Carbon microfibers (CMF) has been used as an adsorbent material for CO₂ and CH₄ capture. The gas adsorption capacity depends on the chemical and morphological structure of CMF. The CMF physicochemical properties change according to the applied stabilization and carbonization temperatures. With the aim of studying the effect of stabilization temperature on the structural properties of the carbon microfibers and their CO₂ and CH₄ adsorption capacity, four different stabilization temperatures (250, 270, 280, and 300 °C) were explored, maintaining a constant carbonization temperature (900 °C). In materials stabilized at 250 and 270 °C, the cyclization was incomplete, in that, the nitrile groups (triple-bond structure, e.g., C≡N) were not converted to a double-bond structure (e.g., C=N), to form a six-membered cyclic pyridine ring, as a consequence the material stabilized at 300 °C resulting in fragile microfibers; therefore, the most appropriate stabilization temperature was 280 °C. Finally, to corroborate that the specific surface area (microporosity) is not the determining factor that influences the adsorption capacity of the materials, carbonization of polyacrylonitrile microfibers (PANMFs) at five different temperatures (600, 700, 800, 900, and 1000 °C) is carried, maintaining a constant temperature of 280 °C for the stabilization process. As a result, the CMF chemical composition directly affects the CO₂ and CH₄ adsorption capacity, even more directly than the specific surface area. Thus, the chemical variety can be useful to develop carbon microfibers with a high adsorption capacity and selectivity in materials with a low specific surface area. The amount adsorbed at 25 °C and 1.0 bar oscillate between 2.0 and 2.9 mmol/g adsorbent for CO₂ and between 0.8 and 2.0 mmol/g adsorbent for CH₄, depending on the calcination treatment applicated; these values are comparable with other material adsorbents of greenhouse gases.

Factors affecting TiO ₂ biomineralization using TiBALDH as precursor.

Peptides and proteins rich in positively charged residues have been the most frequently reported for TiO2 biomineralization since their identification is based on peptide screening on its negatively charged surface. To achieve optimum interaction of the peptides with the biomimetic synthesis precursors rather than interaction with the final product, in this work, a selection of peptides with biomineralization activity was proposed by performing a biopanning directly on the precursor Titanium(IV) bis(ammonium lactate) dihydroxide (TiBALDH). Using two phage display libraries (12- and 7-mer) in different buffer systems, four possible sequences with biomineralization activity of TiO2 were identified: TNWQALAYMQRH (TN), ENHWSLSTLMSS (EN), GLHTSATNLYLH (GL), TWYPNRPPILEL (TW). The selection of buffer and concentration of TiBALDH were vital for a reliable identification. Synthetic peptides with sequences TN and EN, were selected for in vitro biomineralization of TiO2. Both peptides were able to form anatase nanoparticles at room temperature. However, the EN sequence showed lower activity than TN, specially in acetate buffer, requiring a higher concentration to initiate biomineralization. These changes in reactivity can be attributed principally to different states of protonation of the residues mainly due to the glutamic acid in EN. Although the secondary structure determined by circular dichroism results in disordered chains, a common motif could be identified between the two peptides -pol-pol-W-pol-x-x-x-x-M-, where the W and M residues match. The results provide new possibilities for using combinatorial techniques to find new biological templates for nanomaterial synthesis. Resumen. Péptidos y proteínas ricas en residuos con carga positiva han sido frecuentemente reportados para la biomineralización de TiO2, ya que su identificación se basa en la detección de péptidos sobre su superficie con carga negativa. Para alcanzar una interacción óptima del péptido con el precursor biomimético, en lugar de la interacción con el producto final, en este trabajo, se propuso realizar un biotamizado empleando el precursor dihidroxilactatotitanato(IV) de bis-amonio (TiBALDH) para seleccionar péptidos con actividad de biomineralización. Empleamos dos librerías de fago desplegado (12 y 7 residuos) en diferentes soluciones amortiguadoras, identificando cuatro posibles secuencias con actividad biomineralizante de TiO2: TNWQALAYMQRH (TN), ENHWSLSTLMSS (EN), GLHTSATNLYLH (GL), TWYPNRPPILEL (TW). La elección del amortiguador y la concentración de TiBALDH fueron vitales para una selección confiable. Los péptidos sintéticos TN y EN, fueron escogidos para la biomineralización de TiO2 in vitro. Ambos péptidos fueron capaces de formar nanopartículas de anatasa a temperatura ambiente, sin embargo, la secuencia EN mostró menor actividad que TN, especialmente en amortiguador de acetatos, requiriendo una concentración mayor para iniciar la biomineralización. Estas diferencias de reactividad pueden ser atribuidas principlamente a los estados de protonación de los residuos de ácido glutámico en EN. Aunque la estructura secundaria determinada por dicroísmo circular mostró cadenas desordenadas, se identificó un motivo común entre los dos péptidos—pol-pol-W-pol-x-x-x-x-M-, donde los aminoácidos W y M coinciden. Los resultados abren nuevas posibilidades para usar técnicas combinatorias para hallar nuevas plantillas biológicas para la síntesis de nanomateriales.