Evaluation of the adsorption and degradation performance of lanthanum-modified mesoporous carbon nitride composite materials for tetracycline wastewater treatment

Abstract

Lanthanum-modified mesoporous graphite nitride carbon composites (La-g-C₃N₄) were synthesized using a thermal shrinkage polymerization method. The samples underwent characterization through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmet–Teller (BET) analysis. The results revealed that the La₃₀-g-C₃N₄ sample displayed a more porous layered morphology with a uniform pore structure. The BET surface area of the sample was found to be 38.6 m² g⁻¹, which is 5.8 times higher than that of the undoped sample g-C₃N₄. The sample exhibited a type IV isotherm, indicating its mesoporous nature with a pore size distribution ranging from 3 to 20 nm. The application of these materials was investigated for the degradation of tetracycline (TC) and acidic fuchsin (AF) in simulated wastewater. The results demonstrated that the La₃₀-g-C₃N₄ sample exhibited rapid and efficient degradation, along with excellent adsorption capacity for both TC and AF. Within 5 minutes, the degradation efficiency of the La₃₀-g-C₃N₄ sample for TC and AF was measured to be 83.1% and 74.1%, respectively, with corresponding adsorption capacities of 63.9 mg g⁻¹ and 129.4 mg g⁻¹. The kinetic and thermodynamic analysis of the adsorption process revealed that the adsorption of TC and AF by La₃₀-g-C₃N₄ followed the quasi-second-order kinetics and Langmuir adsorption isotherm model, indicating a predominantly single-layer chemical adsorption process. Furthermore, the composite material exhibited good cycling stability and maintained excellent adsorption performance even after six repeated uses.