Polymeric g‐C3N4 is a promising visible‐light‐responsive photocatalyst; however, the fast recombination of charge carriers and moderate oxidation ability remarkably restrict its photocatalytic ...oxidation efficiency towards organic pollutants. To overcome these drawbacks, a self‐modification strategy of one‐step formaldehyde‐assisted thermal polycondensation of molten urea to prepare carbon‐deficient and oxygen‐doped g‐C3N4 (VC‐OCN) is developed, and the carbon vacancy concentration is well‐controlled by changing formaldehyde dosage. The VC‐OCN catalysts exhibit interesting carbon vacancy concentration‐dependent photocatalytic removal efficiency to p‐nitrophenol (PNP) and atrazine (ATN), in which VC‐OCN15 with appropriate carbon vacancy concentration displays significantly higher pollutant removal efficiency than bulk g‐C3N4. The apparent first‐order rate constant of VC‐OCN15 for PNP and ATN removal is 4.4 and 5.2 times higher than that of bulk g‐C3N4. A combination of the experimental results and theoretic calculations confirm that the synergetic effect of carbon vacancies and oxygen doping sites can not only delay the recombination of charge carriers but also facilitate adsorption of oxygen molecules on the carbon vacancies, which leads to the generation of plentiful active oxygen species including not only superoxide anion radicals but also indirectly formed hydroxyl radicals and singlet oxygen. These active oxygen species play a dominant role in the removal of target pollutants.
A strategy of one‐step formaldehyde‐assisted thermal polycondensation of molten urea to prepare carbon‐deficient and oxygen‐doped g‐C3N4 (VC‐OCN) is developed, in which carbon vacancy concentration is controllable. At a suitable carbon vacancy concentration, the VC‐OCN exhibits a significantly higher photocatalytic oxidation capacity to organic pollutants than bulk g‐C3N4, attributed to the synergetic effect of carbon vacancies and oxygen doping sites.
The concentrations and spatial occurrences of 17 legacy per- and polyfluoroalkyl substances (PFAS) and 4 emerging PFAS in the coastal water-dissolved phase, surface sediment phase and suspended ...particulate matter (SPM) in the coastal areas of Bohai Bay were investigated. In addition, the partition behaviors of PFAS in the water-SPM system and water-sediment system and the potential sources of PFAS in the marine environment were revealed. The total concentrations of PFAS (∑PFAS) in the water-dissolved phase, surface sediment and SPM were 20.5–684 ng/L, 2.69–25.0 ng/g dry weight (dw) and 4.39–527 ng/g dw, respectively. The level of PFAS contamination in the coastal areas of Shandong Province was higher than that in other areas. The average partition coefficients (log Kd) of PFAS in the water-SPM system and water-sediment system were 1.56–3.57 and 0.72–2.95, respectively. Long-chain PFAS and PFECHS (perfluoroethylcyclohexane sulfonate) have a higher log Kd than that of short-chain PFAS. PFAS with short carbon chains were mainly detected in the water-dissolved phase, but long-chain PFAS mainly occurred in the surface sediment and SPM phases. Source analysis based on the positive matrix factorization (PMF) model found that erosion inhibitor factories, aqueous film-forming foam factories, metal plating plants, fluoropolymer chemical manufacture and food contact materials were the main sources of PFAS in Bohai Bay. These results improved our understanding of the partitioning behavior and sources of PFAS in aquatic environments.
∑PFAS (ng/L) and composition profile in water dissolved phase in the coastal area of Bohai bay, China. Display omitted
•Occurrences and sources of PFAS in water, surface sediment and SPM of Bohai bay were investigated.•HFPO-DA and Cl-PFAESs were ubiquitous in water dissolved phase.•Short-chain PFAS were mostly presented in water, while long-chain PFAS prevailed in sediment and SPM.•AFFFs factories, metal plating plants, FP manufacture and food contact materials are the key contributing to PFAS.
The occurrence, partition behaviors and potential source of legacy and emerging PFAS in coastal areas were investigated.
Biomolecular receptors such as nucleic acids that switch between two or more conformations upon binding to a specific target can be used to build specific and sensitive biosensors. In this work, ...based on the electrochemical dual-signaling ratiometric strategy and triple-helix molecular switch, we developed a selective, reusable, and simple electrochemical DNA (E-DNA) biosensor for target DNA (T-DNA) detection. A hairpin DNA capture probe labeled with methylene blue (MB-DNA) self-assembles on the surface of a gold electrode (GE) through Au–S bond, and then a single-strand DNA modified with two ferrocenes (Fc-DNA) on each end to enhance the oxidation signal hybridizes with the MB-DNA to form a triple-helix conformation. When T-DNA exists, the Fc-DNA hybridizes with T-DNA disassembling the triple-helix stem and allowing the MB-DNA to revert to its hairpin structure. Hence, the Fc tags diffuse away from the GE surface while the MB tags remain affixed close to it, resulting in a decrease in the peak current of Fc (I Fc) and an increase in that of MB (I MB). The linear relationship between the value of I MB/I Fc and the T-DNA concentration is observed from 0.5 to 80 pM, and the limit of detection is as low as 0.12 pM. The developed E-DNA biosensor may have great potential in the electrochemical detection of a wide range of analytes and be a biosensing platform for early clinical diagnosis and biomedical research.
Because of the intrinsic importance of nucleic acids as biotargets, the simple and sensitive detection of nucleic acids is very essential for biological studies and medical diagnostics. In this work, ...a novel, simple, and selective electrochemical DNA biosensor for the sensitive detection of target DNA (T-DNA) has been developed based on the dual-signaling electrochemical ratiometric method and exonuclease III (Exo III)-assisted target recycling amplification strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The stem-loop (hairpin) DNA capture probe (HP), which was labeled by thiolated methylene blue (MB) at the 3′-protruding termini and ferrocene (Fc) in the middle of the loop, first self-assembled on the gold electrode surface via a Au–S bond. In the presence of T-DNA, the T-DNA hybridized with HP, which triggered the Exo III cleavage process and accompanied the release of T-DNA. As a result, the MB tags were away from and the Fc tags close to the gold electrode surface, leading to the decrease of the oxidation peak current of MB (I MB) and the increase of that of Fc (I Fc). The value of ΔI Fc/|ΔI MB| (ΔI Fc and ΔI MB are the change values of the oxidation peak currents of Fc and MB, respectively) is linear with the concentration of T-DNA from 0.01 pM to 0.8 pM. The detection limit (4.16 fM) of the developed method is much lower than that of the most reported electrochemical DNA biosensors. This strategy provides a simple and sensitive approach for the detection of T-DNA and has promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.
Nanoporous PdCu alloys (NP-PdCu) with uniform PdCu alloy ligament (~
6
nm) and predetermined bimetallic ratio are prepared by selectively dealloying PdCuAl ternary alloys in an alkaline solution. ...NP-PdCu exhibit greatly enhanced electrocatalytic activity for formic acid and methanol oxidation compared with nanoporous Pd (NP-Pd). Moreover, the structure stability of NP-PdCu is also greatly enhanced. The electrochemical surface area of NP-PdCu is well-maintained after 10,000 potential cycles from 0.6 to 0.9
V (vs. RHE) in 0.5
M H
2SO
4 aqueous solution, while that of NP-Pd drops dramatically after 5000
cycles. The NP-PdCu will be promising anode catalysts for fuel cell-related technology.
► The nanoporous PdCu alloys show much improved electrocatalytic activities for small organic molecules oxidation compared with nanoporous pure Pd. ► The nanoporous alloys can reduce the amount of the used noble Pd. ► The nanoporous PdCu alloys show much improved structure stability compared with nanoporous Pd.
Taking TdT-mediated hemin/G-quadruplex DNAzyme nanowires as NADH oxidase and HRP-mimicking DNAzyme, a novel DNA-based electrochemical method has been developed for sensitive and selective assay of ...alkaline phosphatase (AP) activity. The double-stranded DNA (dsDNA) probe consisted of thiol-functionalized DNA1 and 3′-phosphorylated DNA2, was immobilized on a gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode. In the presence of AP, 3′-phosphoryl end of DNA2 was dephosphorylated. Terminal deoxynucletidyl transferase (TdT) catalyzed the sequential addition of deoxynucleotides (dTTPs) at 3′-OH end of DNA2 to extend DNA2 with a poly-T sequence. Then, G-rich DNA3 strand hybridized with the poly-T sequence of DNA2. Upon addition of hemin, the hemin/G-quadruplex DNAzyme was formed. In the presence of NADH, the hemin/G-quadruplex DNAzyme oxidased NADH to NAD+, accompanied by the formation of H2O2 which was further catalyzed by hemin/G-quadruplex DNAzyme (served as a HRP-mimicking DNAzyme) with the thionine (Thi) as electron transfer mediator, leading to the amplified electrochemical signal. Under optimized conditions, the response peak current was linear with the concentration of AP in the range from 0.1UL−1 to 5UL−1 with the detection limit of 0.03UL−1. Also, the developed biosensor possessed good selectivity, reproducibility and stability, and simple sensing structure, showing promising practical applications in AP activity assay.
•A novel DNA-based electrochemical method for alkaline phosphatase activity assay.•TdT-mediated hemin/G-quadruplex DNAzyme nanowires as signal amplification elements.•The developed method shows excellent analytical performance.
A nanoporous PdNi (NP-PdNi) alloy with uniform structure dimension is easily fabricated by one-step mild dealloying of a PdNiAl precursor alloy. NP-PdNi consists of an interconnected nanoscaled ...network backbone and bicontinuous hollow channels in all three dimensions with a typical ligament size of around 5 nm. Electrochemical measurements indicated that the NP-PdNi alloy has superior electrocatalytic activity towards oxygen reduction reaction (ORR) with much higher specific and mass activities as well as higher methanol tolerance compared with Pt/C catalysts. Importantly, NP-PdNi suffers less loss of the ORR activity and the electrochemical surface area of metal upon 5000 potential cycles in acid solution than Pt/C, indicating a better catalytic durability. The NP-PdNi alloy holds great application potential as a cathode electrocatalyst in the fuel cell related technology with unique ORR performance, high structure stability, and easy preparation.
Perfluoroalkyl acids (PFAAs) are a group of emerging persistent organic pollutants (POPs), which have been ubiquitously detected in the environmental media. However, national scale investigations on ...their occurrence and distribution in drinking water are still insufficient. In this study, we detected the 17 priority PFAAs in drinking water from 79 cities of 31 provincial-level administrative regions throughout China, and investigated their occurrence and distribution. Additionally, we also analyzed the influencing factors on their profiles, such as the existence of industrial sources, socioeconomic factors (population density and GDP), and assessed levels of risk associated with contaminated drinking water. On the national scale, the sum concentrations of the 17 PFAAs (∑17PFAAs) in drinking water was in a range of 4.49–174.93 ng/L with a mean value of 35.13 ng/L. Among the 17 individual PFAAs, perfluorobutanoic acids (PFBA) was the most abundant individual PFAAs with the median concentration of 17.87 ng/L, followed by perfluorooctanoic acid (PFOA, 0.74 ng/L), perfluorononanoic acid (PFNA, 0.40 ng/L) and perfluorooctane sulfonic acid (PFOS, 0.25 ng/L). The geographic distribution characteristic of ∑17PFAAs in drinking water was in a descending order of Southwestern China (57.67 ng/L) > Eastern coastal China (32.85 ng/L) > Middle China (29.89 ng/L) > Northwestern China (28.49 ng/L) > Northeastern China (22.03 ng/L), and in general, the existence of the industrial sources could positively affect the contamination levels of PFAAs in drinking water. The pollution level of PFAAs in drinking water also varied among the three different city levels (medium-sized city > big city > town). In towns, the positive correlations were observed between the population density and the ∑17PFAAs (R2 = 0.45, p < 0.01), and the individual concentration of PFHxA, PFBS, and PFOA (p < 0.01). Moreover, besides PFAAs in Yunnan, Jiangsu, and Jiangxi, concentrations of related PFAAs in drinking water from 28 provinces were less than the suggested drinking water advisories. The relatively higher concentrations of PFAAs in Yunnan, Jiangsu, and Jiangxi suggest that further studies focusing on their sources and potential health risk to humans are needed.
Display omitted
•The nationwide occurrence of PFAAs in drinking water of China was investigated.•PFBA, PFOA, and PFHxS were dominated components in drinking water.•PFAAs concentration in drinking water varied among different regions and city levels of China.•PFAAs in drinking water might not pose a serious risk in most sample sites.
Deep learning promotes the breakthrough of emotion recognition in many fields, especially speech emotion recognition (SER). As an important part of speech emotion recognition, the most relevant ...acoustic feature extraction has always attracted the attention of existing researchers. Aiming at the problem that the emotional information contained in the current speech signals is distributed dispersedly and cannot comprehensively integrate local and global information, this paper presents a network model based on a gated recurrent unit (GRU) and multi-head attention. We evaluate our proposed emotion model on the IEMOCAP and Emo-DB corpora. The experimental results show that the network model based on Bi-GRU and multi-head attention is significantly better than the traditional network model at detecting multiple evaluation indicators. At the same time, we also apply the model to a speech sentiment analysis task. On the CH-SIMS and MOSI datasets, the model shows excellent generalization performance.
► Nanoporous PdCu alloys with predetermined alloy ratios are successfully fabricated by a simple dealloying process. ► The alloy ratio has a significant effect on both catalytic activity and ...catalytic behavior of the alloy catalyst for formic acid electro-oxidation. ► Nanoporous PdCu alloy with appropriate alloy ratio has greatly enhanced electrocatalytic activity towards formic acid oxidation and resistance to CO poisoning.
In this work, nanoporous PdCu alloys (np-PdCu) with predetermined bimetallic ratios are fabricated by selectively dealloying PdCuAl ternary alloys in 1.0
M NaOH solution. Electron microscope and X-ray diffraction characterizations show that the nanoporous metals have three-dimensional bicontinuous ligament-pore structure with uniform ligament size. Electrochemical measurements demonstrate that np-PdCu has greatly enhanced electrocatalytic activity and structure stability towards formic acid oxidation (FAO) compared with nanoporous Pd (np-Pd). The surface specific activities of the nanoporous metals follow the order that np-Pd
50Cu
50
>
np-Pd
75Cu
25
>
np-Pd
30Cu
70
>
np-Pd. The peak current density on np-Pd
50Cu
50 shows the highest value, which is about six times of that on np-Pd. The alloy ratio also has a significant effect on the electrocatalytic behavior of the PdCu alloy towards FAO. When the Cu content is lower than 50
at.%, the FAO is mainly through the direct pathway; when the Cu content reaches 70
at.%, the FAO through the CO pathway increases. Moreover, electrochemical stripping experiment and continuous potential scan demonstrate that np-Pd
50Cu
50 has a better resistance to CO poisoning and enhanced structure stability compared with other alloy samples. These results indicate the potential application of the np-Pd
50Cu
50 in direct formic acid fuel cell.
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