Adsorption Potential of Contaminants with Activated Carbon Monoliths from Dried Fruit Epicarp of Lecythis minor

Lecythis minor is a tree commonly known as Monkey pot tree. Its fruits are composed of urn-shaped epicarps, which are bulky ligneous capsules of slow degradation. Activated carbon monoliths were prepared from this fruit epicarp (bioresidue, the source of lignocellulosic matter) by chemical activation with ${\mathrm{H}}_3{\mathrm{PO}}_4$. The activation conditions were optimized using a central composite design, considering parameters of temperature, time, and chemical ratio as variables, and iodine and methylene blue number ($IN$ and MBN), along with yield ($Y$), as responses. The best conditions for activation were 532°C ($T$), 1.5 h ($t$), and 1.5-g ${\mathrm{H}}_3{\mathrm{PO}}_4/1\text{-}\mathrm{g}$ raw matter (chemical ratio, CR), with response values of 996 mg $\mathrm{I}/1\text{-}\mathrm{g}$ activated carbon (AC) ($IN$), 361-mg $\mathrm{MB}/1\text{-}\mathrm{g}$ AC (MBN), and 42% ($Y$). Likewise, the physicochemical/surface characterization of the activated carbon Lecythis minor (ACLM) allowed establishing that it developed micro- and mesopores ($V_{micro}=0.72{\mathrm{cm}}^3/\mathrm{g}$; $V_{meso}=0.87{\mathrm{cm}}^3/\mathrm{g}$), as well as ultra-microporosity, a BET surface area of $\mathrm{2,164}{\mathrm{m}}^2/\mathrm{g}$, and a total pore volume of $1.7{\mathrm{cm}}^3/\mathrm{g}$; also, the removal percentages of the emerging contaminants diclofenac and cephalexin in water were above 96%. It is concluded that fruit epicarp of L. minor is a natural-origin resource to produce AC monoliths, with satisfactory yield, desirable surface development, and high thermal stability, capable of adsorption and removal of pharmaceutical products, and other emergent contaminants from water bodies.

The development of activated carbons from agricultural residues, following processes that maximize their potential as adsorbents, has great potential for the removal of pollutants in water bodies. The above takes into account that in tropical countries there are residues that are totally wasted and that can be investigated by researchers following the methods listed in this work. The pollutants that can be adsorbed vary; for example, chemical residues and medicines that are excreted from the body or that are not properly disposed, dyes, or any other residue that, due to its dimensional characteristics, is complex to capture with other techniques for cleaning water bodies (e.g., mechanical means or filters). The solution to the removal of emerging pollutants is within everyone’s reach.