Enrico Andreoli

Cross-Linking Amine-Rich Compounds into High Performing Selective CO2 Absorbents

Amine-based absorbents play a central role in CO2 sequestration and utilization. Amines react selectively with CO2, but a drawback is the unproductive weight of solvent or support in the absorbent. Efforts have focused on metal organic frameworks (MOFs) reaching extremely high CO2 capacity, but limited selectivity to N2 and CH4, and decreased uptake at higher temperatures. A desirable system would have selectivity (cf. amine) and high capacity (cf. MOF), but also increased adsorption at higher temperatures. Here, we demonstrate a proof-of-concept where polyethyleneimine (PEI) is converted to a high capacity and highly selective CO2 absorbent using buckminsterfullerene (C60) as a cross-linker. PEI-C60 (CO2 absorption of 0.14 g/g at 0.1 bar/90°C) is compared to one of the best MOFs, Mg-MOF-74 (0.06 g/g at 0.1 bar/90°C), and does not absorb any measurable amount of CH4 at 50 bar. Thus, PEI-C60 can perform better than MOFs in the sweetening of natural gas.

Preparation and evaluation of polyethyleneimine-single walled carbon nanotube conjugates as vectors for pancreatic cancer treatment

High quality single-walled carbon nanotubes (SWNTs) were obtained following a new purification procedure, based on using Cl2 gas at high temperature. Cl2-treated SWNTs were fluorinated and modified with branched polyethyleneimine (PEI) to afford covalently functionalised PEI-SWNTs, which were then tested for cytotoxicity both in vitro (HPNE and BxPC3 pancreatic cell lines) and in vivo (BxPC3 xenografts from nude mice) to establish that functionalization with lower molecular weight PEI (600 and 1800 Da) achieved higher cell viability in MTT assay. A shortened version of the nanotubes, PEI(1800)-cut-SWNT (1800 Da branched PEI), was also prepared and tested for cellular internalization in the BxPC3 adenocarcinoma cell line. Laser confocal imaging of the cells after incubation in the presence of RhoB-PEI(1800)-cut-SWNT (covalently labelled with rhodamine B) indicates that the PEI(1800)-cut-SWNTs can reach both the cytoplasm and nucleus of pancreatic cancer cells.

Polyethyleneimine functionalised nanocarbons for the efficient adsorption ofcarbon dioxide with a low temperature of regeneration

Polyethyleneimine (PEI) conjugates with a range of nanocarbons (NCs) have been prepared, and their performances with regard to carbon dioxide absorption and liberation are compared. PEI-functionalised multi-walled carbon nanotubes (PEI-MWNTs) prepared by the reaction of branched PEI (25,000 Da) with F-MWNTs in the presence of pyridine, showed a lower CO2 capacity at 25 °C (5 wt%, 1.1 mmol CO2/g adsorbent) as compared to PEI-SWNTs (9.2 wt%, 2.1 mmol CO2/g adsorbent), consistent with the interior layers of the MWNTs adding weight to the base NC without adding functionality. PEI-functionalised graphite/graphene was prepared by three routes: fluorinated graphite intercalation compounds, prepared from natural graphite powder, were reacted with PEI in EtOH with pyridine; exfoliated natural graphite powder was reacted with Boc–Phe(4-N3)–OH, and subsequently PEI to give PEI-Phe(4-N-G); graphite oxide (GO) was reacted with PEI in the presence of NEt3 to give PEI-GO. The CO2 capacity of PEI-GO at 25 °C (8 wt%, 1.8 mmol CO2/g adsorbent) was comparable to that of PEI-SWNTs making GO a valid and cheaper alternative to the SWNT scaffold. The temperature of CO2 desorption of the PEI-NCs was 75 °C, providing a lower energy load for regeneration compared to current amine-based scrubbing units. The rate of CO2 uptake is seen to depend on the curvature of the NC substrate.

Effect of spray-drying and cryo-milling on the CO2 absorption performance of C60 cross-linked polyethyleneimine

The high CO2 capacity of PEI-C60 conjugates is impeded by a slow rate of absorption. A limiting factor to this rate is proposed to be the surface area available for the rapid contact between amine functional groups of PEI and CO2. Increasing the surface area by spray-drying a solution of reagents is proposed as a route to larger surface area products. In this work we investigate process changes to control absorption chemistry. Reagent solutions were spray-dried in different experimental conditions of concentration, drying temperature, and feed pressure. The results indicate that the rate of CO2 absorption at room temperature can be improved by a factor of 2.5 times by spray drying the product when compared to the product obtained using sonication. Given the rubbery nature of PEI-C60 the surface area, and hence CO2 capacity, could be increased using cryogenic grinding in liquid nitrogen; however, the results show that this has limited effect on the surface area of the absorbent prepared using sonication. Only compared to the hard chunks obtained via stir bar synthesis was the surface area doubled, in contrast to the rubbery product obtained using ultrasonication the area did not change significantly. Interestingly, doubling the surface area, the rate of absorption of wet CO2 at high temperature did not change, while that at low temperature doubled in rate, consistent with the presence of diffusion limitations manly at low temperature.

Defining a performance map of porous carbon sorbents for high-pressure carbon dioxide uptake and carbon dioxide–methane selectivity

The relative influence of heteroatom doping, surface area, and total pore volume of highly microporous carbon materials on CO2 uptake capacity, and the CO2/CH4 selectivity, at high pressure (≤30 bar) is presented. The separation of CO2 from natural gas (natural gas sweetening) is an important application that requires high CO2 uptake in combination with high CO2/CH4 selectivity. Porous carbon (PC), N-doped PC (NPC), and S-doped PC (SPC) materials are prepared using KOH oxidative activation at different temperatures. The surface chemical composition was determined by XPS, while the surface areas, total pore volume, and pore size distributions were obtained by analyzing N2 adsorption–desorption isotherms with support from SEM and TEM. The CO2 and CH4 uptake was determined by volumetric uptake measurements (sorption and desorption). Contrary to previous proposals that N- or S-doping results in high uptake and good selectivity, we show it is the Σ(O,N,S) wt% that is the defining factor for CO2 uptake, of which O appears to be the main factor. Based upon the data analyzed, a performance map has been defined as a guide to designing/choosing materials for both future studies and large scale fluid bed applications using pelletized materials. For CO2 uptake at 30 bar any material with a surface area >2800 m2 g−1 and a total pore volume >1.35 cm3 g−1 is unlikely to be bettered. Such a material is best prepared by thermal activation between 700–800 °C and will have a carbon content of 80–95 wt% (as determined by XPS). While it has been assumed that the parameters that make a good CO2 adsorbent are the same as those that make a material with high CO2/CH4 selectivity, our results indicate instead that for the best selectivity at 30 bar a surface area >2000 m2 g−1 and a total pore volume >1.0 cm3 g−1 and a carbon content of <90 wt% are necessary.

Easily Regenerated Readily Deployable Absorbent for Heavy Metal Removal from Contaminated Water

Although clean and abundant water is the keystone of thriving communities, increasing demand and volatile climate patterns are depleting rivers and aquifers. Moreover, the quality of such water sources is threatened by noxious contaminants, of which heavy metals represents an area of growing concern. Recently, graphene oxide (GO) has been suggested as an adsorbent; however, a support is desirable to ensure a high surface area and an immobile phase. Herein, we described the preparation and characterization of a supported-epoxidized carbon nanotube (SENT) via the growth of multi walled carbon nanotubes (MWNTs) onto a quartz substrate. Subsequent epoxidation provides sufficient functionality to enable adsorbent of heavy metals (Cd2+, Co2+, Cu2+, Hg2+, Ni2+, and Pb2+) from aqueous solution with initial concentrations (60–6000 ppm) chosen to simulate high industrial wastewater contamination. The SENT adsorption efficiency is >99.4% for all metals and the saturation concentration is significantly greater than observed for either GO or acid treated MWNTs. The SENT adsorbent may be readily regenerated under mild conditions using a globally available household chemical, vinegar. 1 g of SENT has the potential to treat 83,000 L of contaminated water down to WHO limits which would be sufficient for 11,000 people.

Nanostructured fusiform hydroxyapatite particles precipitated from aquaculture wastewater

The present work represents a new approach for the isolation of uniform nano particulate hydroxyapatite (HAp). The chemical characterization of a calcium phosphate product obtained from industrial trout farm aquaculture wastewater by two different routes, washing either with a basic aqueous medium (washNaOH) or followed by a further washing with ethanol (washEtOH), is explored. Characterization of the isolated materials includes morphology studies (SEM and TEM), structural (XRD, electron diffraction), compositional (EDX) and thermogravimetric analysis (TGA). The obtained products are a mixture of different compounds, with hydroxyapatite the predominant phase. The morphology is unusually nanometric size with fusiform shaped particles, such characteristics are ordinarily only obtained by synthetic routes. This process of phosphate precipitation represents a unique self-sufficient process to be compared to conventional chemical or biological practices for precipitating phosphate.

Post-Synthetic Ligand Exchange in Zirconium-Based Metal-Organic Frameworks: Beware of The Defects!

Post-synthetic ligand exchange in the prototypical zirconium-based metal-organic framework (MOF) UiO-66 was investigated by in situ solution 1 H NMR spectroscopy. Samples of UiO-66 having different degrees of defectivity were exchanged using solutions of several terephthalic acid analogues in a range of conditions. Linker exchange only occurred in defect-free UiO-66, whereas monocarboxylates grafted at defect sites were found to be preferentially exchanged with respect to terephthalic acid over the whole range of conditions investigated. A 1:1 exchange ratio between the terephthalic acid analogue and modulator was observed, providing evidence that the defects had missing-cluster nature. Ex situ characterisation of the MOF powders after exchange corroborated these findings and showed that the physical-chemical properties of the MOF depend on whether the functionalisation occurs at defective sites or on the framework.