Electron Transfer Interactions Research Articles

The Effect of Different Solvents in Natural Dyes from Roselle (Hibiscus Sabdariffa) and Green Tea Leaves (Camellia Sinensis) for Dye-Sensitized Solar Cell

A dye-sensitized solar cell (DSSC) fabricated using anthocyanin or chlorophyll natural dye extract coming from Roselle (Hibiscus Sabdariffa) and Green Tea leaves (Camellia Sinensis). Both dye pigmentations were extracted using different alcohol-based solvent, namely, ethanol, methanol and mixed (ethanol + methanol) to identify whether the different solvents give the effect during the dye extraction. The performance of the electron transfer interaction between the natural dye and Titanium Dioxide (TiO2) was determined. The photovoltaic response of DSSC was collected by recording the data of I-V characteristic under illumination. The DSSC using the Roselle dye extract yielded the following results; Voc = 0.001 V, Jsc = 0.00868(mA/cm2), FF = 0.3554 and η = 0.00142% which is coming from the mixed solvent. On the other hand, the green tea dye extract yielded the following results; Voc = 0.3985, Jsc = 0.000797 (mA/cm2), FF = 0.3985 and η = 0.0000752% which is coming from the methanol solvent.

New complexes driven by an unsymmetrical tetracarboxylate for highly selective detection of acetylacetone in aqueous solution

Two novel complexes based on an unsymmetrical tetracarboxylate, namely, [Cd2(bptc)(bpp)(H2O)2]n·nH2O (1, H4bptc ​= ​2,3,3′,4′-biphenyl tetracarboxylic acid; bpp ​= ​1,3-bis(4-pyridyl) propane), [Cu(H2bptc)(phen)] (2, phen ​= ​1,10-phenanthroline) have been solvothermally synthesized with the aid of N-donor ligands. The structures, CHN analysis, IR analysis, thermal stabilities and photoluminescence properties of title complexes were investigated. Single-crystal X-ray diffraction analysis indicates that complex 1 demonstrates a novel 3-D network with (4, 5, 5) -connected (3ˑ4ˑ5ˑ6ˑ82) (3ˑ42ˑ5ˑ63ˑ83) (3ˑ43ˑ52ˑ63ˑ7) topology. Whereas complex 2 only possesses a mononuclear structure. Photoluminescence studies indicate that complex 1 shows a strong green light emission, while 2 exhibits blue emissions. Moreover, the luminescence properties of 2 can be utilized to sensitively and selectively detect acetylacetone in aqueous solution with the detection limit of 61.3 ​ppb. In addition, the probable mechanisms are also detailedly investigated, which indicate that the static photo-competitive absorption, photoinduced electron transfer and H-bonding interaction between sensor and analyte may be the main reasons for the fluorescence quenching effect.

Selective dual detection of Hg2+ and TATP based on amphiphilic conjugated polythiophene-quantum dot hybrid materials.

The design of multifunctional sensors based on biocompatible hybrid materials consisting of conjugated polythiophene-quantum dots for multiple environmental pollutants is a promising strategy for the development of new monitoring technologies. Herein, we present a new approach for the "on-off-on" sensing of Hg2+ and triacetone triperoxide (TATP) based on amphiphilic polythiophene-coated CdTe QDs (PQDs, PLQY ∼78%). The emission of the PQDs is quenched by Hg2+ ions via electron transfer interactions. Based on the strong interaction between TATP and Hg2+ ions, the addition of TATP to the PQD-Hg2+ complex results in a remarkable recovery of the PQD emission. Under the optimized conditions, the PQD sensor shows a good linear response to Hg2+ and TATP with detection limits of 7.4 nM and 0.055 mg L-1, respectively. Furthermore, the "on-off-on" sensor demonstrates good biocompatibility, high stability, and excellent selectivity in the presence of other metal ions and common explosives. Importantly, the proposed method can be used to determine the level of Hg2+ and TATP in environmental water samples.

Identifying potential regulatory interactions of peroxiredoxin PRXQ

Peroxiredoxins (Prxs) are cysteine-based peroxide-reducing enzymes that have been extensively studied over the past two decades. The reduction of the Prx disulfide form is dependent on electron donating enzymes to shift the Prx back into a catalytically active state. However, this reaction is poorly understood and reductant enzymes for this reaction to reduce the Prx disulfide bond have received little attention. Prxs from the bacterium Xanthomonas campestris (XcPrxQ) were used to assess how reductants affect Prx turnover by identifying potential electron transfer interactions between Prxs and reductants, Glutaredoxins (Grxs) and Thioredoxins (Trxs). To examine potential interactions between PrxQ and reducing proteins, we used PrxQ, Grx, and Trx mutants to determine the effect of specific cysteines in each of the proteins. Mutant and wildtype proteins were expressed in E. coli and purified using anion-exchange and gel filtration chromatography and purity was verified by SDS-PAGE. The results clarified the role of the two cysteines in PrxQ, C48 and C84, which are thought to participate in the reduction reaction of hydrogen peroxide. They also show Trx and Grx proteins from the same bacterium are possible reductants for Prx turnover, as reactions with PrxQ have produced complex formation at a larger molecular weight, suggesting the reductant binding to PrxQ and reducing its disulfide bond. This study is significant because it reveals potential binding interactions between reductants and Prxs that regulate Prx turnover into a catalytically active state, allowing the enzyme to break down peroxide and prevent oxidative damage, as well as highlighting Trxs in bacteria as a potential drug target due to their regulation of hydrogen peroxide levels in pathogenic strains.

Oxygen-directed porous activation of carbon nanospheres for enhanced capacitive energy storage

Carbonaceous materials attract various attentions as supercapacitor electrode due to their low cost, high stability, and large specific surface area. However, the enhancement of energy storage for carbon electrode is limited by the difficulty in constructing the carbon surface well-compatible for ions and electrons transfer, and by the unclear mechanism. Herein, we develop an oxygen-modulated porous activation strategy (OMPA), by which the transport of electrons and ions can be simultaneously accelerated at the as-produced carbon electrode surface. The key to OMPA lies in the preoxidation of carbon nanospheres (CN), followed by activation with potassium hydroxide. The surface oxygen on oxygen-functionalized CN (OCN) can enable the activated OCN (AOCN) with optimized hierarchical porosities dominated by K+-matched micropore of 0.66 nm, and with an electron transfer interaction with the reserved oxygen. These prominent structures effectively arouse the electrons and ions transfer in the AOCN, as revealed by kinetics analyses and theory calculation. Thu, the AOCN as a supercapacitor electrode delivers a specific capacitance of 282 F g−1 at 0.5 A g−1, maintaining 67% after current density magnifying by 60 times. This work supplies the guidance to rationally design advanced carbon materials as supercapacitors electrode via precisely-tailoring surface characteristic.

On the role of non-diagonal system-environment interactions in bridge-mediated electron transfer.

Bridge-mediated electron transfer (ET) between a donor and an acceptor is prototypical for the description of numerous most important ET scenarios. While multi-step ET and the interplay of sequential and direct superexchange transfer pathways in the donor-bridge-acceptor (D-B-A) model are increasingly understood, the influence of off-diagonal system-bath interactions on the transfer dynamics is less explored. Off-diagonal interactions account for the dependence of the ET coupling elements on nuclear coordinates (non-Condon effects) and are typically neglected. Here, we numerically investigate with quasi-adiabatic propagator path integral simulations the impact of off-diagonal system-environment interactions on the transfer dynamics for a wide range of scenarios in the D-B-A model. We demonstrate that off-diagonal system-environment interactions can have profound impact on the bridge-mediated ET dynamics. In the considered scenarios, the dynamics itself does not allow for a rigorous assignment of the underlying transfer mechanism. Furthermore, we demonstrate how off-diagonal system-environment interaction mediates anomalous localization by preventing long-time depopulation of the bridge B and how coherent transfer dynamics between donor D and acceptor A can be facilitated. The arising non-exponential short-time dynamics and coherent oscillations are interpreted within an equivalent Hamiltonian representation of a primary reaction coordinate model that reveals how the complex vibronic interplay of vibrational and electronic degrees of freedom underlying the non-Condon effects can impose donor-to-acceptor coherence transfer on short timescales.

A Quenched Annexin V-Fluorophore for the Real-Time Fluorescence Imaging of Apoptotic Processes In Vitro and In Vivo.

Annexin‐based probes have long been used to study apoptotic cell death, which is of key importance to many areas of biological research, drug discovery, and clinical applications. Although apoptosis is a dynamic biological event with cell‐to‐cell variations, current annexin‐based probes are impractical for monitoring apoptosis in real‐time. Herein, a quenched annexin V‐near‐infrared fluorophore conjugate (Q‐annexin V) is reported as the first OFF‐ON annexin protein‐based molecular sensor for real‐time near‐infrared fluorescence imaging of apoptosis. Q‐annexin V is non‐fluorescent in the extracellular region, due to photoinduced electron transfer interactions between the conjugated dye and amino acid quenchers (tryptophan and tyrosine). The probe becomes highly fluorescent when bound to phosphatidylserines on the outer layer of cell membranes during apoptosis, thereby enabling apoptosis to be monitored in real‐time in 2D and 3D cell structures. In particular, Q‐annexin V shows superior utility for in vivo apoptosis fluorescence imaging in animal models of cisplatin‐induced acute kidney injury and cancer immune therapy, compared to the conventional polarity‐sensitive pSIVA‐IANBD or annexin V‐Alexa647 conjugates.

Effects of biochar on catalysis treatment of 4-nonylphenol in estuarine sediment and associated microbial community structure.

The effect of pyrolysis temperature on the generation of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge biochar (SSB) and the removal of hazardous chemicals from esturine sediments by SSB and sodium percarbonate (SPC), exemplified by 4-nonylphenol (4-NP) were studied. SSB synthesized at 500°C (SSB500) achieved the highest 4-NP degradation efficiency of 73%, at pH0 9.0 in 12h of reaction time. The enhanced 4-NP degradation was attributed to the SSB500 activation activation of SPC that produced sufficient •OH and CO3-• due to electron-transfer interaction on the Fe-Mn redox pairs. The microbial community diversity and composition of the treated sediment were compared using high-throughput sequencing. Results showed SSB/SPC treatment increased the microbial diversity and richness in the sediments. Proteobacteria were the keystone phylum, while Thioalkalispira genera were responsible for 4-NP degradation in the SSB/SPC treatment. Over all, results revealed the change in the bacterial community during the environmental applications of SSB, which provided essential information for better understanding of the monitoring and improvement of sustainable sediment ecosystems.

Fluorescence detection of histamine based on specific binding bioreceptors and carbon quantum dots

Histamine is primarily found in spoiled food and often used as an indicator of food safety. Compared to various existing methods for analyzing histamine, high-performance liquid chromatography (HPLC) which is accurate but time-consuming, and immunochemical methods that are difficult to produce high specificity and affinity antibodies towards small molecules have been used. In this study, we developed a newly designed, sensitive, and selective fluorescence detection platform for histamine sensing, utilizing carbon quantum dots (CQDs) and synthetic peptides. Specifically, through biopanning approaches, a series of peptides having a high affinity towards immobilized histamine hapten were selected from phage-displayed libraries. Then, CQDs were synthesized by one-pot hydrothermal treatment enabling their fluorescence to be effectively quenched by peptides via the electron transfer interactions. While, in the presence of histamine, fluorescence will be recovered because of the stronger interaction between peptide and target. In this study, from the selectivity tests towards histamine and in contrast to structurally similar compounds, peptide Hisp3 (DIDRAGKASHWP) along with its dipeptide repeat derivative (Hisp3-2-C) were chemically synthesized to be used as promising histamine receptors. Furthermore, the application of peptide along with gold-coated magnetic nanoparticles (MNP@Au NPs) was designed for purification and analysis of fish samples. These results indicate that the CQDs and peptide sensor system could detect histamine at lower concentrations with high sensitivity and selectivity.

Spin-Related Electron Transfer and Orbital Interactions in Oxygen Electrocatalysis.

Oxygen evolution and reduction reactions play a critical role in determining the efficiency of the water cycling (H2 O ⇔ H2 + O2 ), in which the hydrogen serves as the energy carrier. That calls for a comprehensive understanding of oxygen electrocatalysis for efficient catalyst design. Current opinions on oxygen electrocatalysis have been focused on the thermodynamics of the reactant/intermediate adsorption on the catalysts. Because the oxygen molecule is paramagnetic, its production from or its reduction to diamagnetic hydroxide/water involves spin-related electron transfer. Both electron transfer and orbital interactions between the catalyst and the reactant/intermediate show spin-dependent character, making the reaction kinetics and thermodynamics sensitive to the spin configurations. Herein, a brief introduction on the spintronic explanation of the catalytic phenomena on oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is given. The local spin configurations and orbital interactions in the benchmark transition-metal-based catalysts for OER and ORR are analyzed as examples. To further understand the spintronic oxygen electrocatalysis and to develop more efficient spintronic catalysts, the challenges are summarized and future opportunities proposed. Spin electrocatalysis may emerge as an important topic in the near future and help integrate a comprehensive understanding of oxygen electrocatalysis.

An imidazole functionalized copper(II)‐organic framework for highly selective sensing of picric acid and metal ions in water

An imidazole functionalized metal–organic framework (MOF), [Cu(HL)(H2O)]·(H2O)·(DMA) (HBU‐166, H3L = 4,4′,4″‐(1H‐imidazole‐2,4,5‐triyl)tribenzoic acid, DMA = N,N‐dimethylacetamide) was synthesized and characterized by single‐crystal X‐ray diffraction. HBU‐166 was observed as a two‐dimensional MOF and showed good stability in water, an acidic solution (pH = 4), and an alkaline solution (pH = 9). HBU‐166 exhibited ligand‐based luminescence with a blue shift, which could be attributed to the coordination effect. Moreover, HBU‐166 could be applied to detect nitroaromatic compounds (NACs) and metal ions in water with preferable selectivity and sensitivity. In particular, HBU‐166 could be used as a promising luminescent sensor for picric acid (PA) with enhancement of emission intensity. The mechanism for PA detection likely involved electron transfer and weak interaction between ligand and electron‐deficient of NACs at the beginning to increase the emission intensity. Additionally, HBU‐166 exhibited excellent selectivity in the sensing of 4‐nitrophenol and Fe3+ through fluorescence quenching.

Mechanistic investigation of humic substances assisted photodegradation of imipramine under simulated sunlight

Imipramine (IMI) is a frequently prescribed tricyclic antidepressant and widely detected in the natural waters, while the environmental fate of IMI is yet poorly understood. Here, we investigated the photodegradation of IMI under simulated sunlight in the presence of humic substances (HS), typically including humic acid (HA) and fulvic acid (FA). The direct and indirect IMI photodegradation was found to increase both with increasing pH and with deoxygenation of the reaction solutions. The excited triplet state of HS (3HS⁎) was mainly responsible for the photosensitized degradation of IMI according to the steady-state quenching and direct time-resolved experiments. The electron transfer interaction between 3HS⁎ and IMI was observed by laser flash photolysis (LFP) with bimolecular reaction rate constants of (4.9 ± 0.4) × 109 M−1 s−1. Evidence of electron transfer from IMI to 3HS⁎ was further demonstrated by the photoproduct analysis. The indirect photodegradation was triggered off in the side chain of IMI with the nonbonding nitrogen electron transferring to 3HS⁎, followed by hydroxylation, demethylation and cleavage of the side chain. Very important that HS photosystem does not lose its efficiency with decreasing of IMI concentration, meaning that the studied photosystem still be used at environmentally relevant concentrations of IMI. These results suggest that photodegradation could be an important attenuation pathway for IMI in HS-rich and anaerobic natural waters.

Coenzyme Coupling Boosts Charge Transport through Single Bioactive Enzyme Junctions.

SummaryOxidation of formate to CO2 is catalyzed via the donation of electrons from formate dehydrogenase (FDH) to nicotinamide adenine dinucleotide (NAD+), and thus the charge transport characteristics of FDH become essential but remain unexplored. Here, we investigated the charge transport through single-enzyme junctions of FDH using the scanning tunneling microscope break junction technique (STM-BJ). We found that the coupling of NAD+ with FDH boosts the charge transport by ∼2,100%, and the single-enzyme conductance highly correlates with the enzyme activity. The combined flicker noise analysis demonstrated the switching of the coenzyme-mediated charge transport pathway and supported by the significantly reduced HOMO-LUMO gap from calculations. Site-specific mutagenesis analysis demonstrated that FDH-NAD+ stably combined own higher bioactivity and boosts charge transport, and the coupling has been optimized via the natural selection. Our work provides evidence of hydrogen bond coupling in bioactivity but also bridges the charge transport through single-enzyme junctions and enzyme activities.

Guest induced morphology transitions of star shaped pillar[5]arene trimer via endo host-guest and “exo-wall” electron-transfer interactions

Star shape bridged pillar[5]arene trimer (C3-PLT) based on benzene-1,3,5-tricarboxamide (BTAs) was successfully synthesized, which exhibited outstanding guest responsive morphology transition properties. The morphology tuning studies was efficiently achieved with the addition of competitive guest molecules G1 and G2 by various self-assembly mechanisms. C3-PLT itself displays nanofiber morphology through H-type π-π stacking, and this nanofiber morphology can be completely transformed into spherical vesicles by host-guest interaction G1, while upon addition of G2 into C3-PLT by means of “exo-wall” electron-transfer interactions, sheet superstructures can be observed. SEM, 1H NMR, DOSY, fluorescence spectroscopy, and viscosity have verified the formation of supramolecular polymers and morphological transitions between C3-PLT with both guests.

Improved electrochemical performance of graphene oxide supported vanadomanganate (IV) nanohybrid electrode material for supercapacitors

Graphene oxide (GO)-supported polyoxometalates (POMs) have been considered as promising electrode materials for energy storage applications due to their ability to undergo fast and reversible redox reactions. Herein, vanadomanganate-GO composites (K7MnIVV13O38.18H2O-GO with 2:1 and 4:1 ratio) were investigated for use as potential electrode materials in supercapacitors (SCs). The K7MnIVV13O38.18H2O (MnV13) was synthesized and anchored on GO through electron transfer interaction and electrostatic interaction to make the composite electrodes for the present study. All synthesized electrode materials were fully characterized by various techniques, e.g., Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and High Resolution-Transmission Electron Microscopy (HR-TEM). The electrochemical properties of MnV13/GO composites with different MnV13/GO ratios were investigated by two-electrode cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) in different electrolytes. The MnV13/GO composite of ratio 2:1 in 1 M LiCl electrolyte and that of ratio 4:1 in 1 M Na2SO4 electrolyte showed significant specific capacitance values of 269.15 F/g and 387.02 F/g, respectively and energy density of 37.38 Wh/kg and 53.75 Wh/kg, respectively for a scan rate of 5 mV/s. Interestingly, the 1:1 (MnV13/GO) composite in 1 M Na2SO4 and 1 M LiCl electrolytes showed very low specific capacitance values as the deposition of MnV13 on GO was not sufficient, as indicated by FTIR and SEM. Thus, it is evident that the specific capacitance value of these composite materials depends on the amount of MnV13 deposited on GO and these composite materials exhibit the potential to improve the performance of GO-based SCs.

Electrically Tunable Electron Transfer and Binding Interaction between Hydrated Ions and Graphene Oxide.

Density functional theory simulations were carried out to study the binding interaction between hydrated Na+/Cl- and graphene oxide (GO) under electric fields. External electric fields can modify the binding interactions of the hydrated ions with GO. The field-dependent binding energy is mainly controlled by the orbital interaction driven by the field-dependent electron transfer, in which miscellaneous electron-transfer routes in the interfaces between hydrated ions and GO surface were disclosed. The electric field is able to influence the electron-transfer degree for each route, thereby creating various electron acceptor-donor coupling interactions. Furthermore, we preliminarily explored the effect of the electric field on the interlayer structure of bilayer GO with NaCl and water confined inside. Electric fields can enlarge the interlayer spacing through tuning of the hydrated ion-GO interactions. Our simulations present a new understanding of hydrated ion-GO interactions in the presence of an electric field, which is expected to be valuable in the electrical modulation of GO nanomaterials.

(Invited) Large Photoluminescence Enhancement of Monolayer Molybdenum Disulfide Via Molecular Treatment

Molecular interaction is an essential process in various fields such as chemistry, biology and materials science. The interaction of molecules includes: 1) the local electron transfer process, 2) local chemical bonding and 3) assembling to form a structure. All three occur essentially from each molecule’s “recognition” ability. We are trying to extend the molecular interaction system onto inorganic electronic materials to harness the highest-performance of inorganic systems. In this presentation, I will present our recent results of molecular interaction on a semiconducting 2D material, transition metal dichalcogenides (TMDCs).1,2,3 TMDCs are constructed by stacking atomically-thin layers (thickness ~0.7 nm) with van der Waals interaction, and they are expected to generate tiny optoelectronic devices due to their thin nature. Since monolayer TMDC has a direct bandgap, it is a good platform for realizing atomically thin optoelectronic devices. However, an issue is their low luminescence brightness. For example, a representative TMDC, MoS­2, shows photoluminescence (PL) quantum yield of ~1% or less. In this presentation, I will show our recent results of improving the brightness of monolayer MoS2 dramatically (more than 100 times enhancement from the original) via molecular treatments. One method is using a superacid (bis(trifluoromethane)sulfonimide; TFSI) molecule.3 The superacid molecular treatment onto a monolayer MoS2 changes the PL quantum yield of MoS2 from 1% to near-unity. I will discuss the PL enhancement factor in the TFSI treatment on MoS2. The second method is using a redox-active molecule, fluoranil. The fluoranil molecule can reduce the electron concentration of monolayer MoS2, resulting in enhancement of the PL intensity.4 Furthermore, we found that the solvent used for the fluoranil treatment is critical to obtain bright monolayer MoS2. Solvent molecules would screen the charges on fluoranil molecules, as a result, which stabilizes the electron transfer-interaction between fluoranil and MoS2. Keywords: Superacid, redox-active molecules, Transition metal dichalcogenides, Photoluminescence, Transistors

Differences in Applied Redox Potential on Cathodes Enrich for Diverse Electrochemically Active Microbial Isolates From a Marine Sediment.

The diversity of microbially mediated redox processes that occur in marine sediments is likely underestimated, especially with respect to the metabolisms that involve solid substrate electron donors or acceptors. Though electrochemical studies that utilize poised potential electrodes as a surrogate for solid substrate or mineral interactions have shed some much needed light on these areas, these studies have traditionally been limited to one redox potential or metabolic condition. This work seeks to uncover the diversity of microbes capable of accepting cathodic electrons from a marine sediment utilizing a range of redox potentials, by coupling electrochemical enrichment approaches to microbial cultivation and isolation techniques. Five lab-scale three-electrode electrochemical systems were constructed, using electrodes that were initially incubated in marine sediment at cathodic or electron-donating voltages (five redox potentials between −400 and −750 mV versus Ag/AgCl) as energy sources for enrichment. Electron uptake was monitored in the laboratory bioreactors and linked to the reduction of supplied terminal electron acceptors (nitrate or sulfate). Enriched communities exhibited differences in community structure dependent on poised redox potential and terminal electron acceptor used. Further cultivation of microbes was conducted using media with reduced iron (Fe0, FeCl2) and sulfur (S0) compounds as electron donors, resulting in the isolation of six electrochemically active strains. The isolates belong to the genera Vallitalea of the Clostridia, Arcobacter of the Epsilonproteobacteria, Desulfovibrio of the Deltaproteobacteria, and Vibrio and Marinobacter of the Gammaproteobacteria. Electrochemical characterization of the isolates with cyclic voltammetry yielded a wide range of midpoint potentials (99.20 to −389.1 mV versus Ag/AgCl), indicating diverse metabolic pathways likely support the observed electron uptake. Our work demonstrates culturing under various electrochemical and geochemical regimes allows for enhanced cultivation of diverse cathode-oxidizing microbes from one environmental system. Understanding the mechanisms of solid substrate oxidation from environmental microbes will further elucidation of the ecological relevance of these electron transfer interactions with implications for microbe-electrode technologies.

Fluorescence ON-OFF switching, Boolean logic gates like behavior of carbon quantum dots and highly sensitive bovine serum albumin sensing

We demonstrate fluorescence “ON-OFF” switching and photonic logic gates based on fluorescence response of carbon quantum dots (CQDs) in the presence of graphene oxide (GO), reduced graphene oxide (RGO), and bovine serum albumin (BSA). We study the excited state electron and energy transfer interactions among the carbon based materials in detail through steady state fluorescence (SSF) and time resolved fluorescence (TRF) spectroscopy. CQDs function as donor; GO and RGO function as acceptors. SSF results show the fluorescence “turn-OFF” behavior of CQDs in the presence of GO and RGO, and the reason is explained through Stern-Volmer plots. TRF results reveal a decrease in the decay time components of CQDs in the presence of GO and RGO. The gradual recovery of quenched fluorescence of CQDs is observed by the addition of BSA at nanomolar concentrations which shows the highly sensitive “turn-ON” BSA sensing. Single input and two inputs photonic logic gates are implemented based on the fluorescence response of CQDs in the presence of GO, RGO, and BSA in different input combinations. The not, pass1, nor, and implication gates like behavior of CQDs is demonstrated.

Chromate(VI)-induced homogeneous oxidation and photolysis of aqueous tetracycline: Kinetics and mechanism

Tetracycline (TC) and chromate (Cr(VI)) are common organic or inorganic pollutants in the environment, and the interactions between them may mutually alter environmental behaviors and risks. However, the mutual effect between TC and Cr(VI) in aqueous solutions remains unclear. In this study, kinetic experiments, complexation and quenching experiments, electron spin resonance (ESR) analysis, density functional theory (DFT) calculation and identification of products, were performed to investigate the effects and underlying mechanism of Cr(VI) on oxidation and photolysis of TC. The results revealed that Cr(VI) could induce oxidation and photolysis of TC with or without light irradiation and the curve was well fitted by a pseudo first-order kinetic model. Moreover, the change of reaction conditions (such as initial concentration and pH) had great effect on oxidation or photolysis of TC. When Cr(VI) oxidized TC to form Cr(III) and TC radical, Cr(III) complexed with TC to accelerate the oxidation. In addition, oxidation still occurred under simulated irradiation. 1O2 which promoted photolysis of TC increased upon irradiation at higher pH or with the increase of Cr(VI). The participation of Cr(VI) affected self-sensitization and product formation of TC. Therefore, an electron-transfer interaction for photolysis among 1O2 arising from self-sensitization, Cr(VI)/Cr(III) and TC was first proposed. The transformation pathway of TC mainly included five reactions: hydrolysis, hydroxylation, deamination, dehydration and demethylation only for photolysis. This study identified new oxidation and photolysis of TC induced by Cr(VI), which will be helpful to further understand the fate of heavy metals and antibiotics in the natural aquatic environment.