Catalytic Converters for Water Treatment

Abstract

Fresh water demand is driven by human consumption, agricultural irrigation, and industrial usage and continues to increase along with the global population. Improved methods to inexpensively and sustainably clean water unfit for human consumption are desired, particularly at remote or rural locations. Heterogeneous catalysts offer the opportunity to directly convert toxic molecules in water to nontoxic products. Heterogeneous catalytic reaction processes may bring to mind large-scale industrial production of chemicals, but they can also be used at the small scale, like catalytic converters used in cars to break down gaseous pollutants from fuel combustion. Catalytic processes may be a competitive alternative to conventional water treatment technologies. They have much faster kinetics and are less operationally sensitive than current bioremediation-based methods. Unlike other conventional water treatment technologies (i.e., ion exchange, reverse osmosis, activated carbon filtration), they do not transfer contaminants into separate, more concentrated waste streams. In this Account, we review our efforts on the development of heterogeneous catalysts as advanced reduction technologies to treat toxic water contaminants such as chlorinated organics and nitrates. Fundamental understanding of the underlying chemistry of catalytic materials can inform the design of superior catalytic materials. We discuss the impact of the catalytic structure (i.e., the arrangement of metal atoms on the catalyst surface) on the catalyst activity and selectivity for these aqueous reactions. To explore these aspects, we used model metal-on-metal nanoparticle catalysts along with state-of-the-art in situ spectroscopic techniques and density functional theory calculations to deduce the catalyst surface structure and how it affects the reaction pathways and hence the activity and selectivity. We also discuss recent developments in photocatalysis and electrocatalysis for the treatment of nitrates, touching on fundamentals and surface reaction mechanisms. Finally, we note that despite over 20 years of growing research into heterogeneous catalytic systems for water contaminants, only a few pilot-scale studies have been conducted, with no large-scale implementation to date. We conceive of modular, on-or off-grid catalytic units that treat drinking water at the household tap, at a community well, or for larger-scale reuse of agricultural runoff. We discuss how these may be enhanced by combination with photocatalytic or electrocatalytic processes and how these reductive catalytic modules (catalytic converters for water) can be coupled with other modules for the removal of potential water contaminants.

Scaling up Photoelectrocatalytic Reactors: A TiO2 Nanotube-Coated Disc Compound Reactor Effectively Degrades Acetaminophen

“…To better understand the fate of the initial N-organic content, a complete mass balance was conducted (Figure 7b). Compared with the 53% mineralization and volatilization of carbon, only 46% volatilization of nitrogen occurred as the likely result of producing volatile species such as N2 and NOx [53][54][55]. The remaining nitrogen in solution was associated to remaining acetaminophen (0.005 mM), yielded oxamic acid (0.61 µM), and dissolved inorganic nitrogen (0.026 mM); inorganic nitrogen represented 75% of total dissolved nitrogen in solution after photoelectrocatalytic treatment.…”

Promoting selective electroreduction of nitrates to ammonia over electron-deficient Co modulated by rectifying Schottky contacts

“…) was unobvious and covered by the band of NO − species. Based on the above intermediates detected by in situ tests and reported studies [21,47], we deduced the reaction path and carried out the theoretical simulation of Co NSAs and Co/CoO NSAs applied for the electrocatalytic nitrate reduction along this reaction path ( Figure 5(c)). The calculated reaction Gibbs free energies of every process during nitrate reduction were shown.…”

“…Presently, owing to the overuse of nitrogen-based fertilizers and the discharge of industrial and domestic sewage, excessive nitrate (NO 3 − ) exists in surface and underground water, threating human health [20][21][22]. Currently, some commercial technologies, including reverse osmosis, ion exchange and electrodialysis, are used to treat nitrate contamination to produce clean water.…”

Green synthesis of Au decorated CoFe2O4 nanoparticles for catalytic reduction of 4-nitrophenol and dimethylphenylsilane oxidation

“…10,11 In this context, excellent opportunities arise for application of hybrid nanocomposites composed of Au with magnetic oxides in catalysis. 12 Au nanoparticles supported on magnetic oxides may serve to avoid suspension aggregation and catalytic deactivation. 13,14 Meanwhile, the surface coating of magnetic nanoparticles precludes the agglomeration of superparamagnetic nanoparticles enhancing their dispersion in solution.…”