Researchers have found that a one-dimensional, lepidocrocite structured titanium oxide photocatalyst material has the ability to break down two common dye pollutants under the visible light spectrum.
- The material also reduced those dye concentrations in the water by 90% and 64%, respectively, in just 30 minutes, when the starting catalyst to dye mass ratio was 1 to 1.
- The two pollutants are rhodamine 6G and crystal violet, and the solution uses a tiny nanofilament.
THE SIGNIFICANCE: This is being seen as an exciting finding because it helps to address a problem that has been a real challenge for the water treatment process.
- The researchers anticipate that integrating a titanium-oxide photocatalyst into the current processes could improve its effectiveness in removing these chemicals, as well as reducing the amount of energy required to do so.
THE BACKDROP: Discharged in large quantities by textile, cosmetic, ink, paper and other manufacturers, dyes carry high-toxicity and can bring potential carcinogens to wastewater. It has been a major concern for wastewater treatment.
- Wastewater is a major environmental concern worldwide and its existence has long-term impacts on health of humans, aquatic plants and animals. Households and industry generate nearly 380 billion cubic tonnes of wastewater globally each year.
- Only 24% of this is treated sufficiently due to challenges in treatment, including high energy consumption, the existence of residual chemicals, treatment center staffing and the insufficient processing of complex and persistent contaminants, including dyes.
- The most common wastewater treatment methods, such as sedimentation, biological oxidation and chemical-physical treatment, are ineffective at removing dyes, according to the researchers, due to the dyes’ complex molecular structure and water-soluble nature.
THE RESEARCHERS: The researchers were led by Michel Barsoum, Distinguished University professor in the College of Engineering at Drexel University, and his team, including researchers from Drexel’s College of Arts and Sciences.
- The study, recently published in the journal Matter, found that the key to the dye degradation and self-sensitisation process was the ability of the material to generate electron holes and something called “ROS” — hydroxyl , superoxide and singlet oxygen, radicals, as well as electron “holes.”
THE SCIENCE: The process starts with adsorption, where the dye adheres to the surface of the nanofilament, and once illuminated undergoes photocatalysis. The dye sensitizes the nanofilaments to visible light. This process accelerates degradation, allowing the dye to break apart into harmless byproducts such as carbon dioxide and water.
- The two dye targets are commonly appearing dye driven effluents in wastewater. Effluent is different than sewage found in wastewater. Solid waste can be filtered, removed before the water is purified. Effluent is suspended in the water, making it hard to separate and remove.
- Rhodamine 6G is a xanthene-derived dye primarily used in wood processing, paper dyeing, pen ink and cosmetics. Crystal violet, a triphenylmethane dye, is used to dye ink and textiles. These dyes are water soluble and any excess is discharged as effluent.
- Adsorption with clay materials, activated carbon, iron oxide and natural materials such as coffee grounds, has also been used before and exhibit high cationic dye uptake, exchanging ions or forming bonds. However, these materials simply allow separation of the dye from the water — the dye still exists and is simply attached to the adsorbent materials within the wastewater.
- Photocatalysts, long thought to be the key to removing dyes from water, thus far have not produced a sustainable solution. Many photocatalysts typically require UV light treatment, which uses extensive energy. The impact of the new nanofilament resides in its self-sensitisation behaviour, which makes the nanofilament more sensitive to visible light.
- The result: cleaner water without the use of additional toxins or additional energy.
- The team used x-ray diffraction to characterise the arrangement of atoms in the nanomaterial. They further characterised the nanomaterial with scanning and transmission electron microscopy, which sends beams of electrons at the material to form an image.
WHAT THEY SAID:
We are just beginning to uncover the possibilities of this material. As we better understand the processes enabling its behaviour, we anticipate exploring new applications where it could improve the performance of technology that the world needs to move toward a more sustainable future.
— Michel Barsoum
Distinguished Professor, College of Engineering
Drexel University
