Phosphotungstic acid binding in situ to K4Nb6O17 for the effective adsorption-photocatalytic removal of tetracycline.

In this investigation, phosphotungstic acid (H₃PW₁₂O₄₀) was successfully self-assembly implanted into the interspace of K₄Nb₆O₁₇ nanosheet via an impregnation method to form an adsorption-photocatalytic composite, in which n-type semiconductor K₄Nb₆O₁₇ was selected as photo-electron emitter and H₃PW₁₂O₄₀ was particularly used as an electronic transmitter. By characterizing with X-ray diffraction (XRD), transmission (TEM), scan electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectrum (FT-IR), it confirmed that H₃PW₁₂O₄₀ (HPW) was converted to the insoluble tiny particles of K₃PW₁₂O₄₀ (KPW) with the remained primary Keggin group via an ion-exchanged H⁺ of HPW with K⁺ in K₄Nb₆O₁₇ in the implanted process and was firmly bound to the surface of K₄Nb₆O₁₇ to form well sandwich structure. UV-vis diffuse reflectance spectroscopy revealed that the band gap of K₄Nb₆O₁₇-K₃PW₁₂O₄₀ have a slight red shift compared with the single K₄Nb₆O₁₇. Its adsorption-photocatalytic properties were evaluated with the removal of tetracycline as model reaction. Compared with pure K₄Nb₆O₁₇, tetracycline removal rate can be significantly improved for the as-prepared sandwich. Importantly, the removal could still maintain 70% after five reuses in recycle tests at an acidic solution, inferring a good stability which was mainly ascribed to the formation of water-insoluble K₃PW₁₂O₄₀. The separation and transfer process of photogenerated electrons were investigated by surface photovoltage spectroscopy (SPV). It proposed that the KPW anchored firmly on the interlayers of K₄Nb₆O₁₇ through a O-K-O bridge plays a significantly role in promoting the separation of the photogenerated carriers and preventing the leakage and agglomeration of HPW. The present results showed that the strategy of the phosphotungstic acid binding in situ to K₄Nb₆O₁₇ was favorable to promote the hetero-photocatalytic efficiency as well as reusability.Mechanism for tetracycline photodegradation over the K₄Nb₆O₁₇-KPW photocatalytic system<graphic></graphic> [ABSTRACT FROM AUTHOR]