Photocatalytic degradation of commercially sourced naphthenic acids by TiO2-graphene composite nanomaterial

A multi-step approach: Coupling of biodegradation and UV photocatalytic oxidation TiO2 for the treatment of naphthenic acid fraction compounds in oil sands process-affected water

Bitumen extraction in Alberta's oil sands region uses large volumes of water, leading to an abundance of oil sands process-affected water (OSPW). OSPW contains naphthenic acid fraction compounds (NAFCs) which have been found to contribute to OSPW toxicity. This study utilized a multistep treatment, coupling biological degradation with UV photocatalytic oxidation, and nutrient addition to boost the native microbial community's degradation capacity. OSPW initially contained 40-42 mg/L NAFCs with a toxicity of 3.8-3.9 TU. Initial biodegradation (Step 1) was used to remove the easily biodegradable NAFCs (11-25% removal), followed by a light or heavy dose of oxidation (Step 2) to breakdown the recalcitrant NAFCs (66-82% removal). Lastly, post-oxidation biodegradation with nutrients (Step 3) removed the residual bioavailable NAFCs (16-31% removal). By the end of the multistep treatment, the final NAFC concentrations and toxicity ranged from 5.3 to 6.8 mg/L and 1.1-1.2 TU. Analysis showed that OPSW was limited in phosphorus (below detection limit), and the addition of nutrients improved the degradation of NAFCs. Two treatments throughout the multistep treatment never received nutrients and showed minimal NAFC degradation post-oxidation. The native microbial community survived the stress from UV photocatalytic oxidation as seen by the post-oxidation NAFC biodegradation. Microbial community diversity was reduced considerably following oxidation, but increased with nutrient addition. The microbial community consisted predominately of Proteobacteria (Gammaproteobacteria and Alphaproteobacteria), and the composition shifted depending on the level of oxidation received. Possible NAFC-degrading microbes identified after a light oxidation dose included Pseudomonas, Acinetobacter and Xanthomonadales, while Xanthobacteracea and Rhodococcus were the dominant microbes after heavy oxidation. This experiment confirms that the microbial community is capable of degrading NAFCs and withstanding oxidative stress, and that degradation is further enhanced with the addition of nutrients.

β-cyclodextrin modified GO ultrafiltration membranes with enhanced antifouling property for water purification

The study investigated the influence of additives on the fabrication of mixed matrix membranes comprising polyethersulfone (PES), with a specific focus on hydrophilicity, flux, morphology, and antifouling properties. Carboxymethyl modified β-cyclodextrin (CMβ-CD) was used to enhance the dispersion and hydrophilicity of graphene oxide (GO), leading to the formation of a hydrophilic and stable composite nanoparticle (CMCD@GO). The hydrophilicity (WCA <51.5°) and water flux (32.6 L.m-2.h-1) of the modified PES membranes (MCDGO-x) were improved by the incorporation of CMCD@GO nanoparticles, while that of PES membrane was 79.7° and 10.6 L.m-2.h-1. The rate of backscattered light intensity (ΔBS) of MCDGO-x suspensions remains stable, suggesting stable dispersion of CMCD@GO in organic solvents. Compared to the bare PES membrane, the MCDGO-x membrane exhibits a thinner active layer and a finger-like structure. The MCDGO-x membrane exhibited excellent naphthenic acids (NAs) rejection (> 93.2%) due to reduced roughness and higher hydrophilicity, while the GO-modified PES membrane (MGO-5) exhibited lower NAs rejection (87.2%). Furthermore, the MCDGO-5 membrane showed higher flux recovery ratio (FRR) of 79.3% compared to MGO-5 membrane (68.5%) after three cycles, indicating the antifouling performance of MCDGO-x for NAs was significantly improved. The combination of CMβ-CD and GO enhance the flux and antifouling properties of PES ultrafiltration membranes, suggesting significant potential for applications in the purification of oil sands process water and the treatment of oily wastewater.

Efficient removal of naphthenic acids from real petroleum wastewater by natural pyrite activated persulfate system

The petroleum wastewater (PWW) contains a diverse range of recalcitrant organic contaminants. Of particular concern is the removal of naphthenic acids (NAs) due to the high toxicity and persistence. Persulfate (PS) based oxidation processes have shown promising in treating refractory wastewater, while the high costs of prepared catalysts limited their widespread implementation. This study aims to develop a cost-effective natural pyrite activated PS system for PWW treatment. The removal of NAs by pyrite/PS system was initially investigated. More than 90% of cyclohexanoic acid (CHA), a model NA, was removed in pyrite/PS system (2.0 g/L pyrite, 4.0 mM PS) at initial pH of 3-11. Scavenging experiments revealed that Fe(II) on pyrite surface was the reactive site for PS activation to generate reactive species, including sulfate radical (SO4·-), Fe(IV) and hydroxyl radical (·OH) for CHA degradation. Reactions of Fe(III) with S helped restore Fe(II) and enhance PS activation, resulting in the sustained catalytic activity of pyrites over five cycles. Cl-, SO42- and NO3- below 10 mM had minimal impact on CHA degradation in pyrite/PS system. However, over 1 mM of HCO3- inhibited 80% of CHA removal due to the buffer effect to maintain the high solution pH. Removing HCO3- from real PWW restored the removal of CHA and of total organic carbon (TOC) to over 90% and 71.3% in pyrite/PS system, respectively. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results indicated that O2‒6 species including NAs were primarily eliminated through mineralization and oxygen addition. Besides, O3-5S, NO3-5S and N3O2‒4 species were the most susceptible to oxidation in PWW, resulting in the increase of the oxidation level (i.e., O/Cwa) from 0.41 to 0.56 after treatment. This study provides valuable insights into the treatment of NAs in real PWW, and potential application of natural minerals in the treatment of industrial wastewater.

Sorption and desorption of naphthenic acids on reclamation materials: Mechanisms and selectivity of naphthenic acids from oil sands process water

This study investigated the application of materials peat-mineral mix (PT) and Pleistocene fluvial sands from different location (PF-1 and PF-2) obtained from surface mining of oil sands as sorbents of naphthenic acids (NAs) from oil sands process water (OSPW). To understand the sorption properties and mechanisms of NAs in the materials, sorption and desorption studies were performed using decanoic acid (DA) and 5-phenylvaleric acid (PVA). Additionally, the removal efficiency was evaluated using real OSPW to understand the effect of NA structure on sorption. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Langmuir isotherm best fitted the equilibrium data. Maximum sorption capacities for DA and PVA were, respectively, 16.8 × 10³ and 10⁴ mg/kg for PT, 142.9 and 81.3 mg/kg for PF-1, and 600 and 476.2 mg/kg for PF-2. Hydrophobic interactions, hydrogen bonding, and π-π interaction were the main sorption mechanisms. Desorption of model compounds from post-sorption materials was not observed for 14 days. The removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising sorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Sorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important sorption mechanism. The results suggest that some mobility of NAs is expected to take place if the reclamation materials come in contact with OSPW, which might occur in an oil sands reclamation landscape.

Electrochemical treatment of electroplating wastewater using synthesized GO/TiO2 nanotube electrode

The graphene oxide (GO) deposited TiO₂ nanotube (GO/TiO₂) electrode on a titania plate was prepared using a simple anodization method. The morphological and structural properties of TiO₂ and GO/TiO₂ electrodes have been studied using field emission scanning electron microscopy energy dispersive spectroscopy (FESEM-EDS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). FESEM-EDS analysis confirmed that the 13.56% wt of GO nanoparticles was formed over the TiO₂ substrate, with the thickness of the wall to be ∼300 nm. The crystallite size of GO/TiO₂, i.e., 19.53 nm, was confirmed by XRD analysis. Analysis of the UV-DRS spectrum showed the bandgap of the synthesized GO/TIO₂ nanotube electrode to be 3.052 eV. Box-Behnken design (BBD) under response surface methodology (RSM) was used to design the experiments. The effect of operating input parameters like pH, current (i), and degradation time (t) on % COD degradation (X₁) and energy consumed (X₂) were also examined. At optimum process parameters, the value of X₁ and X₂ were 57.61% and 15.00 kWh/m³, respectively. Possible intermediates were identified based on the GC-MS data analysis. Scavenger tests showed that •OH radical plays a major role in electroplating effluents degradation. Based on the results, the EO process using GO/TiO₂ electrodes could be considered a promising technique for electroplating effluent degradation due to high degradation efficiency.

Abiotic and biotic constituents of oil sands process-affected waters

The oil sands in Northern Alberta are the largest oil sands in the world, providing an important economic resource for the Canadian energy industry. The extraction of petroleum in the oil sands begins with the addition of hot water to the bituminous sediment, generating oil sands process-affected water (OSPW), which is acutely toxic to organisms. Trillions of litres of OSPW are stored on oil sands mining leased sites in man-made reservoirs called tailings ponds. As the volume of OSPW increases, concerns arise regarding the reclamation and eventual release of this water back into the environment. OSPW is composed of a complex and heterogeneous mix of components that vary based on factors such as company extraction techniques, age of the water, location, and bitumen ore quality. Therefore, the effective remediation of OSPW requires the consideration of abiotic and biotic constituents within it to understand short and long term effects of treatments used. This review summarizes selected chemicals and organisms in these waters and their interactions to provide a holistic perspective on the physiochemical and microbial dynamics underpinning OSPW .

A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

Titanium Dioxide–Reduced Graphene Oxide Composites for Photocatalytic Degradation of Dyes in Water

Dye wastewater due to industrialization, urbanization and academic activities has become one of the most important environmental issues today. Photocatalytic degradation technology is considered as a promising technology for treating dye wastewater due to its advantages of environmental protection and low energy consumption. Herein, titanium dioxide–reduced graphene oxide composites (TiO2-RGO) were prepared by a one-step hydrothermal method to degrade different dyes (methyl orange, methylene blue and rhodamine B) in water. The structure and morphology of TiO2-RGO were characterized using various technical approaches. The degradation effect of TiO2-RGO on the dye was in accordance with a first-order kinetic reaction. The degradation rate of TiO2-6%RGO for methyl orange at 15 min was 1.67 times higher than that of TiO2, due to the strong electron transport ability and excellent adsorption properties of graphene. TiO2-6%RGO has better degradation performance for fluorescent dyes and anionic azo dyes. Notably, the degradation rate of methyl orange by TiO2-6%RGO photocatalysis for 90 min could reach 96.9%. Meanwhile, the TiO2-6%RGO showed excellent reusability, as the initial degradation rate of 93.2% was maintained after five degradation cycles of methyl orange solution. The present work provides a universal strategy for designing efficient photocatalytic materials.

Preparation and modification methods of defective titanium dioxide-based nanoparticles for photocatalytic wastewater treatment-a comprehensive review

The rapid population growth and industrial expansion worldwide have created serious water contamination concerns. To curb the pollution issue, it has become imperative to use a versatile material for the treatment. Titanium dioxide (TiO₂) has been recognized as the most-studied nanoparticle in various fields of science and engineering due to its availability, low cost, efficiency, and other fascinating properties with a wide range of applications in modern technology. Recent studies revealed the photocatalytic activity of the material for the treatment of industrial effluents to promote environmental sustainability. With the wide band gap energy of 3.2 eV, TiO₂ can be activated under UV light; thus, many strategies have been proposed to extend its photoabsorption to the visible light region. In what follows, this has generated increasing attention to study its characteristics and structural modifications in different forms for photocatalytic applications. The present review provides an insight into the understanding of the synthesis methods of TiO₂, the current progress in the treatment techniques for the degradation of wide environmental pollutants employing modified TiO₂ nanoparticles, and the factors affecting its photocatalytic activities. Further, recent developments in using titania for practical applications, the approach for designing novel nanomaterials, and the prospects and opportunities in this exciting area have been discussed.

Effects of asphaltenes on the photolytic and toxic behavior of bitumen and conventional oil products on saltwater

The effects of asphaltenes on the photolytic and toxic behavior of petroleum oil on seawater was investigated by exposing five original oils and their maltenes to solar irradiation for seven days. Polycyclic aromatic hydrocarbons (PAHs) experienced the fastest photo-oxidation, but negligible photolytic loss was observed for most normal alkanes and all the petroleum biomarkers from tri-cyclic to pentyl-cyclic terpanes in the test total oil and maltenes. The removal of most PAHs from some maltenes was greater than the corresponding total oils. Deasphalting process did not affect the characteristics of naphthenic acid fraction components (NAFCs) in all control samples. In all test oils, solar irradiation formed abundant NAFCs, in particular those only containing oxygen as the heteroatoms (O_o species). The formed O_o species were abundant in congeners having highly saturated congeners, and shifted to a lighter carbon number after exposed. Deasphalting process significantly enhanced the formation of O_o species (o from 2 to 4) for all test oils, in particular for the Cold Lake Blend and Bunker C. The toxicity of exposed maltenes was generally higher than the exposed total oil for most oils, suggesting the aqueous toxicity level was positively related to the formed NAFC intermediates.

Solar-activated zinc oxide photocatalytic treatment of real oil sands process water: Effect of treatment parameters on naphthenic acids, polyaromatic hydrocarbons and acute toxicity removal

Oil sands process water (OSPW) is an industrial process effluent that contains organic compounds such as naphthenic acids (NAs) and polyaromatic hydrocarbons (PAHs), as well as large quantities of inorganic compounds in its mixture. OSPW requires effective treatment for successful reclamation and water reuse. This study investigated the impact of solar-activated zinc oxide (ZnO) photocatalysis on the degradation and removal of NAs and PAHs in OSPW, as well as the elimination of its acute toxicity. With catalyst particles suspended in the effluent (at 1 g/L) under simulated solar radiation of steady irradiance of ~278 W/m², more than 99% removal of NAs was achieved after 4 h of treatment, while nearly all PAHs were simultaneously oxidized within the same reaction time. The photocatalytic treatment appeared to selectively convert classical NAs faster than oxidized NAs. Additionally, NAs with higher double-bond equivalents (DBEs) and higher carbon numbers seemed more susceptible to photocatalytic destruction than others. An overall pseudo first-order rate constant of 1.14 × 10^-2 min^-1, and a fluence-based rate constant of 6.81 × 10^-1 m²/MJ were recorded in apparently hydroxyl radicals (OH) and superoxide (O₂^-) radicals mediated NAs degradation mechanisms. Assessment of the toxicity levels in raw and treated OSPW samples by using Microtox® bioassay indicated that the photocatalytic treatment resulted in ~50% reduction in acute toxicity. Furthermore, we showed that by monitoring the expression levels of key proinflammatory genes using qPCR that treated OSPW significantly reduced the ability of raw OSPW to activate the inflammatory response of immune cells. This indicates that at acute sub-lethal exposure doses, photocatalytic treatment also reduces immunotoxicity. Overall, our results suggest that the ZnO-based photocatalytic degradation of these NAs and PAHs in OSPW could be a significant treatment process aimed at detoxifying OSPW.

Impacts of bioreactor operating parameters on removal efficiency, biodegradation rate, molecular distribution, and toxicity of commercial naphthenic acids

Effects of naphthenic acids (NAs) concentration (50-200 mg NA L^-1; 35-140 mg TOC L^-1) and loading rate (1.4-1249 mg NA L^-1 h^-1; 1-874 mg TOC L^-1 h^-1) on removal efficiency, removal rate, and molecular distribution of NAs, and effluent toxicity were evaluated for biodegradation of commercial NAs mixture in circulating packed bed bioreactors (CPBBs). Increase of NAs concentration and loading rate (shorter residence times) increased the removal rate, while removal efficiency initially declined and then stabilized. The maximum biodegradation rates for 50, 100, 150, and 200 mg NA L^-1 were 128.0, 321.7, 430.2, and 630.0 mg TOC L^-1 h^-1 at loading rates of 218.5, 455.6, 673.5 and 874.0 mg TOC L^-1 h^-1, respectively, with removal efficiencies of 58.6, 70.6, 63.9 and 72.1%. Analysis of influent and treated effluents with gas chromatography-mass spectrometry showed that molecular weight and cyclicity (C and Z numbers) affected the biodegradation, with low molecular weight acyclic NAs (C = 6-12) were the most amenable to biodegradation and those with intermediate and high molecular weights (C = 13-22) and moderate cyclicity (Z = - 4, - 6) were the most recalcitrant. In the biofilm, Proteobacteria and Actinobacteria were the most abundant phyla, and Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria were the dominant classes. Toxicity analyses with Artemia salina and Vibrio fischeri (Microtox) showed that high influent concentrations and loading rates (short residence times) led to higher NAs residual concentration and effluent toxicity. To design and operate large-scale CPBBs, intermediate loading rates and residence times that result in high removal efficiency, reasonable removal rates, and low toxicity are recommended.

Solar photocatalytic treatment of model and real oil sands process water naphthenic acids by bismuth tungstate: Effect of catalyst morphology and cations on the degradation kinetics and pathways

Bitumen extraction from oil sands produces large quantities of oil sands process water (OSPW), which contains recalcitrant naphthenic acids (NAs). In this study, three different morphologies of bismuth tungstate (Bi₂WO₆) photocatalysts were prepared by hydrothermal method. The prepared catalyst was characterized to obtain its structural, textural and chemical properties and tested for the degradation of model NAs and real OSPW under simulated solar irradiation. Nanoplate, flower-like and swirl-like Bi₂WO₆ were prepared and the results showed that the flower-like structure exhibited the highest specific surface area and total pore volume. The highest photocatalytic activity for the degradation of NAs was also demonstrated by the flower-like Bi₂WO₆, achieving complete degradation of cyclohexanoic acid (CHA) at fluence-based rate constant of 0.0929 cm²/J. Superoxide radicals (O₂^•-) and holes were identified as the major reactive species generated during the photocatalytic process. The effect of metallic ions on the degradation rates of S-containing and N-containing NAs differed and the heteroatom was found to be the main reactive site. The by-products of heteroatomic NAs were identified and degradation pathways were reported for the first time. The concentration changes of each byproduct were further estimated by mass balance. This research provides valuable information for the treatment of NAs by engineered passive solar-based approaches.

Progress in Graphene/Metal Oxide Composite Photocatalysts for Degradation of Organic Pollutants

The sewage discharge of industrial wastewater seriously pollutes the water source and rivers, which is very harmful to the health of humans and wildlife. Among those methods for treating wastewater, photocatalysis is a sustainable and environmental-friendly technique for removing the organic pollutants with no secondary pollution. As a popular photocatalyst, graphene/metal oxide nanocomposites have been widely reported in the photocatalysis field. In this review, the recent progress of graphene/metal oxide composites including binary and ternary composites is summarized in detail. The synthesis, microstructure design, and application performance of graphene/TiO2, graphene/ZnO, graphene/SnO2, graphene/WO3, graphene/Fe2O3, and graphene/Cu2O composites are introduced firstly. Then, the synthesis, the selection of components, and the performance of various ternary composites are summarized specifically, including graphene/TiO2-, graphene/ZnO-, graphene/SnO2-, graphene/Cu2O-, graphene/FexOy-, and graphene/Bi-containing ternary composites. At last, the possible research directions of graphene/metal oxide nanocomposites are put forward. The main purpose is to provide a theoretical guidance for designing high-performance graphene/metal oxide photocatalysts for wastewater treatment.

One-step synthesis of Ag2S-TiO2 and its photocatalytic degradation of ethyl paraben wastewater

At first, naked TiO₂ was prepared by sol-gel method. Silver nitrate and thiourea were respectively used as silver source and sulfur source added to form a TiO₂ sol and Ag₂S polymer blend system. Then, the properties of Ag₂S-TiO₂ was one-step synthesized and investigated by photocatalytic experiment and material characterization. According to the characterization results, Ag₂S-TiO₂ is anatase with a band gap of 3.14 eV, a specific surface area of 39.80 m²/g, and an average pore diameter of 3.56 nm. The results of photocatalytic experiments show that Ag₂S-TiO₂ can efficiently remove ethyl paraben within 2 h. Quenching experiments show that both •OH and photogenerated holes have a large effect on photocatalytic performance.

Characterization of ultraviolet-modified biochar from different feedstocks for enhanced removal of hexavalent chromium from water

Biochars produced from different feedstocks via pyrolytic carbonization and ultraviolet (UV) modification were used as alternative adsorbents for aqueous hexavalent chromium (Cr(VI)) remediation. Structural and morphological analysis showed that UV irradiation increased the surface area of biochar and added a large amount of oxygen-containing functional groups on the biochar's surface, resulting in about 2-5 times increase of Cr(VI) removing capacity (14.39-20.04 mg/g) compared to that of unmodified biochars (3.60-8.43 mg/g). The sorption ability among different feedstocks after modification was as follows: corn stack > sawdust > wheat straw. The adsorption kinetics and adsorption isotherm data agreed well with the pseudo-second-order model and Freundlich model, respectively. Experimental and modeling results suggested that the oxygen-containing functional groups and surface areas of biochars were notably increased after UV irradiation, which was mainly governed by surface complexation. X-ray photoelectron spectroscopy analysis showed that reduction occurred during Cr(VI) adsorption. In addition, UV irradiation significantly increased the concentration of dissolved organic matter (DOM) in biochars. The collected outcomes showed that UV-modified biochar was a good material for the removal of hexavalent chromium from aqueous medium. The excellent adsorption capacity, environmental-friendly and low cost properties made the novel material an auspicious candidate for environmental remediation.

Continuous column adsorption of naphthenic acids from synthetic and real oil sands process-affected water (OSPW) using carbon-based adsorbents

In this study, activated petroleum coke (APC) and commercial activated carbon (CAC) were used in a continuous adsorption column for removal of model naphthenic acids and organics from real oil sands process-affected water (OSPW). Diphenylacetic acid and 2-naphthoic acid, two model naphthenic acid (NA) compounds, were removed completely by the APC in a continuous column operation. Due to the complex nature of organics in OSPW, total organic carbon (TOC) was measured to determine the effectiveness of OSPW treatment by APC. The removal of TOC from OSPW at its natural pH 8 by APC was only 25%, whereas acidification at pH 4 followed by APC adsorption removed 96% of the initial TOC. When compared to a commercial activated carbon, the APC showed an average of 20% higher organics removal. The experimental breakthrough curves were better fitted by Thomas model in comparison to Adams-Bohart and Yoon-Nelson models. The regeneration of APC was conducted using methanol with 0.01 wt% NaOH (pH = 11.7) and a total of four cycles of adsorption and regeneration were conducted with marginal loss of adsorption sites.

Titanium Dioxide/Graphene and Titanium Dioxide/Graphene Oxide Nanocomposites: Synthesis, Characterization and Photocatalytic Applications for Water Decontamination

The use of titanium dioxide, TiO2 as a photocatalyst in water decontamination has witnessed continuous interest due to its efficiency, stability, low toxicity and cost-effectiveness. TiO2 use is limited by its large band gap energy leading to light absorbance in the UV region of the spectrum, and by the relatively fast rate of recombination of photogenerated electrons and positive holes. Both limitations can be mitigated by using carbon-TiO2 nanocomposites, such as those based on graphene (G) and graphene oxide (GO). Relative to bare TiO2, these nanocomposites have improved photocatalytic activity and stability under the UV–visible light, constituting a promising way forward for improved TiO2 photocatalytic performance. This review focuses on the recent developments in the chemistry of TiO2/G and TiO2/GO nanocomposites. It addresses the mechanistic fundamentals, briefly, of TiO2 and TiO2/G and TiO2/GO photocatalysts, the various synthesis strategies for preparing TiO2/G and TiO2/GO nanocomposites, and the different characterization techniques used to study TiO2/G and TiO2/GO nanocomposites. Some applications of the use of TiO2/G and TiO2/GO nanocomposites in water decontamination are included.

Petroleomic analysis of the treatment of naphthenic organics in oil sands process-affected water with buoyant photocatalysts

The persistence of toxicity associated with the soluble naphthenic organic compounds (NOCs) of oil sands process-affected water (OSPW) implies that a treatment solution may be necessary to enable safe return of this water to the environment. Due to recent advances in high-resolution mass spectrometry (HRMS), the majority of the toxicity of OSPW is currently understood to derive from a subset of toxic classes, comprising only a minority of the total NOCs. Herein, oxidative treatment of OSPW with buoyant photocatalysts was evaluated under a petroleomics paradigm: chemical changes across acid-, base- and neutral-extractable organic fractions were tracked throughout the treatment with both positive and negative ion mode electrospray ionization (ESI) Orbitrap MS. Elimination of detected OS⁺ and NO⁺ classes of concern in the earliest stages of the treatment, along with preferential degradation of high carbon-numbered O₂^- acids, suggest that photocatalysis may detoxify OSPW with higher efficiency than previously thought. Application of petroleomic level analysis offers unprecedented insights into the treatment of petroleum impacted water, allowing reaction trends to be followed across multiple fractions and thousands of compounds simultaneously.

Structure-reactivity relationship of naphthenic acids in the photocatalytic degradation process

Bitumen extraction in Canada's oil sands generates oil sands process-affected water (OSPW) as a toxic by-product. Naphthenic acids (NAs) contribute to the water's toxicity, and treatment methods may need to be implemented to enable safe discharge. Heterogeneous photocatalysis is a promising advanced oxidation process (AOP) for OSPW remediation, however, its successful implementation requires understanding of the complicated relationship between structure and reactivity of NAs. This work aimed to study the effect of various structural properties of model compounds on the photocatalytic degradation kinetics via high resolution mass spectrometry (HRMS), including diamondoid structures, heteroatomic species, and degree of unsaturation. The rate of photocatalytic treatment increased significantly with greater structural complexity, namely with carbon number, aromaticity and degree of cyclicity, properties that render particular NAs recalcitrant to biodegradation. It is hypothesized that a superoxide radical-mediated pathway explains these observations and offers additional benefits over traditional hydroxyl radical-based AOPs. Detailed structure-reactivity investigations of NAs in photocatalysis have not previously been undertaken, and the results described herein illustrate the potential benefit of combining photocatalysis and biodegradation as a complete OSPW remediation technology.

Fate of oxygenated intermediates in solar irradiated diluted bitumen mixed with saltwater

Two types of diluted bitumen (dilbit) and a light crude oil spiked onto the surface of saltwater were irradiated with natural solar light in Ottawa to assess the impact of sunlight to the fate of oxygenated intermediates. Oxygenated components, including carbonyl polycyclic aromatic hydrocarbons (PAHs) and acidic polar fractions (naphthenic acid fraction compounds, NAFCs), were identified after periods of solar exposure under both winter and summer conditions. Carbonyl PAHs and NAFCs were formed in both seasons; however, light crude and summer irradiation produced higher abundance of them than dilbits and winter exposure. The formed NAFCs were abundant with the congeners containing a heteroatom of oxygen only (O_o species), accompanied by the minor amounts of sulfur- and nitrogen-containing acids. The produced O_o species were predominant with the congeners with light molecular weight, high degree of saturation and heavy oxygen numbers. For both carbonyl PAHs and NAFCs, their abundance continually increased throughout the period of winter exposure. In the summer, some carbonyl PAHs and all O_o species increased during the early exposure period; then they decreased with continued exposure for most oils, illustrating their transitional nature. Oxygenated intermediates thus appear to have been created through the photo-oxidation of non-to medium-polar petroleum hydrocarbons or the intermediates of aldehydes or ketones (O₁). Oil properties, the duration of exposure, exposure season and the chemical structure of these intermediates are critical factors controlling their fate through photo-oxidation. The observed chemical changes highlight the effects of sunlight on the potential behavior, fate and impact of spilled oil, with the creation of new resin group compounds and the reduction of aromatics and saturates. These results also imply that the ecological effects of spilled oil, after ageing in sunlight, depend on the specific oil involved and the environmental conditions.