Adsorb vs. Absorb: What’s the Difference?

Adsorb and absorb sound similar, but they have different meanings. Luckily, you’re not likely to run into the word “adsorb” in everyday conversation. Adsorb, and related words like adsorbate, adsorption, and adsorbent, have narrow applications. You’ll typically see them used in a scientific context, especially in relation to filtration and cooling. 

On the other hand, the word absorb is much more common. An advertisement might boast about absorbent paper towels. Someone can absorb shocking news. A business can even absorb costs associated with a project. Because the word “absorb” has so many figurative uses, it’s much more common to see it in everyday speech. 

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Etymology

Since “adsorb” and “absorb” sound so similar, you may wonder whether they come from the same root word.  

Absorb comes from the Proto-Indo-European root srebh-, meaning “to suck, absorb.” Combined with the prefix ab-, the Latin word absorbere means “to swallow up, devour.” By the 1200’s, the Old French language introduced absorbir and assorbir. The English cognate dates from the early 1400’s. The figurative use of absorb, as in ” to absorb one’s attention,” dates from 1763.

German scientist Heinrich Kayser first combined the prefix ad- with the Latin sorbere in 1881, influenced by the existing verb “to absorb.” According to the Online Etymology Dictionary, the word “adsorb” was first used in English a year later. 

Definitions

Something can be absorbed in both a scientific sense and a figurative sense. 

Merriam-Webster defines the word “absorb” as a verb with the following meanings:

  • to take in (something, such as water) in a natural or gradual way
  • to take in (knowledge, attitudes, etc.)
  • use up, consume
  • to take in and make part of an existent whole
  • to engage or engross wholly
  • to receive without recoil or echo
  • endure, sustain 
  • assume, bear
  • to transform (radiant energy) into a different form especially with a resulting rise in temperature

Adsorb refers to the physical process of adsorption, “the adhesion in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the surfaces of solid bodies or liquids with which they are in contact.” In layman’s terms, adsorption describes a surface phenomenon wherein gas or liquid forms a film on a surface of another liquid or solid material.

Here are a few commonplace examples of adsorption:

  • Silica gel or activated alumina that removes moisture from clothing or electronics
  • Activated charcoal used in water purification
  • Water cooling processes in air conditioning or cold storage

Adsorption attracts and collects a substance on the surface of the adsorbent. It can do this in two ways: chemisorption (resulting from chemical reactions involving covalent bonds) or physisorption (resulting from electrostatic attractions called weak Van der Waals forces).

Encyclopedia Britannica describes the difference between adsorption and absorption this way:

“Adsorption refers to the collecting of molecules by the external surface or internal surface (walls of capillaries or crevices) of solids or by the surface of liquids. Absorption, with which it is often confused, refers to processes in which a substance penetrates into the actual interior of crystals, of blocks of amorphous solids, or of liquids.” 

With adsorption, the molecules collect on the surface through chemical bonds or forces of attraction; with absorption, the molecules get into the interior, beyond the surface. 

Related Words

  • The process of absorption is endothermic, meaning that it absorbs heat. The process of adsorption is exothermic, meaning that it releases heat.
  • An absorbate describes a material being absorbed. 
  • An adsorbate describes a material being adsorbed. 
  • Desorption refers to the release of an adsorbed or absorbed material. 

Synonyms

According to Thesaurus.com, synonyms for absorb include:

  • consume
  • ingest
  • swallow
  • take in
  • assimilate
  • follow
  • get
  • incorporate
  • learn
  • understand
  • employ
  • involve

Synonym.com lists only two synonyms for adsorb:

  • take up 
  • sorb

The Words in Context

“First, the iron powder catalyst helps to adsorb and dissociate nitrogen molecules into atomic nitrogen.”
Chemistry World, “Violent Mechanochemical Impacts Replace…”

“Butyrate leads to an increase of vitamin D. So, the more you have, the more D you absorb.”
Runner’s World, “Better Gut Health Boosts Your Body’s Ability…”

“The team used a process called electrospinning to convert a solution of the polymer into robust mats, which incorporated an extensive network of pores within the polymer’s fibrous structure, creating a vast surface area of 565 square meters per gram of material for adsorbing oil.”
Phys.org, “High-Capacity Oil-Adsorbing Mats Could Be Deployed…”

 “‘Results from our study released today show there is evidence that some sunscreen active ingredients may be absorbed. However, the fact that an ingredient is absorbed through the skin and into the body does not mean the ingredient is unsafe,'” said Dr. Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research, in a recent press release.
ABC News, “Sunscreen Can Be Absorbed in the Bloodstream…”

“Called absorption chillers, the devices use heat from the Sun to boil the refrigerant out of a solution — typically water from a salt solution, or ammonia gas from water.”
Nature, “How Heat From the Sun Can Keep Us All Cool”

“Ferrous sulfate is a common form of supplemental iron with high solubility, meaning that it releases iron ions faster, making it easier to absorb.”
Healthline, “The 10 Best Iron Supplements of 2020”

“Carbon dioxide, the main heat-trapping gas, is produced by animals, including humans, and is absorbed by plants and the oceans. But burning of coal, oil and natural gas since the late 19th century far outstrips what plants and the oceans can remove from the air.”
ABC News, “The Real Math Behind ‘Net Zero…'”

“Most are absorbed by simple diffusion with the molecule passing through the cells of the intestinal epithelium one by one…”
Forbes, “How Do Our Stomachs Absorb Pills?”

Sources: 

  1. www.etymonline.com/word/adsorb
  2. www.etymonline.com/word/absorb
  3. https://www.merriam-webster.com/dictionary/adsorb
  4. https://www.merriam-webster.com/dictionary/absorb
  5. https://www.thoughtco.com/definition-of-adsorption-605820
  6. https://www.forbes.com/sites/quora/2017/03/09/how-do-our-stomachs-absorb-pills/?sh=4e230778606e
  7. https://abcnews.go.com/Technology/wireStory/explainer-real-math-net-carbon-emissions-74678982
  8. https://www.healthline.com/nutrition/best-iron-supplement#_noHeaderPrefixedContent
  9. https://www.nature.com/news/how-heat-from-the-sun-can-keep-us-all-cool-1.21390
  10. https://abcnews.go.com/Health/sunscreen-absorbed-bloodstream-testing-needed/story?id=68442221
  11. https://phys.org/news/2020-07-high-capacity-oil-adsorbing-mats-deployed-oil.html
  12. https://www.chemistryworld.com/news/mechanochemistry-makes-ammonia-under-mild-conditions/4012945.article
  13. https://www.runnersworld.com/news/a34894533/connection-between-vitamin-d-and-gut-health-study/