Application of Nanomaterials in Wastewater Treatment
Water is an indispensable substance in human life and production. With the development of industry, the problem of water pollution is becoming more and more serious. For example, heavy metals in industrial production (such as Pb2+, As3+, Cu2+, Cr6+, Cd2+, Co3+, Mn2+, Hg2+, etc.) enter the natural environment with the discharge of industrial wastewater. Water bodies, causing water heavy metal pollution. Even at low concentrations, heavy metals can cause significant toxicity to microorganisms. A series of problems caused by wastewater discharge are attracting people's attention.
In the past few decades, nanomaterials have been actively researched and developed and successfully applied in many fields such as catalysis, medicine, sensing, and biology. In particular, the application of nanomaterials in water and wastewater treatment has received great attention. Due to the small size of nanomaterials, they have a large specific surface area, so they have strong adsorption capacity and reactivity. More importantly, the mobility of nanomaterials in solution is high. Therefore, various nanomaterials have achieved great success in the removal of heavy metals (Fig. 1), organic pollutants, inorganic anions, bacteria, etc. Based on a large number of studies, nanomaterials show great application prospects in water and wastewater treatment. Currently, the most widely studied nanomaterials for water and wastewater treatment mainly include zero-valent metal nanoparticles, metal oxide nanoparticles, and carbon nanomaterials.
Figure 1: Schematic diagram of a magnetic separator based on magnetic nanoparticles for wastewater treatment
Applications of Nanomaterials in Water and Wastewater Treatment
Silver Nanoparticles
Silver nanoparticles (Silver nanoparticles) are highly toxic to microorganisms and thus have strong antibacterial effects against a variety of microorganisms including viruses, bacteria, and fungi. As a good antibacterial agent, silver nanoparticles have been widely used in water disinfection. For example, adding silver nanoparticles to a ceramic filter composed of clay and sawdust increased the removal efficiency of E. coli. The study also found that filters with higher porosity removed bacteria more efficiently than filters with lower porosity.
Iron Nanoparticles
Various zero-valent metal (such as iron) nanoparticles have different standard reduction potentials. Compared with many redox pollutants, nano-sized zero-valent iron has good potential as a reducing agent. Despite its weak reducing ability, iron has many outstanding advantages for its application in water pollution treatment compared with other metals, including excellent adsorption performance, precipitation and oxidation (in the presence of dissolved oxygen), and low cost. Therefore, nano-sized zero-valent iron (nZVI) nanoparticles have been the most widely studied zero-valent metal nanoparticles.
Zinc Nanoparticles
Although most studies on the degradation of pollutants by zero-valent metal nanoparticles in water and wastewater treatment have focused on iron, zinc has also been considered as an alternative. Zinc has a more negative standard reduction potential than iron and is a stronger reducing agent. Therefore, Zn nanoparticles may degrade pollutants faster than nZVI.
TiO2 Nanoparticles
The electrochemical photolysis of water on TiO2 semiconductor electrodes in 1972
Since then, photocatalytic degradation, as an emerging and promising technology, has attracted widespread attention. In recent years, photocatalytic degradation technology has been successfully applied to the degradation of pollutants in water and wastewater. In the presence of light and catalysts, pollutants can be gradually oxidized into low-molecular-weight intermediate products, and finally converted into CO2, H2O, and anions such as NO3-, PO43-, and Cl-. The photocatalytic properties of TiO2 nanoparticles are capable of killing a variety of microorganisms, such as Gram-negative and Gram-positive bacteria, as well as fungi, algae, protozoa, and viruses.
Zinc Oxide Nanoparticles
In the field of photocatalysis, in addition to TiO2 nanoparticles, ZnO nanoparticles have become the most popular materials for water and Another effective candidate for wastewater treatment. In addition, zinc oxide nanoparticles are environmentally friendly because they are biocompatible, which makes them suitable for water and wastewater treatment.
Iron Oxide Nanoparticles
In recent years, there has been increasing interest in iron oxide nanoparticles for the removal of heavy metals due to their simplicity and availability. Magnetic magnetite (Fe3O4), magnetic magnetite (γ-Fe2O4), and non-magnetic hematite (α-Fe2O3) are often used as nanosorbents. For example, Fe3O4 nanoparticles are usually embedded in a layer of inorganic, organic, or inorganic-organic compounds to form a core-shell structure, which not only avoids the aggregation of nanoparticles but also improves the adsorption of composite particles by increasing the adsorption functional groups on the surface. performance.
Carbon Nanomaterials
Carbon nanomaterials (CNM) for water and wastewater treatment are a strong ability to adsorb various pollutants, fast kinetics, large specific surface area, and selectivity to aromatics. CNMs come in several forms, such as carbon nanotubes (CNTs), carbon beads, carbon fibers, and nanoporous carbons. Among them, CNTs are the most concerned and fastest-growing materials in recent years.
References
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