Efficiency of Bimetallic Nanoparticles for Treatment of Azo Dyes in Water

The development of novel materials for water treatment applications remains a significant need as water resources become increasingly strained and contaminant removal challenges persist. While current commercial water treatment materials and technologies are able to remove a wide range of contaminants, the addition of functionality or performance through material design enables improved contaminant removal and the ability to address particularly recalcitrant contaminants. In particular, the development of nanostructured, reactive materials for water treatment applications holds great promise due to the reactive degradation and improved removal processes that have been demonstrated. Both laboratory-scale and pilot-scale research studies have demonstrated that iron-based nanostructured materials, such as iron nanoparticles, are able to remove a wide variety of water contaminants, including chlorinated organics, pharmaceutical compounds, and heavy metals, through both oxidative and reductive reaction mechanisms. However, iron nanoparticle lifetime remains a challenge particularly in oxidative environments, where the nanoparticles quickly react with water and oxygen to form non-reactive iron oxide compounds. Thus, there remains a need to investigate approaches to extend the lifetime as well as to enhance the performance of iron-based nanoparticles.

In our work, we have focused on the synthesis of bimetallic nanoparticles, which are then used to treat water contaminated by an azo dye (Orange G). These nanoparticles are synthesized in an aqueous solution and result in an alloy morphology. Variation of synthesis parameters can be used to optimize nanoparticle reactivity and understand which parameters are critical to controlling nanoparticle morphology. In our synthesis method, we focus on different combinations of metals, including iron-nickel and iron-cobalt. Thus far, our results have shown that different molar ratios of the metals result in different rates of removal of Orange G from solution, as well as in the overall removal of Orange G from the solution. Within a range of 0.1 to 0.4 mol Ni:mol Fe, lower molar ratios of nickel to iron in the nanoparticle metal combinations have shown higher removal of Orange G. In addition, changing the metals used in synthesis (e.g., from FeNi to FeCo) is a viable option to optimize the reactivity of iron-based nanoparticles. Finally, the types of stabilizers used during aqueous synthesis of the metal nanoparticles may impact the morphology and reactivity of the particles. Currently, stabilizers used in this work are poly(N-vinyl-2-pyrrolidone) (PVP) and amino tris (methylene phosphonic acid) (ATMP). We are beginning to investigate other novel types of stabilizers, such as peptides and peptoids, which have proven to be successful in stabilizing nanoparticles in nanoparticle formation. However, it is unclear how the use of such specialized stabilizers impacts the reactivity of the nanoparticles in water treatment applications.

In this talk, we will present results on several synthesis parameters that have been identified as key to impacting nanoparticle reactivity towards the target water contaminant Orange G, including nanoparticle composition and metal:metal molar ratio in the alloy morphology. Results will be presented for nickel to iron molar ratios in the range of 0 to 0.4 as well as iron to cobalt with a similar range of molar ratios. We will also present results on the characterization of these nanoparticles using techniques such as electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Finally, performance results will be discussed as a function of nanoparticle concentration and Orange G concentration.