Adsorption is a simple yet effective technique for the removal of emerging contaminants. In this study, pure graphitic carbon nitride (g-C(3)N(4)) and nickel-doped g-C(3)N(4) (Ni-g-C(3)N(4)) were synthesized via a thermal polycondensation method and evaluated as adsorbents for doxycycline removal. Structural and morphological characterization was performed using X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The results confirmed the successful incorporation of Ni(2+) into the g-C(3)N(4) matrix, with homogeneous Ni(2+) distribution and no secondary phases. Morphological analysis indicated that nickel doping induced only slight changes in the g-C(3)N(4) morphology. Adsorption experiments revealed that both materials exhibited enhanced adsorption capacity at pH 9, with Ni-g-C(3)N(4) achieving a significantly higher removal efficiency (53.4%) compared to g-C(3)N(4) (14.2%). This improvement was attributed to Ni(2+)-induced positively charged regions, facilitating stronger adsorbate-adsorbent interactions. Kinetic analysis demonstrated that doxycycline adsorption onto Ni-g-C(3)N(4) followed a pseudo-second-order model. Among the tested isotherm models, the Sips model provided the best fit, yielding maximum adsorption capacities of 37.889 mg.g(-1) for g-C(3)N(4) and 116.265 mg.g(-1) for Ni-g-C(3)N(4). Theoretical calculations corroborated experimental findings, confirming that Ni(2+) incorporation in the g-C(3)N(4) structure enhances adsorption capacity by facilitating strong chemical bonds between doxycycline and the Ni-g-C(3)N(4) adsorbent surface.
Langmuir 2025 ; ? (?): ?
