Photochemical hydrogen production from water using three-dimensional Zn-Pd metal-organic frameworks

A Zn-Pd heterometallic metal-organic framework (MOF) based on 3,5-pyridine-dicarboxylic acid (H2-pydc), namely [Zn2(H2O)3{PdCl2(pydc)2}]n (Zn-Pd-2) was successfully synthesized by a slow diffusion method and characterized by single-crystal X-ray diffraction, CHN elemental analysis, FT-IR spectroscopy, thermogravimetric (TG) analysis and N2 gas adsorption measurement. The single-crystal X-ray analysis revealed that the framework morphology of Zn-Pd-2 is as same as that of [Zn2(DMF)3{PtCl2(pydc)2}]n. The Zn-Pd-2 was found to be an effective catalytic performance for the photochemical reduction of water in a well-known photo-system made up of [Ru(bpy)3Cl2] (bpy = 2,2'-bipyridine), MV(2+) (methyl-viologen) and Na2 EDTA (Disodium ethylenediaminetetraacetate); 20.2 turnover based on Zn-Pd-2 was achieved at 4 h irradiation.     

Photochemical hydrogen production from a water-methanol mixture with small particles of iron oxide suspensions

Photochemical hydrogen production has been detected from small particles of doped iron oxide in a methanol-water (1:1) mixture. The systems studied consisted of a pure n-type semiconductor, Fe_2−xNb_xO₃ (x=0.02), a pure p-type semiconductor, La_1−xSr_xFeO₃ (x=0.25), and Mg-doped α-Fe₂O₃. This system was found to be heterogeneous, consisting of both spinel and corundum phase iron oxides, and shows a much higher activity than the pure single phase systems, with either corundum (α-Fe₂O₃) or spinel (Fe_3−xMg_xO_y) structure. The efficiency of the reaction increased substantially when the powders were loaded with Pt. Hydrogen production from these Mg-doped iron oxides is photo-ocatalytic and occurs mainly as a result of bandgap irradiation, but also occurs with sub-bandgap illumination in small amounts. There is a linearly increasing dependence of the H₂ production with increasing light intensity.     

苯基修饰微孔SiO2膜的氢气分离和水煤气变换反应性能

通过正硅酸乙酯与苯基三乙氧基硅烷共水解缩聚反应制备苯基修饰SiO2膜,研究膜材料的氢气渗透和分离性能,并将其作为膜反应器的关键材料应用于水煤气变换反应.结果表明,氢气在苯基修饰SiO2膜中的渗透率随着温度的升高而增大,遵循活化扩散机理,300℃下H2渗透率达到4.67×10-7 mol/(m2·s·Pa),理想分离系数H2/CO、H2/CO2和H2/SF6分别达到10.54、10.50、21.16.在300℃,反应物H2O/CO摩尔比为2∶1的条件下进行水煤气变换反应,膜反应器的CO的转化率比传统固定床反应的CO的转化率高约12％,其原因是苯基修饰的SiO2膜对H2具有一定的选择性.     

Photochemical treatment of phenol aqueous solutions using ultraviolet radiation and hydrogen peroxide

The potential of purifying phenol aqueous solutions (0.0006-0.0064 M) using ultraviolet (UV) radiation and hydrogen peroxide (H2O2; 0.005-0.073 M) was investigated. Although the direct photolysis of phenol and its oxidation by hydrogen peroxide (without ultraviolet light) were insignificant, the combination of UV and H2O2 was extremely effective on phenol degradation. However, the chemical oxygen demand was on no occasion entirely eliminated, indicating the resistance of the intermediate products formed to the photo-oxidation. Increasing the initial concentration of phenol had as a result lower phenol conversions achieved, whereas the increase in hydrogen peroxide initial concentration enhanced significantly the degradation of phenol. In contrast, COD removal was less sensitive to these changes.     

A metal-free polymeric photocatalyst for hydrogen production from water under visible light

The production of hydrogen from water using a catalyst and solar energy is an ideal future energy source, independent of fossil reserves. For an economical use of water and solar energy, catalysts that are sufficiently efficient, stable, inexpensive and capable of harvesting light are required. Here, we show that an abundant material, polymeric carbon nitride, can produce hydrogen from water under visible-light irradiation in the presence of a sacrificial donor. Contrary to other conducting polymer semiconductors, carbon nitride is chemically and thermally stable and does not rely on complicated device manufacturing. The results represent an important first step towards photosynthesis in general where artificial conjugated polymer semiconductors can be used as energy transducers.     

Synthesis of Pt doped Bi2O3/RuO2 photocatalysts for hydrogen production from water splitting using visible light

This study was focused on the preparation of modified bismuth oxide photocatalysts, including Ru and Pt doped Bi2O3, using sonochemically assisted method to enhance their photocatalytic activity. The crystalline phase composition and surface structure of Bi2O3 photocatalysts were examined using SEM, XRD, UV-visible spectroscopy, and XPS. Optical characterizations have indicated that the Bi2O3 presents the photoabsorption properties shifting from UV light region into visible light which is approaching towards the edge of 470 nm. According to the experimental results, visible-light-driven photocatalysis for water splitting with the addition of 0.3 M Na2SO3 and 0.03 M H2C2O4 as sacrificing agents demonstrates that Pt/Bi2O3-RuO2 catalyst could increase the amount of hydrogen evolution, which is around 11.6 and 14.5 micromol g(-1) h(-1), respectively. Plausible formation mechanisms of modified bismuth oxide and reaction mechanisms of photocatalytic water splitting have been proposed.     

Scanning tunneling microscopy with chemically modified tips: discrimination of porphyrin centers based on metal coordination and hydrogen bond interactions

STM gold tips chemically modified with 4-mercaptopyridine (4MP) were found capable of discriminating zinc(II) 5,15-bis(4-octadecyloxyphenyl)porphyrin (Por-Zn) from its metal-free porphyrin (Por-2H) and nickel(II) complexes (Por-Ni) in the mixed monolayers of these compounds, spontaneously formed at the solution/graphite interface. The porphyrin centers in STM images observed with 4MP-modified tips exhibited bright spots, while those measured with unmodified tips exhibited the porphyrin centers as dark depressions. The centers of Por-Zn were brighter than those of Por-2H and Por-Ni, thereby allowing the discrimination of Por-Zn from Por-2H or Por-Ni in mixed monolayers. The changes in the contrasts of porphyrin centers of Por-2H and Por-Zn/ Por-Ni were explained by facilitated electron tunneling due to hydrogen bond and metal coordination interactions, respectively, between porphyrin centers and the pyridyl group of 4MP on the tip.     

Characterization of water in microporous titanium silicates

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Ultrasonic wave field effects on hydrogen production by water electrolysis

In this paper, Electrochemical impedance spectroscopy (EIS) was used to examine polarization impedance phenomena in ultrasonic water electrolysis. The method has been used previously for electrochemical analysis of fuel cells, corrosion, electroplating, etc. However, the EIS method and curvilinear regression have never been used before to analyze the electrochemical reactions which take place during water electrolysis. This study found that when a 2?V potential was applied, the ultrasonic wave field improved activity impedances and concentration impedances and accelerated the rising of hydrogen bubbles during water electrolysis. Ultrasonic power, electrode gap, and electrolyte concentration were the key parameters that affected water electrolysis. At normal temperature, when the electrode gap was 2?mm, the potential 4?V, and electrolyte concentration 40 wt%, the difference in current density between electrolysis without ultrasonic power and electrolysis with ultrasonic power of 225?W was 240?mA/cm². Deducting the power needed for the ultrasonic wave showed an power savings of 3.5?kW and an economical power efficiency of 15%.     

Ab initio study of hydrogen binding on Ca-inserted porphyrin

To study the binding of hydrogen molecules on Ca-inserted porphyrin, we perform ab initio pseudopotential calculations within the local density approximation (LDA). One Ca atom is inserted in the central N₄ cavity formed by the removal of two hydrogen atoms of porphin. By increasing the number of hydrogen molecules, we investigate hydrogen binding on Ca-inserted porphyrin for hydrogen storage. We find that the binding energy of H₂ molecules to the Ca atom is ∼0.25 eV/H₂ up to four hydrogen molecules. When the fifth or sixth H₂ molecule is adsorbed on the Ca atom, the molecule is adsorbed onto Ca-porphyrin with the average binding energy of ∼0.2 eV/H₂. Examining the projected density of states, we study orbital hybridization between the Ca atom and hydrogen molecule. Finally, the possibility of Ca-porphyrin as a hydrogen storage material is discussed.     

Photochemical treatment of 2-chlorophenol aqueous solutions using ultraviolet radiation, hydrogen peroxide and photo-Fenton reaction

In the present work, the photochemical oxidation of 2-chlorophenol aqueous solutions in a batch recycle photochemical reactor using ultraviolet irradiation and hydrogen peroxide was studied. Specifically, the effect of hydrogen peroxide initial concentration (0-10316 mg L(-1)) and 2-chlorophenol initial concentration (150-3000 mg L(-1)) was examined. The process was attended via total organic carbon (TOC), 2-chlorophenol, chloride ion, acetic acid, formic acid and pH measurements. The conversion of 2-chlorophenol observed was always much higher than the corresponding total organic carbon removal, whereas the increase in hydrogen peroxide amount in the solution led to higher values of 2-chlorophenol conversion and total organic carbon removal. Finally, the photo-Fenton reaction was applied to the oxidation of 2-chlorophenol, leading to a higher degree of mineralization of the parent compound.     

On-demand production of hydrogen by reacting porous silicon nanowires with water

On-demand hydrogen generation is desired for fuel cells, energy storage, and clean energy applications. Silicon nanowires (SiNWs) and nanoparticles (SiNPs) have been reported to generate hydrogen by reacting with water, but these processes usually require external assistance, such as light, electricity or catalysts. Herein, we demonstrate that a porous SiNWs array, which is fabricated via the metal-assisted anodic etching (MAAE) method, reacts with water under ambient and dark conditions without any energy inputs. The reaction between the SiNWs and water generates hydrogen at a rate that is about ten times faster than the reported rates of other Si nanostructures. Two possible sources of enhancement are discussed: SiNWs maintain their high specific surface area as they don’t agglomerate, and the intrinsic strain of the nanowires promotes the reactivity. Moreover, the porous SiNWs array is portable, reusable, and environmentally friendly, yielding a promising route to produce hydrogen in a distributed manner.

     

Application of BICOVOX catalyst for hydrogen production from ethanol

Catalytic activity of cobalt-doped bismuth vanadate [Bi₄(V_0.90Co_0.10)₂O_11?δ ; BICOVOX] powder, prepared by a solution combustion synthesis and calcined at 800 °C (BICOVOX-800), for hydrogen production using low-temperature steam reforming of ethanol, has been reported in this paper. The effects of reaction temperature (250–400 °C) and feed concentration (H₂O/EtOH = 2.5:1 and 23:1 mol ratio) on the steady-state ethanol conversion and selectivity of H₂, CO₂, CO, and CH₄ have been investigated (up to 30 h). It is observed that with an increase in reaction temperature and H₂O/EtOH mole ratio, H₂ and CO₂ selectivity increases and CO and CH₄ selectivity decreases. The maximum H₂ selectivity and ethanol conversion are observed to be 63 and 88%, respectively, for H₂O/EtOH = 23:1 mol ratio at 400 °C. The XRD results show that the fresh BICOVOX-800 has pure γ-phase and is highly crystalline. The used catalyst (more than 150 h total) is detected to have less crystallinity and to partially decompose into Bi₂O₃ and BiVO₄ phases.     

Photocatalytic hydrogen production from seawater under full solar spectrum without sacrificial reagents using TiO2 nanoparticles

Photocatalytic water splitting(PWS)has attracted widespread attention as a sustainable method for converting solar to green hydrogen energy.So far PWS research ...     

ZnS/TiO2聚砜纤维复合材料的制备及其光催化水制氢性能的研究

利用高压静电纺丝制备了具有良好耐光降解性能的羧基聚砜电纺纤维毡,利用其为载体用水热反应法制备了ZnS/TiO2聚砜复合光催化材料,得到了分布均匀的ZnS/TiO2聚砜纤维复合材料。通过X射线衍射、光电子能谱、紫外-可见漫反射光谱、热失重、耐紫外光降解实验对复合材料进行了表征。光催化分解水制氢实验表明:ZnS/TiO2含羧基聚砜纤维复合材料的催化效率高于同等条件下粉体ZnS/TiO2,并且具有很好的重复稳定性。     

De novo synthesis of bifunctional conjugated microporous polymers for synergistic coordination mediated uranium entrapment

This work reports a de novo synthesis of novel bifunctional conjugated microporous polymers(CMPs)exhibiting a synergistic-effect involved coordination behavior to uranium.It is highlighted that the synthetic strategy enables the engineering of the coordination environment within amidoxime functionalized CMP frameworks by specifically introducing ortho-substituted amino functionalities,enhancing the affinity to uranyl ions via forming synergistic complexes.The CMPs exhibit high Brunauer-Emmett-Teller(BET)surface area,well-developed three-dimensional(3D)networks with hierarchical porosity,and favorable chemical and thermal stability because of the covalently cross-linked structure.Compared with the amino-free counterparts,the adsorption capacity of bifunctional CMPs was increased by almost 70%,from 105 to 174 mg/g,indicating evidently enhanced binding ability to uranium.Moreover,new insights into coordination mechanism were obtained by in-depth X-ray photoelectron spectroscopy(XPS)analysis and density functional theory(DFT)calculation,suggesting a dominant role of the oxime ligands forming a 1:1 metal ions/ligands(M/L)coordination model with uranyl ions while demonstrating the synergistic engagement of the amino functionalities via direct binding to uranium center and hydrogen-bonding involved secondary-sphere interaction.This work sheds light on the underlying principles of ortho-substituted functionalities directed synergistic effect to promote the coordination of amidoxime with uranyl ions.And the synthetic strategy established here would enable the task-specific development of more novel CMP-based functional materials for broadened applications.     

Enhanced photoelectrochemical hydrogen production from silicon nanowire array photocathode

Herein we report that silicon nanowires (SiNWs) fabricated via metal-catalyzed electroless etching yielded a photoelectrochemical hydrogen generation performance superior to that of a planar Si, which is attributed to a lower kinetic overpotential due to a higher surface roughness, favorable shift in the flat-band potential, and light-trapping effects of the SiNW surface. The SiNW photocathode yielded a photovoltage of 0.42 V, one of the highest values ever reported for hydrogen generation on p-type Si/electrolyte interfaces.     

Techno-economic analysis of green hydrogen production from biogas autothermal reforming

The development and deployment of energy mix hydrogen production technologies, and the prospect of supplying “green” hydrogen to fuel-cell cars are expected to play significant roles in the near future. The sustainability of the process is a key enabler for a hydrogen-including economy. A techno-economic analysis of the BioRobur technology, which involves the green hydrogen production of 100 N m³ H₂/h (5.0 grade), has been performed in this study to provide a basis for comparison between the final cost of the hydrogen and the European target. Moreover, a technology for its eventual implementation has been addressed, in which the weakness and strengths have been identified by means of a SWOT analysis. The cost and supply analysis of this biogas-to-hydrogen production system, via autothermal reforming, indicates that municipal solid waste (MSW) is an important source of the low-cost supply of biogas-derived hydrogen. As far as the market potential is concerned, this analysis suggests that MSW can provide about 286,607 kg/day at 5 €/kg H₂ (delivery cost). Additionally, after 10 years of amortization, the final cost to produce 100 N m³/h of H₂ would be 2.5 €/kg, which is far lower than the European target for the cost of obtaining H₂ through biogas reforming, that is, 5 €/kg of H₂.     

Control of the axial coordination of a surface-confined manganese (III) porphyrin complex

The organization and thermal lability of chloro(5,10,15,20-tetraphenyl porphyrinato)manganese(III) (Cl-MnTPP) molecules on the Ag(111) surface have been investigated under ultra-high vacuum conditions, using scanning tunnelling microscopy, low energy electron diffraction and x-ray photoelectron spectroscopy. The findings reveal the epitaxial nature of the molecule-substrate interface, and moreover, offer a valuable insight into the latent coordination properties of surface-confined metalloporphyrins. The Cl-MnTPP molecules are found to self-assemble on the Ag(111) surface at room temperature, forming an ordered molecular overlayer described by a square unit cell. In accordance with the threefold symmetry of the Ag(111) surface, three rotationally equivalent domains of the molecular overlayer are observed. The primitive lattice vectors of the Cl-MnTPP overlayer show an azimuthal rotation of ±15° relative to those of the Ag(111) surface, while the principal molecular axes of the individual molecules are found to be aligned with the substrate (0(-)11) and ((-)211) crystallographic directions. The axial chloride (Cl) ligand is found to be orientated away from the Ag(111) surface, whereby the average plane of the porphyrin macrocycle lies parallel to that of the substrate. When adsorbed on the Ag(111) surface, the Cl-MnTPP molecules display a latent thermal lability resulting in the dissociation of the axial Cl ligand at ~423 K. The thermally induced dissociation of the Cl ligand leaves the porphyrin complex otherwise intact, giving rise to the coordinatively unsaturated Mn(III) derivative. Consistent with the surface conformation of the Cl-MnTPP precursor, the resulting (5,10,15,20-tetraphenyl porphyrinato)manganese(III) (MnTPP) molecules display the same lattice structure and registry with the Ag(111) surface.