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• Ultralight PAFP/GONRs-A aerogel was prepared facilely by solvothermal polymerization method. • The aerogel showed a low density, large specific surface area and high phosphorus content. • The aerogel presented an unexpectedly high adsorption capacity and selectivity for thorium. • Phosphonic groups play an important role in Th(IV) adsorption. • DFT calculations revealed the coordination modes of Th(IV) with the aerogel, confirming the experimental results. An ultralight three-dimensional porous network phosphonic acid functionalized polymer/graphene oxide nanoribbons aerogel (PAFP/GONRs-A) was prepared using trimethylolpropane trimethacrylate (TRIM) and vinylphosphonic acid (VPA) as monomers via solvothermal polymerization method for thorium capture from aqueous solutions. The synthesized aerogel presented a low density (10.6 mg cm−3), large specific surface area (433.2 m2 g−1) and high phosphorus content (18.2%). The adsorption process of Th(IV) on PAFP/GONRs-A was pH-dependent, spontaneous and endothermic, and well described by the pseudo-second-order kinetic and Langmuir isotherm model. Under optimal experimental conditions (10 mg of adsorbent dosage, 50 mL of solution volume, 240 min of contact time, 298 K of temperature), PAFP/GONRs-A presented an excellent high adsorption capacity of thorium, with maximum capacity of 457.9 mg g−1 at a pH of 3.0, and maximum thorium-selectivity of 87.1% at a pH of 2.0. The values of ΔG for Th(IV) adsorption on PAFP/GONRs-A were calculated to be −21.78, –23.32, −24.87 and −26.41 kJ mol−1 at 283, 298, 313 and 328 K, respectively. Density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) revealed that Th(IV) ions were fixed in aerogel by coordinating with the P = O groups of PAFP/GONRs-A, and both 1:2 ratio of Th(IV) with the P = O ligands on the same graft chain and 1:4 ratio of Th(IV) with P = O ligands on two distinct graft chains could jointly contribute to the adsorption of Th(IV) on PAFP/GONRs-A. This work offers a facile approach for synthesizing the phosphonic acid functionalized graphene oxide nanoribbons aerogel and demonstrates that PAFP/GONRs-A has high potential as a candidate adsorbent for the capture of thorium from aqueous solution. [ABSTRACT FROM AUTHOR]