Engineered biochar via microwave CO and steam pyrolysis to treat carcinogenic Congo red dye.

We developed an innovative single-step pyrolysis approach that combines microwave heating and activation by CO or steam to transform orange peel waste (OPW) into microwave activated biochar (MAB). This involves carbonization and activation simultaneously under an inert environment. Using CO demonstrates dual functions in this approach, acting as purging gas to provide an inert environment for pyrolysis while activating highly porous MAB. This approach demonstrates rapid heating rate (15-120 °C/min), higher temperature (> 800 °C) and shorter process time (15 min) compared to conventional method using furnace (> 1 h). The MAB shows higher mass yield (31-44 wt %), high content of fixed carbon (58.6-61.2 wt %), Brunauer Emmett Teller (BET) surface area (158.5-305.1 m/g), low ratio of H/C (0.3) and O/C (0.2). Activation with CO produces more micropores than using steam that generates more mesopores. Steam-activated MAB records a higher adsorption efficiency (136 mg/g) compared to CO activation (91 mg/g), achieving 89-93 % removal of Congo Red dye. The microwave pyrolysis coupled with steam or CO activation thereby represents a promising approach to transform fruit-peel waste to microwave-activated biochar that remove hazardous dye.