Heterogeneous photodegradation of 1-naphthol with natural iron oxide in water: influence of oxalic acid

The transformation of 1-Naphthol (1-NP) photoinduced by a natural iron oxide (NIO) in aqueous suspension and the influence of oxalic acid have been investigated under monochromatic irradiation (365 nm). The NIO was characterized by X-ray diffraction (XRD), X-ray fluorescence, and Brunauer-Emmett-Teller methods. The XRD result shows that the NIO consists of mixed crystalline hematite. A dark investigation of the system was performed before studying the photochemical behavior. The experiment shows that the NIO possesses a high adsorption capacity for 1-NP and its photodissolution was not observed. Also, the experiment shows that the UV light alone could play an important role in the degradation of 1-NP.After 3 h of irradiation at pH 9.4, 64.2% of 1-NP was degraded. The presence of the NIO was found to promote the photodegradation of 1-NP (72.1%) and the process follows pseudo-first-order reaction kinetics. The photodegradation of 1-NP has been studied at different pH (1.9-12) and catalyst loads (0.5-2.0 g L-1). The results demonstrated that the phototransformation of 1-NP is enhanced by increasing the pH and the optimal initial concentration of the catalyst was found to be 1 g L-1. The involvement of (OH)-O-center dot radicals was ruled out because of the non-influence of tertiobutanol used as a scavenger. The effect of the oxalic acid on the photodegradation of 1-NP by NIO was also investigated. The result revealed that the oxalic acid promoted the photodegradation rate of 1-NP. This investigation will give a new insight to understand the 1-NP photodegradation in natural environment. Measuring chemical oxygen demand also monitors the toxicity of the degraded 1-NP solution and a significant decrease is observed, which implies that the photodegradation through NIO is a safer technique.