Glycerol-based H3PO4-activated carbon as a versatile adsorbent for removal of pollutants from wastewater: A novel synthesis protocol

Aiming at revaluing oversupplied glycerol as a result of biodiesel production, this approach introduces an authentic synthesis protocol for producing glycerol-based activated carbons holding suitable textural/surface properties for an efficient application in the methylene blue and Pb2+ adsorption processes. Typically, glycerol and phosphoric acid were submitted to a polycondensation reaction in order to insert manipulable fractions of C-O-P bridge bonds throughout the whole polymer chain in the form of mono, di and triesters before the traditional carbonization and activation steps. The physicochemical and surface chemistry properties of the ACPs were characterized by means of N2 adsorption/desorption isotherms, thermal analysis, elemental analysis, surface functional groups titration and pHpzc, X-rays diffraction, FTIR spectroscopy and scanning electron microscopy. Indeed, such strategy gave rise to a set of micro/mesoporous activated carbons (ACP) with surface area of up to 1056 m2/g and total acidity, constituted by thermally insensitive carbonyls-/phosphorus-containing functional groups, ranging from 1.63 to 2.32 mmol g−1. Adsorptive features of the obtained series of activated carbons were validated in the methylene blue and Pb2+ removal processes reaching out adsorption capacity of up to 543.3 and 26.5 mg g−1 at 298 K, respectively. Additionally, after confronting experimental data with several isothermal and kinetic theoretical models, it was demonstrated that the adsorption mechanism of both pollutants onto the ACPs is driven by chemisorption up to the monolayer coverage. The thermodynamic study indicated spontaneity of the adsorption processes and suggested a relation between the textural properties and surface functionalities of the ACPs with the enthalpic nature of the adsorbent-adsorbate interactions.