ABSTRACT
The hydrothermal dissolution-recrystallization process is a key step in the crystal structure of titania-based nanotubes and their composition. This work systematically studies the hydrothermal conditions for directly synthesizing anatase TiO2 nanotubes (ATNTs), which have not been deeply discussed elsewhere. It has been well-known that ATNTs can be synthesized by the calcination of titanate nanotubes. Herein, we found the ATNTs can be directly synthesized by optimizing the reaction temperature and time rather than calcination of titanate nanotubes, where at each temperature, there is a range of reaction times in which ATNTs can be prepared. The effect of NaOH/TiO2 ratio and starting materials was explored, and it was found that ATNTs can be prepared only if the precursor is anatase TiO2, using rutile TiO2 leads to forming titanate nanotubes. As a result, ATNTs produced directly without calcination have excellent photocatalytic CO2 reduction than titanate nanotubes and ATNTs prepared by titanate calcination.
ABSTRACT
Here, a novel method for synthesis of heterostructured TiO2-MoO3 (MT) nanosheets photocatalyst by utilizing a facile electrochemical method and examined it's photocatalytic activity by the degradation of tetracycline hydrochloride (TCH), a model of organic pollutants, in the presence of peroxymonosulfate (PMS) under solar light irradiation (SL) was reported for the first time. The influence of several factors on the degradation efficiency including the initial concentration of TCH, solution pH, catalyst dosage, PMS concentration, and the existence of inorganic anions was explored. The MT-15/PMS system displayed a promising photocatalytic performance and up to 97% of TCH was degraded in 90 min the rate of the degradation reaction of MT-15/PMS was the highest (0.05299 min-1) compared to 0.00251, 0.00337, 0.00546, 0.00735, 0.01337min-1of TiO2-P25, TiO2-P25/PMS, MoO3, MoO3/PMS, and MT-15 respectively. The enhancement can be attributed to several reasons. First, the 2D morphology of the optimized heterostructure photocatalyst plays a significant role in providing much more active sites on its surface. Next, the boosted light absorption efficiency and higher photoproduced electron-hole pair separation ability, induced by the unique direct transformation of photogenerated electrons from the valance band of TiO2 to the conduction band of MoO3 via the Ti-O-Mo bond formed at the interface of MT heterostructure. Finally, the appropriate accessible reactive sites for the activation of PMS together with the synergistic effect between activation of PMS and photocatalytic processes eased the production of active species for the degradation of pollutants. Based on the scavenger experiments and EPR analysis, hydroxide and sulfate radicals were found to be the dominant free radical active species in the degradation process. Furthermore, the synergistic degradation reaction mechanism was proposed.
Subject(s)
Environmental Pollutants , Titanium , Peroxides/chemistry , Sulfates/chemistry , Tetracycline , Titanium/chemistryABSTRACT
Design of direct Z-scheme heterojunction photocatalyst is considered as an effective strategy to fully use the high redox potential photogenerated charge carriers. This work reports a novel method for investigating the photosynergistic performance of the Z-scheme MoO3/Bi2O3/g-C3N4 (MBG) photocatalyst with peroxymonosulfate (PMS) for the solar degradation of tetracycline hydrochloride (TCH), a model of organic pollutants in wastewater. The results showed a better strategy to activate PMS via accelerating the redox cycle (Mo6+/Mo5+), which ultimately induces the successive generation of highly reactive oxygen species. The effect of dosage of the catalyst, PMS, pH of the solution, initial concentrations of TCH and the presence of inorganic anions were investigated. It was found that the degradation of the TCH under sunlight irradiation (SL) was strongly enhanced by the presence of the PMS as an electron acceptor. The MBG/PMS/SL system was able to degrade an initial concentration (40 mg/L) of the TCH solution within 140 min. The good reusability and stability of the MBG catalyst were evaluated by recycling the degradation experiment. The main free radicals are OH and SO4â which played an important role in the degradation reaction were identified by scavenger experiments and confirmed by EPR spectroscopy. X-ray photoelectron spectroscopy (XPS) study revealed the role of molybdenum ion in the activation process of PMS. The possible synergistic degradation reaction mechanism was proposed.
