Phosphoric acid adsorbed on silica-ceria matrix obtained by sol-gel method: studies of local structure, texture and acid property

Abstract

Óxidos mistos de SiO 2 /CeO 2 (designados como SC) contendo quantidades variáveis de céria, SC1 = 5,6, SC2 = 8,0 e SC3 = 13,0 (% em massa), foram preparados pelo método de processamento sol-gel e obtidos como sólidos amorfos possuindo áreas superficiais específicas de SC1 = 463, SC2 = 474 e SC3 = 460 m 2 g -1 . Íons fosfatos foram imobilizados na superfície destes sólidos, através da ligação química Ce-O-P, pela imersão de SC em uma solução de ácido fosfórico. Este procedimento produziu sólidos com as seguintes quantidades de P adsorvidas na superfície (em % atômica): SCP1 = 0,60, SCP2 = 0,71 e SCP3 = 1,63. A energia de ligação P 2p 3/2 , obtida por XPS, e o único pico observado em -10 ppm, por NMR de 31 P, revelaram que o fosfato adsorvido na superfície é a espécie H 2 PO 4 -. Utilizando-se piridina como sonda molecular, somente sítios ácidos de Brønsted foram detectados. A determinação das quantidades destes sítios ácidos, feita pela adsorção de NH 3 gasosa sobre a superfície, revelou os seguintes valores para cada sólido tratado com o íon fosfato: SCP1 = 0,37, SCP2 = 0,43 e SCP3 = 0,51 mmol g -1 .SiO 2 /CeO 2 mixed oxide (designated as SC) with variable ceria contents, SC1 = 5.6, SC2 = 8.0 and SC3 = 13.0 wt%, prepared by the sol-gel processing method, were obtained as amorphous solids possessing specific surface areas of SC1 = 463, SC2 = 474 and SC3 = 460 m 2 g -1 . Phosphate ions were immobilized onto the surface of these solids through Ce-O-P bonding by immersing SC into a phosphoric acid solution. Solids with the following P contents were obtained (in atom %): SCP1 = 0.60, SCP2 = 0.71 and SCP3 = 1.63. The binding energy peak P 2p 3/2 at ca. 134.0 eV, observed by XPS, and the 31 P MAS NMR single peak, observed at ca. -10 ppm, revealed that H 2 PO 4 -is the species present on the surface of the matrices. Using pyridine as a molecular probe, only Brønsted acid sites could be detected. The amount of these acid sites, determined by ammonia gas adsorption on the surface, reached the following values for each phosphate-treated solid: SCP1 = 0.37, SCP2 = 0.43 and SCP3 = 0.51 mmol g -1 .

Interfacial Engineering of Nanoporous Architectures in Ga2O3 Film toward Self-Aligned Tubular Nanostructure with an Enhanced Photocatalytic Activity on Water Splitting

“…) species, suggesting that the above phosphorus content revealed by the EDX analysis in the nanotubular structure is only due to adsorption of phosphoric acid from the electrolyte. 50 In line with the SEM topography, TEM examination of the nanotubular structured Ga 2 O 3 film also shows a hollow tube, and the SAED patterns reveal the amorphous characteristic in the as-prepared state of the film (Figure 6a). The XRD patterns of the as-prepared film also reveal the amorphous feature.…”

“…The P 2p XPS spectrum recorded for the phosphorus showed only one photoemission peak centered at 133.1 eV (Figure S6c). This peak can be ascribed to the 2p 3/2 of simply phosphate (PO 4 3– ) species, suggesting that the above phosphorus content revealed by the EDX analysis in the nanotubular structure is only due to adsorption of phosphoric acid from the electrolyte . In line with the SEM topography, TEM examination of the nanotubular structured Ga 2 O 3 film also shows a hollow tube, and the SAED patterns reveal the amorphous characteristic in the as-prepared state of the film (Figure a).…”