Recycling waste nickel-laden biochar to pseudo-capacitive material by hydrothermal treatment: roles of nickel-carbon interaction

Abstract

Abstract Biochar as an absorbent is used to remove heavy metals from industrial wastewater, while the disposal of the residual has received little attention. This study attempted to convert the waste Ni-laden biochar into the pseudo-capacitive materials by hydrothermal treatment, investigated the optimal temperature (90–180 °C) and Ni content (100 and 500 mg g − 1 ), and explored the role of Ni-C interactions in the formation of the pseudo-capacitive materials. The highest pseudo-capacitance of 386.7 F g − 1 was obtained with the highest Ni content and the lowest temperature. The high temperature (180 °C) induced thicker lamellar crystal Ni(OH) 2 , while thinner flower-like Ni(OH) 2 crystal was observed at 90 °C. Low temperature enabled the Ni(OH) 2 crystals to disperse homogeneously on the carbon surface. The infrared spectroscopy showed that Ni promoted the disappearance of functional groups, indicating the catalytic effect of Ni on carbon structure, which also benefited their recrystallization and mutual encapsulation. Moreover, a combination of X-ray diffraction and thermogravimetry verified that Ni inserted into biochar graphite layer and enlarged the layer distance. This study provides a strategy for transforming hazardous nickel-laden biochar into the capacitive material and reveals that nickel can amplify the graphite layer and improve the stability of biochar-based pseudo-capacitive material during the hydrothermal treatment. Graphical Abstract