La_(2)FeMO_(6)双钙钛矿中的不对称氧空位用于促进氧活化和H2S选择性氧化

金属氧化物催化剂表面O_(2)分子的活化对于多相催化中氧化还原反应具有重要意义.硫化氢(H_(2)S)选择性氧化是一个典型的氧化反应,通常用于去除克劳斯工艺尾气中有害的H_(2)S,同时回收化工产品硫磺.受克劳斯反应的热力学限制,工艺尾气中仍有近1%的H_(2)S残留,在焚烧炉中会转化为有害的SO_(x),造成不必要的硫损失以及严重的环境问题.研究表明,氧分子活化解离产生的活性氧物种是H_(2)S选择氧化的关键活性物种.然而,受限于氧分子的低效活化,传统催化剂需提高反应温度以获得令人满意的H_(2)S转化率,这也促进了副反应的进行并生成有害副产物SO_(2).因此,迫切需要在较低温度下实现氧分子的高效活化以促进H_(2)S选择氧化反应的进行,从而最大限度地提高克劳斯工艺硫回收效率并降低运营成本.目前,大多数研究通过引入更多的氧空位促进氧分子的活化及氧化反应的进行,但很少有人考虑氧空位本身结构的影响.近年来,研究者更多地关注不对称氧/空位(M_(1)-O-M_(2)或M_(1)-VO-M_(2)),该特殊结构可以有效地优化氧分子的活化,提高催化性能.本文报道了一种简单的氧空位调控策略用于H_(2)S选择氧化,通过过渡金属(M=Mn,Co和Mo)取代策略在LaFeO_(3)钙钛矿催化剂中引入不对称氧空位,从而激发氧分子活化以促进H_(2)S选择氧化的进行.X射线粉末衍射、Raman光谱及透射电镜结果表明,Mn和Co的引入形成了均匀的La_(2)FeMO_(6)以及La_(2)FeCoO_(6)双钙钛矿相,而Mo的引入则形成了La_(2)Mo_(2)O_(9)和LaFeO_(3)钙钛矿的混相.X射线光电子能谱及M?ssbauerr谱结果表明,Mn取代形成的La_(2)FeMO_(6)双钙钛矿催化剂由于其结构中Mn与Fe的完全交替取代形成了丰富的不对称Fe-VO-Mn位点,结合H_(2)程序升温还原及O_(2)程序升温解吸结果,可以推断不对称空位促进了催化剂上氧分子的活化,进而提高了催化剂的氧迁移率和还原性.模拟计算了氧分子在LaFeO_(3)及La_(2)FeMO_(6)催化剂上的吸附及解离过程,结果表明,氧分子在对称的Fe-VO-Fe位点上具有较高的吸附能及解离能,在不对称的Fe-VO-Mn位点上不存在稳定的吸附态,倾向于直接解离形成活性氧物种.具有丰富不对称Fe-VO-Mn位点的La_(2)FeMO_(6)催化剂的H_(2)S选择氧化低温活性和稳定性显著提高,在较宽的温度窗口内均可保持较好的H_(2)S转化率(>90%)与硫选择性(接近100%).综上,本文通过取代策略实现了对催化剂氧空位结构的调控,揭示了不对称氧空位对氧分子活化行为的促进机制.研究结果不仅为合理设计高效氧化催化剂探明了一条可行的途径,还对氧分子活化过程中氧空位结构的促进机制提供了深入的见解,有望激发更多关于开发氧化还原反应高效催化材料的研究.

Molecular oxygen activation enhancement by BiOBr0.5I0.5/BiOI utilizing the synergistic effect of solid solution and heterojunctions for photocatalytic NO removal

To improve the photocatalytic oxidation reaction activity for NO removal, photocatalysts with excellent activity are required to activate molecular oxygen. Solid solution and heterojunction were suggested as effective strategies to enhance the molecular oxygen activation viaexciton and carrier photocatalysis. In this study, a solid solution and heterojunction containing BiOBr0.5I0.5/BiOI catalyst was synthesized, and it showed improved photocatalytic activity for removing NO. The photocatalytic NO removal mechanism indicated that synergistic effects between the solid solution and heterojunction induced the enhanced activity for molecular oxygen activation. The photogenerated holes, superoxide, and singlet oxygen generated by the carrier and exciton photocatalysis supported the high photocatalytic NO removal efficiency. This study provides new ideas for designing efficient Bi-O-X(X = Cl, Br, I) photocatalysts for oxidation reactions.

Iodine-doping-assisted tunable introduction of oxygen vacancies on bismuth tungstate photocatalysts for highly efficient molecular oxygen activation and pentachlorophenol mineralization

In this work,the tunable introduction of oxygen vacancies in bismuth tungstate was realized via asimple solvothermal method with the assistance of iodine doping.With the predictions afforded bytheoretical calculations,the as-prepared bismuth tungstate was characterized using various tech-niques,such as X-ray diffraction,Raman spectroscopy,scanning electron microscopy,transmissionelectron microscopy,X-ray photoelectron spectroscopy,electron spin resonance spectroscopy,anduV-Vis diffuse reflectance spectroscopy.The different concentrations of the oxygen vacancies onbismuth tungstate were found to be intensely correlated with iodine doping,which weakened thelattice oxygen bonds.Owing to the sufficient oxygen vacancies introduced in bismuth tungstate as aresult of iodine doping,the molecular oxygen activation was remarkably enhanced,thus endowingbismuth tungstate with high activity for the photocatalytic degradation of sodium pentachloro-phenate.More encouraging is the total organic carbon removal rate of sodium pentachlorophenateover iodine-doped bismuth tungstate that exceeded 90%in only 2 h and was 10.6 times higher thanthat of the pristine bismuth tungstate under visible light irradiation.Moreover,the mechanism,through which the degradation of sodium pentachlorophenate over iodine-doped bismuth tung-state is enhanced,was speculated based on the results of radical detection and capture experiments.This work provides a new perspective for the enhanced photocatalytic degradation of organochlo-rine pesticides from the oxygen vacancy-induced molecular oxygen activation over iodine-dopedbismuth tungstate.

DFT Study of Iron Tetraphenylporphyrin Chloride and Iron Pentafluorophenylporphyrin Chloride

The geometry optimizations and the single point energy calculations of iron tetraphenylporphyrin chloride Fe（TPP）Cl and iron tetraphenylporphyrin chloride （Fe（TPP）Cl）, iron pentafluorophenylporphyrin chloride （Fe（TPPF20）Cl） were carried out by using the Density Functional Theory （DFT） UB3LYP with STO-3G^＊ and 6-31G^＊ basis sets, respectively. The electronic properties and the structures of high-lying molecular orbitals were analyzed in detail. The results show that partial spin is transferred from the Fe atom to the porphyrin ring and some electron with the spin opposite to the unpaired electron on the Fe atom is transferred from the porphyrin ring to the Fe atom. The π and σ-type bonding between the Fe atom and the porphyin ring cause the transfer. The fluorination enhances the electron transfer and the chemical stability of the complex. The high stability is important for the complex possessing high catalytic activity. The catalysis mechanism of oxygen molecule activation on the complex surface is also discussed based on the symmetry of the molecular orbitals.

Antioxidation Activities of Low-Molecular-Weight Gelatin Hydrolysate Isolated from the Sea Cucumber Stichopus japonicus

Gelatin extracted from the body wall of the sea cucumber （Stichopus japonicus） was hydrolyzed with flavourzyme. Low-molecular-weight gelatin hydrolysate （LMW-GH） of 700-- 1700 Da was produced using an ultrafiltration membrane bioreaetor system. Chemiluminescence analysis revealed that LMW-GH scavenges high free radicals in a concentration-dependent manner; IC50 value for superoxide and hydroxyl radicals was 442 and 285 μgmL-1, respectively. LMW-GH exhibited excellent inhibitory characteristics against melanin synthesis and tyrosinase activity in B16 cells. Furthermore, LMW-GH notably increased in- traeellular glutathione （GSH）, which in turn suppressed melanogenesis. LMW-GH performs antioxidation activity, holding the potential of being used as a valuable ingredient in function foods, cosmetics and pharmaceuticals or nutriceuticals.

Free radicals, apparent activation energy, and functional groups during low-temperature oxidation of Jurassic coal in Northern Shaanxi

Correlations among free radicals, apparent activation energy, and functional groups during lowtemperature oxidation of Jurassic coal in Northern Shaanxi were investigated by examining three coal samples collected from the Ningtiaota, Jianxin, and Shigetai coal mines. Free radical concentrations at less than 120 ℃ were investigated by electron spin resonance experiments while the thermogravimetric experiments were conducted to analyze apparent activation energies. In addition, Fourier transform infrared spectroscopy was employed to study the spectrum of functional groups generated in coal. The results indicated that, in decreasing order, the apparent activation energies were Shigetai 〉Jianxin 〉 Ningtiaota, indicating that, from 50 to 120 ℃, the Ningtiaota coal sample most easily absorbed and reacted with oxygen while the most resistant was the Shigetai coal sample. Free radical concentrations and line heights increased with increased temperature, and the line width and Lande factor showed irregular fluctuations. Functional group variations were different among these coals, and the phenol and alcohol-associated OHs, carboxyls, and aromatic ring double bonds might have had a major impact on free radical concentrations. These results were meaningful for better consideration and management of coal oxidation at low temperatures.

Study on the Molecular Weight Composition and Antioxidant Activity of Peanut Bioactive Peptides

[ Objective] To prepare peanut bioactive peptides and analyze their molecular weight composition and antioxidant activity. [ Method ] The dialysis bag of 8.0, 3.5 and 1.0 kD were used to classify the hydrolyzate derived from alcalase and flavourzyme, peanut bioactive poptides of differ-ent molecular weight were obtained and then their scavenging capacity of free radicals was measured. The molecular weight composition was stud-ied by Tricine-SDS-PAGE.[Result] The content of peptides 〈 1.0 kD were 76.21% and 83.42% in the total hydrolyzate from alcalase and fla-vourzyme respectively. All hydrolyzate with different molecular grades showed free radical scavenging capacity, which was increased with the reduc- tion of molecular mass. The peptides 〈 1.0 kD exhibited higher radical scavenging capacity of （87.41 ±0.66） % （alcalase） and （67.88 ±0.48）% （ flavourzyme）, respectively. [ Conclusion] Peanut bioactive peptides had strong effect of antioxidant capacity, especially that 〈 1.0 kD, which had great prospect.

Hydrogenation of molecular oxygen to hydroperoxyl： An alternative pathway for O2 activation on nanogold catalysts

Activation of molecular O2 is the most critical step in gold-catalyzed oxidation reactions; however, the underlying mechanisms of this process remain under debate. In this study, we propose an alternative O2 activation pathway with the assistance of hydrogen-containing substrates using density functional theory. It is demonstrated that the co-adsorbed H-containing substrates （R-H） not only enhance the adsorption of O2, but also transfer a hydrogen atom to the adjacent O2, leading to O2 activation by its transformation to a hydroperoxyl （OOH） radical species. The activation barriers of the H-transfer from 16 selected R-H compounds （H2O, CH3OH, NH2CHCOOH, CH3CH=CH2, （CH3）2SiH2, etc.） to the co-adsorbed O2 are lower than 0.50 eV in most cases, indicating the feasibility of the activation of O2 via OOH under mild conditions. The formed OOH oxidant, with an increased O-O bond length of -1.45 A, either participates directly in oxidation reactions through the end-on oxygen atom, or dissociates into atomic oxygen and hydroxyl （OH） by crossing a fairly low energy barrier of 0.24 eV. Using CO oxidation as a probe, we have found that OOH has superior activity than activated O2 and atomic oxygen. This study reveals a new pathway for the activation of O2, and may provide insight into the oxidation catalysis of nanosized gold.

Designed polymeric conjugation motivates tunable activation of molecular oxygen in heterogeneous organic photosynthesis

Photocatalytic oxidative organic reactions are important synthetic transformations,and research on reaction selectivity by reactive oxygen species(ROS)is significant.To date,however,there has rarely been any focus on the directed generation of ROSs.Herein,we report the first identification of tunable molecular oxygen activation induced by polymeric conjugation in nonmetallic conjugated microporous polymers(CMP).The conjugation between these can be achieved by the introduction of alkynyl groups.CMP-A with an alkynyl bridge facilitates the intramolecular charge mobility while CMP-D,lacking an alkynyl group enhances the photoexcited carrier build-up on the surface from diffusion.These different processes dominate the directed ROS generation of the superoxide radical(·O_(2)^(-))and singlet oxygen(^(1)O_(2)),respectively.This theory is substantiated by the different performances of these CMPs in the aerobic oxidation of sulfides and the dehydrogenative coupling of amines,and could provide insight into the rational design of CMPs for various heterogeneous organic photosynthesis.

Insight on the active sites of CoNi alloy embedded in N-doped carbon nanotubes for oxygen reduction reaction

Transition metal alloy electrocatalysts have sparked intense interest for their use in oxygen reduction reaction(ORR).However,there is almost no corresponding research on the alloy active sites.In this study,CoNi alloy nanoparticles embedded in bamboo-like N-doped carbon nanotubes(CoNi-NCTs)as catalysts constructed by a facile pyrolysis of Prussian blue analogs were investigated.The density functional theory calculation reveals that the oxygen molecules are more easily adsorbed on the Ni sites in these catalysts,while the Co sites favor the formation of OOH★intermediates during ORR.In addition,the cooperation of the CoNi alloys with the N-doped carbon benefits electron transfer and promotes electrocatalytic activity.The optimized CoNi-NCT shows remarkable ORR catalytic activity with an half-wave potential(E1/2)of 0.83 V,an onset potential(Eonset)of 0.97 V,and superior durability,all of which surpass the commercial Pt/C catalysts.The assembled zinc-air battery delivers a small charge/discharge voltage gap of 0.86 V at 10 mA cm^(-2),a high-power density of 167 mW cm^(-2),and good stability(running stably over 900 cycles).

Multicolor Luminescent Carbon Nanoparticles： Synthesis, Supramolecular Assembly with Porphyrin, Intrinsic Peroxidase-Like Catalytic Activity and Applications

Luminescent carbon nanoparticles （CNPs） are newcomers to the world of nanomaterials and have shown great impact in health and environmental applications as well as being promising building blocks for future nanodevices because of their fascinating photoluminescence and potential to serve as nontoxic replacements for traditional heavy-metals-based quantum dots. Herein, fluorescent CNPs have been prepared from candle soot by re fluxing with HNO3 and subsequently separated by a single centrifugation. The CNPs can be represented by the empirical formula C1Ho.677Oo.586No.o15Nao.069, and have a size of 20-100 nm, height of 3.0 nm, lifetime of 7.31 ns ＋ 0.06 ns and quantum yield of -1.7%. Further studies demonstrate that： （1）the as-prepared CNPs exhibit excellent stability in biological media and their luminescence intensity does not change with ionic strength or pH in the physiological and pathological range of pH 4.5-8.8; （2） CNPs can act as electron donors and transporters and porphyrin can assemble onto CNPs through electrostatic and ^-stacking interactions to form porphyrin-CNPs supramolecular composites; （3）CNPs have strong intrinsic peroxidase-like activity. Based on this intrinsic peroxidase activity, a simple, cheap, and highly selective and sensitive colorimetric and quantitative assay has been developed for the detection of glucose levels. This assay has been used to analyze real samples, such as diluted blood and fruit juice.

Mechanistic study of copper-catalyzed intramolecular ortho-C-H activation/carbon-nitrogen and carbon-oxygen cyclizations

Intramolecular ortho-C-H activation and C-N/C-O cyclizations of phenyl amidines and amides have recently been achieved under Cu catalysis. These reactions provide important examples of Cu-catalyzed functionalization of inert C-H bonds, but their mechanisms remain poorly understood. In the present study the several possible mechanisms including electrophilic aro- matic substitution, concerted metalation-deprotonation （CMD）, Friedel-Crafts mechanism, radical mechanism, and proton- coupled electron transfer have been theoretically examined. Cu（II）-assisted CMD mechanism is found to be the most feasible for both C-O and C-N cyclizations. This mechanism includes three steps, i.e. CMD with Cu（II）, oxidation of the Cu（II） inter- mediate, and reductive elimination from Cu（III）. Our calculations show that Cu（II） mediates the C-H activation through an six-membered ring CMD transition state similar to that proposed for many Pd-catalyzed C-H activation reactions. It is also in- teresting to find that the rate-limiting steps are different for C-N and C-O cyclizations： for the former it is concerted metalation-deprotonation with Cu（II）, whereas for the latter it is reductive elimination from Cu（III）. The above conclusions are consistent with the experimental kinetic isotope effects （1.0 and 2.1 for C-O and C-N cyclizations, respectively）, substituent effects, and the reactions under O2-free conditions.

Meaningful comparison of photocatalytic properties of {001} and {101} faceted anatase TiO2 nanocrystals

The facet-dependent photocatalytic performance of TiO_2 nanocrystals has been extensively investigated due to their promising applications in renewable energy and environmental fields. However, the intrinsic distinction in the photocatalytic oxidation activities between the {001}and {101} facets of anatase TiO_2 nanocrystals is still unclear and under debate. In this work, a simple photoelectrochemical method was employed to meaningfully quantify the intrinsic photocatalytic activities of {001} and{101} faceted TiO_2 nanocrystal photoanodes. The effective surface areas of photoanodes with different facets were measured based on the monolayer adsorption of phthalic acid on TiO_2 photoanode surface by an ex situ photoelectrochemical method, which were used to normalize the photocurrents obtained from different faceted photoanodes for meaningful comparison of their photocatalytic activities. The results demonstrated that the {001} facets of anatase TiO_2 nanocrystals exhibited much better photocatalytic activity than that of {101} facets of anatase TiO_2 nanocrystals toward photocatalytic oxidation of water and organic compounds with different functional groups(e.g.,–OH, –CHO, –COOH). Furthermore, the instantaneous kinetic constants of photocatalytic oxidation of pre-adsorbates on {001} faceted anatase TiO_2 photoanode are obviously greater than those obtained at {101} faceted anatase TiO_2 photoanode, further verifying the higher photocatalytic activity of {001} facets of anatase TiO_2.This work provided a facile photoelectrochemical method to quantitatively determine the photocatalytic oxidation activity of specific exposed crystal facets of a photocatalyst, which would be helpful to uncover and meaningfully compare the intrinsic photocatalytic activities of different exposed crystal facets of a photocatalyst.

Oxidative polymerization of hydroquinone using deoxycholic acid supramolecular template

Polyhydroquinone (PHQ) is a redox-active polymer with quinone/hydroquinone redox active units in the main chain and may have potential applications as a mediator in biosensors and biofuel cells. By the oxidative polymerization of hydroquinone (HQ), PHQ can be easily synthesized, but the reaction lacks control over the structure of the product. Deoxycholic acid (DCA) was introduced as a supramolecular template to control the reaction. The reaction rate is 14 times of that in deionized water and twice of that in buffer. The DCA template increases not only the reaction rate, but also the molecular weight of the polymer obtained. The template effect of DCA was attributed to the supramolecular assemblies of DCA formed in the solution. Cyclic voltammetry study indicated the resulting PHQ was redox-active. While the supramolecular assemblies of DCA provided a template for the oxidative polymerization of HQ, the protons released as a by-product of the oxidative polymerization of HQ in turn enhanced the self-assembly of DCA. As a result, DCA microfibers form and separate out of the solution.

Cyanide-bridged single molecule magnet based on a manganese(Ⅲ) complex with TTF-fused Schiff base ligand

Reaction of [Mn（TTF-salphen）][OAc] （TTF-salphen2=2,2＇-（（2-（4,5-bis（methylthio）-1,3-dithiol-2-ylidene）-1,3-benzodithiole- 5,6-diyl）bis（nitrilomethylidyne）bis（pbenolate）dianion） and the cyanometalate building blocks [n-Bu4N][（Tp）Fe（CN）3] （Tp =Tris（pyrazolyl）hydroborate） or [n-Bu4N][Ru（salen）（CN）2] （salen2 =N,N＇-ethylenebis（salicylideneimine）dianion） resulted in the formation of two redox-active complexes, the dinuclear heterometallic complex [（Tp）Fe（CN）3Mn（TTF-salphen）＇CH3OH] （1） and the one dimensional complex [Ru（salen）（CN）2Mn（TTF-salphen）]n （2）. Both complexes were characterized by X-ray crystallography and solid state electrochemistry, in addition to static and dynamic magnetic measurements. Antiferromagnetic couplings are found to be operative between metal ion centers bridged by cyanide in both complexes. Complex 1 exhibited field-induced SMM behavior with an energy barrier of 13.8 K. The introduction of the redox-active TTF unit into cyanidebridged complexes with interesting magnetic properties renders them promising candidates for the construction of new hybrid inorganic-organic materials.