Title: photoadsorption fraction
Long Title: IUPAC Gold Book - photoadsorption fraction
DOI: 10.1351/goldbook.14037
Status: current

Definition
Number of entities (atoms, molecules or ions) photoadsorbed per regular surface site at a uniformly irradiated surface of an adsorbent.

Notes
1) Mathematical expression: \(\theta_{\rm{ph}} = N/N^{\rm{ss}}\) with \(N\) the number of entities photoadsorbed and \(N^{\rm{ss}}\) the number of surface sites (mainly regular surface sites, i.e., regular lattice ions or atoms; typically, \(N^{\rm{ss}}\) ca. \(\pu{E15 cm-2}\)). \(\theta_{\rm{ph}}\) is a quantity of dimension one (it is a fractional number).
2) \(\theta_{\rm{ph}}\) has been called photoadsorption number; fraction is preferred. It should not be called capacity, since the term capacity should be reserved for the maximal adsorption number.
3) The photoadsorption fraction, \(\theta_{\rm{ph}}\), is smaller than the photoadsorption capacity, \(\theta_{\rm{max}}\) (i.e., \(\theta_{\rm{ph}} \lt \theta_{\rm{max}}\)).

Related Terms
- photoadsorbed: https://goldbook.iupac.org//terms/view/14032
- photoadsorption area number: https://goldbook.iupac.org//terms/view/14033
- photoadsorption capacity: https://goldbook.iupac.org//terms/view/14034
- regular surface site: https://goldbook.iupac.org//terms/view/14083

Source
- PAC, 2011, 83, 931. 'Glossary of terms used in photocatalysis and radiation catalysis (IUPAC Recommendations 2011)' on page 965 (https://doi.org/10.1351/PAC-REC-09-09-36)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/14037/html
- json: https://goldbook.iupac.org/terms/view/14037/json
- xml: https://goldbook.iupac.org/terms/view/14037/xml

Citation: Citation: 'photoadsorption fraction' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.14037
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Accessed: 2026-06-29T19:17:54+00:00