Preparation of ZnO from 2 D nanosheets to diverse 1 D nanorods and their structure, surface area, photocurrent, optical and photocatalytic properties by simple hydrothermal synthesis

Two–dimensional (2 D) ZnO nanosheets and one–dimensional (1 D) bud−like, grenade−like, prism−like, bamboo−like, brush−like, arrow−like, pencil−like, drip pipe−like, baseball bat−like, gear−like, walking stick−like, taper−like, shuttle−like, and/or hollow tower−like ZnO nanorods (nanotubes) with various tips were synthesized by a simple hydrothermal route from the system of CO(NH2)2N2H4. All the samples exhibit the wurtzite structure of ZnO. With the increase of the amount of N2H4 or decrease of CO(NH2)2, the interplanar spacing of different planes of ZnO increases or decreases simultaneously. FTIR shows that except the nanosheets of S1, all other samples are pure. The average reflectance of S8 reaches about 85% in the wavelengths ranging from 450 to 550 nm, and the reflectance of S3 is about 75%. The Eg values of ZnO from S1–S8 are 3.234, 3.215, 3.223, 3.215, 3.230, 3.243, 3.230 and 3.234 eV respectively. Raman spectra of S1 and S2 are obviously different from those of S3–S8. PL spectra of the ZnO samples exhibit a dominant UV luminescence peak of S1–S7, especially that of S1, S2 and S4. The addition of N2H4 can suppress the defects on the ZnO surface. However, the decrease of CO(NH2)2 introduces the defect. The BET surface area shows that except S1 (55.3 m2/g), S5 is a center of symmetric distribution of surface areas of S2–S8. From above discussion, the density, PL intensity of UV emission, and BET surface area of the ZnO nanorods can be easily tuned by controlling the concentrations of N2H4 and CO(NH2)2. The average values of photocurrent density of S1−S8 are 0.059, 0.170, 0.137, 0.184, 0.215, 0.091, 0.465 and 0.152 μA/cm2, respectively. S4, S2 and S7 possess the rapid photocatalytic activities and decompose 65%, 55% and 50% of MB within 50 min respectively. The order of the average diameters of S3, S4, S5, S6, and S7 agrees with that of photocatalytic efficiency, indicating that the polar (002) plane and/or the nanorod tips affect the photocatalytic activity. The decrease of the amount of CO(NH2)2 introduces the defects, which affects the photocatalytic activity of S8.