Photoreduction of graphite oxide

The photoreduction of graphite oxide (GO) films and solutions by UV light was studied. The electrical resistance of a GO film decreases upon irradiation by more than an order of magnitude. The threshold of photoreduction was determined to be 3.2 eV. The photoreduction is accompanied by an increase in absorption in the visible spectral region, and the CO, CO₂, O₂, and H₂O molecules were found in the gas phase above the irradiated GO film.     

The photoreduction of 8-substituted 5-deazaflavins and the 5-deazaflavin catalyzed photoreduction of methyl viologen

Prolonged illumination of 8-X-5-deazaflavins (X = C1, N(CH₃)₂, NH₂, p-NH₂-C₆H₄) in the presence of an electron donor leads to the formation of a 5,5′-dimer and/or a 6,7-dihydro compound. The course and rate of these photoreductions were established and discussed in terms of electronic and steric effects, exerted by the substituent at position 8 and the electron donor. Pseudo first-order kinetics were found to apply to the photoreduction of 8-X-5-deazaflavins (X = Cl, NH₂, p-NH₂-C₆H₄) while the rate of the photoreduction of 8-X-5-deazaflavin (X = N(CH₃)₂) appeared to contain an autocatalytic element. The catalytic effect of 8-X-5-deazaflavins in the photoreduction of methyl viologen by EDTA was investigated. The substituent effect on the rate of the 8-X-5-deazaflavin mediated photoreduction of methyl viologen by EDTA was found to be comparable with that on the photoreduction rate of 8-X-5-deazaflavin in the presence of EDTA with the exception of 8-X-5-deazaflavin (X = N(CH₃)₂), which showed a remarkable relative enhancement of the reactivity towards methyl viologen photoreduction.     

Photocatalytic Reduction of CO2 over Heterostructure Semiconductors into Value‐Added Chemicals

Photoreduction of CO₂, which utilizes solar energy to convert CO₂ into hydrocarbons, can be an effective means to overcome the increasing energy crisis and mitigate the rising emissions of greenhouse gas. This article covers recent advances in the CO₂ photoreduction over heterostructure‐based photocatalysts. The fundamentals of CO₂ photoreduction and classification of the heterostructured photocatalysts are discussed first, followed by the latest work on the CO₂ photoreduction over heterostructured photocatalysts in terms of the classification of the coupling semiconductors. Finally, a brief summary and a perspective on the challenges in this area are presented.     

Synchronous activation of Ag nanoparticles and BiOBr for boosting solar-driven CO2 reduction

Artificial photosynthesis of valuable chemicals from CO₂ is a potential way to achieve sustainable carbon cycle. The CO₂ conversion activity is still inhibited by the sluggish charge kinetics and poor CO₂ activation. Herein, Ag nanoparticles coupled BiOBr have been constructed by in-situ photoreduction strategy. The crafting of interface between Ag nanoparticles and BiOBr nanosheets, achieving an ultra-fast charge transfer. The BiOBr semiconductor excited electrons and plasmonic Ag nanoparticles generated high-energy hot electrons synchronous accelerates the C=O double bond activation. Thus, the optimized Ag/BiOBr-2 heterostructure shows excellent CO₂ photoreduction activity with CO production of 133.75 and 6.83 µmol/g under 5 h of 300 W Xe lamp and visible light (λ > 400 nm) irradiation, which is 1.51 and 2.81 folds versus the pristine BiOBr, respectively. The mechanism of CO₂ photoreduction was in-depth understood through in-situ FT-IR spectrum and density functional theory calculations. This study provides some new perspectives into efficient photocatalytic CO₂ reduction.     

Efficient detection of CO2 by nanocomposites: Environmental and energy technologies

Nanocomposite materials have received much attention from scientists and engineers interested in the detection and photoreduction of CO₂ compounds. Their interest is due in large part to the unique properties of these materials, including their high degree of photoactivity, thermal stability, high surface area, and malleability. In the present review, we focus on several nanocomposite types used for the detection and photochemical reduction of CO₂: titania-based nanocomposites, chalcogenide-based nanocomposites, LDHs-based nanocomposites, and MOFs-based nanocomposites. More specifically, trends in green synthesis nanocomposites, methods for detecting CO₂ compounds, and the photoreduction of those compounds are summarized in this paper. Several modified approaches to nanocomposite materials have been discussed to achieve optimum results. Generally, we find that the presence of functional active groups, doping metal, and other semiconductor materials act as catalysts, significantly enhancing the photoreduction properties of nano-materials. Moreover, we will also discuss additional challenges, especially in regard to large-scale industrial applications. In our discussion, we will highlight the use of nanocomposite-based materials in the detection and photoreduction of CO₂. It is hoped that our findings will serve as a reference and inspiration for academic researchers and industrial professionals.     

Participation of exciplexes in the photochemical reactions of trinuclear aromatic compounds with N,N′-dimethylaniline in solutions with various polarity

Characteristics of the photoreduction of trinuclear aromatic compounds (phenazine, acridine, and anthracene) by N,N-dimethylaniline (DMA) in media with various polarity (benzene and benzonitrile) were investigated. On the basis of the obtained relationships between the reciprocals of the quantum yields of photoreduction and the reciprocals of the DMA concentration and also on the basis of experiments with biacetyl it was established that the photoreduction is realized with the participation of the lowest excited S₁ and T₁ states. It was shown that the photochemical reduction of the trinuclear aromatic compounds takes place by a mechanism involving an exciplex.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 442–448, July–August, 1990.     

Recent progress on two-dimensional materials confining single atoms for CO2 photoreduction

Photoreduction of CO₂ into value-added products offers a promising approach to overcome both climate change and energy crisis. However, low conversion efficiency, poor product selectivity, and unclear mechanism limit the further advancement of CO₂ photoreduction. The development of two-dimensional (2D) materials and construction of single atom sites are two frontier research fields in catalysis. Combining the advantages of 2D materials and single atom sites is expected to make a breakthrough in CO₂ photoreduction. In this review, we summarized the design and application, proposed challenges and opportunities, and laid a foundation for further research and application of 2D materials confining single atoms (SACs@2D) for CO₂ photoreduction.     

Recent Advances and Future Perspectives of Lead-Free Halide Perovskites for Photocatalytic CO2 Reduction

It is still challenging to design and develop the state-of-the-art photocatalysts toward CO₂ photoreduction. Enormous researchers have focused on the halide perovskites in the photocatalytic field for CO₂ photoreduction, due to their excellent optical and physical properties. The toxicity of lead-based halide perovskites prevents their large-scale applications in photocatalytic fields. In consequence, lead-free halide perovskites (LFHPs) without the toxicity become the promising alternatives in the photocatalytic application for CO₂ photoreduction. In recent years, the rapid advances of LFHPs have offer new chances for the photocatalytic CO₂ reduction of LFHPs. In this review, we summarize not only the structures and properties of A₂BX₆, A₂B(I)B(III)X₆, and A₃B₂X₉-type LFHPs but also their recent progresses on the photocatalytic CO₂ reduction. Furthermore, we also point out the opportunities and perspectives to research LFHPs photocatalysts for CO₂ photoreduction in the future.     

X‐ray photoreduction of U(VI)‐bearing compounds

During XPS analysis, the soft X‐ray‐induced reduction of metals such as Cr(VI) and Ce(IV) in oxides has been reported in the literature and some mechanisms have been proposed to explain this phenomenon. The reduction of U(VI) by the beam during X‐ray Photoelectron Spectroscopy has been already reported in the literature but only for U(VI) sorbed or precipitated onto solids with reducing properties (as micas or pyrites) for whose Fe(II) can also induce the reduction of U(VI), or onto TiO₂ whose the photocatalytic properties are well known. The objective of this paper is to investigate the effects of X‐ray beam on U(VI) bulk compounds (UO₃, UO₂(OH)₂, (UO₂)₂SiO₄, UO₂(CH₃COO)₂ and UO₂C₂O₄). Successive U4f, U5f, C1s XPS spectra were recorded and compared as a function of the irradiation time. The XPS photoreduction of U(VI) into U(IV) is only observed for uranyl compounds containing organic matter (uranyl acetate and uranyl oxalate). Considering the evolution of the C1s signal during the X‐ray irradiation, a significant decrease of the C ? O component simultaneously to the U(VI) reduction is observed, which suggests a desorption of CO or other volatile organic products from the solid surface. All these results on U(VI) bulk compounds indicate the important role of organic carbon species in the photoreduction process and to explain these observations, a photoreduction mechanism has been suggested. Copyright © 2010 John Wiley & Sons, Ltd.     

Identification of Crucial Photosensitizing Factors to Promote CO2-to-CO Conversion

The sensitizing ability of a catalytic system is closely related to the visible-light absorption ability, excited-state lifetime, redox potential, and electron-transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO₂ photoreduction. Herein, a series of Ir(III)-based PSs ( Ir-1 – Ir-6 ) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO₂ photoreduction. Among them, less efficient visible-light absorption capacity results in lower CO yields of Ir-1 , Ir-2 or Ir-4 . Ir-3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the K_obs of Ir-3 is ≈10 times higher than that of Ir-5 , the CO yield of Ir-3 is slightly higher than that of Ir-5 due to the compensation of Ir-5 ’s strong visible-light-absorbing ability. Ir-6 exhibits excellent photocatalytic performance due to the strong visible-light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO₂ photoreduction to CO with Ir-6 can achieve 91.5 μmol, over 54 times higher than Ir-1 , and the optimized TON_C-1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO₂ photoreduction.     

Ultrathin zinc selenide nanosheet-based intercalation hybrid coupled with CdSe quantum dots showing enhanced photocatalytic CO_2 reduction

Fabrication of well-designed heterojunctions is an extraordinarily attractive pathway for boosting the photocatalytic activity toward CO_2 photoreduction.Herein,a novel kind of na nosheet-based intercalation hybrid coupled with CdSe quantum dots(QDs) was successfully fabricated by a facile solvothermal method and served as photocatalyst for full-spectrum-light-driven CO_2 reduction.Ultra-small CdSe QDs were rationally in-situ introduced and coupled with lamellar ZnSe-intercalation hybrid nanosheet,resulting in the formation of CdSe Q.Ds/ZnSe hybrid heterojunction.Significantly,the concentration of Cd~(2+) could change directly the crystallinity and micromorphology of ZnSe intercalation hybrid,which in turn would impact on the photocatalysis activity.The optimized CdSe QDs/ZnSe hybrid-5 composite demonstrated a considerable CO yield rate of the 25.6 μmol g~(-1) h~(-1) without any additional cocatalysts or sacrificial agents assisting,making it one of the best reported performance toward CO_2 photoreduction under full-spectrum light.The elevated CO_2 photoreduction activity could be attributed to the special surface heterojunction,leading to improving the ability of light absorption and promoting the separation/transfer of photogenerated carriers.This present study developed a new strategy for designing inorganic-organic heterojunctions with enhanced photocatalyst for CO_2 photoreduction and provided an available way to simultaneously mitigate the greenhouse effect and alleviate energy shortage pressure.     

Photocatalytic reduction of divalent zinc and cadmium ions in aqueous TiO2 suspensions: an interfacial induced adsorption–reduction pathway mediated by formate ions

A new pathway is described for the photocatalytic reduction of metal ions in organic-loaded aqueous TiO₂ suspensions. Thus, formate ions act as interfacial anchors to initially sequester Zn(II) and Cd(II) ions onto the TiO₂ particle surfaces. Subsequent UV illumination of the suspensions results in the facile photoreduction of these metal ions. In the absence of formate, the metal ions show little proclivity either to adsorb on the TiO₂ particle surfaces or to undergo photoreduction.     

Determination of Metals by Photochemical Precipitation

Abstract

The technique of precipitation from homogeneous solution by photochemical action has been successfully applied to the determination of La, Ba, and In. Precipitation is accomplished through the photoreduction of IO₄ ^? to produce the insoluble iodates. In the case of Zr and Ti, the more soluble periodate is coprecipitated with the iodate and the method is not successful. Cu and Ni cannot be estimated by this method.     

Electronic Interactions on Platinum/(Metal-Oxide)-Based Photocatalysts Boost Selective Photoreduction of CO2 to CH4

By supporting platinum (Pt) and cadmium sulfide (CdS) nanoparticles on indium oxide (In₂O₃), we fabricated a CdS/Pt/In₂O₃ photocatalyst. Selective photoreduction of carbon dioxide (CO₂) to methane (CH₄) was achieved on CdS/Pt/In₂O₃ with electronic Pt−In₂O₃ interactions, with CH₄ selectivity reaching to 100 %, which is higher than that on CdS/Pt/In₂O₃ without electronic Pt−In₂O₃ interactions (71.7 %). Moreover, the enhancement effect of electronic Pt-(metal-oxide) interactions on selective photoreduction of CO₂ to CH₄ also occurs by using other common metal oxides, such as photocatalyst supports, including titanium oxide, gallium oxide, zinc oxide, and tungsten oxide. The electronic Pt-(metal-oxide) interactions separate photogenerated electron-hole pairs and convert CO₂ into CO₂^δ−, which can be easily hydrogenated into CH₄ via a CO₂^δ−→HCOO*→HCO*→CH*→CH₄ path, thus boosting selective photoreduction of CO₂ to CH₄. This offers a new way to achieve selective photoreduction of CO₂.     

Effect of mercaptan on photoreduction of acetone. Non-repair hydrogen transfer reactions

Abstract— Ultraviolet (u.v.) irradiation of solutions of benzhydrol in acetone leads to formation of -2-propanol, benzpinacol and some benzophenone, apparently from the free radicals (CH₃)₂COH, II, and (C₆H₅)₂COH, I. 2-Propanol is formed more rapidly and benzophenone is formed to a much larger extent and persists longer when the solution contains mesityl mercap-tan, as radical II is reduced by mercaptan and radical I is oxidized by thiyl radical. The same hydrogen atom transfer reactions, which retard by a repair mechanism the photoreduction of benzophenone by 2-propanol, accelerate and alter the course of photoreduction of acetone by benzhydrol. Irradiation of acetone leads to 2-propanol, and this is formed more rapidly in the presence of mercaptan. Irradiation of benzophenone in acetone leads to no apparent reaction. The courses of reaction of the several systems are discussed.     

The mechanism of photoreductiom of cyclohexenones to cyclohexanones in isopropyl alcohol

The photoreduction of cyclohexenones in 2-propanol is initiated by H-abstraction at C_β of the enone ³π, π* state, as shown by the reaction course in deuterated solvents.     

Amide-bridged conjugated organic polymers: efficient metal-free catalysts for visible-light-driven CO2 reduction with H2O to CO

The visible-light-driven photoreduction of CO₂ to value-added chemicals over metal-free photocatalysts without sacrificial reagents is very interesting, but challenging. Herein, we present amide-bridged conjugated organic polymers (amide-COPs) prepared via self-condensation of amino nitriles in combination with hydrolysis, for the photoreduction of CO₂ with H₂O without any photosensitizers or sacrificial reagents under visible light irradiation. These catalysts can afford CO as the sole carbonaceous product without H₂ generation. Especially, amide-DAMN derived from diaminomaleonitrile exhibited the highest activity for the photoreduction of CO₂ to CO with a generation rate of 20.6 μmol g⁻¹ h⁻¹. Experiments and DFT calculations confirmed cyano/amide groups as active sites for CO₂ reduction and second amine groups for H₂O oxidation, and suggested that superior selectivity towards CO may be attributed to the adjacent redox sites. This work presents a new insight into designing photocatalysts for artificial photosynthesis.

Amino nitrile-derived conjugated organic polymers can realize the photoreduction of CO₂ with water to CO without H₂ generation efficiently.     

Facilely anchoring Cu2O nanoparticles on mesoporous TiO2 nanorods for enhanced photocatalytic CO2 reduction through efficient charge transfer

Semiconductor-employed photocatalytic CO₂ reduction has been regarded as a promising approach for environmental-friendly conversion of CO₂ into solar fuels. Herein, TiO₂/Cu₂O composite nanorods have been successfully fabricated by a facile chemical reduction method and applied for photocatalytic CO₂ reduction. The composition and structure characterization indicates that the Cu₂O nanoparticles are coupled with TiO₂ nanorods with an intimate contact. Under light illumination, all the TiO₂/Cu₂O composite nanorods enhance the photocatalytic CO₂ reduction. In particular, the TiO₂/Cu₂O-15% sample exhibits the highest CH₄ yield (1.35 µmol g^-1 h^-1) within 4 h irradiation, and it is 3.07 and 15 times higher than that of pristine TiO₂ nanorods and Cu₂O nanoparticles, respectively. The enhanced photoreduction capability of the TiO₂/Cu₂O-15% is attributed to the intimate construction of Cu₂O nanoparticles on TiO₂ nanorods with formed p-n junction to accelerate the separation of photogenerated electron-hole pairs. This work provides a reference for rational design of a p-n heterojunction photocatalyst for CO₂ photoreduction.     

Photoreduction of carbon dioxide by hydrogen and methane

Zirconium oxide is active for photoreduction of gaseous carbon dioxide to carbon monoxide with hydrogen. A stable surface species arises under the photoreduction of CO₂ on zirconium oxide, and it is identified as surface formate by infrared spectroscopy. Adsorbed CO₂ is converted to formate by photoreaction with hydrogen. The surface formate is a true reaction intermediate since CO is formed by the photoreaction of formate and CO₂; surface formate works as a reductant of carbon dioxide to yield carbon monoxide. The dependence on the wavelength of irradiation light shows that a bulk ZrO₂ is not a photoactive species. When ZrO₂ adsorbs CO₂ a new band appears in photoluminescence excitation spectrum. The photoactive species in the reaction that CO₂+H₂ yields HCOO⁻ is presumably formed by the adsorption of CO₂ on ZrO₂ surface. Hydrogen molecules play a role to supply an atomic hydrogen. Therefore, methane molecules can also be used as a reductant of carbon dioxide.     

One-electron reduction of excited NMN and NADP in the presence of amino acids

Excitation of oxidized forms of nicotinamide coenzymes (NADP⁺, NMN⁺) at 254 nm under anaerobic conditions in the presence of EDTA, lysine, serine, glycine leads, in the initial stage of irradiation, to photoreduction of coenzyme. Formation of the photoreduction products was observed by polarographic, spectrophotometric and enzymatic methods. Quantum yields for NMN⁺ and NADP⁺ photoreduction have been calculated and a mechanism proposed. No photoreduction was observed with histidine. Long-term irradiation leads to further reduction of the nicotinamide ring to tetrahydroderivatives absorbing at 280–290 nm. The photochemically generated dimers undergo phototransformation to the parent monomers on irradiation at 365 nm either in the presence or absence of oxygen. The biological significance of the results is discussed.