Formation, speciation and toxicity of CX3R-type disinfection by-products (DBPs) from chlor(am)ination of 2,4-diaminobutyric acid (DAB).

2,4-diaminobutyric acid (DAB), a newly identified algal toxins in water, pose a great threat to human health. DAB may react with chlorine or chloramine to produce CX3R-type disinfection by-products (DBPs) during water treatment processes. This study mainly investigated the formation and speciation of DBPs from chlor(am)ination of DAB. The results revealed that haloacetic acids (HAAs), trihalomethanes (THMs) and haloacetonitriles (HANs) were the main kinds of CX3R-type DBPs generated from DAB during chlor(am)ination, of which dichloroacetic acid yielded the highest. The formation and total toxicity of four CX3R-type DBPs from DAB during chloramination was significantly lower than that during chlorination at each Cl2:N molar ratio. However, more formation of Br-THMs and I-THMs were observed during chloramination in the presence of Br-/I-. Futhermore, the effects of chlor(am)ine dosage, solution pH, reaction time, and the concentration of Br- and I- on the formation and speciation of CX3R-type DBPs were also evaluated during chlor(am)ination. The plausible formation pathways of CX3R-type DBPs from DAB were proposed and verified by theoretical calculation. The quantum chemistry calculations indicate that 1N in DAB and 8N in 2,4-diaminochlorobutyric acid (C4H9O2N2Cl) were more likely to be attacked by electrophiles, supporting the proposed pathway schemes.

Oxidation Mechanisms of the UV/Free Chlorine Process: Kinetic Modeling and Quantitative Structure Activity Relationships.

Recently, the UV/free chlorine process has gained attention as a promising technology for destroying refractory organic contaminants in the aqueous phase. We have developed a kinetic model based on first-principles to describe the kinetics and mechanisms of the oxidation of organic contaminants in the UV/free chlorine process. Substituted benzoic acid compounds (SBACs) were chosen as the target parent contaminants. We determined the second-order rate constants between SBACs and reactive chlorine species (RCS; including [Formula: see text], [Formula: see text] and [Formula: see text]) by fitting our model to the experimental results. We then predicted the concentration profiles of SBACs under various operational conditions. We analyzed the kinetic data and predicted concentration profiles of reactive radicals ([Formula: see text] and RCS), we found that [Formula: see text] was the dominant radicals for SBACs destruction. In addition, we established quantitative structure activity relationships (QSARs) that can help predict the second-order rate constants for SBACs destruction by each type of reactive radicals using SBACs Hammett constants. Our first-principles-based kinetic model has been verified using experimental data. Our model can facilitate a design for the most cost-effective application of the UV/free chlorine process. For example, our model can determine the optimum chlorine dosage and UV light intensity that result in the lowest energy consumption.

Oxidation of Microcystic-LR via the solar/chlorine process: Radical mechanism, pathways and toxicity assessment.

Microcystin-LR (MC-LR) is the most widely distributed and harmful variant toxins released by cyanobacteria, which poses potential threaten to people and aquatic animals when entering natural water. In our research, solar/chlorine process was comprehensively investigated to degrade and detoxify MC-LR. Under the chlorine concentration of 1.0 mg L-1, MC-LR (1.0 µM) was decreased by 96.7%, 26%, and 9% by solar/chlorine process, chlorination, and solar irradiation respectively. Quenching experiments confirmed that reactive chlorine species (RCS) and hydroxyl radical (HO) were the predominant reactive species in solar/chlorine process at neutral condition, and ozone was generated because of the participation of triplet-state oxygen (O(3P)). The respective contributions of each reactive species were calculated with the order as: RCS, HO, ozone, and solar irradiation. The presence of HCO3- and natural organic matter in water inhibited the degradation efficiency of MC-LR. Moreover, the transformation products of MC-LR generated during the solar/chlorine process were identified and a possible pathway was proposed. The hepatotoxicity of MC-LR and its transformation products was compared using protein phosphatase 2A. Our experimental results revealed that the concentration and hepatotoxicity of MC-LR both significantly decreased, and most products were not hepatoxic. Overall, the solar/chlorine process is a promising alternative technology to degrade MC-LR during eutrophication.

Observation and Manipulation of Visible Edge Plasmons in Bi2Te3 Nanoplates.

Noble metals, like Ag and Au, are the most intensively studied plasmonic materials in the visible range. Plasmons in semiconductors, however, are usually believed to be in the infrared wavelength region due to the intrinsic low carrier concentrations. Herein, we observe the edge plasmon modes of Bi2Te3, a narrow-band gap semiconductor, in the visible spectral range using photoemission electron microscopy (PEEM). The Bi2Te3 nanoplates excited by 400 nm femtosecond laser pulses exhibit strong photoemission intensities along the edges, which follow a cos4 dependence on the polarization state of incident beam. Because of the phase retardation effect, plasmonic response along different edges can be selectively exited. The thickness-dependent photoemission intensities exclude the spin-orbit induced surface states as the origin of these plasmonic modes. Instead, we propose that the interband transition-induced nonequilibrium carriers might play a key role. Our results not only experimentally demonstrate the possibility of visible plasmons in semiconducting materials but also open up a new avenue for exploring the optical properties of topological insulator materials using PEEM.

Impact of Chloride Ions on UV/H2O2 and UV/Persulfate Advanced Oxidation Processes.

Chloride ion (Cl-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H2O2 processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl- is present to the rate when Cl- is not present (designated as rRCl-/ rR) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, rRCl-/ rR, can be no larger than 60%. Hence, Cl- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H2O2 process, we found that Cl- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl- will adversely impact organic compounds destruction by the UV/PS and UV/H2O2 processes.

Copper-Vapor-Assisted Rapid Synthesis of Large AB-Stacked Bilayer Graphene Domains on Cu-Ni Alloy.

The synergic effects of Cu85Ni15 and the copper vapor evaporated from copper foil enabled the fast growth of a ≈300 µm bilayer graphene in ≈10 minutes. The copper vapor reduces the growth rate of the first graphene layer while the carbon dissolved in the alloy boosts the growth of the subsequently developed second graphene layer with an AB-stacking order.

Femtosecond laser direct writing of large-area two-dimensional metallic photonic crystal structures on tungsten surfaces.

Metallic photonic crystals (MPCs) and metamaterials operating in the visible spectrum are required for high-temperature nanophotonics, but they are often difficult to construct. This study demonstrates a new approach to directly write two-dimensional (2D) MPCs on tungsten surfaces through the cylindrical focusing of two collinear femtosecond laser beams with certain temporal delays and orthogonal linear polarizations. Results are physically attributed to the laser-induced transient crossed temperature grating patterns and tempo-spatial thermal correlations. Optical properties of the fabricated MPCs are characterized. Such a simple and efficient technique can be used to fabricate large-area, 2D microstructures on metal surfaces for potential applications.

Recent advances in constructed wetlands methane reduction: Mechanisms and methods.

Constructed wetlands (CWs) are artificial systems that use natural processes to treat wastewater containing organic pollutants. This approach has been widely applied in both developing and developed countries worldwide, providing a cost-effective method for industrial wastewater treatment and the improvement of environmental water quality. However, due to the large organic carbon inputs, CWs is produced in varying amounts of CH4 and have the potential to become an important contributor to global climate change. Subsequently, research on the mitigation of CH4 emissions by CWs is key to achieving sustainable, low-carbon dependency wastewater treatment systems. This review evaluates the current research on CH4 emissions from CWs through bibliometric analysis, summarizing the reported mechanisms of CH4 generation, transfer and oxidation in CWs. Furthermore, the important environmental factors driving CH4 generation in CW systems are summarized, including: temperature, water table position, oxidation reduction potential, and the effects of CW characteristics such as wetland type, plant species composition, substrate type, CW-coupled microbial fuel cell, oxygen supply, available carbon source, and salinity. This review provides guidance and novel perspectives for sustainable and effective CW management, as well as for future studies on CH4 reduction in CWs.

A review on the progress of the photocatalytic removal of refractory pollutants from water by BiOBr-based nanocomposites.

Organic matters from various sources such as the manufacturing, agricultural, and pharmaceuticals industries is continuously discharged into water bodies, leading to increasingly serious water pollution. Photocatalytic technology is a clean and green advanced oxidation process, that can successfully decompose various organic pollutants into small inorganic molecules such as carbon dioxide and water under visible light irradiation. Bismuth oxybromide (BiOBr) is an attractive visible light photocatalyst with good photocatalytic performance, suitable forbidden bandwidth, and a unique layered structure. However, the rapid combination of the electron-hole pairs generated in BiOBr leads to low photocatalytic activity, which limits its photocatalytic performance. Due to its unique electronic structure, BiOBr can be coupled with a variety of different functional materials to improve its photocatalytic performance. In this paper, We present the morphologically controllable BiOBr and its preparation process with the influence of raw materials, additives, solvents, synthesis methods, and synthesis conditions. Based on this, we propose design synthesis considerations for BiOBr-based nanocomplexes in four aspects: structure, morphology and crystalline phase, reduction of electron-hole pair complexation, photocorrosion resistance, and scale-up synthesis. The literature on BiOBr-based nanocomposites in the last 10 years (2012-2022) are summarized into seven categories, and the mechanism of enhanced photocatalytic activity of BiOBr-based nanocomposites is reviewed. Moreover, the applications of BiOBr-based nanocomposites in the fields of degradation of dye wastewater, antibiotic wastewater, pesticide wastewater, and phenol-containing wastewater are reviewed. Finally, the current challenges and prospects of BiOBr-based nanocomposites are briefly described. In general, this paper reviews the construction of BiOBr-based nanocomposites, the mechanism of photocatalytic activity enhancement and its research status and application prospects in the degradation of organic pollutants.

Molecular insights into formation of nitrogenous disinfection byproducts from algal organic matter in UV-LEDs/chlorine process based on FT-ICR analysis.

Eutrophication is a globally concerned issue, which brings algal cells and algal organic matter (AOM) into drinking water treatment plants. AOM is an important branch of nitrogenous disinfection byproduct (N-DBP) precursors. The variation of AOM composition in UV-LEDs/chlorine process, and its relationship with N-DBP formation still remain much uncertainty. Herein, we used fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to investigate AOM transformation in UV-LEDs/chlorine process, with UV285 and UV365 as light source, and screen for typical precursors of N-DBPs. We found that more nitrogen-containing compounds were generated after UV-LEDs/chlorine process, leading to the larger formation of N-DBPs in postchlorination. Compounds such as lignin, proteins, and amino sugars tends to be oxidized by reactive species in UV-LEDs/chlorine process. Further, compounds with higher O/C and higher weighted average double bond equivalence (DBEw) are easier to form N-DBPs, including dichloroacetonitrile and trichloronitromethane. Also, influence factors including pH, UV fluence, post-chlorination time and bromide concentration on N-DBP formation were evaluated. The results show that N-DBP formation generally followed the order of UV285/chlorine-postchlorination, UV365/chlorine-postchlorination, and direct chlorination. Our study provides comprehensive information on N-DBP formation from AOM in UV-LEDs/chlorine-postchlorination from molecular levels.

Elimination of ß-N-methylamino-l-alanine (BMAA) during UV/chlorine process: Influence factors, transformation pathway and DBP formation.

As a new cyanobacterial neurotoxin generated by cyanobacteria, BMAA was closely related to amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS/PDC). In this study, the degradation of BMAA by UV/chlorine process was investigated under the impacts of chlorine dosage, NOM dosage, pH and alkalinity. Results showed that only 10% of BMAA was removed by UV irradiation and 46.8% by chlorination in 5 min, however, 98.6% of BMAA was removed by UV/chlorine process in 5 min. The reaction rates were increased under alkaline conditions, but all achieved complete degradation in 5 min. Besides, HCO3- had slight inhibition, while NOM had significant inhibition on the degradation of BMAA. Furthermore, based on the detected degradation products of BMAA during UV/chlorine process, the possible degradation pathways were concluded. Overall, outcomes of this study exhibited that the use of the UV/chlorine process for BMAA degradation was appropriate in practical applications.

Nitrogen conversion from ammonia to trichloronitromethane: Potential risk during UV/chlorine process.

In this study, the potential formation of trichloronitromethane (TCNM) from model organic compounds in ammonia-containing water treated by UV/chlorine process was evaluated. Monochloramine generated from the reaction of chlorine and ammonia can be photolyzed to produce NO2- and reactive nitrogen species (RNS), which play important roles in the formation of TCNM during the subsequent chlorination. The results showed that increase of nitrogen to chlorine molar ratio (from 0 to 1.0) and pH (from 6.5 to 8.0) enhanced the formation of TCNM, mainly due to the increased yield of NO2- and RNS from the photolyzed monochloramine. The formation of TCNM was interestingly found to be linearly correlated with Hammett constants of the model precursors, which is theoretically related to the rate constants of RNS with model compounds. Enhanced formation of TCNM was also observed during the treatment of natural organic matter by UV/chlorine process in ammonia-containing water. The toxicity assessment showed that TCNM significantly increased the genotoxicity of formed DBPs. Furthermore, the electrophilic substitution reaction of •NO2 was proved to more likely occur on the ortho and para position of phenol according to the calculation of Gaussian program, and a possible reaction pathway of phenol and •NO2 was proposed based on the calculated results.

Non-negligible risk of chloropicrin formation during chlorination with the UV/persulfate pretreatment process in the presence of low concentrations of nitrite.

The UV/persulfate (PS) process is a promising water treatment technology, and it can not only effectively degrade contaminants of emerging concern, but also control formation of disinfection byproducts (DBPs). In this study, we investigated the potential and mechanisms of chloropicrin (i.e. trichloronitromethane, TCNM) formation during chlorination that followed UV/PS pretreatment in the presence of low concentrations of nitrite. We found that when nitrite was present in the UV/PS system, unexpected high concentrations of TCNM were formed. The formation potential of TCNM was impacted by operational conditions and water matrix components: (1) high pH enhanced TCNM formation; (2) high UV fluence inhibited TCNM formation; and (3) organic compounds containing phenolic groups enhanced TCNM formation. We discovered that electrophilic substitutions by reactive nitrogen species were favored for phenolic groups, and thus more nitrite-N was transformed to organic nitrogen. We also found that more TCNM was generated from natural organic matter than algal organic matter during chlorination following pretreatment using UV/PS. Accordingly, more attention needs to be paid to TCNM formation, if nitrite is present and the water is pretreated using UV/PS (when applied at upstream of chlorination). For example, we found that if monochloramine was used as a disinfectant downstream of the UV/PS process, the formation of TCNM was reduced.

Photolysis of o-nitrobenzaldehyde in the gas phase: a new OH* formation channel.

Photolysis of gaseous o-nitrobenzaldehyde (o-NBA) with selected different excitation wavelengths (355-400 nm) is investigated, and the nascent OH radical is detected by the single-photon laser-induced fluorescence (LIF) technique. The relative quantum yield and rotational excitation of OH formation are found to be dependent on the excitation energy. The distributions of rotational, spin-orbit, and Lambda-doublet states are obtained at 355-400 nm by analyzing the experimental data. The OH radicals are found to be vibrationally cold at all photolysis wavelengths. The spin-orbit and Lambda-doublet states have nonstatistical distributions. To understand the dissociative process involved in the OH-generating channel, DFT calculations are performed. Based on both experimental and theoretical results, possible photolysis channels of o-NBA leading to the OH fragment are proposed and discussed.

Photodissociation dynamics of alkyl nitrites at 266 and 355 nm: the OH product channel.

Photodissociation of methyl nitrite and n-butyl nitrite at 266 and 355 nm has been investigated in the gas phase at room temperature. OH photoproducts were observed, and their internal state distributions were measured by the one-photon laser-induced fluorescence (LIF) technique. It was found that the nascent OH from the 266 nm photolysis of methyl nitrite was vibrationally cold, and its rotational state distribution conformed to a Boltzmann behavior with a rotational temperature of T(rot) = 2200 +/- 150 K. In contrast, the nascent OH from the 266 nm photolysis of n-butyl nitrite was found to be vibrationally excited, and the measured relative population of v'' = 0:1 was 0.78:0.22. The rotational state distribution of the OH v'' = 1 state conformed to Boltzmann behavior, with a rotational temperature of T(rot) = 1462 +/- 120 K. However, a simple Boltzmann distribution was not found for the OH v'' = 0 state. In the photolysis of n-butyl nitrite at 355 nm, the OH fragment was found to be vibrationally cold and its rotational state distribution showed non-Boltzmann behavior. A photodissociation mechanism involving an intramolecular hydrogen atom transfer process is proposed for the OH product pathway for methyl nitrite, which has been compared with the potential energy surfaces obtained from density functional theory (DFT) calculations. A photodissociation mechanism of n-butyl nitrite is also proposed for the OH product pathway, which differs from that of methyl nitrite due to the effects of the different alkoxy substituents.

Dynamics of OH formation in the photodissociation of o-nitrobenzoic acid at 295 and 355 nm.

Photodissociation dynamics of o-nitrobenzoic acid at 295 and 355 nm is studied by probing the nascent OH photoproduct employing the single-photon laser-induced fluorescence technique. At both of the photolysis wavelengths, the OH fragments are found to be vibrationally cold but have different rotational state distributions. Upon photolysis at 295 nm, the relative population of OH in different rotational states does not follow the Boltzmann equilibrium distribution, whereas upon photolysis at 355 nm, a Boltzmann distribution is observed with a rotational temperature of 1010 +/- 100 K. Between the two spin-orbit states, (2)Pi(3/2) and (2)Pi(1/2), the former is found to be preferentially populated, and the distribution of the Pi(A') state for the Lambda-doublet is dominant at both of the wavelengths studied. Several possible dissociation pathways of o-nitrobenzoic acid leading to formation of the OH fragment are investigated computationally. On the basis of the theoretical and experimental studies, a possible mechanism of OH formation from the photodissociation of o-nitrobenzoic acid at 295 and 355 nm is proposed.

OH produced from o-nitrophenol photolysis: a combined experimental and theoretical investigation.

Photodissociation dynamics of o-nitrophenol in the gas phase at different photolysis wavelengths (361-390 nm) is investigated, and the nascent OH radical is observed by the single-photon laser-induced fluorescence technique. At all the photolysis wavelengths, the OH radicals are formed in vibrationally cold state (upsilon(")=0) and have similar rotational state distributions. The average rotational temperature for all the photolysis wavelengths is approximately 970+/-120 K, corresponding to a rotational energy of 1.9+/-0.2 kcal mol(-1). The spin orbit and Lambda-doublet states of the OH fragments formed in the dissociation are measured to have nonstatistical distributions. To get an insight into the dissociative mechanism leading to OH formation in the photolysis of o-nitrophenol, the potential energy surfaces of the OH-forming channels are mapped by ab initio theoretical calculations. According to both experimental and theoretical results, a possible mechanism for OH formation is proposed.

OH fragment from benzoic acid monomer photolysis: threshold and product state distribution.

Photodissociation dynamics of benzoic acid monomer (BAM) at different ultraviolet excitation wavelengths (280-295 nm) has been investigated. The nascent OH product state distributions were measured using the laser-induced fluorescence (LIF) technique. The rotational state distributions, the Lambda-doublet-state ratio, and spin-orbit state distributions of the OH fragment were also measured at 280-294 nm. The OH fragments are vibrationally cold, and their rotational state distributions are peaked at J'' = 3.5 at each photolysis wavelength. No LIF signal of OH fragments was observed at 295 nm. The photodissociation threshold is determined to be 102.5-103.9 kcal/mol for OH channel. The dissociative state and mechanism have been discussed for OH produced from the photodissociation of BAM.

Synthesis of High-Quality Graphene and Hexagonal Boron Nitride Monolayer In-Plane Heterostructure on Cu-Ni Alloy.

Graphene/hexagonal boron nitride (h-BN) monolayer in-plane heterostructure offers a novel material platform for both fundamental research and device applications. To obtain such a heterostructure in high quality via controllable synthetic approaches is still challenging. In this work, in-plane epitaxy of graphene/h-BN heterostructure is demonstrated on Cu-Ni substrates. The introduction of nickel to copper substrate not only enhances the capability of decomposing polyaminoborane residues but also promotes graphene growth via isothermal segregation. On the alloy surface partially covered by h-BN, graphene is found to nucleate at the corners of the as-formed h-BN grains, and the high growth rate for graphene minimizes the damage of graphene-growth process on h-BN lattice. As a result, high-quality graphene/h-BN in-plane heterostructure with epitaxial relationship can be formed, which is supported by extensive characterizations. Photodetector device applications are demonstrated based on the in-plane heterostructure. The success will have important impact on future research and applications based on this unique material platform.