Yes, you can put lemon juice in a diffuser. Lemon juice can provide a pleasant fragrance and can be used for aromatherapy. You can cut a lemon in half, squeeze the juice into a bowl, filter it to remove impurities and fiber, and add a few drops to the water in your diffuser. However, it is important to check for residue after every use, especially if you add lemon juice with all of its properties.