Controlled evolution of surface microstructure and phase boundary of ZnO nanoparticles for the multiple sensitization effects on triethylamine detection.

In ZnO gas sensors, donor defects (such as zinc interstitials and oxygen vacancies) are considered active sites for the chemical adsorption and ionization of oxygen on the surface of ZnO, which can significantly enhance the sensor's response. However, the influence of the surface microstructure and phase boundaries of ZnO nanoparticles on the chemical adsorption and ionization of surface oxygen has rarely been explored. In this study, we developed a mixed-phase ZnO nanoparticle gas sensor with a rich phase boundary showing 198-50 ppm improvement in response to triethylamine at 340 °C. This is attributed to the generation of defects originating from lattice mismatch at the ZnO - zincite phase boundaries, which providing more active sites for adsorption of oxygen and triethylamine molecules. This work demonstrates a feasible method of combining surface microstructure regulation with pyrolysis strategies to develop ZnO sensors with significantly enhanced gas response performance.

Galvanic replacement-induced preparation of bloom-like Pt23Ni77 for methanol coupled efficient hydrogen production.

Galvanic replacement reaction (GRR) leverages the difference in metal reduction potentials to regulate the structure of nanomaterials. The crucial aspect of constructing highly active catalysts lies in the precise manipulation of both the oxidative dissolution of sacrificial template metals and reductive deposition of alternate metals. Herein, we investigated the morphological transformation of metal Ni as a sacrificial template in the presence of different amounts of H2PtCl6 solution and the Pt4+ substitution of Ni to achieve the redistribution of elements on the catalyst surface, which provides superior performance in both the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER). The uniform distribution of Pt on a three-dimensional transition metal Ni substrate allows for the complete exposure of the noble metal to the catalyst surface. This distribution increases the reaction area, facilitating easy access for reactants and promoting electron transfer. Meanwhile, Pt (1.39 Å) has a larger atomic radius compared to Ni (1.24 Å), and the substitution reaction in the transition metal phase induces strong compressive strain, which effectively regulates the electronic structure of Ni.

Facile electrolysis-solvothermal synthesis of NiOx/graphene for enhanced ethanol oxidation to acetate.

In this work, low-crystalized and defective NiOx/graphene was synthesized by a facile electrolysis-solvothermal method. In the electrolytic process, Ni ions originate from the Ni anode, and graphene is produced from the graphite cathode. Then, Ni ions are reduced into oxides and deposited on graphene in the subsequent solvothermal process. The NiOx/graphene displays excellent electrocatalytic activity and selectivity for ethanol oxidation reaction to acetate. The peak current density was 296.5 mA cm-2 on a glassy carbon electrode. The FE of acetate was more than 93% at the potential range between 1.4 and 1.7 V. We propose that the mechanism is a cooperation between the chemical deprotonating process of ethanol by Ni3+ species and the electrochemical oxidation of the CH3CH2O* intermediate to acetate at the interface between NiOx and graphene.

Effect of boron nitride overlayers on Co@BNNSs/BN-Catalyzed aqueous phase selective hydrogenation of cinnamaldehyde.

The confinement effect known as efficient strategy to enhance the heterocatalytic activity and stability, but a clear view regarding the role of encapsulated overlayers is far from convincing at present, especially, the penetration of substrates with different size. Herein, the experimental evidence about the impacts of BN overlayers on hydrogenation is obtained over Co@BN/BN model catalysts with tuned thinness, in which BN overlayers encapsuled Co particles that dispersed on the defective BN supports, fabricating by the nitridizing of ball-milled BN microplates under NH3 atmosphere. The thinness and crystallinity of BN shells was simply tuned by controlling the pyrolyzed temperature (600-900 °C). The cinnamaldehyde (CAL) selective hydrogenation is taken as probe reaction due to (1) both larger CAL and small H2 molecule involved simultaneously, (2) the middle CC and terminal CO bonds all involved. Combined with structural analysis, the results demonstrate that small H2 molecule can penetrate into the metal-cover interface through the defect sites, then inner Co core dissociate it to atomic H, and the hydrogenation mainly resulting from the spillover of H atoms which occurred on the BN surface. As a result, the thickest BN shells (∼3.4 nm) with ordered-layer-lattice significantly hindered the adsorption and activation of CAL, also the longest H spillover distance led to the lowest activity of Co@BN/BN-900. Instead, Co@BN/BN-600 with merely 2 âˆ¼ 3 overlayers presented the most efficient and highly chemoselective hydrogenation activity. The ultrathin but turbostratic BN overlayers provide more migrating sites also shortened the H spillover distance effectively, and the more favorable CO hydrogenation was also achieved driven by the steric hindrance effect of thinner BN shells. These observations provide new insights towards understanding of confined effect on catalysis process through the accurate regulation of BN shells properties.

Chemical conversion based on the crystal facet effect of transition metal oxides and construction methods for sharp-faced nanocrystals.

In-depth research has found that the nanocrystal facet of transition metal oxides (TMOs) greatly affects their heterogeneous catalytic performance, as well as the property of photocatalysis, gas sensing, electrochemical reaction, etc. that are all involved in chemical conversion processes. Therefore, the facet-dependent properties of TMO nanocrystals have been fully and carefully studied by combining systematic experiments and theoretical calculations, and mechanisms of chemical reactions are accurately explained at the molecular level, which will be closer to the essence of reactions. Evidently, as an accurate investigation on crystal facets, well-defined TMO nanocrystals are the basis and premise for obtaining relevant credible results, and shape-controlled synthesis of TMO nanocrystals thereby has received great attention and development. The success in understanding of facet-dependent properties and shape-controlled synthesis of TMO nanocrystals is highly valuable for the control of reaction and the design of high-efficiency TMO nanocrystal catalysts as well as other functional materials in practical applications.

Gas-Phase Catalytic Dehydration of Glycerol with Methanol to Methyl Glyceryl Ethers over Phosphotungstic Acid Supported on Alumina.

Glycerol can be dehydrated with methanol to produce methyl glyceryl ethers as biologicals and diesel fuel additives. Considering the high efficiency of mass transfer and product separation in the gas-solid catalytic process, a fixed-bed continuous-flow reactor was used to carry out the catalyst evaluation test of the process at 564 K. Compared with zirconium sulfate, lanthanum nitrate, and ammonium molybdate, phosphotungstic acid exhibits a higher target product selectivity. Through loading experiments, it was found that the optimal loading fraction of phosphotungstic acid on alumina is 10 wt %. After the alumina carrier is impregnated with nitric acid, the selectivity and yield of monomethyl glycerol ether can be effectively improved, and it has little effect on other products. A test of the addition amount of cerium nitrate as a promoter was carried out. It was shown in the test that when the addition amount of cerium nitrate is 10 wt %, the catalyst life increases from 2 to 3.5 h and the selectivity of dimethyl glycerol ether increases to 54.51%, which is twice the original. However, the selectivities of monomethyl glycerol ether and trimethyl glycerol ether decrease by one-half each. Through catalyst characterization, it was shown that carbon deposition on the catalyst surface is one of the reasons for catalyst deactivation.

Amorphous Cr2WO6-Modified WO3 Nanowires with a Large Specific Surface Area and Rich Lewis Acid Sites: A Highly Efficient Catalyst for Oxidative Desulfurization.

The oxidative desulfurization (ODS) of fuel oils is of great significance for environmental protection, and the development of efficient ODS heterogeneous catalysts is highly desired. Herein, we have designed and synthesized a novel material of amorphous Cr2WO6-modified WO3 (a-Cr2WO6/WO3) nanowires (3-6 nm) with a large specific surface area of 289.5 m2·g-1 and rich Lewis acid sites. The formation of such a unique nanowire is attributed to the adsorption of Cr3+ cations on non-(001) planes of WO3. In the ODS process, the a-Cr2WO6/WO3 nanowires can efficiently oxidize benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to their corresponding sulfones in a quasi-microemulsion reaction system and possess the highest activity (Ea = 55.4 kJ/mol) for DBT: 99.0% of 15,000 ppm DBT with 2600 ppm S can be removed (70 °C, H2O2 as the oxidant). The improvement in ODS activity from most of WO3 catalysts is owing to the sufficient active sites and enhanced adsorption of DBT on the basis of structural features of a-Cr2WO6/WO3 nanowires. Combined with free radical capture experiments, a possible ODS mechanism of W(O2) peroxotungstate route based on surface -OH groups is reasonably proposed. Moreover, the a-Cr2WO6/WO3 nanowires have good stability and can be synthesized on a large scale, suggesting its potential applications as an efficient heterogeneous catalyst.

CoP/RGO-Pd Hybrids with Heterointerfaces as Highly Active Catalysts for Ethanol Electrooxidation.

The ethanol oxidation reaction is of critical importance to the commercial viability of direct ethanol fuel cell technology. However, owing to the poor C-C bond cleavage capability, almost all ethanol oxidation is incomplete and suffers from low selectivity toward the C1 pathway. Herein, under the support of theoretical calculations that the heterointerfaces between CoP and Pd can reduce the energy barrier of C-C bond cleavage, rich heterointerfaces in CoP/RGO-Pd hybrids were designed to improve ethanol electrooxidation performance through enhancing the selectivity toward the C1 pathway. The experimental results show that the faradaic efficiency of the C1 pathway of CoP/RGO-Pd hybrids is as high as 27.6%, surpassing most reported catalysts in the literature. As a result of this enhancement, CoP/RGO-Pd10 exhibits mass activity as high as 4597 mA·mgPd-1 and specific activity as high as 10 mA·cm-2, which are much higher than those of other Pd-based electrocatalysts.

Removal of trace Cr(VI) from aqueous solution by porous activated carbon balls supported by nanoscale zero-valent iron composites.

In this study, porous activated carbon balls supported by nanoscale zero-valent iron composites (Fe@PACB-700) were used for the first time for the removal of trace Cr(VI) from aqueous solutions. The Fe@PACB-700 composites were prepared by a facile carbothermal reduction method and then characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that nZVI particles have been successfully loaded onto PACBs. Fe@PACB-700 shows an excellent Cr(VI) removal efficiency of 91.2%. The maximum adsorption capacity of Fe@PACB-700 for Cr(VI) is 22.24 mg/g, which is 4.36 times that of PACB. The residual Cr(VI) concentration is below 20 ppb with the use of 0.15 g of Fe@PACB-700, which is much lower than the allowable concentration for Cr(VI) in drinking water (0.05 mg/L). The adsorption of Cr(VI) can be well described by the Langmuir isotherm model and pseudo-second-order kinetic model. Fe@PACB-700 still has a high removal efficiency of 80% after five cycles. Thus, Fe@PACB-700 has a great potential for Cr(VI) removal from aqueous solution. Graphical abstract.

Insight into the Effective Aerobic Oxidative Cross-Esterification of Alcohols over Au/Porous Boron Nitride Catalyst.

Boron nitride (BN) has attracted great attention with an unexpected ability in aerobic catalysis. Still, its related probe reactions are relatively rare, and the effect of the BN-supported metal catalyst on O2 activation is still ambiguous, and opinions are varied. In this work, the porous BN (pBN)-supported Au catalyst with a porous structure and exposed edges exhibits high activity in the oxidative cross-esterification reactions between the aromatic and C1-C3 aliphatic alcohols at ambient temperature. The turnover frequency value for methyl benzoate is 118 h-1 at 30 °C, and the calculated apparent activation energy (Ea, 58 kJ/mol) is comparable to that of AuPd/TiO2, Ru/Al2O3, and PdBiTe catalysts. Combined with temperature-programmed  desorption (TPD) results, the loading of Au enhances the desorption of O2 and the interaction with alcohols; thus, a synergistic effect between the O-rich pBN and Au is considered. The free-radical scavenger can dramatically suppress the conversion (∼6%), suggesting that the reaction proceeds via the O2* radicals. According to the vibration of νO-O, δOO-H, and νB-O-O-B detected by attenuated total reflectance-infrared spectroscopy (ATR-IR), we are prone to consider the oxygen activation route by the edge B atoms. Then, a possible L-H reaction mechanism was proposed: benzyl alcohol and O2 adsorb on the Au/pBN initially, then O2 is converted to O2*, and the α-H elimination proceeds; as the semi-acetal formed, another α-H elimination proceeds and methyl benzoate is finally formed.

N-Doped amorphous MoSx for the hydrogen evolution reaction.

Herein, the functions of a N dopant in crystalline MoS2 catalysts during the electrochemical hydrogen evolution reaction (HER) were reported via a combined experimental and first-principles approach. However, studies on the N doping of amorphous MoSx, which is a more active catalyst, have not been reported to date. In this study, via a simple method, we fabricated N-doped amorphous MoSx for the first time and studied the correlations between the N dopant and the HER performance. Via X-ray photoelectron spectroscopy and theoretical formation energy calculations, we have found that a N dopant in basal plane S2- plays a very important role in the improvement of the HER performance and remains stable during this dynamic transformation process. A N dopant in basal plane S2- can increase the number of active sites toward the HER and enhance the conductivity of the catalysts as well as a N dopant in c-MoS2. In addition to this, the first-principles calculations further suggested that a N dopant in basal plane S2- could improve the activity of unsaturated MoV active sites by bringing its hydrogen adsorption free energy closer to zero. As a result, N-doped amorphous MoSx possesses an overpotential of 143 mV at 10 mA cm-2 and a Tafel slope of 57 mV dec-1, much better than those of a-MoSx. These results provide useful insights for the future development of nonmetal-doped MoSx catalysts in the HER.

Experimental and theoretical investigations of Cs+ adsorption on crown ethers modified magnetic adsorbent.

Carboxyl Fe3O4 nanoparticles (Fe3O4@R-COOH) modified with 18-Crown-6 ether functional groups have been prepared via an amidation reaction and used as bifunctional adsorbent for Cs+. The adsorbent has a superparamagnetic property, allowing an easy recycling, and a high capacity of Cs+ adsorption on the crown ether. The adsorption isotherms and kinetic behaviors agree well with the Langmuir and the pseudo-second-order models. The material exhibits a high selectivity for Cs+ in the solution with co-existing cations (NH4+, Rb+, K+, Na+ and Li+). A theoretical calculation according to density functional theory (DFT) is used to estimate the structure of Cs+ adsorption on crown ether, demonstrating an exothermic process and showing a good agreement with the experimental observations. The adsorption behavior is affected not only by the size of macrocyclic crown ethers, but also by the chelating symmetry and the binding energy. The newly developed adsorbent has a potential application for removing cesium out of wastewater and salt lakes.

Facets Matching of Platinum and Ferric Oxide in Highly Efficient Catalyst Design for Low-Temperature CO Oxidation.

Rational design of supported noble metal is of great importance for highly efficient heterogeneous catalysts. On the basis of the distinct adsorption characteristics of noble metal and transition-metal oxides toward O2 and CO, the overall catalytic performance of CO oxidation reaction could be further modified by controlling the surface property of the materials to achieve optimal adsorption activity. Here, we studied the influence of facets matching between both platinum and ferric oxide support on CO conversion efficiency. It shows that the activities of four catalysts rank following the order of Pt{100}/α-Fe2O3{104} > Pt{100}/α-Fe2O3{001} > Pt{111}/α-Fe2O3{001} > Pt{111}/α-Fe2O3{104}. The strong metal-support interaction and adsorption energy varying with matched enclosed surface are demonstrated by density functional theory based on the projected d-band density of states. Compared with the other three cases, the combination of Pt{100} and α-Fe2O3{104} successfully weakens CO poisoning and provides proper active sites for O2 adsorption. It reveals that the facets matching could be a practicable approach to design catalysts with enhanced catalytic performance.

Glucose-mediated template-free synthesis of hollow CuO microspheres.

In this work, we demonstrated a facile template-free method for the preparation of hollow CuO microspheres via a conventional hydrothermal reaction. The hollow architecture formed directly during the hydrothermal treatment of copper nitrate and glucose, without the use of template, precipitant and calcination process. The effects of reaction time, reaction temperature and glucose concentration were investigated in detail. On the basis of experimental results, the formation of hollow CuO microspheres probably proceeded via self-assemble process and the subsequent Ostwald's ripening. This synthetic strategy strongly depended on the characteristics of copper nitrate, which made it could not extend to other copper salts and/or nitrates. Even though, glucose still showed efficient morphology controlling ability with respect to nanosized transitional metal oxides, which could be used for the controllable synthesis of nanomaterials.

Facile synthesis of self-assembled ultrathin α-FeOOH nanorod/graphene oxide composites for supercapacitors.

A one-pot facile, impurity-free hydrothermal method to synthesize ultrathin α-FeOOH nanorods/graphene oxide (GO) composites is reported. It is directly synthesized from GO and iron acetate in water solution without inorganic or organic additives. XRD, Raman, FT-IR, XPS and TEM are used to characterize the samples. The nanorods in composites are single crystallite with an average diameter of 6nm and an average length of 75nm, which are significantly smaller than GO-free α-FeOOH nanorods. This can be attributed to the confinement effect and special electronic influence of GO. The influences of experimental conditions including reaction time and reactant concentration on the sizes of nanorods have been investigated. It reveals that the initial Fe2+ concentration and reaction time play an important role in the synthetic process. Furthermore, a possible nucleation-growth mechanism is proposed. As electrode materials for supercapacitors, the α-FeOOH nanorods/GO composite with 20% iron loading has the largest specific capacitance (127Fg-1 at 10Ag-1), excellent rate capability (100Fg-1 at 20Ag-1) and good cyclic performance (85% capacitance retention after 2000 cycles), which is much better than GO-free α-FeOOH nanorods. This unique structure results in rapid electrolyte ions diffusion, fast electron transport and high charging-discharging rate. In virtue of the superior electrochemical performance, the α-FeOOH nanorods/GO composite material has a promising application in high-performance supercapacitors.

Facile Fabrication of BCN Nanosheet-Encapsulated Nano-Iron as Highly Stable Fischer-Tropsch Synthesis Catalyst.

The few layered boron carbon nitride nanosheets (BCNNSs) have attracted widespread attention in the field of heterogeneous catalysis. Herein, we report an innovative one-pot route to prepare the catalyst of BCNNSs-encapsulated sub-10 nm highly dispersed nanoiron particles. Then the novel catalyst was used in Fischer-Tropsch synthesis for the first time and it exhibited high activity and superior stability. At a high temperature of 320 °C, CO conversion could reach 88.9%, corresponding catalytic activity per gram of iron (iron time yield, FTY) of 0.9 × 10-4 molCO gFe-1 s-1, more than 200 times higher than that of pure iron. Notably, no obvious deactivation was observed after 1000 h running. The enhanced stability of the catalyst can be ascribed to the special encapsulated structure. Furthermore, the formation mechanism of highly dispersed iron nanoparticle also was elaborated. This approach opens the way to designing metal nanoparticles with both high stability and reactivity for nanocatalysts in hydrogenation application.

Microwave-assisted solvothermal synthesis of Ag-Si codoped TiO2 nanoparticles for enhanced visible light photocatalytic activity.

Ag-Si codoped TiO2 nanoparticles were successfully synthesized via a rapid and energy frugal microwave-assisted solvothermal method. The obtained materials were characterized by XRD, BET, TEM, XPS, and UV-Vis DRS. These characterizations revealed that the obtained materials possessed good crystallinity, small particle size and large surface area. In this system, silicon could enter into the crystal lattice of TiO2, leading to smaller particle size and larger surface area compared to pure TiO2; silver dispersed on the surface of TiO2 particles, contributing to the visible light response and benefiting the efficient separation of photoelectrons and holes. Thus, the synthesized materials should achieve enhanced photoactivity under visible light irradiation, and that was evaluated by the decomposition of Rhodamine B in the aqueous solution. It was found that the Ag-Si codoped TiO2 photocatalyst exhibited higher photocatalytic activity compared with pure TiO2 and Ag or Si doped TiO2. The doping amount of the silver showed significant effect on the photocatalytic activity, and the optimal activity was achieved with Ag content of 1 mol%.

Single-crystal α-Fe2O3 hexagonal nanorings: stepwise influence of different anionic ligands (F- and SCN- anions).

Single-crystal α-Fe(2)O(3) hexagonal nanorings with hexagonal inner hole were synthesized under the stepwise influence of different anionic ligands (F(-) and SCN(-)). This is a new method to design and modify crystal structures of transition metal oxide nanoparticles.

Controllable synthesis and magnetism of iron oxides nanorings.

Hematite (alpha-Fe2O3) nanorings were prepared via a facile hydrothermal route without using any template. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). On the basis of these characterizations and condition experiments, an "oriented dissolution and recrystallization" mechanism under the effect of H2PO4- ions was proposed to explain the formation process of nanoring structure. Magnetite (Fe3O4) nanorings were obtained by reducing alpha-Fe2O3 nanorings, and then maghemite (gamma-Fe2O3) nanorings were obtained by reoxidizing Fe3O4 nanorings. The magnetic properties of these nanorings were investigated, and it was found that these nanorings have higher coercivity and lower saturation magnetization than many other nanostructures of iron oxides. The adsorbed phosphate on the surface and the nanoring morphology might be responsible for this phenomenon. Furthermore, it is interesting to find that the coercivity of the nanorings increased with the increase of d(in)/d(out) (d(in) and d(out) are the inner and outer diameters of the rings, respectively), and a rapid increase was observed at the value of d(in)/d(out) around 0.5.