Green synthesis of metal nanoparticles and application of nanoadditives in diesel fuel: bibliometric analysis

. The problem of obtaining metal nanoparticles considering environmental risks in connection with the use of synthesis products in mixtures of new types of diesel fuel has been studied. An analysis of existing research on these topics was carried out. Based on the data sets obtained using the Dimensions and OpenAlex services, the characteristics of the studies were determined. To analyze the problem of green synthesis of nanoparticles, a dataset of 6,062 journal articles published from 2001 to October 2023 was used. The use of nanoparticles as diesel fuel components was investigated using a dataset of 540 journal articles published from 2005 to October 2023. The leading countries and organizations by the number of publications and citations have been identified. Based on the analysis of co-authorship, the issue of international cooperation is considered. The most significant publications were determined by the number of citations. Using methods of visual analysis of data on research keywords, their trends and prospects were determined. In addition, an assessment was made of the development of the problem of using “green” methods for obtaining nanoparticles used as components of diesel fuel.


Introduction
The problems of obtaining and using nanostructured materials have been the focus of scientific attention for several decades.The fundamental science of nanomaterials is constantly updated with new information.However, the focus of research on these problems is gradually changing.Among the studied aspects of obtaining nanomaterials, their environmental friendliness comes to the fore [1].In addition, the scope of application of nanostructured materials is expanding.In addition to the already traditional areas (structural materials, coatings, pharmaceuticals, etc.), narrower ones are also emerging.These areas include the use of nanoparticles as additives for new types of diesel fuel, increasing engine efficiency, as well as reducing harmful effects on the environment [2].
Bibliometric analysis has recently been increasingly used to determine the characteristics of future scientific research [3].With the advent of accessible electronic databases of scientific publications and new tools (neural networks, machine analysis, etc.) for processing data from such databases, the capabilities of the bibliometric method have expanded.
In this article, bibliometric analysis is used to determine the characteristics, trends and prospects of research on the green synthesis of metal nanoparticles, as well as new types of diesel fuels containing nanoparticles.

Materials and methods
To search and obtain bibliographic data, the services "Dimensions" (by Digital Science, UK) and "OpenAlex" (by OurResearch) were used [4].The search was carried out in Dimensions using the keywords "metal nanoparticles" and "green synthesis" in the "Title" and "Abstract" fields.Search results were limited to journal articles.
The resulting data was exported in CSV format using Dimensions.For subsequent analysis using MS Excel (statistical analysis) and VOSviewer (visual analysis), Dimensions data was supplemented with OpenAlex data.
An analysis of the problem of using nanoparticles as additives for diesel fuel was carried out using the method described above.The keywords used were "nanoparticles", "additive", "diesel", "engine", as well as "green synthesis".
The number of publications and the number of citations were assessed in relation to the characteristics of publications (geography, administrative affiliation, source, year).
Relationships and occurrence of keywords were determined using VOSviewer [5].

Green synthesis of nanoparticles
The resulting data set consisted of bibliographic descriptions of 6,062 journal articles, covering the period from 2001 to October 2023.Among the countries, the leader in the number of publications is India (1,914), followed by China (965) and Iran (524).The largest number of publications was made by authors from King Saud University (Saudi Arabia, 214 publications), the Chinese Academy of Sciences (98) and the Vellore Institute of Technology (India, 88 publications).
Among the sources in terms of the number of publications, the leaders are the Journal of Photochemistry and Photobiology B Biology (176), Molecules (150) and IET Nanobiotechnology (110).
Based on the geographical distribution of publications, it was found that the most active international research collaboration was in India (joint publications with 67 countries), Saudi Arabia (57 countries) and China (55 countries).
The total number of citations of all publications was 275,217 (an average of 45 citations per article).
The most significant publications in terms of the number of citations should be noted.The first of these is a review article on the green synthesis of silver nanoparticles (cited 2963 times) [6].The second article addresses the problem of obtaining metal nanoparticles using plants (cited 2,418 times) [7].The third article presents a simple method for producing gold nanocrystals using bovine serum albumin (cited 2,238 times) [8].
The most cited countries were India (cited 92,294 times), China (41,194) and the USA (26,928).As well as the number of publications, authors from King Saudi University (cited 7,917 times), the Chinese Academy of Sciences (5,894) and the Vellore Institute of Technology (5,857) are also leading in terms of citations.The most significant journals from the point of view of citation were: Journal of Photochemistry and Photobiology B Biology (cited 13,951 times), Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy (13,433) and Colloids and Surfaces B Biointerfaces (9,458).
As a result of analyzing the number of publications (Fig. 1) and citations (Fig. 2) by year, we can conclude that the increasing popularity of this research topic began approximately after 2010.3,780 keywords were found in 6,062 articles, of which 1,059 appeared more than 5 times.The most frequently used keywords were "materials science" (5,701), "chemistry" (5,608) and "nanotechnology" (5,511).Among the methods of using nanoparticles, the first keyword was "catalysis" (10th place among all keywords, 1,899 mentions).In 11th place was the keyword "silver nanoparticles" (1,882), which shows the popularity of this type of nanoparticles in research.The most mentioned research method was "fourier transform infrared spectroscopy", which is associated with the need to determine the composition and mechanism of action of the components of green synthesis.
The general map of occurrence and connection of keywords is shown in Fig. 3.The division into key clusters-topics is clearly visible (chemistry and materials science -red, ecology -yellow, biotechnology -blue, medicine -green).

Nanoparticles as diesel fuel components
The Dimensions search identified 540 articles published between 2005 and October 2023.
66% of the studies were done in India (265), Malaysia (48) and Turkey (44).Among the organizations in terms of the number of publications, the Indian Sathyabama Institute of Science and Technology (28 publications), Saveetha University (24) and Vel Tech University (23) were leaders.The largest number of articles were published in Materials Today Proceedings (64), Fuel (49), and Energy Sources Part A Recovery Utilization and Environmental Effects (26).
The total number of citations to articles on the topic of using nanostructured additives for diesel fuel was 17,182 (an average of 32 citations per article).
The most significant publications in terms of the number of citations were devoted to a review of the use of nanoadditives in the creation of new diesel and biodiesel fuels (cited 334 times) [9], a discussion of the environmental risks of using cerium nanoparticles and cerium oxide as fuel components (cited 297 times) [10], and also the efficiency of using aluminum nanoparticles in diesel and biodiesel fuel (cited 268 times) [11].
In terms of the number of citations, studies from India (8,220), Malaysia (2,263) and Iran (1,384) were in the lead.The most cited organizations were Anna University, Chennai (India, 1,427 citations), University of Malaya (Malaysia, 1420) and King Khaldi University (Saudi Arabia, 1,039).
The graphs of the number of publications (Fig. 4) and the number of citations (Fig. 5) by year show an increasing demand for research on the problem under discussion since approximately 2017.
A total of 481 keywords were identified across 540 articles.139 keywords appeared more than 5 times.The most common keywords found in the articles were "engineering" (531), "chemistry" (506) and "diesel fuel" (504).
The results of the analysis of connections and occurrence of keywords in articles are shown in Fig. 6.The map of occurrence and connections of keywords shows a close connection between nanoparticles and increasing the environmental friendliness and efficiency of using new types of diesel fuel.There is no obvious separation of clusters, as was the case when analyzing publications on green synthesis of nanoparticles.It is assumed that this is due to the rather narrow boundaries of the topic.

Green synthesis of nanoparticles used in diesel fuel
A search using Dimensions revealed single publications devoted to the problem of green methods for obtaining nanoparticles for use as additives for diesel fuel.
It is assumed that this is due to the lack of development of the problem of nanoadditives.At this stage of research, scientists are searching for methods to improve the characteristics of diesel fuel without taking into account the environmental risks of obtaining individual components.
The lack of development of the problem of nanoadditives can be seen in the graphs of the number of publications and citations associated with it (Fig. 4, 5).It is clearly seen that the problem has been actively studied only in the last ~5 years.
It can be assumed that the concentration of efforts on researching green methods for obtaining nanoadditives will begin in the next decade, if the problem of environmental protection does not lose its relevance.

Conclusion
The article examined data obtained using Dimensions and OpenAlex on publications related to the green synthesis of nanoparticles and the use of nanoadditives in the creation of new types of diesel fuel.
A total of 6,062 journal articles on the first topic and 540 articles on the second were reviewed.
Trends and prospects for research in these areas were identified.The problem of using green methods in nanoadditives obtaining is separately considered.
It has been established that both topics are developing.At the same time, the active development of the topic of green synthesis of nanoparticles began around 2010, and nanoadditives -around 2017.
It is noted that in the future it is possible to combine these topics to study the possibilities of obtaining nanoadditives for diesel fuel using green methods.

Fig. 1 .
Fig. 1.Number of publications on green synthesis of nanoparticles by year.

Fig. 2 .
Fig. 2. Number of citations of publications on green synthesis of nanoparticles by year.

Fig. 4 .
Fig. 4. Number of publications related to the use of nanoparticles as diesel fuel components, by year.

Fig. 5 .
Fig. 5. Number of citations of publications related to the use of nanoparticles as diesel fuel components, by year.

Fig. 6 .
Fig. 6.Map of the occurrence of keywords on the topic of using nanoparticles in the creation of new types of diesel fuel.