New advances of heterogeneous photocatalysis for treatment of toxic metals and arsenic

M.I. LITTER; N. QUICI

Nanomaterials for Environmental Protection

John Wiley & Sons

Año: 2014;

One of the current most important environmental problems is the presence of heavy metals and metalloids in water. Some of these species have high mobility in water and represent an environmental threat due to their toxicity for biological organisms. In addition, the loss of raw material in industrial wastes represents a significant economic disadvantage. Metal and metalloid species such as chromium, mercury, uranium and arsenic are considered priority pollutants and the concentration limits of these species in drinking water are becoming more and more stringent. Common techniques used for the removal of metals are precipitation, electrolysis, chemical oxidation, adsorption or chelation, all of them presenting several drawbacks. Advanced Oxidative or Reductive Processes can constitute the basis of alternative water treatment for the removal of these kinds of pollutants. In particular, Heterogeneous Photocatalysis (HP), either Oxidative or Reductive can be successfully employed in the transformation of metals and metalloids. HP is a very well known technology, valuable for purification and remediation of water and air. Several excellent revisions exist on the subject, with different approaches [ - ]. After the HP basic step, i.e., the generation of an electron-hole pair by excitation of a semiconductor with photons of energy higher or equal to its bandgap, some metal or metalloid species can be oxidized by holes or hydroxyl radicals generated (e.g., Pb(II), As(III)) or reduced by conduction band electrons (e. g., Cr(VI), Hg(II), U(VI)) [ ]. Generally, the presence in the medium of an organic donor enhances reductive pathways through the generation of strongly reducing radicals by oxidation of the donor, with a synergistic effect and the possibility of simultaneous treatment of two pollutants. Two of our previous publications [7, ] have dealt with this topic. First, with a detailed review on transition metal ions in photocatalytic systems and, later, the cases of chromium, mercury, lead, uranium, and arsenic were reviewed. In this chapter, we will remind the most important issues and include all the advances made on the topic since 2009 until today with a significant contribution of results from our group.