Competitive photo-degradation performance of ZnO modified bentonite clay in water containing both organic and inorganic contaminants

This study reports the activity difference of zinc oxide modified bentonite clay (Photo-Zn-Bent) photocatalyst when in contact with different environmentally toxic pollutants in a single component and bi-component pollutant systems. The layered structure of purified and swollen nano-bentonite clay (Bent) has tunable interlayer spacing to grow zinc oxide (ZnO) nanoparticles, thereby integrating the adsorbing nature of clay and semiconductor property of ZnO in one hierarchical structure. Initial adsorption studies using methylene blue (MB) showed that the adsorption capacity of Photo-Zn Bent is greater than Bent and ZnO. The photocatalytic pollutant degradation activity of Photo-Zn Bent is compared with ZnO using both single component and bi-component pollutant systems (MB, phenol, mixture of MB and phenol, mixture of phenol and Cr(VI)). We found that Photo-Zn Bent displayed 33% greater MB degradation rate compared to ZnO. Photodegradation efficiency of Photo-Zn-Bent considerably differs for inorganic-organic and organic-organic bicomponent pollutant systems. In bicomponent systems, photodegradation rate of phenol decreased to an extent of 88% in the presence of MB, and increased to 31% in the presence of Cr(VI). On the other hand, photodegradation rate of MB remains unaffected in the presence of phenol, but increased to 56% in the presence of Cr(VI). However, if used in bicomponent pollutant systems for simultaneous cycles, Photo-Zn Bent showed lesser activity after 3 cycles, which in turn gave further insight on to the decay of catalyst with respect to the nature of pollutants.