Synthesis Of ZnAl-LDH/ZnCo₂O₄ Using Pollen As Template And Its Adsorption And Photocatalysis Properties

Hydrotalcite?LDHs? has received widespread attentions in adsorption and photocatalysis, because of its high surface area, good thermal stability, exchangeable interlayer anions and other properties. But LDHs also exists some problems such as layers easy to reunite and difficult to recycle after use.In this paper, the pollen-like ZnCo₂O₄ material was successfully prepared by using pine pollen as the biological template. The morphology, phase composition and physical properties of the as-prepared ZnCo₂O₄ material were investigated by SEM?XRD?FTIR and surface area test. The specific surface area of the as-prepared ZnCo₂O₄ was 89.73 m2/g.Then ZnAl-LDH/ZnCo₂O₄ composite material was synthesized by hydrothermal method with ZnCo₂O₄ as the substrate, and its morphology, phase composition and physical properties were investigated by comprehensive analysis of the testing technologies. The analysis showed that ZnAl-LDH/ZnCo₂O₄ composite material was successfully prepared and still remained the morphology of pine pollen, ZnAl-LDH crystal films dispersed uniformly on the surface of the ZnCo₂O₄ substrate. The specific surface area of the as-prepared ZnAl-LDH/ZnCo₂O₄ composite material was 257.79 m2/g. Then the adsorption of Congo red and doxycycline onto the as-prepared ZnAl-LDH/ZnCo₂O₄ material were systematically investigated. Adsorption experiments results showed that the process of the as-prepared ZnAl-LDH/ZnCo₂O₄ material adsorbing Congo red and doxycycline followed the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum adsorption capacities were 244.49 mg/g and 362.31 mg/g, respectively. In addition, the adsorption capacities of Congo red and doxycycline on the as-prepared ZnAl-LDH/ZnCo₂O₄ material were best in the acid and neutral conditions, respectively. Furthermore, the adsorption process of them on the as-prepared ZnAl-LDH/ZnCo₂O₄ was a spontaneous and endothermic reaction. The as-prepared ZnAl-LDH/ZnCo₂O₄ material can be reused many times and was an excellent adsorbent.Then, ZnAl-CLDH/ZnCo₂O₄ material was obtained by calcining ZnAl-LDH/ZnCo₂O₄ material at different temperatures and its morphology, phase composition and physical properties were investigated by comprehensive analysis of the testing technologies. The analysis showed that ZnAl-CLDH/ZnCo₂O₄ material still maintained the morphology of pine pollen, the phase of ZnAl-LDH was disappeared and converted to Zn O and ZnAl2O4. The specific surface area of the samples obtained at 700? was 48.26 m2/g. Subsequently, the adsorption and catalytic process of Congo red and doxycycline were systematically investigated. Adsorption experiments results showed that the process of the as-prepared ZnAl-CLDH/ZnCo₂O₄ material adsorbing Congo red and doxycycline followed the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum adsorption capacities were 694.44 mg/g and 409.83 mg/g, respectively. The best adsorption properties of Congo red and doxycycline onto ZnAl-CLDH/ZnCo₂O₄ material were at the acid and neutral conditions, respectively. And the adsorption of them on the as-prepared ZnAl-CLDH/ZnCo₂O₄ was spontaneous and endothermic process. In addition, the catalytic activities of the obtained samples for Congo red and doxycycline degradation under simulative sunlight irradiation were also evaluated, and the degradation rate was 87.20% and 98.52%, respectively. And the photocatalytic process all followed first order kinetics. The repeated experiments showed that ZnAl-CLDH/ZnCo₂O₄ as adsorbent and catalyst can be used repeatedl y.In this paper, ZnAl-LDH/ZnCo₂O₄ and ZnAl-CLDH/ZnCo₂O₄ materials were a kind of green, environmentally friendly, efficient and recovery adsorbents. Moreover, ZnAl-CLDH/ZnCo₂O₄ composite material was an efficient catalyst that could be quickly recycled.