Chemical functionalisation of Nerium oleander fibre for the degradation of methylene blue

This work focalises on the extraction of cellulosic fibres from Nerium oleander. The extracted fibres (EC) were functionalised with polyethyleneimine (PEI) and nano-zero-valent copper (nZVCu). The cellulosic substrates were analysed using scanning electron microscope, Fourier transform infrared, thermogravimetric analysis/differential thermogravimetric analysis, and X-ray diffraction (XRD). The EC/PEI/nZVCu nanocomposite demonstrated a wide surface distribution of nZVCu. The XRD pattern of the extracted cellulose demonstrated three main peaks positioned at 15.4°, 22°, and 34.8° which were attributed to (1 1 0), (2 0 0), and (0 4 0) lattice planes of the crystalline cellulose I. The high residual weight (46.46%) noticed for the EC/PEI/nZVCu nanocomposite approved the chemical functionalisation of the cellulosic substrate with inorganic and organic agents. The EC/PEI/nZVCu nanocomposite was applied for the catalytic reduction of methylene blue solution using sodium borohydride (NaBH₄) as a reducing agent. The decolourisation result was affected by several experimental factors including NaBH₄ concentration, initial methylene blue concentration, time, and temperature. A complete decolourisation was achieved after 8 min of reaction (pH = 6, C₀ = 40 mg/L, NaBH₄ = 1 M, T = 20°C). The low calculated E_a value (6.2 kJ mol⁻¹) confirmed the effectiveness of the prepared catalytic system in decolourisation. The catalytic system was non-spontaneous, endothermic, with a reduced disorder.