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Composite materials based on active carbon/TiO2 for photocatalytic water purification
摘要： The present work describes the preparations of active carbon (AC) – titania composites with different AC/TiO2 ratio, their characterization using XRD, BET and SEM and evaluation of adsorption capacity and photocatalytic activity in aqueous solution using azo-dye Acid Orange 7 (AO7). Composite materials based on AC/TiO2 were prepared from commercial active carbon (1737 m2/g) and TiO2 (P25, 45 m2/g) materials by the mixing method. The studied parameters were the ratio of AC/TiO2, hydrothermal treatment and milling of as-prepared composites. The composites show increased BET surface area proportional to the content of AC in the material. The disappearance of AO7 is due to the combination two processes, e. g. adsorption and photocatalytic oxidation which takes place in parallel. Thus the overall removal of AO7 has been corrected on adsorption (measured in dark) to obtain the rate of AO7 disappearance due to photocatalytic oxidation (PO). The optimum ratio of AC/TiO2 was found to be 0.23 where PO rate is only slightly lower than that for P25 and overall AO7 removal is twice higher than for P25 itself. The less intensive (low-frequency) milling of the composite results in the decrease of carbon particle size, increase in AO7 adsorption and decline in the PO of AO7. More intensive milling (high-frequency) results in the decrease of the anatase content, appearance of the small amount of brookite and almost negligible PO rate of AO7. Irradiation of low-frequency milled AC/TiO2 composite in aqueous suspensions resulted in the generation of a comparable concentration of hydroxyl radical spin-adduct (?DMPO-OH) as non-milled composite, high-frequency milled composite revealed substantially lower ?DMPO-OH concentration which can be explained by the increased concentration of carbon-centered radicals in AC acting as scavengers of photogenerated electrons.
关键词： adsorption,Active carbon,P25,EPR spectroscopy,AO7,photocatalytic oxidation
更新于2025-09-23 15:22:29
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Effect of Electron-Nuclear Hyperfine Interactions on Multiple Quantum Coherences in Photogenerated Covalent Radical (Qubit) Pairs
摘要： Ultrafast photo-driven electron transfer reactions starting from an excited singlet state in an organic donor-acceptor molecule can generate a spin-correlated radical pair (RP) with an initially entangled spin state that may prove useful as a two-qubit pair in quantum information protocols. Here we investigate the effects of modulating electron-nuclear hyperfine coupling by rapidly transferring an electron between two equivalent sites comprising the reduced acceptor of the RP. A covalent electron donor-acceptor molecule including a tetrathiafulvalene (TTF) donor, a 4-aminonaphthalene-1,8-imide (ANI) chromophoric primary acceptor, and a m-xylene bridged cyclophane having two equivalent pyromellitimides (PI2), TTF-ANI-PI2, as a secondary acceptor was synthesized along with the analogous molecule having one pyromellitimide (PI) acceptor, TTF-ANI-PI. Photoexcitation of ANI within each molecule results in sub-nanosecond formation of TTF+?-ANI-PI-? and TTF+?-ANI-PI2 -?. The effect of reducing electron-nuclear hyperfine interactions in TTF+?-ANI-PI2 -? relative to TTF+?-ANI-PI-? on decoherence of multiple-quantum coherences has been measured by pulse-EPR spectroscopy. This contribution is especially relevant in the absence of modulation of exchange or dipolar interactions, as with the RP at a fixed distance in the molecules in this work. The theoretical prediction of the contribution from an ensemble of hyperfine interactions to decoherence in these RPs is shown to be less than the full width at half maximum of the quantum beat frequencies measured experimentally. Pulse bandwidth and off-resonant excitation by square microwave pulses are proposed as larger contributors to decoherence in these molecules than the hyperfine interactions, and specific pulse shapes relevant to arbitrary waveform generation are introduced.
关键词： pulse-EPR spectroscopy,photogenerated covalent radical pairs,electron-nuclear hyperfine interactions,multiple quantum coherences,quantum information protocols
更新于2025-09-23 15:21:21
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Guest Inclusion Modulates Concentration and Persistence of Photogenerated Radicals in Assembled Triphenylamine Macrocycles
摘要： Substituted triphenylamine (TPA) radical cations show great potential as oxidants and as spin containing units in polymer magnets. Their properties can be further tuned by supramolecular assembly. Here, we examine how the properties of photogenerated radical cations, intrinsic to TPA macrocycles, are altered upon their self-assembly into 1D columns. These macrocycles consist of two TPAs and two methylene ureas which drive the assembly into porous organic materials. Advantageously, upon activation the crystals can undergo guest exchange in a single-crystal-to-single-crystal transformation generating a series of isoskeletal host-guest complexes whose properties can be directly compared. Photoinduced electron transfer, initiated using 365 nm LED’s, affords radicals at room temperature as observed by EPR spectroscopy. The line shape of the EPR spectra and the quantity of radicals can be modulated by both polarity and heavy atom inclusion of the encapsulated guest. These photogenerated radicals are persistent, with half-lives between 1-7 days and display no degradation upon radical decay. Re-irradiation of the samples can restore the radical concentration back to a similar maximum concentration, a feature that is reproducible over several cycles. EPR simulations of a representative spectrum indicate two species, one containing two N hyperfine interactions and an additional broad signal with no resolvable hyperfine interaction. Intriguingly, TPA analogs without bromine substitution also exhibit similar quantities of photogenerated radicals, suggesting that supramolecular strategies can enable more flexibility in stable TPA radical structures. These studies will help guide the development of new photoactive materials.
关键词： photoinduced electron transfer,supramolecular assembly,radical cations,triphenylamine,EPR spectroscopy
更新于2025-09-12 10:27:22