Rice husk-based pyrogenic carbonaceous material efficiently promoted peroxymonosulfate activation toward the...

Pristine pyrogenic carbonaceous material (BRH) obtained from rice husk and modified with FeCl₃ (BRH-FeCl₃) were prepared and explored as carbocatalysts for the activation of peroxymonosulfate (PMS) to degrade a model pharmaceutical (acetaminophen, ACE) in water. The BRH-FeCl₃/PMS system removed the pharmaceutical faster than the BRH/PMS. This is explained because in BRH-FeCl₃, compared to BRH, the modification (iron played a role as a structuring agent mainly) increased the average pore diameter and the presence of functional groups such as -COO^-, -Si-O^-, or oxygen vacancies, which allowed to remove the pollutant through an adsorption process and significant carbocatalytic degradation. BRH-FeCl₃ was reusable during four cycles and had a higher efficiency for activating PMS than another inorganic peroxide (peroxydisulfate, PDS). The effects of BRH-FeCl₃ and PMS concentrations were evaluated and optimized through an experimental design, maximizing the ACE degradation. In the optimized system, a non-radical pathway (i.e., the action of singlet oxygen, from the interaction of PMS with defects and/or -COO^-/-Si-O^- moieties on the BRH-FeCl₃) was found. The BRH-FeCl₃/PMS system generated only one primary degradation product that was more susceptible to biodegradation and less active against living organisms than ACE. Also, the BRH-FeCl₃/PMS system induced partial removals of chemical oxygen demand and dissolved organic carbon. Furthermore, the carbocatalytic system eliminated ACE in a wide pH range and in simulated urine, having a low-moderate electric energy consumption, indicating the feasibility of the carbocatalytic process to treat water polluted with pharmaceuticals.