Hidróxido duplo lamelar ZnAL com pontos quânticos de carbono: síntese, caracterização e aplicação

Abstract

This study aims to evaluate the influence of adding the carbon quantum dot (CQD) to ZnAl/lamellar double hydroxide, as well as on the physicochemical characteristics (CQD), and its potential application in water treatment. As a form of study and comparison, two materials were synthesized using the coprecipitation method, HDL/ZnAL and the HDL/ZnAl-CQD composite. These materials were subjected to characterizations using various analytical techniques, including X-ray diffraction (XRD), Nitrogen adsorption by the Brunauer, Emmett and Teller method (BET), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (RAMAN ), Scanning Electron Microscopy (SEM), Zero Charge Point (pHpcz) and Transmittance Electron Microscopy (TEM). The results showed that both HDL/ZnAL and HDL/ZnAl-CQD composite were well synthesized. The composite has mesoporous structures, with surface area values of 40.96 m2 /g, pore volume and size of 0.21 cm3 /g, 16.78 nm, respectively. Raman indicated the formation of the graphite structure, attributed to the sp2 plane. The images obtained by SEM showed a material with a surface with a white layer and structures of irregular shapes and varying sizes. pHPZC resulted in a value of 5.07. The TEM image depicted plates with hexagonal shapes and the representation of lamellae typical of HDL structures. The efficiency of HDL/ZnAl-CQD as an adsorbent for dyes, drugs and the herbicide 2,4 D in aqueous solutions was also evaluated. Among the pollutants studied, methylene blue (AM) was chosen as a model pollutant. Kinetic tests showed rapid adsorption phenomena, which reached equilibrium between 45 and 145 min. The experimental data obtained were fitted to the pseudo first-order model, with equilibrium adsorption capacities of 6.50 and 8.00 mg.g-1 for initial adsorbate concentrations of 25 and 50 mg.L-1 , respectively. The isotherms showed behavior similar to Liu's model, characterized by the fact that the HDL/ZnAl-CQD adsorbent is heterogeneous due to the existence of different active sites and with different free energies. The thermodynamic data indicated that the adsorption of AM by the adsorbent is a physical, exothermic, spontaneous and organized process. Additional experimental tests indicated that increasing ionic strength disfavored AM adsorption on the selected adsorbent. The regeneration of the adsorbent with the addition of hydrogen peroxide (H2O2) showed significant performance efficiency after 6 adsorption/desorption cycles, as it had an adsorption reduction of approximately 20% until the sixth cycle. After tests with different aqueous matrices, the adsorbent showed better adsorption with AM in solution with deionized water, reaching a percentage of adsorption of 59.04%. Overall, this study highlights the potential applications of HDL/ZnAl-CQD composite in wastewater treatment. The successful synthesis of HDL/ZnAlCQD adsorbent provides valuable information for the development of customized functional composites for the removal of various pollutants from aqueous solutions.