A KU research team has developed a hybrid material capable of adsorbing pollutants from industrial wastewater using two natural resources of great abundance in the UAE – sand and dates.
Removing pollutants from industrial wastewater safely and affordably is a fundamental concern for governments worldwide. Now, an emerging technology is being explored by researchers at Khalifa University that aims to clean wastewater using two natural resources of great abundance in the UAE – sand and dates.
The KU research team developed a graphene-sand hybrid material capable of adsorbing pollutants, which involves attaching pollutants onto small particles that are then easily removed. While synthesizing graphene-sand adsorbents can be prohibitively expensive, the KU researchers have turned to a previously unused resource – date syrup – to provide the carbon needed to produce the graphene.
“While other routes have been studied, using sugar, for example, as the carbon base for graphene-sand adsorbents, our project aims at utilizing locally available resources for tackling global challenges. As far as we know, we’re the first to use date syrup as a sustainable carbon source,” explained Dr. Fawzi Banat, Professor of Chemical Engineering, at Khalifa University.
Dr. Banat, along with Anjali Edathil, former Research Engineer in the Department of Chemical Engineering, and Shaihroz Khan, visiting Research Assistant, described the in-situ strategy used to produce the graphene-sand hybrid with date syrup in a paper published in Scientific Reports.
Their adsorbent can be used as an environmentally benign and scalable option for decontaminating wastewater, with the adsorption capacity far surpassing that of similar reported graphene-based adsorbents.
“Water is one of the world’s most valuable resources, and only one percent of the global water supply is available for consumption and domestic use,” explained Dr. Banat. “With augmented urbanization and substantial industrialization activity, enormous amounts of hazardous chemicals are discharged into receiving waters every day. Among the emerging inorganic and organic contaminants, heavy metals and dyes are frequently found in industrial effluents, which, if untreated, become a principal concern to the environment and public health. They are non-biodegradable and tend to accumulate in living organisms.”
Numerous efforts have focused on developing cost-effective and appropriate materials and technologies to regulate the amount of these persistent water pollutants to permissible levels before wastewater is discharged to water bodies. Different treatment technologies have been tested, including photodegradation, precipitation, coagulation, membrane separation, and ion exchange. While all work, they suffer from drawbacks in applicability and cost-effectiveness.
Comparatively, the process of adsorption – where a solid holds molecules of a dissolved solid, liquid or gas on its surface by adhesion – is a relatively mature and versatile method for removing pollutants. Traditionally, carbon-rich materials such as charcoal, soot and biochar are used as adsorbents due to their low costs and high surface areas.
“With the advent of nanotechnology, researchers have explored the use of carbon nanomaterials for water purification, with the hope that it may open new fruitful pathways to curb the existing water shortage,” explained Dr. Banat.
“Graphene has attracted tremendous research interest. Its unique physiochemical and mechanical properties have led to its potential as a revolutionary adsorbent for environmental pollutant management. However, a key barrier in the practicality of pristine graphene nanosheets for water purification is its high cost and post-treatment handling, including recovery after the decontamination process.”
Graphene is a novel 2D, one-atom-thick nanomaterial made of carbon atoms arranged in a honeycomb structure. In many cases, such as this one, graphene is organized into sheets a few layers thick rather than existing as a single monolayer. Regardless of organization, however, graphene’s high surface area, combined with its versatile chemistry and highly hydrophobic surface, makes it an ideal adsorbent for removing pollutants. The natural defects and ‘wrinkles’ on its surface act as high-surface-energy adsorption sites for organic pollutants. However, graphene aggregates heavily in water due to the strong forces between the graphene layers.
“To overcome these issues, we can anchor the nanosheets onto an economical and reliable inorganic substrate such as sand,” explained Dr. Banat. “Graphene-sand hybrids not only allow the full expression of the graphene adsorption sites but also ensure dispersibility and easy separation from water.”
Dr. Banat’s research proposes a single-step strategy to develop efficient and eco-friendly graphene sand hybrids using date syrup, a widely available and sustainable carbon source in the Middle East.
Different carbon sources are available in different parts of the world, with several synthetic routes already reported for the preparation of graphene-sand hybrids from sugar, palm sugar, gelatin and asphalt.
Dr. Banat’s team used pyrolysis – the process of chemically decomposing organic materials at high temperatures in the absence of oxygen – to decompose the date syrup, triggering a change of chemical composition and the synthesis of a large volume of graphene material, that subsequently attaches to desert sand without the use of any external chemical agents.
“It is believed that during pyrolysis, the naturally abundant sucrose and fructose molecules in the date syrup undergo complete exfoliation to form graphene nanosheets on the desert sand surface, thereby exposing the powerful adsorption sites concealed in the stacked graphene,” said Dr. Banat.
Dr. Banat’s graphene-sand hybrid adsorbent was tested in the laboratory and showed remarkable efficiency in simultaneously removing both dye and heavy metals from multicomponent systems. The researchers concluded that their adsorbent had great potential as an exceptional material resource of water purification.
“This will undoubtedly open new avenues for the practicability of graphene to curb the existing water shortage,” added Dr. Banat. “We hope our material will help in increasing water resources in the UAE, reducing energy consumption in wastewater treatment processes and be used to convert oily wastewaters from waste to commodity than can be used in applications such as industrial recycling and agriculture.”