Straightforward preparation of highly loaded MWCNT-polyamine hybrids and their application in catalysis

Multiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state ¹³C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), potentiometric titration, and temperature programmed desorption of carbon dioxide (CO₂-TPD). One of the prepared materials was tested as a heterogeneous base catalyst in C-C bond forming reactions such as the Knoevenagel condensation and Henry reaction. Furthermore, two examples concerning a sequential one-pot approach involving two consecutive reactions, namely Knoevenagel and Michael reactions, were reported.

Modification of multi-walled carbon nanotubes by 1,3-diaminopropane to increase CO2 adsorption capacity

Greenhouse gas emissions have increased dramatically over the past years and had a significant impact on global warming. This study investigates the modification of multi-walled carbon nanotubes (MWCNTs) with diamine precursor to improve the carbon dioxide adsorption capacity. To achieve this goal, pristine multi-walled CNTs were functionalized in a two-step process. In the first step, multi-walled carbon nanotubes were functionalized with a mixture of diluted sulfuric and nitric acid (5 M HNO₃/5 M H₂SO₄ with a volume ratio of 1:3) to sequestrate catalytic metal particles and oxidation of MWCNTs. In the second step, oxidized carbon nanotubes were functionalized with 1,3-diaminopropane (DAP) solution to improve the performance of multi-walled CNT in the carbon dioxide adsorption process. Specifications and characteristics of raw and modified carbon nanotubes were determined using FTIR, SEM, TGA, XRD, and N₂ adsorption-desorption isotherms at 77 K. The CO₂ adsorption capacity was measured at 303-323 K and pressures up to 17.3 bar using volumetric method. At 303 K and pressure of 17.3 bar, 92.71 mg g^-1 of CO₂ was adsorbed on MWCNT/DAP, while the CO₂ uptake of raw MWCNT in similar conditions was just 48.49 mg g^-1. The results revealed that amine groups attached to the carbonaceous surfaces during the functionalization process cause the formation of carbon dioxide-adsorption sites on multi-walled CNTs which increased the adsorption capacity of MWCNTs. Experimental data was modeled with Langmuir and Freundlich adsorption isotherms and concluded that the Freundlich model has more fitness with the experimental data.

TiO₂@PEI-Grafted-MWCNTs Hybrids Nanocomposites Catalysts for CO₂ Photoreduction

Anatase (TiO₂) and multiwalled carbon nanotubes bearing polyethylenimine (PEI) anchored on their surface were hybridized in different proportions according to a sol-gel method. The resulting nanocomposites (TiO₂@PEI-MWCNTs), characterized by BET, XRD, XPS, SEM, and UV techniques, were found efficient catalysts for CO₂ photoreduction into formic and acetic acids in water suspension and under visible light irradiation. PEI-grafted nanotubes co-catalysts are believed to act as CO₂ activators by forming a carbamate intermediate allowing to accomplish the first example in the literature of polyamines/nanotubes/TiO₂ mediated CO₂ photoreduction to carboxylic acids.

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO₂ molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO₂ adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

Simultaneous Online Measurement of H2O and CO2 in the Humid CO2 Adsorption/Desorption Process

A dew point meter (DP) and an infrared (IR) CO2 analyzer were assembled in a humid CO2 adsorption/desorption system in series for simultaneous online measurements of H2O and CO2, respectively. The humidifier, by using surface-flushing on a saturated brine solution was self-made for the generation of humid air flow. It was found that by this method it became relatively easy to obtain a low H2O content in air flow and that its fluctuation could be reduced compared to the bubbling method. Water calibration for the DP-IR detector is necessary to be conducted for minimizing the measurement error of H2O. It demonstrated that the relative error (RA) for simultaneous online measurements H2O and CO2 in the desorption process is lower than 0.1%. The high RA in the adsorption of H2O is attributed to H2O adsorption on the transfer pipe and amplification of the measurement error. The high accuracy of simultaneous online measurements of H2O and CO2 is promising for investigating their co-adsorption/desorption behaviors, especially for direct CO2 capture from ambient air.

Ionic liquid functionalization – an effective way to tune carbon dioxide adsorption properties of carbon nanotubes

In this research, the influence of non-covalent functionalization by ionic liquids on carbon dioxide (CO₂) adsorption–desorption properties of multi-walled carbon nanotubes (MWNTs) and partially exfoliated MWNTs (PEMWNTs) has been studied.