In situ UV-vis spectroscopy

In 1993, we examined formation processes of PVP-protected AuPt bimetallic nanoparticles by in-situ UV-Vis spectroscopy during the reduction [53]. Figure 8 shows the in-situ UV-Vis spectra during the simultaneous reduction of Au(III) and Pt(IV) ions. In the case of PVP-protected AuPt bimetallic system, Au(III) ions are... 

Ni(sacsac)P(nBu3)Cl (sacsac = pentane-2,4-dithionate) was activated by AlEt2Cl to form a catalytically active species for the oligomerization of ethene and propene. This study is noteworthy in that it uses in situ UV-VIS spectroscopy to monitor the course of the polymerization. In this reaction, the aluminum reagent serves both to activate the transition metal and to scavenge any moisture present. 

J. van den Broeke, G. Langergraber, A. Weingartner, On-line and in-situ UV/vis spectroscopy for multi parameter measurements a brief review. Spectroscopy Europe, 18(4), 15-18 (2006). 

UV-Vis spectroscopy — Electronic absorption in the UV-Vis range by species generated during electrochemical reactions or being present at the electrochemical interface between the electronically conducting electrode and an ionically conducting phase (electrolyte solution, molten electrolyte, ionic liquid, solid electrolyte) can be studied with in situ UV-Vis spectroscopy in various modes [i-iii] ... 

A probable reaction pathway in this catalytic process is shown in Fig. 14.9. Molecular oxygen and hydrogen react to form H2O2 and H2O over the surface of 2-5 nm Au NPs. The direct formation of H2O decreases H2 efficiency. Hydrogen peroxide formed on the Au surfaces is converted into hydroperoxo species at tetrahedraUy coordinated Ti cation sites. The Ti-hydroperoxo species can subsequently react with C3H1S adsorbed on the Si02 surfaces to form PO. The existence of Ti-hydroperoxo species under reaction conditions were detected by in situ UV-vis spectroscopy [46] (Fig. 14.10). 

A combination of ECESR and in situ UV-Vis spectroscopy has been proposed by Petr et al. [643]. In the case of a cell that was designed to be similar to the ECESR cell proposed by Piette [613], a UV-Vis spectrometer is coupled with the cell via fiber optics. The working electrode is of a minigrid type. A cell design with an electrochemical cell directly coupled with a cuvet fitting into the ESR spectrometer has been described by Friedrich and Baumgarten [644]. 

Both chemical and physical processes take place during calcination and activation. Ligand decomposition from the metal complex can be monitored with in situ vibrational spectroscopy, for example, using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). In the case of a transition metal ion, the metal oxidation state can be tracked as a function of time and temperature using in situ UV-vis spectroscopy. Finally, the formation of metal clusters and nanoparticles can be monitored using XRD, similar to that described for the synthesis of silicalite-1. 

Coke formation has only been studied for H-SAPO-34 catalyst materials and not for H-ZSM-5 zeolites by means of in situ MAS NMR and UV-vis spectroscopies. Thus, catalyst deactivation is discussed for this particular silicoaluminophosphate molecular sieve on the basis of the results shown in Figure 12.19. By adding the capability of in situ UV-vis spectroscopy to the in situ continuous flow MAS... 

This information can be obtained using various techniques. In situ UV-vis spectroscopy, electrochemistry and sur ce studies have been used to characterize electrochromic polymer films iq>on oxidation and reduction. We present here the investigation of BBB, BBL and PPTZPQ. 

The diffusion of anions during doping and dedoping processes at PANI fibers was investigated with in situ UV-vis spectroscopy by Kanamura et al. [489]. Using a cylindrical diffusion model, it was found that the estimated diffusion coefficient increases with the radius of the PANI fiber. Data obtained with PANI prepared in nonaqueous solutions showed a similar dependence, and the overall values of the diffusion coefficient were much smaller. Whereas the kinetic measurements were made in the same solution, it was proposed, that the diffusing species were different. No suggestion of their specific identity was made. 

Modification of PANI-coated electrodes with metal tetrasul-fonated phthalocyanines (MeTSPc), where the metal is cobalt or iron, resulted in significant changes in the electrocatalysis of the reduction of diojygen [504]. Obviously, insertion of the MeTsPc into the polymer occurs [505]. This was supported in an investigation by Coutanceau et al. by the results of in situ UV-vis spectroscopy. The role of the polymer in the mechanism and the kinetics of dioxygen electroreduction seemed to be somewhat difficult to elucidate. Insertion of CoTsPc resulted in a positive shift of the onset of dioxygen reduction. The two-electron pathway that results in hydrogen peroxide as a reduction product remains. 

Elirect evidence of redox mediation between sulfonated PANI and dimercaptane combined in an electrode initially investigated for possible use in secondary batteries [510] was observed with in situ UV-vis spectroscopy [511]. 

In situ UV-vis spectroscopy of PT reported by Onoda et al. [924] revealed the polaron state at 0.4 eV above the valence band and at 0.4 eV below the conduction band with an overall bandgap of 2.1 eV [925]. Interpretation and assigment of UV-vis spectroscopic data can be supported by investigations of model compounds reported by Fichou et al. [926]. Their results obtained with thiophene oligomers strongly support the preceeding band... 

With in situ UV-vis spectroscopy, Zagdrska and Krische [1024] found evidence to indicate a more regular structure of polymers prepared from 4,4 -dibutyl-2,2 -bithiophene and 4,4 -dioctyl-2,2 -bithiophene and modified electrochemically as compared to polymers prepared from 3-alkylthiophenes. Nevertheless, a shorter conjugation length was found. 

Electrooptical properties of composites made of TiC>2 coated with PT based on in situ UV-vis spectroscopy were reported by Rammelt et al. [1097]. Optical properties of poly(3,4-ethylene-dioxythiophene)-sulfated poly(jS-hydroxyether) composite films prepared by electrochemical copolymerization were studied with in situ UV-vis spectroscopy by Yamato et al. [1098]. In the reduced state, a strong absorption around A = 600 nm, assigned to the 7T -) 77 transition, indicating a bandgap of A = 1.6 eV, was found. The actual position of the absorption maximum depended somewhat on the ratio of the components in the composite. The intensity of this band decreased upon oxidation. A fairly broad feature around A = 900-1000 nm appeared. 

Miyashita and Kaneko [1109] studied vapor-deposited films of PPP using cyctic voltammetry and in situ UV-vis spectroscopy. In nonaqueous solutions, reversible anion as well as cation doping and dedoping that involve at least two different doping sites with a dose correlation between electrochemical and spectroscopical data were found. In an aqueous solution, the electrochemical processes were considerably slower. As an explanation, hindered diffusion of hydrated counterions into the film was proposed. Scanning electron microscopy pictures were considered to support this suggestion. The additional optical absorption bands of the doped PPP film were ascribed to transitions from the valence band into the bipolaron state. 

Ding, Z. F., P. F. Brevet, and H. H. Girault, Heterogeneous electron transfer at the polarised water/l,2-dichloroethane interface studied by in situ UV-VIS spectroscopy and differential cyclic voltabsorptometry, Chem Commun, (1997) p. 2059. 

In situ UV-vis spectroscopy was used to monitor the epoxidation reaction of propylene with O2-H2O [15]. Ti-OOH species were formed when O2 and H2O were fed, and their intensity increased gradually with time on stream and then leveled off at about lOOmin (Figure 11.13). Once propylene was introduced to the feed gas, the intensity of Ti-OOH species decreased gradually. This suggests that Ti-OOH species were consumed by propylene and that... 

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