Preparation Of Titanium Pvrophosphate Powder By Sol-Gel Method And Study Of Its Adsorption For Bi³⁺

Bismuth is a rare metal element,which mainly exists in the struture of metal or minerals in environment.Its compound is widely used in the fields of medicine and catalysis.As the extensive use of bismuth and bis muth com pounds,the spread of bismuth-containing compounds in the environment and the exposure of bismuth to organisms have increased.It is recognized that the accumulation of bismuth compounds in the human body will produce toxic effects and cause many diseases,such as nephropathy,osteoarthritis,hepatitis and neuropathology.Therefore,it is crucial to remove bismuth from wastewater.At present,typical methods for removing Bi³⁺from water include solvent extraction,solidoid distill,and adsorption.Among them,adsorption is considered the most ef fe ctive strategy.However,the existing adsorbents have many problems,for exemple complex fabrication and low selectivity to Bi³⁺.Comparatively,titanium pyrophosphate as an adsorbent has the advantages of low cost,easy preparation,and higher selectivity to Bi³⁺.It will be a good adsorbent for Bi³⁺.In this thesis,a sol-gel strategy for titanium pyrophosphate preparation was investigated and,the environmental stability and the adsorption capacity for bismuth were studied.The main content and results are as follows:（1）Ttitanium pyrophosphate powders were prepared by a sol-gel method,and the influence of the sol p H,the proportion of the solvent,and the heat treatment temperature on the morphology of titanium pyrophosphate was investigated.The results have shown th at during the synthesis,the p H value of the sol will affect the morphology of titanium pyrophosphate.Polyhedral titanium pyrophosphate can be prepared when the p H was less than 2.When the p H was greater than 2,titanium pyrophosphate with coral morphology can be prepared.Changing the solvent and the prop ortion of water and eth anol added will have ignorable effect on the shap of titanium phosphate.The increase of heat treatment temperature caused the size of titanium pyrophosphate particles to rise.（2）The acid-base stability of titanium pyrophosphates with various shapes has been compared and the environmental stability of the polyhedral titanium pyrophosphate was systematically studied.The experimental results showed that the order of acid-base stability was polyhedral titanium pyrophosphate>coral titanium pyrophosphate>commercial titanium pyrophosphate.It is also desonstrate that when the p H of the Na Cl solution was in the range of 1-11,the dissolution rate of polyhedral titanium pyrophosphate increased with the rising p H.When the p H was 11,the dissolution rate was the largest,which was 2.19%.Moreover,the dissolution rate of polyhedral titanium pyrophosphate under ultraviolet light was greater than that under dark conditions.The dissolution kinetics fitting showed that a physical diffusion process dominated the dissolution of titanium pyrophosphate.TG/DSC analysis showed that from room temperature to 1000℃,the weight loss rates of polyhedral and coral-shaped titanium pyrophosphates were only 0.75%and 0.84%respectively.This result indicated a good thermal stability of both powders.In contrast,polyhedral titanium pyrophosphate offered a slightly better thermal stability.（3）The thesis systematically studied the selective adsorption performance of polyhedral titanium pyrophosphate to Bi³⁺,investigated the influence of adsorbate solution p H on the adsorption capacity,and performed data fitting for the adsorption process.The adsorption equilibrium constant and the basic thermodynamic constants were obtained.In the selective adsorption experiment of Na⁺,K⁺,Fe³⁺,Cr⁶⁺,Bi³⁺,titanium pyrophosphate exhibited a good selective adsorption for Bi³⁺.Condition optimization experiments showed that the optimal p H was 3.0 and the equilibrium adsorption time was 20min at room temperature.The adsorption kinetics was well in following the linear pseudo-sencond-ord er model,explaining that the adsorption process of Bi³⁺by titanium pyrophosphate was domi nan ted by chemical actions.TheΔG~0 values of the adso rp tion of Bi³⁺by titanium pyrophosphate at 298K,308K,and318K were all negative,illustrating that the adsorption was spontaneous in the temperature range.It is also found that tht absoluteΔG~0 value was increased with the temperature,suggesting that the raising temperature was beneficial to the adsorption of Bi³⁺ions.