Pyrolytic N-doping of silica wastes with urea for tailored morphology, enhanced adsorptive and catalytic degradation of paracetamol and diclofenac

We investigated the effectiveness of N-doping pre-carbonized waste and explored how the nitrogen source and pyrolysis conditions influence the morphology and optical properties of the resulting materials for environmental applications. Ten N-doped materials were obtained by mixing different urea percentages (21.7–78.3 %) with wastes from biogenic silica production. It was revealed that the doping was effective for all samples without affecting the crystalline structure of graphitic carbon. By modulating the urea ratio, it was found that its higher concentrations increased pore size (4.46–4.83 nm) and basicity (6.8–7.1), decreasing the surface area available (894–698 m² g⁻¹). The addition of lower concentrations of urea was shown to decrease the band gap (2.5–2.17 eV), improving the catalytic properties of the materials. The N-doping unlocked carbocatalytic features of the waste-derived materials in photo-assisted reactions, being effective for the degradation of paracetamol and diclofenac in aqueous systems. Thus, this study demonstrates that N-doping not only stabilizes the structures but also allows for the tuning of specific properties to suit targeted applications.