# Engineering Carbon Nitride Quantum Dots via Sulfur Doping for Controlled Reactive Oxygen Species Generation

## TL;DR

This study shows how sulfur-doped carbon nitride quantum dots can be engineered to control the production of reactive oxygen species, useful for biomedical and environmental applications.

## Contribution

First measurement of superoxide and singlet oxygen quantum yields for CNQDs, revealing sulfur doping's dual effect on ROS generation.

## Key findings

- Sulfur doping enhances superoxide generation while suppressing singlet oxygen production in CNQDs.
- CNQDs produce hydrogen peroxide and hydroxyl radicals efficiently under photocatalytic conditions.
- The materials show potential as hypoxia-resistant photosensitizers for photodynamic therapy and pollutant degradation.

## Abstract

Carbon nitride quantum dots (CNQDs) are emerging as versatile photocatalytic materials with promising applications in biomedicine and environmental remediation. In this study, we synthesized pristine and sulfur‐doped CNQDs via a hydrothermal method, and characterized them using transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), and UV–vis absorption spectroscopy. For the first time, the quantum yields of superoxide and singlet oxygen generation were measured for CNQDs. Sulfur doping was found to significantly enhance superoxide generation while concurrently suppressing singlet oxygen production, offering a powerful mechanism for tailoring reactive oxygen species (ROS) output. In addition, all CNQD samples produced hydrogen peroxide and hydroxyl radicals. The ability of these nanomaterials to produce multiple ROS types underscores their potential as hypoxia‐resistant photosensitizers (PSs) for photodynamic therapy (PDT) and as efficient photocatalysts for pollutant degradation.

Pristine and sulfur‐doped carbon nitride quantum dots are prepared via hydrothermal “bottom‐up” synthesis. Quantum yields of superoxide and singlet oxygen generation are measured. Sulfur doping is shown to boost photocatalytic production of superoxide by carbon nitride quantum dots while suppressing singlet oxygen generation. The quantum dots also demonstrate efficient photocatalytic hydrogen peroxide and hydroxyl radical production.