Hybrid CO2-activated system, which consists of precipitation and adsorption was utilized for removal of diclofenac (DCF) from aqueous solution. Diclofenac in CO2-activated system was precipitated by the solubility reduction in water. The effects of temperature, initial DCF concentration and CO2 flow rate on the precipitation efficiencies are investigated. The precipitation of DCF in CO2-activated system results in the reduction of DCF concentration in the aqueous solution less than 5 mg L-1. High initial DCF concentration and high CO2 flow rate achieve a rapid precipitation of DCF in the aqueous solution. Three kinds of adsorbents, chitosan, carbon nanotube and carbon nanofiber were used for the DCF adsorption in CO2-activated system. The carbon-based materials as adsorbents lead to the high adsorption efficiencies of DCF by the protonation of DCF and pi-electron on the aromatic rings of the carbon-based absorbents. Carbon nanofiber in CO2-activated system results in the adsorption efficiency 97.6% and the reduction of DCF concentration less than 0.115 mg L-1. Characterizations of the adsorbents with the zeta-potential, Fourier Transform Infrared spectra and thermogravimetric analysis were also conducted to discuss the DCF adsorption mechanism in CO2-activated system.