Rational design of a cascade CdS/C₃N₄/COF heterostructure for high-performance Cr(VI) photoreduction

Area of Science:

• Materials Science
• Environmental Chemistry
• Catalysis

Background:

• Photocatalytic reduction of toxic hexavalent chromium (Cr(VI)) faces challenges due to inefficient charge separation and recombination in traditional heterojunctions.
• Developing advanced materials is crucial for effective environmental remediation and sustainable chemical processes.

Purpose of the Study:

• To design and synthesize a novel CdS/C3N4/COF cascade heterostructure for enhanced photocatalytic Cr(VI) reduction.
• To investigate the charge transfer dynamics and the role of the covalent organic framework (COF) as an electronic mediator.
• To establish charge-preferential recombination as a design strategy for high-performance photocatalysts.

Main Methods:

• Synthesis of a ternary CdS/C3N4/COF heterostructure.
• Characterization using bond structure analysis, photoluminescence (PL) spectroscopy, and electrochemical methods.
• Photocatalytic Cr(VI) reduction experiments under visible-light irradiation.
• Kinetic and scavenger studies to elucidate reaction mechanisms.

Main Results:

• The CdS/C3N4/COF architecture demonstrated efficient Cr(VI) removal (≈92% in 90 min at pH 3).
• The nanoporous COF acted as an electronic mediator, facilitating preferential recombination of low-energy carriers and enabling an S-scheme charge transfer pathway.
• The ternary heterostructure significantly outperformed binary analogues, confirming the benefits of the engineered cascade architecture.

Conclusions:

• The developed CdS/C3N4/COF photocatalyst effectively removes Cr(VI) via a COF-mediated S-scheme mechanism.
• Charge-preferential recombination is a viable strategy for designing advanced photocatalysts.
• Covalent organic frameworks serve as programmable electronic mediators in complex photocatalytic systems.