Trends in Green Chemistry Research between 2012 and 2022: Current Trends and Research Agenda

Abstract

Traditional chemistry is undergoing a transition process towards a sustained paradigm shift under the principles of green chemistry. Green chemistry is emerging as a pillar of modern chemistry focused on sustainability. In this context, the aim of this study was to analyse green chemistry research and its contributions using quantity, quality, and structural indicators. For this purpose, data were retrieved from Scopus and Web of Science through a structured search equation for the study period, i.e., 2012 to 2022. These data were compiled and processed in Microsoft Excel version 2307, totalling 2450 records. VOSviewer software, version 1.6.18, was used to map the keyword network and for overlay and density visualisations. The results showed that green chemistry is constantly increasing in different fields of knowledge, with new studies in green solvents, eutectic solvents, and education for sustainable development. The number of publications peaked in 2019, slightly decreasing in subsequent years due to the novel coronavirus disease 2019 (COVID-19) pandemic. As visualised through VOSviewer, the keyword “sustainability” is connected to all clusters, and green synthesis, catalysis, sustainability, curriculum, and higher degrees are leading trends in green chemistry research. The study could benefit researchers and professionals interested in green chemistry and sustainability.

1. Introduction

Green chemistry is one of the major steps that humans have taken in their search for a point of balance between chemical processes and the environment in the production of goods and services with the lowest possible impact on ecosystems. From studies assessing how much high school and college students know about green chemistry [1,2,3,4,5] and about its connections and systems thinking in different contexts [6] to in-depth research using computational tools for the rational design of molecules [7] for industrial synthesis with relevant technological applications [8] aimed at improving and aligning conventional procedures with the principles of sustainability, green chemistry research proposes a reference framework for many chemists. These professionals must consider the 12 principles of green chemistry when developing designs, protocols, and methods, given the current warnings and predictions of unsustainability if we continue at this rate of destruction and depletion of resources on our planet [9,10]. Specifically, it focuses on the 12 principles: waste prevention, atomic economy, sustainable synthetic methods, reduction of derivatives, designs for degradation, benign chemical design, real-time analysis for pollution control, accident prevention, catalysis, benign solvents, renewable feedstock, and energy efficiency [9].

Currently, approximately 90% of chemical processes use catalysts to perform reactions with low activation energies and avoid the generation of by-products. However, their conventional use can have negative impacts on the environment due to the toxicity and residues of some tin-based [10] and negative organic [11] catalysts. For this reason, research efforts have shifted towards developing more environmentally friendly, safe, and biodegradable alternatives to reduce the use and manufacture of hazardous materials by minimising waste. Innovative studies have proposed using secondary metabolites and phytochemicals extracted from various plant species as corrosion inhibitors [12], shown the multifaceted potential applicability of hydrotalcite-type anionic clays with high thermal stability, flexible tunability, memory effects, biocompatibility, and easy biodegradation [13], demonstrated the effectiveness of antimony-doped tin catalysts in the decomposition of water contaminants [14], and highlighted laccases, also known as copper oxidases, as green catalysts for bioremediation [15].

Different fields of applied chemistry clearly show interest in developing green and sustainable chemistry. As a case in point, the pharmaceutical industry has been using a highly ecological approach [16] by applying holistic designs to the product life cycle [17]. For example, carbon–carbon bonds can be formed in a reaction of the aromatic nitro group of nitroimidazoles with carbon nucleophiles, yielding imidazole-based pyrimidine hybrids [18]. In addition, supercritical fluid technology and the use of solvents have proven more attractive in research on the efficacy of new drugs [19,20]. In the detergent industry, studies have provided compelling evidence of the suitability and sustainability of bio-base surfactants, especially those with carbohydrate head groups such as alkyl polyglucosides and sucrose esters, as alternatives to conventional petrochemical surfactants [21].

The food industry is researching new methods for protein recovery through electrolyte precipitation, which can replace traditional methods involving alkaline hydrolysis, organic solvents, and precipitation with organic salts, among others. Similarly, studies have evaluated the recovery of bioactive compounds from agro-industry-derived by-products [22]. On a large scale, these agro-industry by-products urgently require green innovation due to their low recovery yields and high environmental impacts, with some concerns about their toxicity [23]. Simultaneously, novel automated methods have been proposed for the analysis of pesticides in food [24]. To the same extent, the packaging industry is moving towards the development of biodegradable films for active packaging based on a mixture of cellulose acetate, polycaprolactone diol, and bio-based plasticisers by researching their profitability and biodegradability under specific conditions [25]. Flame retardants for bioplastics appear to hold promise as sustainable alternatives for many industrial applications [26]. The fashion and personal care industries are not immune to these challenges, showing their concern about their environmental impacts because the demand for products seems inexhaustible. These products require large amounts of natural and synthetic raw materials and chemicals for their treatment. Therefore, a recycling industry must be established for the recovery or conversion of waste materials into valuable products [27,28].

Trends in research show an increasing interest in CO₂ use and conversion into chemical products, albeit limited to a few industrial processes; their main strategic approach is focused on the production of alternative fuels to avoid dependence on fossil fuels [29]. Nevertheless, the oil industry is researching enhanced recovery and developing new deep eutectic solvents using complexes of polybasic acids and Lewis acids with coordinated solvents [30,31]. In synthesis processes, adherence to the principles of green chemistry is becoming more visible. Through novel syntheses, metal-organic structures with high surface areas and porosity for contaminant absorption are now obtained with a 50% reduction in negative environmental impacts thanks to safer procedures, solvents, and auxiliaries [32]. Similarly, polymer manufacturing is more environmentally conscious by consuming less and wasting less [33].

Nanotechnology and biotechnology also satisfactorily contribute to green chemistry through the synthesis of metallic nanoparticles for catalysis, nanoplasmonics, and fuel cells [34]. Research on blue-green-emitting fluorescent copper nanoclusters seeks easier analytical methods for myoglobin and L-thyroxine quantification. Inspired by hybridisation, green-cell-based biosynthesis methods have piqued interest in nanocell hybrids with applications in energy, the environment, and green catalysis [35,36]. Low-toxicity metallic nanoparticles are increasingly used in textile fibres as antibacterial control methods [37]. Nanomaterial synthesis methods use glass tubes designed for nuclear magnetic resonance analysis as reactors to reduce energy use, waste, and pollution [38]. In medicine, threads coated with zinc oxide nanoparticles have been successfully applied as surgical sutures [39]. In the fine chemicals and pharmaceutical industries, biocatalysis has been applied as the main green technology [40]. This increasingly evident transition to green and sustainable chemistry through digitisation enhances the flexibility and transparency of information flows throughout the life cycle of inputs and products [41].

In general, bibliometric and social network analyses have been widely used in the scientific literature in recent years to study trends and patterns. This can be observed in the work of Kahn [42], who conducted a structural analysis of scientific production in a country such as South Africa, and Urhan et al. [43], who explored the connections between climate change and marketing using bibliometrics. From a social perspective, trends and characteristics of research and development conducted on indigenous communities have been analysed [44]. From an environmental standpoint, the relationship between sustainability and Industry 4.0 has been addressed, demonstrating that sustainability is one of the pillars of smart factories [45].

Furthermore, it is worth noting that there are other literature review studies on green chemistry in the scientific literature, such as the one conducted by Sharma and Demir [46]. The identified trends in this study cover the period from 1999 to 2018. Therefore, this present study positions itself within this discussion by providing an update on trends in a fundamentally important research field in terms of sustainability. In this regard, leveraging the importance of bibliometric and social network analyses, this study aims to contribute to green chemistry research by identifying the most active areas of investigation, prominent research references, international scientific collaborations, and current thematic trends within this field of knowledge.

Considering the above, green chemistry pursues a paradigm shift from traditional to environmentally friendly chemical methods to maximise the efficiency of resources while minimising adverse impacts towards achieving sustainability. This approach is focused on promoting an environmentally aware society and fostering credibility and confidence in the use of sustainable materials, technologies, and procedures [47]. Thus, by examining advances in chemistry, the aim of this research is to perform a bibliometric analysis of trends in green chemistry research between 2012 and 2022 using quantity, quality, and structural indicators of green chemistry studies and their contributions. This research may serve as input for other studies on specific topics of interest in the field of green chemistry. To achieve the stated objective, the following research questions are proposed:

• RQ1: What are the years with the highest interest in Green Chemistry?
• RQ2: What type of growth is observed in the number of scientific articles on Green Chemistry?
• RQ3: Who are the main research references in Green Chemistry in terms of productivity and scientific impact?
• RQ4: What is the thematic evolution derived from the scientific production of Green Chemistry?
• RQ5: What are the main clusters of international scientific collaboration in research on Green Chemistry?
• RQ6: What are the main thematic clusters in Green Chemistry?
• RQ7: What are the emerging and growing keywords in the field of Green Chemistry research?

2. Methodology

To achieve the goals set above, the present investigation was designed as a quantitative study using secondary sources of information and a bibliometric analysis to analyse the scientific activity found in the literature. In addition, quality criteria were established in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) 2020 statement.

2.1. Inclusion Criteria

This analysis required defining the topic of interest (green chemistry) and selecting the type of useful information (articles filtered under the criteria of title, keywords, and year of publication). With these input data, the selected databases were searched for bibliographic information using appropriate Boolean operators.

2.2. Exclusion Criteria

The exclusion criteria were applied in 3 complementary screening phases. In the first phase, after excluding all duplicates, texts that did not meet the criteria of this study, such as articles with incomplete metadata, were removed from the sample because they prevented the bibliometric analysis. Subsequently, in the second phase, articles were excluded based on reading their full text; however, this phase is only applicable to systematic literature reviews because they analyse the full content of research articles while bibliometric analysis examines metadata. Lastly, in the third phase, articles that did not fit the scope of this study were excluded based on their titles and abstracts; additionally, records without rigorous methodological criteria and inappropriate document types were excluded.

2.3. Sources of Information

The study was performed using research data from articles published in two of the most important databases of indexed journals, namely Scopus and Web of Science. These databases were chosen due to their extensive coverage of the scientific literature, efficient search and retrieval capabilities, and analytical tools for assessing scientific production. Furthermore, both databases have rigorous selection criteria to ensure the inclusion of high-quality content and are internationally recognised as authoritative sources of information for academic research [48]. These data were analysed based on bibliometric indicators, i.e., statistical data on scientific publications in a specific field of knowledge and on their dissemination. As such, these indicators make it possible to quantify and assess the impact of scientific studies.

2.4. Search Strategies

Records were searched in both databases using two specialised search equations. These equations were derived by considering both the defined inclusion criteria and the search characteristics of each database. Accordingly, the following search equation was used for the Scopus database:

TITLE (“Green Chemistry” OR “Sustainable Chemistry” OR “Green-chemistry”) AND (LIMIT-TO (PUBYEAR, 2022) OR LIMIT-TO (PUBYEAR, 2021) OR LIMIT-TO (PUBYEAR, 2020) OR LIMIT-TO (PUBYEAR, 2019) OR LIMIT-TO (PUBYEAR, 2018) OR LIMIT-TO (PUBYEAR, 2017) OR LIMIT-TO (PUBYEAR, 2016) OR LIMIT-TO (PUBYEAR, 2015) OR LIMIT-TO (PUBYEAR, 2014) OR LIMIT-TO (PUBYEAR, 2013) OR LIMIT-TO (PUBYEAR, 2012))

Similarly, the following search equation was used for Web of Science:

TI = (“Green Chemistry” OR “Sustainable Chemistry” OR “Green-chemistry”) AND (PY = (2022) OR PY = (2021) OR PY = (2020) OR PY = (2019) OR PY = (2018) OR PY = (2017) OR PY = (2016) OR PY = (2015) OR PY = (2014) OR PY = (2013) OR PY = (2012))

2.5. Data Management

From Scopus and Web of Science, 1823 and 1739 records were retrieved, respectively. These records from both databases were compiled in Microsoft Excel spreadsheets into a uniform format to apply the defined exclusion criteria. As a result of this process, a combined database consisting of 2450 records was obtained, which served as the input data for the bibliometric analysis. It is important to note that the search was conducted in October 2022. Data were collected from 2012 to 2022, as this period allows for the examination of the most recent research trends in the field of green chemistry. The processed data were analysed in terms of quantity and quality using a pre-designed Microsoft Excel template for the analysis of keyword frequency and currency. VOSviewer was used to construct keyword co-occurrence, co-authorship, citation, and co-citation maps based on bibliographic data reflecting the productivity, impact, and connectivity between authors [49,50]. To accomplish this, the default or suggested parameters of version 1.6.18 of the software developed by Van Eck and Waltman [51] were employed.

2.6. Assessment of Reporting Bias

In the context of this bibliometric research on green chemistry, this study addresses the assessment of potential reporting biases that may contribute to the lack of synthesis results and subsequent bias risk. It is important to recognise that this study’s inclusion criteria may lead to a bias towards certain synonyms used in the search equation. Likewise, the data collection process may produce an inherent bias towards selecting and excluding certain titles, abstracts, and document types, potentially leading to the omission of information that could be relevant for advancing knowledge in the field of research on green chemistry.

Figure 1 shows the flow diagram of the PRISMA 2020 statement for the literature review process, outlining all the steps of the methodological design.

3. Results and Discussions

In the results and discussions section, a presentation of bibliometric indicators is proposed in three consecutive stages. Firstly, we explore the main authors, journals, and countries that prominently position themselves as research leaders in green chemistry. Subsequently, an analysis of structural indicators within the scientific community was conducted, detailing the co-occurrence network of thematic clusters, research lines, and international co-authorship networks. Lastly, a thematic analysis in terms of keywords in the scientific literature was performed, aiming to comprehend the thematic evolution and, likewise, the key growing and emerging words in the scientific literature on green chemistry.

3.1. Referents for Green Chemistry Research

Figure 2 shows the evolution of studies on green chemistry, highlighting a slight decrease of approximately 10% and 3% in publications from 2013 compared to 2012 and from 2014 compared to 2013, respectively. However, from 2014 to 2019, there was a sustained gradual rebound in the exponential increase in green chemistry research, reaching 74%, equivalent to 306 publications, in contrast to only 175 publications in 2014. In 2020, green chemistry research again decreased by 23% over 2019, recovering slightly in 2021, but only 190 studies in this field of research were published in 2022, a marked decrease of 22% in comparison to 2021.

This variation demonstrates a sustained growth in publications until 2019, except for a slight decrease in 2013. This growth may be associated with a gradual process of environmental awareness in the field of education [52] and in the industry, which show the highest impact and whose research now involves most of the principles of green chemistry proposed by Anastas and Warner in 1998 [53,54]. The proposals set forth in the United Nations (UN) 2030 Agenda for sustainable development also motivated various studies in this field, peaking in 2019.

Considering that scientific publications quickly become outdated, research in the framework of green chemistry is increasing, as shown in Figure 2. This field of research has high potential. From 2020 to 2022, the research output decreased slightly, possibly due to the novel coronavirus disease 2019 (COVID-19) pandemic during this period, when many universities and research centres were forced to interrupt their work. Yet, despite this adversity, the publications continued to share knowledge under the guidelines of green chemistry [55].

Figure 3 presents the analysis of journals that serve as research benchmarks in the scientific production of green chemistry based on publication quantity evaluation as an indicator of scientific productivity and citation count as an index of academic impact. However, it should be noted that high-impact publications may be identified based on their high citation counts due to the topic’s novelty. Consequently, researchers may be more interested in the metric itself than the actual research. Conversely, a low number of citations does not necessarily imply poor quality or a weak contribution to science [56].

In this regard, it is observed that the primary journal within the scientific community is Green Chemistry, which not only stands out as the most productive journal on the topic with nearly 140 articles but also has published the most cited articles in the field, totaling 5862 citations, making it the main research reference. Likewise, within the same group of journals that excel in both productivity and impact, we find ACS Sustainable Chemistry and Engineering, which accounts for a total of 139 articles, ranking as the second most prolific journal in the field and the fourth most cited. Additionally, the Journal of Chemical Education emerges as the third most productive and the fifth with the highest academic impact based on citation quantification.

In contrast, other journals position themselves as benchmarks solely based on the number of citations they have received, indicating their impact, despite having a relatively low quantity of publications. One such example is the journal Chemical Society Reviews, which has published fewer than ten articles but has accumulated approximately 4000 citations. This highlights the scientific dissemination of high-quality articles with a significant impact on the research community.

Furthermore, this bibliometric analysis evaluates aspects associated with scientific productivity and academic impact on a global scale, specifically examining the countries that have led the scientific development of green chemistry, as depicted in Figure 4. The United States has made the most significant contribution to scientific knowledge, producing the highest number of articles (762), which accounts for approximately 35% of the scientific literature. Consequently, the United States also has the highest scientific impact, receiving the most citations. This underscores the importance of the American knowledge base and its influence on the current state of the literature on green chemistry.

Another country that emerges as a crucial player, ranking second in terms of productivity and scientific impact, is India, with over 200 articles and approximately 4000 citations. This indicates the significance of Indian studies among scientific researchers in green chemistry. Additionally, Germany and the United Kingdom are prominent countries that position themselves as leaders in productivity and scientific impact.

Subsequently, in terms of the analysis of key research contributors, this literature review assesses scientific productivity and impact to shed light on the most prominent authors in green chemistry, as detailed in Figure 5. Three groups of authors are distinguished: the primary contributors who are among the most productive and have the highest impact; those who publish sparingly but have a high number of citations; and, conversely, those who have generated a larger volume of knowledge but currently do not stand out in terms of academic impact.

In this regard, Sheldon, R.A., emerges as the principal author, positioned among the top 6 authors who have generated significant knowledge on green chemistry through a greater number of articles. As a result, Sheldon, R.A., has obtained the highest number of citations in their works, approximately 4500, indicating their importance within the scientific and academic community.

On the other hand, there is a subgroup of authors who, although not the most prolific in terms of publications on the topic, have made notable contributions that have transcended the scientific literature, manifested through a high number of citations. Examples of such authors include Wang, Y., Wang, X., and Antonietti, M. Conversely, authors such as Allen, D.T., Licence, P., Subramaniam, B., and Anastas, P.T., despite not having a significant number of citations, currently position themselves as leaders in terms of scientific productivity, shedding light on their tendency towards publication and knowledge generation in the field of green chemistry.

3.2. Structure Indicators of Green Chemistry Research

Figure 6 shows the keyword network related to green chemistry provided by the VOSviewer [57] software for Scopus and Web of Science data, using the following VOSviewer settings to build the co-occurrence map: full count, author keywords that appear at least 6 times, and number of clusters selected based on causal inference. Keywords not related to our study were manually removed.

As a result, 78 words appearing at least 6 times were identified in 5 clusters of the network, totalling 440 and 1221 connections. As the main node in cluster 1, green synthesis occurs 39 times, as indicated in red. In cluster 2, in green, the main node is catalysis, with 33 occurrences; in cluster 3, in blue, the main node is sustainability, with 83 occurrences; in cluster 4, in yellow, the main node is curriculum, with 35 occurrences; and in cluster 5, in purple, the main node is upper-division undergraduate, with 35 occurrences.

Furthermore, through the analysis of the co-occurrence network of keywords and their respective thematic clustering, a total of five lines of research are identified, as shown in Figure 7, one for each previously identified cluster (see Figure 6). The first line of research focuses on assessing circular green innovation for sustainable systems, derived from the blue thematic cluster, and it is closely related to the research line on green catalysis for sustainable biomass conversion, derived from the green thematic cluster.

Additionally, due to a direct relationship between the green and yellow thematic clusters, there is a connection between the last line of research, which involves integrating material sciences into university curricula and incorporating nanotechnology. This, in turn, enhances consistency and integration with the thematic line derived from the purple cluster, which pertains to the development of decision-making skills in final-year university students through laboratory-based instruction in organic and industrial chemistry.

Moreover, the line derived from the green thematic cluster, albeit to a lesser extent, also exhibits a relationship with the thematic line that involves ecologically assisted microwave synthesis of nanoparticles for antibacterial applications, derived from the red thematic cluster.

Cluster 1 has 21 nodes, of which 17 are connected to the main node, including sustainability, catalysis, photocatalysis, nanotechnology, biomass, environment, eco-friendly, antimicrobial, antibacterial activity, silver nanoparticles, toxicity, nanoparticles, gold nanoparticles, and chitosan. Microwave, green solvent, extraction, and deep eutectic solvents are indirectly connected to the main node. Thus, the main node is also directly connected to catalysis, the main node of cluster 2, and sustainability, the main node of cluster 3.

Cluster 2 has 30 nodes with direct connections to nodes such as sustainable chemistry, systems thinking, synthesis, laboratory instruction, organic chemistry, curriculum, second-year undergraduate, upper-division undergraduate, sustainable development, and problem solving, among others, and to the main node of cluster 4, curriculum.

In cluster 3, the main node, sustainability, is connected to 47 nodes, including direct connections to all clusters through their main nodes. Therefore, sustainability is significantly associated with green chemistry. Both cluster 4 and cluster 5, with 28 and 24 nodes, respectively, share and are directly connected to the nodes safety/hazards, problem solving/decision making, first- and second-year undergraduate, laboratory instruction, and organic chemistry.

The overlay visualisation of keywords is shown in Figure 8, which reveals the relationship between terms by year of publication of the article. Trends in green chemistry research are visualised from 2012 to 2022, including recent studies published between 2020 and 2022. Clusters 1 and 2, deep eutectic solvents and green solvents, respectively, encompass studies on multicomponent reactions; cluster 3 includes terms related to education for sustainable development and systemic thinking; and cluster 4 includes research on decision-making and materials science. The highest concentration of connections between words related to the different green chemistry themes is found between 2016 and 2018, and the main node of cluster 3 is connected to the highest number of words.

Figure 9 visually represents the green chemistry keyword density. The density is determined by the colour and area of the nodes; that is, the higher the keyword colour intensity and amplitude are, the higher the number of studies that include the keyword. Conversely, when the colour is light and the amplitude is small, the number of studies that include the keyword is limited. Four trends in green chemistry research were detected: sustainability, sustainable chemistry, green synthesis, and upper-division undergraduate. Sustainability research trends are motivated by the UN 2030 agenda, proposed in 2015 [58,59], towards a gradual transition to environmentally friendly methods, technologies, and procedures in which sustainable chemistry and green synthesis are closely associated from different industrial and educational perspectives.

On the other hand, in terms of the structural analysis of international scientific collaboration, Figure 10 presents the main co-authorship network among countries. In this regard, it is evident that the primary cluster of scientific cooperation is characterised by the colour green, which includes some of the most productive countries (see Figure 4), with a notable emphasis on the relationship between the United States and India.

Within the context of cooperation between these two countries, scientific articles have been produced that have enhanced the existing knowledge surrounding the implementation of green chemistry principles in the pharmaceutical industry [16,60]. This collaboration has been crucial in improving sustainability and reducing costs for active pharmaceutical ingredients [61].

Furthermore, it can be observed that another significant scientific cooperation relationship within the literature on green chemistry exists between the USA and the UK. This partnership encompasses various approaches, such as using green chemistry and engineering to address sustainability challenges in the global use of phosphorus [62]. Additionally, the importance of innovation in green chemistry and engineering for achieving more sustainable development is emphasised [63]. Furthermore, models for decision-making based on green chemistry are proposed for the classification of synthesis protocols of silver nanoparticles into performance-based classes ordered by preferences [64].

3.3. Thematic Components of Green Chemistry Research

Figure 11 shows the most used keywords by year during the study period. In 2012, the most used keyword was organic chemistry. Although organic chemistry lost importance in the following years, interest in this keyword resumed in 2020, thus highlighting the motivation to integrate the principles of green chemistry from undergraduate education to analytical laboratory practices [65]. Even social justice issues have been incorporated into the organic chemistry curriculum to address the history, social, cultural, and environmental impact of compounds, predicting products, and functional groups [66]. In 2013 and 2014, the most used keywords were curriculum and second-year undergraduate. These results highlight the interest in strengthening undergraduate study curricula by including metric disciplines such as chemometrics [67] and designing undergraduate courses aimed at changing attitudes and fostering critical thinking [68,69] towards setting hazard criteria for chemical products and inputs within the framework of the principles of green chemistry.

In 2015, the most used keyword was gold nanoparticles. Research on gold nanoparticles focuses on designing green chemistry-based classification models for synthesis protocols and their applications [64], for example, in modifiers of glassy carbon electrodes for catalytic purposes and in the analysis of complex samples, such as the determination of diethylstilbestrol [70]. In 2016, the most used keyword was upper-division undergraduate. Research on this topic was aimed at providing college students with analytical and instrumental methods and tools for the analysis and discussion of complex problems involving green chemistry [71,72]. In 2017 and 2018, the keyword synthesis and its transition to green synthesis stood out. In particular, green synthesis became relevant in 2021 and 2022 with the emergence of new research on ionic liquids as promising catalysts for organic synthesis [73], on computer-aided prediction for the design of solvent and anti-solvent mixtures to reduce energy consumption [74], on the use of eutectic solvents to improve chitosan film production [75], and on the synthesis of innovative bacterial agents based on hybrid peptides attached to silver nanoparticles [76] and of high-surface graphene oxide to prepare a carbon nanomaterial with potential applications in supercapacitors, programmable adsorbents, and catalysts with a wide range of activities [77].

In 2019, the most used keyword was systems thinking, reflecting research on systemic thinking in science and on the need to direct systemic thinking towards green chemistry, from academic education to industry [78]. Studies also addressed the need to introduce rich contexts associated with the fundamental ideas of chemistry and applicable to various knowledge areas, such as drug products, silanes and their organic modification for coating [79], and water recovery for reuse [80], thereby improving the alignment with reality and with the goals of sustainable development set forth in the UN 2030 agenda [81].

Figure 12 shows the frequency and validity of the keywords based on their concurrency by year. Quadrant I shows the most frequent and current terms, highlighting only green synthesis studies. These studies are motivated by the urgent need to change synthesis methods and procedures towards improving energy use, reducing both energy consumption [82] and the generation of complex waste with low recyclability and natural degradability [83], and outlining viable alternatives focused on reducing or eliminating negative impacts on the environment [84].

Quadrant II shows less frequent but more current terms that have emerged in recent years, such as systems thinking aimed at contextualising the fundamentals of chemistry in real-life events [79]. Another keyword is circular economy, which is based on the optimisation of resources so that they remain longer in the production cycle, finding value in waste. The agro-industry constantly seeks to add value to its waste, for example, by producing edible and inedible oils [85,86]. The mining industry recovers mica from tailings to create mica nanosheets [87]. The textile industry improves process circularity and waste management through sustainable biotextile production [88]. The term nanoparticles is also found in this quadrant, highlighting the contribution of transition nanoparticles for their good electrical, optical, magnetic, and catalytic properties and for their applicability in the fields of environmental and materials science, biomedicine, and catalysis [89,90]. Last, the term ionic liquids is highly attractive in chemistry and engineering. Although its structure and assembly function remain under study [91], its use is geared towards less polluting processes and low energy consumption [92].

Quadrant III includes less frequent and less current terms, such as the term synthesis, which is one of the most commonly used words in chemistry. Synthesis is linked to the design and production of new substances useful for the industry, but this concept has been undergoing a transition towards a new vision based on green synthesis [93]. Nanotechnology has emerged as one of the major advances in chemistry and has greatly contributed to strengthening the foundations of green chemistry. The manipulation of matter at the nanometric scale has been generating revolutionary changes, including the synthesis of metallic nanoparticles through bioreduction using plant extracts to create functional nanostructures [94]. The term gold nanoparticles is associated with this branch of chemistry. In one of these studies, rice seed extracts were used to synthesise gold nanoparticles, whose size can be adjusted by varying the concentration of the silver precursor. When monodisperse, these gold sensors show excellent nanoporosity and an excellent response to glucose detection in a specific range [95]. The term green engineering is also found in this quadrant, which includes green chemistry concepts and advances, implemented and put into practice by engineering, under a framework of technical improvement and economic viability with minimal environmental impact [96]. Therefore, all advances and alignments with the principles of green chemistry lead to the term sustainable development, which seeks to harmonise anthropogenic activities towards rethinking the current society and directing processes into a transition whereby human activities are more respectfully integrated with the environment [97].

Quadrant IV shows more frequent but less current terms, such as curriculum. Research on this topic aims at improving the design of study curricula by introducing specific courses to help students move from the laboratory to the real world and strengthen their skills and awareness in the field of green chemistry [98]. In this context, research regarding the upper undergraduate division shows the need to educate a new generation of highly motivated and responsible scientists to implement the principles of green chemistry and a substantial approach to sustainable development [99]. Other terms found in this quadrant are organic chemistry and laboratory instruction, both of which have strong links complementing each other from theoretical to practical domains. Research on synthesis applying the fundamentals of nanotechnology and catalysis opens up new opportunities [100] in the formative stages of students efforts towards raising green awareness and promoting sustainability thinking and reasoning [101].

4. Conclusions

This bibliometric research reveals that many studies conducted in different fields of knowledge have strong links to the application of the principles of green chemistry. However, in some industrial and educational sectors, this transition process is still laying the foundation for this new paradigm aimed at recovering the balance of our planet. The data analysis revealed sustained exponential growth in quantity until 2019; however, from 2019 to 2022, the research output of green chemistry decreased slightly, possibly due to the COVID-19 pandemic because research centres and universities were forced to cease their activities worldwide. Yet, despite this setback, the contribution of green chemistry to science did not stop. Based on quality indicators, the journals of the UK outperform the journals of the USA, which lead in quantity. Mapping with VOSviewer revealed five clusters, highlighting words such as green synthesis, catalysis, sustainability, curriculum, and upper-division undergraduate, associated with new research on the development of green solvents, eutectic solvents, systems thinking, education for sustainable development, decision-making, and materials science. The term “sustainability” was connected to all clusters, and based on overlay mapping, from 2016 to 2018, green chemistry research was strongly influenced by the UN 2030 agenda and by sustainable development goals, opening up new opportunities for sustainability involving green chemistry.

In this regard, based on the synthesis of results obtained in the present research on trends in green chemistry, it is concluded that future studies should investigate the specificities of the subject in different geographical contexts. This would allow for the identification of chemical characteristics in countries other than the USA, India, and the UK. By doing so, different industrial and educational sectors can overcome their internal limitations and barriers and harness existing knowledge.

Furthermore, it is concluded that other researchers should delve into the different thematic lines identified in this study, as these lines have a high potential for contributing to the various challenges of sustainable development. They can offer solutions to environmental issues through technological innovation, with a particular focus on the role of nanotechnology. This impact extends beyond economic and sustainable development to encompass education, training, and existing knowledge around the matter.

Additionally, future investigations should be grounded in the currently prominent thematic areas. This will contribute to building a solid knowledge foundation on concepts that shape the current state of green chemistry, not only in the literature but in various aspects of the field. It is important to emphasise the significance of green synthesis as a consolidated and growing concept in the scientific literature, as well as its integration with systemic thinking, the circular economy, silver nanoparticles, ionic liquids, and other emerging concepts. These concepts highlight their importance for the near future of theoretical and experimental scientific activity.

On the other hand, this research acknowledges several limitations that need to be understood both in interpreting the obtained results and in overcoming barriers in future investigations. Firstly, using only Scopus and Web of Science databases excludes the entire body of knowledge in other databases that may be equally important for consolidating the literature on green chemistry.

Moreover, the use of the PRISMA methodology, which requires excluding articles based on specific criteria, poses a potential limitation in terms of selection bias in the final inclusion of studies on green chemistry. Consequently, there may be information that other authors consider relevant that is omitted from this study because it was deemed irrelevant to the research objective.

Another noteworthy limitation is the inclusion of articles published between 2012 and 2022, which excludes other documents that may represent valuable theoretical and practical knowledge on earlier aspects of green and sustainable chemistry. Thus, this study may restrict the analysis of texts considered classics in the literature on the subject.

Lastly, similar to any literature review, this study has the limitation that, due to the dynamic and evolving nature of the field, the information will become outdated in future years. Therefore, future studies similar to this will be necessary to update and consolidate the existing knowledge on green chemistry at a specific historical moment.