Xiaofei Zeng

A DIH-based equation for separation of CO2–CH4 in metal–organic frameworks and covalent–organic materials

We develop a new S(DIH) equation based on the difference of isosteric heats (DIH) to calculate the selectivity for CO2 over CH4 in metal–organic frameworks (MOFs) and covalent–organic materials. Using the S(DIH) equation to predict the selectivity requires only the adsorption isotherms of pure components and the DIH of the two components. By comprehensive comparison with the GCMC data in different types of porous materials, including MOFs, ZIFs, COFs and PAFs, it is found that the new S(DIH) equation can predict with high accuracy the selectivity of different types of porous materials for CO2 over CH4 at the low pressure of p = 0–1 bar. Therefore, the new S(DIH) can serve as an efficient tool for the selectivity predictions of porous materials for CO2 over CH4 at p = 0–1 bar, especially for the cases in which experiments can measure the adsorption isotherms and adsorption heats of pure components (such as CO2, CH4, N2 and H2) because the new S(DIH) requires only the adsorption isotherms and adsorption heats of pure components as inputs. In short, the new S(DIH) equation can be considered as a valuable screening tool for obtaining an estimation about the selectivity of a porous material for a certain component of the gas mixture.

Tetrahedral node diamondyne frameworks for CO2 adsorption and separation

The recently reported diamondyne is a fascinating new carbon allotrope with multifunctional applications (J. Mater. Chem. A, 2013, 1, 3851; ibid 2013, 1, 9433). Here we theoretically predict two new tetrahedral node diamondyne (TND) frameworks by replacing the carbon nodes of diamondyne and diamond with the acetylenic linkage (C–CC–C)-formed tetrahedron node. The two resulting theoretical materials (marked as TND-1 and TND-2) exhibit extremely high specific surface areas (SSA) of 6250 and 2992 m2 g−1, respectively. Interestingly, the SSA of TND-1 is calculated to be the highest among all porous carbon materials. By further studying the CO2 capture performance of TND-1 and TND-2, it is found that the CO2 uptake of TND-1 reaches 2461 mg g−1 at 298 K and 50 bar, which outperforms all MOFs, COFs and ZIFs, while the selectivity of TND-2 for CO2/H2 reaches 104 at 35 bar, which is superior to most of the porous materials. In short, the hypothetical TND frameworks are promising candidates for CO2 capture in practical industry.

Enhanced near-infrared shielding ability of (Li,K)-codoped WO3 for smart windows: DFT prediction validated by experiment.

By means of hybrid density functional theory (DFT) computations, we found that (Li,K)-codoped WO3 shows a significantly enhanced near-infrared (NIR) absorption ability for smart windows, and investigated the influence of doping through the analysis of the electronic structures of pure and doped hexagonal WO3. Furthermore, this codoped material, with a hexagonal tungsten bronze nanostructure, was successfully prepared via a simple one-step hydrothermal reaction for the first time. Transmission electron microscopy images showed that the as-prepared products possessed a nanorod-like morphology with diameters of about 5-10 nm. It was demonstrated that (Li,K)-codoped WO3 presents a better NIR absorption ability than pure, Li-monodoped or K-monodoped WO3, which is in good agreement with our theoretical predictions. The experiment and simulation results reveal that this enhanced optical property in NIR can be explained by the existence of high free electrons existing in (Li,K)-codoped WO3.

Unveiling the high-activity origin of single-atom iron catalysts for oxygen reduction reaction

Significance We propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG) supported on nitrogen-doped graphitic carbons, and experimentally demonstrated that the SA-Fe/NG catalyst possesses extremely outstanding catalytic activities for oxygen reduction reaction (ORR) in both acidic and alkaline media. Impressively, both the SA-Fe/NG-based acidic proton exchange membrane fuel cell and Zn-air battery show excellent performance. Combining experimental results and density-functional calculations, we reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N4 active species. The universal surfactant-assisted method can be easily extended to synthesis of other single-atom catalysts, and unveiling the origin of high-ORR activity of SA-Fe/NG will open an approach for developing other heterogeneous catalysts. It is still a grand challenge to develop a highly efficient nonprecious-metal electrocatalyst to replace the Pt-based catalysts for oxygen reduction reaction (ORR). Here, we propose a surfactant-assisted method to synthesize single-atom iron catalysts (SA-Fe/NG). The half-wave potential of SA-Fe/NG is only 30 mV less than 20% Pt/C in acidic medium, while it is 30 mV superior to 20% Pt/C in alkaline medium. Moreover, SA-Fe/NG shows extremely high stability with only 12 mV and 15 mV negative shifts after 5,000 cycles in acidic and alkaline media, respectively. Impressively, the SA-Fe/NG-based acidic proton exchange membrane fuel cell (PEMFC) exhibits a high power density of 823 mW cm−2. Combining experimental results and density-functional theory (DFT) calculations, we further reveal that the origin of high-ORR activity of SA-Fe/NG is from the Fe-pyrrolic-N species, because such molecular incorporation is the key, leading to the active site increase in an order of magnitude which successfully clarifies the bottleneck puzzle of why a small amount of iron in the SA-Fe catalysts can exhibit extremely superior ORR activity.

Synthesis of Transparent Aqueous ZrO2 Nanodispersion with a Controllable Crystalline Phase without Modification for a High-Refractive-Index Nanocomposite Film

The controllable synthesis of metal oxide nanoparticles is of fundamental and technological interest. In this article, highly transparent aqueous nanodispersion of ZrO2 with controllable crystalline phase, high concentration, and long-term stability was facilely prepared without any modification via the reaction of inexpensive inorganic zirconium salt and sodium hydroxide in water under an acid surrounding, combined with hydrothermal treatment. The as-prepared transparent nanodispersion had an average particle size of 7 nm, a high stability of 18 months, and a high solid content of 35 wt %. ZrO2 nanocrystals could be readily dispersed in many solvents with high polarity including ethanol, dimethyl sulfoxide, acetic acid, ethylene glycol, and N, N-dimethylformamide, forming stable transparent nanodispersions. Furthermore, highly transparent polyvinyl alcohol/ZrO2 nanocomposite films with high refractive index were successfully prepared with a simple solution mixing route. The refractive index could be tuned from 1.528 to 1.754 (@ 589 nm) by changing the mass fraction (0-80 wt %) of ZrO2 in transparent nanocomposite films.

Controllable synthesis and evolution mechanism of tungsten bronze nanocrystals with excellent optical performance for energy-saving glass

The controllable synthesis of nanocrystals with a desired structure and morphology is still a great challenge in the chemistry and materials fields. In this work, we report a simple solvothermal method for the controllable synthesis of sodium and cesium doped tungsten bronze nanocrystals (NaxCsyWO3 (NaCWO)) with different morphologies and crystalline phases, through adjusting the amounts of H+ and H2O in the reactive system. Furthermore, ethocel/NaCWO films with high transparency are also fabricated via a solution mixing method. The growth mechanisms of the NaCWO nanocrystals are investigated systematically, and structure–property relationships are also explored. Results indicate that the as-prepared two kinds of crystalline phase NaCWO nanocrystals with four morphologies can be monodispersed in toluene to form transparent nanodispersions. Among these systems, the one with rod-shaped hexagonal nanocrystals exhibits the most excellent near-infrared absorption properties, with 3.5% near-infrared transmittance at 1000 nm, and it simultaneously holds high visible light transmittance of 84% at 440 nm. Owing to the good dispersion of the nanocrystals, the ethocel/NaCWO film with an NaCWO content of 10 per hundred of ethocel resin by weight maintains the same optical performance as the nanodispersion, which is significantly important for the development of NIR absorption materials applied to energy-saving glass, solar collectors, optical filters, etc.

Screening π-conjugated bridges of organic dyes for dye-sensitized solar cells with panchromatic visible light harvesting

Developing highly efficient organic dyes with panchromatic visible light harvesting for dye-sensitized solar cells (DSSCs) is still one of the most important scientific challenges. Here, we design a series of phenothiazine derivative organic dyes with donor-π-acceptor (D-π-A) structure using density functional theory (DFT) and time-dependent DFT (TDDFT) based on experimentally synthesized typical SH-6 organic dyes. Results indicate that the newly designed BUCT13 - BUCT30 dyes show smaller HOMO-LUMO energy gaps, higher molar extinction coefficients and obvious redshifts compared to the SH-6 dye, and the maximum absorption peaks of eight dyes are greater than 650 nm among the newly designed dyes. In particular, BUCT27 exhibits a 234 nm redshift and the maximum molar extinction coefficient with an increment of about 80% compared to the SH-6 dye. BUCT19 exhibits not only a 269 nm redshift and higher molar extinction coefficient with an increment of about 50% compared to the SH-6 dye, but the extremely broad absorption spectrum covering the entire visible range up to the near-IR region of 1200 nm. It is expected that this work can provide a new strategy and guidance for the investigation of these dye-sensitized devices.

Transparent dispersion of nanoparticles and applications to fabricate advanced organic-inorganic composites

How to disperse the inorganic nanoparticles mono-uniformly in the organic matrices is the key challenge of innovation of new generation of organic-inorganic nanocomposites. In this paper, a simple strategic method by incorporating the transparent dispersion of nanoparticles into organic matrix was proposed to prepare transparent organic-inorganic nanocomposites. The transparent dispersions of nanoparticles in liquid solvents were synthesized by our proposed novel high-gravity reaction coupled with extraction-phase transfer (HGRT) technology. By such strategy, the various transparent organic-inorganic nanocomposites with unique functions were fabricated, where the inorganic nanoparticles were all dispersed at the nano-scale. The preparation process principle, scale-up operations and the properties of functional transparent nanoparticle dispersions as well as their applications in the innovation of nanocomposite films for glass energy-saving, nano-lubrications for high railways, advanced transparent flexible optical nanomaterials with the high content of nanoparticles (60 wt%) were reviewed.

Enhanced photochemical performance of hexagonal WO 3 by metal-assisted S–O coupling for solar-driven water splitting

Hybrid density functional calculations was used to comprehensively study the electronic structure of S-, Snand Pb-monodoped and (Sn, S)- and (Pb, S)-codoped hexagonal WO3 (h-WO3) in order to improve their visible light photocatalytic activity. Results indicate that the (Sn, S)- and (Pb, S)-codoped h-WO3 can realize a significant band gap reduction and prevent the formation of empty states in the valence band of h-WO3, while Sn/Pb-monodoped h-WO3 cannot, because in (Sn, S)- and (Pb, S)-codoping, the S-doping introduces the fully occupied S 3p states in the forbidden band gap of h-WO3 and the acceptor metals (Sn and Pb) would assist the coupling of the introduced S with its nearest O. In particular, the (Sn, S)-codoped h-WO3 has the narrowest band gap of 1.85 eV and highest reducing ability among the doped case. Moreover, the calculated optical absorption spectra show that (Sn, S)-codoping can improve the visible light absorption. In short, these results indicate that the (Sn, S)-codoped h-WO3 is a promising material in solar-driven water splitting.摘要本文采用杂化密度泛函理论计算研究了S、Sn、Pb单掺杂和(Sn, S)、(Pb, S)共掺杂六方相三氧化钨(h-WO3)材料的电子结构及其在可见光范围内的光催化特性. 结果表明: (Sn, S)和(Pb, S)共掺杂体系可有效减小h-WO3的带隙, 且能够避免由于Sn、Pb单掺杂形成h-WO3价带中空穴的现象. 这主要是因为在(Sn, S)和(Pb, S)共掺杂体系中, 金属受体(Sn、Pb)杂质的掺入会导致杂质S 原子与邻近的O 原子耦合,形成S–O 键, 该S–O 键的反键轨道在h-WO3的禁带中引入两条完全占据的杂质能级. 值得注意的是, (Sn, S)共掺杂可使h-WO3的带隙减小至1.85 eV, 同时赋予其最高的还原能力. 此外, (Sn, S)共掺杂也提高了h-WO3对可见光的吸收能力. 这些结果表明, (Sn, S)共掺杂h-WO3是一种在太阳光分解水领域有潜在应用前景的材料.

Synthesis of transparent dispersions of aluminium hydroxide nanoparticles.

Transparent dispersions of inorganic nanoparticles are attractive materials in many fields. However, a facile method for preparing such dispersions of aluminium hydroxide nanoparticles is yet to be realized. Here, we report a direct reactive method to prepare transparent dispersions of pseudo-boehmite nanoparticles (1 wt%) without any surface modification, and with an average particle size of 80 nm in length and 10 nm in width, as well as excellent optical transparency over 94% in the visible range. Furthermore, transparent dispersions of boehmite nanoparticles (1.5 wt%) were also achieved after an additional hydrothermal treatment. However, the optical transparency of dispersions decreased with the rise of hydrothermal temperature and the shape of particles changed from rhombs to hexagons. In particular, monodisperse hexagonal boehmite nanoplates with an average lateral size of 58 nm and a thickness of 12.5 nm were obtained at a hydrothermal temperature of 220 °C. The selectivity of crystal growth direction was speculated as the possible formation mechanism of these as-prepared aluminium hydroxide nanoparticles. Besides, two values of 19.6 wt% and 14.64 wt% were separately measured for the weight loss of pseudo-boehmite and boehmite nanoparticles after a continuous heating, indicating their potential flame-resistant applications in the fabrication of plastic electronics and optical devices with high transparency.