Single-Atom Ni Heterogeneous Catalysts Supported UiO-66 Structure: Synthesis and Catalytic Activities

Abstract

Herein, the single-atom Ni site heterogeneous catalysts supported by the UiO-66 structure (University of Oslo-66 metal organic framework) were successfully synthesized by a postsynthetic metalation method, where Ni ions are covalently attached to the missing-linker defect sites at zirconium oxide clusters (Zr6O4(OH)4) in as-prepared UiO-66 structure, [Zr6O4(OH)4(BDC)(DMF)10(OH)10] (BDC (benzene-1,4-dicarboxylate), DMF (dimethylformamide)). The structure properties of the catalysts were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption isotherms (BET), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). It was found that single-atom Ni heterogeneous catalysts supported by the UiO-66 structure, UiO-66/Ni1.0 [Zr6O4(OH)4(C8H4O4)(DMF)10(OH)8Ni2(OH)2(Cl)2], showed a sphere-like morphology with a high specific surface area as well as good thermal stability. Specifically, the as-prepared UiO-66/Ni1.0 exhibited the excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:msub> <a:mrow> <a:mi>E</a:mi> </a:mrow> <a:mrow> <a:mtext>a</a:mtext> </a:mrow> </a:msub> <a:mo>=</a:mo> <a:mn>23.15</a:mn> <a:mtext> </a:mtext> <a:mtext>kJ</a:mtext> <a:mtext> </a:mtext> <a:mtext>mo</a:mtext> <a:msup> <a:mrow> <a:mtext>l</a:mtext> </a:mrow> <a:mrow> <a:mo>−</a:mo> <a:mn>1</a:mn> </a:mrow> </a:msup> </a:math> ), high turnover frequency (76.19 molecules g-1 min-1), and high apparent rate constant ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:msub> <c:mrow> <c:mi>k</c:mi> </c:mrow> <c:mrow> <c:mtext>app</c:mtext> </c:mrow> </c:msub> <c:mo>=</c:mo> <c:mn>0.956</c:mn> <c:mtext>mi</c:mtext> <c:msup> <c:mrow> <c:mtext>n</c:mtext> </c:mrow> <c:mrow> <c:mo>−</c:mo> <c:mn>1</c:mn> </c:mrow> </c:msup> </c:math> ). In addition, methylene blue (MB) was also chosen as the organic dye model for catalytic reduction reaction. The <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:msub> <e:mrow> <e:mi>k</e:mi> </e:mrow> <e:mrow> <e:mtext>app</e:mtext> </e:mrow> </e:msub> </e:math> and TOF for the reduction of MB using UiO-66/Ni1.0 were 0.787 min−1 and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:mn>33.89</g:mn> <g:mo>×</g:mo> <g:msup> <g:mrow> <g:mn>10</g:mn> </g:mrow> <g:mrow> <g:mn>20</g:mn> </g:mrow> </g:msup> </g:math> molecules g−1 min−1, respectively.