A hydrophobic titanium doped zirconium-based metal organic framework for photocatalytic hydrogen peroxide production in a two-phase system†
Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 coupled with the synthesis of valuable products from benzyl alcohol (BA) by a hydrophobic metal organic framework (MOF) is attractive. Herein, a hydrophobic titanium doped zirconium-based MOF (OPA/Zr100−xTix-MOF), whose metal Zr clusters are alkylated by octadecylphosphonic acid (OPA), is synthesized and used for photocatalytic H2O2 production in a two-phase system (water/BA). This allows the formation of H2O2 in the water phase and benzaldehyde, the oxidation product of BA, in the organic phase, respectively. The hydrophobic OPA/Zr92.5Ti7.5-MOF exhibited a remarkable H2O2 production rate of 9.7 mmol L−1 h−1 under the irradiation of visible light (λ > 420 nm), which is about 4.5 times higher than that of the parent zirconium-based MOF (Zr100-MOF). The enhanced activity is attributed to the effective Ti-doping and the unique hydrophobic nature of the catalyst. The Ti species played a role in effectively promoting electron transfer from photoexcited linkers of the MOF to Ti, inhibiting the recombination of photogenerated electron–hole pairs in the hydrophobic MOF matrix. The unique hydrophobic nature, exemplified by a 139° water contact angle, prevented overreduction of H2O2 by spatial separation of the MOF in BA and H2O2 in water. The recycling test of H2O2 production over the catalysts demonstrated that OPA/Zr92.5Ti7.5-MOF displayed good stability. This study has greatly enriched the applications of hydrophobic MOFs in the field of photocatalytic energy production.