Biochar made from the nickel hyperaccumulator <i>Odontarrhena Chalcidica</i> as a sorbent and energy storage material
Creators: name: Smoak, Rachel Annette
Publisher: name: University of Iowa
Year: 2024
Subjects: Alyssum murale
Energy storage
Nickel
Odontarrhena chalcidida
Sorption
Energy
public abstract

description: 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.
description: 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 &gt; 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.
description: <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.
description: 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.