Green Synthesis of Iron Nanoparticle/Clay Composites and Their Effectiveness in Orange II Dye Removal Efficiency

This paper presents a study on orange II sodium salt (OII) degradation based on iron nanoparticles supported by kaolinite clays. The effects of nanoscale iron and initial dye concentration, as well as hydrogen peroxide dosage in a Fenton process, on the degradation of OII were studied. These nanoparticles were synthesized by green methods using coffee bean extract as a natural antioxidant for this process. Aqueous iron chloride was mixed with coffee extract, which is rich in antioxidants, and these antioxidants are responsible for the reduction of metal compounds into nanoparticles. The composite iron nanoparticle-kaolinite composite was synthesized from an aqueous FeCl₃ and kaolinite solution with the added coffee bean extract. The results showed that OII removal efficiency increased with the amount of iron nanoparticles (n-Fe) alone and with the amount iron-supported-kaolinite composite. By increasing the amount of composite, the adsorptive surface area increases as well as the number of active sites, which determine the higher removal efficiency. Regarding H₂O₂ dosage, dye removal was more efficient at lower quantities: 62% removal efficiency with addition of 10 mL H₂O₂, while for the test conducted with 20 mL H₂O₂, removal efficiency was 47%. A possible reason for this behavior can be the n-Fe/ H₂O₂ ratio, which influences the production of degradation products and hinders the degradation. HIGHLIGHTS: • Green synthesized metallic iron nanoparticles (n-Fe) using coffee bean extract as a natural oxidant were used for the removal of Orange II • In order to improve the degradation process, a clay-nanoscale iron composite was used, as well as Fenton oxidation using added H₂O₂. As a support material for the composite, kaolinite was used. The results showed that both reduction and adsorption processes are involved in the dye removal process. Applying Langmuir and Freundlich isothermal models shows monolayer coverage • By comparing the efficiency of the composite alone with the efficiency of the composite with the Fenton process, better results were obtained for the second case which shows the importance of the H₂O₂/Fe system in the degradation process. Also, we may state that the best results were obtained by using n-Fe only • Since the amount of n-Fe present in the composite is low (0.01 g), further experiments should be held concerning the ratios between n-Fe and clay in the composite. Experiments using wastewater containing dyes from a real industrial process should also be done as well, to confirm the activity of this material containing nanoscale iron made using green synthesis in a real wastewater environment, with all the associated ions and compounds.