FeS2 nanosheets (NSs) were produced and exploited as a new catalyst for a chemiluminescence (CL) reaction. The characterization of FeS2 NSs was performed using spectroscopic methods. In this regard, transmission electron microscopy images showed that FeS2 NSs have a length of ~0.5–1 μm. The direct optical band gap energy of FeS2 NSs was found to be 3.45 eV. Prepared FeS2 NSs were used to catalyze the NaHCO3–H2O2 CL reaction. It was found that procaine hydrochloride (PCH) could reduce the intensity of the FeS2 NSs–NaHCO3–H2O2 CL reaction so, with increasing PCH concentrations, the intensity of light emission decreased. Therefore, a simple and sensitive method was introduced to measure PCH with a linear range expanded from 1.00 × 10−6 to 1.00 × 10−3 mol L−1 and an 8.32 × 10−7 mol L−1 limit of detection. Studies related to the effect of foreign species and reaction mechanisms were performed. The application of the approach was verified by quantifying the PCH in the injection
