Macroalgae-based biochar: preparation and characterization of physicochemical properties for potential applications

In this study, we selected five macroalgae species and employed a pyrolysis technique to convert biomass into biochar. Each of the biochar samples was characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS) and microwave plasma atomic emission spectroscopy (MP-AES). The physicochemical properties show that the biochar samples from macroalgae are disordered and porous, relatively high in yield, carbon and nitrogen content, ash and pH, and have elevated oxygen-containing functional groups and inorganic minerals (Ca, Na, Mg, K and P). Because of their porous and disordered structures and abundant functional groups, the biochar samples showed an excellent adsorption efficiency of 100, 98.10, 96.78, 98.09 and 95.47% for Ulva sp., Oedogonium sp., Asparagopsis, Kappaphycus alvarezii and Eucheuma denticulatum, respectively. All biochar samples exhibited negligible amounts of heavy metals (Cd, Cu, Cr, Ni, Pb, As, Zn and Hg), which indicated that biochar is not harmful for plants and crops. The higher ash content in all biochar samples could be advantageous to improve soil quality. Due to the alkaline nature and presence of inorganic minerals, macroalgal biochar could be useful with acidic soil and provide nutritional benefits for crop growth. In this study, we selected five macroalgae species and employed a pyrolysis technique to convert biomass into biochar.