Antifreeze　proteins　(AFPs),　a　type　of　high-efficiency　but　expensive　and　often　unstable　biological　antifreeze,　have　stimulated　substantial　interest　in　the　search　for　synthetic　mimics.　However,　only　a　few　reported　AFP　mimics　display　thermal　hysteresis,　and　general　criteria　for　the　design　of　AFP　mimics　remain　unknown.　Herein,　oxidized　quasi-carbon　nitride　quantum　dots　(OQCNs)　are　synthesized　through　an　up-scalable　bottom-up　approach.　They　exhibit　thermal-hysteresis　activity,　an　ice-crystal　shaping　effect,　and　activity　on　ice-recrystallization　inhibition.　In　the　cryopreservation　of　sheep　red　blood　cells,　OQCNs　improve　cell　recovery　to　more　than　twice　that　obtained　by　using　a　commercial　cryoprotectant　(hydroxyethyl　starch)　without　the　addition　of　any　organic　solvents.　It　is　shown　experimentally　that　OQCNs　preferably　bind　onto　the　ice-crystal　surface,　which　leads　to　the　inhibition　of　ice-crystal　growth　due　to　the　Kelvin　effect.　Further　analysis　reveals　that　the　match　of　the　distance　between　two　neighboring　tertiary　N　atoms　on　OQCNs　with　the　repeated　spacing　of　O　atoms　along　the　c-axis　on　the　primary　prism　plane　of　ice　lattice　is　critical　for　OQCNs　to　bind　preferentially　on　ice　crystals.　Here,　the　application　of　graphitic　carbon　nitride　derivatives　for　cryopreservation　is　reported　for　the　first　time.