Construction of Isoenergetic Band Alignment between CdS QDs and CaFe₂O₄@ZnFe₂O₄ Heterojunction: A Promising Ternary Hybrid toward Norfloxacin Degradation and H₂ Energy Production

Abstract

The increasing demand for clean water triggers advancement in development of nanomaterials for photocatalytic pollutant degradation. Herein, we report for the first time a CdS QDs decorated p-CaFe 2 O 4 @n-ZnFe 2 O 4 heterojunction photocatalyst fabricated via a two-step chemical route, i.e. sol−gel auto combustion and precipitationdeposition methods. The prepared photocatalyst proves to be effective toward degradation of the emerging pollutant norfloxacin under solar light irradiation. Systematic analysis including parameters such as pH, interfering ions, and active species was studied in detail. Photoluminescence, photocurrent study, and activity test reveal that 3%CdS QDs/ CaFe 2 O 4 @ZnFe 2 O 4 has the highest charge separation ability among the prepared composites. Norfloxacin degradation occurs effectively on a ZnFe 2 O 4 surface of CdS QDs/CaFe 2 O 4 @ZnFe 2 O 4 through isoenergetic which is evidenced by AFM analysis and a pn-heterojunction based charge transfer mechanism. The modified band gap alignment and isoenergetic electron transfer from CdS QDs to CaFe 2 O 4 photocatalyst are verified by XPS, Mott−Schottky analysis, and AFM studies. Interestingly, with the introduction of CdS QDs into CaFe 2 O 4 @ZnFe 2 O 4 hybrid the photocurrent density increases from 5.9 mA/cm 2 to 10.39 mA/ cm 2 , which is attributed to isoenergetic charge transfer between CdS QDs and CaFe 2 O 4 . The photocatalytic H 2 evolution rate of 3% CdS QDs/CaFe 2 O 4 @ZnFe 2 O 4 showed 18300 μmol h −1 g −1 , which is 1.4 times greater than that of binary hybrid CaFe 2 O 4 @ZnFe 2 O 4 . Further, 83% photodegradation of 50 ppm norfloxacin has been achieved by the 3% CdS QDs/CaFe 2 O 4 @ ZnFe 2 O 4 ternary nanocomposite after 90 min irradiation, which is 1.28 times that of CaFe 2 O 4 @ZnFe 2 O 4 . Upon vigorous analysis, the outstanding photocatalytic performance is greatly attributed to visible light harnessing ability, ample solar light absorption capacity, low photogenerated electron−hole recombination rate, high concentration of photoexcited electron, and excellent photostability.

Recent Advancement on Ferrite Based Heterojunction for Photocatalytic Degradation of Organic Pollutants: A Review

“…CdS quantum dots decorated by CaFe2O4@ZnFe2O4 prepared by sol-gel auto combustion followed by deposition method and 83% of norfloxacin photodegraded in 90 min under solar irradiation [75]. The maximum degradation were noticed at pH=3, at this pH norfloxacin exist as positively charged species whereas, at this pH heterojunction surface is negatively charged about -12.07 mV as confirmed by zeta potential analysis.…”

NiO Nanosheets Coupled With CdS Nanorods as 2D/1D Heterojunction for Improved Photocatalytic Hydrogen Evolution

“…As shown in Figure 3B, the peak located at 530.6 eV could be attributed to the lattice oxygen of NiO (Wang et al, 2010;Liu et al, 2012;Hu et al, 2018). Figure 3C displays the high-resolution XPS spectra of Cd 3d; the binding energies at 405.2 and 411.9 eV correspond to the Cd 3d 5/2 and Cd 3d 3/2 of the Cd 2+ in CdS nanorods, respectively (Bai et al, 2010;Zhou P. et al, 2017;Behera et al, 2019). The XPS spectrum of S (Figure 3D) presents two peaks at 162.8 and 161.7 eV that were assigned to the characteristic binding energies of S 2p 1/2 and S 2p 3/2 of S 2− .…”

Synthesis of Novel Ternary Dual Z-scheme AgBr/LaNiO3/g-C3N4 Composite with Boosted Visible-Light Photodegradation of Norfloxacin

“…Numerous researches had found that semiconductor photocatalytic technology can be efficacious means of solving the growing environmental pollution and energy crisis around the world [4][5][6][7]. However, common photocatalyst are limited in application for narrow light absorption range, poor stabilization, and lower photodegradation efficiency [8,9].…”