No abstract

Nanosized-photocatalysts with additional magnetic functionality have been studied extensively for many potential applications. Fe 3 O 4 /SiO 2 /TiO 2 core-shell nanoparticles have been evaluated as catalyst for photoreduction of aqueous solution of Ag(I) ions. The nanoparticles was prepared by coating Fe 3 O 4 with SiO 2 and TiO 2 consecutively through sol-gel process followed by microwaveassisted treatment. The prepared nanoparticles were confirmed by XRD and TEM. A photocatalytic reaction was carried out in a batch system with a UV-irradiation wavelength of 340-390 nm. The effects of catalyst loading, irradiation time and solution pH were studied. The Ag(I) photoreduction progress was monitored by AAS. The obtained Fe 3 O 4 /SiO 2 /TiO 2 core-shell nanoparticles can reduce 97% of Ag(I) in the solution whereas unmodified TiO 2 solids can only reduce 37% of the ion. The photocatalytic reaction could be best performed at pH 6, irradiation time of 2 h, and initial Ag(I) concentration of 25 mg/L. The prepared materials could be of interests in the treatment of waste containing toxic heavy metal ions.

Polyaniline (PANI)-sensitized Fe 3 O 4 /SiO 2 /TiO 2 nanoparticles were synthesized and the material then applied as a photocatalyst to reduce Au(III). The Fe 3 O 4 was synthesized through the sono-coprecipitation method using NH 4 OH as a precipitating agent. The coating of SiO 2 and TiO 2 onto the Fe 3 O 4 was then performed via a hydrolysis reaction and sol-gel process using ammonium peroxydisulfate as the initiator of the aniline polymerization. The parameters investigated in this work are the effect of medium acidity, equilibrium state and material responsiveness on visible light. The TEM images show that the photocatalyst had nanosized particles with an approximate size of 20.7 nm. The observed data from the activity test show the optimum pH and contact time of the photoreduction process were 5 and 180 minutes respectively. The effect of light exposure indicated that the polyaniline-sensitized Fe 3 O 4 /SiO 2 /TiO 2 was effective for Au(III) reduction in visible light up to 92% of the initial concentration. The effect of the material revealed that polyaniline-sensitized Fe 3 O 4 /SiO 2 /TiO 2 had better photocatalytic activity than that of TiO 2 and Fe 3 O 4 /SiO 2 /TiO 2 in visible, UV and dark conditions.

The TiO2/Fe3O4 nanoparticle has been successfully synthesized and the material is then applied as a photocatalyst to reduce Pb(II). The Fe3O4 was synthesized through sono-coprecipitation method using NH4OH as a precipitating agent. The coating TiO2 onto Fe3O4 was performed respectively via hydrolysis reaction and sol-gel process using ammonium sulfate and TTIP as a reagent of TiO2. This study investigated several parameters such as the effect of time, equilibrium state and material responsiveness toward ultraviolet light. The XRD measurement indicated the presence of Fe3O4 and TiO2 while TEM image displayed the photocatalyst had a nanosized particle with approximately 60 nm in size. An activity test at pH 4, the equilibrium of photoreduction process showed at 60 minutes. The kinetic parameter of Pb(II) reduction at various catalyst presented that TiO2/Fe3O4 nanoparticle had better reduction rate constant than that of TiO2. Reusing of TiO2/Fe3O4 photocatalysts showed the results of Pb (II) photoreduction were not significantly decrease and the results of photocatalysis were still better than TiO2.

Magnetic photocatalyst of magnetite modified titania composite Fe3O4/TiO2 was prepared by co-precipitation and sol-gel methods followed by calcination at 450 ºC. The produced material was confirmed by XRD, FTIR spectrophotometer, vibrating sample magnetometer and transmission electron microscope. The solid material was tested as a photocatalyst for degradation of nitrobenzene under UV light irradiation. The progress of degradation of nitrobenzene was monitored by using a UV-visible spectrophotometer. The photodegradation of nitrobenzene could be best realized at a medium pH of 7 and 120 min of irradiation. The reaction rate constant of nitrobenzene degradation catalyzed by TiO2 and Fe3O4/TiO2 solids were found to be 0.0058 min-1 and 0.0092 min-1, respectively. The photocatalyst was recoverable by use of a magnetic bar and reusable.