With both global oil consumption and environmental awareness steadily increasing, both economical as well as environmental aspects require an efficient, reliable, and cheap method to remove spilled oil from water. Selective oil absorption is an auspicious technique for this purpose since it is low cost, generally achieves high absorption capacities and offers the opportunity to recycle the working material. Yet, commercial absorption materials still suffer from several shortcomings (e.g. poor oil water selectivity, complicated fabricating process), which is why further advances in material engineering are required in order to obtain applicable oil absorbents.

With the aim of finding an efficient, environmental compatible and economical sorbent material, researchers from the Dalian Polytechnic University (China) have now successfully synthesized a low-cost, organic aerogel based on corn straw and filter paper, which exhibits good performance as an oil sorbent from aqueous media.

The outstanding feature of the synthesized aerogel material is that it originates from corn straw, which is generally considered as a waste product and thus nowadays is still being burned, positively contributing to global greenhouse gas emissions. However, its abundance, low-cost and biodegradability make it an potent raw material for large scale applications. Its main disadvantage — the inherent brittleness of materials originating from it — was overcome by the addition of filter paper pieces to the precursor material leading to the required flexibility of the final aerogel material.

For the preparation of the aerogels, the corn straw was first ground then washed with sodium hydroxide before hydrochloric acid was added. Subsequent filtration and drying led to corn straw particles (P-CS), which were then dispersed in water together with small pieces of commercial filter paper via vigorous stirring. Thereafter, the dispersion was frozen at -25 °C for 12 hours before freeze drying at -55 °C for 36 hours. The final step of the production process, which is shown in the figure below, was the hydrophobization of the corn straw aerogel (A-CS) through chemical vapor deposition of methyltrimethoxysilane (MTMS).

Schematic of hydrophobic corn straw aerogel production process

Analysis of the final freeze-dried aerogel structures unveiled that the material exhibited a porous 3D-structure and a good thermal stability up to 250 °C. Dependent on the solids content and the P-CS:filter paper ratio densities ranging from 14 to 58 mg/cm3 were attained, while porosities between 96 and 99 % were achieved. Water contact angle measurements showed a successful hydrophobization, with measured contact angles reaching values up to 152°.
Investigation of the selectivity and absorptivity for a range of different solvents showed that while water absorptivities were below 1 g/g for the hydrophobized corn straw aerogels (MTA-CS), absoprtivities of organic solvents such as oil or DMF were in the range of 40 g/g. Hence selectivities towards organic solvents were extremely high. Moreover, the MTA-CS did not only absorb the organic phase with a high selectivity, but also in a rapid fashion, leading to fast oil removal from aqueous solutions (see figure below).

Soybean oil removal from water with the MTA-CS for different stages. a) Soybean oil water mixture, b) addition of MTA-CS, c) oil absorption by MTA-CS d) removal of oil soaked MTA-CS

With the novel low cost absorbent material synthesized by the Chinese research team disadvantages of conventional oil absorption were overcome, which might pave the way for the widespread utilization of biodegradable oil sorbents originating from corn straw. Certainly, it will be interesting to see whether novel bio-based oil absorbing materials can outperform their synthetic counterparts (e.g. poly(melamine- formaldehyde), polyurethane and polystyren) in the future.

More details: Yuan Li et al. “Preparation of corn straw based spongy aerogel for spillage oil capture” Korean Journal of Chemical Engineering May 2018, Volume 35, Issue 5, pp 1119–1127, https://link.springer.com/article/10.1007/s11814-018-0010-3

Read more at: http://www.chemengonline.com/inexpensive-renewable-aerogel-shows-promise-handling-oil-spills/?printmode=1

The search for active yet economical water purification strategies is in full swing as increasing industrial activity results in sharp surges in wastewater production, and the ever-growing global population increases demand for clean drinking water.

Commonly, separated, sophisticated absorption processes are deployed to remove either organic or inorganic contaminants from sewage water due to their high efficiency and moderate cost. However, it remains a challenge to devise robust, efficient and economical absorbents for the wide range of trace elements occurring in wastewater. Ideally, novel absorption materials should be able to remove inorganic compounds such as dyes or heavy metals and also be active against harmful viral or bacterial pathogens.

In pursuit of such a material, researchers from Jinan University (China) have synthesized an aerogel structure exhibiting extraordinary dye and heavy metal absorbing properties, by using graphene oxide (GO) and a type of abundant mineral called montmorillonite (MMT). The desired anti-pathogenic activity was realized through equipping the aerogel matrix with a common anti-bacterial agent, resulting in absorbents displaying excellent antibacterial activity against Gram-positive and Gram-negative bacteria.

The aerogel material exhibiting these intriguing properties was manufactured through mixing GO powder, ascorbic acid, and a MMT solution, then inducing gelation through heat treatment at 95 °C. After aging of the hydrogel in a PVA solution for two days, the gel was then freeze dried at -55 °C, resulting in a monolithic aerogel structure, which is shown in the Figure below.

Image of black GO-MMT aerogel placed on top of kapok tree fiber.

Absorption experiments showed that the aerogel absorbents were not only able to remove more than 95 % of methyl orange and methylene blue dyes from aqueous solutions, but also exhibited great properties for the removal of heavy metals from water (e.g. >90 % removal efficiency for chromium ion removal). This activity was found to be stable over numerous absorption/desorption cycles, with sample regeneration being achieved by vigorous shaking. Furthermore, the addition of antibacterial dodecyl dimethyl benzyl ammonium chloride (1227) to the initial precursor solution was found to provide the aerogel with antibacterial activity, which was shown using E. coli and S. aureus bacteria cultures, each losing over 90 % of their cell viability in the presence of the GO-MMT-1227 aerogel material.

Due to these extraordinary findings, the researchers are confident that they have found an efficient, versatile, recyclable, and robust absorbent material, which has the potential to revolutionize water purification. If economical large scale manufacturing and long term stability can be achieved, the novel material might indeed replace state-of-the-art sorbents in wastewater treatment systems.

More details: Yunyun Zhang et al.; The utilization of a three-dimensional reduced graphene oxide and montmorillonite composite aerogel as a multifunctional agent for wastewater treatment, RSC Adv., 2018,8, 4239-4248. https://doi.org/10.1039/C7RA13103H