Hotspots and trends of layered double hydroxide-based adsorbents for polluted water treatment: Insights from bibliometric analysis

Hotspots and trends of layered double hydroxide-based adsorbents for polluted water treatment: Insights from bibliometric analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hotspots and trends of layered double hydroxide-based adsorbents for polluted water treatment: Insights from bibliometric analysis Juliana C. P. L. Paulino, Anamália F. Silva, Danilo H. S. Santos, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2070633/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract The use of layered double hydroxides (LDHs) as adsorbent for water treatment has been gaining relevance in recent years. In this context, this work aimed to map, through a bibliometric study, the extent of research that deals with the theme. The scientific database used was the Web of Science, and the chronology of the search consideredthe period from 1997 to 2022. The bibliometix R-package and VOSviewer software were used in this study. The searches retrieved a total of 663 documents, from 69 countries, distributed among all continents, which China (328), India (51) and Japan (40) were the most productive countries. Important journals in the environmental area and with high impact factor, such as Chemical Engineering Journal (44), Applied Clay Science (38), Journal of Hazardous Materials (35) and Chemosphere (27) most published in the area. The network of keywords used by the authors indicates that the publications retrieved deal mainly with aspects related to the efficiency of (LDHs) in the removal of different pollutants, the composition, the synthesis route and the association with other materials and/or techniques. The result of this study constitutes an important tool for directing future research on the subject. Clays review water pollution adsorption Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. introduction Rapid population growth, uncontrolled exploitation of natural resources, and the use of a wide variety of chemicals in activities essential to humans such as agriculture, industrial processes, among others, have been causing enormous environmental instability worldwide (Koutavarapu et al., 2021). Among the main impacts generated by human intervention on the natural environment, water pollution has stood out as one of the most serious problems of today's society (Nasrollahzadeh et al., 2021). In addition to limiting the availability of an essential resource for human life (Fan and Fang, 2020), the degradation of water quality, interferes with socioeconomic development worldwide, since water plays an important role in several sectors essential to industrial development, functioning as a key element in the production of food and energy, for example (Mao et al., 2015). Moreover, when contaminated, water becomes the primary mode by which potentially toxic chemicals come into contact with the human and animal community, since such substances, when soluble, are more easily transported and distributed through the water cycle (Oller et al., 2011; Yang et al., 2019). The inadequate management of contaminated water by conventional treatment systems has contributed to the expansion of studies dealing with the development of alternative treatment systems that are able to remove the varied classes of pollutants resistant to conventional treatments and ensure that the treated water is healthy for reuse and/or consumption (Kıdak and Doğan, 2018). Among the various technologies that have been evaluated for their efficiency in treating contaminated water, the Adsorption process is most prevalently cited in review papers (Z. Li et al., 2020). This process is preferred over others because it has some important advantages such as relatively simple design, easy operation, high cost-effectiveness, ability to remove pollutants at very low concentrations, low energy consumption, and high availability of raw materials (Fiyadh et al., 2019). Moreover, the adsorption process has a wide applicability, being the most favorable method for removing contaminants of organic and/or inorganic nature (Kim et al., 2022). The efficiency of the adsorption process depends on the surface characteristics of the adsorbent material and how these interact with the specific pollutants to be adsorbed (Fiyadh et al., 2019). Although it is considered the best adsorbent for cleaning liquid solutions, the widespread use of activated carbon is restricted due to its high cost (da Silva Santos et al., 2021; D. H. S. Santos et al., 2020)(Wang, Wang, and Ma, 2010). One ton of such material produced from coconut husk, for example, costs, before shipment, about USD950-1400 (Ahmedna, Marshall, and Rao, 2000). The high cost of producing and marketing AC, in addition to contributing to the lack of access to commercially treated water for a significant fraction of the population in developing countries, given the low per capita income of these countries, also limits the ability of industries to treat their effluents to the required environmental standards prior to disposal-with some industries operating outside legal limits-thereby exacerbating environmental pollution (Ntuli and Hapazari, 2013). In this regard, the interest in the development of unconventional adsorbent materials that are efficient in removing a variety of pollutants of organic and/or inorganic nature, easy to obtain, low toxicity, good regenerative capacity and, in particular, low cost, has been the main object of studies in this area (Kumar et al., 2019). Recent progress in nanoscience and nanotechnology has helped researchers to design nanoscale materials with the desired structure and functionality (Sohrabi et al., 2021). In this perspective, layered double hydroxides (LDHs) have been receiving more and more attention. Layered double hydroxides comprise a class of two-dimensional anionic clays with a structure similar to the mineral hydrotalcite ([Mg 6 Al 2 (OH) 16 ]CO 3 - 4H 2 O) (Mohapatra and Parida, 2016). The general formula of LDHs is represented by the equation M 2+ 1-x M3 + x (OH) 2 .An-x/n.zH 2 O, where M 2+ and M 3+ correspond to di- and trivalent cations, respectively, and An - is an anion. The cations are responsible for the positive charges presented by the lamellae, while the anionic species along with water molecules, present in the interlamellar regiation, makes the material stable (Mishra, Dash, and Pandey, 2018). Commonly known as anionic clays or hydrotalcite-like materials, LDHs are easily synthesized using lowcost materials and unsophisticated equipment (Jijoe et al., 2021). These materials exhibit a unique molecular structure with highly controllable chemical composition of the cationic layers and interlamellar region. Thus, LDHswith different element compositions and metal cation ratios can be produced. These materials exhibit differences in their morphology and crystal structure, which allows them to be designed for a specific purpose (Keyikoglu, Khataee, and Yoon, 2022). The use of LDHsas adsorbent materials in the remediation of environmental problems has been the most commonly reported application in the literature. Although an increasing interest in the use of these materials as adsorbent materials is observed, there is a gap in statistical research trend information on this topic. In this sense, the present work aims, through a bibliometric study, to analyze the scientific guidelines on the suitability of layered double hydroxides (LDHs) as adsorbent agents for contaminants in aqueous media in order to prospect new research directions and/or strategies with potential to boost the use of these materials. 2. Methods 2.1 Bibliometric Analysis This method allows the identification, organization, and evaluation of the constituent elements of a specific study area, and is therefore an important tool for reviews. It is a comprehensive technique related to mathematical and statistical methods to discover the distribution, variation, and quantity of publications in public databases on a given subject (Gallego-Valero, Moral-Parajes, and Román-Sánchez, 2021). 2.2 Data source The Web of Science (WoS) database was used to perform the bibliometric analysis. WoS has high visibility in various fields of knowledge, a selection filter for prestigious publications, and is also widely used to conduct bibliometric studies (Jiang et al., 2018). 2.3 Data selection and processing The sample of documents analyzed in this study was obtained using the terms ("layered double hydroxides" OR "anionic clays" OR "hydrotalcite-like materials") AND ("adsorption" OR 'adsorvent") AND ("treatment OR remediation") AND (water OR "contaminated waters" OR "effluents" OR "wastewater"). The literature search was performed with all the terms that, according to the literature, are commonly used to refer to LDHs in order to obtain results more consistent with reality. The chronology used for the search took into account the date of the first publication retrieved on the subject in the database until March 2022 (1997-2022). The bibliometix R-package and VOSviewer softwares were used for bibliometric analysis and scientific mapping of the retrieved data. 3. Results 3.1 General characteristics of the retrieved samples Through the searches performed in the WoS database, a total of 663 documents were retrieved, of which 89.54% (595 records), the absolute majority, refer to scientific articles, 9.05% (60 records) correspond to review documents, and the less than 2% remaining correspond to the sum of other types of records such as meeting abstracts, book chapters, news, editorial material, among others. Articles printed in English correspond to 98.6% of the total records, followed by articles published in Chinese, 0.9% of the total. The proportion of the sum of the other three languages with retrieved records, which include French, Polish, and Turkish, is less than 0.5 percent. The histogram presented in Figure 1(a) shows the variations in the number of retrieved publications related to the theme between the years 1997 and 2022. The data obtained show, in general, an upward trend. In the first nine years (1997-2005), academic research in this area was in its early stages, with a publication rate of 1.75 papers per year, a negligible figure. In the subsequent years, 2006 to 2015, a greater number of documents were retrieved, reaching an average of 15.5 publications per year, a rate 8.9 times higher than that observed previously (1997-2005). However, in more recent periods (2016 to 2022), the publication rate has increased rapidly and substantially, with the average number of publications being about 3.1 times higher than in the previous period evaluated (2006 to 2015). In the year 2022, by the time the data were surveyed (3/21/2022), 10 studies on the topic had already been published. These results suggest that in the coming years, annual publications on this topic will continue to grow. Characteristics such as high efficiency in the removal of a variety of pollutants, versatility in composition, low cost, low toxicity, regenerative capacity, among others presented by LDHs, added to the increasing disposal of large quantities and varieties of pollutants harmful to the environment, population growth and high demand for water resources, and the commitment to reduce environmental contamination, consequently generate an urgency in the development of new technologies in these areas and corroborate the growth trend observed. 3.2 Relevant countries in research on the topic The papers published on topic in the period 1997-2022 come from a total of 69 countries. Figure 1 (b) shows the map of countries with results in the research, the darker the color of the country/region, the more papers there are in that country/region. Although most studies in this field come from a relatively small number of countries, such as China, India, USA, Japan, Brazil, Saudi Arabia, Australia, France, South Korea and Canada, it is notably explicit that countries from all continents and with a wide diversity of economic and socio-cultural characteristics produce relevant research in this area of knowledge. Figure 2 (a) presents the percentages of the 10 most productive countries/territories on the topic. China is the most prolific territory, accounting for 47.96% of the total, with 318 retrieved papers. The second place is occupied by India (7.69% of the total, 51 papers), followed by Japan with 40 papers, representing 6.03% of the total. Subsequently we have USA (40 documents, 6.03%), Brazil (28 documents, 4.22%), Saudi Arabia (28 documents, 4.22%), Australia (25 documents, 3.77%), France (25 documents, 3.62%), South Korea (24 documents, 3.62%) and Canada (17 documents, 2.56%). The worsening problem of water scarcity in China, caused by serious problems of contamination of drinking water and underground sources by arsenic and fluoride, further associated with rapid economic growth and the large number of industrial production activities in the country, resulted in increased investment in research aimed at the use of advanced technology for water treatment, making this nation a power in this area of technology, which justified the consolidation of China as the country that produces the most on the subject (Wu, 2020). Social network analysis was then applied to analyze the coauthorship relationships among all the producing countries/territories, the results are displayed in Figure 2 (b). Each point represents a node in the network, with nodes being equivalent to countries. The larger the node, the larger the number of cooperations performed by these countries. The lines between the nodes indicate the occurrence of cooperation between the countries, and the thickness of the line is proportional to the number of publications retrieved from these cooperations. Clearly, China, the largest producer of papers on the topic, also has the largest number of collaborations with other countries/territories, given the size of the node in Figure 2(b). The Chinese have produced publications in cooperation with several countries, with their collaborations with the US, India, Saudi Arabia, Canada, Australia, the UK, and Korea standing out as the most intense, a fact denoted by the thickness of the lines of connections. The U.S. presents not very expressive cooperation data, besides interacting with a reduced number of countries/territories, its main productions are the fruit of an intense cooperation with the Chinese, which, according to Figure 2(b), is the most frequent among all the others, with a total of 23 retrieved documents. Figure 3 presents the annual average of document citations. The 10 most frequent cooperation between countries/regions, obtained by the bibliometrix package (version 3.1.4), are summarized in Table 1. Table 1 The cooperation among countries/regions. From To Frequency China USA 23 China Saudi Arabia 17 China Australia 14 China Canada 10 China Korea 10 China United Kingdom 8 India Korea 8 Saudi Arabia Pakistan 7 China India 6 Japan Bangladesh 5 Overall, it is observed that the overall citation of this field shows a zigzag trend and indicates that more and more scholars are paying attention to this field in recent years. The average number of citations peaked in 2001 with average total citations of each article is 200 times. The average of total citations for each article reached 9.52 times per year. The article published by Liang (2017)(Liang et al., 2017) is the most cited. 3.3 Analysis of publications by institutions and authors A total of 765 institutions contributed to the 663 retrieved publications on the topic. The most productive institution was the Chinese Academy of Sciences, which published 45 papers, followed by North China Electric Power University (22), Centre National de la Recherche Scienque CNRS (20), by China University of Geosciences (14) and Tsinghua University (14). The 20 institutions with the highest number of retrieved publications on the topic are summarized in Figure 4. Through the results it was found that 15 of the 20 most productive institutions are from China, the other 5 institutions are distributed among 4 countries: France, Saudi Arabia, India and Egypt. A total of 2,910 researchers participated in the retrieved publications. The authors with the most publications on the topic are shown in Table 2. Researcher Wang XK appears with the highest number of publications (20, 3.01%), followed by Wang XX (13, 1.96%), Qian GR (11, 1.65%), Zhang XL (11, 1.65%), Yu SJ (10, 1.50%). Another important parameter to consider is the number of citations. In this case, Wang XK tops the list with a total number of 1246 citations, Wang XXA was second with the most citations (1099), followed by Hayat T, Yu SJ and Ok YS who had a total of 593, 523 and 497 citations, respectively. 3.4 Main Areas of Study on the Theme The results of the bibliometric analysis allow us to distinguish between the different disciplines to which the scientific articles analyzed belong. It should be noted that an article may belong to more than one category; therefore, the results are analyzed in percentages. In all, 25 different areas of knowledge are covered with publications on the topic. Figure 5 shows the top 10 areas of study. Among the various research areas, the most important are Environmental Sciences with 16.63% of the total, followed by Environmental Engineering (14.07%), Physical Chemistry (13.17%), Chemical Engineering (12.18%), Multidisciplinary Materials Sciences (10.12%), Multidisciplinary Chemistry (6.83%), Water Resources (4.03%), Mining (3.7%), Nanoscience Nanotechnology (2.55%) and Green Sustainble Science Technology (2.49 %). The item identified as "other" (13.99% of the total) includes a wide and diverse range of knowledge areas such as microbiology, mathematics, geology, microscopy, toxicology, biophysics, among others. Table 2 Authors with the most publications on the theme. Author Documents Citations Quantity Percent Wang XK 20 3,01% 1246 Wang XX 13 1,96% 1099 Qian GR 11 1,65% 352 Zhang XL 11 1,65% 181 Yu SJ 10 1,50% 523 Kameda T 9 1,35% 73 Yan LG 9 1,35% 161 Yoshioka T 9 1,35% 73 Zhang J 9 1,35% 225 Chen H 8 1,20% 90 Hayat T 8 1,20% 593 Li J 8 1,20% 95 3.5 Journals that most published on the subject The total number of retrieved documents is distributed among 217 journals. With 6.63% of the total sample of articles (44 documents) the Chemical Engineering Journal, a comprehensive journal for Environmental Chemical Engineering, was the most productive journal, followed by Applied Clay Science (38), Journal of Hazardous Materials (35) and Chemosphere (27). Together, these four journals published 21.49% of the total articles on this research topic. In addition to those mentioned above, other important journals also published within this theme. The information of the 10 journals that publish the most articles on the research topic and their main indexes are summarized in Table 3. Table 3 Journals that have published the most on the subject and their impact factors. Journal Documents IF* Quantity Percent Chemical Engineering Journal 44 6.637% 13.273 Applied Clay Science 38 5.732% 5.467 Journal of Hazardous Materials 35 5.279% 10.588 Chemosphere 27 4.072% 7.086 Journal of Cleaner Production 18 2.715% 9.297 Colloids and Surfacesa Physicochemical and Engineering Aspects 14 2.112% 4.539 Science of the Total Environment 14 2.112% 7.963 Environmental Science and Pollution Research 13 1.961% 4.223 Journal of Environmental Chemical Engineering 13 1.961% 5.876 Desalination and Water Treatment 12 1.810% 1.254 Journal of Materials Chemistry A 9 1.357% 7.393 *Impact Factor 2022. 3.5 The main fields of research The keywords of a scientific document may offer important information about the main ideas and trends of a given theme, and are therefore an extremely important tool in bibliometric analyses. In this paper a total of 1475 keywords were identified, of which the vast majority had only one (1179, 79.7%) or two (210, 14.62%) occurrences, while 69 (4.06%) of the keywords had 5 or more occurrences. Thematic evolution analysis can be used to detect, quantify and visualize specific fields of research, and can visually show the evolution of the theme in recent years. A strategy map shown in Figure 6 divided into four quadrants shows the degree of connection between the clusters and between the keywords in the cluster. The second and third quadrants are the most developed, with strong centrality and high impact being the most relevant for the current field. Similar words are found in the first and fourth quadrants, indicating a certain linearity in the use of HDLs. The strategic diagrams allow visualizing the research field as a set of themes, mapped and classified into four groups, categorized in terms of density and centrality: (I) cluster engine (first quadrant, with high density and strong centrality); (II) highly developed and isolated clusters (second upper left quadrant, with marginal importance for the research field; 'specialized topics'); (III) declining or emerging clusters (third quadrant, with low density and low centrality; 'emerging or disappearing themes'); and (IV) basic and transversal clusters (fourth quadrant, with important but undeveloped themes; 'transversal and general themes') (Alcaide-Muñoz et al., 2017; Cobo et al., 2012). It is noteworthy that the sphere represents a cluster of words (or theme) and the name of each one of these is related to the most recurrent word and/or theme; the volume of the spheres corresponds to the number of associated articles - the larger the sphere, the greater the number of articles that cited that word as a keyword (Cobo et al., 2012, 2011). The detection of the most commonly used keywords in the retrieved documents, limited to the minimum number of 5 occurrences, are presented in Figure 7. Each point represents a node in the network, with the nodes being equivalent to the keywords. The larger the node, the greater the number of links made by these terms. The lines between the nodes indicate the co-occurrence between the keywords, and the thickness of the line is proportional to the quantity with which this co-occurrence is perceived. Visibly, the terms "adsorption", "lamellar double hydroxides", and "water treatment" stand out among the others as the terms that have the largest numbers of links to other keywords. The term "adsorption" is the most highlighted by the retrieved documents with a total of 199 occurrences, which reflects its central position in this high-frequency search field. The top 20 retrieved keywords and their respective occurrence numbers are summarized in Table 4. The co-occurrences between the keywords did not highlight a specific trend in the retrieved papers on the topic, as no significantly thick lines were observed between the terms. These results may indicate that research trends in this area are growing more diverse. The propensity for research on the topic can be identified by analyzing the different groups into which the keywords fall. In all, the terms are comprised in 7 groups identified by distinct colors. Of these, four main groups were observed, chosen by the largest number of keywords included. The first group, colored yellow, comprises a total of 12 keywords and focuses on the determination of the parameters related to the adsorption process due to its conjunction with terms such as "kinetics", "thermodynamics", "isotherm" and "equilibrium". The second group, blue in color, has 17 keywords, and the presence of the terms "composite", "biochar", "memory effect", "magnetic separation of metal ions" and "regeneration" indicate that this group focuses mainly on the production of composite materials and on the properties of LDHs. The third group, colored green, with 13 keywords, focuses on the methods of synthesis and composition of materials, with the presence of the terms "precipitation", "selective adsorption", "calcination", and "engineering". The fourth group, with red coloring, has 14 keywords, and deals with the efficiency of LDHs in the removal of different classes of pollutants due to the adjection of the terms "organic pollutants", "dyes", heavy metals, among others. Table 4 Main keywords and their number of occurrences. Keywords Occurrences Adsorption 199 Layered Double Hydroxides 129 Layered Double Hydroxide 67 Water Treatment 56 Wasterwater Treatment 54 Kinetics 18 Hydrotalcite 30 Sorption 25 Fluorede 23 Wasterwater 17 Phosphate 19 LDH 18 Biochar 15 Photocatalysis 17 Methyl Orange 16 Cr(VI) 13 Removal 13 Dyes 8 Equilibrium 6 Arsenic 15 Some terms such as "phosphate", "phenol", "metal ions", "dyes", "pesticides", among others, used to refer to the wide range of pollutants and/or contaminants present in water, and the terms "biochar", "photocatalysis", "nanomaterials" among others, which refer to the structure and composition of LDHs are found in more than one group in Figure 7. The analysis took into consideration only the distinct terms present in the groups in order to understand the different guidelines of papers retrieved on the topic. Some papers dealing with the different research guidelines related to the topic are summarized in Table 5. Table 5 concisely shows the diversity in the composition of LDHs, as well as their versatility in removing a variety of contaminants in aqueous solution. Furthermore, it can also be seen that the coprecipitation method is the most commonly used for syntheses, a fact elucidated by being a simple method and easy to manipulate in the laboratory (Chang et al., 2005). In this method, the formation of the lamellar structure of the hydroxides occurs in a simple step of precipitation of the bi- and trivalent cations with the interlamellar anion, using the addition of alkaline aqueous solution, in batch (Silva et al., 2021). The number of cycles, a very important data for knowledge of the regeneration capacity and, which can be used for industrial application, is little reported in the researched works. Li et al. (2020) (A. Li et al., 2020), evaluated the recyclability of the ZnAl adsorbent using sodium hydroxide for the adsorption-desorption experiments and, identified that the removal rate of the Congo red dye decreases from 98.01% (1st cycle) to 67.11% after four times of recycling. Just as the adsorption capabilities in pure LDHs are widely investigated, new work involving the production of LDH composites is under increasing development, demonstrating excellent performances in enhancing contaminant removal. In Tolea et al. (2021) (Țolea et al., 2021), LDH -Mg 3 Al was used to support Methyl Trialkyl Ammonium Chloride and increase the adsorption capacity of the new adsorbent material, furthermore, in the same work, two synthetic routes were also investigated and compared for their adsorption capacity as shown in Table 5. Thus, the study identified that functionalization of Mg 3 Al with Methyl Trialkyl Ammonium Chloride (Mg 3 Al-IL-US) increased the adsorption capacity from 143 mg/g to 217 mg/g and presented maximum adsorption capacity of 648 mg/g for sample (Mg 3 Al-IL-COS) obtained by cosynthesis. In the Cl-LDH chloride intercalated LDH-MgAl a slight improvement in phosphate removal was presented, with the value of 63.2 mg/g, when compared to the materials with glycerol (Gly-Cl-LDH) and alanine intercalated (Ala-Cl- LDH), with removal capacity of 55.8 and 58.2 mg/g, respectively (Zhang et al., 2022). However, in the same work, characterization results showed that compared to MgAl-CL, Gly-Cl- LDH and Ala-Cl-LDH have higher porosity and higher specific surface area, in addition to the larger interlayer space for samples with intercalated glycerol and alanine. Table 5 Efficiency of LDHs of varied composition obtained by different synthesis methods, used as adsorbents in the removal of different pollutants. Composition Pollutant Efficiency/adsorption capacity Synthesis method Regeneration cycles References MgFe-Cl Chromates Sulfates 100% 93% coprecipitation - (Matusik and Rybka, 2019) MgFe- CO 3 - Molybdenum 39.9 mg/g coprecipitation - (Golban et al., 2019) MgFe-Cl Nitrate 18.17 mg/g coprecipitation - (L. C. Santos et al., 2020) MgAl-Cl Bright Yellow 115.00 mg/g hydrothermal - (Pourfaraj et al., 2017) CaAl-NO 3 Diy Sunset Yellow 398.41 mg/g coprecipitation - (De Sá et al., 2013) MgAl-CO 3 - Methyl orange 197.62 mg/g urea hydrolysis - (Zaghloul et al., 2020) ZnAl- NO 3 Congo Red diy 625.00 mg/g coprecipitation 4 (Li et al., 2020) ZnFe-NO 3 Methyl orange Methyl blueMalachite green 230.68 mg/g 133.29 mg/g 57.34 mg/g coprecipitation - (Mahmoud et al., 2021) Mg 3 Al-NO 3 Mg 3 Al-IL-US Mg 3 Al-IL-COS Diclofenac 143 mg/g 217 mg/g 648 mg/g coprecipitation ultrasson cossynthesis - (Țolea et al., 2021) MgAl-Cl Gly-Cl-LDH Ala-Cl-LDH Fosfate 63.2 mg/g 55.8 mg/g 58.2 mg/g coprecipitation - (Zhang et al., 2022) 3.6 Insights and prospects The adsorption process is considered the best technique over other contaminated water treatment strategies for its simplicity of operation and universality for common organic and inorganic contaminants (Crini, 2005; Jiang et al., 2018; D. H. S. Santos et al., 2020). However, the production of adsorbent materials with high dispersion of active sites that allow the maximum utilization of their potential, tunability of the composition and electronic state of the adsorption sites on an atomic scale for greater selectivity for a specific pollutant and Stable active sites that guarantee reuse and performance for long-term use has been the major bottleneck in the application and development of this technology(Chen et al., 2022; Keyikoglu et al., 2022). Recent progress in nanoscience and nanotechnology has allowed researchers to design nanosized materials with the desired structure and functionality, and in this sense a growing interest in the use of HDLs for water remediation as an adsorbent has been observed(Jiang et al., 2018). These materials present their unique characteristic structures, such as i) tunability of the elemental composition of the host layer where the metallic cations reside, ii) high ion exchange capacity due to the interchangeability of interlayer anions and iii) controllability of the interlayer distance and dimensions of the material by incorporation of suitable anions (Crini, 2005; Jiang et al., 2018; Keyikoglu et al., 2022). In addition to the type of metal cation, the ratio of divalent and trivalent (M 2+/ M 3+ ) can be regulated. The variety of different types of HDLs with a wide range of elemental compositions that can be produced and its association with other materials has increased interest in research using these materials. It is necessary to understand more objectively what all the aspects involved cause in the material obtained and how this product can be used in its most satisfactory way. 4. Conclusion The survey obtained from the searches in the scientific bases, culminated in the observation of the rising interest of the development of research and technologies that use layered double hydroxides as adsorbent material in the treatment of contaminated water. From 1997 to 2021, a total of 663 papers related to the topic were published in scientific journals indexed to the Web of Science database. A significant increase in the production on the topic was observed in the last 5 years. China was the country that presented the largest number of retrieved publications on the subject, and also the country that has cooperated the most with other nations in the development of new documents, this is important information, since the issue of water pollution affects the whole world. The bibliometric analysis also indicated that the most productive authors were Wang XK, Wang XX, and Qian GR. The journals that published the most on the topic were Chemical Engineering Journal, Applied Clay Science, Journal of Hazardous Materials, and Chemosphere. In addition to the main focus and research trends in the area by using the keywords most frequently found in the retrieved documents were "adsorption." "lamellar double hydroxides" and "water treatment". Through the bibliometric analysis it was possible to verify that LDHs are promising adsorptive agents for the removal of a wide diversity of pollutants present in contaminated water. However, some researches point to the development of composite materials and/or materials with adjusted composition in order to improve even more the efficiency of these materials. Declarations Ethical Approval This material is the authors' own original work, which has not been previously published elsewhere. Consent to Participate Not applied. Consent to Publish Not applied. Author Contributions All authors contributed to the study conception and design. All authors read and approved the final manuscript. JCPLP, AFS, and DHS executed the experiments and manuscript writing; PCN and LM carried out the manuscript interpretation and corrections. Funding The authors thank to National Council for Scientific and Technological Development (CNPq/Brazil), Coordination for the Improvement of Higher Education Personnel (CAPES/Brazil) and Foundation for Research Support of the State of Alagoas (FAPEAL/ Brazil). Competing Interests The authors have no relevant financial or non-financial interests to disclose. Availability of data and materials Data available on request from the authors. References Alcaide-Muñoz, L., Pedro Rodríguez-Bolívar, M., Cobo, M.J., Herrera-Viedma, E., 2017. Analysing the scientific evolution of e-Government using a science mapping approach. https://doi.org/10.1016/j.giq.2017.05.002 Chen, Y., Lin, M., Zhuang, D., 2022. 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J. 215–216, 122–127. https://doi.org/10.1016/J.CEJ.2012.11.024 Golban, A., Lupa, L., Cocheci, L., Pode, R., 2019. Synthesis of MgFe Layered Double Hydroxide from Iron-Containing Acidic Residual Solution and Its Adsorption Performance. Cryst. 2019, Vol. 9, Page 514 9, 514. https://doi.org/10.3390/CRYST9100514 Jiang, M., Qi, Y., Liu, H., Chen, Y., 2018. The Role of Nanomaterials and Nanotechnologies in Wastewater Treatment: a Bibliometric Analysis. Nanoscale Res. Lett. 13, 1–13. https://doi.org/10.1186/S11671-018-2649-4/TABLES/6 Keyikoglu, R., Khataee, A., Yoon, Y., 2022. Layered double hydroxides for removing and recovering phosphate: Recent advances and future directions. Adv. Colloid Interface Sci. 300, 102598. https://doi.org/10.1016/J.CIS.2021.102598 Li, A., Deng, H., Ye, C., Jiang, Y., 2020. Fabrication and Characterization of Novel ZnAl-Layered Double Hydroxide for the Superadsorption of Organic Contaminants from Wastewater. ACS Omega 5, 15152–15161. https://doi.org/10.1021/ACSOMEGA.0C01092/ASSET/IMAGES/ACSOMEGA.0C01092.SOCIAL.JPEG_V03 Liang, H., Gandi, A.N., Xia, C., Hedhili, M.N., Anjum, D.H., Schwingenschlögl, U., Alshareef, H.N., 2017. Amorphous NiFe-OH/NiFeP electrocatalyst fabricated at low temperature for water oxidation applications. ACS Energy Lett. 2, 1035–1042. https://doi.org/10.1021/ACSENERGYLETT.7B00206/SUPPL_FILE/NZ7B00206_SI_001.PDF Mahmoud, R.K., Taha, M., Zaher, A., Amin, R.M., 2021. Understanding the physicochemical properties of Zn–Fe LDH nanostructure as sorbent material for removing of anionic and cationic dyes mixture. Sci. Reports 2021 111 11, 1–19. https://doi.org/10.1038/s41598-021-00437-w Matusik, J., Rybka, K., 2019. Removal of Chromates and Sulphates by Mg/Fe LDH and Heterostructured LDH/Halloysite Materials: Efficiency, Selectivity, and Stability of Adsorbents in Single- and Multi-Element Systems. Mater. (Basel, Switzerland) 12. https://doi.org/10.3390/MA12091373 Pourfaraj, R., Fatemi, S.J., Kazemi, S.Y., Biparva, P., 2017. Synthesis of hexagonal mesoporous MgAl LDH nanoplatelets adsorbent for the effective adsorption of Brilliant Yellow. J. Colloid Interface Sci. 508, 65–74. https://doi.org/10.1016/J.JCIS.2017.07.101 Santos, D.H.S., Duarte, J.L.S., Tonholo, J., Meili, L., Zanta, C.L.P.S., 2020. Saturated activated carbon regeneration by UV-light, H2O2 and Fenton reaction. Sep. Purif. Technol. 250, 117112. https://doi.org/10.1016/j.seppur.2020.117112 Santos, L.C., da Silva, A.F., dos Santos Lins, P.V., da Silva Duarte, J.L., Ide, A.H., Meili, L., 2020. Mg-Fe layered double hydroxide with chloride intercalated: synthesis, characterization and application for efficient nitrate removal. Environ. Sci. Pollut. Res. Int. 27, 5890–5900. https://doi.org/10.1007/S11356-019-07364-4 Țolea, S.N., Cocheci, L., Lupa, L., Vodă, R., Pode, R., 2021. Development of New Efficient Adsorbent by Functionalization of Mg3Al-LDH with Methyl Trialkyl Ammonium Chloride Ionic Liquid. Mol. 2021, Vol. 26, Page 7384 26, 7384. https://doi.org/10.3390/MOLECULES26237384 Zaghloul, A., Benhiti, R., Ait Ichou, A., Carja, G., Soudani, A., Zerbet, M., Sinan, F., Chiban, M., 2020. Characterization and application of MgAl layered double hydroxide for methyl orange removal from aqueous solution. Mater. Today Proc. 37, 3793–3797. https://doi.org/10.1016/J.MATPR.2020.07.676 Zhang, Q., Ji, F., Jiang, L., Shen, Q., Mao, Y., Liu, C., 2022. Glycine- and Alanine-Intercalated Layered Double Hydroxides as Highly Efficient Adsorbents for Phosphate with Kinetic Advantages. Nanomater. (Basel, Switzerland) 12. https://doi.org/10.3390/NANO12040586 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Major revision 27 Oct, 2022 Reviews received at journal 03 Oct, 2022 Reviewers agreed at journal 03 Oct, 2022 Reviewers invited by journal 28 Sep, 2022 Editor assigned by journal 27 Sep, 2022 Submission checks completed at journal 16 Sep, 2022 First submitted to journal 15 Sep, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2070633","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":137186114,"identity":"65eaec2a-0f34-4fd4-82ef-c1d967f5bde2","order_by":0,"name":"Juliana C. P. L. Paulino","email":"","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Juliana","middleName":"C. P. L.","lastName":"Paulino","suffix":""},{"id":137186115,"identity":"99ef1c70-7186-4bfa-9c35-96b60e892b50","order_by":1,"name":"Anamália F. Silva","email":"","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Anamália","middleName":"F.","lastName":"Silva","suffix":""},{"id":137186117,"identity":"cccd2ef9-84f6-48d5-a20c-9e22e9112e69","order_by":2,"name":"Danilo H. S. Santos","email":"","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Danilo","middleName":"H. S.","lastName":"Santos","suffix":""},{"id":137186123,"identity":"487683db-525e-467b-a283-725b09f87bde","order_by":3,"name":"Patrícia C. Nagliate","email":"","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Patrícia","middleName":"C.","lastName":"Nagliate","suffix":""},{"id":137186127,"identity":"c9aace8f-7e6f-4ea3-bedc-73335dc41136","order_by":4,"name":"Lucas Meili","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8UlEQVRIie2OsWoCQRRF7/JgbBbTThCyv7CLEBIi+ZYXBrYSLGy2i0FYG78n9YI/ERmLFWHrTTdWOoMogkzULsWcZi5vONwLBAL/kO4xiE70VR9iVKNG5VXEKVA0TcEukntvUEAQ8jZFqvWvwfdTl6gstmaQQKqoZaxGfiXv92Lovh1WLuecZxOpSDKa14lXGaIH6I/SKhq8YMhRZZVF6m8Z0tZAfzplDN5ZRZG5oghph7EbRuDKKeLvlrh5fotTndmW6eM8V1kZb8QLp41XeeiozdIUOklms3VrBu+JvdBPW6y8yoHzb3FxCQQCgcDd7AGGu0i0vuAtdQAAAABJRU5ErkJggg==","orcid":"","institution":"Federal University of Alagoas","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Lucas","middleName":"","lastName":"Meili","suffix":""}],"badges":[],"createdAt":"2022-09-16 01:44:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2070633/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2070633/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":26726766,"identity":"978608a6-c173-4398-aadd-da0d0d59f8cc","added_by":"auto","created_at":"2022-09-20 20:49:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":133255,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) Number of publications retried between the years 1997 to 2022 (Source: bibliometrix.org); (b) research map that shows all the countries that published on the theme. 1997-2022.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/699ece9a347d09c5a50a45f5.png"},{"id":26726771,"identity":"3d49eaf8-a5e9-4253-92bb-5b7011ffacbe","added_by":"auto","created_at":"2022-09-20 20:49:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":128886,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) 10 main countries in number of documents on the subject; (b) most frequent cooperation network.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/46bdf558975c1616aaccac9d.png"},{"id":26727405,"identity":"a5ce4132-9c2f-4f8e-b950-f0a891a72afb","added_by":"auto","created_at":"2022-09-20 20:54:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":47451,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eAnnual average of document citations (Source: bibliometrix.org).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/89bdc7c5a4b2fa745516526c.png"},{"id":26726770,"identity":"8e56f554-6dc4-487a-828a-a9bb1abcdbe6","added_by":"auto","created_at":"2022-09-20 20:49:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":25664,"visible":true,"origin":"","legend":"\u003cp\u003eThe 20 institutions with the most publications on the subject.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/6f2cc3ff5f0c8bf41477652e.png"},{"id":26727406,"identity":"49b2bf46-c23d-4cfe-bb7c-b475e0ce93a0","added_by":"auto","created_at":"2022-09-20 20:54:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":26233,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMain areas of study on the subject.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/c4d7a2e5aae03aa72498a6ea.png"},{"id":26728277,"identity":"0000f9f3-546f-48cd-bb34-e6c569401cbf","added_by":"auto","created_at":"2022-09-20 20:59:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":51509,"visible":true,"origin":"","legend":"\u003cp\u003eDegree of connection between clusters and between keywords in the cluster. (Source: bibliometrix.org).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/9194172657caca89b3939636.png"},{"id":26726767,"identity":"da3e07fa-0703-472e-afc5-93c349be4dda","added_by":"auto","created_at":"2022-09-20 20:49:17","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":798071,"visible":true,"origin":"","legend":"\u003cp\u003eVisualization of a network related to the most frequently occurring keywords in the retrieved documents.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/38ce53067b480b32be4439ee.png"},{"id":26728311,"identity":"5bcc5537-d924-4d07-b566-48d245800091","added_by":"auto","created_at":"2022-09-20 20:59:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1564358,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2070633/v1/99310a98-98c3-4258-9851-d00703967f29.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hotspots and trends of layered double hydroxide-based adsorbents for polluted water treatment: Insights from bibliometric analysis","fulltext":[{"header":"1. introduction","content":"\u003cp\u003eRapid population growth, uncontrolled exploitation of natural resources, and the use of a wide variety of chemicals in activities essential to humans such as agriculture, industrial processes, among others, have been causing enormous environmental instability worldwide (Koutavarapu et al., 2021). Among the main impacts generated by human intervention on the natural environment, water pollution has stood out as one of the most serious problems of today\u0026apos;s society (Nasrollahzadeh et al., 2021). In addition to limiting the availability of an essential resource for human life (Fan and Fang, 2020), the degradation of water quality, interferes with socioeconomic development worldwide, since water plays an important role in several sectors essential to industrial development, functioning as a key element in the production of food and energy, for example (Mao et al., 2015). Moreover, when contaminated, water becomes the primary mode by which potentially toxic chemicals come into contact with the human and animal community, since such substances, when soluble, are more easily transported and distributed through the water cycle (Oller et al., 2011; Yang et al., 2019).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe inadequate management of contaminated water by conventional treatment systems has contributed to the expansion of studies dealing with the development of alternative treatment systems that are able to remove the varied classes of pollutants resistant to conventional treatments and ensure that the treated water is healthy for reuse and/or consumption (Kıdak and Doğan, 2018). Among the various technologies that have been evaluated for their efficiency in treating contaminated water, the Adsorption process is most prevalently cited in review papers (Z. Li et al., 2020). This process is preferred over others because it has some important advantages such as relatively simple design, easy operation, high cost-effectiveness, ability to remove pollutants at very low concentrations, low energy consumption, and high availability of raw materials (Fiyadh et al., 2019). Moreover, the adsorption process has a wide applicability, being the most favorable method for removing contaminants of organic and/or inorganic nature (Kim et al., 2022).\u003c/p\u003e\n\u003cp\u003eThe efficiency of the adsorption process depends on the surface characteristics of the adsorbent material and how these interact with the specific pollutants to be adsorbed (Fiyadh et al., 2019). Although it is considered the best adsorbent for cleaning liquid solutions, the widespread use of activated carbon is restricted due to its high cost (da Silva Santos et al., 2021; D. H. S. Santos et al., 2020)(Wang, Wang, and Ma, 2010). One ton of such material produced from coconut husk, for example, costs, before shipment, about USD950-1400 (Ahmedna, Marshall, and Rao, 2000). The high cost of producing and marketing AC, in addition to contributing to the lack of access to commercially treated water for a significant fraction of the population in developing countries, given the low per capita income of these countries, also limits the ability of industries to treat their effluents to the required environmental standards prior to disposal-with some industries operating outside legal limits-thereby exacerbating environmental pollution (Ntuli and Hapazari, 2013).\u003c/p\u003e\n\u003cp\u003eIn this regard, the interest in the development of unconventional adsorbent materials that are efficient in removing a variety of pollutants of organic and/or inorganic nature, easy to obtain, low toxicity, good regenerative capacity and, in particular, low cost, has been the main object of studies in this area (Kumar et al., 2019). Recent progress in nanoscience and nanotechnology has helped researchers to design nanoscale materials with the desired structure and functionality (Sohrabi et al., 2021). In this perspective, layered double hydroxides (LDHs) have been receiving more and more attention.\u003c/p\u003e\n\u003cp\u003eLayered double hydroxides comprise a class of two-dimensional anionic clays with a structure similar to the mineral hydrotalcite ([Mg\u003csub\u003e6\u003c/sub\u003eAl\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e16\u003c/sub\u003e]CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e4H\u003csub\u003e2\u003c/sub\u003eO) (Mohapatra and Parida, 2016). The general formula of LDHs is represented by the equation M\u003csup\u003e2+\u003c/sup\u003e\u003csub\u003e1-x\u003c/sub\u003eM3\u003csup\u003e+\u003c/sup\u003e\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e.An-x/n.zH\u003csub\u003e2\u003c/sub\u003eO, where M\u003csup\u003e2+\u003c/sup\u003e and M\u003csup\u003e3+\u003c/sup\u003e correspond to di- and trivalent cations, respectively, and An\u003csup\u003e-\u003c/sup\u003e is an anion. The cations are responsible for the positive charges presented by the lamellae, while the anionic species along with water molecules, present in the interlamellar regiation, makes the material stable (Mishra, Dash, and Pandey, 2018).\u003c/p\u003e\n\u003cp\u003eCommonly known as anionic clays or hydrotalcite-like materials, LDHs are easily synthesized using lowcost materials and unsophisticated equipment (Jijoe et al., 2021). These materials exhibit a unique molecular structure with highly controllable chemical composition of the cationic layers and interlamellar region. Thus, LDHswith different element compositions and metal cation ratios can be produced. These materials exhibit differences in their morphology and crystal structure, which allows them to be designed for a specific purpose (Keyikoglu, Khataee, and Yoon, 2022).\u003c/p\u003e\n\u003cp\u003eThe use of LDHsas adsorbent materials in the remediation of environmental problems has been the most commonly reported application in the literature. Although an increasing interest in the use of these materials as adsorbent materials is observed, there is a gap in statistical research trend information on this topic. In this sense, the present work aims, through a bibliometric study, to analyze the scientific guidelines on the suitability of layered double hydroxides (LDHs) as adsorbent agents for contaminants in aqueous media in order to prospect new research directions and/or strategies with potential to boost the use of these materials.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1 Bibliometric Analysis\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis method allows the identification, organization, and evaluation of the constituent elements of a specific study area, and is therefore an important tool for reviews. It is a comprehensive technique related to mathematical and statistical methods to discover the distribution, variation, and quantity of publications in public databases on a given subject (Gallego-Valero, Moral-Parajes, and Rom\u0026aacute;n-S\u0026aacute;nchez, 2021).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Data source\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Web of Science (WoS) database was used to perform the bibliometric analysis. WoS has high visibility in various fields of knowledge, a selection filter for prestigious publications, and is also widely used to conduct bibliometric studies (Jiang et al., 2018).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.3 Data selection and processing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe sample of documents analyzed in this study was obtained using the terms (\u0026quot;layered double hydroxides\u0026quot; OR \u0026quot;anionic clays\u0026quot; OR \u0026quot;hydrotalcite-like materials\u0026quot;) AND (\u0026quot;adsorption\u0026quot; OR \u0026apos;adsorvent\u0026quot;) AND (\u0026quot;treatment OR remediation\u0026quot;) AND (water OR \u0026quot;contaminated waters\u0026quot; OR \u0026quot;effluents\u0026quot; OR \u0026quot;wastewater\u0026quot;). The literature search was performed with all the terms that, according to the literature, are commonly used to refer to LDHs in order to obtain results more consistent with reality. The chronology used for the search took into account the date of the first publication retrieved on the subject in the database until March 2022 (1997-2022). The bibliometix R-package and VOSviewer softwares were used for bibliometric analysis and scientific mapping of the retrieved data.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 General characteristics of the retrieved samples\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThrough the searches performed in the WoS database, a total of 663 documents were retrieved, of which 89.54% (595 records), the absolute majority, refer to scientific articles, 9.05% (60 records) correspond to review documents, and the less than 2% remaining correspond to the sum of other types of records such as meeting abstracts, book chapters, news, editorial material, among others.\u003c/p\u003e\n\u003cp\u003eArticles printed in English correspond to 98.6% of the total records, followed by articles published in Chinese, 0.9% of the total. The proportion of the sum of the other three languages with retrieved records, which include French, Polish, and Turkish, is less than 0.5 percent. The histogram presented in Figure 1(a) shows the variations in the number of retrieved publications related to the theme between the years 1997 and 2022. The data obtained show, in general, an upward trend. In the first nine years (1997-2005), academic research in this area was in its early stages, with a publication rate of 1.75 papers per year, a negligible figure. In the subsequent years, 2006 to 2015, a greater number of documents were retrieved, reaching an average of 15.5 publications per year, a rate 8.9 times higher than that observed previously (1997-2005). However, in more recent periods (2016 to 2022), the publication rate has increased rapidly and substantially, with the average number of publications being about 3.1 times higher than in the previous period evaluated (2006 to 2015). In the year 2022, by the time the data were surveyed (3/21/2022), 10 studies on the topic had already been published. These results suggest that in the coming years, annual publications on this topic will continue to grow.\u003c/p\u003e\n\u003cp\u003eCharacteristics such as high efficiency in the removal of a variety of pollutants, versatility in composition, low cost, low toxicity, regenerative capacity, among others presented by LDHs, added to the increasing disposal of large quantities and varieties of pollutants harmful to the environment, population growth and high demand for water resources, and the commitment to reduce environmental contamination, consequently generate an urgency in the development of new technologies in these areas and corroborate the growth trend observed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Relevant countries in research on the topic \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe papers published on topic in the period 1997-2022 come from a total of 69 countries. Figure 1 (b) shows the map of countries with results in the research, the darker the color of the country/region, the more papers there are in that country/region. Although most studies in this field come from a relatively small number of countries, such as China, India, USA, Japan, Brazil, Saudi Arabia, Australia, France, South Korea and Canada, it is notably explicit that countries from all continents and with a wide diversity of economic and socio-cultural characteristics produce relevant research in this area of knowledge.\u003c/p\u003e\n\u003cp\u003eFigure 2 (a) presents the percentages of the 10 most productive countries/territories on the topic. China is the most prolific territory, accounting for 47.96% of the total, with 318 retrieved papers. The second place is occupied by India (7.69% of the total, 51 papers), followed by Japan with 40 papers, representing 6.03% of the total. Subsequently we have USA (40 documents, 6.03%), Brazil (28 documents, 4.22%), Saudi Arabia (28 documents, 4.22%), Australia (25 documents, 3.77%), France (25 documents, 3.62%), South Korea (24 documents, 3.62%) and Canada (17 documents, 2.56%).\u003c/p\u003e\n\u003cp\u003eThe worsening problem of water scarcity in China, caused by serious problems of contamination of drinking water and underground sources by arsenic and fluoride, further associated with rapid economic growth and the large number of industrial production activities in the country, resulted in increased investment in research aimed at the use of advanced technology for water treatment, making this nation a power in this area of technology, which justified the consolidation of China as the country that produces the most on the subject (Wu, 2020).\u003c/p\u003e\n\u003cp\u003eSocial network analysis was then applied to analyze the coauthorship relationships among all the producing countries/territories, the results are displayed in Figure 2 (b). Each point represents a node in the network, with nodes being equivalent to countries. The larger the node, the larger the number of cooperations performed by these countries. The lines between the nodes indicate the occurrence of cooperation between the countries, and the thickness of the line is proportional to the number of publications retrieved from these cooperations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eClearly, China, the largest producer of papers on the topic, also has the largest number of collaborations with other countries/territories, given the size of the node in Figure 2(b). The Chinese have produced publications in cooperation with several countries, with their collaborations with the US, India, Saudi Arabia, Canada, Australia, the UK, and Korea standing out as the most intense, a fact denoted by the thickness of the lines of connections. The U.S. presents not very expressive cooperation data, besides interacting with a reduced number of countries/territories, its main productions are the fruit of an intense cooperation with the Chinese, which, according to Figure 2(b), is the most frequent among all the others, with a total of 23 retrieved documents. Figure 3 presents the annual average of document citations. The 10 most frequent cooperation between countries/regions, obtained by the bibliometrix package (version 3.1.4), are summarized in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e The cooperation among countries/regions.\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" style=\"border-collapse: collapse; margin: 0px auto;\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"33.333333333333336%\"\u003e\u003cstrong\u003eFrom\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"33.333333333333336%\"\u003e\u003cstrong\u003eTo\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"33.333333333333336%\"\u003e\u003cstrong\u003eFrequency\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eUSA\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e23\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eSaudi Arabia\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e17\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eAustralia\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e14\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eCanada\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e10\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eKorea\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e10\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eUnited Kingdom\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eIndia\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eKorea\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eSaudi Arabia\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003ePakistan\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e7\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eChina\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eIndia\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e6\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eJapan\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003eBangladesh\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e5\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp skip=\"true\"\u003eOverall, it is observed that the overall citation of this field shows a zigzag trend and indicates that more and more scholars are paying attention to this field in recent years. The average number of citations peaked in 2001 with average total citations of each article is 200 times. The average of total citations for each article reached 9.52 times per year. The article published by Liang (2017)(Liang et al., 2017) is the most cited.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Analysis of publications by institutions and authors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA total of 765 institutions contributed to the 663 retrieved publications on the topic. The most productive institution was the Chinese Academy of Sciences, which published 45 papers, followed by North China Electric Power University (22), Centre National de la Recherche Scienque CNRS (20), by China University of Geosciences (14) and Tsinghua University (14). The 20 institutions with the highest number of retrieved publications on the topic are summarized in Figure 4. Through the results it was found that 15 of the 20 most productive institutions are from China, the other 5 institutions are distributed among 4 countries: France, Saudi Arabia, India and Egypt.\u003c/p\u003e\n\u003cp\u003eA total of 2,910 researchers participated in the retrieved publications. The authors with the most publications on the topic are shown in Table 2. Researcher Wang XK appears with the highest number of publications (20, 3.01%), followed by Wang XX (13, 1.96%), Qian GR (11, 1.65%), Zhang XL (11, 1.65%), Yu SJ (10, 1.50%).\u003c/p\u003e\n\u003cp\u003eAnother important parameter to consider is the number of citations. In this case, Wang XK tops the list with a total number of 1246 citations, Wang XXA was second with the most citations (1099), followed by Hayat T, Yu SJ and Ok YS who had a total of 593, 523 and 497 citations, respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4 Main Areas of Study on the Theme\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe results of the bibliometric analysis allow us to distinguish between the different disciplines to which the scientific articles analyzed belong. It should be noted that an article may belong to more than one category; therefore, the results are analyzed in percentages. In all, 25 different areas of knowledge are covered with publications on the topic. Figure 5 shows the top 10 areas of study. Among the various research areas, the most important are Environmental Sciences with 16.63% of the total, followed by Environmental Engineering (14.07%), Physical Chemistry (13.17%), Chemical Engineering (12.18%), Multidisciplinary Materials Sciences (10.12%), Multidisciplinary Chemistry (6.83%), Water Resources (4.03%), Mining (3.7%), Nanoscience Nanotechnology (2.55%) and Green Sustainble Science Technology (2.49 %). The item identified as \u0026quot;other\u0026quot; (13.99% of the total) includes a wide and diverse range of knowledge areas such as microbiology, mathematics, geology, microscopy, toxicology, biophysics, among others.\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u0026nbsp;Authors with the most publications on the theme.\u0026nbsp;\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" width=\"24.242424242424242%\"\u003e\u003cstrong\u003eAuthor\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\" width=\"50.505050505050505%\"\u003e\u003cstrong\u003eDocuments\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\" width=\"25.252525252525253%\"\u003e\u003cstrong\u003eCitations\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"50%\"\u003e\u003cstrong\u003eQuantity\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"50%\"\u003e\u003cstrong\u003ePercent\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eWang XK\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e20\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e3,01%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1246\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eWang XX\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e13\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,96%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1099\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eQian GR\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e11\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,65%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e352\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eZhang XL\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e11\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,65%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e181\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eYu SJ\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e10\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,50%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e523\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eKameda T\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e9\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,35%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e73\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eYan LG\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e9\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,35%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e161\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eYoshioka T\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e9\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,35%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e73\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eZhang J\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e9\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,35%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e225\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eChen H\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,20%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e90\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eHayat T\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,20%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e593\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"24.242424242424242%\"\u003eLi J\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e1,20%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"25.252525252525253%\"\u003e95\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 Journals that most published on the subject\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe total number of retrieved documents is distributed among 217 journals. With 6.63% of the total sample of articles (44 documents) the Chemical Engineering Journal, a comprehensive journal for Environmental Chemical Engineering, was the most productive journal, followed by Applied Clay Science (38), Journal of Hazardous Materials (35) and Chemosphere (27). Together, these four journals published 21.49% of the total articles on this research topic. In addition to those mentioned above, other important journals also published within this theme. The information of the 10 journals that publish the most articles on the research topic and their main indexes are summarized in Table 3.\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u0026nbsp;Journals that have published the most on the subject and their impact factors.\u003c/p\u003e\n\u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" style=\"border-collapse: collapse; margin: 0px auto;\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\"\u003e\u003cstrong\u003eJournal\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"2\"\u003e\u003cstrong\u003eDocuments\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd rowspan=\"2\"\u003e\u003cstrong\u003eIF*\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cstrong\u003eQuantity\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cstrong\u003ePercent\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eChemical Engineering Journal\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e44\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e6.637%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e13.273\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eApplied Clay Science\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e38\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e5.732%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e5.467\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eJournal of Hazardous Materials\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e35\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e5.279%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e10.588\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eChemosphere\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e27\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e4.072%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e7.086\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eJournal of Cleaner Production\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e18\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e2.715%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e9.297\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eColloids and Surfacesa Physicochemical and Engineering Aspects\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e14\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e2.112%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e4.539\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eScience of the Total Environment\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e14\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e2.112%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e7.963\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eEnvironmental Science and Pollution Research\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e13\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1.961%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e4.223\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eJournal of Environmental Chemical Engineering\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e13\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1.961%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e5.876\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eDesalination and Water Treatment\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e12\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1.810%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1.254\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003eJournal of Materials Chemistry A\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e9\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e1.357%\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e7.393\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp style=\"text-align: center;\"\u003e*Impact Factor 2022.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 The main fields of research\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe keywords of a scientific document may offer important information about the main ideas and trends of a given theme, and are therefore an extremely important tool in bibliometric analyses. In this paper a total of 1475 keywords were identified, of which the vast majority had only one (1179, 79.7%) or two (210, 14.62%) occurrences, while 69 (4.06%) of the keywords had 5 or more occurrences.\u003c/p\u003e\n\u003cp\u003eThematic evolution analysis can be used to detect, quantify and visualize specific fields of research, and can visually show the evolution of the theme in recent years. A strategy map shown in Figure 6 divided into four quadrants shows the degree of connection between the clusters and between the keywords in the cluster.\u003c/p\u003e\n\u003cp skip=\"true\"\u003eThe second and third quadrants are the most developed, with strong centrality and high impact being the most relevant for the current field. Similar words are found in the first and fourth quadrants, indicating a certain linearity in the use of HDLs.\u003c/p\u003e\n\u003cp skip=\"true\"\u003eThe strategic diagrams allow visualizing the research field as a set of themes, mapped and classified into four groups, categorized in terms of density and centrality: (I) cluster engine (first quadrant, with high density and strong centrality); (II) highly developed and isolated clusters (second upper left quadrant, with marginal importance for the research field; \u0026apos;specialized topics\u0026apos;); (III) declining or emerging clusters (third quadrant, with low density and low centrality; \u0026apos;emerging or disappearing themes\u0026apos;); and (IV) basic and transversal clusters (fourth quadrant, with important but undeveloped themes; \u0026apos;transversal and general themes\u0026apos;) (Alcaide-Mu\u0026ntilde;oz et al., 2017; Cobo et al., 2012). It is noteworthy that the sphere represents a cluster of words (or theme) and the name of each one of these is related to the most recurrent word and/or theme; the volume of the spheres corresponds to the number of associated articles - the larger the sphere, the greater the number of articles that cited that word as a keyword \u0026nbsp;(Cobo et al., 2012, 2011).\u003c/p\u003e\n\u003cp\u003eThe detection of the most commonly used keywords in the retrieved documents, limited to the minimum number of 5 occurrences, are presented in Figure 7. Each point represents a node in the network, with the nodes being equivalent to the keywords. The larger the node, the greater the number of links made by these terms. The lines between the nodes indicate the co-occurrence between the keywords, and the thickness of the line is proportional to the quantity with which this co-occurrence is perceived.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVisibly, the terms \u0026quot;adsorption\u0026quot;, \u0026quot;lamellar double hydroxides\u0026quot;, and \u0026quot;water treatment\u0026quot; stand out among the others as the terms that have the largest numbers of links to other keywords. The term \u0026quot;adsorption\u0026quot; is the most highlighted by the retrieved documents with a total of 199 occurrences, which reflects its central position in this high-frequency search field. The top 20 retrieved keywords and their respective occurrence numbers are summarized in Table 4.\u003c/p\u003e\n\u003cp\u003eThe co-occurrences between the keywords did not highlight a specific trend in the retrieved papers on the topic, as no significantly thick lines were observed between the terms. These results may indicate that research trends in this area are growing more diverse. The propensity for research on the topic can be identified by analyzing the different groups into which the keywords fall. \u0026nbsp;In all, the terms are comprised in 7 groups identified by distinct colors. Of these, four main groups were observed, chosen by the largest number of keywords included.\u003c/p\u003e\n\u003cp\u003eThe first group, colored yellow, comprises a total of 12 keywords and focuses on the determination of the parameters related to the adsorption process due to its conjunction with terms such as \u0026quot;kinetics\u0026quot;, \u0026quot;thermodynamics\u0026quot;, \u0026quot;isotherm\u0026quot; and \u0026quot;equilibrium\u0026quot;. \u0026nbsp;The second group, blue in color, has 17 keywords, and the presence of the terms \u0026quot;composite\u0026quot;, \u0026quot;biochar\u0026quot;, \u0026quot;memory effect\u0026quot;, \u0026quot;magnetic separation of metal ions\u0026quot; and \u0026quot;regeneration\u0026quot; indicate that this group focuses mainly on the production of composite materials and on the properties of LDHs. The third group, colored green, with 13 keywords, focuses on the methods of synthesis and composition of materials, with the presence of the terms \u0026quot;precipitation\u0026quot;, \u0026quot;selective adsorption\u0026quot;, \u0026quot;calcination\u0026quot;, and \u0026quot;engineering\u0026quot;. \u0026nbsp;The fourth group, with red coloring, has 14 keywords, and deals with the efficiency of LDHs in the removal of different classes of pollutants due to the adjection of the terms \u0026quot;organic pollutants\u0026quot;, \u0026quot;dyes\u0026quot;, heavy metals, among others.\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u003cstrong\u003eTable 4\u003c/strong\u003e\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003eMain keywords and their number of occurrences.\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003e\u003cstrong\u003eKeywords\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e\u003cstrong\u003eOccurrences\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eAdsorption\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e199\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eLayered Double Hydroxides\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e129\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eLayered Double Hydroxide\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e67\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eWater Treatment\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e56\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eWasterwater Treatment\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e54\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eKinetics\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e18\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eHydrotalcite\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e30\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eSorption\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e25\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eFluorede\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e23\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eWasterwater\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e17\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003ePhosphate\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e19\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eLDH\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e18\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eBiochar\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e15\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003ePhotocatalysis\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e17\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eMethyl Orange\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e16\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eCr(VI)\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e13\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eRemoval\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e13\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eDyes\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e8\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eEquilibrium\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e6\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"50.49261083743843%\"\u003eArsenic\u003cbr\u003e\u003c/td\u003e\n \u003ctd valign=\"top\" width=\"49.50738916256157%\"\u003e15\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;Some terms such as \u0026quot;phosphate\u0026quot;, \u0026quot;phenol\u0026quot;, \u0026quot;metal ions\u0026quot;, \u0026quot;dyes\u0026quot;, \u0026quot;pesticides\u0026quot;, among others, used to refer to the wide range of pollutants and/or contaminants present in water, and the terms \u0026quot;biochar\u0026quot;, \u0026quot;photocatalysis\u0026quot;, \u0026quot;nanomaterials\u0026quot; among others, which refer to the structure and composition of LDHs are found in more than one group in Figure 7. The analysis took into consideration only the distinct terms present in the groups in order to understand the different guidelines of papers retrieved on the topic. Some papers dealing with the different research guidelines related to the topic are summarized in Table 5.\u003c/p\u003e\n\u003cp\u003eTable 5 concisely shows the diversity in the composition of LDHs, as well as their versatility in removing a variety of contaminants in aqueous solution. Furthermore, it can also be seen that the coprecipitation method is the most commonly used for syntheses, a fact elucidated by being a simple method and easy to manipulate in the laboratory (Chang et al., 2005). In this method, the formation of the lamellar structure of the hydroxides occurs in a simple step of precipitation of the bi- and trivalent cations with the interlamellar anion, using the addition of alkaline aqueous solution, in batch (Silva et al., 2021). The number of cycles, a very important data for knowledge of the regeneration capacity and, which can be used for industrial application, is little reported in the researched works. Li et al. (2020) (A. Li et al., 2020), evaluated the recyclability of the ZnAl adsorbent using sodium hydroxide for the adsorption-desorption experiments and, identified that the removal rate of the Congo red dye decreases from 98.01% (1st cycle) to 67.11% after four times of recycling.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eJust as the adsorption capabilities in pure LDHs are widely investigated, new work involving the production of LDH composites is under increasing development, demonstrating excellent performances in enhancing contaminant removal. In Tolea et al. (2021) (Țolea et al., 2021), LDH -Mg\u003csub\u003e3\u003c/sub\u003eAl was used to support Methyl Trialkyl Ammonium Chloride and increase the adsorption capacity of the new adsorbent material, furthermore, in the same work, two synthetic routes were also investigated and compared for their adsorption capacity as shown in Table 5. Thus, the study identified that functionalization of Mg\u003csub\u003e3\u003c/sub\u003eAl with Methyl Trialkyl Ammonium Chloride (Mg\u003csub\u003e3\u003c/sub\u003eAl-IL-US) increased the adsorption capacity from 143 mg/g to 217 mg/g and presented maximum adsorption capacity of 648 mg/g for sample (Mg\u003csub\u003e3\u003c/sub\u003eAl-IL-COS) obtained by cosynthesis. In the Cl-LDH chloride intercalated LDH-MgAl a slight improvement in phosphate removal was presented, with the value of 63.2 mg/g, when compared to the materials with glycerol (Gly-Cl-LDH) and alanine intercalated (Ala-Cl- LDH), with removal capacity of 55.8 and 58.2 mg/g, respectively (Zhang et al., 2022). However, in the same work, characterization results showed that compared to MgAl-CL, Gly-Cl- LDH and Ala-Cl-LDH have higher porosity and higher specific surface area, in addition to the larger interlayer space for samples with intercalated glycerol and alanine.\u0026nbsp;\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u003cstrong\u003eTable 5\u003c/strong\u003e\u003c/p\u003e\n\u003cp style=\"text-align: center;\"\u003e\u0026nbsp;Efficiency of LDHs of varied composition obtained by different synthesis methods, used as adsorbents in the removal of different pollutants.\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003e\u003cstrong\u003eComposition\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e\u003cstrong\u003ePollutant\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e\u003cstrong\u003eEfficiency/adsorption capacity\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003e\u003cstrong\u003eSynthesis method\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e\u003cstrong\u003eRegeneration cycles\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e\u003cstrong\u003eReferences\u003c/strong\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgFe-Cl\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eChromates\u003cbr\u003eSulfates\u003cbr\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e100%\u003cbr\u003e93%\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Matusik and Rybka, 2019)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgFe-\u0026nbsp;CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eMolybdenum\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e39.9 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Golban et al., 2019)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgFe-Cl\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eNitrate\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e18.17 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003e\u0026nbsp;\u003cbr\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(L. C. Santos et al., 2020)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgAl-Cl\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eBright Yellow\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e115.00\u0026nbsp;mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ehydrothermal\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Pourfaraj et al., 2017)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eCaAl-NO\u003csub\u003e3\u003c/sub\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eDiy\u003cbr\u003e\u0026nbsp;Sunset Yellow\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e398.41 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(De S\u0026aacute; et al., 2013)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgAl-CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eMethyl orange\u003cbr\u003e\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e197.62 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003eurea hydrolysis\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Zaghloul et al., 2020)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eZnAl-\u0026nbsp;NO\u003csub\u003e3\u003c/sub\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eCongo Red diy\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e625.00 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e4\u0026nbsp;\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Li et al., 2020)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eZnFe-NO\u003csub\u003e3\u003c/sub\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eMethyl orange\u003cbr\u003eMethyl blueMalachite green\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e230.68 mg/g\u003cbr\u003e133.29 mg/g\u003cbr\u003e57.34 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Mahmoud et al., 2021)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMg\u003csub\u003e3\u003c/sub\u003eAl-NO\u003csub\u003e3\u003c/sub\u003e\u003cbr\u003eMg\u003csub\u003e3\u003c/sub\u003eAl-IL-US\u003cbr\u003eMg\u003csub\u003e3\u003c/sub\u003eAl-IL-COS\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eDiclofenac\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e143\u0026nbsp;mg/g\u003cbr\u003e217\u0026nbsp;mg/g\u003cbr\u003e648 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003eultrasson\u003cbr\u003ecossynthesis\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Țolea et al., 2021)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"15.064102564102564%\"\u003eMgAl-Cl\u003cbr\u003eGly-Cl-LDH\u003cbr\u003eAla-Cl-LDH\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003eFosfate\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"23.878205128205128%\"\u003e63.2 mg/g\u003cbr\u003e55.8 mg/g\u003cbr\u003e58.2 mg/g\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"16.346153846153847%\"\u003ecoprecipitation\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"15.705128205128204%\"\u003e-\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"13.301282051282051%\"\u003e(Zhang et al., 2022)\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003e3.6 Insights and prospects\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe adsorption process is considered the best technique over other contaminated water treatment strategies for its simplicity of operation and universality for common organic and inorganic contaminants (Crini, 2005; Jiang et al., 2018; D. H. S. Santos et al., 2020). However, the production of adsorbent materials with high dispersion of active sites that allow the maximum utilization of their potential, tunability of the composition and electronic state of the adsorption sites on an atomic scale for greater selectivity for a specific pollutant and Stable active sites that guarantee reuse and performance for long-term use has been the major bottleneck in the application and development of this technology(Chen et al., 2022; Keyikoglu et al., 2022).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRecent progress in nanoscience and nanotechnology has allowed researchers to design nanosized materials with the desired structure and functionality, and in this sense a growing interest in the use of HDLs for water remediation as an adsorbent has been observed(Jiang et al., 2018). These materials present their unique characteristic structures, such as i) tunability of the elemental composition of the host layer where the metallic cations reside, ii) high ion exchange capacity due to the interchangeability of interlayer anions and iii) controllability of the interlayer distance and dimensions of the material by incorporation of suitable anions\u0026nbsp;(Crini, 2005; Jiang et al., 2018; Keyikoglu et al., 2022). In addition to the type of metal cation, the ratio of divalent and trivalent (M\u003csup\u003e2+/\u003c/sup\u003eM\u003csup\u003e3+\u003c/sup\u003e) can be regulated.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe variety of different types of HDLs with a wide range of elemental compositions that can be produced and its association with other materials has increased interest in research using these materials. It is necessary to understand more objectively what all the aspects involved cause in the material obtained and how this product can be used in its most satisfactory way.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe survey obtained from the searches in the scientific bases, culminated in the observation of the rising interest of the development of research and technologies that use layered double hydroxides as adsorbent material in the treatment of contaminated water. From 1997 to 2021, a total of 663 papers related to the topic were published in scientific journals indexed to the Web of Science database. A significant increase in the production on the topic was observed in the last 5 years. China was the country that presented the largest number of retrieved publications on the subject, and also the country that has cooperated the most with other nations in the development of new documents, this is important information, since the issue of water pollution affects the whole world. The bibliometric analysis also indicated that the most productive authors were Wang XK, Wang XX, and Qian GR. The journals that published the most on the topic were Chemical Engineering Journal, Applied Clay Science, Journal of Hazardous Materials, and Chemosphere. In addition to the main focus and research trends in the area by using the keywords most frequently found in the retrieved documents were \"adsorption.\" \"lamellar double hydroxides\" and \"water treatment\". Through the bibliometric analysis it was possible to verify that LDHs are promising adsorptive agents for the removal of a wide diversity of pollutants present in contaminated water. However, some researches point to the development of composite materials and/or materials with adjusted composition in order to improve even more the efficiency of these materials.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis material is the authors\u0026apos; own original work, which has not been previously published elsewhere.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applied.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applied.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. All authors read and approved the final manuscript. JCPLP, AFS, and DHS executed the experiments and manuscript writing; PCN and LM carried out the manuscript interpretation and corrections.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank to National Council for Scientific and Technological Development (CNPq/Brazil), Coordination for the Improvement of Higher Education Personnel (CAPES/Brazil) and Foundation for Research Support of the State of Alagoas (FAPEAL/ Brazil).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData available on request from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAlcaide-Mu\u0026ntilde;oz, L., Pedro Rodr\u0026iacute;guez-Bol\u0026iacute;var, M., Cobo, M.J., Herrera-Viedma, E., 2017. Analysing the scientific evolution of e-Government using a science mapping approach. https://doi.org/10.1016/j.giq.2017.05.002\u003c/li\u003e\n \u003cli\u003eChen, Y., Lin, M., Zhuang, D., 2022. Wastewater treatment and emerging contaminants: Bibliometric analysis. Chemosphere 297, 133932. https://doi.org/10.1016/J.CHEMOSPHERE.2022.133932\u003c/li\u003e\n \u003cli\u003eCobo, M.J., L\u0026oacute;pez-Herrera, A.G., Herrera-Viedma, E., Herrera, F., 2011. Science mapping software tools: Review, analysis, and cooperative study among tools. J. Am. Soc. Inf. Sci. Technol. 62, 1382\u0026ndash;1402. https://doi.org/10.1002/ASI.21525\u003c/li\u003e\n \u003cli\u003eCobo, M.J., L\u0026otilde;pez-Herrera, A.G., Herrera-Viedma, E., Herrera, F., 2012. SciMAT: A new science mapping analysis software tool. J. Am. Soc. Inf. Sci. Technol. 63, 1609\u0026ndash;1630. https://doi.org/10.1002/ASI.22688\u003c/li\u003e\n \u003cli\u003eCrini, G., 2005. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog. Polym. Sci. 30, 38\u0026ndash;70. https://doi.org/10.1016/J.PROGPOLYMSCI.2004.11.002\u003c/li\u003e\n \u003cli\u003eDe S\u0026aacute;, F.P., Cunha, B.N., Nunes, L.M., 2013. Effect of pH on the adsorption of Sunset Yellow FCF food dye into a layered double hydroxide (CaAl-LDH-NO3). Chem. Eng. J. 215\u0026ndash;216, 122\u0026ndash;127. https://doi.org/10.1016/J.CEJ.2012.11.024\u003c/li\u003e\n \u003cli\u003eGolban, A., Lupa, L., Cocheci, L., Pode, R., 2019. Synthesis of MgFe Layered Double Hydroxide from Iron-Containing Acidic Residual Solution and Its Adsorption Performance. Cryst. 2019, Vol. 9, Page 514 9, 514. https://doi.org/10.3390/CRYST9100514\u003c/li\u003e\n \u003cli\u003eJiang, M., Qi, Y., Liu, H., Chen, Y., 2018. The Role of Nanomaterials and Nanotechnologies in Wastewater Treatment: a Bibliometric Analysis. Nanoscale Res. Lett. 13, 1\u0026ndash;13. https://doi.org/10.1186/S11671-018-2649-4/TABLES/6\u003c/li\u003e\n \u003cli\u003eKeyikoglu, R., Khataee, A., Yoon, Y., 2022. Layered double hydroxides for removing and recovering phosphate: Recent advances and future directions. Adv. Colloid Interface Sci. 300, 102598. https://doi.org/10.1016/J.CIS.2021.102598\u003c/li\u003e\n \u003cli\u003eLi, A., Deng, H., Ye, C., Jiang, Y., 2020. Fabrication and Characterization of Novel ZnAl-Layered Double Hydroxide for the Superadsorption of Organic Contaminants from Wastewater. ACS Omega 5, 15152\u0026ndash;15161. https://doi.org/10.1021/ACSOMEGA.0C01092/ASSET/IMAGES/ACSOMEGA.0C01092.SOCIAL.JPEG_V03\u003c/li\u003e\n \u003cli\u003eLiang, H., Gandi, A.N., Xia, C., Hedhili, M.N., Anjum, D.H., Schwingenschl\u0026ouml;gl, U., Alshareef, H.N., 2017. Amorphous NiFe-OH/NiFeP electrocatalyst fabricated at low temperature for water oxidation applications. ACS Energy Lett. 2, 1035\u0026ndash;1042. https://doi.org/10.1021/ACSENERGYLETT.7B00206/SUPPL_FILE/NZ7B00206_SI_001.PDF\u003c/li\u003e\n \u003cli\u003eMahmoud, R.K., Taha, M., Zaher, A., Amin, R.M., 2021. Understanding the physicochemical properties of Zn\u0026ndash;Fe LDH nanostructure as sorbent material for removing of anionic and cationic dyes mixture. Sci. Reports 2021 111 11, 1\u0026ndash;19. https://doi.org/10.1038/s41598-021-00437-w\u003c/li\u003e\n \u003cli\u003eMatusik, J., Rybka, K., 2019. Removal of Chromates and Sulphates by Mg/Fe LDH and Heterostructured LDH/Halloysite Materials: Efficiency, Selectivity, and Stability of Adsorbents in Single- and Multi-Element Systems. Mater. (Basel, Switzerland) 12. https://doi.org/10.3390/MA12091373\u003c/li\u003e\n \u003cli\u003ePourfaraj, R., Fatemi, S.J., Kazemi, S.Y., Biparva, P., 2017. Synthesis of hexagonal mesoporous MgAl LDH nanoplatelets adsorbent for the effective adsorption of Brilliant Yellow. J. Colloid Interface Sci. 508, 65\u0026ndash;74. https://doi.org/10.1016/J.JCIS.2017.07.101\u003c/li\u003e\n \u003cli\u003eSantos, D.H.S., Duarte, J.L.S., Tonholo, J., Meili, L., Zanta, C.L.P.S., 2020. Saturated activated carbon regeneration by UV-light, H2O2 and Fenton reaction. Sep. Purif. Technol. 250, 117112. https://doi.org/10.1016/j.seppur.2020.117112\u003c/li\u003e\n \u003cli\u003eSantos, L.C., da Silva, A.F., dos Santos Lins, P.V., da Silva Duarte, J.L., Ide, A.H., Meili, L., 2020. Mg-Fe layered double hydroxide with chloride intercalated: synthesis, characterization and application for efficient nitrate removal. Environ. Sci. Pollut. Res. Int. 27, 5890\u0026ndash;5900. https://doi.org/10.1007/S11356-019-07364-4\u003c/li\u003e\n \u003cli\u003eȚolea, S.N., Cocheci, L., Lupa, L., Vodă, R., Pode, R., 2021. Development of New Efficient Adsorbent by Functionalization of Mg3Al-LDH with Methyl Trialkyl Ammonium Chloride Ionic Liquid. Mol. 2021, Vol. 26, Page 7384 26, 7384. https://doi.org/10.3390/MOLECULES26237384\u003c/li\u003e\n \u003cli\u003eZaghloul, A., Benhiti, R., Ait Ichou, A., Carja, G., Soudani, A., Zerbet, M., Sinan, F., Chiban, M., 2020. Characterization and application of MgAl layered double hydroxide for methyl orange removal from aqueous solution. Mater. Today Proc. 37, 3793\u0026ndash;3797. https://doi.org/10.1016/J.MATPR.2020.07.676\u003c/li\u003e\n \u003cli\u003eZhang, Q., Ji, F., Jiang, L., Shen, Q., Mao, Y., Liu, C., 2022. Glycine- and Alanine-Intercalated Layered Double Hydroxides as Highly Efficient Adsorbents for Phosphate with Kinetic Advantages. Nanomater. (Basel, Switzerland) 12. https://doi.org/10.3390/NANO12040586\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"emvm","sideBox":"Learn more about [Environmental Management](http://link.springer.com/journal/267)","snPcode":"267","submissionUrl":"https://submission.nature.com/new-submission/267/3","title":"Environmental Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Clays, review, water pollution, adsorption","lastPublishedDoi":"10.21203/rs.3.rs-2070633/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2070633/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe use of layered double hydroxides (LDHs) as adsorbent for water treatment has been gaining relevance in recent years. In this context, this work aimed to map, through a bibliometric study, the extent of research that deals with the theme. The scientific database used was the Web of Science, and the chronology of the search consideredthe period from 1997 to 2022. The bibliometix R-package and VOSviewer software were used in this study. The searches retrieved a total of 663 documents, from 69 countries, distributed among all continents, which China (328), India (51) and Japan (40) were the most productive countries. Important journals in the environmental area and with high impact factor, such as Chemical Engineering Journal (44), Applied Clay Science (38), Journal of Hazardous Materials (35) and Chemosphere (27) most published in the area. The network of keywords used by the authors indicates that the publications retrieved deal mainly with aspects related to the efficiency of (LDHs) in the removal of different pollutants, the composition, the synthesis route and the association with other materials and/or techniques. The result of this study constitutes an important tool for directing future research on the subject.\u003c/p\u003e","manuscriptTitle":"Hotspots and trends of layered double hydroxide-based adsorbents for polluted water treatment: Insights from bibliometric analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-09-20 20:49:14","doi":"10.21203/rs.3.rs-2070633/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2022-10-27T09:03:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2022-10-03T09:28:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"24da8229-ab69-4eec-a46b-da62771e80d6","date":"2022-10-03T09:01:59+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-09-28T07:49:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-09-28T00:47:53+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2022-09-16T09:41:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Management","date":"2022-09-16T01:40:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"emvm","sideBox":"Learn more about [Environmental Management](http://link.springer.com/journal/267)","snPcode":"267","submissionUrl":"https://submission.nature.com/new-submission/267/3","title":"Environmental Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"73cc460b-b28a-4727-b179-c8a36fd60976","owner":[],"postedDate":"September 20th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2022-12-09T01:44:19+00:00","versionOfRecord":[],"versionCreatedAt":"2022-09-20 20:49:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2070633","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2070633","identity":"rs-2070633","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}