A Facile and Low-Energy Consumption Preparation Method for Biochar via the Hofmeister Effect for Dye Adsorption and the Electrode of Supercapacitor

Abstract

Activated biochar has exhibited huge potential in high performance adsorbent and supercapacitor. However, the single pyrolysis process usually could provide poor pore structure, limited surface area and insufficient surface oxygen-containing groups. Herein, we innovatively propose a facile and low-energy consumption preparation method to provide biochar with high surface area and sufficient oxygen-containing groups via gelling at room temperature, conventional drying method and one-step carbonization at 350 °C. Specially, bamboo powder, a byproduct of bamboo processing, and poly(vinyl alcohol) (PVA) were selected as the raw materials. Potassium nitrate with the strong salting-out effect was introduced into the bamboo/PVA solution at the presence of CaCl2 to lead to the sol–gel transition to form the bamboo/PVA blocks at room temperature. The bamboo/PVA blocks could be dried by the conventional drying method without the collapse of pore structure. Bamboo/PVA blocks were carbonized at 300–450 °C and the characterization indicated that the BCM-350 had significant structural advantages: the specific surface area of 907.18 ± 28.31 m2/g, the rich N/O codoped surface functional groups, and the unique micromesoporous hierarchical structure. The biochar showed excellent performance in both environmental and energy applications. For pollutant removal, it exhibited a high adsorption capacity of 569.69 ± 60.92 mg/g for methyl orange dye. As a supercapacitor electrode, it showed a high specific capacitance of 120.82 ± 0.064 mF/cm2 and excellent rate performance. The whole process is free of freezing-drying and supercritical drying process and the carbonization process is just at 350 °C. This work provided a facile and low-energy consumption preparation method for biochar.