Synthesis of Photocatalytic Titania/Zero-valent Iron Nanocomposites for Remediation of Nitrate and Nitrite in Wastewater

• Main Authors: Chih-Ping Liou, 劉志平
• Other Authors: 林錕松
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/53686288853578243094

碩士 === 元智大學 === 化學工程與材料科學學系 === 96 === The main objectives of the present study were to prepare surface-modified zero-valent iron nanoparticles for the remediation of nitrate and nitrite in wastewater. The experimental part contains the synthesis of the material, identification and application to treat with nitrate and nitrite wastewater. Prepare surface-modified zero-valent iron nanoparticles by coating polyethyleneimine (PEI) and titania nanofilms. Coating titania part, Titanium isopropoxide (TTIP) and Tetrabutyl orthotitanate (TBOT) were used as the precursors to synthesize titania/zero-valent iron nanocomposites. Characterization of PEI/Fe(0) and TiO2/Fe(0) reacted with nitrate and nitrite wastewater were also investigated by precision instrument. In addition, this study was also carried out to provide information concerning the removal efficiencies and mechanism in the chemical reductive treatment processes for nitrate and nitrite wastewaters. By FE-SEM and TEM analyses, spherical zero-valent iron nanoparticles have a diameter around 80~100 nm. In addition, zero-valent iron nanoparticles coated with PEI in the form of spherical particles with diameter around 20-30 nm were also measured by FE-SEM and TEM microphotos. PEI/Fe(0) has a characteristic peak of Fe(0) at 2θ = 44.59o and 64.62o identified by XRD patterns and surface area of 53.4 m2/g measured by BET isotherms was also investigated. From ESCA spectra, the main species on PEI/Fe(0) surface were Fe3O4 and α-FeOOH. Using TTIP as the precursor to synthesize TiO2/Fe(0) nanocomposites, after calcined at 500oC for 2 h, the single phase of TiO2/Fe(0) nanocomposites became armophous to anatase. By TEM and FE-SEM analyses, TiO2 coating was enwrapped on the zero-valent iron nanoparticles, forming core-shell structure of TiO2/Fe(0) nanocomposites, after calcined at 500oC for 2 h, the TiO2 shell becomes relatively loose and possesses aperture structure with diameter around 20-30 nm. TiO2/Fe(0) nanocomposites has a characteristic peak of anatase TiO2 at 2θ = 25.7o identified by XRD patterns and surface area of 84.8 m2/g was measured by BET isotherms. By using X-ray absorption near edge structure (XANES), the valence and framework of TiO2/Fe(0) are similar with Ti(IV) structures. The EXAFS data revealed that TiO2/Fe(0) had a first shell of Ti-O bonding with bond distances of 1.94 Å and coordination numbers was 3.40. Using TBOT as the precursor to synthesize anatase TiO2/Fe(0) nanocomposites and without heat treatment. By TEM and SEM analyses, the core Fe(0) with diameter around 50 nm and the anatase TiO2 shell relatively loose and possesses aperture structure. TiO2/Fe(0) nanocomposites has characteristic peak of anatase TiO2 and Fe(0) at 2θ = 25.24o、37.82°、48.04° and 2θ = 25.42°、37.82°、48.04° identified by XRD patterns, respectively. Surface-modified zero-valent iron nanoparticles reaction with nitrate and nitrite solution of 60 mg/L as N. The concentrations of the nitrate and nitrite solution were decreased obviously. After 30 min, the nitrate and nitrite removal efficiency were 50 and 70%, respectively. After 3 h, the nitrate and nitrite removal efficiency reached 100%. TiO2/Fe(0) nanocomposites reaction with nitrate and nitrite solution of 60 mg/L as N. After 3 h, the nitrate and nitrite removal efficiency were only 40 and 23%, respectively. According to the mass balance of nitrogenous species during the reactions for the surface-modified zero-valent iron nanoparticles, around 70% nitrate and nitrite were converted to ammonia. It appeared that some of the nitrate and nitrite was converted to nitrogen gas.