Photocatalytic Degradation Of Perfluorooctanoic Acid Research Articles

Efficient photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticle modified titanium dioxide

Perfluorooctanoic acid (PFOA) is potentially toxic and exceptionally stable attributed to its robust CF bond, which is hard to be removed by UV/TiO2 systems. In this research, bismuth nanoparticle (Bi NP) modified titanium oxides (Bi/TiO2) were synthesized by a simple photochemical deposition-calcination method and were applied as photocatalysts for the first time to degrade PFOA. The removal rate of 50 mg/L PFOA reached 99.3 % with 58.6 % defluorination rate after 30 min of irradiation via a mercury lamp. Bi/TiO2 exhibited superior performance in PFOA degradation compared to commercial photocatalysts (TiO2, Ga2O3, Bi2O3 and In2O3). In addition, Bi/TiO2 showed high degradation activity under actual sunlight, achieved 100 % removal rate and 59.3 % defluorination rate within 2 h. Bi NPs increase the light trapping ability of Bi/TiO2 and promote the separation of photogenerated electron-hole pairs via local surface plasmon resonance (LSPR) effect, which results in more photogenerated holes (h+) and hydroxyl radicals (OH). Combined with DFT calculations and intermediate detections, the degradation reaction is initiated from the oxidation of the PFOA carboxyl group via h+, followed by the loss of the CF2 unit step by step with the participation of OH. This work presents a novel approach for the practical implementation of TiO2-based photocatalysts to achieve highly efficient photocatalytic degradation of perfluorocarboxylic acids (PFCAs).

Zinc oxide@citric acid-modified graphitic carbon nitride nanocomposites for adsorption and photocatalytic degradation of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a highly persistent organic pollutant of global concern. A novel nanocomposite composed of ZnO nanoparticles and citric acid-modified g-C3N4 was synthesized by ball milling process. The synthesized nanocomposite was more efficient than pure ball-milled ZnO nanoparticles for PFOA elimination under visible light irradiation. The optimal hybrid photocatalyst, produced by the addition of 5 wt% of citric acid-modified g-C3N4, demonstrated significantly better performance for PFOA removal than pure ZnO nanoparticles under UV irradiation, with the apparent rate constants of 0.468 h−1 and 0.097 h−1, respectively. The addition of peroxymonosulfate (0.53 g L−1) significantly increased PFOA removal, clarifying the crucial effect of sulfate radicals on PFOA photodegradation. In comparison, citric acid-modified g-C3N4 was not effective for PFOA elimination under visible light irradiation, even with the addition of peroxymonosulfate. Further experiments under dark conditions identified surface adsorption on hybrid photocatalyst as a key process in total PFOA removal. In summary, PFOA removal by ZnO@citric acid-modified graphitic carbon nitride nanocomposites is due to the combined action from adsorption and photodegradation, with adsorption as the dominating mechanism.

Size-selective trapping and photocatalytic degradation of PFOA in Fe-modified zeolite frameworks

Removal and destruction of perfluorooctanoic acid (PFOA) are challenging due to its extreme persistence and dilute concentrations. This study investigated dual-function adsorptive-photocatalytic zeolite materials to selectively adsorb and degrade PFOA via tuning pore structures and doping transition metals. It is found that the pore opening is critical in the size-selective trapping of PFOA, while the iron doped zeolites present excellent adsorption of PFOA (>80 mg g−1) combining hydrophobic and electrostatic interactions. The formation of PFOA-iron complexes has reduced bond dissociation energy of C−F, calculated from density functional theory, for favorable stepwise defluorination (over 60% defluorination in 4 hours) by superoxide radicals and ligand-to-metal charge transfer. This mechanistic investigation extends the potential of the concentrate-and-degrade concept to remove PFOA selectively and effectively from contaminated water.

Fabrication of OVs enriched BiOCl microflowers doped with Fe3+ for effective destruction of two typical contaminants

ABSTRACT In this study, a one-step solvothermal method was used to fabricate Fe3+ doped BiOCl microflowers with abundant oxygen vacancies (OVs) in the presence of glacial acetic acid. Various analytical techniques were employed to characterize the structural, morphological, and optical properties of the prepared samples. The presence of OVs was confirmed by low temperature electron paramagnetic resonance (EPR) analysis. The photocatalytic results show that Fe3+ doped BiOCl photocatalysts have higher activity than the bare BiOCl, and 10% Fe3+/BiOCl exhibits the highest photocatalytic performance, the photocatalytic efficiency of this sample is 2.3 and 1.1 times higher than that of the blank BiOCl toward photocatalytic degradation of perfluorooctanoic acid (PFOA) and rhodamine B (RhB), respectively. Furthermore, Fe3+ doped BiOCl demonstrates excellent reusability. Based on the experimental observations, an enhancement mechanism for the photocatalytic activity of Fe3+ doped BiOCl was reasonably elucidated.

Boosting PFOA photocatalytic removal from water using highly adsorptive and sunlight-responsive ZIF67/MIL-100(Fe) modified C3N4

Per- and polyfluoroalkyl substances (PFAS) are widely used in many industrial and food processes. Their discharge into the environment shows a serious threat because of their toxicity, non-biodegradability and high mobility in water and soil. Photocatalytic reaction is confirmed an effective way for the degradation of PFOA. Photocatalytic materials with multifunctional properties can boost the generation of oxidizing materials, enhance the degradation efficiency of target pollutants. Herein, we report an easy-synthesis of ZIF67@C3N4 and MIL-100(Fe)@C3N4 by in-situ hydrothermal growth route for the photocatalytic degradation of perfluorooctanoic acid (PFOA). Unlike bare g-C3N4, ZIF67@C3N4 and MIL-100(Fe)@C3N4 composites exhibit higher specific surface areas which enhanced the adsorption properties. Moreover, the formed heterojunction systems boost the visible light responsive and the separation of photo-induced electrons, allowing excellent degradation of PFOA. Besides the same response to spectrum below 420 nm as C3N4, ZIF67@C3N4 holds a certain light absorption capacity between 500 and 600 nm, proving that ZIF67@C3N4-X has better light utilization capacity than ZIF67 and C3N4. With the increase of MIL-100(Fe) addition, the red-shift becomes significant. Through the preliminary photocatalytic tests using methylene blue as a representative organic pollutant, the results showed that ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% are the most effective. When ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% were applied comparatively towards the photocatalytic oxidation of PFOA, the results showed that the removal rates reached 79.2% and 60.5%, respectively, which is much higher than bare C3N4. The quenching tests indicated that photo-induced h+ played a major role in the photocatalytic degradation of PFOA by ZIF67@C3N4-24.4%, while O2- and h+ participated equality towards the PFOA degradation in MIL-100(Fe)@C3N4-70% system. Besides the photonic effects, it was suggested that the adsorption and electron shuttle effect also played significant role on the excellent removal of PFOA, wherein the adsorption e behavior of catalysts help the accumulation of PFOA nearby the photoactive C3N4 area. In addition, this process promoted further mineralization of generated intermediate products, making the system more sustainable.

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

Perfluorooctanoic acid is ubiquitous in water bodies and is detrimental to the health of organisms. Effectively removing perfluorooctanoic acid (PFOA), a persistent organic pollutant, has been a hot topic around the world. With traditional physical, chemical, and biological methods, it is difficult to effectively and completely remove PFOA, the costs are high, and it is easy to cause secondary pollution. There are difficulties in applying some technologies. Therefore, more efficient and green degradation technologies have been sought. Photochemical degradation has been shown to be a low-cost, efficient, and sustainable technique for PFOA removal from water. Photocatalytic degradation technology offers great potential and prospects for the efficient degradation of PFOA. Most studies on PFOA have been conducted under ideal laboratory conditions at concentrations that are higher than those detected in real wastewater. This paper summarizes the research status of the photo-oxidative degradation of PFOA, and it summarizes the mechanism and kinetics of PFOA degradation in different systems, as well as the influence of key factors on the photo-oxidative degradation and defluoridation process, such as system pH, photocatalyst concentration, etc. PFOA photodegradation technology's existing problems and future work directions are also presented. This review provides a useful reference for future research on PFOA pollution control technology.

Photocatalytic Degradation of Perfluorooctanoic Acid on Pb-doped TiO2 Coated with Reduced Graphene Oxide.

Poor reactivity of extraordinarily strong per- and polyfluoroalkyl substances (PFAS) with TiO2 makes it necessary to advance photocatalytic materials. In this present work, lead (Pb)-doped TiO2 coated with reduced graphene oxide (TiO2 -Pb/rGO) was prepared using hydrothermal method and then its photocatalytic activity with various PFAS in water, especially perfluorooctanoic acid (PFOA), was investigated. PFAS decomposition kinetics by TiO2 -Pb/rGO was compared to neat TiO2 , Pb-doped TiO2 (TiO2 -Pb) and rGO-coated TiO2 (TiO2 /rGO). TiO2 -Pb/rGO (0.33 g/L) under UV showed superior removal of PFOA (10 mg/L) at 98% after 24 hr, following TiO2 -Pb/UV at 80%, TiO2 /rGO/UV at 70%, TiO2 /UV at <10%, and UV at <10%. Doping of TiO2 with Pb and introduction of rGO to TiO2 greatly changed the physicochemical properties of TiO2 and the subsequent charge transfer mechanism. Radical scavenger experiments indicated that holes, superoxide radical anion, and singlet oxygen were responsible for the observed PFOA decomposition. Decomposition of PFOA by TiO2 -Pb/rGO under UV led to formation of short-chain perfluorocarboxylic acids (PFCAs) as reaction intermediates through step-by-step removal of CF2 units. Polyfluoroalkyl substance (6:2 fluorotelomer sulfonate (6:2FTS)) and long-chain PFCAs such as PFOA were significantly removed and defluorinated by TiO2 -Pb/rGO while it was ineffective towards perfluorosulfonic acids and short-chain PFCAs. Removal kinetics decreased in order of 6:2FTS > PFOA >> PFOS > PFHpA ≈ PFHxS ≈ PFBA ≈ PFBS. Pb doping to TiO2 /rGO showed better performance than Fe doping. Overall, this study implied that proper designing of TiO2 photocatalytic materials enables to expedite decomposition of persistent organic pollutants in water, in particular highly challenging fluorinated chemicals.

Morphological Regulation of Bis-muth Oxychloride and Its Photocatalytic Degradation of Perfluorooctanoic Acid

Morphological Regulation of Bis-muth Oxychloride and Its Photocatalytic Degradation of Perfluorooctanoic Acid

Photocatalytic degradation of perfluorooctanoic acid (PFOA) via MoS2/rGO for water purification using indoor fluorescent irradiation

The current investigation focussed on the facile synthesis of MoS2/rGO nanocomposite with different weight percentages of MoS2 (1%, 5% and 15% w.r.t. to rGO) prepared via hydrothermal methods. The effective incorporation of MoS2 on the GO structures was substantially confirmed via various characterization tools via attenuated total reflectance-Fourier transform infrared (ATR-FTIR), ultraviolet-visible spectroscopy(UV–VIS), scanning electron microscope (SEM), transmision electron microscope (TEM), x-ray diffractometry (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), surface area and pore analyzer, zeta potential and x-ray photoelectron spectroscopy (XPS). The nanocomposites were applied as photocatalysts to degrade perfluorooctanoic acid (PFOA) using a photoreactor equipped with an 18-watt fluorescent lamp. MoS2/rGO-15 showed superior photocatalytic properties for degrading PFOA, with kinetic rate constant k = 0.0758 min−1, and t ½ = 1.524 h under fluorescent light evaluated by using the Langmuir-Hinshelwood (L-H) model. The reusability studies indicated that the MoS2/rGO-15 composites can be reused for up to six cycles. Real water sample analysis revealed that MoS2/rGO-15 is efficient in degrading PFOA in a river water sample with a 77% degradation percentage. Thus, this research proposed a sustainable solution for photocatalytic degradation of PFOA in water purification under fluorescent light.

Titanium oxide improves boron nitride photocatalytic degradation of perfluorooctanoic acid

Boron nitride (BN) has the newly-found property of degrading recalcitrant polyfluoroalkyl substances (PFAS) under ultraviolet C (UV-C, 254 nm) irradiation. It is ineffective at longer wavelengths, though. In this study, we report the simple calcination of BN and UV-A active titanium oxide (TiO2) creates a BN/TiO2 composite that is more photocatalytically active than BN or TiO2 under UV-A for perfluorooctanoic acid (PFOA). Under UV-A, BN/TiO2 degraded PFOA ∼ 15 × faster than TiO2, while BN was inactive. Band diagram analysis and photocurrent response measurements indicated that BN/TiO2 is a type-II heterojunction semiconductor, facilitating charge carrier separation. Additional experiments confirmed the importance of photogenerated holes for degrading PFOA. Outdoor experimentation under natural sunlight found BN/TiO2 to degrade PFOA in deionized water and salt-containing water with a half-life of 1.7 h and 4.5 h, respectively. These identified photocatalytic properties of BN/TiO2 highlight the potential for the light-driven destruction of other PFAS.

Application of machine learning algorithms in predicting the photocatalytic degradation of perfluorooctanoic acid

ABSTRACT Perfluorooctanoic acid (PFOA) is used in a variety of industries and is highly persistent in the environment, with potential human health risks. Photocatalysis has been extensively used for the decomposition of various organic pollutants, yet its simulation and modeling are challenging. This research aimed to establish different machine learning (ML) algorithms which can simulate and predict the photocatalytic degradation of PFOA. The published results were used to estimate and predict the photocatalytic degradation of PFOA. Statistical criteria including the coefficient of determination (R2 ), mean absolute error (MAE), and mean squared error (MSE) were considered in assessing the best method of modeling. Among the seven ML algorithms pre-screened, Adaptive Boosting (AdaBoost), Gradient Boosting Machine (GBM), and Random Forest (RF) showed the best performance and were chosen for deep modeling and analysis. Grid search was used to optimize the models developed by AdaBoost, GBM, and RF; and permutation variable importance (PVI) was used to analyze the relative importance of different variables. Based on the modeling results, GBM model (R2 = 0.878, MSE = 106.660, MAE = 6.009) and RF model (R2 = 0.867, MSE = 107.500, MAE = 6.796) showed superior performances compared with AdaBoost model (R2 = 0.574, MSE = 388.369, MAE = 16.480). Furthermore, the PVI results suggested that the GBM model provided the best outcome, with the light irradiation time, type of catalyst, dosage of catalyst, solution pH, irradiation intensity, initial PFOA concentration, oxidizing agents (peroxymonosulfate, ammonium persulfate, and sodium persulfate), irradiation wavelength, and solution temperature as the most important process variables in decreasing order.

Efficient photocatalytic degradation of PFOA in N-doped In2O3/simulated sunlight irradiation system and its mechanism

In this work, the kinetics and mechanisms of photocatalytic degradation of perfluorooctanoic acid (PFOA) by nitrogen-doped indium trioxide (N-doped In2O3 or NH4NO3-In2O3) under Xe lamp irradiation were systematically investigated. Nitrogen originating from various inorganic and organic nitrogen compounds was doped into In2O3 to examine the catalytic effect. The NH4NO3-In2O3 catalyst was characterized by SEM, TEM, FT-IR, UV-DRS, BET surface area, XPS, and XRD, and showed the best catalytic performance. After 18 h of irradiation, PFOA was almost completely degraded with addition of 5 mg catalyst, while it was hardly degraded by simulated sunlight alone. The low photocatalytic degradation efficiency of PFOA was observed in different natural waters, which was due to the inhibitory effect of high pH and common anions like SO42−. The calculation results of Materials Studio showed that a shoulder-to-shoulder π system between nitrogen atom and oxygen atom (NO π*) was formed after nitrogen doping into interstitial sites of In2O3, therefore resulting in a reduction in band gap energy. Occupied NO π* states were responsible for the red shift, while unoccupied NO π* levels restrained the recombination of electrons (e−) and holes (h+). Nitrogen doping reduced the excitation energy for electronic transition, and thus accelerated the reaction. According to mass spectrometry analysis, decarboxylation and elimination were still the main photodegradation pathways of PFOA. To the best of our knowledge, this report is the first to explore the reaction mechanisms of PFOA in an N-doped In2O3/Xe lamp irradiation system.

Synthesis of samarium doped ferrite and its enhanced photocatalytic degradation of perfluorooctanoic acid (PFOA)

A novel samarium doped ferrite composite material was prepared successfully by using the chemical co-precipitation method, which was used for the photocatalytic degradation of perfluorooctanoic acid (PFOA). The samarium doped ferrite was characterized by XRD, FT-IR, SEM, XPS, UV–vis and VSM. The results revealed the catalyst could be a typical soft magnetic material with a spinel structure, which has uniform particle size (100–200 nm), and good photoresponse in the wavelength range of 200–700 nm. Satisfactory photocatalytic activity of the samarium doped ferrite material was verified, that is the PFOA (0.5 mmol L−1) with degradation efficiency of 48.61% could be achieved in 120 min under UV irradiation at 185 nm. After conducting the cycle experiments, excellent stability and good magnetic recovery performance of the samarium doped ferrite were found. The free radical capture test signified that the h+ and •OH could play major roles in the PFOA initial oxidation, simultaneously. Moreover, possible mechanisms of the PFOA degradation was studied by analyzing the intermediate products using the HPLC method. These results suggest that samarium doped ferrite is a promising photocatalyst in the PFOA wastewater treatment.

Mechanism insights into the facet-dependent photocatalytic degradation of perfluorooctanoic acid on BiOCl nanosheets

Photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS) remains insufficient. It is vital to investigate the structure–activity relationship between exposed facets and photocatalytic activity of PFAS. In this study, BiOCl nanosheets with predominantly exposed {010} or {001} facets (i.e. {010}-BiOCl or {001}-BiOCl) were synthesized via the hydrothermal method and applied for the photodegradation of perfluorooctanoic acid (PFOA). We observed that the degradation rate constant of PFOA via the {010}-BiOCl (0.0954 min−1) was 2.64-fold better than that of the {001}-BiOCl (0.0361 min−1) in photocatalytic activity. Density functional theory calculation results revealed that the higher catalytic activity of {010}-BiOCl was attributed to the in-situ generated surface oxygen vacancies (OVs) and the strong interaction with PFOA molecules via the bidentate adsorption configuration. {010}-BiOCl nanosheets with OVs exhibited the highest adsorption capacity (55.6 mg g−1h−1) and lowest adsorption energy (-0.399 eV) for PFOA molecules. The electron spin resonance spectroscopy and radical scavenging experiments showed that both photogenerated holes and surface hydroxyl radicals were generated on {010} facets that contributed to the degradation of PFOA; while only photogenerated holes were formed on {001} facets. Interestingly, F− ions as the by-products were prone to attaching to the BiOCl facets to block the catalytic sites. To recover the catalytic performance, we adopted a simple chemical precipitation approach to precipitate the F− by using Ca2+ ions. Our findings provide fundamental insights into the interface reactions during the photocatalytic degradation of PFOA.

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

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.

Enhanced photocatalytic degradation of perfluorooctanoic acid by Ti3C2 MXene-derived heterojunction photocatalyst: Application of intercalation strategy in DESs

In-situ construction of heterojunction photocatalyst on two-dimensional (2D) Ti3C2 MXene substrate has been proved to be a feasible method to enhance the photocatalytic degradation of organic pollutants. However, the limited interlayer spacing of 2D Ti3C2 hinders the in-situ growth of TiO2 photocatalyst. Herein, the intercalation strategy was developed in deep eutectic solvents (DESs) method to achieve interlayer expansion of Ti3C2 and improve Ti3C2-derived photocatalyst performance. Because of the intercalation of choline cations, the DESs method synthesized Ti3C2 (Ti3C2-DES) had the larger c-lattice parameter than that of traditional HF method synthesized Ti3C2 (Ti3C2-HF). The interlayer space of Ti3C2-DES could be intercalated with more water molecule for oxidization of the Ti atoms, which remarkably promoted the in-situ growth of TiO2 crystals. The formed heterojunction between (001) and (101) facets enhanced carriers separation. The Ti3C2 substrate with excellent conductivity further promoted carriers transfer. As a result, Ti3C2/TiO2 photocatalyst exhibited superior perfluorooctanoic acid (PFOA) removal performance (almost 100% removal efficiency and 49% defluorination efficiency within 16 h) compared with the traditional Ti3C2-HF/TiO2 (22% removal efficiency and 12% defluorination efficiency within 16 h). This study provides a feasible strategy for enhancing photocatalytic degradation of PFOA by Ti3C2 MXene-derived heterojunction photocatalyst.

Enhanced photocatalytic degradation of perfluorooctanoic acid using carbon-modified bismuth phosphate composite: Effectiveness, material synergy and roles of carbon

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) are recalcitrant to conventional wastewater treatment processes. In search for a more effective technology, we prepared a carbon sphere (CS) modified bismuth phosphate composite photocatalyst (BiOHP/CS) through a hydrothermal process. BiOHP/CS was able to adsorb > 99% of PFOA in 2 h (dosage = 1.0 g/L, initial PFOA = 200 µg/L, pH = 7.0), and subsequently, in situ decompose adsorbed PFOA nearly completely in 4 h of UV irradiation. The PFOA degradation rate was ~18 times greater than that by neat BiOHP. Advanced spectroscopic analyses and density functional theory calculations revealed that the carbon modification not only enhances the PFOA adsorption capacity, but also facilitates a side-on adsorption configuration of PFOA on the photoactive sites. While only the head carboxylate group was involved in PFOA adsorption on neat BiOHP, both the CF2/CF3 entities and the head carboxylate group participated in adsorption of PFOA on BiOHP/CS, which facilitates the subsequent photocatalytic cleavage of the CF bonds. Photoluminescence emission analysis and density of states calculations confirmed the CS-facilitated side-on adsorption mode and CS-enhanced separation of electrons and holes. In addition, the CS modification facilitates activation of PFOA by changing the electron distribution of the C-F bond, and enhances the stability and reusability of BiOHP by preventing photo-corrosion of the composite material. Overall, the findings provide important insights into the roles of carbonaceous modification and adsorption configurations in enhanced photocatalytic destruction of PFOA, which may guide future design and fabrication of environment-friendly adsorptive photocatalysts.

Tailoring photocatalysts and elucidating mechanisms of photocatalytic degradation of perfluorocarboxylic acids (PFCAs) in water: a comparative overview

AbstractA perfluorooctanoic acid (PFOA), as the most important representative of perfluorocarboxylic acids (PFCAs), is environmentally persistent and bioaccumulative. Among treatment techniques for PFOA decomposition, photocatalytic degradation of PFOA has received considerable attention. A series of candidate photocatalytic materials, including TiO2‐, carbonaceous‐, Ga2O3‐, In2O3‐based, etc., have been successfully proposed to eliminate PFOA. Overall, there are two types of mechanisms for photocatalytic degradation of PFCAs, including conventional mechanism and charge transfer mechanism. For a conventional mechanism, the mechanism of PFOA photodegradation over bulk TiO2 via two pathways: photo‐redox and β‐scission. For the charge transfer mechanism, the PFOA degradation pathway in water‐soluble H3PW12O40 is mainly via charge‐transfer excited complex ([PW12O40]3−*). Finally, attention on critical challenges and prospects for photodegradation of PFOA are also intensified. © 2020 Society of Chemical Industry

Enhanced adsorption and photocatalytic degradation of perfluorooctanoic acid in water using iron (hydr)oxides/carbon sphere composite

Perfluorooctanoic acid (PFOA) has been widely detected in aquatic systems. Yet, cost-effective technologies for degrading PFAS have been lacking. We prepared and tested an adsorptive photocatalyst consisting of iron (hydr)oxides and carbon spheres (FeO/CS) through a one-step hydrothermal process. Characterization results revealed that the presence of carbon spheres affected the crystal formation of iron (hydr)oxides, and resulted in mutually modified mixed phases ferrihydrite and carbon spheres. FeO/CS was able to effectively adsorb and then degrade the pre-sorbed PFOA under simulated solar light. FeO/CS(1:1), prepared at an Fe:Glucose molar ratio of 1:1, showed the highest PFOA adsorption capacity and photoactivity. At a dosage of 1.0 g/L, FeO/CS(1:1) adsorbed nearly all 200 µg/L of PFOA within 1 h, and when the PFOA-laden FeO/CS(1:1) was subjected to simulated solar light at neutral pH, 95.2% of pre-concentrated PFOA was photodegraded and 57.2% defluorinated in 4 h. The efficient degradation also regenerated the material, allowing for repeated uses of the material without chemical regeneration. The much enhanced adsorption and photocatalytic activity of FeO/CS was attributed to: 1) CS facilitated formation of ferrihydrite, leading to adsorption of PFOA via binuclear and bidentate complexation, and 2) a hybrid ferrihydrite-CS structure, enabling multi-point, corporative adsorption of PFOA, and increasing direct electron extraction from PFOA under solar light irradiation. Moreover, OH radicals played an important role in PFOA degradation. Lastly, a photodegradation mechanism is proposed based on experimental findings and density functional theory calculations.

Improved photocatalytic degradation of perfluorooctanoic acid on oxygen vacancies-tunable bismuth oxychloride nanosheets prepared by a facile hydrolysis.

Oxygen vacancies (OVs) defective BiOCl nanosheets are important for developing efficient hole (h+) oxidation. Herein, a facile hydrolysis without the use of organic solvent was developed for preparing OVs-controllable BiOCl nanosheets, which was then applied to degrade perfluorooctanoic acid (PFOA), a typical persistent organic pollutant, which is resistance to the oxidation by hydroxyl radicals (OH). As changing the alkali source in the preparation process, the ratio of OVs in BiOCl nanosheets increases from 0.573 to 0.981, and the photocatalytic performance of BiOCl for the degradation and defluorination of PFOA increases by 3-4 times. A linear relationship between the photocatalytic degradation of PFOA and the OVs amount in BiOCl was observed. The introduction of OVs in BiOCl not only offers localized states for trapping photo-generated electrons, but also acts as active sites for adsorbing PFOA, both of which are helpful to improve the h+-oxidation of PFOA. The photocatalytic degradation of PFOA was more effective at pH 4.6 compared to other previously reported highly acidic and alkaline conditions. These factors ultimately guaranteed the improved degradation and defluorination of PFOA over OVs-rich BiOCl nanosheets. This work provides a readily achievable tactic to induce OVs formation on nanocrystals for enhanced photocatalytic water treatment.