How does phosphoric acid interact with cherry stones? A discussion on overlooked aspects of chemical activation

The fabrication of activated carbon (AC) is widely carried out by the so-called chemical activation method, in which the biomass substratum is put in touch with an impregnating chemical agent prior to the carbonization stage. Even though this methodology is known for a long time, there are many features that are still poorly understood, particularly those regarding the details of the underlying mechanisms involved during the interaction of the activating agent with the precursor, eventually leading to the development of AC. Previous research conducted in the laboratories dealt with the use of cherry stones (CS) and phosphoric acid, toward ACs with tailored porous structures, finding out that the experimental variables of the impregnation stage were crucial for their eventual characteristics. Thus, the results obtained at that time deserved further discussion, with the aim at unraveling the true nature of those findings. With such purpose, the authors comment further on the CS and H3PO4 in non-conventional impregnation methodologies, performed in the previous works. Four series of H3PO4-impregnated products were prepared in a previous research, using a wide range of impregnation strategies, aiming at controlling the loading of H3PO4 on the lignocellulosic substratum. Herein, with the mass uptake as the main, it was possible to link the uptake with the chemical changes of H3PO4 in agreement with essential chemistry knowledge. Mass gain is strongly dependent on the impregnation method, and interesting insights arise on the basis of the mass changes of CS after impregnation.