Blue Fluorescence Emission Research Articles

An Innovative Microwave-Assisted One-Step Green Synthetic Approach of Biowaste Derived Fluorescent Carbon-Dot Invisible Ink for Currency Anti-Counterfeiting Applications

The quest for the design and synthesis of carbon dots with anti-counterfeit properties that are derived via green, environmentally friendly and economical procedures is a continuous process. Carbon dots (C-dots) derived from biowaste are cheap to synthesize, possess good photo-stability and high synthetic yield, making them applicable in the anti-counterfeiting of currency. Herein, we report a novel eco-friendly, cheaper, and faster method for the synthesis of carbon dots with strong photoluminescence properties from monkey orange fruit (Strychnos spinosa) biowaste. The presence of the hydroxyl and carbonyl functional groups of the carbon dots were determined by the Fourier transform infrared spectroscopy (FTIR). The carbon dots showed strong blue emission fluorescence (emission wavelength of 452[Formula: see text]nm) when excited at 330[Formula: see text]nm. The morphology and size were determined by the atomic force microscopy (AFM) which indicated amorphous and spherical nanoparticles with an average size of less than 2[Formula: see text]nm. The no-crystallinity of the as-prepared carbon dots was confirmed using X-ray diffraction which showed the graphite-like structure. The carbon dots were produced and demonstrated good photo and chemical stability as well as high covert properties. The anti-counterfeiting of currency application by the synthesized carbon dots was demonstrated when the subsequent gel ink printed on the currency showed excellent chemical stability when exposed to washing with water, ethanol, and acetone. It also showed superior photostability when exposed to UV light at 365[Formula: see text]nm and daylight for an extended period of up to 6[Formula: see text]h. This work provides a facile, economical, and green approach for large scale production of carbon dots from the abundant biowaste.

One-step preparation of N-doped grapheme quantum dots with high quantum yield for bioimaging and highly sensitive electrochemical detection of isoniazid.

Conventional techniques for synthesizing GQDs have a poor quantum yield (QY) that restricts their biological applications. Herein, we present a rapid, cost-effective and high quantum yield synthesis of nitrogen-doped graphene quantum dots (N-GQDs) through a scientific microwave reactor. The reaction parameters like microwave irradiation time, temperature, precursor concentration and pressure were optimized for achieving high quantum yield. The prepared N-GQDs exhibit bright blue fluorescence and excitation independent emission property with a quantum yield of 42.81%. In-vivo investigations on C. elegans revealed that the as-prepared N-GQDs are exceptionally biocompatible and maintain the normal physiological functioning of the primary and secondary targeted organs in nematodes. The synergetic effect of intestinal barrier and defecation behavior mitigates N-GQDs translocation into reproductive organs of nematode. In addition, the N-GQDs modified GCE was tested for electrochemical sensing characteristics towards the anti-tuberculosis drug isoniazid (INZ). The N-GQDs showed appreciable electrocatalytic performance towards INZ with high sensitivity (3.76μAμM-1cm-1). The differential pulse voltammetry (DPV) analysis of N-GQDs exhibit a lower detection limit of 10.91nM for INZ. The N-GQDs modified sensor exhibits good reproducibility, excellent anti-interference ability and excellent analytical performance for INZ in real samples like human blood serum and urine samples.

Simple One-step Solid-state Synthesis of Highly Crystalline N Doped Carbon Dots As Selective Turn Off-sensor for Picric Acid and Metanil Yellow.

A simple one-step solid-state pyrolysis method has been employed to synthesize highly crystalline nitrogen-doped carbon dots using adipic acid and urea as carbon and nitrogen sources. The prepared carbon dots displayed UV emission ( λex = 290nm and λem = 370nm) and blue fluorescence emission ( λex = 360nm and λem = 420nm). These crystalline nitrogen-doped carbon dots exhibited a quantum yield of 6% with tryptophan as standard at 370nm emission and 14% with quine sulfate as standard at 420nm emission. The synthesized carbon dots were spherical, having a mean particle diameter of 2.56 ± 0.57nm. The prepared carbon dots have large functional groups on their surface, which renders excellent water solubility to them. Carbon dots was used as selective and sensitive turn off sensor for detection of picric acid Metanil yellow with the linear response for picric acid ranging from 2μM to 22μM and 2-45μM with a detection limit of 0.06μM and 0.45μM and for Metanil yellow ranging from 1μM to 30μM with a detection limit of 0.32μM. The mechanism for detecting metanil yellow is proposed to be the inner filter effect. At the same time, it is both the inner filter effect and FRET for picric acid. The actual sample application of carbon dots as a nanosensor was tested to detect metanil yellow as an adulterant in turmeric powder.

A fluorescence and phosphorescence dual-signal readout platform based on carbon dots/SiO2 for multi-channel detections of carbaryl, thiram and chlorpyrifos

In this work, a fluorescence and phosphorescence dual-signal readout platform for multi-channel detections of carbaryl, thiram and chlorpyrifos was constructed by confining carbon dots (CDs) in SiO2 nanoparticles. The CDs were synthesized by a simple hydrothermal treatment of fresh pomegranate seeds, L-aspartic acid and L-tryptophan (PAT-CDs). PAT-CDs embedded in SiO2 nanoparticles (PAT-CDs@SiO2) emitted blue fluorescence and very long lifetime green phosphorescence in aqueous solution. Accordingly, one detection channel for carbaryl on the PAT-CDs@SiO2 platform was developed with a ratiometric approach applying dual-signal readouts from two emission wavelengths. Moreover, two detection channels for thiram and chlorpyrifos with a fluorescence and phosphorescence dual-signal readout strategy were built on the PAT-CDs@SiO2 platform. Finally, the proposed multi-channel detection method recovered carbaryl, thiram and chlorpyrifos in tap and pork samples in the range of 90% and 110%. Therefore, multi-channel detection functions can be potentially integrated onto CDs based platforms due to their high performances and possible multi-signal readouts.

One-step Synthesis of Biomass-Based Carbon Dots for Detection of Metal Ions and Cell Imaging

Biomass-based carbon dots (Bio-CDs) were prepared from dehydroabietic acid using a one-step hydrothermal process. Characterization by TEM, XPS and FTIR spectroscopy showed that the Bio-CDs are spherical nanoparticles containing mainly C, N and O elements, with functional groups such as amino and carbonyl groups on their surface. The optical properties of the Bio-CDs were studied in detail. A solution of Bio-CDs exhibited excitation-dependent blue fluorescence emission. The solution showed excellent photostability under ultraviolet light and the fluorescence intensity could be enhanced by decreasing the temperature. The intensity of fluorescence emission of the solution was essentially unchanged over the pH range 3.91–8.69, and in the presence of different anions and cations, other than Fe3+ and Pb2+. Fe3+ and Pb2+ ions, respectively, quenched and enhanced the intensity of the fluorescence emission of the solution, allowing sensitive and selective detection of Fe3+ (LOD = 2.33 μM, Em = 437 nm) and of Pb2+ (LOD = 0.27 μM, Em = 437 nm and LOD = 0.33 μM, Em = 500 nm). As a further demonstration of potential applications, the Bio-CDs were shown to have low cytotoxicity and to stain cell nuclei as effectively as the commonly used nuclear stain 4′,6-diamino-2-phenylindole (DAPI), demonstrating their promise in the field of cell imaging.

Triple-emission nitrogen and boron co-doped carbon quantum dots from lignin: Highly fluorescent sensing platform for detection of hexavalent chromium ions

Considering that hexavalent chromium ions (Cr6+) with high toxicity poses a huge threat to human health and the ecological environment, constructing a rapid and accurate sensing platform is of great significance in detecting the toxic substance. The novel nitrogen and boron co-doped carbon quantum dots (N, B-CQDs) from lignin are synthesized as fluorescent sensors for the detection of Cr6+. The synthetic processes involve the acid hydrolysis step followed by the hydrothermal treatment step. Lignin is firstly depolymerized by cleaving ether bonds in the acidolysis, and N, B-CQDs are consequently formed by the aromatic re-fusion of lignin nanoparticles in the hydrothermal process. The lignin-derived N, B-CQDs show triple emission of purple, blue and green fluorescence under the excitation of 300, 330, and 490 nm, respectively. The triple-emission N, B-CQDs are applied for the triple-channel detection of Cr6+, which exhibit highly sensitive and selective fluorescence quenching for Cr6+ with good linearity (R2 ≤ 0.996) and very low limit of detection as 0.054, 0.049, and 0.077 μM under the excitation of 300, 330 and 490 nm, respectively. The utilization of renewable lignin as CQDs-based fluorescent sensors opens a new avenue for the rapid and accurate detection of Cr6+ through a multichannel sensing platform.

CES 2022: Less is More

AbstractScaled‐down show still delivers top‐notch exhibits and innovation aplenty.

Glutathione-stabilized copper nanoclusters mediated-inner filter effect for sensitive and selective determination of p-nitrophenol and alkaline phosphatase activity

A simple and highly selective fluorescence biosensor has been exploited for p-nitrophenol (p-NP) and alkaline phosphatase (ALP) activity detection based on the glutathione-stabilized copper nanoclusters (GSH-CuNCs) mediated-inner filter effect (IFE). The GSH-CuNCs were prepared by employing GSH as stabilizer and ascorbic acid (AA) as reductant. The obtained GSH-CuNCs exhibited a strong blue fluorescence emission at 420 nm with an excitation wavelength of 365 nm, which overlapped largely with the absorption spectra of p-nitrophenol (p-NP). Therefore, the luminescence of GSH-CuNCs could be quenched by p-NP through inner filter effect. In addition, ALP catalyzed the substrate p-nitrophenyl phosphate (p-NPP) to form p-nitrophenol (p-NP), which also leading to the fluorescence quenching of GSH-CuNCs. The fluorescent strategy was realized for the sensitive determination of p-NP and ALP activity with the promising limit of detection of 20 nM (for p-NP) and 0.003 mU⋅mL−1 (for ALP). Furthermore, the method could be applied to detect the p-NP content in river water samples and ALP activity in human serum samples.

Multifunctional ratiometric fluorescent sensing platform constructed by grafting various response groups on carbon dots with bromine active site for biosensing and bioimaging

Multifunctional sensing platform with the advantages of simplicity, convenience and efficiency is critical to the improvement of application in biosensing and bioimaging. However, the lack of easily modified scaffold materials seriously hinders its various responsive sensing development. To solve this issue, a novel kind of carbon dots (namely rCDs) with easily modified bromine substitution site was developed by one-step solvothermal treatment of citric acid, ethylenediamine and 4-bromo-1,8-naphthalic anhydride. Benefiting from the maintained structure of naphthalimide structure with bromine substitution site to contribute responsive yellow-green fluorescence emission and the stable blue fluorescence emission from citric acid and ethylenediamine, dual emissive ratiometric sensors based on rCDs could be conveniently fabricated by avoiding the combination of two components with distinct emission wavelength together. As proof, three ratiometric fluorescent probes for sensing formaldehyde (rCDs-FA), HSO3- (rCDs-HSO3-) and pH (rCDs-pH) featuring high stability, selectivity and biocompatibility were simply prepared. Moreover, the as-obtained probes were successfully applied to monitor dynamic variations of formaldehyde, HSO3- and pH changes in living cells. Taken together, the established multifunctional ratiometric fluorescent sensing platform could be simply and effectively regulated through changing the grafted response groups. This work would provide a universal method to design more biosensing or bioimaging platforms by adjusting response groups in the future.

A Water-Stable 2-Fold Interpenetrating cds Net as a Bifunctional Fluorescence-Responsive Sensor for Selective Detection of Cr(III) and Cr(VI) Ions.

Reactions of ZnSO4∙7H2O, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H2bdc) afforded a luminescent coordination polymer, [Zn(Br-1,3-bdc)(NI-mbpy-34)]n (1), under hydro(solvo)thermal conditions. Single-crystal X-ray structure analysis revealed that 1 features a three-dimensional (3-D) 2-fold interpenetrating cds (or CdSO4) net topology with the point symbol of (65·8), where the Zn(II) centers are considered as 4-connected square-planar nodes. X-ray powder diffraction (XRPD) patterns and thermogravimetric (TG) analysis confirmed that 1 shows high chemical and thermal stabilities. Notably, 1 displayed solvent dependent photoluminescence properties; the fluorescence intensity and emission maximum of 1 in different solvent suspensions varied when a solvent was changed. Furthermore, the H2O suspension of 1 exhibited blue fluorescence emission and thus can be treated as a selective and sensitive fluorescent probe for turn-on detection of Cr3+ cations through absorbance caused enhancement (ACE) mechanism and turn-off detection of Cr2O72−/CrO42− anions through collaboration of the absorption competition and energy transfer process, with limit of detection (LOD) as low as μM scale.

Acid-directed synthesis of three Cd-based metal–organic frameworks with luminescence and catalytic CO2transformation properties

This paper shows an example of acid-directed hydrothermal synthesis of three different Cd(ii)-MOFs based on the same mixed ligands. Two of them show blue fluorescence emissions and high activities in the CO2cycloaddition with epoxybutanes.

Syntheses, crystal structures and properties of three compounds based on the dicarboxylate ligand with S-S flexible linkage

Three new compounds, [MnL(2, 2΄-bipy)2]n·1.5nH2O (1), Co(4, 4ˊ-bipy)(H2O)4·2HL (2) and 2HL·(4, 4ˊ-bipyH)·2H2O (3) (H2L = 2,2΄-dithiosalicylic acid, 2, 2΄-bipy = 2, 2΄-bipyridine, 4, 4΄-bipy = 4, 4΄-bipyridine), have been synthesized by hydrothermal and evaporation methods. Structural determination reveals that compound 1 shows a one-dimensional chain structure with L2- ligands adopting bridging coordination modes, compound 2 features a mononuclear structure with uncoordinated HL- anions, balancing the charges, compound 3 is a new inclusion compound of HL- anions and 4, 4ˊ-bipyH cation with π-π stacking interactions. In compounds 1-3, the flexible S-S linkages can make H2L ligands present different conformations of dihedral angles between the terminal benzene rings. The S-O hypervalent bonds can stabilize the conformations. Thermogravimetric analyses and fluorescent measurements of compounds 1 and 2 have been performed. Compounds 1 and 2 exhibit broad blue fluorescent emission bands at 420 nm and 424 nm, respectively.

A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium.

Hydro(solvo)thermal reactions of Cd(NO3)2, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H2bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H2O)]∙2H2O}n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (44·62), where the Cd(II) center adopts a {CdO5N2} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH2Cl2, H2O, CH3OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H2O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO42− and 14.91 μM for Cr2O72−, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr3+, Fe3+, and Al3+ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr3+, 3.82 μM for Fe3+, and 3.37 μM for Al3+, mainly through an absorbance-caused enhancement (ACE) mechanism.

Spiro Compounds for Organic Light-Emitting Diodes

ConspectusThe development of cutting-edge optoelectronic devices is rapidly changing science and technology. The organic light-emitting diodes (OLEDs), as one of the most applicable techniques of organic electronics, are experiencing the process of materials’ upgrade. Among all the organic units to construct OLED materials, the spiro structure and its derived compounds have been widely studied due to the good thermal stability and unique orthogonally rigid structure. It had shown great potential in first generation fluorescent OLEDs (FOLEDs) and second generation phosphorescent OLEDs (PhOLEDs). Recently, it has achieved outstanding performance in third generation thermally activated delayed fluorescence (TADF) OLEDs, which is attributed to its orthogonal structure caused by the spiro atom; thus the spiro compound can innately separate the hole and electron which is beneficial for minimizing the singlet–triplet splitting energy (ΔEST). The most classic aromatic spiro unit is 9,9′-spriobifluorene (SBF), which was first reported in 1930. The study of aromatic spiro compounds is closely related to the development of organic semiconductors; now, the structure–property relationship of spiro compounds is getting clearer and attracting wide attention from the material community.In this Account, we briefly summarize the efforts on the functionalization and application of spiro compounds in OLEDs. The functionalization of spiro compounds in our group mainly focuses on the development of electron-rich spiro backbone and the adjustment of different substitution positions. In this regard, we have systematically studied the electron-rich spiro backbones which could greatly facilitate the carrier injection/transport and the new derivation positions (C1, C3, and C4 at fluorene moiety) can markedly affect the energy levels of triplet excitons, which is crucial for host materials in OLEDs, especially for the blue ones. The two main methods, i.e., backbone modification and position engineering, can cooperate to construct a rigid scaffold to realize spatial donor/acceptor intramolecular interaction, which confines the donor/acceptor distance. Afterward, the application of spiro compounds in OLEDs is elucidated from FOLEDs to PhOLEDs, then to TADF OLEDs. The spiro[acridine-9,9′-fluorene] (SAF) unit is our first example to enhance the performance of blue and violet fluorescent emitters, which have reached the theoretical upper limit of FOLEDs. For PhOLEDs, the spiro-type compounds are mainly used as host materials. The substitution positions of the SBF unit are thus thoroughly investigated to afford host materials with high triplet energy. And the SAF unit is modified to form ambipolar host materials to balance hole/electron injection for better white PhOLEDs. During this research, we understood the importance of the orthogonal arrangement in the spiro structure for ambipolar material design. Finally, TADF materials based on the spiro compounds are also presented. The spiro materials used in TADF are usually performed as an individual donor or acceptor before our contribution. Our tendency is to utilize the through-space charge transfer, i.e., charge transfer occurring between the spatial-close donor and acceptor, to construct efficient TADF materials, which paves a new avenue for the future study of spiro compounds.

Nitrogen, boron-doped Ti3C2 MXene quantum dot-based ratiometric fluorescence sensing platform for point-of-care testing of tetracycline using an enhanced antenna effect by Eu3.

The Ti3C2 MXene quantum dots (Ti3C2 MQDs) derived from Ti3C2 MXene have received much attention because of their remarkable advantages in biosensing. Nevertheless, the functionalization of Ti3C2 MQDs to improve their properties is just in its infant stage. Herein, we firstly synthesized nitrogen and boron co-doped Ti3C2 MQDs (N, B-Ti3C2 MQDs) with good water solubility, strong stability, and high optical characteristics. The N, B-Ti3C2 MQDs exhibit excitation wavelength-dependent blue photoluminescence with optimal excitation/emission peaks at 335/439nm. Nowadays, the development of fast and real-time detection of tetracycline (TC) in animal derived food is very essential. In this work, a novel point-of-care testing (POCT) platform was established based on ratiometric fluorescence method using N, B-Ti3C2 MQDs coupled with Eu3+. Upon addition of TC in the Eu3+/N, B-MQDs system, blue fluorescence emission of N, B-Ti3C2 MQDs was quenched and red fluorescence emission of Eu3+ was enhanced gradually, which was ascribed to the synergistic inner filter effect and antenna effect. Moreover, we prepared test papers with N, B-Ti3C2 MQDs and Eu3+ for TC detection based on the change of fluorescence color, which could be recognized by color recognizer app installed in the smartphone. Therefore, great promise for POCT of TC is givenwith the merits of simplicityand visible detection possibility.The proposed method demonstrated a low detection limit of 20nM. Applicationof the platform for TC quantification in milk samples opened a novel means for the potential use ofN, B-Ti3C2 MQDs in food safety.

Synthesis of fluorescent carbon quantum dots from Jatropha fruits and their application in fluorometric sensor for the detection of chlorpyrifos

In this study, we have synthesized fluorescent carbon quantum dots (J-CQDs) from Jatropha fruit by using a one-pot hydrothermal approach, for the first time. The as-synthesized J–CQDs exhibited bright blue fluorescence emission with a high quantum yield of 13.7 %. Furthermore, the synthesized fluorescent J-CQDs have been used as a fluorometric sensor for the detection of pesticides. The sensing of pesticides is based on the irreversible catalytic inhibition of acetylcholinesterase (AChE) enzyme with a controlled fluorescence quenching process. The thiocholine was mainly triggered by the decomposition of DTNB to form yellow-colored TNBA. Further, TNBA gradually quenched the fluorescence emission spectra of added J-CQDs via dynamic quenching. The catalytic activity of AChE was inhibited in the presence of OPs, leading to the recovery of the fluorescence signal. Thus, a sensitive and selective nanoprobe was designed for the sensing of OPs (chlorpyrifos) along with a detection limit 2.7 ng/mL. Apart from this, the proposed sensing method has been successfully applied for pesticide detection in environmental and agricultural samples with acceptable recovery. Thus, the delivered result suggests that our probe is simple in design, having a short reaction time, and could be proficiently used in further analytical and environmental applications in the future.

Efficiency Breakthrough of Fluorescence OLEDs by the Strategic Management of “Hot Excitons” at Highly Lying Excitation Triplet Energy Levels

AbstractAggregation‐induced emission (AIE) and hybridized local and charge‐transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) by harnessing “hot excitons” at the high‐lying triplet exciton states (Tn, n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of Tn→Tn−1. Herein, experimental results and theoretical calculations demonstrate the “hot exciton” process between the high‐lying triplet state T3 and the lowest excited singlet state S1 in an AIE material 4⁗‐(diphenylamino)‐2″,5″‐diphenyl‐[1,1″:4′,1″:4″,1′″:4′″,1⁗‐quinquephenyl]‐4‐carbonitrile (TPB‐PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the “hot exciton” process and inhibit the T3→T2 loss by doping a blue fluorescent emitter in TPB‐PAPC. Finally, the doped TPB‐PAPC blue OLEDs achieve a maximum external quantum efficiency (EQEmax) of 9.0% with a small efficiency roll‐off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2‐(4‐(10‐(3‐(9H‐carbazol‐9‐yl)phenyl)anthracen‐9‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQEmax of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high‐performance “hot exciton” molecules and the fabrication of high‐performance blue fluorescence OLEDs.

Cr(VI) removal by cellulose-based composite adsorbent with a double-network structure

A cellulose-based composite adsorbent (PEI-PAM-CF) was fabricated via a facile cross-linking of polyethyleneimine/polyacrylamide (PEI/PAM) and cellulose using epichlorohydrin as the cross-linker. It possessed a double-network structure and emitted blue fluorescence. Compared with the control samples (PEI-CF and PAM-CF), the PEI-PAM-CF showed a synergy effect for the Cr(VI) removal. It can effectively remove Cr(VI) at low concentration with no structure destroyed for the adsorbent. Other coexisting anions (NO 3 - , Cl - , H 2 PO 4 - and CH 3 COO - ) and cations (Na + , K + , Mg 2+ , Ca 2+ and Cr 3+ ) had no significant effect on Cr(VI) removal except SO 4 2- . After five adsorption/desorption cycles, the Cr(VI) removal only decreased with a loss of 7%, suggesting that the PEI-PAM-CF had good regeneration performance. Most importantly, the electrostatic adsorption mechanism between Cr(VI) and the PEI-PAM-CF was revealed by a reversible fluorescence “on-off-on” phenomenon and the DFT calculation. The adsorption sites on the PEI-PAM-CF were attributed to the amino groups of the PEI and PAM. Hence, the PEI-PAM-CF was potential for the treatment of Cr(VI)-containing wastewater at low concentration. • A cellulose-based composite adsorbent with a dual-network structure was prepared. • The adsorbent PEI-PAM-CF can effectively uptake the low concentration Cr(VI). • A synergy effect was observed after adding PEI and PAM together. • The proposed electrostatic adsorption mechanism was clarified. • The DFT calculation was performed to study the adsorption sites.

Promoting Room Temperature Phosphorescence through Electron Transfer from Carbon Dots to Promethazine.

Room temperature phosphorescence (RTP) as a fascinating phenomenon shows great potential toward multiple applications. Howbeit, it is challengeable to improve the phosphorescence efficiency of carbon dots (CDs) owing to their short lifetime. Herein, we proposed a facile, rapid, and gram-scale strategy to synthesize the cross-linked carbon dots (named N-CDs) with both bright blue fluorescence and green RTP emissions. To be specific, the polymer of polyethylenimine (PEI) served as the cross-linking agent and carbon source, during which process phosphoric acid accelerated the formation of the compact carbon core within 30 s. Subsequently, the cross-linked carbon dots with the rigid network formed a small singlet-triplet energy splitting (ΔEST) of 0.490 eV, thus exhibiting a long RTP lifetime of 429.880 ms while coated on the filter paper through the hydrogen bonds. Taking advantage of the double luminescence, we successfully achieved the dual-channel detection of promethazine by N-CDs. The fluorescence of N-CDs was obviously quenched by promethazine through the electron-transfer process, displaying the linear range from 0.4 to 8 mM. Significantly, the electron transfer (ET) from carbon dots to promethazine boosted their phosphorescence efficiency and prolonged the lifetime to 565.190 ms, and the enhanced phosphorescence facilitated the sensitive recognition of promethazine with the concentration range of 1-3000 μM. Meanwhile, the possible autofluorescence interference from biological samples could be avoided through this RTP assaying mode, providing the more accurate results. Also, their RTP and fluorescence endowed the current N-CDs with the ability of dual-signal painting and imaging. This strategy may broaden the new approaches to produce the long-lifetime and high-efficiency RTP material toward the sensing purpose.

Comparison of two diphenyl polyenes as acid-sensitive additives during the biodegradation of a thermoset polyester polyurethane coating.

Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers. 1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases. Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N.albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator. Our experiments confirm that N.albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.