The presence of pharmaceuticals in natural waters has been the subject of numerous studies in the last decade due to their potential negative effects on human health and the environment. Indeed, the intensive use of pharmaceuticals leads to their presence in municipal wastewater. Unfortunately, international and national regulations still do not require continuous monitoring of the presence of pharmaceuticals in natural waters and drinking water, so wastewater treatment plants do not focus on removing them from wastewater. Diclofenac, 2-[2-(2,6-dichloroanilino)phenyl]acetic acid (DCF), is a nonsteroidal compound used as an analgesic, anti-inflammatory, and antipyretic drug and is therefore commonly found in wastewater. Due to its properties, DCF remains biologically active in the aquatic environment and easily enters the food chain. Therefore, DCF should be removed from wastewater before it is discharged into water bodies. Adsorption is an efficient and simple method that can be used to remove DCF from water. In this study, the possibility of removing DCF by adsorption on activated carbon is investigated. Modified hazelnut shell (MHS), modified commercial activated carbon Cullar (MC) and unmodified commercial activated carbon Cullar (C) were batch tested as adsorbents. The tested adsorbents were characterised by FTIR, zeta potential and pHpzc, while the adsorbent efficiency was tested in the pH range from 2 to 10 and described by isothermal studies. Among the tested adsorbents, the maximum uptake of 48.7 mg g–1 was found when modified activated carbon Cullar was used, while both Freundlich and Langmuir isotherm models fitted well to the data. Modified activated carbon from hazelnut shells showed effective removal of DCF.Prisutnost farmaceutskih spojeva u prirodnim vodama tema je brojnih znanstvenih istraživanja tijekom prošlog stoljeća zbog njihova potencijalnog negativnog utjecaja na zdravlje ljudi i okoliš. Naime, česta i prekomjerna uporaba lijekova uzrokuje njihovu čestu pojavu u komunalnim otpadnim vodama. Nažalost, međunarodne i nacionalne regulative ne nalažu kontinuirano praćenje prisutnosti lijekova u prirodnoj i pitkoj vodi, pa stoga ni procesi pročišćavanja otpadnih voda nisu usmjereni na njihovo uklanjanje iz otpadnih voda. Diklofenak (DCF), 2-[2-(2,6-dikloroanilino)fenil]octena kiselina nesteroidni je spoj koji se upotrebljava kao analagetik, protuupalni i antipiretski lijek te se često može naći u otpadnim vodama. Zbog svojih karakteristika DCF ostaje biološki aktivan u vodenom okolišu i lako ulazi u hranidbeni lanac. Stoga je DCF nužno ukloniti iz otpadnih voda prije njihova ispuštanja u vodna tijela. Adsorpcija je učinkovita i jednostavna metoda kojom se DCF može učinkovito ukloniti iz vode. Cilj ovog istraživanja je ispitati mogućnost uklanjanja DCF-a adsorpcijom na modificirane ljuske lješnjaka, modificirani i izvorni oblik komercijalnog aktivnog ugljena Cullar (Cadriano, Italija). Svojstva adsorbensa ispitana su FTIR spektroskopijom, analizom zeta-potencijala i pHpzc. Učinkovitost adsorbensa ispitana je u području pH vrijednosti od 2 do 10 te opisana izotermnim modelima. Među ispitanim adsorbensima, najveća količina DCF-a od 48,7 mg g–1 adsorbirana je na modificirani aktivni ugljen Cullar, dok su dobiveni rezultati dobro opisani i Freundlichovom i Langmuirovom izotermom. Značajne količine DCF-a adsorbirane su i na modificirani aktivni ugljen iz ljuski lješnjaka
