Investigating structural, optical and photocatalytic properties of hydrothermally synthesized ZnO nanorod arrays with various aspect ratios

ZnO nanorods with various aspect ratios (by changing the time of growth between 0-240 min) were synthesized using hydrothermal method and were investigated using XRD, SEM, UV–Vis and PL. It was found that growth time is directly coupled with the length, orientation and aspect ratio of the nanorod arrays. The optical transmittance of the NR arrays indicated a regular decrement of average transmittance with increasing the aspect ratio of NRs in the visible range. The optical constants (absorption coefficient, extinction coefficient and refractive index) can be account as a function of refractive index were determined. The porous ZnO nanorod with the thickness of ∼ 1560 nm and texture coefficient of 0.96 for (002) plane exhibits the average visible transmittance <60%, refractive index 1.34, packing density 0.26 and lowest optical band gap, was fabricated in the longest time of hydrothermal growth (240 min). As the growth time was increased, the photoluminescence properties was sustained a general weakening tendency and a red-shift of UV-emission peak position. The UV-assisted photocatalytic degradation of 4-Nitrophenol (4-NP) of ZnO NRs were investigated. The considerable photocatalytic performance of ZnO NRs with highest aspect ratio was explained by its porosity and optical characteristics.