Macroemulsion-mediated synthesis of fibrous ZnO microrods and their surface morphology contribution to the high photocatalytic degradation rate

In this work, fibrous ZnO microrods were synthesized through a macroemulsion-mediated solvothermal method using two different precursors: zinc nitrate and zinc acetate. Initially, we optimized urea concentration using the zinc acetate precursor, producing homogeneous ZnO microrods. We then applied this optimum condition to synthesize ZnO using zinc nitrate. XRD and Raman spectroscopy analyses confirmed that both precursors resulted in ZnO with a wurtzite crystal structure. Raman spectroscopy also reveals the presence of the B-1L silent mode in both samples, which is caused by crystal defects. Morphological observation using FESEM shows that both samples have rod shapes with different diameters and lengths but similar aspect ratios. Moreover, the detailed morphology indicates that the ZnO synthesized using zinc acetate has a more uniform fibrous morphology than the ZnO synthesized using zinc nitrate. The uniform fibrous morphology might be induced by the organic counterions, the acetate ion (CH3COO-), in the mixture during the synthesis process. The uniform fibrous ZnO microrod provides excellent properties, including a higher surface area, smaller bandgap energy, and higher total density of defects. The photocatalytic activity of the synthesized ZnO was determined through in situ observation using time-dependent photoluminescence spectroscopy measurements. The photocatalytic test shows that the uniform fibrous ZnO microrods have higher photocatalytic efficiency (73.82%) within 60 minutes of irradiation and a higher photodegradation rate (k = 0.1745 min(-1)). The recovery test confirmed that the ZnO_Ac_U2 photocatalyst also has higher stability. The higher photocatalytic activity might be due to the synergistic effect among the higher surface area, smaller bandgap energy, higher total density of defects, and uniform fibrous morphology. Moreover, the in situ measurement using time-dependent photoluminescence spectroscopy can collect data at decent intervals, resulting in a more reliable value of the rate constant.