Molecular Oxygen Activation by Citric Acid Boosted Pyrite-Photo-Fenton Process for Degradation of PPCPs in Water.

Pyrite has been used in photo-Fenton reactions for the degradation of pollutants, but the application of photo-Fenton processes with extra H 2 O 2 in real water/wastewater treatment has still been limited by the economic cost of H 2 O 2 and artificial light sources. Herein, citric acid (CA) and simulated/natural sunlight are used to develop a pyrite-based photo-Fenton system (pyrite-CA-light) in situ generating H 2 O 2 through the enhanced activation of molecular oxygen. The degradation of pharmaceuticals and personal care products (PPCPs), especially acetaminophen (APAP) as the main target pollutant, in the pyrite-CA-light system was investigated. The effects of influencing factors such as various organic acids, APAP concentration, pH, pyrite dosage, CA concentration and co-existing anions (HCO 3 - , Cl - , NO 3 - , SO 4 2- and H 2 PO 4 - ) were examined. At a pyrite dosage of 0.1 g L -1 , CA concentration of 0.6 mM and an initial pH of 6.0, the degradation efficiency of APAP (30 μM) was 99.1% within 30 min under the irradiation of xenon lamp (70 W, λ ≥ 350 nm). Almost the same high efficiency of APAP degradation (93.9%) in the system was achieved under natural sunlight irradiation (ca. 650 W m -2 ). The scavenging experiments revealed that the dominant active species for degrading APAP was hydroxyl radical (HO • ). Moreover, a quantitative structural-activity relationship (QSAR) model for pseudo-first-order rate constants ( k obs ) was established with a high significance (R 2 = 0.932, p = 0.001) by using three descriptors: octanol-water partition coefficient (log K ow), dissociation constant (pK a ) and highest occupied molecular orbital (HOMO). This work provides an innovative strategy of the photo-Fenton process for the degradation of PPCPs using natural minerals and ordinary carboxylic acid under sunlight.