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Graphical abstract Highlights • Noble-metal-free CdS/Ni 9 S 8 /Al 2 O 3 catalyst was developed for the photoreduction of CO 2. • The Al 2 O 3 support enhanced the separation of the photogenerated electron-hole pairs. • The Al 2 O 3 support promoted the CO 2 adsorption and activation on the catalyst. • The Al 2 O 3 support facilitated the production of protons for reducing CO 2. Abstract Noble-metal-free photocatalysts are promising for economic and efficient conversion of solar energy into chemical energies. Herein, a highly efficient CO evolution, with an evolution rate of 12.1 μmol h−1, is achieved from the visible-light-driven photoreduction of CO 2 with H 2 O on a noble-metal-free CdS/Ni 9 S 8 /Al 2 O 3 photocatalyst. The CO evolution on CdS/Ni 9 S 8 /Al 2 O 3 is comparable to that on the noble-metal-based CdS/Pt/Al 2 O 3 photocatalyst (10.6 μmol h−1), but 11 times higher than that on the Al 2 O 3 -free CdS/Ni 9 S 8 (1.1 μmol h−1) photocatalyst. The Al 2 O 3 support facilitates the separation of the photogenerated electron-hole pairs, CO 2 adsorption and production of protons for reducing CO 2 , thus enhancing the CO evolution. These results will open a new door for rationally fabricating efficient noble-metal-free photocatalysts, and favor the transition to solar energy economy. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MoO 3 @ZIF-8 core-shell nanorods were prepared by a facile method. • Properties of MoO 3 @ZIF-8 core-shell nanorods were confirmed by imperative measurements. • Enhanced photocatalytic performance were measured under the same condition. • The mechanism of the enhanced photocatalytic performance was discussed in detail. Abstract Recently, hexavalent chromium (Cr(VI)) in wastewater has become a threat to the ecosystem and human health. The synthesis of high-performance and recyclable photocatalysts still remains a challenge. The photoreduction efficiency of Cr(VI) is inhibited by the high rate of recombination of electron-hole pairs and the low adsorption capacity of Cr(VI). In this study, three-dimensional (3D) MoO 3 /ZIF-8 core-shell nanorod composite photocatalysts were prepared via a facile two-step method and applied to the reduction of Cr(VI). The chemical state of the elements, microstructure, surface elements, and optical properties of the MoO 3 /ZIF-8 core-shell nanorods were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy. The as-prepared MoO 3 @ZIF-8 catalysts displayed superior photocatalytic activity for Cr(VI) reduction under visible light, compared to the pure ZIF-8 and MoO 3 nanowires. Further, MoO 3 @ZIF-8 (with 15% of ZIF-8) exhibited the best photocatalytic activity, and promoted 100% reduction of Cr(VI) (15 mg L−1) within 45 min. The 3-D core-shell structure not only provided a large surface area, but also separated the electron-hole pairs effectively. The photocatalytic activity of the composite remained almost unchanged after four cycles. The mechanism of Cr(VI) reduction is also discussed in detail. [ABSTRACT FROM AUTHOR]

Deoxygenation of graphene oxide is a low-cost and effective way to yield graphene (i.e., reduced graphene oxide - RGO) for many applications. However, choices of reduction approach and reduction time need consideration due to damaging pre-existing materials on electronic devices. Here, we found a facile and eco-friendly route that was based on the photo-oxidation of ethanol (diluted in water) on a catalytic TiO 2 film to rapidly induce the formation of RGO within 15 min under UV (20 mW/cm 2 ) or sun lights (1 sun = 100 mW/cm 2 ). Our reduction route was indirectly activated by chain reactions of ethanol and TiO 2 (so-called domino effect) because the GO deoxygenation occurred even when the samples were placed around and not in contact with TiO 2 film. To obtain the highest reduction, the samples should stay on the catalytic film to receive lights for activation and acceleration of reactions. Furthermore, effects of exposure time (1–20 min), ethanol concentration (14.3–100%), and light intensity on RGO quality explored with the use of chemiresistive devices. The results of demonstrative sensing measurements towards NO 2 and NH 3 indicate that our method is promising for electrical applications using solution processable RGO. [ABSTRACT FROM AUTHOR]

The anaerobic photocatalysed reduction of methylene blue, MB, by glycerol to leuco methylene blue, LMB, is studied using UV-absorbing, P25 TiO 2 , and visible-absorbing, CdS, semiconductor powder particles as the photosensitizer. In both cases, the photo-reductive bleaching of the dye to LMB, is very rapid, typically <2 min. The photobleaching of the MB is readily and simply reversed in the dark by allowing air into the system, so as to let the ambient oxygen to oxidise the photogenerated LMB back to its original blue, oxidized form, MB. Action spectra are recorded for both systems and reveal no evidence of dye-sensitisation, nor dye photolysis over the time scale of the reaction (i.e. ca. 2 min). Instead, the action spectra exhibit spectral profiles that match very well that of the diffuse reflectance spectra of the respective semiconductor photocatalysts. The MB/glycerol system appears to offer a simple, quick, unambiguous way to assess the photocatalytic activity of both visible and UV absorbing photocatalyst powders using a dye, such as MB. [ABSTRACT FROM AUTHOR]

Zinc sulfur quantum dots‐reduced graphene oxide (ZnS QDs‐rGO) composites are successfully synthesized by a one‐step hydrothermal method. The ZnS QDs are well scattered on the surface of the wrinkled rGO with smaller particle size compared with initial ZnS QDs. The influence of the content of rGO in composites on the photocatalytic effect is also investigated in detail. The ZnS QDs‐1.0% rGO has the highest photocatalytic activity and the degradation kinetics of methylene blue is more consistent with the zero order kinetic model than the pseudo first order kinetic model in this experiment. The mechanism for the enhancement of photocatalytic activity is mainly due to promoting separation of the photogenerated carriers with the introduction of rGO and the increase in specific surface area of ZnS QDs due to decrease in size. These results reveal that the effective synergistic action between ZnS QDs and rGO is the key factor to determine the photocatalytic degradation efficiency of the ZnS QDs‐rGO composites. [ABSTRACT FROM AUTHOR]

Mercury (Hg) in the Arctic is a significant concern due to its bioaccumulative and neurotoxic properties, and the sensitivity of Arctic environments. Previous research has found high levels of Hg in snowpacks with high chloride (Cl − ) concentrations. We hypothesised that Cl − would increase Hg retention by decreasing Hg photoreduction to Hg(0) in melted Arctic snow. To test this, changes in Hg photoreduction kinetics in melted Alert, NU snow were quantified with changing Cl − concentration and UV intensity. Snow was collected and melted in Teflon bottles in May 2014, spiked with 0–10 μg/g Cl − , and irradiated with 3.52–5.78 W·m − 2 UV (280–400 nm) radiation in a LuzChem photoreactor. Photoreduction rate constants ( k ) (0.14–0.59 hr − 1 ) had positive linear relationships with [Cl − ], while photoreduced Hg amounts (Hg(II) red ) had negative linear relationships with [Cl − ] (1287–64 pg in 200 g melted snow). Varying UV and [Cl − ] both altered Hg(II) red amounts, with more efficient Hg stabilisation by Cl − at higher UV intensity, while k can be predicted by Cl − concentration and/or UV intensity, depending on experimental parameters. Overall, with future projections for greater snowpack Cl − loading, our experimental results suggest that more Hg could be delivered to Arctic aquatic ecosystems by melted snow (smaller Hg(II) red expected), but the Hg in the melted snow that is photoreduced may do so more quickly (larger k expected). [ABSTRACT FROM AUTHOR]

Abstract: Bioinspiration is an attractive way to develop new robust chemistry. In biological cell, chemical reactions form complex networks (e.g. signaling and metabolic) that communicate with each other and control cell division, growth, and interaction with environment. Thus, combining multiple chemical subsystems into a single network is an attractive way to design a chemical system with new functions. In this paper, we combined two chemical networks: i) a photocatalytic oxidation/ reduction on TiO2 particles, and ii) an autocatalytic formation of enzyme trypsin (Tr) from its precursor trypsinogen (Tg). Moreover, we put the combined network in hydrogel media, where all reactions are coupled to diffusion, to achieve a photocatalytic regulation of an autocatalytic wave. We showed that TiO2 particles affected the fluorescence quenching of Tr, but, without irradiation, had no effect on the autocatalytic formation of Tr. With irradiation, however, a cascade of photocatalytic reactions causes media acidification that suppress the autocatalytic formation of Tr and propagation of the autocatalytic wave. [ABSTRACT FROM AUTHOR]

Composite of silver, zinc sulfide and multi-walled carbon nanotubes (Ag-ZnS-MWCNTs) was synthesized sonochemically using a direct immersion ultrasonic probe and characterization results (XRF, XRD, FE-SEM, EDX, and DRS) showed the success of composite synthesis. The photocatalytic activity of the Ag-ZnS-MWCNTs composite was tested using Rhodamine B (Rh-B) degradation under visible light irradiation. The effects of four key operational variables (Rh-B and Ag-ZnS-MWCNTs concentration, pH, and visible light exposure time) on treatment process were analyzed and optimized using Response Surface Methodology (RSM). The maximum removal efficiency of 87.53% was obtained at optimum condition (4 mg L −1 of Rh-B, 1.25 g L −1 of Ag-ZnS-MWCNTs, at pH = 9, and an irradiation time of 116 min). In continuation of our investigations, a novel kinetics model was developed based on the proposed mechanism for the photocatalytic process. Eventually, byproducts produced within the photocatalytic degradation of Rh-B dye were identified by gas chromatography–mass spectrometry (GC–MS) technique. [ABSTRACT FROM AUTHOR]

Perfluorooctanesulfonate (PFOS) is a toxic, bioaccumulative, and highly persistent anthropogenic chemical. Hydrated electrons (ℓaq-) are potent nucleophiles that can effectively decompose PFOS. In previous studies, ℓaq- are mainly produced by photoionization of aqueous anions or aromatic compounds. In this study, we proposed a new photolytic strategy to generate eaq– and in turn decompose PFOS, which utilizes nitrilotriacetic acid (NTA) as a photosensitizer to induce water photodissociation and photoionization, and subsequently as a scavenger of hydroxyl radical (•OH) to minimize the geminate recombination between •OH and ℓaq-. The net effect is to increase the amount of eaq– available for PFOS degradation. The UV/NTA process achieved a high PFOS degradation ratio of 85.4% and a defluorination ratio of 46.8% within 10 h. A pseudo-first-order rate constant (k) of 0.27 h–1 was obtained. The laser flash photolysis study indicates that ℓaq- is the dominant reactive species responsible for PFOS decomposition. The generation of eaq– is greatly enhanced and its half-life is significantly prolonged in the presence of NTA. The electron spin resonance (ESR) measurement verified the photodissociation of water by detecting •OH. The model compound study indicates that the acetate and amine groups are the primary reactive sites. [ABSTRACT FROM AUTHOR]

The exposure of TiCl 3 to the plasma electric discharge burned in moisten air lead to the formation of TiO 2 nanopowder for short exposure time (<30 min). However, as expected for longer exposure time, the N-doped TiO 2 was formed. The synthesized powder for three exposure times was characterized by X-ray diffraction (XRD), FTIR spectroscopy, and nitrogen physisorption. The nitrogen loading was confirmed by X-ray photoelectron spectroscopy (XPS) analysis and the redshift response of doped photocatalyst was evaluated through the discoloration of aqueous Remazol Brilliant Blue-R dye under daylight. As a result, the textural analysis revealed the mesoporous materials with a specific surface area of 157 m 2  g −1 . The chemical states of nitrogen have been assigned to N–Ti–O and O–N–O in the TiO 2 lattice. The photo-degradation rates of RBB-R dye were 62; 76 and 81%, respectively, for the sample exposed during 20, 30 and 60 min. The observed enhanced photocatalytic activity is mainly attributed to the increasing amount of Nitrogen loaded that shift the photocatalytic response in the visible region of light. [ABSTRACT FROM AUTHOR]

A bifunctional CuO-Fe 3 O 4 material was synthesized and employed for the photocatalytic degradation of p-arsanilic acid (p-ASA) under visible light irradiation and simultaneous removal of the released inorganic arsenic by adsorption from solution. The effects of major factors, including solution pH, bicarbonate ion, halide ion and humic acid, on the p-ASA degradation were investigated. Under various water quality conditions, an excellent removal of p-ASA could always be achieved by the CuO-Fe 3 O 4 photocatalytic process and p-ASA could be completely converted to As(V) within 36 min. Simultaneously, the released As(V) could be adsorbed onto the surface of CuO-Fe 3 O 4 nanoparticles with high efficiency above 95% at initial pH range from 4 to 7. The presence of humic acid significantly weakened the degradation of p-ASA by scavenging OH, and slightly inhibited the As(V) removal. On the basis of the UV–vis, FTIR, XPS analysis and the major degradation products detected, the mechanism of the p-ASA photocatalytic degradation and the released As(V) adsorption by CuO-Fe 3 O 4 nanoparticles was given, and the degradation pathway of p-ASA during the photocatalytic process was also taken into consideration. Combined with the photocatalytic property and the high adsorption capacity of As(V), the synthesized magnetic CuO-Fe 3 O 4 nanoparticles have significant potential applications for controlling the risk of p-ASA in wastewater. [ABSTRACT FROM AUTHOR]

Bi 2 O 2 CO 3 with a narrow band gap ( Eg ∼ 2.93 eV) was self-assembled by Bi 2 O 2 CO 3 nanosheets via a hydrothermal method, and the β-Bi 2 O 3 /Bi 2 O 2.33 @Bi 2 O 2 CO 3 composites were further fabricated using Bi 2 O 2 CO 3 as template by slow thermal decomposition for 4 h, described as: Bi 2 O 2 CO 3 → β-Bi 2 O 3 /Bi 2 O 2.33 @Bi 2 O 2 CO 3 (300 °C) → β-Bi 2 O 3 /Bi 2 O 2.33 (320 °C) → β-Bi 2 O 3 (350 °C). Deep investigation towards the generation and existence of β-Bi 2 O 3 and Bi 2 O 2.33 on the surfaces and interfaces of Bi 2 O 2 CO 3 were also carefully conducted by XRD, HRTEM and XPS analysis. In comparison with pure Bi 2 O 2 CO 3 , β-Bi 2 O 3 /Bi 2 O 2.33 @Bi 2 O 2 CO 3 displayed superior photocatalytic degradation efficiency and stability to cationic dyes under visible-light irradiation. Especially, the as-prepared BOC–300 °C with relatively high specific surface area (12.11 m 2 g −1 ) could entirely remove Rh-B and MB in 45 min and 60 min, which were approximately 4.7 and 6.6 times as high as that of pure Bi 2 O 2 CO 3 , respectively. Further study demonstrated that the enhanced photocatalytic degradation efficiency of β-Bi 2 O 3 /Bi 2 O 2.33 @Bi 2 O 2 CO 3 is surely owing to the well matched band gap and p - n heterojunction, which made it possible for much faster charge transfer rather than electron-hole pairs recombination process. [ABSTRACT FROM AUTHOR]

Ag-decorated S-doped g-C 3 N 4 composites with different % w/w Ag were synthesized via chemical reduction method. The Ag/S-doped g-C 3 N 4 composites were used as photocatalysts for aqueous bisphenol A (BPA) degradation under solar irradiation. Investigation of the photocatalysts using various characterization methods including X-ray diffractometry, scanning electron microscopy and transmission electron microscopy indicated that the Ag nanoparticles (average size = 10–20 nm) were well-crystalline and uniformly distributed on the S-doped g-C 3 N 4 (SCN) surface. The photocatalytic performance of SCN was ∼3 times more efficient than that of the g-C 3 N 4 , while the Ag/SCN with 12% w/w Ag (Ag-SCN-12) exhibited the highest photocatalytic activity for BPA degradation followed by 8% w/w Ag/SCN, 4% w/w Ag/SCN, SCN, and Ag. The effects of pH and Ag-SCN-12 loading on photocatalytic BPA degradation were also investigated. The results showed that the Ag-SCN-12 was highly stable (<40 µg L −1 Ag leaching) and could be reused for at least 4 cycles without significant deterioration to its catalytic activity. The incorporation of Ag into the SCN enhanced the photocatalytic activity of SCN due to the improved electron-hole pair separation and decreased electron-hole pair recombination rate as evidenced by the photoluminescence emission study. The predominant reactive oxygen species (ROS) generated by the Ag-SCN-12 photocatalytic system was O 2 − which formed secondary ROS ( OH, and 1 O 2 ) for BPA degradation. The mechanism of ROS generation during the photocatalytic process is also proposed. Based on the BPA degradation intermediates identified using the LC/MS/MS, the BPA degradation pathways in the photocatalytic system are elucidated. [ABSTRACT FROM AUTHOR]

In this work, ZnO nanoneedles were synthesized employing a co-precipitation method. Further, white cement composites were prepared with ZnO filler of 5%, 10% and 15% by weight ratio. With the increasing concentration of ZnO in cement matrix the synergetic effect between ZnO and white cement matrix was observed through FE-SEM and UV–visible. We studied the photocatalytic degradation of pollutant (Rhodamine 6G) using ZnO nano-needles embedded in white cement matrix under ultraviolet irradiation (UV) along with enhanced hydrophobic nature and the antimicrobial property of the cement. The pseudo-first order kinetics was found in a photocatalytic process, and degradation rate constant was enhanced up to 0.147 min −1 for ZnO modified cement which was significantly higher than the pure cement (0.037 min −1 ). Antimicrobial studies were performed using bacterial strains Escherichia.coli (JM109, Promega Gram negative), Bacillus subtilis (MTCC121, Gram-positive) and fungal strain Aspergillus niger (MTCC281) for all the composites. A significant improvement in bacterial and fungal degradation was observed in ZnO modified cement than control and pure cement in a dose-dependent manner. [ABSTRACT FROM AUTHOR]

A novel ternary Ag/Ag 2 CO 3 /BiVO 4 plasmonic heterojunction photocatalyst was successfully fabricated by a precipitation method over BiVO 4 , followed by light reduction. The obtained composites were characterized by various measurements and the photocatalytic performances of the as-prepared composites were assessed by the degradation of tetracycline (TC) under visible-light illumination. The ternary plasmonic heterojunction photocatalyst exhibits higher and wider absorption in the visible and ultraviolet regions than the pure BiVO 4 and it displays superior performance in the degradation of tetracycline. The highest efficiency of Ag/Ag 2 CO 3 /BiVO 4 photocatalyst to degrade TC is up to 94.9% at 150 min. On the basis of the obtained experimental results, the probable photocatalytic mechanism of the enhanced activity is discussed. The degradation of tetracycline is not only influenced by OH, but also caused by valence-band holes (h + ). Therefore, the improved photocatalytic activity of Ag/Ag 2 CO 3 /BiVO 4 is due to the enhanced absorbance under the visible light, the facilitated charge transfer and the inhibited recombination of electron-hole pairs. The likely degradation pathway was proposed on the basis of the intermediate products detected by GC–MS. Moreover, the surface plasmon resonance and the electric field enhancement were simulated by the three dimensional finite difference time domain (FDTD) method. [ABSTRACT FROM AUTHOR]

This paper demonstrates the preparation of pure TiO, 40% of BiO in TiO and Ag loaded BiO/TiO nanocomposites by the hydrothermal method followed by the photoreduction process. The crystal structure, morphology and composition of the samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy respectively. The dispersion of Ag nanoparticles on the surface of BiO/TiO nanocomposites are found to bring the conduction band near to the valence band, resulting in the narrow band gap compared to pure TiO and BiO/TiO nanocomposites. The XRD analysis demonstrated that silver nanoparticles were dispersed finely on the surface of BiO/TiO nanocomposites. All the characterization results revealed that the Ag/BiO/TiO nanocomposites were smaller crystallite size, stronger absorbance in the visible region and greater surface area than pure TiO and BiO/TiO nanocomposites. The photoluminescence intensity decreases with an increase in the UV-illumination time of Ag loaded BiO/TiO revealing a decrease in the recombination rate of electron-hole pairs. In order to test them as a photocatalyst, methyl orange was used as a standard. The photocatalytic degradation of methyl orange shows that the ABT5 sample exhibits the maximum degradation efficiency of 99% within 180 min of irradiation. [ABSTRACT FROM AUTHOR]

Kinetic insight into photoinduced Fe-based atom transfer radical polymerization (ATRP) involving monomer-mediated photoreduction was performed by modeling approach for the first time. Preliminary numerical analysis of number-average molar mass (Mn) derivation in this specific system was given. Simulation results provided a full picture of reactant concentration and reaction rate throughout the entire polymerization. Methyl 2,3-dibromoisobutyrate (MibBr2) generated from methyl methacrylate (MMA)-mediated photoreduction as the leading factor for the deviation of Mn from theoretical value was confirmed by reaction contributions in α-bromophenylacetate (EBPA) containing system. Reasonable predictions were made with respect to the polymerizations under a variety of initial conditions. Results show that increasing light intensity will shorten transition period and increase steady state polymerization rate; decreasing catalyst loading will cause the decrease in polymerization rate and Mn deviation; varying initiation activity will slightly increase the time to attain steady state of dispersity (Mw/Mn) evolution and enormously change the fraction of reaction contributions; increasing targeted chain length will extend transition period, decrease steady state polymerization rate, increase Mn deviation degree with same reaction contributions, and decrease the time to attain the steady state of Mw/Mn. The numerical analysis presented in this work clearly demonstrates the unique ability of our modeling approach in describing the kinetics of photoinduced Fe-based ATRP of MMA. © 2017 American Institute of Chemical Engineers AIChE J, 2017 [ABSTRACT FROM AUTHOR]

Development of novel hybrid photocatalysts with high efficiency and durability for photocatalytic hydrogen generation is highly desired but still remains a grand challenge currently. In the present work, TiO 2 -doped microporous zeolite SSZ-13 with varying amounts of TiO 2 were prepared using solid state dispersion (SSD) method, as photocatalysts for the evolution of photocatalytic degradation of methylene blue and H 2 evolution under UV–vis irradiation. The incorporation of P25 into SSZ-13 zeolite significantly enhanced the photocatalytic activity for H 2 evolution (reduction) and degradation of methylene blue (oxidation). And the most efficient photocatalyst was proven to 60%TiO 2 loading, whose H 2 generation (126.7 μmol/h) was profoundly enhanced for 3 times with respect to P25 (37.2 μmol/h) and degradation rate of methylene blue was 96% within 2.5 h. The photocatalysts were characterized by XRD, SEM, BET, UV–vis and PL. The results showed TiO 2 were well dispersed on the surface of zeolite and the strong interaction between P25 and SSZ-13 zeolite, which improved significantly photocatalytic performance of P25. This study suggested the potential photocatalytic application of microporous zeolite SSZ-13 as a catalyst carrier. [ABSTRACT FROM AUTHOR]

This study reports an easy synthesis protocol of a novel bimetallic silver halide (Au/AgBr–Ag) plasmonic heterostructure as a visible light induced photocatalyst. In this process, first CTAB capped Au NPs were coated with AgBr, and then Ag nanoparticles were formed on the surface of AgBr by photoreduction, while exposing to daylight at room temperature. The presence of Au and Ag improves the visible absorption ability of NPs and avoids charge recombination of the semiconductor AgBr during photoexcitation, which in turn enhances 16 and 8.9 fold the photocatalytic efficiency of Rhodamine B dye degradation under visible light irradiation compared to that of pure AgBr and AgBr/Ag, respectively. The recycling tests of the photocatalyst show only ∼8.7% decrease in efficiency after the 5th cycle of reuse without changing the morphology. During the photocatalytic process, active superoxide radicals (O2Ṗ−) play a major role, proved through scavenger trapping and photoluminescence experiments. The presence of two plasmonic metals (Au and Ag) in the heterostructure helps to improve visible light absorption as well as avoid charge recombination of the semiconductor AgBr to act as a better photocatalyst. Since this heteronanostructure can be easily synthesized by a one-step method, this study could provide a new approach for the development of efficient bimetallic/semiconductor halide plasmonic photocatalysts with enhanced visible absorption and better charge separation. [ABSTRACT FROM AUTHOR]

Photocatalytic reduction of CO2 to CO proceeded by visible light ( λ>400 nm) using mesoporous graphitic carbon nitride (C3N4) coupled with a RuII-ReI binuclear complex ( RuRe) containing a photosensitizer and catalytic units. The selectivity to CO exceeded 90 % during the initial stage. Photocatalytic reactions (including isotope tracer experiments) and electrochemical measurements revealed that the reaction proceeded according to a two-step photoexcitation of C3N4 and the RuII photosensitizer unit, that is, it followed the Z-Scheme mechanism. Modification of C3N4 with highly dispersed silica was found to improve the ability of C3N4 to accommodate RuRe, which enhanced the photocatalytic activity for CO production. [ABSTRACT FROM AUTHOR]

This work shows a novel artificial donor-catalyst- acceptor triad photosystem based on a mononuclear C5H5- RuH complex oxo-bridged TiO2 hybrid for efficient CO2 photoreduction. An impressive quantum efficiency of 0.56% for CH4 under visible-light irradiation was achieved over the triad photocatalyst, in which TiO2 and C5H5-RuH serve as the electron collector and CO2-reduction site and the photonharvester and water-oxidation site, respectively. The fast electron injection from the excited Ru2+ cation to TiO2 in ca. 0.5 ps and the slow backward charge recombination in half-life of ca. 9.8 ms result in a long-lived D+-C-A- charge-separated state responsible for the solar-fuel production. [ABSTRACT FROM AUTHOR]

The flavodiiron proteins (FDPs) Flv1 and Flv3 in cyanobacteria function in photoreduction of O2 to H2O, without concomitant formation of reactive oxygen species, known as the Mehler-like reaction. Both Flv1 and Flv3 are essential for growth under fluctuating light (FL) intensities, providing protection for PSI. Here we compared the global transcript profiles of the wild type (WT), Δflv1 and Δflv1/Δflv3 grown under constant light (GL) and FL. In the WT, FL induced the largest down-regulation in transcripts involved in carbon-concentrating mechanisms (CCMs), while those of the nitrogen assimilation pathways increased as compared with GL. Already under GL the Δflv1/Δflv3 double mutant demonstrated a partial down-regulation of transcripts for CCM and nitrogen metabolism, while in FL conditions the transcripts for nitrogen assimilation were strongly down-regulated. Many alterations were specific only for Δflv1/Δflv3, and not detected in Δflv1, suggesting that certain transcripts are affected primarily because of the lack of flv3. By constructing the strains overproducing solely either Flv1 or Flv3, we demonstrate that the homo-oligomers of these proteins also function in acclimation of cells to FL, by catalyzing reactions with as yet unidentified components, while the presence of both Flv1 and Flv3 is a prerequisite for the Mehler-like reaction and thus the electron transfer to O2. Considering the low expression of flv1, it is unlikely that the Flv1 homo-oligomer is present in the WT. [ABSTRACT FROM AUTHOR]

Proton-coupled electron transfer (PCET), a ubiquitous phenomenon in biological systems, plays an essential role in copper nitrite reductase (CuNiR), the key metalloenzyme in microbial denitrification of the global nitrogen cycle. Analyses of the nitrite reduction mechanism in CuNiR with conventional synchrotron radiation crystallography (SRX) have been faced with difficulties, because X-ray photoreduction changes the native structures of metal centers and the enzyme-substrate complex. Using serial femtosecond crystallography (SFX), we determined the intact structures of CuNiR in the resting state and the nitrite complex (NC) state at 2.03- and 1.60-Å resolution, respectively. Furthermore, the SRX NC structure representing a transient state in the catalytic cycle was determined at 1.30-Å resolution. Comparison between SRX and SFX structures revealed that photoreduction changes the coordination manner of the substrate and that catalytically important His255 can switch hydrogen bond partners between the backbone carbonyl oxygen of nearby Glu279 and the side-chain hydroxyl group of Thr280. These findings, which SRX has failed to uncover, propose a redoxcoupled proton switch for PCET. This concept can explain how proton transfer to the substrate is involved in intramolecular electron transfer and why substrate binding accelerates PCET. Our study demonstrates the potential of SFX as a powerful tool to study redox processes in metalloenzymes. [ABSTRACT FROM AUTHOR]

The ability to drive reactivity using visible light is of importance for many disciplines of chemistry and has significant implications for sustainable chemistry. Identifying photochemically active compounds and understanding photochemical mechanisms is important for the development of useful materials for synthesis and catalysis. Here we report a series of photoactive diphenyltellurophene compounds bearing electron-withdrawing and electron-donating substituents synthesized by alkyne coupling/ring closing or palladium-catalyzed ipso-arylation chemistry. The redox chemistry of these compounds was studied with respect to oxidative addition and photoelimination of bromine, which is of importance for energy storage reactions involving X2. The oxidative addition reaction mechanism was studied using density functional theory, the results of which support a three-step mechanism involving the formation of an initial ¹ association complex, a monobrominated intermediate, and finally the dibrominated product. All of the tellurophene derivatives undergo photoreduction using 430, 447, or 617 nm light depending on the absorption properties of the compound. Compounds bearing electron-withdrawing substituents have the highest photochemical quantum efficiencies in the presence of an alkene trap, with efficiencies of up to 42.4% for a pentafluorophenyl-functionalized tellurophene. The photoelimination reaction was studied in detail through bromine trapping experiments and laser flash photolysis, and a mechanism is proposed. The photoreaction, which occurs by release of bromine radicals, is competitive with intersystem crossing to the triplet state of the brominated species, as evidenced by the formation of singlet oxygen. These findings should be useful for the design of new photochemically active compounds supported by main-group elements. [ABSTRACT FROM AUTHOR]

Photocatalytic degradation of bisphenol A (BPA) in waters and wastewaters in the presence of titanium dioxide (TiO) was performed under different conditions. Suspensions of the TiO were used to compare the degradation efficiency of BPA (20 mg L) in batch and compound parabolic collector (CPC) reactors. A TiO catalyst supported on glass spheres was prepared (sol-gel method) and used in a CPC solar pilot plant for the photodegradation of BPA (100 μg L). The influence of OH·, O, and h on the BPA degradation were evaluated. The radicals OH· and O were proved to be the main species involved on BPA photodegradation. Total organic carbon (TOC) and carboxylic acids were determined to evaluate the BPA mineralization during the photodegradation process. Some toxicological effects of BPA and its photoproducts on Eisenia andrei earthworms were evaluated. The results show that the optimal concentration of suspended TiO to degrade BPA in batch or CPC reactors was 0.1 g L. According to biological tests, the BPA LC in 24 h for E. andrei was of 1.7 × 10 mg cm. The photocatalytic degradation of BPA mediated by TiO supported on glass spheres suffered strong influence of the water matrix. On real municipal wastewater treatment plant (MWWTP) secondary effluent, 30 % of BPA remains in solution; nevertheless, the method has the enormous advantage since it eliminates the need of catalyst removal step, reducing the cost of treatment. [ABSTRACT FROM AUTHOR]

The direct decarboxylative arylation of α-amino acids has been achieved via visible light-mediated photoredox catalysis. This method offers rapid entry to prevalent benzylic amine architectures from an abundant biomass, specifically α-amino acid precursors. Significant substrate scope is observed with respect to both the amino acid and arene components. [ABSTRACT FROM AUTHOR]

The kinetics of the photoreductionof four benzophenone derivativesby isopropyl alcohol was examined in acetonitrile, namely, tetra-meta-trifluoromethyl-, di-para-trifluoromethyl-,di-para-methoxy benzophenone, and, for comparison,the unsubstituted molecule itself. The basic spectroscopic (absorptionand phosphorescence spectra) and photophysical (quantum yields andexcited state energies) properties were established, and the key kineticparameters were determined by the laser flash photolysis transientabsorption technique. The rate coefficients of both the primary andsecondary photoreduction reaction show remarkable dependence on ringsubstitution. This substantial effect is caused by the considerablechange in the activation energy of the corresponding process. Theexperimental results as well as DFT quantum chemical calculationsclearly indicate that these benzophenone derivatives all react as n–π* excited ketones, and the rate as wellas the activation energy of the reduction steps change parallel withthe reaction enthalpies, the determining factor being the stabilityof the forming aromatic ketyl radicals. The secondary photoreductionof benzophenones by the aliphatic ketyl radical formed in the primarystep occurs via a hydrogen bonded complex. The binding energy of thehydrogen bonded complex between the aliphatic ketyl radical reactantand a solvent molecule is a critical parameter influencing the observablerate of the secondary photoreduction. [ABSTRACT FROM AUTHOR]

Bromate reduction in water by ultraviolet irradiation using medium-pressure lamps (UV-M) emitting light in the range of 200–600 nm has been investigated. Effects of certain experimental parameters including the initial bromate concentration, UV light intensity, initial pH, and presence of dissolved organic and inorganic carbon and nitrate on the kinetics and efficiency of UV irradiation for bromate reduction were evaluated. Experimental results showed that UV-M irradiation achieved complete destruction of bromate and almost total conversion of bromate into bromide for the initial bromate concentrations ranging from 10 to 1000 μg/L under different pH conditions. A simple kinetic model for bromate destruction was developed. Bromate decay with time during UV-M irradiation follows pseudo-first-order kinetics. The observed rate constant (kobs) decreased with increasing bromate concentrations upto 100 μg/L and then it becomes constant at 0.058 min−1 for higher bromate concentrations. Increasing the UV light intensity resulted in the increase of the rate of bromate destruction. The kobs increased linearly with increasing light intensity. A UV dose of 1000 mJ/cm2 was sufficient to reduce the bromate concentration to less than 10 μg/L within 10 min. The presence of dissolved organic carbon or carbonate/bicarbonate slowed the bromate reduction rate due to absorption of non-negligible fraction of UV light by these compounds. Presence of nitrate affects both the kinetics and efficiency of bromate reduction. [ABSTRACT FROM AUTHOR]

We report photocatalytic H2 production by hydrogenase (H2ase)-quantum dot (QD) hybrid assemblies. Quenching of the CdTe exciton emission was observed, consistent with electron transfer from the quantum dot to H2ase. GC analysis showed light-driven H2 production in the presence of a sacrificial electron donor with an efficiency of 4%, which is likely a lower limit for these hybrid systems. FTIR spectroscopy was employed for direct observation of active-site reduction in unprecedented detail for photodriven H2ase catalysis with sensitivity toward both H2ase and the sacrificial electron donor. Photosensitization with Ru(bpy) 32+ showed distinct FTIR photoreduction properties, generating all of the states along the steady-state catalytic cycle with minimal H2 production, indicating slow, sequential one-electron reduction steps. Comparing the H2ase activity and FTIR results for the two systems showed that QDs bind more efficiently for electron transfer and that the final enzyme state is different for the two sensitizers. The possible origins of these differences and their implications for the enzymatic mechanism are discussed. [ABSTRACT FROM AUTHOR]

Interactions of externally added plastoquinone (PQ) derivatives (PQ0-PQ3) with the photosystem II (PSII) acceptor side were investigated in PSII membrane fragments prepared from spinach by measuring the photoreduction rates of PQ derivatives at various PQ concentrations, and the following results were obtained.From the kinetic analysis, all the PQ derivatives (PQ0-PQ3) except PQ3 were shown to accept electrons at two sites (the QB site and the PQ site) as in the case of Synechococcus vulcanus PSII particles with benzoquinone derivatives [Satoh et al. (1995) Plant Cell Physiol. 36: 597].Affinities of PQ derivatives at the QB site increased as the length of the isoprene side chain got longer, while those at the PQ site were not very much different for all the PQ derivatives tested in this study.The inhibitory effect of DCMU was noncompetitive, and, therefore, the affinity of PQ3 for the PQ site was determined while that for the QB site could not be estimated presumably due to its fairly high affinity to the site.Based on the results obtained using PQ derivatives, the mechanism of interaction of an authentic PQ, PQ9, at the QB site is discussed. [ABSTRACT FROM AUTHOR]

19 examples [ABSTRACT FROM AUTHOR]

A tandem ring expansion/oxidation arylation reaction of small sized ring substituted alkenes and allenes are developed. [ABSTRACT FROM AUTHOR]