Regulating Platinum Active Species on the Side Chains of Hydrazone-Linked Covalent Organic Frameworks for Photocatalytic Hydrogen Generation

Abstract

Herein, a pair of hydrazone-linked covalent organic frameworks (COFs) were constructed with identical main-chain backbone and distinctive side chains (denoted as BTB-COF and BTD-COF), respectively. With H₂PtCl₆ as the co-catalyst precursor, BTD-COF with ethoxy side chains demonstrated superior photocatalytic H₂ production performance yielding 3708 μmol·g⁻¹·h⁻¹ under visible light irradiation, which was 3.0 times higher than that of its analogue BTB-COF with thioether side chains (1236 μmol·g⁻¹·h⁻¹). Comprehensive studies on the composites of platinum nanoparticles (Pt NPs) with COFs after photocatalytic H₂ generation had revealed the impacts of side chains on the photocatalytic process and the anchoring of Pt NPs within COFs. By contrast with the divalent oxidized-state of Pt on BTB-COF, Pt NPs anchored on BTD-COF existed as metallic Pt⁰ with an uniform size of 2.7 nm, agreeing well with the diameter of pore channels. The nature of metallic Pt⁰ NP was greatly beneficial for the surface charge transfer process and had consequently enhanced the photogenerated carrier separation efficiency, which was supported by the density functional theory calculations. This work elucidates the impacts of side chains on the H₂ generation performance of COFs under visible light, which will further spur the structural evolution of functional COFs materials.

Keywords

Covalent organic frameworks / Side chain engineering / Photocatalytic hydrogen generation / Hydrazone linkages / Coordination interaction / Platinum active species / Surface charge transfer / Photogenerated carrier separation

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