Dissertation
Biochar made from the nickel hyperaccumulator Odontarrhena Chalcidica as a sorbent and energy storage material
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2022
DOI: 10.25820/etd.006614
Abstract
Sustainable development requires new ways to produce the materials that society needs and wants. Agromining, or farming for metals, is a novel method of metal production using hyperaccumulating plants. These plants can accumulate levels of metals in their biomass higher than in commercially-mined ores without toxic side effects. The metal is then extracted from the plants and used to make products. However, despite the prevalence of metal-carbon materials, no value-added products have been made directly from hyperaccumulator biomass using the whole plant as a resource. This work demonstrates the first syntheses of value-added products through direct pyrolysis of the nickel (Ni) hyperaccumulator <i>Odontarrhena chalcidica</i> into biochar.
The biochar was first evaluated as a Ni(II) sorbent to enhance its Ni concentration. High-temperature biochar pyrolyzed at 900°C sorbed aqueous Ni(II) better than biochar pyrolyzed at a lower temperature. The best-performing biochar had 41 mg hyperaccumulated Ni (g biochar)⁻¹ and sorbed an additional 51 mg Ni (g biochar)⁻¹ for a total concentration of 92 mg Ni (g biochar)⁻¹. Similar biochars without hyperaccumulated Ni sorbed 154 mg Ni (g biochar)⁻¹, which was competitive with the highest-performing Ni sorbents in the literature and the highest of any unmodified, plant-based biochar. The biochars removed Ni(II) from the solution by combining cation exchange and precipitation mechanisms driven by their intrinsically high cation exchange capacities and alkaline pH values. Fast kinetics allowed the biochar to remove Ni(II) from solutions with pH > 2 typically within 15 minutes. The biochars were also able to extract metals from multi-metal solutions. Together, these characteristics indicate that <i>O. chalcidica</i> biochar is a candidate sorbent for the treatment of metals-contaminated wastewater.
<i>O. chalcidica</i> biochar was also examined by cyclic voltammetry and galvanostatic cycling to determine its potential application as an energy storage material. Biochars with hyperaccumulated Ni demonstrated faradaic charge storage and outperformed biochars with similar concentrations of Ni added after pyrolysis, indicating that hyperaccumulators may have enhanced energy storage properties compared to other metal-carbon composites. Normalized by the mass of Ni, 900°C biochar containing hyperaccumulated Ni that underwent KOH activation was the highest-performing material observed. It possessed a consistent specific capacity of 540 mAh (g Ni)⁻¹ between 4 and 10 A (g biochar⁻¹ and a capacity retention of 64% of maximum capacity after 2000 cycles at 10 A (g biochar)⁻¹. Normalized by the total mass of biochar material, the sample with the highest Ni concentration (containing hyperaccumulated and added Ni) performed best, with a maximum specific capacity of 32 mAh (g biochar)⁻¹ at 4 A (g biochar)⁻¹ and capacity retention of 68% of maximum capacity after 2000 cycles at 10 A (g biochar)⁻¹. Both materials compared favorably to other Ni-carbon energy storage materials reported in the literature, showing the efficacy of <i>O. chalcidica</i> biochar as an energy storage material.
The work presented in this dissertation demonstrates that value-added products can be synthesized directly from agromined hyperaccumulator biomass. It also offers a potential alternative production process for types of materials that are already in demand and shows that possibilities exist to grow advanced, green materials.
Details
- Title: Subtitle
- Biochar made from the nickel hyperaccumulator Odontarrhena Chalcidica as a sorbent and energy storage material
- Creators
- Rachel Annette Smoak
- Contributors
- Jerald L Schnoor (Advisor)David M Cwiertny (Committee Member)Gregory H LeFevre (Committee Member)Syed Mubeen (Committee Member)Michelle M Scherer (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Summer 2022
- DOI
- 10.25820/etd.006614
- Publisher
- University of Iowa
- Number of pages
- xviii, 197 pages
- Copyright
- Copyright 2022 Rachel Annette Smoak
- Language
- English
- Description illustrations
- illustrations (chiefly color), charts, graphs
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
- As the world advances, we need new ways to make materials. One new strategy is using plants known as hyperaccumulators to mine for metals. Hyperaccumulator plants can hold higher concentrations of metals in their tissues than in the ores we mine. We can remove the metal and use it to create products. However, we have never made a product that uses both the metal and the plant as a resource despite many uses for materials made from metal and carbon. This work discusses the first products created using both the nickel (Ni) and the carbon of the Ni hyperaccumulator Odontarrhena chalcidica as resources. To make these products, I heated O. chalcidica plants without oxygen to create biochar. The biochar quickly and effectively removed Ni and other metals from water and simulated acid mine drainage. The biochar had properties that could make it helpful in removing metal pollutants from water or in making acidic soil less toxic to plants. I also found that energy could be stored in the O. chalcidica biochar like energy is stored in a battery. Biochar made from plants that hyperaccumulated Ni stored energy better than biochar made from plants without Ni even when similar levels of Ni were added to the latter. This shows that hyperaccumulator biochar may be an excellent material for future energy storage technologies. My research shows that we can make valuable products from Ni hyperaccumulator plants and that better ways exist to make the materials we need now and in the future.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984284951302771
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