Strategies And Properties Of Green Synthesis Of Bayerite In An Aqueous Two-phase System At Room Temperature

Micro-nano materials have a wide range of applications in the fields of catalysis,energy conversion and storage,and their morphology control is of great significance for the efficient utilization of the materials themselves.In the preparation of micro-nano materials by traditional liquid-phase precipitation method,it is often difficult to control the precipitation rate,which leads to the difficulty of morphology control.In this dissertation,the reaction system was extended to an aqueous two-phase system(ATPS)based on the traditional liquid-phase system to control the precipitation process,and a variety of amphoteric(hydro)oxides with different morphologies were prepared.The main results are as follows:(1)The phase diagram of ethanol-Na Al O2 was drawn and fitted by cloud point titration using cheap Na Al O2 and nontoxic,green small molecular alcohol as materials at room temperature and atmospheric pressure.The fitting results(the correlation coefficient R2 =0.9835)have a high correlation with cloud point data.It was proved by FT-IR that the upper and lower layers of the ethanol-Na Al O2 ATPS had similar compositions with the homogeneous phase system(HPS).When the mass fraction of ethanol(W1)is gradually increased in the Na Al O2 solution with a certain mass fraction(W2),the solution can be transformed from HPS to ATPS.(2)Bayerite with different morphologies and well crystallization was rapidly prepared in ethanol-Na Al O2 system with ethyl acetate(EA)as precipitant at room temperature and atmospheric pressure.The products were characterized by XRD,SEM and TEM.The study found that the phase of the product did not change with the W1 and the precipitation time.And the sample prepared in the HPS had a flake-like structure with a size distribution of tens to hundreds of nanometers.In addition,the samples prepared in the metastable phase(between HPS and ATPS)and ATPS were solid microspheres with uniform particle size with 3~5 μm.For the samples prepared in the ATPS,ethanol participates in the self-assembly and cross-linking process of bayerite microspheres through Al-O-C bond.The mild synthesis strategy was further extended to rapidly prepare other amphoteric oxide microspheres.Sn O2 microspheres with smooth surface and particle size distribution of 0.2~1 μm,Si O2 microspheres with 1~2 μm and flower-like Zn O microspheres(particle sizes ranging from 7~8 μm and 4~5 μm)with hierarchical structure were successfully prepared.In addition,the synthesis strategy was extended to use inorganic aluminum salts as precursors,sodium acetate and sodium propionate as precipitants to react at 80 ℃,aluminum hydroxide acetate(AHA)and aluminum propionate(AP)with different morphologies were successfully prepared.The difference in morphology is highly correlated with the reaction system.(3)The double hydrolysis reaction of the ethanol-Na Al O2 ATPS was deeply studied,and a series of bayerites with hierarchical structure were prepared.The samples were characterized by XRD,SEM,TEM and N2 adsorption-desorption.The effects of different precipitation systems,Na Al O2 concentrations,alcohol/water ratio and the precipitant types on the morphologies and structures of the products were studied.Studies have shown that the morphologies of bayerite in the HPS were random nanoflakes,and the size of nanoflakes increases with the increase of W2.However,the samples in the ATPS can proceed a certain degree of self-assembly to form a sphere-like or microsphere structure(EA as precipitant).At a certain W2 and with the increase of W1,the precipitation system changed from HPS to ATPS,and the morphologies of bayerite changed from irregular nanoflakes to microspheres.However,the microsphere structure was defective when W1 is too high.The degree of self-assembly for microspheres was increased and the defect structure of bulk phase was reduced by adding acid-reduced organic acid esters(ethyl acetate,ethyl propionate,ethyl isobutyrate and ethyl pivalate)in the precursor solution with the same composition.In addition,the weaker the acidity of the organic acid ester in the ATPS,the lower the yield of bayerite.The hydrogenation performance of 2-ethylanthraquinone was evaluated after theη-Al2O3 loaded with Pd prepared by the scale-up experiment(the raw material of the typical small test was enlarged by 10 times).The results shown that the best sample had the highest hydrogenation efficiency(12.7 g/L)when the hydrogenation time was 150 min,which was higher than the performance of commercial γ-Al2O3 as the carrier reported in the literature(8.5 g/L).Therefore,the work in this dissertation is of great significance for the development of novel high-performance and low-cost hydrogenated activated alumina support materials,and the synthesis strategy of ATPS provides a new idea for the regulation of the morphology and structure of micro-nano materials.