Key Takeaways & Executive Findings
- •• • Chemical propulsion and photocatalytic degradation dominate current MNR research, as revealed by data-driven quantitative analysis, indicating a focused research trajectory toward energy-efficient and reactive systems. • • Self-driven magnetorobots achieve recyclable and scalable micro/nanoplastic removal from nonmarine waters, addressing a critical gap in conventional filtration methods that fail to capture particles below 5 mm. • • Metal-organic framework-based autonomous microrobots enable radioactive uranium preconcentration, demonstrating high selectivity and efficiency in treating radionuclide-contaminated wastewater, a niche where traditional sorbents are often inefficient. • • Zerovalent-iron/platinum Janus micromotors with spatially separated functionalities achieve efficient water decontamination, exemplifying the design principle of integrating catalytic and adsorptive domains to enhance overall removal kinetics.
Abstract
Conventional wastewater treatment technologies face persistent challenges including incomplete removal of emerging contaminants, secondary pollution, and low energy efficiency. Micro-nano robots (MNRs), leveraging their self-propulsion, precise navigation, and high specific surface area, offer a transformative approach for targeted pollutant sequestration and degradation. This review systematically examines the operational mechanisms and propulsion strategies of MNRs in wastewater remediation. Through a data-driven bibliometric analysis, we identify chemical propulsion and photocatalytic degradation as the predominant research foci. We critically evaluate the performance of various MNR designs—including chemically driven, magnetically driven, and light-driven systems—for the removal of organic pollutants, heavy metals, microplastics, radioactive nuclides, and pathogenic microorganisms. Representative studies demonstrate removal efficiencies exceeding 90% for specific contaminants, such as uranium preconcentration via metal-organic framework-based microrobots and microplastic removal using self-driven magnetorobots. Despite these advances, MNRs face intrinsic trade-offs between propulsion efficiency and environmental compatibility, as well as challenges in coordinating actuation and control in complex aqueous matrices. We propose future directions emphasizing sustainable energy-harvesting systems and intelligent, reconfigurable multifunctional designs. This review provides a systematic framework and forward-looking perspective to accelerate the translation of MNR technology from laboratory innovation to practical wastewater treatment applications.
1. Introduction
Conventional wastewater treatment technologies—including adsorption, oxidation, UV treatment, flocculation, activated sludge, and membrane filtration—are increasingly inadequate against the rising complexity of pollutants. Emerging contaminants such as microplastics, pharmaceuticals, and endocrine disruptors evade traditional barriers, while processes like activated sludge generate secondary pollution and demand high energy inputs. The inability to precisely target sub-micron contaminants in heterogeneous matrices underscores a critical technological bottleneck.
Micro-nano robots (MNRs) address this bottleneck by converting chemical or external physical energy into autonomous motion, enabling active navigation and targeted interaction with pollutants. Unlike passive nanomaterials, MNRs exhibit enhanced mass transfer and can be functionalized for selective adsorption or catalytic degradation. This review systematically evaluates the current state of MNR applications, identifies key challenges in efficiency-compatibility and actuation-control coordination, and outlines future directions for sustainable and intelligent MNR design, providing a roadmap for translating this disruptive technology into practical wastewater treatment solutions.
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LV Haolong, JIAN Yang, HUANG Hui, REN Hongqiang (2026). Micro-nano Robots for Wastewater Treatment: Current Application Status and Prospects. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025091801
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Frequently Asked Questions
What are the primary bottlenecks preventing the scale-up of micro-nano robots from laboratory to industrial wastewater treatment?
The main bottlenecks include the intrinsic trade-off between propulsion efficiency and environmental compatibility, as well as the difficulty in coordinating actuation and control in complex, large-volume wastewater matrices. For instance, chemical propulsion often relies on fuels like hydrogen peroxide, which are toxic and impractical at scale. Additionally, the long-term stability and reusability of MNRs in real wastewater conditions remain unproven. Research must focus on developing biocompatible fuels and robust, recoverable designs to overcome these hurdles.
How do micro-nano robots achieve selective removal of specific pollutants, such as heavy metals or radionuclides, compared to conventional sorbents?
MNRs can be functionalized with specific recognition elements, such as metal-organic frameworks (MOFs) or ion-imprinted polymers, that exhibit high affinity for target ions. For example, MOF-based microrobots have demonstrated efficient uranium preconcentration, achieving high distribution coefficients even at trace concentrations. Their self-propulsion enhances mass transfer and reduces diffusion limitations, leading to faster kinetics and higher uptake capacities than passive sorbents. Furthermore, the ability to navigate and collect pollutants enables localized treatment, minimizing secondary contamination.
What are the most promising propulsion mechanisms for practical wastewater treatment, considering energy efficiency and environmental safety?
External field-driven mechanisms, particularly magnetic and light-driven propulsion, are most promising because they eliminate the need for chemical fuels, avoiding secondary pollution. Magnetic propulsion offers precise control and deep tissue penetration, while photocatalytic propulsion can simultaneously drive motion and degrade pollutants. However, the energy requirements for large-scale magnetic fields or light penetration in turbid water remain challenging. Hybrid systems that combine multiple driving forces may offer a balanced solution.
How do micro-nano robots address the removal of microplastics, which are notoriously difficult to capture due to their small size and low concentration?
Self-driven magnetorobots have been engineered to capture microplastics via electrostatic or hydrophobic interactions, achieving efficient removal from nonmarine waters. Their autonomous motion allows them to actively encounter and adhere to microplastics, overcoming the limitations of passive filtration. The magnetic core enables easy retrieval and recyclability, making the process scalable. However, the efficiency depends on the surface chemistry and the ability to release captured plastics for disposal, which requires further optimization.
What are the key performance metrics used to evaluate the efficiency of micro-nano robots in pollutant degradation, and how do they compare to conventional methods?
Key metrics include degradation rate constants (e.g., first-order kinetics), removal efficiency percentages, and mineralization rates. For instance, photocatalytic micromotors have achieved degradation rates of organic dyes exceeding 90% within minutes, significantly faster than passive photocatalysts due to enhanced mass transfer. Additionally, the figure of merit often includes the turnover frequency and the energy consumption per order of pollutant removal. Comparative studies indicate that MNRs can reduce treatment times by up to an order of magnitude, though energy costs for external fields must be factored into overall efficiency.
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