In this work, biochar (BC) was synthesized from the thermal decomposition of banana peels and modified by different percentages of ZnO NPs using the wet impregnation method. The ZnO_x/BC_1-x nanocomposites’ (x = 0.00, 0.10, 0.20, 0.30, 0.50, 1.00 as a weight) physical and chemical properties were estimated utilizing X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N₂ sorption, Transmission electron microscopy (TEM), and zeta potential. The synthesized nanocomposites were utilized as adsorbents for eliminating methylene blue toxic dye from water. Through the adsorption batches, several parameters have been tested, such as the impact of x value, duration time, adsorbent dose, initial pH, dye concentration, and medium temperature. Compared to the tested nanocomposites, the ZnO_0.10/BC_0.90 nanocomposite revealed the best adsorption efficiency (96.5 %) with a high adsorption capacity reaching 118.8 mg/g. To ensure accurate identification of adsorption process behavior, the adsorption isotherms, kinetic models, and thermodynamic studies were investigated. Langmuir and pseudo-2^nd order were discovered to be the most appropriate models that ascribe the adsorption behavior. Furthermore, the thermodynamic study reveals that the MB uptake on the nanocomposites is both spontaneous and exothermic.