Trends in ion exchange: Analysis of the literature

Ion exchange is an elegant concept whose simplicity has allowed a wide range of applications in separations (e.g., water treatment, chromatography, radiochemistry, food processing), catalysis and synthesis. The objective of this Perspective is to map its origin and present status, then propose a trajectory into the future. This is addressed with data mined from the open literature as reported in the Web of Science Core Collection (Clarivate Analytics) via a search of the keyword "ion exchange" for the period 1900-1960, then narrowed to 1941-1960, followed by subsequent 20-year periods to the present day. Data are sorted into the top ten WoS Categories, Research Areas, Publication Titles and Countries, then further defined with additional keywords. Interest in ion exchange was found to be constant across the vicennial periods as the number of references kept pace with growth in the chemical (open) literature. The period to 1960 had 1213 references with chemistry the dominant area (60.9%) and engineering at only 4.5% of the papers; resins were the dominant material with membranes a distant second. The period 1961-1980 had 5175 references with chemistry retaining its top ranking but engineering significantly increasing; resins and membranes were the primary materials while separations dominated and catalysis barely registered. There were 21,901 references in 1981-2000 with environmental science appearing as a research area for the first time; resins ended the century as they began - the primary material - but by a small margin over membranes. The 21st century (2001-2020) began with 52,187 references, chemistry held steady compared to the preceding period while engineering and materials science increased significantly and environmental science doubled its percentage, joined by water resources; membranes continued their upward trend, surpassing resins. Output from China increased to outperform the USA. In the last three years of that period, environmental science made a stronger showing and energy fuels replaced biotechnology. In comparing the vicennial periods, the rise of engineering, materials science and ecology combined with water was impressive. In comparing Research Areas in the initial period with those from the latest, it is seen that chemistry fell from 61% to 41% while engineering increased from 4% to 25%. Applications were more likely to involve membranes. Separations remained steady from the initial to the current period while catalysis moved equal to them, Examining the most cited papers in the latest period shows an emphasis on metal-organic frameworks, tailored materials, membranes for energy and environmental applications, and to an array of applications in environmental remediation. Ion exchange is applied as a preparative technique in, for example, batteries, photocatalysts, electrocatalysts, supercapacitors, and perovskite nanocrystals. Ion exchange is thus poised to continue well into the 21st century. It has flourished by its ability to adapt. As the analysis of the literature shows, it will continue to flourish.