Self-cleaning materials have gained considerable attention for both their unique properties and practical applications in energy and environmental areas. Recent examples of many TiO2-derived materials have been illustrated to understand the fundamental principles of self-cleaning hydrophilic and hydrophobic surfaces. Various models including those proposed by Wenzel, Cassie-Baxter and Miwa-Hashimoto are discussed to explain the mechanism of self-cleaning. Examples of semiconductor surfaces exhibiting the simultaneous occurrence of superhydrophilic and superhydrophobic domains on the same surface are illustrated, which can have various advanced applications in microfluidics, printing, photovoltaic, biomedical devices, anti-bacterial surfaces and water purification. Several strategies to improve the efficiency of photocatalytic self-cleaning property have been discussed including doping with metals and non-metals, formation of hetero-junctions between TiO2 and other low bandgap semiconductors, and fabrication of graphene based semiconductor nano-composites. Different mechanisms such as band-gap narrowing, formation of localized energy levels within the bandgap and formation of intrinsic defects such as oxygen vacancies have been suggested to account for the improved activity of doped TiO2 photocatalysts. Various preparation routes for developing efficient superhydrophilic–superhydrophobic patterns have been reviewed. In addition, reversible photo-controlled surfaces with tuneable hydrophilic/hydrophobic properties and its technological applications are discussed. Examples of antireflective surfaces exhibiting self-cleaning properties for the applications in solar cells and flat panel displays have also been provided. Discussion is provided on TiO2 based self-cleaning materials exhibiting hydrophilic and underwater superoleophobic properties and their utilities in water management, antifouling applications and separation of oil in water emulsions are discussed. In addition, ISO testing methods (ISO 27448: 2009, ISO 10678: 2010 and ISO 27447: 2009) for analysing self-cleaning activity and antibacterial action have also been discussed. Rapid photocatalytic self-cleaning testing methods using various photocatalytic activity indicator inks such as resazurin (Rz), basic blue 66 (BB66) and acid violet 7(AV7) for a broad range of materials such as commercial paints, tiles and glasses are also described. Various commercial products such as glass, tiles, fabrics, cement and paint materials developed based on the principle of photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. The wide ranges of practical applications of self-cleaning photocatalytic materials suggest further development to improve their efficiency and utilities. It was concluded that a rational fabrication of multifunctional photocatalytic materials by integrating biological inspired structures with tunable wettability would be favorable to address a number of existing environmental concerns.

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Self-Cleaning Applications of TiO2 by Photo-Induced Hydrophilicity and Photocatalysis

In recent years, the area of developing visible-light-active photocatalysts based on titanium dioxide has been enormously investigated due to its wide range of applications in energy and environment related fields. Various strategies have been designed to efficiently utilize the solar radiation and to enhance the efficiency of photocatalytic processes. Building on the fundamental strategies to improve the visible light activity of TiO2-based photocatalysts, this Perspective aims to give an insight into many contemporary developments in the field of visible-light-active photocatalysis. Various examples of advanced TiO2 composites have been discussed in relation to their visible light induced photoconversion efficiency, dynamics of electron–hole separation, and decomposition of organic and inorganic pollutants, which suggest the critical need for further development of these types of materials for energy conversion and environmental remediation purposes.

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New Insights into the Mechanism of Visible Light Photocatalysis

Fabrication and characterization of Fe 3 O 4 @SiO 2 @TiO 2 @Ho nanostructures as a novel and highly efficient photocatalyst for degradation of organic pollution

Surface and interface engineering of hierarchical photocatalysts

Photocatalytic degradation of Acephate, Omethoate, and Methyl parathion by Fe3O4@SiO2@mTiO2 nanomicrospheres.

Cobalt(II) phthalocyanine-sensitized hollow Fe3O4@SiO2@TiO2 hierarchical nanostructures: Fabrication and enhanced photocatalytic properties

Microstructure, optical and electrical properties of nitrogen doped sp2-rich a-C thin films grown by facing-target magnetron sputtering

The invention discloses a magnetic composite photocatalyst as well as a preparation method and application of the photocatalyst. The preparation method of the magnetic composite photocatalyst comprises the following steps: (1) preparing meso-tetra(4-carboxyl phenyl) porphyrin; (2) preparing meso-tetra(4-carboxyl phenyl) porphyrinozinc which is called ZnTCPP for short; (3) preparing Fe3O4 with the diameter of 350-400nm; (4) preparing a Fe3O4@TiO2 magnetic material; and (5) soaking the Fe3O4@TiO2 magnetic material in the ZnTCPP ethanol solution, stirring, reducing pressure to remove a solvent, cleaning with solid ethanol, washing, and drying, thus obtaining the magnetic composite photocatalyst. The magnetic composite photocatalyst has both visible-light response and magnetic response, is convenient to use and is obvious in catalytic effect; the magnetic composite photocatalyst is easy to separate by utilizing magnetic effect; toxicity is low, separation is thorough, environment friendliness can be realized, the magnetic composite photocatalyst has multifunctionality and high stability, and the degradation rate on methylene blue reaches up to more than 85%.

Jing-Long Wu

Papers

Cobalt(II) phthalocyanine-sensitized hollow Fe3O4@SiO2@TiO2 hierarchical nanostructures: Fabrication and enhanced photocatalytic properties

Microstructure, optical and electrical properties of nitrogen doped sp2-rich a-C thin films grown by facing-target magnetron sputtering

Magnetic composite photocatalyst as well as preparation method and application of photocatalyst