Adsorption of Pb2+ ion using coal fly ash/g-C3N4/Bi2O2CO3 and re-use of spent adsorbent for photocatalytic and forensic applications

Here, the application of a novel coal fly ash/graphitic carbon nitride/Bismuth oxy carbonate (CFA/g-C ₃ N ₄ /Bi₂O₂CO₃) composite for Pb(II) removal from aqueous solutions is reported. The composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and other techniques. The factors affecting the Pb(II) removal performance in batch adsorption experiments, including contact time, adsorbent dosage, and solution pH, were evaluated using the response surface methodology (RSM) approach with central composite design (CCD). The analysis revealed that under optimal conditions for Pb(II) removal (107.6 min, 24.35 mg, pH 6.62, at 25 ºC), Pb(II) removal performance reached 100%. Kinetic studies indicated a rapid adsorption process, well-conformed with the pseudo-second order model. Isotherm analysis affirmed the applicability of the Langmuir model, suggesting a monolayer adsorption with a maximum adsorption capacity of 60.29 mg g⁻¹. The adsorption process was endothermic and spontaneous. The Pb ²⁺ ion-loaded spent adsorbent (CFA/g-C ₃ N ₄ /Bi ₂ O ₂ CO ₃ @Pb ²⁺ ) was then reused to degrade rhodamine B (RhB). The photocatalytic experiments for RhB over CFA/g-C₃N₄/Bi₂O₂CO₃@Pb²⁺ under optimal conditions demonstrated excellent photocatalytic performance (< 99%) and high reusability (up to 5 cycles). This highlights that the CFA/g-C ₃ N ₄ /Bi₂O₂CO₃@Pb²⁺ is a potential photocatalyst for dye remediation in wastewater treatment applications. Additionally, CFA/g-C ₃ N ₄ /Bi₂O₂CO₃@Pb²⁺ demonstrated to be responsive for latent fingerprint (LFP) detection on a variety of substrates. As a result, it is a useful labeling agent for LFP detection in forensic authentication.