Umapada Pal
(Benemérita) Universidad Autónoma de Puebla, Physics Department, Faculty Member
- Professor, Autonomous University of Puebla, Mexico, work on nanomaterials (all type) and their applicationsedit
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Graphene oxide (GO) was prepared by modified Hummer's method to produce reduced graphene oxide (RGO) following standard thermal and chemical reduction processes. Prepared RGO colloids were utilized to fabricate RGO films over glass... more
Graphene oxide (GO) was prepared by modified Hummer's method to produce reduced graphene oxide (RGO) following standard thermal and chemical reduction processes. Prepared RGO colloids were utilized to fabricate RGO films over glass and FTO coated glass substrates through drop-coating. A systematic study was performed to evaluate the effect of reduction degree on the optical and electrical properties of the RGO film. We demonstrate that both the reduction process (thermal and chemical) produce RGO films of similar optical and electrical behaviors. However, the RGO films fabricated using chemically reduced GO colloid render better performance in dye sensitized solar cells (DSSCs), when they are used as counter electrodes (CEs). It has been demonstrated that RGO films of optimum thicknesses fabricated using RGO colloids prepared using lower concentration of hydrazine reducer have better catalytic performance in DSSCs due to a better catalytic interaction with redox couple. The bett...
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Well-crystalline SnO2 nanoparticles of 4-5 nm size with different In contents were synthesized by hydrothermal process at relatively low temperature and characterized by transmission electron microscopy (TEM), microRaman spectroscopy and... more
Well-crystalline SnO2 nanoparticles of 4-5 nm size with different In contents were synthesized by hydrothermal process at relatively low temperature and characterized by transmission electron microscopy (TEM), microRaman spectroscopy and photoluminescence (PL) spectroscopy. Indium incorporation in SnO2 lattice is seen to cause a lattice expansion, increasing the average size of the nanoparticles. The fundamental phonon vibration modes of SnO2 lattice suffer a broadening, and surface modes associated to particle size shift gradually with the increase of In content. Incorporation of In drastically enhances the PL emission of SnO2 nanoparticles associated to deep electronic defect levels. Although In incorporation reduces the band gap energy of SnO2 crystallites only marginally, it affects drastically their dye degradation behaviors under UV illumination. While the UV degradation of methylene blue (MB) by undoped SnO2 nanoparticles occurs through the production of intermediate byproduc...
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Mixed oxide nanoparticles containing Ti, Si, and Al of 8-15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles... more
Mixed oxide nanoparticles containing Ti, Si, and Al of 8-15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microRaman spectroscopy, and diffuse reflectance spectroscopy (DRS). Dye removal abilities of the nanoparticles from aqueous solutions were tested for different cationic dyes. While all the mixed oxide nanoparticles revealed high and fast adsorption of cationic dyes, the particles containing Ti and Si turned out to be the best. The adsorption kinetics and equilibrium adsorption behavior of the adsorbate - adsorbent systems could be well described by pseudo-second-order kinetics and Langmuir isotherm model, respectively. Estimated thermodynamic parameters revealed the adsorption process is spontaneous, driven mainly by the electrostat...
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Understanding the variations of the near electric field around plasmonic nanoparticles is very important for several applications where the interactions occur close to the surface of the nanoparticle.
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The relation between the morphological and textural properties and the performance of ZnO-based dye-sensitized solar cells is explored using ZnO materials prepared by a sonochemical method as a function of pH.
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ZnO nanostructures containing doped with different atom % of Nb are fabricated through ultrasound assisted hydrolysis in water. Effects of Nd incorporation on the structure, morphology, defect structure, optical, and magnetic behaviors of... more
ZnO nanostructures containing doped with different atom % of Nb are fabricated through ultrasound assisted hydrolysis in water. Effects of Nd incorporation on the structure, morphology, defect structure, optical, and magnetic behaviors of the nanostructures have been studied utilizing X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy and magnetometry. We demonstrate that while Nb incorporation in ZnO nanostructures drastically modify their morphology and crystallinity, it does not affect the band gap energy of of ZnO significantly. While Nb incorporation in small concentration creates higher oxygen vacancy related defects in ZnO nanostructures, which are responsible for their visible emissions, incorporation of Nb in higher concentration reduces those defect structures from the band gap of the nanostructures. While oxygen vacancies have been frequently associated to the ferromagnetic behavior of ZnO nanostructures, our results indicate that a mere prese...
Fabrication of phase-pure well-crystalline BiFeO submicroparticles in large scale is of great importance for the utilization of this rhombohedrally distorted perovskite material in applications such as memory storage and spintronic... more
Fabrication of phase-pure well-crystalline BiFeO submicroparticles in large scale is of great importance for the utilization of this rhombohedrally distorted perovskite material in applications such as memory storage and spintronic devices and visible photocatalyst for the degradation of organic pollutants. In fact, because of the narrow temperature range of phase stabilization, the fabrication of phase-pure BiFeO in large scale remained elusive. We present the synthesis of phase-pure BiFeO particles of submicrometric dimensions (246-330 nm average size) through the adjustment of oxidizing/reducing agent ratio in solution combustion process utilizing glycine as reducing agent and nitrate precursors as oxidizing agent. Utilizing X-ray diffraction and Raman spectroscopy, we demonstrate that the BiFeO submicroparticles synthesized at equivalence ratio (Φ) close to 0.5 do not contain undesired impurities such as BiFeO and BiFeO. Moreover, the submicroparticles are highly crystalline, po...
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Through this brief review, we provide a comprehensive historical background of the development of nanostructured hydroxyapatite (nHAp), and its application potentials for controlled drug delivery, drug conjugation, and other biomedical... more
Through this brief review, we provide a comprehensive historical background of the development of nanostructured hydroxyapatite (nHAp), and its application potentials for controlled drug delivery, drug conjugation, and other biomedical treatments. Aspects associated with efficient utilization of hydroxyapatite (HAp) nanostructures such as their synthesis, interaction with drug molecules, and other concerns, which need to be resolved before they could be used as a potential drug carrier in body system, are discussed. This review focuses on the evolution of perceptions, practices, and accomplishments in providing improved delivery systems for drugs until date. The pioneering developments that have presaged today's fascinating state of the art drug delivery systems based on HAp and HAp-based composite nanostructures are also discussed. Special emphasis has been given to describe the application and effectiveness of modified HAp as drug carrier agent for different diseases such as b...
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A facile surfactant free wet-precipitation process was employed to prepare hydroxyapatite (HAp) nanoparticles.
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We study the optical response of eccentric nanoshells (i.e., spherical nanoparticles with an eccentric spherical inclusion) in the near and the far field through finite-difference time-domain simulations. Plasmon hybridization theory is... more
We study the optical response of eccentric nanoshells (i.e., spherical nanoparticles with an eccentric spherical inclusion) in the near and the far field through finite-difference time-domain simulations. Plasmon hybridization theory is used to explain the obtained results. The eccentricity generates a far-field optical spectrum with various plasmon peaks. The number, position, and width of the peaks depend on the core offset. Near-field enhancements in the surroundings of these structures are significantly larger than those obtained for equivalent concentric nanoshells and, more importantly, they are almost independent of the illumination conditions. This opens up the door for using eccentric nanoshells in applications requiring intense near-field enhancements.
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... U. Pal1,2*, O. V??zquez-Cuchillo3, A. Bautista-Hern??ndez2, and JF Rivas-Silva2 ... Phys. 76, 708 (1994). [7] GW Arnold, JA Border, J. Appl. Phys. 48, 1488 (1977). [8] U. Pal, A. Bautista-Hern??ndez, L. Rodr??guez-Fern??ndez, JC... more
... U. Pal1,2*, O. V??zquez-Cuchillo3, A. Bautista-Hern??ndez2, and JF Rivas-Silva2 ... Phys. 76, 708 (1994). [7] GW Arnold, JA Border, J. Appl. Phys. 48, 1488 (1977). [8] U. Pal, A. Bautista-Hern??ndez, L. Rodr??guez-Fern??ndez, JC Cheang-Wong, J. Non-Cryst. Sol. 275, 65 (2000). ...
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Here, we report the synthesis of uniform alpha-GaO(OH) nanorods on Si substrates at low temperature (200 degrees C) using solvothermal technique. alpha-GaO(OH) uniform nanorods is converted to beta-Ga2O3 after annealing at 900 degrees C... more
Here, we report the synthesis of uniform alpha-GaO(OH) nanorods on Si substrates at low temperature (200 degrees C) using solvothermal technique. alpha-GaO(OH) uniform nanorods is converted to beta-Ga2O3 after annealing at 900 degrees C under ambient atmosphere. A series of electron microscopy characterizations including scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) are used to understand the growth mechanism of alpha-GaO(OH) nanorods formation. This nanostructure emits defect-related strong PL emissions at blue (492 nm) and green (522 nm) regions and the relative intensities of these emissions peaks can be modified by varying the reaction conditions. Similarly, we also observed room temperature cathodoluminescence (CL) and the uniform CL contrast of the nanorods in their CL image indicates a homogeneous defect distribution along the nanorods.
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we have explored for the first time the structure of 1–2 nm bimetallic AuPd nanoparticles using HREM at a series of tilting angles from an electron beam. From the experiment, we observe that the addition of a second metal allows the... more
we have explored for the first time the structure of 1–2 nm bimetallic AuPd nanoparticles using HREM at a series of tilting angles from an electron beam. From the experiment, we observe that the addition of a second metal allows the nanoparticles to reach a quasispherical shape. That shape can be explained in terms of a dodecahedron, which is very close to a spherical shape along its fivefold axis. The majority of the particles in the experiment correspond to a dodecahedral shape. Also, monometallic DFT (Au) and EAM (Pd) calculations demonstrate that the structure is stable. Therefore the missing regular solid has been found. The shape for very small particles corresponds to a Platonic solid and larger particles correspond to Archimedean solids. We conclude that in the very small
size range of both mono- and bimetallic nanoparticles, the complete sequence of structures that is formed corresponds to the following sequence: atoms-clusters-Platonic solids-Archimedean solids, defected structures (twins, stacking faults, etc.), and finally bulk-like structures.
size range of both mono- and bimetallic nanoparticles, the complete sequence of structures that is formed corresponds to the following sequence: atoms-clusters-Platonic solids-Archimedean solids, defected structures (twins, stacking faults, etc.), and finally bulk-like structures.
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We predict general trends for surface segregation in binary metal clusters based on the difference between the atomic properties of the constituent elements. The energetically most favorable site for a guest atom on a pure metal cluster... more
We predict general trends for surface segregation in binary metal clusters based on the difference between the atomic properties of the constituent elements. The energetically most favorable site for a guest atom on a pure metal cluster is determined considering the attractive and repulsive contributions of the cohesive energy of an atom in the cluster. It is predicted that for adjacent elements in a period of the periodic table, the bimetallic system would be more stable if the component with smallest valence electron density is placed on the surface. On the other hand, in bimetallic clusters built with elements of only one group, the trend to be in the volume (of the atomic component with smaller core density) will be higher for that cluster with atomic components most separated in the group. Such chemical ordering trends in the lowest energy configurations of Pt-Au, Pt-Pd, and Pt-Ni binary alloy clusters are verified for their 561 atom systems through a simulated annealing process. Some of our atomistic predictions are verified through quantum mechanical calculations.
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The optical constants (the refractive index n and the absorption const'ant K ) and absorption coef-ficients CT are measured on CdTe thin films in the wavelength range 500 to 2000 nm. Some param-eters which affect these... more
The optical constants (the refractive index n and the absorption const'ant K ) and absorption coef-ficients CT are measured on CdTe thin films in the wavelength range 500 to 2000 nm. Some param-eters which affect these optical properties of thin films, such as the film thickness, ...
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... Ası mismo, la existencia de una banda de energıa prohibida (ver Fig. 5) nos demuestra el carácter semiconductor de los materiales AlP, GaAs y AlAs reportados en este estudio. ... Page 6. 14 A. BAUTISTA-HERN ´ANDEZ, L. P ÉREZ-ARRIETA,... more
... Ası mismo, la existencia de una banda de energıa prohibida (ver Fig. 5) nos demuestra el carácter semiconductor de los materiales AlP, GaAs y AlAs reportados en este estudio. ... Page 6. 14 A. BAUTISTA-HERN ´ANDEZ, L. P ÉREZ-ARRIETA, U. PAL, AND JF RIVAS-SILVA ...
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We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5–23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of... more
We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5–23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of the reaction mixture have been studied. Formation and growth dynamics of the Au nanoparticles in the colloids were studied using transmission electron microscopy and UV-Vis optical absorption spectroscopy techniques. While the reductor content and, hence, the nucleation and growth rates of the nanoparticles could be controlled by controlling the PE content in the reaction solution, the stability of the nanoparticles depended strongly on the pH of the reaction mixture. The mechanisms of Au ion reduction and stabilization of Au nanoparticles by potato starch have been discussed. The use of common natural solvent like water and biological reductor like PE in our synthesis process opens up the possibility of synthesizing Au nanoparticles in fully green (environmental friendly) way, and the Au nanoparticles produced in such way should have good biocompatibility.