Synthesis of Porous Octahedral ZnO/CuO Composites from Zn/Cu-Based MOF-199 and Their Applications in Visible-Light-Driven Photocatalytic Degradation of Dyes

Abstract

In the present paper, a porous octahedral (ZnO/CuO) composite is synthesized from zinc/copper-based metal-organic framework-199, and its applications in visible-light-driven photocatalytic degradation of dyes are demonstrated. The precursors of Zn-BTC, Cu-BTC, and Zn/Cu-BTC (BTC: benzene-1,3,5-tricarboxylate) were synthesized using a microwave-assisted method. Benzene-1,3,5-tricarboxylate acts as a sacrificial template and was removed from the precursors via thermal decomposition to form CuO, ZnO, and ZnO/CuO. ZnO/CuO with a large specific surface area of 32.5 m 2 ·g –1 is composed of porous octahedral particles of 5–10 μ m in diameter. Methylene blue (MB) was utilized as the dye model for photocatalytic degradation reactions. The porous octahedral ZnO/CuO exhibits superior visible-light-driven photocatalytic degradation of MB compared with single CuO or ZnO. The kinetic model of photocatalytic degradation was proposed as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mfenced open="(" close=")"><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:msub></mml:mrow></mml:mfenced><mml:mo>×</mml:mo><mml:mi mathvariant="normal">ln</mml:mi><mml:mi>C</mml:mi><mml:mo>+</mml:mo><mml:mi>C</mml:mi><mml:mrow><mml:mo>=</mml:mo></mml:mrow><mml:mrow><mml:mo>−</mml:mo></mml:mrow><mml:msub><mml:mrow><mml:mi>k</mml:mi></mml:mrow><mml:mrow><mml:mtext>r</mml:mtext></mml:mrow></mml:msub><mml:mi>t</mml:mi><mml:mo>+</mml:mo><mml:mfenced open="(" close=")"><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:msub></mml:mrow></mml:mfenced><mml:mo>×</mml:mo><mml:mi mathvariant="normal">ln</mml:mi><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mtext>e</mml:mtext></mml:mrow></mml:msub><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mtext>e</mml:mtext></mml:mrow></mml:msub></mml:math>, where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow><mml:mrow><mml:mtext>L</mml:mtext></mml:mrow></mml:msub></mml:math> is the Langmuir equilibrium constant and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mtext>e</mml:mtext></mml:mrow></mml:msub></mml:math> is the MB concentration at equilibrium. The model significantly fits the kinetic data. In addition, the acquired catalyst manifests excellent photocatalytic degradation for several other dyes including phenol red, methyl orange, and Congo red.