Sol gel method is a simple a low cost technique, which gives possibility to deposit coatings with definitely chemical and phase composition at low temperatures. Here we report an application of sol gel method by dip coating technique to prepare a several type of nanosized coatings: (a) one-component coatings such as TiO2 and Nd doped TiO2 (b) two types of bi-component layers, which contain as underlayer SiO2 and upper layer TiO2 or CeO2. The coatings were characterized by XRD, SEM and AFM analyses. The XRD data revealed anatase phase for TiO2 and Nd doped TiO2 coatings. The presence of cubic CeO2 and SiO2 crystallographic phases were proved in SiO2/CeO2 sample. The morphological investigations of the coatings revealed that they have relatively dense surface. The anticorrosion properties were estimated by exposing the samples to the action of salty solution of 3.5% NaCl and was evaluated by their weight losses. Corrosion attack induces insignificant alteration of the surface morphology of both Nd doped TiO2 samples and multilayer barrier coatings. Pits and other significant visible signs of corrosion are not found according to AFM and SEM analyses. The results proved that the investigated bi-component oxide coatings on the base of titania and ceria deposited on SiO2 exhibit better corrosion resistance than the noncoated steel and one component samples. These type of oxide coatings could be perspective for various applications in industry due to their good anticorrosion properties.
Author: Stambolova I.
CoO/Al2O3, CuO/Al2O3 AND NiO/Al2O3 CATALYSTS FOR PHOTODEGRADATION OF MALACHITE GREEN DYE UNDER UV-IRRADIATION
CoO, CuO or NiO supported on Al2O3 photocatalysts were prepared by impregnation and then calcination at 400oC for 3 hours. The obtained samples were physico-chemically studied by Powder X-ray diffraction analysis, X-ray photoelectron spectroscopy and Scanning electron microscopy. The photocatalytic oxidative degradation of aqueous solution of Malachite Green (MG) dye as pollutant using CoO, CuO or NiO supported on Al2O3 under UV irradiation was tested. The results determined that the highest degree of degradation of MG dye after 120 minutes was achieved using NiO/ Al2O3 photocatalyst (82%) than that the other materials CuO/Al2O3 (64%), CoO/Al2O3 (59%) and Al2O3 (50%). The calculated apparent rate constants increasing in the order: Al2O3 (2.7×10-3 min-1)<CoO/Al2O3 (3.9×10-3 min-1)<CuO/Al2O3 (4.1×10-3 min-1)<NiO/Al2O3 (8.4×10-3 min-1).
NICKEL FERRITE-ACTIVATED CARBON MATERIALS – PREPARATION AND PHOTOCATALYTIC EFFICIENCY FOR CLEANING OF MALACHITE GREEN AND REACTIVE BLACK 5 DYES UNDER UV-ILLUMINATION
Nickel ferrites having different stoichiometry supported on activated carbon (Ni0.25Fe2.75O4-AC, Ni0.5Fe2.5O4-AC, NiFe2O4-AC) were prepared by co-precipitation using nitrate precursors and activated carbon from peach stones and calcination procedure in nitrogen atmosphere. The physicochemical properties of these materials were studied by powder X-ray diffraction analysis (PXRD) and Mössbauer spectroscopy. The presence of spinel ferrite and additional hematite phases was established by PXRD. The photocatalytic properties of the so synthesized nickel ferrite-AC materials were tested and compared in oxidative degradation of Malachite Green (MG) and Reactive Black 5 (RB5) dyes under UV-light irradiation. The photocatalytic tests show that investigated samples lead to much higher degree of degradation of MG (86%-92%) compared with that of RB5 (17%-35%) due to their structure. The results proved that nickel ferrite-AC materials are more efficient photocatalysts for removal of MG as model contaminant from aqueous solution under UV light than RB5.
EFFECT OF La DOPING AND THERMAL TREATMENT ON THE PHOTOCATALYTIC ACTIVITY OF ZnO FOR DEGRADATION OF REACTIVE BLACK 5 DYE
The La-doped powder-form ZnO samples were prepared by impregnation using appropriate amounts of aqueous solutions of La(NO3)3. The non-impregnated and impregnated zinc oxide materials were then thermally treated at different temperatures – 350oC and 450oC in air atmosphere. The phase composition and structure of the obtained catalysts were characterized by powder X-ray diffraction analysis (PXRD), EPR and X-ray photoelectron spectroscopy. The PXRD results gave evidence that the average crystallite size of nanosized ZnO phase was varying within the range of 10-14 nm. The present work was focused on the influence of La doping and calcination temperatures on the photocatalytic activities of zinc oxide samples in the reaction of oxidative degradation of industrial textile azo dye Reactive Black 5 (RB5) under UV-light irradiation. The photocatalytic activity tests showed that the La doped ZnO photocatalysts are superior to the non-doped samples and are applicable to decontamination of the textile waste waters.
New type of photocatalyst containing copper oxide hydrate crystalline phase and additional amount of copper sulfate 2+ hydroxide was prepared by thermal decomposition of copper sulfate. The EPR detected presence of Cu ions. Photocatalytic degradation of two different model pollutants Reactive Black 5 (RB5) and Malachite Green (MG) in aqueous solution under UV illumination was investigated. The copper oxide containing catalyst showed four times higher photocatalytic activty with respect to RB5 than that to MG dye.
The catalyst exhibited much higher adsorption capacity to RB5 than to MG dye. The degree of degradation of MG dye is 18%, rate constant is 1.7х10 -3 min-1 while the degree of degradation of RB5 dye is 90%, rate constant is 8х10-3 min-1 after 2 hours of illumination.