Novel microwave assisted synthesis of ZnS nanomaterials.

A novel ambient pressure microwave assisted technique is developed in which silver and indium-modified ZnS is synthesized. The as-prepared ZnS is characterized by x-ray diffraction, UV-vis spectroscopy, x-ray photoelectron spectroscopy and luminescence spectroscopy. This procedure produced crystalline materials with particle sizes below 10 nm. The synthesis technique leads to defects in the crystal which induce mid-energy levels in the band gap and lead to indoor light photocatalytic activity. Increasing the amount of silver causes a phase transition from cubic blende to hexagonal phase ZnS. In a comparative study, when the ZnS cubic blende is heated in a conventional chamber furnace, it is completely converted to ZnO at 600 °C. Both cubic blende and hexagonal ZnS show excellent photocatalytic activity under irradiation from a 60 W light bulb. These ZnS samples also show significantly higher photocatalytic activity than the commercially available TiO(2) (Evonik-Degussa P-25).

Effect of N-doping on the photocatalytic activity of sol-gel TiO2.

In order to study the visible light photocatalytic activity of nitrogen doped titanium dioxide, the interaction between nitrogen dopant sources and titania precursors during sol-gel synthesis is investigated. N-TiO(2) was synthesised using the sol-gel method using 1,3-diaminopropane as a nitrogen source. Samples were annealed several temperatures and the percentage of rutile present determined by X-ray diffraction to be 0% (500°C), 46% (600°C), and 94% (700°C). The reducing amounts of anatase at higher temperatures are studied using FTIR, which suggests the absence of any polymeric chains formed by the chelating agents, which would normally extend anatase-to-rutile transformation temperatures. Differential scanning calorimetry shows that crystalliation occurs before 500°C, providing the crystalline form determined by XRD at 500°C. Increased temperature also resulted in diminished visible light absorption capability, with only the 500°C sample showing significant absorption in the visible region. XPS studies revealed that nitrogen remained within the TiO(2) lattice at higher temperatures. Consequent with the reduced visible light absorption capacity, photocatalytic activity also reduced with increased annealing temperature. Degradation kinetics of methylene blue, irradiated with a 60 W house-bulb, resulted in first order degradation rates constants of 0.40 × 10(-2), 0.19 × 10(-2), and 0.22 × 10(-2)min(-1) for 500, 600, and 700°C respectively. Degradation of Degussa P25 was minimal under the same conditions, and that of undoped TiO(2) was 0.02 × 10(-2)min(-1). Similarly, using 4-chlorophenol under solar irradiation conditions, the N-doped sample at 500°C substantially out-performed the undoped sample. These results are discussed in the context of the effect of increasing temperature on the nature of the band gap.