Effect of the pH of an Aqueous Solution on the Structural, Optical, and Photoresponse Properties of Hydrothermally Grown ZnO Nanorods and the Fabrication of a High Performance Ultraviolet Sensor

Of the various parameters related to the hydrothermal method for growing ZnO nanorods, the pH of the aqueous solution has a pronounced effect on the growth rate, morphology, and photoresponse of the fabricated ZnO nanorods. Here, we investigated the effects of the pH of the aqueous solution on the structural, optical, and photoresponse properties of hydrothermally grown ZnO nanorods. When the pH of the solution was kept at 8, the ZnO nanorods exhibited improved vertical orientation, a higher growth rate, and directional growth along the (002) plane confirmed by scanning electron microscopy. In contrast, the growth rate of the ZnO nanorods grown at a pH of 10 was lower, as the ZnO nanorods were dissolved because of the presence of excessive OH (-) ions in the solution. The ultraviolet (UV) sensor based on the ZnO nanorods grown at a pH of 8 showed higher photoresponsivity as compared to those of the sensors based on the ZnO nanorods grown at pH values of 7, 9, and 10. Thus, the use of an aqueous solution with the optimal pH values (8 in this case) resulted in uniform ZnO nanorods, which could be employed to fabricate a high-performance UV sensor suitable for use in practical applications.