. Introduction
Water is the major resource of life on the earth; as a consequence, sustainable growth of civilization is heavily influenced by availability of water resources with the required quality. In modern civilization, inadequate assess to clean water and sanitation are two most pervasive problem leading to water scarcity, even in the regions currently considered as water rich[1-3]. Estimated 1.2 billion people lack access to safe drinking water; millions of people die annually- 3900 children per day from the diseases transmitted through unsafe drinking water [4-6]. In both developing and industrialized nations, a growing number of contaminates are entering in fresh water; from traditional compounds to micro/nano pollutants. Common …show more content…
However, the main limitations for large scale practical applications of semiconductor oxide photocatalysts are as follows: (1) high recombination rate of electronic–hole pairs resulting in low quantum yield for binary metal oxide photocatalyst. (2) The limitation in the harvesting of visible light. Generally, wide bandgap semiconductor oxides are employed as photocatalysts, for example, the bandgap value of anatase TiO2 is 3.2 eV, and the corresponding absorption wavelength is 387.5 nm, resulting in limited light absorption of the UV region [31-34]. However, the solar spectrum comprises of only 5–7% of UV light, while 46% and 47% of the spectrum consists of visible light and infrared radiation, respectively. (3) Poor selective adsorption of organic pollutants from aqueous phase [35]. (4) The photocatalytic treatment of a high concentration of organic pollutants from industrial waste poisons the photocatalyst resulting in deactivation [36]. (5) Difficult isolation and recovery of photocatalysts from the reaction mixture is not easy. Conventional technique such as filtration and sedimentation are not efficient because of the nano-size of the photocatalyst particles. This limitation hinders the economics and sustainability of heterogeneous photocatalyst for water purification process [37-39]. Furthermore, immobilization of photocatalyst on different supports also reduces the effective surface are for photocatalytic reaction thus reducing the overall efficiency of photocatalytic system. So, an ideal and green heterogeneous phtotocatalyst must therefore possess some unambiguous features including stability in aqueous phase, high activity, chemical inertness, low-cost, photostability, non-toxicity, efficient recovery and reasonable recyclability for efficient water purification process