Advances in Photo-catalytic Materials for Environmental Applications

Abstract

INTRODUCTIONOver two thirds of Earth's surface is covered by water; less than a third is taken up by land. As Earth's population continues to grow, people are putting ever-increasing pressure on the planet's water resources. In a sense, our oceans, rivers, and other inland waters are being "squeezed" by human activities-not so they take up less room, but so their quality is reduced. Poorer water quality means water pollution. We know that pollution is a human problem because it is a relatively recent development in the planet's history: before the 19 th century Industrial Revolution, people lived more in harmony with their immediate environment. As industrialization has spread around the globe, so the problem of pollution has spread with it. When Earth's population was much smaller, no one believed pollution would ever present a serious problem. It was once popularly believed that the oceans were far too big to pollute. Today, with around 7 billion people on the planet, it has become apparent that there are limits. Pollution is one of the signs that humans have exceeded those limits.Water pollution can be defined in many ways. Usually, it means one or more substances have built up in water to such an extent that they cause problems for animals or people. Water pollution almost always means that some damage has been done to an ocean, river, lake, or other water source. A 1969 United Nations report defined ocean pollution as: "The introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities, including fishing, impairment of quality for use of sea water and reduction of amenities."Most water pollution doesn't begin in the water itself. Take the oceans: around 80 percent of ocean pollution enters our seas from the land. Virtually any human activity can have an effect on the quality of our water environment. When farmers fertilize the fields, the chemicals they use are gradually washed by rain into the groundwater or surface waters nearby. Sometimes the causes of water pollution are quite surprising. Chemicals released by smokestacks (chimneys) can enter the atmosphere and then fall back to earth as rain, entering seas, rivers, and lakes and causing water pollution. That's called atmospheric deposition. Water pollution has many different causes like: Sewage, Nutrients, Chemical waste, radioactive waste, Oil pollution, Plastics and Alien species. The common pollutants include toxic organic compounds like chlorinated and non-chlorinated aliphatic and aromatic compounds, dyes, inorganic compounds like heavy metals, noxious gases like NO x , SO x , CO and NH 3 , and pathogens like bacteria, fungi and viruses. ABSTRACTThe growth of industry worldwide has extremely increased the generation and accumulation of waste by products. This has caused severe environmental problems that have become a major concern. Because of this, photo-catalytic polluta...

Recent Review of Titania-Clay-Based Composites Emerging as Advanced Adsorbents and Photocatalysts for Degradation of Dyes over the Last Decade

“…The dye pollutants get adsorbed on its exterior where redox reactions transpire as a result of generation of electrons from conduction band (CB) and holes from valence band (VB). The resultant products finally detach from the photocatalyst and are discarded into the aqueous media [53]. The reaction mechanism can be simplified as follows: (3) Photocatalyst + UV Vis ⟶ Hole s VB + e CB Hole s VB + e CB ⟶ E Δ h Hole s VB + H 2 O ⟶ O ∙ H + H + e CB + O 2 ⟶ O ∙ 2 O ∙ H + Dye ⟶ H 2 O + C O 2 O…”

Photocatalytic Degradation of Congo Red Dye via Multi-Walled Carbon Nanotubes Modified CuO and ZnO Nanoparticles under Visible Light Irradiation

“…It believes that both large numbers of defects and acceptor states are responsible for improving photocatalytic performance. The presence of ZnO defects serves as an electron acceptor or a hole donor to promote the position of the carrier charges and thus prolonged separation by trapping at energy levels close to the conductive or valence bands, respectively [62]. Photogenerated electrons (eCb -) can also react with electron acceptors such as O2 adsorbed on the nanocomposite surface or dissolved in water, reducing it to radical anion O2superoxide.…”