Intelligent photoresponsive isotropic semiconductor micromotors are developed by taking advantage of the limited penetration depth of light to induce asymmetrical surface chemical reactions. Independent of the Brownian motion of themselves, the as-proposed isotropic micromotors are able to continuously move with both motion direction and speed just controlled by light, as well as precisely manipulate particles for nanoengineering.

Light-Steered Isotropic Semiconductor Micromotors

In this work, water-fuelled TiO2/Pt Janus submicromotors with light-controlled motions have been developed by utilizing the asymmetrical photocatalytic water redox reaction over TiO2/Pt Janus submicrospheres under UV irradiation. The motion state, speed, aggregation and separation behaviors of the TiO2/Pt Janus submicromotor can be reversibly, wirelessly and remotely controlled at will by regulating the “on/off” switch, intensity and pulsed/continuous irradiation mode of UV light. The motion of the water-fuelled TiO2/Pt Janus submicromotor is governed by light-induced self-electrophoresis under the local electrical field generated by the asymmetrical water oxidation and reduction reactions on its surface. The TiO2/Pt Janus submicromotors can interact with each other through the light-switchable electrostatic forces, and hence continuous and pulsed UV irradiation can make the TiO2/Pt Janus submicromotors aggregate and separate at will, respectively. Because of the enhanced mass exchange between the environment and active submicromotors, the separated TiO2/Pt Janus submicromotors powered by the pulsed UV irradiation show a much higher activity for the photocatalytic degradation of the organic dye than the aggregated TiO2/Pt submicromotors. The water-fuelled TiO2/Pt Janus submicromotors developed here have some outstanding advantages as “swimming” photocatalysts for organic pollutant remediation in the macro or microenvironment (microchannels and microwells in microchips) because of their small size, long-term stability, wirelessly controllable motion behaviors and long life span.

Light-controlled propulsion, aggregation and separation of water-fuelled TiO2/Pt Janus submicromotors and their “on-the-fly” photocatalytic activities

Conventional photocatalytic micromotors are limited to the use of specific wavelengths of light due to their narrow light absorption spectrum, which limits their effectiveness for applications in biomedicine and environmental remediation. We present a multiwavelength light-responsive Janus micromotor consisting of a black TiO2 microsphere asymmetrically coated with a thin Au layer. The black TiO2 microspheres exhibit absorption ranges between 300 and 800 nm. The Janus micromotors are propelled by light, both in H2O2 solutions and in pure H2O over a broad range of wavelengths including UV, blue, cyan, green, and red light. An analysis of the particles’ motion shows that the motor speed decreases with increasing wavelength, which has not been previously realized. A significant increase in motor speed is observed when exploiting the entire visible light spectrum (>400 nm), suggesting a potential use of solar energy, which contains a great portion of visible light. Finally, stop–go motion is also demonstrated...

/pdf/multiwavelength-light-responsive-au-b-tio2-janus-micromotors-4418ibxydk.pdf

Multiwavelength Light-Responsive Au/B-TiO2 Janus Micromotors

Hierarchical MoS2 nanosheets integrated Ti3C2 MXenes for electrocatalytic hydrogen evolution

Swarming and collective migration of micromotors under near infrared light

Highly crystalline mesoporous TiO2 was prepared by a facile sol–gel process in the presence of poly(oxyethylene-23) lauryl ether (Brij-35) surfactant. The pore size distribution of the samples became wider as the amount of Brij-35 increased. When the sample was prepared with moderate concentration of Brij-35, the sample had a bimodal pore size distribution with the small pores at 7 nm and the large pores at 20 nm. The photocatalytic activity was evaluated by the degradation of methylene blue under UV irradiation. The sample with large pore size and wide pore size distribution showed higher photocatalytic activity. The crystalline mesoporous TiO2 with large pore size and wide pore size distribution showed higher photocatalytic activity.

Effects of pore size on the photocatalytic activity of mesoporous TiO 2 prepared by a sol–gel process

TiO2 microspheres with tunable particle size were prepared in alcohols without a template via a facile non-aqueous sol–gel process, on the basis of an ester elimination mechanism. The diameter of TiO2 microspheres in the range of 0.4–2.9 μm was controlled by the ratio of methanol in the solvent.

Template-free synthesis of TiO2 microspheres with tunable particle size via a non-aqueous sol–gel process

Hierarchical flower-like nickel hydroxychloride microspheres were prepared by forced hydrolysis reaction of nickel chloride hexahydrate in ethanol via a facile template-free solvothermal process. The flower-like nickel hydroxychloride microspheres, which were prepared with low concentration of Ni without adding H2O, were composed of crumpled nanosheets with random orientation. The aggregation growth and the dissolution–recrystallization process were involved in the formation of the flower-like nickel hydroxychloride microspheres. The flower-like β-Ni(OH)2 microspheres were prepared by nickel hydroxychloride microspheres treated with high concentration of KOH. The β-Ni(OH)2 microspheres prepared with higher concentration of KOH showed better electrochemical performance, while the β-Ni(OH)2 microspheres prepared with lower concentration of KOH showed better adsorption activity for acid fuchsine.

Synthesis of nickel hydroxychloride microspheres via a facile template-free process and their conversion to β-Ni(OH)2 microspheres

Size-controlled hematite mesocrystals were prepared by forced hydrolysis of FeCl3via a facile hydrothermal process. The particle size of the hematite mesocrystals were well-controlled by the ratio of ethanol to water. As the ratio of ethanol increased, the particle size of the hematite mesocrystals increased from 0.5 to 1.5 μm without losing their internal mesocrystalline structure. The sizes of the hematite particles were also affected by the concentrations of KOH and formic acid. Goethite rods were prepared with 0.26 M KOH.

Size-controlled synthesis of hematite mesocrystals

A top-down synthetic method was developed for the fabrication of sponge-like Mn3O4 composed of Mn3O4 nanocrystals by decomposition of manganese formate at 200 °C. The samples were characterized in terms of their structural and morphological properties by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) studies. TEM and SEM images showed that the morphology of sponge-like Mn3O4 structures was mostly retained from the morphology of the manganese formate precursor, which was controlled by the solvothermal process. Large sponge-like Mn3O4 structures exhibiting crystallographic symmetry were prepared under solvothermal treatment for a long time. The XRD pattern showed that the Mn3O4 exhibit a tetragonal hausmannite structure. The results of N2 adsorption analysis indicated that the sponge-like Mn3O4 nanostructures possess high surface area. The possible formation mechanism of Mn3O4 nanostructures has been discussed.

/pdf/top-down-synthesis-of-sponge-like-mn3o4-at-low-temperature-3k9ptmk6pj.pdf

Top-down synthesis of sponge-like Mn3O4 at low temperature

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