In this thesis, two new heterogeneous catalysts, TiO 2 -Nb 2 O 5 and Fe-g-C 3 N 4 /CF were prepared, and their application were investigated. In the first project, heterogeneous TiO 2 -Nb 2 O 5 nanocatalysts were prepared and analyzed by FT-IR, pyridine adsorption, XRD, TGA, FE-SEM, EDAX, TEM and BET methods and elemental mapping. Then, the performance of these nanocatalysts was investigated for preparation of one of the most attractive and functional organic materials called 5-hydroxymethylfurfural from pure fructose and glucose. With fructose as the raw material, 78% yield and 82% selectivity was obtained. When glucose used as the starting material, 56% efficiency and 84% selectivity was observed. This reaction was carried out in aqueous solvent and 2-butanol was applied as the extraction phase. In the second project, heterogeneous Fe-g-C 3 N 4 /CF catalysts were prepared using inexpensive materials such as carbon fiber and melamine, and investigated by FT-IR, FE-SEM, XRD, XPS, UV-visible DRS, EDAX, elemental mapping, and BET. Subsequently, the performance of this catalyst examined in the presence of visible light and hydrogen peroxide for degradation of methylene blue, rhodamine B, and methyl orange as harmful pollutants in the industrial effluents.