Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO₄-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics

Abstract

The synergistically MXene (Ti 3 C 2 T x ) co-catalystdecorated BiVO 4 -based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti 3 C 2 T x ) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO 4 phase and MXene (Ti 3 C 2 T x ) and also the antisymmetric (834 cm −1 ) and symmetric stretching (715 cm −1 ) of tetrahedral VO 4 and D (1330 cm −1 ) and G (1570 cm −1 ) bands corresponding to MXene (Ti 3 C 2 T x ) in the Raman spectrum. The worm-like structures of BiVO 4 nanocrystals grew onto the lamellar sheets of MXene (Ti 3 C 2 T x ), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m 2 g -1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V 5+ and Ti 3+ states, and the uniform distribution of BiVO 4 nanocrystals over lamellar sheets of MXene (Ti 3 C 2 T x ) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti 3 C 2 T x ) to BiVO 4 . Further, the higher degree of band bending at the BiVO 4 /MXene (Ti 3 C 2 T x ) heterojunction, revealed from the Mott−Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.

Synthesis and Photocatalytic Application of Magnetic CoFe2O4/Conjugated Poly(vinyl chloride) Derivative Nanocomposite

“…The contamination of waterbodies by high toxicity Cr(VI) can induce irreversible detriment to the aquatic ecological environment, bringing bad illnesses to human being. Hence, it is worldwide taken as a priority to remedy Cr(VI) pollution in various bodies of water. − By contrast, Cr(III) is far lower in toxicity and an essential element of the human body, and it is readily eliminated from water through precipitating with alkali ( K sp ⊖ (Cr(OH) 3 ) = 6.3 × 10 –31 ) . Therefore, reducing Cr(VI) to Cr(III) is a method often applied to treat Cr(VI)-contaminated waterbodies.…”