Location: Commodity Utilization Research
2013 Annual Report
Because of known difficulty in recovering water-soluble fullerene NMs, reliable analytical methods needed to be established first. Water-soluble fullerene NMs were prepared by stirring bulk fullerene in water for several weeks in the dark. In addition, concentrated and more regularly shaped fullerene NMs were prepared by adding naturally occurring surfactants. Additional stock solution was prepared by sonicating fullerene-containing toluene layer in a large volume of water. After testing different recovery methods, repeated recovery using toluene and salt was determined to be most reliable. Then, analytical techniques were developed to separate and recover fullerene NMs in toluene layer using liquid chromatography with photodiode array detector.
We then conducted experiments to test how fast, how strongly, and how much of fullerene NMs will become trapped in biochar. After 3 days of mixing in water, fullerene NMs were strongly attached to biochar, and could not be removed from biochar, even using a harsh recovery method involving hot toluene. Smaller fullerene NMs were especially tightly bound on biochar, suggesting penetration into pores. All biochars strongly removed fullerene NMs from water, but biochars made at higher temperatures were most effective. Interestingly, biochars made at low temperature decreased the size of water soluble NMs by releasing surfactants. Structure and amount of biochar surfactants were studied using a fluorescence-based imaging technique. Further experiments are being conducted using different salts and pH to understand the chemistry of biochar-NMs interactions, and to visualize the attachment of NMs on biochars using transmission electron microscopy (TEM). Parallel batch experiments were conducted on cerium oxide NMs by the collaborator having an access to a highly sensitive mass spectrometric analyzer for metal NMs. Because smaller NMs are expected to be more toxic, separate methods were developed to prepare cerium oxide NMs having different size. Concurrently with the decrease in size, electric charge (zeta potential) of cerium oxide NMs became more negative with higher pH and surfactant concentrations. The property of NMs suspension did not change over time, making it suitable for the use in biochar experiments. These observations along with TEM imaging confirmed that higher pH and surfactant concentration made NMs more soluble in water. Based on these results for NMs sequestration by biochar, greenhouse experiments were started to test bioavailability of cerium oxide and fullerene NMs on corn, soybean, lettuce, and tomato by the collaborator. Effects of 0.5 to 5% biochar (with respect to the weight of soil) are studied on the crop yield, NMs accumulation, reactive oxygen species production, water evaporation, and photosynthesis. This project was monitored via conference calls, email communications, and face-to-face discussions at two technical conferences and a review panel meeting. Members of this project sponsored a symposium at a professional conference, and contributed a book chapter on topics addressing both NMs and biochar.
Agricultural Research Service' Principal Investigator is monitoring activities.