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. 2025 Feb 4;41(4):2480-2491.
doi: 10.1021/acs.langmuir.4c04175. Epub 2025 Jan 26.

Design of S-Scheme CuInS2/CeO2 Heterojunction for Enhanced Photocatalytic Degradation of Pharmaceuticals in Wastewater

Olalekan C Olatunde  1 , Ibrahim Waziri  2 , Damian C Onwudiwe  1 , Tunde L Yusuf  3
Affiliations

Design of S-Scheme CuInS2/CeO2 Heterojunction for Enhanced Photocatalytic Degradation of Pharmaceuticals in Wastewater

Olalekan C Olatunde et al. Langmuir. .

Abstract

The release of common medications and illegal drugs into the environment could be potentially harmful to the ecosystem and hamper the behavior and growth of plants and animals. These pollutants gain access to water through sewage and factory discharges and have been found to exceed safety limits in water bodies. Therefore, there is an urgent need for improved wastewater purification systems. In this study, semiconductor-based heterojunction photocatalyst CuInS2/CeO2, synthesized through a facile solvothermal process, was explored for the photocatalytic degradation of ciprofloxacin, commonly used antibiotics. Studies on the electronic properties of the heterojunction revealed interfacial characteristics that were suitable for enhanced charge carrier separation and transport and a potential S-scheme charge transfer mechanism. The heterojunction achieved ∼90% efficiency for the degradation of CIP compared to 60% and 12% reported for CeO2 and CuInS2, respectively. This shows an improvement in the activity, which results from the improved charge carrier properties of the heterojunction. Further investigation of the charge transfer mechanism through radical scavenging experiments identified •OH, O2•-, and h+ as active species contributing to the catalyst's efficacy. Based on X-ray photoelectron spectroscopy analysis, a proposed S-scheme charge transfer mechanism was suggested for the CuInS2/CeO2 heterojunction. The findings indicate the potential of the CuInS2/CeO2 heterojunction as a promising photocatalyst for treating waste effluents from the pharmaceutical industry.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) XRD spectra of CeO2, CuInS2, and CuInS2/CeO2, (b) Raman spectra of CeO2, CuInS2, and CuInS2/CeO2, and (c) FTIR spectra of CeO2, CuInS2 and 1.5CuInS2/CeO2, and (d) BET plot for CeO2, CuInS2, and CuInS2/CeO2 heterojunctions at different weight ratios.
Figure 2
Figure 2
SEM micrographs of (a) CeO2, (b) CuInS2, and (c) 1.5CuInS2/CeO2. The TEM micrographs of (d) CeO2, (e) CuInS2, (f) 1.5CuInS2/CeO2, and (g) EDS of 1.5CuInS2/CeO2.
Figure 3
Figure 3
(a) Survey scan of CeO2, CuInS2, and 1.5CuInS2/CeO2; (b) High resolution scan of Cu 2p, (c) In 3d, (d) S 2p, (e) Ce 3d, (f) and O 1s.
Figure 4
Figure 4
(a) EIS spectra of CeO2, CuInS2, and CuInS2/CeO2 heterojunctions; (b) Photocurrent density of CeO2, CuInS2, and CuInS2/CeO2 heterojunctions; (c) UV–vis spectra of CeO2, CuInS2, and CuInS2/CeO2 heterojunctions; (d) Photoluminescence spectra of CeO2, CuInS2, and 1.5CuInS2/CeO2 (excited at 325 nm).
Figure 5
Figure 5
Mott–Schottsky plot for (a) CeO2 and (b) CuInS2 and Tauc plot for (c) CeO2, (d) CuInS2, and (e) band alignment in the 1.5CuInS2/CeO2 heterojunction.
Figure 6
Figure 6
(a) Photocatalytic degradation profile of CIP by CeO2, CuInS2, and CuInS2/CeO2; (b) Pseudo-first order kinetics plot for CIP degradation; (c) Effect of catalyst dosage on the degradation of CIP; (d) TOC removal by CuInS2/CeO2 in synthetic and real water samples.
Figure 7
Figure 7
(a) Degradation efficiency of 1.5CuInS2/CeO2 for other antibiotics; (b) Stability test for 1.5CuInS2/CeO2; (c) XRD spectra of 1.5CuInS2/CeO2 before and after 5 catalytic cycles.
Figure 8
Figure 8
(a) Radical scavenging experiment; (b) Proposed S-scheme charge transfer mechanism for CuInS2/CeO2 heterojunction.
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