Efficient Photocatalytic Degradation of Malachite Green and Cr(VI) Using Co-MOF and Bacterial Cellulose@Co-MOF Biocomposite: A Green Approach

The persistent presence of synthetic dyes such as malachite green (MG) and inorganic heavy metals such as Cr-(VI) in industrial effluents poses a major environmental threat due to their toxicity and resistance to biodegradation. Their high solubility and bright colors make removal difficult, necessitating efficient and sustainable remediation techniques. Photocatalysis is an environmentally friendly water treatment technique that uses light energy to activate a photoactive catalyst, degrading pollutants into less harmful products, such as carbon dioxide and water. This study investigates the photocatalytic degradation of MG and Cr-(VI) using cobalt-based metal-organic frameworks (Co-MOF) and a bacterial cellulose-supported composite (BC@Co-MOF). The catalyst was synthesized using the precipitation method. The BC@Co-MOF composites were prepared using an in situ synthesis method. The as-synthesized materials were characterized by using a scanning electron microscope, energy dispersive X-ray spectrometry, powder X-ray diffractometer, photoluminescence spectroscopy, UV-diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, porosimetry, and thermogravimetric analysis. The effect of initial concentration of the target pollutant, solution pH, and source of light on the photocatalytic degradation was studied. The nanofibrous BC@Co-MOF composite enhanced the catalytically active sites, improved mass transfer, and facilitated efficient photodegradation. In the presence of UV radiation, BC@Co-MOF 6H demonstrated the highest 92.52% degradation of MG and 82.06% degradation of Cr-(VI) in 60 min under optimum conditions (10 ppm and neutral pH of the solution). The photocatalytic degradation of MG followed pseudo-first-order kinetics. The radical scavenger studies revealed the dominance of h⁺ radicals for the degradation of MG, whereas for the degradation of Cr-(VI), ^•O₂ ^-, and h⁺ were the dominant reactive species. The underlying mechanism for the degradation of MG was proposed with the help of LC-MS analysis. The photocatalytic degradation of an aqueous solution containing a mixture of MG and Cr (VI), in the presence of BC@Co-MOF 6H and under solar light, showed 88.36 and 81.65% degradation of MG and Cr (VI), respectively. The degradation of the mixed pollutants revealed the synergistic effect of adsorption and photodegradation. The BC@Co-MOF 6H catalyst exhibited excellent photocatalytic activity when reused for up to 4 cycles. The BC@Co-MOF 6H catalyst also exhibited promising results for the treatment of real-time industrial effluent, indicating its practical applicability. Furthermore, phytotoxicity studies confirmed the safe nature of treated water, making BC@Co-MOF a green, recyclable, and highly effective photocatalyst for wastewater treatment.