Terminal Defects Research Articles

On image transformation for partial discharge source identification in vehicle cable terminals of high‐speed trains

AbstractPartial discharge (PD) detection of cable terminals is crucial for the safe operation of the traction power system in trains. However, similar PD signals in complex train‐operating environments cause difficulty to recognise the insulation defects. Therefore, a PD signal image transformation recognition method is proposed for PD detection of cable terminal defects to identify defects in cable terminals with similar PD characteristics accurately. In the proposed method, the raw PD signals are firstly transformed to images via the Gramian angular field (GAF) representation. This can reveal the discriminative characteristics embedded in the original PD signals and subsequently facilitate differentiating the PD sources, which exhibit similar characteristic in the time domain. The obtained GAF representation of PD signals (named as PD GAF images) is extracted from local and global features to train an efficient MobileVIT model, which is then utilised to identify similar types of PD sources in cable terminals. The results show that the proposed method achieves 97.5% recognition accuracy in the field experiment, which is superior to other methods.

Modulating Dual Functionalities of Hydrazide Derivatives for Iodide Oxidation Suppression and Defect Passivation in Printable Mesoscopic Perovskite Solar Cells

AbstractThe oxidation of iodide ions during annealing in air and rich defects generated at crystal terminations in perovskite are major limitations for achieving high photovoltaic performance in printable mesoscopic perovskite solar cells (p‐MPSCs). Here, the dual role of hydrazide derivatives in inhibiting iodide oxidation and passivating crystal termination defects is reported and how the dual role is affected by the substituent is studied. It's found that varying the hydrazide derivative from formylhydrazine (FH) to benzhydrazide (BH) and then to 4‐tert‐butylbenzhydrazide (TBBH) by introducing phenyl and 4‐tert‐butylphenyl substituents enhances the electron donating ability of hydrazides due to substituent electronic effect. The tailored hydrazides present enhanced iodide oxidation suppression and defect passivation capabilities, which lowers the trap density of perovskite in p‐MPSCs significantly. As the most effective additive, TBBH improves the power conversion efficiency of the p‐MPSC from 18.66% to 20.30%, and the resulted device maintains 90% of its initial efficiency after 500 h tacking at maximum power point at 55 ± 5 °C under simulated 1 sun illumination.

Field strength prediction of 220 kV cable oil terminal defects based on multivariate nonlinear regression model

During the installation of a cable oil terminal, it is easy to leave scratches on the main insulation owing to uneven forces when removing the semi-conductive layer. Scratch defects cause field intensity distortion, which leads to partial discharge and insulation failure. This study attempts to establish a simulation model of a 220 kV cable terminal to determine the effect of the length, depth, and position of the scratch on the maximum field strength at the defect. The simulation and experiment demonstrate that the maximum field strength at the defect increases with greater length and decreases as the depth increases. Therefore, a prediction method for the terminal defect field strength based on a multivariate nonlinear regression model was proposed in this study. When the defect is located at 20 mm from the root of the stress cone, the maximum field strength is 14.5 MV/m when the length and depth are 2 mm and 1 mm, respectively. The maximum field strength at the defect was predicted based on the length, depth, and position of the scratch defect to evaluate the severity of the defect.

Immunodeficiency: Complement disorders.

The complement system is an important component of innate and adaptive immunity that consists of three activation pathways. The classic complement pathway plays a role in humoral immunity, whereas the alternative and lectin pathways augment the innate response. Impairment, deficiency, or overactivation of any of the known 50 complement proteins may lead to increased susceptibility to infection with encapsulated organisms, autoimmunity, hereditary angioedema, or thrombosis, depending on the affected protein. Classic pathway defects result from deficiencies of complement proteins C1q, C1r, C1s, C2, and C4, and typically manifest with features of systemic lupus erythematosus and infections with encapsulated organisms. Alternative pathway defects due to deficiencies of factor B, factor D, and properdin may present with increased susceptibility to Neisseria infections. Lectin pathway defects, including Mannose-binding protein-associated serine protease 2 (MASP2) and ficolin 3, may be asymptomatic or lead to pyogenic infections and autoimmunity. Complement protein C3 is common to all pathways, deficiency of which predisposes patients to severe frequent infections and glomerulonephritis. Deficiencies in factor H and factor I, which regulate the alternative pathway, may lead to hemolytic uremic syndrome. Disseminated Neisseria infections result from terminal pathway defects (i.e., C5, C6, C7, C8, and C9). Diagnosis of complement deficiencies involves screening with functional assays (i.e., total complement activity [CH50], alternative complement pathway activity [AH50], enzyme-linked immunosorbent assay [ELISA]) followed by measurement of individual complement factors by immunoassay. Management of complement deficiencies requires a comprehensive and individualized approach with special attention to vaccination against encapsulated bacteria, consideration of prophylactic antibiotics, treatment of comorbid autoimmunity, and close surveillance.

The ABCF ATPase New1 resolves translation termination defects associated with specific tRNAArg and tRNALys isoacceptors in the P site.

The efficiency of translation termination is determined by the nature of the stop codon as well as its context. In eukaryotes, recognition of the A-site stop codon and release of the polypeptide are mediated by release factors eRF1 and eRF3, respectively. Translation termination is modulated by other factors which either directly interact with release factors or bind to the E-site and modulate the activity of the peptidyl transferase center. Previous studies suggested that the Saccharomyces cerevisiae ABCF ATPase New1 is involved in translation termination and/or ribosome recycling, however, the exact function remained unclear. Here, we have applied 5PSeq, single-particle cryo-EM and readthrough reporter assays to provide insight into the biological function of New1. We show that the lack of New1 results in ribosomal stalling at stop codons preceded by a lysine or arginine codon and that the stalling is not defined by the nature of the C-terminal amino acid but rather by the identity of the tRNA isoacceptor in the P-site. Collectively, our results suggest that translation termination is inefficient when ribosomes have specific tRNA isoacceptors in the P-site and that the recruitment of New1 rescues ribosomes at these problematic termination contexts.

Visual localization and quantitative detection method for thermal defects in cable terminals of high-speed trains based on a temperature derivative

Abstract Cable terminal defect detection plays an important role in ensuring the safe and stable operation of high-speed trains (HST). In this paper, a numerical model of the electromagnetic thermal field of overheating defects of cable terminal shielding grids and a method of detecting internal defects of cable terminals - even-order temperature derivative (EOTD) is proposed for quantitative detection of internal defective structures of vehicle-mounted cable terminals. Firstly, a numerical model of the electromagnetic thermal field of cable terminals under the condition of leakage current is constructed, through which the temperature field distribution characteristics of different defective structures are analyzed. Then, the intuitive location of the defective region is obtained by investigating the derivative characteristics of the temperature image, and the depth and intensity of the defects are quantitatively assessed by using the main side peak (MSP) distances and the MSP values extracted from the derivative curves. Finally, the simulation and experimental results achieve the identification of defect structures and the quantitative detection of defect depth and intensity, proving the effectiveness and accuracy of the proposed method.

The ABCF ATPase New1 resolves translation termination defects associated with specific tRNAArg and tRNALys isoacceptors in the P site.

The efficiency of translation termination is determined by the nature of the stop codon as well as its context. In eukaryotes, recognition of the A-site stop codon and release of the polypeptide are mediated by release factors eRF1 and eRF3, respectively. Translation termination is modulated by other factors which either directly interact with release factors or bind to the E-site and modulate the activity of the peptidyl transferase center. Previous studies suggested that the Saccharomyces cerevisiae ABCF ATPase New1 is involved in translation termination and/or ribosome recycling, however, the exact function remained unclear. Here, we have applied 5PSeq, single-particle cryo-EM and readthrough reporter assays to provide insight into the biological function of New1. We show that the lack of New1 results in ribosomal stalling at stop codons preceded by a lysine or arginine codon and that the stalling is not defined by the nature of the C-terminal amino acid but rather by the identity of the tRNA isoacceptor in the P-site. Collectively, our results suggest that translation termination is inefficient when ribosomes have specific tRNA isoacceptors in the P-site and that the recruitment of New1 rescues ribosomes at these problematic termination contexts.

Expression of human RECQL5 in Saccharomyces cerevisiae causes transcription defects and transcription-associated genome instability

RECQL5 is a member of the conserved RecQ family of DNA helicases involved in the maintenance of genome stability that is specifically found in higher eukaryotes and associates with the elongating RNA polymerase II. To expand our understanding of its function we expressed human RECQL5 in the yeast Saccharomyces cerevisiae, which does not have a RECQL5 ortholog. We found that RECQL5 expression leads to cell growth inhibition, increased genotoxic sensitivity and transcription-associated hyperrecombination. Chromatin immunoprecipitation and transcriptomic analysis of yeast cells expressing human RECQL5 shows that this is recruited to transcribed genes and although it causes only a weak impact on gene expression, in particular at G + C-rich genes, it leads to a transcription termination defect detected as readthrough transcription. The data indicate that the interaction between RNAPII and RECQL5 is conserved from yeast to humans. Unexpectedly, however, the RECQL5-ID mutant, previously shown to have reduced the association with RNAPII in vitro, associates with the transcribing polymerase in cells. As a result, expression of RECQL5-ID leads to similar although weaker phenotypes than wild-type RECQL5 that could be transcription-mediated. Altogether, the data suggests that RECQL5 has the intrinsic ability to function in transcription-dependent and independent genome dynamics in S. cerevisiae.

Assessment of dental mobility in elderly and senile patients with various types of dentition defects

Objective. To determine the differences in the degree of tooth mobility in elderly patients with various types of dentition defects. To establish and differentiate the degree of tooth mobility in relation to the type of dentition defect in elderly and senile patients. Materials and methods. 500 patients aged 60 to 75 divided into 4 groups were examined. In the first group of patients, terminal defects were revealed (on one or both sides). The second group consisted of patients with included defects (on one or both sides). The third group was presented by combined defects (included and not included). Patients with single standing teeth constituted the fourth group. Patients with complete absence of teeth were excluded from the study. The assessment of dental mobility was carried out using the Periodotest device. All studies on dental mobility were conducted as part of the initial examination of the patient. To obtain objective data, periotestometry was performed 2 times in each patient. Average periotestometry data were calculated for each patient. The average readings of periotestometry for different groups of patients were determined. Results. On the basis of the data obtained while comparing the results of periotestometry, in relation to the type of dentition defect, statistically significant differences were established (p 0.001) (method used: the Kraskel – Wallis criteria). The results of periotestometry obtained in patients of group 4 were significantly higher than in representatives of other examined groups. The least mobility according to the results of periotestometry was observed in groups 2 and 3. Conclusions. The study revealed significant differences in the degree of tooth mobility in relation to the type of dentition defect. In patients with single standing teeth, 2–3 degree of their mobility was determined, while patients with included defects had 1–2 degree of the mobility of existing teeth. The obtained data of periotestometry indicate the need to use unloading dentures in elderly patients, in order to preserve the remaining teeth in patients with single-standing teeth, as well as in patients with terminal defects of the dentition.

Tailoring the optoelectronic properties of monolayer BA2PbI4/MoS2 heterojunction through terminal variations and defect engineering

In light of the inherent challenge posed by the simultaneous pursuit of structural stability and favorable optoelectronic characteristics in two-dimensional organic-inorganic halide perovskites, the construction of heterojunctions emerges as a promising strategy for mitigating electronic deficiencies and enhancing overall performance. Furthermore, defect engineering stands as a commonly employed technique to fine-tune the photoelectric properties of materials. In this study, we systematically investigate the pivotal vacancy defects, namely VBA and VI, within the monolayer BA2PbI4/MoS2 heterojunction system, employing first-principles calculations. Our computational findings illuminate the conductivity of MoS2 can be modulated when it interfaces with distinct surface terminations of 2D BA2PbI4, thereby exerting influence over electron flow within MoS2. Additionally, we observe a progressive transformation of p-type doped MoS2 into a heavily doped material as the concentration of BA vacancy defects increases. To further optimize the optoelectronic properties, we strategically introduce the I vacancy (Pb-Pb dimer) defect, effectively transitioning the indirect bandgap heterojunction into a direct one. Our study underscores the profound impact of different surface terminations and defect configurations on the physical attributes of the heterojunction, offering valuable insights for the fabrication of high-performance photoelectric materials.

Regulated Dual Defects of Bridging Organic and Terminal Inorganic Ligands in Iron-based Metal-Organic Framework Nodes for Efficient Photocatalytic Ammonia Synthesis.

Engineering advantageous defects to construct well-defined active sites in catalysts is promising but challenging to achieve efficient photocatalytic NH3 synthesis from N2 and H2O due to the chemical inertness of N2 molecule. Here, we report defective Fe-based metal-organic framework (MOF) photocatalysts via a non-thermal plasma-assisted synthesis strategy, where their NH3 production capability is synergistically regulated by two types of defects, namely, bridging organic ligands and terminal inorganic ligands (OH- and H2O). Specially, the optimized MIL-100(Fe) catalysts, where there are only terminal inorganic ligand defects and coexistence of dual defects, exhibit the respective 1.7- and 7.7-fold activity enhancement comparable to the pristine catalyst under visible light irradiation. As revealed by experimental and theoretical calculation results, the dual defects in the catalyst induce the formation of abundant and highly accessible coordinatively unsaturated Fe active sites and synergistically optimize their geometric and electronic structures, which favors the injection of more d-orbital electrons in Fe sites into the N2 π* antibonding orbital to achieve N2 activation and the formation of a key intermediate *NNH in the reaction. This work provides a guidance on the rational design and accurate construction of porous catalysts with precise defective structures for high-performance activation of catalytic molecules.

Regulated Dual Defects of Bridging Organic and Terminal Inorganic Ligands in Iron‐based Metal‐Organic Framework Nodes for Efficient Photocatalytic Ammonia Synthesis

AbstractEngineering advantageous defects to construct well‐defined active sites in catalysts is promising but challenging to achieve efficient photocatalytic NH3 synthesis from N2 and H2O due to the chemical inertness of N2 molecule. Here, we report defective Fe‐based metal‐organic framework (MOF) photocatalysts via a non‐thermal plasma‐assisted synthesis strategy, where their NH3 production capability is synergistically regulated by two types of defects, namely, bridging organic ligands and terminal inorganic ligands (OH− and H2O). Specially, the optimized MIL‐100(Fe) catalysts, where there are only terminal inorganic ligand defects and coexistence of dual defects, exhibit the respective 1.7‐ and 7.7‐fold activity enhancement comparable to the pristine catalyst under visible light irradiation. As revealed by experimental and theoretical calculation results, the dual defects in the catalyst induce the formation of abundant and highly accessible coordinatively unsaturated Fe active sites and synergistically optimize their geometric and electronic structures, which favors the injection of more d‐orbital electrons in Fe sites into the N2 π* antibonding orbital to achieve N2 activation and the formation of a key intermediate *NNH in the reaction. This work provides a guidance on the rational design and accurate construction of porous catalysts with precise defective structures for high‐performance activation of catalytic molecules.

Defect Identification Method of Cable Termination based on Improved Gramian Angular Field and ResNet

Background: This paper proposes a defect identification method for vehicle-mounted cable terminals in electric multiple units (EMUs) based on the improved Graham angle field and residual network to address the issue of low recognition accuracy caused by the lack of partial discharge (PD) and identification data for Ethylene Propylene Rubber (EPR) cable terminal defects. Methods: The improved Gramian angular field (IGAF) characteristic transformation method was used to transform the PD one-dimensional time-series signal into a two-dimensional one after cable terminals with four common insulation defects were constructed, and a PD detection platform was built. Finally, an anti-aliasing downsampling module and attention mechanism were added to the residual network ResNet101 model. The Center loss and Softmax loss functions were integrated to increase accuracy for training and recognition classification. Topological feature images improved the distinguishability of defect categories. Results: The test results showed that the diagnostic method has an accuracy rate of 97.3% for identifying PD at the cable terminal. Conclusion: The proposed diagnosis model has higher recognition accuracy and better balance than other conventional fault diagnosis methods, making it suitable for diagnosing high-voltage cable faults in EMU trains.

AP-2α/AP-2β Transcription Factors Are Key Regulators of Epidermal Homeostasis

AP-2 transcription factors regulate ectodermal development, but their roles in epidermal homeostasis in adult skin are unknown. We find that AP-2α is the predominant AP-2 family member in adult epidermis, followed by AP-2β. Through inactivation of AP-2α, AP-2β, or both in keratinocytes, we assessed the effects of a gradient of epidermal AP-2 activity on skin function. We find that (i) loss of AP-2β in keratinocytes is compensated for by AP-2α, (ii) loss of AP-2α impairs terminal keratinocyte differentiation and hair morphogenesis, and (iii) the combined loss of AP-2α/AP-2β results in more severe skin and hair abnormalities. Keratinocyte differentiation defects precede progressive neutrophilic skin inflammation. Inducible inactivation of AP-2α/AP-2β in the adult phenocopies these manifestations. Transcriptomic analyses of epidermis lacking AP-2α or AP-2α/AP-2β in keratinocytes demonstrate a terminal keratinocyte differentiation defect with upregulation of alarmin keratins and of several immune pathway regulators. Moreover, our analyses suggest a key role of reduced AP-2α-dependent gene expression of CXCL14 and the keratin 15 gene K15 as an early pathogenic event toward the manifestation of skin inflammation. Thus, AP-2α and AP-2β are critical regulators of epidermal homeostasis in adult skin.

Radiological assessment of long-term outcomes of restorative treatment in patients with shortened dental arches

Restoring the integrity of the dentition with orthopedic structures should be carried out strictly according to indications, taking into account the condition of the supporting teeth and/or teeth limiting the defect. To conduct a retrospective analysis of the results of orthopedic treatment of patients with shortened dentition according to clinical and radiological methods. The material for the study was data from cone beam computed tomography (CBCT) of 126 patients with shortened dentition (most patients with the absence of a second molar, as well as the absence of the first and second molars), who sought a consultation about missing teeth in the orthopedic and surgical department of the Federal State Budgetary Institution National Medical Research Center TsNIISiCHLKh Ministry of Health of Russia. At the stages of treatment for patients in the study group, insufficient attention is paid to the restoration of terminal defects of the dentition in the upper and lower jaws, especially the restoration of second molars. This may be due to improper planning of dental treatment and insufficient motivation of the patient to carry out comprehensive dental rehabilitation. According to CT studies, the number of complications of orthopedic treatment in the area of supporting teeth and/or teeth limiting the included defect or terminal defect of the dentition in the masticatory region increases depending on the period of use of the orthopedic structure. The use of cantilever structures leads to functional overload of the supporting teeth. Neglecting the restoration of a full dentition and prosthetics of end defects of the dentition leads to dentoalveolar advancement of antagonists of missing teeth and the appearance of complications such as functional overload of supporting teeth and resorption of alveolar bone.

RNA Pol II Assembly Affects ncRNA Expression.

RNA pol II assembly occurs in the cytoplasm before translocation of the enzyme to the nucleus. Affecting this assembly influences mRNA transcription in the nucleus and mRNA decay in the cytoplasm. However, very little is known about the consequences on ncRNA synthesis. In this work, we show that impairment of RNA pol II assembly leads to a decrease in cryptic non-coding RNAs (preferentially CUTs and SUTs). This alteration is partially restored upon overcoming the assembly defect. Notably, this drop in ncRNAs is only partially dependent on the nuclear exosome, which suggests a major specific effect of enzyme assembly. Our data also point out a defect in transcription termination, which leads us to propose that CTD phosphatase Rtr1 could be involved in this process.

Genome-wide regulation of Pol II, FACT, and Spt6 occupancies by RSC in Saccharomyces cerevisiae

RSC (remodels the structure of chromatin) is an essential ATP-dependent chromatin remodeling complex in Saccharomyces cerevisiae. RSC utilizes its ATPase subunit, Sth1, to slide or remove nucleosomes. RSC has been shown to regulate the width of the nucleosome-depleted regions (NDRs) by sliding the flanking nucleosomes away from NDRs. As such, when RSC is depleted, nucleosomes encroach NDRs, leading to transcription initiation defects. In this study, we examined the effects of the catalytic-dead Sth1 on transcription and compared them to those observed during acute and rapid Sth1 depletion by auxin-induced degron strategy. We found that rapid depletion of Sth1 reduces recruitment of TBP and Pol II in highly transcribed genes, as would be expected considering its role in regulating chromatin structure at promoters. In contrast, cells harboring the catalytic-dead Sth1 (sth1-K501R) exhibited a severe reduction in TBP binding, but, surprisingly, also displayed a substantial accumulation in Pol II occupancies within coding regions. The Pol II occupancies further increased upon depleting endogenous Sth1 in the catalytic-dead mutant, suggesting that the inactive Sth1 contributes to Pol II accumulation in coding regions. Notwithstanding the Pol II increase, the ORF occupancies of histone chaperones, FACT and Spt6 were significantly reduced in the mutant. These results suggest a potential role for RSC in recruiting/retaining these chaperones in coding regions. Pol II accumulation despite substantial reductions in TBP, FACT, and Spt6 occupancies in the catalytic-dead mutant could indicate severe transcription elongation and termination defects. Such defects would be consistent with studies showing that RSC is recruited to coding regions in a transcription-dependent manner. Thus, these findings imply a role for RSC in transcription elongation and termination processes, in addition to its established role in transcription initiation.

Different bonding modes modulate the structure and properties of g-C3N4-Based materials

Composite precursors with hydrogen bonding interactions (Fe(OH)3/DCDA) and chemical bonding interactions (Fe(OH)3/PA/DCDA) were constructed by simple hydrothermal method, respectively, and then the corresponding photocatalysts (Fe2O3/g-C3N4 and Fe2O3/C/g-C3N4) were calcined under N2 atmosphere to study the effect of different bonding types of precursors on the structure and performance of the photocatalysts. It is shown that the strong chemical bonding interaction between -CHO in Fe(OH)3/PA and -NH2 in DCDA causes the calcined Fe2O3/C/g-C3N4 to exhibit a lower density of terminal amino defects compared to the weak hydrogen bonding interaction, which greatly facilitates the photogenerated electron-hole separation. In addition, the strong chemical bonding interactions in the precursors would also cause incomplete polymerization during calcination, leading to the formation of porous structures in the catalyst Fe2O3/C/g-C3N4, which increases the specific surface area on the one hand and enhances the photoavailability on the other. Therefore, the prepared Fe2O3/C/g-C3N4 has good photocatalytic activity and can degrade 51.28 % of MB solution after 60 min of continuous irradiation under visible light, which is 2.8 times higher than that of g-C3N4.

Pregnancy Termination and Postnatal Major Congenital Heart Defect Prevalence After Introduction of Prenatal Cardiac Screening

Prenatal cardiac screening of the first and second trimesters has had a major impact on postnatal prevalence of congenital heart defects (CHDs), rates of termination of pregnancy (TOP), and outcomes among children born alive with CHDs. To examine the prenatal and postnatal incidence of major CHDs (ie, necessitating intervention within the first year of life), detection rate trends, rates of TOP, and the association of cardiac screening with postnatal outcomes. In this cross-sectional study, 3827 fetuses with antenatally diagnosed major CHDs in the Czech Republic (population 10.7 million) between 1991 and 2021 were prospectively evaluated with known outcomes and associated comorbidities. Prenatal and postnatal prevalence of CHD in an unselected population was assessed by comparison with a retrospective analysis of all children born alive with major CHDs in the same period (5454 children), using national data registry. Data analysis was conducted from January 1991 to December 2021. Prenatal detection and postnatal prevalence of major CHDs and rate of TOPs in a setting with a centralized health care system over 31 years. A total of 3 300 068 children were born alive during the study period. Major CHD was diagnosed in 3827 fetuses, of whom 1646 (43.0%) were born, 2069 (54.1%) resulted in TOP, and 112 (2.9%) died prenatally. The prenatal detection rate increased from 6.2% in 1991 to 82.8% in 2021 (P < .001). Termination of pregnancy decreased from 70% in 1991 to 43% (P < .001) in 2021. Of 627 fetuses diagnosed in the first trimester (introduced in 2007), 460 were terminated (73.3%). Since 2007, of 2066 fetuses diagnosed in the second trimester, 880 (42.6%) were terminated, resulting in an odds ratio of 3.6 (95% CI, 2.8-4.6; P < .001) for TOP in the first trimester compared with the second trimester. Postnatal prevalence of major CHDs declined from 0.21% to 0.14% (P < .001). The total incidence (combining prenatal detection of terminated fetuses with postnatal prevalence) of major CHD remained at 0.23% during the study period. In this cross-sectional study, the total incidence of major CHD did not change significantly during the 31-year study period. The prenatal detection of major CHD approached 83% in the current era. Postnatal prevalence of major CHD decreased significantly due to early TOPs and intrauterine deaths. The introduction of first trimester screening resulted in a higher termination rate in the first trimester but did not revert the overall decreasing trend of termination for CHDs in general.

Intramolecular engineering of defective terminations within triazine-based conjugated polymers for augmented photocatalytic H2 production and Cr(VI) reduction

In this study, enhanced intramolecular polarization of π-conjugated electrons in triazine-based conjugated polymers (TCPs) was modulated by incorporating –NH2/-CN terminations. The electron-abundant –NH2 groups and the electron-deficient –CN groups lead to the delocalization of the π-conjugated electrons on the plane of the conjugated polymer by the push-and-pull effect. The resultant A-TCP-C configuration expands the photoresponsive regions and form spatially separated electron-hole centers as the charge-transfer channels for electron shuttling. The π-conjugated electrons polarized delocalization system induces the asymmetrical distribution of electrostatic potential and creates intramolecular electric field to facilitate the activation of the conjugated electrons over the plane from π to π* states by accumulating valence electrons on the benzene ring near –NH2 terminals, which reduce the activation energy barrier and thus offer profitably condition for the visible light excitation process. Additionally, the exposed –NH2/-CN terminal defects create high-energy adsorption sites for the preconcentration of target substances. This optimization of thermodynamically and kinetically accessible pathways enabled preferential reactant accumulation and charges transfer. The as-synthesized A-TCP-C20 polymer exhibits a photocatalytic activity of removing 95.8% Cr(VI) within 40 min and a H2 production ability of 1919.0 μmol g−1 h−1, which is 6 folds and 260 folds over the pristine TCP, respectively. Our work presents a facile and directional structure arrangement can be devised to simultaneously optimize active species binding, transfer, and activation on TCPs surface sites.