Reed biochar by microwave-assisted pyrolysis for the removal of tetracycline in water

This study uses reed straw and phosphoric acid to synthesize reed biochar and modified reed biochar through tubular furnace pyrolysis and microwave-assisted pyrolysis, respectively. The effects of pyrolysis temperature and phosphorous acid on the structure, composition, porosity, and adsorption performance of tetracycline (TC) were further investigated. The results showed that the modified biochar prepared by microwave-assisted pyrolysis had better performance. At a pyrolysis temperature of 500 °C, the microwave-prepared phosphorus-modified biochar MHP500 demonstrated a yield of 55.2 %, boasted a large specific surface area of 1692 m²/g, featured a high carbon content of 45.6 % and exhibited a heightened degree of aromatization. Through EDS mapping observation, it was innovatively discovered that the carbon content within the surface pores of the MHP500 material was higher than that outside the pores. This indicates that during the construction of carbon materials through microwave-assisted pyrolysis, heat diffuses from the interior to the exterior of the material, leading to a higher degree of carbonization within the material. The dosage of 0.25 g/L of MHP500 and the initial solution pH of 5, contributed to a removal of 95 % TC within 1 h for a 200 mL solution at an initial TC concentration of 50 mg/L. The adsorption process of TC by the materials followed a Elovich model. The Langmuir model could better describe the adsorption behavior with charcoal materials. The reusability of MHP500 was sound, maintaining 80 % for TC removal even after three adsorption-desorption cycles.