CSIR – National Institute for Interdisciplinary Science and Technology (NIIST)

Council of Scientific & Industrial Research (CSIR), Govt.Of India Thiruvananthapuram.

Dark-Catalysis: Novel approach for industrial dye-removal


Dr. Satyajit Shukla on 26th November 2013 at 2:30 pm

The carcinogenic and health-hazardous organic-synthetic-dyes in the industrial waste-water pollute the surface- and ground-water affecting the under-water photosynthesis activity and life-sustainability. Removing the organic-synthetic-dyes from the industry effluents and aqueous solutions is, hence, of prime importance. Photocatalysis using the nanocrystalline semiconductor titania (TiO2) has been widely investigated for this purpose. This mechanism has been, however, associated with the several major drawbacks which include the need for an exposure to the external-radiation for generating the electron-hole (e-/h+) pairs, reducing the band-gap energy of photocatalyst via costlier dopants, and the difficulties in the catalyst-separation following the dye-removal treatment. In order to overcome these major drawbacks associated with the photocatalysis mechanism, we have developed a novel dye-removal technology based on the dark-catalysis mechanism which utilizes the hydrothermally processed nanotubes of semiconductor-oxides such as the hydrogen titanate (H2Ti3O7) and anatase-TiO2. The dark-catalysis process consists of “two-step” and “one-step” dye-removal methods. In the “two-step” dye-removal method, the organic-synthetic-dye is adsorbed on the surface of nanotubes-based adsorbent in the dark-condition in one aqueous solution and then decomposed in another aqueous solution also in the dark-condition. On the other hand, in the “one-step” dye-removal method, the dye-adsorption and the dye-decomposition simultaneously take place in one aqueous solution in the dark-condition. The dye-removal via the dark-catalysis mechanism has been demonstrated using the basic and reactive dyes. It has been shown that the hydrothermally processed semiconductor-oxides nanotubes can surface-adsorb an organic-synthetic-dye in the dark-condition with very high dye-adsorption capacity (105-140 mg•g-1) at the initial solution-pH of ~10. In order to improve the efficiency of adsorbent-separation from the treated aqueous solution, a magnetic dye-adsorbent catalyst has been newly developed which allows the separation of nanotubes-based dye-adsorbent using an external magnetic field. New approaches for the recycling of semiconductor-oxides nanotubes-based magnetic / non-magnetic dye-adsorbents have also been developed. The comparison shows that relative to the photocatalysis mechanism, the dark-catalysis process is safer, simpler, highly efficient, and scalable as required for its commercialization in the near-future.