A green and economic approach to synthesize magnetic Lagenaria siceraria biochar (γ-Fe 2 O 3 -LSB) for methylene blue removal from aqueous solution.

In the printing and textile industries, methylene blue (a cationic azo dye) is commonly used. MB is a well-known carcinogen, and another major issue is its high content in industrial discharge. There are numerous removal methodologies that have been employed to remove it from industrial discharge; however, these current modalities have one or more limitations. In this research, a novel magnetized biochar (γ-Fe2 O3 -LSB) was synthesized using Lagenaria siceraria peels which were further magnetized via the co-precipitation method. The synthesized γ-Fe2 O3 -LSB was characterized using FTIR, X-ray diffraction, Raman, SEM-EDX, BET, and vibrating sample magnetometry (VSM) for the analysis of magnetic properties. γ-Fe2 O3 -LSB showed a reversible type IV isotherm, which is a primary characteristic of mesoporous materials. γ-Fe2 O3 -LSB had a specific surface area (SBET  = 135.30 m2 /g) which is greater than that of LSB (SBET  = 11.54 m2 /g). γ-Fe2 O3 -LSB exhibits a saturation magnetization value (Ms) of 3.72 emu/g which shows its superparamagnetic nature. The batch adsorption process was performed to analyze the adsorptive removal of MB dye using γ-Fe2 O3 -LSB. The adsorption efficiency of γ-Fe2 O3 -LSB for MB was analyzed by varying parameters like the initial concentration of adsorbate (MB), γ-Fe2 O3 -LSB dose, pH effect, contact time, and temperature. Adsorption isotherm, kinetic, and thermodynamics were also studied after optimizing the protocol. The non-linear Langmuir model fitted the best to explain the adsorption isotherm mechanism and resulting adsorption capacity ( q e =54.55 mg/g). The thermodynamics study showed the spontaneous and endothermic nature, and pseudo-second-order rate kinetics was followed during the adsorption process. Regeneration study showed that γ-Fe2 O3 -LSB can be used up to four cycles. In laboratory setup, the cost of γ-Fe2 O3 -LSB synthesis comes out to be 162.75 INR/kg which is low as compared to commercially available adsorbents. The results obtained suggest that magnetic Lagenaria siceraria biochar, which is economical and efficient, can be used as a potential biochar material for industrial applications in the treatment of wastewater.