A survey on application of mesoporous materials in chemistry

aDepartment of Industrial Engineering, Iran University of Science and Technology, Tehran, Iran bDepartment of Chemistry, Iran University of Science and Technology, Tehran, Iran C H R O N I C L E A B S T R A C T Article history: Received January 5, 2019 Received in revised form February 20, 2019 Accepted February 20, 2019 Available online February 22, 2019 Mesoporous materials are substances whose pores maintain diameters between 2 and 50 nm, according to IUPAC nomenclature. This paper presents a comprehensive scientometrics on the existing trend on mesoporous materials in chemistry. The study uses Web of Science database as the primary source of value added articles and performs different methods for detecting highly cited articles, most active countries, etc. The search of articles using Web of Science was accomplished with two keywords “Mesoporous materials” and “Chemistry”. In Web of Science, there were about 800 articles related to these keywords over the period 1900-2019. Then the articles were arranged according to the citation order in non-increasing order, and among them, we found about 200 highly cited articles. According to our survey, green chemistry, water, heterogeneous catalysis and aqueous-solution build a structure on mesoporous materials. Moreover, conversion, guest molecules, triblock, oxidation, heterogeneous catalysts set the corner of other structure of the study. The survey also indicates that there were three clusters associated with mesoporous materials in chemistry. In the first cluster silica appears to be the most important word followed by molecular-sieves and MCM41. Organic-group is the most important word in the second cluster followed by hybrid materials. In cluster 3, nanoparticles appears to be the most important word followed by functionalization. In our study, absorption, nanoparticles and drug-delivery are detected as the emerging keywords and future studies could be concentrated on these subjects.


Introduction
Mesoporous materials are substances whose pores maintain diameters between 2 and 50 nm, according to IUPAC nomenclature. 1 According to IUPAC, microporous materials contain pores smaller than 2 nm in diameter, while macroporous materials are with pores bigger than 50 nm in diameter.Most mesoporous materials include different kinds of silica and alumina with similarly-sized mesopores.There are several evidences of mesoporous oxides of niobium, tantalum, titanium, zirconium, cerium and tin but the flagship of mesoporous materials is mesoporous carbon with direct implementation in energy storage facilities. 2 This paper presents a comprehensive scientometrics on the existing trend on mesoporous materials in chemistry.The study uses Web of Science database as the primary source of value added articles and performs different methods for detecting highly cited articles, most active countries, etc.

The bibliographic study
In this study, we have used Web of Science database as the primary source of gathering data and the collected information are used through Biblioshiny tool available in R-software package for processing the data.

The themes in reviewed articles
The search of articles on the Scopus site was accomplished with two keywords "Mesoporous materials" and "Chemistry".In Web of Science, there were about 750 articles related to these keywords.Then the articles were arranged according to the citation non-increasing order, and among them, we have reported about 200 highly cited articles.Table 1 demonstrates some of the most cited references associated with the application of mesoporous materials in chemistry.As we can observe from the results of Table 1, mesoporous materials, molecular-sieves and silica are three well-recognized keywords used in the literature.Fig. 1 shows the most important words used overtimes.Moreover, Fig. 1 demonstrates the trend and various words used in the literature.Fig. 2 presents the conceptual structure map of the proposed study.According to our survey, green chemistry, water, heterogeneous catalysis and aqueous-solution build a structure on mesoporous materials.Moreover, conversion, guest molecules, triblock, oxidation, heterogeneous catalysts set the corner of other structure of the study.

Country Scientific Production
According to Fig. 3, the distribution of scientific production by various countries and as we can observe, the largest scientific productions are associated with United States, China and Australia.

Corresponding author's country
Our survey demonstrates that researchers from the China have maintained the most contribution in this field followed by the researchers from the United States and Germany.Fig. 4 shows the details of our survey.Moreover, we see a good collaboration between most countries with other countries.

Collaboration network and Cluster classification
Fig. 6 shows the Author's Collaboration Network.As we can observe from the results of Table 2 and Fig. 7, there are three clusters associated with mesoporous materials in chemistry.In the first cluster, silica appears to be the most important word followed by molecular-sieves and MCM-41.Organic- group is the most important word in the second cluster followed by hybrid materials.In cluster 3, nanoparticles appears to be the most important word followed by functionalization.In terms of the average citation, papers published by researchers in Canada, Australia, and France have received the highest citations.Fig. 8 shows the results of the collaborations among various countries.As we can observe from the results of Fig. 8, there was a strong collaboration from the researchers in the United States from one side and other countries which was the highest to Canada, Australia and China, respectively.

Thematic map
Co-word analysis draws clusters of keywords considered as themes.][205][206][207][208][209] Thematic map is a very intuitive plot and we can analyze themes according to the quadrant in which they are placed:  Hence, the themes with the highest internal coherence and closest relationship to other themes appear in the first quadrant (the upper right part of the graph) and this includes complexes and mesoporous molecular-sieves and these two keywords are considered as motor keywords.In the second quarter, chemistry as a general word plays the basic role for scientific development.Themes in this quadrant are important for a research field but are not developed and they are considered as emerging areas of research.This group includes Absorption, Nanoparticles and Drug-delivery.This quadrant includes transversal and general, basic themes, which include conversion and thin-films.

Conclusion
This study has tried to provide a comprehensive view of the scientific papers between 1900 to the first month of 2019 on mesoporous materials in chemistry.This research has shown researchers from China, Germany, Spain, United Kingdom and Australia have contributed the most in this area.Moreover, green chemistry, water, heterogenous catalysis and aqueous-solution have built a structure on mesoporous materials.In addition, the themes with the highest internal coherence and closest relationship to other themes have included complexes and mesoporous molecular-sieves and these keywords were considered as motor keywords.Absorption, Nanoparticles and Drug-delivery were detected as the emerging keywords and future studies could be concentrated on these issues.

Fig. 1 .Fig. 2 .
Fig. 1.Demographic of the trend of different words used in literature

Fig. 4
Fig. 4 Corresponding author's country 2.4.The frequency distribution of sources In this research, most articles from the sources shown in Fig. 5 are from the Journal of Chemistry-A European Journal with 64 articles, followed by Angewandte Chemie-International Edition with 47 articles.

Fig. 8 .
Fig. 8. Country Collaboration map Fig. 9 demonstrates how many articles have been written by the authors with the highest number of articles during the time, and how many citations each one received.The size of each circle indicates the number of articles and the amount of boldness of the circles indicates the number of citations in that year.

Table 1
The most popular keywords used in studies associated with mesoporous materials

Table 2
Demographic of three clusters