Two-dimensional　(2D)　perovskites　have　recently　garnered　widespread　attention　for　their　favorable　properties,　such　as　stability.　However,　their　application　in　photoelectric　fields　is　typically　limited　by　the　low　mobility　of　charge　carriers.　Herein,　a　range　of　2D　lead-free　double　perovskites　are　fabricated　using　substituted　aliphatic　diamine　cations.　This　modification　leads　to　distortions　in　the　octahedral　structure　of　2D　perovskites,　enhancing　the　connectivity　of　atomic　orbitals　at　band　edges.　Notably　(NH3(CH2)3NH3)2AgBiBr8,　with　minimized　layer　spacing　compared　to　reported　2D　lead-free　double　perovskites,　shows　the　highest　carrier　mobility,　surpassing　its　3D　counterpart.　(NH3(CH2)3NH3)2AgBiBr8　displays　excellent　activity　and　stability　in　photocatalytic　selective　oxidation,　achieving　a　toluene　conversion　up　to　100%　with　a　benzoic　acid　selectivity　of　99%　under　visible　light　irradiation.　Lower　hydrophilicity　as　well　as　higher　toluene　adsorption　capacity　with　the　diamine　cation　substitutions　could　be　responsible　for　the　boosted　photocatalytic　performances.　©　2023　The　Author(s)