Pinggui Tang

Electrocatalytic Cobalt Nanoparticles Interacting with Nitrogen-Doped Carbon Nanotube in Situ Generated from a Metal–Organic Framework for the Oxygen Reduction Reaction

A metal organic framework (MOF), synthesized from cobalt salt, melamine (mela), and 1,4-dicarboxybezene (BDC), was used as precursor to prepare Co/CoNx/N-CNT/C electrocatalyst via heat treatment at different temperature (700-900 °C) under nitrogen atmosphere. Crystallites size and microstrain in the 800 °C heat-treated sample (MOFs-800) were the lowest, whereas the stacking fault value was the highest among the rest of the homemade samples, as attested to by the Williamson-Hall analysis, hence assessing that the structural or/and surface modification of Co nanoparticles (NPs), found in MOFs-800, was different from that in other samples. CNTs in MOFs-800, interacting with Co NPs, were formed on the surface of the support, keeping the hexagonal shape of the initial MOF. Among the three homemade samples, the MOF-800 sample, with the best electrocatalytic performance toward oxygen reduction reaction (ORR) in 0.1 M KOH solution, showed the highest density of CNTs skin on the support, the lowest ID/IG ratio, and the largest N atomic content in form of pyridinic-N, CoNx, pyrrolic-N, graphitic-N, and oxidized-N species. Based on the binding energy shift toward lower energies, a strong interaction between the active site and the support was identified for MOFs-800 sample. The number of electron transfer was 3.8 on MOFs-800, close to the value of 4.0 determined on the Pt/C benchmark, thus implying a fast and efficient multielectron reduction of molecular oxygen on CoNx active sites. In addition, the chronoamperometric response within 24 000 s showed a more stable current density at 0.69 V/RHE on MOFs-800 as compared with that of Pt/C.

Co-intercalation of Acid Red 337 and a UV absorbent into layered double hydroxides: enhancement of photostability.

Organic-inorganic hybrid pigments with enhanced thermo- and photostability have been prepared by co-intercalating C.I. Acid Red 337 (AR337) and a UV absorbent (BP-4) into the interlayer of ZnAl layered double hydroxides through a coprecipitation method. The obtained compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric-differential thermogravimetric-differential thermal analysis, UV-visible spectroscopy, and the International Commission on Illumination (CIE) 1976 L*a*b* color scales. The results show the successful co-intercalation of AR337 and BP-4 into the interlayer region of layered double hydroxides (LDHs) and reveal the presence of host-guest interactions between LDH host layers and guest anions of AR337 and BP-4 and guest-guest interactions between AR337 and BP-4. The intercalation can improve the thermostability of AR337 due to the protection of LDH layers. Moreover, the co-intercalation of AR337 and BP-4 not only markedly enhances the photostability of AR337 but also significantly influences the color of the hybrid pigment.

Controllable Synthesis and Gas-Sensing Properties of Zinc Oxide Nanocrystals With Exposed Different Percentage of Facets

A facile and controllable one-step hydrothermal method to synthesize nanodisks and nanorods of zinc oxide with exposed different crystal facets of (0001), (11̅00), (011̅0), and (101̅0) has been realized. It was found that the average percentage of exposed (0001) crystal facets follows the order of nanodisks > nanorods-1 > nanorods-2 > nanorods-3, while the average percentage of exposed (11̅00), (011̅0), and (101̅0) crystal facets decreases monotonically. The sensing tests to NO2 indicate that the nanodisks exhibit higher sensitivity. It has also been validated that the (0001) crystal facet has the highest surface energy and the lowest binding energy, which is considered to be the key factor of high gas-sensing by the calculations of density functional theory. This finding will open a new window to explore the relationship between gas-sensing and exposed facets and will be useful for designing gas-sensing materials with specifically exposed surfaces.

Synthesis and applications of layered double hydroxides based pigments.

Layered double hydroxides (LDHs) have attracted a great deal of attention owing to their structural anisotropy, anion-exchange capability and compositional flexibility and have been widely investigated as catalysts, adsorbents, anion-exchangers, polymer additives, optical materials, and so on. The intercalation of chromophores into the interlayer galleries of LDHs has drawn considerable interest since it can result in a kind of functional pigments showing different photophysical and photochemical properties from the pristine chromophores due to the host-guest and guest-guest interactions. This paper reviews recent patents progress made for the synthesis and applications of LDHs based pigments. The potentional applications and the future development are also discussed.

Layered Double Hydroxides as Flame Retardant and Thermal Stabilizer for Polymers

Layered double hydroxides (LDH) has wide applications as non-toxic and halogen-free flame retardant for various resins and highly efficient thermal stabilizer for halogen-containing polymers. This review will discuss some public patents and relevant papers on the flame retardancy and the thermal stability of LDH/polymer composites when the LDHs with different chemical compositions are used as the additive in the polymer matrix. We have summarized these related LDHs in two tables: one for flame retardant and the other for thermal stabilizer.

Antioxidant intercalated Zn-containing layered double hydroxides: preparation, performance and migration properties

A straightforward preparation of the antioxidant anion 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (DBHP), intercalated into layered double hydroxides (DBHP-LDH) via a co-precipitation method, and adjusting the (Mg, Zn, Al) metal ratio was reported. The influence of the Zn-containing LDH composition was studied by measuring the thermal stability and the DBHP anti-migration ability when dispersed into polypropylene (PP). The overall crystallinity of α-PP is found to remain similar with the dispersion of DBHP-LDH particles, but shaper diffraction peaks indicate the presence of larger crystallized domains, most probably arising from an anisotropic connection of smaller coherent PP domains with the help of PP chains diffusing inside the layered inorganic structure. The latter is acting as a coalescent agent yielding an intercalated PP nanocomposite structure with extended interfaces inducing a shift in the glass transition temperature to a higher temperature. The radical-scavenging activity of DBHP when interleaved between LDH layers is found to be conserved while an optimized cation composition for MgZnAl–DBHP is found for the thermo-oxidative stability in association with a lower DBHP migration among the PP nanocomposite series, making the resulting PP nanocomposite a highly promising candidate for possible applications.

Novel Carbon Paper@Magnesium Silicate Composite Porous Films: Design, Fabrication, and Adsorption Behavior for Heavy Metal Ions in Aqueous solution

It is of great and increasing interest to explore porous adsorption films to reduce heavy metal ions in aqueous solution. Here, we for the first time fabricated carbon paper@magnesium silicate (CP@MS) composite films for the high-efficiency removal of Zn2+ and Cu2+ by a solid-phase transformation from hydromagnesite-coated CP (CP@MCH) precursor film in a hydrothermal route and detailedly examined adsorption process for Zn2+ and Cu2+ as well as the adsorption mechanism. The suitable initial pH range is beyond 4.0 for the adsorption of the CP@MS to remove Zn2+ under the investigated conditions, and the adsorption capacity is mainly up to the pore size of the porous film. The composite film exhibits excellent adsorption capacity for both of Zn2+ and Cu2+ with the corresponding maximum adsorption quantity of 198.0 mg g-1 for Zn2+ and 113.5 mg g-1 for Cu2+, which are advantageous over most of those reported in the literature. Furthermore, the adsorption behavior of the CP@MS film follows the pseudo-second-order kinetic model and the Langmuir adsorption equation for Zn2+ with the cation-exchange mechanism. Particularly, the CP@MS film shows promising practical applications for the removal of heavy metal ions in water by an adsorption-filtration system.

Fabrication and Adsorption Behavior of Magnesium Silicate Hydrate Nanoparticles towards Methylene Blue

Magnesium silicate as a high-performance adsorption material has attracted increasing attention for the removal of organic dye pollution. Here, we prepared a series of magnesium silicate hydrates (MSH) in a hydrothermal route, and carefully investigated the corresponding adsorption behavior towards methylene blue (MB) as well as the effect of surface charge on adsorption capacity. The results show that surface charge plays a key role in the adsorption performance of MSH for MB, a negative surface charge density follows the increase of Si/Mg feeding ratio from 1.00 to 1.75, and furthermore the higher negative charge favors the improvement of the adsorption capacity. Among four investigated samples (MSH = 1.00, 1.25, 1.50, and 1.75), MSH-1.75 has the highest negative surface charge and shows the largest adsorption capacity for MB. For example, the equilibrium adsorption quantity is 307 mg·g−1 for MSH-1.75, which is 35% higher than that of 227 mg·g−1 for MSH-1.00. Besides, for MSH-1.75, the as-prepared sample with negative charge exhibits ca. 36% higher adsorption quantity compared to the sample at the zero point of charge (pHZPC). Furthermore, magnesium silicate hydrate material with Si/Mg feeding ratio = 1.75 demonstrates the promising removal efficiency of beyond 98% for methylene blue in 10 min, and the maximum adsorption capacity of 374 mg·g−1 calculated from the Langmuir isotherm model.

Design and Synthesis of Cobalt-Based Electrocatalysts for Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) is the crucial step of various renewable energy conversion and storage technologies such as fuel cells and air-batteries. Cobalt-based electrocatalysts including oxides/chalcogenides and Co-Nx /C, one kind of non-precious metal electrocatalysts with competitive activity, enhanced durability, and acceptable cost, have been proposed as the potentially interesting alternatives to Pt-based electrocatalysts. In this account, we summarized the synthesis methods and the corresponding main impact factors including ligand effect, particle size effect, crystal structure, nanostructure, defects and active centers related to the ORR performance on both of oxides/chalcogenides and Co-Nx /C. Some special points have been discussed on design and synthesis of low-cost and high-performance cobalt-based electrocatalysts with enhanced electrocatalytic activity. Also, the current challenges and future trends are proposed for improving the performance of Co-involving electrocatalysts.