PHOTOCATALYTIC REDUCTION of carbon dioxide to formaldehyde was investigated on four semiconductor photocatalysts (FeS, FeS/FeS2, NiO and TiO2). The reaction was carried out in continues flow of CO2 gas bubbled into the reactor. Semiconductor photocatalysts were characterized by X-Ray diffraction (XRD) and Diffuse Reflectance Spectroscopic (DRS) methods. Sulfide ion was used as hole scavenger. The results show that the TiO2 has greater PHOTOCATALYTIC activity compared to the other photocatalysts, for example, maximum formaldehyde concentration were 720 and 380 ppm on TiO2 and NiO, respectively.Addition of carbonate ion causes an increase (around two times) in the concentration of formaldehyde. The yield of the formaldehyde decreased with decreasing concentration of the sulfide ion and the pH of the reaction mixture (from 700 ppm to 500 ppm). This investigation demonstrates that under ultraviolet radiation, carbon dioxide can be reduced to formaldehyde on semiconductor photocatalysts. This reaction could have been a possible chemical route to photosynthesis on the early Earth.

In this paper, the effect of PHOTOCATALYTIC REDUCTION on hydrophilicity of graphene oxide nanosheets is presented. The graphene oxide nanosheets were prepared by oxidation and exfoliation of natural graphite. The prepared samples were exposed to UV irradiation in presence of TiO2 nanoparticles. Raman spectroscopy and atomic force microscopy show that roughness of the surface is increased due to increasing irradiation. Also, the hydrophilicity of samples by measuring the contact angle of micro-liter droplets of deionized water, showed that by increasing exposure time up to 8 hours the contact angle of samples in crease from about 27 degrees to about 89 degrees.

Background and Objectives: Pollution of water resources to nitrate is an environmental problem in many parts of the world. This problem possibly causes diseases such as methemoglobinemia, lymphatic system cancer and Leukemia. Hence, nitrate control and removal from water resources is necessary. Considering that application of nanomaterials in treatment of environmental pollutants has become an interesting method, in this research use of Ag-doped TiO2 nanoparticles synthesized through photodeposition produced under UV irradiation was studied for removal of nitrate from aqueous solutions.Materials and Methods: Three nitrate concentrations of 20, 50, and 100 mg/L were considered. In order to determine the effect of Ag-doped TiO2 nanoparticles on nitrate removal, dosages of 0.1, 0.4, 0.8 and 1.2 g/L nanoparticles were used; pH range of 5-9 was also considered. The effect of Ag-doped TiO2 nanoparticles both in darkness and under UV irradiation was studied. Moreover, the presence of chloride and sulfate anions on the system removal efficiency was investigated.Results: The optimum performance of nitrate removal (95.5%) was obtained using nitrate concentration of 100 mg/L, in acidic pH and 0.8 g/L Ag-TiO2. Increase of nanoparticle dosage up to 0.8 g/L, increased the removal efficiency, but for 1.2 g/L dosage of nanoparticles, the removal efficiency decreased. Maximum REDUCTION performance without nanoparticles, under UV irradiation and under darkness conditions were 32% and 23.3%, respectively. In addition, we found that presence of sulfate and chloride anions in aqueous solution reduced efficiency of nitrate removal.Conclusion: Results of this study showed that Ag-doped TiO2 nanoparticles may be efficiently used for nitrate removal from aqueous solutions.