Enhanced Photocatalytic Degradation of Perfluorooctanoic Acid by Mesoporous Sb2O3/TiO2 Heterojunctions

Abstract

Perfluorooctanoic acid (PFOA), a typical perfluorinated carboxylic acid, is an emerging type of permanent organic pollutants that are regulated by the Stockholm Convention. The degradation of PFOA, however, is quite challenging largely due to the ultra-high stability of C-F bonds. Compared with other techniques, photocatalytic degradation offers the potential advantages of simple operation under mild conditions as well as exceptional decomposition and defluorination efficiency. Titanium dioxide (TiO2) is one of the most frequently used photocatalysts, but so far, the pristine nanosized TiO2 (e.g., the commercial P25) has been considered inefficient for PFOA degradation, since the photo-generated hydroxyl radicals from TiO2 are not able to directly attack C-F bonds. Mesoporous Sb2O3/TiO2 heterojunctions were therefore rationally designed in this work, of which the confined Sb2O3 nanoparticles in mesoporous TiO2 framework could not only tune the band structure and also increase the number of active sites for PFOA degradation. It was found that, after loading Sb2O3, the absorption of UV light was enhanced, indicating a higher efficiency of light utilization; while the band gap was reduced, which accelerated the separation of photo-generated charge carriers; and most importantly, the valence band edge of the Sb2O3/TiO2 heterojunction was significantly lifted so as to prevent the occurrence of hydroxyl radical pathway. Under the optimal ratio of Sb2O3–TiO2, the resulting catalysts managed to remove 81.7% PFOA in 2 h, with a degradation kinetics 4.2 times faster than the commercial P25. Scavenger tests and electron spin resonance spectra further revealed that such improvement was mainly attributed to the formation of superoxide radicals and photo-generated holes, in which the former drove the decarboxylation from C7F15COOH–C7F15•, and the latter promoted the direct electron transfer for the conversion of C7F15COO−–C7F15COO•. The Sb2O3/TiO2 photocatalysts were highly recyclable, with nearly 90% of the initial activity being retained after five consecutive cycles, guaranteeing the feasibility of long-term operation.

Innovative Nanocomposites for Enhanced Photocatalytic Removal of Hazardous Pollutants: Probing the Role of CuO/Fe2O3 and MXene Synergy

“…The photocatalytic performance strongly depends upon the band gap energy, morphology, surface modification, and active sites for the adsorption process. First, 2D sheets of MXene facilitate the fastest charge transport proficiency and offer a large surface area, the MXene became a good supporting agent for CF composite and significantly improved the adsorption ability of CF/MXene composite. , Second, introducing CF into MXene nanosheets avoids the restacking of MXene layers and increases the surface area of the ternary nanocomposite. Third, MXene, with outstanding electric conductivity, has the potential to capture excited electrons, act as a good electron transporter, and move the charges toward reactive sites for chemical reactions.…”

Research Updates on the Mechanism and Influencing Factors of the Photocatalytic Degradation of Perfluorooctanoic Acid (PFOA) in Water Environments

“…Yao et al selected a removal rate of PFOA between 20 and 120 min to calculate degradation kinetics and the process of pseudo-first-order kinetics and mesoporous TiO 2 films of 6.3 × 10 −3 min −1 and 3%-Sb 2 O 3 /TiO 2 12.6 × 10 −3 min −1 [46]. It was found that with the addition of 3.6 mmol/L of the PFOA, the degradation rate constantly increases from 0.48/h to 0.88/h [30,87].…”

Insights into Photo/Electrocatalysts for the Degradation of Per- and Polyfluoroalkyl Substances (PFAS) by Advanced Oxidation Processes

“…Based on the mechanisms of photocatalytic AOPs for PFAS degradation, strategies for constructing photocatalysts to enhance the degradation process can be summarized as follows: (1) increase the yield of ROS through element doping, introducing heterojunctions, etc. [26,[70][71][72][73]; (2) increase the rate of reaction between ROS and PFASs by using composite materials and controlling their morphology [38]; and (3) expand degradation pathways by generat- In electrocatalytic processes, oxidation primarily occurs on the anode. Therefore, the choice of anode materials (i.e., electrocatalysts) plays a crucial role in electrocatalytic AOPs for PFAS degradation.…”

“…(1) increase the yield of ROS through element doping, introducing heterojunctions, etc. [26,[70][71][72][73]; (2) increase the rate of reaction between ROS and PFASs by using composite materials and controlling their morphology [38]; and (3) expand degradation pathways by generating multiple ROS from advanced photocatalysts [74]. Currently, commonly used photocatalysts for PFAS degradation include titanium dioxide (TiO 2 ), indium oxide (In 2 O 3 ), gallium oxide (Ga 2 O 3 ), bismuth (Bi)-based materials, and their composites [27,75].…”

“…These carbon materials allow for uniform dispersion of TiO 2 nanoparticles on a hydrophobic surface, leading to an increased PFAS adsorption rate and improved photocatalytic degradation with minimized risk of secondary pollution and good stability. Heterojunctions between TiO 2 and other semiconductors can enhance the electron-hole separation efficiency and improve the photocatalytic degradation performance [26,28,71]. For instance, Sb 2 O 3 −TiO 2 heterojunctions use Sb 2 O 3 nanoparticles confined within the mesoporous TiO 2 framework to adjust the band structure, increase the number of active sites for PFAS degradation, enhance UV absorption, and improve light utilization (Figure 4b) [71].…”