Ultrasmall cobalt boride-decorated P, K-doped gC3N4 for plasmon-driven degradation of high concentration tetracycline

The widespread contamination of aquatic ecosystems by pharmaceutical pollutants, particularly tetracycline (TC) antibiotics, poses significant environmental risks. gC3N4 is widely studied as a photocatalyst for environmental remediation, yet its practical use remains limited. To overcome these limitations, we developed gC3N4 by co-doping phosphorus (P) and potassium (K), and further decorating with ultrasmall cobalt boride (CoB) nanoparticles. Elemental co-doping with P and K modulates the electronic structure of gC3N4 by narrowing the bandgap, introducing shallow impurity bands, and enhancing charge separation through directional charge redistribution, supported by spectroscopic analysis and DFT simulations. The introduction of plasmonic CoB nanoparticles leads to the formation of Schottky junctions, while also inducing localized surface plasmon resonance (LSPR) that significantly amplifies the photocatalytic activity. CoB/P-K-gC3N4 exhibited a 21-fold increase in TC degradation rate compared to pristine gC3N4, where 84.8 % of 100 ppm TC was degraded using 10 mg of photocatalyst in one hour, achieving high removal activity of 7.1 mgpollutant/gcatalyst/min. The catalyst also demonstrated excellent structural stability and sustained photocatalytic efficiency over multiple reuse cycles. Electrochemical studies showed a higher charge carrier density along with a noticeable decline in charge transfer resistance, while photoluminescence and time-resolved fluorescence analysis confirmed a suppressed electron-hole recombination rate. This study demonstrates the synergistic interplay of co-doping and plasmonic enhancement in advancing next-generation photocatalysts for sustainable water purification.