除尘 is a verb-object compound meaning 'to remove dust' or 'to dust'. It is a separable verb (离合词): the object 尘 can move away from 除 when you add a measure word, a verb aspect marker, or a complement in between. For example, 除了尘 means 'dusted' (completed action), and 除一下尘 means 'dust quickly'. In informal speech you might hear it split, but in technical or formal contexts it's often kept together (e.g., 除尘器 'dust remover').