[en] Boron carbide (B₄C) is an excellent covalent carbide that finds applications in industries and nuclear power plants. The present synthesis methods of boron carbide are expensive and involve the use of toxic chemicals that adversely affect environment. In the present work, we report for the first time the use of the hydrothermal method for converting the cellulose from cotton as the carbon precursor for B₄C. The carbon precursor is converted into functionalized porous carbonaceous material by hydrothermal treatment followed by sodium borohydride. It is further treated with boric acid to make it a B₄C precursor. The precursor is characterized by UV–visible diffuse reflectance, Raman, Fourier transform infrared, photoluminescent and energy dispersive spectroscopy. The morphology and structure analysis is carried out using field emission scanning electron microscopy and x-ray diffraction techniques. The results of structural and optical characterization of the sample synthesized are compared with the commercial B₄C. The thermal stability of the sample is studied by thermogravimetric analysis. The sample annealed at 700 °C is found to be B₄C devoid of amorphous carbon with a yield of 44.7%. The analysis reveals the formation of boron carbide from the sample. (paper)