Fourier Transform Raman Studies of Methyl Red Adsorbed on γ-Alumina and Silica-Alumina

Abstract

Fourier transform Raman spectra of methyl red adsorbed on untreated and pretreated γ-alumina and silicaalumina calcined at 900 o C under 1 atm steam flowing were recorded. Spectral analysis shows that the active species adsorbed on γ-alumina was to be deprotonated methyl red, and on silica-alumina to be di-protonated. This indicates that γ-alumina adapted in this work holds Brönsted basicity, and silica-alumina Brönsted acidity. Raman intensities of methyl red on pretreated γ-alumina are about three times stronger than on untreated γ-alumina, while spectral features are unchanged. For silica-alumina, spectral features show modified vibrational characteristics upon surface hydroxylations generated from pretreatment. Consequently, the acidity loss for silica-alumina and the basicity gain for γ-alumina were observed by increasing the surface hydroxyl groups on the catalysts through pretreatment of the steam calcination.

Thermal response and thermochromism of methyl red-based copolymer systems – coupled responsiveness in critical solution behaviour and optical absorption properties

“…Considering previous studies 58,59,61–63 about vibrational and vibronic behaviour of azobenzenes, the first possibility is the most probable explanation. Thus, we attribute these spectral features to vibronic sub-bands.…”

“…1400 cm −1 ) in the parent compound (MR). 62,63 Even though the energy difference between the sub-bands is higher than the energy of the –NN– stretching mode, coupling of the involved vibrational modes is likely to influence the observed maximum. This is indicated by significant broadening of the sub-bands and their apparent overlap, which is apparent even in the derivative spectra.…”

Highly Sensitive and Full Range Detectable Humidity Sensor using PEDOT:PSS, Methyl Red and Graphene Oxide Materials

“…Band at 1395 cm −1 shows a strong characteristic N = N stretching and a weak band at 1419 cm −1 is assigned to the CH 3 symmetric deformation. The band at 1085 cm −1 is CH 3 rocking and band at 1341 cm −1 is attributed to C − O – H while 1312 cm −1 band is amine N − C 29 . These bands suggest that methyl red thin film has no impurities and contamination.…”

Remoción De Colorantes Azo Con Alginato: Relación Entre Estructura De Colorante Y Eficiencia De Remoción

“…Se obtuvieron espectros UV-visible del Rmetilo de experimentos similares a los realizados con los otros colorantes. Park et al (2004) han reportado que en el intervalo de pH = 4 a 6 existen los mayores cambios en la distribución electrónica del Rmetilo y que se deben a la existencia de las especies aniónica y protonada de este compuesto, dado que su pKa es de 5.02 (García-Heras et al 2005). Experimentalmente se encontró que valores menores y mayores a este pH produjeron espectros de absorción electrónica muy diferentes, a pH = 4, λ max = 525 nm (disolución color rojo) y a pH = 6, λ max = 431 nm (disolución color naranja).…”

“…Esto explicaría la baja afinidad del Rmetilo por el ALG. Además, el Rmetilo es más pequeño que los anteriores colorantes y tiene menos tendencia a agregarse por la disminución en su planaridad molecular a pH = 7 por la predominancia de la especie aniónica (Park et al 2004). Lo anterior resulta en un eficiencia de remoción del 14.9 % a pH = 7 y F.I.…”