Photoelectrocatalytic degradation of pharmaceuticals promoted by a metal-free g-C3N4 catalyst

Graphitic carbon nitride (g-C3N4) recently emerged as a remarkable photoelectrocatalyst for water treatment. Advanced oxidation processes (AOPs) consisting of photoelectrocatalytic (PEC) systems are being researched towards the development of sustainable strategies for the complete removal of refractory contaminants from effluents of urban wastewater treatment plants (WWTPs). This work consists of the optimisation of a PEC system, composed of a boron-doped diamond (BDD) anode, titanium cathode, and a suspended g-C3N4 photoelectrocatalyst, for the treatment of both synthetic and real urban waste waters spiked with pharmaceutical active compounds (PhACs). Different working parameters were considered and optimised to improve degradation and mineralisation rates, such as the cathode material, anode-to-cathode distance, electrolyte resistivity, and matrix composition. The optimal conditions allowed removals of 100 % diclofenac, 88 % fluoxetine and 77 % ibuprofen in the complex wastewater matrix. Moreover, it was observed that the presence of other refractory organic molecules offered a greater impediment to PEC treatment than residual co-existing substances. The main oxidative agents were investigated by scavenging experiments, showing that generated holes and reactive oxyspecies, i.e. hydroxyl and superoxide radicals, take a major role in the degradation of PhACs. The recyclability of the g-C3N4 suspension as photoelectrocatalyst in the PEC process provides a promising perspective for the development of wastewater treatment units.