Solar light based degradation of organic pollutants using ZnO nanobrushes for water filtration

In this work, we report an effective water filtration system based on the photocatalytic performance of semiconducting dense nano-brushes under natural sunlight. During thin-film photocatalysis, which is usually performed by a deposited layer of photocatalyst, a stagnant boundary layer is created near the catalyst which adversely affects the rate of adsorption because of diffusional restrictions. One strategy that may be used is to disrupt this laminar boundary layer by creating a super-dense nanostructure near the surface of the catalyst. Furthermore, it is useful to fabricate a structured filter element for the passage of water with the use of nanostructures protruding out of the surface. Herein, dye remediation is performed by solar means. This remediation was initially limited to a lower efficiency because of diffusional restrictions but has now become a fast process due to microhole incorporation in the filter materials with protruding dense nanostructures. Theoretical analysis predicts that there is an optimal film thickness that yields the maximum adsorption and also a highly nonlinear behaviour of diffusivity with respect to the fraction adsorbed. The effect of increased surface area due to microholes on the fraction adsorbed is also investigated and it is found that there is an optimum value of hole diameter for maximum adsorption.