Fabrication and functionalization of biological graphene aerogel by reusing microorganism in activated sludge and ionic dyes

Abstract A novel biological graphene aerogel (BGA) was fabricated by using bacteria in waste activated sludge (AS) as cross-linker, and ionic dye as surface charge modification reagent. Through rheological measurement and electron microscopy, this AS-BGA was confirmed an elastic porous structure with packing bacteria inside graphene oxide (GO) sheets. A variety of chemical elemental analysis demonstrated that GO was reduced by the bacteria to reduced graphene oxide (rGO) alongside the gelation process. Further, methylene blue (MB), methyl orange (MO) and Congo red (CR) were used to alter GO’s surface charge owing to the electrostatic and π-π stacking effect. Accordingly, the surface electronic properties of the AS-BGA prepared by the functionalized GO exhibited a consistent change, i.e., electronegativity was enhanced by anionic MO and CR, meanwhile neutralized by cationic MB. Thereby, the adsorption capability of the AS-BGA with the optimal functionalization conditions through MO was increased 1.24-fold higher than the unfunctionalized one. Furthermore, the raw material and energy consumptions related to the synthesis of AS-BGA was analyzed by the life cycle assessment method. This study points to the reuse of the excess bacteria and organic compounds to derive adsorbents for sustainable wastewater treatment, by exploiting graphene materials in an exquisite way.