1：Experimental Design and Method Selection:

A one-pot hydrothermal method was used to synthesize carbon dots from catechol as a single carbon source, without doping or modification. The method involves hydrolysis, polymerization, carbonization under high temperature and pressure.

2：Sample Selection and Data Sources:

Catechol was used as the carbon source; real water samples (tap water) were collected for application testing.

3：List of Experimental Equipment and Materials:

Chemicals included catechol, various salts (e.g., NaCl, FeCl3), and sodium hypochlorite; equipment included a Teflon-lined stainless steel autoclave, dialysis membrane, UV-Vis spectrophotometer (Shimadzu UV-2600), fluorescence spectrophotometer (Shimadzu RF-6000), FTIR spectrophotometer (Thermo Fisher Scientific iN10 Nicolet micro FTIR), XPS spectrograph (Thermo Fisher Scientific ESCALAB250Xi), TEM (JEOL JEM-2100), and XRD diffractometer (Rigaku SmartLab 9 kW).

4：Experimental Procedures and Operational Workflow:

Catechol was dissolved in water, heated in an autoclave at 200°C for 24 hours, cooled, dialyzed, and vacuum-dried to obtain CDs. For ClO? detection, CDs solution was mixed with ClO? standards in phosphate buffer, incubated for 10 minutes, and fluorescence intensity measured at 323 nm excitation.

5：Data Analysis Methods:

Quantum yield was calculated using L-tyrosine as a standard; fluorescence quenching was analyzed with linear regression for sensitivity; selectivity was assessed by testing interference from other ions.