Biochar pyrolyzed with concentrated solar radiation for enhanced nitrate adsorption

Abstract

Biochar has been recognized as an effective soil amendment for reducing nitrogen leaching in agriculture, but its large-scale implementation is impeded by the costly production process due to high energy requirements for thermal decomposition of feedstock. This study aimed to develop a novel pyrolysis system utilizing concentrated solar radiation to produce biochar and explore the potential of solar-pyrolyzed biochar for nitrate adsorption. Results showed that the solar-pyrolyzed biochar exhibited a maximum adsorption capacity of 35.59 mg/g for nitrate, significantly higher than two out of the three commercially available biochars in America that are selected for comparison. The Fourier-transform infrared (FTIR) analysis suggested a variety of oxygen-containing polar functional groups present in the solar-pyrolysis biochar, which enhances its affinity for nitrate and other hydrophilic ions. The X-ray diffraction (XRD) analysis revealed that the solar pyrolysis biochar was an amorphous material with a poorly crystalline, carbon-rich phase, indicating a high degree of carbonization and recalcitrance, as confirmed by Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analysis. The porous structure of the solar-pyrolysis biochar suggested a larger specific surface area, which could benefit adsorption. Although further experiments are required to determine the stability and cost-effectiveness of a scaled-up solar-pyrolysis apparatus, these findings provide hope for a more sustainable and high-performing biochar production process in the future.