Comparative studies of physicochemical and adsorptive properties of biochar materials from biomass using different zinc salts as activating agents

The challenge nowadays still to find an economical way for the production of biochar materials with specific characteristics, rich in nitrogen, sulfur, or other surface functional groups for a specific purpose, as well as providing a clear understanding of the mechanisms occurring in the process preparation, when it is used different chemical agents, and, produce highly porous materials. This study displays the influence of different zinc salts (Cl-, SO42-, PO43- and NO3-) at the different quantities on the physical-chemical and adsorptive properties of the biochar materials produced via conventional heating. The biochar materials (ZnACs) are characterized by FTIR spectroscopy, DRX, X-Ray Fluorescence, nitrogen-adsorption/desorption analyses, FESEM-EDS, TGA/DTG, CHNS elemental analysis, pHzpc, hydrophobic properties, total basicity, and acidity groups. The Adsorption studies of emerging organic contaminants, pharmaceutical molecules, and anionic and cationic dyes on the ZnACs carbons were carried out at the following conditions: C0 = 300.0 mg L−1, T = 25 °C, adsorbent mass = 30.0 mg and t = 20 h. It appeared that although all the salts have zinc and even in the same molar amounts, the preparation process led to biochar materials with different textural characteristics and surface functional groups. The biochars also presented good adsorption capacities for removing pharmaceuticals, EOCs, and dyes from aqueous media. Notwithstanding, the biochar prepared with Zn(NO3)2 and ZnCl2 show the best textural characteristics and adsorption performance for all tested classes of adsorbates. The adsorbed amount (qe) is > 200 mg g−1 for ZnNAC2 and ZnCAC1. [Display omitted] •Different zinc salts were employed as activating agents in the preparation of the biochar materials.•The smaller the number of valence electrons in the counterions is, the greater is the SBET and Vp.•High surface area for ZnCl2 (1220 m2 g−1) and Zn(NO3)2 (323 m2 g−1) was obtained.•The preparation process leads to biochars with different textural characteristics and functional groups.•Zn(NO3)2 and ZnCl2 based biochars show good adsorption performance and Qe > 200 mg g−1 for ZnNAC2 and ZnCAC1.