Synthesis of MOF on MOF photocatalysts using PCN-134 as seed through epitaxial growth strategy towards nizatidine degradation

MOF on MOF composites illustrated superb functional scalability, but few MOF on MOF composites had been applied in the direction of photocatalytic degradation. In this work, a series of P21-X (X = 1, 2, 3, 4) composites were synthesized and optimized with PCN-134 as the MOF seed and PCN-222 as the secondary MOF by an epitaxial growth method and applied to the photocatalytic degradation of nizatidine (NZT). P21-X had excellent substantial adsorption and photocatalytic properties. P21-3 exhibited the highest removal of 90.81% for NZT. The mechanism of P21-3 producing 1O2 was probed. Based on the results of UPLC-HRMS, the NDMA was not produced during the degradation process and rational pathways for degradation of NZT were proposed. The environmental toxicity of NZT degradation products was evaluated using ECOSAR, T.E.S.T. software and Vibrio fischeri luminescence inhibition, the results showed that the toxicity of the reaction solution was diminished after 120 min of photodegradation by P21-3. Moreover, given the strong anti-interference performance of 1O2, the photocatalytic degradation system constructed with P21-3 could be free from the interference of common anions, cations and dissolved organic matters. As a result, the photocatalytic activity of the system remained high removal of NZT in tap water, river water and seawater. The results demonstrated that the MOF on MOF composites P21-3, synthesized by the epitaxial growth method, had enhanced photodegradation capability. The current study not only avoids the generation of toxic by-products in the photocatalytic degradation process but also broadens the application area of MOF on MOF composites.