2D MXene-derived Nb2O5/C/Nb2C/g-C3N4 heterojunctions for efficient nitrogen photofixation†
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Abstract
Due to the rather high 940.95 kJ mol−1 thermodynamic cleavage energy of the N–N triple bond, developing a robust catalytic process for N2 reduction under mild conditions is a continuing scientific challenge. Here, 2D MXene-derived niobium pentoxide/carbon/niobium carbide/graphite-like carbon nitride (Nb2O5/C/Nb2C/g-C3N4) heterojunctions were explored as photocatalysts for N2 reduction in water. Nb2O5/C/Nb2C/g-C3N4 heterojunctions were prepared by uniformly growing Nb2O5 on Nb2C and then forming g-C3N4 nanosheets in situ on Nb2O5/C/Nb2C. With an optimized Nb2O5/C/Nb2C : g-C3N4 ratio of 1 : 1, Nb2O5/C/Nb2C/g-C3N4 showed a high nitrogen reduction rate (0.365 mmol h−1 gcat−1), which was 9.1 times as high as that of the MXene derived Nb2O5/g-C3N4 composite. It is worth mentioning that the enhanced performance of Nb2O5/C/Nb2C/g-C3N4 should be attributed to the enhancement in photogenerated electron and hole separation efficiency caused by the short-range directional charge transmission over the close contact between Nb2O5 and conductive Nb2C as well as the Schottky junction formed at the Nb2O5/Nb2C interface. By further changing the pH of the catalytic system, the concentration of reactive electrons was adjusted and the energy barrier of proton reduction was improved. With the optimized pH of 9 adjusted with NaOH solution, the nitrogen reduction efficiency could be further promoted 2.5 times (0.927 mmol h−1 gcat−1).
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