CuS/KTa_0.75Nb_0.25O₃ nanocomposite utilizing solar and mechanical energy for catalytic N₂ fixation

This work synthesized a novel CuS/KTa_0.75Nb_0.25O₃ (KTN) heterojunction composite and firstly applied it in photocatalytic and piezocatalytic reduction of N₂ to NH₃. XRD, Raman, XPS, SEM, and TEM analyses indicate that CuS nanoparticles closely adhered to the surface of KTN nanorods, which facilitates the migration of electrons between the two semiconductors. Mott-Schottky and valence band XPS analysis shows that KNbO₃ shows a higher conduction band than CuS, indicating that CuS mainly acts as electron trappers to capture the photogenerated electrons from KTN. Because of the great enhanced spatial separation of photogenerated charge carriers, the CuS/KTN presents much higher performance than pure KNT, which is further confirmed by ¹H NMR analysis of the reaction solution. An interesting finding is that synthesized CuS/KTN not only performs well under light irradiation but also can work in an ultrasonic bath, indicating its great potential in photo/piezocatalytic conversion of N₂ to NH₃. The optimal 10 %CuS/KTN shows an NH₃ production rate of 36.2 μmol L^-1 g^-1 h^-1 under ultrasonic vibration, which reaches 7.4 times that of KTN. The electrons generated by KTN through the piezoelectric effect can be captured by CuS, which endows the electrons a longer life to participate in the reaction, thereby improving the catalytic reaction performance.