Metal-Oxide-Based Microjets for the Simultaneous Removal of Organic Pollutants and Heavy Metals

Orbits, Spirals, and Trapped States: Dynamics of a Phoretic Janus Particle in a Radial Concentration Gradient

A long-standing goal in colloidal active matter is to understand how gradients in fuel concentration influence the motion of phoretic Janus particles. Here, we present a theoretical description of the motion of a spherical phoretic Janus particle in the presence of a radial gradient of the chemical solute driving self-propulsion. Radial gradients are a geometry relevant to many scenarios in active matter systems and naturally arise due to the presence of a point source or sink of fuel. We derive an analytical solution for the Janus particle's velocity and quantify the influence of the radial concentration gradient on the particle's trajectory. Compared to a phoretic Janus particle in a linear gradient in fuel concentration, we uncover a much richer set of dynamic behaviors including circular orbits and trapped stationary states. We identify the ratio of the phoretic mobilities between the two domains of the Janus particle as a central quantity in tuning their dynamics. Our results provide a path for developing optimum protocols for tuning the dynamics of phoretic Janus particles and mixing fluid at the microscale. In addition, this work suggests a method for quantifying the surface properties of phoretic Janus particles, which have proven to be challenging to probe experimentally.

UHPLC-QTOF-MS-Based Targeted Metabolomics Provides Novel Insights into the Accumulative Mechanism of Soil Types on the Bioactive Components of Salvia miltiorrhiza

The root of Salvia miltiorrhiza Bunge (SMB) has been widely used to treat cardiovascular diseases. However, the contents of secondary metabolites in the roots from different production areas are significantly different, and the impact of soil factors on this accumulation remains unclear. Therefore, this study aimed to elucidate the regularity of variation between the active components and soil factors through targeted metabolomics and chemical dosimetry. Soils were collected from five different cities (A, B, C, D, and E) and transplanted into the study area. The results showed that there were significant differences in the soil fertility characteristics and heavy metal pollution levels in different soils. Ten water- and twelve lipid-soluble metabolites were identified in SMBs grown in all soil types. SMBs from D cities exhibited the highest total tanshinone content (p < 0.05). The salvianolic acid B content in SMBs from E cities was the highest (p < 0.05). Interestingly, correlation analysis revealed a significant negative correlation between the accumulation of lipid-soluble and water-soluble metabolites. Double-matrix correlation analysis demonstrated that available potassium (AK) was significantly negatively correlated with salvianolic acid B (r = -0.80, p = 0.0004) and positively correlated with tanshinone IIA (r = 0.66, p = 0.008). Conversely, cadmium (Cd) and cuprum (Cu) were significantly positively and negatively correlated with salvianolic acid B (r = 0.96, p < 0.0001 and r = 0.72, p = 0.0024) and tanshinone IIA (r = 0.40, p = 0.14 and r = 0.73, p = 0.0018), respectively. Mantel's test indicated that AK (r > 0.52, p < 0.001), Cu (r > 0.60, p < 0.005), and Cd (r > 0.31, p < 0.05) were the primary drivers of the differences in the active components of SMBs. These findings provide a theoretical framework for modulating targeted metabolites of SMB through soil factors, with significant implications for the cultivation and quality control of medicinal plants.

Advanced materials for micro/nanorobotics

Autonomous micro/nanorobots capable of performing programmed missions are at the forefront of next-generation micromachinery. These small robotic systems are predominantly constructed using functional components sourced from micro- and nanoscale materials; therefore, combining them with various advanced materials represents a pivotal direction toward achieving a higher level of intelligence and multifunctionality. This review provides a comprehensive overview of advanced materials for innovative micro/nanorobotics, focusing on the five families of materials that have witnessed the most rapid advancements over the last decade: two-dimensional materials, metal-organic frameworks, semiconductors, polymers, and biological cells. Their unique physicochemical, mechanical, optical, and biological properties have been integrated into micro/nanorobots to achieve greater maneuverability, programmability, intelligence, and multifunctionality in collective behaviors. The design and fabrication methods for hybrid robotic systems are discussed based on the material categories. In addition, their promising potential for powering motion and/or (multi-)functionality is described and the fundamental principles underlying them are explained. Finally, their extensive use in a variety of applications, including environmental remediation, (bio)sensing, therapeutics, etc., and remaining challenges and perspectives for future research are discussed.

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

Comprehensive Understanding of Self-Propelled Janus Pt/Fe2O3 Micromotor Dynamics: Impact of Size, Morphology, and Surface Structure

The increasing use of plastics has led to the accumulation of plastic waste in the oceans, resulting in significant global environmental challenges associated with microplastic pollution. Micromotors, capable of capturing and removing microplastics from aquatic systems, have emerged as a promising solution to addressing this problem. This research aims to analyze the factors affecting the speed of micromotors, including size, morphology, and surface structure, while elucidating the underlying mechanisms governing micromotor propulsion to develop efficient and ecofriendly micromotors. In this study, we systematically manipulate various parameters by modifying the synthesis method of hematite-based micromotors, subsequently comparing their propulsion speeds and uncovering the precise role of these parameters in determining the micromotor performance. Furthermore, we shed light on the intricate interplay between drag force and propulsive force, demonstrating how these forces vary under different H2O2 conditions. These findings provide valuable insights into the design of efficient micromotors tailored for dynamic aquatic environments.

Multifunctional Biotemplated Micromotors for In Situ Decontamination of Antibiotics and Heavy Metals in Soil and Groundwater

The ubiquitous pollution by antibiotics and heavy metal ions has posed great threats to human health and the ecological environment. Therefore, we developed a self-propelled tubular micromotor based on natural fibers as an active heterogeneous catalyst for antibiotic degradation and adsorbent for heavy metal ions in soil/water. The prepared micromotors can move in the presence of hydrogen peroxide (H2O2) through a bubble recoil mechanism. The MnO2 NPs and MnFe2O4 NPs loaded on the hollow fibers not only enabled self-driven motion and magnetic control but also served as activators of peroxymononsulfate (PMS) and H2O2 to produce active free radicals SO4•- and •OH. Benefiting from the self-propulsion and bubble generation, the micromotors can effectively overcome the disadvantage of low diffusivity of traditional heterogeneous catalysts, achieving the degradation of more than 90% TC in soil within 30 min. Meanwhile, due to the large specific surface area, abundant active sites, and strong negative zeta potential, the micromotors can effectively adsorb heavy metal ions in the water environment. In 120 min, self-propelled micromotors removed more than 94% of lead ions, an increase of 47% compared to static micromotors, illustrating the advantages of on-the-fly capture. The prepared micromotors with excellent catalytic performance and adsorption capacity can simultaneously degrade antibiotics and adsorb heavy metal ions. Moreover, the magnetic response enabled the micromotors to be effectively separated from the system after completion of the task, avoiding the problem of secondary pollution. Overall, the proposed micromotors provide a new approach to the utilization of natural materials in environmental applications.

Bubble-propelled micromotors for ammonia generation

Micromotors have emerged as promising tools for environmental remediation, thanks to their ability to autonomously navigate and perform specific tasks at the microscale. In this study, we present the development of MnO2 tubular micromotors modified with laccase for enhanced oxidation of organic pollutants by providing an additional oxidative catalytic pathway for pollutant removal. These modified micromotors exhibit efficient ammonia generation through the catalytic decomposition of urea, suggesting their potential application in the field of green energy generation. Compared to bare micromotors, the MnO2 micromotors modified with laccase exhibit a 20% increase in rhodamine B degradation. Moreover, the generation of ammonia increased from 2 to 31 ppm in only 15 min, evidencing their high catalytic activity. To enable precise tracking of the micromotors and measurement of their speed, a deep-learning-based tracking system was developed. Overall, this work expands the potential applicability of bio-catalytic tubular micromotors in the energy field.

Light-Powered Self-Adaptive Mesostructured Microrobots for Simultaneous Microplastics Trapping and Fragmentation via in situ Surface Morphing

Microplastics, which comprise one of the omnipresent threats to human health, are diverse in shape and composition. Their negative impacts on human and ecosystem health provide ample incentive to design and execute strategies to trap and degrade diversely structured microplastics, especially from water. This work demonstrates the fabrication of single-component TiO2 superstructured microrobots to photo-trap and photo-fragment microplastics. In a single reaction, rod-like microrobots diverse in shape and with multiple trapping sites, are fabricated to exploit the asymmetry of the microrobotic system advantageous for propulsion. The microrobots work synergistically to photo-catalytically trap and fragment microplastics in water in a coordinated fashion. Hence, a microrobotic model of "unity in diversity" is demonstrated here for the phototrapping and photofragmentation of microplastics. During light irradiation and subsequent photocatalysis, the surface morphology of microrobots transformed into porous flower-like networks that trap microplastics for subsequent degradation. This reconfigurable microrobotic technology represents a significant step forward in the efforts to degrade microplastics.

Confined Tri-Functional FeOx @MnO2 @SiO2 Flask Micromotors for Long-Lasting Motion and Catalytic Reactions

H₂ O₂ -fueled micromotors are state-of-the-art mobile microreactors in environmental remediation. In this work, a magnetic FeO_x @MnO₂ @SiO₂ micromotor with multi-functions is designed and demonstrated its catalytic performance in H₂ O₂ /peroxymonosulfate (PMS) activation for simultaneously sustained motion and organic degradation. Moreover, this work reveals the correlations between catalytic efficiency and motion behavior/mechanism. The inner magnetic FeO_x nanoellipsoids primarily trigger radical species (^• OH and O₂ ^•- ) to attack organics via Fenton-like reactions. The coated MnO₂ layers on FeO_x surface are responsible for decomposing H₂ O₂ into O₂ bubbles to provide a propelling torque in the solution and generating SO₄ ^•- and ^• OH for organic degradation. The outer SiO₂ microcapsules with a hollow head and tail result in an asymmetrical Janus structure for the motion, driven by O₂ bubbles ejecting from the inner cavity via the opening tail. Intriguingly, PMS adjusts the local environment to control over-violent O₂ formation from H₂ O₂ decomposition by occupying the Mn sites via inter-sphere interactions and enhances organic removal due to the strengthened contacts and Fenton-like reactions between inner FeO_x and peroxides within the microreactor. The findings will advance the design of functional micromotors and the knowledge of micromotor-based remediation with controlled motion and high-efficiency oxidation using multiple peroxides.

Nanostructured Hybrid BioBots for Beer Brewing

The brewing industry will amass a revenue above 500 billion euros in 2022, and the market is expected to grow annually. This industrial process is based on a slow sugar fermentation by yeast (commonly Saccharomyces cerevisiae). Herein, we encapsulate yeast cells into a biocompatible alginate (ALG) polymer along Fe₃O₄ nanoparticles to produce magneto/catalytic nanostructured ALG@yeast-Fe₃O₄ BioBots. Yeast encapsulated in these biocompatible BioBots keeps their biological activity (growth, reproduction, and catalytic fermentation) essential for brewing. Catalytic fermentation of sugars into CO₂ gas caused a continuous oscillatory motion of the BioBots in the solution. This BioBot motion is employed to enhance the beer fermentation process compared to static-free yeast cells. When the process is finished, magnetic actuation of BioBots is employed for their retrieval from the beer samples, which avoids the need of additional filtration steps. All in all, we demonstrate how an industrial process such as beer production can be benefited by miniaturized autonomous magneto/catalytic BioBots.

Precisely controlled and deeply penetrated micro-nano hybrid multifunctional motors with enhanced antibacterial activity against refractory biofilm infections

The biofilm resistance of microorganisms has severe economic and environmental implications, especially the contamination of facilities associated with human life, including medical implants, air-conditioning systems, water supply systems, and food-processing equipment, resulting in the prevalence of infectious diseases. Once bacteria form biofilms, their antibiotic resistance can increase by 10-1,000-fold, posing a great challenge to the treatment of related diseases. In order to overcome the contamination of bacterial biofilm, destroying the biofilm's matrix so as to solve the penetration depth dilemma of antibacterial agents is the most effective way. Here, a magnetically controlled multifunctional micromotor was developed by using H₂O₂ as the fuel and MnO₂ as the catalyst to treat bacterial biofilm infection. In the presence of H₂O₂, the as-prepared motors could be self-propelled by the generated oxygen microbubbles. Thereby, the remotely controlled motors could drill into the EPS of biofilm and disrupt them completely with the help of bubbles. Finally, the generated highly toxic •OH could efficiently kill the unprotected bacteria. This strategy combined the mechanical damage, highly toxic •OH, and precise magnetic guidance in one system, which could effectively eliminate biologically infectious fouling in microchannels within 10 min, possessing a wide range of practical application prospects especially in large scale and complex infection sites.

Biomass-derived nanocellulose aerogel enable highly efficient immobilization of laccase for the degradation of organic pollutants

Laccase is a promising biocatalyst for pollutant degradation and water purification. However, laccase can only improve the stability of enzyme activity and achieve its significant catalytic effect after effective immobilization. Herein, we report a general strategy to integrate nanocellulose aerogel and laccase for high-efficiency degradation of organic pollutants. Biomass-derived functional bacterial cellulose (BC) aerogel with a nanonetwork structure and high porosity was prepared by biosynthesis, solvent replacement, and atom transfer radical polymerization (ATRP) procedures. Subsequently, a biocatalyst platform was fabricated by "coupling" ATRP-modified BC aerogel with abundant active sites with laccase through ion coordination. The results demonstrated the biocatalyst platform not only has good biological affinity, but also has high enzyme load and structural stability. Meanwhile, the degradation rates of reactive red X-3B and 2, 4-dichlorophenol reached 94.5% and 85.2% within 4 h, respectively. The strategy disclosed herein could provide a practical method for the degradation of organic pollutants.

Shape-preserving conversion of calcium carbonate tubes to self-propelled micromotors

The self-assembly of inorganic structures beyond the euhedral shape repertoire is a powerful approach to grow hierarchically ordered materials and mesoscopic devices. The hollow precipitate tubes in chemical gardens are a classic example, which we produce on Nafion membranes separating a CaCl₂-containing gel from a Na₂CO₃ solution. The resulting CaCO₃ microtubes are conical and consist of either pure vaterite or calcite. The process also forms branched T- and Y-shaped structures. The metastable vaterite polymorph can be converted to Mn-based structures without loss of the macroscopic shape. In H₂O₂ solution, the resulting tubes self-propel by the release of O₂ bubbles, which for branched structures causes rotation. The tubes can contain multiple bubbles which are ejected in a quasi-periodic fashion (e.g. in groups of four). The addition of surfactants causes the accumulation of bubble trails and bubble rafts that interact with the moving tubes and give rise to distinct motion patterns.

Micromotor-in-Sponge Platform for Multicycle Large-Volume Degradation of Organic Pollutants

The presence of organic pollutants in the environment is a global threat to human health and ecosystems due to their bioaccumulation and long-term persistence. Hereby a micromotor-in-sponge concept is presented that aims not only at pollutant removal, but towards an efficient in situ degradation by exploiting the synergy between the sponge hydrophobic nature and the rapid pollutant degradation promoted by the cobalt-ferrite (CFO) micromotors embedded at the sponge's core. Such a platform allows the use of extremely low fuel concentration (0.13% H₂ O₂ ), as well as its reusability and easy recovery. Moreover, the authors demonstrate an efficient multicycle pollutant degradation and treatment of large volumes (1 L in 15 min) by using multiple sponges. Such a fast degradation process is due to the CFO bubble-propulsion motion mechanism, which induces both an enhanced fluid mixing within the sponge and an outward flow that allows a rapid fluid exchange. Also, the magnetic control of the system is demonstrated, guiding the sponge position during the degradation process. The micromotor-in-sponge configuration can be extrapolated to other catalytic micromotors, establishing an alternative platform for an easier implementation and recovery of micromotors in real environmental applications.

Pick up and dispose of pollutants from water via temperature-responsive micellar copolymers on magnetite nanorobots

Nano/micromotor technology is evolving as an effective method for water treatment applications in comparison to existing static mechanisms. The dynamic nature of the nano/micromotor particles enable faster mass transport and a uniform mixing ensuring an improved pollutant degradation and removal. Here we develop thermosensitive magnetic nanorobots (TM nanorobots) consisting of a pluronic tri-block copolymer (PTBC) that functions as hands for pollutant removal. These TM nanorobots are incorporated with iron oxide (Fe3O4) nanoparticles as an active material to enable magnetic propulsion. The pickup and disposal of toxic pollutants are monitored by intermicellar agglomeration and separation of PTBC at different temperatures. The as-prepared TM nanorobots show excellent arsenic and atrazine removal efficiency. Furthermore, the adsorbed toxic contaminants on the TM nanorobots can be disposed by a simple cooling process and exhibit good recovery retention after multiple reuse cycles. This combination of temperature sensitive aggregation/separation coupled with magnetic propulsion opens a plethora of opportunities in the applicability of nanorobots in water treatment and targeted pollutant removal approaches.

Halloysite-Based Nanorockets with Light-Enhanced Self-Propulsion for Efficient Water Remediation

Halloysite-based tubular nanorockets with chemical-/light-controlled self-propulsion and on-demand acceleration in velocity are reported. The nanorockets are fabricated by modifying halloysite nanotubes with nanoparticles of silver (Ag) and light-responsive α-Fe₂O₃ to prepare a composite of Ag-Fe₂O₃/HNTs. Compared to the traditional fabrication of tubular micro-/nanomotors, this strategy has merits in employing natural clay as substrates of an asymmetric tubular structure, of abundance, and of no complex instruments required. The velocity of self-propelled Ag-Fe₂O₃/HNTs nanorockets in fuel (3.0% H₂O₂) was ca. 1.7 times higher under the irradiation of visible light than that in darkness. Such light-enhanced propulsion can be wirelessly modulated by adjusting light intensity and H₂O₂ concentration. The highly repeatable and controlled "weak/strong" propulsion can be implemented by turning a light on and off. With the synergistic coupling of the photocatalysis of the Ag-Fe₂O₃ heterostructure and advanced oxidation in H₂O₂/visible light conditions, the Ag-Fe₂O₃/HNTs nanorockets achieve an enhanced performance of wastewater remediation. A test was done by the catalytic degradation of tetracycline hydrochloride. The light-enhanced propulsion is demonstrated to accelerate the degradation kinetics dramatically. All of these results illustrated that such motors can achieve efficient water remediation and open a new path for the photodegradation of organic pollutions.

Manganese-Based Micro/Nanomotors: Synthesis, Motion, and Applications

As emerging micro/nano-scale devices, micro/nanomotors have been innovatively applied in the environmental and biomedical applications. In this paper, the recent advances of Mn-based micro/nanomotors (Mn-micro/nanomotors) in catalytic oxidation of organic contaminants and the mechanisms in decomposition of H₂ O₂ (e.g., the generation of O₂ bubbles and reactive oxygen species) are reviewed. The intrinsic characteristics and synthetic strategies of Mn-based materials are discussed, aiming to gain comprehensive understandings on the asymmetric design of micro/nanomotors. Mn-micro/nanomotors have many advantages such as flexible structures, biocompatibility, powerful motion, long lifetime, and low-cost as compared to noble-metal micro/nanomotors. These merits fulfil Mn-micro/nanomotors great promises from proof-of-concept studies to realistic applications, including pollutant decomposition, trace detection of heavy metal ions, oil removal, drug delivery, isolation of biological targets, and killing bacteria and cancer cells. The great flexibility in fabrication enables diverse and innovative strategies to address challenges for Mn-micro/nanomotors, including high consumption of H₂ O₂ and non-directional motion. Meanwhile, a perspective of Mn-micro/nanomotors in water remediation by coupling the motors with other Fenton/Fenton-like systems to enhance the catalytic activity and to yield more reactive oxygen species is presented. Directions to the design of on-demand H₂ O₂ -fueled Mn-micro/nanomotors for advanced purification of organic contaminants in aquatic systems are also proposed.

Hyperporous magnetic catalyst foam for highly efficient and stable adsorption and reduction of aqueous organic contaminants

The facile and low-cost fabrication of free-standing magnetic catalysts with high catalytic efficiency, rapid reaction rate and excellent recoverability has been pursued for various catalysis applications, e.g., treating aqueous organic 4-nitrophenol pollutants. Here, we design and fabricate a free-standing nickel-coated hyperporous polymer foam (Ni-HPF) with adjustable shapes and sizes, hierarchical multiscale porous structures, abundant catalytical interfaces and excellent super-paramagnetic properties. Due to the synergistical effect of abundant binding sites and highly catalytic reduction, the as-prepared Ni-HPF has demonstrated high conversion efficiency (> 90% at extremely low concentration of 7.5 μM) and rapid reaction rate (2.58 × 10^-3 s^-1) for the reduction of organic 4-nitrophenol. Moreover, the magnetic catalyst also holds excellent recoverability (>80% conversion rate even after 1000 cycles) and good reproducibility (>80% conversion rate after 3 months of storage). As such, this work with novel material design and working principle could provide a wide range of potential applications in water purification, chemical catalysis and energy storage devices.

Rational Fabrication of Multiple Dimensional Assemblies from Tryptophan-Based Racemate

Fabricating structural complex assemblies from simple amino acid-based derivatives is attracting great research interests due to their easy accessibility and preparation. However, the morphological regulation of racemates (an equimolar mixture of enantiomers) were largely overlooked. In this work, through rational modulation of kinetic and thermodynamic parameters, we achieved multiple dimensional architectures employing tryptophan-based racemate (RPWM). Upon assembling, 1D bundled nanofibers, 2D lamellar nanostructure and 3D urchin-like microflowers could be obtained depending on the solvents used. The corresponding morphology evolutions were successfully illustrated by changing the enantiomeric excess (ee) value. Moreover, for RPWM, uniform 0D nanospheres were formed in H 2 O under 4 ℃, which could spontaneously convert into lamella under ambient temperature. Taking advantages of its temperature-responsive phase change behavior, RPWM assemblies exhibited excellent removal efficiency for organic dye RhB, and could be reused for several consecutive cycles without significant changes in its removal performance. Taken together, it's rational to envision that the engineering of racemates assembly pathways can greatly increase the robustness in a wide variety of supramolecular materials and further lead to their blooming versatile applications.

A critical review on metal complexes removal from water using methods based on Fenton-like reactions: Analysis and comparison of methods and mechanisms

Metals mainly exist in the form of complexes in urban wastewater, fresh water and even drinking water, which are difficult to remove and further harm human health. Fenton-like reaction has been used for the removal of metal complexes. Effective removal of metal complexes using Fenton-like reaction requires the removal of both metals and organic ligands, meanwhile, the fate of metals and organic pollutions must be clearly understood. Thus, this review summarizes the relevant research on metal complex removal from using Fenton-like reactions in the past ten years, with the detailed removal approaches and mechanisms analyzed. Electro-, photo-, microwave/ultrasound-Fenton reactions or the synergistic Fenton reaction have been shown to exhibit excellent metal complex treatment capabilities. Furthermore, various catalysts, such as transition metals, bimetals and metal-free catalytic systems can expand the potential applications of Fenton-like reactions. Novel Fenton reaction methods without the addition of metals or H₂O₂, with construction of a dual active center catalyst, or with the introduction of other free radicals, are all worthy of further investigation. Due to increasing levels of environmental metal and organic pollutions remediation requirements, more research is required for the development of economical and efficient novel Fenton-like processes.

Highly efficient and selectivity removal of heavy metal ions using single-layer NaxKyMnO2 nanosheet: A combination of experimental and theoretical study

Manganese oxides (MnO₂) are widely applied in heavy metal ions removal due to their low-cost, environmental-friendly and biocompatibility. However, the adsorption capacity of MnO₂ need to be further improved to satisfy the demand of practical application. Herein, a highly dispersed single layer Na_xK_yMnO₂ nanosheet was synthesized by a facile wet-chemical method with sodium dodecyl sulfonate as surfactant. The high surface specific area, excellent dispersibility and abundant oxygen vacancies endowed Na_xK_yMnO₂ nanosheets with potential in heavy metal ions adsorption. The adsorption experiments results showed that Na_xK_yMnO₂ nanosheets possessed high efficiency and selectivity towards lead ion (Pb²⁺) with a high adsorption capacity of 2091.8 μmol g^-1. The Na_xK_yMnO₂ also showed an excellent reusability with the removal rate of 95.4% for Pb²⁺ even after five cycles. Moreover, both the theoretical calculation and experimental data illustrated that the single layer Na_xK_yMnO₂ nanosheets possess high selectivity to Pb²⁺ adsorption.

Dual-stimuli-responsive CuS-based micromotors for efficient photo-Fenton degradation of antibiotics

Antibiotics as emerging pollutants in water pose great risks to human health. Due to their persistence in the environment, advanced oxidation processes (AOPs) have been proposed for the degradation of antibiotics. Therefore, developing efficient catalysts for AOPs becomes critical for the removal of antibiotics. Herein, we develop self-propelled CuS-based micromotors (CuS@Fe₃O₄/Pt) as active heterogenous catalysts for efficient photo-Fenton degradation of antibiotics. Combining the merits of conventional heterogenous and homogenous catalysts, the prepared micromotors are easy to recycle and free of secondary pollution risks, while demonstrating high degradation efficiency due to self-induced intensification of mass transfer via autonomous motion and microbubble generation. The H₂O₂ in the Fenton reagents can serve as the fuel for the micromotors to drive their self-propulsion by bubbles generated from catalytic decomposition of H₂O₂ by the platinum layer. The dual-stimuli-responsiveness of the micromotors to magnetic field and light irradiation allows multi-modes of propulsion and guidance in different systems. The efficient photothermal effect of CuS enables the micromotors to achieve collective phototactic motion toward light, whereas magnetic responsiveness facilitates the recovery and collection of the micromotors. The synergistic effect of CuS and Fe₃O₄ NPs in H₂O₂ under visible light irradiation generates a large amount of OH· and ·O₂^- to effectively degrade tetracycline within several minutes. With these advantages, the dual-stimuli-responsive CuS-based micromotors provide a new strategy for enhanced degradation of antibiotics in water purification applications.

Simultaneous Removal of Antibiotics and Heavy Metals with Poly(Aspartic Acid)-Based Fenton Micromotors

The discharge of diverse pollutants has led to a complex water environment and posed a huge health threat to humans and animals. Self-propelled micromotors have recently attracted considerable attention for efficient water remediation due to their strong localized mass transfer effect. However, a single functionalized component is difficult to tackle with multiple contaminants and requires to combine different decontamination effects together. Here, we introduced a multifunctional micromotor to implement the adsorption and degradation roles simultaneously by integrating the poly(aspartic acid) (PASP) adsorbent with a MnO₂ -based catalyst. The as-prepared micromotors are well propelled in contaminated waters by MnO₂ catalyzing hydrogen peroxide. In addition, the catalytic ramsdellite MnO₂ (R-MnO₂ ) inner layer is decorated with Fe₂ O₃ nanoparticles to improve their catalytic performance, contributing to an excellent degradation ability with 90% tetracycline (TC) removal in 50 minutes by enhanced Fenton-like reactions. Combining the attractive adsorption capability of poly (aspartic acid) (PASP), the composite micromotors offer an efficient removal of heavy metal ions in short time. Moreover, the designed micromotors are able to simultaneously remove antibiotic and heavy metals in mixed contaminants circumstance just in single treatment. This multifunctional micromotor with distinctive decontamination ability exhibits a promising prospective in treating multiple pollutants in the future.

Insight into the co-adsorption behaviors and interface interactions mechanism of chlortetracycline and lead onto struvite loaded diatomite

Finding effective methods for simultaneous removal of antibiotics and heavy metals has attracted increasing concerns. Herein, we investigated the co-adsorption behaviors of chlortetracycline (CTC) and Pb (II) onto struvite loaded diatomite (SD) in aqueous solution, and their interface interactions mechanism was investigated using crystal and microstructure analysis combined with density functional theory (DFT) calculations. The adsorption capacity at equilibrium of CTC increased from 44.28 to 87.58 mmol/kg with the presence of Pb (II), but the adsorption capacity at equilibrium of Pb (II) decreased from 4289.70 to 3559.9 mmol/kg with the presence of CTC. Besides, the effect of environmental factors (solution pH and humic acid) was also evaluated. Microstructure analysis for recovered products demonstrated that the interface interactions brought by the surface Pb(II) of Pb₅(PO₄)₃OH and carbonyl-O of CTC could facilitate the removal of CTC but inhibit the removal of Pb(II) by suppressing the crystal growth of Pb₅(PO₄)₃OH, especially the orientation growth of (0 0 1) crystal plane. DFT calculations gave theoretical support for the interface interactions between Pb₅(PO₄)₃OH and CTC.

Facile synthesis of 2Dα-MnO2nanosheets for the removal of heavy metal ions

Removal of heavy metal ions (HMIs) has attracted great attentions due to the fact that they have serious effect on environment and human beings. Manganese oxide (MnO₂) was widely used as absorbent for the HMIs removal on account of its low-cost, eco-friendly and biocompatibility. The modification of morphological and structure is recognized as the effective route to improve the adsorption capacity. In this work, 2Dα-MnO₂nanosheets were synthesized by hydrothermal method with Al³⁺additive. With the merits of high specific surface area, high dispersity in aqueous solution and abundant surface defects, 2Dα-MnO₂nanosheets exhibited excellent HMIs adsorption performance. The maximum adsorption capacity of 2Dα-MnO₂nanosheets reached 1.604 mmol g^-1(Pb²⁺) and 0.813 mmol g^-1(Cd²⁺), respectively and can maintain stable after five cycles. Besides, the established adsorption kinetics fitted well with pseudo-second-order adsorption kinetics model. Based on the above results, 2Dα-MnO₂is efficient for the removal of HMIs and possesses remarkable practical application potential.

3D printing of functional microrobots

3D printing (also called "additive manufacturing" or "rapid prototyping") is able to translate computer-aided and designed virtual 3D models into 3D tangible constructs/objects through a layer-by-layer deposition approach. Since its introduction, 3D printing has aroused enormous interest among researchers and engineers to understand the fabrication process and composition-structure-property correlation of printed 3D objects and unleash its great potential for application in a variety of industrial sectors. Because of its unique technological advantages, 3D printing can definitely benefit the field of microrobotics and advance the design and development of functional microrobots in a customized manner. This review aims to present a generic overview of 3D printing for functional microrobots. The most applicable 3D printing techniques, with a focus on laser-based printing, are introduced for the 3D microfabrication of microrobots. 3D-printable materials for fabricating microrobots are reviewed in detail, including photopolymers, photo-crosslinkable hydrogels, and cell-laden hydrogels. The representative applications of 3D-printed microrobots with rational designs heretofore give evidence of how these printed microrobots are being exploited in the medical, environmental, and other relevant fields. A future outlook on the 3D printing of microrobots is also provided.

Recent development of autonomously driven micro/nanobots for efficient treatment of polluted water

Autonomously propelled micro/nanobots are one of the most advanced and integrated structures which have been fascinated researchers owing to its exceptional property that enables them to be carried out user-defined tasks more precisely even on an atomic scale. The unique architecture and engineering aspects of these manmade tiny devices make them viable options for widespread biomedical applications. Moreover, recent development in this line of interest demonstrated that micro/nanobots would be very promising for the water treatment as these can efficiently absorb or degrade the toxic chemicals from the polluted water based on their tunable surface chemistry. These auto propelled micro/nanobots catalytically degrade toxic pollutants into non-hazardous compounds more rapidly and effectively. Thus, for the last few decades, nanobots mediated water treatment gaining huge popularity due to its ease of operation and scope of guided motion that could be monitored by various external fields and stimuli. Also, these are economical, energy-saving, and suitable for large scale water treatment, particularly required for industrial effluents. However, the efficacy of these bots hugely relies on its design, characteristic of materials, properties of the medium, types of fuel, and surface functional groups. Minute variation for one of these things may lead to a change in its performance and hinders its dynamics of propulsion. It is deemed that nanobots might be a smart choice for using these as the new generation devices for treating industrial effluents before discharging it in the water bodies, which is a major concern for human health and the environment.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Evaluation of CNT-COOH/MnO2/Fe3O4 nanocomposite for ibuprofen and paracetamol removal from aqueous solutions

The nanocomposite CNT-COOH/MnO₂/Fe₃O₄ was synthesized and characterized by different techniques, namely X-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller analysis, magnetic measurement, point of zero charge and hydrophobicity index. Analyzes revealed the groups -COOH, MnO₂ and Fe₃O₄ attached to the carbon nanotubes, the acidic character of the obtained nanocomposite and its stability. The surface area for the obtained nanocomposite was 114.2 m² g^-1. The prepared nanocomposite was used for adsorption of ibuprofen and paracetamol from aqueous solution. Isotherm, kinetic and thermodynamic parameters were determined for predicting the ibuprofen and paracetamol adsorption on synthetized nanocomposite. The equilibrium data obtained from adsorption were well represented by Langmuir model and kinetics data were well fitted by the pseudo-second order model. The maximum adsorption capacity obtained for ibuprofen and paracetamol was 103.093 mg g^-1, 80.645 mg g^-1 respectively. The thermodynamic analysis showed that the adsorption process for both pollutants was spontaneous and endothermic. The synthetized nanocomposite can be a suitable new absorbent for ibuprofen and paracetamol removal from aqueous solutions due to its high adsorbing capacity and it can be separated by an external magnetic field.

Chiral poly(amide-imide)/ZnS nanocomposite as a new adsorbent for simultaneous removal of cationic dyes from aqueous solution

A new adsorbent, poly(amide-imide)/zinc sulfide nanocomposite (PAI/ZnS NC), was fabricated and identified by Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission-scanning electron microscopy, and transmission electron microscopy. Then, the obtained NC was applied for the simultaneous removal of auramine O (AO) and rhodamine B (RB) dyes from aqueous solution via the interactions of hydrogen bonding, π– π stacking, and Lewis acid–base interaction. The effects of operational variables including pH, PAI/ZnS NC mass, AO and RB concentration, and sonication time on removal efficiency were examined and optimized values were found to be 8.0, 16 mg, 11 mg L−1, and 6 min, respectively. The adsorption capacities of PAI/ZnS NC for the removal of AO and RB dyes were found to be 70.92 and 91.74 mg g−1, respectively. Ultraviolet–visible spectrophotometer was used to determine the amount of residual dye in solution. Fitting the experimental equilibrium data to isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich reveals the suitability of the Langmuir model with high correlation coefficients ( R2 = 0.998 for AO and R2 = 0.999 for RB). Pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models applicability was tested and the pseudo-second-order equation controls the kinetics of the adsorption process. Furthermore, this study establishes that PAI/ZnS NC can be successfully applied as a low-cost adsorbent and conserve its high efficiency after nine cycles for the removal of AO and RB dyes.

Effective Removal of Clenbuterol and Ractopamine from Water with a Stable Al(III)-Based Metal-Organic Framework

Clenbuterol (CLE) and ractopamine (RAC) are two kinds of typical β₂-adrenergic agonists which pose a serious threat to the health of human beings. In this work, 10 kinds of metal-organic frameworks (MOFs) with high stability and various pore features are screened to assess adsorption performance for CLE and RAC. An Al(III)-MOF (BUT-19) with abundant ethyl groups exhibits exceptional performance in removing CLE and RAC from water. The maximum adsorption capacity for CLE and RAC are up to 294.1 and 366.3 mg/g under the optimum adsorption conditions, respectively. Meanwhile, the adsorption mechanism effects of pH, temperature, and coexisted ions are investigated systematically. It is found that the MOF pore size and weak hydrogen-bond interactions between CLE/RAC molecules and the MOF are the main causes leading to the extraordinary adsorption. This study provides a new idea for the purposeful design and synthesis of MOFs for removing environmental pollutants and sheds light on the depuration of contaminated water.

Fluorescent multi-component polymer sensors for the sensitive and selective detection of Hg2+/Hg+ ions via dual mode fluorescence and colorimetry

Fluorescent multi-component polymers, which are sensitive and selective to Hg2+/Hg+ through fluorescence and colorimetry, were synthesized by the Heck coupling reaction.

Fabrication, application, optimization and working mechanism of Fe2O3 and its composites for contaminants elimination from wastewater

Fe₂O₃ and its composites have been extensively investigated and employed for the remediation of contaminated water with the characteristics of low cost, outstanding chemical stability, high efficiency of visible light utilization, excellent magnetic ability and abundant active sites for adsorption and degradation. In this review, the potentials of Fe₂O₃ in water remediation were discussed and summarized in detail. Firstly, various synthesis methods of Fe₂O₃ and its composites were reviewed and compared. Based on the structures and characteristics of the obtained materials, their applications and related mechanisms in pollutants removal were surveyed and discussed. Furthermore, several strategies for optimizing the remediation processes, including dispersion, immobilization, nano/micromotor construction and simultaneous decontamination, were also highlighted and discussed. Finally, recommendations for further work in the development of novel Fe₂O₃-related materials and its practical applications were proposed.

Magnetically steerable iron oxides-manganese dioxide core-shell micromotors for organic and microplastic removals

Because of micro/nanoscale manipulation and task-performing capability, micro/nanomotors (MNMs) have attracted lots of research interests for potential applications in biomedical and environmental applications. Owing to the low-cost, good motion behavior, and environmental friendliness, various low-cost metal oxides based MNMs become promising alternatives to the precious metal based MNMs, in particular for environmental remediation applications. Hereby, we demonstrate the facile and scalable fabrication of two types of bubble-propelled iron oxides-MnO₂ core-shell micromotors (Fe₃O₄-MnO₂ and Fe₂O₃-MnO₂) for pollutant removal. The Fe₂O₃-MnO₂ micromotor exhibits efficient removals of both aqueous organics and suspended microplastics via the synergy of catalytic degradation, surface adsorption, and adsorptive bubbles separations mechanisms. The adsorptive bubbles separation achieved more than 10% removal of the suspended microplastics from the polluted water in 2 h. We clarified the major contributions of different remediation mechanisms in pollutants removals, and the findings may be beneficial to a wide range of environmental applications of MNMs.

Controllable and Continuous Hollow Fiber Swimmers Based on the Marangoni Effect

The rapid response movement caused by the Marangoni effect, a surface tension gradient-induced mass transfer behavior, has spurred considerable promise for diverse applications from microrobots and microreactors to smart drug delivery. Herein, we fabricated an aligned hollow fiber swimmer that showed self-propel movement on a water surface based on the Marangoni effect. By rational designing of an aligned hollow microstructure and an optimized geometrical shape, this swimmer can move continuously for more than 600 s and the maximum angular velocity can reach 22 rad·s^-1. The movement process of the swimmer is clearly monitored by infrared imaging and the process fluid migration. Moreover, this swimmer exhibited a highly controllable motion mode induced by a magnetic field and a concentration gradient. We designed a novel continuous motion system under the heat conversion from solar energy illumination into mechanical energy. This swimmer shows potential application prospects in controlled cargo transportation and convenient energy conversion systems.

Cubic nano-silver-decorated manganese dioxide micromotors: enhanced propulsion and antibacterial performance

The increasing threat of antibiotic-resistant bacterial strains represents the current antibacterial dilemma and requires novel bactericidal treatment to circumvent this problem. In this work, an efficient strategy for killing bacteria using PEDOT/MnO₂@Ag micromotors is reported based on the intense motion-induced convection and excellent sterilization ability of silver (Ag) ions. A distinctive inner surface structure with cubic Ag nanoparticle growth and dispersion in the MnO₂ layer was constructed by simple cathodic co-electrodeposition. Due to the synergistic catalytic reaction of both MnO₂ and Ag, the micromotors can rapidly swim in very low concentrations of hydrogen peroxide (H₂O₂). The antibacterial efficiency of the micromotors was evaluated with the Escherichia coli (E. coli) model. The continuous movement of micromotors, corresponding to violent mass transfer, along with the on-the-fly release of silver ions, greatly enhanced bacteria killing efficacy, with about 14% increase in bacterial death in 0.2% H₂O₂ solution as compared to no motors. Such proposed micromotors could be ideal candidates for combating antibiotic-resistant bacteria in the fields of biomedical and environmental applications.

Autonomous Motion of Bubble-Powered Carbonaceous Nanoflask Motors

We report a carbonaceous nanomotor with a characteristic flask-like hollow structure that can autonomously move under the propulsion of oxygen bubbles. The carbonaceous nanoflask (CNF) motor was fabricated by encapsulating platinum nanoparticles (Pt NPs) into the hollow cavity of the CNF. The internally encapsulated Pt NPs act as catalysts to decompose hydrogen peroxide (H₂O₂) fuel into oxygen bubbles. The generated oxygen bubbles recoil the motion of the CNF motors. Besides, the velocity of CNF motors can be controlled by adjusting the concentration of the H₂O₂ solution. The motion velocity increases with the increase of H₂O₂ concentration, up to 109.25 μm s^-1 at 10% H₂O₂. This study provides important implications for understanding the motion behaviors of nanomotors with an internal cavity, and the self-propelled CNF motors as smart carrier systems have potential applications in the future.

Visible-Light-Driven Water-Fueled Ecofriendly Micromotors Based on Iron Phthalocyanine for Highly Efficient Organic Pollutant Degradation

The light-driven micromotor has been demonstrated to have great potential in the environmental remediation field. However, it is still challenging to develop highly efficient, ecofriendly, and visible-light-powered micromotors for organic pollutant degradation. In this paper, we report an ecofriendly micromotor based on iron phthalocyanine (FePc) and gelatin, which exhibits the visible-light-driven self-propulsion behavior using water fuel based on the photocatalytic reaction and self-diffusiophoresis mechanism. Fast motion behavior is observed which induces the rapid agitation of the solution. This, together with the excellent photocatalytic activity, makes the FePc-based micromotor highly efficient when utilized in the degradation of organic pollutants with a normalized reaction rate constant of 2.49 × 10^-2 L m^-2 s^-1, which is by far the fastest and is far superior than the stationary counterpart. The external fuel-free propulsion and the high efficiency in pollutant degradation make the current micromotor potentially attractive for environmental remediation.

Hotspots on the Move: Active Molecular Enrichment by Hierarchically Structured Micromotors for Ultrasensitive SERS Sensing

Surface-enhanced Raman scattering (SERS) is recognized as one of the most sensitive spectroscopic tools for chemical and biological detections. Hotspots engineering has expedited promotion of SERS performance over the past few decades. Recently, molecular enrichment has proven to be another effective approach to improve the SERS performance. In this work, we propose a concept of "motile hotspots" to realize ultrasensitive SERS sensing by combining hotspots engineering and active molecular enrichment. High-density plasmonic nanostructure-supporting hotspots are assembled on the tubular outer wall of micromotors via nanoimprint and rolling origami techniques. The dense hotspots carried on these hierarchically structured micromotors (HSMs) can be magnet-powered to actively enrich molecules in fluid. The active enrichment manner of HSMs is revealed to be effective in accelerating the process of molecular adsorption. Consequently, SERS intensity increases significantly because of more molecules being adjacent to the hotspots after active molecular enrichment. This "motile hotspots" concept provides a synergistical approach in constructing a SERS platform with high performance. Moreover, the newly developed construction method of HSMs manifests the possibility of tailoring tubular length and diameter as well as surface patterns on the outer wall of HSMs, demonstrating good flexibility in constructing customized micromotors for various applications.

Near-Infrared Light-Powered Janus Nanomotor Significantly Facilitates Inhibition of Amyloid-β Fibrillogenesis

Inspired by the natural motors, artificial nanomotors (NMs) have emerged as intelligent, advanced, and multifunctional nanoplatforms that can perform complex tasks in living environments. However, the functionalization of these fantastic materials is in its infancy, hindering the success of this booming field. Herein, an inhibitor-conjugated near-infrared (NIR) laser-propelled Janus nanomotor (JNM-I) was constructed and first applied in the modulation of amyloid-β protein (Aβ) aggregation which is highly associated with Alzheimer's disease (AD). Under NIR light illumination, JNM-I exhibited efficient propulsion through the "self-thermophoresis" effect, and the active motion of JNM-I increased the opportunity of the contacts between the immobilized inhibitors and Aβ species, leading to an intensification of JNM-I on modulating the on-pathway Aβ aggregation, as evidenced by the distinct changes of the amyloid morphology, conformation, and cytotoxicity. For example, with a NIR irradiation, 200 μg/mL of JNM-I increased the cultured SH-SY5Y cell viability from 68% to nearly 100%, but it only protected the cells to 89% viability without an NIR irradiation. Meanwhile, the NIR irradiation effectively improved the blood-brain barrier (BBB) penetration of JNM-I. Such a JNM-I has connected artificial nanomotors with protein aggregation and provided new insight into the potential applications of various nanomotors in the prevention and treatment of AD.

Effective removal of inorganic and organic heavy metal pollutants with poly(amino acid)-based micromotors

The increasing extent of heavy metal pollution all over the world has resulted in many serious environmental and public health problems. To solve these problems, effective technologies for water treatment are urgently needed. Recent efforts have focused on the development of self-driven micro/nanomotors for eliminating inorganic and organic pollutants in an aqueous system. These synthetic micro/nanomotors can increase mass transfer through the transportation of reactive species, leading to higher decontamination rates. Here, we report a surface-tunable poly(amino acid) (PAA)-based micromotor. The property of the outer layer can be adjusted by changing the type and proportion of amino acids according to real requirements. Three kinds of micromotors are fabricated, which consist of a microtube composed of PAAs (i.e., polyaspartic acid (PAsp), polycysteine (PCys) or a copolymer of both (PAsp-Cys)), a thin Ni intermediate layer, and a Pt inner layer. Due to the presence of various side-chain functional groups (e.g., amino, carboxyl, and sulfhydryl) on the surface of the poly(amino acid)s, these micromotors can be used as effective scavengers for the removal of heavy metals (i.e., Cd2+, Pb2+ and methylmercury). Compared with PAsp and PCys micromotors, the PAsp-Cys micromotor shows good acid resistance and can simultaneously adsorb various kinds of heavy metals with high removal efficiency. The outer layer of the surface-tunable micromotor has good biocompatibility and adsorption efficiency, which holds considerable promise for environmental and biomedical applications.