Magnetic modification of pine needle-derived activated carbon for dye removal with facilitated recovery from wastewater

Biomass based activated carbon as an adsorbent attained significant attention in today’s world for the industrial waste water treatment due to its sustainable nature, high surface area and adsorption ability. In the present study, activated carbon (AC) was developed from of Pinus roxburghii (Chir Pine) dry needle biomass and was magnetically modified through physical activation. The iron oxide nanoparticles were integrated by in-situ technique to impart improved magnetic separability. The prepared samples of magnetic modified activated carbon (MMAC) were systematically characterized for evaluating the surface morphology, presence of surface functional groups, crystalline structure and magnetic properties. The obtained results confirmed regular tubular vacant spaces, which were later on magnetically modified by dispersing Fe₃O₄ nanoparticles in the hollow spaces of AC to obtain strong magnetic responsiveness. The adsorption studies were performed using Malachite Green (MG) industrial dye. The batch adsorption of MG dye from the aqueous solution demonstrated AC’s maximum Langmuir adsorption capacity of Q max of 416.93 mg/g while the optimized magnetic composite (MMAC3) retained a highly competitive capacity of 369.47 mg/g. AC required complex filtration for recovery and the MMAC3 exhibited high magnetic saturation of 1.22 emu/g using the external magnet from the aqueous solution. Non-linear kinetic analysis and multi-model equilibrium isotherm evaluations (including Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich) were conducted to rigorously define the physical and mass-transfer parameters driving the adsorption capacity. Thermodynamic investigations confirmed that Malachite Green sequestration by both AC and the MMAC 3 composite is a spontaneous, endothermic and entropy-driven physisorption process. The most important finding of the regeneration experiments is the impressive cyclic stability of both the matrices used, with each matrix maintaining more than 80% of the initial adsorption ability after five cycles. Although AC was slightly superior in the amount adsorbed, MMAC 3 stands out because of the capability of fast magnetic separation, making it ideal for large-scale water treatments. As seen from the experimental results, magnetic separation can be performed very efficiently without any additional use of energy-consuming methods such as centrifugation or filtration. This makes the proposed product environmentally friendly.