Constructed zinc oxide/polydopamine S-scheme heterojunction via d-π electronic coupling for enhanced carbon dioxide...

Constructing inorganic-organic hybrid S-scheme heterojunction has emerged as a pivotal strategy for achieving high photocatalytic activity, yet their practical implementation is hindered by intrinsic limitations of charge recombination, lattice mismatch and low interfacial charge transfer efficiency in conventional systems. Herein, we present a zinc oxide/polydopamine (ZnO/PDA) S-scheme heterojunction engineered through in-situ polycondensation, leveraging strong electronic coupling between Zn²⁺ vacant d-orbitals and PDA's conjugated π-system. This S-scheme electron migration pathway creates an efficient interfacial charge-transfer channels and suppresses photocarrier recombination, even more endowing the heterojunction with stronger oxidation-reduction ability. Meanwhile, PDA's porous architecture and amine-functionalized surface synergistically enhance CO₂ trapping and adsorption, achieving 17-fold increase in CO₂ adsorption capacity for optimized ZP10 composite versus pristine ZnO. Correspondingly, this composite demonstrates dramatically improved photocatalytic performance, yielding CO and CH₄ at rates of 133 and 71 μmol h^-1 g^-1 respectively, representing enhancements of 19-fold and 6-fold compared to pristine ZnO. Combined experimental and theoretical analyses reveal a stepwise CO₂ reduction mechanism that the conversion of CO₂ to CO and CH₄ on the ZnO/PDA surface undergoes a intermediate state evolution process of CO₂ → CO₂^- → ^⁎COOH→^⁎CO → CO and CO₂ → CO₂^- → ^⁎COOH→^⁎CHO → ^⁎CH₃O → ^⁎CH₃ → CH₄. This work provides a generalizable framework for designing inorganic-organic hybrid S-scheme heterojunction that simultaneously optimize charge dynamics and reactant activation energetics in photocatalytic systems.