Synthesis of ZrO2/MgAl-LDH composites and evaluation of its isotherm, kinetics and thermodynamic properties in the adsorption of congo red dye

Abstract

Recently, the treatment of waste water by Zr-based adsorbents had significantly attracted wide interest among researchers owing to its distinct features. The unique properties of Zr such as thermal stability, large size, high positive charge, greater mechanical rigidity and acid-base nature are mainly responsible for its diverse application. In this work, designing of the new adsorbent material containing tetravalent Zr metal oxide layered double hydroxide (LDH) composite for the removal of anionic dye was studied. The modification of LDH was conducted via the urea hydrolysis method by using zirconium salts as a precursor material. The adsorption efficiency of the as-synthesized material represented as ZrO2/MgAl-LDH was investigated for the decontamination of congo red (CR) dye from an aqueous medium. The adsorbent ZrO2/MgAl-LDH composite was characterized by several instrumental techniques including powder X-ray diffraction (P-XRD), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy(FT-Ir), scanning emission microscopy(SEM), energy dispersive X-ray(EDX), transmission emission microscopy(TEM) and thermogravimetric analysis(TGA). The influence of several experimental factors on the adsorption equilibrium studies such as pH, temperature, initial dye concentration, contact time, adsorbent dosages, and interfering ions are examined under optimized conditions. The thermodynamic study manifests the spontaneous and endothermic nature of the sorption process. Additionally, based on fitting the experimental data with different models the isotherm and kinetics mechanism are found to be more appropriate with Langmuir isotherm, Redlich-Peterson isotherm, and pseudo-second-order kinetics. The spectral analysis further indicates the oxidizing nature of the material, therefore favoring the adsorption of anionic dye. The maximum dye removal efficiency of ZrO2/MgAl-LDH reached up to 97.19% under the optimum reaction condition (initial dye concentration = 50 mg/L, contact dosages = 0.02 g, temperature = 303 K). In addition, the maximum monolayer adsorption capacity (qmax= 169.42 mg) for CR adsorption also reveals its superiority in adsorption test. Moreover, the adsorbent can be easily retrieved and reused up to fifth cycle. Therefore, the characterization and experimental results of ZrO2/MgAl-LDH affirms its potential application for effective decontamination of waste water.