Preparation And Application Of Lithium Niobate-type Negative Ion Materials

Negative air ions can purify water and air.Therefore,the production of negative air ions is an effective way to improve people’s life.A commonly used artificial production method is negative ion functional materials,which mainly prepared from natural minerals that can release negative ions.It has problems such as large differences in negative ion release performance,difficulty in mining,small output,and hard artificial synthesis,limiting application and development of negative ion functional materials.Therefore,it is valuable to study new-type negative ion functional materials that are easy to synthesize.Tourmaline is a typical natural mineral that can release negative ions.Due to its permanent electrostatic field,piezoelectric effect and pyroelectric effect,tourmaline can ionize the surrounding air to generate negative air ions when the surrounding environment changes.Lithium niobate ferroelectric material has the largest spontaneous polarization(P_s≈71×10^–6C/cm²),and has good physical and chemical stability.Polarized lithium niobate can have strong and stable internal electric field.We speculated that it has the conditions of generating negative ions.Therefore,in this thesis,we select lithium niobate as the basic material for the preparation of a new negative ion functional material.The main research results are as follows:（1）The preparation process of the lithium niobate polarized powder was designed.Lithium niobate powder was synthesized by the solid-phase method at 720℃for 4 h.The polarized lithium niobate powder was prepared by the electric field polarization of 2.8 kV/mm.Its average negative ion release amount was 239 ions/cm³,and no negative ions were released from the unpolarized powder,indicating that the method for preparing negative ion powder from polarized lithium niobate is feasible.（2）The grain size of lithium niobate was changed by setting different temperature regimes,and the effect of grain size on the release performance of powder anion was studied.The results show that with the increase of the grain size of lithium niobate powder,the number of negative ions released was higher.We measured that the initial average negative ion release amount of polarized lithium niobate powder prepared at 720℃for 4 h and afterwards 1100℃for 2 h was810 ions/cm³,relatively the highest.The negative ion release performance of polarized lithium niobate powder was improved,which also provided a reference for subsequent temperature system settings.（3）Lithium niobate was doped with neodymium ions,zinc ions and magnesium ions,respectively.The variables including doping element,doping amount,and polarization electric field were controlled separately to observe the changes in the negative ion release performance of lithium niobate.We obtained the parameters for the highest initial average negative ion release from lithium niobate,which is the polarized lithium niobate powder with 1（mol）%magnesium doped under an electric field of 2.8 kV/mm（referred to as 1%MLN）.Its initial average negative ion release was measured to be 2982 ions/cm³.The reason why the release amount of negative ions varies with three variables was analyzed.The polarizing electric field was not as large as possible,which is related to the breakdown of the material.Among the three doping elements,the negative ion release performance of the magnesium-doped lithium niobate polarized powder was relatively better,and it is speculated that the possible reason is related to the smaller radius of magnesium ions.With the increase of the content of magnesium-doped lithium niobate,the release performance of negative ions first increases and then decreases.It is speculated that when the dosage is different,magnesium ions occupy different positions in the lattice,which makes the electric dipole moments and defects formed in the lattice changing,resulting in different polarization effects.（4）The durability of negative ion release performance of the well-performing magnesium-doped lithium niobate was evaluated.The results show that the 1%MLN polarized powder prepared under the electric field of 1.7-2.8 kV/mm released about 80%of the initial negative ion release amount after 200 days,indicating that its negative ion release performance is durable.（5）Finally,we used 1%MLN polarized powder to carry out the purification experiment of dye waste solution.The results show that 1%MLN polarized powder has good purification effect on methylene blue solution.1 g of 1%MLN polarized powder can purify up to 97%of200 ml of methylene blue solution with a concentration of 10 mg/L.The purification of methylene blue by 1%MLN polarized powder may be a combination of adsorption and degradation.The degradation of methylene blue is the result of the release of negative ions.Ultrasound and friction can stimulate its negative ion release performance.