One-step synthesized 3D-structured MOF foam for efficient and convenient catalytic reduction of nitrogen-containing aromatic compounds

Metal Organic Frameworks (MOFs) receive increasing attention for 4-nitrophenol (4-NP) reduction; however the existing studies of using MOFs for 4-NP reduction all involve with noble metals. Moreover, the reported MOFs are very fine powders which are inconvenient for realistic implementation. Thus, the present study proposes to develop a MOF foam which exhibits macroscale features of foam and microscale functionalities of MOFs. Specifically, a Cu foam is selected as the macroporous substrate which serves as a porous support and the metal source for synthesizing Cu-based MOF, HKUST-1, via an one-step electrochemical method. The resulting HKUST-1 foam can act as a convenient catalyst for reduction of 4-NP to 4-AP in either batch-type or flow-thru-type reactions. The corresponding activation energy (E_a) of 4-NP reduction (43.3 kJ/mol) is also significantly lower than E_a values of reported catalysts, including noble metal catalysts, whereas the corresponding TOF (48.3 min⁻¹) is higher than many other catalysts. HKUST-1 foam can also efficiently catalyze reduction of methylene blue (MB) to fully decolorize its color. In addition, HKUST-1 foam could be reused over multi-cycles and retain its activity for reduction of 4-NP and MB. These features validate that HKUST-1 foam is a practical, convenient, and reusable catalyst for reduction of 4-NP.