Facile synthesis of ultrathin two-dimensional nanosheets-constructed MCo₂O₄ (M = Ni, Cu, Zn) nanotubes for efficient photocatalytic oxygen evolution

Abstract

Hierarchical nanosheets-assembled nanotubes are of great interest for their unique physicochemical properties as well as their potential applications in a variety of fields. However, the synthesis of hierarchical mixed transition-metal oxides-based nanosheets-assembled nanotubes for highly efficient photocatalytic oxygen evolution is rarely reported. Herein, a simple and versatile approach was developed to synthesize hierarchical nanosheets-constructed MCoO (M = Ni, Cu, Zn) nanotubes. Core-shell polyacrylonitrile (PAN)/M-cobalt hydroxide ultrathin nanosheet composite nanofibers were first synthesized by hydroxylation reaction between PAN/M-cobalt acetate hydroxide precursors and NaBH. After calcination, these nanofibers as precursors were easily transformed into the corresponding hierarchical nanosheets-constructed MCoO nanotubes. By applying a photocatalyst, the resultant MCoO nanotubes, particularly the CuCoO nanotubes, exhibited high photocatalytic activity and cycle stability toward water oxidation reaction with O generation rates of 51.1 mmol g h under visible light irradiation, which is higher than most reported catalysts. This approach is very versatile and can be applied to synthesize other hierarchical multi-element oxides-based nanosheets-constructed nanotubes for advanced applications.

Selective Photocatalytic Hydrogenation of α,β-Unsaturated Aldehydes on Au/CuCo2O4 Nanotubes under Visible-Light Irradiation

“…Scheme 2 illustrates a proposed mechanism of photocatalysis on Au/CuCo 2 O 4 nanotubes. As reported in the literature, 27 the valence band (VB) and conduction band (CB) of CuCo 2 O 4 are at 2.66 and 1.30 eV, respectively. The photoexcitation processes in the Au/CuCo 2 O 4 nanotubes are proposed in Scheme 2.…”

“…CuCo 2 O 4 hollow nanotubes were prepared as previously described in the literature. 27 Then, photoinduced reduction was implemented to decorate the gold nanoparticles (Au NPs) onto the CuCo 2 O 4 nanotubes. Figure 1a,b shows the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of CuCo 2 O 4 .…”

“…The EDX elemental mapping (Figure S2) confirms the uniform distribution of the elements Cu, Co, and O on the nanotube surface. 27 A photoinduced reduction method was applied to load the gold nanoparticles (Au NPs) onto the CuCo 33,34 It has been reported that "hot" electrons of Au NPs could be created upon irradiation, which facilitates chemical reactions. 29 When Au/CuCo 2 O 4 was treated with HCl aqueous solution to obtain pure Au NPs from Au/CuCo 2 O 4 , the LSPR of Au can be clearly seen to be around 525 nm (Figure S6).…”

“…Next, the precipitate and NaBH 4 (5 mg) were added into ethanol (10 mL) and stirred for 5 min at room temperature. Finally, the collected products were washed with water, dried at 40 °C, and calcinated at 400 °C for 2 h. 27 Synthesis of Au/CuCo 2 O 4 Nanotubes. Au/CuCo 2 O 4 nanotubes were synthesized using the photoinduced reduction method as follows: CuCo 2 O 4 nanotubes (100 mg) were dispersed in 25 mL (1 mM HAuCl 4 ) of ethanol solution under magnetic stirring.…”

“…Next, the precipitate and NaBH 4 (5 mg) were added into ethanol (10 mL) and stirred for 5 min at room temperature. Finally, the collected products were washed with water, dried at 40 °C, and calcinated at 400 °C for 2 h …”