This work presents an extensive study on the effect of various parameters (concentration, solvents, infrared irradiation, salts, and temperature variation) on the barium oxide nanoparticles decorated multi-wall carbon nanotubes. A simple and effective technique involving infrared irradiation and diazonium chemistry was utilized. The materials were characterized using X-ray photoelectron spectroscopy, Raman spectroscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, powder X-ray diffraction, thermogravimetric analysis and ultraviolet–visible spectrophotometry. A homogeneous distribution of amorphous barium oxide nanoparticles onto carbon nanotubes was observed. Particles size varies from 3–18 nm (Gaussian mean diameter ∼11.7 nm). Thermogram showed that nanoparticles act as a catalyst to decompose nanotubes even at lower temperature. A common dye pollutant that is methylene blue was considered to evaluate the ability of the present composite for water purification for the first time. As our technique is also applicable to bulk synthesis, it can be worthful for wide range of nanotechnological applications.