Development of efficient methods for CO 2 recovery from industrial waste gases etc. is extremely important in relation to both reutilization of CO 2 as carbon resources 1 and environmental issue concerned with the greenhouse effect. 2 One of the most commonly used processes for CO 2 recovery is chemically reversible CO 2 fixation by primary or secondary amines based on CO 2 fixation by amines at room temperature to give ammonium carbamates, and CO 2 release from ammonium carbamates upon heating. 3 Application of CO 2 fixation in functional polymers has been also examined, 4 for instance, copolymers of styrene bearing pendant amino groups fixed CO 2 under ambient conditions. 4b A more attractive process may be CO 2 fixation by tertiary amines giving zwitterion adducts that may provide a more easily handled fixation-release treatment, since these zwitterions could release CO 2 at reduced temperatures owing to their lability (primary-(secondary) amines; at >100°C). Furthermore, this process can provide zwitterions having a unique reactivity. However, detailed studies concerning CO 2 fixation by tertiary amines and its application to functional polymers have not been carried out. Here we report a new type of reversible CO 2 fixation by amidine derivatives and by polymers bearing an amidine moiety both in solution and solid state.In the course of the study of CO 2 fixation by tertiary amines, there has been one example of CO 2 fixation by 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) to afford the zwitterion adduct. 5 Assuming the reasons why DBU can react with CO 2 are its high nucleophilicity and stabilization of the cation species by delocalization in the amidine moiety, we constructed the idea that amidine derivatives with higher nucleophilicity may provide a success of CO 2 fixation. N-Methyltetrahydropyrimidine (MTHP) containing an amidine structure was synthesized, 6 since it would have higher nucleophilicity due to decrease in the steric hindrance around the nitrogen atom of imine moiety. CO 2 fixation using MTHP was performed in N,N-dimethylformamide (DMF) at 25°C under atmospheric pressure. 7 Fixing efficiency (%, mmol of CO 2 /mmol of MTHP) was estimated from the weight increase in the reaction mixture. When CO 2 was bubbled into a DMF solution of MTHP, a white precipitate was formed immediately, and the weight increase in the reaction mixture ceased after 1 h to afford the corresponding zwitterion adduct (MTHP)CO 2 ) in quantitative fixing efficiency. On the other hand, DBU needed 100 h to fix CO 2 in 89% fixing efficiency, 8 thus, MTHP proved to be an excellent agent for CO 2 fixation. The IR spectrum of MTHP)CO 2 showed two absorption bands assignable to the CO 2 moiety at 1689 and 1389 cm -1 . The 1 H NMR spectrum of MTHP)CO 2 showed that the signal of the imine proton was shifted to lower field (0.57 ppm) compared with MTHP and the 13 C NMR spectrum showed a signal attributable to the carbonyl group at 161.3 ppm.Reversibility of CO 2 fixation by MTHP was examined ( Figure 1): The obtained zwitterion addu...

The effect of grain size on the thermoelectric properties of n-type nanocrystalline bismuth-telluride based thin films is investigated. We prepare the nanocrystalline thin films with average grain sizes of 10, 27, and 60 nm by a flash-evaporation method followed by a hydrogen annealing process. The thermoelectric properties, in terms of the thermal conductivity by a differential 3 method, the electrical conductivity, and the Seebeck coefficient are measured at room temperature and used to evaluate the figure of merit. The minimum thermal conductivity is 0.61 W m −1 K −1 at the average grain size of 10 nm. We also estimate the lattice thermal conductivity of the nanocrystalline thin films and compare it with a simplified theory of phonon scattering on grain boundaries. For nanosized grains, the lattice thermal conductivity of nanocrystalline thin films decreases rapidly for smaller grains, corresponding to the theoretical calculation. The figure of merit is also decreased as the grain size decreases, which is attributed to the increased number of defects at the grain boundaries.

Copolymers bearing DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and DBN (1,5-diazabicyclo[4.3.0]non-5-ene) moieties fixed carbon dioxide under atmospheric pressure. The copolymers bearing DBN moieties fixed carbon dioxide faster than those bearing DBU moieties owing to the lower steric hindrance around the imine structure. These copolymers held trapped CO 2 under a N 2 flow at 25 °C, whereas the corresponding lowmolecular weight amidines release trapped CO 2 under the same conditions. The trapped CO 2 in the copolymers was quantitatively released by a N 2 flow at 120 °C. The CO 2 trapping efficiency of a copolymer bearing DBN moieties is competitive with that of an amidine-containing polymer, whereas the preparative method for the copolymer bearing DBN is easier. The higher CO 2 trapping abilities of the DBN derivatives were supported by computational calculation.

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