This work demonstrates an easy and green method to synthesize alum doped nanopolyaniline (NDPANI). Nanopolyaniline was synthesized by using a template free interfacial polymerization of aniline using APS as oxidant. An environment friendly and nontoxic substance, potash alum, in contrast to hazardous mineral acid, was used as a dopant to create positive charge in the polymer backbone. This material promises a greener method for selective removal of anionic dyes like Orange-II (O-II) and Mordant Yellow (MY) from wastewater. The synthesized alum doped nanopolyaniline (NDPANI) was characterized by FTIR, X-ray fluorescence (XRF), SEM, and DLS. The adsorption was studied by variation of adsorbent dosage, pH, temperature, time, and initial concentration of anionic dyes under different reaction conditions. Adsorption of dye follows pseudo-second-order kinetics. Langmuir isotherm was found to be the best fitting model with the maximum adsorption capacity for O-II being 667 mg/g at 308 K. The thermodynamic parameters such as the Gibbs free energy change (Delta G degrees), enthalpy change (Delta H degrees), and entropy changes (Delta S degrees) were calculated and revealed that the adsorption process is spontaneous and endothermic in nature. The material exhibits enhanced dye adsorption capacity and can be used for removal of O-II effectively.