Hydroxyapatite Modification And Their Properties For Formaldehyde Catalytic Oxidation

Formaldehyde (HCHO) is one of the most common indoor air pollutants. It emits from building and decorating materials, as well as some consumer products. HCHO is considered to be carcinogenic and teratogenic to human beings. Short exposure to HCHO could cause irritation allergies, and long term exposure elevates the possibility of fatal hazards. Because of the toxicity of HCHO and the existing common contact ways, the elimination of HCHO has long been a great concern.Among all the current technologies for HCHO removal, catalytic oxidation is a promising method for its efficiency, convenience and cleanliness. In order to avoid the drawbacks such as high cost and unsafety of conventional catalysts, hydroxyapatite (HAP), which is non-toxic and safe with various sources, is chosen as the main component of the catalytic system. Modifications of HAP were adopted to design the catalysts. The structure and properties for HCHO oxidation of the catalysts were examined. The main contents of the work are as follows:Organic modification of HAP:Organic compounds, such as sodium citrate, CTAB and SDS were added during the procedure of HAP synthesis. The structure of modified HAP was established and identified by various characterization Techniques (XRD, BET, and IR etc.). The main structural difference caused by the modification of organic compounds turned out to be the specific surface area and pore structure. Sodium citrate modified HAP, with the largest specific surface area and pore volume as well as the smallest pore size, presented the best activity with the complete conversion temperature of240℃. Further investigation of the sodium citrate modified sample was performed.Doping of transition metals:Transition metals (Mn, Co, and Cu etc), instead of noble metal, were chosen as doping elements to further develop the catalytic activity of HAP. It was shown that the doping of transition metal significantly improved the performance of HAP. Among all the samples, Cu doped HAP (CuHAP) showed the best performance with the complete conversion temperature at180℃. Based on this result, different methods including ion exchange, co-precipitation and impregnation were used for the preparation of CuHAP to adjust the location and species of Cu on HAP. Methods of characterization including XRD, H2-TPR, EPR and XPS were used to relate the Cu species&locations with the catalytic activity. It was concluded that highly dispersed Cu species were mainly responsible for the activity.As a non-precious metal material, HAP presented considerable activity for HCHO catalytic oxidation. And it has been found by the present work that its activity can be significantly improved by the modification of organic compounds and metals. Therefore, as a promising material for HCHO catalytic oxidation, HAP is worth exploring.