Superhydrophobic TiO 2 with great application potential is mainly obtained by surface modification with low surface energy organics, which is easily degraded under sunlight irradiation, which results in the loss of superhydrophobic properties. Herein, we developed a room-temperature pulsed chemical vapor deposition (pulsed CVD) method to develop amorphous TiO 2 -deposited TiO 2 nanoparticles. The ultraviolet stability/ultraviolet-induced reversible wettability switch had been simultaneously realized by different and controllable deposition cycles of amorphous TiO 2 . The superhydrophobic properties of the organic-free TiO 2 were determined by the micrometer− nanometer−sub-nanometer multiscale structure, the multiscale pore structure, and the large Young's contact angle resulting from carboxylic acid adsorption. Also, we found that the adsorption rate and adsorption stability of oxygen and water at the surface oxygen vacancies were the key to facilitate the reversible switching between superhydrophilic and superhydrophobic states, which was well demonstrated by experimental characterization and theoretical simulation. In addition, we also found that the resistance of dense amorphous TiO 2 films on the TiO 2 surface to the migration of photogenerated electrons and holes was the key to maintain the stable superhydrophobic properties of superhydrophobic TiO 2 under ultraviolet illumination. The powders were strongly ground and the coating surface was rubbed on the surface of the sandpaper, which still maintained superhydrophobic properties, providing favorable conditions for the application of superhydrophobic TiO 2 . This work modulates the ultraviolet stability and dark/ultraviolet-induced switchable superhydrophobicity/superhydrophilicity of coated TiO 2 by simply adjusting the number of deposition times in a pulsed CVD process for the first time, thus contributing to the development of organic-free superhydrophobic TiO 2 .
Engineering a heterojunction on a TiO 2 surface (such as SnO 2 /TiO 2 ) is an effective strategy to enhance photocatalytic activity, by facilitating charge separation. However, the traditional fabrication for heterojunctions is usually operated in an aqueous environment, with the drawback of homogeneous nucleation of SnO 2 , which lowers photocatalytic efficiency. Herein, we develop a low-temperature pulsed chemical vapor deposition method that dispersedly deposits SnO 2 on anatase TiO 2 . By regulating the pretreatment temperatures of TiO 2 , we can tune the deposition process of SnO 2 on TiO 2 and achieve the best photocatalytic performance over deposition on 200 °C pretreated TiO 2 . Intrinsically, proper structural hydroxyls offer effective sites to boost the adsorption of Sn species via Ti−O−Sn to form a SnO 2 /TiO 2 heterojunction, which enhances photocatalysis. However, a higher surface coverage of hydroxyls from free or physically adsorbed H 2 O leads to homogeneous nucleation of SnO 2 . On the basis of these principles, we demonstrate a hydroxyl-mediated formation mechanism for a SnO 2 / TiO 2 heterojunction.
Low-cost and simple strategies to synthesize highly efficient and robust oxidative electrocatalysts for commercial largescale water electrolysis are still a challenge. Here, we reported a reductive H 2 plasma surface modification strategy, where a defectrich amorphous NiFe coating layer can be anchored and interact with porous Co 3 O 4 nanoarrays. The plasma-modified surface can promote the reconstruction process to generate high-valence and ultra-active species, thus forming abundant active centers and oxygen vacancies with high electrocatalytic activity. The H 2 −NiFe/ Co 3 O 4 composite reveals excellent bifunctional electrocatalytic ability, and ultralow overpotentials of 233 and 273 mV are required to reach 100 and 1000 mA cm −2 , respectively, for oxygen evolution, while the urea oxidation reaction (UOR) requires the potentials of 1.315 and 1.420 V to reach 10 and 1000 mA cm −2 , respectively. The superior electrocatalytic stability is confirmed by a 240 h longterm test at 1 A cm −2 for the oxygen evolution reaction and the consecutive multistep chronoamperometric tests for the UOR. This work provides an easily scalable and energy-efficient surface modification method to fabricate a robust bifunctional catalyst, while the atomic species and configuration can also be flexibly adjusted, which is suitable to be extended to various application fields.
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