Electron donor-acceptor metal-organic frameworks for efficient photocatalytic reduction and oxidation

It is a great challenge to obtain a broad-spectrum light response and high redox capability in photocatalysis. Unlike the traditional process of expanding the light spectrum of a photocatalyst often leads to a decrease in oxidation or reduction potential, here we proposed a mixed-ligand strategy to improve the light response and photocatalytic redox performances simultaneously. Tetrad (4-carboxyphenyl) porphyrin (TCPP, electron donor) and N, N'-bis (5-diphenylphthalic acid)-naphthlimide (NDI, electron acceptor) were coordinated with Zr (IV) clusters to produce electron donor-acceptor (D-A) metal-organic frameworks (ML-MOFs). As photocatalysts, the ML-MOFs exhibited higher photocatalytic efficiency in the generation of nicotinamide adenine dinucleotide phosphate (NADH) in the absence of any noble metals. Refractory antibiotic tetracycline hydrochloride (TCH) was almost completely degraded within 30 min with an amazing kinetic constant of 0.08229 min^-1, far exceeding that of the single-ligand MOFs and other noble-metal-free photocatalysts. The experimental and theoretical evidence indicated the D-A structure in ML-MOFs achieved larger dipole moments and enlarged built-in electric fields, which greatly improved the charge separation and transfer efficiency, conferring them with boosting photocatalytic oxidation and reduction performances. This research presents a new stratagem for the preparation of advanced photocatalysts with both photocatalytic oxidation and reduction ability and makes a significant step towards energy conversion and environmental governance via photocatalysis.