Borophosphate glass as an active media for CuO nanoparticle growth: an efficient catalyst for selenylation of oxadiazoles and application in redox reactions

Abstract

Herein, we report the preparation of CuO@ borophosphate nanoparticles (CuOnano@glass) and their wide catalytic applications. The glass annealing, under a controlled atmosphere, enables the growth of copper nanoparticles on the glass surface (not within) by an uncommon bottom-up process. Following the thermal annealing of metallic nanoparticles under air atmosphere, supported copper oxide nanoparticles CuONPs on the glass surface can be obtained. The approach enables the glass matrix to be explored as a precursor and a route for the synthesis of supported copper-based nanoparticles in a solvent-free process without immobilization steps or stabilizing agents. In order to demonstrate the wide synthetic utility of this CuONPs glass-based catalyst, one-pot three-component domino reactions were performed under an air atmosphere, affording the desired selenylated oxadiazoles in good to excellent yields. We also extended the application of these new materials as a glass-based catalyst in the phenol hydroxylation and the reduction of 4-nitrophenol.

Figure 1

Powder X-ray diffraction analysis of copper-doped borophosphate glass annealed under (a) ${\text{H}}_2$ (g) gas at 430 ${}^{\circ }\text{C}$ for 15 min (JCPDS file (${\text{Cu}}^0$): 04-0836, (b) metallic copper nanoparticles [sample (a)] annealed under air atmosphere for 1 h at $400{}^{\circ }\text{C}$ (JCPDS file (CuO): 80-1917. Graph in insert: (c) borophosphate glass doped without annealing (as-prepared glass sample).

Figure 2

SEM images of CuO nanostructures supported on 6 mol% (${\text{Cu}}^{2+}$ ions) copper-doped borophosphate glass annealed for 60 min under air atmosphere (main scale bar $1\mu \text{m}$). Picture in insert: unannealed glass sample (scale bar $1\mu \text{m}$).

Figure 3

Raman spectra for the copper-doped (6 mol% copper ions) borophosphate glass samples with ${\text{Al}}_2{\text{O}}_3$ (10 mol%): (a) unannealed (as-prepared), (b) annealed at 430 ${}^{\circ }\text{C}$ under hydrogen for 45 min; and (c) sample (b) with further oxidation, annealing under air atmosphere for 60 min. Graph in insert: detail of Raman spectrum for sample (c) for region of CuO Raman-active modes.

Figure 4

UV–Vis spectra for ${\text{Al}}_2{\text{O}}_3$ (10 mol%) Cu-doped glass: (a) 45 min at $430{}^{\circ }\text{C}$ under ${\text{H}}_2$ (g) atmosphere, (b) unannealed glass sample. Inset: (c) the derivative of the curve of sample (a) showing the maximum of surface plasmon resonance (${\text{SPR}}_{\mathit{max}}$) peak.

Scheme 1

Scope of oxadiazole 1 and aryl iodides $2{.}^{a,b}$.

Scheme 2

Gram-scale reaction.

Scheme 3

Plausible proposal for the reaction mechanism.

Figure 5

Effect CuOnano@glass catalyst at copper wt% (glass mass) on the phenol hydroxylation reaction at $50{}^{\circ }\text{C}$ (a) 1.09 mg (25 mg ), (b) 2.17 (50 mg), (c) 3.26 mg (75 mg), and (d) 4.34 (100 mg). Graph in insert: effect of phenol: ${\text{H}}_2{\text{O}}_2$ ratio in the catalytic reaction.

Figure 6

(A) Typical UV–Vis absorption spectra for 4-nitrophenol reduction by CuOnano@glass catalyst with 0.43 mg of copper (10 mg of glass) and (B) Effect of CuOnano@glass catalyst mass at copper wt% (glass mass) on normalized absorbance ($\text{A}/{\text{A}}_0$) versus time (min) for (a) 0.09 mg (2 mg), (b) 0.22 mg (5 mg), (c) 0.43 mg (10 mg), (d) Undoped borophosphate glass, and (e) Without catalyst. Graphic in insert: evolution of ${\text{k}}_{\mathit{app}}$ as a function of copper amount.