This research aims to develop low-toxicity, cost-effective, and reusable biobased materials by combining natural biopolymers with graphene oxide. Therefore, chitosan/kappa carrageenan (CS/kCar) and chitosan/kappa carrageenan/graphene oxide (CS/kCar@GO) nanocomposites were synthesized and applied for the effective removal of As(III), Cr(VI), and F from aqueous solutions. The results showed that the maximum removal for As(III) (79%), Cr(VI) (99%), and F (36%) was achieved at pH 5.0, 7.0, and 3.0, respectively. The data were best fitted by pseudo-second-order (PSO) kinetics and the Langmuir isotherm model, indicating adsorption capacities of 2.44 for As(III), 2.82 for Cr(VI), and 32.63 mg/g for F from the optimal CS/kCar@GO composite. According to the thermodynamic analysis, the adsorption of heavy metals and fluoride ions on the CS/kCar@GO nanocomposite was endothermic and spontaneous in all cases. Reuse of CS/kCar@GO for up to 10 cycles after regeneration demonstrated the effectiveness of this adsorbent.