Water is one of mankind’s major problems. It is vital to identify new methods to purify water and to decontaminate and reuse wastewater, at lower costs than at present, while minimising energy use, the use of chemical agents, and the environmental impact of the decontamination process itself.

Solar photocatalysis has demonstrated enormous potential for wastewater disinfection and detoxification. It is an environmentally benign and sustainable process, which makes use of minimal energy and material resources, and is capable of removing both micro-organisms and persistent organic compounds, without introducing additional chemical agents or toxic substances. The process allows the total removal of pollutants (mineralising them to CO 2 and water), with minimal production of sludge or other by-products, the disposal of which is an additional problem in conventional treatment techniques.

Because of this great potential, demonstrators and pilot plants have been built, but have not reached commercial viability due to two fundamental barriers:

The lack of inexpensive, efficient photocatalysts that are easy to produce on a large scale. Efficient photocatalysts do exist, but they are synthesised by high-cost processes that are very difficult to industrialise and reproduce on a large scale, and require expensive and scarce materials. Current efficiency requires long photocatalyst-pollutant contact times and, therefore, long residence times in the photoreactor (>1h), which are unfeasible in large-scale industrial wastewater treatment plants.

The difficulty in recovering the catalyst from the medium at the end of the process. Solar reactors keep the photocatalyst in suspension in the medium to be treated, and require expensive and complex processes to separate it after treatment.

The Nanobac project aims to overcome these two barriers. It revolves around the development of new technologies for the large-scale production of nanostructured materials using low-cost, high-productivity techniques. Strategies for doping and stabilisation of ultra-reactive faces will make it possible to obtain efficient materials, with accelerated degradation kinetics that reduce the residence time of contaminants in the reactor, bringing it to values compatible with profitable commercial exploitation. The technology aims to achieve the self-assembly of nanoparticles into larger, hollow and porous structures that allow easy separation from the reaction medium. In addition, economical techniques for deposition and immobilisation of the photocatalyst on various substrates will be developed, allowing the design of reactors based on impregnated walls, which are much simpler to operate.

With this starting photocatalyst, the design of a complete wastewater treatment system based on an efficient and economic solar photoreactor will be undertaken. A commercially available system will be demonstrated, in which both the photocatalyst and the photoreactor will be multifunctional in nature, capable of fully degrading and mineralising a wide range of pollutants.

The techniques developed have a strong cross-cutting character. From the point of view of market orientation and commercial exploitation, the project can be considered articulated around two axes: a direct axis, which leads to the development of commercial wastewater treatment plants, exploited by Alquimia, and a transversal axis, which will exploit the materials and production techniques developed in Nanobac in all those markets that are directly accessible for the new photocatalyst material (associated with its low cost/high productivity manufacturing route). The transversal axis targets the construction markets (photocatalytic glass and ceramics for windows, building envelopes, and flooring), biomedical applications (especially biosensors), and energy (through the production of photocatalytic solar hydrogen), as well as environmental applications other than water treatment: in particular, the treatment of confined atmospheres (e.g. aircraft cockpits) and air purification in domestic applications are strongly growing markets, which demand increasing amounts of photocatalyst.