Importance of Micropore–Mesopore Interfaces in Carbon Dioxide Capture by Carbon‐Based Materials

Mesoporous carbonaceous materials (Starbons®) derived from low‐value/waste bio‐resources separate CO₂ from CO₂/N₂ mixtures. Compared to Norit activated charcoal (AC), Starbons® have much lower microporosities (8–32 % versus 73 %) yet adsorb up to 65 % more CO₂. The presence of interconnected micropores and mesopores is responsible for the enhanced CO₂ adsorption. The Starbons® also showed three–four times higher selectivity for CO₂ adsorption rather than N₂ adsorption compared to AC.     

Efficient CO2 capturer derived from as-synthesized MCM-41 modified with amine

A new strategy to synthesize a highly efficient CO(2) capturer by incorporating tetraethylenepentamine (TEPA) into as-synthesized MCM-41 (AM) is reported. The amine guest can be distributed in the micelle of the support, forming a web within the mesopore to trap CO(2) molecules and resulting in a high adsorption capacity for CO(2) up to 237 mg g(-1). Four samples of the as-synthesized MCM-41 with a different amount or type of surfactant are employed as supports to investigate the influence of micelles on the CO(2) adsorption, and the spokelike structure of the micelle in the channel of the support is proven to be essential to the distribution of guest amine. Among these supports, the AM sample is the most competitive due to the advantages of energy and time saving in preparation of the support along with the resulting higher CO(2) adsorption capacity. At the optimal loading of 50 wt % TEPA, the AM-50 sample exhibits a high adsorption capacity of 183 mg g(-1) in the sixth adsorption cycle at 5 % CO(2) concentration.     

Insights into the Oxidative Dehydrogenation of Amines with Nanoparticulate Iridium Oxide

The aerobic oxidation of amines offers a promising route towards many versatile chemical compounds. Within this contribution, we extend our previous investigations of iridium oxide‐catalyzed alcohol oxidation to amine substrates. In addition to demonstrating the versatility of this catalyst, particular attention is focused on the mechanisms of the reaction. Herein, we demonstrate that although amines are oxidized slower than the corresponding alcohols, the catalyst has a preference for amine substrates, and oxidizes various amines at turnover frequencies greater than other systems found in the open literature. Furthermore, the competition between double amine dehydrogenation, to yield the corresponding nitrile, and amine–imine coupling, to yield the corresponding coupled imine, has been found to arise from a competitive reaction pathway, and stems from an effect of substrate‐to‐metal ratio. Finally, the mechanism responsible for the formation of N‐benzylidene‐1‐phenylmethanamine was examined, and attributed to the coupling of free benzyl amine substrate and benzaldehyde, formed in situ through hydrolysis of the primary reaction product, benzyl imine.     

Carbon‐Dot‐Sensitized,Nitrogen‐Doped TiO2 in Mesoporous Silica for Water Decontamination through Nonhydrophobic Enrichment–Degradation Mode

Mesoporous silica synthesized from the cocondensation of tetraethoxysilane and silylated carbon dots containing an amide group has been adopted as the carrier for the in situ growth of TiO₂ through an impregnation–hydrothermal crystallization process. Benefitting from initial complexation between the titania precursor and carbon dot, highly dispersed anatase TiO₂ nanoparticles can be formed inside the mesoporous channel. The hybrid material possesses an ordered hexagonal mesostructure with p6mm symmetry, a high specific surface area (446.27 m² g^?1), large pore volume (0.57 cm³ g^?1), uniform pore size (5.11 nm), and a wide absorption band between λ=300 and 550 nm. TiO₂ nanocrystals are anchored to the carbon dot through Ti?O?N and Ti?O?C bonds, as revealed by X‐ray photoelectron spectroscopy. Moreover, the nitrogen doping of TiO₂ is also verified by the formation of the Ti?N bond. This composite shows excellent adsorption capabilities for 2,4‐dichlorophenol and acid orange 7, with an electron‐deficient aromatic ring, through electron donor–acceptor interactions between the carbon dot and organic compounds instead of the hydrophobic effect, as analyzed by the contact angle analysis. The composite can be photocatalytically recycled through visible‐light irradiation after adsorption. The narrowed band gap, as a result of nitrogen doping, and the photosensitization effect of carbon dots are revealed to be coresponsible for the visible‐light activity of TiO₂. The adsorption capacity does not suffer any clear losses after being recycled three times.     

Enhanced CO2 Adsorption over Polymeric Amines Supported on Heteroatom‐Incorporated SBA‐15 Silica: Impact of Heteroatom Type and Loading on Sorbent Structure and Adsorption Performance

Silica supported amine materials are promising compositions that can be used to effectively remove CO₂ from large stationary sources, such as flue gas generated from coal‐fired power plants (ca. 10 % CO₂) and potentially from ambient air (ca. 400 ppm CO₂). The CO₂ adsorption characteristics of prototypical poly(ethyleneimine)–silica composite adsorbents can be significantly enhanced by altering the acid/base properties of the silica support by heteroatom incorporation into the silica matrix. In this study, an array of poly(ethyleneimine)‐impregnated mesoporous silica SBA‐15 materials containing heteroatoms (Al, Ti, Zr, and Ce) in their silica matrices are prepared and examined in adsorption experiments under conditions simulating flue gas (10 % CO₂ in Ar) and ambient air (400 ppm CO₂ in Ar) to assess the effects of heteroatom incorporation on the CO₂ adsorption properties. The structure of the composite adsorbents, including local information concerning the state of the incorporated heteroatoms and the overall surface properties of the silicate supports, are investigated in detail to draw a relationship between the adsorbent structure and CO₂ adsorption/desorption performance. The CO₂ adsorption/desorption kinetics are assessed by thermogravimetric analysis and in situ FT‐IR measurements. These combined results, coupled with data on adsorbent regenerability, demonstrate a stabilizing effect of the heteroatoms on the poly(ethyleneimine), enhancing adsorbent capacity, adsorption kinetics, regenerability, and stability of the supported aminopolymers over continued cycling. It is suggested that the CO₂ adsorption performance of silica–aminopolymer composites may be further enhanced in the future by more precisely tuning the acid/base properties of the support.     

Molecular‐Level Insights into Intrinsic Peroxidase‐Like Activity of Nanocarbon Oxides

Nanocarbon oxides have been proved to possess great peroxidase‐like activity, catalyzing the oxidation of many peroxidase substrates, such as 3,3′,5,5′‐tetramethylbenzidine (TMB) and o‐phenylenediamine dihydrochloride (OPD), accompanied by a significant color change. This chromogenic reaction is widely used to detect glucose and occult blood. The chromogenic reaction was intensively investigated with density functional theory and molecular‐level insights into the nature of peroxidase‐like activity were gained. A radical mechanism was unraveled and the carboxyl groups of nanocarbon oxides were identified as the reactive sites. Aromatic domains connected with the carboxyl groups were critical to the peroxidase‐like activity.     

Halogen‐Free Synthesis of Carbamates from CO2 and Amines Using Titanium Alkoxides

A direct synthesis of carbamates from amines and carbon dioxide in the presence of Ti(OR)₄ (R=n Bu ( 1 ), Me ( 2 ), Et ( 3 ), n Pr ( 4 )) was investigated. Aniline was reacted with titanium n ‐butoxide ( 1 ) in the presence of carbon dioxide (5 MPa) to give the corresponding n ‐butyl N ‐phenylcarbamate (BPC) in nearly quantitative yield (99 %) within 20 min. Furthermore, 1 could be regenerated upon reaction with n ‐butanol during water removal. The recovered 1 could then be reused in a subsequent reaction.     

Ternary Sn‐Ti‐O Electrocatalyst Boosts the Stability and Energy Efficiency of CO2 Reduction

Simultaneously improving energy efficiency (EE) and material stability in electrochemical CO₂ conversion remains an unsolved challenge. Among a series of ternary Sn‐Ti‐O electrocatalysts, 3D ordered mesoporous (3DOM) Sn_0.3Ti_0.7O₂ achieves a trade‐off between active‐site exposure and structural stability, demonstrating up to 71.5 % half‐cell EE over 200 hours, and a 94.5 % Faradaic efficiency for CO at an overpotential as low as 430 mV. DFT and X‐ray absorption fine structure analyses reveal an electron density reconfiguration in the Sn‐Ti‐O system. A downshift of the orbital band center of Sn and a charge depletion of Ti collectively facilitate the dissociative adsorption of the desired intermediate COOH* for CO formation. It is also beneficial in maintaining a local alkaline environment to suppress H₂ and formate formation, and in stabilizing oxygen atoms to prolong durability. These findings provide a new strategy in materials design for efficient CO₂ conversion and beyond.     

Boron‐Functionalized Graphene Oxide‐Organic Frameworks for Highly Efficient CO2 Capture

The capture and storage of CO₂ have been suggested as an effective strategy to reduce the global emissions of greenhouse gases. Hence, in recent years, many studies have been carried out to develop highly efficient materials for capturing CO₂. Until today, different types of porous materials, such as zeolites, porous carbons, N/B‐doped porous carbons or metal‐organic frameworks (MOFs), have been studied for CO₂ capture. Herein, the CO₂ capture performance of new hybrid materials, graphene‐organic frameworks (GOFs) is described. The GOFs were synthesized under mild conditions through a solvothermal process using graphene oxide (GO) as a starting material and benzene 1,4‐diboronic acid as an organic linker. Interestingly, the obtained GOF shows a high surface area (506 m² g⁻¹) which is around 11 times higher than that of GO (46 m² g⁻¹), indicating that the organic modification on the GO surface is an effective way of preparing a porous structure using GO. Our synthetic approach is quite simple, facile, and fast, compared with many other approaches reported previously. The synthesized GOF exhibits a very large CO₂ capacity of 4.95 mmol g⁻¹ at 298 K (1 bar), which is higher those of other porous materials or carbon‐based materials, along with an excellent CO₂/N₂ selectivity of 48.8.     

Base‐Promoted Coupling of Carbon Dioxide,Amines, and N‐Tosylhydrazones: A Novel and Versatile Approach to Carbamates

A base‐promoted three‐component coupling of carbon dioxide, amines, and N‐tosylhydrazones has been developed. The reaction is suggested to proceed via a carbocation intermediate and constitutes an efficient and versatile approach for the synthesis of a wide range of organic carbamates. The advantages of this method include the use of readily available substrates, excellent functional group tolerance, wide substrate scope, and a facile work‐up procedure.     

Base‐Promoted Coupling of Carbon Dioxide,Amines, and Diaryliodonium Salts: A Phosgene‐ and Metal‐Free Route to O‐Aryl Carbamates

A phosgene‐ and metal‐free synthesis of O‐aryl carbamates is realized through a three‐component coupling of carbon dioxide, amines and diaryliodonium salts. The reaction only requires a base as the promoter, providing access to a diverse array of O‐aryl carbamates in moderate to high yields with excellent chemoselectivity.     

Molecular‐Level Understanding of the Carbonisation of Polysaccharides

Understanding of both the textural and functionality changes occurring during (mesoporous) polysaccharide carbonisation at the molecular level provides a deeper insight into the whole spectrum of material properties, from chemical activity to pore shape and surface energy, which is crucial for the successful application of carbonaceous materials in adsorption, catalysis and chromatography. Obtained information will help to identify the most appropriate applications of the carbonaceous material generated during torrefaction and different types of pyrolysis processes and therefore will be important for the development of cost‐ and energy‐efficient zero‐waste biorefineries. The presented approach is informative and semi‐quantitative with the potential to be extended to the formation of other biomass‐derived carbonaceous materials.     

Insights into the Temperature‐Dependent “Breathing” of a Flexible Fluorinated Metal–Organic Framework

The framework expansion and contraction upon carbon dioxide uptake was studied in a partially fluorinated metal–organic framework, FMOF‐2. The results show framework expansion and contraction (breathing) as a function of pressure and temperature. Even at temperatures as low as ?30 °C, two phase transitions seem to take place with a pressure step (corresponding to the second transition) that is greatly dependent on temperature. This behavior is described by the model proposed by Coudert and co‐workers showing that the material seems to undergo two phase transitions that are temperature‐dependent. The isosteric heats of adsorption at high pressures show a minimum that is concurrent with the region of CO₂ loadings where the second pressure step occurs. It was deduced that these lower enthalpy values are a consequence of the energy cost related to the expansion or reopening of the framework. Lastly, the large and reversible breathing behavior may be a product of the combination of the high elasticity of zinc (II) coordination and the apparent high flexibility of the V‐shaped organic building block.     

An ATR‐FTIR Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines,Part II

This paper reports on an ATR‐FTIR spectroscopic investigation of the CO₂ absorption characteristics of a series of heterocyclic diamines: hexahydropyrimidine (HHPY), 2‐methyl and 2,2‐dimethylhexahydropyrimidine (MHHPY and DMHHPY), hexahydropyridazine (HHPZ), piperazine (PZ) and 2,5‐ and 2,6‐dimethylpiperazine (2,6‐DMPZ and 2,5‐DMPZ). By using in situ ATR‐FTIR the structure–activity relationship of the reaction between heterocyclic diamines and CO₂ is probed. PZ forms a hydrolysis‐resistant carbamate derivative, while HHPY forms a more labile carbamate species with increased susceptibility to hydrolysis, particularly at higher CO₂ loadings (>0.5 mol CO₂/mol amine). HHPY exhibits similar reactivity toward CO₂ to PZ, but with improved aqueous solubility. The α‐methyl‐substituted MHHPY favours HCO₃^? formation, but MHHPY exhibits comparable CO₂ absorption capacity to conventional amines MEA and DEA. MHHPY show improved reactivity compared to the conventional α‐methyl‐ substituted primary amine 2‐amino‐2‐methyl‐1‐propanol. DMHHPY is representative of blended amine systems, and its reactivity highlights the advantages of such systems. HHPZ is relatively unreactive towards CO₂. The CO₂ absorption capacity C_A (mol CO₂/mol amine) and initial rates of absorption R_IA (mol CO₂/mol amine min^?1) for each reactive diamine are determined: PZ: C_A=0.92, R_IA=0.045; 2,6‐DMPZ: C_A=0.86, R_IA=0.025; 2,5‐DMPZ: C_A=0.88, R_IA=0.018; HHPY: C_A=0.85, R_IA=0.032; MHHPY: C_A=0.86, R_IA=0.018; DMHHPY: C_A=1.1, R_IA=0.032; and HHPZ: no reaction. Calculations at the B3LYP/6‐31+G** and MP2/6‐31+G** calculations show that the substitution patterns of the heterocyclic diamines affect carbamate stability, which influences hydrolysis rates.     

醇胺溶液吸收二氧化碳的实验研究

CO2的减排和有效利用受到人们的广泛关注.以二乙醇胺(DEA)、三乙醇胺(TEA)、N-甲基二乙醇胺(MDEA)溶液为对象,采用鼓泡吸收装置考察了醇胺的种类及浓度对CO2吸收速率和吸收容量的影响,研究了吸收前后溶液pH的变化,以及醇胺溶液再生后的情况.实验表明,醇胺溶液浓度增大有利于CO2的吸收,相同条件下DEA和TEA的吸收效果好于MDEA,醇胺溶液吸收CO2后pH由接近于11降至7左右,TEA的再生效果好于DEA.