Novel Cu(OH)₂/BC: a nano biocomposite for water cleansing

Bismarck Brown G is a carcinogenic cationic dye that continues to contaminate water sources despite regulations limiting its use. In this study, copper hydroxide (Cu(OH)₂) nanoparticles were grown on the surface of Nigella sativa (black cumin) seeds to develop a Cu(OH)₂/BC composite in an eco-friendly and sustainable manner for the removal of the dye from water. The composite was characterized using Fourier transform-infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, differential scanning calorimetry techniques, and Brunauer-Emmett-Teller gas adsorption analysis, which confirmed the successful integration of Cu(OH)₂ with the BC matrix. The prepared Cu(OH)₂/BC had a specific surface area, pore volume, and average pore diameter of ~ 86 m² g⁻¹, 0.092 cc g⁻¹, and 1.932 nm, respectively, with numerous functional groups on its surface. Due to these properties, the resulting composite was used for the adsorption of Bismarck Brown G (BBG) dye. Almost complete (~ 99.0%) dye removal was achieved at an optimized dose of 3 g L⁻¹, pH = 7, in 150 min, and at a temperature of 30 °C. The adsorption isotherm followed the order of fitting: Langmuir > Freundlich > Temkin. The isotherm results indicated chemisorption (with some physisorption) on a heterogeneous surface. The kinetics followed the pseudo-second order model. Thermodynamic analysis confirmed a spontaneous, exothermic, and predominantly chemisorption-driven mechanism. In conclusion, the Cu(OH)₂/BC nanocomposite shows potential to serve as an efficient, cost-effective, eco-friendly, and scalable adsorbent material for industrial wastewater treatment.