Solar light photodegradation of nicotine in the presence of aged polystyrene microplastics

Limited information exists on the potential of aged microplastics to induce photodegradation of organic pollutants under sunlight irradiation. In this work, nicotine (NIC), a widespread emerging contaminant, was used as a model organic substrate to investigate this innovative degradation process. Polystyrene (PS) pellets were artificially aged and became rich in oxygenated moieties with their carbonyl index reaching 0.43 ± 0.04 after 4 d of aging. The degradation of NIC photosensitized by aged PS at different pH values was monitored for 6 h under simulated sunlight irradiation (650 W/m²). The maximum degradation rate was observed at pH = 11 (75 % NIC removal from a 10 mg L^-1 solution containing 50 g L^-1 aged PS pellets), suggesting that the unprotonated NIC is the most photoreactive form. Increasing the PS load from 50 to 200 g L^-1 accelerated NIC degradation. The addition of 2.5 mg L^-1 humic acids had a slight enhancement role (82 % NIC degradation), which confirms their effectiveness as photosensitizers. NIC photosensitization by aged PS was also studied in the presence of t-butanol (55 % NIC removal in solutions containing 100 mg L^-1 t-butanol) and in anoxic conditions (NIC solution purged with N₂; 95 % NIC removal), to gain insight into the respective roles of the potentially formed ^•OH and ¹O₂. The main photo-produced reactive species involved in NIC degradation likely were the triplet states of the PS beads (³PS*). Differently from most advanced oxidation processes, NIC's photodegradation by aged PS was not affected by increasing amount of chloride and we observed negligible differences between NIC degradation in ultra-pure water and seawater. The effectiveness of irradiated PS towards NIC photodegradation was also investigated in tap water and secondary wastewater. Overall, the possibility to decontaminate polluted water with waste-derived materials is interesting in the framework of circular economy.