Engineering of visible light photocatalytic activity in SnO2 nanoparticles: Cu2+-integrated Li+, Y3+ or Zr4+ dopants

Integration between Cu2+ ions and Li+, Y3+ or Zr4+ ions was strongly enhanced the visible light absorption and the sunlight photocatalytic properties of nanocrystalline SnO2. Nanopowders of SnO2, Sn0.97Cu0.03O2, Sn0.95Cu0.03Li0.02O2, Sn0.95Cu0.03Y0.02O2 and Sn0.95Cu0.03Zr0.02O2 compositions were synthesized via coprecipitation method. Dominant crystallographic planes of SnO2 tetragonal rutile structure were clearly detected in the XRD patterns with absence of any secondary phases or impurities. The FTIR profiles show a strong appearance of the characteristic vibrational absorption modes of SnO2 in all compositions which prove their good crystallinity. The TEM images demonstrate that the agglomerated nanoparticles observed for pure SnO2 were converted to regular nanospherical-shaped with slight degree of agglomeration due to Cu doping or (Cu, Li), (Cu, Y) and (Cu, Zr) codoping. Pure SnO2 possesses UV band gap energy of 3.6 eV while Sn0.97Cu0.03O2, Sn0.95Cu0.03Li0.02O2, Sn0.95Cu0.03Y0.02O2 and Sn0.95Cu0.03Zr0.02O2 compositions exhibit visible light band gap energies of 2.97 eV, 2.7 eV, 2.6 eV and 2.6 eV, respectively. The photocatalytic tests confirmed that 97% of Congo red and 91% of Rhodamine B dyes were decomposed in the presence of Sn0.95Cu0.03Li0.02O2 catalyst after 90 min of solar irradiation. Sn0.95Cu0.03Li0.02O2 has considerable activity above 87% over long photodegradation time for four successive tests. For Sn0.95Cu0.03Li0.02O2 catalyst, the high generation of the charge carriers due to extending of the band gap to visible light spectrum plus suppression of charge carriers' recombination by Cu2+-Cu+ trap states and high defects formation lead to its high photocatalytic activity.