Web of Science is a globally renowned comprehensive academic information resource database, covering numerous disciplines. The literature it includes has high academic influence and wide representativeness, effectively reflecting the cutting-edge trends and development directions of international academic research. This article conducts a bibliometric analysis using Web of Science as the data source. In the advanced search interface of Web of Science, the search conditions are set as: the subject contains “Micro nano bubble”, “nano bubble”, and “micro bubble”, and on the basis of the above search results, further search for literature with the full text containing “degradation”. The search mode is set to exact match, and the search time range is from the establishment of the database to 1 April 2025. After the search, a total of 509 articles related to the management of hazardous waste in small and micro enterprises were obtained. After duplicate removal using Note Express software, 508 articles were finally obtained for subsequent in-depth analysis. The search scope is set as “subject” (TS): TS = [“Micro nano bubble” or “nano bubble” or “micro bubble” AND TS = (“degradation”)]. The specific screening items are shown in Table 1, excluding irrelevant research topics and directions such as “endocrinology and metabolism” and “agriculture”, while Table 1 presents the final data results.

Compared with traditional bibliometric methods, visualization methods can more intuitively present citation information of literature and its inherent hierarchical structure, facilitating in-depth exploration of interaction relationships in complex networks. This paper, by means of the scientific knowledge mapping method, uses CiteSpace and VOSviewer software to conduct trend analysis of publications, research institutions, scholars, and keyword co-occurrence analysis based on the obtained 508 related literature data, and draw corresponding knowledge maps, thereby comprehensively and intuitively presenting the research situation in this field.

Authors and their collaborations within a certain research field are key factors in promoting academic progress and spreading knowledge. Bibliometric analysis can identify authors who have contributed to a specific research field and their collaboration patterns. Table 2 shows the top 20 authors who have published the most papers in photocatalytic oxidation of volatile organic compounds (VOCs). There are 16 authors from China, demonstrating China’s outstanding contributions to this field. Hu Liming from Tsinghua University has published the most papers, with a total of 10. His most influential paper studied the characteristics of ozone MNBs, including their bubble number, size distribution, and zeta potential. The experiment investigated the ozone MNBs’ mass transfer rate. They used ozone MNBs to deal with water contaminated with organic matter, which showed significant purification efficiency. They also conducted the column tests to research the efficiency of ozone MNBs in the remediation of groundwater contaminated with organic matter. Field monitoring was carried out on a site contaminated with trichloroethylene (TCE). The results indicated that ozone MNBs could significantly enhance the remediation efficiency and are an innovative in-situ remediation technology of groundwater contaminated with organic matter (Hu and Xia, 2018). His team mainly focuses on the ozone MNB technology application in groundwater pollution treatment, confirming the groundwater pH influence and salinity on the treatment capacity of the technology (Xia and Hu, 2019; Li et al., 2013). They believe that ozone MNBs have great oxidation capacity and low secondary pollution (Cao et al., 2023), and possess the ability to transport and dissolve in porous media (Li et al., 2014), making it a promising in-situ remediation technology of groundwater contaminated with organic matter. Fan Wei from Jiangnan University ranks second with eight papers. The representative research direction of this author with the second-highest influence integrates MNB and photocatalytic technology. They found that the MNBs’ interfacial photoelectric effect was also proved to be beneficial for pollutant degradation. MNBs guided strong light scattering, increasing 54.8% of the light path length in the photocatalytic medium at 700 nm and strengthening the photocatalyst light adsorption (Fan et al., 2021; Fan et al., 2019).

The author collaboration distribution map can well reflect the cooperation and joint research in environmental industrial pollution treatment using MNB technology (Figure 1). Each node’s size in the figure represents the paper number published by the author (the larger node means that the author has published more papers), while the connecting lines represent the authors’ collaboration. Figure 1 shows the degree of author collaboration, with several closely collaborating author groups emerging, including the teams of Ma Xing and Zheng Chan, as well as Li Jia and Lan Ziwei. Unlike the author with the highest volume of publications, their main research direction is nanomotors (Ma et al., 2016; Ye et al., 2021; Yang et al., 2023a). The closeness of the connections between different authors is shown in the figure, meaning that the international cooperation intensity in this field still needs to be strengthened. Analyzing the collaboration level among researchers is important because such collaboration not only helps to collect expertise from different disciplines, promoting innovation and progress, but also improves the reliability, quality and efficiency of research through peer review, knowledge transfer and resource sharing, etc. Moreover, collaboration can promote the scientific research internationalization, help solve complicated interdisciplinary problems, and accelerate the transformation of research outcomes into practical applications, especially in the fields of pollution control and environmental protection.

Research institution analysis provides information on the most influential and productive research institutions in a certain research field, which could make scholars well understand the current situation and field trends, and guide how to solve important problems and promote innovation. Figure 2 shows the knowledge domain of collaborative organizations using the software VOSviewer. Every circular node represents an organization, and the circle size indicates the published paper number. Inter-institutional collaboration is represented by a line between two nodes, with the thickness of the line indicating the degree of collaboration. The CAS occupies the highest ranking and has published the most papers in Table 3, which has a critical academic influence. In its latest research, it reviewed the benefits of MNB in the cleaning process, then analyzed in depth the factors affecting its cleaning effect and the possible mechanisms involved. Additionally, it summarized the production and application of MNB in various cleaning scenarios and elaborated on its applications in semiconductor cleaning (Takahashi et al., 2015), membrane cleaning (Lee et al., 2015) and metal cleaning (Ulatowski et al., 2024). In its latest research, it was found that the MNB technology enhanced the vacuum ultraviolet degradation rate by improving the mixing and mass transfer within the solution, optimizing the light performance in the solution, and increasing the dissolved oxygen level (El Aswar et al., 2025). Moreover, as shown in Figure 2, the CAS, Shanghai University, and Tongji University have relatively close cooperative relationships. Their works mainly focus on the application of MNB technology in treating polycyclic aromatic hydrocarbon pollution in groundwater, where the technology can enhance the surfactants transfer and thus improving the degradation capacity (Dai et al., 2023; Han et al., 2025).

Journals in a research field help researchers understand the main academic resources and knowledge dissemination channels. The h-index is a hybrid quantitative indicator which could be used to evaluate the academic output quantity and quality. It was proposed by George Hirsch, a physicist at the University of California, San Diego, in 2005. As it can be seen in Table 4, the analysis of the journals has identified the top ten publications with the highest citation counts in the field of MNB technology for environmental pollution degradation. Chemical Engineering Journal is the journal with the highest number of articles published in this field, with 21 articles, and it is also the publication with the highest citation count, indicating its importance in the field. Next are Separation and Purification Technology and Ultrasonics Sonochemistry, which have published 18 and 13 articles respectively. Additionally, although ACS Nano has only published seven research papers on MNBs, its citation count ranks second, suggesting that this publication is highly trusted by readers in the field and the articles published in it have significant influence within the field.

The different colored areas in the Figure 3 represent the different research preferences of various publications on the article’s research direction. The publications in the red area led by Ultrasonics Sonochemistry mainly focus on the generation mechanism and methods of MNBs. Ultrasonics Sonochemistry mainly uses ultrasound to generate MNBs for water pollution treatment, with two main approaches: activating intermediate substances [such as quantum dots (Entezari and Ghows, 2011), nanomaterials (Bao et al., 2023), etc.] to enhance their oxidation capacity and enhancing the generation of free radicals through sonochemistry (Pétrier et al., 2010), to strengthen the effect of wastewater treatment. The publications in the yellow area led by Separation and purification technology mainly focus on the technology of using MNBs to clean dirt. This journal mainly studies the use of MNB technology to clean filter membranes, solve the problem of membrane fouling, thereby improving the stability of the membrane and enhancing the degradation capacity of water treatment (Duan et al., 2025; Duan et al., 2022; Mo et al., 2024). The publications in the green area led by Acs nano mainly focus on the R&D of water treatment materials and equipment. This journal mainly studies the nanoscale micro-motors application in water pollution treatment (Villa et al., 2018; Zhang et al., 2024; Soler et al., 2013). The publications in the blue area led by Chemical engineering journal have a relatively comprehensive research direction, covering various aspects of MNB technology.

By conducting a statistical analysis of the published paper number from 1995 to 2025, the status, maturity and development trend of MNB technology research achievements can be clearly shown. Figure 4 presents the research result distribution on MNB technology in environmental treatment based on the time series. From 1995 to 2007, less than five articles on MNB technology were published each year. From 2008 to 2017, this field showed a overall slow growth trend, and the annual publication volume in this field exceeded 10 for the first time in 2017. After that, research related to MNB technology gradually became a hot topic, which is inseparable from the pollution control and environmental protection policies of many countries as well as major technological breakthroughs. From 2017 to 2024, the published paper number increased significantly, with an annual publication volume of over 50 for five consecutive years, and the publication volume reached 80 in 2024. As of 2025, 508 papers have been published in VOCs photocatalytic oxidation research. The continuous increase in the number of papers in this field indicates that researchers have paid more attention to the application of MNB technology in environmental pollution degradation.

Based on the timeline (Figure 5), the development process of MNB technology has been sorted out, covering its key progress from the theoretical assumption to the exploration of applications in multiple fields such as water treatment and disinfection, demonstrating the continuous expansion of its application boundaries and the deepening of research. In the theoretical assumption stage, Parker et al. first hypothesized the MNBs existence in 1994, laying the theoretical foundation for subsequent related research and opening the door to the study of this special type of bubble (Parker et al., 1994). During the early application exploration period of MNB technology (1999–2007), Ishida et al. imaged bulk MNBs using atomic force microscopy (AFM), providing a direct understanding of the physical morphology of MNBs (Ishida et al., 2000). Chu et al. reported the application of ozone MNBs in dye removal and water disinfection, expanding the application ideas of MNBs in water treatment (Chu et al., 2007).

From 2009 to 2018, it was the development period of MNB technology. Tasaki et al. studied the degradation effect of MNBs under ultraviolet (UV) irradiation on methyl orange, exploring the water treatment technology of light-MNB synergy (Utaka et al., 2009). In 2011, the first review on the application of MNB technology in water treatment was conducted, systematically summarizing the application achievements and prospects of this technology in water treatment at that time. In 2016, Agarwal et al. reviewed the history of MNBs, retrospectively summarizing its development trajectory from a more macroscopic perspective (Agarwal et al., 2016).

As shown in the figure, it is the time distribution map of key words related to MNB technology. During the explosive period after 2018, due to its excellent mass transfer ability and the ability to produce active oxidative species, MNB technology was coupled with different environmental pollution degradation technologies and applied in multiple fields. There were studies on the degradation of aniline using non-thermal plasma/MNBs, further enriching the technical means of MNBs in the treatment of refractory organic pollutants. In 2019, Fenton/MNBs were used for dye separation and microplasma bubbles for inactivating microorganisms, exploring new directions for the combination of MNBs with other technologies. MNBs were used to enhance the degradation of oxytetracycline under visible light, broadening the application scope of MNBs in the field of photocatalytic degradation. In 2021, it was found that MNBs could promote the photocatalytic disinfection of microbial spores, and the stability of oxygen-containing MNBs in fresh water was confirmed, providing new evidence for their application in the disinfection field. In 2022, the exploration of ultraviolet C (UV-C)/hydrogen peroxide (H₂O₂)/MNBs as a new disinfection technology further explored the potential of MNBs in disinfection technology innovation.

From 2023 to 2025, the development of MNB technology has been rapid, and research has delved deeper. The focus of research on the applicability of MNB technology has mainly been on exploring the coupling effect of MNBs with other technologies. In previous studies, it was found that MNBs can effectively enhance gas mass transfer and the production of active species. Scholars have thus focused on the coupling effect between MNBs and various oxidants, using the strong oxidation effect of MNBs to activate different oxidants (such as persulfate, ferrous ions, and nano zero-valent iron) and treat complex pollutants in different media, continuously expanding the application scope of MNB technology. Jing et al. utilized MNBs to enhance the immobilized Chlorella technology. Thanks to the excellent mass transfer capacity of MNBs, the biomass of Chlorella increased by 2.48 times, significantly improving the removal efficiency of ofloxacin (Jing et al., 2025). Chi et al. studied the degradation of tetracycline, a commonly used antibiotic in wastewater, using a system based on zero-valent nano-iron assisted by MNBs. MNBs can serve as an ideal carrier for zero-valent nano-iron. When they burst, they generate shock waves and highly reactive substances (such as •OH), which can significantly enhance the degradation efficiency (Chi et al., 2024). Table 5 presents a portion of the relevant research on MNB technology in various application scenarios over the past 2 years.

Meanwhile, due to the mature development of ozone MNB technology, in recent studies, scholars no longer confine their research to the laboratory and have conducted many practical application studies, mainly exploring the influence of factors such as air intake rate, air intake volume, and pollutant concentration (Hu et al., 2023; Zhao et al., 2024a). Ponce-Robles et al. actively promoted the practical application of MNB technology. By adjusting the size of ozone MNBs, the air intake volume, and the air intake rate, they conducted experiments in large-scale pharmaceutical wastewater. They replaced the traditional tertiary sewage treatment equipment with ozone MNB technology, which enhanced the treatment capacity and reduced costs (Ponce-Robles et al., 2023).

In the keyword spectrum diagram, VOSviewer has classified the keywords. Co-occurrence analysis of keywords helps to understand the basic themes and concepts in the literature or dataset. It assists researchers in positioning their research, decision-making, and collaboration to achieve a more comprehensive understanding of the challenges and opportunities in a specific field or topic. As shown in Figure 6, the keywords in the MNB field are divided into five categories. The three main categories are the red area led by “degradation”, which mainly focuses on the application of MNB technology to assist other different treatment technologies, such as non-thermal plasma bubbles, advanced oxidation, photocatalysis, etc., and ultimately focuses on the degradation effect of pollutants. The second category is the pink area, mainly summarizing the development of ozone MNB technology. The combination of ozone and MNB technology is the most developed technology. Between these two areas is the purple area, mainly summarizing the core keywords of MNB technology, “oxides” and “reactive oxygen species”. Next, we will further analyze the three key categories.

First, let’s discuss the purple area section (Figure 6), which outlines the core principle of MNB technology. Now, two representative views explains the generation of reactive oxygen species (ROS) during MNB oxidation: one is the view of interface ion accumulation during the MNB contraction process (Takahashi et al., 2007a; Yang et al., 2023d). As MNBs contract, the surface Zeta potential increases with the increase in the contraction rate, which is inversely proportional to the bubble size. This indicates that the surface charge migration rate is insufficient to counteract the increase in the MNB contraction rate, leading to the accumulation of charges at the gas-liquid interface and the formation of a high chemical potential (Takahashi et al., 2015). According to this theory, under a wide range of pH conditions, MNBs carry a negative charge. Therefore, during the bubble contraction process, OH⁻ is more easily adsorbed onto the bubble surface than H⁺, resulting in an interface environment with high ion concentration and a double-layer structure (Takahashi et al., 2007b). When ozone gas diffuses and dissolves into the liquid phase within MNBs, the high concentration of OH⁻ at the interface triggers the ozone self-decomposition chain reaction, leading to the generation of ·OH (Cheng et al., 2018; Khuntia et al., 2012; Cheng et al., 2019). This theory is applicable to ozone MNBs. Since ozone itself is a highly reactive oxidizing species, when ozone gas diffuses and dissolves into the liquid phase within MBs, the high concentration of OH⁻ at the interface triggers the ozone self-decomposition chain reaction, leading to the generation of •OH (Cheng et al., 2018; Khuntia et al., 2012; Cheng et al., 2019). During the accumulation of air and oxygen MNBs at the bubble interface, the reaction between oxygen and OH⁻ is slow and inefficient, and thus cannot generate a large amount of reactive oxygen free radicals. Zhao et al. revealed the main free radicals produced and the pathways of ozone generating free radicals (Equations 1–4) when using ozone MNB technology to treat tetracycline wastewater, verifying the working mechanism of ozone MNBs (Zhao et al., 2024b). 2 O 3 → 1 O 2 + 2 O 2 (1) O 3 + OH 2 ‐ → · OH + · O 2 ‐ + O 2 (2) O 3 · ‐ → O · ‐ + O 2 (3) O · ‐ + H 2 O → · OH + OH ‐ (4)

The other view is the adiabatic compression during the MNB collapse process (Shi et al., 2021; Yasui et al., 2016; Zhou et al., 2020). As MNBs contract, the reduction in volume increases the internal gas pressure. Before reaching the critical collapse state, MNBs typically withstand an internal pressure of 0.83–1.65 MPa, which is over 50 times the atmospheric pressure (Yasui et al., 2019). At this point, ozone molecules remain in a dense state, colliding more frequently in a smaller space, resulting in a higher energy state. Simultaneously, the MNB wall contraction speed reaches 90 m/s, raising the critical temperature inside the bubble to 3,000 K and the temperature of the liquid near the bubble to 360 K. Although these extreme conditions of high temperature and pressure only last for approximately 19 picoseconds, a quasi-adiabatic compression effect is formed at the MNB interface, which is sufficient to trigger the thermal decomposition of gas molecules, thereby leading to the generation of free radicals. The applicability of this theory is not only limited to ozone MNBs, but also applies to MNBs composed of oxygen and air. Although the free radical yield of oxygen is far less than that of ozone, with the support of adiabatic compression theory, it can be coupled with different types of other technologies (such as advanced oxidation, photocatalysis, etc.) to enhance the oxidation capacity and assist other water treatment technologies. Considering the cost, oxygen MNBs are cheaper than ozone MNBs and more suitable for coupling with other technologies. Li et al. found in the experiment of using divalent iron to catalyze the treatment of 4,4′-sulfonyl diphenol (BPS) that the degradation efficiency of pollutants increased by 35% after the addition of MNBs for co-treatment (Li et al., 2025a). El Aswad et al. utilized MNBs to assist in the ultraviolet photocatalytic degradation of sulfamethazine in water, doubling the degradation efficiency (El Aswar et al., 2025). During the treatment process, the presence of hydroxyl radicals was detected using pCBA, CCl₄, and MDE probe compounds to identify •OH, •O₂ ⁻, and ¹O₂ respectively. The discovery of hydroxyl radicals indicates that the energy and free radicals generated during the collapse of MNBs are conducive to the oxidative degradation of water pollution. This inexpensive and simple bubble technology is expected to become an auxiliary means to enhance existing environmental pollution treatment technologies and engineering.

The red area of the keyword spectrum (Figure 6) mainly focuses on the application of MNB technology in combination with various other technologies. It summarizes the excellent auxiliary degradation ability of MNBs. The functionalization of MNBs, their ability to generate reactive oxygen species (ROS), and their light scattering effect also contribute to assisting oxidation degradation reactions. Specifically, for instance, in the Fenton reaction, a Fe(II) catalytic layer can be constructed on the surface of MNBs, which not only adsorbs pollutants but also promotes the Fenton reaction in situ while adsorbing pollutants (Zhang et al., 2022a), thereby enhancing the oxidation reaction rate (Yi et al., 2023). Additionally, during the interface contraction process of MNBs, ROS can also be generated at the interface, directly leading to the degradation of pollutants (Wu et al., 2019). Moreover, the light scattering effect at the interface of MNBs can effectively extend the effective path length of light, thereby improving the photocatalytic efficiency (Fan et al., 2021). These indicate that the application of MNBs plays a crucial role in enhancing oxidation performance.