Synthesis of γ-Al₂O₃ nanopowder by the sol-gel method: Effect of different acid precursors on the superficial, morphological and structural properties

Arquímedes Cruz-López,Odilón Vázquez Cuchillo,Isaías Juárez Ramírez,Lilia M. Bautista-Carrillo,Elvira Zarazua-Morin 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.5

The main aim of this investigation is to study the effect of three acid precursors (nitric acid, acetic acid and citric acid) during the synthesis of γ-Al2O3 nanopowder by the sol-gel method. The TEM analyses showed that the γ-Al2O3 prepared by using the strongest acid were irregular nanofibers with a length of 50 nm and a diameter of 5 nm, while the γ-Al2O3 prepared with citric acid showed agglomerates. On the other hand, the SEM analyses showed very similar morphologies. The N2-physisorption analyses confirmed that there is a relationship between the acidity and the surface area; and between the presence of mesopores and micropores on the surface of the synthesized Al2O3. The effect of the acid strength on the surface area was as follows: nitric acid (347 m2·g−1) > acetic acid (252 m2·g−1) > citric acid (164 m2·g−1). In addition, the XRD results confirmed that for all the samples thermally treated at 600 oC, the main phase was γ-Al2O3; nevertheless, the thermal analyses showed that the γ-Al2O3 synthesized with the weakest acid was not stable above 600 oC. The main aim of this investigation is to study the effect of three acid precursors (nitric acid, acetic acid and citric acid) during the synthesis of γ-Al2O3 nanopowder by the sol-gel method. The TEM analyses showed that the γ-Al2O3 prepared by using the strongest acid were irregular nanofibers with a length of 50 nm and a diameter of 5 nm, while the γ-Al2O3 prepared with citric acid showed agglomerates. On the other hand, the SEM analyses showed very similar morphologies. The N2-physisorption analyses confirmed that there is a relationship between the acidity and the surface area; and between the presence of mesopores and micropores on the surface of the synthesized Al2O3. The effect of the acid strength on the surface area was as follows: nitric acid (347 m2·g−1) > acetic acid (252 m2·g−1) > citric acid (164 m2·g−1). In addition, the XRD results confirmed that for all the samples thermally treated at 600 oC, the main phase was γ-Al2O3; nevertheless, the thermal analyses showed that the γ-Al2O3 synthesized with the weakest acid was not stable above 600 oC.

Low Wavenumber Raman Modes and Plasmon Resonance in Cd Nanoparticles Obtained in Extract of Opuntia ficus-indica Plant

M. Cortez-Valadez,L. P. Ramírez-Rodríguez,J.-G. Bocarando-Chacon,M. FLORES-ACOSTA,S. VELUMANI,R. Ramírez-Bon 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2015 NANO Vol.10 No.7

"Cadmium colloidal crystalline nanoparticles were obtained by a simple green synthesis method employing the plant extract of Opuntia ficus-indica. The plant extract reduces the Cd ions and stabilizes the size of cadmium colloidal particles at the nanometric level. The size and morphology of agglomerates of nanoparticles of about 100 nm were analyzed by field-emission scanning electron microscopy (FESEM). The size, shape and crystalline structure of the Cd nanoparticles were determined from TEM analysis. The results show that Cd nanoparticles with hexagonal crystalline structure and average size 2–3 nm were obtained by this green synthesis method. The optical absorption spectrum of the colloidal solution containing the cadmium nanoparticles displays an optical absorption band centered at 236 nm, which was attributed to the plasmon resonance of the Cd colloidal nanoparticles. Mie theory for colloidal systems was applied to reproduce theoretically the plasmon resonance absorption data of the Cd colloidal nanoparticles. Furthermore, the Raman spectrum of powder from dried samples after reduction of cadmium ions, displays a low wavenumber vibration mode centered at 114 cm-1, assigned to the Cd nanoparticles. Density functional theory (DFT) calculations at local spin density approximation (LSDA) level were performed to determine the structure and vibrational properties of small clusters of cadmium consisting of 3–10 atoms. Radial breathing modes with frequencies between 90 cm-1 and 120 cm-1 were found to be the most active Raman modes of the low-energy Cdn clusters."

Challenges managing COVID vaccine-induced immune thrombotic thrombocytopenia in low-middle income countries

Céleo Ramírez,Ramón Jeremías Soto Hernández,Reyna M. Durón 대한백신학회 2021 Clinical and Experimental Vaccine Research Vol.10 No.3

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is an extremely rare complication associated with the adenovirus-vectored coronavirus disease 2019 (COVID-19) ChAdOx1 nCoV-19 (AZD1222) vaccine. It is characterized by venous thrombosis, mainly cerebral venous sinus thrombosis, moderate to severe thrombocytopenia, and rarely, thrombosis in cerebral arteries. This syndrome is similar to the heparin-induced thrombocytopenia and presents mostly among women aged 18–55 years, without previous exposure to heparin, usually 5 to 20 days after vaccination. However, cases have been reported in men and older adults [1-4]. Unlike COVID-19, this adverse effect might not represent a public health problem in itself, but it is already causing vaccine hesitancy in population groups susceptible to severe COVID-19, and poses a challenge in low resource settings [5]. The first case reports showed evidence that VITT has a mortality around 40% [1-3]. So far, cases have been reported and treated in hospitals of highly developed countries with first-rate health systems that facilitate early detection and treatment of this severe adverse event. VITT is confirmed by using PF4-dependent enzyme-linked immunosorbent assay (ELISA) assay, which allows the differential diagnosis from other causes of thrombosis in patients with a history of ChAdOx1 nCoV-19 vaccination in previous days. However, it is likely that a large number of hospitals in many low-middle income countries do not have approved PF4-dependent ELISA assays for accurate diagnosis, nor immunoglobulins, glucocorticoids, and non-heparin anticoagulants needed for the treatment of this condition [1-4]. In times of this COVID-19 pandemic and precision medicine, problems and solutions should be considered global. Policies related to COVID-19 need to be addressed considering varied public health and socioeconomic contexts. The ChAdOx1 nCoV-19 vaccine is one of the most used vaccines in low-middle income countries, where special testing to confirm VITT is not widely available. Therefore, real figures are unknown, and underreporting of this adverse effect should be considered. Patient information, government, and hospital preparedness in these countries are needed to diagnose and manage VITT adequately, and to reduce morbidity and mortality from this complication. These strategies will have a positive impact on public acceptance and adherence to COVID vaccination.

COVID-19 vaccination policies and the new challenges of international travel

Céleo Ramírez,최준낙,Reyna M. Durón 대한백신학회 2022 Clinical and Experimental Vaccine Research Vol.11 No.2

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Particle size effect of LiAlSiO₄on the thermal expansion of SiC porous materials

I. Juárez-Ramírez,K. Matsumaru,K. Ishizaki,L.M. Torres-Martínez 한양대학교 세라믹연구소 2008 Journal of Ceramic Processing Research Vol.9 No.5

This paper reports the effect of the particle size of LiAlSiO4 on the thermal expansion and Young’s modulus of low thermal expansion (LTE) coefficient of porous materials using silicon carbide (SiC), vitrified bonding material (VBM) and lithium aluminum silicate (LiAlSiO4) at 850 oC. According to the XRD results, there is no reaction between the raw materials during the sintering process. SEM analysis revealed the presence of an internal porous structure with a pore size less than 4 micrometers. It was found that decreasing the particle size of LiAlSiO4 by almost 4 times reduces the porosity, keeping a low thermal expansion coefficient, but the Young’s modulus increases 50%. This paper reports the effect of the particle size of LiAlSiO4 on the thermal expansion and Young’s modulus of low thermal expansion (LTE) coefficient of porous materials using silicon carbide (SiC), vitrified bonding material (VBM) and lithium aluminum silicate (LiAlSiO4) at 850 oC. According to the XRD results, there is no reaction between the raw materials during the sintering process. SEM analysis revealed the presence of an internal porous structure with a pore size less than 4 micrometers. It was found that decreasing the particle size of LiAlSiO4 by almost 4 times reduces the porosity, keeping a low thermal expansion coefficient, but the Young’s modulus increases 50%.

Thermo and pH-Responsive Poly(DEGMA-co-OEGMA)-b-Poly(DEAEM) Synthesized by RAFT Polymerization and Its Self-Assembly Study

Ángela M. López,Antonio Tirado-Guizar,Angel Licea-Claverie,Alejandro Ramírez-Jiménez 한국고분자학회 2022 Macromolecular Research Vol.30 No.12

Drug delivery and release systems using stimuli-responsive nanostructures based on amphiphilic copolymers have gained great importance. In this work copolymers from oligo(ethylene glycol) methyl ether methacrylate (OEGMA) and di(ethylene glycol) methyl ether methacrylate (DEGMA) as thermo-responsive moiety and block copolymers incorporating N,N′-diethylaminoethyl methacrylate (DEAEM) as pH-responsive one, were synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT) using 5-amino-4-methyl-4-(propylthiocarbonothioylthio)- 5-oxo pentanoic acid as chain transfer agent (CTA). The number average molecular weights (Mn), and dispersity Đ confirmed a good RAFT control. Polymers were characterized by Fourier transform infrared spectroscopy using a attenuated total reflection (FTIR-ATR), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscope (TEM), and Turbidimetry. Their self-assembly behavior is described by its hydrodynamic diameter (Dh), its ζ-potential and as well as its cloud point temperature (Tcp). The results showed thermo-responsive and pH-responsive systems with Tcp in phosphate-buffered saline (PBS) pH=7.4 around 37 and 42℃ the isoelectric point was found in a pH range between 7.0 and 7.5, further the critical micelle concentration (CMC) indicated very low values between 5.85 to 4.20 × 10-4 mg mL-1. The developed block copolymeric systems have potential to be used for drug transport and delivery.

Occurrence of Squash yellow mild mottle virus and Pepper golden mosaic virus in Potential New Hosts in Costa Rica

Ruth M. Castro,Lisela Moreira,María R. Rojas,Eduardo Hernández,Floribeth Mora,Pilar Ramírez,Robert L. Gilbertson 한국식물병리학회 2013 Plant Pathology Journal Vol.29 No.3

Leaf samples of Solanum lycopersicum, Capsicum annuum,Cucurbita moschata, Cucurbita pepo, Sechium edule and Erythrina spp. were collected. All samples were positive for begomoviruses using polymerase chain reaction and degenerate primers. A sequence of ~1,100 bp was obtained from the genomic component DNA-A of 14 samples. In addition, one sequence of ~580 bp corresponding to the coat protein (AV1) was obtained from a chayote (S. edule) leaf sample. The presence of Squash yellow mild mottle virus (SYMMoV) and Pepper golden mosaic virus (PepGMV) were confirmed. The host range reported for SYMMoV includes species of the Cucurbitaceae,Caricaceae and Fabaceae families. This report extends the host range of SYMMoV to include the Solanaceae family, and extends the host range of PepGMV to include C. moschata, C. pepo and the Fabaceae Erythrina spp. This is the first report of a begomovirus (PepGMV)infecting chayote in the Western Hemisphere.

LA EDUCACIÓN SUPERIOR CHILENA EN PERSPECTIVA : ENTREVISTA CON JOSÉ JOAQUÍN BRUNNER

Oswaldo Méndez-Ramírez Institute of Iberoamerican Studies Pusan Universit 2013 International Journal of Latin American Studies Vol.3 No.1

Resumen. En el contexto del proyecto de investigación: Educación superior en Chile: ¿crisis o fortalecimiento del neoliberalismo?; el pasado 17 de abril del 2012, se realizó la entrevista que a continuación se trascribe al Doctor José Joaquín Brunner, Profesor Investigador en la Universidad Diego Portales. La Entrevista se llevó a cabo en la ciudad de Santiago de Chile, en las instalaciones de dicha universidad. Abstract. In the context of the research project: Higher Education in Chile: Crisis or strengthening of neoliberalism?; the follow interview was made to José Joaquín Brunner (Ph.D), research professor in Diego Portales University, this year on April 17th. The interview was conducted in the city of Santiago de Chile. Palabras clave: Educación superior, calidad educativa, neoliberalismo, posmodernismo, equidad. Key Words: Higher education, quality of education, neoliberalism, postmodernism, equity.

Construcciones conceptuales sobre la educación superiores y calidad educativa en estudiantes universitarios chilenos

Oswaldo Méndez Ramírez 한국외국어대학교 중남미연구소 2012 중남미연구 Vol.31 No.3

The present manuscript explores the representations that students of the University of Chile have with regard to the incentive concepts: “higher education” and “quality of education”. It is a qualitative study that allowed access to conceptual constructs and processes definition of individuals; using the technique of natural semantic networks. The population was made up of students currently enrolled in studies of history; psychology and educational psychology at the University of Chile. The sample was comprised of a total of 70 students. Derived from the analysis, were found three concepts in common: learning, inequality and opportunity. The results led to interpret that the students of the University of Chile, a high quality education must be a right and be an education that promotes learning, combat inequality and provides opportunities.

Bi2InTaO7 compounds as promising photocatalysts for marine plankton removal

Leticia M. Torres-Martínez,Isaías Juárez-Ramírez,Juan S. Ramos-Garza,Francisco Vázquez-Acosta,Ricardo Gómez,ZhengYi Fu,Soo Wohn Lee 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.1

The removal of marine plankton, red (Amphidium carterae), and green (Tetraselmis suecica) tide algae, by heterogeneous photocatalysis was carried out using pyrochlore-type semiconductors. The semiconductor, Bi2InTaO7 , was prepared by the solgel method and a solid state reaction. The XRD patterns evidence formation of the pyrochlore phase in the sol-gel materials calcined at low temperatures (600-800 oC). Nanostructured sol-gel materials were observed by SEM. The sol-gel preparation allowed the formation of the pyrochlore-type compound with specific surface areas (7-13 m2g−1) higher than the solid obtained by solid state preparation (< 5 m2g−1). Band gap (Eg) values between 2.1-2.7 eV determined by UV-Vis spectroscopy were obtained. Bi2InTaO7 photocatalysts prepared by the sol-gel method were able to eliminate Tetraselmis suecica and Amphidium carterae algae totally after 50 minutes of UV-irradiation, whereas Bi2InTaO7 by solid state preparation needed more than 1 h.