ETCHING METHOD FOR ELECTROLESS PLATING

An etching method using a photocatalyst, which provides an etched surface with a proper roughness, a photocatalytic etching method capable of responding even in an ultraviolet light range as well as a visible light range, and a method for performing photocatalytic etching using a titanium dioxide sol containing a large amount of brookite phase having excellent dispersibility and photocatalytic efficiency are provided. An etching method for electroless plating comprises the steps of: dipping a plastic part into a colloidal solution in which nano-sized titanium dioxide is suspended in a sol state; and irradiating a light source onto the plastic part dipped into the colloidal solution. The titanium dioxide sol is prepared by a preparation process of the titanium dioxide sol comprising the steps of: mixing a neutralizer with an aqueous titanyl chloride solution, thereby neutralizing the aqueous titanyl chloride solution to obtain a titanium dioxide-based hydrate; cleaning and filtering the titanium dioxide-based hydrate; dipping, stirring and dissolving the titanium dioxide-based hydrate in an aqueous solution into which hydrogen peroxide is dissolved in 8 to 10 times of moles as compared with the moles of titanyl chloride ions; and injecting a solution in which the titanium dioxide-based hydrate is dissolved into the aqueous hydrogen peroxide solution into an autoclave, subjecting the solution to hydrothermal synthesis to obtain a titanium dioxide sol.