Novel microwave assisted synthesis of ZnS nanomaterials

Abstract

A novel ambient pressure microwave-assisted technique is developed in which silver and indium modified ZnS is synthesised. The as prepared ZnS is characterised 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 watt light bulb. These ZnS samples also show significantly higher photocatalytic activity compared to the commercially available TiO 2 (Evonik-Degussa P-25).

Solar photocatalysis for water disinfection: materials and reactor design

“…Disinfection of drinking water using solar energy is not a recent development and has been practiced in ancient cultures for centuries. McGuigan et al 3 has recently traced the historical 15 development of solar water disinfection. SODIS, more specifically, is a procedure which uses only sunlight and plastic bottles, designed for drinking water purification in remote regions in which sunlight is plentiful.…”

“…The major challenge remains the significant time (up to 6 hours) taken to fully inactivate the pathogens in water. Furthermore, only small bottle-sized volumes 15 of water can be treated in the SODIS protocol, described above. Another disadvantage is the variation in treatment time recently highlighted by Byrne et al 4 The treatment time is dependent on a number of variable factors such as solar irradiance and starting water quality.…”

“…However, introduction of artificial UV light sources is not practical in remote areas where there is a lack 70 of power supplies. Utilisation of the main part of the solar spectrum by the development of photocatalysts (Figure 2) that can yield high photocatalytic activity under visible light 7,[11][12][13][14][15][16][17][18][19][20][21] would be highly beneficial in remote regions. Hydroxyl radicals have the most positive electrochemical 10 reduction potential (+2.8 V vs. normal hydrogen electrode (NHE)) among other substances generally employed for water disinfection, e.g.…”

“…TiO 2 photocatalysis, therefore, has real potential for disinfection of resistant microorganisms. 7,[22][23][24][25][26] In addition to the hydroxyl radicals, other 15 oxidative species such as superoxide anions and singlet oxygen can also be created ( Figure 2). The first report of TiO 2 photocatalytic inactivation of bacteria was in 1985 by Matsunaga et al 27 , and since then a large number of microorganisms have been reported to be photocatalytically 20 inactivated.…”

“…Glass cylinders were coated with TiO 2 using a previously characterised sol-gel method 39 and annealed at 500 °C. This cycle was repeated three times resulting in a thin film of average 15 thickness of 600 nm crystallized in the anatase phase. Photodegradation of 4-chlorophenol and carbaryl under solar irradiation in a parabolic solar collector was found to be comparable to P25 TiO 2 in suspension.…”