•3DOM LaMnAl11O19 is prepared using the polymethyl methacrylate-templating method.•Pd/3DOM LaMnAl11O19 is prepared via polyvinyl alcohol-protected reduction route.•0.97 wt% Pd/3DOM LaMnAl11O19 performs the best in methane combustion.•0.97 wt% Pd/3DOM LaMnAl11O19 is catalytically stable in methane combustion.•3DOM structure, Pd NPs, Oads, reducibility, and Pd–support interaction govern the activity.Three-dimensionally ordered macroporous (3DOM) LaMnAl11O19 and 0.97 wt% Pd/3DOM LaMnAl11O19 samples with a good-quality 3DOM structure have been prepared using the poly(methyl methacrylate) (PMMA)-templating and polyvinyl alcohol (PVA)-protected reduction methods, respectively. The Pd nanoparticles (NPs) with a size of 2–5 nm were uniformly dispersed on the macropore wall surface of 3DOM LaMnAl11O19. Due to the highest adsorbed oxygen species concentration and the best low-temperature reducibility, the 0.97 wt% Pd/3DOM LaMnAl11O19 sample showed the best catalytic activity for methane combustion, with the reaction temperatures (T10%, T50%, and T90%) required for achieving methane conversions of 10, 50, and 90% being 259, 308, and 343 °C at SV = 20,000 mL/(g h), respectively. The 0.97 wt% Pd/3DOM LaMnAl11O19 catalyst was catalytically stable, whereas the 0.98 wt% Pd/3DOM Mn2O3 sample was partially deactivated after 50 h of methane oxidation. The introduction of 3.0 vol% H2O or 2.0 vol% CO2 to the reaction system resulted in the reversible deactivation of 0.97 wt% Pd/3DOM LaMnAl11O19, but the addition of 100 ppm SO2 led to the irreversible deactivation of the catalyst. It is concluded that the good-quality 3DOM structure, uniformly dispersed Pd NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pd NPs and 3DOM LaMnAl11O19 were accountable for the good catalytic performance of 0.97 wt% Pd/3DOM LaMnAl11O19.Download full-size image

Ordered mesoporous Mn2O3 (meso-Mn2O3) and meso-Mn2O3-supported Pd, Pt, and Pd-Pt alloy x(PdyPt)/meso-Mn2O3; x = (0.10−1.50) wt%; Pd/Pt molar ratio (y) = 4.9−5.1 nanocatalysts were prepared using KIT-6-templated and poly(vinyl alcohol)-protected reduction methods, respectively. The meso-Mn2O3 had a high surface area, i.e., 106 m2/g, and a cubic crystal structure. Noble-metal nanoparticles (NPs) of size 2.1−2.8 nm were uniformly dispersed on the meso-Mn2O3 surfaces. Alloying Pd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd5.1Pt)/meso-Mn2O3 gave the best performance; T10%, T50%, and T90% (the temperatures required for achieving methane conversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of 20000 mL/(g·h). The effects of SO2, CO2, H2O, and NO on methane combustion over 1.41(Pd5.1Pt)/meso-Mn2O3 were also examined. We conclude that the good catalytic performance of 1.41(Pd5.1Pt)/meso-Mn2O3 is associated with its high-quality porous structure, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interactions between Pd-Pt alloy NPs and the meso-Mn2O3 support.Alloying Pd with Pt enhanced the catalytic performance in methane combustion. 1.41(Pd5.1Pt)/meso-Mn2O3 showed the highest activity because of its large surface area, high Oads concentration, good low-temperature reducibility, and strong Pd-Pt alloy and Mn2O3 interactions.Download high-res image (124KB)Download full-size image

•Ordered mesoporous Cr2O3 (meso-Cr2O3) is fabricated via the KIT-6-templating route.•xAu1Pd2/meso-Cr2O3 are prepared using the polyvinyl alcohol-protected reduction method.•The 1.95Au1Pd2/meso-Cr2O3 sample performs the best for toluene oxidation.•Oads concentration, low-temp. reducibility, and AuPd–Cr2O3 interaction govern the activity.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au, Pd, and Au–Pd (0.90 wt% Au/meso-Cr2O3, 1.00 wt% Pd/meso-Cr2O3, and xAu1Pd2/meso-Cr2O3 (x = 0.50–1.95 wt%) catalysts were prepared using the KIT-6-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is found that the meso-Cr2O3 with a high surface area of 74 m2/g was rhombohedral in crystal structure and the noble metal nanoparticles (NPs) with a size of 2.9–3.7 nm were uniformly dispersed on the surface of meso-Cr2O3. The 1.95Au1Pd2/meso-Cr2O3 sample performed the best: the T10%, T50%, and T90% (temperatures required for achieving toluene conversions of 10, 50, and 90%) were 87, 145, and 165 °C at a space velocity of 20,000 mL/(g h), respectively, and the apparent activation energy was the lowest (31 kJ/mol) among all of the samples. The effect of moisture on the catalytic activity of the 1.95Au1Pd2/meso-Cr2O3 sample was also examined. It is concluded that the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3 was associated with its small Au–Pd particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3.Three-dimensionally ordered mesoporous Cr2O3 (meso-Cr2O3) and its supported Au–Pd (xAu1Pd2/meso-Cr2O3) catalysts were prepared using the KIT-6-templating and PVA-protected reduction methods, respectively. The small noble metal particle size, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and meso-Cr2O3 were responsible for the excellent catalytic performance of 1.95Au1Pd2/meso-Cr2O3.

Binuclear iron phthalocyanine/reduced graphene oxide (bi-FePc/RGO) nanocomposite with good electrocatalytic activity for ORR in alkaline medium was prepared in one step. High angle annular dark field image scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy element mapping results show bi-FePc was uniformly distributed on RGO. An obvious cathodic peak located at about −0.23 V (vs. SCE) in CV and an onset potential of −0.004 V (vs. SCE) in LSV indicate the as-prepared bi-FePc/RGO nanocomposite possesses high activity which is closed to Pt/C for ORR. The ORR on bi-FePc/RGO nanocomposite follows four-electron transfer pathway in alkaline medium. Compared with Pt/C, there is only a slight decrease (about 0.02 V vs. SCE) for bi-FePc/RGO nanocomposite when the methanol exists. The excellent activity and methanol tolerance in alkaline solutions proves that bi-FePc/RGO nanocomposite could be considered as a promising cathode catalyst for alkaline fuel cells.

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and their supported gold and palladium alloy (zAuxPdy/CZY; z = 0.80–0.93 wt%; x or y = 0, 1, 2) nanoparticles (NPs) were prepared using the cetyltrimethyl ammonium bromide-assisted hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of toluene. It is shown that the CZY in zAuxPdy/CZY was cubic in crystal structure, surface areas of CZY and zAuxPdy/CZY were in the range 68–77 m2 g−1, and the Au–Pd NPs with a size of 4.6–5.6 nm were highly dispersed on the surface of CZY nanorods. Among all the samples, 0.90Au1Pd2/CZY possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and performed the best: T50% and T90% (temperatures required for achieving toluene conversions of 50 and 90%) were 190 and 218 °C at a space velocity of 20000 mL (g h)−1, respectively. The partial deactivation due to water vapor introduction was reversible. The active sites might be the surface oxygen vacancies on CZY, oxidized noble metal NPs, and/or interfaces between noble metal NPs and CZY. The apparent activation energies (37–43 kJ mol−1) obtained over 0.90–0.93AuxPdy/CZY were much lower than that (88 kJ mol−1) obtained over CZY for toluene oxidation. It is concluded that the excellent catalytic performance of 0.90Au1Pd2/CZY was associated with its high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd NPs and CZY nanorods as well as good dispersion of Au–Pd NPs.

We have previously developed bare narrow-bore capillary chromatography. In this work, high-performance DNA separation was realized for a size range of 10–800 base pairs (bp) utilizing bare narrow-bore capillary chromatography with 750 nm-radius capillaries. Separation behavior of double-stranded DNA (dsDNA) fragments was investigated over a range of eluent concentrations and elution pressures. DNA molecules were hydrodynamically separated in a size-dependent manner in free solution without any sieving matrices, with the longer fragments being eluted out from the capillary earlier. It was found that the eluent concentration variously influenced the transport behavior for different-sized DNA fragments depending upon the configuration of DNA molecules and the association of counterions. Ionic strength of the solutions strongly impacted DNA persistence length. Enhanced elution pressure could shorten analysis time with a slight loss in resolution. Excellent efficiency of two million theoretical plates per meter was achieved, which indicates the enormous potential of bare narrow-bore capillary chromatography for the analysis of DNA fragments. These findings would be useful in understanding the transport behavior of DNA fragments in confined dimensions for chromatography in free solution.

Substitution reaction, as one of the most powerful and efficient chemical reactions, has been widely used in various syntheses, including those for the design and preparation of functional molecules or materials. In the past decade, a class of newly developed inorganic–organic hybrid materials, namely metal–organic materials (MOMs), has experienced a rapid development. MOMs are composed of metal-containing nodes connected by organic linkers through strong chemical bonds, and can be divided into metal–organic frameworks (MOFs) and metal–organic polygons/polyhedra (MOPs) with infinite and discrete structural features, respectively. Recent research has shown that the substitution reaction can be used as a new strategy in the synthesis and modification of MOFs and MOPs, particularly for pre-designed ones with desired structures and functions, which are usually difficult to access by a direct one-pot self-assembly synthetic approach. This review highlights the implementation of the substitution reaction in MOFs and MOPs. Examples of substitution reactions at metal ions, organic ligands, and free guest molecules of MOFs and MOPs are listed and analyzed. The changes or modifications in the structures and/or properties of these materials induced by the substitutions, as well as the nature of the associated reaction, are discussed, with the conclusion that the substitution reaction is really feasible and powerful in synthesizing and tailoring MOMs.

The Ce0.6Zr0.3Y0.1O2 (CZY) nanorods and its supported nanosized gold (xAu/CZY, Au loading (x) = 0.4–4.7 wt %) were prepared using the cetyltrimethylammonium bromide-assisted hydrothermal and polyvinylpyrrolidone-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous analytical techniques, and their catalytic activities were evaluated for the oxidation of CO and toluene. It is shown that the CZY in xAu/CZY was cubic in crystal structure, surface areas of CZY and xAu/CZY were in the range of 68–79 m2/g, and the Au nanoparticles (NPs) with a size of 3.1–3.9 nm were well dispersed on the surface of CZY nanorods. Among the xAu/CZY samples, the 4.7Au/CZY sample possessed the highest adsorbed oxygen concentration and the best low-temperature reducibility, and showed the highest catalytic activity at a space velocity of 20 000 mL/(g h): the T50% and T90% (temperatures required for achieving reactant conversions of 50 and 90%) were 32 and 60 °C for CO oxidation and 218 and 265 °C for toluene oxidation, respectively. Deactivation of water vapor addition was reversible, a result due to the competitive adsorption of H2O and toluene as well as oxygen on the sample surface. The apparent activation energies (27–37 and 39–53 kJ/mol) obtained over xAu/CZY were lower than those (42 and 88 kJ/mol) obtained over CZY for CO and toluene oxidation, respectively. On the basis of the characterization results and activity data, we conclude that the excellent catalytic performance of 4.7Au/CZY was associated with its higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au NPs and CZY nanorods as well as better Au NPs dispersion.

Pressure-induced transport of double-stranded DNA (dsDNA) from 10 base pairs (bp) to 1.9 mega base pairs (Mbp) confined in a 750-nm-radius capillary was studied using a hydrodynamic chromatographic technique and four distinct length regions (rod-like, free-coiled, constant mobility, and transition regions) were observed. The transport behavior varied closely with region changes. The rod-like region consisted of DNA shorter than the persistence length (∼150 bp) of dsDNA, and these molecules behaved like polymer rods. Free-coiled region consisted of DNA from ∼150 bp to ∼2 kilo base pairs (kbp), and the effective hydrodynamic radius RHD of these DNA scaled to L0.5 (L is the DNA length in kbp), a characteristic property of freely coiled polymers. Constant mobility region consisted of DNA longer than ∼100 kbp, and these DNA had a constant hydrodynamic mobility and could not be resolved. Transition region existed between free-coiled and constant mobility regions. The transport mechanism of DNA in this region was complicated, and a general empirical equation was established to relate the mobility with DNA length. Understanding of the fundamental principles of DNA transport in narrow capillary channels will be of great interest in the development of “lab-on-chip” technologies and nongel DNA separations.

•3DOM CoFe2O4 is fabricated via the polymethyl methacrylate-templating route.•MnOx/3DOM CoFe2O4 is prepared by the incipient wetness impregnation method.•Pd–Pt/MnOx/3DOM CoFe2O4 is obtained using the PVA-protected reduction method.•1.87Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 performs excellently in CH4 combustion.•Pd–Pt alloy, Oads, reducibility, and metal-support interaction govern the activity.Three-dimensionally ordered macroporous (3DOM) CoFe2O4, zMnOx/3DOM CoFe2O4 (z = 4.99–12.30 wt%), and yPd–Pt/6.70 wt% MnOx/3DOM CoFe2O4 (y = 0.44–1.81 wt%; Pd/Pt molar ratio = 2.1–2.2) have been prepared using the polymethyl methacrylate microspheres-templating, incipient wetness impregnation, and bubble-assisted polyvinyl alcohol-protected reduction strategies, respectively. All of the samples were characterized by means of various techniques. Catalytic performance of the samples was measured for methane combustion. It is shown that the as-prepared samples exhibited a high-quality 3DOM structure (103 ± 20 nm in pore size) and a surface area of 19–28 m2/g, and the noble metal or alloy nanoparticles (NPs) with a size of 2.2–3.0 nm were uniformly dispersed on the macropore wall surface of 3DOM CoFe2O4. The loading of MnOx on CoFe2O4 gave rise to a slight increase in activity, however, the dispersion of Pd–Pt NPs on 6.70MnOx/3DOM CoFe2O4 significantly enhanced the catalytic performance, with the 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 sample showing the highest activity (T10% = 255 °C, T50% = 301 °C, and T90% = 372 °C at a space velocity of 20,000 mL/(g h)). We believe that the excellent catalytic activity of 1.81Pd2.1Pt/6.70MnOx/3DOM CoFe2O4 was related to its well-dispersed Pd–Pt alloy NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between MnOx or Pd–Pt NPs and 3DOM CoFe2O4.

Ordered intermetallic nanomaterials are of considerable interest for fuel cell applications because of their unique electronic and structural properties. The synthesis of intermetallic compounds generally requires the use of high temperatures and multiple-step processes. The development of techniques for rapid phase- and size-controlled synthesis remains a formidable challenge. The intermetallic compound Pt1Bi2 is a promising candidate catalyst for direct methanol fuel cells because of its high catalytic activity and excellent methanol tolerance. In this work, we explored a one-step, facile and ultrafast phase- and size-controlled process for synthesizing ordered Pt–Bi intermetallic nanoparticles (NPs) within seconds in microfluidic reactors. Single-phase Pt1Bi1 and Pt1Bi2 intermetallic NPs were prepared by tuning the reaction temperature, and size control was achieved by modifying the solvents and the length of the reaction channel. The as-prepared Pt–Bi intermetallic NPs exhibited excellent methanol tolerance capacity and high electrocatalytic activity. Other intermetallic nanomaterials, such as Pt3Fe intermetallic nanowires with a diameter of 8.6 nm and Pt1Sn1 intermetallic nanowires with a diameter of 6.3 nm, were also successfully synthesized using this method, thus demonstrating its feasibility and generality.

Substitution reaction, as one of the most powerful and efficient chemical reactions, has been widely used in various syntheses, including those for the design and preparation of functional molecules or materials. In the past decade, a class of newly developed inorganic–organic hybrid materials, namely metal–organic materials (MOMs), has experienced a rapid development. MOMs are composed of metal-containing nodes connected by organic linkers through strong chemical bonds, and can be divided into metal–organic frameworks (MOFs) and metal–organic polygons/polyhedra (MOPs) with infinite and discrete structural features, respectively. Recent research has shown that the substitution reaction can be used as a new strategy in the synthesis and modification of MOFs and MOPs, particularly for pre-designed ones with desired structures and functions, which are usually difficult to access by a direct one-pot self-assembly synthetic approach. This review highlights the implementation of the substitution reaction in MOFs and MOPs. Examples of substitution reactions at metal ions, organic ligands, and free guest molecules of MOFs and MOPs are listed and analyzed. The changes or modifications in the structures and/or properties of these materials induced by the substitutions, as well as the nature of the associated reaction, are discussed, with the conclusion that the substitution reaction is really feasible and powerful in synthesizing and tailoring MOMs.