WO2021067786A1 - Système de dégradation de contaminants chimiques dans l'eau - Google Patents

Système de dégradation de contaminants chimiques dans l'eau Download PDF

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Publication number
WO2021067786A1
WO2021067786A1 PCT/US2020/054048 US2020054048W WO2021067786A1 WO 2021067786 A1 WO2021067786 A1 WO 2021067786A1 US 2020054048 W US2020054048 W US 2020054048W WO 2021067786 A1 WO2021067786 A1 WO 2021067786A1
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Prior art keywords
reactor
boron nitride
photocatalyst
pfoa
nitride photocatalyst
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PCT/US2020/054048
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English (en)
Inventor
Michael S. Wong
Kimberly N. HECK
Bo Wang
Lijie DUAN
Sujin GUO
Paul Westerhoff
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William Marsh Rice University
Arizona State University
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Publication of WO2021067786A1 publication Critical patent/WO2021067786A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/30—Treatment of water, waste water, or sewage by irradiation
    • C02F1/32—Treatment of water, waste water, or sewage by irradiation with ultraviolet light
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/12—Halogens or halogen-containing compounds
    • C02F2101/14—Fluorine or fluorine-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/36—Organic compounds containing halogen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/001—Runoff or storm water
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C02F2103/343—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 from the pharmaceutical industry, e.g. containing antibiotics
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/10—Photocatalysts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/30—Wastewater or sewage treatment systems using renewable energies
    • Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy

Definitions

  • Conventional methods and systems for treating wastewater may employ coagulation, sedimentation, granular media filtration, reverse osmosis, ion exchange, adsorption (e.g, activated carbon), ultraviolet light radiation, ultrasonic energy, and other chemical-intensive processes to remove contaminants from water.
  • Conventional separation techniques may generate waste streams that often require additional processing to treat the removed contaminants, such as regenerative treatments to destroy the contaminants ⁇
  • Advances in the water industry also include the development and use of photocatalysts, such as titanium dioxide, to detoxify contaminants from water.
  • Fig. 9 illustrates PFOA concentration over time using for BN.
  • Fig. 10 illustrates the rate of reaction for BN loading.
  • Fig. 11 illustrates PFOA concentration over time using for Ti0 2 .
  • Fig. 12 illustrates the rate of reaction for T1O2 loading.
  • Fig. 13 illustrates terephthalic acid ( ⁇ OH probe) generation of radicals by both
  • Fig. 14 illustrates HPLC-DAD-detected PFOA concen tration-time and fluoride concentration profiles using BN, with and without 254 nm irradiation.
  • Fig. 15 illustrates HPLC-DAD-detected PFOA concentration-time and fluoride concentration profiles using T1O2., with and without 254 nm irradiation
  • Fig. 16 illustrates HPLC-MS detected concentration-time profiles of PFOA and byproducts for BN, with corresponding total fluorine balance.
  • Fig. 17 illustrates HPLC-MS detected concentration-time profiles of PFOA and byproducts for T1O2, with corresponding total fluorine balance.
  • TBA as hole, superoxide/hydroperoxyl and hydroxyl radical scavengers, respectively.
  • Fig. 21 illustrates XPS of B Is binding energies at different reaction times.
  • Fig. 22 illustrates XPS of N Is binding energies at different reaction times.
  • Fig. 23 illustrates absorbance spectra of BN through DR-UV.
  • Fig. 24 illustrates the Raman spectra of as-received and ball milled BN.
  • Fig. 25 illustrates the PFOA concentration-time profiles using as-received and ball milled BN.
  • Fig. 28 illustrates the PFOA concentration-time profiles in SDW with reinjections of PFOA for the BN case.
  • Fig. 29 illustrates the fluoride concentration profiles of the SDW with reinjections of PFOA for the BN case.
  • Fig. 30 illustrates the GenX and fluoride concentration- time profiles using BN with 254 nm irradiation.
  • Fig. 31 illustrates the PFOA sorption isotherm obtained using the BN as the sorbent with the initial PFOA concentration in the range of 25-300 mg/L and the initial pH of 3 at 30 °C.
  • Embodiments disclosed herein are directed to a photocatalytic system that may degrade chemicals, such as pollutants typically found in driniking water or municipal and industrial wastewaters, thereby detoxifying the chemicals.
  • Embodiments disclosed herein may provide a broad set of stakeholders (e.g., industrial organizations, governmental organizations, and citizens) a secure source of clean water. Embodiments disclosed herein may broaden access to clean drinking water by cleaning water from a variety of potential sources (e.g., groundwater from wells, saltwater, brackish water, or recycled industrial water). Some embodiments of the present disclosure may be modular systems that offer compact embodiments of catalytic treatment systems. These modular systems may provide drinking water from the scale of a household, to a neighborhood to a remote town. In addition, these modular embodiments may also provide access to clean water in the event of a natural disaster.
  • stakeholders e.g., industrial organizations, governmental organizations, and citizens
  • Embodiments disclosed herein may broaden access to clean drinking water by cleaning water from a variety of potential sources (e.g., groundwater from wells, saltwater, brackish water, or recycled industrial water).
  • Some embodiments of the present disclosure may be modular systems that offer compact embodiments of catalytic treatment systems
  • Embodiments herein may relate to the design and manufacture of multifunctional nanomaterials to adsorb a wide variety of pollutants, including: oxo- anions, total dissolved solids, nitrates, salts, organics, foulants, sealants, viruses and microbes, among others. These nanomaterials may be immobilized in membranes that are packaged into system modules. The use of modules offers flexibility of targeted pollutant(s) and end-use application capacity or scale of delivered water rate. Novel photonic, catalytic, and/or photocatalytic engineered nanomaterials (ENMs) described herein may introduce new approaches to transform water treatment from a large, chemical- and energy-intensive process toward compact physical and catalytic systems. These innovations may benefit multiple stakeholders, from rural communities and locations hit by natural disasters to hydraulic fracturing oil and gas sites, where reuse of produced waters minimizes regional environmental impacts.
  • EPMs photocatalytic engineered nanomaterials
  • Perfluoroc arboxylic acids (PFOA) part of the Per/polyfluorocarboxylic substances (PFAS) family, is an example of a particularly harmful contaminant found in the water supply.
  • PFAS Perfluoroc arboxylic acids
  • PFAS Per/polyfluorocarboxylic substances
  • Concern over water contamination by harmful contaminants, such as PFOA highlights the need for effective treatment approaches provided by embodiments of the present disclosure.
  • PFOA perfluorinated compounds
  • Conventional PFOA degradation methods include advanced oxidation processes (AOPs).
  • AOPs advanced oxidation processes
  • UV-C irradiation with high spectral irradiance decompose PFOA via photolysis.
  • Photocatalytic degradation of contaminants in aqueous liquids presents advantages over other methods. Advantages of photocatalysis include using ambient conditions for reaction, air as the oxidant, and light as the energy source. Photocatalysis also directly destroys targeted contaminants, thus rendering the contaminant non-toxic without additional processing. For example, physical separation methods often produce waste streams and may require regenerative treatments to destroy the separated contaminants ⁇
  • Boron Nitride is generally considered an electrical insulator, due to its wide band gap.
  • BN has also been investigated previously for its use in thermal (i.e., non-photo) catalysis.
  • BN is also conventionally understood to act as a support material, wherein an active material (typically group 8b metals) is immobilized upon it.
  • BN has also been proposed to treat organic compounds in water due to its high hydrophobicity and surface area. However, these methods only remove the organic compounds and do not detoxify them (i.e., further treatment remains necessary).
  • Embodiments disclosed herein are directed to treating contaminants in an aqueous liquid with boron nitride (BN) photocatalysts.
  • the BN photocatalyst may be activated by a light source (i.e., irradiated), including an ultraviolet light source, in the presence of an oxidant.
  • the oxidant may be the ambient air, or may be provided by an oxidant source connected via flow line, wherein the oxidant (e.g., the added air or oxygen) flows into the system.
  • the BN photocatalyst degrades the contaminants upon activation by the light, thereby decreasing the toxicity of the aqueous liquid.
  • Embodiments disclosed herein may include treating contaminants in an aqueous liquid with BN-Ti02 photocatalysts.
  • the oxidant may be the ambient air, or may be provided by an oxidant source connected via flow line, wherein the oxidant (e.g., the added air or oxygen) flows into the system.
  • Both the BN photocatalyst and the Ti02 photocatalyst may be present in the same system to degrade the contaminants upon activation by the light, thereby decreasing the toxicity of the aqueous liquid.
  • boron nitride acts as a photocatalyst for degrading contaminants, such as PFOA, in an aqueous solution without the use of additional chemicals. It has been found that BN photocatalyst is active for the heterogeneous photodegradation of PFOA and may be as much as four times more effective than conventional photocatalysts, such as T1O2. In addition to degradation of stable and recalcitrant compounds like PFOA, embodiments of the present disclosure may also be used for the degradation of less-stable compounds, such as 1, 4-dioxane, pharmaceuticals, pesticides, and chlorinated solvents.
  • less-stable compounds such as 1, 4-dioxane, pharmaceuticals, pesticides, and chlorinated solvents.
  • Photocatalytic reactor configurations may vary with light sources (ambient light, sunlight, ultraviolet light), photocatalyst handling (photocatalyst coated on or as a particulate suspended in a slurry, or coated on an immobilized surface), sources of wastewater (industrial runoff, sewage from cities), and sources of oxidants (ambient air, oxygen line).
  • light sources ambient light, sunlight, ultraviolet light
  • photocatalyst handling photocatalyst coated on or as a particulate suspended in a slurry, or coated on an immobilized surface
  • sources of wastewater industrial runoff, sewage from cities
  • sources of oxidants ambient air, oxygen line
  • the BN photocatalyst may be present in one or more various forms, including in particulate form, coated on reactor surfaces, such as fixed-geometry surfaces, fluidized media, and contained in polymer nano-composites.
  • the particular form of the BN photocatalyst used within a water treatment system is not particularly limited, other than the need to have sufficient surface area for contact with the reactants, oxygen and the contaminant(s), as well as sufficient exposure of the BN photocatalyst to light.
  • the BN photocatalyst may be present in a coating that is disposed on one or more surfaces within a reactor.
  • BN photocatalyst for example, may be incorporated into a paste and deposited on a surface within or to be disposed within a reactor.
  • the paste may be prepared in some embodiments by mixing BN photocatalyst nanopowders with a binder, such as polyethylene glycol, and condensed by evaporation until a target viscosity and BN photocatalyst content is reached.
  • the paste may then be disposed on various surfaces by methods understood by those skilled in the art with the benefit of the present disclosure, such as fluidized bed coating, spray coating, and roller coating methods.
  • BN photocatalyst may be present on particles (i.e., particulate support materials), that may be used in a slurry reactor or fixed bed reactor, for example.
  • BN photocatalyst may be applied to, deposited upon, or otherwise associated with suitable particulate support materials by various methods understood by those skilled in the art.
  • Particulate support materials may include, among other compounds, silica, alumina, titania, and mixtures of these particulate support materials, therein.
  • the size of the support materials may be in a range from lOnm to 10mm, for example, depending upon the reactor type (fixed bed or slurry).
  • the support materials are preferably low surface area support materials, and the BN photocatalyst may be disposed largely on an exterior or exposed portion of the particle such that the BN may be exposed to light during use.
  • particulate materials of sufficient strength should be used, such that contact with other catalyst particles does not result in damage to the catalyst that may render the catalyst unsuitable for the intended reaction.
  • BN particles themselves may be useful as a slurry or fixed bed catalyst.
  • BN photocatalyst may be present on fixed-geometry surfaces.
  • fixed-geometry surfaces may include immobilized surfaces, walls of the reactor, the outside surface of the light source, optical fiber structures, polymer rods, fixed bed membranes, and other equivalent means that may be coated with BN photocatalyst. These surfaces may be immobilized within a system and configured to allow a flow of a fluid across the outside surface area of the fixed- geometry surface.
  • BN photocatalyst may be applied to the outside surface area of the fixed-geometry surface by coating methods understood by those skilled in the art.
  • the fixed-geometry surface is the light source configured to conduct light waves through the inside of the structure, thereby exposing and activating the BN photocatalyst.
  • the BN photocatalyst may be disposed largely on the external surface of the support material or fixed geometry surfaces in a manner providing a large surface area and efficient exposure or the BN photocatalyst to light.
  • the slurry reactor may also be configured for fluid communication with an oxidant source, such as a flow line to the reactor, an open surface of the reactor to the ambient air where agitation or other interaction with the ambient air may result in dissolution of oxygen within the aqueous liquid, or other equivalent means that may result in oxygen being dissolved in the aqueous liquid upstream before introduction of the aqueous liquid into the reactor.
  • an oxidant source such as a flow line to the reactor, an open surface of the reactor to the ambient air where agitation or other interaction with the ambient air may result in dissolution of oxygen within the aqueous liquid, or other equivalent means that may result in oxygen being dissolved in the aqueous liquid upstream before introduction of the aqueous liquid into the reactor.
  • Embodiments of the present disclosure may also include reactors configured to hold a stationary photocatalyst, such as the BN photocatalyst coated fixed-geometry surfaces as described above.
  • Photocatalytic reactors with fixed, or stationary catalysts may be operated with batch, semi-batch, and continuous flow processing.
  • the BN photocatalyst coated fixed-geometry surface may be fitted to be disposed in the reactor, wherein an aqueous liquid, such as wastewater, may be in fluid communication with the BN photocatalyst coated fixed-geometry surface.
  • the reactor may be configured with a light source, such as an ultraviolet lamp, which may be internal or external to the reactor.
  • the reactor may also be configured for fluid communication with an oxidant source, such as a flow line to the reactor, an open surface of the reactor to the ambient air where agitation or other interaction with the ambient air may result in dissolution of oxygen within the aqueous liquid, or other equivalent means that may result in oxygen being dissolved in the aqueous liquid upstream before introduction of the aqueous liquid into the reactor.
  • an oxidant source such as a flow line to the reactor, an open surface of the reactor to the ambient air where agitation or other interaction with the ambient air may result in dissolution of oxygen within the aqueous liquid, or other equivalent means that may result in oxygen being dissolved in the aqueous liquid upstream before introduction of the aqueous liquid into the reactor.
  • embodiments disclosed herein may include a slurry reactor system 100.
  • an oxidant is present in the slurry reactor 12.
  • the oxidant source may come from a line (not shown) to supply the oxidant, such as oxygen.
  • the slurry reactor 12 may also be open to the surrounding environment wherein ambient air may act as the oxidant.
  • the wastewater 14 enters through line 11 into a slurry reactor 12.
  • the wastewater 14 from line 11 mixes with fluidized media, herein BN photocatalyst coated particles 13, to create a slurry.
  • BN photocatalyst is coated on particles using methods understood by those skilled in the art.
  • BN By pre-mixing BN nanopowders and the support materials with water, and then evaporating and calcining in the air atmosphere, BN might be coated on the support surface.
  • the BN coating may also be polymer nano-composites wherein a paste is prepared by mixing BN nanopowders with a binder, such as polyethylene glycol, among others, and may be condensed by evaporation. The paste may then be applied to a particle surface to create BN photocatalyst coated particles 13.
  • wastewater 14 flows inside the slurry reactor 12 and passes over the BN photocatalyst coated particles 13.
  • light source 15 exposes the contents of the reactor 12 to light waves, preferably ultraviolet light.
  • ultraviolet light mono- or poly-chromatic
  • the activated BN photocatalyst particles 13 then catalyze the reaction of the oxidant and contaminants, thereby degrading the water contaminants.
  • a BN coating may be deposited and immobilized onto a fixed surface, such as glass, metal, or substrate.
  • fiber optic reactor system 200 depicts optical fiber rods 22 as a surface for the BN photocatalyst coating 23.
  • BN photocatalyst coating 23 may be applied directly to the surface configured to direct ultraviolet light from a light source 25 to the BN photocatalyst coating 23 in the presence of the wastewater 26.
  • the wastewater 26 enters the fiber optic reactor system 200 through line 21 and into the fiber optic reactor 27.
  • fiber optic reactor 27 is configured to draw an oxidant from a source, such as the ambient air via an open reactor vessel.
  • the wastewater 26 passes over the BN photocatalyst coating 23 in the presence of ultraviolet light waves, and an oxidant source.
  • the ultraviolet light waves originate from a light source 25, such as a lamp.
  • the BN photocatalyst coating 23 reacts with the light waves and oxidant to degrade the contaminants in the wastewater via pathways described herein.
  • the treated wastewater 28 flows out of the fiber optic reactor 27 though line 29.
  • Fig. 1 and Fig. 2 show embodiments of single-phase reactor systems. It will be understood by those in the art that embodiments of the present disclosure may be 2-, 3-, or multiple-phase reactor systems.
  • Loading of the photocatalyst may impact the activity and rate of PFOA loss.
  • loading a quartz cell with a solid can lead to suspension turbidity which can negatively affect light flux throughout the reaction vessel.
  • Fig. 4 shows exploratory experiments wherein the BN photocatalyst mass was varied between 0-100 mg to determine the optimum BN photocatalyst load mass. The maximum rate of PFOA loss was observed between 50-100 mg BN photocatalyst. Therefore, the mass of photocatalysts (in the case of the experiment, h-BN) used for each experiment was kept at 50 mg.
  • Embodiments of the present disclosure may apply the load ratio captured in the experiment to maximize the photocatalysis pathways of BN while not affecting the light flux through the reaction vessel.
  • PFOA degradation can undergo stepwise decarboxylation/defluorination in which PFOA composes to perfluorheptanoic acid (Cl), which decomposes to perfluorohexanoic acid (C6), and so on.
  • the shorter chain homologues of PFOA may react directly with the surface B-H bonds formed during irradiation with the UV light.
  • the surface bound fluoride may be released from the BN surface as the concentrations of PFOA and its fragments decrease.
  • the present disclosure does not require the use of additional chemicals, unlike most conventional treatment technologies require; water with atmospheric air is effective for the degradation of PFOA by the photocatalytic BN and a UV-C light source.
  • BN advantageous photocatalytic properties with PFOA may be, in part, due to its hydrophobic surface.
  • PFAS is a surfactant with a polar headgroup and non-polar carbon-fluorine chain.
  • PFAS hydrophobic moiety interacts with the otherwise hydrophobic surface of BN.
  • Other photocatalysts are usually metal oxides (e.g., titanium dioxide) and as such exhibit surface charge and are not considered hydrophobic in nature.
  • metal oxides e.g., titanium dioxide
  • oxidation of the surface by light produces oxygen functional groups that increase polarity, and thus would not maintain their hydrophobicity.
  • the unique hydrophobic surface of BN, and its ability to attract PFAS is a distinctive quality of its ability to bring PFAS compounds close enough to the surface to facilitate heterogeneous catalysis.
  • BN powder, ⁇ lpm, 98% purity, lot number STBH7651
  • titanium dioxide TiC , P25 nanopowder, ⁇ 21 nm particle size, >99.5%
  • silicon dioxide SiC , nanopowder, 10-20 nm particle size, 99.5% purity
  • DI water deionized water
  • X-ray photoelectron spectroscopy (XPS) data was obtained using a PHI Quantera System with monochromatic A1 KR radiation.
  • XPS samples were prepared by placing 50 mg of material in an 80°C oven overnight to evaporate water before analysis.
  • DR-UV of the powders was obtained by diluting with 60 wt% BaSCri, pressing into a wafer, and measured using a Shimadzu UV-2450 spectrometer. Nitrogen physisorption was performed following 5 hours (“h”) of evacuation at 150°C and BET surface areas are shown below in Table 3.
  • Raman spectra was collected from 100 /cm to 3200 /cm on a Raman microscope with 532 nm excitation.
  • the photocatalytic reactor used was fabricated. It was equipped with six 4W
  • Table 4 shows the reported literature values of PFOA photocatalysts using UVC irradiation.
  • the optimum amount of photocatalyst (2.5 g/L BN, or 0.5 g/L T1O2) was added to a 100 mL quartz round bottom flask containing 20 mL of DI 3 ⁇ 40 spiked with 50 ppm (0.12 mM) PFOA and capped with a septum before placing in the reactor box and turning on light and stirring.
  • Initial pH for most experiments was 6.5. Aliquots were removed and filtered with 0.20 pm syringe filters.
  • Optimal loadings of BN and T1O2 were determined by dosing the reactor with varied masses of photocatalyst, then choosing the concentration at which the rate of PFOA disappearance was maximum, as shown in Figs. 9-12.
  • the mobile phase was 50 v% acetonitrile and 50 vol% of 5 mmol/L Na 2 HP0 4 with a flow rate of 0.8 mL/min, a sample injection volume of 50 pL, and detected at 210 nm.
  • concentration of released fluoride was measured by ion chromatography (IC, (Dionex Aquion, 4 x 250 mm IonPac AS23, AERS 500 Carbonate Suppressor). pH measurements were recorded using an Orion Star A111 pH probe. Chemical actinometry using potassium ferrioxalate actinometer to determine photons adsorbed in the flasks in the photoreactor was done using standard methods.
  • the rate of photons adsorbed was determined to be 2.6 pEin/L/s. Defining an apparent quantum yield (QY) as molecules of PFOA degraded per photon reaching the reaction fluid: where D
  • PFOA concentration-time profiles are shown using BN (Fig. 14) and Ti02 (Fig. 15) with and without 254 nm irradiation. Also shown in Fig. 14 and Fig. 15 are the fluoride concentration profiles for BN (Fig. 14) and Ti02 (Fig. 15). PFOA concentrations unexpectedly decreased with irradiation time using BN. PFOA did not degrade with 254 nm light without BN or T1O2. PFOA had a half-life of 1.2h for BN in the reaction system, exhibiting a photocatalytic rate of 0.24 mg of PFOA/Lmin.
  • fluoride ions were detected after irradiation began.
  • 240 min. about 52% of the total initial fluorine was released as F for BN, as compared to about 40% for T1O2.
  • PFOA concentrations were not measurable in the BN case, suggesting the formation of shorter-chain PFAS byproducts.
  • Fig. 16 shows concentration profiles that typify reactions occurring in series (i.e., PFOA is degrading in a stepwise fashion over BN).
  • Fig. 17 shows PFOA is also degrading and forming shorter chain intermediates over Ti0 2 .
  • EDTA ethylenediaminetetraacetic acid
  • SOD superoxide dismutase
  • TBA ⁇ t ⁇ -butanol
  • TBA had a partial inhibitory effect, indicating that ⁇ H radicals are also involved in PFOA degradation. In all, this suggests a co dependent mechani sm, as shown in Fig. 20, in which holes and radical species degrade PFOA and related byproducts, rather than a single radical that is responsible for defluorination.
  • XPS was performed on BN before and at different reaction times, as shown in Fig. 21 and Fig. 22.
  • Fig. 21 and Fig. 22 show XPS of B Is (Fig. 21) and N Is (Fig. 22) binding energies at different reaction times. The higher binding energy shifts of the B Is and N Is peaks (after 180 min.) to the formation of surface B-F and N-F bonds, respectively.
  • PFOA and its shorter chain homologues can react directly with surface fi ll bonds formed during irradiation.
  • the binding energy peaks shifted back after 360 min., and may be as a result of the release of the surface-bound fluoride into solution from the BN surface as the concentrations of PFOA and its fragments decreased.
  • a reductive reaction pathway over in-situ hydrogenated BN sites may be coexisting with the photo-oxidative pathway (the oxidative pathway being shown in Fig. 20).
  • the B-H surface species would be regenerated via photocatalyzed reaction with either proton or water species, as has been reported for BN and fluorinated BN in photocatalyzed water splitting.
  • the XPS results imply concurrent hydrodefluorination during BN catalyzed PFOA photodegradation.
  • the BN band gap should be too wide for 254 nm light absorption, yet PFOA underwent apparent photocatalytic degradation over BN.
  • the absorbance spectrum of BN was measured, as shown in Fig. 23, as well as for T1O2, as shown in Fig. 26, through DR-UV.
  • T1O2 has a wide absorbance throughout the UV region, extending from 200 to 400 nm.
  • the BN spectrum showed a small peak absorbance at 208 nm.
  • BN had very small, but non-zero, absorbance at 254 nm, which may be due to defects within BN, such as edge defects.
  • the Raman spectra of the BN material was collected, which arises from in-plane vibrations of N and B in opposing directions. Its broadness and location are measures of defectiveness. As shown in Fig. 24, the BN (as received) was relatively defective. The full width at half-maximum was 12/cm, which was broader than the value of the bulk powder. The E2 g mode blue- shifted to 1367/cm, from 1371/cm for bulk BN.
  • the resulting material After introducing defects via ball milling, the resulting material showed an increased absorbance in the UV-C range, as seen in Fig. 23, and a broader E2 g Raman peak, and a slight blue-shift was observed, as seen in Fig. 24.
  • the ball milled BN showed improved performance for PFOA degradation.
  • the photocatalytic degradation rate increased from 0.24 to 0.44 mg of PFOA/Lmin after ball milling. These rates are 2 to 4 times greater than that of T1O2.
  • the apparent quantum yields for as -received BN and ball milled BN were calculated to be 0.4% and 0.7%, respectively, higher than the value of 0.18% for T1O2.
  • BN surface defects are necessary for light absorption and photodegradation capacity and predict that large- surface area BN, with high surface defect content, will show higher PFOA photodegradation activity.
  • Fig. 27 shows the PFOA photodegradation rates over as-received BN and T1O2 in DI water and SDW.
  • BN outperformed T1O2, whose level of degradation after 120 min. dropped to 15%.
  • Fig. 28 shows the PFOA concentration time profiles in SDW with reinjections of PFOA for the BN case.
  • BN maintained activity following three cycles of PFOA degradation over 19 h, during which time the T1O2 was able to degrade only the initial spike over 16 h, as seen in Fig. 28.
  • Fig. 29 shows the corresponding fluoride concentration profiles of the SDW with reinjections of PFOA for the BN case. As shown in Fig.
  • the level of free fluoride in the BN system was 48 ppm, representing about 43% of the total fluorine added, while the T1O2 system had 25 ppm F ⁇ , representing about 74% of the initial fluorine added.
  • FIG. 30 shows the GenX and fluoride concentration-time profiles using BN with 254 nm irradiation. As shown in Fig. 30, roughly 20% degraded in 2 h under the same reaction conditions, with an estimated half-life of at least 5 hours. This is the first reported heterogeneous photocatalytic decomposition of GenX.
  • Systems herein may be effective for other fluorinated compounds and other contaminants.
  • the system directly and efficiently degrades persistent organic pollutants directly rendering them nontoxic. There is no need to pretreat the water with another technology. The technology does not require additional solvents. Furthermore, there is no need to use chemical additives.
  • Embodiments of the present disclosure may provide a secure source of clean, safe water to a broad set of stakeholders (e.g., industrial organizations, governmental organizations, and citizens).
  • Embodiments of the present disclosure offer flexibility of targeted pollutant(s) and end-use application capacity or scale of delivered water rate.
  • Embodiments of the present disclosure may transform water treatment from a large, chemical- and energy-intensive process toward compact physical and catalytic systems.
  • Embodiments of the present disclosure may be applicable in the treatment of wastewater, thereby providing potable water to serve stakeholders from households, to neighborhoods, and to remote towns. Scalability may be achieved in a wide variety of applications with proper unit design.
  • Embodiments of the present disclosure may also provide access to drinking water during times of natural disasters. Natural disasters may destroy existing wastewater treatment facilities, leaving the affected population vulnerable to contaminants in the drinking water. Some embodiments of the present disclosure may be implemented on the fly with commercially available supplies to set up a wastewater treatment system, therein providing the population with access to clean water.

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  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Catalysts (AREA)
  • Physical Water Treatments (AREA)

Abstract

Un système de dégradation de contaminants peut comprendre un réacteur contenant un photocatalyseur au nitrure de bore. Le système de réacteur peut être configuré pour recevoir un liquide aqueux comprenant au moins un contaminant, et peut également comprendre une source de lumière configurée pour diriger la lumière vers le photocatalyseur au nitrure de bore, et une source d'oxydant en communication fluidique avec le réacteur.
PCT/US2020/054048 2019-10-02 2020-10-02 Système de dégradation de contaminants chimiques dans l'eau WO2021067786A1 (fr)

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