Photocatalytic selective oxidation of 2-phenoxy-1-phenylethanol coupled with Cd-MOF/S/Ni–NiO for hydrogen evolution performance and mechanism

Abstract

In this study, Cd-MOF/S/Ni–NiO (MOF = metal–organic framework) composite materials were prepared using a hydrothermal synthesis method and employed for the high-efficiency photocatalytic oxidation of the lignin β-O-4 model compound 2-phenoxy-1-phenylethanol, coupled with water splitting hydrogen evolution. The Cd-MOF/S/Ni–NiO composite material retained the petal-like morphology of Cd-MOF, with Ni-BTC acting as the precursor for Ni–NiO, effectively preventing metal agglomeration. Without the addition of Ni–NiO, the main photocatalytic oxidation products of 2-phenoxy-1-phenylethanol were phenol and acetophenone, and only 2.6% of 2-phenoxy-1-phenylethanone was produced, with a hydrogen production rate of 102 μmol g⁻¹ h⁻¹. However, after the addition of 1 mmol Ni–NiO, 2-phenoxy-1-phenylethanol was almost completely converted, with phenol and acetophenone yields of 30% and 32%, respectively. The yield of 2-phenoxy-1-phenylethanone increased to 62%, and the hydrogen production rate reached 1058 μmol g⁻¹ h⁻¹. It was found that the addition of an appropriate amount of Ni–NiO facilitated the formation of the oxidation product of 2-phenoxy-1-phenylethanone. The reaction mechanism was subsequently verified, revealing that h⁺ is the main oxidizing species in the photocatalytic oxidation of 2-phenoxy-1-phenylethanol. This work demonstrates a dual-optimized catalytic system for the highly selective oxidation of lignin β-O-4 model compounds, coupled with simultaneous hydrogen production, providing new insights into the high-value application of lignin in the catalytic conversion of polymetallic oxides.