Cyano-bearing conjugated polycarbazoles PHN-1 and PHN-2 were efficiently prepared in high yields from corresponding monomers with paraand meta-configuration by oxidative coupling polymerization at room temperature, respectively. PHN-1 with para-configuration exhibits higher porosity than meta-configuration counterpart PHN-2. Cyano groups in the polymers were further converted to conjugated polycarbazoles containing tetrazole (PHN-1-TZ and PHN-2-TZ) or amidoxime groups (PHN-1-AO and PHN-2-AO) after treatment with NaN3/NH4Cl3 and hydroxylamine aqueous solution, respectively. Up to 55.0% enhancement of CO2 uptake at 298 K and 1.0 bar found for PHN-2-TZ (4.93 wt%) after post-modification from PHN-2 (3.18 wt%) is ascribed to tetrazole groups with basic feature and acidic hydrogen, which show high affinities to CO2 not only by the Lewis acid–Lewis base and local-dipole-quadrupole interactions but also through the hydrogen bonding with oxygen atoms of CO2 . In the real seawater with excess uranium (8.02 ppm), a maximum uranium extraction uptake of 119.4 mg g-1 for PHN-1-AO greatly higher than ~10 mg g-1 for the PHN-1 (about) at room temperature is due to the strong chelating interaction between the amidoxime groups and uranium.