Using iron (III) acetylacetonate as both a cross-linker and micropore former to develop polyimide membranes with enhanced gas separation performance

Facile Modification of Flexible Electrodes via Laser Transfer

In this work, we report the modification of commercially available electrochemical electrodes with tin oxide (SnO₂) and Pd doped SnO₂ (Pd-SnO₂) via pulsed laser-induced forward transfer (LIFT). The pulsed light irradiation working as in situ pulsed photo-thermal treatment allows for the transfer of SnO₂ and Pd-SnO₂ from UV absorbing metal complex precursors onto flexible, commercially available screen-printed electrodes. The laser transfer conditions are optimized and the material transferred under different conditions is evaluated morphologically and chemically, and its functionality is tested against the detection of copper ions. For example, by applying laser fluences in the range 100–250 mJ/cm², the shape and the size of the transferred features ranges from nano-polyhedrons to near corner-grown cubic Pd-SnO₂ or near cubic Pd-SnO₂. In addition, the EDX analysis is consistent with the XPS findings, i.e., following laser transfer, Pd amounts lower than 0.5% are present in the Pd-SnO₂ pixels. First sensing tests were carried out and the transferred Pd-SnO₂ proved to enhance the cathodic peak when exposed to Cu(II) ions. This photo-initiated fabrication technology opens a promising way for the low-cost and high-throughput manufacturing of metal oxides as well as for electrodes for heavy metal ion detection.

Thermally Stable Cross-linked P84 with Superior Membrane H2/CO2 Separation Properties at 100 °C

Polymers with a strong size-sieving ability and superior H₂/CO₂ selectivity are of great interests for pre-combustion CO capture at 100 °C or above. Polyimides (such as Matrimid^® and 6FDA-durene) have been cross-linked using diamines and show superior H₂/CO₂ selectivity. However, these cross-linked polymers cannot be used for the pre-combustion CO₂ capture because of the lack of thermal stability at 100 C. Herein we demonstrate that commercial P84™ can be chemically cross-linked using 1,4-butanediamine (BuDA) to achieve robust H₂/CO₂ separation properties at 100 °C to 150 °C. The cross-linked P84 were thoroughly evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The effects of the cross-linking time on the physical properties and H₂/CO₂ separation properties at various temperatures were determined and interpreted using a free volume model. An exemplary sample based on P84 crosslinked by BuDA for 6 h exhibits a H₂ permeability of 47 Barrers (1 Barrer = 3.35 × 10^-16 mol m/m²·s·Pa) and H₂/CO₂ selectivity of 14 at 100 °C, which is on the Robeson's upper bound, indicating their potential for practical applications.

Chemical Crosslinking of 6FDA-ODA and 6FDA-ODA:DABA for Improved CO₂/CH₄ Separation

Chemical grafting or crosslinking of polyimide chains are known to be feasible approaches to increase polymer gas-pair selectivity and specific gas permeance. Different co-polyimides; 6FDA-ODA and 6FDA-ODA:DABA were synthesized using a two-step condensation method. Six different cross-linkers were used: (i) m-xylylene diamine; (ii) n-ethylamine; and (iii) n-butylamine, by reacting with 6FDA-ODA’s imide groups in a solid state crosslinking; while (iv) ethylene glycol monosalicylate (EGmSal); (v) ethylene glycol anhydrous (EGAn); and (vi) thermally labile iron (III) acetylacetonate (FeAc), by reacting with DABA carboxyl groups in 6FDA-ODA:DABA. The gas separation performances were evaluated by feeding an equimolar CO₂ and CH₄ binary mixture, at a constant feed pressure of 5 bar, at 25 °C. Fractional free volume (FFV) was calculated using Bondi’s contribution method by considering the membrane solid density property, measured by pycnometer. Other characterization techniques: thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) were performed accordingly. Depending on the type of amine, the CO₂/CH₄ selectivity of 6FDA-ODA increased between 25 to 100% at the expense of CO₂ permeance. We observed the similar trend for 6FDA-ODA:DABA EGmSal-crosslinked with 143% selectivity enhancement. FeAc-crosslinked membranes showed an increment in both selectivity and CO₂ permeability by 126% and 29% respectively. Interestingly, FeAc acted as both cross-linker which reduces chain mobility; consequently improving the selectivity and as micro-pore former; thus increases the gas permeability. The separation stability was further evaluated using 25–75% CO₂ in the feed with CH₄ as the remaining, between 2 and 8 bar at 25 °C. We also observed no CO₂-induced plasticization to the measured pressure with high CO₂ content (max. 75%).