Photocatalytic removal of methylmercury assisted by UV-A irradiation

The present study evaluates the removal of methylmercury from aqueous solutions by TiO2 photocatalysis using UV-A irradiation. To assess the weight of the variables pH and amount of catalyst, a factorial design was used when planning the experiments. Methylmercury was determined by the difference between total mercury and inorganic mercury. The optimal conditions for methylmercury removal are low amounts of catalyst and an alkaline pH. Under optimal conditions, more than 95% of methylmercury removal was achieved after 2 min irradiation. Methylmercury can be removed in the presence of nitrogen or oxygen under different mechanism pathways. In the presence of nitrogen, the reaction proceed by forming water soluble compounds, such as methanol or more oxidised moieties. In the presence of oxygen, the reaction slows due to competition between oxygen and Hg (II) for conduction band electrons. In saturated oxygen solutions, the main reaction products were CH4, CO and CO2. To recover the reduced mercury released from the reactor, copper powder was arranged in a trapping device amalgamating Hg0, achieving above 90% of retention yield.