Comparison and mechanism of photocatalytic activities of N-ZnO and N-ZrO2 for the degradation of rhodamine 6G

Abstract

N-doped ZnO (N-ZnO) and N-doped ZrO2 (N-ZrO2) are synthesized by novel, simple thermal decomposition methods. The catalysts are evaluated for the degradation of rhodamine 6G (R6G) under visible and UV light. N-ZnO exhibits higher dye degradation under both visible and UV light compared to N-ZrO2 due to possessing higher specific surface area, lower crystalline size, and lower band gap. However, it is less reusable than N-ZrO2 and its photocatalytic activity is also deteriorated at low pH. At the same intensity of 3.5 W/m(2), UVC light is shown to be a better UV source for N-ZnO, while UVA light is more suitable for N-ZrO2. At pH 7 with initial dye concentration of 10 mg/L, catalyst concentration of 1 g/L, and UVC light, 94.3 % of R6G is degraded by N-ZnO within 2 h. Using UVA light under identical experimental conditions, 93.5 % degradation of R6G is obtained by N-ZrO2. Moreover, the type of light source is found to determine the reactive species produced in the R6G degradation by N-ZnO and N-ZrO2. Less oxidative reactive species such as superoxide radical and singlet oxygen play a major role in the degradation of R6G under visible light. On the contrary, highly oxidative hydroxyl radicals are predominant under UVC light. Based on the kinetic study, the adsorption of R6G on the catalyst surface is found to be the controlling step.

The interplay between morphology and photocatalytic activity in ZnO and N-doped ZnO crystals

“…In this way, the N percentage in this method synthesis could be considered elevated [52,80,81]. [30,46,47] Sudrajat and Babel [53] confirmed that adsorption of Rhodamine 6G on the ZnO:Nmaterials surface is the rate determining step in the degradation mechanism. In this way, SSA and the availability of surface functional groups play a crucial role in the photocatalytic activity of ZnO:N. Moreover, the same authors showed that highly oxidative hydroxyl radicals are principallyresponsible for Rhodamine 6G degradation under UV light.…”

“…The results allow the essential comprehension of the dye degradation mechanism associated with the photocatalytic activity of the generated p-type semiconductor [52]. Sudrajat and Babel [53] successfully synthesized ZnO:N and ZnO 2 :N materials and compared the mechanism of their photocatalytic activities for the degradation of Rhodamine 6G. From these works, it is possible to conclude that not only specific surface area, band gap values, midgap energetic levels (energetic inner levels) created by the doping process influence the photocatalytic activity of materials, but also morphology plays a major role in defining the semiconductor properties.…”

“…In this way, SSA and the availability of surface functional groups play a crucial role in the photocatalytic activity of ZnO:N. Moreover, the same authors showed that highly oxidative hydroxyl radicals are principallyresponsible for Rhodamine 6G degradation under UV light. On the other hand, superoxide radical and singlet oxygen which is classified as less oxidative reactive species play a major role in Rhodamine 6G mechanism degradation under visible light [53].…”

A novel visible light active N-doped ZnO for photocatalytic degradation of dyes

“…To study the effect of operating parameters on the dye degradation by N-ZnO under visible and UVC light, the experiments were performed by varying key operating parameters, namely, dye concentration (5-25 mg/L), catalyst concentration (0.5-2.5 g/L), pH (5)(6)(7)(8)(9), and salinity (0.3-9.6 g/L NaCl). The kinetics of dye degradation were studied by adopting the Langmuir-Hinshelwood pseudo first order kinetic model.…”

“…Among semiconductors, ZnO appears suitable for photocatalysis applications [4][5][6]. Due to its lower cost, higher mobility of charge carriers, and ability to absorb a larger fraction of solar spectrum, ZnO is often preferred to TiO 2 [7].…”