Nanomaterials and Nanotechnologies in Wastewater Treatment: Insights from a Bibliometric Analysis (1997‑2016)

Background

The advent of nanomaterial and nanotechnology terminology has spurred interdisciplinary research across chemistry, materials science, medicine, electronics, photonics, and environmental science. The exceptional surface‑area‑to‑volume ratios and reactivity of NNs make them ideal candidates for addressing the growing challenge of wastewater discharge and resource recovery. As global populations rise and living standards improve, the volume of municipal and industrial effluents threatens ecosystems and potable water supplies. Advanced, cost‑effective, and environmentally friendly treatment technologies are therefore essential.

Nanoparticles can be employed as adsorbents, membrane modifiers, photocatalysts, disinfectants, and sensors, offering high performance across a spectrum of contaminant classes. However, the increasing prevalence of engineered nanoparticles in commercial products raises concerns about their fate and potential impacts within wastewater treatment systems. A systematic, quantitative assessment is thus required to guide future research and policy decisions.

Bibliometric analysis has proven invaluable for mapping scientific fields, identifying emerging trends, and forecasting future directions. Tools such as CiteSpace provide visualizations of co‑citation networks, keyword bursts, and collaboration patterns, enabling researchers to make data‑driven decisions. In light of the exponential growth in NN‑related publications, this paper conducts a comprehensive bibliometric and visual analysis of the literature from 1997 to 2016.

Methods

Data Sources

We queried the Science Citation Index Expanded (SCI) on 30 June 2017 using the search string “nano*” AND (“wastewater treatment” OR “sewage treatment” OR “wastewater disposal” OR “sewage disposal”). This strategy retrieved 2,604 records spanning 1997‑2016, ensuring coverage of the most relevant peer‑reviewed literature.

Bibliometric Analysis

Bibliometric analysis applies statistical techniques to publication data, enabling quantitative assessment of publication trends, citation impact, and collaborative networks. Social network analysis, implemented via Gephi, was used to map co‑authorship among the most productive countries and institutions.

Visualization Analysis

Visual representations were generated using CiteSpace for keyword co‑occurrence and burst detection, and ArcGIS to map institutional geographic distribution.

Results and Discussion

Publication Characteristics

Of the 2,604 records, 2,393 (91.9%) were original research articles, while reviews and proceedings papers accounted for 7.45% and 5.45% respectively. English dominated the literature (98.96%), with Chinese contributions at 0.71%; other languages collectively comprised less than 0.4%.

The annual publication trajectory (Figure 1) demonstrates an exponential rise from an average of five papers per year in the early 1990s to 138 in 2011, and a subsequent rapid acceleration. The fitted curve confirms the field’s sustained growth trajectory.

The annual publication number of the top six productive countries during 1997–2016. TP: the total number of publications. The number after the country is the total publications of this country in this field over the time span

China dominated the field with 962 papers (40.2% of the total), followed by the United States (324) and Iran (140). While the United States exhibited a steady increase, China’s surge is linked to national strategic plans prioritizing environmental nanomaterials. Other leading nations—India, South Korea, and Spain—showed modest growth, maintaining a significant gap relative to the top two.

Country and Institutional Contributions

Out of 2,391 articles with complete author affiliations, 83 countries contributed, with the top 20 accounting for 83.95% of all publications. China led in quantity, yet the United States achieved a higher h‑index (55 versus China’s 62) and a broader collaboration network, suggesting a higher proportion of high‑impact work.

The top 30 countries’ collaboration network (Figure 2) reveals a dense partnership between the United States and China, comprising 66 joint papers. China also collaborates extensively with Hong Kong, Saudi Arabia, and the United Kingdom, whereas the United States maintains a more diverse, albeit less dense, international network.

The cooperation network of the top 30 productive countries/territories

Institutional analysis identified 1,871 active research entities, predominantly clustered in Europe, East Asia, and North America. Two‑thirds of the top 30 institutions were Chinese, with the Chinese Academy of Sciences, Tongji University, and Harbin Institute of Technology leading publication output. A high proportion (54.75%) of papers involved multi‑institutional collaborations. While Chinese institutions show robust intra‑national links, their overseas collaboration remains limited.

The cooperation network of the top 30 productive institutions

Subject Categories and Journal Landscape

The literature spans 44 subject categories. Engineering leads (1,069 papers), followed by Chemistry (757) and Environmental Sciences & Ecology (702). The upward trend in Chemistry after 2011 reflects a growing emphasis on the mechanistic understanding of NNs in wastewater contexts.

These 2,393 articles appear in 449 journals. The top 20 journals contribute 47.2% of all publications. RSC Advances (108 papers) is the most prolific, followed by Desalination (97) and Desalination and Water Treatment (96). The prevalence of high‑impact factor journals (IF 4.2‑9.5) underscores the field’s credibility and scientific rigor.

Timeline view of a network related to co‑occurring keywords

Keyword Evolution and Emerging Themes

Keyword burst analysis (Figure 4) identified 20 terms with the strongest attention spikes between 1998 and 2016. Long‑lasting bursts in nanofiltration (14 years), reverse osmosis (10 years), and ultrafiltration (13 years) highlight sustained interest in membrane technologies. Recent bursts in composite, graphene, and sewage sludge point to evolving research foci toward advanced nanocomposites and sludge valorisation.

High‑frequency keywords such as adsorption, degradation, nanofiltration, TiO₂, and photocatalysis dominated early stages, whereas newer terms—carbon nanotube, graphene oxide, magnetic nanoparticle—signal a shift toward novel nanostructures and functionalization strategies.

Highly Cited Works

Top ten highly cited papers, sourced from Environmental Science & Technology and Water Research, collectively demonstrate the field’s emphasis on contaminant removal and material innovation. Graphene‑based studies, magnetic nanoparticles, and carbon nanotube research appear prominently, reflecting their transformative potential. Simultaneously, several high‑impact papers raise awareness of the environmental and health risks associated with nanoparticle release.

Current Applications and Future Directions

Four application domains—adsorption, membrane filtration, photocatalysis, and sensing—emerge as the core of current research. While these technologies have matured, challenges such as nanoparticle recovery, cost‑effective synthesis, and regulatory compliance persist.

Adsorption

Carbon‑based nano‑adsorbents (e.g., aerogels, CNTs, graphene) exhibit superior specific surface areas and active sites, enabling efficient removal of heavy metals and organic pollutants. Nonetheless, aggregation, regeneration complexity, and scale‑up obstacles remain. Strategies to immobilise nanoparticles within pellets or beads can mitigate recovery issues, though they introduce mass‑transfer limitations.

Membrane Filtration

Nanofiber, nanocomposite, and thin‑film nanocomposite (TFN) membranes incorporate inorganic nanoparticles (Al₂O₃, SiO₂, zeolite, TiO₂) to enhance hydrophilicity, reduce fouling, and improve flux. TFN membranes, pioneered by Hoek’s group, demonstrate notable performance gains. Future work should focus on elucidating the precise interactions between nanomaterials and polymer matrices, and on integrating antimicrobial nanoparticles (e.g., Ag) to counter biofouling.

Sensor and Detection

Nanomaterials serve as platforms for detecting trace organic contaminants (PAHs, PCBs, PBDEs) and pathogens. CNTs, Au‑TiO₂ composites, and graphene oxide have enabled sub‑nanogram per milliliter detection limits. However, challenges persist in mitigating false positives in complex wastewater matrices and in developing portable, reusable sensor devices.

Conclusions

This bibliometric survey reveals a rapidly expanding field, with China leading in publication volume and the United States achieving a higher relative h‑index and broader international collaboration. Key nanomaterials—graphene, carbon nanotubes, magnetic nanoparticles, and silver nanoparticles—remain at the forefront of research. While laboratory demonstrations abound, large‑scale commercial deployment is limited, largely due to recovery challenges and potential environmental risks. Addressing these gaps—through scalable synthesis, robust recovery technologies, and comprehensive risk assessment—will be essential for translating nanotechnology innovations into practical wastewater treatment solutions.

Abbreviations

CP:

The number of internationally collaborative publications

FP:

The number of publications as first author’s country

NNs:

Nanomaterials and nanotechnologies

R (%):

The rank (the ratio of the number) of a certain item

R(h-index):

The rank (the value of h-index) of a certain item’s

RP:

The number of publications as corresponding author’s country

SP:

The number of single country publications

TP:

The number of total publications