Visible-light driven phosphotungstic acid/tubular C3N4 heterojunction photocatalyst for efficient cleavage of C–C bond in lignin

The photocatalytic cleavage of C α -C β bonds in lignin holds considerable potential for the production of value-added chemicals. Lignin consists of phenylpropane units interconnected by a variety of complex chemical bonds. Specifically, C-O bonds are more prevalent and relatively easier to cleave, whereas C–C bonds exhibit higher bond energy, rendering them more difficult to cleavage under conventional conditions. This study presents a phosphotungstic acid/phosphoric acid-functionalized porous tubular C 3 N 4 composite photocatalyst (PW/P-TCN). H 3 PO 4 modified PW/P-TCN surfaces enhance O 2 adsorption, improve separation and transfer of photogenerated carriers, and increase exposure of active sites. This promotes reactant adsorption and significantly boosts photocatalytic efficiency. Through this strategy, 1,2-diphenylethanol (DPol), used as a typical model substrate, is fully converted into aromatic monomers, achieving a DPol conversion rate of 99.9 %. Mechanistic studies reveal that C α -C β bond cleavage primarily involves the photo-oxidation mechanism mediated by electron-hole coupling. The construction of the PW/P-TCN heterojunction is essential for simultaneously sustaining robust reduction and oxidation capabilities. Natural lignin samples are applied to the photocatalytic system, and successful C–C bond cleavage depolymerization is achieved under optimal reaction conditions. This study offers valuable insights for the design of more economical and efficient photocatalysts for lignin depolymerization.