Insight into Fe-O-Bi electron migration channel in MIL-53(Fe)/Bi4O5I2 Z-scheme heterojunction for efficient photocatalytic decontamination.

Building a heterojunction is a fascinating option to guarantee sufficient carrier separation and transfer efficiency, but the mechanism of charge migration at the heterojunction interface has not been thoroughly studied. Herein, MIL-53(Fe)/Bi4O5I2 photocatalyst with a Z-scheme heterojunction structure is constructed, which achieves efficient photocatalytic decontamination under solar light. Driven by the newly-built internal electric field (IEF), the formation of Fe-O-Bi electron migration channel allows for rapid separation and transfer of charge carriers at the heterojunction interface, confirmed by the material characterization and density functional theory (DFT) calculation. The narrower band gap and improved visible light response also contribute to the enhanced photocatalytic activity of composite materials. With levofloxacin as the target pollutant, the optimal MIL-53(Fe)/Bi4O5I2 achieves complete removal of pollutant within 150 min, the photocatalysis rate of which is ca. 4.4 and 26.0 times that of pure Bi4O5I2 and MIL-53(Fe), respectively. Simultaneously, the optimal composite material exhibits satisfactory photodegradation of seven fluoroquinolones, and the photocatalysis rates are as follows: lomefloxacin > ciprofloxacin > enrofloxacin > norfloxacin > pefloxacin > levofloxacin > marbofloxacin. DFT calculations reveal a positive relationship between degradation rate and Fukui index (ƒ0) of main carbon atoms in seven fluoroquinolones. This study sheds light on the existence of electron migration channels at Z-scheme heterojunction interface to ensure sufficient photoinduced carrier transfer, and reveals the influence of pollutant structure on photolysis rate.

Enhanced biomethane production from Scenedesmus sp. using polymer harvesting and expired COVID-19 disinfectant for pretreatment.

This study evaluates the repurposing of expired isopropanol (IPA) COVID-19 disinfectant (64% w/w) to pretreat algal biomass for enhancing methane (CH4) yield. The impact of harvesting methods (centrifugation and polymer flocculation) and microwave pretreatment on CH4 production from Scenedesmus sp. microalgal biomass were also investigated. Results show minimal impact of harvesting methods on the CH4 yield, with wet centrifuged and polymer-harvested biomass exhibiting comparable and low CH4 production at 66 and 74 L/kgvolatile solid, respectively. However, microalgae drying significantly increased CH4 yield compared to wet biomass, attributed to cell shrinkage and enhanced digestibility. Consequently, microwave and IPA pretreatment significantly enhanced CH4 production when applied to dried microalgae, yielding a 135% and 212% increase, respectively, compared to non-pretreated wet biomass. These findings underscore the advantage of using dried Scenedesmus sp. over wet biomass and highlight the synergistic effect of combining oven drying with IPA treatment to boost CH4 production whilst reducing COVID-19 waste.

Tuning Electrical and Mechanical Properties of Metal-Organic Frameworks by Metal Substitution.

Metal-organic frameworks (MOFs), synthesized by the self-assembly of organic ligands and metal centers, are structurally designable materials. In the current study, first-principles calculation based on density functional theory (DFT) was performed to investigate the intrinsic mechanical and electrical properties and mechanical-electrical coupling behavior of MOF-5. To improve the conductivity of MOF-5, homologous elements of Cu, Ag, and Au were adopted to replace the Zn atom in MOF-5, reducing the band gap and improving its electrical performance. Cu-MOF-5 and Au-MOF-5, with stable structures, exhibit better conductivity. The intrinsic mechanical properties such as independent elastic constants of MOF-5 and M-MOF-5 (M = Cu, Ag, Au) were obtained. MOF-5 and Cu-MOF-5 were experimentally synthesized to demonstrate the reduction in the band gap after metal substitution. The study of the strain effect of MOF-5 and Cu-MOF-5 proves that strain engineering is an effective method to regulate the band gap and this modulation is repeatable. This study clarifies the tunability of the band gap of MOF-5 with metal substituents and provides an efficient strategy for the development of new types of MOFs with desired physical properties using the combination of theoretical prediction and experimental synthesis and validation.

Elevated nitrate promoted photodegradation of PAHs in aqueous phase: Implications for the increased nutrient discharge.

Polycyclic aromatic hydrocarbons (PAHs) are frequently released in aqueous phase by oil spill or from other sources, and photochemical oxidation is one of their major weathering processes. In this study, the photochemical behavior of phenanthrene (PHE, as a representative PAH) were studied and the effects of nitrogenous compounds were evaluated. The results showed that nitrate was an effective photosensitizer for improving the photodegradation of PHE, but the promoting effect was less effective in seawater due to the presence of halogen ions; the ammonia played a negligible role on PHE degradation. The photochemical ionization was a key process for PHE degradation, it can be retarded due to the quenching of triplet excited state by dissolved oxygen, and the inhibition was most prominent in fresh water. The presence of nitrate increased the steady state concentration of •OH from 2.08 × 10-15 M to 1.04 × 10-14 M in fresh water, and from 1.5 × 10-16 M to 2.08 × 10-15 M in seawater. The secondary-order reaction rate constant between PHE and •OH (k•OH,PHE) was determined as 5.70 × 109 M-1 s-1. Similar trend was observed for 1O2. The contribution of •OH to PHE removal was more prominent in fresh water than in seawater due to the quenching effects of halogen, and the increasing of nitrate enlarged the contribution of •OH. Two possible PHE degradation pathways were proposed based on GC-MS analysis and DFT calculation. The Quantitative Structure-activity Relationship (QSAR) evaluation showed that some degradation intermediates were more toxic than PHE, but the total environmental risk was still diminished due to the low percentage of toxic intermediates. This study provided theoretical and experimental insights into the influence of nitrogenous compounds on the photodegradation of PHAs in water environment.

Semiconducting mineral induced photochemical conversion of PAHs in aquatic environment: Mechanism study and fate prediction.

Semiconducting minerals (such as iron sulfides) are highly abundant in surface water, but their influences on the natural photochemical process of contaminants are still unknown. By simulating the natural water environment under solar irradiation, this work comprehensively investigated the photochemical processes of anthracene (a typical Polycyclic Aromatic Hydrocarbons) in both freshwater and seawater. The results show that the natural pyrite (NP) significantly promotes the degradation of anthracene under solar illumination via 1) NP induced photocatalytic degradation of anthracene, and 2) Fenton reaction due to the NP induced photocatalytic generation of H2O2. The material characterization and theoretical calculation reveal that the natural impurity in NP enlarges its band gap, which limits the utilization of solar spectra to shorter wavelength. The contribution of generated reactive intermediates on anthracene degradation follows the order of 1O2 >OH > O2- in freshwater and O2- >1O2 >OH in seawater. The photochemically generated H2O2 is a vital source for OH generation (from Fenton reaction). The steady-state concentration of OH, 1O2 and O2- in freshwater were monitored as 3.0 × 10-15 M, 1.1 × 10-13 M, and 4.5 × 10-14 M, respectively. However, the OH concentration in seawater can be negligible due to the quenching effects by halides, and the 1O2 and O2- concentrations are higher than that in freshwater. An anthracene degradation kinetic model was built based on the experimentally determined reactive intermediates concentration and its second order rate constant with anthracene. Moreover, the anthracene degradation pathway was proposed based on intermediates analysis and DFT calculation, and its toxicity evolution during the photochemical process was assessed by quantitative structure-activity relationship (QSAR) based prediction. This finding suggests that the natural semiconducting minerals can affect the fate and environmental risks of contaminants in natural water.

Ceftriaxone sodium degradation by carbon quantum dots (CQDs)-decorated C-doped α-Bi2O3 nanorods.

A novel carbon quantum dots decorated C-doped α-Bi2O3 photocatalyst (CBO/CQDs) was synthesized by solvothermal method. The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies. The ceftriaxone sodium degradation rate constant (k) of CBO/CQDs was 11.4 and 3.2 times that of pure α-Bi2O3 and C-doped α-Bi2O3, respectively. The interstitial carbon doping generated localized states above the valence band, which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes; the loading of CQDs improved the charge carrier separation and extended the visible light response; the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers. The •O2 - and h+ were identified as the dominant reactive species in ceftriaxone sodium degradation, and the key role of •O2 - was further investigated by NBT transformation experiments. The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack, and intermediates analysis was conducted to explore the possible degradation pathways. The toxicity evaluation revealed that some degradation intermediates possessed high toxicity, thus the contaminants require sufficient mineralization to ensure safe discharge. The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of α-Bi2O3, which provides references for future studies.

Enhanced removal of humic substances in effluent organic matter from a leachate treatment system via biological upgradation of molecular structure.

Biological upgradation (BU) process was proposed, with the goal of converting the molecular structure, for improving the coagulation effect on humic substances (HS) in effluent organic matter from the membrane bioreactor of a leachate treatment system. Enhancement of coagulation effect was observed with the improvement of chemical oxygen demand and HS removal efficiency from 45.5% and 56.5% to 80.0% and 92.6% (Fe dosage was 400 mg·L-1), respectively, which was approximately 30-40% higher than the other available researches. Variations in molecular weight (MW) and carboxyl contents of fulvic acid (FA) and humic acid (HA) were analysed by size exclusion chromatography coupled with dissolved organic carbon detection, potentiometric titration and Fourier transform infrared spectroscopy. The obtained results indicated that BU process led to the growth of MW of HS, of which the larger MW (1650 Da) FA and HA raised from 19.07 and 0.34 mgC·L-1 to 71.67 and 1.58 mgC·L-1, respectively, as well as increases in the carboxyl contents of FA and HA from 6.70 and 6.28 meq·gC-1 to 11.84 and 8.71 meq·gC-1, respectively. Because of this, a stronger binding effect between Fe and HS might be formed that improved the coagulation effect.

Molecular Analyses of Petroleum Hydrocarbon Change and Transformation during Petroleum Weathering by Multiple Techniques.

Various analytical techniques are used to study the weathering process of four crude oils, i.e., Iranian light crude oil, Daqing crude oil, Shengli crude oil, and Tahe crude oil. The molecular composition and structural information of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and heteroatom compounds were characterized by gas chromatography-flame ionization detector (GC-FID), gas chromatography-mass spectrometry (GC-MS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), respectively. The results showed that the weathering loss of n-alkanes was related to the molecular weight, and the low-molecular-weight (LMW) n-alkanes were more volatile. The loss degree of LMW naphthalene and alkylation homologues in PAHs was also higher. With the increase in the alkylation degree, the weathering resistance ability of PAHs was enhanced. In the negative-ion ESI FT-ICR MS mode, a total of 16 classes of compounds were detected for neutral nitrogen compounds and acidic compounds in the four crude oils. With the increase in weathering time, the relative abundances of NO, NO2, and O3S compounds gradually increased. In particular, the NO and NO2 compounds with different condensation degrees increased significantly. These results indicated that in addition to the volatilization of hydrocarbon compounds, nitrogen compounds were also oxidized to a certain extent during the weathering process. The provided information would enrich the understanding of the short-term weathering process of petroleum hydrocarbons.

Interaction-sedimentation strategy for highly efficient removal of refractory humic substances in biologically treated wastewater effluent: from mechanistic investigation to full-scale application.

Based on the accurate characterization of the binding sites of humic substances (HS) and their binding coefficients with ferric ions (Fe(III)), a coupled interaction-sedimentation (CIS) technology was proposed for dealing with HS in the biologically treated wastewater effluent (BTWE) from a full-scale antibiotic production wastewater treatment plant. The infrared spectral and carbon-13 nuclear magnetic resonance characteristics showed that (i) protonated carboxyl groups in HS were the main binding sites for Fe(III) and HS, (ii) one carboxyl group of HS interacted with one ferric ion, (iii) the Fe(III)-binding ability of fulvic acids (FA) was 2.8 times as much as that of humic acids (HA) when FA and HA coexisted, and (iv) the presence of non-humic substances in the effluent organic matter (EfOM) amplified the Fe(III)-binding ability difference between FA and HA to 4.9 times. Afterwards CIS technology was successfully optimized and applied in engineering-scale and superior HS and EfOM removal efficiencies of 94.2% and 84.0% were reached, respectively. The CIS technology and its engineering application in this study not only fulfill the direct discharging standard for antibiotic production wastewater, but also have the potential for replication in broader advanced treatments for BTWE.

Highly efficient AgBr/h-MoO3 with charge separation tuning for photocatalytic degradation of trimethoprim: Mechanism insight and toxicity assessment.

A highly solar active AgBr/h-MoO3 composite was constructed by a facile precipitation method, and the charge separation tuning was achieved by photoreduction of AgBr. The photoreduced Ag0 on AgBr/h-MoO3 acted as charge transfer bridge to form Z-scheme heterostructure, while the high degree of Ag reduction converted the material into type-II heterostructure. The synthesized optimal material promoted charge separation and visible light activity due to the incorporation of highly solar active AgBr, which showed ca. 2 times activity on trimethoprim (TMP) degradation than h-MoO3. The contribution of reactive species on TMP degradation followed the order of O2- >1O2 > h+, which agree well with the proposed charge separation mechanism. The photocatalytic degradation mechanism of TMP was proposed based on the radical quenching, intermediate analysis and DFT calculation. The toxicity analysis based on QSAR calculation showed that part of the degradation intermediates are more toxic than TMP, thus sufficient mineralization are required to eliminate the potential risks of treated water. Moreover, the material showed high stability and activity after four reusing cycles, and it is applicable to treat contaminants in various water matrix. This work is expected to provide new insight into the charge separation tuning mechanism for the AgX based heterojunction, and rational design of highly efficient photocatalysts for organic contaminants degradation by solar irradiation.

Surface modification of BiOBr/TiO2 by reduced AgBr for solar-driven PAHs degradation: Mechanism insight and application assessment.

A novel solar active AgBr/BiOBr/TiO2 catalyst was synthesized by a facile coprecipitation method for solar-driven water remediation. The synthesized material composed of flower-like TiO2 nanoparticles loaded on BiOBr nanosheets and with homogeneous surface distributed Ag/AgBr nanoparticles. The internal electric field between BiOBr/TiO2 heterojunction greatly facilitated the charge carrier migration; the introduction of narrow band gap semiconductors (AgBr and BiOBr) promoted the visible light adsorption; and the Ag/AgBr nanoparticles acted as photosensitizer to further improve the light utilization. The new material showed 7.6- and 4.0-times activity of pure TiO2 and BiOBr under solar light, and the contribution of reactive species on anthracene degradation followed the order of h+ >O2•-> •OH. The degradation mechanism and pathway were proposed based on intermediates analysis and DFT calculation. The QSAR analysis revealed that the environmental risks of contaminants were greatly reduced during the photocatalysis process but some intermediates were still toxic. The high photocatalytic activity, stability and adaptability all indicated that this new material owns great application potential for cost-effective photocatalytic remediation of persistent organic contaminants under solar light.

Comprehensive evaluation of substrate materials for contaminants removal in constructed wetlands.

Considerable number of studies have been carried out to develop and apply various substrate materials for constructed wetlands (CWs), however, there is a lack of method and model for comprehensive evaluation of different types of CWs substrates. To this end, this article summarized nearly all the substrate materials of CWs available in the literatures, including natural materials, agricultural/industrial wastes and artificial materials. The sources and physicochemical properties of various substrate materials, as well as their removal capacities for main water contaminants including nutrients, heavy metals, surfactants, pesticides/herbicides, emerging contaminants and fecal indicator bacteria (FIB) were comprehensively described. Further, a scoring model for the substrate evaluation was constructed based on likely cost, availability, permeability, reuse and contaminant removal capacities, which can be used to select the most suitable substrate material for different considerations. The provided information and constructed model contribute to better understanding of CWs substrate for readers, and help solve practical problems on substrates selection and CWs construction.

Highly active WO3@anatase-SiO2 aerogel for solar-light-driven phenanthrene degradation: Mechanism insight and toxicity assessment.

The global energy crisis and water pollution drive the researchers to develop highly effective and less energy intensive water purification technologies. In this study, a highly active WO3@TiO2-SiO2 nanocomposite was synthesized and used for photocatalytic degradation of persistent organic pollutants under simulated solar light. The optimum WO3@TiO2-SiO2 prepared with 2 wt% WO3 loading and calcination at 800 °C exhibited higher photocatalytic activity, as the rate constant (k1) for phenanthrene degradation was ∼7.1 times of that for the commercial TiO2 (P25). The extremely large specific surface area (>400 m2/g) of WO3@TiO2-SiO2 afforded it with enlarged pollutants adsorption performance and abundant active surface sites. The heterojunction of anatase with SiO2 as well as loading of WO3 decreased the band gap energy (Eg) of TiO2, which extended the utilization spectrum of TiO2 to visible region. Formation of Ti-O-Si band indicated the excess charges can cause Brønsted acidity due to the absorption of protons to compensate the charges. Moreover, the migration of photo-excited electrons from the conduction band of anatase to WO3 and holes in the opposite direction restrained the electron-hole recombination. The photocatalytic degradation mechanism and pathway for phenanthrene degradation were proposed based on experimental analysis and density functional theory (DFT) calculation, and the toxicities of the degradation intermediates were evaluated by quantitative structure-activity relationship (QSAR) analysis. WO3@TiO2-SiO2 also showed good separation (settling) performance and high stability. Our work is expected to offer new insight into the photocatalytic mechanism for WO3, TiO2 and SiO2 based heterojunctions, and rational design and synthesis of highly efficient photocatalysts for environmental application.

Particle morphomics by high-throughput dynamic image analysis.

A novel omics-like method referred to as "particle morphomics" has been proposed in the present study. The dynamic images of >2,000,000 particles per sample in sediments, soils and dusts were collected by a Sympatec GmbH QICPIC particle size and shape analyzer, and the morphological descriptors of each particle including equivalent diameter, sphericity, aspect ratio and convexity were extracted as the "particle morphome". Various multivariate analyses were adopted to process the high-throughput data of particle morphome including analyses of alpha and beta diversities, similarity, correlation, network, redundancy, discretion and principal coordinate. The outcome of particle morphomics could estimate the morphological diversity and sketch the profile of morphological structure, which aided to develop a morphological fingerprint for specific particle samples. The distribution and properties of particle assemblages of specific morphology could also be evaluated by selecting particles with respect to filter criteria. More importantly, the particle morphomics may be extended to investigate and explain the biogeochemical and environmental processes involved with particle morphology if linked with external variables.

Pilot investigation on formation of 2,4,6-trichloroanisole via microbial O-methylation of 2,4,6-trichlorophenol in drinking water distribution system: An insight into microbial mechanism.

Taste & odor (T&O) problems in drinking water are always complained by customers. Recent studies have indicated biofilms in drinking water distribution system (DWDS) are always ignored as potential sources of T&O compounds. In this paper, the formation of 2,4,6-trichloroanisole (2,4,6-TCA), one of the dominant T&O compounds, was investigated in a pilot-scale DWDS. The addition of precursor 2,4,6-trichlorophenol (2,4,6-TCP) of 0.2 mg/L induced the formation of 2,4,6-TCA with a maximum yield of ∼400 ng/L, and the formation kinetics can be described by a pseudo-first-order kinetic model. Effects of water distribution factors such as pipe material, temperature, flow velocity, and residual chlorine on the formation of 2,4,6-TCA were evaluated, and the pipe material was found to have the most remarkable effect. Ductile iron and stainless steel pipes produced much more 2,4,6-TCA than polyethylene (PE) pipe. The biofilm microbial communities on the three types of pipe walls were then comprehensively analyzed by heterotrophic plate count and 16S rRNA/ITS1 genes high throughput sequencing. The links between the 2,4,6-TCA formation potential and the microbial activity in genus and enzymatic levels in DWDS have been revealed for the first time. According to the characteristics of microbial assemblages of producing 2,4,6-TCA, quorum-sensing (QS) bacterial signaling system and extracellular DNA (eDNA) may be two promising targets for biofilm treatment and 2,4,6-TCA control in DWDS.

Photocatalysis of bisphenol A by an easy-settling titania/titanate composite: Effects of water chemistry factors, degradation pathway and theoretical calculation.

Bisphenol A (BPA) is a widely concerned endocrine disrupting chemical and hard to be removed through conventional wastewater treatment processes. In this study, we developed a TiO2 decorated titanate nanotubes composite (TiO2/TNTs) and used for photocatalytic degradation of BPA. TEM and XRD analysis show that the TiO2/TNTs is a nano-composite of anatase and titanate, with anatase acting as the primary photocatalytic site and titanate as the skeleton. TiO2/TNTs exhibited excellent photocatalytic reactivity and its easy-settling property leaded to good reusability. After 5 reuse cycles, TiO2/TNTs also could photo-degrade 91.2% of BPA with a high rate constant (k1) of 0.039 min-1, which was much better than TiO2 and TNTs. Higher pH facilitated photocatalysis due to more reactive oxygen species produced and less material aggregation. The presence of NaCl and CaCl2 showed negligible effects on BPA degradation, but NaHCO3 caused an inhibition effect resulting from consumption of ·OH. Humic acid inhibited degradation mainly due to blockage of the active sites of TiO2/TNTs. Degradation pathway was well interpreted through theoretical calculation. Hydroxyl radical played the dominate role in BPA photodegradation, and the atoms of BPA with high Fukui index based on density-functional theory (DFT) calculation are the radical easy-attacking (f0) sites. Considering the good photocatalytic reactivity, reusability, stability and settle property, TiO2/TNTs promises to be an efficient alternative for removal of organic compounds from wastewaters.

Application of magnetic OMS-2 in sequencing batch reactor for treating dye wastewater as a modulator of microbial community.

The potential and mechanism of synthesized magnetic octahedral molecular sieve (Fe3O4@OMS-2) nanoparticles in enhancing the aerobic microbial ability of sequencing batch reactor (SBR) for treating dye wastewater have been revealed in this study. The addition of Fe3O4@OMS-2 of 0.25g/L enhanced the decolorization of SBRs with an operation cycle of 24h by more than 20%. The 16S rRNA gene high-throughput sequencing indicated Fe3O4@OMS-2 increased the microbial richness and diversity of SBRs, and more importantly, promoted the potential dye-degrading bacteria. After a series of enriching and screening, four bacterial strains with the considerable decolorizing ability were isolated from SBRs, designating Alcaligenes faecalis FP-G1, Bacillus aryabhattai FP-F1, Escherichia fergusonii FP-D1 and Rhodococcus ruber FP-E1, respectively. The growth and decolorization of these pure strains were promoted in the presence of Fe3O4@OMS-2, which agrees with the result of high-throughput sequencing. Monitoring dissolved Fe/Mn ions and investigating the change of oxidation states of Fe/Mn species discovered OMS-2 composition played the critical role in modulating the microbial community. The significant enhancement of Mn-oxidizing/-reducing bacteria suggested microbial Mn redox may be the key action mechanism of Fe3O4@OMS-2, which can provide numerous benefits for the microbial community and decolorization of SBRs.

Effects of oil dispersants on photodegradation of parent and alkylated anthracene in seawater.

This study investigated effects of three model oil dispersants on photodegradation of two model PAHs (anthracene and 9,10-dimethyanthracene (9,10-DMA)) under simulated sunlight. All three dispersants, i.e. Corexit EC9500A, Corexit EC9527A and SPC 1000, promoted the photolysis rate of 9,10-DMA, following the order of Corexit EC9500A > Corexit EC9527A > SPC 1000. The photodegradation rate was well interpreted by a two-stage, first-order kinetic law with a faster initial photolysis rate in the presence of the dispersants. Span 80, Tween 85 and kerosene were found as the key dispersant components, of which Span 80 and Tween 85 promoted the photodegradation by boosting absorbance of solar irradiation while kerosene by dispersing more PAHs in the upper layer of the water column. Dissolved oxygen (DO) inhibited photolysis of anthracene regardless of dispersant resulting from quenching the excited states of the PAH, while DO facilitated photolysis of 9,10-DMA due to the formation singlet oxygen (1O2) radicals in the presence of oil dispersants. The other ROS, i.e. •O2- and •OH, played a negligible role on the photodegradation of anthracene and 9,10-DMA. Fluorescence analysis showed that more anthracene was associated with dispersant than 9,10-DMA, which favored the direct transfer of energy to anthracene, while energy is more likely transferred to oxygen to form 1O2 in the case of 9,10-DMA. Direct photolysis dominated the photodegradation of anthracene and 9,10-DMA. Both direct ionization of anthracene and the electron transfer from excited 9,10-DMA to oxygen can lead to formation of the corresponding PAH radical cations. Overall, the oil dispersants accelerated the photolysis rates of the PAHs without altering the degradation pathway. The findings are useful for understanding photochemical weathering of dispersed oil components in the environment.

An overview of nanomaterials applied for removing dyes from wastewater.

Organic dyes are one of the most commonly discharged pollutants in wastewaters; however, many conventional treatment methods cannot treat them effectively. Over the past few decades, we have witnessed rapid development of nanotechnologies, which offered new opportunities for developing innovative methods to treat dye-contaminated wastewater with low price and high efficiency. The large surface area, modified surface properties, unique electron conduction properties, etc. offer nanomaterials with excellent performances in dye-contaminated wastewater treatment. For examples, the agar-modified monometallic/bimetallic nanoparticles have the maximum methylene blue adsorption capacity of 875.0 mg/g, which are several times higher than conventional adsorbents. Among various nanomaterials, the carbonaceous nanomaterials, nano-sized TiO2, and graphitic carbon nitride (g-C3N4) are considered as the most promising nanomaterials for removing dyes from water phase. However, some challenges, such as high cost and poor separation performance, still limit their engineering application. This article reviewed the recent advances in the nanomaterials used for dye removal via adsorption, photocatalytic degradation, and biological treatment. The modification methods for improving the effectiveness of nanomaterials are highlighted. Finally, the current knowledge gaps of developing nanomaterials on the environmental application were discussed, and the possible further research direction is proposed.

Transport of multi-walled carbon nanotubes stabilized by carboxymethyl cellulose and starch in saturated porous media: Influences of electrolyte, clay and humic acid.

This study investigated the transport behaviors of carboxymethyl cellulose (CMC) and starch stabilized multi-walled carbon nanotubes (MWNTs) through a saturated quartz sand column in the presence of electrolytes, model clays, and natural organic matter (humic acid) through column breakthrough experiments and model simulations. Both stabilizers, CMC and starch, greatly enhanced the breakthrough of MWNTs, with a full breakthrough plateau (C/C0) ranging from 0.69 to 0.90 at ionic strength from 0.3 to 10mM. Between the two stabilizers, CMC was more effective in resisting particle deposition, and thus CMC-stabilized MWNTs were more transportable through the medium. While non-stabilized MWNTs were much less transportable and were vulnerable to electrolyte effects (especially Ca2+), the stabilized counterparts were much more resistant to the coagulation effects of electrolytes. The presence of colloidal clay particles showed contrasting effects on the transport of bare and stabilized MWNTs. The full breakthrough C/C0 of bare MWNTs was suppressed by kaolinite and montmorillonite particles from 0.33 to <0.15 with 5mg/L clay, indicating that the presence of both clays enhanced the aggregation and deposition of MWNTs. However, kaolinite particles facilitated the transport of stabilized-MWNTs, while montmorillonite weakened the breakthrough of stabilized MWNTs. Humic acid had less effect on the mobility of stabilized-MWNTs than that of bare MWNTs. The advection-dispersion transport model incorporated with the filtration theory was able to simulate the breakthrough curves and quantitatively interpret the particle deposition. The results can facilitate our understanding of fate and transport of stabilized carbon nanotubes in the environment.