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Rodríguez-Hueso JE, Borbón-Nuñez HA, Ponce-Pérez R, Hoat DM, Takeuchi N, Tiznado H, Guerrero-Sánchez J. Atomic-scale study of TiO 2-GR nanohybrid formation by ALD: the effect of the gas phase precursor. Nanoscale Adv 2023; 5:5476-5486. [PMID: 37822911 PMCID: PMC10563838 DOI: 10.1039/d3na00729d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Accepted: 09/07/2023] [Indexed: 10/13/2023]
Abstract
In the present work, we report on a theoretical-computational study of the growth mechanism of the TiO2-Graphene nanohybrid by atomic layer deposition. Hydroxyl groups (OH) are anchoring sites for interacting with the main ALD titanium precursors (Tetrakis (dimethylamino) Titanium, Titanium Tetrachloride, and Titanium Isopropoxide). Results demonstrate that the chemical nature of the precursor directly affects the reaction mechanism in each ALD growth step. Tetrakis(dimethylamino)titanium is the precursor that presents a higher affinity (lower energy barriers for the reaction) to hydroxylated graphene in the growth process. A complete reaction mechanism for each precursor was proposed. The differences between precursors were discussed through the non-covalent interactions index. Finally, the water molecules help reduce the energy barriers and consequently favor the formation of the TiO2-graphene nanohybrid.
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Affiliation(s)
- Jonathan E Rodríguez-Hueso
- Centro de Investigación Científica y de Educación Superior de Ensenada,Carretera Tijuana-Ensenada 3918 Apdo. Postal 22860 Ensenada B.C. Mexico
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
| | - H A Borbón-Nuñez
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
- CONAHCyT- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
| | - R Ponce-Pérez
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
| | - D M Hoat
- Institute of Theoretical and Applied Research, Duy Tan University Ha Noi 100000 Viet Nam
- Faculty of Natural Sciences, Duy Tan University Da Nang 550000 Viet Nam
| | - N Takeuchi
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
| | - H Tiznado
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
| | - Jonathan Guerrero-Sánchez
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México Km.107, Apdo. Postal 14. Carretera Tijuana-Ensenada Ensenada Baja California Mexico
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Vazquez JL, López J, Bohórquez C, Lizarraga E, Blanco E, Can-Uc B, Romo O, Nedev N, Farías MH, Tiznado H. O 3-Annealing Effect on the Etching Resilience of a TiO 2/Al 2O 3 filter Prepared by Atomic Layer Deposition. ACS Appl Mater Interfaces 2023; 15:40942-40953. [PMID: 37590996 DOI: 10.1021/acsami.3c07586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/19/2023]
Abstract
This research investigates the improvements of ozone (O3) annealing on the optical and etching characteristics of TiO2/Al2O3 multilayer band-pass filters designed for potential optoelectronic applications. The band-pass filters were fabricated using atomic layer deposition (ALD), and their performance was systematically analyzed after the addition of O3 annealing at moderate temperatures (up to 300 °C). Results reveal that O3 annealing improves the optical transmittance of the multilayers by approximately 40% without significant spectral changes (∼6 nm). The observed enhancement in the transmittance is attributed to the improved stoichiometry of TiO2. By filling in the oxygen vacancies created during the fabrication process, it reduces its extinction coefficient. Furthermore, the O3 annealing enhances the stability of TiO2 against wet etching, improving the uniformity of etched surfaces. Etching on the ozone-annealed multilayer was up to 8 times more homogeneous, as observed in the roughness. The relatively short duration of the O3 annealing process, approximately 1.6 h, makes it a cost-effective alternative compared to using ozone in the ALD process, which can last several hours for thick optical coatings.
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Affiliation(s)
- Jorge Luis Vazquez
- Centro de Investigación Científica y de Educación Superior de Ensenada-CICESE. Ensenada 22860, México
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
| | - Javier López
- CONAHCYT - Centro de Nanociencias y Nanotecnología, UNAM, Km 107 Carretera Tijuana-Ensenada s/n., C.P. 22800, Ensenada 04510, México
| | - Carolina Bohórquez
- Centro de Investigación Científica y de Educación Superior de Ensenada-CICESE. Ensenada 22860, México
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
| | - Eder Lizarraga
- Universidad Autónoma de Baja California, Unidad Valle de las Palmas, Blvd. Universitario 1000, C.P. 22260 Tijuana 22260, Baja California, México
| | - Eduardo Blanco
- Departamento de Física de la Materia Condensada, Universidad de Cádiz, E11519 Puerto Real, España
| | - Bonifacio Can-Uc
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
| | - Oscar Romo
- Centro de Investigación Científica y de Educación Superior de Ensenada-CICESE. Ensenada 22860, México
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
| | - Nicola Nedev
- Universidad Autónoma de Baja California, Instituto de Ingeniería, Blvd. Benito Juárez s/n, C.P. 21280, Mexicali 21280, Baja California, México
| | - Mario H Farías
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
| | - Hugo Tiznado
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología (CNyN), Km 107 Carretera Tijuana-Ensenada s/n, C.P. 22800, Ensenada 04510, Baja California, México
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3
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Paez-Ornelas JI, Fernández-Escamilla HN, Borbón-Nuñez HA, Tiznado H, Takeuchi N, Guerrero-Sánchez J. A first-principles study of the atomic layer deposition of ZnO on carboxyl functionalized carbon nanotubes: the role of water molecules. Phys Chem Chem Phys 2021; 23:3467-3478. [PMID: 33507181 DOI: 10.1039/d0cp05283c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The formation of heterostructures that combine a large surface area with high surface activity has attracted the attention of the scientific community due to the unique properties and applications of these heterostructures. In this work, we describe - at the atomic level - the full reaction mechanisms involved in the atomic layer deposition of a hybrid ZnO/CNT inorganic structure. First, the pristine CNTs are chemically activated with a carboxylic acid, a process unique to carbon materials. Diethylzinc (DEZ) and water are used as gas-phase precursors to form ZnO. Our findings show that DEZ is physically adsorbed on the CNTs during the exposure of the first precursor. The ligand-exchange to generate chemisorbed ethyl zinc on the O side of the COOH group needs to overcome an energy barrier of 0.06 eV. This is a very small energy if compared to the values (0.5-0.6 eV) obtained in previous studies for OH functionalized surfaces. The height of the barrier is associated with the C[double bond, length as m-dash]O side, which mediates the H proton's exchange from the OH group to the C2H5 ligand. Furthermore, upon exposure to the oxidizing agent (H2O), ethyl zinc exchanges its last ligand as ethane, and it accepts a hydroxyl group through a self-limiting reaction with an energy barrier of 0.88 eV. Notice that the energy barrier of the second ligand-exchange is larger than of the first. We have also analyzed the effect in the saturation of the second precursor: as the quantity of water molecules increases, the long-range interactions tend to repel them. However, the energy barrier of the second ligand-exchange decreases from 1.53 eV to 0.88 eV for one and two water molecules, showing a clear dependence on the oxidizing agent. Non-covalent interactions are used as a tool to visualize the driving forces that take place during each partial reaction in real space. Our study points out the importance of using the right functionalization agent to achieve a controlled and conformal ALD growth at the initial steps of the formation of hybrid ZnO/CNT structures, as well as the role played by the oxidizing agent to lower the energy barrier on the second ALD step.
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Affiliation(s)
- J I Paez-Ornelas
- Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera, Tijuana-Ensenada 3918, Apdo. Postal 22860, Ensenada, B.C., Mexico
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López-Medina J, Carvalho WOF, Vazquez-Arce J, Moncada-Villa E, Oliveira ON, Farías MH, Tiznado H, Mejía-Salazar JR. Refractive index of ZnO ultrathin films alternated with Al 2O 3 in multilayer heterostructures. Nanotechnology 2020; 31:505715. [PMID: 33025922 DOI: 10.1088/1361-6528/abb42f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The design of optoelectronic devices made with ZnO superlattices requires the knowledge of the refractive index, which currently can be done only for films thicker than 30 nm. In this work, we present an effective medium approach to determine the refractive index of ZnO layers as thin as 2 nm. The approach was implemented by determining the refractive index of ZnO layers ranging from 2 nm to 20 nm using spectroscopic ellipsometry measurements in multilayers. For a precise control of morphology and thickness, the superlattices were fabricated with atomic layer deposition (ALD) with alternating layers of 2 nm thick Al2O3 and ZnO, labeled as N ZnO-Al2O3, where N = 10, 20, 30, 50, 75 and 100. The total thickness of all superlattices was kept at 100 nm. The approach was validated by applying it to similar superlattices reported in the literature and fitting the transmittance spectra of the superlattices.
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Affiliation(s)
- J López-Medina
- CONACYT - Centro de Nanociencias y Nanotecnología, UNAM. Km 107 Carretera Tijuana-Ensenada s/n. B.C., C.P. 22800, México
| | - William O F Carvalho
- National Institute of Telecommunications (Inatel), 37540-000, Santa Rita do Sapucaí, MG, Brazil
| | - J Vazquez-Arce
- Centro de Investigación Científica y Educación Superior de Ensenada-CICESE. Ensenada, 22860, México
| | - E Moncada-Villa
- Escuela de Física, Universidad Pedagógica y Tecnológica de Colombia, Avenida Central del Norte 39-115, Tunja, Colombia
| | - Osvaldo N Oliveira
- Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970, São Carlos, SP, Brazil
| | - M H Farías
- Universidad Nacional Autónoma de México, Centro de Nanociencias y Nanotecnología, Km 107 Carretera Tijuana-Ensenada s/n, Ensenada, B.C., C.P. 22800, México
| | - H Tiznado
- Universidad Nacional Autónoma de México, Centro de Nanociencias y Nanotecnología, Km 107 Carretera Tijuana-Ensenada s/n, Ensenada, B.C., C.P. 22800, México
| | - J R Mejía-Salazar
- National Institute of Telecommunications (Inatel), 37540-000, Santa Rita do Sapucaí, MG, Brazil
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Garibo D, Borbón-Nuñez HA, de León JND, García Mendoza E, Estrada I, Toledano-Magaña Y, Tiznado H, Ovalle-Marroquin M, Soto-Ramos AG, Blanco A, Rodríguez JA, Romo OA, Chávez-Almazán LA, Susarrey-Arce A. Green synthesis of silver nanoparticles using Lysiloma acapulcensis exhibit high-antimicrobial activity. Sci Rep 2020; 10:12805. [PMID: 32732959 PMCID: PMC7393152 DOI: 10.1038/s41598-020-69606-7] [Citation(s) in RCA: 143] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Accepted: 07/15/2020] [Indexed: 01/01/2023] Open
Abstract
The scientific community is exploiting the use of silver nanoparticles (AgNPs) in nanomedicine and other AgNPs combination like with biomaterials to reduce microbial contamination. In the field of nanomedicine and biomaterials, AgNPs are used as an antimicrobial agent. One of the most effective approaches for the production of AgNPs is green synthesis. Lysiloma acapulcensis (L. acapulcensis) is a perennial tree used in traditional medicine in Mexico. This tree contains abundant antimicrobial compounds. In the context of antimicrobial activity, the use of L. acapulcensis extracts can reduce silver to AgNPs and enhance its antimicrobial activity. In this work, we demonstrate such antimicrobial activity effect employing green synthesized AgNPs with L. acapulcensis. The FTIR and LC-MS results showed the presence of chemical groups that could act as either (i) reducing agents stabilizing the AgNPs or (ii) antimicrobial capping agents enhancing antimicrobial properties of AgNPs. The synthesized AgNPs with L. acapulcensis were crystalline with a spherical and quasi-spherical shape with diameters from 1.2 to 62 nm with an average size diameter of 5 nm. The disk diffusion method shows the magnitude of the susceptibility over four pathogenic microorganisms of clinical interest. The antimicrobial potency obtained was as follows: E. coli ≥ S. aureus ≥ P. aeruginosa > C. albicans. The results showed that green synthesized (biogenic) AgNPs possess higher antimicrobial potency than chemically produced AgNPs. The obtained results confirm a more significant antimicrobial effect of the biogenic AgNPs maintaining low-cytotoxicity than the AgNPs produced chemically.
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Affiliation(s)
- Diana Garibo
- Cátedras Conacyt-Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Departamento de Microbiología, Ensenada, Baja California, México. .,Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México.
| | - Hugo A Borbón-Nuñez
- Cátedras Conacyt-Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, México
| | - Jorge N Díaz de León
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México
| | - Ernesto García Mendoza
- Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Baja California, México
| | - Iván Estrada
- Cátedras Conacyt-Centro de Investigación en Materiales Avanzados S.C. (CIMAV), Departamento de Ingeniería de Materiales y Química, Chihuahua, México
| | - Yanis Toledano-Magaña
- Universidad Autónoma de Baja California (UABC), Escuela de Ciencias de la Salud, Unidad Valle Dorado, Ensenada, México
| | - Hugo Tiznado
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México
| | - Marcela Ovalle-Marroquin
- Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Ensenada, Baja California, México
| | | | - Alberto Blanco
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México
| | - José A Rodríguez
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México
| | - Oscar A Romo
- Universidad Nacional Autónoma de México (UNAM), Centro de Nanociencias y Nanotecnología, Ensenada, Baja California, México
| | - Luis A Chávez-Almazán
- Secretaría de Salud de Guerrero, Banco de Sangre Regional Zona Centro, Chilpancingo de los Bravo, Guerrero, México
| | - Arturo Susarrey-Arce
- Mesoscale Chemical Systems, MESA+ Institute, University of Twente, Drienerlolaan 5, 7522 NB, Enschede, The Netherlands
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Guerrero-Sánchez J, Borbon-Nunez HA, Tiznado H, Takeuchi N. Understanding the first half-ALD cycle of the ZnO growth on hydroxyl functionalized carbon nanotubes. Phys Chem Chem Phys 2020; 22:15333-15339. [PMID: 32409803 DOI: 10.1039/d0cp00817f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report the adsorption of diethylzinc on hydroxyl functionalized carbon nanotubes. This study intends to understand, at the atomic level, the initial stages of ZnO formation by atomic layer deposition. Our study begins with the molecule physisorbed on the nanotube (initial state of the reaction). The final state of this reaction is when the H atom of the hydroxyl group is abstracted and migrates to one ethyl group of diethylzinc. The oxygen atom relaxes towards the nanotube and forms a strong bond with a carbon atom, while the remaining part of the molecule forms a bond with the H atom and physisorbs on top of the ZnO unit. The probability for this process to happen is very high since the energy to desorb the diethylzinc molecule is higher than the energy needed to break down the O-H bond. Non-covalent interactions and charge density distributions are plotted to confirm the break-down, formation of bonds, and repulsion during the reaction pathway.
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Affiliation(s)
- J Guerrero-Sánchez
- Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Apartado Postal 14, Ensenada Baja California, Código Postal 22800, Mexico.
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Romero-Núñez A, Gómez-Cortés A, Tiznado H, Díaz G. Ni-doped ceria nanorods for the WGS reaction: Effect of Ni distribution in methane suppression. Catal Today 2020. [DOI: 10.1016/j.cattod.2018.09.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Soto G, Pahuamba E, Ramírez F, Cruz-Reyes J, del Valle M, Tiznado H. Swirling fluidized bed plasma reactor for the preparation of supported nanoparticles. RQUIM 2019. [DOI: 10.24275/rmiq/mat886] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Can-Uc B, López J, Lizarraga-Medina EG, Borbon-Nuñez HA, Rangel-Rojo R, Marquez H, Tiznado H, Jurado-González JA, Hirata-Flores G. Third-order nonlinear optical properties of a multi-layer Al 2O 3/ZnO for nonlinear optical waveguides. Opt Express 2019; 27:17359-17368. [PMID: 31252946 DOI: 10.1364/oe.27.017359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 05/10/2019] [Indexed: 06/09/2023]
Abstract
This is a report of a study of the nonlinear optical properties of samples based on multiple Al2O3/ZnO bilayers fabricated by atomic layer deposition (ALD) in silica. The multi-layer configuration for samples consists of alternated layers of constant thickness of Al2O3 (Δx) and ZnO (Δy) nanolaminates with a total thickness of ∼ 500 nm. The physical properties of the samples were characterized by means of TEM, spectrophotometry and variable angle spectroscopic ellipsometry. The absorptive and refractive contributions to the nonlinearity of the samples were studied by means of z-scan technique using a 100 fs at 800 nm. The nonlinear parameters, β and n2, are studied using different values of the layers thickness, Δx and Δy, in the nanolaminated stack. The possible applications in optical signal processing system are discussed by means of the figures of merit W and T.
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Fuentes I, Rodriguez JL, Tiznado H, Romo-Herrera JM, Chairez I, Poznyak T. Terephthalic acid decomposition by photocatalytic ozonation with V xO y/ZnO under different UV-A LEDs distributions. CHEM ENG COMMUN 2019. [DOI: 10.1080/00986445.2019.1581617] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Affiliation(s)
- Iliana Fuentes
- Lab. de Ing. Química Ambiental, ESIQIE—Instituto Politécnico Nacional, Zacatenco, México, México
- UPIBI—Instituto Politécnico Nacional, Ticomán, Unidad Profesional Interdisciplinaria de Biotecnología, México, México
| | - Julia L. Rodriguez
- Lab. de Ing. Química Ambiental, ESIQIE—Instituto Politécnico Nacional, Zacatenco, México, México
| | - Hugo Tiznado
- Centro de Nanociencias y Nanotecnología CNyN Universidad Nacional Autónoma de México, Carretera Tijuana a Ensenada, Ensenada, Baja California, México
| | - José M. Romo-Herrera
- Centro de Nanociencias y Nanotecnología CNyN Universidad Nacional Autónoma de México, Carretera Tijuana a Ensenada, Ensenada, Baja California, México
| | - Isaac Chairez
- UPIBI—Instituto Politécnico Nacional, Ticomán, Unidad Profesional Interdisciplinaria de Biotecnología, México, México
| | - Tatyana Poznyak
- Lab. de Ing. Química Ambiental, ESIQIE—Instituto Politécnico Nacional, Zacatenco, México, México
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11
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Contreras E, Dominguez D, Tiznado H, Guerrero-Sanchez J, Takeuchi N, Alonso-Nunez G, Contreras OE, Oropeza-Guzmán MT, Romo-Herrera JM. N-Doped carbon nanotubes enriched with graphitic nitrogen in a buckypaper configuration as efficient 3D electrodes for oxygen reduction to H 2O 2. Nanoscale 2019; 11:2829-2839. [PMID: 30676594 DOI: 10.1039/c8nr08384c] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Herein, a series of N-doped carbon nanotube (CNx) samples were obtained by modifying the synthesis temperature. Consequently, the proportion of graphitic nitrogen (Ngraph) in the samples was systematically increased as a function of temperature. This allowed evaluation of the role of the CNx graphitic nitrogen in the oxygen reduction reaction (ORR). A correlation between the Ngraph content and the ORR onset potential was observed, which shifted to more positive potentials with an increase in kinetic current density (jk); this showed that Ngraph played a significant catalytic role in the ORR. The samples with high Ngraph content favored the two-electron pathway for the ORR not only in basic media (pH = 13) but also in neutral media (pH = 7), representing an attractive alternative for wastewater remediation through the on-site generation of H2O2. The energetic calculations showed that the formation of H2O2 must be favorable in the presence of graphitic nitrogen sites. Finally, the performance of the buckypaper arrangement was evaluated, and the CNx buckypaper showed a higher cathodic current peak as compared to CNx traditional ink dispersions. Overall, this study not only sheds light on the role of Ngraph in the ORR, but also demonstrates that CNx buckypaper is an efficient 3D electrode for electrocatalytic applications.
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Affiliation(s)
- Enrique Contreras
- Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Posgrado en Ciencias en Nanociencias, Carretera Ensenada-Tijuana No. 3918, Zona Playitas, CP 22860, Ensenada, BC, Mexico
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12
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Aguilar CM, Chairez I, Rodríguez JL, Tiznado H, Santillán R, Arrieta D, Poznyak T. Inhibition effect of ethanol in naproxen degradation by catalytic ozonation with NiO. RSC Adv 2019; 9:14822-14833. [PMID: 35516308 PMCID: PMC9064194 DOI: 10.1039/c9ra02133g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 05/07/2019] [Indexed: 12/07/2022] Open
Abstract
This work evaluated the inhibition effect of low molecular weight alcohol (ethanol) on naproxen (NAP) degradation by conventional and catalytic ozonation. The reaction system considered the ethanol as complementary organic matter in water. The conventional ozonation and in the presence of nickel oxide (O3–NiO) achieved 98% NAP degradation during the first 15 min of reaction despite the presence of ethanol. However, NAP degradation presented a delaying effect during the first minutes of treatment with this alcohol. The latter phenomenon indicates that ethanol concentration played a meaningful role in ozonation effectiveness in comparison with the presence of NiO catalyst. The presence of NiO did not generate differences in the byproducts in comparison with conventional ozonation. The intermediates were detected using the Electrospray Ionization Mass Spectrometry technique and have only one aromatic ring in their chemical structure. In samples without ethanol, these byproducts appeared only in the first 5 min of reaction. The TOC study demonstrated the increment of 25% in the mineralization degree with the presence of NiO due to the formation of ·OH species. Ethanol concentration as organic matter delayed the NAP elimination and O3–NiO increased the mineralization degree and oxidation state of byproducts.![]()
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Affiliation(s)
| | - Isaac Chairez
- Departamento de Bioprocesos
- UPIBI-Instituto Politécnico Nacional
- 07340 Mexico
- Mexico
| | | | - Hugo Tiznado
- Universidad Nacional Autónoma de Mexico
- Centro de Nanociencias y Nanotecnología
- 22860 Ensenada
- Mexico
| | - Ricardo Santillán
- Lab. de polímeros
- ESIQIE-Instituto Politécnico Nacional
- 07738 Mexico
- Mexico
| | - Daniel Arrieta
- Centro de Nanociencias y Micro y Nanotecnologías CNMN-Instituto Politécnico Nacional
- 07738 Mexico
- Mexico
| | - Tatiana Poznyak
- Lab. Ing. Química Ambiental
- ESIQIE-Instituto Politécnico Nacional
- 07738 Mexico
- Mexico
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13
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Aguilar CM, Rodríguez JL, Chairez I, Tiznado H, Poznyak T. Naphthalene degradation by catalytic ozonation based on nickel oxide: study of the ethanol as cosolvent. Environ Sci Pollut Res Int 2017; 24:25550-25560. [PMID: 26832864 DOI: 10.1007/s11356-016-6134-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 01/19/2016] [Indexed: 06/05/2023]
Abstract
Naphthalene (NA) is a polycyclic aromatic hydrocarbon with toxic properties in aquatic systems. Ozonation (O3) and catalytic ozonation (O3-cat) processes are attractive alternatives of degradation for this kind of compound. NA (20 mg L-1) degradation by conventional and catalytic ozonation in the presence of a cosolvent (ethanol) was the aim of this study. This solution was proposed to simulate some aspects of real wastewaters where not only water acts as solvent. Two proportions of the mixture ethanol/water were selected (30:70 and 50:50) with the purpose of studying the cosolvent effect on NA degradation system by ozonation. O3-cat process used nickel oxide as catalyst (0.1 g L-1). The degradation analysis of NA by O3-cat in two different proportions of cosolvent showed that in the case of 30:70 (ethanol/water), a 95 % of NA elimination in 60 min was obtained, while in the case 50:50 (ethanol/water), only 55 % was achieved. The O3 process showed similar results of degradation to the initial compound in comparison with catalytic system. According to these results, there is an inhibition effect in pollutant removal by ethanol due to the higher ethanol concentration; the lower elimination rate of NA was obtained (by 40 % during the 60 min). The by-products analysis of ozonation process detected oxalic and formic acids. Treatments with NiO presented less production of organic acids in comparison with conventional ozonation process. The high concentration of ethanol has a relevant factor in the elimination of NA and formation of organic acids; samples with 50 % of cosolvent have showed a higher concentration of organic acids. X-ray photoelectron spectroscopy (XPS) study of O3-cat of diluent (O3-NiO control) and O3-NA-NiO showed the presence of -CO3 absorbed on catalyst due to ethanol decomposition.
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Affiliation(s)
- C Marissa Aguilar
- Departamento de Bioprocesos, UPIBI-Instituto Politécnico Nacional, Ticoman, 07340, México, D.F., México
| | - Julia L Rodríguez
- Lab. Ing. Química Ambiental, ESIQIE-Instituto Politécnico Nacional, Zacatenco, 07738, México, D.F., México.
| | - Isaac Chairez
- Departamento de Bioprocesos, UPIBI-Instituto Politécnico Nacional, Ticoman, 07340, México, D.F., México
| | - Hugo Tiznado
- Universidad Nacional Autónoma de México, Centro de Nanociencias y Nanotecnología, Km. 107 Carretera Tijuana a Ensenada, 22860, Ensenada, Baja California, México
| | - Tatyana Poznyak
- Lab. Ing. Química Ambiental, ESIQIE-Instituto Politécnico Nacional, Zacatenco, 07738, México, D.F., México
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14
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Romo-Herrera JM, Contreras OE, Domínguez D, Rodríguez JR, Alonso-Nuñez G, Muñoz-Muñoz F, Tiznado H. Insulating Carbon Nanotubes by Atomic Layer Deposition for Electrical Wiring Purposes. J Nanosci Nanotechnol 2015; 15:6774-6778. [PMID: 26716242 DOI: 10.1166/jnn.2015.10331] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Carbon Nanotubes (CNTs) are coated by an insulator (Al2O3) shell using the atomic layer deposition (ALD) technique. This is achieved in large quantities (tens of milligrams per batch) for electrical wiring purposes. Here we present a transmission electron microscopy (TEM) characterization together with a detailed high resolution elemental analysis by in-column energy dispersive X-ray spectroscopy (EDXS). An excellent conformality of the insulator around the CNTs is obtained. Moreover, the elemental maps show the composition of the shell while the line scan analyses demonstrate an abrupt shell-CNT interface achieved by our ALD approach.
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15
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González EAZ, García-Guaderrama M, Villalobos MR, Dellamary FL, Kandhual S, Rout NP, Tiznado H, Arizaga GGC. Potassium titanate as heterogeneous catalyst for methyl transesterification. POWDER TECHNOL 2015. [DOI: 10.1016/j.powtec.2015.04.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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16
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Tiznado H, Domínguez D, Muñoz-Muñoz F, Romo-Herrera J, Machorro R, Contreras O, Soto G. Pulsed-bed atomic layer deposition setup for powder coating. POWDER TECHNOL 2014. [DOI: 10.1016/j.powtec.2014.07.034] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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17
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Rodríguez JL, Valenzuela MA, Tiznado H, Poznyak T, Flores E. Synthesis of nickel oxide nanoparticles supported on SiO2 by sensitized liquid phase photodeposition for applications in catalytic ozonation. ACTA ACUST UNITED AC 2014. [DOI: 10.1016/j.molcata.2014.04.028] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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18
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Durán A, Tiznado H, Romo-Herrera JM, Domínguez D, Escudero R, Siqueiros JM. Nanocomposite YCrO3/Al2O3: Characterization of the Core–Shell, Magnetic Properties, and Enhancement of Dielectric Properties. Inorg Chem 2014; 53:4872-80. [DOI: 10.1021/ic4029589] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- A. Durán
- Universidad Nacional Autónoma de México, Centro de Nanociencias y
Nanotecnología, Km. 107 Carretera Tijuana-Ensenada, Apartado Postal
14, C. P. 22800, Ensenada, B. C. México
| | - H. Tiznado
- Universidad Nacional Autónoma de México, Centro de Nanociencias y
Nanotecnología, Km. 107 Carretera Tijuana-Ensenada, Apartado Postal
14, C. P. 22800, Ensenada, B. C. México
| | - J. M. Romo-Herrera
- Universidad Nacional Autónoma de México, Centro de Nanociencias y
Nanotecnología, Km. 107 Carretera Tijuana-Ensenada, Apartado Postal
14, C. P. 22800, Ensenada, B. C. México
| | - D. Domínguez
- Universidad Nacional Autónoma de México, Centro de Nanociencias y
Nanotecnología, Km. 107 Carretera Tijuana-Ensenada, Apartado Postal
14, C. P. 22800, Ensenada, B. C. México
| | - R. Escudero
- Universidad Nacional Autónoma de México, Instituto
de Investigaciones en Materiales, Apartado
Postal 70-360, México, D. F. 04510, México
| | - J. M. Siqueiros
- Universidad Nacional Autónoma de México, Centro de Nanociencias y
Nanotecnología, Km. 107 Carretera Tijuana-Ensenada, Apartado Postal
14, C. P. 22800, Ensenada, B. C. México
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19
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Rodríguez JL, Valenzuela MA, Pola F, Tiznado H, Poznyak T. Photodeposition of Ni nanoparticles on TiO2 and their application in the catalytic ozonation of 2,4-dichlorophenoxyacetic acid. ACTA ACUST UNITED AC 2012. [DOI: 10.1016/j.molcata.2011.11.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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20
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Soto G, Tiznado H, Contreras O, Pérez-Tijerina E, Cruz-Reyes J, Del Valle M, Portillo A. Preparation of a Ag/SiO2 nanocomposite using a fluidized bed microwave plasma reactor, and its hydrodesulphurization and Escherichia coli bactericidal activities. POWDER TECHNOL 2011. [DOI: 10.1016/j.powtec.2011.07.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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21
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Camarena JP, Espinoza-Gómez H, Somanathan R, Tiznado H, Vélez-López E, Romero-Rivera R, Martínez-López MA, Avalos-Borja M, Bek A, Alonso-Nuñez G, Rogel-Hernández E. Molecular assembly of multi-wall carbon nanotubes with amino crown ether: synthesis and characterization. J Nanosci Nanotechnol 2011; 11:5539-5545. [PMID: 21770216 DOI: 10.1166/jnn.2011.3430] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Synthetic methodology and physicochemical characterization of multi-wall carbon nanotubes (MWCNTs) functionalized with a crown ether molecule is reported. The MWCNTs were synthesized by spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. The nanotubes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxidation of MWCNTs was carried out by 8 h of sonication in a mixture of sulfuric and nitric acid (3:1). The MWCNT-COOH was amidated with 4-aminobenzo-15-crown-5 under mild reaction conditions using N,N'-dicyclohexylcarbodiimide and dimethylaminopyridine as catalyst and dimethylformamide as solvent, at room temperature for 24 h. The amidation product was characterized by scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a mass spectrometry study to determine the fragmentation pattern being m/z 309, 177 and 149 the most important ions.
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Affiliation(s)
- J P Camarena
- Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Ave. Calzada Tecnológico 14418 Mesa de Otay, Tijuana, CP 22390, BC, México
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22
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Lew CM, Liu Y, Day B, Kloster GM, Tiznado H, Sun M, Zaera F, Wang J, Yan Y. Hydrofluoric-acid-resistant and hydrophobic pure-silica-zeolite MEL low-dielectric-constant films. Langmuir 2009; 25:5039-5044. [PMID: 19344154 DOI: 10.1021/la803956w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A new technique for the silylation of pure-silica-zeolite MEL low-k films has been developed in which the spin-on films are calcined directly in trimethylchlorosilane or 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in order to protect the films against corrosive wet etch chemicals and ambient moisture adsorption. In an alternative procedure, HMDS is also added to the zeolite suspension before film preparation. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, water-soak tests, and HF etch tests are performed to characterize the films. The dielectric constant is as low as 1.51, and the films resist HF attack up to 5.5 min. These properties are highly desirable by the semiconductor industry for next-generation microprocessors.
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Affiliation(s)
- Christopher M Lew
- Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, California, USA
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23
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Tiznado H, Bouman M, Kang BC, Lee I, Zaera F. Mechanistic details of atomic layer deposition (ALD) processes for metal nitride film growth. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.molcata.2007.06.010] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Abstract
The surface chemistry of atomic layer depositions (ALD) of titanium nitride films using alternate doses of TiCl4 and NH3 was characterized by using X-ray photoelectron spectroscopy. The nature of the species deposited by each half-reaction was explored first. Evidence was obtained for the partial loss of chlorine atoms and the reduction of the metal during the adsorption of the TiCl4. Subsequent ammonia treatment removes most of the remaining chlorine and leads to the formation of a nitride. Both half-reactions were proven self-limited, stopping after the deposition of submonolayer quantities of the materials. Repeated ALD cycles were shown to lead to the buildup of thick films. However, those films display a Ti3N4 layer on top of the expected TiN. The data suggest that the reduction of the Ti4+ species may therefore occur during the TiCl4, not NH3, dosing step. The incorporation of impurities in the films was also investigated. Chlorine is only deposited on the surface, and in negligible quantities. This Cl appears to originate from readsorption of the HCl byproduct, and could be removed by light sputtering, heating, or further ammonia treatment. Oxygen incorporation, on the other hand, was unavoidable and was determined to possibly come from diffusion from the underlying substrate.
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Affiliation(s)
- Hugo Tiznado
- Department of Chemistry, University of California, Riverside, California 92521, USA
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25
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Jiao J, Anariba F, Tiznado H, Schmidt I, Lindsey JS, Zaera F, Bocian DF. Stepwise Formation and Characterization of Covalently Linked Multiporphyrin−Imide Architectures on Si(100). J Am Chem Soc 2006; 128:6965-74. [PMID: 16719477 DOI: 10.1021/ja060906q] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A major challenge in molecular electronics and related fields entails the fabrication of elaborate molecular architectures on electroactive surfaces to yield hybrid molecular/semiconductor systems. A method has been developed for the stepwise synthesis of oligomers of porphyrins linked covalently via imide units. A triallyl-porphyrin bearing an amino group serves as the base unit on Si(100), and the alternating use of a dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) and a porphyrin-diamine for reaction enables the rapid and simple buildup of oligomers composed of 2-5 porphyrins. The properties of these porphyrin "multad" films on Si(100) were interrogated using a variety of techniques. The charge densities of the redox-active porphyrin oligomers were determined via electrochemical methods. The stepwise growth was evaluated in detail via Fourier transform infrared (FTIR) spectroscopy and by selected X-ray photoelectron spectroscopic (XPS) studies. The morphology was probed via AFM methods. Finally, the thickness was evaluated by using a combination of ellipsometry and AFM height profiling, accompanied by selected XPS studies. Collectively, these studies demonstrate that high charge density, ultrathin, multiporphyrin films of relatively well-controlled thickness can be grown in a stepwise fashion using the imide-forming reaction. The increased charge densities afforded by the porphyrin multads may prove important for the fabrication of molecular-based information-storage devices. This bottom-up process for construction of surface-tethered molecular architectures complements the top-down lithographic approach for construction of functional devices with nanoscale dimensions.
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Affiliation(s)
- Jieying Jiao
- Department of Chemistry, University of California, Riverside, CA 92521-0403, USA
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26
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Wei L, Tiznado H, Liu G, Padmaja K, Lindsey JS, Zaera F, Bocian DF. Adsorption Characteristics of Tripodal Thiol-Functionalized Porphyrins on Gold. J Phys Chem B 2005; 109:23963-71. [PMID: 16375385 DOI: 10.1021/jp0537005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
X-ray photoelectron and Fourier transform infrared spectroscopy studies are reported for self-assembled monolayers (SAMs) of two tripodal thiol-functionalized metalloporphyrins (Zn and Cu) and three benchmark tripods on gold substrates. The tripodal unit common to all five molecules is 1-(phenyl)-1,1,1-tris(4-mercaptomethylphenyl)methane (Tpd). Both porphyrins contain S-acetyl-protected thiols and are linked to the 4-position of the phenyl ring of Tpd via a phenylethyne group. The benchmark molecules include (1) two tripods containing a bromine atom at the 4-position of the apical phenyl ring, one a free thiol and the other its S-acetyl-protected analogue, and (2) a S-acetyl-protected tripod containing a phenylethyne unit at the 4-position of the apical phenyl group. Together, the spectroscopic studies reveal that none of the five tripodal molecules bond to the gold surface via all three sulfur atoms. Instead, the average number of bound thiols ranges from 1.5 to 2, with the porphyrinic molecules generally falling at the middle to upper end of the range and the smallest benchmark tripods falling at the lower end. Similar surface binding is found for the S-acetyl-protected and free benchmark tripods, indicating that the presence of the protecting group does not influence binding. Furthermore, the surface binding characteristics of the SAMs are not sensitive to deposition conditions such as solvent type, deposition time, or temperature of the solution.
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Affiliation(s)
- Lingyun Wei
- Department of Chemistry, University of California, Riverside, California 92521-0403, USA
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27
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Abstract
Characterization of palladium catalysts, supported on alumina and alumina modified by zirconia added by impregnation, was performed by CO adsorption from 143 to 298 K and monitored by infrared spectroscopy. It was found that the population of the Al3+ octahedral sites in the alumina decreased by the addition of zirconia. In contrast to the case of the pure alumina support, where stabilization of Pd+ was observed, Pd2+ was formed preferentially on samples where zirconia was added, and higher crystallinity in the metallic palladium was observed. Studies of CO adsorption at low temperatures (143 K) gave a better description of the surface species, since at higher temperatures (298 K) the reaction of the CO with some of the palladium oxide particles led to the partial reduction of the latter.
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Affiliation(s)
- Hugo Tiznado
- Programa de Posgrado en Física de Materiales, CICESE, Ensenada, B.C. 22860, Mexico.
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28
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Roth KM, Yasseri AA, Liu Z, Dabke RB, Malinovskii V, Schweikart KH, Yu L, Tiznado H, Zaera F, Lindsey JS, Kuhr WG, Bocian DF. Measurements of electron-transfer rates of charge-storage molecular monolayers on Si(100). Toward hybrid molecular/semiconductor information storage devices. J Am Chem Soc 2003; 125:505-17. [PMID: 12517164 DOI: 10.1021/ja021169a] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Redox kinetics were measured for two electroactive molecules attached to Si(100) surfaces, a ferrocene (Fc-BzOH) and a Zn(II) trimesitylporphyrin (Por-BzOH). Each molecule was derivatized with a benzyl alcohol linker for attachment to the Si surface via the formation of a Si-O bond. A complete protocol was developed for the preparation of stable Si(100) surfaces derivatized with the electroactive molecules. The redox-kinetic measurements were performed on the resulting Fc-BzOH and Por-BzOH monolayers to probe (1) the rate of electron transfer (k0) for oxidation in the presence of applied potentials and (2) the rate of charge dissipation after the applied potential is disconnected (in the form of a charge-retention half-life t1/2). The k0 values for the two types of monolayers were found to be similar to one another as were the t1/2 values. Perhaps more importantly, the electron-transfer rates for both the Fc-BzOH and the Por-BzOH monolayers differ from the charge-dissipation rates by approximately 6 orders of magnitude and are strongly dependent on the surface concentration of the electroactive species. For the Por-BzOH monolayers on Si(100), the k0 and t1/2 values and their trends as a function of surface coverage were determined to be similar to those previously measured for the analogous thiol-derivatized molecule assembled on Au(111). In contrast, the Fc-BzOH monolayers on Si(100) were found to exhibit much slower electron-transfer and charge-dissipation rates than those in the corresponding thiol-Au(111) case. Two alternative hypotheses are advanced to explain both the diminution in rates with increased surface coverage and the contrasting behavior with the analogous thiols on Au, one based on space-charge effects at the monolayer-solution interface, and a second relying on changes in distance of the redox centers from the surface as modulated by the orientation of the linking chains. Collectively, the ability to prepare and study stable, electroactive molecular media on Si(100) is likely to be key in the development of hybrid molecular/semiconductor devices.
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Affiliation(s)
- Kristian M Roth
- Department of Chemistry, University of California, Riverside 92521-0403, USA
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