Air Purifier and Dehumidifier look similar but the uses and specification are different. You can research about differences between both products.
Air Purifier and Dehumidifier both can reduce the allergens, both are helpful for those who suffer from asthma and allergens problems. An air purifier can remove dust and many allergens from air & clean the air of a particular area. While dehumidifier can remove (humidity) moisture from the air,
An air purifier has an inbuilt filter. Which removes many particles like dust, smoke, etc from the air. An air purifier is helpful to stop mold growth, but it cannot stop excess moisture in humidity area. An air purifier can clear the air but it cannot stop returning of mold.
The Portable dehumidifier can control excess moisture or humidity from your room, bedroom, home, office, storage room, basement, etc. Excess moisture can grow mold bacteria. A dehumidifier cannot clean the air but it can able to maintain a clean environment. You can take benefit of both products if you are suffering from air quality problems or bad smell.
Various types of Dehumidifiers available in the market like portable, desiccant, etc. all are different from each other but all are helpful to reduce the humidity level from an air.
To get a better result from air purification you have to change its filter every six months. If there are plates instead of filter, then they need to be cleaned in every week by removing the plates from the unit. While to get a better result from a dehumidifier you have to clean the coils, filter, etc parts every few months.
Peoples who suffer from asthma or any type of allergies problems, an air purifier can help those peoples by cleaning the air in which they are breathing. While a dehumidifier is beneficial to remove excess humidity from air & stop the growth of mold and dust.
You can use either both or one of them to get better air quality & for controlling humidity in a particular area.