“Immobilization of TiO2/ZnO Nanocomposites on Kaolin for Tannery Wastewater Treatment: A Comprehensive Synthesis and Characterization Study”

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“Immobilization of TiO2/ZnO Nanocomposites on Kaolin for Tannery Wastewater Treatment: A Comprehensive Synthesis and Characterization Study”


This study investigates the adsorption effects of selected physicochemical parameters from tannery wastewater onto beneficiated kaolin and various nanocomposites, including kaolin/TiO2, kaolin/ZnO, and kaolin/TiO2/ZnO. The nanocomposites were prepared using wet impregnation methods, and their properties were characterized through various techniques such as X-ray diffraction (XRD), nitrogen gas adsorption-desorption Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), High Resolution Scanning Electron Microscopy (HRSEM), Energy Dispersive X-ray spectroscopy (EDX), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). The results revealed the morphology, phase identification, surface area, functional groups, and adsorption process of the nanoadsorbents.

The crystallite size of synthesized TiO2 (at pH 4-12) and ZnO (at pH 6-12) calcined at 450 °C ranged from 5.67 to 15.02 nm and 11.84 to 24.82 nm, respectively, as determined by XRD patterns. HRSEM and HRTEM further confirmed the plate-like kaolinite, tetragonal anatase, and hexagonal zincite shapes of kaolin, TiO2, and ZnO. The BET results indicated increased surface areas of kaolin/TiO2 and kaolin/ZnO nanocomposites compared to beneficiated kaolin, and XRD and HRTEM showed the distribution of TiO2 and ZnO nanoparticles within the kaolin framework, which was further corroborated by EDX analysis.

The adsorption method explored the influence of experimental parameters, such as contact time, adsorbent dosage, and temperature. Adsorption isotherm studies were conducted at different temperatures (30-70 °C) and fitted to Jovanovic, Halsey, Flory-Huggins, and Redlich-Peterson isotherm models. Jovanovic isotherm model best fitted the data within the studied temperature range, while the Flory-Huggins isotherm model explained the spontaneous adsorption system. Kinetic adsorption models (fractional power, Bangham, and Avrami) and adsorption mechanism determinations (Boyd and intra-particle diffusion) were applied to experimental results at different contact times, showing that the kinetic adsorption process followed the Bangham kinetic model. The rate-determining step in the adsorption of tannery wastewater onto the adsorbents was found to be external mass transfer, as the plots of Boyd and intra-particle diffusion did not pass through the origin.

Thermodynamic studies indicated that the adsorption system is temperature-dependent, with an increase in temperature resulting in an increase in pollutant adsorption, signifying an endothermic and spontaneous adsorption process. The calculated thermodynamic parameters, change in enthalpy (∆H) and change in entropy (∆S) from Vant’s Hoff plots, confirmed the spontaneity of the adsorption process. The synthesized nanocomposites were presented with a mechanistic pathway, and the resulting nanocomposite filter demonstrated resistance to temperatures above 900 °C. The flow rate of the filter pot was optimized by adjusting the proportion of kaolin and sawdust, serving as a controller for the flow rate and percentage porosity of the filter pot.

The bactericidal effects of TiO2 and ZnO nanoparticles in the composites were observed, explaining the nanoscale and physicochemical properties of the nanoparticles along with the surface area of the kaolin. The filtrates obtained using the nanocomposite filter pots showed concentrations of investigated physicochemical parameters below WHO and NESREA standards, suggesting that the filter pots nanocomposites could be a potentially safe and viable adsorbent in water filters for water purification systems.

“Immobilization of TiO2/ZnO Nanocomposites on Kaolin for Tannery Wastewater Treatment: A Comprehensive Synthesis and Characterization Study”

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