Complete Removal Of Template Research Articles

Amine functionalized AFI type microporous SAPO-5 materials: preparation, unique method on template extraction, characterization and its catalytic application on epoxide ring opening

Microporous AFI type silicoaluminophosphate (SAPO-5) having aminosilane functionality in the framework was prepared by in-situ (direct co-condensation) approach under hydrothermal conditions. The template (structure directing agent) presents within the channels of synthesized aminosilane modified SAPO-5 framework was selectively removed by a unique method using acidic ethanol extraction. Before and after the template extraction, presence of AFI type phase of SAPO-5 was confirmed through powder XRD pattern. The complete removal of template from the channels of framework was confirmed through FT-IR, 13C MAS NMR and N2 sorption studies. The covalent bonding of aminosilane functionality within the organic–inorganic hybrid SAPO-5 framework was evident through 29Si MAS NMR and 13C MAS NMR studies. The final material was utilized for selective synthesis of 1-phenoxy-2-propanol (99%) via propylene oxide ring opening with phenol under solvent free conditions in liquid phase medium.

Effect of thermal treatment on surface and bulk properties of Fe/ZSM-5 zeolites prepared by different methods

Fe/ZSM-5 samples (5 wt.% Fe) prepared by in situ incorporation using TPABr template under hydrothermal conditions (Fe–ZSM-5 in), chemical liquid deposition (Fe–ZSM-5 imp) and solid–solid (Fe–ZSM-5 ss) interaction were characterized by N 2 physisorption, TG/DSC, X-ray diffraction, FTIR spectroscopy, UV–Vis diffuse reflectance spectroscopy and 57Fe Mössbauer spectroscopy techniques. Calcination at 550 °C leads to almost complete removal of template that was associated with dislodgment of significant fraction of Fe to external positions as recognized for the in situ prepared sample (Fe–ZSM-5 in). This sample showed an increase in lattice volume suggesting the presence of the majority of Fe ions in tetrahedral positions inside zeolite channels and offered as well the lowest crystallites size (75 nm) and maximum S BET (453 m 2/g) between all samples. On the other hand, Fe–ZSM-5 ssbef, resulting from solid–solid interaction and subjected to heat treatment in vacuum at 200 °C, measured the lowest mean pore radius ( r −; 23 Å), and pore volume ( V p; 0.3887 cm 3/g), giving a hint about the probability of finding neutral iron oxide nanoparticles (α-Fe 2O 3) as a separate phase that has been validated by Mössbauer (IS = 0.3 mm/s, QS = −0.2 mm/s, H eff = 520 kOe) and UV–Vis (400 nm) investigations. This sample also demonstrated that the majority of Fe occupied framework positions beside a fraction identified as small oligonuclear oxo-iron ions ( Fe x 3 + – O ; 290 nm). Interestingly, Fe–ZSM-5 ssaft, resulting from solid–solid interaction and subjected to air calcination at 550 °C, measured maximum V p (0.6380 cm 3/g) and r − (39 Å) values, reflecting the enforced location of Fe in this sample leading to an effective pore widening and thus a pronounced mesoporosity is attained. IR bands due to ν asT–O in ZSM-5 (1105 cm −1) showed a shift to lower wave numbers (1059 cm −1) following Fe incorporation reflecting the extent of exchanging Fe in this sample (Fe–ZSM-5 ssaft), unlike the rest of the samples which showed splitting, which accounted for the presence of residual Al 3+ beside Fe 3+ ions in the same site. Mössbauer data of this sample confirmed the latter result and indicated the maximum lattice imperfection and showed as well the lowest degree of crystallinity. The Fe–ZSM-5 impaft sample, subjected to heat treatment at 550 °C, showed α-Fe 2O 3 species where that heated at 110 °C presented the lowest S BET (361 m 2/g). More correlations were evaluated and discussed on the effect of thermal treatment on the existence of various Fe species (either framework or non-framework), their electronic states and local structures.

Evaluation of methods aimed at complete removal of template from molecularly imprinted polymers.

Polymers imprinted with clenbuterol were used to study the influence of various post-polymerization treatments [e.g., thermal annealing, microwave assisted extraction (MAE), Soxhlet extraction and supercritical fluid template desorption] on the bleeding of residual template. The aim of the study was to reduce the bleeding to levels that would allow the use of the materials as affinity phases for extraction of clenbuterol from bovine urine at concentrations below 1 ng ml-1. After treatment, the clenbuterol imprinted polymers were packed into solid-phase extraction columns and the bleeding was estimated by quantifying the amount of template released in 10 ml of methanol-acetic acid (9 + 1 v/v). This was followed by an assessment of selectivity and recovery in comparison with non-treated material. The lowest bleeding level was found after MAE using 100% trifluoroacetic acid for 3 x 20 min at 100 degrees C. The collected eluate contained in this case 3 ng ml-1 of clenbuterol. The same material was subsequently used for the extraction of clenbuterol from spiked bovine urine. The resulting selectivity and recovery were lower compared with those obtained using the untreated material. A milder but still efficient method to reduce the bleeding level was found to be MAE with formic acid. In this case a bleeding level of 14 ng ml-1 was found after only a 1 h extraction time. In a second model system, using a polymer imprinted with L-phenylalanine anilide, the bleeding was reduced to a similar level by extensive on-line washing in good swelling solvents containing acid or base additives and after thermal annealing of the polymers in the dry state.