Magnetic Fe3O4 nanoparticles loaded papaya (Carica papaya L.) seed powder as an effective and recyclable adsorbent material for the separation of anionic azo dye (Congo Red) from liquid phase: Evaluation of adsorption properties

Abstract

Magnetic adsorbents have recently gotten a lot of attention because of their eco-friendliness, ease of separation, and inexpensive cost. In this work, a new magnetic Fe3O4 loaded papaya seed powder (Fe3O4-PSP) was successfully synthesized and utilized as a biosorbent to eliminate Congo Red (CR) from the liquid phase. The prepared Fe3O4-PSP was characterized by BET, FE-SEM/EDX, VSM, XRD, pHPZC, and FT-IR analysis. Batch tests were carried out to assess the influence of several adsorption factors like temperature (303–333 K), pH function (2.0–10.0), CR initial concentration (100–400 mg/L), Fe3O4-PSP mass (0.01–0.08 g/30 mL), and contact time (0–420 min). The pHPZC of Fe3O4-PSP was computed at 5.4. Four kinetic models were used to analyze the kinetic data, and the most appropriate model with an R2 value of 0.9991 was the pseudo-second-order. In accordance with the intra-particle diffusion model, the adsorption follows a three-step mechanism. The adsorption equilibrium data were examined using Dubinin-Radushkevich (D-R), Freundlich, Langmuir, and Temkin models and the adsorption data were well represented by the Langmuir isotherm (R2 = 0.9962). The saturated adsorption efficiency of Fe3O4-PSP calculated from the Langmuir model was 216.9 mg/g at 303 K. The data was examined using error and regression coefficient functions, such as the χ2 and SSE, to define the best-suitable isotherm and kinetic models. Hydrogen bonding and electrostatic interactions between CR and Fe3O4-PSP are responsible for the primary adsorption mechanism. The thermodynamic factors ΔSo (64.8 J/mol K), ΔGo (−1.1997 ∼ 3.1439 kJ/mol for 303 ∼ 333 K), and ΔHo (18.4 kJ/mol) revealed that the adsorption of CR onto Fe3O4-PSP was feasible, spontaneous, and endothermic. The saturation magnetization of Fe3O4-PSP was found to be 54.4 emu/g. An external magnetic field can regenerate and easily separate Fe3O4-PSP from an aqueous solution with no weight loss. According to the findings, Fe3O4-PSP is a potentially recyclable adsorbent for removing CR dye from contaminated water.