In this work, we describe a simple and general procedure for the purification of carbon dots. Following a hydrothermal heating procedure, the reaction mixture usually contains unreacted starting material and by-products alongside the carbon dots, which often appear among otherwise intense photoluminescence. The proposed purification method is based on a solid phase extraction technique, where the reaction mixture is absorbed on porous alumina and the carbon dots are isolated from the by-products and unreacted organics using proper solvents, and are finally recovered from the alumina using a simple extraction.