Low-cost adsorbents prepared from brewer's spent grain for pollutants removal

Biosorbents have been an alternative to activated carbon, especially agro-industrial wastes, as they are abundant in the environment and have low cost; however, raw lignocellulosic wastes have low specific surface area. In this sense, this work proposes the synthesis of low-cost adsorbents from brewery spent grain (BSG) to remove different pollutants from the aqueous matrix. Thermogravimetric (TGA) analyses were performed to determine the temperature of the thermal treatments. The adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), specific surface area, pore volume, scanning electron microscopy (SEM), and X-ray diffractometry (XDR). The point of zero charge (pHPZC) was also determined to know the adsorbents' surface charge distribution. The adsorption assays were carried out to individual solutions of methylene blue, reactive red 120, Cr6+, caffeine, phosphate, and ammonium, in a Wagner shaker, at 30 rpm for 1 h. The FTIR spectra showed stretching and deformation bands between 3323.79 and 898 cm(-1) that can be attributed to different functional groups present on the surface, related to cellulose, lignin, and hemicellulose. The thermal and acid treatments were able to cause morphological changes and improve the raw BSG structural characteristics, by increasing (above 100%) the pore volume and specific surface area. The pHPZC ranged between 5.58 and 7.89 with values approximately neutral, which indicate that the BSG has an amphoteric character. Finally, the adsorption performance varied from 7.63 to 99.37%, according to pollutant type, which demonstrates that the raw and functionalized BSG can be potential biosorbents.