Synergistic effect of anisotropic ZnO nanoparticle shape on its photocatalytic performance for drug degradation in water

Increasing environmental issues have emerged due to various pharmaceutical wastes. These wastes are difficult to remove by treatment due to their continuous consumption and long-term persistence. We have synthesized two different shapes of zinc oxide (ZnO) nanoparticles as catalysts—nanorod (ZnO–NR) and oval-shape (ZnO–OS). A comparative performance of these two catalyst shapes on photocatalytic degradation of rifampicin (RIF) in water—a first-line anti-tuberculosis drug, was carried out. ZnO–NR showed three times higher normalized first-order degradation rate constant of RIF under UV light than that with ZnO–OS. This is due to: (i) specific surface area and specific pore volume of ZnO–NR being 25 and six times higher, respectively, than ZnO–OS; (ii) oxygen vacancy in ZnO–NR being 1.7 times higher than ZnO–OS; (iii) slightly lower band gap energy in ZnO–NR than ZnO–OS, adding to carrier concentration; and (iv) ZnO–NR additionally showing 12.4% chemisorbed oxygen also. Towards RIF degradation, ZnO–NR shows a much improved synergistic effect than ZnO–OS under UV light, as ZnO–NR under UV light is found to give 2.7 times higher degradation than when the catalyst and UV act independently and hence only additively. Therefore, this study is helpful in tuning the shape-dependent chemical reactivity of nanoparticles in water treatment.