Excitation-emission Matrix Fluorescence Spectra Research Articles

Mechanistic insights of efficient aromatic organic compounds oxidation using biochar derived from coking wastewater sludge

Coking wastewater sludge possessed potential environmental hazards and pyrolysis was a desirable approach which could converted it into one functional carbonous material. The sludge-based biochar (SC-N3) originated from the feedstock of sludge from the regenerated water treatment had various iron-containing species and exhibited the effective catalytic ability. Compared with the degradation of the four pollutants (i.e., phenol, pyridine, quinoline and indole) alone, the mixed of the four pollutants in simulated coking wastewater exhibited a prominent different degradation trend, where the removal rates of indole and quinoline were enhanced from 45% and 30% to 98.9% and 82.3%, respectively. The quinone intermediates from phenol degradation, played a critical role in enhancing the removal rates of indole and quinoline as the electron transfer medium. Both the free radical pathway dominated by •OH and non-radical pathway with 1O2 play the main role in indole degradation, while •OH was the main factor in the catalytic degradation of phenol, quinoline and pyridine. By analysis the intermediates elucidated by Fourier transform ion cyclotron resonance mass spectrometry and three-dimensional excitation-emission matrix fluorescence spectra, the degradation molecular characteristics and pathways of the four pollutants in simulated coking wastewater were deciphered. The findings indicated that the catalyst SC-N3 prepared from the coking wastewater sludge presented unique catalytic properties and possessed a promising application in the degradation of refractory wastewater.

S-type heterojunction enhance the photocatalytic activity of TiO2/AgBr/Ag using loofah sponge as template towards ciprofloxacin degradation

Photocatalyst TiO2/AgBr/Ag (TBA) composites using loofah sponge as a template were successfully prepared for the first time. The photocatalytic activities of the TBA composites were evaluated by removing ciprofloxacin (CIP) under visible light. The PDOS shows that the valence band edge of TBA-30 is primarily composed of Ti 3d atom states, with small contributions from O 2p atom states. The conduction band edge is dominated by Ag 4d and O 2p atom states, with minor contributions from Br 4p atom states. TBA-30 composites demonstrate outstanding photocatalytic performance, degrading 87% of the target within 180 min. The degradation rate of CIP decreased to 70.19% after five runs, Furthermore, the TOC removal efficiency of CIP reached 84.2% in the end. CIP intermediates and degradation pathway were determined by GC-MS. Three-dimensional excitation-emission matrix fluorescence spectra (3D EEM) were used to study the degradation of CIP molecules. Trapping experiments and electron paramagnetic resonance (EPR) characterisation identified superoxide (·O2-) and photogenerated holes (h+) as the primary active radicals. Furthermore, formed S-type heterojunction and Ag as the electron capture site enhanced the separation efficiency of photoinduced electron-hole pairs. The DFT calculation was used to study the electron transport performance of TBA-30 by calculating the charge density difference.

Simultaneous degradation and rejection of PPCPs from wastewater in a 3DEO-FO-RO process

This study established a novel three-dimensional electrochemical oxidation coupled with forward osmosis and reverse osmosis (3DEO-FO-RO) system with the purpose to achieve simultaneous degradation and rejection of pharmaceuticals and personal care products (PPCPs) in wastewater. 18 frequently detected PPCPs were selected as the target pollutants to prepare the synthetic wastewater with a concentration of 200 μg/L for each pollutant. Ti/IrO2–Ta2O5–SnO2 mesh anode, titanium mesh cathode and Sn–Sb–Bi/γ-Al2O3 particles electrodes were integrated in the 3DEO-FO reactor. Experimental results demonstrated that degradation efficiency exceeding 98.5 % and rejection exceeding 99.4 % for each PPCP were achieved simultaneously in the 3DEO-FO-RO processes at a current density of 1 mA/cm2 after 8 h treatment. Despite variations in applied current density, the 3DEO-FO-RO processes exhibited superior PPCPs removal efficiencies, particularly for refractory compounds, compared to the 2DEO-FO-RO processes. Increased hydroxyl radical (·OH) generation in the 3D reactor was considered to be responsible for the excellent performance. Furthermore, results derived from ultraviolet (UV) absorption spectra and fluorescence excitation-emission matrix (EEM) spectra provided additional validation for the effective removal of PPCPs in the 3DEO-FO-RO processes, along with evidence indicating the decomposition of PPCPs into smaller constituents. Ultimately, the 3DEO-FO-RO process demonstrated its capacity in removing PPCPs from actual secondary effluent from a wastewater treatment plant. This integrated system coupling 3D EO with FO-RO membranes can provide an efficient approach for simultaneous degradation and rejection of trace contaminants for wastewater reuse.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature.

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

Engineering highly dispersed AgI nanoparticles on hierarchical In2S3 hollow nanotube to construct Z-scheme heterojunction for efficient photodegradation of insecticide imidacloprid

Increasing the exposure of active sites and improving the intrinsic activity are necessary considerations for designing a highly efficient photocatalyst. Herein, an In2S3/AgI stable Z-scheme heterojunction with highly dispersed AgI nanoparticles (NPs) is synthesized by the mild self-templated and in-situ ion exchange strategy. Impressively, the optimized In2S3/AgI-300 Z-scheme heterojunction exhibits superior photodegradation activity (0.020 min−1) for the decomposition of insecticide imidacloprid (IMD), which is extremely higher than that of pure In2S3 (0.002 min−1) and AgI (0.013 min−1). Importantly, the three-dimensional excitation-emission matrix (3D EEMs) fluorescence spectra, high-resolution mass spectrometry (HRMS), the photoelectrochemical tests, radical trapping experiment, and electron spin resonance (ESR) technique are performed to clarify the possible degradation pathway and mechanism of IMD by the In2S3/AgI-300 composite. The enhanced photocatalytic performance is attributed to the highly dispersed AgI NPs on hierarchical In2S3 hollow nanotube and the construction of In2S3/AgI Z-scheme heterojunction, which can not only increase active site exposure, but also improve its intrinsic activity, facilitating rapid charge transfer rate and excellent electron-hole pairs separation efficiency. Meanwhile, the practical application potential of the In2S3/AgI-300 composite is systematically investigated. This study opens a new insight for designing catalysts with high photocatalytic performance through a convenient approach.

Ceramic membrane reactor integrated with UV/O3/Catalyst Beads for treating real textile wastewater: Enhanced effluent quality, fouling control and molecular transformations of DOM

A ceramic membrane reactor (CMR) was employed to treat real textile wastewater with the simultaneous use of UV, O3, and photocatalytic beads for dissolved organic matter (DOM) transformation and membrane fouling control. The O3 treatment exhibited high performance in color removal. Simultaneous use of UV and ozonation (UV/O3) resulted in 91% and 64% color and chemical oxygen demand (COD) removal, respectively, and delayed (3-fold) fouling time compared to UV alone. A combination of TiO2-loaded polymeric beads with UV/O3 (UV/O3/Beads) further enhanced the color (96%) and COD (86%) removal as well as improved fouling control by 9-folds compared to the control (Air alone) experiment. Three-dimensional excitation-emission matrix (3-D EEM) fluorescence spectra revealed minimum DOM and synergistic effects of UV, O3, and photocatalytic beads (UV/O3/Beads) in the degradation of fluorescent DOM. The •OH radicals were leading in degrading organic pollutants during the treatment. Transformations of heteroatomic DOMs were confirmed by the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). S-containing compounds in the treated samples appeared in a reduced state (lower H/C and O/C ratios), indicating the transformation of R–SO3 to R–S–R. Whereas N-containing DOM was mostly oxidized. UV/O3 rapidly transformed dye molecules to colorless, creating suitable conditions for photocatalytic beads for accelerated degradation of pollutants. Also, the PTR-TOF-MS analysis revealed the successful removal of toxic VOCs (Methanethiol, Allylamine, Cyclohexenes, Butanes, Propanes, and Hydrazines) from wastewater by the UV/O3/Beads treatment. Based on these findings, DOM transformations could be better understood, and the simultaneous application of heterogeneous photocatalysis and UV/O3 could be safely recommended as a promising technology for treating industrial wastewater.

Rapidly identifying the geographical origin of Lilium bulbs by nano-effect excitation-emission matrix fluorescence combined with chemometrics

Lilium bulbs (LB) are a highly nutritious food, and their quality and price are influenced by origin. The present study proposed a nano-effect excitation-emission matrix fluorescence (EEMF) combined with chemometrics strategy for rapidly identifying the geographical origin of LB. Nano-effect EEMF spectra of 280 LB samples from different origins were collected after reaction with bovine serum albumin-modified gold and silver nanoclusters (BSA-AuAgNCs). Further, partial least squares-discrimination analysis (PLS-DA) and principal component analysis-linear discriminant analysis (PCA-LDA) were used to establish classification models for identifying the geographical origin of LB based on the obtained nano-effect EEMF spectra. The result showed that PCA-LDA model gained the optimal performance, and the classification accuracy of the training set and the prediction set was 95.9% and 90.5%, respectively. The nano-effect EEMF spectra was based on the reaction of BSA-AuAgNCs with the components, such as phenolic acids, in LB through hydrogen bonding, which amplified the spectral difference. This study demonstrated that the proposed strategy is effective for identifying the geographical origins of LB, which provides a new idea for the geographic traceability of other foods.

Transformation of organic carbon through medium pressure (polychromatic) UV disinfection of wastewater effluent during wet weather events

An observed decrease in total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations following wastewater disinfection with medium pressure (MP, polychromatic) ultraviolet (UV) irradiation during wet weather flows is investigated. When antecedent rainfall in the previous 7-days was >2 in (5 cm), TOC and DOC concentrations decreased dramatically following MP-UV disinfection. Organic carbon surrogate measurements of biological oxygen demand (BOD), TOC, DOC, turbidity, UVA – 254 nm, SUVA (specific UVA), scanning UV–Visible spectra (200–600 nm), fluorescence excitation-emission matrix (EEM) spectra, and light scattering data are presented for wastewater resource recovery facility (WRRF) influent, secondary effluent (pre-UV-disinfection), and MP-UV-disinfected (final effluent) samples. TOC and DOC in wastewater influent and secondary effluent (i.e., pre-UV disinfection) correlated with antecedent rainfall conditions. The percent TOC and DOC removal through secondary treatment (i.e., from influent to effluent pre-UV) and the percent TOC and DOC removal through MP-UV disinfection (i.e., from effluent pre-UV to effluent post-UV) were compared and the latter approached 90 % through MP-UV disinfection during high antecedent rainfall conditions. Spectroscopy (UV, visible, or fluorescence) was performed on samples after filtration through 0.45 μm filters, i.e., the operationally defined DOC fraction of aquatic carbon. Scanning UV–visible spectra indicated transformation of an unidentified wastewater component into light-scattering entities regardless of antecedent rainfall conditions. The types of organic carbon (diagenetic, biogenic, or anthropogenic) and the significance of wet weather are discussed. An organic carbon contribution via infiltration and inflow was attributed as a source-of-interest in this research.

Anti-interference and non-destructive identification of textile fabrics using front-face excitation-emission matrix fluorescence spectroscopy combined with multi-way chemometrics

The identification of trace textile fabrics discovered at crime scenes plays a crucial role in the case of forensic investigations. Additionally, in practical situations, fabrics may be contaminated, making identification more challenging. To address the aforementioned issue and promote the application of fabrics identification in forensic analysis, front-face excitation-emission matrix (FF-EEM) fluorescence spectra coupled with multi-way chemometric methods were proposed for the interference-free and non-destructive identification of textile fabrics. Common commercial dyes in the same color range under different materials (cotton, acrylic, and polyester) that cannot be visually distinguished were investigated, and several binary classification models for the identification of dye were established using partial least squares discriminant analysis (PLS-DA). The identification of dyed fabrics in the presence of fluorescent interference was also taken into consideration. In each kind of pattern recognition model mentioned above, the classification accuracy (ACC) of the prediction set was 100%. The alternating trilinear decomposition (ATLD) algorithm was executed to separate mathematically and remove the interference, and the classification model based on the reconstructed spectra attained an accuracy of 100%. These findings indicate that FF-EEM technology combined with multi-way chemometric methods has broad prospects for forensic trace textile fabric identification, especially in the presence of interference.

Effects of paddy irrigation-drainage system on water quality and productivity of small rivers in the Himi region of Toyama, Central Japan

The aim of this study was to clarify the impact of differences between historical and recently introduced irrigation and drainage management systems on water quality in the rivers around paddy fields. We investigated the seasonal variation in nutrients concentration and dissolved organic carbon (DOC) components in single- (used for intake only) and dual-purpose (used for both intake and drainage) channels during a 4-year period in the Himi region of Toyama, Central Japan. The system of dual-purpose channel has traditionally been used in the region of this study. A total of 197 three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra of DOM in waters were applied for the parallel factor analysis (PARAFAC) modeling. Based on the 3DEEM and PARAFAC, the abundance of terrestrial humic-like components in the dual-purpose channel was significantly higher than that in the single-purpose channel. The even long-chain n-fatty acids derived associated with rice cropping in sediments of the dual-purpose channels were 22−30-fold higher than that of the single-purpose channel. In addition, the turbidity values of the river waters had significantly positive linear correlations with concentrations of K+, DOC, and humic-like components. These observations indicate that the dissolved nutrient concentrations in the river water were higher in the dual-purpose channel compared to those of the single-purpose channel, which may be supplied by leaching from the inflow of soil particles from the paddy fields. During the mid-irrigation period, the quantity of epiphytic chlorophyll a on artificial substrate tiles in the dual-purpose channel were 3.1–4.1-fold higher than that in the single-purpose channel. This study clear that the input of paddy drainage during the irrigation season significantly changes the DOC components in river waters and irrigation management is strongly linked to the primary production in agricultural channels. Therefore, it is important to consider the impact of the introduction of different irrigation and drainage management systems on water quality and productivity in order to maintain the riverine ecosystems around rice paddies, which are based on historical water use systems.

Base-activated persulfate strategy for ceramic membrane cleaning after treatment of natural surface water

The natural organic matters (NOM) have been proved to form the hydraulically irreversible membrane fouling, which limit the application of the membrane in water treatment processes. To solve the membrane fouling caused by NOM, a novel one-step chemical cleaning method for the ceramic membrane derived from the base-activated persulfate oxidation process was developed in this study. When the SiC ceramic membranes was used to filtrate practical river water, the permeate flux dropped 65% as ΔTMP reached 30 kPa. After 2 h immersion of the fouled membrane in the cleaning solution (2 mM PMS and 8 mM NaOH), the flux recovery rate nearly reached 100%. Direct backwash of the membrane by the above cleaning solution further reduced the cleaning time to 25 mins, while achieving similar cleaning effect. Then the cleaned membranes were immersed in NaClO solution to release all the residual foulants, but the fluorescence excitation-emission matrix spectra (EEM) and total organic carbon (TOC) of the solution were found insignificant, which demonstrated the base-activated persulfate strategy had effectively removed the irreversible membrane fouling. Free radical quenching experiments were carried out and·O2- was identified as the dominant ROS responsible for the removal of the membrane foulants. The permeate flux and filtration efficiency of the SiC membrane were stable after 5 consecutive fouling-cleaning cycles, and the membrane structure was not damaged. In summary, the base-activated persulfate strategy is an efficient and cleaner method for SiC membrane cleaning, which is potential to be applied in practical membrane water treatment process.

Performance of resin adsorption and ozonation pretreatment in mitigating organic fouling of reverse osmosis membrane

Effective pretreatment of reverse osmosis (RO) influent is of great importance for reducing membrane fouling risks during coking wastewater desalination. In this study, the combined resin adsorption and ozonation pretreatment was investigated on alleviating RO membrane organic fouling. The performance of combined process was compared with only resin adsorption or ozonation, which was evaluated in terms of changes in chemical oxygen demand (COD), ultraviolet-visible index, and three-dimensional excitation-emission matrix fluorescence spectra. RO membrane fouling tests were conducted to examine the effects of pretreatment on flux decline and filtration resistance. The surface morphology and functional groups of membrane before and after fouling was characterized by scanning electron microscopy and infrared spectroscopy. The correlation between major organic matter in the wastewater and normalized RO membrane flux was established via multiple linear regression equations. The results showed that ozonation was more effective in removing COD and fluorescent organics than resin adsorption. Moreover, the combined bifunctional resin adsorption/ozonation unit showed the best performance, with COD and UV254 removal rates of 49.4 % and 88.0 %, respectively. The fluorescence intensity of each component decreased significantly. Meanwhile, the polysaccharide and protein components of the RO membrane fouling layer were effectively reduced by 67.2 % and 80.8 %, respectively. Most importantly, the combined pretreatment substantially reduced the decline in membrane flux and filtration resistance. Meanwhile, the fulvic acid-like organics in the wastewater showed high correlations with normalized membrane flux. The regression equation was beneficial for RO membrane fouling evaluation.

Impact of different classification schemes on discrimination of proteins with noise-contaminated spectra using laboratory-measured fluorescence data

Biological agents are important to detect and identify with respect to environmental contamination and public health. Noise contamination in fluorescent spectra is one of the contributors to the uncertainties of identification. In order to investigate the noise-tolerant capability provided by laboratory-measured excitation-emission matrix (EEM) fluorescence spectra that are used as a database, fluorescence properties of four proteinaceous biotoxin samples and ten harmless protein samples were characterized by EEM fluorescence spectra, and the predicting performance of models trained by laboratory-measured fluorescence data was tested and verified from validation data with noise-contaminated spectra. By means of peak signal of noise (PSNR) as an indicator of noise levels, the potential impact of noise contaminations on the characterization and discrimination of these samples was evaluated quantitatively. Different classification schemes utilizing multivariate analysis techniques of Principal Component Analysis (PCA), Random Forest (RF), and Multi-layer Perceptron (MPL) coupled with feature descriptors of differential transform (DT), Fourier transform (FT) and wavelet transform (WT) were conducted under different PSNR values. We systematically analyzed the performance of classification schemes by the case study at 20 PSNR and by statistical analysis from 1-100 PSNR. The results show that the spectral features with EEM-WT decreased the demanding number of input variables while retaining high performances in sample classification. The spectral features with EEM-FT presented the worst performance although having the largest number of features. The distributions of feature importance and contribution were found sensitive to noise contaminations. The classification scheme of PCA prior to MPL with EEM-WT as input presented an improvement in lower PSNR. These results indicate that robust features extracted by corresponding techniques are critical to enhancing the spectral differentiation capabilities among these samples and play an important role in eliminating the noise effect. The study of classification schemes for discriminating protein samples with noise-contaminated spectra presents tremendous potential for future developments in the rapid detection and identification of proteinaceous biotoxins based on three-dimensional fluorescence spectrometry.

Water-soluble brown carbon in atmospheric aerosols from the resource-dependent cities: Optical properties, chemical compositions and sources

As a vital type of light-absorbing aerosol, brown carbon (BrC) presents inherent associations with atmospheric photochemistry and climate change. However, the understanding of the chemical and optical properties of BrC is limited, especially in some resource-dependent cities with long heating periods in northwest China. This study showed that the annual average abundances of Water-soluble BrC (WS-BrC) were 9.33±7.42 and 8.69±6.29 µg/m3 in Baotou and Wuhai and the concentrations, absorption coefficient (Abs365), and mass absorption efficiency (MAE365) of WS-BrC presented significant seasonal patterns, with high values in the heating season and low values in the non-heating season; while showing opposite seasonal trends for the Absorption Ångström exponent (AAE300-400). Comparatively, the levels of WS-BrC in developing regions (such as cities in Asia) were higher than those in developed regions (such as cities in Europe and Australia), indicating the significant differences in energy consumption in these regions. By combining fluorescence excitation-emission matrix (EEM) spectra with the parallel factor (PARAFAC) model, humic-like (C1 and C2) and protein-like (C3) substances were identified, and accounted for 61.40%±4.66% and 38.6%±3.78% at Baotou, and 60.33%±6.29% and 39.67%±4.17% at Wuhai, respectively. The results of source apportionment suggested that the potential source regions of WS-BrC varied in heating vs. non-heating seasons and that the properties of WS-BrC significantly depended on primary emissions (e.g., combustion emissions) and secondary formation.

Pd nanoparticles decorated BiVO4 pine architectures for photocatalytic degradation of sulfamethoxazole

Sulfamethoxazole (SMX) has been extensively detected in wastewater treatment plant effluents and surface water. Because of its potential risks to ecology and health, treatment for eliminating SMX is urgently required. In this study, we report the application of Pd nanoparticles decorated on BiVO4 pine architecture for the photocatalytic degradation of SMX. The results showed that the barer BiVO4 and Pd–BiVO4 eliminated SMX under visible-light irradiation. After 210 min of irradiation, 98.8% of SMX was substantially eliminated by Pd–BiVO4, whereas bare BiVO4 can degraded approximately 36.3% of SMX. Pd–BiVO4 also exhibited a high mineralization rate (84% of total organic carbon (TOC) removal) compared to bare BiVO4 (51% of TOC removal). Through three-dimensional excitation-emission matrix fluorescence spectra, SMX with high fluorescence intensity can be degraded to non-fluorescence intermediate products, further confirming the high mineralization of SMX over Pd–BiVO4 catalyst. Well-dispersed Pd nanoparticles on the {040} facet of BiVO4 pine architecture can support the recombination of photogenerated charge carriers because of the formation of the Schottky junction at the Pd–BiVO4 interface. Besides, the active species trapping tests indicated that •O2− and h+ radicals dominate SMX photodegradation over Pd–BiVO4. The main degradation intermediates of SMX in the reaction solution was also identified through ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. This investigation can provide insight into designing metallic/semiconductor junctions for antibiotic elimination in water media.

Characterization of DOM and disinfection by-products precursors in biological activated carbon filter backwash water from drinking water treatments

Abstract Biological activated carbon filter backwash water (BAC FBW) removes pollutants from BAC filters in drinking water treatment plants. Characterizing the dissolved organic matter (DOM) in BAC FBW is of great significance for the recycling and treatment of backwash water. DOM pollution was monitored over a year using three-dimensional excitation–emission matrix fluorescence spectra. The dissolved organic carbon (DOC) concentration and fluorescence results showed that the DOC concentration reached the lowest value of 1.95 mg/L in the summer. The relative abundances of fluorescence components had a direct relationship with temperature variations. The soluble microbial products were enhanced greatly during cold seasons, while fulvic-acid-like and humic-acid-like compounds remained constant. Disinfection by-products (DBPs) formation potential and cytotoxicity were evaluated. The total haloacetonitriles (HANs), trihalomethanes (THMs), halonitromethanes (HNMs), and haloacetaldehyde (HALs) formation potentials ranged from 35.5 to 47.3 μg/L, 95.1 to 126 μg/L, 4.95 to 8.06 μg/L, and 43.4 to 53.0 μg/L in BAC FBW, respectively. Among all DBPs included in the calculation, the order of contribution to cytotoxicity was HANs > HALs > THMs > HNMs, respectively. Especially, HANs were much higher than the other DBPs, which should be controlled to avoid the biological risk of effluent quality.

Truxene-linked di-coumarin-mono-corrole tetrad: Synthesis, photophysical properties and application in Triplet−Triplet annihilation upconversion

Triplet−triplet annihilation upconversion (TTA-UC) has drawn widespread interest because of its great potential applications. However, it is still a challenge to design and synthesize efficient triplet photosensitizers without heavy atoms for TTA-UC. In this work, a triplet photosensitizer tetrad 2C-T-Cor based on two coumarin moieties and one corrole moiety with a truxene as the bridge was synthesized and used in TTA-UC as a novel heavy atom-free organic photosensitizer (perylene bisimide (PBI) was used as triplet acceptor). The photophysical properties were investigated by means of steady-state UV–Vis absorption and fluorescence spectroscopy, nanosecond time-resolved transient absorption spectroscopy, three-dimensional excitation emission matrix fluorescence spectra, and cyclic voltammetry. With photo-excitation of the coumarin unit at 420 nm, the intramolecular singlet–singlet energy transfer takes place from the coumarin moiety to the corrole unit with a transfer efficiency of 63.9%. Electrochemical study indicated that the intramolecular electron transfer was thermodynamically prohibited in toluene owing to the positive ΔGCS for charge-separation. A triplet excited state was investigated for 2C-T-Co via nanosecond time-resolved transient absorption and the triplet lifetime is 118 μs. 2C-T-Co can act as the triplet photosensitizer for the application of TTA-UC, and the upconversion quantum yield of 0.98% was observed.

Rapid identification and semi-quantification of adulteration in walnut oil by using excitation–emission matrix fluorescence spectroscopy coupled with chemometrics and ensemble learning

Walnut oil (WNO) is a high-quality vegetable oil with high nutritional value, but it may be the target for adulteration and mislabeling. Therefore, this work proposes the use of excitation–emission matrix fluorescence (EEMF) spectroscopy coupled with chemometrics and ensemble learning to identify and semi-quantify the adulterated WNO. Herein, a total of 711 vegetable oil samples were analyzed. A five-component alternating trilinear decomposition (ATLD) completed the EEMF spectra characterization of 426 pure oil samples and provided chemically meaningful information. Five authenticity identification methods, including eXtreme gradient boosting (XGB), gradient boosting decision tree (GBDT), random forest (RF), multi-way partial least squares discriminant analysis (N-PLS-DA), and k-nearest neighbor (k-NN), were used for the discrimination of WNO and counterfeited WNO. Besides, PLS regression (PLSR) models were established to semi-quantify the adulterated levels of WNO concentration in edible blended oils. The results showed that ensemble methods obtained better performance, with the correct classification rate (CCR) of cross-validation being ranged 82.7–100 %, and the value of RMSEP is less than 12.8 %. These results suggest that EEMF combined with chemometrics and ensemble methods can be used as a promising tool for rapid authenticity identification in commercial edible vegetable oils.

Melamine foam derived nitrogen and boron co-doped metal-free electrode for enhanced electro-Fenton degradation of metronidazole

In this work, a melamine foam derived nitrogen (N) and boron (B) co-doped metal-free electrode was prepared by accessible method and applied in heterogeneous electro-Fenton (EF) system. Overcoming the metal ion leaching and harsh operating conditions of most transition metal electrodes, the prepared metal-free electrode (NB/CF40) possessed an excellent EF performance for degradation of metronidazole (MTZ) in a wide range of pH (3–11), maintaining great reusability even after ten runs with higher mineralized current efficiency (MCE) and lower energy consumption (EC). Significantly, the NB/CF40 has excellent decontamination performance for actual wastewater containing MTZ analyzed by quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and three-dimensional excitation-emission matrix fluorescence spectra (3D EEMs). According to experimental results, characterization analysis and density functional theory (DFT) calculations, EF reaction mechanism by NB/CF40 cathode was proposed, in which the active sites of BCCC-graphitic N and BCCC-pyridinic N configurations contributed to the improvement of EF performance by affecting the charge density of nearby carbon framework, adsorption of O2, and desorption of *OOH. This work offers a new idea for the remediation of wastewater by the efficient metal-free EF system in a wide pH range.

Enriched surface oxygen vacancies of Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction with boosted visible-light photocatalytic degradation for levofloxacin: Performance, degradation pathway and mechanism insight

Exploring effective approach to promote more comprehensive charge transfer and efficient spatial charge separation is considered to be a prospective strategy to reinforce photocatalytic degradation activity. Herein, the oxygen vacancy modified Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction photocatalyst was successfully fabricated via a facile solvothermal method. The chemical structure, morphology, and optical properties of the photocatalyst were characterized in detail. The optimized Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction displayed the maximum photocatalytic efficiency (84.3 %) for the degradation of levofloxacin (LEV), which was significantly higher than that of pure Bi2WO6 (45.1 %), oxygen vacancy modified Bi2WO6 (69.4 %), and NH2-MIL-68(In) (49.3 %). Importantly, the high-resolution mass spectrometry (HRMS), three-dimensional excitation-emission matrix (3D EEMs) fluorescence spectra, the photo-electrochemical and photo-luminescence measurement, radical trapping test, and electron spin resonance (ESR) technique were carried out to illuminate the probable degradation pathway and mechanism of the LEV. The improved photocatalytic efficiency can be ascribed to the synergetic effect between oxygen vacancy and the Z-scheme heterojunction, which can serve as trapping centers to enhance the generation of photoexcited electrons and accelerate the charge transfer. Meanwhile, the effects of pH, photocatalyst dose, LEV concentration and different kinds of harmful organic pollutants were systematically explored from the practical application. This study offers a novel perspective for the integration of defect engineering and Z-scheme heterojunction in efficient organic pollutants degradation.