Efficient and environmentally friendly ways to eliminate pollution

Contamination of air and water by pesticides, pharmaceuticals, heavy metals, toxic gases and volatile organic compounds (VOCs) is a serious and growing public health concern. As a result, various decontamination methods such as chlorination, adsorption and oxidation have been developed; however, the most commonly used methods cannot remove all contaminants. Newer methods using nanomaterials have attracted much attention in recent years as the substances with unique structures could provide efficient, environmentally friendly and cost-effective ways to remediate pollution.

In a new study, Virender Sharma, PhD, professor in the Department of Environmental and Occupational Health at the Texas A&M School of Public Health, and other researchers from the School of Public Health and the University of Cincinnati investigated the state-of-the-art research on environmental decontamination using black phosphorous (BP). Their study, published in the Chemical Engineering Journal, reviewed the studies of BP-based nanomaterials in decontamination of water and air as well as research on improving BP’s stability and possible future uses of these materials.

BP is a two-dimensional nanomaterial consisting of ultrathin layers of phosphorous with a folded hexagonal structure that resembles a honeycomb. Like graphene, BP has unusual physical, chemical and electrical properties that give tremendous potential for use in a variety of applications. One property of BP is its ability to trap heavy metals, organic pollutants and VOCs on its surface, largely due to its high surface area. Additionally, BP shows strong absorption of ultraviolet light, suggesting that it could be useful in solar cells and as a photocatalyst for pollution remediation.

The researchers reviewed several studies on the use of BP-based composites to decontaminate water. One study examined the use of a single layer BP composite to remove arsenic and chromium from water, and found that the material was highly effective. Another study looked at removing dioxin from polluted water, and noted that BP doped with calcium atom performed well. They also reviewed an article comparing the performance of a BP-based composite against that of metal oxides and graphene at removing organic dyes and found that BP performed better than the other materials.

Research shows that BP is a promising material for cleaning polluted water, and the research team found similar results for decontaminating air. One study investigated the adsorption of VOCs from the air. VOCs present a risk to public health and are a concern near petrochemical plants and other industrial facilities. For example, people living in and around Deer Park, Texas, were warned to stay indoors due to high levels of benzene in the air following the Intercontinental Terminals Co fire in early 2019. Another study reviewed by Sharma and colleagues examined the adsorption of toxic gases like hydrogen sulfide, hydrogen cyanide and ammonia using BP treated with different metals. That study found that BP composites treated with platinum, aluminum and nickel were most effective at trapping toxic gases on their surfaces.

Another promising technique for pollution remediation is photocatalysis, in which materials known as photocatalysts get rid of pollutants in the presence of light. One study found that BP-based materials perform extremely well at removing dyes from water under ultraviolet light; however, the material’s performance was degraded after several runs as BP dissolved into the water. That study found that treating BP with titanium dioxide made the material much more stable and that it could maintain its high performance over a long time. Other studies looked at improving BP’s photocatalytic performance by combining it with materials like silver nanoparticles and found that the resulting materials were well-suited for eliminating organic pollutants like BPA from water. Studies of BP’s photocatalytic abilities in the air found that BP-based materials could eliminate nitric oxide from the air, oxidizing it into less harmful compounds, and that the materials were stable for a long time.

The researchers also found several studies focusing on the ways to address BP’s deterioration in water or humid air and thus improve its stability. These studies involved the use of solvents to prepare BP-based materials, combining BP with graphene to protect the BP, coating BP sheets with aluminum oxide or titanium dioxide and various other chemical techniques. They also found that studies identified thermal and electron beam treatments as possible future avenues of research.

In their review of recent literature, Sharma and colleagues found that most of the studies reviewed dealt with single pollutants at high concentrations in otherwise pure air and water. Thus, additional research dealing with multiple contaminants, lower concentrations and the presence of organic matter and particulates in air and water is needed.

Although the body of research on BP-based pollution remediation is expanding, the field is still relatively new and plenty of work remains. However, the body of research thus far shows that BP-based materials hold promise as an effective method for remediating pollution.