Few-layer NbOCl2 nanosheets as acidifying agents for pH clocks

• NbOCl2 nanosheets serve as a novel acidifying agent that enables controlled H+ release, overcoming the limitations of inorganic and organic acids in spectral analysis. • The material exhibits a smooth extinction spectrum with distinct identification windows (400–410 nm and 410–900 nm), facilitating precise pH clock monitoring. • Transient absorption studies reveal size-dependent carrier dynamics, linking H+ release to reduced absorption and providing mechanistic insights. • NbOCl2 offers a safe, simple, and effective platform for advancing spectroscopic detection technologies in acid-sensitive applications.