Considering the headspace of the photoreactor (5 ml) and the amount of photocatalyst used (0.42 mg), we can calculate that the O2 production is 110 μmol(O2) g(catalyst) -1 . Through an analysis of the derivative of the O2 formation data, the O2 production rate (e.g. μmol(O2) g(catalyst) -1 min -1 ) can also be calculated.