Abstract
The nanostructure of ZnAl-layered double hydroxide (ZnAl-LDH) was designed to promote the catalytic performance of Mo-based ZnAl-LDH (Mo/ZnAl-LDH) catalysts, in a catalytic wet air oxidation (CWAO) process, under room temperature and pressure, in degradation of dye wastewater. Four most commonly used preparation methods, traditional precipitation (TP), hydrothermal synthesis (HS), sol-gel (SG), and urea co-precipitation (UC) were employed to prepare the ZnAl-LDH. The resulting Mo/ZnAl-LDH samples were contrasted through surface area, crystal structure, chemical state, and morphology. The degradation of cationic orchid X-BL, under room temperature and pressure, was developed to determine the catalytic activity of these Mo/ZnAl-LDH samples. The results showed that the nanostructure of ZnAl-LDH, prepared by HS, enhanced the adhesion of the catalytic active component, thus Mo/ZnAl-LDH had the highest catalytic activity of 84.2% color removal efficiency and 73.9% total organic carbon removal efficiency. Specific Mo species, such as Na2Mo2O7, Mo dispersion, and O2− ions were proved to be related with catalytic performance. These findings preliminarily clarified that LDHs preparation methods make a difference in the performance of Mo/LDHs.
Highlights
Catalytic wet air oxidation (CWAO) is an effective method for organic wastewater treatment in the 21st century [1,2], which allows the use of less severe reaction conditions
All catalyst exhibited the diffraction lines arising from the Na2 MoO4 phase (JCPDS 12-0773), located at 2θ = 16.95◦, 27.76◦, 35.66◦, 48.98◦, 52.18◦, and 57.27◦
Mo-SG and Mo-urea co-precipitation (UC) have extremely sharp and narrow diffraction spectra and exhibit high characteristic peaks of Na2 MoO4, which indicates that Mo-SG
Summary
Catalytic wet air oxidation (CWAO) is an effective method for organic wastewater treatment in the 21st century [1,2], which allows the use of less severe reaction conditions. It is suited to the decomposition of refractory pollutants, even, thereby, reducing the capital and operating costs [3]. The choice of the catalyst in the CWAO process is significant and, seeking an effective, robust, and low-cost catalyst, has been a research hotspot [4,5,6]. Heterogeneous catalysts containing small amounts of molybdenum oxides, and clay-immobilized molybdenum, have attracted considerable attention because of their wide structural variety and specific properties. To promote the catalytic activity of Mo-Zn-Al-O catalyst, attention has been focused on the nanostructure design
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