TiO2-assisted degradation of a perfluorinated surfactant in aqueous solutions treated by gliding arc discharge

Recent advances on PFAS degradation via thermal and nonthermal methods

Per- and polyfluoroalkyl substances (PFAS) are a set of synthetic chemicals which contain several carbon-fluorine (C-F) bonds and have been in production for the past eight decades. PFAS have been used in several industrial and consumer products including nonstick pans, food packaging, firefighting foams, and carpeting. PFAS require proper investigations worldwide due to their omnipresence in the biotic environment and the resulting pollution to drinking water sources. These harmful chemicals have been associated with adverse health effects such as liver damage, cancer, low fertility, hormone subjugation, and thyroid illness. In addition, these fluorinated compounds show high chemical, thermal, biological, hydrolytic, photochemical, and oxidative stability. Therefore, effective treatment processes are required for the removal and degradation of PFAS from wastewater, drinking water, and groundwater. Previous review papers have provided excellent summaries on PFAS treatment technologies, but the focus has been on the elimination efficiency without providing mechanistic understanding of removal/degradation pathways. The present review summarizes a comprehensive examination of various thermal and non-thermal PFAS destruction technologies. It includes sonochemical/ultrasound degradation, microwave hydrothermal treatment, subcritical or supercritical treatment, electrical discharge plasma technology, thermal destruction methods/incinerations, low/high-temperature thermal desorption process, vapor energy generator (VEG) technology and mechanochemical destruction. The background, degradation mechanisms/pathways, and advances of each remediation process are discussed in detail in this review.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

In-liquid plasma: a novel tool in the fabrication of nanomaterials and in the treatment of wastewaters

Attempts to generate plasma in liquids have been successful and various devices have been proposed.

Degradation of triclosan in aqueous solution by dielectric barrier discharge plasma combined with activated carbon fibers

The degradation of triclosan (TCS) in aqueous solution by dielectric barrier discharge (DBD) plasma with activated carbon fibers (ACFs) was investigated. In this study, ACFs and DBD plasma coexisted in a planar DBD plasma reactor, which could synchronously achieve degradation of TCS, modification and in situ regeneration of ACFs, enhancing the effect of recycling of ACFs. The properties of ACFs before and after modification by DBD plasma were characterized by BET and XPS. Various processing parameters affecting the synergetic degradation of TCS were also investigated. The results exhibited excellent synergetic effects in DBD plasma-ACFs system on TCS degradation. The degradation efficiency of 120 mL TCS with initial concentration of 10 mg L(-1) could reach 93% with 1 mm thick ACFs in 18 min at input power of 80 W, compared with 85% by single DBD plasma. Meanwhile, the removal rate of total organic carbon increased from 12% at pH 6.26-24% at pH 3.50. ACFs could ameliorate the degradation efficiency for planar DBD plasma when treating TCS solution at high flow rates or at low initial concentrations. A possible degradation pathway of TCS was investigated according to the detected intermediates, which were identified by liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) combined with theoretical calculation of Gaussian 09 program.

Plasmacatalytic removal of lead acetate assisted by precipitation

The Gliding Arc Discharge (GAD) is an efficient non-thermal plasma technique able to degrade organic compounds dispersed in water at atmospheric pressure. The degradation of the organometallic lead acetate (PbAc) in aqueous solution was performed by two distinct plasmageneous processes: GAD and GAD/TiO2. The global oxidation of the organic matter was followed by Chemical Oxygen Demand (COD) and the mineralization was determined by the Total Organic Carbon (TOC). The Pb(2+) ions released during the degradation process were measured by Atomic Absorption Spectroscopy (AAS). For 2h of GAD treatment, the degradation rate of PbAc (10mM) reached 83% and for the same duration of GAD/TiO2 process ([TiO2]=1gL(-1)), it reached 93%. The release of Pb(2+) ions in the solution was respectively of 95% and 57% for GAD and GAD/TiO2 processes. The released Pb(2+) ions were removed by precipitation process in a basic medium at pH=11.1. A reaction mechanism was proposed to explain the PbAc molecule degradation and the Pb(2+) elimination.

Plasma-TiO2 catalytic method for high-efficiency remediation of p-nitrophenol contaminated soil in pulsed discharge

Nonthermal discharge plasma and TiO(2) photocatalysis are two techniques capable of organic pollutants removal in soil. In the present study, a pulsed discharge plasma-TiO(2) catalytic (PDPTC) technique by combining the two means, where catalysis of TiO(2) is driven by the pulsed discharge plasma, is proposed to investigate the remediation of p-nitrophenol (PNP) contaminated soil. The experimental results showed that 88.8% of PNP was removed within 10 min of treatment in PDPTC system and enhancing pulse discharge voltage was favorable for PNP degradation. The mineralization of PNP and intermediates generated during PDPTC treatment was followed by UV-vis spectra, denitrification, total organic carbon (TOC), and CO(x) selectivity analyses. Compared with plasma alone system, the enhancement effects on PNP degradation and mineralization were attributed to more amounts of chemically active species (e.g., O(3) and H(2)O(2)) produced in the PDPTC system. The main intermediates were identified as hydroquinone, benzoquinone, catechol, phenol, benzo[d][1, 2, 3]trioxole, acetic acid, formic acid, NO(2)(-), NO(3)(-), and oxalic acid. The evolution of the main intermediates with treatment time suggested the enhancement effect of the PDPTC system. A possible pathway of PNP degradation in soil in such a system was proposed.

Photocatalytic decomposition of perfluorooctanoic acid by iron and niobium co-doped titanium dioxide

The photocatalytic decomposition of perfluorooctanoic acid (PFOA) in aqueous solution using Fe and Nb co-doped TiO(2) (Fe:Nb-TiO(2)) prepared by sol-gel method was investigated. The photocatalytic activity of Fe:Nb-TiO(2) towards PFOA degradation was compared to that of pure TiO(2) synthesized using the same method, and that of the commercially available TiO(2) photocatalyst, Aeroxide TiO(2) P25 (AO-TiO(2) P25). The photocatalysts were characterized by XRD, DRS, BET-N(2) adsorption isotherm, and SEM-EDX techniques and the data were correlated to the photocatalytic activity. Fe:Nb-TiO(2) showed the highest activity compared to the undoped TiO(2) and the commercially available TiO(2). Such activity was attributable to the effects of co-doping both on the physico-chemical properties and surface interfacial charge transfer mechanisms. Perfluorocarboxylic acids (PFCAs) with shorter carbon chain length and fluoride ions were identified as photocatalytic reaction intermediates and products.

Ultrasonic synthesis and photocatalytic characterization of H3PW12O40/TiO2 (anatase)

A novel H(3)PW(12)O(40)/TiO(2) (anatase) composite photocatalyst was prepared by a high-intensity ultrasonic method using a lower temperature (80 degrees C) and was characterized by XRD and FT-IR. Its photocatalytic activity, using solar light, was evaluated through the degradation of organic dye methylene blue (MB) in aqueous. When MB solution (50mg/l, 200 ml) containing H(3)PW(12)O(40)/TiO(2) (anatase) (0.4 g) was degraded by solar irradiation after 90 min, the removal of concentration and TOC of MB reached 95% and 73%, respectively. The photocatalyst activity of H(3)PW(12)O(40)/TiO(2) (anatase) was much higher than TiO(2) which was prepared in the same way. H(3)PW(12)O(40)/TiO(2) remained efficient after five repeated experiments.