Thesis defence in the University of Oulu

Doctoral Candidate

Master of Science Tuula Selkälä

Faculty and research unit

University of Oulu Graduate School, Faculty of Technology, Fibre and Particle Engineering Research Unit

Field of study

Process Engineering

Date and time of the thesis defence

19.2.2021 12:00

Place of the thesis defence

Linnanmaa, auditorium L10. Remote connection: https://oulu.zoom.us/j/65663410763

Topic of the dissertation

Cellulose nanomaterials and their hybrid structures in the removal of aqueous micropollutants

Opponent

Professor Aji P Mathew, Stockholm University

Custos

Professor Henrikki Liimatainen, University of Oulu

Nanoscale wood fibers remove drug and dye residues from water

Micropollutants are synthetic or natural organic compounds that are present in the environment at
very low concentrations. They end up in nature via industrial and domestic wastewaters, for
example, and are suspected of having adverse effects on the environment and biota. Conventional
wastewater treatment processes fail to remove them completely and therefore there is an urgent
need for new technical solutions that improve the treatment processes at wastewater treatment
plants and/or at the point source. Biobased cellulose nanomaterials provide an environmentally
friendly option for micropollutant removal from water due to their inherent properties, such as
customizability and high reactive surface area.

In this work, a urea–lithium chloride (LiCl) deep eutectic solvent (DES)-based pretreatment for
the preparation of anionic cellulose nanomaterials was developed. Moreover, three different
concepts (batch, precipitation, filtration) were developed where an investigation was made of the
suitability of charged cellulosic nanomaterials prepared with DES pretreatments for the removal
of ionizable micropollutants (pharmaceutical, dyes), either alone or in combination with natural
inorganic materials. According to the results, urea–LiCl DES acted as a non-reactive solvent that
swelled the fiber matrix and allowed carboxylation of the fiber surface with succinic anhydride.
Based on concept testing, anionic and cationic cellulosic nanomaterials were capable of binding
ionizable micropollutants to themselves. Increasing the dose of cellulosic nanomaterial improved
the removal of the micropollutant but complicated the separation of the exhausted material from
the treated water. The intensity of the interaction was mainly dependent on the pH of the solution,
which affected the charge of both the adsorbent and the micropollutant. In addition, combining the
cellulosic nanomaterial with natural inorganic particles or materials facilitated the separation of
both from the treated water and in some cases, improved the purification result.

This work provides new insights into the interaction of organic compounds and cellulose
nanoparticles in different removal concepts and demonstrates the suitability of charged cellulosic
nanomaterials and their hybrid structures for reducing ionizable micropollutants from aqueous
solutions.

 

Dissertation

Last updated: 8.2.2021