Based on increased contamination and pure water demand, water purification (from chemical contaminants) and disinfection (from microorganisms) is a common practice. Different methods are used, such as chlorination, ozonation, heating, adsorption and others. However, each of these methods has advantages and shortcomings.  Cost and hazardous side products are examples of such difficulties. To avoid such shortcomings, more economic and environmentally friendly processes are being assessed, most notably solar energy driven mineralization of the contaminants and organisms. The solar process demands photo-catalysts that are safe, economic, re-usable and soundly effective. Semiconductors nanoparticles are studied, such as ZnO nano-particles, and show high promise.  Unfortunately, these systems have high band gap values (~3.2 eV) and demand radiations in the UV region, which is not highly present in the oncoming solar radiations (only ~5%).  Therefore, researchers need to either use the 5% UV tail or activate the semiconductor particle with sensitizers. Both strategies have been examined in these laboratories. ZnO nano-particles exhibit soundly high efficiency in water disinfection from both Gram+ and Gram– bacteria.  Sensitizing ZnO nano-particles to visible solar light has also been effective. Quantum dot particles (such as CdS) and metal-based molecules (such as ruthenium compounds) were reported in solar energy conversion (Graetzel solar cells) and water purification. As per water purification purposes, we have found that such sensitizers should not be used as they may degrade into hazardous materials in water. Replacing such synthetic sensitizers with natural product dyes, commonly used in food and beverage, have been investigated here. Examples are anthocyanin and curcuma dyes. These two natural dyes have been anchored to ZnO nano-particles. The resulting composites have been characterized and effectively examined in visible light photo-degradation of different water organic contaminants, such as phenols, chlorinated phenols, waste pharmaceuticals, pesticides and other organics. Moreover, the sensitized particles are effective in killing and for the first-time complete mineralizing of bacteria in water leaving no organic stuff. The natural dye sensitizer itself does not yield hazardous organics as it degrades away into minerals. Regeneration of the sensitized photo-catalyst can be achieved by adding trace amounts of the photo-catalytic suspension.  Results on different organic contaminant degradations and bacterial complete mineralization will be presented, together with mechanistic models. Methods to recover the nano-particles from the purified water will also be presented. Fate of the sensitizer molecules themselves will be discussed. Ability of some contaminant molecules themselves to self-sensitize their own photo-degradation will be also highlighted. Future prospects of using natural dye sensitizers in wide scale water purification and establishing joint collaboration will also be discussed.        

Key words: Natural Dye sensitizers; Photo-catalysis; Water purification & disinfection; ZnO; Self-sensitizaion.

Conference Title

INTERNATIONAL CONFERENCE ON ENERGY, ENVIRONMENT AND STORAGE OF ENERGY

Conference Country

Turkey

Conference Date

June 5, 2020 - June 7, 2020

Conference Sponsor

Erciyes University, Erciyes, Kayseri, Turkey

Additional Info

Conference Website