A variable temperature infrared spectroscopy study of NaY zeolite dehydration

Thermal analysis by variable temperature infrared spectroscopy with a button sample holder and Peltier heating/cooling

An apparatus and methodology for variable temperature infrared spectroscopy measurements of neat samples contained in a button sample holder are described. Sample heating and cooling are achieved by applying voltage to stacked Peltier thermoelectric devices. Between 0 and 150 °C, samples can be heated and cooled at 2 °C s^-1 rates, facilitating temperature step heating/cooling profiles with minimal delay between isothermal infrared spectrum measurements. Examples of correlating temperature-dependent spectral variations with specific sample changes are provided for α-quartz heating/cooling, ibuprofen melting, and acetylsalicylic acid thermal decomposition. Trends in α-quartz infrared spectra obtained with a step heating/cooling temperature profile are used to evaluate spectrum measurement reproducibility. Detection of vibration band intensity variations of less than 1% resulting from a 10 °C sample temperature increment illustrates the measurement sensitivity. By comparing infrared spectra obtained at different temperatures, reversible and irreversible sample changes are identified. Infrared spectra acquired during linear ramp heating are employed to determine the ibuprofen melting point, which confirms the temperature measurement accuracy of the apparatus. Selective analysis is demonstrated by determining isoconversion effective activation energies for processes involved in the thermal decomposition of the acetylsalicylic acid component of a commercial pharmaceutical tablet.

Thermal behavior of natural stellerite: high-temperature X-ray powder diffraction and IR spectroscopy study

The thermal behavior of stellerite from the Savinskoye deposit (Transbaikalia, Russia), Ca_7.69Na_0.25K_0.06(Si_56.24Al_15.76)O₁₄₄·53.39H₂O, was investigated by in situ high-temperature X-ray powder diffraction (HTXRPD) and ex situ HT infrared (IR) spectroscopic analysis. Four different HTXRPD experimental procedures were used to study the thermal behavior of the powder samples: (1) RT-750 °C, (2) RT-220 °C -RT, (3) 200-350-RT °C, and (4) 350-700 °C. Electron probe microanalysis and single-crystal X-ray diffraction were preliminary used to determine the chemical composition and crystal structure of stellerite. The A → B phase transition (Fmmm → Amma) starts at ∼110 °C and is completed at about 140 °C (in situ HTXRPD) and 200 °C (ex situ HTIR) depending on the experimental conditions. It involves a cell volume decrease of 5.8% (Experiment 1). The thermal expansion of stellerite is more pronounced along the b and c axes, with αa: αb: αc (× 10^-5) = 2.50:-25.52:-6.84 at 100 °C, 0.44:-21.75:-25.64 at 150 °C after the completion of the phase transition, and 3.06:-1.86:-16.94 at 500 °C. The reverse B → A transition occurs at temperatures below 100 °C during slow cooling (Experiment 2), however, it does not occur upon rapid cooling (Experiment 3). The B → D phase transition above 300 °C is not observed (Experiment 4). The temperature barrier of phase transition in the ex situ HTIR spectroscopy experiment is shifted towards high temperatures. The heating above 200 °C leads to an increase of 3430 cm^-1 and a decrease of 3600 and 3260 cm^-1 bands, which correspond to the stretching vibration of H₂O. The heating above 400 °C causes complete dehydration of the stellerite.

Mid-infrared spectroscopy of liquids by using a modified button sample holder

A new approach for mid-infrared spectroscopy measurements of liquids is described. Thin layers of liquid samples are analyzed by using a modified button sample holder that incorporates a reservoir. To obtain spectra, buttons containing liquid samples are placed at the infrared beam focus of a praying mantis diffuse reflection optical system. Infrared radiation absorption path lengths can be adjusted by changing the quantity of liquid added to the reservoir. Thin film transflection spectra are similar to those obtained by transmission measurements. Transflection spectra of thicker layer liquids also resemble transmission measurements, but with increased relative intensities for low absorptivity peaks. Unlike transmission measurements, transflection spectra retain overlapping peak profiles for highly absorbing vibration bands due to multiple path length dynamic range effects. For a fixed effective path length (i.e. constant liquid volume), linear calibration plots of absorbance or integrated absorbance versus concentration are obtained. The button sample holder provides a methodology that is complementary to the transmission cell and attenuated total reflection (ATR) techniques for infrared analyses of neat solids and liquids, and is especially useful for characterizing thick samples and high absorptivity bands.

Chabazite Synthesis and Its Exchange with Ti, Zn, Cu, Ag and Au for Efficient Photocatalytic Degradation of Methylene Blue Dye

A chabazite-type zeolite was prepared by the hydrothermal method. Before ion exchange, the chabazite was activated with ammonium chloride (NH₄Cl). The ion exchange process was carried out at a controlled temperature and constant stirring to obtain ion-exchanged chabazites of Ti⁴⁺ chabazite (TiCHA), Zn²⁺ chabazite (ZnCHA), Cu²⁺ chabazite (CuCHA), Ag⁺ chabazite (AgCHA) and Au³⁺ chabazite (AuCHA). Modified chabazite samples were characterized by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), N₂ adsorption methods and UV–visible diffuse reflectance spectroscopy (DRS). XRD results revealed that the chabazite structure did not undergo any modification during the exchange treatments. The photocatalytic activity of chabazite samples was evaluated by the degradation of methylene blue (MB) in the presence of H₂O₂ under ultraviolet (UV) light illumination. The photodegradation results showed a higher degradation efficiency of modified chabazites, compared to the synthesized chabazite. CuCHA showed an efficiency of 98.92% in MB degradation, with a constant of k = 0.0266 min⁻¹ following a first-order kinetic mechanism. Then, it was demonstrated that the modified chabazites could be used for the photodegradation of dyes.

Characteristics of poly-silicate aluminum sulfate prepared by sol method and its application in Congo red dye wastewater treatment

A novel method for synthesizing poly-silicate aluminum sulfate coagulant (PSAS) using a silica-alumina sol was reported. Herein, two modalities (nSiO₂/nNa₂O: 1.11 and 3.27) of self-made water glasses were used as the silica source for synthesizing the sol precursor. Then, the PSAS_1.11 and PSAS_3.27 with different basicity were obtained by controlling the Al molar ratio of precursor to aluminum sulfate. The results showed that the PSAS_1.11 coagulant prepared with low modulus water glass (LMWS, 1.11) has low turbidity and good stability. Using low modulus water glass, the effect of the Al molar ratio of precursor to aluminum sulfate on the basicity and stability of PSAS_1.11 with Al/Si of 20 and the effect of the molar ratio of aluminum to silicon on the basicity and stability of PSAS_1.11 were studied, respectively. Based on XRD and Fourier infrared (FTIR) characterization of the sol precursor and PSAS_1.11, the synthesis mechanism of PSAS by the silica-alumina sol method was discussed. Al species distribution of PSAS_1.11 was determined using the Al-Ferron timed spectrophotometric method. Moreover, the performance of PSAS_1.11 coagulant was examined, regarding its efficiency towards color removal of Congo red. The results showed that PSAS_1.11 coagulant with Al/Si of 20 and Al molar ratio of 1/12 exhibits excellent performance, and the color removal rate reached 98.6% at an initial pH of 11 and coagulant dosage of 40 mg L⁻¹ (Al mg L⁻¹). Finally, the PSAS coagulant mechanism was discussed in detail through infrared characterization, ²⁷Al NMR, Raman, morphology and mapping of the flocs.

A novel method for synthesizing poly-silicate aluminum sulfate coagulant (PSAS) using a silica-alumina sol was reported.

A high sensitivity variable temperature infrared spectroscopy investigation of kaolinite structure changes

A new approach for thermal analysis based on variable temperature infrared spectroscopy is described and evaluated. Diffuse reflection optics are employed with a sample heating system that does not employ a sealed environmental chamber. Rather than using a sample cup, a thin layer of solid particles is loaded into a "button" sample holder. The new design minimizes spectral artifacts and provides enhanced optical throughput compared to other designs, but necessitates a more restrictive sample heating temperature range. Results obtained while monitoring solid-state temperature-dependent changes are used to assess the sensitivity of the method. Infrared spectrum changes associated with reversible and irreversible kaolinite structure changes are described and characterized. Subtle temperature-dependent sample changes are revealed by positive and negative difference spectrum residuals, which are obtained by subtracting infrared spectra obtained at different temperatures. Scan-to-scan infrared spectrum relative standard deviations at 30 and 150 °C were less than 1.0%, which was slightly higher than the ambient temperature reproducibility.