Sustainable Facilities Management in the Built Environment: A Mixed-Method Review

: The signiﬁcance of facilities management practices in the built environment and the changing focus to include sustainability principles have been acknowledged. However, there is no consensus on the sustainability principles needed to ensure maximal beneﬁts in the built environment. Few studies have systematically analysed and visualised the trends in facilities management sustainability research. This study thus explored facilities management research and its evolving focus over the past decade regarding sustainability. With a focus on the built environment, an exploratory study using scientometrics and content analysis was undertaken based on the extant literature from 2012 to 2022 published in the Scopus database. Keywords including “sustainable facilities management” and “built environment” were used to identify journal articles and conference papers. Interlinks were mapped and visualised using VOSviewer and complemented with ﬁndings from the content analysis. Findings showed that current research pathways centred around four clusters, including planning and implementation, community-oriented smart facilities management, innovativeness, and environmental and corporate energy management. These core research focus areas were mostly concentrated in the United Kingdom. The core researchers, institutions, funders, and sources were established. Future research gaps and directions based on knowledge areas and methodological and collaborative endeavours were highlighted. The study offers insights to facilities managers, researchers, analysts, and policymakers on the trajectory of sustainable facilities management research and the extent to which the sustainable development agenda has been embraced. The relations between SFM research and opportunities or areas of stronger focus given contemporary occurrences were identiﬁed.


Introduction
The relevance of facilities management practices in the built environment has been recognised for decades.The global facility management market exceeded $1 trillion in 2022, may hit $2 trillion by 2027, and is projected to reach $119.4 billion by 2030 [1].The growth trajectory has been attributed to global trends including increasing investments in the real estate and construction industries, cloud deployments due to COVID-19, prominent remote working, and outsourcing trends [2].The facilities management sector contributes towards the realisation of many sustainable development goals (SDGs) [3,4].As a key component of the built environment and the services that help maintain and run the infrastructure, the facilities management industry plays a crucial role in meeting environmental challenges and organisations' and stakeholders' obligations (core and non-core activities) [5].
Facilities management integrates concerns from people, workplaces, and resources.Adequately managed facilities help to save on the costs of managing both the premises and equipment and boost employee morale while elevating their efficiency and engagement at the workplace [2].With rising industrialisation, crime risks, the need to adopt a personalised, safe, and hygienic environment for employees, and the growth of security and technology awareness, new directions for sustainability have been the focus of more studies in the built environment.Moreover, with the tremendous rise in the use of fourthrevolution technologies, the transition of facility management over the years has altered the way enterprises operate [2].Thus, the evolution of real estate models and increased focus on IT infrastructure, improved employee engagement, and health and wellness, while ensuring environmental sustainability, impact facilities management practice.
Consequently, sustainability concerns in facilities management have received increased attention in academic research.Concurring with this view, Opoku and Lee [4] edited and published twelve papers in a recent special issue of the Sustainability journal, titled "The Future of Facilities Management: Managing Facilities for Sustainable Development."In their editorial piece, the importance of sustainable facilities management (SFM) to cater for the future in relation to the SDGs was emphasised.On their part, in their review of the evolution of FM, Bröchner et al. [6] expressed that opportunities for FM research are partly concerned with sustainability, combining environmental and social aspects, and advocated that policies and schemes for sustainable buildings should be more clearly linked to sustainable FM.Therefore, research collating new sustainability perspectives and principles is relevant to ensuring that key issues are not omitted in decision-making, planning, and forecasting for the future.
Previous studies have been undertaken on facilities management and incorporating sustainability perspectives.However, some have focused on developing countries [7][8][9], have a singular focus, for example, outsourcing [10], a safety management framework [11], life cycle assessment and energy consumption [9,12], and green leasing [13].Further, studies that acknowledge the relevance of attention to public facilities have a limited focus on sustainability.For example, Galamba and Nielsen [14] focused on capabilities for public in-house facilities management geared towards social sustainability, while Ighravwe and Oke [15] and Mewomo et al. [16] paid little attention to different aspects of sustainability in their studies on factors that affect facilities management practices/approaches in public and private buildings in developing countries (Nigeria and South Africa, respectively).Similarly, Ganisen et al. [17] examined FM considerations to achieve sustainability (environmental, economic, and social) of building facilities, while Lee and Kang [18] evaluated innovation characteristics as predictors for SFM adoption; thus, they did not explore sustainability principles relevant to FM in the built environment.
From the above, it appears that there is no consensus on the sustainability principles to ensure maximal benefits in public facilities and buildings.This view was supported by Collins et al. [9], who opined that little consistency exists on how to bridge the gap between SFM and sustainable buildings.Further, most studies have used case studies or surveys to examine SFM variables and contexts.Few studies have systematically analysed and visualised the trends in facilities management sustainability research, a gap that this study fills.According to Mendes et al. [19], existing evidence can be identified and updated through a systematic review where the topic is relevant and topical, and new research is continuously emerging, such as the current study.
Therefore, a sequential explanatory mixed-method review entailing scientometric and content analyses was used in this study to map and analyse the knowledge paths to make them visible and understandable within the bigger picture of sustainability research [20].The focus was on the built environment, which contributes greatly to energy consumption, accounting for 36% of final energy use [21].Additionally, buildings in most developed countries, for example, the United States (US), consume 88% of portable water supplies, 68% of all electricity, 12% of freshwater supplies, 40% of raw materials, and are responsible for 20% of solid waste streams (US Green Building Council, cited in Darko et al. [22]).Although sustainability is not only environmentally inclined, the concern is great and can be a starting point for building on other elements, including social and economic.Moreover, assets and buildings account for most of the energy and material use in society [22,23].The specific objectives are to understand the publication trend, core authors and institutions on the topic of SFM, the methods employed, and how research around sustainability in facilities management has been understood over the past decade.To achieve these objectives, this study built and visualised the network of publications shaping the discussion on SFM and mapped the clusters of thematically related publications.The main development paths and themes of SFM research and the strategic principles they embody were identified.Subsequently, the key contributions were further analysed using content analyses, with the complement of articles identified via citation and hand searches.The study provides evidence on who and what is driving sustainability research and initiatives in facilities management.The study identifies principles that have been the nexus of SFM research to continuously advance sustainability imperatives, support facilities management practices, and fulfil stakeholders' needs, especially in public buildings.The remaining sections of the paper present a review of the literature, the methods used in conducting the study, the findings, and the conclusions drawn from both phases of the research.

Sustainable Facilities Management
Facilities management balances three aspects, including human resources, people (employees and employers), human resources and sociological aspects, work activities and resources (productivity and costs), and work environment (architecture and engineering) [12].The function is responsible for the systems and processes that determine areas such as energy management, utilities performance, environmental and waste management, and recycling practices [24].It is practised in various sectors/industries where manufacturing, production of physical structures, and operational/administrative activities are involved.Its roots lie in the custodial role of a building caretaker concerned with operational issues of maintenance, utility management, and costing but have evolved as the nature of businesses has moved from core competence to critical business and support services; thus, workplace and productivity concerns [25,26].Moreover, work is no longer a place but an activity that can be conducted anywhere [5].Due to the changing nature of FM, facilities managers are increasingly engaged with the evolving sustainability agenda and developing sustainability policies within their organisations [24].
Facilities management contributes to the realisation of SDG 6 (sustainable management of water and sanitation), SDG 7 (clean and affordable energy), SDG 9 (sustainable and resilient infrastructure), SDG 12 (responsible consumption and production), SDG 13 (climate action), SDG 15 (life on land and biodiversity), SDG 16 (peace, justice, and strong institution), and SDG 17 (partnership for the goals) [3,4].These underlie the Brundtland Report's definition of sustainable development as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs" [27].Therefore, SDG initiatives aim to develop meaningful action and progress in sectors that will still be critical to humanity in the future.In this context, sustainability was identified as one of the key areas in which FM professionals must develop their capabilities to meet the challenges, demands, and opportunities for sustainable development [3].
The SFM concept integrates FM and sustainable development by adopting technology and innovative business practices that balance the social, economic, and environmental impacts of business decisions [4].It broadly encompasses flexible design and renovations to enhance building longevity, site development to promote liveable communities, waste management, energy efficiency, thermal comfort, indoor air quality, water reuse, use of environmentally friendly materials, and a circular economy through recycling practices during construction, demolition, renovation, and occupancy [18].
Sustainable facilities management aims to ensure workspaces have a minimal or positive impact on the environment.Opoku and Lee [4] provided definitions and explanatory notes on the significance of incorporating sustainability into facilities management.Fauzi et al. [28] argued that in addition to the maximisation of economic value and minimisation of economic and social costs, sustainability has become a strategic imperative for businesses as they increasingly recognise that aligning business operations with sustainable ways adds more value.Managed proactively, a SFM service can reduce costs and provide long-term value [29,30].Sustainable facilities management is important as typical buildings consume more resources and energy than necessary, negatively impact the environment, and generate lots of waste [18,23].
Other literature has highlighted the importance of basing FM research on an understanding of the fundamental forces that shape change and long-term sustainability, for instance, digitisation, proptech, and post-pandemic consequences [6,31,32].With the increase in wellbeing and ergonomic concerns, given the recent incidence of the COVID-19 pandemic and work-from-home adjustments, the employees and society have become the main concerns, leading to increased interest in public facilities management.Therefore, the adoption of sustainable practices can help in addressing FM challenges and simplifying its function at different levels (strategic, tactical, and operational levels) [3,4] and in regard to various principles, which will be highlighted in this study.

Related Research and Gaps
Empirical and review studies exist on SFM, as reviewed in this section.With a focus on human resource coordination at the strategic (policy planning), tactical (awareness), and operational levels (implementation and future improvement), Talib et al. [3] evaluated SFM initiatives for the tourism sector using partial least squares structural equation modelling.However, the findings of the quantitative study among 34 respondents from one hotel in Malaysia may not be generalisable.Likewise, Potkany et al. [12] examined the role of facilities management in ensuring sustainability at the different phases of a building's life cycle, and Collins et al. [9] explored the integration of SFM and sustainable building in the design and management of buildings in a case study of six buildings.However, while these studies advocated for the integration of design through maintenance and eventual decommissioning, the focus was on energy consumption and green buildings, respectively.Other studies also provided insights into practice areas where facilities management could incorporate sustainability elements.For example, Gluch and Svensson [8] used a case study to examine institutional responsibilities and contributed some layered understandings of institutional work related to change in construction in general and specifically in public SFM in Sweden.On their parts, Galamba and Nielsen [14] and Okoro and Musonda [26] examined the role of facilities managers and the competencies needed for SFM.
Ighravwe and Oke [15] addressed how to select an adequate maintenance strategy for public buildings by using multicriteria decision-making models in a quantitative study in Nigeria.The study identified factors that affect facilities management in both public and private buildings, including corruption, insufficient funding, a poor or lack of maintenance culture, poor handling and misuse of the facilities, and a lack of maintenance information.However, the study did not have a core sustainability focus; one of the maintenance strategies identified, namely, corrective maintenance from condition assessment, does not necessarily have a sustainability or futuristic focus.A similar study in South Africa established factors affecting facilities management practices in developing countries using a survey and factor analysis [16].While the study focused on public buildings and FM practices, the elements of sustainability received little attention.Further, Pinti et al. [33] conducted a systematic review and comparative thematic analysis of BIM-FM research for public and private organisations, thus, not necessarily focusing on sustainable FM in public buildings.Another review study [7], focused on Europe, found that research on SFM was limited and that most primary research addressed environmental sustainability.The study focused on publications from 2007 to 2012, hence the need to update the state-ofthe-art evidence.
Sustainable FM can be into building performance; sustainability tools and standards; user perception, satisfaction, and productivity; sustainability management; construction and sustainable building materials; building design and sustainability; urban development; and the benefit of green buildings [7].Collins et al.'s study [9], which explored the gap between sustainable buildings and sustainable FM, observed that there is a need to bridge the traditional gap between design, construction, and FM demands with more effective solutions based on life cycle assessments.The adoption of SFM practices will reduce energy, water, and waste in the maintenance and operation of buildings; however, organisational and management support is required for the smooth adoption of SFM practices and processes [10,34].In addition, since sustainability entails the preservation of resources for future generations, a continuous update of the state-of-the-art and directions on facilities management is warranted to provide current evidence to inform decision-making and future planning.The synthesis of existing knowledge in a field of research is a significant contribution to both theory and practice [35].Therefore, the current study updates the evidence on SFM in the built environment using a review of sustainability indicators and concerns in facility management practice and recommends future research directions.

Research Design
This research adopted a secondary approach using scientometric and content analyses.Secondary research entails summarising, collating, or analysing existing research data or field observations by other authors to identify gaps in the knowledge, re-interpreting and offering different perspectives, and highlighting future directions [36].It is an exercise that applies the same basic research principles as primary studies and follows steps in the inquiry process when a systematic process is followed [37], as presented in Figure 1.
user perception, satisfaction, and productivity; sustainability management; construction and sustainable building materials; building design and sustainability; urban development; and the benefit of green buildings [7].Collins et al.'s study [9], which explored the gap between sustainable buildings and sustainable FM, observed that there is a need to bridge the traditional gap between design, construction, and FM demands with more effective solutions based on life cycle assessments.The adoption of SFM practices will reduce energy, water, and waste in the maintenance and operation of buildings; however, organisational and management support is required for the smooth adoption of SFM practices and processes [10,34].In addition, since sustainability entails the preservation of resources for future generations, a continuous update of the state-of-the-art and directions on facilities management is warranted to provide current evidence to inform decisionmaking and future planning.The synthesis of existing knowledge in a field of research is a significant contribution to both theory and practice [35].Therefore, the current study updates the evidence on SFM in the built environment using a review of sustainability indicators and concerns in facility management practice and recommends future research directions.

Research Design
This research adopted a secondary approach using scientometric and content analyses.Secondary research entails summarising, collating, or analysing existing research data or field observations by other authors to identify gaps in the knowledge, re-interpreting and offering different perspectives, and highlighting future directions [36].It is an exercise that applies the same basic research principles as primary studies and follows steps in the inquiry process when a systematic process is followed [37], as presented in Figure 1.To develop a comprehensive general framework of factors considered in sustainabilityinclined research in facilities management, the study was conducted in a sequential explanatory two-phase design, guided by aspects of the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA) guidelines [38].A systematic approach was followed to identify literature, update it, and classify information on how a particular research topic is evolving based on the overall conclusions from previous studies using scientometric analysis (quantitative analyses of selected publications) [19].Scientometrics is concerned with the quantitative analysis of textual characteristics of scientific literature to evaluate the development of a field, the influence of publications, authorship patterns, and the production and dissemination of knowledge [39].This approach to the literature review and information visualisation allows for the understanding of scientific disciplines and produces a persistent and shared knowledge space for researchers to keep track of the development of knowledge more effectively [40].A subsequent content analysis (qualita-tive in nature) was used to analyse and situate the documents within the themes identified in the first quantitative phase, as was performed in previous studies [35,41].
Data were collected through an initial integrative review of articles related to the topic to refine the research purpose through hand searching using Google Scholar, Google, and Science Direct.A subsequent systematic approach was used to identify materials relevant to the study in the Scopus database two months later.Thus, the study included materials published up to 2022.A qualitative synthesis was thereafter conducted using content analysis to identify, categorise, and describe the factors from the SFM research [37].These stages were used to ensure that new publications and relevant insights were not missed.Thus, a considerable number of documents were identified on the subject area to perform quantitative and qualitative analyses and draw reliable conclusions on SFM research in the built environment.

Database Selection
An initial integrative search was conducted using Google, Google Scholar, and Science Direct to establish the gaps in previous studies and refine the research problem and questions.These materials were included in the problem formulation stage to gain clarity on the research direction and then in the integration and discussion section.For the bibliometric aspect, the Scopus database was used to identify materials for this study.The database is among the largest curated abstract and citation databases of high quality, with a wide global and regional coverage of scientific or peer-reviewed literature, including journals, conference proceedings, and books [42,43].It ensures the highest quality data are indexed through rigorous content selection and re-evaluation by an independent Content Selection and Advisory Board.Additionally, extensive quality assurance processes continuously monitor and improve all data elements in Scopus.The database offers comprehensive author and institution profiles, obtained from advanced profiling algorithms and manual curation, ensuring high precision and recall.
Although Kumpulainen and Seppänen [44] posited that bibliometric results depend on the citation index selected and relevant articles may be missed, the Scopus database was still used to delineate the search to the built environment and obtain data for the visualisation of networks in the VOSviewer version 1.6.18software used.The preliminary integrative review also served to uncover relevant articles that could have been missed.

Search Strategy-Criteria and Procedure
For the identification, search, selection, and evaluation of studies, the PRISMA systematic approach helped to identify the evidence and where it fell short, avoid bias, and include the right information to answer the research questions [45].It allowed for the rigorous search, screening, and selection of relevant scientific articles based on their eligibility (inclusion and exclusion criteria); thus, reducing potential bias [41].
The preliminary integrative search was undertaken in October 2022.Google, Google Scholar, and Science Direct were used to identify materials for inclusion, as was carried out by Mendes et al. [19].Fifteen articles were retrieved on facilities management sustainability in the built environment using hand and citation searches.Citation searching was used to identify articles that have been cited by identified publications.Subsequently, in December 2022, a systematic review was undertaken in Scopus.The criteria for inclusion and exclusion were as presented in Figure 1.
The advanced search function was used to retrieve 208 documents using the keywords "sustainable facilities management" and "built environment."Documents were limited to "all open access" and the eleven-year (2012-2022) period.The search elicited journal articles and conference papers published in the following years: 2009, 2012, and 2014-2022.To ensure that relevant and current knowledge was included, the 2009 document was removed.Thus, pre-2012 (N = 1), as shown in Figure 1, was removed.The period was limited to obtaining relevant materials and their current contribution to the sustainability debate.This was to capture as much recent literature as possible given the increasing relevance of sustainability in facilities management, the futuristic nature of the topic, and the need to examine contemporary issues to inform further research directions.Therefore, studies from 2012 to date were retained and used for the bibliometric analysis.
Other inclusion criteria were applied, including document type (articles and conference papers were selected).Conference papers were included because conferences play an important role in sustainability research [27].Subsequently, documents that were published in the final stage in journals and conference proceedings (source type) and in the English language were selected.These filters, as applied, are presented in the search string below: "sustainable facilities management", "built environment" AND (LIMIT-TO (OA, "all")) AND (LIMIT-TO (PUBYEAR, 2022) OR LIMIT-TO (PUBYEAR, 2021) OR LIMIT-TO (PUB-YEAR, 2020) OR LIMIT-TO (PUBYEAR, 2019) OR LIMIT-TO (PUBYEAR, 2018) OR LIMIT-TO (PUBYEAR, 2017) OR LIMIT-TO (PUBYEAR, 2016) OR LIMIT-TO (PUBYEAR, 2015) OR LIMIT-TO (PUBYEAR, 2014) OR LIMIT-TO (PUBYEAR, 2012)) AND (LIMIT-TO (DOC-TYPE, "ar") OR LIMIT-TO (DOCTYPE, "cp")) AND (LIMIT-TO (PUBSTAGE, "final")) AND (LIMIT-TO (SRCTYPE, "j") OR LIMIT-TO (SRCTYPE, "p")) Further, title and abstract screening of each of the 77 articles was performed to ensure the inclusion of relevant materials.Ten documents that were not relevant to facilities management, the built environment, or facilities (for example, households, food and agriculture, and leather manufacturing) were removed.The focus was on buildings and the built environment, and the literature that was not related to SFM was excluded.

Visualisation
The bibliometric information gathered from the Scopus database were analysed and visualised using VOSviewer software.This software has been widely used for quantitative analysis involving technical construction, pictorial imaging, and bibliometric network mapping.Other network visualisation tools such as Cite Spec or Gephi exist; however, VOSviewer was used because of its user-friendly interface and multiple network visualisation tools, such as keyword clusters, to identify research themes.In addition, CitNet-Explorer only measures direct citations of individual publications; it does not show links between authors and sources [46].
The sample data in txt format were exported to Excel as a csv file for further cleaning and management of graphs and charts, and then imported into the VOSviewer software for mapping and visualisation.Different units of analysis were used, including documents, sources, cited sources, countries, and terms used in the abstracts, titles, and keywords of the articles, to create output networks of citations, co-citations, co-authorship, and keywords [43].
Cluster analysis was used to generate social network maps (consisting of nodes and links) showing occurrences and collaborations among countries, institutions, and keywords by VOSviewer [47].The size of the nodes shows the number of publications or frequency; the larger the node, the greater the publication frequency.The links between nodes represent relationships of collaboration, co-occurrence, or co-citations, and the colour of the nodes and lines represents different clusters [47].Co-citation occurs when two documents receive a citation from the same third document [48].This provides insight into how authors, as domain experts, connect ideas between published works [40].
Citation analysis was also undertaken using bibliographic coupling to establish the most cited documents and the relationships between the documents.Bibliographic coupling occurs when two studies cite the same third document; this was relevant to the cited authors, institutions, and countries [48].Closely related documents are cited together.

Content Analysis
A subsequent integrative approach was taken to identify and review more studies using content analysis.According to Mendes et al. [19], a systematic review can be updated and supported when:

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The topic is still relevant to policy and practice, and preliminary searches suggest that there are new studies suitable for inclusion.

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The original review included limited data, and an update could provide valuable additional information.

•
Influential studies were omitted from the original conclusions.
Content analysis has been used to review sustainability research [49] and in a subsequent review phase to establish the underlying meaning and authors' views [6].Content analysis entails a "subjective interpretation of the content of text data through the systematic classification process of coding and identifying themes and patterns" [49].A deductive approach was employed to decipher explanations based on the established theoretical perspectives from the bibliometric phase.It is a top-down approach to understanding the latent content within a priori or predetermined codes for the data [50].It helps to sort data into topical categories of interest based on the study's aim and objectives.
Content analysis was therefore used to analyse the top ten most cited articles from the bibliometric phase, which were then analysed within the context of the identified themes to situate core publications within the identified sustainability themes and the principles they embody.This technique led to the identification of relevant sources for interesting, relevant, and significant contributions through other platforms, including Google, Google Scholar, and Science Direct.
Out of the 67 articles used in the bibliometric analysis, the top ten most cited articles, cited at least 22 times, were then analysed, visualised, and synthesised using content analysis.The time span selected for the content analysis ranged from 2012 to 2020.It was acknowledged that publications in 2021 and 2022 were not included in the content analysis.These documents had not yet been cited much, as they were published recently [48].Other articles were included from the initial hand and citation searching and used in the discussion and integration of findings.The content analysis followed the process explained in Bingham and Witkowsky [50], including the following:

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Data organisation and attribute codes (the most cited publications);

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Sorting the data into relevant topical categories (SFM sustainability principles and application areas); • Coding (pre-identified themes from the bibliometric cluster analysis); • Identifying themes and findings (sustainability principles and indicators related to the themes); • Applying theory to explain findings (integration of the findings from the bibliometric phase and content analysis).
Therefore, the process involved categorising, tagging, and thematic analysis of the selected documents to understand what they represent and where they fit within the pre-identified themes.

Reliability
Methodology, reporting, and transparency are critical in discerning the quality and usefulness of content analysis and allowing for replication [51].A systematic and reproducible methodology for searching previous publications related to the subject was used [36].In addition, efforts were made to select relevant articles for the study and critically analyse and present the evidence in a clear manner, thus enhancing reliability [38].Further, for the qualitative synthesis of results, intersubjectivity of data analysis dealing with latent content deserving interpretations was pursued by discursive alignment of interpretation [51].The systematic procedures in this study enhanced the replicability and, therefore, the reliability [52].The triangulation of methods (using bibliometrics and content analysis) also enhanced the credibility of the findings.

Results
The results are presented in this section.For the scientometric analysis, publication characteristics were tabulated and presented in graphs, including the annual trend, authors, sources, funders, affiliations, and keywords [47].The content analysis follows, with the most frequently co-cited documents revealed.

Publication Timeline
The study examined the publication history of SFM research between 2012 and 2022.Over the years, as shown in Figure 2, publications increased steadily from 2014 to 2017, dropped in 2019 and 2020, and increased again exponentially in 2021.This sharp increase could be attributed to the increased focus on health and wellbeing post-pandemic.One 2013 document indexed in Scopus was a book chapter by Tucker, M., which was excluded from the bibliometrics based on the criteria.It is evident that sustainability research in facilities management is growing year after year.
fore, the reliability [52].The triangulation of methods (using bibliometrics and content analysis) also enhanced the credibility of the findings.

Results
The results are presented in this section.For the scientometric analysis, publication characteristics were tabulated and presented in graphs, including the annual trend, authors, sources, funders, affiliations, and keywords [47].The content analysis follows, with the most frequently co-cited documents revealed.

Publication Timeline
The study examined the publication history of SFM research between 2012 and 2022.Over the years, as shown in Figure 2, publications increased steadily from 2014 to 2017, dropped in 2019 and 2020, and increased again exponentially in 2021.This sharp increase could be attributed to the increased focus on health and wellbeing post-pandemic.One 2013 document indexed in Scopus was a book chapter by Tucker, M., which was excluded from the bibliometrics based on the criteria.It is evident that sustainability research in facilities management is growing year after year.The social networks of maps showing the collaborations among authors were examined.Out of 216 authors, the top 10 authors with at least two documents and ten citations were identified.These are presented in Table 1.The top 10 most prolific authors contributed 51% (34 out of 67) of the papers.Notably, the most prolific authors, equally earning the most publications (6) and citations (255), were Parlikad and Xie, followed by Lu (5 documents, 233 citations) and Schooling (4 documents, 126 citations).The social networks of maps showing the collaborations among authors were examined.Out of 216 authors, the top 10 authors with at least two documents and ten citations were identified.These are presented in Table 1.The top 10 most prolific authors contributed 51% (34 out of 67) of the papers.Notably, the most prolific authors, equally earning the most publications (6) and citations (255), were Parlikad and Xie, followed by Lu (5 documents, 233 citations) and Schooling (4 documents, 126 citations).Collaborations were also strongest among these four authors, as indicated by the total link strength (TLS) ranging from 12 to 15.For the analysis of the co-citation of authors (those cited together), ten met the threshold with a minimum number of 19 citations.The top three co-cited authors were Elmualim, Valle, and Shah, with 52, 40, and 39 citations, respectively.

Co-Authorship among Organisations
With a minimum threshold of two documents per organisation, and at least one citation, seven organisations met the requirement out of 152.These were all higher education institutions independently conducting research on this topic.There was little or no indication of collaboration among the institutions, as can be seen in the TLS of 0 (Table 2).Universities in the UK are particularly influential, including University College London with 40 citations and Liverpool John Moores University with 27 citations.Note: TLS-total link strength.

Funding Organisations
The funding agencies were examined.This was important because funding agencies support relevant research to inform strategic decisions and maximise scientific impacts [53].In addition, the funding increases academic or scholarly outputs in the recipient institutions or countries [54].
Over the period investigated, there was funding for SFM research in the built environment.These included public bodies and higher education institutions.The top funders were the Engineering and Physical Sciences Research Council (EPSRC) in the UK (seven documents), the Ministry of Higher Education in Malaysia (four documents) and the University of Cambridge, UK (three documents) (Figure 3).These correspond with the results of the highest publication outputs from the UK and Malaysia.Thus, supportive funding increased productivity in the SFM research field in these countries.

Analysis of Sources
The top five sources responsible for the publication of 42% (28) of the papers were Sustainability (8), IOP Conference Series: Earth and Environmental Science (7), Facilities (6), International Journal of Sustainable Built Environment (3), and International Journal of Sustainable Construction Engineering and Technology (4).The CiteScore of the journals is shown in Figure 4.The CiteScore reflects the yearly average number of citations to recent articles published in the journals.Sustainability and Facilities had the highest and most stable CiteScore metrics over the years investigated.

Analysis of Country Networks
Keeping the minimum to at least three documents and six citations per country, the co-authorship of countries was visualised (Figure 5).The larger nodes indicate a higher frequency of occurrence of documents from that country.Out of 33 countries, the top two countries with the highest number of documents were the United Kingdom (26) and Malaysia (16).

Analysis of Country Networks
Keeping the minimum to at least three documents and six citations per country, the co-authorship of countries was visualised (Figure 5).The larger nodes indicate a higher frequency of occurrence of documents from that country.Out of 33 countries, the top two countries with the highest number of documents were the United Kingdom (26) and Malaysia (16).Further, with a minimum of three documents per country, the citations among countries were analysed using bibliographic coupling.For each of the countries, the total strength of the bibliographic coupling links with other countries was calculated.This showed the relationship between the documents when two studies cite the same third document; this was relevant to the cited authors, institutions, and countries [48].Closely related documents are cited together.The results showed that the UK had the strongest links, followed by Australia and China (Table 3).Further, with a minimum of three documents per country, the citations among countries were analysed using bibliographic coupling.For each of the countries, the total strength of the bibliographic coupling links with other countries was calculated.This showed the relationship between the documents when two studies cite the same third document; this was relevant to the cited authors, institutions, and countries [48].Closely related documents are cited together.The results showed that the UK had the strongest links, followed by Australia and China (Table 3).Note: TLS-total link strength.

Analysis of Research Techniques
The methods used in the publications included cross-case analysis, artificial neural networks, fuzzy analytical network processing, fuzzy expert systems, graph theory, linear regression, a matrix approach, structural equation modelling, and a theoretical model with a TLS value of 5. Others were case studies, conceptual framework/model development, and interpretative structural modelling, with a TLS value of 4.

Keyword Analysis
The VOSviewer software can be used to identify the most occurring keywords, which represent the topics being studied, as suggested by the authors to best represent their research [55].Moreover, in bibliometric analysis, a network graph of keyword co-occurrences reflects hot topics [47].The keywords were analysed with all the author keywords.
Keeping the minimum TLS at 3, the top keywords were analysed.Terms including sustainable development, facilities management, sustainability, and facility management were also excluded as they appeared mostly given the general search scope [35].For each of the remaining 178 keywords, the frequency of occurrence was established.The most frequently occurring keywords were digital twin (6), building information modelling (5), asset management (4), sustainable development (3), anomaly detection (3), building information modelling (2), energy efficiency (2), and sustainability assessment (2).Alternatively, the least occurring keywords (appearing only once) were public universities, public buildings, life cycle costing, workplace indoor environmental quality, Green Star post-pandemic, machine learning, and LEED, among others.Some of these concepts, for example, green star accreditation and LEED (Leadership in Energy and Environmental Design), appeared in research in the 2000s, as reported by Brochner et al. [6].
Further, the total strength of the co-occurrence links among keywords was calculated by the software using the normalisation of associations and a full counting algorithm.Out of these, 70 keywords were linked and formed four clusters.These are presented in Figure 6.The most prominent keywords and linkages are visible.
Cluster 1-Strategic SFM perspective (red-coloured).This cluster was observed to include terms related to strategic planning and implementation, with the concerns of the public and information power at the uppermost level of consideration.The items were twenty-two and included inter alia, asset information modelling and requirements, asset maintenance, best practices, a case study, building information modelling, built asset management, client requirements, a conceptual framework, decision support systems, the development process, employers' information, a fm-dp integration framework, healthcare, hierarchy-based information, information integration, KPIs, operational information, organisational performance, and property development.
pandemic, machine learning, and LEED, among others.Some of these concepts, for example, green star accreditation and LEED (Leadership in Energy and Environmental Design), appeared in research in the 2000s, as reported by Brochner et al. [6].
Further, the total strength of the co-occurrence links among keywords was calculated by the software using the normalisation of associations and a full counting algorithm.Out of these, 70 keywords were linked and formed four clusters.These are presented in Figure 6.The most prominent keywords and linkages are visible.Cluster 1-Strategic SFM perspective (red-coloured).This cluster was observed to include terms related to strategic planning and implementation, with the concerns of the public and information power at the uppermost level of consideration.The items were twenty-two and included inter alia, asset information modelling and requirements, asset maintenance, best practices, a case study, building information modelling, built asset management, client requirements, a conceptual framework, decision support systems, the development process, employers' information, a fmdp integration framework, healthcare, hierarchy-based information, information integration, KPIs, operational information, organisational performance, and property development.
Cluster 2-Community-oriented smart FM (green-coloured).Cluster 2 contained 18 items, including ablution space, asset management, BIM, building and city levels, building information modelling, cognitive building, design, digital twin, heritage buildings, hygiene, IOT, Malaysia, mosques, openBIM, operation and maintenance, pre-construction, sensors, and value management.The items in this cluster are related to the smart preservation of public buildings for the health and wellbeing of their users on a larger scale.
Cluster 3-Innovative maintenance management (blue-coloured).Items grouped under this theme were sixteen and related to innovative tools and systems for fault detection and water management.The items include anomaly detection, augmented reality, building information modelling, condition monitoring, industry foundation classes, information systems, operation and maintenance management, operations and maintenance, return on investment, Shewhart control charts, smart maintenance, smart meters, task-technology fit, and water management.
Cluster 2 contained 18 items, including ablution space, asset management, BIM, building and city levels, building information modelling, cognitive building, design, digital twin, heritage buildings, hygiene, IOT, Malaysia, mosques, openBIM, operation and maintenance, pre-construction, sensors, and value management.The items in this cluster are related to the smart preservation of public buildings for the health and wellbeing of their users on a larger scale.
Cluster 3-Innovative maintenance management (blue-coloured).Items grouped under this theme were sixteen and related to innovative tools and systems for fault detection and water management.The items include anomaly detection, augmented reality, building information modelling, condition monitoring, industry foundation classes, information systems, operation and maintenance management, operations and maintenance, return on investment, Shewhart control charts, smart maintenance, smart meters, task-technology fit, and water management.
Cluster 4-Environmental and corporate energy management (yellow-coloured).Cluster 4 included fourteen items, including building maintenance, building performance, commercial properties, elements, energy efficiency, framework, green building, greenhouse gas emissions, management policy, office buildings, performance measures, strategic sustainability, structural equation modelling, and sustainability assessment.These items relate to environmental and corporate focus in facilities management with the aim of maximising efficiency and sustainability in energy management.

Content Analysis Findings
Content analysis was used for further qualitative synthesis.The top ten most cited works were further analysed to decipher what each entailed in terms of methods and focus.These were also classified according to the themes emerging from the bibliometric phase to further understand what each theme embodies in the author's views and findings.The results are briefly outlined below, as presented in Table 4:

•
Ashworth et al. [23] developed a system for information management useful to clients and facilities managers and identified information flow for effective FM and cost reduction in the long run.

•
Bröchner et al. [6] identified eight SFM categories as fundamental forces that shape change and future FM, including sustainability tools and standards, building performance, user perception and productivity, satisfaction, sustainability management in the built environment, construction and sustainable building materials, building design and sustainability, green building benefits, and urban sustainability.

•
Lu et al. [56] tested digital technology integration in operations and maintenance of buildings and cities, bridging the gap between humans and buildings/cities.
• Xie et al. [57] focused on the use of augmented reality for anomaly detection in operations and maintenance; identified SFM indicators/principles included users' satisfaction and building performance in relation to users' thermal comfort.

•
Moretti et al. [58] focused on technology integration in cognitive buildings and building performance as an SFM focus.

•
Lu et al. [59] demonstrated the use of technology (digital twin) in FM functions and sustainable operations and maintenance.

•
Thatcher and Milner [60] identified SFM concepts including indoor environmental quality, user satisfaction, productivity, wellbeing, and perception.

•
Darko et al. [22] identified building energy efficiency, water efficiency, environmental sustainability, and life cycle cost reduction.

•
Elmualim et al. [24] focused on policy and drivers for SFM and identified that the three main sustainability concepts for facilities managers are energy management, waste and recycling management, and carbon footprint.
The areas of consensus among the authors (most-cited) were highlighted, along with the key sustainability themes and principles that emerged from the cluster analysis.Ashworth et al. [23], with 23 citations, developed and tested a framework for increased collaboration and information centralisation to meet clients', organisations', and facilities management needs.This aligned with the first theme, a strategic SFM perspective, and the view expressed by Opoku and Lee [4] that SFM connotes adopting innovative business practices that balance the economic impacts of business decisions.
There was agreement among four of the studies published in 2019 and 2020 on the orientation of SFM towards the community's needs and comfort while introducing or adopting smart systems for FM.The studies included Bröchner et al. [6], Lu et al. [56], Xie et al. [57], and Moretti et al. [58].The efficacy of smart systems in facilities management functions while taking into cognisance the systems' performance in ensuring optimal comfort for the users was explored, thus bridging the gap between human relationships with buildings and cities; thus innovative systems for facilities management, with social considerations [4].
Linking with the third theme, Lu et al. [59] investigated the role of the digital twin in FM without focusing on the impact on people or society.The remaining four studies [22,24,60,61] focused on environmental and corporate issues in FM, including green building, indoor environmental quality, and corporate productivity and wellbeing.Additionally, in one of the studies, Thatcher and Milner [60] identified users' satisfaction (social sustainability) and indoor environmental quality (environmental sustainability) as SFM concerns, thus suggesting a crosslink between two themes-community-oriented smart FM and environmental and corporate energy management.As advocated by Elmualim et al. in their 2021 study, a balanced approach that takes into consideration the wider social and economic aspects of sustainability is desirable.The increased attention to societal impact and users' comfort/satisfaction supports the increased research and citations based on these studies.Policies and schemes to support SFM should be linked to all aspects of sustainability more clearly to achieve wider and more balanced desirable impacts, a view supported by Bröchner et al. [6].
The above findings are further integrated with the results from the bibliometric stage in the next section.This is done with further reference to other pieces of the literature identified from the hand and citation searches.

Discussion and Integration of Findings from the Cluster and Content Analyses
The cluster analysis findings revealed four clusters into which the published research of the last decade could be classified.The most cited documents also aligned with the cluster themes, including a strategic SFM perspective, community-oriented smart FM, innovative maintenance management, and environmental and corporate energy management.This grouping is different from the findings in Bröchner et al.'s [6] review, which was based on published research from the 1970s to the 2010s and revealed eight categories of SFM, including sustainability tools and standards, building performance, user perception and productivity, satisfaction, sustainability management in the built environment, construction and sustainable building materials, building design and sustainability, green building benefits, and urban sustainability.However, the findings on the most frequently occurring keywords in the current study (including sustainability assessment, digitisation, and energy efficiency) are consistent.The SFM themes are further discussed hereunder.

Strategic SFM Perspective
The first cluster-themed strategic SFM perspective underlies the principle described in Svensson et al. [62] as "the big perspective approach," whereby alignment of an organisation's mission with strategic initiatives while paying attention to stakeholders is critical.This involves strategic FM planning and implementation with the parties involved; employers and clients need to manage and integrate information to achieve sustainable operational performance (preserving the assets and operations for use by future generations).This view was shared by Ashworth et al. [23], who opined that information centralisation is critical to SFM.Svensson et al. [62] further linked this to the institutional theory, where actors' and scholars' attention can be redirected to "the purposive, distributed and agentic dimensions of institutional change."Gluch and Svensson [8] also emphasised the role of multi-level institutional actors in promoting new practices in a specific organisational setting to ensure sustainability.Moreover, effective management, with communication at the centre of it, contributes to sustainable development implementation even with multiple actors or stakeholders [34,63].
Therefore, the lack of collaboration among the authors as observed in the publication trend is worrisome since sustainability crosses borders and requires cooperation and collective effort towards attaining set goals.Perhaps the low level of collaboration is because facilities management is perceived as conservative, non-value-adding, or unavoidable liabilities, as opined by Opoku and Lee [4] and Baaki et al. [25].Researchers should collaborate more in pinpointing factors that affect individuals' abilities to shape sustainability-oriented facilities management and practices to help sustain the efforts of those who are trying.Likewise, the private and public sectors (including non-academic institutions) should be involved in finding ways to ensure facilities management practices are implemented with a view to long-term sustainability.
Further, the first cluster also includes integration of facilities management throughout the asset and property design, development, and maintenance phases, as supported in the content analysis.This finding aligns with Potkany et al.'s [12] and Collins et al.'s [9] results about the critical role of facilities management in ensuring sustainability at the different phases of a building's life cycle.However, Nazeer et al. (2019) [64] submitted that SFM practices may be challenging in the health sector because of the building engineering system, facility type, organisation's business sector, and culture.However, they found that identifying applications for energy-saving measures and proper waste storage and transportation systems are significant sustainable FM services to ensure sustainable FM in healthcare buildings.
Concurring with these views, Rodriguez-Trejo et al. [65] agreed that adherence to client requirements during the operational phase could be challenging.The authors advocated putting in place a structured information delivery and decision support system, within digitally enabled (BIM) protocols, established at the project's inception phase, which could assist to prevent information loss, coordinate the project delivery in line with the client's requirements, and anticipate the impacts of planning decisions on the operational performance of buildings.Such a system will assist in translating priorities into objective parameters and information categories.Effective information management during operational facilities management can help to consider practitioner and user needs, improve asset performance during use, and reduce environmental impact [6,66].

Community-Oriented Smart FM
The second cluster is themed community-based smart FM suggested that since digitisation is important going forward, it is crucial to ensure SFM linkages to the needs of the broader society, city, or community in addition to smart systems.The theme deals with the way facilities management practices link to impacts on the building and society.It also includes public entities in the operation and management of buildings and the use of digitisation for the operation and maintenance of buildings and community buildings.These findings are consistent with the view that public facilities management uniquely aligns building projects and FM with the policies of sustainable development at the societal level [14].The need for FM to adapt models that suit the needs of the community settings in which it operates was also highlighted in Nazeer et al. [64].Opportunities are created by digitisation, which in turn supports sustainability through building design, workplace change and culture, performance measurement, and the urban context [6].These digitisation processes should, however, be relatable and consider broader awareness, impacts, and social sustainability.For example, in their case study of the development of a digital twin (a digital replica of physical assets, processes, and systems), Lu et al. [56] concluded that in addition to supporting heterogeneous data sources, effective data querying and analysis, and decision-making processes in operations and maintenance, digitisation bridges the gap between human relationships, buildings, and cities.Moreover, there is an increased awareness of cleanliness and the need to preserve healthy spaces for work and habitation, given the pandemic and lockdown experiences [32].Hence, policies and practices should be clearly and equally linked to sustainability concerning individual and broader societal goals.

Innovative Maintenance Management
The third cluster contained items regarding innovativeness in maintenance management processes and practices to ensure productive and lasting performance of buildings during the operation and maintenance phases.As supported in Okoro et al. [67] and Opoku and Lee [4], SFM incorporates adopting technology and innovative business practices that balance various impacts of business decisions, including inter alia, economic aspects like return on investment, as classified in this cluster.The link to return on investment also indicates that cost savings are an important target in sustainable building operations and maintenance.As found by Alsharif et al. [30], cost notably emerged as a dominant influence on facilities and project management decision makers' choices; it plays an important role in shaping the decision-making process alongside other key organisational factors.
Further, the third cluster reflects that accessibility to data or information using technology is critical for improving conditions and sustainability assessment.This view was supported by Araszkiewicz [68], which demonstrated the effectiveness of digital techniques in integrating data for the building lifecycle and providing information and decision support to facility management and maintenance.Similarly, Lu et al. [59] found that a novel digital twin-based anomaly detection process flow was effective in continuously detecting an anomaly in HVAC pumping, thus contributing to automated asset monitoring in operations and maintenance.Likewise, in Xie et al. [57], an augmented reality system was successfully applied to facilities' inspection and maintenance by highlighting failed assets and supporting other FM functions (recording, communication, and verification).Other studies have also advocated the use of innovative systems to ensure SFM practices [18,69].

Environmental and Corporate Energy Management
The fourth cluster emerged as relating to environmental and corporate focus in facilities management with the aim of maximising efficiency and sustainability in energy management.Four of the most cited studies also supported energy management as an important SFM focus [22,24,60,61].Buildings account for a significant amount of energy use [22,23].Thus, waste and energy management in the built environment is crucial to ensuring that resources are preserved for future generations [22,23].SFM efforts through energy efficiency can reduce unsustainable energy needs and costs, improve business competitiveness and air quality, and mitigate climate change.Araszkiewicz's [68] case study of an office building in Amsterdam supported the idea that SFM can be better aligned with corporate environmental, social, and governance goals; this helps to provide a positive image for customers, investors, and organisations.Facilities managers have responsibilities related to the sustainability of their organisations in areas including energy management, waste management, recycling, and health and safety [6].
Sustainable development is also closely linked to the concept of the green economy, described as an economy that results in improved human wellbeing as well as social equity while significantly reducing environmental risks and ecological scarcities [70].Green buildings promote environmental and indoor quality, which fosters the wellbeing and productivity of workers in the long run [60].Potkany et al. [12] concur that SFM should adopt a life cycle perspective to reduce or save energy and costs.Further, energy use monitoring in buildings can be improved by wireless sensors; this is directly relevant to sustainability efforts [6].More smart monitoring tools and systems should be used for energy management.

Knowledge Pathways
It is notable that higher education institutions and public buildings were not prominent in the clusters.Higher education institutions appeared only once in the frequency analysis, in Alsharif et al. [30].The initial hand searching, however, revealed some studies on facilities management in higher education, but without a sustainability focus [71] or facilities management perspective [63].More research is needed to support policy making in higher education in facilities management practice with a clear sustainability focus.Also, outsourcing was not prominent in the network clusters.One would have expected it to be related to the hygiene and health aspects in Cluster 2. Outsourcing was critical to organisations with the return to work after the COVID-19 lockdowns.According to O'Bierne [32], citing recent Citron Hygiene research, more than half (53%) of facilities managers who were involved in the study reported that they gained valuable support working with outsourced service providers, and two-fifths (40%) reported that they represent good value for money.Therefore, research on outsourcing will still be important for workplace hygiene as well as the wellbeing and productivity of employees.
Further, some of the least frequently occurring keywords, such as machine learning, post-pandemic, and life cycle costing, did not appear in the clusters.One study was found through hand searching that dwelt on water management in public places during the COVID-19 pandemic [69].More collaborative research is therefore needed on these areas, as they are topical and will influence workplace core business processes in the future.
Further, the role of legislation in enforcing sustainability imperatives was highlighted.However, Elmualim et al. [24] argued that regulations are biased towards environmental sustainability, with less attention given to wider social and economic aspects of sustainability.Therefore, more research into policies and regulations is needed to continue supporting the focus on societal and economic sustainability imperatives in facilities management.Persistence is crucial with the continuously evolving focus on facilities management, workplace goals, and societal implications [6].
Furthermore, although there has been somewhat equal attention (increased research/ citations) to societal impact (as much as environmental) in facilities management functions in recent research, this is most likely because of the need for corporate social responsibility within organisations during the COVID-19 pandemic.Organisations tried to balance business outcomes with the wellbeing and relations between corporations, customers, and communities [72].It is notable that corporate social responsibility did not appear in the clusters; it appeared in only one study [29].Therefore, more research is needed on this topic as business environments continue to evolve to accommodate contemporary needs.
Additionally, the competencies needed for SFM were not highlighted.According to Galamba and Nielsen [14], effective management and technology use require specific capabilities.Facilities managers and employees can be empowered through collaboration, planning, and education to acquire the know-how and understanding of technologies for sustainability.

Methodological Coverage
The studies analysed were conducted using case studies (mostly observations and reporting of implementation processes), theoretical modelling, and quantitative studies (which entailed statistical analysis including regression and structural equation modelling).
No study was found that used interviews to explore perceptions of sustainability perspectives and implications for the future.Future studies could therefore employ interviewing as a technique to obtain in-depth views, which could reveal how individuals or organisations are contributing to the sustainability agenda in the facilities management arena.

Publication Patterns-Countries, Institutions and Funders
The research on sustainability is geographically diverse, covering 33 countries on different continents.While the number of authors is increasing, they are drawn from a small number of organisations in these countries.Universities in the UK are particularly influential, including University College London and Liverpool John Moores University, which are the most cited organisations.The collaboration links also indicate much association between the UK, Australia, and China.It is also notable that the top ten institutions were universities.More collaboration among private and public institutions (including non-academic institutions) is needed since sustainability touches all and should be a collective effort.In addition, results indicated that funded authors are more prolific in the SFM research area.More agencies should provide funding to support up-and-coming researchers in contributing to the realisation of SDGs relevant to facilities management in the built environment.

Conclusions
The study sought to establish the publication trend and how the knowledge around SFM has been shaped over the years.The productivity and scientific impact of authors, organisations, countries, sources, funding agencies, and knowledge patterns were examined.The discussion on sustainability in facilities management practice was articulated for information, decision-making, and future research.
Integrative hand and citation searches were conducted using articles from Google, Google Scholar, and Science Direct.These articles were used in the initial scoping to refine the study's purpose.Articles indexed in Scopus were subsequently identified and analysed systematically and sequentially using bibliometric and content analyses.The study built and visualised the publication networks of authors, institutions, sources, and thematic areas.The main development paths and themes of SFM research and the strategic principles they embody were identified in the first qualitative phase (bibliometric analysis).These included four clusters: strategic SFM perspective, community-oriented smart facilities management, innovative maintenance management, and environmental and corporate energy management.A further qualitative analysis was used to understand the latent meaning of the identified themes in the context of the authors and to draw conclusions and recommend further research pathways, methodological aspects, and collaboration patterns.The findings support the idea that more collaboration is needed beyond higher education institutions.In addition, the adoption of case studies and applied research over statistical methods was highlighted; more in-depth studies are needed to obtain information on SFM practices.
The study provided evidence on what is driving sustainability initiatives in facilities management and strategies in the built environment.As the goal of sustainability is to meet the needs of the present without compromising the ability of future generations to meet their needs, the current study can be the basis for future discussions on relevant sustainability concepts in the facilities management space.
The SFM principles could be beneficial to policymakers to continuously advance sustainability imperatives, support facilities management practices, and fulfil stakeholders' needs while reducing costs, especially in the built environment.Policymakers aiming to promote sustainable practices can develop suitable policies and incentives in certain areas, for example, corporate social responsibility, and further explore ways to achieve this within their communities and jurisdictions.
The study also provided a valuable reference for industry practitioners in SFM-related organisations to plan better with a futuristic focus and make informed decisions about business goals, strategies, project performance, and productivity, taking the employees' wellbeing into account.Sustainability policies can be enacted within organisations to encourage commitment to certain standards to meet business objectives while being conscious of social and environmental obligations.
Further, the bibliometric analysis of the existing and recent knowledge on SFM provided a helpful and seminal reference for researchers and scholars in SFM research communities to deepen their understanding of the major issues that influence SFM decision-making.The study also identified knowledge gaps (areas with the least attention), which could be the focus of many studies in the future.
Furthermore, the gaps identified could be the basis for funding support from various agencies, especially for funders seeking to maximise the impact of their funding in sustainability research fields.The information is envisaged as being beneficial in determining where to channel and commit resources to make the highest impact.
The study's limitations lie in the data and methods used.First, from the database used for the bibliometric aspect of the research, although more databases were used to identify sources integratively, the researcher may have missed some articles inadvertently.Secondly, by restricting the search to the built environment, some studies, for example, focused on buildings, may have been excluded from the bibliometric analysis.Therefore, the studies used are not exhaustive.Future studies could include a more specific focus on buildings or public facilities and other spheres/industries such as manufacturing and tourism.Thirdly, the data analysis techniques are not exhaustive; further studies could adopt other review methods or primary research approaches like interviews (an identified methodological gap) to identify concerns and concepts in SFM.Notwithstanding, future research could embrace these trends in SFM as its relevance and visibility continue to grow.

Figure 1 .
Figure 1.Research procedure adopted.To develop a comprehensive general framework of factors considered in sustainability-inclined research in facilities management, the study was conducted in a sequential explanatory two-phase design, guided by aspects of the "Preferred Reporting Items for

Sustainability 2023 , 26 Figure 3 .Figure 3 .
Figure 3. Funding organisations.5.1.5.Analysis of SourcesThe top five sources responsible for the publication of 42% (28) of the papers were Sustainability (8), IOP Conference Series: Earth and Environmental Science(7), Facilities (6), International Journal of Sustainable Built Environment (3), and International Journal of Sustainable Construction Engineering and Technology (4).The CiteScore of the journals is shown in Figure4.The CiteScore reflects the yearly average number of citations to re-

Table 1 .
Author co-authorship and co-citation analysis.
Note: TLS-total link strength.

Table 4 .
Perspectives from highly cited works in SFM research.