Effect of cetylpyridinium chloride on surface passivation and photocatalytic activity of ZnO nanostructures

• Surfactant-assisted synthesis of shape-controlled ZnO nanostructures.
• Use of cetylpyridinium chloride favors the formation of pyramidal-shaped particles.
• Defect band intensity changes with the change in shape of ZnO particles.
• Amount of defect strongly influences photocatalytic activity of ZnO nanostructures.
• Recyclable photocatalyst for the degradation of organic contaminants under UV light.

We report a facile soft-chemical approach for the preparation of water dispersible ZnO nanostructures by using cationic surfactant, cetylpyridinium chloride (CPC) as a shape directing agent. XRD and TEM analysis reveal the formation of highly crystalline single-phase hexagonal wurtzite ZnO nanostructures. It has been observed that the addition of surfactant strongly affects size and shape of ZnO particles. The presence of CPC predominantly favors the formation of pyramidal-shaped nanoparticles (10–20 nm), whereas roughly spherical nanoparticles (∼10 nm) were formed in absence of CPC. These ZnO nanostructures show good aqueous colloidal stability, which is important for their photocatalytic applications. Optical studies confirmed that the concentration of CPC controls both bandgap and intensity of defect-related emission of ZnO nanostructures. Further, we have explored the photocatalytic activity of these ZnO nanostructures using methyl orange and methylene blue as model dyes. It has been observed that the concentration of defect present on the surface of ZnO nanostructures strongly influences the photocatalytic degradation of organic dyes. The nearly complete mineralization of treated organic dye by ZnO photocatalyst was confirmed from the significant reduction in chemical oxygen demand (COD) values. Further, the photodegradation efficiency of organic dye is also found to be dependent on other parameters, such as nature and concentration of dye and amount of photocatalyst. More ever, these nanostructures could be promising recyclable photocatalyst for degradation of organic contaminants under UV light.