Continuous flow mechanochemical synthesis of Zr-MOF as effective catalyst for 4-nitrophenol reduction

Nitroaromatic compounds (NACs) are a group of organic chemicals containing one or more nitro functional groups attached to an aromatic ring. These compounds are considered emerging pollutants (EPs) in wastewater due to their potential environmental and human health impacts. These NACs can enter wastewater through various sources, including the production and use of explosives, dyes, pesticides, or pharmaceuticals. 4-nitrophenol (4-NP) is considered a priority pollutant due to its toxicity and potential environmental and health hazards. Thus, its removal is crucial. For that purpose, a novel strategy to carry out Zr-MOFs syntheses has been developed employing I-CHEM technology (Impact Continuous flow Heated Mechanochemistry), an improved wet-milling process. The resulting materials have demonstrated efficacy as catalysts in the reduction of 4-NP towards 4-aminophenol (4-AP), a precursor to paracetamol. Notably, the most promising outcomes were achieved with Zr-MOF prepared through continuous flow mechanochemical processes utilizing Zr-methacrylate clusters as precursor (Zr-MOF/2@RL). 4-NP removal was successfully carried out at room temperature, with an outstanding optimal time of removal of 14 min, 30% faster than with synthesized by conventional methodologies. These findings underscore the innovation brought about by the I-CHEM synthetic approach, where more effective collisions are reached, as well as opening avenues for broader applications of MOFs. The wet-mechanochemical procedure not only demonstrates its novelty, but also presents the potential for scalability under continuous flow conditions, further enhancing the feasibility of largescale production.