Reduction of Bromate by Cobalt-Impregnated Biochar Fabricated via Pyrolysis of Lignin Using CO₂ as a Reaction Medium

In this study, pyrolysis of lignin impregnated with cobalt (Co) was conducted to fabricate a Co-biochar (i.e., Co/lignin biochar) for use as a catalyst for bromate (BrO₃^-) reduction. Carbon dioxide (CO₂) was employed as a reaction medium in the pyrolysis to induce desired effects associated with CO₂; (1) the enhanced thermal cracking of volatile organic compounds (VOCs) evolved from the thermal degradation of biomass, and (2) the direct reaction between CO₂ and VOCs, which resulted in the enhanced generation of syngas (i.e., H₂ and CO). This study placed main emphases on three parts: (1) the role of impregnated Co in pyrolysis of lignin in the presence of CO₂, (2) the characterization of Co/lignin biochar, and (3) evaluation of catalytic capability of Co-lignin biochar in BrO₃^- reduction. The findings from the pyrolysis experiments strongly evidenced that the desired CO₂ effects were strengthened due to catalytic effect of impregnated Co in lignin. For example, the enhanced generation of syngas from pyrolysis of Coimpregnated lignin in CO₂ was more significant than the case without Co impregnation. Moreover, pyrolysis of Coimpregnated lignin in CO₂ led to production of biochar of which surface area (599 m² g^-1) is nearly 100 times greater than the biochar produced in N₂ (6.6 m² g^-1). Co/lignin biochar produced in CO₂ also showed a great performance in catalyzing BrO₃^- reduction as compared to the biochar produced in N₂.