Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review

Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies. The advantages of ZnO nanomaterials over other semiconductors, and their structure-dependent properties, make them important building blocks in nanotechnology as multifunctional materials. Moreover, it has been confirmed that ZnO nanomaterials can exhibit high performance in photodegradation of organic dyes for treatment of industrial effluent. The wurtzite structure of ZnO contains polar and nonpolar planes; the low surface energy and thermodynamic stability of the nonpolar planes enable formation of one-dimensional (1D) ZnO structures, which are desirable compared with zero-dimensional (0D) and two-dimensional (2D) nanoarchitectures. Also, relative to other forms, the superiority of 1D ZnO nanostructures in dye photodegradation makes them promising as a future research direction and for commercial use. Therefore, understanding the design and synthesis of 1D ZnO nanomaterials is of critical importance for the development of novel and high-performance photocatalysts. Rational design of 1D ZnO nanophotocatalysts is thus required to enhance their photodegradation activity via efficient separation of charge carriers, increased surface-to-volume ratio, enhanced light absorption capacity, and improved stability/reusability. We briefly describe herein the most widely applied synthesis methods, including vapor-phase and solution-based strategies, to understand different methods for tailoring 1D ZnO nanophotocatalysts. Moreover, to elucidate the effect of their physical/chemical properties on the photodegradation efficiency, all the modification methods are categorized into four different approaches, viz. (1) morphology control, (2) induction of defects, (3) modulation by doping, and (4) formation of hybrids and heterojunctions. An overview of all aspects of charge generation, separation, and transfer during dye photodegradation by engineered 1D ZnO nanomaterials is also provided. Graphical abstract