Effectively　reducing　the　concentration　of　nitrogen-containing　compounds　(NCCs)　remains　a　significant　but　challenging　task　in　environmental　restoration.　In　this　work,　a　novel　step-scheme　(S-scheme)　SnO2@MCr　heterojunction　was　successfully　fabricated　via　a　facile　hydrothermal　method.　At　this　heterojunction,　MIL-101(Cr)　octahedrons　are　decorated　with　highly　dispersed　SnO2　quantum　dots　(QDs,　approximate　size　3　nm).　The　QDs　are　evenly　wrapped　around　the　MIL-101(Cr),　forming　an　intriguing　zero-dimensional/three-dimensional　(0D/3D)　S-scheme　heterostructure.　Under　simulated　sunlight　irradiation　(280　nm　＜　lambda　＜　980　nm),　SnO2@MCr　demonstrated　superior　photoactivity　toward　the　denitrification　of　pyridine,　a　typical　NCC.　The　adsorption　capacity　and　adsorption　site　of　SnO2@MCr　were　also　investigated.　Tests　using　20%SnO2@MCr　exhibited　much　higher　activity　than　that　of　pure　SnO2　and　MIL-101(Cr);　the　reduction　ratio　of　Cr(VI)　is　rapidly　increased　to　95%　after　sunlight　irradiation　for　4　h.　The　improvement　in　the　photocatalytic　activity　is　attributed　to　(i)　the　high　dispersion　of　SnO2　QDs,　(ii)　the　binding　of　the　rich　adsorption　sites　with　pyridine　molecules,　and　(iii)　the　formation　of　the　S-scheme　heterojunction　between　SnO2　and　MIL-101(Cr).　Finally,　the　photocatalytic　mechanism　of　pyridine　was　elucidated,　and　the　possible　intermediate　products　and　degradation　pathways　were　discussed.