Substitutes apatites for energy production and absorption

Hydroxyapatite (HA: Ca10(PO4)6(OH)2) is a widely used biomaterial for the repair and regeneration of bone defects; however HA is also recognized as a very interesting material for environmental purification due to its ability to easily absorb a number of inorganic compounds as well as different organic substances such as proteins and bacteria. In this respect, specific ion substitutions in the lattice of HA can enable specific functionality so to open the way to multi-functional and multi-purpose applications. In particular, the substitution of Calcium ions (Ca2+) with Ti4+ ions can be performed during synthesis at low temperature; the ionic substitution destabilize the HA lattice and yields an atomic re-arrangement that yields a decrease of the energy gap of the band structure of HA. In this condition, Ti-HA gathers photoelectronic properties that are promising for implementation into new dye-sensitized solar cells (DSSCs) for energy production, that are among the most advanced and promising ways of providing electricity in the absence of a main power supply. These new devices can also take advantage of the absorbing properties of HA to achieve new tools for photo-degradation of several organic substances and purifications of surfaces from bacteria.
The new Ti-HA phase is obtained also by heterogeneous nucleation on natural fibres, made electroconductive by coating with conductive polymers such as polypyrrole and polyalanine.
Moreover Titanium-substituted HA is also able to absorb light in the ultraviolet region; this is a very relevant feature in the view of the serious damages that may affect the skin of people over-exposed to sun radiation, spanning from burns, erythema, and skin cancer. In this respect the development of new biocompatible media for skin protection has a huge socio-economic impact and can be enhanced by exploiting the multi-functional properties of Ti-HA.