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In order to address the current energy and environmental challenges, photoelectrochemical (PEC) water splitting has been widely studied, and the key point about the efficient PEC process is how to develop highly active photoanode catalysts. In this article, we report a two-step hydrothermal and electrodeposition approach to prepare a cobalt (oxy)-hydroxide (CoOOH)-modified Ti-Fe2O3-In2O3 electrode by synergy of electron modulation and a heterojunction structure for promoting PEC water splitting. Under a bias of 1.23 V vs RHE, the optimized Ti-Fe2O3-In2O3/CoOOH photoanode demonstrated remarkable photocurrent density and hydrogen evolution rate as high as 1.33 mA cm–2 and 22.8 μmol cm–2 h–1, which was 5.11-fold and 5.14-fold that of bare α-Fe2O3, respectively. Characterization results indicate that Ti-doping will alter the electronic structure and improve the charge carrier density, whereas the construction of a heterojunction can realize the spatial separation of charge carriers. Meanwhile, the outer CoOOH ultrathin layer can provide a large amount of oxygen evolution reaction sites and promote the surface reaction. This work suggests that the PEC performance of Fe2O3-based photoanodes can be improved effectively by the synergy of electronic modulation and heterojunction construction. [ABSTRACT FROM AUTHOR]

Hierarchical TiO2 was prepared via hydrolysis method and characterized by XRD, N2 adsorption–desorption, UV–vis diffusion, and NH3–TPD. With the increase of calcination temperature, the surface area and surface hydroxyls of prepared materials decrease rapidly. The photoactivity was evaluated using the self-sensitized photodegradation of rhodamine B under visible light. The fresh samples show higher activity than P-25 due to higher surface area and more effective light utilization. After stored in air for ca. half a year, the materials show significantly increased photoactivity, due to the prebonding of water on surface bridging hydroxyls, which induces water-mediated adsorption switch from covalent mode to electrostatic one. Water treatment further promotes the photoactivity of stored samples, because more water are bonded on TiO2 surface. It is found that the water-mediated effect closely depends on the surface area and amount of surface bridging hydroxyls. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) severely limits the efficiency of proton exchange membrane (PEM) electrolyzers due to slow reaction kinetics. IrO 2 is currently a commonly used anode catalyst, but its large-scale application is limited due to its high price and scarce reserves. Herein, we reported a practical strategy to construct an acid OER catalyst where Iridium oxide loading and iridium element bulk doping are realized on the surface and inside of W 18 O 49 nanowires by immersion adsorption, respectively. Specifically, W 0.7 Ir 0.3 O y has an overpotential of 278 mV at 10 mA·cm -2 in 0.1 M HClO 4 . The mass activity of 714.10 A·g Ir -1 at 1.53 V vs. the reversible hydrogen electrode (RHE) is 80 times that of IrO 2 , and it can run stably for 55 h. In the PEM water electrolyzer device, its mass activity reaches 3563.63 A·g Ir -1 at the cell voltage of 2.0 V. This improved catalytic performance is attributed to the following aspects: (1) The electron transport between iridium and tungsten effectively improves the electronic structure of the catalyst; (2) the introduction of iridium into W 18 O 49 by means of elemental bulk doping and nanoparticles supporting for the enhanced conductivity and electrochemically active surface area of the catalyst, resulting in extensive exposure of active sites and increased intrinsic activity; and (3) during the OER process, partial iridium elements in the bulk phase are precipitated, and iridium oxide is formed on the surface to maintain stable activity. This work provides a new idea for designing oxygen evolution catalysts with low iridium content for practical application in PEM electrolyzers.

Dynamic reconstruction of catalyst active sites is particularly important for metal oxide-catalyzed oxygen evolution reaction (OER). However, the mechanism of how vacancy-induced reconstruction aids OER remains ambiguous. Here, we use Co 3 O 4 with Co or O vacancies to uncover the effects of different defects in the reconstruction process and the active motifs relevant to alkaline OER. Combining in situ characterization and theoretical calculations, we found that cobalt oxides are converted to an amorphous [Co(OH) 6 ] intermediate state, and then the mismatched rates of *OH adsorption and deprotonation lead to irreversible catalyst reconstruction. The stronger *OH adsorption but weaker deprotonation induced by O defects provides the driving force for reconstruction, while Co defects favor dehydrogenation and reduce the reconstruction rate. Importantly, both O and Co defects trigger highly OER-active bridge Co sites in reconstructed catalysts, of which Co defects induce a short Co-Co distance (3.38 Å) under compressive lattice stress and show the best OER activity (η 10 of 262 mV), superior to reconstructed oxygen-defected Co 3 O 4 -V O (η 10 of 300 mV) and defect-free Co 3 O 4 (η 10 of 320 mV). This work highlights that engineering defect-dependent reconstruction may provide a rational route for electrocatalyst design in energy-related applications.

Dispersing single palladium atoms on a support is promising to minimize the usage of palladium and improve the selectivity for alkyne semihydrogenation, but its activity is often very low as a result of unfavorable H 2 activation. Here, we load palladium onto α-Fe 2 O 3 (012) to construct highly active and stable single-site Pd-Fe pairs with luxuriant d-electron domination near the Fermi level driven by strong electronic coupling and prove that Pd-Fe pairs cooperatively adsorb H 2 and dissociate an H─H bond, whereas solo Pd sites enable preferential desorption of C═C intermediate, thus achieving both high activity and high selectivity for alkyne hydrogenation. This catalyst exhibits state-of-the-art performance in purifying acetylene of ethylene stream, with 99.6% and 100% conversion and 96.7% and 94.7% selectivity at 353 and 393 K, respectively, and excellent stability with negligible activity decay after a 200 h test. This single-site pair inherits the advantage but overcomes the weakness of both Pd ensemble and single Pd atoms, enabling ultralow-Pd-loading catalysts for selective hydrogenation.

The development of highly active, universal, and stable inexpensive electrocatalysts/cocatalysts for hydrogen evolution reaction (HER) by morphology and structure modulations remains a great challenge. Herein, a simple self-template strategy was developed to synthesize hollow Co-based bimetallic sulfide (MxCo3-xS4, M = Zn, Ni, and Cu) polyhedra with superior HER activity and stability. Homogenous bimetallic metal-organic frameworks are transformed to hollow bimetallic sulfides by solvothermal sulfidation and thermal annealing. Electrochemical measurements and density functional theory computations show that the combination of hollow structure and homoincorporation of a second metal significantly enhances the HER activity of Co3S4. Specifically, the homogeneous doping in Co3S4 lattice optimizes the Gibbs free energy for H* adsorption and improves the electrical conductivity. Impressively, hollow Zn0.30Co2.70S4 exhibits electrocatalytic HER activity better than most of the reported nobel-metal-free electrocatalysts over a wide pH range, with overpotentials of 80, 90, and 85 mV at 10 mA cm(-2) and 129, 144, and 136 mV at 100 mA cm(-2) in 0.5 M H2SO4, 0.1 M phosphate buffer, and 1 M KOH, respectively. It also exhibits photocatalytic HER activity comparable to that of Pt cocatalyst when working with organic photosensitizer (Eosin Y) or semiconductors (TiO2 and C3N4). Furthermore, this catalyst shows excellent stability in the electrochemical and photocatalytic reactions. The strategy developed here, i.e., homogeneous doping and self-templated hollow structure, provides a way to synthesize transition metal sulfides for catalysis and energy conversion.

Defects are critically important for metal oxides in chemical and physical applications. Compared with the often studied oxygen vacancies, engineering metal vacancies in n-type undoped metal oxides is still a great challenge, and the effect of metal vacancies on the physiochemical properties is seldom reported. Here, using anatase TiO2, the most important and widely studied semiconductor, we demonstrate that metal vacancies (VTi) can be introduced in undoped oxides easily, and the presence of VTi results in many novel physiochemical properties. Anatase Ti0.905O2 was synthesized using solvothermal treatment of tetrabutyl titanate in an ethanol-glycerol mixture and then thermal calcination. Experimental measurements and DFT calculations on cell lattice parameters show the unstoichiometry is caused by the presence of VTi rather than oxygen interstitials. The presence of VTi changes the charge density and valence band edge of TiO2, and an unreported strong EPR signal at g = 1.998 presents under room temperature. Contrary to normal n-type and nonferromagnetic TiO2, Ti-defected TiO2 shows inherent p-type conductivity with high charge mobility, and room-temperature ferromagnetism stronger than Co-doped TiO2 nanocrystalline. Moreover, Ti-defected TiO2 shows much better photocatalytic performance than normal TiO2 in H2 generation (4.4-fold) and organics degradation (7.0-fold for phenol), owing to the more efficient charge separation and transfer in bulk and at semiconductor/electrolyte interface. Metal-defected undoped oxides represent a unique material; this work demonstrates the possibility to fabricate such material in easy and reliable way and thus provides new opportunities for multifunctional materials in chemical and physical devices.

In this work, we demonstrate a convenient, efficient, and environmentally benign strategy to achieving antimicrobial and antiadhesive purposes using a silver-zwitterion nanocomposite. The synthesis of the nanocomposite relies on loading zwitterionic polymer brushes with Ag(+) precursor ions, followed by their in situ reduction to Ag nanoparticle by ultraviolet (UV) irradiation. Both poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA) have been studied as matrices for the embedding of silver. Well-dispersed silver nanoparticles are embedded into pCBMA matrices. The obtained pCBMA-silver hybrid (CB-Ag) is capable of killing bacteria upon contact and releasing dead bacteria under wet conditions. Results suggest the feasibility of using this nanocomposite system as a robust and reliable antimicrobial and antiadhesive platform for the prevention of microbial colonization.

A computational study using a hybrid DFT method (M06) on the cyclopropanation of endo-dicyclopentadiene with Simmons-Smith zinc carbenoids is reported. Each channel proceeds via the methylene-transfer mechanism with a reactant complex (RC) and subsquently a asynchronous transition state (TS). The channels with monomeric IZnCH(2)I attacking the double bonds from the exo-face have a much lower barrier (about 16.17-18.43 kcal/mol) in the gas phase, compared with the channels from the endo-face (21.80-31.13 kcal/mol). Thus, P1 and P3 are the primary cyclopropanated compounds, and P5 is the sole final product, representing remarkable stereospecificity. When considering the bulk solvent effect of diethyl ether, the barriers are decreased about 0.50-7.77 kcal/mol due to more "destabilization" of RC than TS. The solvated (ICH(2))(2)Zn can further reduce the barriers about 0.18-2.30 kcal/mol. In addition, the solvated IZnCH(2)I and (ICH(2))(2)Zn do not change the reaction pathways and retain the stereospecificity. Our computational results agree with the experimental observations quite well and suggest that both IZnCH(2)I and (ICH(2))(2)Zn might be the active species in the real reaction system. Regarding the solvent effect, the polar continuum model is more realistic than the direct involvement of diethyl ether molecules.

Modulation of anatase toward highly active facets has been attracting much attention, but the mechanism and photoactivity are still ambiguous. Here we demonstrate the inherent mechanisms for facets nucleation and morphology evolution, and clarify some vital influences of facets and surface nature on the photoactivity. Simply tuning the Ti/F ratio in the synthetic mixture leads to single anatase crystal exposed with different facets like {001}, {010}, or {110}. And complex sphere structure exposed with {001} facets can be formed by secondary nucleation and growth. Prolonging the hydrothermal treatment time causes selective etching on {001} facets, whereas defluorination via thermal calcination produces many pores on the surface. The photodegradation of positively and negatively charged, and zwitterionic dyes indicates that the type of reactant, adsorption mode and surface area play significant roles in photocatalysis. This work makes a step toward understanding the formation of facet-mediated structure and designing highly active materials for environmental remediation, hydrogen production, and dye-sensitized solar cells., (© 2012 American Chemical Society)

Preadsorbed water along with surrounding bulk water significantly modulates the surface electronic structure of TiO(2), switches the adsorption mode of dyes, and promotes dye sensitization of TiO(2) under visible-light irradiation. This opens a door toward facile improvement in the efficiency of photodegradation of dyes and dye-sensitized solar cells under visible-light irradiation without any complicated and expensive surface modulation.

Ion pair "leakage" pathways, located computationally by means of multidimensional potential energy surface scans, rationalize the unsymmetrical D-label scrambling observed experimentally in the DCl addition products of nortricyclene and norbornene. "Classical" addition transition structures can interconvert ("leak") to symmetrical nonclassical 2-norbornyl ion pair species, either TS's or a minimum, before products form.

A novel plasma reduction method has been developed to reduce supported noble-metal ions without the use of any reducing chemicals. H2PtCl6, PdCl2, AgNO3, and HAuCl4 supported on nonporous TiO2 and porous gamma-Al2O3 and HZSM-5 were reduced using an Ar glow discharge plasma. Optical absorption spectra and X-ray photoelectron spectroscopy show that the supported metal ions are completely reduced to metallic species. Transmission electron microscopy shows that the prepared metals are amorphous clusters and homogeneously distributed with nanoscale sizes. X-ray diffraction also confirms that the plasma-reduced metals exist as small crystallites or amorphous clusters. Thermal annealing of plasma-reduced samples at elevated temperature transforms the clusters into crystals with a slight increase in particle sizes, but the sizes are still smaller than those of H2-reduced metals. O2 glow discharge plasma can also reduce noble-metal ions, accompanied by production of a small amount of oxides. Plasma reduction is very promising for the preparation of metal nanoparticles and supported metal catalysts.

NiO-loaded semiconductors have been extensively used as the photocatalysts for water splitting. The metal-support interface is an important factor affecting the efficiency. In the present work, the pretreatment methods were studied to produce a more desirable metal-support interface using Ta2O5 and ZrO2 as the support. The traditional method includes a thermal decomposition, reduction at 773 K, and oxidation at 473 K (R773-O473). The thermal decomposition of Ni(NO3)2 makes the Ni atoms migrate into the bulk of the supports, resulting in a diffused interfacial region. Alternatively, a cold plasma treatment was used to replace the thermal decomposition. Metal salts are quickly decomposed by glow discharge plasma treatment at room temperature, avoiding the thermal diffusion of Ni atoms. With the sequent R773-O473 treatment, a clean metal-support interface is produced. Moreover, the metal particles have optimal shapes with a larger surface. In photocatalysis, the clean metal-support interface is more favorable for the charge separation and transfer, and the increased metal surface provides more active sites. NiO/Ta2O5 and NiO/ZrO2 prepared with the plasma treatment exhibit higher activity for photocatalytic hydrogen generation from pure water and methanol solution, respectively. This work shows the potential of cold plasma treatment in the preparation of metal-loaded catalysts and nanostructured materials.