Nanomaterials are the main players that promise profits through their nano-enabled applications in multiple fields.
Nanomaterials have been used in many environmental applications such as the treatment of contaminated water for drinking, agriculture and more recent application than conventional means.
The explosive development in nanotechnology research has presented new strategies for environmental remediation.
Some of these applications use the properties of the nanomaterials that relate to their high specific surface areas, such as fast dissolution, high reactivity and strong sorption.
Others take advantage of their discontinuous properties, such as superparamagnetic, localized surface plasmon resonance (SPR), and quantum confinement effect.
Most applications discussed in this article are still in the stage of research and development.
Water pollution is the most difficult environmental challenge facing society.
Therefore, the release of pollutants from sewage or industrial wastewater must be considered a threat to the environment.
Characterizing the physical, chemical and biological aspects of raw water and treated water is crucial to ensure that they are safe for disposal in the aquatic or desert environment.
Water pollution
The leaching of pollutants into groundwater from sewage or industrial water causes serious health problems, which may be used by humans for drinking and other purposes in some areas.
It is worth mentioning that a man cannot live more than three days without water.
Heavy metals are likely to be the most common water problem consumers face.
Heavy metals (such as arsenic, zinc, iron, manganese, aluminum, cadmium, lead, etc.) cause many health problems if found in drinking water at concentrations higher than permitted.
Titanium dioxide nanoparticles
Titanium dioxide nanoparticles, also called ultrafine titanium dioxide, are particles of titanium dioxide (TiO2) with diameters less than 100 nm.
Ultrafine TiO2 is used in sunscreens due to its ability to block UV radiation while remaining transparent on the skin.
Its photocatalytic sterilizing properties also make it useful for many applications.
Nanoparticles of TiO2 are found different in their surface-to-volume ratio, their properties change so that they acquire catalytic ability.
Activated by sunlight’s ultraviolet (UV) component, they break down toxins or enhance other relevant reactions.
Titanium oxide photocatalysts have been broadly studied for solar energy conversion and environmental applications in the past several decades, because of their high chemical stability, good photoactivity, relatively low cost and non-toxicity.
Photocatalytic oxidation process
In the photocatalytic oxidation process, organic pollutants are cracked in the presence of semiconductor photocatalysts, an energetic light source, or an oxidant such as oxygen or air.
Only photons with energies greater than the bandgap energy (ΔE) can result in the excitation of valence band (VB) electrons that then promote possible reactions.
Recently, advanced oxidation processes (AOPs) using (TiO2) have been used successfully to toxic pollutants removal from industrial wastewater.
TiO2 features as a photocatalytic agent
1. High photochemical reactivity.
2. High photocatalytic activity.
3. Low cost.
4. Stability in aquatic systems.
5. Low environmental toxicity.
Mechanism of dye degradation upon irradiation
Photocatalytic oxidation is an AOP for the elimination of trace pollutants and microbial pathogens.
It is a valuable pretreatment for hazardous and nonbiodegradable pollutants to enhance their biodegradability.
Photocatalysis can also be used as a polishing step to treat recalcitrant organic compounds.
The major barrier to its wide application is slow kinetics, due to limited light fluence and photocatalytic activity.
Current research focuses on increasing photocatalytic reaction kinetics and photoactivity range.
Gold nanoparticles
The modification of the Au surface with appropriate chemical species can improve separation and preconcentration efficiency, and analytical selectivity.
Making gold (AuNPs), is considered one of the wide selections of core resources available, coupled with tunable surface properties in the form of inorganics or inorganic-organic amalgams, and has been described as an excellent platform for a broad range of analytical methods.
Advantages of Gold (AuNPs)
1. High surface-to-volume ratio.
2. Easy surface modification.
3. Simple synthesis methods.
The AuNPs have been applied successfully used in:
1. Removal of peptides.
2. Removal of proteins.
3. Removal of heavy metal ions.
4. Removal of polycyclic aromatic hydrocarbons (PAHs).
Zerovalent iron nanoparticles
Elemental iron has been used as an ideal candidate for remediation, for the following reasons:
1. Low-cost,
2. Extremely easy to prepare and apply to a variety of systems.
3. No toxicity is induced by its usage.
The idea of using metals such as iron as remediation is dependent on reduction-oxidation reactions, in which a neutral electron donor (a metal) chemically reduces an electron acceptor (a pollutant).
Nanoscale iron particles have surface areas greater than larger-sized powders, which leads to enhanced reactivity for the redox process.
Zero valent iron nanoparticles applications:
1. Decomposition of halogenated hydrocarbons to benign hydrocarbons.
2. Remediation of heavy metals.
3. Solvents dichlorination
A significant loss of reactivity can occur before the particles can reach the target contaminant.
In addition, zero-valent iron nanoparticles tend to flocculate when added to water, resulting in a reduction in the effective surface area of the metal.
Therefore, the effectiveness of remediation depends on the accessibility of the contaminants to the nanoparticles, and the maximum efficiency of remediation will be achieved only if the metal nanoparticles can effectively migrate without oxidation to the contaminant or the water–contaminant interface.
To overcome such difficulties, a regularly used strategy is to integrate iron nanoparticles within support materials, such as polymers, porous carbon and polyelectrolytes.
Finally, Nanotechnology for water and wastewater management is depending on the matchless properties of nanomaterials and their conjunction with current treatment technologies presents great chances to revolutionize water and wastewater treatment.
Nanotechnology has shown huge possibilities in water treatment technologies.
The recent development of nanotechnology has raised the possibility of environmental decontamination through several nanomaterials cutting the process and tools.
Another nanomaterials application in the water treatment field may be discussed in another article.
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