Synthesis Of Mesoporous Al-based Spinel And Its Surface Chemical Properties

As a kind of important inorganic functional material, spinel-type metal oxides have beenextensively applied to optical, electrical, magnetic, catalytic and many other fields for itsexcellent physical and chemical properties. However, due to the material prepared bytraditional method of high temperature solid phase sintering exist many shortcomings such aspoor uniformity, smaller specific surface area and so on, its applications are limited. On theother hand, spinel-type materials with special structure often show many excellent propertieswhich are superior to other materials. Therefore, there is urgent need to design or develop amore practical and versatile new method to synthesize spinels. Up to now, research on thesurface chemical properties of spinel-type mineral is relatively few, and determining thesurface complexation constants of spinel can provide a theoretical basis and guidance in usingand developing this kind of material, therefore it has a very vital significance.In this study, five kinds of mesoporous nano ZnAl₂O₄, CuAl₂O₄, CoAl₂O₄, MnAl₂O₄andZn₂TiO₄were synthesized through a coprecipitation method using simple mixed templatesconsisting of butylamine and a n-alkanol （hexanol, decanol, dodecanol）. Powder X-raydiffraction, Fourier transform infrared spectroscopy （FTIR）, thermogravimetric and differentialthermal analysis （TG/DTA）, high resolution transmission electron microscopy （HRTEM） andnitrogen adsorption-desorption techniques were used to characterize the prepared samples. Theresults indicate that all the prepared spinels are mesoporous materials and they have good porestructure, larger specific surface area and an amount of pore volume.Mesoporous zinc aluminate spinels with adjustable pore size have been successfullysynthesized. All the texture parameters of the obtained ZnAl₂O₄spinel, such as specificsurface area, pore diameter and volume, show a regular augmentation with increasing thecarbon chain length of the alkanol. Sample prepared with dodecanol and calcinated at500℃has the highest specific surface area of298m²·g^-1. The obtained mesoporous ZnAl₂O₄spinelshows excellent thermal stability, even the samples calcinated at800℃,its specific surfacearea still surpass150m²·g^-1. Further more, the pore size distribution is relatively uniform andchanges from3.1to12.1nm. We proposed the mesoporous ZnAl₂O₄formation mechanism, the formation of the mesoporous mainly by synergistically function between a short carbon chainbutylamine and the alcohols with proper carbon chain length to form micelles of volumeexpansion, and eventually formed the holes.We investigated the effect of the amount of water used on the textures of mesoporousCuAl₂O₄, the results show that when the water consumption of120mL mesoporous structureCuAl₂O₄samples could not formed, and when the dosage of water decreases gradually from80mL to40mL, the pore size of the samples increased from9.3nm to17.4nm. The optimal waterconsumption is80mL, at this time, the specific surface area is109m²·g^-1, the pore size is9.4nm and pore volume is0.341cm3·g^-1. The absorption of butyl and octyl xanthate fromaqueous solution onto the synthesized mesoporous CuAl₂O₄solid surfaces was studied by acontinuous, online, in situ attenuated total reflection Fourier transform infrared spectroscopy（ATR-FTIR） technique. The adsorption results show that mesoporous CuAl₂O₄has a highchemisorption capacity for xanthate, which reaches236and300mg·g^-1for butyl and octylxanthate, respectively, within100min. The adsorption kinetics can be described by apseudo-second-order reaction model.Thes experimental results show that the mixed templates composed of butylamine and an-alkanol can help to form mesoporous MnAl₂O₄, experiments without using a template orusing other templates to synthesis mesoporous MnAl₂O₄were all unsuccessfull. MesoporousMnAl₂O₄shows a excellent selectively catalytic reduction ability to NO in low temperature of150℃. Zn₂TiO₄can form when temperature is higher than800℃, and mainly caused by thesintering reaction of mesophase Zn₂Ti₃O₈and ZnO. Zn₂TiO₄and Zn₂Ti₃O₈showed anexcellent photocatalytic effect to Rhodamine （RB） under visible light irradiation,5mg·L-1RBcan be completely degradated within60min when1mg·mL-1Zn₂Ti₃O₈is used.Finally, by using the automatic potentiometric titration technique and WinSGW software,we determined the surface acid-base equilibrium constants of the four prepared mesoporousspinels ZnAl₂O₄, CuAl₂O₄, CoAl₂O₄, and MnAl₂O₄. As the used spinels minerals weremesoporous materials with high purity, the obtained relevant surface acid-base equilibriumconstant has universalism. As well konw, the surface acid-base equilibrium constants are veryfundamental to further studing surface chemical properties of spinel.