Influence of acids, bases and surfactants on the photocatalytic degradation of a model dye rhodamine B

Photocatalytic materials and additional components, especially promoters, play a pivotal role in the success of photocatalysed environmental remediation processes. To understand the influence of acid promoters in the absence and presence of surfactants, photocatalytic degradation of a model dye rhodamine B (RhB) was studied by UV-photocatalysis (254 nm UV source) with the subsequent addition of each of 0.01 mol dm^− 3 of nitric acid (HNO₃), sulphuric acid (H₂SO₄), hydrochloric (HCl), citric acid and acetic acid. Furthermore, the effect of 0.01 mol dm^− 3 of sodium hydroxide (NaOH) and sodium carbonate (Na₂CO₃), as well as surfactants, including the cationic cetrimonium bromide (CTAB), anionic sodium dodecylsulphate (SDS) and non-ionic surfactant tween 80, were analyzed using a UV–Visible spectrophotometer. The k_obs. values for photodegradation of RhB under UV-irradiation was heavily dependent on type of acid and base. Pre-micellar, micellar and post-micellar concentrations of surfactants were also analyzed for their effects on the photodegradation of RhB. Concentrations at and above the critical micelle concentration (CMC) were found to suppress the photocatalytic degradation of RhB in the presence of a promoter (HNO₃). Micellar solubilization is responsible for the changes in the photocatalytic activity. Nonionic micelles are unable to protect the dye over longer times due to autooxidation process. The resulting degradation products of RhB by [rad]OH were identified by LC-MS and GC–MS analysis and accordingly a schematic degradation pathway was proposed.