Germanane in photocatalysis
22 August 2014 - Chemical Zoo
New in the family of graphene / graphane like materials is germanane (GeH). It was invented in 2013 by Goldberger et al. (DOI). Synthesis of precursor CaGe2 is accomplished by heating elemental calcium and germane at 1000°C for 18 hours. This compound is a typical Zintl compound with the calcium atoms in between 2D germanium layers. When treated with HCl for an extended time (-40°C / 8 days), hydrogen replaces calcium and germanane is formed. The ion-exchange expands a layer from 5 to 5.5 Angstrom. Properties reported in 2013: surface stable over months, loses hydrogen at 200°C and can be exfoliated with scotch tape to single layers on silicon. The band gap is 1.58 eV.
A recent publication by Zhenhua Liu et al. (DOI) has more on properties. One change was made in the synthetic procedure , mercury was used as a flux in the CaGe2 reaction and later removed by ultracentrifugation. Compared to nitrogen doped (ammonia exposed) titanium oxide oxidation of Rhodamine B by visible light by germanane (in water) is 6 times as fast. Photocatalytic water splitting was also tested. A solution of germanane in water under irradiation did nothing but adding methanol as a so-called hole-scavenger saved the day with lots of hydrogen generation. These hole scavengers prevent the recombination of the electron/hole pair formed after a photon strikes the catalyst surface, increasing the catalyst efficiency. No reference catalyst was tested making for certain the finding cannot be graded against other catalysts that exist in the literature.