Introduction and Quantification of Sulfide Ion Defects in Highly Crystalline CdS for Photocatalysis Applications

• Published in: Physica status solidi. A, Applications and materials science Vol. 221; no. 12
• Main Author: Nagakawa, Haruki
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.06.2024
• Subjects: Amorphization; cadmium sulfides; Catalytic activity; Control methods; Crystal defects; Defect annealing; defect engineering; Electron traps; Grinding; hydrogen productions; Hydroxylation; Oxidation; Photocatalysis; Photocatalysts; Photodegradation; Submerging; Surface defects
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.202400213

To evaluate and diversify, control methods for surface defects in photocatalysts have surged because of their significant effect on carrier dynamics and reactivity. Sulfide photocatalysts, wherein anion defects act as electron traps, are not as extensively researched as oxide photocatalysts, and therefore, the knowledge of defects remains incomplete. Herein, simple treatments such as grinding, alkali immersion, and annealing are used to introduce surface defects into CdS, which is a representative sulfide photocatalyst. Moreover, Pt‐loaded CdS is prepared by reducing Pt ions using electrons trapped in the defects. The amount of defects on the CdS surface is successfully estimated by quantifying the amount of unreacted Pt ions through the absorbance of the reaction solution. The results indicate that the defect density can be increased using any of these employed methods. The surface state varies with the introduction method, leading to significant changes in photocatalytic activity. Grinding induces particle refinement and amorphization, alkali immersion induces oxidation and hydroxylation, and annealing enables the formation of a sulfurized surface. These surface conditions degrade the photocatalytic activity, and therefore, introduction of defects under relatively mild conditions is preferred. Herein, the sample calcined at 473 K shows the highest photocatalytic activity. Sulfide ion defects are introduced on the surface of highly crystalline CdS via grinding, alkali immersion, and annealing. Different surface states are observed based on the introduction method; however, in all the cases, the introduced defects act as electron traps. The defect density is determined from the number of Pt ions reduced by the trapped electrons.