NANOSTRUCTURED POROUS SEMICONDUCTORS AS EMERGING MATERIALS IN ENVIRONMENTAL TECHNOLOGY: SYNTHESIS, PROPERTY AND APPLICATIONS

• Published in: International journal of energy, environment, economics Vol. 23; no. 4-5; p. 545
• Main Authors: Sohn, Hiesang, Lee, Kimoon
• Format: Journal Article
• Language: English
• Published: Hauppauge Nova Science Publishers, Inc 2015
• Subjects: Alloys; Alternative energy sources; Chemical contaminants; Design engineering; Efficiency; Electric properties; Environmental impact; Environmental restoration; Environmental science; Light; Metal oxide semiconductors; Morphology; Nanostructure; Photocatalysis; Porosity; Porous materials; Remediation; Renewable resources; Self assembly; Semiconductors; Solar energy; Water shortages
• ISSN: 1054-853X

As global environmental issues increasingly attracted our attention, there have been significant concerns on the porous semiconductors including silicon, metal oxide, chalcogenides, and their alloy/composites since their high surface areas, large pore volumes and unique photo-electric property endow them with superior functions for the improvement of environment and conservation technologies. Hence, there has been considerable effort to design, fabricate, and manipulate porous semiconductors with effective harvest of photon energy, reduced recombination of photogenerated charge carriers, optimized crystalline structure, and maximized active sites. This article covers the recent progress in the fabrication and property of nanostructured porous semiconductors and their applications in the environmental science and technology. Firstly, the grounding principles of porous semiconductor in the environmental science are briefly discussed. Beginning with defining and describing key components in the photocatalytic phenomena (e.g., photon energy (h v), energy band gap (Eg), energy diagram and working mechanisms in the photocatalysis), the working principles of the usage of semiconductors, such as light-induced chemical transformations by their electronic structure, in the environmental technology are reviewed. In addition, basic theories on the porosity and pore structure of porous materials are discussed. Secondly, it is overviewed the preparation techniques for nanostructured porous semiconductors based on various synthetic routes. Beginning with a description of conventional preparation method for porous semiconductor such as porosification process, it is discussed the two general approaches (top-down and bottom-up method) to prepare porous semiconductor. Top-down method employs sacrificial template such as surfactants, inorganic salts, or inorganic/organic walls to prepare mesoporous semiconductor. Bottom-up method employs nano-building blocks to construct complex macroscopic architectures of porous semiconductor through self-assembly of building blocks. In addition, it is discussed recently developed non-conventional approaches to prepare porous semiconductors such as porous silicon, germanium and their alloys. Thirdly, the properties of porous semiconductor are discussed. Particularly, the effects of chemical composition, size effect, porosity on optical and photocatalytic properties are mainly discussed. We discuss the quantum mechanical effect of porous semiconductor on their optical properties, since it provides grounding in the design, fabrication and theory of photocatalysts and other applications. Specifically, it is discussed regarding the band gap engineering through the regulation of the size, morphology and pore structure of building block and the products. In addition, the structure-property relationship in the porous semiconductor is discussed to elucidate unique size/shape/pore structure-dependent physico-chemical properties. In the end, the potential and specific applications in the environmental technology are discussed to elucidate: the performance of the porous semiconductors; their issues and challenges; and identify potential research applications and directions. Specifically, photocatalyst, energy application and environmental remediation are discussed in the first. Energy application encompasses harvesting solar energy through the hydrogen generation and CO2 conversion. In addition, environmental remediation covers how the porous semiconductors are employed in sensing and detoxification of contaminants in water and air. Meanwhile, we discuss the current challenges and problems of porous semiconductors encountered in such applications. It is expected that this article not only provides some useful pointers but also suggests directions in the design and fabrication of the nanostructured porous semiconductors for environmental applications by closely linking materials science with the environmental technology.