This study is focused on the application of activated carbon nanoadsorbent derived from Ocimum basilicum Linn (sweet basil) leaves for the removal of methyl orange dye from an aqueous solution. The Ocimum basilicum Linn leaves are dried, powdered, cured with H2SO4, and thermally treated to form an activated carbon biosorbent. Sorbent characterization studies like scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy have revealed the adsorption of the methyl orange dye from their aqueous solution in the batch mode process. The biosorbent has shown a maximum adsorption capacity of 1.54 mg g−1 at 10 mg l−1 concentration, 1.2 g sorbent dosage, pH of 3, contact time of 180 min, and pHpzc at 3.9. Experimental results are analyzed using equilibrium models and it is found that the Langmuir isotherm model and kinetic model fit well and also the results have corresponded well with pseudo-first order. The intraparticle diffusion (IPD) mechanism has shown that pore diffusion occurs at a slower rate. The Elovich model has displayed that adsorption is affected by film diffusion. From the statistical optimization studies, it is demonstrated that Box–Behnken model can correlate the good agreement between experimental and predicted values. The highest adsorption capacity for the nanoadsorbent was found using quadrate models and optimizing the variables at a time of 237 min, initial dye concentration of 5.31 mg l−1, adsorbent dose of 1.22 g, and pH of 4.23.