Kinetic investigation of Cu(II) ions photoreduction in presence of titanium dioxide and formic acid

The photoreduction of Cu(II) in presence of an organic species as sacrificial agent has been investigated by many research groups but some controversial results are reported in literature. In this work, the photoreduction process of Cu(II) in presence of formic acid is investigated aiming at clarifying the reaction mechanism and assess the reaction kinetics. The effect of operating conditions such as TiO2 load, initial concentration of sacrificial agent, pH and ionic strength was studied. The results of the work are: (1) the system reactivity does not depend neither on pH (in the range 2.0–3.5) nor on ionic strength of the solution; (2) formic acid is adsorbed on TiO2 surface; (3) the nature of anionic species can influence the Cu(II) photoreduction (e.g. the addition of sulphate or phosphates reduces the reaction rates); and (4) FA can be completely mineralized during this photoxidation process; for example, this is observed for a TiO2 load of 0.1 g/L after a reaction time of about 240 min. A simplified kinetic model is developed to describe the behavior of the system and validated by analysing the data collected during the experimental work.