Multiple-Emitting Luminescent Metal-Organic Framework as an Array-on-a-MOF for Rapid Screening and Discrimination of Nitroaromatics.

Fluorescence array technologies have attracted great interest in the sensing field because of their high sensitivity, low cost, and capability of multitarget detection. However, traditional array sensing relies on multiple independent sensors and thus often requires time-consuming and laborious measurement processes. Herein, we introduce a novel fluorescence array strategy of the array-on-a-metal-organic framework (MOF), which integrates multiple array elements into a single MOF matrix to achieve facile sensing and discrimination of multiple target analytes. As a proof-of-concept system, we constructed a luminescent MOF containing three different emitting channels, including a lanthanide ion (europium/Eu3+, red emission), a fluorescent dye (7-hydroxycoumarin-4-acetic acid/HCAA, blue emission), and the MOF itself (UiO-66-type MOF, blue-violet emission). Five structurally similar nitroaromatic compounds (NACs) were chosen as the targets. All three channels of the array-on-a-MOF displayed rapid and stable fluorescence quenching responses to NACs (response equilibrium achieved within 30 s). Different responses were generated for each channel against each NAC due to the various quenching mechanisms, including photoinduced electron transfer, energy competition, and the inner filter effect. Using linear discriminant analysis, the array-on-a-MOF successfully distinguished the five NACs and their mixtures at varying concentrations and demonstrated good sensitivity to quantify individual NACs (detect limit below the advisory concentration in drinking water). Moreover, the array also showed feasibility in the sensing and discrimination of multiple NACs in real water samples. The proposed "array-on-a-MOF" strategy simplifies multitarget discrimination procedures and holds great promise for various sensing applications.

Intrinsic Peroxidase-like Activity of Polystyrene Nanoplastics Mediates Oxidative Stress.

Nanoplastics represent a global environmental concern due to their ubiquitous presence and potential adverse impacts on public and environmental health. There is a growing need to advance the mechanistic understanding of their reactivity as they interact with biological and environmental systems. Herein, for the first time, we report that polystyrene nanoplastics (PSNPs) have intrinsic peroxidase-like activity and are able to mediate oxidative stress. The peroxidase-like activity is dependent on temperature and pH, with a maximum at pH 4.5 and 40 °C. The catalytic activity exhibits saturation kinetics, as described by the Michaelis-Menten model. The peroxidase-like activity of PSNPs is attributed to their ability to mediate electron transfer from peroxidase substrates to H2O2. Ozone-induced PSNP aging can introduce oxygen-containing groups and disrupt aromatic structures on the nanoplastic surface. While ozonation initially enhances peroxidase-like activity by increasing oxygen-containing groups without degrading many aromatic structures, extended ozonation destroys aromatic structures, significantly reducing this activity. The peroxidase-like activity of PSNPs can mediate oxidative stress, which is generally positively correlated with their aromatic structures, as suggested by the ascorbic acid assay. These results help explain the reported oxidative stress exerted by nanoplastics and provide novel insights into their environmental and public health implications.

Revealing Molecular Structures of Nitrogen-Containing Compounds in Dissolved Black Carbon Using Ultrahigh-Resolution Mass Spectrometry Combined with Thermodynamic Calculations.

Landscape wildfires generate a substantial amount of dissolved black carbon (DBC) annually, yet the molecular nitrogen (N) structures in DBC are poorly understood. Here, we systematically compared the chemodiversity of N-containing molecules among three different DBC samples from rice straw biochar pyrolyzed at 300, 400, and 500 °C, one leached dissolved organic carbon (LDOC) sample from composted rice straw, and one fire-affected soil dissolved organic matter (SDOMFire) sample using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). N-Containing molecules contributed 20.0%, 36.1%, and 43.7% of total compounds in Combined DBC (pooling together the three DBC), LDOC, and SDOMFire, respectively, and molecules with fewer N atoms had higher proportions (i.e., N1 > N2 > N3). The N-containing molecules in Combined DBC were dominated by polycyclic aromatic (62.2%) and aromatic (14.4%) components, while those in LDOC were dominated by lignin-like (50.4%) and aromatic (30.1%) components. The composition and structures of N-containing molecules in SDOMFire were more similar to those in DBC than in LDOC. As the temperature rose, the proportion of the nitrogenous polycyclic aromatic component in DBC significantly increased with concurrent enhanced oxidation and unsaturation of N. As indicated by density functional theory (DFT)-based thermodynamic calculations, the proportion of aliphatic amide N decreased from 23.2% to 7.9%, whereas that of nitroaromatic N increased from 10.0% to 39.5% as the temperature increased from 300 to 500 °C; alternatively, the proportion of aromatic N in the 5/6 membered ring remained relatively stable (∼31%) and that of aromatic amide N peaked at 400 °C (32.7%). Our work first provides a comprehensive and thorough description of molecular N structures of DBC, which helps to better understand and predict their fate and biogeochemical behavior.

Efficient Catalytic Oxidation of Ethylene at 0 °C on an in Situ Carbon Modified Pt Catalyst Supported on SBA-15.

The design of efficient catalysts for catalytic ethylene (C2H4) oxidation is of crucial importance for extending the shelf life of fruits and vegetables. Herein, a carbon modified SBA-15 supported Pt catalyst (Pt/CSBA-15) was prepared in situ by a facile solid phase grinding-infiltration-inert atmosphere calcination method. Characterization results reveal that in the Pt/CSBA-15 catalysts thin carbon layers are successfully formed in the hexagonal pores of SBA-15. Additionally, Pt particles are well dispersed in the channels of SBA-15, and Pt/CSBA-15 has a smaller Pt particle size than the catalyst without carbon modification (i.e., Pt/SBA-15). O2 is more feasibly adsorbed and activated on small-sized Pt particles, and in situ formed carbon species enhance the hydrophobicity of catalysts. As a result, both 3Pt/CSBA-15 and 5Pt/CSBA-15 are able to maintain 100% conversion of 50 ppm of C2H4 for more than 7 h at 0 °C. 3Pt/CSBA-15 even achieves 81.5% C2H4 conversion and 71.6% CO2 yield after 20 h, exhibiting much more prominent catalytic performances than 3Pt/SBA-15. DFT calculations and in situ FTIR measurements confirm that small-sized Pt particles possess strong O2 affinity to promote O2 adsorption, and in situ formed hydrophobic carbon layers efficiently suppress competitive H2O adsorption. Such a unique one-step catalyst preparation method for regulating the size of metal particles and the hydrophobicity of catalysts can be perfectly utilized to develop simple and efficient hydrophobic catalysts applied in low-temperature oxidation of C2H4.

Benzenepoly(carboxylic acid)s as Exclusive Intrinsic Markers to Assess Riverine Export of Dissolved Black Carbon.

Landscape fires annually generate large quantities of black carbon. The water-soluble fraction of black carbon (i.e., dissolved black carbon/DBC) is an important constituent of the dissolved organic carbon (DOC) pool, playing a crucial role in the global budget of refractory carbon and climate change. A key challenge in constraining the flux and fate of riverine DBC is to develop targeted and accurate quantification methods. Herein, we report that benzenepentacarboxylic acid (B5CA) intrinsically present in DBC can be used as an exclusive and holistic marker (representing both condensed aromatics and less-/nonaromatic fractions) for DBC quantification. B5CA was universally detected in water extractions of biochar and fire-affected soils with relatively large abundance but not produced by nonthermogenic processes. It has good mobility in the environment as it is not readily precipitated by cations or adsorbed by common geosorbents. B5CA also represents the recalcitrant components of DBC with excellent stability against photodegradation and biodegradation. Applying B5CA as the DBC marker in surface waters of the Changjiang River (i.e., the third largest river in the world), we calculate the DBC concentration in the downstream Changjiang River to be 4.8 ± 5.5% of the DOC flux. Our work provides a simple and reliable approach for the accurate quantification and source tracking of DBC in the soil and aquatic carbon pools.

Comparing Photoactivities of Dissolved Organic Matter Released from Rice Straw-Pyrolyzed Biochar and Composted Rice Straw.

Here, we systematically compared the photoactivity and photobleaching behavior between dissolved black carbon (DBC) from rice straw biochar and leached dissolved organic carbon (LDOC) from rice straw compost using complementary techniques. The Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed that DBC was dominated by polycyclic aromatic (55.1%) and tannin-like molecules (24.1%), while LDOC was dominated by lignin-like (58.9%) and tannin-like molecules (19.7%). Under simulated sunlight conditions, DBC had much higher apparent quantum yields for 3DOM* and 1O2 but much lower apparent quantum yields for •OH than LDOC. After a 168 h irradiation, the total number of LDOC formulas identified by FT-ICR MS decreased by 40.1% with concurrent increases in O/C and H/C ratios and also decreases in double bond equivalence minus oxygen (DBE - O) and average molecular weight identified by gel permeation chromatography. However, despite the large decreases in UVA254 and DOC, the total number of DBC formulas decreased only by 12.0% with nearly unchanged O/C ratio, DBE - O values, molecular weight distribution, and benzenepolycarboxylic aromatic condensation (BACon) index regardless of the decreased percentage of condensed aromatic carbon (ConAC %). Compared with LDOC, the photolysis of DBC was much less oxidative and destructive mainly via breakup of a small portion of the highly condensed aromatic rings, probably accompanied by photodecarboxylation.

High-Throughput Method for Natural Organic Matter Hydrophobicity Assessment Using an Ionic Liquid-Based Aqueous Two-Phase System.

Hydrophobicity of natural organic matter (NOM) is one of its fundamental properties that influence the environmental fate of pollutants and the performance of many water treatment unit processes. In this study, a high-throughput method was developed for NOM hydrophobicity measurement based on the phase separation technique in the 96-well format. It measures the partition coefficients of NOM (KATPS,IL) in an ionic liquid (IL)-based aqueous two-phase system (ATPS). The ATPS was made of 1-butyl-3-methylimidazole bromide solution and a salt solution containing potassium phosphate monobasic and potassium phosphate dibasic. The partition of NOM in IL-based ATPS is mainly affected by its hydrophobicity. log KATPS,IL linearly correlated with the commonly used NOM hydrophobicity scales, including (O + N)/C, O/C, and aromatic carbons. KATPS,IL provided a more accurate assessment of NOM hydrophobicity than spectroscopic indices. Furthermore, KATPS,IL can predict the organic carbon-water partition coefficients for hydrophobic organic chemical sorption to NOM based on the two-phase system model. The high-throughput KATPS,IL measurement and the two-phase system model can be applied to real surface water samples. Our results suggest that the proposed high-throughput method has great potential to be applied to monitor NOM hydrophobicity for environmental risk assessment and water treatment purposes.

Two-Phase System Model to Assess Hydrophobic Organic Compound Sorption to Dissolved Organic Matter.

The equilibrium partition of organic compounds to dissolved organic matter (DOM) is an essential process that affects their environmental risks. Traditional models cannot accurately assess this process as the variability of DOM is not properly accounted for. The two-phase system (TPS) model was developed with the consideration of the variability that stems from both organic compounds and DOM. In this study, we examined the applicability of the TPS model for the prediction of the organic carbon-water partition coefficient (KOC) of hydrophobic organic compound (HOC) sorption to aquatic and sediment DOM using a diverse set of 17 organic compounds and 53 DOM samples. The TPS model showed good predictive power (RMSE < 0.20) without calibration, outperforming currently used linear free energy relationship models (RMSE > 0.28). The significance of DOM properties in the sorption behavior was quantitatively analyzed based on the TPS model. The spatial pattern of KOC for HOC sorption to aquatic DOM in Lake Taihu, the third largest freshwater lake in China, was assessed using the TPS model. Our results suggest that the TPS model has great potential to facilitate the routine assessment of the partition behavior of HOCs in aquatic systems for environmental risk assessment.

Dissolved Black Carbon Facilitates Photoreduction of Hg(II) to Hg(0) and Reduces Mercury Uptake by Lettuce (Lactuca sativa L.).

Here, we investigated the photoreduction of Hg(II) (Hg(NO3)2) mediated by dissolved black carbon (DBC, <0.45 µm size fraction) collected from water extracts of biochar derived by pyrolyzing crop residues (rice, soybean, and peanut). Under simulated sunlight conditions, the presence of 5 mg C/L DBC significantly facilitated the production of Hg(0) from Hg(II) (initially at 10 nmol/L) with a reduction ratio of 73 ± 4% in 5.3 h. Inhibition of photolysis-induced reactive oxygen species by a quencher or removal of dissolved oxygen indicated that Hg(II) was mainly reduced by superoxide anion (O2•-). Reduction by electrons transferred from photoexcited DBC components or by organic free radicals produced from photo-Fenton-like reactions was also proposed to play a role. Contrary to dissolved humic substances, the DBC-mediated photoreduction of Hg(II) led to unique positive mass-independent isotopic fractionation (MIF) of Hg(0) (Δ199Hg = 1.8 ± 0.3‰), which was attributed to the dominance of secondary Hg(II) reduction by O2•-. The leachate from soil amended with rice biochar at 1-5% mass ratios exhibited significantly higher photocatalytic efficiency than that from unamended soil (wherein the reduced Hg(0) increased from 27 ± 1 to 63 ± 2% in maximum), and the efficiency positively correlated with the percentage of amended biochar. Under natural illumination conditions, the total mercury and/or methylmercury uptake by roots, shoots, and leaves of lettuce (Lactuca sativa L.) grown in water extracts of rice biochar-amended soil was consistently lower (up to 70 ± 20%) than that without the biochar amendment. The findings highlight that DBC might play an important and previously unrecognized role in the biogeochemical cycle and the environmental impact of mercury.

Role of Extracellular Polymeric Substances in Microbial Reduction of Arsenate to Arsenite by Escherichia coli and Bacillus subtilis.

We show that arsenate can be readily reduced to arsenite on cell surfaces of common bacteria (E. coli or B. subtilis) or in aqueous dissolved extracellular polymeric substances (EPS) extracted from different microorganisms (E. coli, B. subtilis, P. chrysosporium, D. gigas, and a natural biofilm) in the absence of exogenous electron donors. The efficiency of arsenate reduction by E. coli after a 7-h incubation was only moderately reduced from 51.3% to 32.7% after knocking out the arsenic resistance genes (arsB and arsC). Most (>97%) of the reduced arsenite was present outside the bacterial cells, including for the E. coli blocked mutant lacking arsB and arsC. Thus, extracellular processes dominated arsenate reduction. Arsenate reduction was facilitated by removing EPS attached to E. coli or B. subtilis, which was attributed to enhanced access to reduced extracellular cytochromes. This highlights the role of EPS as a permeability barrier to arsenate reduction. Fourier-transform infrared (FTIR) combined with other chemical analyses implicated some low-molecular weight (<3 kDa) molecules as electron donors (reducing saccharides) and electron transfer mediators (quinones) in arsenate reduction by dissolved EPS alone. These results indicate that EPS act as both reducing agent and permeability barrier for access to reduced biomolecules in bacterial reduction of arsenate.

Prediction of Apolar Compound Sorption to Aquatic Natural Organic Matter Accounting for Natural Organic Matter Hydrophobicity Using Aqueous Two-Phase Systems.

The equilibrium partitioning of organic compounds to natural organic matter (NOM) plays a key role in their environmental fate as well as bioavailability. In this study, a prediction model for organic compound sorption to NOM was theoretically derived based on two-phase systems. In this model, the hydrophobicity of NOM was scaled by their partition coefficients in an aqueous two-phase system (KATPS) and that of organics was scaled by their octanol-water partition coefficients (KOW). The model uses only KATPS and KOW as variables. Coefficients in the model were determined using a data set including the organic carbon-water partition coefficient (KOC) of four polycyclic aromatic hydrocarbons (PAHs) sorption to 10 NOM samples collected from surface waters. The resulting model was validated using additional NOM samples and reference NOM, which suggested good prediction power for PAH sorption to aquatic NOM. The model performance was compared with commonly used linear free energy relationship models, and its applicability was discussed. Sorption behavior unexpected by this model is attributed to additional sorption mechanisms other than partitioning. Overall, this approach allows prediction of KOC for apolar organic compound sorption to aquatic NOM simply using their respective partition coefficients in two-phase systems based on a specific model.

Sunlight-Mediated Lead and Chromium Release from Commercial Lead Chromate Pigments in Aqueous Phase.

Lead chromate pigments are included in a group of the most widely used pigments, which account for 3% of worldwide lead consumption. This study reports the photoactivity of commercial lead chromate pigment (i.e., chrome yellow) under simulated sunlight. It underwent photodissolution in the presence of organic acid and dissolved organic matter in the aqueous phase, releasing Pb(II) and Cr(III). Pb(II) was released more readily than Cr(III) which mainly formed hydroxides and oxides. The photodissolution can be activated by light with a wavelength <514 nm. The reaction is mediated by the reduction of Cr(VI) in the pigment by self-generated electrons. The kinetics were mainly affected by the electron-hole separation efficiency which can be enhanced by electron donors. The reaction rate decreases with increasing solution pH as the photodissolution process consumes protons. The photodissolution of the chrome yellow pigment was further confirmed in a river water sample under natural sunlight, with 11.28% of lead and 2.56% of chromium released in 7 h. This study highlights the importance of considering photochemical processes in risk assessments and regulations of commercial semiconductor pigments, which are currently based on their solubility.

Dissolved Black Carbon as an Efficient Sensitizer in the Photochemical Transformation of 17ß-Estradiol in Aqueous Solution.

Dissolved black carbon (DBC) is an important component of the dissolved organic matter (DOM) pool. Nonetheless, little is known about its role in the photochemical processes of organic contaminants. This study investigated the effect of DBC on the phototransformation of 17ß-estradiol in aqueous solutions under simulated sunlight. Four well-studied dissolved humic substances (DHS) were included as comparisons. DBC acted as a very effective sensitizer to facilitate the phototransformation of 17ß-estradiol. The apparent quantum yield for 17ß-estradiol phototransformation mediated by DBC was approximately six times higher than that by DHS at the same carbon concentration. Quenching experiments suggested that direct reaction with triplet-excited state DBC (3DBC*) was the predominant pathway of 17ß-estradiol phototransformation. The higher mediation efficiency of DBC than DHS is likely due to the higher contents of aromatic groups and smaller molecular sizes, which facilitated the generation of 3DBC*. The apparent quantum yield of triplet-excited states production for DBC was 4-8 times higher than that for DHS. The results suggest that 3DBC* may have a considerable contribution to the overall photoreactivity of triplet-excited state DOM in aquatic systems. Our findings also imply that DBC can play an important role in the phototransformation of organic contaminants in the environments.

Threshold Concentrations of Silver Ions Exist for the Sunlight-Induced Formation of Silver Nanoparticles in the Presence of Natural Organic Matter.

Sunlight-induced photoformation of silver nanoparticles (nAg), mediated by natural organic matter (NOM), is significantly affected by the concentration of Ag(I) and chloride. The initial photoformation rates of nAg in Suwannee River humic acid (SRHA) and Suwannee River natural organic matter (SRNOM) solutions were examined under simulated sunlight irradiation. A critical induction concentration (CIC) of Ag(I) (10 mg/L for SRHA and 5 mg/L for SRNOM, respectively) was observed, below which the nAg formation was minimal. The threshold is attributed to the interplay of reduction and oxidation reactions mediated by NOM, reflecting the need to achieve sufficiently fast growth of silver clusters to outcompete oxidative dissolution. The CIC can be reduced by scavenging oxidative radicals or be increased by promoting singlet oxygen and hydrogen peroxide generation. The presence of chloride effectively reduced the CIC by forming AgCl, which facilitates reduction reactions and provides deposition surfaces. SRNOM is more efficient in mediating photoformation of nAg than SRHA, owing to their differed phototransient generation. These results highlight prerequisites for the photoformation of nAg mediated by NOM, in which the photochemistry and solution chemistry are both important.

Dissolved Mineral Ash Generated by Vegetation Fire Is Photoactive under the Solar Spectrum.

Vegetation fire generates vast amounts of mineral ash annually that can be readily mobilized by water or wind erosion. Little is known about the photoactivity of dissolved mineral ash in aquatic systems and its ability to mediate redox reactions of environmental pollutants. This study reports that dissolved mineral ash derived from pyrolysis of biomass is photoactive under simulated sunlight, generating reactive oxygen species. It can mediate the photoreduction of hexavalent chromium (Cr(VI)) in the presence of electron donors; for example, phenols and dissolved organic matter, at pH 4.7. The reaction kinetics followed the Langmuir-Hinshelwood model, suggesting a heterogeneous photocatalytic reaction. The enhancement of reduction efficiency was linearly correlated with the one-electron reduction potential of phenols. The synergy between dissolved mineral ash and phenols is attributed to the inhibition of electron-hole recombination. The reduction rate decreases with increasing solution pH, owing to the decreased reduction potential and surface adsorption of Cr(VI). The silicon and silicon carbide components are most likely responsible for the photocatalytic activity of dissolved mineral ash. Our results suggest that dissolved mineral ash is a natural photocatalyst that can mediate redox reactions of pollutants in sunlit aquatic systems, playing an overlooked role in natural attenuation and aquatic photochemistry.

Sunlight Promotes Fast Release of Hazardous Cadmium from Widely-Used Commercial Cadmium Pigment.

Cadmium pigments are widely used in the polymer and ceramic industry. Their potential environmental risk is under debate, being the major barrier for appropriate regulation. We show that 83.0 ± 0.2% of hazardous cadmium ion (Cd2+) was released from the commercial cadmium sulfoselenide pigment (i.e., cadmium red) in aqueous suspension within 24 h under simulated sunlit conditions. This photodissolution process also generated sub-20 nm pigment nanoparticles. Cd2+ release is attributed to the reactions between photogenerated holes and the pigment lattices. The photodissolution process can be activated by both ultraviolet and visible light in the solar spectrum. Irradiation under alkaline conditions or in the presence of phosphate and carbonate species resulted in reduced charge carrier energy or the formation of insoluble and photostable cadmium precipitates on pigment surfaces, mitigating photodissolution. Tannic acid inhibited the photodissolution process by light screening and scavenging photogenerated holes. The fast release of Cd2+ from the pigment was further confirmed in river water under natural sunlight, with 38.6 ± 0.1% of the cadmium released within 4 h. Overall, this study underscores the importance to account for photochemical effects to inform risk assessments and regulations of cadmium pigments which are currently based on their low solubility.

Photochemistry of Dissolved Black Carbon Released from Biochar: Reactive Oxygen Species Generation and Phototransformation.

Dissolved black carbon (BC) released from biochar can be one of the more photoactive components in the dissolved organic matter (DOM) pool. Dissolved BC was mainly composed of aliphatics and aromatics substituted by aromatic C-O and carboxyl/ester/quinone moieties as determined by solid-state nuclear magnetic resonance. It underwent 56% loss of absorbance at 254 nm, almost complete loss of fluorescence, and 30% mineralization during a 169 h simulated sunlight exposure. Photoreactions preferentially targeted aromatic and methyl moieties, generating CH2/CH/C and carboxyl/ester/quinone functional groups. During irradiation, dissolved BC generated reactive oxygen species (ROS) including singlet oxygen and superoxide. The apparent quantum yield of singlet oxygen was 4.07 ± 0.19%, 2-3 fold higher than many well-studied DOM. Carbonyl-containing structures other than aromatic ketones were involved in the singlet oxygen sensitization. The generation of superoxide apparently depended on electron transfer reactions mediated by silica minerals in dissolved BC, in which phenolic structures served as electron donors. Self-generated ROS played an important role in the phototransformation. Photobleaching of dissolved BC decreased its ability to further generate ROS due to lower light absorption. These findings have significant implications on the environmental fate of dissolved BC and that of priority pollutants.

Enhanced Adsorption of Hydroxyl- and Amino-Substituted Aromatic Chemicals to Nitrogen-Doped Multiwall Carbon Nanotubes: A Combined Batch and Theoretical Calculation Study.

A large effort is being made to develop nanosorbents with tunable surface chemistry for enhanced adsorption affinity and selectivity toward target organic contaminants. Heteroatom N-doped multiwall carbon nanotubes (N-MCNT) were synthesized by chemical vapor deposition of pyridine and were further investigated for the adsorptive removal of several aromatic chemicals varying in electronic donor and acceptor ability from aqueous solutions using a batch technique. Compared with commercial nondoped multiwall carbon nanotubes (MCNT), N-MCNT had similar specific surface area, morphology, and pore-size distribution but more hydrophilic surfaces and more surface defects due to the doping of graphitic and pyridinic N atoms. N-MCNT exhibited enhanced adsorption (2-10 folds) for the π-donor chemicals (2-naphthol and 1-naphthalmine) at pH ∼6 but similar adsorption for the weak π-donor chemical (naphthalene) and even lower adsorption (up to a 2-fold change) for the π-acceptor chemical (1,3-dinitrobenzene). The enhanced adsorption of 2-naphthol and 1-naphthalmine to N-MCNT was mainly attributed to the favored π-π electron-donor-acceptor (EDA) interaction between the π-donor adsorbate molecule and the polarized N-heterocyclic aromatic ring (π-acceptor) on N-MCNT. The proposed adsorption enhancement mechanisms were further tested through the pH effects on adsorption and the density function theory (DFT) calculation. The results show for the first time that the adsorptive interaction of π-donor aromatic compounds with carbon nanomaterials can be facilitated by N-doping.

Molybdenum doping leads to faster photo-dissolution of commercial molybdate red pigment than chrome yellow pigment under sunlight irradiation.

The photo-dissolution of lead chromate pigments poses specific environmental hazards. In this study, we report that doping molybdenum in lead chromate pigments, resulting in commonly known molybdate red pigment, increases the risk of heavy metal leaching when exposed to light. Commercial molybdate red pigments undergo photo-dissolution when exposed to simulated sunlight and exhibit lower photostability compared to lead chromate pigments such as chrome yellow. After 24 hours of irradiation, the leaching rates of toxic lead and chromium from molybdate red pigments were 2.98 and 3.70 times higher, respectively, than those from chrome yellow pigments. The primary factor leading to decreased pigment photostability is the activation of pigment semiconductors facilitated by molybdenum doping. Molybdate red pigments exhibit a broader light absorption spectrum and more efficient separation and transfer of photogenerated charge carriers than chrome yellow pigments, boosting the photochemical activity. To the best of our knowledge, this is the first study to illustrate the doping effect on the photostability of commercial inorganic pigments and the consequent heavy metal leaching. Our results suggest that Mo doping reduces the photostability of lead chromate pigments, highlighting the potential elevated environmental risks associated with complex inorganic pigments.

Cotransport of nanoplastics and plastic additive bisphenol AF (BPAF) in unsaturated hyporheic zone: Coupling effects of surface functionalization and protein corona.

The ecological risk of combined pollution from microplastics (MPs) and associated contaminants usually depends on their interactions and environmental behavior, which was also disturbed by varying surface modifications of MPs. In this study, the significance of surface functionalization and protein-corona on the cotransport of nanoplastics (NPs; 100 nm) and the related additive bisphenol AF (BPAF) was examined in simulated unsaturated hyporheic zone (quartz sand; 250-425 µm). The electronegative bovine serum albumin (BSA) and electropositive trypsin were chosen as representative proteins, while pristine (PNPs), amino-modified (ANPs), and carboxyl-modified NPs (CNPs) were representative NPs with different charges. The presence of BPAF inhibited the mobility of PNPs/CNPs, but enhanced the release of ANPs in hyporheic zone, which was mainly related to their hydrophobicity changes and electrostatic interactions. Meanwhile, the NPs with high mobility and strong affinity to BPAF became effective carriers, promoting the cotransport of BPAF by 16.4 %-26.4 %. The formation of protein-coronas altered the mobility of NPs alone and their cotransport with BPAF, exhibiting a coupling effect with functional groups. BSA-corona promoted the transport of PNPs/CNPs, but this promoting effect was weakened by the presence of BPAF via increasing particle aggregation and hydrophobicity. Inversely, trypsin-corona aggravated the deposition of PNPs/CNPs, but competition deposition sites and increased energy barrier caused by coexisting BPAF reversed this effect, facilitating the cotransport of trypsin-PNPs/CNPs in hyporheic zone. However, BPAF and protein-coronas synergistically promoted the mobility of ANPs, owing to competition deposition sites and decreased electrostatic attraction. Although all of the NPs with two protein-coronas reduced dissolved BPAF in the effluents via providing deposition sites, the cotransport of total BPAF was improved by the NPs with high mobility (BSA-PNPs/CNPs) or high affinity to BPAF (BSA/trypsin-ANPs). However, the trypsin-PNPs/CNPs inhibited the transport of BPAF due to their weak mobility and adsorption with BPAF. The results provide new insights into the role of varying surface modifications on NPs in the vertical cotransport of NPs and associated contaminants in unsaturated hyporheic zone.