Ash based nanocomposites for photocatalytic degradation of textile dye pollutants: A review

Ash is a highly available industrial and agricultural waste by-product. Giving insights into the huge generation of ash and environmental concern of disposal issue, aesthetic attention has been drawn on the sustainable utilization of ash as a renewable supporting material in the synthesis of photocatalytic nanocomposites. Coal fly ash, rice husk ash and volcanic ash are currently being investigated for their potential to be applied as an effective precursor material for photocatalyst preparation, owing to their advantages of high adsorption capability, high ion-exchange capacity, significant specific surface area and high reusability. The novelty of these studies is that prepared ash based photocatalysts could provide a synergistic effect of the adsorption capacity of ash and the photocatalytic activity of photocatalysts to enhance the overall degradation efficiency of dye. Exploring the possible usage of these abundant by-products not only solving the environmental problem but also highlighting its further economic value of utilization with the concept of "waste to wealth". This paper presents a fundamental information pertaining to the basic principles of photocatalysis and semiconductor based photocatalysts. A brief overview of the role of ash based nanocomposites in terms of the preparation methods and conditions, morphologies, physiochemical properties and their photocatalytic performances on the degradation of dye pollutants is highlighted. The optimization, mechanism and stability study are also reviewed. The finding showed that the porous structure and the presence of aluminosilicate in the ash greatly enhance the adsorption capacity of the total composite in the dye degradation process. The photocatalytic performance was dependent on the calcination temperature, catalyst loading, solution pH, initial dye concentration and light source. However, reusability test indicated the high stability of the prepared ash based composites, with most of the dye degradation efficiency greater than 80% even after a few successive regeneration cycles.