Synthesis And Properties Of Lanthanum Hydroxide Podwers By Microwave Hydrothermal Method

As one of the important rare earth material，lanthanum hydroxide (La(OH)3)is widely and deeply applied by the scientists to their studies in many areas. Dueto the special electronic and microstructure structures of La(OH)3,the materialhas a board application outlook in the aspects of usage on the electrical property,magnetic property and photocatalytic property. Nevertheless, There still remainsfurther investigations on the exploration of a simplified synthesis process, greenand economic techniques when developing phase, control of microstructure andcrystal growth, which are believed to be very necessary for lanthanum hydroxidepowders. In this dissertation, La(OH)3micro/nanocrystal with micro/nanorods,micro/nanosheets, nanospheres and flower were synthesized by a microwavehydrothermal method using La(NO3)3·6H2O and KOH as raw materials. On thisbasis, we investigated influence technological factors on Synthesis of La(OH)3powders which including precursor solution pH, alkalinity sources, La3+/OH-ratio of amount of substance, reaction temperature, reaction time andconcentration of the precursor solution. There are three templates as controllingthe morphology of La(OH)3, which are EDTA, PVP, HMTA. The phasecomposition, morphology and optical properties of as-prepared samples werecharacterized by X-ray diffraction (XRD), field emission scanning electronmicroscopy (FESEM), ultraviolet–visible spectroscopy (UV-Vis) and test ofphotocatalysis, respectively. The following are the main results and conclusions:In microwave hydrothermal system, without any templates, we successfullyobtained La(OH)3micro/nanocrystal (rods, sheets) by controlling differentreaction conditions, which were precursor solution pH, alkalinity sources,La3+/OH-ratio of amount of substance, reaction temperature, reaction time and concentration of the precursor solution. Results showed that the growth unit,crystal nucleation and crystallization were found to play key roles in differenttechnological conditions to change the products phases and morphologies.Besides, Photocatalytic degradation of methyleneblue under UV light showedthat different technological conditions had vary results on photocatalyticproperties for preparing La(OH)3. photocatalytic properties had relationshipswith crystallization, specific surface area and grain size of La(OH)3powders.La(OH)3micro/nanocrystal were synthesized with flowerlikes, nanospheres,nanosheet by adding different templates. This suggested that adding differenttemplates for the preparation of different morphologies of La(OH)3nanocrystalsplayed a pivotal role. UV-Vis absorption spectra showed that adding differenttemplates all had good absorbation to UV light. Photocatalytic degradation ofmethyleneblue showed that the photocatalytic activity of La(OH)3with templateswere obviously improved under ultraviolet light for21min, which photocatalyticdegradation rate of La(OH)3powders was99%. This showed the addingtemplates could improve the photocatalytic activity of the La(OH)3powders. Allin all, photocatalytic degradation rate was nanospheres (EDTA)> nanosheets(PVP)> flowerlikes (HMTA)> nanorod(without template).Adding different amounts of EDTA were successfully prepared purenanospheres La(OH)3powders, which size, crystallinity and dispersibility hadchanged. This indicated that Adding different amounts of EDTA have animportant influence on morphology of La(OH)3powders In addition,photocatalytic degradation of methyleneblue under ultraviolet light showed thatadding0.02g/ml EDTA could obtain spherical structure, good dispersion andcrystallinity, and its photocatalysis was best.