Vacancy-Engineered 1D Nanorods with Spatially Segregated Dual Redox Sites for Visible-Light-Driven Cooperative CO₂ Reduction

Abstract

Cooperative CO 2 photoreduction with tailored organic synthesis offers a potent avenue for harnessing concurrently generated electrons and holes, facilitating the creation of both solar fuels and specialized chemical compounds. However, controlling the crystallization and morphologies of metal-free molecular nanostructures with exceptional photocatalytic activities toward CO 2 reduction remains a significant challenge. These hurdles encompass insufficient CO 2 activation potential, sluggish multielectron processes, delayed charge-separation kinetics, inadequate storage of long-lived photoexcitons, unfavorable thermodynamic conditions, and the precise control of product selectivity. Here, melem oligomer 2D nanosheets (MNSs) synthesized through pyrolysis are transformed into 1D nanorods (MNRs) at room temperature with the simultaneous engineering of vacancies and morphology. Transient absorption spectral analysis reveals that vacancies in MNRs trap charges, extending charge carrier lifetimes. Additionally, carbon vacancies enhance CO 2 adsorption by increasing amine functional centers. The photocatalytic performance of MNRs for CO 2 reduction coupled with benzyl alcohol oxidation is approximately ten times higher (CH 3 OH and aromatic aldehyde production rate 27 ± 0.5 and 93 ± 0.5 mmol g –1 h –1, respectively) than for the MNSs (CH 3 OH and aromatic aldehyde production rate 2.9 ± 0.5 and 9 ± 0.5 mmol g –1 h –1, respectively). The CO 2 reduction pathway involved the carbon-coordinated formyl pathway through the formation of *COOH and *CHO intermediates, as mapped by in situ Fourier-transform infrared spectroscopy. The superior performance of MNRs is attributed to favorable energy-level alignment, enriched amine surfaces, and unique morphology, enhancing solar-to-chemical conversion.