality factor Q is nearly constant in Cu²⁺ substituted Co-ferrite. The toroidal core data showed that the density and shrinkage of Co_1 − xCu_xFe₂O₄ (0≤x ≤ 0.5) ferrites increased with increasing quantity of Cu ions.     

Mesoporous assembly of 2D manganate nanosheets intercalated with cobalt ions

Mesoporous compound of cobalt-layered manganese oxide was synthesized by self-assembly reaction between 2D manganate nanosheets and cobalt ions. It was found that 2D manganate nanosheets are interstratified with cobalt ions, leading to the formation of porous intercalation heterostructure with expanded surface area of ∼ 44-100 m²/g. The mesopores with the average diameters of ∼ 11-17 nm originate from the house-of-cards type stacking of the layered manganate crystallites. Co K- and Mn K-edge X-ray absorption spectroscopy revealed that both the cobalt and manganese ions are stabilized in octahedral symmetry with the mixed oxidation states of Mn³⁺/Mn⁴⁺ and Co²⁺/Co³⁺. Considering high oxidation states of component metal ions, this porous material is expected to be very useful as redox catalysts and/or lithium intercalation electrodes.     

EPR and optical absorption studies of Cu ions in alkaline earth alumino borate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu²⁺ ions in alkaline earth alumino borate glasses doped with different concentrations of CuO have been studied. The EPR spectra of all the glasses exhibit the resonance signals, characteristic of Cu²⁺ ions present in axially elongated octahedral sites. The number of spins participating in the resonance has been calculated as a function of temperature for calcium alumino borate (CaAB) glass doped with 0.1 mol% of CuO. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures (T) and from the 1/χ-T graph, the Curie temperature of the glass has been evaluated. The optical absorption spectra of all the glasses show a single broad band, which has been assigned to the ²B_1g → ²B_2g transition of the Cu²⁺ ions. The variation in the intensity of optical absorption with the ionic radius of the alkaline earth ion has been explained based on the Coulombic forces. By correlating the EPR and optical absorption spectral data, the nature of the in-plane σ bonding between Cu²⁺ ion and the ligands is estimated. From the fundamental ultraviolet absorption edges of the glasses, the optical energy gap (E_opt) and the Urbach energy (ΔE) are evaluated. The variation in E_opt and ΔE is explained based on the number of defect centers in the glass.     

The microwave-assisted synthesis and characterization of Zn1 − xCoxO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn_1 − xCo_xO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn_1 − xCo_xO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn_1 − xCo_xO nanoparticles. The XRD study shows that for Co doping up to 5%, Co²⁺ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn_1 − xCo_xO (x = 1-5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co²⁺ ions in the tetrahedral sites. The Raman study shows that the linewidth of E₂^low mode increases with Co concentration, which further indicates the incorporation of Co²⁺ ions into the ZnO host matrix.     

Novel biopolymer-coated hydroxyapatite foams for removing heavy-metals from polluted water

3D-macroporous biopolymer-coated hydroxyapatite (HA) foams have been developed as potential devices for the treatment of lead, cadmium and copper contamination of consumable waters. These foams have exhibited a fast and effective ion metal immobilization into the HA structure after an in vitro treatment mimicking a serious water contamination case. To improve HA foam stability at contaminated aqueous solutions pH, as well as its handling and shape integrity the 3D-macroporous foams have been coated with biopolymers polycaprolactone (PCL) and gelatine cross-linked with glutaraldehyde (G/Glu). Metal ion immobilization tests have shown higher and fast heavy metals captured as function of hydrophilicity rate of biopolymer used. After an in vitro treatment, foam morphology integrity is guaranteed and the uptake of heavy metal ions rises up to 405 μmol/g in the case of Pb²⁺, 378 μmol/g of Cu²⁺ and 316 μmol/g of Cd²⁺. These novel materials promise a feasible advance in development of new, easy to handle and low cost water purifying methods.     

A combination of bioleaching and bioprecipitation for deep removal of contaminating metals from dredged sediment

A linked microbial process comprising bioleaching with sulfate-oxidizing bacteria and bioprecipitation with sulfate-reducing bacteria operating sequentially was investigated to deeply remove contaminating metals from dredged sediment. The results showed that sediment bioleaching resulted in a sharp decrease in sediment pH from an initial pH ∼7.6 to pH ∼2.5 within 10-20 days, approximately 65% of the main heavy metals present (Zn + Cu + Cr) were solubilized, and most of the unsolubilized metals existed in residual form of sediment. The acidic leachate that resulted from sediment bioleaching was efficiently stripped of metal sulfates using a bioprecipitation reactor when challenged with influent as low as pH ∼3.7. More than 99% of Zn²⁺, 99% of Cu²⁺ and 90% of Cr³⁺ were removed from the leachate, respectively, due to the formation of ZnS, Cu₂S and CrOOH precipitates, as confirmed by SEM-EDS and XRD detection. It was also found that alkalization of bioleached sediment using Ca(OH)₂ excluded the risk of sediment re-acidification. The ability of the combined process developed in this study to deeply remove heavy metals in insoluble sulfides or hydroxides forms makes it particularly attractive for the treatment of different types of metal contaminants.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Enhanced crystal grain size by bromine doping in electrodeposited Cu2O

Extremely large crystal grains are obtained by bromine doping in electrodeposited Cu₂O on indium tin oxide (ITO) substrate through an acetate bath. The grains are as large as 10,000 μm² in area, or ~ 100 μm in linear dimension, while the film is only 1-5 μm thick. The enhanced grain size is explained by the effect of over-potential for the Cu²⁺/Cu⁺ redox couple on nucleation density of Cu₂O on ITO substrate. The over-potential is a function of several deposition conditions including solution pH, deposition potential, deposition temperature, bromine precursor concentration, and copper precursor concentration. In addition, undoped Cu₂O displays a high resistivity of 100 MΩcm. Bromine doping in Cu₂O significantly reduces the resistivity to as low as 42 Ωcm after vacuum annealing. Br-doped Cu₂O shows n-type behavior.     

Structural aspects of adamantine like multinary chalcogenides

The present state of knowledge of structure, phase relations and metal ordering in 2(ZnX)_x(CuBX₂)_1 − x (B = Ga, In and X = S, Se, Te) and Cu₂Zn_xFe_1 − xSnS₄ multinary compounds is discussed. The chemical disorder process in 2(ZnX)_x(CuBX₂)_1 − x alloys leads to a phase separation, i.e. in a certain composition range (2-phase field) two phases, tetragonal domains and a cubic matrix, coexist. Its width depends on the three-valent cation only and is independent from the size of anion. In the subsolidus region of the 2(ZnX)_x(CuBX₂)_1 − x system the stability range of tetragonal mixed crystals as well as the miscibility gap is decreasing, the stability range of cubic mixed crystals is increasing. The process of structural disorder in 2(ZnX)_x(CuBX₂)_1 − x as well as Cu₂Fe_1 − xZn_xSnS₄ alloys is connected to the cation substructure. In tetragonal 2(ZnX)_x(CuInX₂)_1 − x alloys a non-random Zn distribution on the both cation positions of the chalcopyrite-type structure was revealed, whereas a random distribution of Zn and Cu on two different sites of the kesterite type structure was obtained in Cu₂ZnSnS₄ in contradiction to literature. The crossover from stannite (x = 0) to kesterite (x = 1) in Cu₂Fe_1 − xZn_xSnS₄ is considered as a three-stage process of cation restructure involving Cu⁺, Zn²⁺ and Fe²⁺, whereas Sn⁴⁺ does not take part in this process. In tetragonal 2(ZnX)_x(CuInX₂)_1 − x alloys the anion displacement is decreasing with increasing ZnX content in CuInX₂ indicating a decreasing tetragonal distortion. Here the disorder process in the cation substructure and the displacement process in the anion substructure are coupled.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Utilization of lignocellulosic natural fiber (jute) components during a microbial polymer production

Lignocellulosic fiber (jute), a low cost natural complex carbon source, was introduced in a fermentation medium to observe the effects of its constituents on the production of a commercially potent bacterial extracellular polysaccharide (EPS) synthesized by Bacillus megaterium RB-05. It has been found that among all the fiber components the bacterium has utilized cellulose most for the EPS production. Maximum polymer yield of 0.297 g g^− 1 substrate was found after 72 h fermentation. Consumption of fiber components was typically driven by in situ bacterial enzyme activity as EPS production was found significantly (p < 0.05) accelerated from 36 h onwards with considerable cellulase activity. Utilization of fiber components during different fermentation hours were characterized using scanning electron microscopy, FT-IR spectroscopy, X-ray diffraction, tensile property, and contact angle measurement.