Serial nanomaterial synthesis from Ilex paraguariensis biomass for efficient Cr6+ adsorption and detection

This study presents the use of Ilex paraguariensis, an agro-industrial waste, to obtain multiple nanomaterials through serial processes. The materials synthesized included organic-coated magnetite (Fe3O4@YM), Carbon dots (CD), SiO2 materials, and a magnetite-CD composite (Fe3O4@CD). The characterization of these materials showed that they have nanosphere-like geometries with mean diameters ranging from 4.5 nm to 19.7 nm. The versatility of these materials was demonstrated by using them to develop both Cr6+ adsorbents and sensors. CDs were used as Cr6+ sensors, while all Fe or Si-containing materials were used as Cr6+ adsorbents. CD showed a fluorescence-based method for Cr6+ quantification in the range 1.00–243.00 μM with a detection limit of 0.58 μM. Of all the adsorbents, Fe3O4@YM and Fe3O4@CD showed the highest number of adsorption sites at 161.29 and 312.50 mg Cr6+ g−1, which was attributed to the higher surface area and concentration of carboxylic and phenolic groups on the latter material. The economic feasibility of the materials was evaluated through the intensive enhancement price for the adsorption process (φ). It was found that the materials with the highest adsorption capacity are not necessarily the ones with the lowest required economic investment. Fe3O4@YM was shown to have higher economic feasibility considering both synthesis and adsorption processes with values of 8.4 and 5.8 mg Cr6+ USD−1. This approach demonstrates the potential of using agro-industrial residues for the green synthesis of multiple nanomaterials with different applications, useful for fully developing a remediation process.