Investigating Adsorption of Carbamazepine with Adsorbents Developed from Flax Shives with X-ray Spectroscopy

Carbamazepine (CBZ), a pharmaceutical used in the treatment of epilepsy, is also used for the treatment of some diseases or symptoms such as alcoholism, opiate withdrawal, and depression. Unfortunately, this drug has often been detected in rivers and surface waters, thus raising concern regarding its impact on the environment. A recent paper discusses how flax shives (the material left after fiber is extracted from flax stems) have been used to remove CBZ from simulated wastewater. Catherine Niu, a professor at the College of Engineering of the University of Saskatchewan in Canada and co-author of this paper, spoke to Spectroscopy about how she and her associates used X-ray photoelectron spectra and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis in their research.

Your paper (1) discusses how adsorbents based on hydrochars and steam activated hydrochars developed from flax shives were used to adsorb carbamazepine (CBZ) from simulated contaminated water. What made you decide that using flax shives would be an effective way to accomplish this?

Flax shives containing cellulosic components have been abundantly generated as a byproduct after flax fiber is extracted, which have not been effectively utilized. Previously research showed that cellulosic components or their derivatives have potential for removing pharmaceutical or related chemicals from water. The decision of using flax shives as a feedstock to make hydrochars and steam activated hydrochars adsorbents to remove pharmaceuticals in this work was made in order to develop novel uses of the material for water treatment. In addition, the results from this work may be transferable to treat other agricultural byproducts containing cellulosic components.

Please describe the mechanisms of CBZ adsorption.

The results obtained from this work show π-π electron donor-acceptor interaction may play an important role on the adsorption mechanism of CBZ on the above-mentioned adsorbents. Hydrophobic interaction also contributed while the roles of hydrogen bonding and electrostatic attraction between CBZ and adsorbents with opposite charges is insignificant. Pore filling may also contribute to the ability of flax shives to act as adsorbents.

You used X-ray photoelectron spectra and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis in your research. What do these techniques reveal about the adsorption process you were studying?

These spectral analyses provided evidence indicating that the adsorption mechanism of π-π electron donor-acceptor interaction may play an important role in the adsorption of CBZ on the above-mentioned adsorbents. This interaction provides a mechanism whereby CBZ adsorbs to the cellulose of the flax shives.

What advantages do these spectroscopy techniques offer that other techniques available may have lacked?

Experiments of adsorption of pharmaceuticals from water by adsorbents are able to demonstrate whether the adsorbents can adsorb the pharmaceuticals or not. However, other methods have not been able to provide adequate information on what reasons or the mechanism that causes the pharmaceuticals to be adsorbed on the surface of the adsorbents. The aforementioned spectroscopy techniques may provide information to assist of understanding the adsorption mechanisms, which is what we are interested in learning.

How was the Canadian Light Source (CLS) essential for this research?

The Canadian Light Source (CLS) was required in order to utilize the near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis. Without this source there would not be sufficient X-ray energy to complete this analysis. This work actually provided the detailed evidence that a π-π electron donor-acceptor interaction may play a critical role in the adsorption mechanism of CBZ on the abovementioned adsorbents. This mechanism may also be present for other similar pharmaceutical molecular structures.

How does your research differ from what was previously done by yourself or others?

This work used flax shives as a feedstock to make hydrochars and steam activated hydrochars for CBZ pharmaceutical contaminant adsorption. To the best knowledge of the authors of this work, such an adsorption system has not been reported prior to this published research work.

Were there any particular limitations or challenges you encountered in your work?

We encountered challenges to effectively desorb adsorbed carbamazepine from the loaded adsorbents. This limits the regeneration of the adsorbents for reuse. If we are not able to regenerate the adsorbents they will have a one-use only limited applicability. In addition, we were interested in how to reduce the uses of acid and thermal energy in the process of developing the adsorbents. For us to learn how to minimize the use of energy and chemicals in this process is an ongoing challenge.

Can you please summarize the feedback that you have received regarding this work?

This work has made contributions to demonstrate flax shives were successfully made into adsorbents which adsorbed carbamazepine with capacity and speed comparable with some other commercial adsorbents reported. The mechanisms which may play important roles in the adsorption were explored. However, there are the abovementioned challenges which still need to be addressed to optimize this process for real-world application.

Can this work translate to detecting other pharmaceuticals in water, or even detecting them in other classical elements (earth, air)?

This work may be transferable to detect other pharmaceuticals similar to carbamazepine in water or in earth after earth samples are dissolved in water. However, this question needs to be verified by future research.

What are the next steps in this research?

The next steps are to address the challenges and limits described in the previous answers and to continue to find ways to enhance adsorption capacity. Choices of additional feedstocks and pharmaceuticals will also be investigated. If successful, collaboration may be established with industrial partners to develop a pilot or an industrial scale water treatment process. We are hopeful that this research will be fruitful.

Reference

(1) Aghababaei, A.; Babu Borugadda, V.; Dalai, A.; Hui Niu, C. An Investigation on Adsorption of Carbamazepine with Adsorbents Developed from Flax Shives: Kinetics, Mechanisms, and Desorption. Chem. Eng. Res. Des. 2023, 189, 138–155, DOI: 10.1016/j.cherd.2022.11.008

Dr. Catherine Niu is a professor in the Department of Chemical and Biological Engineering at the University of Saskatchewan. She obtained her Ph.D. in chemical engineering from McGill University in Canada. In addition, she received her bachelor and master's degrees in chemical engineering from Sichuan University in P.R. China. Dr. Niu has passion on biosorption and adsorption research. Her research area focuses on biosorption which utilizes inexpensive non-living biomaterials called biosorbents to sequester chemicals of interest. Biosorbents are prepared from the naturally abundant or waste biomass of algae, moss, fungi, bacteria or waste parts of plants and animals, which act just as adsorbents of biological origin. Dr. Niu's research includes developing and characterizing novel biosorbents, optimizing biosorption processes, and studying the adsorption kinetics, equilibrium, mechanism, and desorption. The diversified and promising applications of biosorption technology lead to the development of her research projects in the areas of water treatment, gas purification, biochemical adsorption, and more.