Preparation And Application Of Hydroxyapatite With Piezoelectric Catalytic Activity

In recent years,the extensive research interest in hydroxyapatite（HAP）has been sparked by its utilization as an environmental protection intelligent material,which boasts remarkable biocompatibility and a variety of physical and chemical properties.However,its piezoelectric properties have not been fully explored so far.The purpose of this work is to develop a simple method to prepare HAP with good piezoelectric catalytic activity,and explore its potential applications in the degradation of organic pollutants and the generation of H₂O₂and other aspects.In this work,HAP was prepared by a simple chemical precipitation method and calcined at 200℃in an atmospheric atmosphere.The specific research contents include the following three parts:（1）Hydroxyapatite（HAP）was synthesized by a series of aqueous precipitation steps using calcium nitrate and diamine hydrogen phosphate as calcium and phosphorus sources,respectively,and further introduced a certain degree of oxygen vacancy defects through calcination to give better catalytic performance.The piezoelectric catalytic effect of gold nanoparticles was verified by the deposition experiment of gold nanoparticles and piezoelectric force microscopy（PFM）.Systematic study of the factors influencing the piezoelectric catalytic degradation of HAP,such as catalyst,dye concentration,temperature,initial p H,atmosphere and ultrasonic power,was conducted using Rhodamine B（Rh B）and other model pollutants as substrates.To delve deeper into the universality of catalytic degradation of HAP obtained,piezoelectric degradation tests were carried out on 5 mg/L rhodamine B（Rh B）,methylene blue（MB）,methyl orange（MO）and crystal violet（CV）.After 30 minutes of ultrasonic treatment,the degradation rates were 92%,88%,86%and 90%,respectively.And from the perspective of practical application,some anions and cations were quantitatively introduced to simulate the degradation of organic dyes in natural water environments,which proves that the material is more suitable for application in low salt water environments.Experiments of recycling also demonstrated the reusability and durability of the materials.The reactive oxygen species（ROS）that play a role in the piezoelectric catalytic degradation reaction were studied through free radical capture experiments and electron spin resonance（ESR）spectroscopy,and the results confirmed that OH plays a dominant role in the degradation reaction.（2）It was found that H₂O₂ played a role as an intermediate product in the reaction system.Therefore,the production of H₂O₂was preliminarily evaluated.Within 30 minutes,the cumulative concentration of H₂O₂ in pure water reached 152.24μmol/L.The generation path and oxygen source of hydrogen peroxide were explored,and determined that dissolved oxygen is the source of oxygen generated by H₂O₂,as well as the conversion process of dissolved oxygen through two consecutive single electron reduction to produce H₂O₂.The corresponding parameters were further optimized,and the quenching experiment showed that the quenching of·OH was beneficial to the accumulation of H₂O₂.The reduction experiment of potassium permanganate also confirmed the electron source in the generation reaction of H₂O₂.Based on the results of the free radical capture experiment in the previous chapter,a piezoelectric catalytic degradation mechanism of HAP was proposed.At the same time,relevant experiments have also confirmed that the generated H₂O₂ can stably exist in the reaction system and has good decomposition resistance.This study provides a new approach for the clean and environmentally friendly synthesis of H₂O₂.（3）Hydroxyapatite is often used as a filler in toothpastes,mainly acting as a friction agent in traditional theories.If piezoelectric hydroxyapatite is introduced into toothpaste,it will have significant development potential.We propose a non-destructive,biocompatible,cost-effective,and time efficient tooth whitening strategy based on the piezoelectric catalytic effect generated by piezoelectric nanoparticles.When H₂O₂ generated through HAP piezoelectric catalysis is decomposed into water,it releases active oxygen,which can oxidize and degrade the chromatin on the surface of teeth,achieving visual decolorization and whitening.The tooth cleaning experiment has confirmed that the piezoelectric catalytic effect of HAP can be extended to the field of whitening toothpaste,and the soybean germination toxicity experiment also shows that HAP is safe and reliable during use,providing a potential piezoelectric abrasive for the removal of extrinsic pigments from teeth.