Photocatalytic degradation of microcystins from a field-collected cyanobacterial assemblage by 3D printed TiO2 structures using artificial versus solar irradiation.

Microcystins (MCs) from freshwater cyanobacteria cause adverse effects to humans and ecological receptors through multiple exposure routes requiring adaptable and diverse treatment technologies. Photocatalysis of MCs using TiO₂ is a promising technology; however, TiO₂ photocatalysts as unbound nanoparticles in suspension are impractical to deploy. 3D Printing (3DP) provides a means to immobilize TiO₂, producing deployable photocatalyst structures with extensive geometric freedom. The objective of this proof-of-concept experiment was to incrementally increase the environmental complexity (e.g., broad-spectrum fluorescent lamps and outdoor solar; filtered cell lysate and algal assemblage as the source of MCs) while comparing photocatalysis rates of MCs by 3DP TiO₂ structures using polylactic acid (PLA) as the binder. Degradation half-lives of MCs were shorter in TiO₂ embedded in 3DP PLA relative to PLA-only controls with differences in half-lives ranging from 3.6 to 10h. The one exception was the outdoor solar and an algal assemblage, where significant differences could not be discerned due to the already rapid photolysis rates. Ultimately, photocatalysis rates (half-life = 1.9-11.6h) were comparable to those previously published for TiO₂ 3DP structures in a laboratory environment and TiO₂ fixed-films (half-life = 2-13h) demonstrating feasibility of 3DP to immobilize TiO₂ photocatalysts under a range of conditions. This is the first time that MC concentrations from a field-collected HAB were photocatalytically degraded in both solar simulated light and sunlight using a custom-made advanced photocatalytic nano-composite with enhanced performance through high surface area design enabled by 3D printing. These data inform future development of scalable, retrievable, and operationally flexible structures with immobilized TiO₂.