Photoreaction Process Research Articles

Direct Observation of the Triplet Metal-Centered State in [Ru(bpy)3]2+Using Time-Resolved Infrared Spectroscopy

[Ru(bpy)3]2+ is well-known as a prototype for the Ru(II) complexes used in a wide variety of photofunctional materials. The triplet metal-centered (3MC) state is important in this complex, since it dominates the phosphorescence lifetime and photoreaction processes. Despite this, the 3MC state has not yet been observed by spectroscopic methods. In the present study, we demonstrated that time-resolved infrared vibrational spectroscopy enables observations of the 3MC state. A vibrational band at 1599 cm−1 was found to exhibit unique temporal behavior that differed from that of other bands assignable to the triplet metal-to-ligand charge-transfer (3MLCT) state. This unique behavior was assessed under various experimental conditions and it was concluded that the band arises from the short-term population (∼23 ps) of the 3MC state during relaxation to the bottom of the 3MLCT state. These results agree with [Fe(bpy)3]2+ spectra, which show that the 5MC state is the most stable excited state.

Facet-dependent photocatalytic performance of TiO2: A DFT study

The facet-dependent photocatalytic activity of TiO2 has been found in CO2 photoreduction. However, which facet is more reactive and the nature of its dramatically different activity are still in the great debate. Utilizing density functional theory, two key photocatalytic steps (photo-generated electrons transfer and photoreaction) are investigated on anatase TiO2 (001) and (101) facets to unravel such puzzles. The photo-generated electrons transfer (within the bulk, from bulk to surface and across the surface) has similar transfer barrier, indicating that the experimentally observed different activity may not be dominated by photo-generated electrons transfer, and the photoreaction process could be the rate-limiting step. The possible CO2 photoreduction reaction paths have been extensively examined and large barrier difference on two facets is obtained. The facts that the higher conduction band minimum can generate more strongly reductive electrons, the lower reaction barrier can lead to the faster reaction rate and the product adsorption can have more suitable properties give rise to a higher activity on (101) facets than that on (001) facets.

Synergistic photocatalysis of Cr(VI) reduction and 4-Chlorophenol degradation over hydroxylated α-Fe2O3 under visible light irradiation

A series of Fe2O3 materials with hydroxyl are synthesized in different monohydric alcohol (C2–C5) solvents by solvothermal method and characterized by XRD, BET, XPS, TG and EA. The amount of hydroxyl is demonstrated to be emerged on the surface of the as-synthesized Fe2O3 particles and their contents are determined to be from 7.99 to 3.74wt%. The Cr(VI) reduction experiments show that the hydroxyl content of Fe2O3 samples exacts great influence on the photocatalytic activity under visible light irradiation (λ>400nm) and that the Fe2O3 sample synthesized in n-butyl alcohol exhibits the optimal photocatalytic activity. The synergistic photocatalysis for 4-Chlorophenol (4-CP) degradation and Cr(VI) reduction over above Fe2O3 sample is further investigated. The photocatalytic ratio of Cr(VI) reduction are enhanced from 24.8% to 70.2% while that of 4-CP oxidation are increased from 13.5% to 47.8% after 1h visible light irradiation. The Fe2O3 sample keeps good degradation rates of mixed pollutants after 9 runs. The active oxygen intermediates O2−, OH and H2O2 formed in the photoreaction process are discovered by ESR measurement and UV–vis test. The photocatalytic degradation mechanism is proposed accordingly.

Photo-Degradation of Reactive Yellow 14 Dye (A Textile Dye) Employing ZnO as Photocatalyst

In this paper, the reactive yellow 14 dye solution was removed from aqueous solution in the presence of commercial ZnO (mean crystallite size is 44.116 nm) under the UV A light. The decolourization of dye process was obeyed to pseudo-first orderkinetics. The optimum conditions of decolourization for this dye such as: initial dye concentration 50 mg/L, best dose of ZnO 350 mg/100mL and initial pH of aqueous solution of dye 6.75 were studied. Activation energies for dye were found to be 27.244 kJmol-1. The photoreaction process was observed to be endothermic reaction and less randomness.

Redox-induced reversible intramolecular carbon–nitrogen bond formation of an azopyridylruthenium complex: Control of carbonyl ligand photoreactivity caused by structural change of the complex

Intramolecular carbon–nitrogen bond formation between a carbonyl and proximal azopyridine ligand by ligand-based reduction led to the formation of a novel ruthenium complex containing a bidentate carbamoyl ligand. Reversible C–N bond formation and cleavage reactions were confirmed by chemical and electrochemical redox reactions. The change in character of the CO moiety based on intramolecular structural change affects the CO ligand photoreactivity. The molecular structures of the carbamoyl compound and photoreaction products were determined by X-ray crystallography to confirm the present photoreaction process.

One-pot solvothermal synthesis of highly efficient, daylight active and recyclable Ag/AgBr coupled photocatalysts with synergistic dual photoexcitation

Abstract Efficient light harvesting has been considered to be critical for manipulating the photocatalytic behavior of photocatalysts, because it directly determines the generation of reactive redox charge carriers involved in photoreaction process. In this study, we present a successful example on efficient conversion of solar energy by Ag/AgBr coupled photocatalysts that hold unique synergistic dual photoexcitation. A series of Ag/AgBr coupled photocatalysts were controllably synthesized by an easily manipulated mild solvothermal process. The physicochemical properties of the as-prepared Ag/AgBr coupled photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). The results showed the solvothermal reaction time played key role for control of crystalline structure, morphology, composition, and visible light absorption ability of the resulting photocatalysts. The as-prepared Ag/AgBr coupled photocatalysts exhibited remarkable photocatalytic performance and good reusability for decomposing organic dyes in aqueous solution under the irradiation of commercial 20 W cool daylight fluorescent lamp, owing to the synergistic dual photoexcitation cooperating between plasmonic Ag nanoparticles and narrow-band-gap AgBr.

In-situ FTIR spectroscopic study of the mechanism of photocatalytic reduction of NO with methane over Pt/TiO2 photocatalysts

Photo-selective catalytic reduction of nitric oxide (NO) with methane (CH4) over TiO2 and Pt/TiO2 photocatalysts was studied at reaction temperatures of 25, 50, and 100 °C. The activity of Pt/TiO2 in NO reduction was better than that of TiO2. Conversion of NO by use of Pt/TiO2 and UV irradiation was up to 86.4 %. In-situ Fourier-transform infrared spectroscopy was successfully used to monitor the photoreaction process on TiO2 and Pt/TiO2 photocatalysts. During irradiation with UV light, bidentate nitrite disappeared and bidentate nitrate, monodentate nitrate, and isocyanate, an important intermediate, were generated. Adsorbed NH2 was found to be the final product of NO reduction after UV irradiation. We concluded that NO could be effectively reduced by CH4 under light irradiation at temperatures below 100 °C. A possible reaction mechanism is proposed on the basis of the intermediates and products generated by the photocatalyst under UV light irradiation.

The role of organic ligands in iron cycling and primary productivity in the Antarctic Peninsula: A modeling study

Iron (Fe) is the limiting nutrient for primary productivity in the Southern Ocean, with much of the dissolved iron (dFe) bound to organic ligands or colloids. A Fe model for the Southern Ocean (SOFe) is developed to understand the role of bacteria and organic ligands in controlling Fe cycling and productivity. The model resolves the classical food web and microbial loop, including three types of nutrients (N, Si, Fe) and two types of Fe ligands. Simulations of the zero-dimensional (0-D) model are calibrated with detailed results of shipboard grow-out incubation experiments conducted with Antarctic Peninsula phytoplankton communities during winter 2006 to provide the best estimate of key biological parameters. Then a one-dimensional (1-D) model is developed by coupling the biological model with the Regional Oceanic Modeling System (ROMS) for a site on the Antarctic Peninsula shelf, and the model parameters are further calibrated with data collected from two surveys (summer 2004 and winter 2006) in the area. The results of the numerical simulations agree reasonably well with observations. An analysis of the 1-D model results suggests that bacteria and organic ligands may play an important role in Fe cycling, which can be categorized into a relatively fast mode within the euphotic zone dominated by photo-reactions (summer d Fe residence time about 600 days) and complexation and a slow mode below with most of the dFe biologically complexed (summer dFe residence time >10 years). The dFe removal from the euphotic zone is dominated by colloidal formation and further aggregations with additional contribution from biological uptake, and an increase of organic ligands would reduce Fe export. The decrease of Fe removal rate over depth is due to the continuous dissolution and remineralization of particulate Fe. A number of sensitivity experiments are carried out for both 0-D and 1-D models to understand the importance of photo-reactive processes in primary productivity, bacterial activity, Fe speciation, and dFe residence time within the euphotic zone. The bio-availability of ligand-bound Fe (FeL) is critical to modeled high primary productivity, which is consistent with both shipboard measurements and field observations. In addition, model productivity is sensitive to photoreaction rates if FeL is not directly available for phytoplankton uptake.

One-step nano-engineering of dispersed Ag–ZnO nanoparticles' hybrid in reduced graphene oxide matrix and its superior photocatalytic property

Reduced graphene oxide (rGO) has been engineered with a hybrid of dispersed Ag and ZnO nanoparticles by a one-step hydrothermal technique using graphene oxide, AgNO3 and Zn(CH3COO)2 precursors without adding any external toxic reagent. Formation of the Ag–ZnO–rGO hybrid is confirmed from X-ray diffractometry, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The hybrid shows an enhanced and faster ultraviolet photocatalytic property i.e. 97.2% degradation of methyl orange in 90 minutes as compared to the values of 56%, 84% and 60% by bare ZnO, Ag–ZnO and ZnO–rGO, respectively. The enhanced photocatalytic property is due to an efficient charge transfer process from ZnO to both Ag and rGO. This result would be beneficial for synthesizing efficient ZnO-based ternary photocatalysts with different combinations of metal and graphene, and understanding their photocatalytic performance in photoreaction processes.

Photochemical Engineering of Graphene Oxide Nanosheets

Many unique properties of graphene oxide (GO) strongly depend on the oxygenated functional groups and morphologies. Here, the photoreaction process is demonstrated to be very useful to control these factors. We report the fast, simple production of nanopores in porous GO via photoreaction in O2 under UV irradiation at room temperature. Quantitative analysis using X-ray photoelectron spectroscopy showed that nanopores were produced in areas of oxygenated groups (sp3 carbon bonds), creating porous reduced graphene oxide (rGO). The photoreaction mechanism was proposed on the basis of changes in the number of oxygenated groups. Proton conduction occurred at the basal plane of epoxide groups in virgin GO, even at low humidity, and at carboxyl groups for porous rGO at high humidity. Thus, GO and rGO samples with various morphologies, oxygenated functional groups, and conduction types can be easily fabricated by controlling the photoreaction conditions.

Cell adhesion control on photoreactive phospholipid polymer surfaces

Non-invasive and effective cell recovery from culture substrates is important for the passage and characterization of cells. In this study, a photoreactive polymer surface, which uses UV-irradiation to control substrate cell adhesion, was prepared. The photoreactive phospholipid polymer (PMB-PL) reported herein, was composed of a both 2-methacryloyloxyethyl phosphorylcholine (MPC) unit as a cytocompatible unit and methacrylate bearing a photolabile nitrobenzyl group. The PMB-PL polymer was used to coat a cell culture substrate thus affording a photoreactive surface. Surface analysis of the PMB-PL coating indicated a strong photoresponse owing to the sensitivity of the PL unit. Before light exposure, the PMB-PL surface provided cell adhesion. Following UV-irradiation, the PMB-PL coating was converted to a neutral ζ-potential and hydrophilic surface. The photoreactive surface conversion process allowed for the detachment of adhered cells from the PMB-PL surface while maintaining cell viability. This study demonstrates the promise and significance of the PMB-PL photoreactive surface as a method to control cell attachment and detachment for cell function investigation.

Field‐induced photo‐reactive alignment technology for the vertical‐alignment liquid‐crystal mode

Abstract— An advanced vertical‐alignment liquid‐crystal (VA‐LC) technology based on field‐induced photo‐reactive alignment (FPA) as an advanced alignment mode for VA is proposed. FPA realizes uniform alignment and a faster rising response time, especially at high voltage. This technology can generate a pre‐tilt angle only by using photo‐reactive alignment material so that the tact time is shorter and the long‐term reliability is higher than that of conventional photo‐reactive processes, which require additional photo‐reactive monomers. The advanced hybrid FPA was developed by adopting both the tilted alignment with a pre‐tilt angle and conventional vertical alignment. By using an advanced hybrid structure, the response time and contrast ratio can be further improved.

Metastable polymorphic form of isopropylbenzophenone derivative directly obtained by the solid-state photoreaction investigated by ab initiopowder X-ray diffraction analysis

The crystalline state of 2-(2,4,6-triisopropybenzoyl)((S)-1-phenylethyl)benzamide (1) is known to undergo a diastereospecific Norrish type II photocyclization under UV irradiation, giving a single photoproduct (R,S)-cyclobutenol (2). Its polycrystalline form (2A) has a different X-ray diffraction pattern from the known polymorph 2B, which is obtained from recrystallization of the photoproduct. Such a polymorphic phenomenon, which is the result of a solid-state photoreaction, is, in itself, highly interesting and the structure of the photoproduct 2A should directly lead to the photoreaction mechanism. Thus, the crystal structure of 2A has been directly determined from the powder X-ray diffraction data. Interestingly, the crystal packing has been retained during the photoreaction process and, although the powder X-ray diffraction pattern is significantly different, there are only minor structural changes. The comparison of the crystal structures of 1 and 2A reveals the photoreaction mechanism. The lattice energy calculations of the polymorphic forms of 2A and 2B reveals that 2A, which is obtained only by the solid-state photoreaction, is less stable than 2B, which is why it is not reformed on recrystallization.

Fe2O3-Pillared Rectorite as an Efficient and Stable Fenton-Like Heterogeneous Catalyst for Photodegradation of Organic Contaminants

An efficient Fe(2)O(3)-pillared rectorite (Fe-R) clay was successfully developed as a heterogeneous catalyst for photo-Fenton degradation of organic contaminants. X-ray diffraction analysis and high-resolution transmission electron microscope analysis clearly showed the existence of the Fe(2)O(3) nanoparticles in the Fe-R catalyst. The catalytic activity of the Fe-R catalyst was evaluated by the discoloration and chemical oxygen demand (COD) removal of an azo-dye rhodamine B (RhB, 100 mg/L) and a typical persistent organic pollutant 4-nitrophenol (4-NP, 50 mg/L) in the presence of hydrogen peroxide (H(2)O(2)) under visible light irradiation (lambda > 420 nm). It was found that the discoloration rate of the two contaminants was over 99.3%, and the COD removal rate of the two contaminants was over 87.0%. The Fe-R catalyst showed strong adsorbability for the RhB in the aqueous solution. Moreover, the Fe-R catalyst still showed good stability for the degradation of RhB after five recycles. Zeta potential and Fourier transform infrared spectroscopy were used to examine the photoreaction processes. Finally, a possible photocatalytic mechanism was proposed.

Electronic Spectra of Two Long-Lived Photoproducts: Double-Proton Transfer in 7-Hydroxyquinoline Dimer in a 2-Methyltetrahydrofuran Glass Matrix

Photoreactions of 7-hydroxyquinoline (7-HQ) in low-temperature (77-100 K) 2-methyltetrahydrofuran glass matrices are investigated using electronic spectroscopy. We have observed fluorescence excitation and fluorescence spectra of two long-lived species generated by irradiation of UV light (230-400 nm). The dominant species responsible for the fluorescence spectrum between 470 and 600 nm was assigned to the S(1)-->S(0) (pipi*) transition of the keto form of cyclic 7-HQ dimer [(7-HQ)(2)] produced by excited-state double-proton transfer, the corresponding S(1)-S(0) fluorescence excitation spectrum of which was detected between 360 and 510 nm. Temperature dependence of the fluorescence excitation spectra showed the occurrence of keto --> enol isomerization in the S(0) state of (7-HQ)(2) due to a back double-proton transfer. A very slow rate for the keto --> enol isomerization implies that the potential barrier height for the back double-proton transfer reacion is substantially high. Theoretical calculations at the MP2/aug-cc-pVDZ level of theory indicate that the enol and keto forms of cyclic (7-HQ)(2) are nonplanar, therefore a large change in the geometry is necessary for the back double-proton transfer. A second long-lived species that emits between 410 and 600 nm has been tentatively assigned to the D(3)(2A'') --> D(0)(1A'') transition of the 7-quinolinoxyl radical on the basis of calculated electronic transition energies for possible candidates obtained by MS-CASPT2/aug-cc-pVDZ level calculations as well as IR study of 7-HQ in argon matrices [Sekine, M.; Nagai, Y.; Sekiya, H.; Nakata, M. J. Phys. Chem. A 2009, 113, 8286]. Photoreaction processes leading to the two long-lived species have been discussed.

Photoreactions and Structural Changes of Anabaena Sensory Rhodopsin

Anabaena sensory rhodopsin (ASR) is an archaeal-type rhodopsin found in eubacteria. The gene encoding ASR forms a single operon with ASRT (ASR transducer) which is a 14 kDa soluble protein, suggesting that ASR functions as a photochromic sensor by activating the soluble transducer. This article reviews the detailed photoreaction processes of ASR, which were studied by low-temperature Fourier-transform infrared (FTIR) and UV-visible spectroscopy. The former research reveals that the retinal isomerization is similar to bacteriorhodopsin (BR), but the hydrogen-bonding network around the Schiff base and cytoplasmic region is different. The latter study shows the stable photoproduct of the all-trans form is 100% 13-cis, and that of the 13-cis form is 100% all-trans. These results suggest that the structural changes of ASR in the cytoplasmic domain play important roles in the activation of the transducer protein, and photochromic reaction is optimized for its sensor function.

Degradation of 2, 4-D acid using Mn2+ as catalyst under UV irradiation

In this paper, the oxidative degradation of 2, 4-dichlorophenoxyacetic acid (2, 4-D) using Mn2+/H2O2 reagent under UV irradiation was studied. The results show that 2, 4-D was degraded more completely in Mn2+/H2O2 solution than traditional Fenton solutions. The effects of the concentration of Mn2+, H2O2 and pH were also investigated. And under the optimal condition of \( c_{Mn^{2 + } } \) 1.48×10−4 mol/L, \( c_{H_2 O_2 } \) 8.99×10−5 mol/L and pH 3.38, the formation of ·OH was the most, both the decomposition rate of H2O2 and the degradation rate of 2, 4-D were the fastest. In addition, the photoreaction process was monitored using spin-trapping electron paramagnetic resonance (EPR), and the results indicated that the oxidative process was predominated mainly by the hydroxyl radical (·OH) gennerated in the system.

Photodegradation of bisphenol-A in a batch TiO 2 suspension reactor

In this work, the photocatalytic behaviors of bisphenol-A (BPA), which has been listed as one of endocrine disrupting chemicals, were carried out in a batch TiO 2 suspension reactor. The photodegradation efficiency has been investigated under the controlled process parameters including initial BPA concentration (i.e., 1–50 mg L −1), TiO 2 dosage (i.e., 5–600 mg/200 cm 3), initial pH (i.e., 3–11), and temperature (i.e., 10–70 °C). It was found that the optimal conditions in the photoreaction process could be coped with at initial BPA concentration = 20 mg L −1, TiO 2 dosage = 0.5 g L −1 (100 mg/200 cm 3), initial pH = 7.0, and temperature = 25 °C. According to the Langmuir–Hinshelwood model, the results showed that the photodegradation kinetics for the destruction of BPA in water also followed the first-order model well. The apparent first-order reaction constants ( k obs), thus obtained from the fittings of the model, were in line with the destruction-removal efficiencies of BPA in all the photocatalytic experiments. Based on the intermediate products identified in the study, the possible mechanisms for the photodegradation of BPA in water were also proposed in the present study.

Identification of FTIR Bands Due to Internal Water Molecules around the Quinone Binding Sites in the Reaction Center from Rhodobacter sphaeroides

The bacterial reaction center (RC) is a membrane protein complex that performs photosynthetic electron transfer from a bacteriochlorophyll dimer to quinone acceptors Q(A) and Q(B). Q(B) accepts electrons from the primary quinone, Q(A), in two sequential electron transfer reactions coupled to uptake of a proton from solution. It has been suggested that water molecules along the proton uptake pathway are protonated upon quinone reduction on the basis of FTIR difference spectra [Breton, J., and Nabedryk, E. (1998) Photosynth. Res. 55, 301-307]. We examined the possible involvement of water molecules in the photoreaction processes by studying (18)O water isotope effects on FTIR difference spectra resulting from formation of Q(A)(-) and Q(B)(-). Continuum bands in D(2)O due to Q(B)(-) formation in the 2300-1800 cm(-1) region did not show spectral shifts by (18)O water in the wild-type (WT) RC, suggesting that these bands do not originate from (protonated) water. In contrast, the Q(B)(-)/Q(B) spectrum of the EQ-L212 mutant RC showed a spectral shift of a band near 2100 cm(-1) due to (18)O water substitution, consistent with protonation of internal water. FTIR shifts due to (18)O water were also observed following formation of Q(A)(-) and Q(B)(-) in the spectral region of 3700-3500 cm(-1) characteristic of weakly hydrogen bonded water. The water responsible for the Q(B)(-) change was localized near Glu-L212 by spectral shifts in mutant RCs. The weakly hydrogen bonded water perturbed by quinone reduction may play a role in stabilizing the charge-separated state.

Three-dimensional micropatterning of bioactive hydrogels via two-photon laser scanning photolithography for guided 3D cell migration

Micropatterning techniques that control three-dimensional (3D) arrangement of biomolecules and cells at the microscale will allow development of clinically relevant tissues composed of multiple cell types in complex architecture. Although there have been significant developments to regulate spatial and temporal distribution of biomolecules in various materials, most micropatterning techniques are applicable only to two-dimensional patterning. We report here the use of two-photon laser scanning (TPLS) photolithographic technique to micropattern cell adhesive ligand (RGDS) in hydrogels to guide cell migration along pre-defined 3D pathways. The TPLS photolithographic technique regulates photo-reactive processes in microscale focal volumes to generate complex, free from microscale patterns with control over spatial presentation and concentration of biomolecules within hydrogel scaffolds. The TPLS photolithographic technique was used to dictate the precise location of RGDS in collagenase-sensitive poly(ethylene glycol- co-peptide) diacrylate hydrogels, and the amount of immobilized RGDS was evaluated using fluorescein-tagged RGDS. When human dermal fibroblasts cultured in fibrin clusters were encapsulated within the micropatterned collagenase-sensitive hydrogels, the cells underwent guided 3D migration only into the RGDS-patterned regions of the hydrogels. These results demonstrate the prospect of guiding tissue regeneration at the microscale in 3D scaffolds by providing appropriate bioactive cues in highly defined geometries.