**1. Introduction**

Lignin has been studied by different researchers over the years; the first output was published in 1908, and to date, a total of 74,191 documents mentioning "lignin" have been published, according to the Web of Science database (WOS). **Figure 1** presents a treemap with the published documents distributed by the WOS categories (from 1908 to 2023): Biotechnology Applied Microbiology (9440), Energy fuels (9362), Materials Science Paper Wood (9256), Chemistry Multidisciplinary (8935), Chemical Engineering (8564), to mention just a few.

A search for the word "lignin-first" revealed a smaller number of documents, totaling 127. But what was quite impressive was the date of the first document, in 1997 (**Figure 2**). The main articles were published in the last 6 years, reaching a total of 122. This fact reveals the increasing importance of the "lignin-first" approach within the research community.

#### **Figure 1.**

*TreeMap chart adapted from WOS searching results using the word "lignin" (www.webofscience.com; accessed on September 30, 2022).*

**Figure 2.**

*The number of publications that mention the word "lignin-first" and their citations over the years. Adapted from WOS (www.webofscience.com; accessed on September 30, 2022).*

The topic "lignin nanoparticles" is also an increasing one (**Figure 3**), and the search provided a total of 373 documents during the period from 2008 to 2022 (September). The most highly cited papers number 10, with 332 articles and 32 review papers recorded. The distribution between the WOS categories was as follows: Chemistry Multidisciplinary (123), Polymer Science (81), Materials Science Multidisciplinary (59), and Biochemistry Molecular Biology (51). Although the year 2022 has not ended, it is possible to see the growing tendency for the number of publications and citations of this topic (**Figure 3**).

According to these results, it is clear that lignin is still an exciting research topic. To reinforce this, at the moment, a European Cooperation in Science & Technology is being developed within this theme, called "*LignoCost - Pan-European Network on the Sustainable Valorisation of Lignin*" (COST Action CA17128, https://lignocost.eu/), to establish a network between different researchers having a focus on lignin valorization and its sustainable industrial application. One of the Working Groups is devoted to making a Wikilignin database where relevant works are being compiled.

*Lignin as Feedstock for Nanoparticles Production DOI: http://dx.doi.org/10.5772/intechopen.109267*

**Figure 3.**

*The number of publications that mention "lignin nanoparticles" and their citations over time. Adapted from WOS. (www.webofscience.com; accessed on September 30, 2022).*
