Photocatalytic degradation of micropollutants under visible light irradiation

Many organic wastewater contaminants are not removed by biological degradation treatment in wastewater treatment plants (WWTP), and thus are persistent in WWTP effluents at ng/L to μg/L levels. In particular, large efforts have been made in these last decades to study the amount and potential risks of antibiotics in the environment. Ciprofloxacin (CP) is an antibiotic that belongs to the family of medications known as quinolones. CP is the most prescribed fluoroquinolone in Europe. The discharge into surface waters and in WWTPs of antibiotics may give rise to ecotoxicological effects and antibacterial resistance. As far as the decontamination issue is concerned, heterogeneous photocatalytic processes are quite eco-friendly in comparison with chemical depollution methods. The objective of this work is to assess the photocatalytic efficiency of LaFeO3 nanopowder to decontaminate water from micropollutants under Visible light irradiation. The optical band-gap energy of LaFeO3 nanopowder is 2.54 eV [1]. The photocatalytic activity was tested on 4-Nitrophenol which is a compound representing an important group of water pollutants and the antibiotic Ciprofloxacin. The photocatalytic degradation reactions were carried out using a Rayonet reactor equipped with 8 lamps (8 W) emitting in the Visible region. A solution was prepared using 100 mL of distilled water, the initial concentration of 4-Nitrophenol (4-NP) was 1.4 x10-4 mol L-1. The initial concentration of H2O2 was 0.005 mol L-1. The catalyst powder (0.03 g L-1) was added to the resulting solution in a cylindrical Pyrex. The initial concentrations for the suspension of CP were: 5.0 x10-6 mol L-1 for CP, 0.0026 mol L-1 for H2O2, and 0.13 g L-1 for LaFeO3. Both suspensions were magnetically stirred for 30 min prior to illumination. Subsequently, irradiation was performed on continuously stirred suspension. The temperature increment during the degradation tests was monitored and it never reached temperature higher than 40°C. The degradation of 4-NP and CP was followed by taking 3 mL of the suspension at regular time intervals, and centrifuged for 10 min to separate the catalyst. Their concentration was calculated according to the variation in absorbance of the irradiated solution. The degradation efficiency using LaFeO3 in presence of H2O2 under Visible light irradiation (6 h) is more than 90% for both compounds, much higher than that with H2O2 under Visible light. For the sake of comparison, the experiments were also carried out under dark, and both 4-NP and CP were not significantly converted.