Environmental Engineering Reference
In-Depth Information
11
Destruction of chloroorganic compounDs
with nanophotocatalysts
Rashid A. Khaydarov, Renat R. Khaydarov, and Olga Gapurova
Institute of Nuclear Physics, Uzbekistan Academy of Sciences, Tashkent, Uzbekistan
11.1
introDuction
Photocatalysis based on the application of nanocatalysts is a very promising method for the treatment of contaminated water,
air, and land. Photocatalytic systems equipped with artificial ultraviolet (UV) light systems can be applied at ambient tempera-
ture to degrade various chemical and microbiological pollutants: organic materials, organic acids, estrogens, pesticides, dyes,
crude oil, microbes (including viruses and chlorine-resistant organisms), and inorganic substances.
There are several potential photocatalysts, but the most widespread substance is nano titanium dioxide. Nanosized particles
are preferred to bulk TiO
2
because they are significantly more reactive than larger particles due to their larger surface area. TiO
2
is chemically stable and has a high ability to break molecular bonds leading to degradation. To avoid free nanoparticles in water,
nano TiO
2
particles are usually immobilized on a substrate or integrated into thin films and other materials. On the other hand,
the lifetime of nanoparticles before their agglomeration can be easily regulated [1], and the nanoparticles can be transformed
into large particles that are absolutely safe for the environment. This method opens an opportunity to increase the efficiency of
catalysts significantly by using colloidal nanophotocatalysts (NPC) homogeneously dispersed on the surface of land to be
treated. At present, the development of new types of NPCs with enhanced catalytic properties is a challenge, as they have many
applications in science and technology.
This chapter deals with a new method for the destruction of chloroorganic compounds that is based on the use of colloidal
nanocarbon-metal compositions (NCMC) as NPC dispersed on polluted land, soil, and water. Dichlorodiphenyltrichloroethane
(DDT), aldrin, lindane, and polychlorinated biphenyls (PCBs) have been chosen as the chloroorganic compounds to test NPC
efficiency.
The production and agricultural use of DDT was banned in the early 1970s. The environmental distribution and effects
of DDT arise from its unusual chemical stability and hence its persistence. DDT and some of the breakdown products of
DDT, principally dichlorodiphenyldichloroethylene (DDE), are highly persistent in soil, sediment, and biota as they are
relatively resistant to breakdown by the enzymes and higher organisms found in the soil. Thus contamination by these
substances can last long after DDT application.
Aldrin is an organochlorine insecticide that was widely used until the 1970s, when it was banned in most countries. Before
the ban, it was heavily used as a pesticide to treat seed and soil. In soil, on plant surfaces, or in the digestive tracts of insects,
aldrin oxidizes to epoxide dieldrin, which is a stronger insecticide. Like related polychlorinated pesticides, aldrin is highly
lipophilic. Its solubility in water is only 0.027 mg/l, which exacerbates its persistence in the environment. It was banned by the
Stockholm Convention on Persistent Organic Pollutants.
