Metal-modified sludge-based biochar enhance catalytic capacity: Characteristics and mechanism

The improvement of the catalytic performance of sludge-based biochar plays an important role in the catalytic application of biochar. This work aimed to use transition metals and rare earth elements (Fe, Ce, La, Al, Ti) to modify sludge and prepare modified biochar with better catalytic performance through pyrolysis. Through the Fourier transform infrared spectrometer, Raman spectrometer, and X-ray photoelectron spectroscopy, the effects of different metal modifications on the surface morphology, molecular structure, element compositions, and valence of elements of biochar were comprehensively investigated. The results showed that metal elements were successfully modified onto the surface of biochar as metal oxides. Although the highest intensity of persistent free radicals was detected in blank-biochar by electron spin resonance, the intensities of hydroxyl radicals catalyzed by modified biochars in H₂O₂ system were higher than that catalyzed by blank-biochar, indicating that the catalytic performance of modified biochar was mainly related to the metal oxide loaded and the defect structure on the surface of metal-modified biochar. Furthermore, in the H₂O₂ system, the degradation efficiencies of tetracycline catalyzed by the biochars within 4 h were 51.7% (blank-biochar), 90.7% (Fe-biochar), 69.0% (Ce-biochar), 59.9% (La-biochar), 58.0% (Al-biochar), 58.0% (Ti-biochar), respectively, suggesting that Fe-biochar not only possessed the best catalytic performance but also shortened the reaction time. This research not only provided the possibility for recycling the waste activated sludge, but also proposed a modification method to improve the catalytic performance of biochar.