Heptazine-based　conjugated　polymeric　carbon　nitrides　(PCNs)　are　promising　metal-free　photocatalysts,　yet　their　synthesis　is　challenging　due　to　the　electron-deficiency　and　insolubility　of　heptazine　units.　Indeed,　heptazine-containing　polymers　have　only　been　prepared　through　nucleophilic　substitution　with　amines　by　using　toxic　cyameluric　chloride　as　the　starting　material.　Herein,　we　report　the　novel　and　environmentally　friendly　method　for　preparing　heptazine-based　mesoporous　PCNs　with　hydrazone　links　formed　through　a　simple　Schiff　base　condensation　of　melem-NH2　and　aldehydes.　Unlike　cyameluric　chloride,　melem-NH2　is　non-toxic,　stable,　and　can　be　readily　obtained　from　melem　and　hydrazine　in　solution.　We　demonstrate　that　the　hydrazone　linkages　and　the　heptazine　units　synergistically　enhance　the　photocatalytic　activity　of　PCNs　in　visible-light-driven　aerobic　oxidation　of　benzyl　alcohol　to　benzaldehyde.　In　particular,　the　polymer　constructed　from　melem-NH2　and　p-phthalaldehyde　shows　17　times　more　activity　than　graphitic　carbon　nitride　(g-C3N4).　©　2020　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim