Finally, bulk OVs are healed by O2 introduction at 400°C (eqn. 3). As elaborated above, the OVs of the temperature treated BiOCl samples are located in the bulk rather than at the surface. To further confirm this point, we also measured transmission FTIR spectra of all BiOCl samples pressed into KBr pellets in the evacuated sample compartment of the FTIR spectrometer at reduced pressure of <5 mbar at 298 K (Fig. ). The peak at 2332 cm -1 results from CO2 physisorption from the residual gas . Interestingly, there are no indications of CO2 chemisorption in the region of 2260-2270 cm -1 , although that would have been expected