Currently we present a simple technique to prepare nitrogen doped- carbon quantum dots (N-CQD) from spoiled/expired cough syrup. As prepared N-CQD was then utilised as a reducing agent to obtain nanostructured β-MnO2. The physicochemical properties of N-CQD and β-MnO_2-CQD particles were characterised by using various techniques. The dye removal efficiency of β-MnO_2-CQD was studied using methylene blue (MB). The absorption results show that dye concentrations, nanocomposites dosage, pH, conductivity, and temperature affected the dye removal capacity of the β-MnO2-CQD. The adsorption isotherm and kinetics model agreed well with Langmuir and pseudo-second order, respectively.