Understanding CO2 capture kinetics and energetics by ionic liquids with molecular dynamics simulation

Room temperature ionic liquids (ILs) are recognized to be potential media for CO₂ capture, but the interaction nature is less documented which hinders the future development of ILs with high CO₂ solvation capability. Here, through all atom molecular dynamics (MD) simulations, the solvation process of CO₂ with four representative ILs, [EMIM][BF₄], [BMIM][BF₄], [EMIM]CL and [BMIM]CL was systematically studied. Our data clearly reflect the fact that hydrophobic components from both cations and anions dominate CO₂ solvation because IL–CO₂ attraction is mainly driven by the van der Waals attractions. Consequently, cations with longer alkyl chain (for instance, [BMIM]⁺ than [EMIM]⁺) and anions with higher hydrophobicity (for instance, [BF₄]⁻ than CL⁻) effectively enhance CO₂ solvation. For all the ILs under study, addition of water into ILs abates CO₂ solvation through regulating the anion–CO₂ interactions. Moreover, it is worth mentioning that ILs with a hydrophobic anion ([BF₄]⁻ in this study) are more resistant to the existence of water to capture CO₂ than ILs with a hydrophilic anion (Cl⁻ in this study). Free energy decomposition analyses were conducted which support the above findings consistently. Generally, it is predicted that cations with long alkyl chain, anions with high hydrophobicity, and ILs with smaller surface tension are potentially effective CO₂ capturing media. Our present study helps the deep understanding of the CO₂ capturing mechanism by ILs and is expected to facilitate the future design and fabrication of a novel IL medium for gas capture and storage.

The interactions between ionic liquids (ILs) and CO₂ were studied by molecular dynamics simulations. Several key characters, including the volumes of cations and anions, the length of the alkyl chain have been assessed on CO₂ capture capability.     

Systematic investigation of CO2 : NH3 ice mixtures using mid-IR and VUV spectroscopy – part 1: thermal processing

The adjustment of experimental parameters in interstellar ice analogues can have profound effects on molecular synthesis within an ice system. We demonstrated this by systematically investigating the stoichiometric mixing ratios of CO₂ : NH₃ ices as a function of thermal processing using mid-IR and VUV spectroscopy. We observed that the type of CO₂ bonding environment was dependent on the different stoichiometric mixing ratios and that this pre-determined the NH₃ crystallite structure after phase change. The thermal reactivity of the ices was linked to the different chemical and physical properties of the stoichiometric ratios. Our results provide new details into the chemical and physical properties of the different stoichiometric CO₂ : NH₃ ices enhancing our understanding of the thermally induced molecular synthesis within this ice system.

The stoichiometric mixing ratio of CO₂ : NH₃ ices determines both the initial chemical and physical properties of the ices and their evolution through thermal processing including CO₂ bonding environment, NH₃ crystallite size and amount of residue.     

Promoting dry reforming of methane via bifunctional NiO/dolomite catalysts for production of hydrogen-rich syngas

Extensive effort has been focused on the advancement of an efficient catalyst for CO₂ reforming of CH₄ to achieve optimum catalytic activity together with cost-effectiveness and high resistance to catalyst deactivation. In this study, for the first time, a new catalytic support/catalyst system of bifunctional NiO/dolomite has been synthesized by a wet impregnation method using low-cost materials, and it shows unique performance in terms of amphoteric sites and self-reduction properties. The catalysts were loaded into a continuous micro-reactor equipped with an online GC-TCD system. The reaction was carried out with a gas mixture consisting of CH₄ and CO₂ in the ratio of 1 : 1 flowing 30 ml min⁻¹ at 800 °C for 10 h. The physicochemical properties of the synthesized catalysts were determined by various methods including X-ray diffraction (XRD), N₂ adsorption–desorption, H₂ temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of CO₂ (TPD-CO₂), and temperature-programmed desorption of NH₃ (TPD-NH₃). The highest catalytic performance of the DRM reaction was shown by the 10% NiO/dolomite catalyst (CH₄ & CO₂ conversion, χCH₄; χCO₂ ∼ 98% and H₂ selectivity, S_H2 = 75%; H₂/CO ∼ 1 : 1 respectively). Bifunctional properties of amphoteric sites on the catalyst and self-reduction behaviour of the NiO/dolomite catalyst improved dry reforming of the CH₄ process by enhancing CH₄ and CO₂ conversion without involving a catalyst reduction step, and the catalyst was constantly active for more than 10 h.

Catalytic conversion of methane dry reforming via NiO/Dolomite catalysts.     

Cooperative CO2 absorption by amino acid-based ionic liquids with balanced dual sites

In this study, a variety of functionalized ILs with dual sites including amino acid group (AA) and basic anion (R) were synthesized to investigate the suppression and cooperation between the sites in CO₂ absorption. The basic anions selected in this study with different basicity include sulfonate (Su), carboxylate (Ac), imidazolium (Im), and indolium (Ind). These ILs ([P₆₆₆₁₄]₂[AA–R]) were applied to CO₂ absorption. The results present that CO₂ capacity increases first and then decreases later with the continuous increase in the activity of the anion site. Combined with CO₂ absorption experiments, IR and NMR spectroscopic analyses and DFT calculation demonstrate that the ability of one site to capture CO₂ would be suppressed when the activity of another site is much stronger. Thus, the cooperation of dual site-functionalized ILs and high CO₂ capacity might be achieved through balancing the two sites to be equivalent. Based on this point, [P₆₆₆₁₄]₂[5Am–iPA] was further synthesized by taking the advantage of the conjugated benzene ring. As expected, [P₆₆₆₁₄]₂[5Am–iPA] showed capacity as high as 2.38 mol CO₂ per mol IL at 30 °C and 1 bar without capacity decrease even after 10 times recycling performance of CO₂ absorption and desorption.

Cooperative CO₂ absorption by anion functionalized ILs with dual sites including amino acid group (AA) and basic anion (R) could be achieved through regulating the relative activation of two sites.     

Absorption and thermodynamic properties of CO2 by amido-containing anion-functionalized ionic liquids

In this contribution, two kinds of amido-containing anion-functionalized ionic liquids (ILs) were designed and synthesized, where the anions of these ILs were selected from deprotonated succinimide (H-Suc) and o-phthalimide (Ph-Suc). Then, these functionalized ILs were used to capture CO₂. Towards to this end, solubility of CO₂ in the ILs was determined at different temperatures and different CO₂ partial pressures. Based on these data, chemical equilibrium constants of CO₂ with the ILs were derived at different temperatures from the “deactivated IL” model. The other thermodynamic properties such as reaction Gibbs energy, reaction enthalpy, and reaction entropy in the absorption were also calculated from the corresponding equilibrium constant data at different temperatures. It was shown that these anion-functionalized ILs exhibited high CO₂ solubility (up to 0.95 mol CO₂ mol⁻¹ IL) and low energy desorption, and enthalpy change was the main driving force for CO₂ capture by using such ILs as absorbents. In addition, the interactions of CO₂ with the ILs were also investigated by ¹H NMR, ¹³C NMR, and FT-IR spectroscopy.

Amido-containing anion-functionalized ionic liquids exhibit high CO₂ absorption capacity and low desorption energy.     

Inorganic carbonate composites as potential high temperature CO2 sorbents with enhanced cycle stability

A calcium magnesium carbonate composite (CMC) material containing highly porous amorphous calcium carbonate (HPACC) and mesoporous magnesium carbonate (MMC) was synthesized. CMCs with varying HPACC : MMC mol ratios and high BET surface area (over 490 m² g⁻¹) were produced. The CMCs retained the morphology shared by HPACC and MMC. All these materials were built up of aggregated nanometer-sized particles. We tested the CO₂ uptake properties of the synthesized materials. The CMCs were calcined at 850 °C to obtain the corresponding calcium magnesium oxide composites (CMOs) that contained CaO : MgO at different mol ratios. CMO with CaO : MgO = 3 : 1 (CMO-3) showed comparable CO₂ uptake at 650 °C (0.586 g g⁻¹) to CaO sorbents obtained from pure HPACC (0.658 g g⁻¹) and the commercial CaCO₃ (0.562 g g⁻¹). Over 23 adsorption–desorption cycles CMOs also showed a lower CO₂ uptake capacity loss (35.7%) than CaO from HPACC (51.3%) and commercial CaCO₃ (79.7%). Al was introduced to CMO by the addition of Al(NO₃)₃ in the synthesis of CMC-3 to give ACMO after calcination. The presence of ∼19 mol% of Al(NO₃)₃ in ACMO-4 significantly enhanced its stability over 23 cycles (capacity loss of 5.2%) when compared with CMO-3 (calcined CMC-3) without adversely affecting the CO₂ uptake. After 100 cycles, ACMO-4 still had a CO₂ uptake of 0.219 g g⁻¹. Scanning electron microscope images clearly showed that the presence of Mg and Al in CMO hindered the sintering of CaCO₃ at high temperatures and therefore, enhanced the cycle stability of the CMO sorbents. We tested the CO₂ uptake properties of CMO and ACMO only under ideal laboratory testing environment, but our results indicated that these materials can be further optimized as good CO₂ sorbents for various applications.

A Ca/Mg/Al oxide composite was synthesised and showed a high CO₂ uptake of 0.537 g g⁻¹ at 650 °C with high uptake even after 100 cycles.     

Hydrothermal synthesis of nitrogen-doped ordered mesoporous carbon via lysine-assisted self-assembly for efficient CO2 capture

Nitrogen-doped ordered mesoporous carbons (NOMCs) were synthesized by single-step hydrothermal self-assembly using F127 as a soft template, hexamine as a formaldehyde source, l-lysine as a polymerization catalyst, and 3-aminophenol as both carbon and nitrogen sources. The microstructure of the NOMCs was characterized by XRD, N₂ adsorption/desorption, TEM, FTIR, and XPS. The results indicated that the obtained NOMCs exhibited a large specific surface area, uniform pore size distribution and highly ordered 2-D hexagonal mesostructure (P6mm). Besides, the nitrogen was uniformly doped into the carbon framework in the form of various nitrogen species. The adsorption isotherms of CO₂ and N₂ were also determined and could be well fitted by a DSL model. The capture capacity of CO₂ was affected by both the nitrogen content and mesostructure of the adsorbents. Overall, NOMC-L-0.5 displayed excellent CO₂ capture capacity (0 °C, 3.32 mmol g⁻¹; 25 °C, 2.50 mmol g⁻¹), and still demonstrated great regenerability with only 2% loss after several CO₂ adsorption/desorption cycles. Moreover, the CO₂/N₂ selectivity calculated by IAST was as high as 43.2 at 25 °C in a typical composition of flue gas (binary mixtures with 15% CO₂). The superior adsorption performance enables NOMCs to be a promising CO₂ adsorbent in practical applications.

Synthesis process of nitrogen-doped ordered mesoporous carbon through lysine-assisted single-step hydrothermal self-assembly for CO₂ capture.     

An amine-bifunctionalization strategy with Beta/KIT-6 composite as a support for CO2 adsorbent preparation

An amine-bifunctionalized composite strategy was used to fabricate grafted-impregnated micro-/mesoporous composites for carbon dioxide capture. The micro-/mesoporous Beta/KIT-6 (BK) composite containing a high-silica zeolite with a three-dimensional twelve-membered ring crossing channel system and cubic structural silica was used as a support, and 3-aminopropyltrimethoxysilane (APTS) and tetraethylenepentamine (TEPA) were used as the grafted and impregnated components, respectively. The amine efficiency, adsorption kinetics, thermal stability, regeneration performance, and the effects of impregnated amine loadings (30–60%) and temperatures (40–90 °C) on the CO₂ adsorption performance were investigated using a thermal gravimetric analyzer (TGA) in the mixed gases (15 vol% CO₂ and 85 vol% N₂). At 60 °C, the bifunctionalized Beta/KIT-6 (1 mL APTS g⁻¹ BK) displayed the highest CO₂ adsorption capacity of 5.12 mmol g⁻¹ at a TEPA loading of 50%. The kinetic model fitting results showed that the CO₂ adsorption process was a combination of physical and chemical adsorption, wherein the chemical adsorption is dominant. After five adsorption/desorption cycle regenerations, the saturated adsorption capacity of the composite material was 4.86 mmol g⁻¹, which was only 5.1% lower than the original adsorption capacity. The composites demonstrated excellent CO₂ adsorption performance, indicating the promising future of these adsorbents for CO₂ capture from actual flue gas after desulfurization.

CO₂ adsorption curves of A-BK-TEPA-50 at 40, 60, 75, 80 and 90 °C.     

Insights into the specific heat capacity enhancement of ternary carbonate nanofluids with SiO2 nanoparticles: the effect of change in the composition ratio

Ternary carbonate nanofluids have proven to be a promising high temperature thermal energy storage and transfer medium for solar thermal power. For the ternary carbonate K₂CO₃–Li₂CO₃–Na₂CO₃ (4 : 4 : 2, mass ratio) with SiO₂ nanoparticles prepared using a two-step solution method, the enhancement of the specific heat capacity was up to 113.7% at 540 °C compared to the ternary carbonate prepared by a direct mixing method. The present work aims to give insights into the marked enhancement of specific heat capacity. The effect of evaporation temperature on the nanostructures formed in ternary carbonate nanofluids is discussed for the enhancement of specific heat capacity. More importantly, based on an analysis of inductively coupled plasma atomic emission spectrometry, it is revealed that the composition ratio of the ternary carbonate, which can influence its specific heat capacity, was changed during the evaporation process in an electrothermal drier. Besides a difference in the solubility of the carbonates in water, it is demonstrated that the heating mode can affect the composition ratio of mixed molten salts.

The specific heat capacity of a ternary carbonate-SiO₂ nanofluid is enhanced by 113.7% at 540 °C.     

Unraveling the mechanism of CO2 capture and separation by porous liquids

Carbon dioxide (CO₂) emissions intensify the greenhouse effect so much that its capture and separation are needed. Porous liquids, possessing both the porous properties of solids and the fluidity of liquids, exhibit a wide range of applications in absorbing CO₂, but the mechanism of gas capture and separation demands in-depth understanding. To this end, we provide a molecular perspective of gas absorption in a porous liquid composed of porous organic cages dissolved in a size-excluded solvent, hexachloropropene, by density functional theory for the first time. In this work, different conformations were considered comprehensively for three representative porous organic cages and molecules. Results show that chloroform, compared to CO₂, tends to enter the cage due to stronger C–H⋯π interaction and the optimal capacity of each cage to absorb CO₂ through hydrogen bonding and π–π interaction is 4, 2 and 4 equivalents, respectively. We hope that these discoveries will promote the synthesis of similar porous liquids that are used to capture and separate gases.

A POC-type porous liquid has the ability to absorb CO₂ and the cage provides a cavity for absorption. The dominant interaction between CO₂ and the cage is π–π interaction. The optimal capacities of the three porous organic cages are 4, 2 and 4 eq.     

Functional utilization of biochar derived from Tenebrio molitor feces for CO2 capture and supercapacitor applications

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost. Fabrication of eco-friendly and cost-effective biochar from high potential biomass Tenebrio molitor feces can not only realize the functional application of waste, but also a potential way of future carbon capture and energy storage technology. In this study, a novel KOH activation waste-fed Tenebrio molitor feces biochar (TMFB) was developed and investigated in terms of CO₂ capture and electrochemical performance. When activated at 700 °C for 1 h, the specific surface area of the feces biochar (TMFB-700A) increased significantly from 232.1 to 2081.8 m² g⁻¹. In addition, well-developed pore distribution facilitates CO₂ capture and electrolyte diffusion. TMFB-700A can quickly adsorb a large amount of CO₂ (3.05 mol kg⁻¹) with excellent recycling performance. TMFB-700A also exhibited promising electrochemical performance (335.8 F g⁻¹ at 0.5 A g⁻¹) and was used as electrode material in a symmetrical supercapacitor. It provided a high energy density of 33.97 W h kg⁻¹ at a power density of 0.25 kW kg⁻¹ with 90.47% capacitance retention after 10 000 charge–discharge cycles. All the results demonstrated that TMFB could be a potential bifunctional material and provided valuable new insights for Tenebrio molitor feces high-value utilization.

Biochar has attracted great interest in both CO₂ capture and supercapacitor applications due to its unique physicochemical properties and low cost.     

Knitting polycyclic aromatic hydrocarbon-based microporous organic polymers for efficient CO2 capture

In order to achieve efficient CO₂ capture, four novel microporous organic polymers, based on distinct polycyclic aromatic hydrocarbons such as fluoranthene, binaphthalene, naphthalene and phenanthrene, were successfully prepared by the solvent knitting method. N₂ sorption isotherms indicate that these polymers are predominately microporous with ultrahigh BET surface area i.e., 1788 m² g⁻¹ for fluoranthene-based Polymer 1, 1702 m² g⁻¹ for binaphthalene-based Polymer 2 and objective CO₂ uptake capacity of 24.79 wt% and 20.19 wt% (273.15 K/1.00 bar) respectively. While compared with the former two polymers, though 1227 m² g⁻¹ and 978 m² g⁻¹ are moderate in surface area, however the naphthalene-based Polymer 3 and phenanthrene-based Polymer 4 still exhibit CO₂ adsorption of up to 17.44 wt% and 18.15 wt% respectively under the similar conditions. Moreover, the H₂ storage and CH₄ adsorption in these polymers can be 2.20 wt% (77.3 K/1.13 bar) and 2.79 wt% (273.15 K/1.00 bar). More significantly, the electron-rich PAHs are proved to be new building blocks that provide a wealth of chances to produce hypercrosslinked polymers with efficient gas adsorption capacity, which are greatly influenced by the porous nature of polymers. Given the merits including mild reaction conditions, low cost, high surface area, impressive gas absorption performance, high thermal stability, these polymers are considered to be promising candidates for CO₂ capture and energy storage under more practical conditions.

In order to achieve efficient CO₂ capture, four novel microporous organic polymers, based on distinct polycyclic aromatic hydrocarbons, were successfully prepared by the solvent knitting method.     

Fabrication of graphite via electrochemical conversion of CO2 in a CaCl2 based molten salt at a relatively low temperature

Fabrication of graphite by electrochemical splitting of CO₂ in a CaCl₂ molten salt is a promising approach for the efficient and economical utilization of CO₂. Systematically understanding the graphitization mechanism is of great significance to optimize the process. In this work, how pulse parameter and type of anode affect morphologies and crystallinity of graphite nanostructures were both investigated. The results indicate that the optimum current efficiency, energy consumption and highest degree of graphitization can be achieved by employing an appropriate pulse current parameter (T_on : T_off = 120 : 5), and with the utilization of a RuO₂–TiO₂ inert anode. The microstructure and morphologies show noticeable change by varying electrolytic conditions. In addition, the present study provides an insight into facile ways to improve the graphitization degree by electrochemical conversion of CO₂ at a relatively low temperature.

Fabrication of graphite by electrochemical splitting of CO₂ in a CaCl₂ molten salt is a promising approach for the efficient and economical utilization of CO₂.     

An organic–inorganic hybrid K2TiF6 : Mn4+ red-emitting phosphor with remarkable improvement of emission and luminescent thermal stability

A new type of monoethanolamine (MEA) and Mn⁴⁺ co-doped KTF : MEAH⁺, Mn⁴⁺ (K₂TiF₆ : 0.1MEAH⁺, 0.06Mn⁴⁺) red emitting phosphor was synthesized by an ion exchange method. The prepared Mn⁴⁺ co-doped organic–inorganic hybrid red phosphor exhibits sharp red emission at 632 nm and the emission intensity at room temperature is 1.43 times that of a non-hybrid control sample KTF : Mn⁴⁺ (K₂TiF₆ : 0.06Mn⁴⁺). It exhibits good luminescent thermal stability at high temperatures, and the maximum integrated PL intensity at 150 °C is 2.34 times that of the initial value at 30 °C. By coating a mixture of KTF : MEAH⁺, Mn⁴⁺, a yellow phosphor (YAG : Ce³⁺) and epoxy resin on a blue InGaN chip, a prototype WLED (white light-emitting diode) with CCT = 3740 K and R_a = 90.7 is assembled. The good performance of the WLED shows that KTF : MEAH⁺, Mn⁴⁺ can provide a new choice for the synthesis of new Mn⁴⁺ doped fluoride phosphors.

KTF : MEAH⁺, Mn⁴⁺ exhibits good luminescent thermal stability at high temperatures, and the maximum integrated PL intensity at 150 °C is 2.34 times the initial value at 30 °C.     

Activity of La0.75Sr0.25Cr0.5Mn0.5O3−δ, Ni3Sn2 and Gd-doped CeO2 towards the reverse water-gas shift reaction and carburisation for a high-temperature H2O/CO2 co-electrolysis

The syngas mixture of CO and H₂, e.g. from natural gas reforming, is currently an important feedstock supplier for the synthesis of numerous chemicals. In order to minimize fossil source dependency and reduce global warming, alternative processes to produce syngas, such as high-temperature co-electrolysis of H₂O and CO₂via the internal reverse water-gas shift (RWGS) reaction, may be meaningful. In this study, the influence of the H₂ : CO₂ ratio on the activity, selectivity and stability of the as-prepared La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) and Ni₃Sn₂ as well as commercial Ni and Gd-doped CeO₂ (GDC₂₀) powder materials for the reverse RWGS reaction was investigated in a tubular quartz glass reactor at 700 °C and 800 °C and ambient pressure. The highest conversion factor close to the maximum value of 50% for CO was yielded for the LSCrM, Ni and GDC₂₀ samples by applying a 0.5 : 0.5 H₂ : CO₂ feed ratio at 800 °C. Similar activity was calculated for the Ni₃Sn₂ alloy after normalization to the Ni mass content. Moreover, all the investigated catalysts exhibited higher selectivity for CO and H₂O products than Ni, with which CH₄ molar concentrations up to 0.9% and 2.4% were collected at 800 °C and 700 °C, respectively. The influence of feed pressure on the carburisation process was inspected in a tubular Ni–Cr reactor. Under a carbon-rich gas mixture at 3 bar and 700 °C, large amounts of graphitic carbon were deposited solely on the Ni sample after 100 h of exposure time. After the exposure of the powder materials to 0.5 : 0.5 and 0.9 : 0.1 H₂ : CO₂ atmospheres for 300 h at 700 °C and 10 bar, traces of amorphous carbon were surprisingly detected only on Ni₃Sn₂ powder via Raman microscopy. Thus, because GDC₂₀ ist not active for electrochemical H₂ production, LSCrM or a mixture of both LSCrM and GDC₂₀ materials appears to be the most promising candidate for Ni substitution in high-temperature H₂O/CO₂ co-electrolysis.

LSCrM_, Ni₃Sn₂ and GDC₂₀ powders show high activity and selectivity for the RWGS reaction.     

Catalytic conversion of CO2 into propylene carbonate in a continuous fixed bed reactor by immobilized ionic liquids

In this study, functionalized composite catalysts, namely, ILs (ILX/(ZnBr₂)₂), with hydroxyl, carboxyl and amino groups immobilized on a molecular sieve (MCM-22) support were synthesized with the help of a silane coupling agent, 3-chloropropyltriethoxysilane (CPTES). Cycloaddition of CO₂ and propylene oxide (PO) was carried out in a fixed bed reactor. The results show that MCM-22-CPTES-[AeMIM][Zn₂Br₅] demonstrates the best catalytic properties for this reaction. A high selectivity and yield of propylene carbonate (PC) could be reached at 130 °C under a CO₂ pressure of 2.0 MPa, with a LHSV of 0.75 h⁻¹ and a molar ratio of CO₂/PO of 3 : 1. The yield stabilized at 61.6% after 50 h in the fixed bed reactor.

In this study, functionalized composite catalysts, namely, ILs (ILX/(ZnBr₂)₂), with functional groups immobilized on a molecular sieve (MCM-22) support were synthesized with the help of a silane coupling agent, 3-chloropropyltriethoxysilane (CPTES).     

Biowaste-derived 3D honeycomb-like N and S dual-doped hierarchically porous carbons for high-efficient CO2 capture

Considering the characteristics of abundant narrow micropores of <1 nm, appropriate proportion of mesopores/macropores and suitable surface functionalization for a highly-efficient carbon-based CO₂ adsorbent, we proposed a facile and cost-effective strategy to prepare N and S dual-doped carbons with well-interconnected hierarchical pores. Benefiting from the unique structural features, the resultant optimal material showed a prominent CO₂ uptake of up to 7.76 and 5.19 mmol g⁻¹ at 273 and 298 K under 1 bar, and importantly, a superb CO₂ uptake of 1.51 mmol g⁻¹ at 298 K and 0.15 bar was achieved, which was greatly significant for CO₂ capture from the post-combustion flue gases in practical application. A systematic study demonstrated that the synergetic effect of ultramicroporosity and surface functionalization determined the CO₂ capture properties of porous carbons, and the synergistic influence mechanism of nitrogen/sulfur dual-doping on CO₂ capture performance was also investigated in detail. Importantly, such as-prepared carbon-based CO₂ adsorbents also showed an outstanding recyclability and CO₂/N₂ selectivity. In view of cost-effective fabrication, the excellent adsorption capacity, high selectivity and simple regeneration, our developed strategy was valid and convenient to design a novel and highly-efficient carbonaceous adsorbent for large-scale CO₂ capture and separation from post-combustion flue gases.

We proposed a facile and cost-effective strategy to prepare N/S dual-doped carbons with abundant micropores of <1 nm, appropriate proportion of meso/macropores and suitable surface functionalization for highly efficient CO₂ capture.     

Reduced graphene oxide decorated with octahedral NiS2/NiS nanocrystals: facile synthesis and tunable high frequency attenuation

Reduced graphene oxide (RGO) decorated with octahedral NiS₂/NiS nanocrystals were fabricated via a facile synthetic strategy. By appropriate adjustment of the weight ratio of GO and NiS₂/NiS nanocrystals, RGO–NiS₂/NiS nanocomposites with an excellent microwave absorption performance were achieved. As expected, RGO–NiS₂/NiS nanocomposites in a polyvinylidene fluoride (PVDF) matrix with different mass fractions (5, 10, 15, 20 wt%) possess effective absorption in the high frequency range with a thin thickness (1.5 mm) compared with those of octahedral NiS₂/NiS nanocrystals. It was revealed that RGO–NiS₂/NiS nanocomposites with a GO : NiS₂/NiS weight ratio of 1 : 4 exhibited the most prominent microwave absorption property. The optimal effective frequency bandwidth of this sample covers 4.32 GHz at a thin coating layer of 1.5 mm (15 wt%). The corresponding reflection loss value can reach −32.2 dB at 14.32 GHz. Moreover, the fundamental attenuation mechanisms are also discussed in detail.

Reduced graphene oxide (RGO) decorated with octahedral NiS₂/NiS nanocrystals were fabricated and they possessed an excellent microwave absorption performance in the high frequency range.     

Direct synthesis of shaped MgAPO-11 molecular sieves and the catalytic performance in n-dodecane hydroisomerization

In industrial application, molecular sieves are usually used in a certain shape. This requires the addition of binder and causes the reduction of both the molecular sieve content and catalytic performance. Herein, pseudo-boemite was mixed with deionized water at room temperature, followed by the drop-wise addition of phosphoric acid, magnesium acetate solution, hydrofluoric acid, di-n-propylamine and 1-ethyl-3-methyl imidazolium bromide with vigorous stirring. The molar ratio of Al₂O₃ : P₂O₅ : MgO : HF : DPA : [EMIm]Br : H₂O in the gel was 1 : 1 : 0.03 : 0.18 : 0.4 : 1 : 45. Then the gel was dried, extruded and directly crystallized to form a shaped MgAPO-11 molecular sieve. X-ray diffraction, scanning electron microscopy, N₂ adsorption, ammonia temperature programmed desorption, pyridine adsorption infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to investigate the physicochemical properties of the samples. X-ray diffraction, scanning electron microscopy and N₂ adsorption tests show that the shaped MgAPO-11 molecular sieve is fully crystallized and possesses hierarchical porosity. Mg is incorporated into the molecular sieve framework and the Pt catalyst supported by the obtained shaped MgAPO-11 exhibits excellent catalytic performance with n-dodecane conversion of 94% and isomer selectivity of 95% at 280 °C. Such a method for the direct synthesis of shaped molecular sieves shows potential for the green synthesis of molecular sieves in industry.

Shaped MgAPO-11 with hierarchical pores can be directly synthesized via a solid transformation route. Fewer synthesis steps and superior catalytic performance make the route possess great potential in practical applications.     

Synthesis of alkyl polyglycosides using SO3H-functionalized ionic liquids as catalysts

An effective process for synthesis of alkyl polyglycosides (APG) was developed using SO₃H-functionalized ionic liquids (SFILs) as catalysts. Four SFILs, [PSmim][HSO₄], [PSmim][pTSA], [PSPy][HSO₄] and [PSPy][pTSA], were designed and synthesized for APG synthesis. The results indicated that [PSmim][HSO₄] shows the best catalytic performance among these four SFILs, which has a great agreement with the order of their acidities. When the [PSmim][HSO₄] was used as catalyst, the reaction time could be decreased from 24 h to 8 h, and molar ration of n-octanol to glucose could be decreased from 5 : 1 to 3 : 1 under the optimization reaction conditions. In addition, the [PSmim][HSO₄] could be easily regenerated and recycled at least 5 times with slight decrease in catalytic activity. Moreover, the catalytic mechanism of [PSmim][HSO₄] was further investigated by molecular simulation. The high catalytic activity of [PSmim][HSO₄] is attributed to hydrogen bonds between [PSmim][HSO₄] and glucose and n-octanol, which could accelerate the protonation of glucose and removal of hydrogen ions from the hydroxyl in n-octanol.

Alkyl polyglycosides (APG), produced from glucose and fatty alcohols, are one kind of renewable green non-ionic surfactants. It is of great significance to develop a green catalyst reaction system for synthesis of alkyl polyglycosides.