Adsorption of nitrophenol onto a novel Fe3O4-κ-carrageenan/MIL-125(Ti) composite: process optimization, isotherms, kinetics, and mechanism

Water pollution is a dreadful affair that has incessantly aggravated, exposing our planet to danger. In particular, the persistent nitro aromatic compound like nitrophenols causes anxiety to the researchers due to their hazardous impacts, excessive usage, and removal difficulty. For this purpose, a novel multi-featured composite was constructed based on κ-Carrageenan (κ-Carr), MOF (MIL-125(Ti)), and magnetic Fe 3 O 4 for efficient adsorptive removal of o-nitrophenol (o-NP). Interestingly, BET measurements revealed the high surface area of Fe 3 O 4 -κ-Carr/MIL-125(Ti) of about 163.27 m 2 /g, while VSM showed its excellent magnetic property (20.34 emu/g). The comparison study pointed out the synergistic effect between Fe 3 O 4 , κ-Carr, and MIL-125(Ti), forming a composite with an excellent adsorption performance toward o-NP. The adsorption data obeyed pseudo-second-order kinetic model, and Freundlich isotherm model was better fitted than Langmuir and Temkin. Furthermore, Langmuir verified the supreme adsorption capacity of o-NP onto Fe 3 O 4 -κ-Carr/MIL-125(Ti) since the computed q max  reached 320.26 mg/g at pH 6 and 25 °C. Furthermore, the XPS results postulated that the adsorption mechanism pf o-NP proceeded via H-bonding, π - π interaction, and electron donor–acceptor interactions. Interestingly, Fe 3 O 4 -κ-Carr/MIL-125(Ti) composite retained good adsorption characteristics after reusing for five cycles, suggesting its viable applicability as an efficient, renewable, and easy-separable adsorbent for removing nitro aromatic pollutants.