查看更多>>摘要：The carbon source,graphitization degree and microstructure of pure carbon materials have strong effects on their electrical conductivity,impedance matching and electromagnetic(EM)waves absorption properties.A novel microstructure nitrogenous porous carbon(NPC)material with excellent EM waves absorption properties was synthesized by carbonizing polyaniline(PANI)fiber clusters.When the filler loading is only 30 wt%,the widest effective absorption bandwidth(EAB)reached 5.5 GHz from 12.41 GHz to 17.91 GHz(almost the entire Ku band)with a thickness of only 1.5 mm and the EAB/thickness was up to 3.67 GHz/mm,which is not inferior or even better than many composites with complex structure.The nitrogen atoms in NPC lattice reduced its graphitization degree.The synergistic effect of optimized impedance matching and enhanced dielectric loss improved EM waves absorption of NPC.The EM waves dissipation mechanisms of NPC material mainly include dipole polarization,interface polarization and conductance loss.The synthesized NPC is a potential EM waves absorption material.
查看更多>>摘要：Chrysolepic acid(CA)is a widely-used chemical product and considered hazardous for ecosystem and human health,which makes its removal as important as its sensing.In this work,a composite structure(denoted as Tb-COF,with a structural composition of C_(162)H_(120)N_(18)O_(12)Br3·C_(21)HgNsO_(12)Tb1)was synthesized,consisting of an ionic covalent organic framework(denoted as I-COF,with a structural composition of C_(162)H_(120)N_(18)O_(12)Br6)and a terbium-based dopant/emitter(denoted as Tb(DPA)_3~(3-),DPA = pyridine-2,6-dicarboxylic acid).Tb-COF was identified by means of single crystal analysis,infrared(IR)spectra,X-ray diffraction(XRD),porosity analysis,SEM(scanning electron microscope)/TEM(transmission electron microscope)and elemental composition analysis.The dopant loading level in Tb-COF was determined as 41%.Both green emission from Tb-based dopant and red emission from I-COF host were observed.The presence of CA quenched I-COF emission but enhanced dopant emission,resulting in ratiometric sensing signal.A linear calibration curve was demonstrated,with fitting equation of I/I0 = 1.223 + 6.709 × 10~5 M~(-1)[CA],R~2 = 0.996,within [CA] region of 0-9 μM.The key sensing/adsorption process was revealed as the adsorption of I-COF micropores for CA molecules,which endowed Tb-COF with a good selectivity over competing species.I-COF adsorption/removal feature for CA was tentatively evaluated.
查看更多>>摘要：Good indoor air environment is of great significance for the health and comfort assurance of occupants.In this work,a series of bismuth self-doping Bi2MoO6/diatomite(BD-X)composites with different proportions of bismuth and molybdenum source were prepared via a mild solvothermal process.Under visible light irradiation,the BD-3 sample exhibited the optimal formaldehyde(HCHO)mineralization performance,and the corresponding calculated rate constant was up to 3.2 times higher than that of bare Bi2MoO6(B).The introduction of diatomite as catalyst carrier could not only contribute to the dispersion of nano-scale Bi2MoO6 photocatalyst,but also promote the exposure of(001)crystal plane of Bi2MoO6.In particular,the molybdenum vacancy generated with increasing the proportion of bismuth source,which effectively facilitated the separation of photogenerated carriers.Moreover,the photogenerated holes(h~+)played the major role in the photocatalytic degradation process.Overall,this research would provide a novel binary composite photocatalyst derived from natural mineral for the high-efficient mineralization of formaldehyde under visible light.
查看更多>>摘要：Heteroatomic mesoporous ZSM-5(Zeolite Socony Mobil-5)as an important catalyst is widely applied in catalytic field,however,its catalytic performance in VOCs oxidation is not clear.Particularly,the effects of the metal ionic radius at lattice site on surface active oxygen and reducibility of ZSM-5 are confused.Herein,Cu-,Mn-,Cr-and Co-doped mesoporous ZSM-5 were synthesized by a hydrothermal method to investigate the effects and altered mechanisms for hexane oxidation via the catalysts containing transition metals with different ionic radii at lattice sites in mesoporous ZSM-5,and the physical/chemical characteristics of all the catalysts were characterized.The results show that surface active oxygen species and low-temperature reducibility as critical factors in hexane oxidation are relevant to the transition metal ion radius.And,moderate-length ionic radius can significantly facilitate the increase in the amount and transfer capacity of the surface reactive oxygen species and the reducibility of catalysts,which exhibits a typical volcano-type curve relationship.Among the prepared catalysts,Cu-HZ(tetra-coordination Cu~(2+)radius: 0.57 A),which possesses the largest concentration of superficial lattice oxygen,the highest reducibility and an adequate degree and strength for surface acidity,exhibits the highest catalytic activity,the highest CO2 yield and selectivity.Additionally,compared with the supported mesoporous ZSM-5,the reaction mechanism of hexane oxidation over doped mesoporous ZSM-5 can be intensified by the synergistic effects between the lattice transition metal atom as the acidic adsorption site and the surface reactive oxygen generated by lattice doping of transition metal.We believe that this work can provide new insights into the design of catalysts for VOC degradation.
查看更多>>摘要：Metal-organic frameworks(MOFs)are a class of crystalline and porous adsorbents,with wide-ranging applications in gas separations,membrane materials as well as sensors.Commonly used batch synthesis techniques for MOF production are limited by low productivity,high operating costs,and slow crystallization timescales,severely impeding the large-scale manufacturing of these materials.However,batch synthesis is a useful and easy technique to screen multiple reaction parameters to find an optimal chemistry.Therefore,in this study,we have used the batch process and screened a multidimensional reaction space consisting of 45 sample variations based on the crystallinity,yield,and instantaneous precipitation,which could lead to tube clogging under flow conditions.We have found one optimized reaction chemistry,that could be used in flow conditions,which in this study is a novel millifluidic droplet-based reactor for the continuous synthesis of HKUST-1 crystals.The biphasic flow in the millifluidic reactor consisted of droplets of the reactant solution,dispersed in a continuous phase of silicone oil.We investigate the differences in the quality and quantity of HKUST-1 synthesized via the continuous and batch techniques.Moreover,we have demonstrated that the HKUST-1 samples prepared via the continuous synthesis in a droplet based millifluidic reactor,at an ultra-low residence time exhibit excellent physical properties comparable to that obtained for the samples prepared by the traditional batch process.A clean,easy-to-install,and reusable millifluidic reactor presented in this work may pave the path for an economically viable,large-scale synthesis of HKUST-1.
查看更多>>摘要：In this paper,a new post-functionalized nano-platform of Tb~(3+)@UiO-66-DPA had been synthesized and characterized by FTIR spectra,PXRD,SEM,TGA and XPS.With the multi-functionalized nano-platform of Tb~(3+)@UiO-66-DPA,the selective detection and identification of two typical simulants(diethyl chlorophosphate,DCP,and 2-chloroethyl ethyl sulfide,CEES)of chemical warfare agents(nerve agents and mustard gas)had been realized.DCP sensitized and enhanced the'antenna effect'of Tb~(3+)@UiO-66-DPA through the inhibition of non-radiative deactivation vibrational energy transfer pathways,and the quantitative assay of CEES was achieved through the new Cu~(2+)-mediated luminescent assay method.This study would provide a reliable and effective methodology to detect nerve agent and mustard gas simulants simultaneously via the excellent multi-functional lanthanide nano-materials platform.
查看更多>>摘要：A simple and scalable method is presented for preparing propane dehydrogenation catalysts with superior catalytic properties.Pt distribution is significantly improved when the platinum precursor and a large amount of NaCl are introduced into the MFI zeolite by impregnation,and after calcining and fixing the active components in the insoluble form,the excess of inert salt is washed with water.NaCl promotes Pt dispersion,prevents sintering during calcination,and effectively suppresses zeolite acidity.Washing after the calcination of Pt-containing catalysts further increases the catalyst activity and stability due to the redispersion of water-soluble chlorinated Pt compounds.High external surface acid site concentrations,Na/Pt atomic ratios of 40-70,calcination temperatures of 400-500 ℃,washing with water,and the order of component introduction when the excess NaCl and the precursor of Pt are calcined jointly contribute to improved Pt dispersion and catalyst stability.
查看更多>>摘要：Since the catalytic activity and the stability of silica-bound organometallic complexes are affected by their interactions with hydroxyl groups on the surface,isolated hydroxyls are often created prior to the introduction of catalytic species.Here,we investigate a method to remove the indigenous hydroxyls and create new isolated hydroxyls by grafting organo-trimethoxysilane(R-TMS)to generate a silicon T~2 site,(≡SiO-)2SiR(-OH).We used in situ ~(29)Si solid-state NMR experiments to monitor the evolution of T~n sites,(≡SiO-)nSiR(-OH)_(3-n)(n = 1,2,3).The study indicates that i)the grafting proceeds in a consecutive manner as T~1 → T~2 → T~3,and ii)the kinetics depend on the type of functional groups in the silane.However,the rates of T~1 formation and T~2 → T~3 conversion are also controlled to a significant extent by the entropy loss associated to the initial silane binding and the spatial arrangement of surface hydroxyls,respectively.The grafting of R-TMS with a basic functional group leads to a lower concentration of T~1 sites.The nucleophilicity of the functional group facilitates the grafting process by lowering the enthalpy barrier,while the T~1 formation rate is more influenced by the entropy barrier than the T~1 → T~2 conversion rate.Thus,the basic functional group promotes the T~1 → T~2 conversion more than the T~1 formation,resulting in a lower concentration of T~1 sites.
查看更多>>摘要：Traditional zeolite synthesis requires usage of the organic structure-directing agent(OSDA)which is capital-intensive and non-eco-friendly.Seed-assisted zeolite synthesis can reduce or eliminate OSDAs,making it a green and economical approach.Seed-assisted synthesis conditions reside in a high-dimensional chemical space where a brute-force search is unfeasible.Here we utilize archived experiment records to build machine learning models for predicting crystallization tendency.Effects of seed physicochemical properties,gel compositions as well as crystallization conditions are calibrated.In particular,seed framework density,NaOH concentration in the gel and crystallization time have synergistic influences on the zeolite transformation.The machine learning model is interpreted with domain knowledge to obtain chemical hypothesis.The hypothesis is verified by follow-up experiments,distilling zeolite transitions that had been overlooked previously.
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