Electron Quenchers Research Articles

Performance of new CO2 based mixture in CMS Improved Resistive Plate Chambers in HL-LHC environment

Resistive Plate Chamber (RPCs) detectors in the Compact Muon Solenoid operate with a gas mixture composed of 95.2% of C2H2F4, which provides a high number of ion-electron pairs, 4.5% of iC4H10, which ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4 is known to be a Greenhouse gas with a global warming potential (GWP) of 1430. Consequently, several ECO-friendly alternatives to C2H2F4 have been investigated in recent years. In this context, a short-mid term approach for the upcoming years of Large Hadron Collider (LHC) operation could be to focus on reducing the GWP of the RPC gas mixture by replacing C2H2F4 with CO2. The studies are conducted at the CERN Gamma Irradiation Facility in the North Area of the Super Proton Synchrotron (SPS), where a 13.6 TBq radiation source and a muon beam from SPS mimic the conditions of Phase-II (i.e. High-Luminosity (HL)) of the LHC. This paper presents the performance of a 1.4 mm gap RPC with three different CO2 based mixtures (30 and 40% of CO2; 0.5 and 1% of SF6) under high gamma background conditions with the perspectives for the longevity campaign.

Extended study of the influence of europium doping on phosphate glass

The phosphate glasses with various Eu2O3 concentrations (0.1–3.0 w/w%) were synthesized and studied regarding the influence of europium dopant on the properties of irradiated phosphate glasses. During studies, samples were irradiated using two types of ionizing radiation sources (β− and γ), with obtained doses up to 40 kGy. TL studies were investigated using various methods, such as TL response vs. radiation dose and the TMax-Tstop method. To further investigate, if increasing the europium concentration affects the structure of electron traps, Computer Glow Curve Deconvolution studies linked with various heating rates methods were applied –increasing the concentration of dopant does not influence the number and energy of electron traps in irradiated samples. This fact was also supported by the results of the thermoluminescence spectrum – where no additional signals, besides wide signals from native glass were observed. OSL and IRSL studies were also conducted, for OSL we observed quenching of the signals, similar as in the TLD case. For IRSL studies all samples didn't display any signals. Finally, to understand if Eu3+ also has a “protective” effect, decreasing the yield of generating F-centers during irradiation, UV-VIS spectroscopy was used. It was established that samples doped with europium oxide possess ca. 20% lower signals at F-center maximum (at 475 nm), the building-up maximum at 320 nm was observed, characteristic of the absorption band of Eu2+. All data indicate that europium in phosphate glass is taking the role of an efficient electron quencher. This quenching phenomenon occurs in three ways: first (direct) when the ion reduction process (Eu3+→Eu2+) competes with the formation of F-centers, and second (indirect) when during heating electrons coming from F-centers were quenched by near Eu3+ ions. The third mechanism of quenching occurs through the electron's non-radiative transition induced by increased stress in the glass matrix caused by a large ionic radius of the dopant.

Enhanced photocatalytic removal of bromate in drinking water by Au/TiO2 under ultraviolet light.

The photo-reduction of bromate (BrO3 -) has attracted much attention due to the carcinogenesis and genotoxicity of BrO3 - in drinking water. In this study, a heterojunction photocatalyst was developed by depositing Au nanoparticles (NPs) onto P25 TiO2 NPs through a one-pot, solvent-thermal process. Due to the unique properties of Au, the Au NPs deposited on the TiO2 surface created a Schottky barrier between the metal and the semiconductor, leading to an effective separation of photo-generated charge carriers as the Au nanoparticles served as electron sinks. The Au/TiO2 photocatalyst demonstrated efficient reduction of BrO3 - under UV light illumination without the need for sacrificial agents. The effect of different Au loading of Au/TiO2 was systematically investigated for its influence on the generation of electrons and the reduction ability of BrO3 -. The results indicate that the 1% Au/TiO2 catalyst exhibited a higher concentration of localized electrons, rendering it more effective in BrO3 - removal. The photocatalytic efficiency for BrO3 - reduction decreased upon the addition of K2S2O8 as an electron quencher, suggesting that the primary factor in this photo-reduction process was the availability of electrons. These findings hold promise for the potential application of the Au/TiO2 catalyst in the removal of BrO3 - from drinking water through photo-reduction.

Integration of TiO2 QDs with brown TiO2: S-scheme photocatalysts with boosted activity for simulated sunlight-driven N2 fixation without hole quencher

An alternative strategy to solve the energy consumption and pollution problems caused by traditional ammonia production is photocatalytic N2 fixation. Therefore, the rational design and facile synthesis of photocatalysts for the efficacious ammonia production is an active research hotspot. In this research, TiO2 QDs (TQDs) and brown TiO2 (BTO) nanoparticles were combined through a facile hydrothermal method. The optimal homojunction TQDs/BTO (1:1) photocatalyst with QDs size of about 4.5 nm was utilized for ammonia production, for the first time, with the activity of 11844 µmol L−1 g−1, which was almost 14.5, 4.46, and 3.07-folds as large as TiO2 (P25), TQDs, and BTO materials, respectively. In addition, the presence of hydrazine intermediate in the ammonium formation pathway and the impact of hydrogen-free solvents, electron quencher, and acidic and basic solutions on ammonia production were investigated. The electrochemical and spectroscopic characterizations confirmed that the boosted ability of photocatalyst is related to the boosted adsorption of N2 molecules and effective segregation/transfer of charge carriers. Consequently, the S-scheme TQDs/BTO (1:1) homojunction photocatalyst could be a suitable photocatalyst in N2 fixation technology, with high stability for repeated use and a facile synthesis route.

Performance studies of RPC detectors operated with C2H2F4 and CO2 gas mixtures

Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of 90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation.

The stimulation of peroxymonosulfate via novel Co0.5Cu0.5Fe2O4 heterogeneous photocatalyst in aqueous solution for organic contaminants removal

The abundance of organic pollutants in the aqueous system has posed a serious threat to human health. Here, Co0.5Cu0.5Fe2O4 magnetic nanoparticles (NPs) were successfully synthesized for antibiotic degradation. The properties of the as-prepared photocatalyst were tested by diverse characterization techniques. The effects of the concentration of photocatalyst (20–100 mg L−1) and peroxymonosulfate (PMS) (20–80 mg L−1), and the pH (3–9) of solution on the degradation of tetracycline (TC) in aqueous solution by Co0.5Cu0.5Fe2O4/PMS/light system were investigated comprehensively. The results showed that Co0.5Cu0.5Fe2O4 NPs possessed remarkable photocatalytic performance over a wide pH range with the help of PMS and visible light irradiation. The degradation rate of TC could reach 86.0% at 40 min in the optimized conditions (TC = 10 mg L−1, catalyst = 60 mg L−1, PMS = 60 mg L−1, pH = 7). In addition, the active species quenching experiment demonstrated that h+, SO•4–, and •OH were generated in the degradation progress. Interestingly, h+ served as a conqueror in the reaction system, which benefited from the increased separation capability of electron-hole pairs due to the role of PMS as an electron quencher. Meanwhile, an improved PMS-assisted photocatalytic degradation of the TC reaction mechanism has been presented. Various TC intermediates were also uncovered, and probable degradation pathways were proposed. Furthermore, the Co0.5Cu0.5Fe2O4/PMS/light system was able to degrade a variety of organic pollutants, including naproxen sodium, naproxen, carbamazepine, ofloxacin, and flurbiprofen. The excellent degradation of various organics and high recyclability underline potential applications of Co0.5Cu0.5Fe2O4 NPs.

Hot electron-induced electrochemiluminescence of polystyrene modified electrode for rutin determination

• The spin-coating strategy is chosen to prepare the insulating layer, which is much simpler and controllable. • Polystyrene insulating layer can generation stable HECL. • Owing to the quenching effect on the SO 4 − radical, the present sensing platform was applied for the determination of rutin. For hot electron-induced electrochemiluminescence (HECL), developing facile and controllable insulating layer on the electrode surface is key to the effective electron tunneling. Herein, a polystyrene modified glassy carbon electrode based the spin-coating was proposed for HECL. The constructed interface was characterized by atomic force microscopy (AFM). And HECL performance was investigated in details using the system of Ru(bpy) 3 2+ and S 2 O 8 2− . The as-prepared film shows the stable and reproducible HECL performance and the HECL mechanism was discussed using ECL spectra and hydrated electron quenchers. Finally, on the basis of the inhibition of SO 4 − , the present polystyrene film was applied to the detection of rutin in the range of 0.1–1.3 μM with a detection limit of 90 nM (S/N = 3).

The role of biochar in the photocatalytic treatment of a mixture of Cr(VI) and phenol pollutants: Biochar as a carrier for transferring and storing electrons

Biochar (BC) is widely used to remove environmental pollutants due to its photocatalytic activity. However, the mechanism of BC in photocatalysis remains unclear. In this study, soybean straw biochar (D500), dewatered sludge biochar (S500) and TiO2/BC composite catalysts were prepared to test their photocatalytic activity in the photocatalysis-dark reaction using phenol and Cr(VI) as the representative pollutants. D500 had a good graphitized structure, layered structure and more active sites, which led to good photocatalytic activity. Compared with D500, S500 did not have a similar structure, resulting in a lack of photocatalytic activity. In addition, the efficiency of Cr(VI) and phenol removal using D500/TiO2 as a catalyst was higher than that obtained using D500 and TiO2, respectively. TiO2 coupled with D500 increased the generation of photoexcited electrons and reduced the recombination of e−-h+ pairs. The removal efficiency of TiO2/D500 for Cr(VI) (80.4 %) and phenol (77.7 %) in the hybrid systems was higher than that of Cr(VI) and phenol in unitary systems. This difference was mainly attributed to the inhibition of e−-h+ pair recombination by phenol and Cr(VI), which function as electron quenchers and hole quenchers, respectively. Furthermore, D500 stored electrons under light and released these electrons under dark conditions. When D500 was combined with TiO2, the electrons on the biochar activated the catalytic redox activity of TiO2, thereby removing pollutants under dark conditions. Meanwhile, TiO2/D500 also exhibited good reusability and stability. In summary, this study provides new insight into the role of biochar in photocatalysis.

In situ preparation of g-C3N4 nanosheet/FeOCl: Achievement and promoted photocatalytic nitrogen fixation activity

Climate change, global warming, and population growth have led researchers to use eco-sociable procedures for the N2 reduction reaction. It has discovered that N2 molecule can be transformed into NH3 in ambient circumstances with nanocomposites upon visible irradiation. In this research paper, a new visible-light-driven photocatalyst was constructed, with various weight percents of FeOCl particles (10, 20, 30, and 40%) that have adhered on NS-CN. Subsequently, multiple features of the nanocomposites were assayed in detail. The results illustrated that the NS-CN/FeOCl (20%) system has remarkable photoactivity in the NH4+ production reaction in comparison with the NS-CN and CN, which showed 2.5 and 8.6 higher activity, respectively. The durability of NS-CN/FeOCl (20%) system, as a substantial factor, was assayed for 5 recycles. Moreover, the effect of electron quenchers, pH of media, and solvent was studied. At last, a feasible Z-scheme mechanism for the remarkable improvement of N2 fixation efficiency was offered.

Excitons with Reverse Rectifying Characteristics for Superior Solar Photocatalysis

AbstractThis study demonstrates an inverted energy‐gradient hybrid nanoparticle architecture that supports the formation of 2D excitons in the nanoshell domain. The developed geometry places a wide‐gap semiconductor quantum dot (ZnS, Eg= 3.68 eV) at the core of the nanocomposite particle in order to funnel the photoinduced energy into the low‐gap (CdS, Eg= 2.42 eV) shell layer. This inverted band regime helps to extract the photogenerated excitons into the shell and hence increases the exciton transport quantum efficiency, hereby leading to the superior photocatalytic efficiency for photoredox reactions over the nanohybrid. To demonstrate bandgap engineering and photoinduced charge carrier delocalization, we employed steady‐state and time‐resolved emission and absorption techniques in the presence and absence of an electron quencher (4‐nitrophenol) and hole quencher (4‐methoxyphenol). The significant suppression of band‐edge emissions and the decrement of the fluorescence lifetimes demonstrated the key role of nanoshell on the transfer of photogenerated charge carriers from core to the surface of the photocatalyst. Detailed investigations of the photocatalytic activity of ZnS@CdS and kinetic study of the reactions were also carried out under solar radiation. The contribution of O2•− and •OH to photocatalytic reactions revealed respectively via luminol chemiluminescence and terephthalic acid photoluminescence techniques.

Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation

Bromate (BrO3−), an oxyhalide disinfection by-product (DBP) in drinking water, has been demonstrated to be carcinogenic and genotoxic. In the current work, metallic Ag and reduced graphene oxide (RGO) co-modified BiVO4 was successfully synthesized by a stepwise chemical method coupling with a photo-deposition process and applied in the photo-reduction of BrO3− under visible light irradiation. In this composite, metallic Ag acted as an electron donor or mediator and RGO enhanced the BrO3− adsorption onto the surface of catalysts as well as an electron acceptor to restrict the recombination of photo-generated electron-hole pairs. The Ag@BiVO4@RGO composite exhibited greater photo-reduction BrO3− performance than pure BiVO4, Ag@BiVO4 and RGO@BiVO4 under identical experimental conditions: initial BrO3− concentration 150 μg/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (λ > 420 nm). The photoluminescence spectra (PL), electron-spin resonance (ESR), photocurrent density (PC) and electrochemical impedance spectroscopy (EIS) measurements indicated that the modified BiVO4 enhanced the photo-generated electrons and separated the electron-hole pairs. The photocatalytic reduction efficiency for BrO3− removal decreased with the addition of electron quencher K2S2O8, suggesting that electrons were the primary factor in this photo-reduction process. The declining photo-reduction efficiency of BrO3− in tap water should attribute to the consumption of photo-generated electrons by coexisting anions and the adsorption of dissolved organic matter (DOM) on graphene surface. The overall results indicate a promising application potential for photo-reduction in the DBPs removal from drinking water.

Understanding the Origin of the Photocatalytic CO2 Reduction by Au- and Cu-Loaded TiO2: A Microsecond Transient Absorption Spectroscopy Study

Recent photocatalytic data for CO2 reduction by H2O using simulated sunlight have shown that, while TiO2 Evonik P25 containing Au nanoparticles (NPs; Au/P25) generates considerably higher amounts of hydrogen than methane, when P25 contains Au–Cu alloy NPs the selectivity toward methane increases dramatically. To gain insight into this photocatalytic behavior, in the present work we have performed a transient absorption spectroscopy study in the microsecond time scale of three samples, namely, Au/P25, Cu/P25, and (Au, Cu)/P25 using 355 (UV) and 532 nm (visible) lasers. The transient spectra exhibit as common features a narrower peak at about 320 nm and a broad band from 400 to 800 nm. Using oxygen as electron quencher and methanol as hole quencher, the transient signals have been assigned to charge separation. Several cases were observed, including: (i) absence of quenching attributed to the lack of accessibility of the quencher to the site, (ii) quenching of the signal, or (iii) increase of the transient signal intensity attributed to less charge recombination by removal of one of the charge carriers. Of relevance to understand the origin of the photocatalytic CO2 reduction by H2O is the quenching of the charge separated state by these two reagents. In this way, it was observed that H2O exerts a remarkable influence to the transient signal, quenching its intensity in the three samples at the two irradiation wavelengths, except for (Au, Cu)/P25 upon 532 nm excitation. Importantly, the distinctive behavior due to the presence of Cu has been attributed to the observed quenching by CO2 of the broad 400–800 nm band when excitation is performed with UV 355 nm light.

Molecule-like CdSe Nanoclusters Passivated with Strongly Interacting Ligands: Energy Level Alignment and Photoinduced Ultrafast Charge Transfer Processes

Semiconductor nanoclusters (SCNCs) are promising electronic materials for use in solid-state device fabrication, where device efficiency is strongly controlled by charge generation and transfer from SCNCs to their surroundings. In this paper we report the excited-state dynamics of molecule-like 1.6 nm diameter CdSe SCNCs, which are passivated with the highly conjugated ligand phenyldithiocarbamate. Femtosecond transient absorption studies reveal subpicosecond hole transfer (τ ≈ 0.9 ps) from a SCNC to its ligand shell based on strong electronic interaction and hole delocalization, and subpicosecond hot electron transfer (τ ≈ 0.2 ps) to interfacial states created by charge separation. A series of control experiments were performed by varying SCNC size (1.6 nm vs 2.9 nm) and photon energy of the pump laser (388 nm vs 490 nm) as well as addition of electron quencher (benzoquinone) and hole quencher (pyridine), which rules out alternative mechanisms and confirms the critical role of energy level alignment between the SCNC and its passivating ligands. Understanding such charge carrier transfer dynamics across the SCNC–organic molecule interface is very important to various physical phenomena such as hot carrier relaxation and multiple exciton generation, which together could aid in the design of high-efficiency solar cells and photocatalysts.

Double channel emission from a redox active single component quantum dot complex.

Herein we report the generation and control of double channel emission from a single component system following a facile complexation reaction between a Mn(2+) doped ZnS colloidal quantum dot (Qdot) and an organic ligand (8-hydroxy quinoline; HQ). The double channel emission of the complexed quantum dot-called the quantum dot complex (QDC)-originates from two independent pathways: one from the complex (ZnQ2) formed on the surface of the Qdot and the other from the dopant Mn(2+) ions of the Qdot. Importantly, reaction of ZnQ2·2H2O with the Qdot resulted in the same QDC formation. The emission at 500 nm with an excitation maximum at 364 nm is assigned to the surface complex involving ZnQ2 and a dangling sulfide bond. On the other hand, the emission at 588 nm-with an excitation maximum at 330 nm-which is redox tunable, is ascribed to Mn(2+) dopant. The ZnQ2 complex while present in QDC has superior thermal stability in comparison to the bare complex. Interestingly, while the emission of Mn(2+) was quenched by an electron quencher (benzoquinone), that due to the surface complex remained unaffected. Further, excitation wavelength dependent tunability in chromaticity color coordinates makes the QDC a potential candidate for fabricating a light emitting device of desired color output.

Study of the factors influencing the photo-stability of Ag@AgBr plasmonic photocatalyst

The factors that influence the photo-stability of Ag@AgBr plasmonic photocatalyst, such as light resource, electron/hole quencher, dye sensitizer, and atmosphere environment, were investigated in detail. It was revealed that Ag@AgBr can remain stable under weak light sources while it will become unstable under strong light sources. Electron quenchers are favorable to improving the stability of Ag@AgBr while hole quenchers do the opposite. Acting as a sensitizer, acid orange 7 dye is detrimental to the stability of Ag@AgBr. As for the atmospheric environment, air and oxygen-rich atmospheres are more favorable for keeping the stability of Ag@AgBr than vacuum atmosphere.

Spectroscopy and Femtosecond Dynamics of Water Soluble Type I CdSe/ZnS Core–Shell Quantum Dot

Thiol-capped type I CdSe/ZnS core–shell quantum dot nanostructures have been synthesized at low temperature in water; and then characterized by steady-state absorption and photoluminescence (PL) studies and high resolution TEM (HRTEM) measurements. On excitation of CdSe quantum dot predominantly surface state emission was detected, however on ZnS shell formation prominent exciton emission of CdSe with much higher overall quantum yield was observed. Femtosecond up-conversion measurements reveal that exciton emission found to decay much faster as compared to that of surface state emission. Lifetime of CdSe exciton emission found to increases with ZnS shell thickness. Femtosecond transient absorption studies have been carried out on these QD and core–shell material at 400 nm laser light and monitored the transients in the visible region to study charge carrier dynamics in ultrafast time scale. On laser excitation electron–hole pairs are generated which are detected by induced absorption signal for the charge carriers in visible region and immediate bleach at excitonic position for both QD and QD core–shell. Carrier quenching studies has been carried out for both CdSe and CdSe/ZnS by using benzoquinone (BQ, electron quencher) and pyridine (Py, hole quencher) suggest that although CdSe/ZnS form type I core–shell, still both electron and hole found to be leaked through ZnS shell from CdSe core.

Photochemical Evidence of Electronic Interwall Communication in Double‐Wall Carbon Nanotubes

Single- and double-wall carbon nanotubes (CNTs) having dimethylanilino (DMA) units covalently attached to the external graphene wall have been prepared by the reaction of the dimethylaminophenylnitronium ion with the corresponding CNT. The samples have been characterized by Raman and XPS spectroscopies, thermogravimetry, and high-resolution transmission electron microscopy in which the integrity of the single or double wall of the CNT and the percentage of substitution (one dimethylanilino group every 45 carbons of the wall for the single- and double-wall samples) has been determined. Nanosecond laser flash photolysis has shown the generation of transients that has been derived from the charge transfer between the dimethylanilino (as the electron donor) to the CNT graphene wall (as the electron acceptor). Importantly, the lifetime of the double-wall CNT is much shorter than that monitored for the single-wall CNT. Shorter-lived transients were also observed for the pentyl-esterified functionalized double-wall CNT with respect to the single-wall analogue in the presence of hole (CH(3)OH) and electron quenchers (O(2), N(2)O), which has led to the conclusion that the inner, intact graphene wall that is present in double-wall CNT increases the charge mobility significantly, favoring charge recombination processes. Considering the importance that charge mobility has in microelectronics, our finding suggests that double-wall CNT or two-layer graphene may be more appropriate to develop devices needing fast charge mobility.

Broadband Spectral Probing Revealing Ultrafast Photochemical Branching after Ultraviolet Excitation of the Aqueous Phenolate Anion

Electron photodetachment from the aromatic anion phenolate excited into the π-π* singlet excited state (S(1)) in aqueous solution is studied with ultrafast transient absorption spectroscopy with a time resolution of better than 50 fs. Broad-band transient absorption spectra from 300 to 690 nm are recorded. The transient bands are assigned to the solvated electron, the phenoxyl radical, and the phenolate S(1) excited state, and confirmation of these assignments is achieved using both KNO(3) as electron quencher and time-resolved fluorescence to measure singlet excited state dynamics. The phenolate fluorescence lifetime is found to be short (∼20 ps) in water, but the fast decay is only in part due to the electron ejection channel from S(1). Using global target analysis, two electron ejection channels are identified, and we propose that both vibrationally hot S(1) state and the relaxed S(1) state are direct precursors for the solvated electron. Therefore, electron ejection is found just to compete with picosecond time scale vibrational relaxation and electronic radiationless decay channels. This contrasts markedly with <100 fs electron detachment processes for inorganic anions.

Charge carrier dynamics in thiol capped CdTe quantum dots

We report the ultrafast charge carrier relaxation dynamics of mercaptopropionic acid capped CdTe quantum dot (QD) using femtosecond transient absorption spectroscopy by exciting the particles with 400 nm laser light and monitoring the transients in the visible to near IR region. Cooling dynamics and population dynamics in different quantized states of the charge carriers were monitored by following the growth kinetics of the bleach at different excitonic positions. The cooling time second and first excitonic states were found to be 150 fs and 500 fs, respectively, which increases non-linearly with its size. Defect states of QD surface play an important role in the cooling dynamics of the charge carriers. Quenching studies have been carried out to find out cooling and trapping dynamics of the individual charge carriers. Electron and hole cooling time were measured to be 700 fs and 150 fs for the first excitonic state using quenchers. Trapping dynamics of electron and hole have been determined by monitoring transient signal at 1000 nm and by using hole and electron quencher, respectively. Electron and hole trapping times have been found to be 700 fs and 1 ps, respectively, in CdTe QD.

Photo-degradation of curcumin in the presence of TiO2 nanoparticles: Fundamentals and application

Photo-degradation of curcumin in the presence of TiO2 nanoparticles has been studied in water–methanol and water–acetonitrile mixed solvents. Curcumin was found to form charge transfer (CT) complexes with TiO2 nanoparticles. The binding constant of the CT complexes has been determined. Curcumin was found to undergo photo-degradation under UV–vis and only visible light irradiations. Photo-degradation was investigated in the presence of external electron quenchers like methyl violegen and dissolved oxygen and hole quenchers like iodide ions in a de-aerated condition. The presence of oxygen was found to enhance the photo-degradation processes. The photo-degradation was found to be completely quenched in the presence of iodide ions in both the solvent mixtures in a de-aerated condition. A reaction pathway for the photo-degradation of curcumin in the presence of TiO2 nanoparticles has been proposed. This study has been successfully applied to remove the yellow turmeric stain from cotton fabrics.