Roles of cocatalysts in photocatalysis and photoelectrocatalysis.

Since the 1970s, splitting water using solar energy has been a focus of great attention as a possible means for converting solar energy to chemical energy in the form of clean and renewable hydrogen fuel. Approaches to solar water splitting include photocatalytic water splitting with homogeneous or heterogeneous photocatalysts, photoelectrochemical or photoelectrocatalytic (PEC) water splitting with a PEC cell, and electrolysis of water with photovoltaic cells coupled to electrocatalysts. Though many materials are capable of photocatalytically producing hydrogen and/or oxygen, the overall energy conversion efficiency is still low and far from practical application. This is mainly due to the fact that the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously. Water splitting is a thermodynamically uphill reaction, requiring transfer of multiple electrons, making it one of the most challenging reactions in chemistry. This Account describes the important roles of cocatalysts in photocatalytic and PEC water splitting reactions. For semiconductor-based photocatalytic and PEC systems, we show that loading proper cocatalysts, especially dual cocatalysts for reduction and oxidation, on semiconductors (as light harvesters) can significantly enhance the activities of photocatalytic and PEC water splitting reactions. Loading oxidation and/or reduction cocatalysts on semiconductors can facilitate oxidation and reduction reactions by providing the active sites/reaction sites while suppressing the charge recombination and reverse reactions. In a PEC water splitting system, the water oxidation and reduction reactions occur at opposite electrodes, so cocatalysts loaded on the electrode materials mainly act as active sites/reaction sites spatially separated as natural photosynthesis does. In both cases, the nature of the loaded cocatalysts and their interaction with the semiconductor through the interface/junction are important. The cocatalyst can provide trapping sites for the photogenerated charges and promote the charge separation, thus enhancing the quantum efficiency; the cocatalysts could improve the photostability of the catalysts by timely consuming of the photogenerated charges, particularly the holes; most importantly, the cocatalysts catalyze the reactions by lowering the activation energy. Our research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible. All of these findings suggest that dual cocatalysts are necessary for developing highly efficient photocatalysts for water splitting reactions.

Stability of MoS2 Nanocatalysts for the Slurry-Phase Catalytic Hydrogenation of Anthracene.

The stability of both the structure and activity of MoS2 nanocatalysts is crucial for minimizing the catalyst cost of the slurry-phase (SP) catalytic hydrogenation. MoS2-GP and MoS2-SP catalysts were, respectively, obtained by gas-phase (denoted as GP) and SP aging of fresh MoS2 catalysts. The MoS2-SP catalyst demonstrated a comparable catalytic hydrogenation activity to that of the fresh MoS2 catalyst, which is about 1.7 times of that for the MoS2-GP catalyst. After 12 cycles of the MoS2-SP catalyst, the obtained Cy12 catalyst demonstrates a retention of 92.0% of its initial catalytic activity. The MoS2-SP catalyst exhibits an impressive stability of catalytic hydrogenation. The MoS2-SP catalyst exhibits average stacking layers of 3.3 and an average slab of 5.2 nm and exposes 14.0% of active sites. The MoS2-SP catalyst can serve as a highly active and stable catalyst for catalytic hydrogenation. This finding can offer valuable insights into the stability of the hydrogenation catalyst in SP hydrogenation technology.

A theoretical study on the mechanism of photocatalytic oxygen evolution on BiVO4 in aqueous solution.

The oxygen evolution reaction (OER) is regarded as one of the key issues in achieving efficient photocatalytic water splitting. Monoclinic scheelite BiVO(4) is a visible-light-responsive semiconductor which has proved to be effective for oxygen evolution. Recently, the synthesis of a series of monoclinic BiVO(4) single crystals was reported, and it was found that the (010), (110), and (011) facets are highly exposed and that the photocatalytic O(2) evolution activity depends on the degree of exposure of the (010) facets. To explore the properties of and photocatalytic water oxidation reaction on different facets, DFT calculations were performed to investigate the geometric structure, optical properties, electronic structure, water adsorption, and the whole OER free-energy profiles on BiVO(4) (010) and (011) facets. The calculated results suggest both favorable and unfavorable factors for OER on the (010) and the (011) facets. Due to the combined effects of the above-mentioned factors, different facets exhibit quite different photocatalytic activities.

Visible light driven overall water splitting using cocatalyst/BiVO4 photoanode with minimized bias.

BiVO4 and many other semiconductor materials are ideal visible light responsive semiconductors, but are insufficient for overall water splitting. Upon loading water oxidation cocatalyst, for example Co-borate (denoted as CoBi) used here, onto BiVO4 photoanode, it is found that not only the onset potential is negatively shifted but also the photocurrent and the stability are significantly improved. And more importantly, PEC overall water splitting to H2 and O2 is realized using CoBi/BiVO4 as photoanode with a rather low applied bias (less than 0.3 V vs. counter electrode) in a two-electrode scheme, while at least 0.6 V is needed for bare BiVO4. This work demonstrates the practical possibility of achieving overall water splitting using the PEC strategy under a bias as low as the theoretical minimum, which is the difference between the flat band and proton reduction potential for a photoanode thermodynamically insufficient for water reduction. As long as the water oxidation overpotential is overcome with an efficient cocatalyst, the applied bias of the whole system is only used for that thermodynamically required for the proton reduction.

Constructing layer-by-layer self-assembly MoS2/C nanomaterials by a one-step hydrothermal method for catalytic hydrogenation of phenanthrene.

Layer-by-layer self-assembly MoS2/C nanomaterials are constructed through the electrostatic adsorption between MoS2 nuclei with positive charge and C nuclei with negative charge using a facile one-step hydrothermal method. The layer-by-layer self-assembly MoS2/C catalysts with high exposure of catalytic hydrogenation active sites exhibit enhanced catalytic performance in phenanthrene hydrogenation.

Carnitine-acylcarnitine translocase deficiency caused by SLC25A20 gene heterozygous variants in twins: a case report.

The current case report describes the clinical, biochemical and genetic characteristics of carnitine-acylcarnitine translocase deficiency (CACTD) in infant male and female twins that presented with symptoms shortly after elective caesarean delivery. The clinical manifestations were neonatal hypoglycaemia, arrhythmia and sudden death. The age of onset was 1.5 days and the age of the death was 1.5-3.5 days. Dried blood filter paper analysis was used for the detection of acylcarnitine. Peripheral venous blood and skin samples were used for next-generation sequencing. The twins and their parents underwent gene analysis and whole exome sequencing analyses of the solute carrier family 25 member 20 (SLC25A20; also known as carnitine-acylcarnitine translocase) gene. Both infants carried compound heterozygous variants of the SLC25A20 gene: variant M1:c.706_707insT:p.R236L fs*12 and variant M2:c.689C>G:p.P230R. The M1 variant was paternal and had not been previously reported regarding CACTD. The M2 variant was maternal. CACTD has severe clinical manifestations and a poor prognosis, which is manifested as hypoketotic hypoglycaemia, hyperammonaemia, liver function damage and elevated creatine kinase.

Slurry-Phase Hydrogenation of Different Asphaltenes to Liquid Fuels on Dispersed MoS2 Nanocatalysts.

Asphaltene, the most complex and recalcitrant fraction of heavy oil, was investigated in this study to gain new insights into its structure and reactivity. Two types of asphaltenes, ECT-As and COB-As, were extracted from ethylene cracking tar (ECT) and Canada's oil sands bitumen (COB), respectively, and used as reactants for slurry-phase hydrogenation. Characterization of ECT-As and COB-As was carried out by a combination of techniques, including XRD, elemental analysis, simulated distillation, SEM, TEM, NMR, and FT-IR, to gain insights into their composition and structure. A dispersed MoS2 nanocatalyst was used to study the reactivity of ECT-As and COB-As under hydrogenation conditions. The results showed that under optimal catalytic conditions, the vacuum residue content of hydrogenation products could be reduced to less than 20%, and the products contained over 50% light components (gasoline and diesel oil), indicating that ECT-As and COB-As were effectively upgraded. The characterization results indicated that ECT-As contained a higher aromatic carbon content, shorter alkyl side chains, fewer heteroatoms, and less highly condensed aromatics than COB-As. The light components (gasoline and diesel oil) of ECT-As hydrogenation products mainly consisted of aromatic compounds with 1-4 rings, with the alkyl chains mainly composed of C1-C2, while light components of COB-As hydrogenation products were mainly composed of aromatic compounds with 1-2 rings and C11-C22 paraffins. The characterization of ECT-As and COB-As and their hydrogenation products revealed that ECT-As was an "archipelago type" asphaltene, composed of multiple small aromatic nuclei interconnected through short alkyl chains, while COB-As was an "island type" asphaltene, with long alkyl chains connected to aromatic nuclei. It is suggested that the structure of asphaltene has a significant impact on both its reactivity and product distribution.

Crystal facet dependence of water oxidation on BiVO4 sheets under visible light irradiation.

Monoclinic BiVO(4) crystals with preferentially exposed (040) facets were hydrothermally synthesized by using a trace amount of TiCl(3) as the directing agent; this function was confirmed by X-ray diffraction patterns (XRD) and high-resolution transmission electron microscopy (HRTEM). The effects of the directing agent TiCl(3) and the pH values applied during synthesis have been studied, and the optimized BiVO(4) sample with highly exposed (040) facet could be obtained by using 1.2 at.% of TiCl(3) as the directing agent at a pH value of 2. Some complementary techniques were also applied to exclude the effects of the structural and physical property changes, such as surface area and hydrophilicity. The photocatalytic activity of oxygen evolution on BiVO(4) is found to be proportionally correlated with the exposed surfaces of the (040) facet. It is assumed that the active sites with a BiV(4) structure on the exposed (040) facet is assigned to be responsible for the high activity of O(2) evolution.

Direct synthesis of shaped MgAPO-11 molecular sieves and the catalytic performance in n-dodecane hydroisomerization.

In industrial application, molecular sieves are usually used in a certain shape. This requires the addition of binder and causes the reduction of both the molecular sieve content and catalytic performance. Herein, pseudo-boemite was mixed with deionized water at room temperature, followed by the drop-wise addition of phosphoric acid, magnesium acetate solution, hydrofluoric acid, di-n-propylamine and 1-ethyl-3-methyl imidazolium bromide with vigorous stirring. The molar ratio of Al2O3 : P2O5 : MgO : HF : DPA : [EMIm]Br : H2O in the gel was 1 : 1 : 0.03 : 0.18 : 0.4 : 1 : 45. Then the gel was dried, extruded and directly crystallized to form a shaped MgAPO-11 molecular sieve. X-ray diffraction, scanning electron microscopy, N2 adsorption, ammonia temperature programmed desorption, pyridine adsorption infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to investigate the physicochemical properties of the samples. X-ray diffraction, scanning electron microscopy and N2 adsorption tests show that the shaped MgAPO-11 molecular sieve is fully crystallized and possesses hierarchical porosity. Mg is incorporated into the molecular sieve framework and the Pt catalyst supported by the obtained shaped MgAPO-11 exhibits excellent catalytic performance with n-dodecane conversion of 94% and isomer selectivity of 95% at 280 °C. Such a method for the direct synthesis of shaped molecular sieves shows potential for the green synthesis of molecular sieves in industry.

Highly Effective Pd/MgO/γ-Al2O3 Catalysts for CO Oxidative Coupling to Dimethyl Oxalate: The Effect of MgO Coating on γ-Al2O3.

The support of MgO/γ-Al2O3 was initially prepared by a multiple impregnation method and Pd was placed on the surface of the MgO/γ-Al2O3 support via incipient wetness impregnation. Pd/MgO/γ-Al2O3 (Pd/MAO) catalysts were systematically characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), CO2-temperature-programmed desorption (TPD), transmission electron microscopy (TEM), CO-Fourier transform infrared (CO-FTIR), and X-ray photoelectron spectroscopy (XPS) and tested in the CO oxidative coupling to dimethyl oxalate (DMO) reaction. Compared to Pd/γ-Al2O3, the catalytic activities of the Pd/MAO catalysts improved significantly. The Pd/MAO catalyst with a 30% mass ratio of Mg to γ-Al2O3 delivers 3 times higher STY of DMO than that of Pd/γ-Al2O3. It has been demonstrated that MgO covered γ-Al2O3 layer-by-layer forming MAO supports, which can increase surface basicity and the interaction between Pd particles and the MAO supports. Moreover, the relationship between metal and support interaction and catalytic performance was discussed.

(2-{[2-(2-Amino-ethyl-amino)-eth-yl]imino-meth-yl}phenolato)nickel(II) chloride dihydrate.

In the title complex, [Ni(C(11)H(16)N(3)O)]Cl·2H(2)O, the Ni(II) ion is coordinated within a distorted square-planar environment. In the crystal, inter-molecular N-H⋯Cl, N-H⋯O, O-H⋯O, O-H⋯Cl and weak C-H⋯O hydrogen bonds link the components into a two-dimensional network parallel to (001).

Dichlorido[tris-(1H-benzimidazol-2-ylmeth-yl)amine-κN,N,N,N]iron(III) chloride tetra-hydro-furan monosolvate monohydrate.

In the title compound, [FeCl(2)(C(24)H(21)N(7))]Cl·C(4)H(8)O·H(2)O, the Fe(III) atom is coordinated by four N atoms of the polybenzimidazole ligand and two Cl atoms in a distorted octa-hedral environment. The cation, anion, the uncoordinated water mol-ecule and the THF solvent molecule are linked by hydrogen bonds into a three-dimensional network structure. The THF molecule is disordered with two sets of sites in a 0.58 (1):0.42 (2) ratio..

(RS)-3-Acetyl-2-methyl-4-(3-nitro-phen-yl)-1,4,5,6,7,8-hexa-hydro-quinolin-5-one.

In the title compound, C(18)H(18)N(2)O(4), the nitro group, a methyl group, the acetyl group and some atoms of the dihydro-quinolinone group are disordered over two sites with the ratio of occupancies fixed at 0.57:0.43. The relationship between the major and minor components of disorder is that of diastereomers. In the crystal structure, inter-molecular N-H⋯O, weak C-H⋯O and C-H⋯π inter-actions link the mol-ecules into two-dimensional layers running parallel to the (010) plane.

Aqua-(picolinato N-oxide-κO,O)(pyridine-2,6-dicarboxyl-ato-κO,N,O')iron(III) monohydrate.

In the title compound, [Fe(C(6)H(4)NO(3))(C(7)H(3)NO(4))(H(2)O)]·H(2)O, the Fe(III) ion is coordinated by two O and one N atoms from a pyridine-2,6-dicarboxyl-ate ligand, by two O atoms from a picolinate N-oxide ligand and by one water O atom in a distorted octa-hedral geometry [Fe-O = 1.940 (3)-2.033 (3) Šand Fe-N = 2.057 (4) Å]. In the crystal structure, the coordinated and solvent water mol-ecules contribute to the formation of O-H⋯O hydrogen bonds, which link the mol-ecules into layers parallel to the ab plane.

Synthesis of discrete aluminophosphate -CLO nanocrystals in a eutectic mixture.

Extra-large-pore aluminophosphate -CLO (i.e., DNL-1) nanocrystals were synthesized in a eutectic mixture composed of diethylamine hydrochloride (DEAC) and ethylene glycol (EG) with 1-methylimidazole (1-MIm) as an additional amine using both conventional and microwave heating. The effects of the synthesis parameters, such as the amount of 1-MIm and the P/Al ratio, on the formation of DNL-1 nanocrystals were studied. The products were characterized using a variety of techniques. XRD, DLS, SEM and TEM results indicate that the as-synthesized DNL-1 nanocrystals have good crystallinity and narrow particle size distributions, and their average particle size was controlled in the 100-220nm range by simply adjusting the amount of 1-MIm. TG-DSC and N2 adsorption analyses reveal that the as-synthesized DNL-1 nanocrystals exhibit good thermal stability and the calcined samples possess high BET surface areas and large pore volumes. In addition, the cooperative structure-directing effects of 1-MIm and the eutectic mixture cation (DEA(+)) in the formation of DNL-1 nanocrystals were discussed.

Photoelectrochemical water oxidation on photoanodes fabricated with hexagonal nanoflower and nanoblock WO3.

Hexagonal nanoflower WO3 arrays have been prepared by using RCOO(-) as the structure directing agent in the microwave-assisted hydrothermal synthesis process. The photoelectrochemical performance of the synthesized hexagonal flower-like WO3 electrode was enhanced compared with the block-like WO3 film.

Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO4.

Charge separation is crucial for increasing the activity of semiconductor-based photocatalysts, especially in water splitting reactions. Here we show, using monoclinic bismuth vanadate crystal as a model photocatalyst, that efficient charge separation can be achieved on different crystal facets, as evidenced by the reduction reaction with photogenerated electrons and oxidation reaction with photogenerated holes, which take place separately on the {010} and {110} facets under photo-irradiation. Based on this finding, the reduction and oxidation cocatalysts are selectively deposited on the {010} and {110} facets respectively, resulting in much higher activity in both photocatalytic and photoelectrocatalytic water oxidation reactions, compared with the photocatalyst with randomly distributed cocatalysts. These results show that the photogenrated electrons and holes can be separated between the different facets of semiconductor crystals. This finding may be useful in semiconductor physics and chemistry to construct highly efficient solar energy conversion systems.

Visible light driven H(2) production in molecular systems employing colloidal MoS(2) nanoparticles as catalyst.

Colloidal MoS(2) nanoparticles with diameters of less than 10 nm were prepared with a simple solvothermal method and demonstrated high efficiency in catalyzing H(2) evolution in Ru(bpy)(3)(2+)-based molecular systems under visible light.