Facile preparation of protonated hexaniobate nanosheets and its enhanced photocatalytic activity

Exfoliated hexaniobate nanosheets E-H₂K₂Nb₆O_17-x (E-HKNO) with broad light absorption (up to 850 nm) and high adsorption properties were prepared via ion exchange and transient annealing processes with micron-size K₄Nb₆O₁₇ powders as the precursor. The as-prepared E-HKNO nanosheets show excellent visible light photodegradation performances when compared to degussa P25, which was evaluated in terms of degradation of Rhodamine B (Rh B). High adsorption and broad light absorption characteristics could be attributed to the exfoliation behavior and the reduction of surface Nb⁵⁺ to Nb⁴⁺, which was confirmed by x-ray photoelectron spectroscopy (XPS) and Raman spectra. From the Mott-Schottky analysis, the E-HKNO is an n-type semiconductor and has a higher flat band voltage (-0.46 V versus RHE at pH = 7), compared with K₄Nb₆O₁₇. In addition, the electrochemical impedance spectroscopy (EIS) indicates that the E-HKNO nanosheets have an increased semiconductor-electrolyte charge transfer resistance, which is not conducive to the separation of photogenerated carriers (e^--h⁺). Accordingly, a small amount of holes scavenger (EDTA) was added to improve the photodegradation performance of the E-HKNO, since the holes scavenger can inhibit the recombination of the photogenerated carriers. This work provides not only a facile method for the preparation of an efficient E-HKNO nanosheets photocatalyst, but also new insights for further enhancing the photodegradation performance by adding trace scavenger.