Pyrolysis-free synthesis of a high-loading single-atom Cu catalyst for efficient electrocatalytic CO2-to-CH4 conversion

Electrocatalytic CO2-to-CH4 conversion provides a promising means of addressing current carbon resource recycling and intermittent energy storage. Cu-based single-atom catalysts have attracted extensive attention owing to their high intrinsic activity toward CH4 production; however, they suffer from uncontrollable metal loading and aggregation during the conventional pyrolysis process of carbon-based substrates. Herein, we developed a pyrolysis-free method to prepare a single-atom Cu catalyst anchored on a formamide polymer substrate with a high loading amount and well atomic dispersion through a mild polycondensation reaction. Owing to the isolation of copper active sites, efficient CO2-to-CH4 conversion is achieved over the single-atom Cu catalyst, along with the significant suppression of C-C coupling. As a result, the optimal single-atom catalyst with 5.87 wt% of Cu offers high CH4 faradaic efficiencies (FEs) of over 70% in a wide current density range from 100 to 600 mA cm-2 in the flow cell, together with a maximum CH4 partial current density of 415.8 mA cm-2. Moreover, the CH4 FE can reach 74.2% under optimized conditions in a membrane electrode assembly electrolyzer. This work provides new insights into the subtle design of highly efficient electrocatalyst for CO2 reduction.

Modified melamine-based porous organic polymers with imidazolium ionic liquids as efficient heterogeneous catalysts for CO2 cycloaddition

The chemical conversion of carbon dioxide (CO2) into highly value-added products not only alleviates the environmental issues caused by global warming but also makes an impact on economic benefits in the world. The synthesis of cyclic carbonates by the cycloaddition of CO2 with epoxides is one of the most attractive methods for CO2 conversion. However, the development of green and highly efficient heterogeneous catalysts is considered to be a great challenge in catalysis. In this work, alkenyl-modified melamine-based porous organic polymer (MPOP-4A) was firstly synthesized by a one-pot polycondensation method, and it was again modified with imidazolium-based ionic liquids to obtain final modified catalyst (MPOP-4A-IL). Various analytical techniques were used to confirm structure and chemical composition of the prepared materials. The MPOP-4A-IL catalyst synthesized by the post-modification strategy with imidazolium-based ionic liquids exhibited enhanced catalytic activity for CO2 cycloaddition reaction. The enhanced catalytic performance could be attributed to the presence of abundant active sites in their structure such as hydrogen bond donors (HBD), nitrogen (N) sites, and nucleophilic groups for an effective chemical reaction. The MPOP-4A-IL catalyst was found to be metal-free, easy to recycle and reuse, and has good versatility for a series of different epoxides. The interaction of MPOP-4A-IL catalyst with epoxide and CO2 was further verified by density functional theory (DFT) calculations, and the possible mechanism of the CO2 cycloaddition reaction was proposed.

Porous organic polymers (POPs) for environmental remediation

Modern global industrialization along with the ever-increasing growth of the population has resulted in continuous enhancement in the discharge and accumulation of various toxic and hazardous chemicals in the environment. These harmful pollutants, including toxic gases, inorganic heavy metal ions, anthropogenic waste, persistent organic pollutants, toxic dyes, pharmaceuticals, volatile organic compounds, etc., are destroying the ecological balance of the environment. Therefore, systematic monitoring and effective remediation of these toxic pollutants either by adsorptive removal or by catalytic degradation are of great significance. From this viewpoint, porous organic polymers (POPs), being two- or three-dimensional polymeric materials, constructed from small organic molecules connected with rigid covalent bonds have come forth as a promising platform toward various leading applications, especially for efficient environmental remediation. Their unique chemical and structural features including high stability, tunable pore functionalization, and large surface area have boosted the transformation of POPs into various macro-physical forms such as thick and thin-film membranes, which led to a new direction in advanced level pollutant removal, separation and catalytic degradation. In this review, our focus is to highlight the recent progress and achievements in the strategic design, synthesis, architectural-engineering and applications of POPs and their composite materials toward environmental remediation. Several strategies to improve the adsorption efficiency and catalytic degradation performance along with the in-depth interaction mechanism of POP-based materials have been systematically summarized. In addition, evolution of POPs from regular powder form application to rapid and more efficient size and chemo-selective, "real-time" applicable membrane-based application has been further highlighted. Finally, we put forward our perspective on the challenges and opportunities of these materials toward real-world implementation and future prospects in next generation remediation technology.

One-step synthesis of nitrogen-rich organic polymers for efficient catalysis of CO2 cycloaddition

Nitrogen-rich organic polymer poly(chloride triazole) (PCTs) was synthesized by a one-step method as metal-halogen-free heterogeneous catalyst for the solvent-free CO2 cycloaddition. PCTs had abundant nitrogen sites and hydrogen bond donors, exhibited great activity for the cycloaddition of CO2 and epichlorohydrin, and achieved 99.6% yield of chloropropene carbonate under the conditions of 110 ℃, 6 h, and 0.5 MPa CO2. The activation of epoxides and CO2 by hydrogen bond donor and nitrogen sites was further explained by density functional theory (DFT) calculations. In summary, this study showed that nitrogen-rich organic polymer is a versatile platform for CO2 cycloaddition, and this paper provides a reference for the design of CO2 cycloaddition catalysts.

Pyridine-based conjugated microporous polymers as adsorbents for CO2 uptake via weak supramolecular interaction

Two pyridine-based conjugated microporous polymers with high micro-porosity exhibited a high CO2 capture value via weak supramolecular interaction.

Design and construction of a hydrophilic coating on macroporous adsorbent resins for enrichment of glycopeptides

Although macroporous adsorbent resins (MARs) have been commercialized and widely applied in industrial and life fields, it is still of necessity to develop simple approaches to functionalize MARs. One of the most widely used methods to realize excellent fouling resistance performance is surface modification of hydrophilic polymers on substrates to fabricate an anti-biofouling coating. Herein, three kinds of hydrophilic poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) MAR were designed and facilely prepared by coating a layer of porous organic polymers (POPs) via either an epoxy-amine ring-opening polymerization or amine-aldehyde condensation reaction using isophthalaldehyde (IPA), 1,4,7,10-tetraazacyclododecane (cyclen), melamine and 1,3,5-triglycidyl isocyanurate (TGIC) as precursors. By taking advantage of their merits, such as large surface area, excellent hydrophilicity and unbiased affinity toward all types of glycopeptide, three functionalized hydrophilic MARs were successfully applied to capture glycopeptides from complex samples as hydrophilic interaction liquid chromatography (HILIC) sorbents. A total of 694 N-glycopeptides and 372 N-glycosylation sites were identified from 2 μL of human serum digest with poly(TC)@MAR, which were not only more than those of poly(MT)@MAR (286 N-glycosylation sites and 547 N-glycopeptides) and poly(IM)@MAR (669 N-glycopeptides and 355 N-glycosylation sites), but also more than those of other reported HILIC materials. This work provided a new and simple way to synthesize enrichment materials for liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) analysis of glycoproteomes.

Micro- and Ultramicroporous Polyaminals for Highly Efficient Adsorption/Separation of C1-C3 Hydrocarbons and CO2 in Natural Gas

This paper presents a series of micro- and ultramicroporous polyaminals with BET surface areas up to 1304 m² g^-1, which are prepared from two triazine-based tetraamines and three dialdehydes or monoaldehyde through the A₄ + B₂ or A₄ + B₁ aminalization reaction. It is interesting to find that the para-substituted monomers are favorable to force the linking struts apart in the network to generate micropores (1.22 nm), whereas the meta-substituted monomers make the pores in the network squeezed by the twisted linking struts, resulting in the formation of ultramicropores (0.52 nm). Besides, the adsorption behaviors of the major components of natural gas, such as propane (C₃H₈), ethane (C₂H₆), methane (CH₄), and carbon dioxide (CO₂), are significantly different, strongly depending on the polarizabilities, critical temperatures, molecular sizes of gases, porosity parameters of polymers, and the interaction between gases and the polymer skeleton. At 298 K/1 bar, the polymers show high uptake for C₃H₈ (114.5 cm³ g^-1) and C₂H₆ (84.2 cm³ g^-1). Moreover, the adsorption selectivities of C₃H₈/CH₄, C₂H₆/CH₄, C₃H₈/C₂H₆, C₃H₈/CO₂, C₂H₆/CO₂, and CO₂/CH₄ also reach 296.3, 23.1, 9.0, 22.1, 4.1, and 5.0, respectively, exhibiting promising applications in adsorption/separation of C₁-C₃ hydrocarbons and stripping CO₂ gas from natural gas under the ambient condition.

A Pd NP-confined novel covalent organic polymer for catalytic applications

A novel unsymmetrical covalent organic polymer was synthesized via nucleophilic substitution reaction of 2,4,6-trichloro-1,3,5-triazine with p-amino phenol.

Carbazole-functionalized hyper-cross-linked polymers for CO2 uptake based on Friedel-Crafts polymerization on 9-phenylcarbazole

To systematically explore the effects of the synthesis conditions on the porosity of hyper-cross-linked polymers (HCPs), a series of 9-phenylcarbazole (9-PCz) HCPs (P1-P11) has been made by changing the molar ratio of cross-linker to monomer, the reaction temperature T 1, the used amount of catalyst and the concentration of reactants. Fourier transform infrared spectroscopy was utilized to characterize the structure of the obtained polymers. The TG analysis of the HCPs showed good thermal stability. More importantly, a comparative study on the porosity revealed that: the molar ratio of cross-linker to monomer was the main influence factor of the BET specific surface area. Increasing the reaction temperature T 1 or changing the used amount of catalyst could improve the total pore volume greatly but sacrificed a part of the BET specific surface area. Fortunately changing the concentration of reactants could remedy this situation. Slightly changing the concentration of reactants could simultaneously obtain a high surface area and a high total pore volume. The BET specific surface areas of P3 was up to 769 m2 g-1 with narrow pore size distribution and the CO2 adsorption capacity of P11 was up to 52.4 cm3 g-1 (273 K/1.00 bar).