ABSTRACT
In the last decade, the rapid growth in urbanization and industrialization resulting in the production of numerous hazardous pollutants, like gas fumes, smoke, dyes, and persistent organic pollutants, due to which environmental pollution has risen to its maximum. Inappropriate dumping of industrial effluents and poor waste-water management are the major factors that are responsible for the increase in water pollution at a frightening level. According to the reports of WHO, approximately 80% of diseases are water-borne and around 3.1% of deaths occur due to unhygienic water. So, there is an urgent need to improve the quality of water. Treatment of pollutants present in wastewater is a challenging task, so in this regard, several technologies have been developed. Among all the reported technologies, photocatalytic treatment of wastewater by utilizing nanoscale semiconductors possesses several advantages due to the large surface area and high surface activity of nanoparticles and utilization of solar energy. Apart from possessing appropriate band-gap energy, an ideal semiconductor should possess properties, such as excellent photo-activity, biological and chemical non-reactivity, ability to utilize a broad solar spectrum and inexpensive non-toxic. According to the literature, TiO2 not only possesses the characteristics of an ideal semiconductor but also appears as one of the most efficient photocatalysts, which is able to mineralize many of the organic pollutants existing in wastewater completely. However, TiO2 faces few drawbacks such as it can absorb photons only under UV radiation and easy recombination of the photogenerated electrons and holes occurs. A few countermeasures have been suggested to extend the wavelength range of the photo-activation toward the visible light region in order to utilize solar energy by modifying TiO2 photocatalyst via doping and coupling to reduce pollutant levels in aqueous streams. There are numerous factors, like the intensity of light, nature of photocatalyst, dopant concentration, initial concentration of the pollutants, and pH of the waste-water, which govern the photocatalytic degradation of pollutants present in wastewater are also discussed.
