A　facile　gaseous　CO2　mediated　solid-to-solid　transformation　principle　is　adopted　to　insert　additional　CO32−　anions　into　the　thin　single-crystal　nanosheets　of　Bi2O2CO3,　which　is　built　of　periodic　arrays　of　intrinsic　CO32−　anions　and　(Bi2O2)2+　layers.　The　additional　CO32−　anions　create　abundant　defects.　The　Bi2O2CO3　nanosheets　with　rich　interlayer　CO32−　exhibit　superior　electronic　properties　and　charge　transfer　kinetics　than　the　pristine　single-crystal　2D　Bi2O2CO3　and　display　enhanced　catalytic　activity　in　photocatalytic　CO2　reduction　reaction　and　the　photocatalytic　oxidative　degradation　of　organic　pollutants.　This　work　thus　illustrates　interlayer　engineering　as　a　flexible　means　to　build　layered　2D　materials　with　excellent　properties.　©　2024　Wiley-VCH　GmbH.