Nanostructured SnO₂–ZnO Heterojunction Photocatalysts Showing Enhanced Photocatalytic Activity for the Degradation of Organic Dyes

Abstract

Nanoporous SnO(2)-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO(2) particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO(2) particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO(2)-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO(2) nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV-visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO(2)-ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO(2), that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO(2)-ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO(2)-ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO(2) and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO(2)-ZnO photocatalyst because of the energy difference between the conduction band edges of SnO(2) and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO(2)-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.

Effect of heating on the structural and optical properties of TiO2 nanoparticles: antibacterial activity

“…4. The wavelength of transmittance edge was determined by extrapolating the sharply rising part and horizontal part of the UV-Vis curves, showing the transmittance edge (as wavelength) according to pervious finding (Uddin et al 2012). The transmittance edge determination and band gap energy calculation was on the basis of transmittance edge as shown in Fig.…”

Nano-sized SnO₂ Photocatalysts: Synthesis, Characterization and Their Application for the Degradation of Methylene Blue Dye

“…Moreover, the pH of the solution affected the formation of hydroxyl radicals by the reaction between hydroxide ions and photo-induced holes on the SnO 2 surface. The positive holes are considered as the major oxidation steps at low pH, whereas hydroxyl radicals are considered as the predominant species at neutral or high pH levels [27]. It would be expected that the generation of •OH were higher due to the presence of more available hydroxyl ions on the SnO 2 surface.…”

“…Furthermore, to date, many SnO 2 -based coupled semiconductor composite photocatalysts, such as SnO 2 -TiO 2 [23][24][25][26], SnO 2 -ZnO [27][28][29][30][31] or SnO 2 -CuO [32] have been extensively studied for their high photocatalytic activities. But the study about SnO 2 [33][34][35][36][37] is especially less.…”

ZnO/SnO2 Heterojunctions Sensors with UV-Enhanced Gas-Sensing Properties at Room Temperature

“…Among the MOS, zinc oxide (ZnO) and tin oxide (SnO2) are n-type wide band-gap semiconductors (Eg = 3.2 and 3.6 eV, at 300 K) [4,5]. These compounds have attracted much interest due to their wide range of applications, mainly as chemoresistors [1,6].…”

“…The heterojunctions have been prepared by a variety of physical and/or chemical routes [4,5,[9][10][11]. Recently, we reported the UV-assisted gas sensing properties of ZnO/SnO2 heterojunctions prepared via conventional hydrothermal method [9].…”