Green four-component reaction and dye adsorption studies of new ZnCoAl-LDH and ZnCoCr-LDH materials

Abstract

The present work aims to synthesis two LDH materials such as ZnCoAl-LDH and ZnCoCr-LDH to investigate their catalytic effect and the adsorption properties. The as-produced materials were prepared by Co-precipitation method and their structures were confirmed using various complementary characterization techniques mainly scanning electron microscopy (SEM) and element mapping, Energy-dispersive X-ray spectroscopy (EDX), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray diffraction (DRX), and Thermogravimetric Analysis (TGA/DTG). However, the LDH materials were tested in four-component reaction as a heterogeneous catalyst. For this purpose, the elaborated catalyst was used to produce dihydropyran-pyrazole derivatives under green condition. The structure of both dihydropyrano-pyrazoles was characterized based on 1D, 2D NMR. Otherwise, the adsorption potential of ZnCoAl-LDH and ZnCoCr-LDH was evaluated by removing Congo red (CR), as an anionic dye, from an aqueous solution. The effects of influential adsorption parameters such as pH, initial CR concentration, contact time and adsorbent dosage on CR removal were investigated. ZnCoCr-LDH proved more effective at adsorbing CR, with maximum removal of 98 % observed at pH 2, while ZnCoAl-LDH showed 93 % removal. The adsorption isotherms of the system were described using Langmuir, Temkin and Freundlich models. The maximum adsorption capacity of ZnCoAl-LDH and ZnCoCr-LDH was calculated on the basis of the Langmuir isotherm and amounted to 272.756 mg/g and 391. 920 mg/g respectively. The Freundlich model also shows a good fit for ZnCoAl-LDH (R² = 0.999), although it is generally less relevant than the Langmuir model. However, the adsorption kinetics of CR on the surface of ZnCoAl-LDH materials was defined by the PFO model, while ZnCoCr-LDH followed the PSO model.