Project 4: Designing the next generation of highly selective sorbents for water remediation

Removing metals and other chemicals that can contaminate drinking water is critical for public health, but traditional approaches to filter and remove neurotoxic metals are not sufficiently selective in the presence of other non-toxic ions, which frequently occur at higher concentrations, have similar chemical structures, and compete for sorption sites. 

Our Goals   

This project aims to develop a drinking water filter technology that 

  • selectively removes neurotoxic oxo-anions from drinking water by adsorption
  • can be used for a variety of water treatment systems (e.g., individual households, on well water, small-scale community systems or schools)
  • are more effective, efficient, and sustainable than existing technologies.

Our Approach

Recent advances in polymer- and nano- science allow for unprecedented bottom-up capabilities to thermodynamically model, characterize, and controllably synthesize adsorbents. Project 4 is designing selectively adsorptive polymers based on the waste bio-polymer chitosan and metal oxides particles. By selectively exposing different surfaces of the metal oxide particles, we are able to exploit chemical behavioral differences such as polarity, charge distribution, size, and hydrophobicity between the target oxoanion metal pollutants and other naturally occurring competing ions, to generate highly selective and tunable polymeric and nano-surfaces.    

Project 4 Team

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Recent Publications

Srishti Gupta, Ngan Anh Nguyen, and Christopher L. Muhich. 7/2022. “Surface water H-bonding network is key controller of selenate adsorption on [012] α-alumina: An Ab-initio study.” Journal of Colloid and Interface Science, 617, Pp. 136-146. Publisher's VersionAbstract
Selenate adsorption onto metal oxide surfaces is a cost-effective method to remove the toxin from drinking water systems. However, the low selectivity of metal oxides requires frequent sorbent replacement. The design of selective adsorbents is stymied because the surface factors controlling selenate adsorption remain unknown. We calculate adsorption energies of selenate on the (0 1 2) α-Al2O3 surface using density functional theory to unravel the physics that controls adsorption. Our model is validated against experiment by correctly predicting selenate removal efficiency as a function pH. We find that the selenate adsorption energy on the anhydrous α-Al2O3 surface is surprisingly anti-correlated with the fully solvated adsorption energy; therefore, the direct interaction between adsorbate and sorbent is eliminated as the controlling mechanism. Rather, the change in number of surface hydrogen bonds after adsorption is the factor most correlated with the adsorption energy (R2 > 0.8); and is thus determined to be the factor controlling selenate adsorption. We find that pH affects adsorption by controlling the number of surface protons available for H-bonding to selenate. This work demonstrates that adsorption prediction should not be made based on gas phase sorption energies and suggests that surface engineering which increases surface protonation may be an effective strategy for increasing selenate sorption.
Chu C, Huang D, Gupta S, Weon S, Niu J, Stavitski E, Muhich C, and Kim JH. 8/30/2021. “Neighboring Pd single atoms surpass isolated single atoms for selective hydrodehalogenation catalysis.” Nat Commun, 30, 12(1), Pp. 5179.Abstract

Single atom catalysts have been found to exhibit superior selectivity over nanoparticulate catalysts for catalytic reactions such as hydrogenation due to their single-site nature. However, improved selectively is often accompanied by loss of activity and slow kinetics. Here we demonstrate that neighboring Pd single atom catalysts retain the high selectivity merit of sparsely isolated single atom catalysts, while the cooperative interactions between neighboring atoms greatly enhance the activity for hydrogenation of carbon-halogen bonds. Experimental results and computational calculations suggest that neighboring Pd atoms work in synergy to lower the energy of key meta-stable reactions steps, i.e., initial water desorption and final hydrogenated product desorption. The placement of neighboring Pd atoms also contribute to nearly exclusive hydrogenation of carbon-chlorine bond without altering any other bonds in organohalogens. The promising hydrogenation performance achieved by neighboring single atoms sheds light on a new approach for manipulating the activity and selectivity of single atom catalysts that are increasingly studied in multiple applications.

Baiyang Chen, Jingyi Jiang, Xin Yang, Xiangru Zhang, and Paul Westerhoff. 2021. “Roles and Knowledge Gaps of Point-of-Use Technologies for Mitigating Health Risks from Disinfection Byproducts in Tap Water: A Critical Review.” Water Res, 200, Pp. 117265. Publisher's VersionAbstract
Due to rising concerns about water pollution and affordability, there is a rapidly-growing public acceptance and global market for a variety of point-of-use (POU) devices for domestic uses. However, the efficiencies and mechanisms of POU technologies for removing regulated and emerging disinfection byproducts (DBPs) are still not systematically known. To facilitate the development of this field, we summarized performance trends of four common technologies (i.e., boiling, adsorption, membrane filtration, and advanced oxidation) on mitigating preformed DBPs and identified knowledge gaps. The following highest priority knowledge gaps include: 1) data on DBP levels at the tap or cup in domestic applications; 2) certainty regarding the controls of DBPs by heating processes as DBPs may form and transform simultaneously; 3) standards to evaluate the performance of carbon-based materials on varying types of DBPs; 4) long-term information on the membrane performance in removing DBPs; 5) knowledge of DBPs' susceptibility toward advanced redox processes; 6) tools to monitor/predict the toxicity and diversity of DBPs formed in waters with varying precursors and when implementing different treatment technologies; and 7) social acceptance and regulatory frameworks of incorporating POU as a potential supplement to current centralized-treatment focused DBP control strategies. We conclude by identifying research needs necessary to assure POU systems protect the public against regulated and emerging DBPs.
Paul Westerhoff, Pedro JJ Alvarez, Jaehong Kim, Qilin Li, Alessandro Alabastri, Naomi J Halas, Dino Villagran, Julie Zimmerman, and Michael S Wong. 2021. “Utilizing the broad electromagnetic spectrum and unique nanoscale properties for chemical-free water treatment.” Current Opinion in Chemical Engineering, 33. Publisher's VersionAbstract
Clean water is critical for drinking, industrial processes, and aquatic organisms. Existing water treatment and infrastructure are chemically intensive and based on nearly century-old technologies that fail to meet modern large and decentralized communities. The next-generation of water processes can transition from outdated technologies by utilizing nanomaterials to harness energy from across the electromagnetic spectrum, enabling electrified and solar-based technologies. The last decade was marked by tremendous improvements in nanomaterial design, synthesis, characterization, and assessment of material properties. Realizing the benefits of these advances requires placing greater attention on embedding nanomaterials onto and into surfaces within reactors and applying external energy sources. This will allow nanomaterial-based processes to replace Victorian-aged, chemical intensive water treatment technologies.
J Kidd, P Westerhoff, and A Maynard. 4/22/2021. “Survey of Industrial Perceptions for the Use of Nanomaterials for In-Home Drinking Water Purification Devices.” NanoImpact, 22, 100320, Pp. 1-6. Publisher's VersionAbstract

As businesses, specifically technology developers and industrial suppliers, strive to meet growing demand for higher quality drinking water, the use of engineered nanomaterials in commercial point-of-use (POU) in-home water purification devices are becoming an increasingly important option. Anecdotally, some businesses appear wary of developing and marketing nanomaterial-enabled devices because of concerns that they will face onerous regulation and consumer pushback. However, little of substance is known about business perceptions of and attitudes toward the use of engineered nanomaterials in POU water purification devices, or how these compare with consumer perceptions. To address this knowledge-gap, we administered a 14-question survey among 65 participants from US-based industrial companies focused on drinking water purification. Our results indicate that the dominant concerns for businesses are costs and public perceptions associated with nanomaterial-enabled POU devices for drinking water purification. Cost-specific barriers include competition from more conventional technologies, and tensions between operational versus capital costs. 57% of respondents were concerned or very concerned that public perceptions will influence the long-term viability of nanomaterial-enabled POU devices for drinking water purification. 49% of respondents stated that government regulation of nanomaterials would be the preferred approach to ensure public safety, followed by the certification of POU devices (28%). When asked about specific nanomaterials and their potential use in POU devices for drinking water purification, respondents ranked carbon nanotubes as the nanomaterial with highest concern for environmental health and safety, followed by silver, titanium dioxide, zinc oxide, and copper. Respondents ranked nanoclays as the nanomaterial with highest likelihood for public acceptance, followed by silica, cerium oxide, titanium dioxide, and aluminum oxide

    Holly E Rudel, Mary Kate M Lane, Christopher L Muhich, and Julie B Zimmerman. 2020. “Toward Informed Design of Nanomaterials: A Mechanistic Analysis of Structure-Property-Function Relationships for Faceted Nanoscale Metal Oxides.” ACS Nano.Abstract
    Nanoscale metal oxides (NMOs) have found wide-scale applicability in a variety of environmental fields, particularly catalysis, gas sensing, and sorption. Facet engineering, or controlled exposure of a particular crystal plane, has been established as an advantageous approach to enabling enhanced functionality of NMOs. However, the underlying mechanisms that give rise to this improved performance are often not systematically examined, leading to an insufficient understanding of NMO facet reactivity. This critical review details the unique electronic and structural characteristics of commonly studied NMO facets and further correlates these characteristics to the principal mechanisms that govern performance in various catalytic, gas sensing, and contaminant removal applications. General trends of facet-dependent behavior are established for each of the NMO compositions, and selected case studies for extensions of facet-dependent behavior, such as mixed metals, mixed-metal oxides, and mixed facets, are discussed. Key conclusions about facet reactivity, confounding variables that tend to obfuscate them, and opportunities to deepen structure-property-function understanding are detailed to encourage rational, informed design of NMOs for the intended application.
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