RCIPL
Repositório Institucional do Politécnico de Lisboa
Entradas recentes
Carbon aerogels and xerogels: next-generation materials for sustainable energy and environmental solutions
Publication . Tomić, David; Radinović, Kristina; Mladenović, Dušan; Milikić, Jadranka; Santos, Diogo; Pombeiro, Armando; Paul, Anup; Sljukic Paunkovic, Biljana
Abstract
Carbon aerogels and xerogels, with their 3D porous architectures, ultralow density, high surface area, and excellent conductivity, have emerged as multifunctional materials for energy and environmental applications. This review highlights recent advances in the synthesis of these materials via polymerisation, drying, and carbonisation, as well as the role of novel precursors such as graphene, carbon nanotubes, and biomass. Emphasis is also placed on doped and metal-decorated carbon gels as efficient electrocatalysts for oxygen reduction reactions, enabling four- and two-electron pathways for energy conversion and the production of green H2O2, respectively. Aerogels’ high specific capacitance and stability also position them as promising materials for supercapacitors. The versatility of carbon aerogels and xerogels offers exciting prospects for future innovations in catalysis, energy storage, and sustainable technologies.
Low-cost transition metals (Fe, Ni, Co) on carbon aerogel for water electrolysis and supercapacitor applications
Publication . Mladenović, Dušan; Martins, Marta; Samanci, Meryem; Charneca, Miguel; Paul, Anup; Santos, Diogo M. F.; Bayrakçeken, Ayşe; Ślijukić, Biljana
Abstract
Cost-effective transition metals (TM = Fe, Ni, Co) were immobilized on carbon aerogel (CA) using microwave irradiation, followed by nitrogen doping into one catalyst series through heat treatment. The physical characterization of the synthesized catalysts included N2 sorption, inductively coupled plasma-mass spectrometry, X-ray diffraction analysis, transmission electron microscopy, Raman spectroscopy, FTIR spectroscopy, and X-ray photoelectron spectroscopy. Co/CA displayed the best performance for oxygen evolution reaction (OER) electrocatalysis in alkaline water electrolysis, followed by Ni/CA. Co/CA exhibited a small Tafel slope of 110 mV dec−1 and required an overpotential of just 276 mV to reach 10 mA cm−2, lower than that of the commercial IrO2 electrocatalyst. Additionally, Co/CA and Ni/CA demonstrated excellent long-term stability during OER, with activity increasing over time. Capacitance measurements also showed the potential of TM/CA materials as supercapacitor electrodes. Fe/CA achieved the highest performance, with a specific capacitance of 322 F g-1 at a moderate current of 1 A g-1. It retained up to 96 % of its capacitance over 1000 cycles, indicating excellent stability.
Adenine tagged Mn-based coordination polymer for conversion of carbon dioxide to cyclic carbonates under atmospheric pressure
Publication . Eskemech, Alehegn; Bhakhar, Rubi; Biswas, Pritam; Karmakar, Anirban; Krishnan, Venkata; Koner, Rik Rani
Abstract
Natural processes collectively balance the global carbon cycle, effectively controlling atmospheric carbon dioxide (CO2) levels. However, excessive CO2 emissions due to industrialization and population growth have disrupted natural processes by increasing the atmospheric CO2 concentration. To address this issue, CO2 capture and conversion have been implemented. Metal–organic frameworks (MOFs)/coordination polymers (CPs) with bioligands, such as amino acids and nucleobases, are receiving much interest. However, bio-MOFs are not much reported due to the lack of control over their coordination with metal ions. In this work, we have developed an adenine-tagged Mn-CP with dominant basic sites, [Mn(IPT2–)(Ade)(DMF)]n (IPT2– = isophthalate; Ade = adenine; DMF = N,N′-dimethylformamide). The analysis of isosteric heat (Qst) of CO2 adsorption supported the presence of strong interactions between CO2 and Mn-CP. Mn-CP demonstrated moderate to outstanding performance in coupling CO2 with smaller and larger epoxides at ambient pressure under neat conditions. The thermodynamic activation parameters indicate that Mn-CP operates through an associative mechanism (ΔS⧧ = −283.4 J mol−1 K−1), with a reduced kinetic barrier characterized by ΔH⧧ of 17.28 kJ mol–1 and Ea of 20.5 kJ mol–1. The catalytic efficiency of Mn-CP was particularly notable in the coupling reaction of epichlorohydrin and CO2, yielding 92% of the corresponding cyclic carbonate under atmospheric pressure.
Heterometallic CuCd and Cu2Zn complexes with o-vanillin and its Schiff-base derivative: slow magnetic relaxation and catalytic activity associated with Cu(II) centres
Publication . Vassilyeva, Olga Yu; Nesterova, Oksana V.; Bienko, Alina; Komarnicka, Urszula K.; Buvaylo, Elena A.; Vasylieva, Svitlana M.; Skelton, Brian W.; Nesterov, Dmytro S.
Abstract
In this work, two novel heterometallic mixed-ligand mixed-anion complexes [CuIICdIIClL(o-Van) (OAc)]·3H2O (1) and [CuII2ZnIICl2L2(o-Van)(OAc)] (2) were prepared by reacting fine copper powder and Cd(II) or Zn(II) acetate with an ethanol solution of the Schiff-base ligand HL formed in situ in the condensation reaction of 2-hydroxy-3-methoxy-benzaldehyde (o-VanH) and CH3NH2·HCl. The compounds were thoroughly characterized by elemental analysis, FT-IR, UV/Vis and EPR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction, revealing the neutral molecular nature of both the compounds. Catalytic properties of 1 and 2 were studied in the oxidation of hydrocarbons with H2O2 under mild conditions, showing the maximum reaction rate of 4 × 10−5 M s−1 and TOF up to 640 h−1. Both compounds undergo complex transformations in solution as evidenced by kinetic analysis and time-dependent UV/Vis spectroscopy, indicating that the reduced Cu(I) form of 1 is unexpectedly unfavorable. Complex 1 demonstrates slow magnetic relaxation dominated by the direct relaxation process between T = 1.8 and 7 K under an external DC field of 0.2 and 0.4 T, a very rarely observable effect in the coordination compounds of Cu(II).
Complex 2 possesses weak ferromagnetism (J = 4.50 cm−1, zJ’ = −0.201 cm−1 for H = −JS1S2 formalism) occurring through the Cu–O–Cu pathways. Theoretical CASSCF, DFT and TDDFT calculations were applied to investigate the electronic structures of 1 and 2 and rationalize their behavior in solution.
A 3D MOF with Cu20/Cu6 clusters: self-assembly, CO2 encapsulation, structural features, and magnetic properties
Publication . Sliwa, Ewelina I.; Nesterov, Dmytro S.; Klak, Julia; Kirillov, Alexander M.; Smolenski, Piotr
Abstract
Molecular design of multicopper clusters has been of increasing importance in inorganic chemistry, biomedical science, and functional materials. Herein, two new copper compounds were self-assembled from copper(II) monofluoroacetate or trifluoroacetate, elemental copper, and 1,3,5-triaza-7-phosphaadamantane (PTA). The reaction starting from copper(II) monofluoroacetate yielded a tetranuclear cluster, [Cu4II(μ3-OH)2(μ-L)6(PTA=O)2] (1), where L is monofluoroacetate(1−) and PTA=O is the oxide of PTA. Formation of 1 involves the oxidation of PTA and the incorporation of μ3-OH– ligands. In contrast, a similar reaction with copper(II) trifluoroacetate produced a unique three-dimensional metal–organic framework (3D MOF), formulated as [{Cu20II(CO3)(μ3-O)2(μ3-OH)22(μ-L′)12}{Cu6I(μ3-PTA)6(CH3CN)12}]n·6n(L′)·3n(H2O)·2n(CH3CN) (2), where L′ is trifluoroacetate. It comprises Cu20 clusters, with an encapsulated carbonate anion fixed from atmospheric CO2, which are bridged by {Cu6I(PTA)6} units into a 3D MOF. Control experiments confirmed that carbonate originates from ambient CO2 rather than from added carbonate salts. Both 1 and 2 were fully characterized, and their magnetic properties were investigated, revealing dominant antiferromagnetic interactions within the Cu4 and Cu20 clusters, respectively. Density functional theory (DFT) calculations confirmed the antiferromagnetic ground spin state of 1 and disclosed the stability of the Cu20 core in 2. This work highlights the influence of fluorinated carboxylates and atmospheric conditions on the assembly and architecture of multicopper clusters, and extends their family to new examples.