Consecutive Charging of a Perylene Bisimide Dye by Multistep Low‐Energy Solar‐Light‐Induced Electron Transfer Towards H2 Evolution

A photocatalytic system containing a perylene bisimide (PBI) dye as a photosensitizer anchored to titanium dioxide (TiO₂) nanoparticles through carboxyl groups was constructed. Under solar‐light irradiation in the presence of sacrificial triethanolamine (TEOA) in neutral and basic conditions (pH 8.5), a reaction cascade is initiated in which the PBI molecule first absorbs green light, giving the formation of a stable radical anion (PBI^.?), which in a second step absorbs near‐infrared light, forming a stable PBI dianion (PBI^2?). Finally, the dianion absorbs red light and injects an electron into the TiO₂ nanoparticle that is coated with platinum co‐catalyst for hydrogen evolution. The hydrogen evolution rates (HERs) are as high as 1216 and 1022 μmol h^?1 g^?1 with simulated sunlight irradiation in neutral and basic conditions, respectively.     

Spin–Orbit Charge-Transfer Intersystem Crossing in Anthracene–Perylenebisimide Compact Electron Donor–Acceptor Dyads and Triads and Photochemical Dianion Formation

Perylenebisimide ( PBI )–anthracene ( AN ) donor–acceptor dyads/triad were prepared to investigate spin–orbit charge-transfer intersystem crossing (SOCT-ISC). Molecular conformation was controlled by connecting PBI units to the 2- or 9-position of the AN moiety. Steady-state, time-resolved transient absorption and emission spectroscopy revealed that chromophore orientation, electronic coupling, and dihedral angle between donor and acceptor exert a significant effect on the photophysical property. The dyad PBI-9-AN with orthogonal geometry shows weak ground-state coupling and efficient intersystem crossing (ISC, Φ_Δ=86 %) as compared with PBI-2-AN (Φ_Δ=57 %), which has a more coplanar geometry. By nanosecond transient absorption spectroscopy, a long-lived PBI localized triplet state was observed (τ_T=139 μs). Time-resolved EPR spectroscopy demonstrated that the electron spin polarization pattern of the triplet state is sensitive to the geometry and number of AN units attached to PBI . Reversible and stepwise generation of near-IR-absorbing PBI radical anion ( PBI^−⋅ ) and dianion ( PBI²⁻ ) was observed on photoexcitation in the presence of triethanolamine, and it was confirmed that selective photoexcitation at the near-IR absorption bands of PBI^.− is unable to produce PBI²⁻ .     

Steering spatially separated dual sites on nano-TiO2 through SMSI and lattice matching for robust photocatalytic hydrogen evolution

Spatial isolation of different functional sites at the nanoscale in multifunctional catalysts for steering reaction sequence and paths remains a major challenge. Herein, we reported the spatial separation of dual-site Au and RuO₂ on the nanosurface of TiO₂ (Au/TiO₂/RuO₂) through the strong metal-support interaction (SMSI) and the lattice matching (LM) for robust photocatalytic hydrogen evolution. The SMSI between Au and TiO₂ induced the encapsulation of Au nanoparticles by an impermeable TiO_x overlayer, which can function as a physical separation barrier to the permeation of the second precursor. The LM between RuO₂ and rutile-TiO₂ can increase the stability of RuO₂/TiO₂ interface and thus prevent the aggregation of dual-site Au and RuO₂ in the calcination process of removing TiO_x overlayer of Au. The photocatalytic hydrogen production is used as a model reaction to evaluate the performance of spatially separated dual-site Au/TiO₂/RuO₂ catalysts. The rate of hydrogen production of the Au/TiO₂/RuO₂ is as high as 84 μmol h⁻¹ g⁻¹ under solar light irradiation without sacrificial agents, which is 2.5 times higher than the reference Au/TiO₂ and non-separated Au/RuO₂/TiO₂ samples. Systematic characterizations verify that the spatially separated dual-site Au and RuO₂ on the nanosurface of TiO₂ can effectively separate the photo-generated carriers and lower the height of the Schottky barrier, respectively, under UV and visible light irradiation. This study provides new inspiration for the precise construction of different sites in multifunctional catalysts.     

Efficient Photoredox Cycles to Control Perylenediimide Self-Assembly**

Photoreduction of perylenediimide (PDI) derivatives has been widely studied for use in photocatalysis, hydrogen evolution, photo-responsive gels, and organic semiconductors. Upon light irradiation, the radical anion (PDI⋅⁻) can readily be obtained, whereas further reduction to the dianion (PDI²⁻) is rare. Here we show that full 2-electron photoreduction can be achieved using UVC light: 1) in anaerobic conditions by ‘direct photoreduction’ of PDI aggregates, or 2) by ‘indirect photoreduction’ in aerobic conditions due to acetone ketyl radicals. The latter strategy is also efficient for other dyes, such as naphthalenediimide (NDI) and methylviologen (MV²⁺). Efficient photoreduction on the minute time-scale using simple LED light in aerobic conditions is attractive for use in dissipative light-driven systems and materials.     

Efficient One-Pot Microwave-Assisted Hydrothermal Synthesis of Nitrogen-Doped TiO2 for Hydrogen Production by Photocatalytic Water Splitting

Develop a photocatalyst system for solar energy conversion to electric energy or chemical energy is a topic of great interest for fundamental and practical importance. In this study, nitrogen-doped TiO₂ with high hydrogen production by photocatalytic water splitting were prepared by microwave-assisted hydrothermal method using titanium sulfate as precursor in the presence of urea. The nitrogen doped TiO₂ prepared in this study was pure anatase phase with a high surface area (372?m²?g^?1) and showed a very high hydrogen evolution rate of water splitting reaction under UV light irradiation (4,386?μmol?g^?1?h^?1) and visible light irradiation (185?μmol?g^?1?h^?1) which was about 15?times higher than commercial TiO₂ (Degussa P25).     

Photocatalytic Activity for Water Decomposition to Hydrogen over Nitrogen‐doped TiO2 Nanoparticle

Nitrogen-doped TiO2 nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV-Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 ℃. XPS studies indicate that the nitrogen atom enters the TiO2 lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N-doped samples from 44.61 to 38.27 m2/g are smaller than that of Degussa TiO2. UV-Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO2 annealed for 2 h at 400 ℃ under gas of NH3/N2 (V/V＝1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N-doped TiO2 nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ＞400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N-doped TiO2 annealed at 700 ℃.     

Photoexcitation of aqueous suspensions of titanium dioxide nanoparticles: an electron spin resonance spin trapping study of potentially oxidative reactions

It is well‐established that exposure of aqueous suspensions of titanium dioxide (TiO₂) nanoparticles to ultraviolet A (UVA) light produces reactive oxygen species which leads to biological damage. However, there is disagreement in the literature as to the exact nature of these species and how they are formed. Using a number of different spin traps (i.e. PBN, POBN, DMPO, DEPMPO), we have shown that the primary damaging species produced on irradiation of an aqueous suspension of TiO₂ is the hydroxyl radical, which is formed at the valence band hole under both aerobic and hypoxic conditions. Hydroxyl radical production is enhanced by the presence of oxygen which probably reacts with the conduction band electrons or resultant Ti³⁺, inhibiting hole‐electron recombination, although we find no evidence of reaction of oxygen to form free superoxide radical anions or of the formation of any other radical at that site. The present results suggest that the resulting O₂ ^?? species may not be as labile as previously thought and may possibly undergo further reduction to the O ₂ ^2? dianion. Hydroxyl radicals formed at the surface of the TiO ₂ readily react with substrates containing an abstractable hydrogen to produce secondary radicals that, in biological systems, could lead to cell damage.     

Ag@AgCl修饰的锐钛矿相TiO2纳米管的制备及其光催化性能

首先采用水热合成法和双氧水处理制备了具有锐钛矿相的TiO2纳米管,然后通过沉淀和光化学反应将Ag@AgCl纳米粒子负载于其上,从而制得TiO2纳米管负载的表面等离子体光催化剂.结果表明,经Ag@AgCl纳米粒子修饰后,锐钛矿相TiO2纳米管因表面等离子共振效应而对可见光具有明显的响应,光生电子-空穴对更容易分离,因而T...     

Disclosing Support-Size-Dependent Effect on Ambient Light-Driven Photothermal CO2 Hydrogenation over Nickel/Titanium Dioxide

The size of support in heterogeneous catalysts can strongly affect the catalytic property but is rarely explored in light-driven catalysis. Herein, we demonstrate the size of TiO₂ support governs the selectivity in photothermal CO₂ hydrogenation by tuning the metal-support interactions (MSI). Small-size TiO₂ loading nickel (Ni/TiO₂-25) with enhanced MSI promotes photo-induced electrons of TiO₂ migrating to Ni nanoparticles, thus favoring the H₂ cleavage and accelerating the CH₄ formation (227.7 mmol g⁻¹ h⁻¹) under xenon light-induced temperature of 360 °C. Conversely, Ni/TiO₂-100 with large TiO₂ prefers yielding CO (94.2 mmol g⁻¹ h⁻¹) due to weak MSI, inefficient charge separation, and inadequate supply of activated hydrogen. Under ambient solar irradiation, Ni/TiO₂-25 achieves the optimized CH₄ rate (63.0 mmol g⁻¹ h⁻¹) with selectivity of 99.8 %, while Ni/TiO₂-100 exhibits the CO selectivity of 90.0 % with rate of 30.0 mmol g⁻¹ h⁻¹. This work offers a novel approach to tailoring light-driven catalytic properties by support size effect.     

CdS Reinforced with CoSX/NiCo-LDH Core-shell Co-catalyst Demonstrate High Photocatalytic Hydrogen Evolution and Durability in Anhydrous Ethanol

At present, inefficient charge separation of single photocatalyst impedes the development of photocatalytic hydrogen evolution. In this work, the CoS_X/NiCo-LDH core-shell co-catalyst was cleverly designed, which exhibit high activity and high stability of hydrogen evolution in anhydrous ethanol system when coupled with CdS. Under visible light (λ≥420 nm) irradiation, the 3 %Co/NiCo/CdS composite photocatalyst exhibits a surprisingly high photocatalytic hydrogen evolution rate of 20.67 mmol g⁻¹ h⁻¹, which is 59 times than that of the original CdS. Continuous light for 20 h still showed good cycle stability. In addition, the 3 %Co/NiCo/CdS composite catalyst also shows good hydrogen evolution performance under the Na₂S/Na₂SO₃ and lactic acid system. The fluorescence (PL), ultraviolet-visible diffuse reflectance (UV-vis) and photoelectrochemical tests show that the coupling of CdS and CoS_X/NiCo-LDH not only accelerates the effective transfer of charges, but also greatly increases the absorption range of CdS to visible light. Therefore, the hydrogen evolution activity of the composite photocatalyst has been significantly improved. This work will provide new insights for the construction of new co-catalysts and the development of composite catalysts for hydrogen evolution in multiple systems.     

Electrons and Hydroxyl Radicals Synergistically Boost the Catalytic Hydrogen Evolution from Ammonia Borane over Single Nickel Phosphides under Visible Light Irradiation

From the perspective of tailoring the reaction pathways of photogenerated charge carriers and intermediates to remarkably enhance the solar-to-hydrogen energy conversion efficiency, we synthesized the three low-cost semiconducting nickel phosphides Ni₂P, Ni₁₂P₅ and Ni₃P, which singly catalyzed the hydrogen evolution from ammonia borane (NH₃BH₃) in the alkaline aqueous solution under visible light irradiation at 298 K. The systematic investigations showed that all the catalysts had higher activities under visible light irradiation than in the dark and Ni₂P had the highest photocatalytic activity with the initial turnover frequency (TOF) value of 82.7 min⁻¹, which exceeded the values of reported metal phosphides at 298 K. The enhanced activities of nickel phosphides were attributed to the visible-light-driven synergistic effect of photogenerated electrons (e⁻) and hydroxyl radicals (^.OH), which came from the oxidation of hydroxide anions by photogenerated holes. This was verified by the fluorescent spectra and the capture experiments of photogenerated electrons and holes as well as hydroxyl radicals in the catalytic hydrogen evolution process.     

Isoprene Heterogeneous Uptake and Reactivity on TiO2: A Kinetic and Product Study

The heterogeneous interaction of isoprene with TiO₂ surfaces was studied under dark and UV light irradiation conditions. The experiments were conducted at room temperature, using zero air as bath gas, in a flow reactor coupled with a SIFT‐MS (selected‐ion flow‐tube mass spectrometer) and a FTIR spectrometer for the gas‐phase monitoring of reactants and products. The steady‐state uptake coefficient and the yields of the products formed were measured as a function of TiO₂ mass (9–120 mg), light intensity (37–112 W m⁻²), isoprene concentration (36–12000 ppb), and relative humidity (0.01–90% of RH). Under dark and dry conditions, isoprene was efficiently and reversibly adsorbed on TiO₂. In contrast, under humid conditions, isoprene uptake was diminished, pointing to competitive adsorption with water molecules. In the presence of UV light irradiation, isoprene reacted on the surface of TiO₂. The reactive steady‐state uptake coefficient, γ_ss, was independent of RH under most ambient relative humidity conditions (>50%). However, γ_ss was strongly dependent on isoprene initial concentration according to the empirical expression: γ_ss = (2.0 × 10⁻⁴) × [isoprene] with n = 0.35 and 0.28 for 37 and 112 W m⁻² irradiation conditions, respectively. In addition to the kinetics, a detailed product study was performed. The gas‐phase oxidation products were mostly CO₂ (ca. 90% of the carbon mass balance) and a large variety of carbonyl compounds (methyl vinyl ketone, acetone, methacrolein, formaldehyde, acetaldehyde, propanal, traces of butanal, and pentanal), the distribution of which was investigated as a function of mineral oxide mass, isoprene concentration, and RH. Furthermore, the surface‐adsorbed products were determined employing off‐line HPLC chromatography; their concentrations were inversely dependent on RH and decreased to background levels at RH greater than 30%. Finally, the reaction mechanism and possible implications of isoprene reaction on TiO₂ are briefly discussed.     

Novel Photodynamic Therapy Using Water-dispersed TiO2–Polyethylene Glycol Compound: Evaluation of Antitumor Effect on Glioma Cells and Spheroids In Vitro

Titanium dioxide (TiO₂) is thought to be a photocatalytic agent excited by UV light. Our aim was to investigate the photocatalytic antitumor effect of water-dispersed TiO₂ nanoparticles on C6 rat glioma cells and to evaluate the treatment responses by the spheroid models. Water-dispersed TiO₂ nanoparticles were constructed by the adsorption of chemical modified polyethylene glycol (PEG) on the TiO₂ surface (TiO₂/PEG). Each monolayer and spheroid of C6 cells was coincubated with various concentrations of TiO₂/PEG and subsequently irradiated with UV light. Damage of the cells and spheroids was evaluated sequentially by staining with the fluorescent dyes. The cytotoxic effect was correlated with the concentration of TiO₂/PEG and the energy dose of UV irradiation. More than 90% of cells were killed after 13.5 J cm⁻² of UV irradiation in the presence of 500 μg mL⁻¹ TiO₂/PEG. The irradiated spheroids in the presence of TiO₂/PEG showed growth suppression compared with control groups. In TiO₂/PEG-treated spheroids, the number of Annexin V-FITC-stained cells gradually increased during the first 6 h, and subsequently propidium iodide-stained cells appeared. The results of this study suggest that newly developed photoexcited TiO₂/PEG have antitumoral activity. Photodynamic therapy utilizing this material can be a clue to a novel therapeutic strategy for glioma.     

MOFs Conferred with Transient Metal Centers for Enhanced Photocatalytic Activity

Highly effective photocatalysts for the hydrogen‐evolution reaction were developed by conferring the linkers of NH₂‐MIL‐125(Ti), a metal–organic framework (MOF) constructed from TiO_x clusters and 2‐aminoterephthalic acid (linkers), with active copper centers. This design enables effective transfer of electrons from the linkers to the transient Cu²⁺/Cu⁺ centers, leading to 7000‐fold and 27‐fold increase of carrier density and lifetime of photogenerated charges, respectively, as well as high‐rate production of H₂ under visible‐light irradiation. This work provides a novel design of a photocatalyst for hydrogen evolution using non‐noble Cu²⁺/Cu⁺ as co‐catalysts.     

Effect of HF treatment on the activity of TiO2 thin films for photocatalytic water splitting

The effects of HF treatment on the activity of TiO₂ thin films for the photocatalytic water splitting reaction have been investigated. TiO₂ thin films treated with HF solution (HF-TiO₂) were found to exhibit a remarkable enhancement of the photocatalytic activity for H₂ evolution from a methanol aqueous solution, as well as efficient photoelectrochemical performance under UV light irradiation as compared with the untreated TiO₂. Moreover, Pt-loaded HF-TiO₂ thin films were found to act as efficient and stable photocatalysts for the decomposition of water under UV light irradiation. The mechanistic insights obtained in the present study will be useful in the design of highly efficient photocatalysts for the decomposition of water.     

Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution

Post-coordination design on covalent organic frameworks (COFs) is an efficient strategy for elevating the photocatalytic activity of organic moiety. However, the rigid skeletons and densely layered stacking of two-dimensional (2D) COFs cannot be flexibly adapted for specific conformations of metal complexes, thereby impairing the metal-COF cooperation. Here, we adopt a solvothermal method to immobilize nickel(II) ions into a 2,2′-bipyridine-containing 2D COF, forming a stable coordination motif. Such the complex remarkably enhances the photocatalytic performance, giving an optimized H₂ evolution rate of as high as 51 300 μmol h⁻¹ g⁻¹, 2.5 times higher than the pristine COF. The evolved hydrogen gas can also be detected upon 700-nm light irradiation, while its analog synthesized by the traditional coordination method is photo-catalytically inert. This work provides a strategy for optimizing the metal-COF coordination system and strengthening a synergy for electronic regulation in photocatalysis.     

可见光驱动的光催化产氢同时诱导低能核反应嬗变钾为钙

报道了曙红、氯铂酸钾、氧化石墨烯和三乙醇胺混合物悬浮体系在可见光照射条件下将钾嬗变为钙的现象.在大于440 nm光照的条件下,反应体系可以产生大量的氢气,同时体系中的部分钾原子转变为钙元子.在反应过程中,悬浮混合物中的钙元素浓度持续增加,同时伴随发生质子的还原为氢和部分质子反应为氦3和氦4的反应.分析表明,在自然界的某种环境和条件下,钙有可能通过在温和条件下的低能核反应(LENR)经历钾的嬗变生成,这个过程可能与光催化产氢过程中生成的负氢有关.     

Pt deposited TiO2 catalyst fabricated by thermal decomposition of titanium complex for solar hydrogen production

C, N codoped TiO₂ catalyst has been synthesized by thermal decomposition of a novel water-soluble titanium complex. The structure, morphology, and optical properties of the synthesized TiO₂ catalyst were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the Pt deposited TiO₂ catalysts synthesized at different temperatures was evaluated by means of hydrogen evolution reaction under both UV–vis and visible light irradiation. The investigation results reveal that the photocatalytic H₂ evolution rate strongly depended on the crystalline grain size as well as specific surface area of the synthesized catalyst. Our studies successfully demonstrate a simple method for the synthesis of visible-light responsive Pt deposited TiO₂ catalyst for solar hydrogen production.     

Facile Synthesis of Thermal‐ and Photostable Titania with Paramagnetic Oxygen Vacancies for Visible‐Light Photocatalysis

A novel dopant‐free TiO₂ photocatalyst (V_o^.‐TiO₂), which is self‐modified by a large number of paramagnetic (single‐electron‐trapped) oxygen vacancies, was prepared by calcining a mixture of a porous amorphous TiO₂ precursor, imidazole, and hydrochloric acid at elevated temperature (450 °C) in air. Control experiments demonstrate that the porous TiO₂ precursor, imidazole, and hydrochloric acid are all necessary for the formation of V_o^.‐TiO₂. Although the synthesis of V_o^.‐TiO₂ originates from such a multicomponent system, this synthetic approach is facile, controllable, and reproducible. X‐ray diffraction, XPS, and EPR spectroscopy reveal that the V_o^.‐TiO₂ material with a high crystallinity embodies a mass of paramagnetic oxygen vacancies, and is free of other dopant species such as nitrogen and carbon. UV/Vis diffuse‐reflectance spectroscopy and photoelectrochemical measurement demonstrate that V_o^.‐TiO₂ is a stable visible‐light‐responsive material with photogenerated charge separation efficiency higher than N‐TiO₂ and P25 under visible‐light irradiation. The V_o^.‐TiO₂ material exhibits not only satisfactory thermal‐ and photostability, but also superior photocatalytic activity for H₂ evolution (115 μmol h^?1 g^?1) from water with methanol as sacrificial reagent under visible light (λ>400 nm) irradiation. Furthermore, the effects of reaction temperature, ratio of starting materials (imidazole:TiO₂ precursor) and calcination time on the photocatalytic activity and the microstructure of V_o^.‐TiO₂ were elucidated.     

The Hexacyanodiborane(6) Dianion [B2(CN)6]2−

Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B₂(CN)₆]²⁻ that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H₃O)₂[B₂(CN)₆] starts at 200 °C. The [B₂(CN)₆]²⁻ dianion is readily accessible starting from 1) B(CN)₃²⁻ and an oxidant, 2) [BF(CN)₃]⁻ and a reductant, or 3) by the reaction of B(CN)₃²⁻ with [BHal(CN)₃]⁻ (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an S_N2 mechanism.