This loofah-inspired gel uses sunlight to purify water

Here is an affordable spongy alternative to expensive water purifiers.
Rupendra Brahambhatt
Loofah sponge-inspired hydrogel.
Loofah sponge-inspired hydrogel.

Adapted from ACS Central Science 2023

We previously reported about a pufferfish-inspired hydrogel that purifies water using sunlight. The researchers have now proposed an improved version of the gel, which is capable of purifying water at a rate enough to meet a person’s daily water demand.

Unlike the previous gel, the improved version can work in cloudy conditions. This has been made possible by its loofah-inspired design that has an open-pore network interconnected by cellulose fibers. The network allows rapid liquid permeation.

One of the study authors and a postdoctoral research associate at Princeton University, Xiaohui Xu, told IE, “Water scarcity is one of the global challenges. To alleviate this, we developed a solar absorber gel for water purification. The previous gel worked great, but we want to further enhance the water release rate to meet daily water demand. 

She further added, “We noticed natural loofah has rapid liquid permeation. So inspired by loofah, we developed this second-generation hydrogel for water purification.” 

The researchers believe that besides providing clean water access in a sustainable and low-cost way to the world’s population, the enhanced version of the hydrogel could also be employed in various applications related to chemical separation, drug delivery, and smart sensors. 

How did scientists create the loofah-inspired gel?

The previously developed hydrogel was mainly composed of poly(N-isopropyl acrylamide) or PNIPAm. This gel could be placed in a water source in the evening, and it released the purified water when exposed to sunlight. 

However, due to its closed pores, the previous version of the PNIPAm gel released water slowly, and therefore, it wasn’t able to remove enough water to meet even a day’s demand of a person. The researchers added some additional coatings to PNIPAm gel to provide a loofah-like open pore structure.

“The (enhanced) hydrogel uniquely integrates the attributes of PNIPAm, polydopamine (PDA), and poly (sulfobetaine methacrylate) (PSBMA). The PDA and PSBMA coatings on the hydrogel’s inner pores endow the gel with photothermal properties, pollutant-removing ability, and anti-oil- and bio-fouling characteristics,” Xu told IE

According to the researchers, the open pore network allows the loofah-inspired hydrogel to release water at a rate four times that of the previously developed PNIPAm gel.

Water purification using loofah-inspired hydrogel?

This loofah-inspired gel uses sunlight to purify water
Eco-friendly white loofah sponge.

Xu and her team tested the enhanced PNIPAm gel at room temperature under artificial light having the same intensity as sunlight. They first allowed the hydrogel to absorb water and then placed it under the light to measure the speed at which it released clean water

Surprisingly, within 10 minutes, the loofah-inspired hydrogel discharged 70 percent of the water it imbibed. Even under low light conditions that mimicked a cloudy day environment, the gel released the same amount of absorbed water in just 15 to 20 minutes. 

Also, similar to its previous version, the hydrogel successfully purified heavily polluted water samples containing microplastics, metals, dyes, and oil. For instance, it turned a dirty water sample containing chromium at 40 ppm (parts per million) into clean water with chromium restricted at 0.007 ppm, which is considered safe to drink. 

Since the loofah-inspired hydrogel uses only sunlight, it could be a boon for parts of the world that don’t have clean drinking water. Many underdeveloped regions that can’t afford expensive water treatment plants or solutions that require a lot of energy can reap the benefits of this low-cost, low-energy innovation. 

The researchers also reveal that the limitation of the hydrogel is that it can reject bacteria but does not have the bacterial-killing ability yet. “We are currently trying to endow the hydrogel with antibacterial properties, so the hydrogel can quickly kill water-born bacteria and deliver safe water. We are also working on the purification of PFAS- contaminated water,” said Xu.

The study is published in the journal ACS Central Science.

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