Visible light driven TiO₂/Pt micromotor with directional motion

Abstract

Light-driven micromotors show transformative potential for biomedical and environmental applications due to their biocompatibility, sustainability, and energy efficiency. However, conventional systems that rely on ultraviolet or infrared light face critical limitations, including biotoxicity and thermal damage. We present a TiO₂/Pt Janus micromotor enabling highly efficient surfactant-free propulsion under visible light (455 nm) through synergistic bandgap engineering and asymmetric catalysis. Platinum-mediated Schottky junctions extend optical absorption into the visible spectrum, achieving active propulsion in pure water at low intensities of 30 mW cm⁻². Motion control is demonstrated through speed modulation via light intensity adjustment, real-time start-stop switching, and hydrogen peroxide co-catalyst acceleration. The micromotors maintain exceptional multi-cycle stability while achieving trajectory straightness. Compared to systems driven by 365 nm light, the enhancement in directional persistence is significant, enabling precise directional motion control through internal chemical propulsion mechanisms without depending on external fields or physical guides, thereby overcoming the rapid deactivation characteristic of conventional systems. This fuel-free design establishes a biocompatible microactuation platform with minimized thermal effects, enabling applications in targeted drug delivery, minimally invasive surgery, and environmental remediation. Our work advances visible-light-controlled micromotors toward practical implementation.

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Introduction

In micro and nanosystems, breakthroughs in optical drive technology drive smart micromotors from concept to practical application.^1–8 Currently, mainstream light-driven technology relies mainly on light sources that are not easily obtained from sunlight, such as infrared and ultraviolet. While long-wave infrared radiation enables precise particle manipulation through controlled thermal gradients,^9,10 and short-wave ultraviolet light facilitates charge carrier separation for electric field-mediated motion control, these approaches face fundamental challenges in biomedical applications.^11,12 However, visible light (455 nm), with its moderate wavelength, exhibits a more comprehensive advantage in terms of biocompatibility and energy cleanliness. In terms of biosafety, visible light avoids the risk of DNA damage or apoptosis and other carcinogenic risks that may be triggered by high-energy photons of UV light,^13,14 and its moderate energy has a low risk of causing damage to biological tissues, making it especially suitable for biological applications,^15–18 thus breaking the limit of biotoxicity of traditional UV-driven motors. In addition, compared to infrared light, the thermal effect of visible light is weaker, which can effectively avoid secondary damage caused by overheating local tissues. At the same time, the easy accessibility of visible light, its low equipment cost, and the high popularity of light sources is its significant advantages.^19–21 Furthermore, visible light-driven micromotors demonstrate unprecedented operational versatility.^22,23 Unlike peroxide-dependent or pH-constrained systems, our developed platforms achieve stable propulsion in pure aqueous media. Powered by biocompatible and environmentally friendly fuel sources, they are optimal for practical applications.^24,25

Although visible light demonstrates superior biocompatibility and solar compatibility compared to UV/IR alternatives, its inherent photocatalytic efficiency remains constrained by fundamental material limitations.^26–29 This challenge has catalyzed breakthroughs in semiconductor engineering, with titanium dioxide (TiO₂) emerging as a pivotal platform for the development of visible-light micromotors.^30–32 Despite its wide bandgap of ∼3.2 eV, which typically limits activation to UV light, advanced material modification strategies are expanding the role of TiO₂ in visible-light energy conversion. Strategies such as energy band engineering and surface modification can effectively enhance the application share of visible light in light control.^33,34 Its properties in photocatalytic decomposition, as well as its eco-friendliness, self-cleaning/sterilization, are excellent.³⁵ Light field regulation of superstructured surfaces³⁶ and ultra-immersed interface regulation³⁷ offer innovative paths for developing solar-powered, environmental remediation,³⁸ and targeted delivery of functional micro and nanosystems.³⁹

Motion directionality is usually a challenge that light-controlled micromotors confront. Currently, magnetic integration is still required in many studies to achieve directional motion in micro and nanomotors,^40,41 which not only complicates the control system but also reduces the size advantage of these motors to some extent.^42–44 In this paper, we propose using a single light field to control the micromotor, enabling directional motion under visible light modulation and thereby strengthening the advantages of light field control.

In this study, we report a novel approach to fabricate a Janus micromotor system, TiO₂/Pt Janus micromotors, constructed from half-covered titanium dioxide microspheres and platinum layers, which can be efficiently driven in a pure water environment under both UV and blue light with a wavelength of 365 nm and 455 nm. Herein, strategies including doping modulation, heterojunction construction, and morphological design were synergistically employed to mitigate the bandgap limitation of TiO₂, thereby enabling efficient visible-light-driven propulsion.^45–47 Platinum doping effectively extends the light absorption of TiO₂ into the visible spectral region, resulting in blue-light photoinduced charge separation, generating a directional electrophoretic force to propel the TiO₂/Pt Janus micromotors. The system features, therefore, a directional motion under visible light (455 nm), characterized by its high degree of straightness in trajectory. Compared to systems driven by 365 nm light, the enhancement in directional persistence is significant, enabling precise directional motion control through internal chemical propulsion mechanisms without depending on external fields or physical guides.^48–50 This behavior has been thoroughly quantified using several statistical approaches and notably complements the speed regimes typically reported in previous studies on directed motion.^6,51 With a light irradiation with an intensity of 30 mW cm⁻², the Janus motors produce a microscopic asymmetric chemical reaction-guided self-electrophoretic motion in water. Directional motion reversal of the micromotor is achievable through light switching, while its speed is efficiently modulated by light intensity control. Meanwhile, the controlling effect of blue light on these micromotors remains stable over multiple cycles, demonstrating their robust motion stability and extended operational lifetime. Significantly, this TiO₂/Pt Janus micromotor system exhibits exceptionally high catalytic activity. This enables efficient propulsion in pure water under low-intensity blue light, eliminating the need for additional surfactants or toxic chemical fuels. These combined features endow the micromotor with excellent biocompatibility, addressing key limitations inherent in conventional chemical micromotor systems.⁵²

Results and discussion

TiO₂ microparticles were synthesized via a modified hydrothermal reaction,⁵³ followed by annealing at an optimized temperature to ensure catalytic activity. The overall fabrication process is shown in Fig. 1A. The microspheres were dispersed in aqueous solution and uniformly coated on a silicon wafer. Platinum (Pt) was then deposited onto the dried TiO₂-coated substrate using physical vapor deposition (PVD) under high vacuum conditions, thus forming the TiO₂/Pt Janus structure. Finally, the TiO₂/Pt Janus micromotors were collected from the substrate by sonication in deionized water, followed by centrifugation.

Fig. 1 (A) Schematic of the TiO₂/Pt micromotor fabrication process for visible-light-driven (455 nm) propulsion. (B) SEM image of a spherical TiO₂/Pt Janus micromotor. (C–E) Corresponding EDS elemental mapping for (C) Ti, (D) Pt, and (E) O (scale bar: 500 nm). (F) Raman spectra of pure TiO₂ (red) and the TiO₂/Pt Janus micromotors (black). (G) UV-Vis absorption spectra of pure TiO₂ (red) and TiO₂/Pt Janus micromotors (black).

The morphology of the TiO₂/Pt Janus micromotors was characterized by scanning electron microscopy (SEM). As shown in Fig. 1B, the TiO₂ particles are non-smooth spheres exhibiting a hedgehog-like structure, which significantly increases their relative surface area.⁴⁵ The particle size of the TiO₂/Pt Janus micromotors was determined through analysis of SEM images using ImageJ software. Statistical processing of 120 particles indicated an average diameter of 2.5 μm. Energy dispersive X-ray spectroscopy (EDS) mapping (Fig. 1C–E) confirmed the composition distribution: Ti and O were uniformly dispersed throughout the particles, while Pt localized exclusively on one hemisphere of the hedgehog-shaped TiO₂ spheres. This asymmetric Pt deposition establishes the TiO₂/Pt Janus structure, enabling directional motion. The performance of TiO₂ micromotors is highly dependent on their crystal structure. To identify the crystalline phase and evaluate the structure-performance relationship, Raman spectra of both TiO₂ micromotors and TiO₂/Pt Janus micromotors were analyzed. As shown in Fig. 1F, characteristic B_1g, E_g and A_1g peaks appear in both samples, confirming the successful synthesis of the hedgehog-shaped TiO₂ microspheres. The peak positions indicate that the synthesized TiO₂ microspheres adopt the rutile phase.⁵⁴ Compared with anatase-phase TiO₂, nanostructured rutile photocatalysts exhibit higher visible-light absorbance and superior chemical stability.^46,55 Critically, peak position analysis confirms structural stability: the deposited Pt layer neither alters the chemical structure of the TiO₂ microspheres nor undergoes structural changes itself.

Absorption spectra reflects the photoresponsive properties, reveals the energy conversion mechanism, and guides structural optimization. Fig. 1G shows the UV-visible absorption spectra of both samples. Pure TiO₂ microspheres exhibit UV absorption owing to the intrinsic bandgap of TiO₂. Crucially, the TiO₂/Pt Janus micromotors demonstrate significantly enhanced absorption at 455 nm compared to pure TiO₂ microspheres. To further verify the photocatalytic properties of both systems, we performed motion comparison experiments under identical environmental conditions (as detailed in the SI). The TiO₂/Pt Janus micromotors show photoactive motion compared to pure TiO₂ micromotors under the same illumination, light intensity, and solution environment. This indicates effective suppression of electron–hole recombination in the Janus structures, preventing rapid annihilation of photogenerated carriers. Consequently, the extended lifetime of charge carriers enables higher photocatalytic activity in TiO₂/Pt micromotors relative to their pure TiO₂ counterparts.

Further the motion tests performed on TiO₂/Pt Janus micromotors (Fig. 2B) demonstrated effective movement in pure water, attributing the propulsion to photoelectrophoresis. Meanwhile, the detailed propulsion mechanism is schematically depicted in Fig. 2A. Upon illumination with bandgap light, electrons (e⁻) are excited from the valence band to the conduction band of TiO₂, generating holes (h⁺) in the process.⁵⁶ The spatial separation of these oppositely charged carriers is essential to prevent recombination and prolong their availability for photoelectric conversion and catalytic reactions.^57,58

Fig. 2 (A) Principle schematic of catalytic TiO₂/Pt Janus micromotor driven by 455 nm light in water. (B) Motion trajectory schematic of a light-driven (455 nm) TiO₂/Pt Janus micromotor in water (Scale bar: 10 μm).

Herein, Pt serves as an electron “one-way gate”: its lower Fermi level relative to the conduction band minimum of TiO₂ creates a high Schottky barrier at the TiO₂/Pt interface,^47,59 establishing a unidirectional electron transfer channel from TiO₂ to Pt.⁶⁰ Consequently, charge separation occurs across the micromotor structure, establishing a self-built electric field that further accelerates carrier separation. Notably, higher work function of Pt (φ_TiO2 = 4.20 eV, φ_Pt = 5.65 eV, φ_Pd = 5.30 eV, φ_Au = 5.21 eV, φ_Ag = 4.26 eV),⁶¹ generates a larger upward Schottky band bending. This facilitates efficient electron accumulation in the Pt layer while confining photogenerated electrons and preventing hole recombination. The spatially separated carriers then drive redox reactions: holes on TiO₂ mediate oxidation, while accumulated electrons on Pt catalyze hydrogen evolution.

2H₂O − 4e⁻ → 4H⁺ + O₂

2H⁺ + 2e⁻ → H₂

The redox reaction rate asymmetry between hemispheres drives electron accumulation on the Pt side, producing a net negative surface charge on the Janus micromotors. Under an applied electric field, these negatively charged micromotors undergo directional propulsion via electrophoresis.⁶²

Propulsion of noble-metal micromotors under 455 nm light originates from surface plasmon resonance (SPR)-induced hot electrons, whose interfacial transfer and carrier dynamics generate motive force.⁶³ To verify this mechanism, control experiments were conducted for PS/Pt Janus microspheres under 365 nm and 455 nm illumination, respectively. As illustrated in Fig. 3C and D, and Video S2, PS/Pt particles exhibited only Brownian motion under both wavelengths, whereas TiO₂/Pt Janus micromotors demonstrated sustained directional motion at constant speed. This distinction arises because significant SPR requires noble metal nanostructures within their characteristic resonance ranges with around a wavelength of 520 nm for Au nanoparticles.⁶⁴ In comparison, platinum exhibits negligible SPR in the visible region (455 nm).⁶⁵ Consequently, insufficient hot electrons are generated to enable propulsion via plasmonic mechanisms at this wavelength. These results rule out Pt-induced self-thermophoresis as a propulsion mechanism, confirming that the observed directional motion stems from the electrophoretic effect.

Fig. 3 (A) Speed dependence of TiO₂/Pt Janus micromotors on 455 nm light intensity in pure water. (B) Speed variation in aqueous NaCl solutions under 455 nm illumination. (C and D) Trajectories of TiO₂/Pt and PS/Pt micromotors in pure water under 365 nm light and 455 nm light, respectively. (Scale bars: 10 μm).

Electrolyte (NaCl) was introduced at concentrations of 10⁻³, 10⁻², 10⁻¹, and 1 mmol L⁻¹ into solutions containing TiO₂/Pt Janus micromotors to further validate the theoretical interpretation.⁶⁶ Motion speed measurements under different ionic strengths (Fig. 3B) revealed a significant negative correlation with NaCl concentration. According to electrophoresis theory,^67,68 increased ionic strength compresses the electric double layer, reducing zeta potential and weakening the local electric field strength. This directly diminishes electrophoretic mobility. Crucially, when particle motion relies on self-generated ionic gradients, elevated salt concentrations diminish this gradient, thereby decreasing propulsion speed. Experimentally, speed progressively reduced with increasing NaCl concentration, with nearly complete motion cessation observed at the highest concentration (1 mmol L⁻¹). This concentration-dependent speed suppression aligns precisely with theoretical predictions for the compression of electric double layers. After ruling out interference from other driving mechanisms, this further confirms that the driving mechanism of this micromotor is self-electrophoretic propulsion.

The propulsion of the micromotor is driven by electrophoresis, with motion speed serving as a direct indicator of its intensity. Electrophoresis drives propulsion of the micromotor, where speed serves as a direct measure of propulsion intensity. As quantified in Fig. 3A, TiO₂/Pt Janus micromotors exhibit light intensity-dependent speed in aqueous environments under 455 nm illumination, showing a linear correlation between speed and incident light intensity.^69–71

Here, ζ denotes the zeta potential of the Janus micromotors. E is the generated electric field. And μ are the dielectric constant and viscosity of the aqueous medium, respectively.

The electrophoretic driving force depends critically on the self-generated electric field strength (E), as given in eqn (1). which reflects the magnitude of the photogenerated current. This current, representing photon-induced electron excitation, scales directly with light intensity, as described by eqn (2).⁷²

Zeta potential measurements (SI) reveal that TiO₂/Pt Janus microspheres with −66.3 ± 3.5 mV possess a significantly more negative surface potential than pure TiO₂ with −54 mV after the deposition of Pt. The narrow standard deviation of 3.5 mV confirms the uniform and stable integration of Pt on the TiO₂ surfaces.

Light intensity I of 455 nm light exhibits positive correlations with both photon flux (Φ) and zeta potential (ζ). By adjusting light intensity, we concurrently control photon flux and ζ potential. This dual control alters the strength of the self-generated electric field through photocurrent generation and the surface electrochemical properties. As a result, both electrophoretic mobility and the diffusion coefficient are impacted, allowing for precise speed modulation of the micromotors by adjusting the intensity of incident light.

Repeated activation/deactivation cycles were performed on TiO₂/Pt Janus micromotors, with speed profiles and kinematic states analyzed during illumination transitions. As shown in Fig. 4A–D, micromotors immediately initiate directional motion upon illumination and revert to Brownian diffusion when light is terminated, which demonstrates reversible on/off switching capability for the operational stability of visible light (455 nm)-controlled micromotors. Particle trajectories during 5–10 switching cycles were tracked using ImageJ software (30 fps acquisition) with manual displacement calibration. To quantitatively validate the micromotor motion, trajectories of 15 individual micromotors (n = 15) were tracked over a period of 15 seconds, and their mean-square displacement (MSD) was calculated (Fig. 4F). The diffusion coefficient D was then derived using the equation D = MSD/iΔt,³³ where the factor of 4 accounts for motion in two dimensions and Δt denotes the time interval (Fig. 4G). MSD analysis revealed significantly increased mobility under illumination at 30 mW cm⁻² compared to dark conditions (0 mW cm⁻²), coupled with a substantial rise in the diffusion coefficient, confirming the presence of light-driven propulsion. Fig. 4E contrasts the disordered jitter in darkness with sustained unidirectional motion during illumination. The micromotors exhibit high reversibility and precise control across multiple switching cycles, demonstrating robust operational stability under visible light actuation.

Fig. 4 (A and B). Trajectories in pure water with 455 nm light (A) off and (B) on. (C and D) Trajectories in low-concentration H₂O₂ solution with light (C) off and (D) on (scale bar: 10 μm). (E) Mean-squared displacement (MSD) versus time interval (Δt) derived from trajectory analysis. (F) Speed-time profile showing on/off motion control in pure water (no additives) under 455 nm illumination. G. Diffusion coefficient of TiO₂/Pt Janus micromotors under different UV intensities, determined from the MSD plots (analyzed from 15 micromotors).

It is confirmd that the non-electrochemical decomposition of hydrogen peroxide at low concentrations negligibly affects propulsion.⁷³ Thus, the self-electrophoresis mechanism remains dominant for micromotors in low-concentration H₂O₂ environments. To enhance propulsion speed, a 1 μL aliquot of H₂O₂ (at incremental concentrations of 2.5%, 5%, and 7.5%) was introduced into 9 μL of the TiO₂/Pt Janus micromotor solution, yielding final H₂O₂ concentrations of 0.25%, 0.5%, and 0.75% (Video S5). Resulting velocities were compared against deionized water controls. Fig. 5A illustrates the proposed reaction mechanism of TiO₂/Pt Janus micromotors in low-concentration H₂O₂ environments. Fig. 5B demonstrates modest speed increases across concentrations. Notably, in 0.75% H₂O₂, speed approximately doubled versus pure water under identical illumination. This enhancement is attributed to accelerated hole consumption via the reaction (2H₂O₂ + 2h⁺ = 2H⁺ + O₂ + 2H₂O),^62,73 which suppresses electron–hole recombination, promotes electron accumulation, and amplifies the self-electrophoretic effect.

Fig. 5 (A) Operational mechanism of visible-light-driven TiO₂/Pt Janus micromotors in low-concentration H₂O₂. (B) Speed comparison of TiO₂/Pt Janus micromotors in pure water versus low-concentration H₂O₂ solution at equivalent TiO₂ densities under 455 nm illumination.

Since UV light is the common light source for TiO₂-basedmicromotors,^52,74–76 we compared propulsion under UV (365 nm) versus visible light (455 nm) using identical experimental conditions with constant micromotor concentration and the same platform. Video S4 shows representative trajectories. Multiple replicate experiments enabled root-mean-square deviation (RMSD) analysis, which quantifies positional variance between actual trajectories and ideal linear paths (Fig. 6). MATLAB-processed RMSD data (SI) demonstrate consistently higher values under UV illumination across different intensities (Fig. 6A and B), correlating with erratic motion characterized by frequent directional changes and rotation. While the addition of H₂O₂ at different concentrations increased velocities under both wavelengths (Fig. 6C and D), 455 nm illumination consistently maintained significantly lower RMSD values than 365 nm. This demonstrates enhanced directional control under visible-light illumination, characterized by near-linear trajectories. Statistical analysis of directional change timing indicates the straight trajectory persists for approximately five minutes of motion (SI). To analyze the temporal evolution of micromotor directionality throughout its trajectory. Define the angle theta between the theoretical direction of motion (with the platinum-covered side pointing toward the titanium dioxide bare leakage side) and the actual direction of motion as shown by the motion trajectory, referred to as the direction deviation angle. The theoretical model is illustrated in Fig. 6E. The sine of (cos) represents the direction of the motion, and the closer cos is to 1 the stronger the directionality, a cosine value greater than 0.8 is defined as the strongly controllable directional regime. (SI) Previous studies have shown that, using identical directional research models, within the speed range of 3–14 μm s⁻¹, the directional controllability of motion increases with speed.⁷⁷ This study further reveals that at sufficiently low speeds, the directional controllability also increases as the speed decreases. Combined with statistical analysis of steering time points, it is concluded that the micromotors in this study demonstrate strongly controllable directionality during motions under five minutes. As shown in Fig. 6F, the motion is slower in 455 nm light than in 365 nm light with the same light intensity, and accordingly, the directionality is stronger. We propose that the reduced speed under 455 nm illumination mitigates the impact of directional fluctuations on trajectory straightness. Statistical analysis confirms that 455 nm-driven micromotors maintain straighter paths with minimal deviation across equivalent displacement ranges.

Fig. 6 (A) Micromotor trajectories under varying 365 nm UV light intensities with corresponding real-time RMSD (root-mean-square deviation). (B) RMSD distributions for three micromotor ensembles under different 365 nm UV light intensities. (C) Comparative trajectories and real-time RMSD under 365 nm UV versus 455 nm visible light. (D) RMSD analysis of multiple micromotors under 365 nm ultraviolet and 455 nm visible light in pure water and H₂O₂ solutions of varying concentrations. (E) Directional deviation angle (θ) defined as the angle between theoretical and actual motion vectors. (F) Speed versus directional persistence for TiO₂/Pt Janus micromotors under 455 nm (yellow) and 365 nm (blue) illumination.

Conclusions

This work reports on visible light-driven TiO₂/Pt Janus micromotors powered solely by 455 nm wavelength illumination. These micromotors achieve efficient propulsion in pure water without requiring additional chemical fuels, demonstrating excellent environmental adaptability. Experimental results confirm that their motion is based on a self-electrophoretic mechanism through salt experiments. By gradually adding NaCl to the TiO₂/Pt Janus micromotors, the motor mobility decreases. Notably, the TiO₂/Pt Janus micromotors exhibit superior speed and directional persistence compared to PS/Pt spheres of equivalent volume. Their speed is tunable by modulating the intensity of the 455 nm light source, which is governed by the self-electrophoretic mechanism. The micromotors maintain stable activity over multiple cycles, confirming robust motion stability and extended particle longevity. While the addition of hydrogen peroxide as a co-catalyst enhances propulsion speed, the system operates self-sufficiently in pure water. Under 455 nm illumination, the micromotors notably display clearer directional persistence and improved trajectory straightness compared to systems driven by UV light (365 nm). While existing literature has addressed the relationship between speed and motion straightness predominantly at high speeds, this work, employing the same motion model, establishes that excellent trajectory straightness is also achievable in the low-speed domain. The addition of hydrogen peroxide as a co-catalyst can enhance the micromotor speed of motion, which is beneficial for future speed control. Overcoming the complex problem of light-controlled micromotor directionality will facilitate subsequent research to enhance micromotor control.

This work reveals that platinum doping effectively extends the photoabsorption range of titanium dioxide into the visible spectrum, enabling visible-light control of Janus microspheres. This expands the visible-light receptor options for micromotor manipulation while establishing a fuel-free aqueous propulsion system. By eliminating the need for chemical fuel, our TiO₂/Pt Janus micromotors achieve environmentally friendly performance.

Materials and methods

Materials and experiments

Concentrated sulfuric acid (98 wt%) and hydrochloric acid (40 wt%) are purchased from Sigma Aldrich. Tetrabutyl titanate (99 wt%), oleic acid (85 wt%), and absolute ethanol (99.7 wt%) are purchased from Sinopharm Chemical Reagent Co. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) images are obtained using a TESCAN GAIA3 Electron Microscope System. Raman spectra are recorded with an Oxford Instruments WITec alpha300 R confocal Raman imaging microscope. The Zeta potential is measured using a DLS Nanoparticle Analyzer (Dynamic Light Scattering). Light at 455 nm is illuminated from a Thorlabs M455L4. An inverted optical microscope (Osbalin IX73) equipped with a LUCPLFLN40XPH and a 20.7-megapixel color-cooled micro-imaging camera (DP74-CU) along with the image analysis software cellSens Entry version. Additionally, ImageJ software was utilized to analyze motion trajectories, while Origin software was employed to analyze statistical data.

Preparation of anatase titanium dioxide particles by hydrothermal synthesis

Precursor solution preparation: at room temperature, 40 mL of oleic acid was mixed with 4 mL of concentrated hydrochloric acid (HCl, 37 wt%) and stirred magnetically for 10 minutes to form a homogeneous solution. Subsequently, 8 mL of tetrabutyl titanate (TBOT) was added dropwise while continuously stirring for 30 minutes to ensure uniform dispersion of the titanium source.

Hydrothermal reaction: the precursor mixture was transferred to a 100 mL PTFE liner and sealed in a stainless steel autoclave, which was then placed in an oven at 180 degrees centigrade for 3 h. After the reaction, the autoclave was cooled to room temperature.

Separation of products: the resulting suspension was centrifuged at 1500 rpm for 3 min, and the supernatant was discarded. Subsequently, the precipitate was washed alternately with deionized water and acetone (7000 rpm, 5 min per time), and this process 3 to 5 times to eliminate residual impurities. Finally, the washed samples were dried in an oven at 60 degrees centigrade overnight to obtain a white powder. This powder was then transferred to a muffle furnace and heated to 450 degrees centigrade at a rate of 5 degrees centigrade per min under an air atmosphere, where it was calcined for 2 hours to promote crystal transformation and enhance crystallinity.

Preparation of TiO₂/Pt Janus nanoparticles: the anatase TiO₂ particles (average particle size of about 3 μm), which were hydrothermally synthesized and calcined, were dispersed in de-ionized water and prepared into a suspension with a mass concentration of 5 mg μL⁻¹. The suspension was uniformly coated on ultrasonically cleaned quartz glass slides using a spin-coating method, followed by acetone and ethanol, and then dried in an oven at 60 degrees centigrade for 10 min to form a TiO₂ layer with uniform thickness. The platinum layer was deposited using magnetron sputtering with a DC magnetron sputtering deposition system that employed 99.99% pure Pt as the sputtering source. Before the deposition, the vacuum chamber was pumped to 3.0 × 10⁻³ Pa, and high-purity argon (99.999%) was introduced to achieve a working air pressure of 0.5 Pa. The quartz substrate, which was loaded with a TiO₂ film, was fixed on a rotating sample stage. The sputtering power was set to 100 W, and the deposition time was 15 minutes, resulting in a Pt metal layer with a thickness of 20–30 nm on the TiO₂ surface. The thickness of the platinum layer could be precisely controlled by adjusting the sputtering parameters, such as power and time. Finally, the resulting Janus structure was separated, and the coated quartz substrate was immersed in deionized water and treated with an ultrasonic processor (90 W) for 3 min to detach the surface-adhered TiO₂/Pt composite particles from the substrate and to uniformly disperse them in the aqueous solution.

Author contributions

X. G. was responsible for the experimental part, data analysis, and wrote the original manuscript. Z. W. participated in data analysis, discussion of results, and revision of the manuscript. Y. Z. was responsible for helping to prepare micromotors. T. Y. proposed the idea for the experiment, designed the experimental protocol, discussed the results, reviewed the manuscript, and received financial support.

Conflicts of interest

There are no conflicts to declare.

Data availability

All experimental and simulation data supporting this study are fully available without restriction under the https://doi.org/10.1039/d5nr03324a in the Figshare repository. Per Nanoscale Horizons’ open science policy, no access barriers or embargo periods apply to these data.

Supplementary information (SI) is available. See DOI: https://doi.org/10.1039/d5nr03324a.

Acknowledgements

T. Y. acknowledges fundings from the National Natural Science Foundation of China (52405474), the Fundamental Research Funds for the Central Universities (2024ZYGXZR076), the Guangdong Regional Joint Youth Foundation (2022A1515110906). The authors would like to thank Prof. Jincheng Lei for Raman access, Yide Hu for providing the Raman measurement data, Prof. Jun Liu for SEM access, and Fangkun Li for providing the SEM measurement data.

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