Cyclic voltammetry (CV) and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to investigate the effect of major urine compounds on the electro-oxidation activity of urea using a nickel cobaltite (NiCoO ) catalyst. As a substrate, carbon paper exhibited better benchmark potential and current values compared with stainless steel and fluorine-doped tin oxide glass, which was attributed to its greater active surface area per electrode geometric area. CV analysis of synthetic urine showed that phosphate, creatinine, and gelatin (i.e., proteins) had the greatest negative effect on the electro-oxidation activity of urea, with decreases in peak current up to 80% compared to that of a urea-only solution. Further investigation of the binding mechanisms of the deleterious compounds using in situ ATR-FTIR spectroscopy revealed that urea and phosphate weakly bind to NiCoO through hydrogen bonding or long-range forces, whereas creatinine interacts strongly, forming deactivating inner-sphere complexes. Phosphate is presumed to disrupt the interaction between urea and NiCoO by serving as a hydrogen-bond acceptor in place of catalyst sites. The weak binding of urea supports the hypothesis that it is oxidized through an indirect electron transfer. Outcomes of this study contribute to the development of electrolytic systems for treating source-separated urine.

Regulated oxidized pollutants in drinking water can have significant health effects, resulting in the need for ancillary treatment processes. Oxoanions (e.g., nitrate) are one important class of oxidized inorganic ions. Ion exchange and reverse osmosis are often used treatment processes for oxoanions, but these separation processes leave behind a concentrated waste product that still requires treatment or disposal. Photocatalysis has emerged as a sustainable treatment technology capable of catalytically reducing oxoanions directly to innocuous byproducts. Compared with the large volume of knowledge available for photocatalytic oxidation, very little knowledge exists regarding photocatalytic reduction of oxoanion pollutants. This study investigates the reduction of various oxoanions of concern in drinking water (nitrate, nitrite, bromate, perchlorate, chlorate, chlorite, chromate) using a commercial titanium dioxide photocatalyst and a polychromatic light source. Results showed that oxoanions were readily reduced under acidic conditions in the presence of formate, which served as a hole scavenger, with the first-order rate decreasing as follows: bromate > nitrite > chlorate > nitrate > dichromate > perchlorate, corresponding to rate constants of 0.33, 0.080, 0.052, 0.0074, 0.0041, and 0 cm/photons × 10, respectively. Only bromate and nitrite were reduced at neutral pH, with substantially lower rate constants of 0.034 and 0.0021 cm/photons × 10, respectively. No direct relationship between oxoanion physicochemical properties, including electronegativity of central atom, internal bond strength, and polarizability was discovered. However, observations presented herein suggest the presence of kinetic barriers unique to each oxoanion and provides a framework for investigating photocatalytic reduction mechanisms of oxoanions in order to design better photocatalysts and optimize treatment.

The photocatalytic conversion ofN-hydroxy-carbamates toN-hydroxy-oxazolidinones using metal–organic frameworks is reported herein.

Two-dimensional molybdenum disulfide (MoS 2 ) is emerging as a catalyst for energy and environmental applications. Recent studies have suggested the stability of MoS 2 is questionable when exposed to oxidizing conditions found in water and air. In this study, the aqueous stability of 2H-and 1T-MoS 2 and 2H-MoS 2 protected with a carbon shell was evaluated in the presence of model oxidants (O 2 , NO 2 À , BrO 3 À ). The MoS 2 electrocatalytic performance and stability was characterized using linear sweep voltammetry and chronoamperometry. In the presence of dissolved oxygen (DO) only, 2H-and 1T-MoS 2 were relatively stable, with SO 4 2À formation of only 2.5% and 3.1%, respectively. The presence of NO 2 À resulted in drastically different results, with SO 4 2À formations of 11% and 14% for 2H-and 1T-MoS 2 , respectively. When NO 2 À was present without DO, the 2H-and 1T-MoS 2 remained relatively stable with SO 4 2À formations of only 4.2% and 3.3%, respectively. Similar results were observed when BrO 3 À was used as an oxidant. Collectively, these results indicate that the oxidation of 2H-and 1T-MoS 2 can be severe in the presence of these aqueous oxidants but that DO is also required. To investigate the ability of a capping agent to protect the MoS 2 from oxidation, a carbon shell was added to 2H-MoS 2 . In a batch suspension in the presence of DO and NO 2 À , the 2H-MoS 2 with the carbon shell exhibited good stability with no oxidation observed. The activity of 2H-MoS 2 electrodes was then evaluated for the hydrogen evolution reaction by a Tafel analysis. The carbon shell improved the activity of 2H-MoS 2 with a decrease in the Tafel slope from 451 to 371 mV dec À1 . The electrode stability, characterized by chronopotentiometry, was also enhanced for the 2H-MoS 2 coated with a carbon shell, with no marked degradation in current density observed over the reaction period. Because of the instability exhibited by unprotected MoS 2 , it will only be a useful catalyst if measures are taken to protect the surface from oxidation. Further, given the propensity of MoS 2 to undergo oxidation in aqueous solutions, caution should be used when describing it as a true catalyst for reduction reactions (e.g., H 2 evolution), unless proven otherwise. rsc.li/rsc-advances 9324 | RSC Adv., 2020, 10, 9324-9334This journal is Fig. 8 Chronoamperometry of 2H-MoS 2 and 2H-MoS 2 /C0.1 electrodes in the absence and presence of NO 2 À (7.14 mM). The applied potential was À0.5 V vs. RHE. Samples were degassed with N 2 prior to measurement. The observed noise in current density is due to effects from stirring.9332 | RSC Adv., 2020, 10, 9324-9334This journal is