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Understanding the possible role of physicochemical properties in determining the toxicity of ZnO nanomaterials (NMs) is crucial for the safe use of ZnO-based materials. In this study, we synthesized four types of ZnO NMs, and characterized them as ZnO nanorods (NRs; length 400-500 nm, diameter 150-200 nm), ZnO Mini-NRs (length 50-100 nm, diameter 15-20 nm), amorphous ZnO microspheres (a-ZnO MS) and crystalline ZnO MS (c-ZnO MS; the a/c-ZnO MS are nanoflowers with an extensive growth of sheet-like structures). ZnO NMs and ZnO Mini-NRs were significantly more cytotoxic than a/c-ZnO MS, and this trend was similar in both HepG2 cells and human umbilical vein endothelial cells. Intracellular reactive oxygen species was only modestly induced by c-ZnO MS, whereas intracellular Zn ions were dose-dependently increased in HepG2 cells by the exposure of all types of ZnO NMs. The expression of endoplasmic reticulum stress marker DDIT3 was induced following an order of ZnO NRs > a-ZnO MS > c-ZnO MS > ZnO Mini-NRs, and the apoptosis gene CASP12 was induced following an order of a-ZnO MS > ZnO NRs > c-ZnO MS > ZnO Mini-NRs. Combined, these results suggested that ZnO NM-induced cytotoxicity and expression of endoplasmic reticulum stress-apoptosis genes could be influenced by the size and shape of ZnO NMs.

Two copper borates, CuB 2 O 4 and Cu 3 B 2 O 6 , produce either H 2 or O 2 under visible light in the presence of sacrificial agents. Both copper borates exhibit intrinsic midgap states between the valence bands and conduction bands. However, structural differences in the two compounds lead to midgap states with remarkably different photocatalytic behaviors. In CuB 2 O 4 , the midgap states facilitate visible light absorption and enhance photocatalytic activity, while in Cu 3 B 2 O 6 they act as trap states that reduce photocatalytic activity.

Tungsten trioxide (WO 3 ) has been conceived as a promising photoanode material for photoelectrochemical (PEC) water oxidation. Therefore, many efforts have been made to improve its PEC performances. Herein, a novel heterojunction is fabricated through combining rocksalt CoO (R-CoO) or blende CoO (B-CoO) nanosheets with WO 3 nanoplates using a spin-coating method. The typical type II heterojunctions, e.g., WO 3 /R-CoO and WO 3 /B-CoO, both have exhibited higher photocurrent densities than pristine WO 3 photoanode. The photocurrent densities of WO 3 /R-CoO, WO 3 /B-CoO and WO 3 are 0.53 mA cm -2 , 0.45 mA cm -2 and 0.31 mA cm -2 at 1.23 V vs. reversible hydrogen electrode, respectively. For the WO 3 /R-CoO photoanode, the surface charge separation efficiency is 50.95% and the photoconversion efficiency is 0.062%, which are both higher than the WO 3 and WO 3 /B-CoO photoanodes. The enhanced PEC performances are due to the type II heterojunction between WO 3 and R-CoO (or B-CoO), which facilitates the absorption of visible light and charge transport. The better performance of WO 3 /R-CoO than that of WO 3 /B-CoO may be due to the deeper valence band position of R-CoO. Our work demonstrates that R-CoO (or B-CoO) can couple with WO 3 to form a type II heterojunction to improve the PEC water oxidation performance.