Photogenerated Hydroxyl Radicals Research Articles

Engineering a staggered type-II Bi2WO6/WO3 heterojunction with improved photocatalytic activity in wastewater treatment

In recent years, the removal organic pollutants from wastewater by advanced oxidation processes, especially photocatalysis, has become a meaningful approach due to its eco-friendliness and low cost. Herein, staggered type-II Bi2WO6/WO3 heterojunction photocatalysts were prepared by a facile hydrothermal route and investigated by modern physicochemical methods (X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption-desorption, and diffuse reflectance spectroscopy). The optimized BWOW-5 photocatalyst exhibited a H2O2-assisted photocatalytic methylene blue removal efficiency of 94.1% (k = 0.01414 min−1) within 180 min under optimal reaction conditions, which is much higher than that of unmodified Bi2WO6 and WO3 due to efficient separation of the photogenerated charge carriers. The trapping experiments demonstrated that photogenerated hydroxyl radicals and holes play a key role in the photodegradation reaction. Moreover, the optimized BWOW-5 heterojunction photocatalyst exhibited excellent activity in the H2O2-assisted degradation of other pollutants, namely phenol, isoniazid, levofloxacin, and dibenzothiophene with the removal rate of 63.1, 73.6, 95.0, and 72.4%, respectively. This investigation offers a design strategy for Bi2WO6-based multifunctional photocatalytic composites with improved activity for organic pollutant degradation.

Modulation of cell death mechanisms via α-Ag2WO4 morphology-dependent factors

The cytotoxic of α-Ag2WO4 synthesized in different morphologies (cuboidal (AW-C), hexagonal rod-like (AW-HRL) and nanometric rod-like (AW-NRL) was analyzed to understand the impact of morphological modulation on the toxicity of 3 T3 cell lines in the dark and when photoactivated by visible light. Pathways of toxicity were examined, such as parameters and electrostatic interaction, uptake, ion release and ROS production. Cytotoxicity was observed for all samples after reaching concentrations exceeding 7.8 μg/mL. Uptake tests demonstrated that the samples were not internalized by cells, likely due to their negative surface charge. AW-NRL exhibited autophagy in the absence of light and during photoactivation, primarily attributed to its ability to generate singlet oxygen. Analyzing intercellular ROS and RNS production, AW-HRL induced an increase in NO through exposure to photo-generated hydroxyl radicals, while AW-NRL showed increases only at non-photoactivated concentrations and AW-C did not exhibit increases. Interestingly, in the dark, these cells showed a low propensity for apoptosis, with late apoptosis and necrosis being more pronounced. When photoactivated, this behavior changed, revealing predominantly apoptotic and late apoptotic cell death. There is a need for an understanding of how morphology can alter the biological properties of α-Ag2WO4 to predict and optimize its effects on cellular responses.

Strategic rationalization for improved photocatalytic decomposition of toxic pollutants: Immobilizing Bi2Te3 nanorods and V2O5 nanoparticles over MoS2 nanosheets

Researchers have become increasingly interested in solar energy based on semiconductor photocatalysts to remove hazardous pollutants and clean the environment. In this work, an efficient MoS2-Bi2Te3-V2O5 nanocomposite has been prepared through wet impregnation method. MoS2-Bi2Te3-V2O5 photocatalyst was utilized to decompose the MB and Rh B dyes. The photocatalytic efficiency (Rh B) of MoS2-Bi2Te3-V2O5 nanocomposite (95.19 %) was higher than 2.70 times of Bi2Te3 nanorods, 1.55 times of V2O5 nanoparticles, 1.68 times of MoS2 nanosheets, 1.50 times of MoS2-Bi2Te3, and 1.21 times of MoS2-V2O5 nanocomposite, respectively. Recycling tests conducted on the MoS2-Bi2Te3-V2O5 nanocomposite revealed its high stability and durability. The outcomes obtained from the scavenger test suggest that the photogenerated hydroxyl radicals play a chief role in the photocatalytic performance of Rh B dye in the MoS2-Bi2Te3-V2O5 nanocomposite, respectively. The enhanced photocatalytic performance of the MoS2-Bi2Te3-V2O5 nanocomposite is ascribed to the strong hybrid formation of Bi2Te3, V2O5, and MoS2 nanosheets, respectively. Consequently, the straightforward and readily synthesized MoS2-Bi2Te3-V2O5 nanocomposite can serve as an economical, highly effective material for environmental applications.

Surface electronic state modulation promotes photoinduced aggregation and oxidation of trace CO for lossless purification of H2 stream

Although photogenerated hydroxyl radicals can oxidize CO without H2 consumption, the nonselective collision severely lowers photocatalytic photon utilization. We here demonstrate that electronic state modification of TiO2 resulted from magnesium doping can promote hydroxyl radical generation by weakening the adsorption of oxygen species and facilitating semiconductor-cocatalyst interfacial electron transfer. Importantly, the partial deprivation of electronic cloud from cationic sites can strengthen σ-donation and π-backdonation that synergistically promote the electrostatic interaction for aggregating CO in the vicinity of semiconductor. The resulted photocatalyst thus exhibits growing superiority over common counterpart in target reaction as CO concentration lowers. By these merits, CO in H2 stream can be reduced to < 1 × 10−6 with efficient photon utilization.

Photocatalytic degradation of aromatic pollutants using plasmonic Cu–Ag nanocomposites

Commercially viable solutions are required for the environmental pollution challenges that are plaguing the global community. Development of cost-effective and visible light active photocatalysts for degrading persistent organic pollutants was attempted herein. Copper (Cu) and silver (Ag) nanoparticles and their nanocomposites at various ratios were explored for pollutant degradation in presence of visible light. Para-nitrophenol (p-NP) was used as a model pollutant to compare the catalytic activities of the nanomaterials. The silver rich nanocomposite (CuAg2) was found to be the most active photocatalyst because of its stronger ability to harvest light and synergistic charge transfer between Cu and Ag. CuAg2 could photocatalytically mineralize pharmaceutical compounds such as sulfamethoxazole (SMX) and norfloxacin (NOR) in presence of a small amount of H2O2. Photogenerated hydroxyl radicals were found to be responsible for the degradation of the pollutants. Moreover, the CuAg2 could be used as a surface enhanced Raman spectroscopy (SERS) substrate for detecting the pollutants. Operando catalytic activity studies also could be conducted using the CuAg2. Finally, liquid chromatography-mass spectrometry (LC-MS) was used to understand the possible degradation pathways for SMX and NOR.

Direct photoconversion of nitrite to dinitrogen on Pd/TiO2 coupled with photooxidation of aquatic pollutants

Nitrate (NO3−) and nitrite (NO2−) are ubiquitous aquatic pollutants and should be controlled for water quality. Although diverse methods of nitrate/nitrite reduction have been developed, most require chemical reductants and external energy inputs. Nitrite is oxidized by photogenerated hydroxyl radicals (•OH) in an aqueous suspension of Pd-loaded TiO2 (Pd/TiO2) with producing nitrate as a major product. The main photoconversion product of nitrite is changed from nitrate to N2 on Pd/TiO2 in the presence of aquatic pollutants (arsenite (As(III)) or 4-chlorophenol (4-CP)) which can suppress the photooxidation of NO2− by scavenging holes/•OH. The photogenerated H2 on Pd/TiO2 serves as a main reductant and was immediately consumed for reducing nitrite to N2. The presence of As(III) or 4-CP also enhanced the durability of Pd/TiO2 by efficiently scavenging hole/•OH that may oxidize Pd nanoparticles. The proposed process can be a viable treatment option for nitrite-contaminated water containing various aquatic pollutants.

In situphotogenerated hydroxyl radicals in the reaction atmosphere for the accelerated crystallization of solution-processed functional metal oxide thin films

We propose a disruptive method to accelerate the crystallization at low temperatures of functional metal oxide films whereby hydroxyl radicals (•OH) are photogeneratedin situfrom the atmosphere where solution-deposited layers are UV-irradiated.

Electron flux at the Schottky junction of Bi NPs and WO3-supported g-C3N4: an efficient ternary S-scheme catalyst for removal of fluoroquinolone-type antibiotics from water.

Recently, global-scale attempts have been conducted to develop clean technologies and affordable materials to remediate pharmaceutical contaminants of water resources that are resistant to the biodegradation. In line with global efforts, this study reports a facile method to fabricate Bi nanocrystals in situ decorated on WO3 nanoplates and its composite with graphitic carbon nitride (WO3/Bi/g-C3N4) for photocatalytic degradation of fluoroquinolone-type antibiotics (ciprofloxacin and ofloxacin). The designed ternary S-scheme WO3/Bi/g-C3N4 composite material was fully characterized by physicochemical and electrochemical analysis. Depositing the cost-effective and earth-abundant Bi nanocrystals onto WO3 via a facile reduction route has been shown to increase the boosting of electron flux at their interface (Schottky junction). The S-scheme separation is confirmed by the calculation of band positions and the analysis of photogenerated hydroxyl radicals and holes. The complete removal of contaminants was obtained over the WO3/Bi/g-C3N4 photocatalyst after 90 min under visible light irradiation. The present work would provide a rational route for developing Bi NP-based photocatalysis to replace metallic Au, Pt, and Ag NPs.

In-grown flower like Al-Li/Th-LDH@CNT nanocomposite for enhanced photocatalytic degradation of MG dye and selective adsorption of Cr (VI)

Inner transition metal ions doped layered double hydroxides–embedded in CNTs have attracted increasing attention for wastewater treatment and renewable energy recently. In this work, the nanostructures of Al-Li/Th-LDH@CNT consisting of flower-like morphology were successfully synthesized by the elegant combination of exfoliated Al-Li/Th LDHs nano-sheets and F-CNTs using the hydrothermal method. The as-synthesized Al-Li@ThLDH-CNT nanocomposite is employed for MG dye photodegradation and selective adsorption of Cr (VI) ions. The Al-Li/Th-LDH@CNT nanocomposite has exhibited excellent visible-light-induced photocatalytic activity towards Malachite green (MG) dye, and almost 98% of (MG) dye is decolorized within 45 min. Studies probing the mechanism demonstrate that the photogenerated hydroxyl radical and holes play a vital role in the MG dye degradation process. Furthermore, the Al-Li/Th-LDH@CNT was tested to examine its selective adsorption behavior towards different metal ions at ultra-low trace levels by the ICP-MS technique. The adsorption behavior of Al-Li/Th-LDH@CNT displayed high removal percentage towards Cr6+ (94.1%), while as 86.7% and 83% for Al-Li and Al-Li-CNT adsorbents and the maximum adsorption capacities of Al-Li, Al-Li-CNT, and Al-Li/Th-LDH@CNT were found to be 156.2, 163.3 and 172.4 mg/g respectively. Thus, preparing layered structure composite using a simple engineered route may open a new strategy to synthesize advanced materials having improved synergistic catalytic properties, which could be effectively used as highly efficient probes for environmental applications.

Photo-generated hydroxyl radicals contribute to the formation of halogen radicals leading to ozone depletion on and within polar stratospheric clouds surface

Polar stratospheric clouds (PSCs), of which the surface is a dynamic liquid water layer and might consist of aqueous HNO3 and H2O2, is a well-known key meteorological condition contributing to the ozone hole in the polar stratosphere. PSCs has been considered to provide abundant surface for the heterogeneous reactions causing the formation of the Cl2 and HOCl, which are further photolyzed into Cl and ClO radicals leading to the ozone destruction. Here we demonstrated that the sunlight drives the massive and stable production of OH radicals in aqueous HNO3 and its main photo-induced byproduct HNO2. We also found that the photo-generated OH radicals in aqueous HNO3, HNO2 and H2O2 have the remarkable capability to react with the dissolved HCl, Cl− and Br− to form halogen radicals. In addition, we observed that the H2O2 can react with dissolved HCl and Br− in darkness to form and release Cl2 and Br2 gases, which could further be photolyzed into reactive halogen radicals whenever sunlight is available. All these findings suggest that, except for the well-known heterogeneous reactions, photochemical reactions involving the aqueous HNO3 and H2O2 on and within PSCs surface might constitute another important halogen activation pathway for ozone destruction. This study may shed deeper insights into the mechanism of halogen radicals resulting in ozone depletion in polar stratosphere.

Generation and photogeneration of hydroxyl radicals and singlet oxygen by particulate matter and its inorganic components

Polluted air containing particulate matter (PM) is a huge environmental problem in the city of Kraków, Poland. PM causes numerous negative health effects including infection of the respiration system and cardiovascular disorders. The development of autoimmune disorders can be facilitated by redox active transition metals due to the generation of reactive oxygen species (ROS) and induction of oxidative stress, which results in lipid peroxidation, protein oxidation and severe oxidative modification of DNA. Our goal was to study ROS generation (in particular, HO• and 1O2) in the presence of PM collected via different procedures at different locations in Kraków. Scanning electron microscopy analysis confirmed that in all collected samples, aggregates of small grains could be observed. Cold plasma treatment was used to remove parts of the organic matter and to uncover inorganic compounds which become more relevant following plasma treatment. All samples were photoactive and showed hydroxyl radical generation. Singlet oxygen production studies indicated that during plasma treatment, unsaturated organic species are produced that intensify the generation of 1O2. Generation of hydroxyl radicals and singlet oxygen in vitro was confirmed using human epithelial cell line A549.

Removal of Chlorinated Organic Pollutants from Groundwater Using a Vacuum-UV-Based Advanced Oxidation Process

The presence of chlorinated organic compounds, such as trichlorethylene (TCE) and tetrachlorethylene (PCE), in water sources requires particular attention due to their slow rate of decomposition, carcinogenicity, and toxicity. Advanced oxidation processes (AOPs) have been addressed for treating such organic pollutants, most commonly using UV-C radiation (254 nm) with the addition of different chemicals (e.g., TiO2 and H2O2). Although these previous AOP studies were proven to be effective, chemical dosing often complicates the treatment process and increases its costs. The current study examines the removal kinetics of TCE and PCE under combined UV-C/vacuum-UV radiation in different water matrixes (distilled water, synthetic solutions, and real groundwater). Faster degradation of both pollutants and their transformation products were observed in the presence of vacuum-UV radiation (using Hg lamps emitting at 185 and 254 nm), with the most significant effect in distilled-water solutions. In more realistic water matrixes (groundwater), pollutants removal still occurred but at lower efficiency due to the presence of interfering compounds that react with the photogenerated hydroxyl radicals and/or absorb UV/vacuum-UV radiation. An investigation of the effect of such substances enabled to identify the main interfering compounds (e.g., carbonate system ions and chloride) and to develop an appropriate pretreatment for their removal, improving the treatment effectiveness.

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.

Unprecedented arsenic photo-oxidation behavior of few- and multi-layer Ti3C2Tx nano-sheets

Water contaminated by arsenic is a tremendous risk for health and environment due to its toxic and carcinogenic nature thus asking for more advanced and efficient removal strategies. Therefore, the aim of this study is to investigate for the first time the photo-oxidation performance of few- and multi-layer Ti3C2Tx nano-sheets (Mxenes) regarding the arsenic removal from synthetic arsenic solutions. Few-layer Mxene nano-sheets have the capability to efficiently oxidize highly toxic As(III) to less harmful As(V) and possess at the same time a notable adsorption capability for both species (about 44% for As(III) and 50% for As(V)). The quantification of photogenerated hydroxyl radicals verified that few-layer Mxene nano-sheets are capable to generate 4 times more hydroxyl radicals compared to multi-layer Mxene nano-sheets. The increase amount of produced •OH radicals observed for few-layer Mxene nano-sheets can be attributed to its higher content of available active TiO2 sites, which provide more redox reaction sites thus improving the photocatalytic behavior. Moreover, the detected -OH surface terminations verified on the few-layer MXene nano-sheets promote their significant adsorption capacity. Thereby, our results demonstrate that especially few-layer Mxene nano-sheets are a promising candidate for an efficient arsenic removal due to its unprecedented dual effect of adsorption/photo-oxidation regarding this toxic contaminant.

Photocatalytic degradation of malachite green dye using chitosan supported ZnO and Ce–ZnO nano-flowers under visible light

Two types of chitosan-based composites (chitosan/ZnO and chitosan/Ce–ZnO composites) were synthesized under microwave irradiation and characterized as advanced catalysts of enhanced photocatalytic activity under the visible light. The morphological investigation reflected the formation of ZnO and Ce doped ZnO at stunning micro flowers of nano limps. Additionally, the optical studies reflected a reduction in the bandgap of ZnO from 3.3 eV to 2.85 eV and 2.5 eV after supporting it onto chitosan chains and after doping it with cerium, respectively. The synthetic composites were applied in photocatalytic removal of malachite green dye under a visible light source. The synthetic CH/ZnO and CH/Ce–ZnO showed enhancement in the photocatalytic removal of M.G by 54% and 87%, respectively, as compared to the pure ZnO. The synthetic composites are of high stability and can be reused for five photocatalytic degradation cycles at stunning removal percentages. The main oxidizing radicals during the removal of M.G by CH/ZnO are the generated electron-hole pairs as well as the hydroxyl radicals. The effective species in CH/Ce–ZnO photocatalytic system are the photogenerated hydroxyl radicals followed by the electron-hole pairs.

Synthesis of activated carbon-supported TiO2-based nano-photocatalysts with well recycling for efficiently degrading high-concentration pollutants

It is highly desired to develop efficient TiO2-based nano-photocatalysts with excellent recycling properties for practical application to degrade high-concentration pollutants. Herein, TiO2 nanoparticles have been successfully modified by coupling activated carbon (AC), constructing heterojunction with SrTiO3 and modifying with phosphoric acid. It is clearly demonstrated that the as-prepared nano-photocatalysts exhibit exceptional photoactivities for degrading high-concentration pollutants like 2,4-dichlorophenol (2,4-DCP) and bisphenol A (BPA), both with ∼3-time activity enhancement compared to commercial P25 TiO2. Based on the surface photovoltage responses and the fluorescence spectra related to the formed OH amounts, it is deduced that the exceptional photocatalytic activities are attributed to the coupled AC for accepting electrons and promoting reactant adsorption, to the formed SrTiO3 for inhibiting the anatase TiO2 crystallite growth to increase the surface area and promoting the charge separation, and to the modified phosphate groups for promoting the adsorption of O2 to enhance the charge separation. Furthermore, it is demonstrated through the radical trapping experiments that the photogenerated hydroxyl radicals could be dominant for the photocatalytic degradation of 2,4-DCP. This work would provide a feasible route to obviously enhance the photocatalytic activities of TiO2-based nano-photocatalysts for the environmental remediation with good recycling properties.

Microwave-Assisted Synthesis of Porous Aggregates of CuS Nanoparticles for Sunlight Photocatalysis.

Solvated two-dimensional nanosheets of copper hydroxy dodecylsulfate in 1-butanol react with thiourea under microwave irradiation to yield surfactant-free porous aggregates of CuS nanoparticles. These aggregates exhibit excellent photocatalytic activity toward degradation of methylene blue, methyl orange, and 4-chlorophenol in natural sunlight. While the high surface area (14.74 m2 g–1) and porosity increase the active reaction centers for adsorption and degradation of organic molecules, quantum confinement results in a low recombination of photogenerated electrons and holes. Chemical and photogenerated hydroxyl radicals cause the oxidation of the dyes and 4-chlorophenol.

Solar Energy Harvesting with Carbon Nitrides and N‐Heterocyclic Frameworks: Do We Understand the Mechanism?

AbstractThe photocatalytic splitting of water into molecular hydrogen and molecular oxygen with sunlight is the dream reaction for solar energy conversion. For decades, transition metal oxide semiconductors and supramolecular organometallic structures have been extensively explored as photocatalysts for solar water splitting. More recently, polymeric materials consisting of triazine or heptazine building blocks have attracted considerable attention as hydrogen‐evolution photocatalysts. The mechanism of hydrogen evolution with these materials is discussed throughout the current literature in terms of the familiar concepts developed for photoelectrochemical water splitting with semiconductors since the 1970s. We discuss in this Minireview an alternative mechanistic paradigm for photoinduced water splitting with carbon nitrides, which focusses on the specific features of the photochemistry of aromatic N‐heterocycles in aqueous environments. Using ab initio electronic‐structure calculations, it is shown that a water molecule which is hydrogen‐bonded to an N‐heterocycle can be decomposed into hydrogen and hydroxyl radicals by two simple sequential photochemical reactions. This concept is illustrated by the discussion of excited‐state reaction paths and their energy profiles for hydrogen‐bonded complexes of pyridine, triazine and heptazine with a water molecule. It is shown that the excited‐state hydrogen‐transfer and hydrogen‐detachment reactions are essentially barrierless, in sharp contrast to water oxidation in the electronic ground state, where high barriers prevail. We also discuss in some detail the products of possible reactions of the highly reactive photogenerated hydroxyl radicals with the chromophores. We hypothesize that the challenge of efficient solar hydrogen generation with carbon nitride materials is less the decomposition of water as such, but rather the controlled recombination of the photogenerated radicals to the closed‐shell products H2 and H2O2.

Facile synthesis of cation doped ZnO-ZnCo2O4 hetero-nanocomposites for photocatalytic decomposition of aqueous organics under visible light

Heterostructured cation doped ZnO-ZnCo2O4 nanocomposites having different cobalt loading were synthesized in a facile co-precipitation method followed by calcination at an optimum temperature. The structural features of the nanocomposites were confirmed using various characterization techniques. The morphologies of the heterostructured nanocomposites were changed from mixed structure (flakes and nano-rod) to spherical shape (cation doped ZnO-ZnCo2O4 to ZnCo2O4) when the cobalt composition varied from 10% to 50% of cobalt. The catalyst with 20% cobalt content exhibited the highest visible light photocatalytic performance towards degradation of Methyl Orange dye (MO dye) (92% degradation) and 2-chlorophenol (2-CP) (∼100% degradation). The rate-constant values for MO dye, and 2-CP degradations were 0.0177 min−1 and 0.0263 min−1 respectively, which are significantly higher than recent published materials, revealed by a comparison study. The enhanced photocatalytic activity is due to the heterojunction interfaces, which help to separate and transfer electron-hole pair as evidenced from PL spectra. Active species trapping experiments revealed that photogenerated hydroxyl radical played key role in degradation reaction. Moreover, the degradation products of MO dye and 2-CP were analyzed using mass spectroscopy, and their probable degradation pathways were arrived accordingly.

Photocatalytic degradation and mineralization of perfluorooctanoic acid (PFOA) using a composite TiO2 −rGO catalyst

The inherent resistance of perfluoroalkyl substances (PFASs) to biological degradation makes necessary to develop advanced technologies for the abatement of this group of hazardous substances. The present work investigated the photocatalytic decomposition of perfluorooctanoic acid (PFOA) using a composite catalyst based on TiO2 and reduced graphene oxide (95% TiO2/5% rGO) that was synthesized using a facile hydrothermal method. The efficient photoactivity of the TiO2-rGO (0.1gL−1) composite was confirmed for PFOA (0.24mmolL−1) degradation that reached 93±7% after 12h of UV–vis irradiation using a medium pressure mercury lamp, a great improvement compared to the TiO2 photocatalysis (24±11% PFOA removal) and direct photolysis (58±9%). These findings indicate that rGO provided the suited properties of TiO2-rGO, possibly as a result of acting as electron acceptor and avoiding the high recombination electron/hole pairs. The release of fluoride and the formation of shorter-chain perfluorocarboxilyc acids, that were progressively eliminated in a good match with the analysed reduction of total organic carbon, is consistent with a step-by-step PFOA decomposition via photogenerated hydroxyl radicals. Finally, the apparent first order rate constants of the TiO2-rGO UV–vis PFOA decompositions, and the intermediate perfluorcarboxylic acids were found to increase as the length of the carbon chain was shorter.