Tag Archives: Polymer

Efficient Removal of Heavy Metal Ions from Water by Nanoporous Thin Films

Posted on November 13, 2017 by | 1 comment

The term heavy metal refers to any metallic chemical element that is toxic or poisonous at low concentrations. The most common heavy metals include mercury (Hg), arsenic (As), chromium (Cr), cadmium (Cd) and lead (Pb).

Heavy metals are natural components of Earth’s crust. They are non-degradable. They enter our bodies via food, drinking water and air. At very low concentrations, some heavy metals, such as copper and zinc, are essential to maintain the metabolism of the human body. However, at higher concentrations they can cause poisoning and put our lives at risk. For example, high levels of lead (II) cations can hinder brain development in children who drink from contaminated sources and cause organ damage to people of all ages. Similarly, water supplies contaminated with cadmium (II) cations cause the weakening of bones and damage our kidneys and livers.

Heavy metals are dangerous because they tend to bioaccumulate. In other words, their concentrations increase in our bodies over time. They are stored faster than they are broken down or excreted.

Heavy metals can enter a water supply by industrial and consumer waste, or from acidic rain breaking down soils and releasing heavy metals into streams, groundwater and other water sources.

In order to remove the heavy metals from our water supplies, Weidman and co-workers functionalized nanoporous thin films of poly(acrylic acid) (PAA) with glutathione and cysteamine. Glutathione and cysteamine are peptides that exist in many organisms to counter the accumulation of heavy metal ions. For example, glutathione, which is found in many plants and animals, can bind to the metal ions and remove the ions from transport pathways within the organism.

Coupling glutathione to PI−PS−PAA films can remove over 93% of heavy metal ions for drinkable water. (Source: Weidman et al., 2017)

Unlike the conventional packed bed processes, which require long residence times for effective removal of heavy metals; the nanoporous films have a lot of built-in functional groups, which allow the coupling of glutathione and cysteamine to the groups. The ready attachment of glutathione and cysteamine to the films enable efficient removal of toxic heavy metals from water supplies.

The thin films were tested with cadmium (Cd2+) and lead (Pb2+) ions. Results showed that the films could remove over 93% of the heavy metal ions. Furthermore, in mixed ion solutions, the capacity and removal rates of the films did not reduce. After repeatedly regenerating the films, the films showed no loss in capacity.

The percent of metal removed in the solution containing cysteamine-functionalized films (left) and in the solution containing glutathione-functionalized films (right). (Source: Weidman et al., 2017)

In conclusion, these thin films provide a sustainable platform for the efficient purification of lead- and cadmium- contaminated water sources to safe levels.

-Jennifer Liu-

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Stretching the Mussels

Posted on November 6, 2017 by | 1 comment

Many everyday products such as tire rubber rely on their ability to stretch. These materials are mainly consisted of a type of polymer called the elastomer which  can flex without breaking and return to the original form. However, a big limitation of elastomer materials is the lack of strength. A group of researchers has developed a tough but still flexible elastomer but they were inspired by an unusual creature, the mussel.

Mussels (Wikimedia Commons)

Elastomers are structurally shapeless polymer strands with only a few chemical cross-links in between, In order to strengthen the elastomer, the density of the strands must be increased but a denser and more structured polymer would result in a stiffer and more brittle material.

Mussels form a tough and flexible polymer to secure to the surfaces in rough intertidal zones. The researcher at UC Santa Barbara’s Materials Research Laboratory were inspired by this natural polymer and they developed a way to maintain elasticity while increasing strengths in elastomeric polymers.

The research focused on a dry polymeric system which is different from previous research which was limited to wet systems. The researchers utilized a mussel inspired iron coordination complexes into a dry polymeric system. The iron coordination provides a self-healing mechanism which can reform broken cross-links therefore maintaining the material’s flexibility but increases the toughness.

They found that the iron incorporated polymers do not store energy when it is stretched. It disperses the energy then slowly recovers to the original shape. This material can be very useful in everyday uses to absorb contact such as the inside of a helmet or the coating of a phone case.

Polymers that contain metal coordination are not widely used and researched. This research opens up possibilities to change a polymer’s properties by the uses of metals. Further research into this field has the potential to optimize functionality and durability in many everyday applications.

Science discovers can come from anywhere. Chemistry advancements often happen in the laboratory but the inspiration is  all around us. This research’s method of developing a tough elastomer will allow for more research into the relationship between elasticity and strength of elastomers.

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A New Wastewater Treatment Strategy by a Porous β-cyclodextrin Polymer

Posted on October 21, 2017 by | 1 comment

Micropollutants are residue from substances, used everyday in modern society, including pharmaceuticals and personal care products (PPCPs), hormones, pesticides and industrial chemicals. According to University of Georgia Office of Research, 90% of consumed prescription drugs ultimately end up in our waste water. Micropollutants are hazardous, persistent, and not bio-degradable. They cannot be removed with conventional waste water treatment technologies. The continued release of micropollutants with wastewater effluent can cause long-term hazards such as rise of antibiotic-resistant organisms and reproductive and developmental abnormalities on sensitive species.

Wastewater treatment plant (Photo source: IWA)

Activated carbons are the most common materials used to remove organic pollutants from water. However, they have several deficiencies, including slow pollutant uptake (of the order of hours), poor removal of relatively hydrophilic micropollutants and poor regeneration performance. Since activated carbons bind to most substances through London dispersion forces, they adsorb larger molecules and non-polar molecules preferentially.

Scientists from Cornell University had synthesized porous β-cyclodextrin-containing polymers (P-CDPs) to remove the micropollutants from water. β-cyclodextrin (β-CD) is an inexpensive, sustainably produced cyclic macromolecule of glucose. It was crosslinked with rigid aromatic groups, providing a high-surface-area polymer of β-CD containing pores of 1.8–3.5 nm diameter. The resulting polymer can rapidly remove a variety of organic micropollutants with adsorption rate constants 15 to 200 times greater than those of activated carbons. In addition, the polymer can be easily and repeatedly regenerated by rinsing the polymer with methanol at room temperature while with no loss in performance. Finally, it can rapidly remove a complex mixture of organic micropollutants, including aromatic model compounds, pesticide, plastic components and pharmaceuticals, at environmentally relevant concentrations. The porous cyclodextrin-based polymers offer a rapid, flow-through water treatment.

P-CDPs were derived from nucleophilic aromatic substitution of hydroxyl (-OH) groups of β-CD by tetrafluoroterephthalonitrile (1) (Fig. a). The side groups of the P-CDPs, including fluoride (-F), cyano (-CN) and hydroxyl (-OH) groups, can bind to pollutants of different sizes and hydrophobicities through London dispersion forces and ionic, covalent and hydrogen bonds.

Figure a | Left, synthesis of the high-surface-area porous P-CDP from β-CD and 1. Right, schematic of the P-CDP structure. (Alsbaiee et al., 2016)

β-CD and 1 were polymerized in a suspension of potassium carbonate (K2CO3) in tetrahydrofuran (THF) at 80 °C to provide a pale-yellow precipitate, which proved to be the P-CDPs. P-CDPs obtained from 1:β-CD ratio of 3:1 exhibited the highest surface areas. A cost analysis of P-CDP indicates raw materials costs of US dollar (USD) 3.70 per kg.

Existing biological wastewater treatment plants are not specifically designed to remove micropollutants, and conventional activated carbons have poor removal performance and slow pollutant uptake. Therefore, the P-CDP, which can remove a wide range of micropollutants, presents a possible solution for wastewater treatment.

-Jennifer Liu-

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