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• Modified g-C 3 N 4 nanostructures was fabricated by a preorganization approach. • g-C 3 N 4 photocatalysts demonstrate improved degradation and hydrogen production. • Nanostructure engineering accelerates charge carrier dynamics. • Tunable band structure and high-performance solar photocatalysis are achieved. Pristine graphitic carbon nitride (g-C 3 N 4) suffers from poor photocatalytic activity due to its limited light adsorption, small specific surface area and feasible recombination of photogenerated charge carriers. One practical approach to solve the problem of low solar-to-hydrogen efficiency is nanostructuring the morphology of g-C 3 N 4 to enhance its light-harvesting property and boost the rate of charge-carrier transportation. Here, we present a strategy to optimize the textural properties and catalytic performance of g-C 3 N 4 via using oxamide (OA) as a chemical modifier in the precursor solution, which significantly make the light absorption edge shift from 440 to 650 nm. Moreover, the nanostructure of the resultant g-C 3 N 4 can be easily tuned with increasing the amount of oxamide. The morphological features of g-C 3 N 4 materials change from sheet-like structure to tubular structure, porous nanotube and eventually interconnected porous sheet. More interestingly, the unique g-C 3 N 4 nanostructure offers advantages of a broader solar absorption spectrum and accelerates charge carrier dynamics that are favorable for advancing photocatalytic performance. The findings provide insightful information that can be used to understand the structure-property relationship in g-C 3 N 4 nanostructures for improved solar-to-fuel conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • A nearly total conversion and > 98% selectivity of C-C bond cleavage is achieved. • Sufficient superoxide radicals are necessary for highly selective C-C bond cleavage under visible light. • Efficient photocatalytic C-C bonds breaking towards lignin β -O-4 model compounds. • Ru single atoms outperform the nanoparticles for photocatalytic C-C bond cleavage. • C β -H extraction by photogenerated hole is the critical step of the transformation. The selective cleavage of the C C bonds in lignin is highly pursued to obtain aromatic monomers from renewable resources but remains challenging due to their high dissociation energies and steric hindrance between bulky aromatic groups. Herein, a mesoporous carbon nitride-supported ruthenium single-atom photocatalyst (Ru 1 /MCN) is reported for efficient oxidative C α -C β bonds scissoring towards lignin β -O-4 model compounds with high activity and selectivity under visible–light irradiation and room temperature. With this strategy, a nearly total conversion of > 99% and > 98% selectivity of C C bond cleavage can be achieved upon 2–phenoxy–1–phenylethanol. In-depth investigations verify that the C β -H extraction by photogenerated holes is the critical step of the transformation, which directly generates the C β radical intermediates and thus promotes the selective C α -C β bonds breaking by coupling with superoxide radicals induced by photogenerated electrons. This work explores the potential of single-atom catalysts for photocatalytic production of aromatics from renewable biomass feedstocks. [ABSTRACT FROM AUTHOR]