Microemulsion as solvent for naphthoquinones extraction from walnut (Juglans mandshurica Maxim) green husk using high voltage electrical discharge

•An efficient method for obtaining naphthoquinones from walnut husk was developed.•High voltage electric discharge extraction with microemulsion was explored.•The effects of microemulsion formula and discharge conditions were investigated.•High voltage electric discharge with microemulsion shows favorable superiority.