Proposal and application of a novel extraction and purification technology for juglone from Juglans mandshurica waste branches: Reverse micellar microemulsion combined with magnetic solid phase extraction

A reverse micellar microemulsion combined with magnetic solid phase extraction (RMM-MSPE) technology was developed for the extraction and purification of juglone from Juglans mandshurica. Reverse micellar microemulsion (RMM) (Tween 80: n-propanol: n-hexane: 0.05 mol/L KCl aqueous solution = 27:13.5:4.5:55; w/w/w/w) was used to extract juglone based on microwave. The optimum conditions were a pH of 5.6, a liquid-solid ratio of 20:1 (mL/g), temperature of 40 °C, time of 63 s, and power of 400 W. Graphene oxide/nano diamonds/ Fe3O4 (GO/ND/Fe3O4) was prepared as adsorbent and applied to purify juglone by magnetic solid-phase extraction (MSPE). The optimum adsorption conditions were time of 14 h, solid to liquid ratio of 30 mg/mL, pH of 5.5 and shaker speed of 200 r/min. Anhydrous methanol provided the best desorption of juglone and the optimum conditions were a desorption time of 16 h, pH of 8, and the solid-liquid ratio of 40 mg/mL. The purity of juglone was 69.08% and the recovery yield was 78.67%. RMM and GO/ND/Fe3O4 could be reused three times and eight times after the first use, respectively. The proposed RMM-MSPE is a green and efficient alternative method for extraction and purification of juglone.