Halloysite based nanocomposites and photocatalysis: A Review

Heterogeneous photocatalysis is an efficient, relatively cheap and environmentally friendly technology for decomposing various organic and air pollutants. Halloysite is a natural clay mineral usually in the form of nanotubes that has many applications as well as potential uses including photocatalysis. In this paper the photocatalytic activities of halloysite-based nanocomposites in combination with various photocatalysts that have been synthesized and tested in decomposing organic and air pollutants are reviewed. Many photocatalysts have been synthesized and among them TiO2 in the form of anatase, or rutile, or a mixture of both is the most common photocatalyst due to its effectiveness and low cost. Researches by many investigators are summarized and discussed. The possibilities and limitations of halloysite-based nanocomposites for future applications are also discussed and new fields of research are proposed. It is suggested that Halloysite-based nanocomposites are more promising in positively charged organic substrates like tetracycline and Rhodamine B where the organic pollutant is attracted by halloysite's negatively charged external surfaces close to the photocatalysts, than neutral like paracetamol or negatively charged which that attraction does not occur.