Sorption-oxidation mechanism for the removal of arsenic (III) using Cu-doped ZnO in an alkaline medium.

1-D oxides Zn1-xCuxO and spherical composites Zn1-xCuxO/CuO were obtained by thermolysis of formate-glycolate complexes Zn1-xCux (HCOO)(OCH2CH2O)1/2 (0 ≤ x ≤ 0.15). The structural and property characteristics showed that Cu was introduced into the Zn site of the ZnO lattice to form the Zn0.95Cu0.05O solid solution. The concentration of copper in the precursors regulates the topological and structural features of the formation of Zn1-xCuxO oxides, which determine their sorption and photocatalytic properties. The materials were tested in As3+ photooxidation reaction under UV and visible radiation. It has been established that Cu+ is an effective dopant in the composition of 1-D oxide Zn1-xCuxO (0 ≤ x < 0.1). The presence of Cu2+ in the shell of Zn1-xCuxO/CuO composite reduces the photoactivity of the material. The maximum efficiency of arsenic extraction (up to 80% for Zn0.95Cu0.05O) was achieved from dilute arsenic-containing solutions (3.8 mg/L As) and an adsorbent concentration of 0.8 g/L for 24 h. In saturated solutions (380 mg/L As) this value is reduced by a factor of 100. According to XPS data, the primary process is As3+ sorption on the catalyst surface followed by its oxidation to As5+. Using the EPR method it was found that singly charged oxygen vacancies V O + $$ {V}_O^{+} $$ associated with Cu in Zn1-xCuxO are directly involved in the photostimulated oxidation of As3+. PRACTITIONER POINTS: Two types of Zn1-x Cux O photocatalysts were obtained by thermolysis of the Zn1-x Сux (HCOO)(OCH2 CH2 O)1/2 complex (0 ≤ x ≤ 0.15) in air. Sorption of arsenic from dilute solutions reaches 80% on 1-D oxide Zn0.95 Cu0.05 O. Sorption of As3+ on the catalyst surface is at primary process followed by its oxidation to As5+ . Removal of As3+ from alkaline solutions occurs due to successful combination of sorption and photocatalytic properties of the 1-D oxides Zn1-x Cux O.

Coagulation removal of nickel (II) ions by ferric chloride: Efficiency and mechanism.

Removal of heavy metal ions, in particular, divalent nickel ions from natural and wastewater, is of great importance for the environment. Nickel (II) ions are very toxic and provoke many diseases. The purpose of this work was to study the possibility of removing toxic nickel (II) ions from polluted water using an iron (III) chloride (FeCl3) coagulant. It is shown that the removal of nickel ions from aqueous solution by iron (III) hydroxide precipitate formed during the coagulation process at pH 7 and 8 is described with satisfactory accuracy by the classical adsorption isotherms of Freundlich, Langmuir, and Dubinin-Radushkevich. The studies performed with the use of X-ray powder diffraction and thermal analyses, IR, Raman, and Mössbauer spectroscopy have shown that the uptake of nickel ions by iron (III) hydroxide precipitate is due to simple physical adsorption and is not accompanied by the formation of mixed iron and nickel compounds. No alloying of the formed iron (III) hydroxide precipitate with nickel ions takes place either. The formed iron (III) hydroxide precipitate is a two-line ferrihydrite having the gross formula Fe2 O3 × 3H2 O. Its sorption capacity for nickel ions is almost an order of magnitude higher than that of some mineral and carbon sorbents, and at pH 7 and 8, it is 60.5 and 141.9 mg/g, respectively. PRACTITIONER POINTS: Coagulant FeCl3 cleans contaminated solutions from Ni(II) ions. Iron (III) hydroxide precipitated at pH 7 and 8 is a two-line ferrihydrite Fe2 O3  × 3H2 O. Removing of Ni(II) ions is described by classical adsorption isotherms. The most complete removal of Ni(II) ions occurs at pH = 8.

Self-Assembly of Ag2S Colloidal Nanoparticles Stabilized by MPS in Water Solution.

Self-assembly of colloidal Ag2S nanoparticles (NPs) was studied in the presence of (3-mercaptopropyl)trimethoxysilane (MPS). Solutions with different molar ratios of Ag2S/MPS were prepared. The appearance of nano- and microtubes was detected. Self-organized NPs were studied with optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HRTEM). Silicon nuclear magnetic resonance spectroscopy (29Si NMR) was used to study polycondensation of MPS molecules. Geometrical parameters of the nano- and microtubes depended on the molar ratio of Ag2S/MPS. The scheme and mechanism of self-assembly of Ag2S NPs in nanotubes in the presence of MPS were proposed. The effect of MPS on the preservation of the initial stoichiometry of Ag2S NPs was discussed.