Strain Engineering in Amino-Confined CdS Enables Kinetically Coupled Methanol and Ammonia Oxidation for Photocatalytic Formamide Synthesis

Abstract Photocatalytic synthesis of formamide (FA) through C─N bond construction from carbon and nitrogen-containing small molecules offers a sustainable route for converting solar energy into value-added chemicals. However, selective C─N coupling is often limited by mismatched reaction kinetics between carbon and nitrogen substrates. Here, we develop a CdS−diethylenetriamine (CdS − D) composite with an amino-confined, compressively strained interface for FA synthesis from methanol and ammonia. Local strain promotes methanol C─H activation, while surface amino groups transiently retain methanol-derived species near the interface, improving their temporal overlap with nitrogen-derived intermediates and favoring productive C─N coupling over competing pathways. CdS − D achieves an FA production rate of 8.51 mmol g − 1 h − 1 with 84.47% selectivity, 49 times that of pristine CdS, without cocatalysts or external oxidants. This work elucidates how amino confinement and compressive strain mitigate the kinetic disparity between methanol and ammonia oxidation and promote productive interfacial radical conversion, offering a viable strategy for the selective photocatalytic synthesis of value-added amides from simple molecular feedstocks.