Study on boron and fluorine-doped C3N4 as a solid activator for cyclohexane oxidation with H2O2 catalyzed by 8-quinolinolato ironIII complexes under visible light irradiation

This paper discloses that boron and fluorine-doped carbon nitride (C3N4BF), as a solid activator, can efficiently accelerate the relatively inert 5,7-dichloro-8-quinolinolato iron(III) complex (FeIII(Qb)3) to photo-catalyze the oxidation of cyclohexane to cyclohexanol and cyclohexanone by hydrogen peroxide (H2O2) in acetonitrile (MeCN) under visible light irradiation and achieve 25.87 % cyclohexane conversion, which is almost twice as high as without it and obviously higher than the results obtained using ordinary C3N4 as an activator or under thermo-catalysis. Furthermore, its such activation effect on FeIII(Qb)3 photocatalysis is also observed in the H2O2-involved oxidation of other substrates such as toluene, ethylbenzene, benzyl alcohol and thioanisole. UV–vis and PL spectra, photocurrent transient measurements and theoretical calculations support that C3N4 and especially C3N4BF can form strong π-π stacking interactions with FeIII(Qb)3, thus inducing a weakly structural distortion of FeIII(Qb)3 and enhancing its photo-reductive activation via capturing the photo-generated electrons of the activator. As a result, the synergistic catalytic effect of FeIII(Qb)3 with C3N4/especillly C3N4BF can significantly accelerate the above thermo-/especially photo-oxidations.