Acid–base sensor based on sol–gel encapsulation of bromothymol blue in silica: application for milk spoilage detection

Stocker, Mariele K.; Sanson, Murilo L.; Bernardes, Arthur A.; Netto, Antonio Marchi; Brambilla, Rodrigo

doi:10.1007/s10971-021-05529-7

Cited by 5 publications

(4 citation statements)

References 22 publications

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“…[14] Another recently reported silica-encapsulated pH indicator comprised silica capsules bearing bromothymol blue prepared by the Stöber sol-gel method, and these were dispersed in high density polyethylene for use in monitoring milk spoilage. [15] Polymer-based packaging polyethylene is an inert, easily moldable material that meets the specifications of the food industry while being permeable to gases and compatible with silica. Note that simply mixing the silica with polyethylene in the molten state requires a high degree of polyethylene processing because the silica produced by the sol-gel process is hygroscopic.…”

Section: Introductionmentioning

confidence: 99%

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Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

Heck

Santos

2023

Macro Reaction Engineering

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A number of colorimetric pH indicators (phenolphthalein, bromocresol green, 4‐nitrophenol, phenol red, and bromothymol blue) are encapsulated within silica particles via an acid‐catalyzed sol–gel process. The fabricated indicator is added during ethylene polymerization with a metallocene (Cp2ZrCl2) catalyst. Introduction of the indicator into the silica matrix affects the surface area, probably by partially blocking some of the pores. The encapsulated pH indicator reduces the catalytic activity by up to 17%, whereas adding a solution of the indicator reduced the catalytic activity by up to 34%. The crystallinities of the samples containing the silica‐encapsulated pH indicators are lower than those of the samples to which the pH indicator is added in solution form. The prepared encapsulated colorimetric pH indicators are analyzed by diffuse reflectance UV‐vis spectroscopy. The measured color values are distributed according to the CIE Lab lightness psychometric color space. Addition of the indicator in solution form (free) to the ethylene polymerization reaction does not result in indicator activity in acidic or alkaline media. The pH indicators incorporated into the polyethylene show color changes when exposed to acidic and alkaline media. Samples to which the unencapsulated pH indicators (free) are added exhibit lower catalytic activities and higher crystallinities than the samples containing the encapsulated pH.

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Section: Introductionmentioning

confidence: 99%

“…[ 14 ] Another recently reported silica‐encapsulated pH indicator comprised silica capsules bearing bromothymol blue prepared by the Stöber sol‐gel method, and these were dispersed in high density polyethylene for use in monitoring milk spoilage. [ 15 ]…”

Section: Introductionmentioning

confidence: 99%

Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

Heck

Santos

2023

Macro Reaction Engineering

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“…To date, many studies have attempted to elucidate the influence of precursors on the hydrolysis, condensation reactions, and crosslinking by applying different characterization and analysis techniques, including gas chromatography (GC) [ 21 ], nuclear magnetic resonance 29 Si NMR [ 22 , 23 ], Raman spectroscopy [ 24 ], and Fourier transform infrared spectroscopy (FTIR) [ 25 , 26 ]. Among these approaches, FTIR not only provides complementary information on the bonds and structures formed during the synthesis process but also, when combined with deconvolution methods, yields valuable data on the microstructure of siliceous materials [ 27 , 28 , 29 ]. Knowledge obtained by these means is of major interest because it allows for the prediction of: (i) the physical properties of xerogels derived from their structure [ 30 ]; (ii) the catalytic activity of metals supported in silica matrices [ 31 ]; and (iii) the correlation of the silica species in the membrane of a fiber optic sensor with its efficacy [ 32 ].…”

Section: Introductionmentioning

confidence: 99%

Hybrid Xerogels: Study of the Sol-Gel Process and Local Structure by Vibrational Spectroscopy

et al. 2021

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The properties of hybrid silica xerogels obtained by the sol-gel method are highly dependent on the precursor and the synthesis conditions. This study examines the influence of organic substituents of the precursor on the sol-gel process and determines the structure of the final materials in xerogels containing tetraethyl orthosilicate (TEOS) and alkyltriethoxysilane or chloroalkyltriethoxysilane at different molar percentages (RTEOS and ClRTEOS, R = methyl [M], ethyl [E], or propyl [P]). The intermolecular forces exerted by the organic moiety and the chlorine atom of the precursors were elucidated by comparing the sol-gel process between alkyl and chloroalkyl series. The microstructure of the resulting xerogels was explored in a structural theoretical study using Fourier transformed infrared spectroscopy and deconvolution methods, revealing the distribution of (SiO)4 and (SiO)6 rings in the silicon matrix of the hybrid xerogels. The results demonstrate that the alkyl chain and the chlorine atom of the precursor in these materials determines their inductive and steric effects on the sol-gel process and, therefore, their gelation times. Furthermore, the distribution of (SiO)4 and (SiO)6 rings was found to be consistent with the data from the X-Ray diffraction spectra, which confirm that the local periodicity associated with four-fold rings increases with higher percentage of precursor. Both the sol-gel process and the ordered domains formed determine the final structure of these hybrid materials and, therefore, their properties and potential applications.

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“…Thymol blue has also been used to detect CO 2 via pH in a europium polymer composite film [40,41]. Bromothymol blue has been used with high density polythethylene (HDPE), ethylene-vinyl acetate (EVA), and silica to detect spoiled milk via pH changes [42] and combined with carbon nanotubes to detect epinephrine [43]. The well-known pH indicator phenolphthalein has been functionalized with formaldehyde and immobilized in diacetylcellulose to create an optical sensor [44] as well as electrospun with poly(acrylonitrile-co-vinyl acetate) (PAN) in N, N-dimethylformamide (DMF) to develop halochromic nanosensors [45].…”

Section: Introductionmentioning

confidence: 99%

3D Printed Chromophoric Sensors

2021

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Eight chromophoric indicators are incorporated into Sylgard 184 to develop sensors that are fabricated either by traditional methods such as casting or by more advanced manufacturing techniques such as 3D printing. The sensors exhibit specific color changes when exposed to acidic species, basic species, or elevated temperatures. Additionally, material properties are investigated to assess the chemical structure, Shore A Hardness, and thermal stability. Comparisons between the casted and 3D printed sensors show that the sensing devices fabricated with the advanced manufacturing technique are more efficient because the color changes are more easily detected.

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Acid–base sensor based on sol–gel encapsulation of bromothymol blue in silica: application for milk spoilage detection

Cited by 5 publications

References 22 publications

Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

Hybrid Xerogels: Study of the Sol-Gel Process and Local Structure by Vibrational Spectroscopy

3D Printed Chromophoric Sensors

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