Impact on the Photocatalytic Dye Degradation of Morphology and Annealing-Induced Defects in Zinc Oxide Nanostructures

Abstract

In this study, three different morphologies, nanoflower (NF), nano sponge (NS), and nano urchin (NU), of zinc oxide (ZnO) nanostructures were synthesized successfully via a mild hydrothermal method. After synthesis, the samples were annealed in the atmosphere at 300, 600, and 800 °C. Although annealing provides different degradation kinetics for different morphologies, ZnO NS performed significantly better than other morphologies for all annealing temperatures we used in the study. When the photoluminescence, electron paramagnetic resonance spectroscopy, BET surface, and X-ray diffraction analysis results are examined, it is revealed that the defect structure, pore diameter, and crystallinity cumulatively affect the photocatalytic activity of ZnO nanocatalysts. As a result, to obtain high photocatalytic activity in rhodamine B (RhB) degradation, it is necessary to develop a ZnO catalyst with fewer core defects, more oxygen vacancies, near band emission, large crystallite size, and large pore diameter. The ZnO NS-800 °C nanocatalyst studied here had a 35.6 × 10–3 min–1 rate constant and excellent stability after a 5-cycle photocatalytic degradation of RhB.

Phase controlled green synthesis of wurtzite (P63mc) ZnO nanoparticles: interplay of green ligands with precursor anions, anisotropy and photocatalysis

“…The smaller difference in the UV absorption shift (Fig. 11a) in the case of Zn-SL and Zn-NR, while the slightly higher difference in the case of Zn-AC after adsorption–desorption equilibrium indicate the differences in the extent of adsorption of dye on the catalyst surface primarily due to the different morphologies of the catalysts or the polar (002) or non-polar (100) facets of the wurtzite ( P 63 mc ) crystals, as reported by Kislov and Mclaren et al 20,47,52 This observation is also consistent with the pseudo-first order kinetics of dye degradation (Fig. 11b) with a nearly linear fit ( R 2 of 0.95–0.99) of the time ( t ) vs. ln( C / C 0 ) curve.…”

“…This clearly indicates that in the absence of the catalyst, the necessary OH˙ radicals leading to the degradation reaction were supplied through homolytic fission of the peroxide linkage in H 2 O 2 by the sunlight. 47,55–58 The proposed mechanism for the degradation process is given below. 56 ZnO + hv (sunlight) → ZnO (h + ) + ZnO (e − )ZnO (h + ) + H 2 O → OH˙ + H + ZnO (e − ) + O 2 → O 2 ˙ − O 2 ˙ − + H 2 O → OOH˙ + OH − OOH˙ + H 2 O → OH˙ + H 2 O 2 H 2 O 2 + hv → OH˙ + OHOH˙ + RhB (dye) → CO 2 + H 2 O…”

“…S2 and S1 †) very high rates constants "k" (Table S1 †) in the range of 0.28606 to 1.81453 min −1 with nearly 100% RhB degradation in just 75 min by the Zn-AC catalyst, which is higher rate (Table 3) than that in previous studies. 47 The large difference in the degradation percentage (rate constant "k") under dark and light conditions indicates the underlying fundamental mechanism of dye degradation, where the initiation of the process as the rst step is the absorption of light by the catalyst for the generation of charge carriers, i.e., electron-hole pairs. 48 On the contrary, the 10% degradation of the dye under dark conditions may be due to the residual absorption of light during the whole experiment.…”

TiO2 Phase Ratio’s Contribution to the Photocatalytic Activity

“…Dyes such as thymol blue, carmine, indigo red, red 120, rhodamine B, methylene blue, and eriochrome black-T are most often used in the textile industry . When they get into wastewater, they become dangerous and cause serious harm to aquatic flora, fauna, and humans. , Photocatalysis is a well-known method, and its history began at the beginning of the 20th century. − However, it reasonably still attracts a lot of attention as an advanced oxidation process used for the photodegradation of toxic compounds and dyes. − To ensure a photocatalytic process, two conditions must be met, using light as an electron exciter and a semiconductor as a process catalyst. Simultaneously, photocatalysts must have electronic structure, charge transport characteristics, and light-absorbing properties.…”

Recent Advances in Photochargeable Integrated and All-in-One Supercapacitor Devices

“…Research in the conversion and storage of renewable energy has gained vast acceleration since 2008 with the global energy crisis regarding environmental issues and economic depression due to the exploitation of carbon-based fuels. − On the basis of the report of the International Energy Agency (IEA), the capacity of renewable energy is expected to double in the next five years to decrease the use of coal in the electricity generation process to keep global warming at 1.5 °C . Thanks to the enormous development in materials science and high-tech energy systems, many sustainable energy applications have been reported by incorporating hydropower, biomass, geothermal, wind, solar, and ocean energies. , Among all, solar power is the most valuable renewable energy source as it is a continuous power supply to the Earth (3.8 × 10 23 kW). , Therefore, the scientific community has been urged to seek new developments to utilize solar power for energy conversion and storage applications, such as photovoltaic (PV) devices, typically solar cells; − photoelectrochemical (PEC) H 2 generation; − photocatalytic systems; − photorechargeable batteries; − and optoelectronics. , Although solar light can be used directly, its unbalanced intermittency regularly affects energy harvest, and a huge energy potential remains untapped. Thus, capturing, converting, and storing solar energy in a single and compact system is of great interest for long-term solution.…”