Scientists Eye Cheaper Adsorbent

Algae-based material shows promise as a cost-effective replacement for activated carbon.

By Seán Ottewell, Editor at Large

A team of researchers from the Chemistry for Technologies Laboratory and the Department of Mechanical and Industrial Engineering, University of Brescia, Brescia, Italy, has developed a new class of low-cost and sustainable materials that they believe could replace activated carbon in many wastewater and air pollution treatment applications.

The synthesis method is simple and easy to scale up.

Today wastewater treatment encompasses many different technologies, including membrane filtration, ion-exchange, coagulation, adsorption, flocculation, microbiological or enzymatic decomposition, and advanced oxidation (For more on this topic, see, “Understand Industrial Wastewater Treatment”).

Each technology varies in degree of success, but adsorption often is favored more than others because of its simplicity, ease of operation, ability to respond rapidly to changing conditions, insensitivity to toxicity, and high efficiency and convenience.

One of the most commonly used adsorbents is activated carbon, well-known for its high adsorption capacity for dyes, organic contaminants and heavy metals. However, it is expensive to produce and regenerate, and can pose disposal problems.

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This was the starting point for the Italian researchers. They considered various natural resources and byproducts from industrial processes that could be used as cost-effective and more environmentally-friendly replacements. The result is an easily synthesized, porous, low-cost hybrid material that can act as adsorbent and filter for organic compounds removal, both from the air and wastewater.

The hybrid material is obtained by combining sodium alginate —a naturally occurring, highly abundant and inexpensive polysaccharide — with the amorphous silica fume, a byproduct derived from ferrosilicon or silicon metal alloy processing.

Sodium alginate, readily extracted from various species of algae and seaweeds, has long been the focus of intensive research due to its gelling capacity, film forming, emulsion stabilizing, biocompatibility, and non-toxicity properties. However, its mechanical strength often is an issue; research to overcome the problem includes cross linking, blending with hydrophilic materials and nano-reinforcement to produce nano-composites.

Also included in this research is alginate’s ability to form organic/inorganic composites — particularly with silica. These composites offer many advantages in terms of chemical and mechanical stability. They already are being investigated for possible applications in the fields of biomedicine, biocatalysis, bioseparation and biosensing. However, manufacture of such composites can involve solvents and precipitating agents that impact both their environmental and economic benefits.

What the Italian researchers have achieved is a simple, patent-pending synthesis of a new porous hybrid material using sodium alginate and silica fume. The material is consolidated by the gelling properties of alginate and by decomposition of sodium-bicarbonate controlled porosity at low temperatures (70–80°C). The structural, thermal, and morphological characterization shows that the material is a mesoporous (having pore diameters of 2–50nm) organic/inorganic hybrid. An article in Frontiers in Chemistry describes the research.

“This paper shows the simple synthesis of a new porous hybrid material, obtained by using low cost and byproduct materials,” says lead author, Elza Bontempi from the University of Brescia. “The material was designed on the basis of the European Commission’s request to develop an affordable, sustainable and innovative design-driven material solution that can reduce the concentration of particulate matter in urban areas.”

“The article reports preliminary results about the new material’s capability to capture particulate matter. It can also be used for wastewater remediation. In particular, its ability to replace activated carbon is demonstrated,” she adds.

The synthesis method is simple and easy to scale up. Taking advantage of the gelling properties of alginate, the researchers combined it with the decomposition of food-grade sodium bicarbonate (baking soda) to consolidate the material. Testing of wastewater pollution was performed using methylene blue dye as a model pollutant. The hybrid material adsorbed and removed the dye, even at high concentrations, with 94% efficiency. Further, coating the material with a 100-nm thin film of titania imparts good photo degradation of pollutants (more than 20%).

Analyses have revealed that, compared with activated carbon, production of the hybrid material consumed less energy while leaving a much smaller carbon footprint. The material also demonstrated encouraging capabilities for trapping diesel-exhaust-fume particulate matter.

The hybrid material can be applied as a coating, used for spraying or brushing, or 3-Dprinted. This means it could be used to cover external building surfaces to remove particulate matter, as well as in the design of novel water filtration units. This versatility, says Bontempi, makes it an exciting new addition to the toolkit for reducing air and water pollution.


Ottewell2Seán Ottewell is Chemical Processing's Editor at Large. You can email him at sottewell@putman.net.

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