Biochar is a cost-effective and porous material with high carbon content. It is considered as an effective supporting matrix owing to its high specific surface area and notable ion exchange ability. In this work, a porous biochar support was fabricated from pistachio residues using pyrolysis procedure. Subsequently, various crystalline phases and morphologies of MnO2 were deposited onto the biochar support through chemical protocols with Mn(Ac)2, KMnO4, and MnSO4 as Mn source. The N2 adsorption-desorption experiments were employed to characterize the porosities and specific surface areas of the synthesized nanocomposites. It is found that the γ-MnO2/biochar composite possessed the higher surface area than the δ-MnO2 and α-MnO2 samples. The adsorption features of the composite materials in the removement of target dye from aqueous solution were also examined. Based on the experimental results, the γ-MnO2/biochar sample showed the highest efficiency for removal of target dye. In addition, the experimental data exhibited a good correlation (R2 greater than 0.99) with the pseudo-second-order kinetic model, indicating a chemical adsorption approach for dye adsorption.