Sequential Carbonization from Hyperaccumulator to Prepare Functional Biochar for Efficient Azo Dye Degradation

Abstract

Dye-containing wastewater is one of the most heavily industrial pollutants. "Waste treatment wastewater" is an ecofriendly water management strategy. In this study, we used hyperaccumulator (Sedum alfredii) residues to prepare a series of functional biochars by hydrothermal carbonization pretreatment (HTP) combined with pyrolysis. The removal efficiency of different biochar for azo dye acid orange 7 (AO7) via activated peroxymonosulfate (PMS) was evaluated. Compared with the original biochar (SABC-8)/PMS system (10%), the functionalized biochar (SAHC200-8)/PMS system removed 99.7% of AO7 (50mg L-1) within 30 minutes with the apparent rate constant (Kobs) of 0.1333 min-1. Despite the presence of multiple reactive oxygen species (ROSs) in the reaction solution, the relative contribution of nonradical electron transfer was quantified to be the largest ([[EQUATION]]=86.56%) instead of 1O2 by the competition kinetics. In-situ Raman and electrochemical tests further revealed the electron transfer-driven mechanism for the oxidation of AO7 in the biochar/PMS system. This work highlights the importance of HTP as a pretreatment for regulating the graphitic domains of biochar and proposes a method for preparing effective catalysts from hyperaccumulators.

Keywords: Hyperaccumulator, Biochar, SR-AOPS, competitive kinetics, Electron transfer pathway