Phosphoric acid functionalized graphene oxide: a highly dispersible carbon-based nanocatalyst for the green synthesis of bio-active pyrazoles

•Novel phosphonic acid functionalized carbocatalysts were designed and prepared.•Catalyst preparation procedure was simple and flexible in controlling the functionalization level.•The catalyst showed high activity toward catalytic synthesis of pyrano[2,3-c]pyrazole derivatives.•The developed water-tolerant catalyst can be simply retrieved (≥95%) and repetitively used.