Transparent conductive oxide (TCO) films and transparent oxide semiconductor (TOS) films have been widely adopted in solar cells, flat panel displays, smart windows, and transparent flexible electronic devices due to their advantages of high transparency and good conductivity and so on. Most of TCO and TOS films are mainly derived from indium oxide, zinc oxide and tin oxide. Among these materials, the In element is toxic, rare and expensive for indium oxide film, which will cause environmental pollution; zinc oxide film is sensitive to acid or alkali etchants, resulting in a poor formation of film patterning; tin oxide film is not only non-toxic, eco-friendly, and cheap but also has good electrical properties and strong chemical stability. Thus, tin oxide has a great potential for developing the TCO and TOS films. At present, the film is prepared mainly by the vacuum deposition technique. The drawbacks of this technique are complex and expensive equipment system, high energy consumption, complicated process and high-cost production. However, compared with the vacuum deposition technique, the sol-gel method has attracted extensive attention because of its virtues such as simple process and low cost. In this paper, we review the development status and trend of TCO and TOS films. First, the structural characteristics, conductive mechanism, element doping theory and carrier scattering mechanism of tin oxide thin films are introduced. Then the principle of sol-gel method and correlative film fabrication techniques are illustrated. Subsequently, the application and development of tin oxide-based thin films prepared by sol-gel method in n-type transparent conductive films, thin-film transistors and p-type semiconductor films in recent years are described. Finally, current problems and future research directions are also pointed out.

Moving bed biofilm reactors (MBBRs) are often used in wastewater treatment. Using MBBR carriers with a porous surface is beneficial to the adhesion of microorganisms and the growth of biofilms. Polyethylene (PE) carriers with highly open and connected pores are designed by constructing a co-continuous structure of PE/polyethylene oxide (PEO) blend, which was followed by the removal of PEO with water. It is found that the extrudates of PE/ PEO (w/w, 4/6) blend exhibit a co-continuous pore structure; however, PEO cannot create a porous surface. The polar rigid filler calcium carbonate (CaCO 3 ) is proposed to be preferentially distributed in the PEO phase, thus increasing its surface energy, reaching a goal of a porous surface successfully on the base of retaining the internal co-continuous porous structure. The content and size of CaCO 3 can further tune the morphology and pore size of the porous surface. The prepared PE porous carriers display a 200 μm-thick biofilm comprising a large number of filamentous bacteria and a small number of coccal and rob bacteria after an MBBR experiment for 30 days, which is also observed within the carriers as revealed by confocal laser scanning microscopy.