Publications

Aiming to transition towards sustainable design processes, plasma doping methods have been investigated as ultra-fast and solvent-free alternatives to chemical doping strategies. Despite their advantages, the current state-of-the-art plasma-doped materials present low doping percentages. Consequently, their acceptance as a replacement to conventional methods is still disfavoured. In this work, we propose a change in the paradigm by presenting a new approach termed high-performance plasma doping (HPPD) capable of intensively doping material lattices. To do so, HPPD exploits the higher number of available sites in vacancy-engineered materials for introducing dopants through non-thermal plasma (NTP) treatment. For this purpose, hydroxyapatite (HAp) is presented as a representative case example of successful HPPD. Thus, HAp disks with OH- lattice vacancies are prepared and treated for short times with NTP. All the HPPD samples are oxygen-doped successfully, displaying conductivity enhancement of up to one order of magnitude. In addition, doping for the entire material bulk is achieved, reaching a doping replacement efficiency of 50%. The proposed mechanism, based on oxygen diffusion through the OH- HAp columns, is corroborated through density functional theory (DFT) calculations. Results reveal the key role of lattice vacancies as charge imbalances, exercising an electronic pull on reactive gas species. Further assessment of the HPPD HAp is done through catalytic CO2 conversion reactions. Thus, the synthesis of C1-C3 products (including ethanol and formic acid, among others) from CO2 under mild conditions (150 degrees C and 6 bar of CO2) is achieved, realizing a total yield of 537.85 +/- 3.40 mu mol gc-1. Finally, the implications of HPPD and its extension towards other materials are discussed and highlighted by performing a state-of-the-art comparison.

JTD Keywords: Co2, Congo red, Conversion, Nanoparticles, Oxide, Photocatalytic degradation, Sites, Surface, Tio2

Permanently polarized hydroxyapatite (p-HAp) has been reported as a feasible green alternative to conventional catalysts for the selective conversion of CO2 into highly valuable chemical products. However, structural control and enhanced electrical properties achieved on p-HAp clearly contrast with other reported catalytic systems, where hydroxyapatite mainly acts as a support receiving much less attention. In this work we take advantage of the knowledge obtained on p-HAp to develop an HAp-based catalytic system composed of TiO2 nanoparticles deposited on p-HAp. It is important to stress that p-HAp is not only considered as a mechanical support but has been put in the spotlight for catalyst preparation and as an active catalytic part. Therefore, the use of p-HAp in this system has unveiled exceptional synergies with TiO2 attributed to the enhanced electrical properties of p-HAp, capable of attracting the photo-electrons generated in TiO2 nanoparticles avoiding electron-hole recombination. CO2 fixation reactions carried out under mild conditions (120 degrees C, 6 bar and under UV exposure) result in complete selectivity control of the C2 products, shifting from ethanol (201 mu mol g(catalyst)(-1)) for p-HAp alone to acetic acid (381 mu mol g(catalyst)(-1)) when TiO2 nanoparticles are loaded in the system. Considering the challenging CO2 activation energy and the high control of the selectivity achieved, we do believe that this novel approach can be considered as a starting point to explore other systems and reactions where control of the crystal structure and the enhanced electrical properties of HAp can play a crucial role in the final products, reaction conditions, yields and selectivities.

JTD Keywords: Behavior, Cobalt, Conversion, Methane, Ni, Oxidation, Performance, Reduction, Syngas production, Tio2