Research On Synthesis Of Titania Nanostructures And Their Photocatalytic Degradations Of 4-chloronitrobenzene

Organic contaminations in aquatic environment must be removed because it is a serious threat to human health and water environment. Heterogeneous photocatalysis using nanosized TiO2-based catalysts is a potential technique for degradation of such organic pollutants. Unfortunately, it is still not applied in practical wastewater treatment due to its low quantum yield, wide band gap, hard recovery and etc. In order to overcome these problems, this paper will be focused on the synthesis of nano- and/or micro-sized titania with different morphologies and their photocatalytic degradation of 4-chloronitrobenzene (4-CNB). Finally, the degradation pathway and mechanism of photocatalytic oxidation of 4-CNB will be discussed.Titanate nanorods have been successfully synthesis through a simple hydrothermal method using commercial titania powders as precursor and sodium hydroxide as solvent. The as-prepared nanorods have a diameter about 50-150 nm and the length of the rods can be reached to several micrometers, such large aspect ratio is good for separating the solid catalyst form reaction solution. The titanate nanorods process excellently stable thermal ability, which has been proved by XRD, SEM, FTIR, and BET analysis. The photocatalytic experiments showed that the photocatalytic reaction followed pseudo first-order kinetics. The titanate nanords calcined at 500°C exhibited the highest oxidation activity, which was nearly twice more than that of commercial"TIANDA"titania powder. Finally, the influence of different catalyst dosage, concentration of 4-CNB and the solution pH on the photocatalytic efficiency were investigated.Large-scale fan-shaped rutile TiO2 nanostructures have been synthesized by means of a simple hydrothermal method using only TiCl4 as titanium source and chloroform/water as solvents. Structural characterization indicates that the fan-shaped TiO2 nanostructures are composed of several TiO2 nanorods with diameters of about 5 nm and lengths of 300-350 nm. The photocatalytic acivtity was low due to its rutile phase. Nevertheless, this simple method might useful for the synthesis of other inorganic materials.TiO2 hollow microspheres were synthesized by a hydrothermal method using potassium titanium oxalate as titanium source. The TiO2 hollow microspheres, which had an average external diameter of 1.75 ?m and an average interior diameter of 1.4 ?m, were composed of numerous TiO2 nanoparticles with an average diameter of 6.5 nm. Photocatalysis experiments indicated that the TiO2 hollow microspheres calcined at 500 ?C exhibited the highest photocatalytic activity, which was about 2 and 1.5 times higher than that of the uncalcined sample and Degussa P25, respectively. In addition, it was demonstrated that these TiO2 hollow microspheres could be recycled easily without decreasing their photocatalytic activity after 6 times of use.TiO2 solid microspheres have been synthesized on large scale by a simple hydrothermal method without using any surfactants or templates. Results indicate that the TiO2 microspheres, with the diameter of 0.8-1.2μm, are composed of numerous TiO2 nanocrystals with an average diameter of 5.6 nm. The titania solid microspheres calcined at 500°C show the same photocatalytic activity to the P25. Finally, it only needed 4 h to completely separate the solid catalyst from the reaction solution by gravity.Mesoporous TiO2 microspheres were successfully fabricated by a series of hydrolysis methods using porous SiO2 as the template. The as-prepared mesoporous TiO2 microspheres process high BET surface area (376.7 cm2/g) and uniform pore distribution, both of which are good for adsorption. The adsorption rate of 4-CNB was about 90% after 1 h adsorption.Core/shell/shell structured Fe3O4/SiO2/TiO2 composites with enhanced photocatalytic activity and fast magnetic separation have been successfully synthesized through a serial of sol-gel processes. The as-obtained core/shell/shell structure is composed of a central magnetite core with an average diameter of ca. 200 nm, interlayer of silica with a thickness of ca. 59 nm, and an outer layer of titania with a tunable thickness range from ca. 12.6 to 14.7 nm. Thanks to the interlayer of SiO2, the chemical and thermal stability of Fe3O4 core, as well as the photocatalytic efficiency of the TiO2 shell were significantly enhanced, respectively. Photocatalysis experiments showed that the photocatalytic efficiency of the Fe3O4/SiO2/TiO2 calcined at 500°C was higher than that of commercial photocatalyst Degussa P25. The photocatalytic activity increases with a decreased thickness of the TiO2 shell. In addition, it was demonstrated that the Fe3O4/SiO2/TiO2 composites could be recycled easily by applying an external magnetic field without decreasing their photocatalytic activity during eighteen cycles of use. It will be an ideal recyclable catalyst for wastewater treatment in the future.The photocatalytic degradation of 4-CNB was studied using powder TiO2 as photocatalyst under different atmospheres (nitrogen, oxygen, and ozone). The total organic carbon (TOC) and inorganic anions (chloride, nitrate, and nitrite anions) were measured to monitor the mineralization process, while the degradation of 4-CNB and the formation of intermediates were followed by HPLC and LC–MS, respectively. Several free radicals such as·OH and·O2- were detected and identified in these three different photocatalytic reaction systems by using electron paramagnetic resonance (EPR) technique.