Room temperature electrodeposition of photoactive Cd(OH)2 nanowires

Cd(OH)₂ nanowires (NWs) were successfully prepared by room temperature electrogeneration of base using Cd(NO₃)₂ aqueous electrolyte and Anodic Alumina Membrane (AAM) as template. Cd(OH)₂ films have been also deposited on tin-doped indium oxide (ITO) for comparison. SEM analysis shows high quality deposits made of closely packed nanowires (NWs) into AAM and uniform flake-like surface on ITO. XRD analysis reveals that Cd(OH)₂ films on ITO are polycrystalline, while the nanowires grow along the preferential directions [1 0 0] and [1 1 0]. Photoelectrochemical measurements show that Cd(OH)₂ NWs are photoactive materials with indirect and direct band gap of 2.15 and 2.75 eV, respectively.     

Trace Cd,Co, and Pb elements distribution during Sulcis coal pyrolysis: GFAAS determination with slurry sampling technique

A simple and fast method based on graphite furnace atomic absorption spectrometry (GF AAS) and slurry sampling technique (SlS) was developed to determine trace Cd, Co and Pb in high-sulphur coal (Sulcis, Italy) and coal chars derived at 600, 750 and 950 °C under N₂ atmosphere for developing a clean coal for electricity production. The proposed method was then coupled to a four-step sequential chemical extraction method for assessment of metals distribution in coaled samples. The slurries were prepared by varying sample mass (1–50 mg), volume (1–3 mL) and kind of dispersing medium (1% v/v Triton X-100 and 2 N HNO₃), and sonication time (5–30 min). Pyrolysis/atomization temperatures as well carrier gas flow rate were optimised. Pd(NO₃)₂ and NH₄H₂PO₄ were employed to stabilize Cd and Pb, respectively, in the pyrolysis stage of furnace program. The use of HNO₃ as dispersing agent was found to be effective in lowering the high level of background absorption on the Cd analytical signal produced by raw coal matrix. Conversely, coal charred samples did not show significantly level of background interferences, so that Triton X-100 dispersing agent could be used for all analytes. Calibration curve against acid-matched standards was allowed for Cd, whereas the standard addition calibration was used for Co and Pb owing to chemical matrix interferences. The precision, expressed as relative standard deviation (% RSD, n = 5), was better than 5% for Cd, Co, and Pb at 1, 10, and 15 μg L^? 1 levels, respectively. The accuracy of the analytical method was checked by analyzing a BCR No. 182 steam coal certificated reference material and the results were in good agreement with certificated and informed values. The solid detection limits (3σ_blank) were as low as 0.001 Cd, 0.01 Co, and 0.01 Pb mg kg^? 1, using 30 mg sample mass and slurry concentration of 30 m v^? 1 for Cd, and 50 mg sample mass and 50 m v^? 1 slurry concentration for Co and Pb. The content of elements in Sulcis coal was found to be 0.33 Cd, 4.0 Co, and 3.8 Pb mg kg^? 1 and mostly associated to sulphates and di-sulphides as indicated by the leaching test. Under pyrolysis conditions Cd significantly volatilised (about 64%) at temperature higher than 600 °C, whereas residue chars at 950 °C are enriched in Co and Pb up to 20%. The proposed method is suitable for routine metals monitoring in coaled samples.     

Vapour pressures,densities, and viscosities of the (water + lithium bromide + potassium acetate) system and (water + lithium bromide + sodium lactate) system

Measurements of thermophysical properties (vapour pressure, density, and viscosity) of the (water + lithium bromide + potassium acetate) system LiBr:CH₃COOK = 2:1 by mass ratio and the (water + lithium bromide + sodium lactate) system LiBr:CH₃CH(OH)COONa = 2:1 by mass ratio were measured. The system, a possible new working fluid for absorption heat pump, consists of absorbent (LiBr + CH₃COOK) or (LiBr + CH₃CH(OH)COONa) and refrigerant H₂O. The vapour pressures were measured in the ranges of temperature and absorbent concentration from T = (293.15 to 333.15) K and from mass fraction 0.20 to 0.50, densities and viscosities were measured from T = (293.15 to 323.15) K and from mass fraction 0.20 to 0.40. The experimental data were correlated with an Antoine-type equation. Densities and viscosities were measured in the same range of temperature and absorbent concentration as that of the vapour pressure. Regression equations for densities and viscosities were obtained with a minimum mean square error criterion.     

Construction of Cd(II)–ferrocenesuccinate coordination complexes via changing adjuvant ligands and anions

Seven Cd(II)–ferrocenesuccinate coordination complexes with the formulas [Cd(η²-FcCOC₂H₄COO)₂(pbbbm)]₂ (1), [Cd(η²-FcCOC₂H₄COO)(pbbbm)Cl]₂ (2), [Cd(η²-FcCOC₂H₄COO)(pbbbm)I]₂ (3), {[Cd(η²-FcCOC₂H₄COO)₂(btx)₂]₂(CH₃OH)_0.5} (4), [Cd(η²-FcCOC₂H₄COO)₂(bix)]₂(H₂O) (5), {[Cd(η²-FcCOC₂H₄COO)(bbbm)_1.5Cl] · (CH₃OH)_0.5}_n (6), and {[Cd(η²-FcCOC₂H₄COO)(mbbbm)Cl] · (H₂O)_2.75}_n (7) [pbbbm = 1,4-Bis(benzimidazole-1-ylmethyl)benzene), btx = 1,4-bis(triazol-1-ylmethyl)benzene), mbbbm = 1,3-bis(benzimidazole-1-ylmethyl)benzene), bix = 1,4-bis(imidazol-1-ylmethyl)benzene, bbbm = 1,1-(1,4-Butanediyl)bis-1H-benzimidazole)] have been synthesized and characterized. Single-crystal X-ray analysis reveals that complexes 1–5 are all dimers and bridged by pbbbm, btx and bix, respectively. But the five complexes present some differences in their dimeric conformations, which can be ascribed to the impacts of adjuvant ligands and counter anions. In contrast to complexes 1–5, both 6 and 7 are of 1-D structures (with the same counter anions), and the former is double ladder-like structure only bridged by bbbm, while the latter is chain-like structure bridged by chlorine anions and adjuvant ligand mbbbm. Notably, various π–π interactions are found in complexes 1–7, and they have significant contributions to molecular self-assembly processes. The electrochemical studies of complexes 1–7 in DMF solution display irreversible redox waves and indicate that the half-wave potentials of the ferrocenyl moieties in these complexes are all shifted to positive potential compared with that of ferrocenesuccinate.     

Remediation of Cd2+ in aqueous systems by alkali-modified (Ca) biochar and quantitative analysis of its mechanism

Co-pyrolysis of straw and Ca(OH)₂ is a feasible modification method to improve the adsorption capacity of biochar for Cd. However, few studies have quantitatively analyzed the contribution of different adsorption mechanisms of alkali-modified biochar. In this study, the alkali-modified (Ca) biochar were prepared by co-pyrolyzing lime (Ca(OH)₂) and soybean straw (SBB) or rape straw (RSB) at 450 °C. The adsorption mechanism was investigated by a series of experiments and was provided by quantitative analysis. The maximum adsorption capacities of Cd²⁺ by Ca-SBB and Ca-RSB were calculated to be 78.49 mg g^?1 and 49.96 mg g^?1, which were 1.56 and 1.48 times higher than SBB (50.40 mg g^?1) and RSB (33.79 mg g^?1), respectively. Compared with the original biochar (SBB, RSB), alkali-modified biochar (Ca-SBB and Ca-RSB) were found to have faster adsorption kinetics and lower desorption efficiencies. The mechanism study indicated that Ca(OH)₂ modification effectively enhanced the contribution of ion exchange and decreased the contribution of functional groups complexation. After Ca(OH)₂ modification, precipitation and ion exchange mechanisms dominated Cd^2 + absorption on Ca-SBB, accounting for 49.85% and 34.94% of the total adsorption, respectively. Similarily ion exchange and precipitation were the main adsorption mechanism on Ca-RSB, accounting however for 61.91% and 18.47% of total adsorption, respectively. These results suggested that alkali-modified biochar has great potential to adsorp cadmium in wastewater.     

Controllable growth of gold nanowires and nanoactuators via high-frequency AC electrodeposition

An electrochemical deposition method using high-frequency alternating current (AC) signal is reported here for the in situ synthesis and assembly of Au nanowires and nanoactuators on microelectrodes without using any masks or templates. High conductivity of 3.79 ± 0.14 × 10⁷ Ω^− 1 m^− 1 is achieved on the Au nanowires assembled between electrodes. Au nanoactuators with expansion ratio of more than 500% can be fabricated at higher frequency. The actuators can act as claws to grab SiO₂ nanoparticles in a water solution when driven by an alternating electric field. Disconnected nanowires and nanoparticles which self-aligned around the electrodes were also obtained at lower gold ion concentration, indicating a different current transfer mode in AC electrodeposition.     

Effect of heating on speciation of copper in Si/Al/Ca-based environmental matrices

X-ray absorption spectroscopy is used to investigate the speciation of sorbed copper in heated fly ash. CuO and Cu(OH)₂ are determined to be the principal copper species in the Cu-sorbing fly ash heated at 500 °C for 2 h. Heating the Cu-sorbing fly ash to 900 °C or 1100 °C can result in the formation of CuSO₄, representing 41% and 32% of the total copper, respectively. Ash sintering and/or co-melting at 900 and 1100 °C occur, thereby triggering chemical reaction between CuO/Cu(OH)₂ and sulfur compounds.     

Determination of trace amounts of cadmium by modified graphite furnace atomic absorption spectrometry after liquid phase microextraction

A simple and powerful microextraction technique was used for determination of cadmium in water samples using liquid phase microextraction (LPME) followed by graphite furnace atomic absorption spectrometry (GF-AAS). In a preconcentration step, cadmium was extracted from a 2 mL of its aqueous sample in the pH = 6 as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) cationic complex into a 4 µL drop of nitrobenzene and ammonium tetraphenylborate as counter ion. In the drop, the cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) ammonium tetraphenylborate ion associated complex was formed. After extraction, the microdrop was retracted and directly transferred into a graphite tube modified by [Pd_(c) + Pd_(i)]. Some effective parameters on extraction and complex formation, such as type and volume of organic solvent, pH, concentration of chelating agent and counter ion, extraction time and stirring rate were optimized. Under the optimum conditions, the enrichment factor and recovery were 390 and 78%, respectively. The calibration graph was linear in the range of 0.01–1 µg L^− 1 with correlation coefficient of 0.9952 under the optimum conditions of the recommended procedure. The detection limit based on the 3Sb criterion was 0.0065 µg L^− 1 and relative standard deviation (RSD) for eight replicate measurements of 0.1 µg L^− 1 and 0.4 µg L^− 1 cadmium was 6.4 and 5.8% respectively. The characteristic concentration was 0.0014 µg L^− 1 equivalent to a characteristic mass of 5.6 fg. In order to evaluate the accuracy and recovery of the presented method the procedure was applied to the analysis of reference materials and seawater.     

Preparation of Ag2Se and Ag2Se1 − xTex nanowires by electrodeposition from DMSO baths

We have developed a novel electrochemical route to fabricate highly ordered stoichiometric Ag₂Se nanowire arrays by electrodeposition from non-aqueous dimethyl sulfoxide (DMSO) solutions. Cyclic voltammetry technique was used to study this cathodic deposition process. X-ray energy dispersion analysis shows that stoichiometric Ag₂Se nanowires can be obtained in a wide range of deposition condition. X-ray diffraction and electron diffraction patterns demonstrate that the as-deposited nanowires are [0 0 2] oriented orthorhombic β-Ag₂Se. Furthermore, ternary Ag₂Se_1 − xTe_x nanowires have been electrodeposited in mixed SeCl₄–TeCl₄ DMSO solutions.     

One-step synthesis of poly(thionine)-Au nano-network and nanowires and its application for non-enzyme biosensing of hydrogen peroxide

We describe the preparation of novel poly(thionine)-Au materials, where the poly(thionine)-Au nano-network and nanowires have been synthesized in aqueous solution via the polymerization of thionine using HAuCl₄ as the oxidant in a single reaction setup. The synthesis process does not require templates, nor does it require large amounts of organic solvents or electrochemical methods. The morphology of the nanocomposites can be controlled by varying the thionine/HAuCl₄ ratio. The resulting poly(thionine)-Au network was used to fabricate a novel non-enzyme hydrogen peroxide (H₂O₂) biosensor. In pH 7.0 phosphate buffer, almost interference-free determination of H₂O₂ was realized at − 0.1 V versus Ag/AgCl with a linear of 1 × 10^− 4 to 5 × 10^− 2 M, a correlation coefficient of 0.998 and a response time of < 2 s. The developed biosensor showed a detection limit of 0.2 μM (S/N = 3) with very good stability, reproducibility and high selectivity.     

About the OH yield in the radiolysis of an aqueous/H2O2 system. Its optimisation for water treatment

Unless the radiolytic reducing species are neutralised or converted into oxidising species, an EB remediation system cannot be considered a true Advanced Oxidation Processes (AOP). A water/H₂O₂ system irradiated by UVC mercury lamps constitutes a widely used OH production method. Employing H₂O₂ in radiolysis as well, an enhancement of the oxidative efficiency of an EB treatment can be obtained. Pulse radiolysis measurements of an aerated aqueous/H₂O₂/KSCN system have been systematically undertaken to assess the optimal H₂O₂ concentration. By linearly fitting a competition kinetics relationship, it is found that the scavengeable extra-yield of OH is ΔG(OH)=0.24 μmol J^?1 (R=0,9958), while the maximum experimental yield is measured G(OH)_max=(0.52±0.02) μmol J^?1 when [H₂O₂]=5–10 mM. Exceeding these concentrations the OH yield drops off.     

Potentiostatically deposited nanostructured α-Co(OH)2: A high performance electrode material for redox-capacitors

A high specific capacitance was obtained for α-Co(OH)₂ potentiostatically deposited onto a stainless-steel electrode in 0.1 M Co(NO₃)₂ electrolyte at −1.0 V vs. Ag/AgCl. The structure and surface morphology of the obtained α-Co(OH)₂ were studied by using X-ray diffraction analysis and scanning electron microscopy. A network of nanolayered α-Co(OH)₂ sheets was obtained; the average thickness of individual α-Co(OH)₂ sheets was 10 nm, and the thickness of the deposit was several micrometers. The capacitive characteristics of the α-Co(OH)₂ electrodes were investigated by means of cyclic voltammetry and constant current charge–discharge cycling in 1 M KOH electrolyte. A specific capacitance of 860 F g⁻¹ was obtained for a 0.8 mg cm⁻² α-Co(OH)₂ deposit. The specific capacitance did not decrease significantly for the active mass loading range of 0.1–0.8 mg cm⁻² due its layered structure, which allowed easy penetration of electrolyte and effective utilization of electrode material even at a higher mass. This opens up the possibility of using such materials in supercapacitor applications.     

Electrochemical characterization of vertical arrays of tin nanowires grown on silicon substrates as anode materials for lithium rechargeable microbatteries

Vertical arrays of one-dimensional tin nanowires on silicon dioxide (SiO₂)/silicon (Si) substrates have been developed as anode materials for lithium rechargeable microbatteries. The process is complementary metal-oxide-semiconductor (CMOS) compatible for fabricating on-chip microbatteries. Nanoporous anodized aluminum oxide (AAO) templates integrated on SiO₂/Si substrates were employed for fabrication of tin nanowires resulting in high surface area of anodes. The microstructure of these nanowire arrays was investigated by scanning electron microscopy and X-ray diffraction. The electrochemical tests showed that the discharge capacity of about 400 mA h g⁻¹ could be maintained after 15 cycles at the high discharge/charge rate of 4200 mA g⁻¹.     

Hydrothermal synthesis and thermochemistry of metalloborophosphate of Na2[CuB3P2O11(OH)]·0.67H2O

The pure hydrated metalloborophosphate sample, Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O, has been synthesized and characterized by XRD, FT-IR, DTA-TG techniques, and chemical analysis. The molar enthalpies of solution of Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O(s) in 1 mol · dm^?3 HCl (aq), of Cu(OH)₂ (s) in (HCl + H₃BO₃) (aq), and of NaH₂PO₄·2H₂O (s) in (HCl + H₃BO₃ + Cu(OH)₂) (aq) were measured, respectively. With the incorporation of the previously determined enthalpy of solution of H₃BO₃ (s) in 1 mol · dm^?3 HCl (aq), together with the use of the standard molar enthalpies of formation for NaH₂PO₄·2H₂O (s), Cu(OH)₂ (s), H₃BO₃ (s), and H₂O (l), the standard molar enthalpy of formation of ?(4988.4 ± 2.5) kJ · mol^?1 for Na₂[CuB₃P₂O₁₁(OH)]·0.67H₂O at T = 298.15 K was obtained on the basis of the appropriate thermochemical cycle.     

Fabrication of metal-shelled coaxial nanowires and annealing-induced formation of metal nanoparticles for catalytic applications: Growth and characteristics of SnO2-branched nanostructures

We have fabricated SnO₂ branches on SiO_x stem nanowires, via a novel multi-step process. With the SnO₂ branches having diameters in the range 20–80 nm, X-ray diffraction, transmission electron microscopy and selected area diffraction pattern coincidentally revealed that the branches were crystalline rutile SnO₂ structures. We suggested that a Ag-catalyzed base-growth vapor–liquid–solid growth mechanism was responsible for the growth of SnO₂ branches. Photoluminescence analysis indicated that the Ag-coated SiO_x nanowires exhibited emission bands centered at 2.6 eV and 3.1 eV, presumably from the SiO_x core nanowires. Subsequent annealing induced 2.4-eV band, whereas the growth of SnO₂ branches induced 2.1-eV band. For the branched product, we have investigated the O₂ and NO₂ sensing properties. A linear relationship between sensitivity and the O₂ gas concentration was observed, which demonstrates its potential application to chemical sensors.     

Synthetic procedures and structural features of new di- and tri-nuclear chelate compounds of Cd(II) with sulfur and nitrogen donor ligands

Cd(dmpymt)₂ reacts with CdCl₂, CdBr₂·4H₂O, CdI₂, 2,2′-bipyridine and 1,10-phenanthroline to give the dimeric chelates [Cd(dmpymt)(bpy)Cl]₂ and [Cd(dmpymt)(phen)Cl]₂, as well as the tri-nuclear complexes [Cd₃(dmpymt)₄(bpy)₂Br₂] and [Cd₃(dmpymt)₄(bpy)₂I₂] (dmpymtH = 4,6-dimethylpyrimidine-2-thione; bpy = 2,2′-bipyridine; phen = 1,10-phenantroline). In all complexes the Cd(II) centers present the coordination number six. The new compounds are examples of the managing of the final aggregation state of thiolate metal complexes by introducing co-ligands to block specific coordination sites of the metal center.     

Helicity-induced two-layered Cd(II) coordination polymers built with different kinked dicarboxylates and an organodiimidazole

A new ligand bis-(4-imidazol-1-yl-phenyl)-diazene (azim), incorporating an azo moiety at the center and two imidazole groups at the terminals has been designed and synthesized. Under solvothermal conditions, this ligand reacts with Cd(NO₃)₂·6H₂O and different angular aromatic dicarboxylates to form layered coordination polymers: [Cd(azim)(bcp)]_n (1) and {[Cd(azim)(oba)](H₂O)}_n (2) [bcpH₂ = 1,3-bis-(4′-carboxy phenoxy)benzene; oba = 4,4′-oxybis(benzoate)]. Both 1 and 2 have been characterized by single-crystal X-ray diffraction technique, elemental analysis, PXRD and IR spectroscopy. The structure of each polymer looks like 2D grid where two layers are interpenetrated in a “cloth-like” topology. Both the structures contain single- and double-stranded helical coils where the pitches as well as the width are controlled by the carboxylate co-ligands. The hydrogen-bonding interactions between adjacent layers extend these structures to overall 3D supramolecular architectures.     

Application of Box–Behnken design in the optimisation of an on-line pre-concentration system using knotted reactor for cadmium determination by flame atomic absorption spectrometry

The present paper proposes an on-line pre-concentration system for cadmium determination in drinking water using flame atomic absorption spectrometry (FAAS). Cadmium(II) ions are retained as 1-(2-pyridylazo)-2-naphthol (PAN) complex at the walls of a knotted reactor, followed of elution using hydrochloric acid solution. The optimization was performed in two steps using factorial design for preliminary evaluation and a Box–Behnken design for determination of the critical experimental conditions. The variables involved were: sampling flow-rate, reagent concentration, pH and buffer concentration, and as response the analytical signal (absorbance). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line pre-concentration system, precision, effect of other ions in the pre-concentration system and accuracy. Using the optimized experimental conditions, the procedure allows cadmium determination with a detection limit (3 σ / S) of 0.10 μg L^− 1, a quantification limit (10 σ / S) of 0.33 μg L⁻¹, and a precision, calculated as relative standard deviation (RSD) of 2.7% (n = 7) and 2.4% (n = 7) for cadmium concentrations of 5 and 25 μg L^− 1, respectively. A pre-concentration factor of 18 and a sampling frequency of 48 h⁻¹ were obtained. The recovery for cadmium in the presence of several ions demonstrated that this procedure could be applied for the analysis of water samples. The method was applied for cadmium determination in drinking water samples collected in Salvador City, Brazil. The cadmium concentrations found in five samples were lower than the maximum permissible levels established by the World Health Organization.     

Preparation,crystal structure and infrared spectroscopy of the new compound Rb4Be(SeO4)2(HSeO4)2·4H2O

A new compound, Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O, crystallizes in a comparatively wide concentration range from mixed beryllium rubidium selenate solutions (from solutions containing 29.06 mass% beryllium selenate and 25.75 mass% rubidium selenate up to solutions containing 12.53 mass% beryllium selenate and 55.32 mass% rubidium selenate).Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O crystallizes in the acentric orthorhombic space group Pmn2₁ (a = 32.607(4), b = 10.676(2), c = 6.069(1) Å, V = 2112.8 ų, Z = 4, R1 = 0.047 for 4059 F_o > 4σ(F_o) and 311 variables). The crystal structure is composed of Be(H₂O)₄ tetrahedra arranged in layers at x = 0 and x = ½, alternating with broad layers built up from SeO₄ and HSeO₄ selenate tetrahedra and Rb cations. The beryllium–water layers are linked to the rest of the structure via hydrogen bonds only. The H₂O molecules as well as the OH molecules of the acid HSeO₄ groups form strong to very strong hydrogen bonds with donor–acceptor distances between 2.58 and 2.74 Å.Vibrational spectra (infrared and Raman) of Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O are presented and discussed in the region of the fundamentals of both the selenate and the beryllium tetrahedra (skeleton motions) as well as in the region of the OH vibrations at ambient and liquid nitrogen temperature (LNT). The appearance of four Raman bands corresponding to ν₁ of the selenate ions reflects the existence of four crystallographically different selenate tetrahedra in the structure. The spectroscopic experiments reveal that the ν₁ modes of the selenate ions appear at higher frequencies than some components of ν₃. Bands of an AB doublet structure (2950, 2390 cm^?1) arising from the OH stretching modes of the HSeO₄^- ions are recognized in the infrared spectra. The appearance of two infrared bands (1308, 1250 cm^?1) corresponding to δ(OH) (in-plane bending modes of the OH groups) confirms the structural data regarding the existence of two crystallographically different OH groups. The water librations are also briefly commented. The appearance of a band at a comparatively large wavenumber (1013 cm^?1) corresponding to rocking librations of the water molecules indicate that strong hydrogen bonds are formed in the title compound.