Studies of the adsorption properties of methylene blue onto the low-cost Torreya grandis aril biochar without activation

Conventional adsorbents dependent on chemical activation suffer from high costs and environmental burdens, limiting their practical application. In this study, biomass raw materials sourced from Torreya grandis arils (TGA) were used to synthesize biochar adsorbents via adjusting carbonization temperatures and heating rates with no chemical activation involved, ensuring eco-friendliness and cost-effectiveness. Adsorbents were characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effects of key factors including initial methylene blue (MB) concentration, solvent species, carbonization temperatures, and heating rates were investigated. The obtained results demonstrated that the prepared adsorbents exhibit excellent adsorption efficiency toward MB, with a maximum experimental adsorption capacity of 287.70 mg/g for pyrolyzed TGA conducted at a heating rate of 4 °C/min and a carbonization temperature of 275 °C. Meanwhile, the pseudo-second-order kinetic model (R2 > 0.994) and Langmuir isotherm model (R2 > 0.990) provide satisfactory descriptions of the adsorption data. Thermodynamic parameters confirmed the adsorption was spontaneous, endothermic, and disorder-increasing, involving both chemisorption and physisorption. This study demonstrates that non-activated TGA biochar, with its simple preparation process, low cost, and high adsorption efficiency, has great potential as an economical and eco-friendly alternative for eliminating textile dyes from wastewater.