Intensification of photocatalytic processes for niche applications in the area of water, wastewater and air treatment [preface]

Photocatalysis and photoelectrocatalysis are attractive technologies with potential applications in several fields, such as environmental technology, chemical synthesis, energy, and medicine. Although thousands of research papers have been published reporting promising results, actual industrial applications still remain limited, principally in the area of environmental remediation. The lack of knowledge on photoreactor design among the wider scientific and industrial community and integration with conventional technologies are some of the factors that are limiting the adoption of these emerging technologies for remediation purposes

Emerging advanced oxidation processes for the elimination of micro-pollutants

Emerging advanced oxidation processes for the elimination of micro-pollutant

AOPs: recent advances to overcome barriers in the treatment of water, wastewater and air

AOPs: recent advances to overcome barriers in the treatment of water, wastewater and ai

Treatment of winery wastewater by sulphate radicals: HSO5−/transition metal/UV-A LEDs

© 2016 Elsevier B.V.In this study, the effectiveness of the HSO5-/M n+/UV process on the treatment of winery wastewater (WW) was investigated. The optimal operating conditions were determined: [HSO5-]=2.5mM; [M2(SO4) n ]=1.0mM; pH=6.5 and reaction temperature=323K. Under the given conditions, 51%, 42% and 35% of COD removal was achieved using respectively Fe(II), Co(II) and Cu(II) as catalysts. Different UV sources were tested with the previously selected optimal conditions in order to increase the treatment efficiency. The highest COD removal (82%) was achieved using a UV-A LEDs system (70W/m2). These conditions were also promising for the treatment of WW with COD concentrations of 5000mg O2/L, reaching 79% and 64% of COD and TOC removal, respectively, after 180min of treatment. At 323K, the most effective treatment was obtained when Co(II) was used as catalyst (79% and 64% of COD and TOC removal), while at ambient temperature (293K) the highest COD (65%) and TOC (52%) removals were obtained with Fe(II) catalyst. Moreover, it was demonstrated that the use of HSO5-/M n+ in several consecutive doses was more efficient than adding the reagents as a single dose at the beginning of the reaction. A comparison between the performance of the HSO5-/Fe(II)/UV-A LED process and the conventional photo-Fenton demonstrated important advantages associated with the HSO5-/Fe(II)/UV-A LED process, including the absence of the costly pH adjustment and of the hydroxide ferric sludge which characterise the photo-Fenton treatment process. The HSO5-/M n+/UV-A LED process demonstrates a high COD and TOC removal efficiency, and it can be considered a promising technology for application in real scale agro-food wastewater treatment plants

Size-Tunable Hydrothermal Synthesis of SnS₂ Nanocrystals with High Performance in Visible Light-Driven Photocatalytic Reduction of Aqueous Cr(VI)

SnS₂ nanocrystals with adjustable sizes were synthesized via a hydrothermal method from the aqueous solution of common and inexpensive SnCl₄·5H₂O, thioacetamide and citric acid, simply by varying the reaction temperature and reaction time. The structures, Brunauer–Emmett–Teller (BET) specific surface areas and optical properties of the resultant SnS₂ nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption/desorption isotherms, and UV–vis diffuse reflectance spectra. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. It was found that the photocatalytic activities of SnS₂ nanocrystals in aqueous suspension depended on their synthesis conditions. The product synthesized under suitable hydrothermal conditions (for example, at 150 °C for 12 h) not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability. Our photocatalytic results suggested that SnS₂ nanocrystals are a promising photocatalyst in the efficient utilization of solar energy for the treatment of Cr(VI)-containing wastewater

Catalytic processes and new materials and technologies in water/wastewater treatment [Editorial]

Catalytic processes and new materials and technologies in water/wastewater treatment [Editorial

Near real-time measurement of carbonaceous aerosol using microplasma spectroscopy: Application to measurement of carbon nanomaterials

<p>A sensitive, field-portable microplasma spectroscopy method has been developed for real-time measurement of carbon nanomaterials. The method involves microconcentration of aerosol on a microelectrode tip for subsequent analysis for atomic carbon using spark emission spectroscopy (SES). The spark-induced microplasma was characterized by measuring the excitation temperature (15,000–35,000 K), electron density (1.0 × 10¹⁷–2.2 × 10¹⁷ cm⁻³), and spectral responses as functions of time and interelectrode distance. The system was calibrated and detection limits were determined for total atomic carbon (TAC) using a carbon emission line at 247.856 nm (C I) for various carbonaceous materials including sucrose, EDTA, caffeine, sodium carbonate, carbon black, and carbon nanotubes. The limit of detection for total atomic carbon was 1.61 ng, equivalent to 238 ng m⁻³ when sampling at 1.5 L min⁻¹ for 5 min. To improve the selectivity for carbon nanomaterials, which mainly consist of elemental carbon (EC), the cathode was heated to 300°C to reduce the contribution of organic carbon to the total atomic carbon. Measurements of carbon nanotube aerosol at elevated electrode temperature showed improved selectivity to elemental carbon and compared well with the measurements from the thermal optical method (NIOSH Method 5040). The study shows the SES method to be an excellent candidate for development of low-cost, hand-portable, real-time instrument for measurement of carbonaceous aerosols and nanomaterials.</p

Hydroxyl Radical Oxidation of Cylindrospermopsin (Cyanobacterial Toxin) and Its Role in the Photochemical Transformation

Cylindrospermopsin (CYN), an alkaloid guanidinium sulfated toxin, is produced by a number of cyanobacteria regularly found in lakes, rivers, and reservoirs. Steady-state and time-resolved radiolysis methods were used to determine reaction pathways and kinetic parameters for the reactions of hydroxyl radical with CYN. The absolute bimolecular reaction rate constant for the reaction of hydroxyl radical with CYN is (5.08 ± 0.16) × 10⁹ M^–1 s^–1. Comparison of the overall reaction rate of CYN with hydroxyl radical with the individual reaction rate for addition to the uracil ring in CYN indicate the majority of the hydroxyl radicals (84%) react at the uracil functionality of CYN. Product analyses using liquid chromatography–mass spectrometry indicate the major products from the reaction of hydroxyl radical with CYN involve attack of hydroxyl radical at the uracil ring and hydrogen abstraction from the hydroxy-methine bridge linking the uracil ring to the tricyclic guanidine functionality. The role of hydroxyl radical initiated pathways in the natural organic matter (NOM) photosensitized transformation of CYN were evaluated. Scavenger and trapping experiments indicate that hydroxyl radical mediated transformations account for approximately ∼70% of CYN destruction in surface waters under solar irradiation in the presence of NOM. The absence of solvent isotope effect indicates singlet oxygen does not play a significant role in the NOM sensitized transformation of CYN. The primary degradation pathways for HO• mediated and NOM photosensitized destruction of CYN involve destruction of the uracil ring. The fundamental kinetic parameters determined from these studies are critical for the accurate evaluation of hydroxyl-radical based technologies for the remediation of this problematic cyanotoxin in drinking water and important in the assessment of the environmental oxidative transformation of uracil based compounds

Future trends in photocatalysis for environmental applications

Future trends in photocatalysis for environmental application

A Mechanistic Understanding of Hydrogen Peroxide Decomposition by Vanadium Minerals for Diethyl Phthalate Degradation

The interaction of naturally occurring minerals with H₂O₂ affects the remediation efficiency of polluted sites in in situ chemical oxidation (ISCO) treatments. However, interactions between vanadium­(V) minerals and H₂O₂ have rarely been explored. In this study, H₂O₂ decomposition by various vanadium-containing minerals including V­(III), V­(IV), and V­(V) oxides was examined, and the mechanism of hydroxyl radical (^•OH) generation for contaminant degradation was studied. Vanadium minerals were found to catalyze H₂O₂ decomposition efficiently to produce ^•OH for diethyl phthalate (DEP) degradation in both aqueous solutions with a wide pH range and in soil slurry. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analyses, and free radical quenching studies suggested that ^•OH was produced via single electron transfer from V­(III)/V­(IV) to H₂O₂ followed a Fenton-like pathway on the surface of V₂O₃ and VO₂ particles, whereas the oxygen vacancy (OV) was mainly responsible for ^•OH formation on the surface of V₂O₅ particles. This study provides new insight into the mechanism of interactions between vanadium minerals and H₂O₂ during H₂O₂-based ISCO