Detection of Hydrogen Phosphate ($${\text{HPO}}_{4}^{{2 - }}$$) and Hydrocarbonate ($${\text{HCO}}_{3}^{ - }$$) Using Cetyltrimethylammonium Bromide-Capped 1,10-Phenanthroline Nanoparticles for Environmental Monitoring

Cetyltrimethylammonium bromide (CTAB)-capped 1,10-phenanthroline nanoparticles (1,10-PHTNPs) were synthesized using a reprecipitation method and characterized by spectroscopic and surface charge analyses, confirming a stable colloidal suspension (average size of 141 nm, zeta potential of +42 mV). The sensing mechanism is based on fluorescence quenching through electrostatic interactions between the cationic nanoparticles and $${\text{HPO}}_{4}^{{2 - }}$$ / $${\text{HCO}}_{3}^{ - }$$ ions. The nanoparticles exhibited structured excitation at 380 nm with enhanced emission at 454 nm. Stern–Volmer constants were 4.4 × 103 M–1 for $${\text{HCO}}_{3}^{ - }$$ and 1.82 × 104 M–1 for $${\text{HPO}}_{4}^{{2 - }}$$ , with corresponding detection limits of 4.09 × 10–6 M and 8.24 × 10–7 M, respectively. Recovery studies with spiked tap and river water samples showed recoveries of 95–102% (relative standard deviation < 4%), confirming the probe’s applicability for real-world sample analysis. These results demonstrate that CTAB-capped 1,10-PHTNPs are promising fluorescent probes for trace-level detection of $${\text{HPO}}_{4}^{{2 - }}$$ and $${\text{HCO}}_{3}^{ - }$$ ions in aqueous environments.