Transparent conductors as solar energy materials: A panoramic review

Design, and Applications Shutao Wang,†,‡ Kesong Liu, Xi Yao, and Lei Jiang*,†,‡,§ †Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, and ‡Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, BeiHang University, Beijing 100191, People’s Republic of China Department of Biomedical Sciences, City University of Hong Kong, Hong Kong P6903, People’s Republic of China

Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications

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

The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.

Hydrophilic and superhydrophilic surfaces and materials

Their Applications Kesong Liu,†,∥ Moyuan Cao,† Akira Fujishima, and Lei Jiang*,†,‡ †Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, PR China ‡Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China Research Institute for Science and Technology, Photocatalysis International Research Center, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan Institute for Superconducting and Electronic Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia

Bio-Inspired Titanium Dioxide Materials with Special Wettability and Their Applications

Wetting properties of gas diffusion layers: Application of the Cassie–Baxter and Wenzel equations

Superhydrophobic TiO2 coatings formed through a non-fluorinated wet chemistry route

Sol–gel TiO2 thin films have been loaded with platinum clusters through a photo-platinization method using water/ethanol platinum solutions. The morphological and physico-chemical properties of platinized films as well as the chemical state of platinum clusters have been studied by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. These characterizations show that morphological and physico-chemical properties are strongly influenced by the water/ethanol composition of the platinum solution and temperature of the post-platinization heat-treatment, which in turn determines the photocatalytic performances of platinized films. UV-assisted photocatalytic reactions induced by platinized films follow bi-regime kinetics. The first regime is characterized by a rather high rate constant, while long term UV exposition promotes a more or less pronounced deceleration of the photocatalytic reaction. Optimization of the photocatalytic activity requires a platinization in presence of a water excess followed by a heat-treatment in the 250–400 °C thermal range. Films processed in such conditions exhibit rate constants in the first and second photocatalysis regime which are four times and three times greater, respectively, than the rate constant measured for non-platinized films.

The photocatalytic activity of sol–gel derived photo-platinized TiO2 films

Investigation on AlN epitaxial growth and related etching phenomenon at high temperature using high temperature chemical vapor deposition process

Sol–gel TiO 2 thin films have been loaded with platinum nano-particles via their immersion within a Pt 4+ precursor liquid solution exposed to UV light. Mechanisms involved in the photo-induced formation of platinum particles have been studied by UV/visible spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscopy. According to studied mechanisms, it is shown that the amount, size, and structural state of photo-generated platinum particles dispersed at a solid surface can flexibly be monitored.

G. Berthomé

Papers

Wetting properties of gas diffusion layers: Application of the Cassie–Baxter and Wenzel equations

Superhydrophobic TiO2 coatings formed through a non-fluorinated wet chemistry route

The photocatalytic activity of sol–gel derived photo-platinized TiO2 films

Investigation on AlN epitaxial growth and related etching phenomenon at high temperature using high temperature chemical vapor deposition process

Mechanisms involved in the platinization of sol–gel-derived TiO2 thin films