Preparation process of functionalized superparamagnetic adsorbents with diphenyldimethoxysilane (DPDMS) as precursor, for removing oil stains from water with a capacity of adsorption in the range 2.0 to 4.0 g of oil/g of adsorbent, the said process comprising: a. synthesis of superparamagnetic iron oxide nanoparticles (CoFe 2 O 4) with a spinel crystal structure, using Co 2+ and Fe 3+ metal salts, which may be sulfates, chlorides, nitrates, acetates, in a molar concentration range from 0.01 to 1 mol/l and co-precipitation of metal (II/III) ions in a basic aqueous medium having a pH value from 9 to 12, at an elevated temperature, and in this way the formation of superparamagnetic product, using metal hydroxides, such as NaOH or KOH in a molar range 0.25 to 3.0 mol/L, as a precipitation reagent; b. colloidal stabilization of CoFe 2 O 4 nanoparticles in acidic aqueous medium having a pH in the range from 2 to 4; c. surface functionalization of nanoparticles using colloidal solution of CoFe 2 O 4 nanoparticles in weight concentration 0.05 to 0.10 g/ml, tetra-alkoxide precursor tetraethoxysilane (TEOS) in the mol ratio R (H 2 O:TEOS) in the range of 40 to 1050 and di-alkoxide precursor diphenyldimethoxysilane (DPDMS) in mol ratio P (TEOS:DPDMS) 0.25, 0.5, 1 or 2, with an alcoholic medium that consists of a mixture of lower alcohols namely methanol, ethanol, propanol or butanol in the concentration range 0.1 to 1.0 mol%, the alkaline catalyst ammonia in a concentration range 0.001 to 0.010 mol%, water in the concentration range from 0.005 to 0.10 mol%, and the process parameters, which are: temperature of the reaction is in range 25 °C to 50 °C, reaction time in range of 1 hour to 72 hours, and the pH value of the medium in the range of 2.0 to 11.0. a. synthesis of superparamagnetic iron oxide nanoparticles (CoFe 2 O 4) with a spinel crystal structure, using Co 2+ and Fe 3+ metal salts, which may be sulfates, chlorides, nitrates, acetates, in a molar concentration range from 0.01 to 1 mol/l and co-precipitation of metal (II/III) ions in a basic aqueous medium having a pH value from 9 to 12, at an elevated temperature, and in this way the formation of superparamagnetic product, using metal hydroxides, such as NaOH or KOH in a molar range 0.25 to 3.0 mol/L, as a precipitation reagent; b. colloidal stabilization of CoFe 2 O 4 nanoparticles in acidic aqueous medium having a pH in the range from 2 to 4; c. surface functionalization of nanoparticles using colloidal solution of CoFe 2 O 4 nanoparticles in weight concentration 0.05 to 0.10 g/ml, tetra-alkoxide precursor tetraethoxysilane (TEOS) in the mol ratio R (H 2 O:TEOS) in the range of 40 to 1050 and di-alkoxide precursor diphenyldimethoxysilane (DPDMS) in mol ratio P (TEOS:DPDMS) 0.25, 0.5, 1 or 2, with an alcoholic medium that consists of a mixture of lower alcohols namely methanol, ethanol, propanol or butanol in the concentration range 0.1 to 1.0 mol%, the alkaline catalyst ammonia in a concentration range 0.001 to 0.010 mol%, water in the concentration range from 0.005 to 0.10 mol%, and the process parameters, which are: temperature of the reaction is in range 25 °C to 50 °C, reaction time in range of 1 hour to 72 hours, and the pH value of the medium in the range of 2.0 to 11.0.