فهرست مطالب shiva salem

The current research uses silica nanoparticles produced from rice husk through conventional and sonochemical precipitation to treat industrial tannery wastewater. The effects of NaOH concentration, precipitation pH, and ageing time on adsorption properties were studied via the central composite design (CCD) method. The obtained results indicated that rice husk ash, as a precursor used in the preparation of silica, should be dissolved in the dilute NaOH solution, 0.5 mol L-1, and precipitation pH should be controlled at the level of 9.0 to achieve an adsorbent with proper performance. Although the surface area of powder produced conventionally is larger than that obtained by the sonochemical method, the pore size distribution plays an effective role in the adsorption of Cr III compounds. The precipitation under sonication leads to large pores distributed in the 4-38 nm range, facilitating the diffusion of chromium compounds even in acidic environments.</em>

Among the photocatalysts, Titanium dioxide (TiO2) is mostly used for wastewater treatment. Nevertheless, large band gap, rapid recombination of electron–hole along with difficult separation process limits TiO2 applications in industrial scale. In this study, the photocatalytic activity and separation of TiO2 were improved by combined application of Fe3O4 and graphene oxide. X-ray powder diffraction (XRD), scanning electron microscopy (FESEM), and magnetization measurement (VSM) was utilized to characterize the sample and the photocatalytic degradation of methylene blue under visible light irradiation was evaluated by UV-vis spectrophotometer. The results indicate the successful preparation of purified TiO2/Fe3O4/GO nanocomposite by a two-step sol gel-hydrothermal method. The enhanced photocatalytic activity of nanocomposite is attributed to the simultaneous application of iron oxide and graphene oxide. The maximum photocatalytic decoloration (90%) is achieved within 80 min under lamp irradiation. The superparamagnetism of nanocomposites provided a convenient route for separation of the catalyst from the reaction mixture by an external magnet.

Recently, CoAl2O4, MgAl2O4 and ZnAl2O4 have been considered as the most widely used spinel structures in industrial applications as catalysts, basic catalysts and pigments especially at nano scale. Studies have shown that the composites including the combination of different types of spinels have more desirable properties in comparison to the absolute spinels. In this research review paper, the structures, properties, advantages and disadvantages of the neat spinels have been studied. Moreover, the effect of cations replacement, M=Zn, Mg, Mn, Ba, Sr, in CoxM1-xAl2O4 structures has been evaluated as one of the novel methods of spinel improvement. The results show that these replacements strongly improve the characteristics of the new combined spinels structures. For example; Increasing Zn cation results in reducing the toxicity and cobalt aluminate pigment production costs and leads to control the phenomenon of ion exchange between tetrahedral and octahedral position.

Solar energy is one of the best possible solutions that can be applied as renewable energy resources. In recent years¡ few technologies are used for manufacturing of solar cells. In the first-generation solar cell is mainly made by crystalline silicon wafer with 300-400 µm thickness. In the second and third technologies fabrication of solar cells is based on the deposition of semiconductors on the glass¡ metal or polymer substrates. The thickness of these coating is around 3-5 µm. The cost of raw materials in second and third technologies is less than the first generation. Moreover¡ the size of these solar cells is approximately 100 times larger than the first one. It should be noted that the efficiency of the first generation in comparison to the other technologies are high due to the high quality raw materials which are used in the fabrication. It is expected that the differences between the efficiency of these for technologies will be decreased by the time and other technologies will be replaced by the first generation. In this research¡ the structure of different technologies has been studied and the possible methods for improvement of the solar cells efficiency have been introduced.

In present investigation the effect of calcination time of nano-sized CoAl2O4 pigment on thermal behaviour of a typical transparent frit was investigated. The nano-sized cobalt-aluminate spinels were prepared by combustion method and calcined for 1 and 2 h at 800 and 1000 ˚C. The calcined powders were added to an industrial transparent frit and the thermal behaviours of modified glazes were studied by hot stage microscopy, HSM. The thermal properties are described in terms of height percentage and contact angle as a function of temperature. In order to obtain the parameters of Vogel-Fulcher-Tamman equation, the glass transition temperature, softening point and the temperature where samples form a half-sphere shape during HSM analysis were measured and the molten phase viscosity was predicted as a function of temperature. The results indicated that the calcination of cobalt–aluminate at 1000 ˚C during 1 h provides the best thermal properties.