Banca de QUALIFICAÇÃO: MARIA JOSEÍTA DOS SANTOS COSTA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE: MARIA JOSEÍTA DOS SANTOS COSTA
DATA: 03/03/2023
HORA: 08:30
LOCAL: Auditório Geratec - Universidade Estadual do Piauí
TÍTULO: Simple method for preparing CuWO4 photoelectrodes with p-type or n-type behavior: experimental and theoretical studies
PALAVRAS-CHAVES: doping semiconductor oxide; photoelectrodes; solar energy; copper tungstate; polymeric precursor method
PÁGINAS: 37
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Eletroquímica
RESUMO:

Solar water splitting is an alternative method to produce H₂ using sunlight and specialized semiconductors. Many semiconductor oxides have been used as photocatalysts in these reactions, and strategies have been developed to improve the efficiency of the catalytic process. Ionic doping in semiconductors is considered efficient strategy to enhance the charge transport and avoiding its rapid recombination. This study, a simple polymeric precursor method was employed for the fabrication of pristine copper tungstate (CuWO₄) film and that of varying doping concentration (1%, 3%, and 5%) of lithium (Li:CuWO₄) and magnesium (Mg:CuWO₄). Films were prepared from copper-tungsten citrate resin and thermal treated at 500°C/2h. The chemical composition, valence state, optical, morphological and structural properties of the synthesized materials were characterized using X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), diffuse reflectance spectroscopy (DRS), field emission–scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), respectively. Spherical shaped nanostructures were observed, just like confirmed triclinic structure and the presence of dopants with elongation of crystalline lattice. DRS spectra confirmed the chemical composition of films and greater evidence of the Mg dopant. The impurities occupied interstitial sites in the host CuWO₄ lattice and induced shift for lower optical band gap energy. The presence of dopants was clearly observed with photoelectrochemical response, modifying n-type behavior of host film for p-type in the doped CuWO₄ films. Pristine CuWO₄ electrodes reached higher anodic photocurrent density of 20 mA cm^-2 at 1.0 V vs. Ag/AgCl (0.1 mol L^-1 Na₂SO₄), while Li:CuWO₄ and Mg:CuWO₄ electrodes obtained higher cathodic photocurrent density of 123 and 78 mA cm^-2 at -0.4 V vs. Ag/AgCl (0.1 mol L^-1 Na₂SO₄),  respectively. Doping with Li or Mg in host CuWO₄ electrodes favored the inhibition of the charge recombination and efficient applied bias photon-to-current efficiency for hydrogen evolution reaction. Moreover, density functional theory (DFT) calculations were carried out to model structures and to understand theoretically the alterations of the doped CuWO­₄ structures experimentally obtained, besides electronic properties from the analysis of density of states (DOS) and projected density of states (PDOS). Therefore, CuWO₄ films are promising for potential application in water splitting and photocatalytic process.

MEMBROS DA BANCA:
Presidente - 794.918.553-87 - REGINALDO DA SILVA SANTOS - UESPI
Interno - 1553988 - EDSON CAVALCANTI DA SILVA FILHO
Interno - 756.483.183-91 - GERALDO EDUARDO DA LUZ JUNIOR - UESPI
Interno - 1722880 - JOSY ANTEVELI OSAJIMA FURTINI
Externo ao Programa - 840.043.633-49 - LAÉCIO SANTOS CAVALCANTE - UESPI