Hydroxyapatite-based biphasic catalysts with plasticity properties and its potential in carbon dioxide fixation

Permanently polarized hydroxyapatite, an outstanding catalytic material for carbon and nitrogen fixation

“…The apparition of those new species was attributed to the rearrangement of the OH − groups, which acted as water substitutes and provided the structural integrity for the new phase stabilization, rather to the introduction of disordered PO 4 3− tetrahedra. 30 As it is discussed below, far from being an inconvenient, the coexistence of controlled amounts of Bru is desired for specific applications. In this sense, the polarization treatment offered an easy synthesis route for obtaining such biphasic samples.…”

“…comparable to Fourier Transform Infrared Spectroscopy, FTIR); and (2) it supplies unequivocal crystallographic details, complementing the information provided by X-ray diffraction (XRD) technique. 30,35 Thus, most of the HAp characteristic diffraction peaks overlap in position with the reflections of other calcium phosphate salts. This is illustrated in Fig.…”

“…3, which compares the wide angle X-ray diffraction (WAXD) patterns of pp-HAp without and with Bru at the surface. 30 The peaks identified at 2y = 31.81, 32.21, and 33.01 correspond to reflections of HAp (JCPDS card number 9-0432), whereas the most significant peaks of Bru appear at 2y = 291, 311, 351, 421, and 511 (JCPDS card number 72-0713).…”

“…4). 30 Moreover, Raman spectroscopy provides valuable information about the crystallinity and presence of disordered species through the analysis of the full half maximum width (FWHM) of each vibration, the presence of OH À vacancies through the area of the O-H peak, and the OH À orientation/ polarization through the peak intensity (Fig. 4).…”

“…:CH 2 + CH 3 CH 2 OH -CH 3 CH(OH)CH 3 (6) pp-HAp prepared through the TSP was found to exhibit remarkable boosted catalytic activity for carbon fixation, representing a feasible, cheap and non-toxic alternative to the conventional catalysts. 17,19,30 Moreover, the utilization of pp-HAp presents an important advantage with respect to HAp polarized by ultrasonic induced stress, as no electric field has to be applied during the whole reaction, the final net energetic balance is clearly favourable for pp-HAp. The catalytic conversion of CO 2 and CH 4 into ethanol under mild reaction conditions (low pressure and temperature comprised between 95 and 140 1C) has recently been reported.…”