Germanane and butyl-functionalized germanane as visible-light photocatalysts for the degradation of water pollutants

Germanane, a two-dimensional Ge lattice in which each atom is hydrogen-terminated in the z-direction, possesses a remarkable combination of electronic and optical properties that are attractive for applications ranging from chemical sensing to electrocatalysis and photocatalysis. In this work, we studied germanane (GeH) and the novel butyl-functionalized germanane (GeBu_xH_(1−x)) as photocatalysts for water purification under visible light irradiation and utilizing challenging conditions in terms of photocatalyst loading (1 mg per g of aqueous solution containing 200 ppm of pollutant). The synthesized GeH and GeBu_xH_(1−x) have significantly higher specific surface area (121 m² g⁻¹ and 76 m² g⁻¹, respectively) than other germanane derivatives reported to date and display optical band gaps suitable for visible light absorption (1.40 eV and 1.55 eV, respectively). In terms of photocatalytic performance, GeH displayed the best activity in the degradation of rhodamine B (61% removal after 3 h under visible radiation), while GeBu_xH_(1−x) proved to be the best photocatalyst for the degradation of phenol (33% removal after 3 h under visible radiation). In both cases, the activity under visible radiation surpassed that of P25 TiO₂ and could be enhanced significantly by sonication in water before interaction with the pollutants. Recycling tests showed that GeH could be reused with no or negligible loss of photocatalytic activity, whereas GeBu_xH_(1−x) showed a minor decrease in activity upon reuse.