Efficient electrocatalysis for denitrification by using TiO2 nanotube arrays cathode and adding chloride ions

Electrocatalysis is emerging as a promising alternative to bacterial denitrification for removing nitrate and ammonia from sewage. The technology is highly efficient and robust in actual wastewater treatment scenarios; however, there may be the generation of harmful intermediates (such as nitrite) on the traditional cathode material. In this study, we demonstrated that TiO2 nanotube arrays can be used as an effective cathode to reduce nitrate to ammonia without generation of nitrite. Alongside this, the addition of chloride ions in the solution can further oxidize ammonia to N2. We looked into the key factors influencing the electrocatalytic denitrification, including the current density (2–10 mA/cm2), initial pH values (3–11), and types of anions (HCO3−, Cl−, SO42−). The results showed that 90.8% of nitrate and 59.4% of total nitrogen could be removed in 1.5 h under optimal conditions, with degradation kinetic constants of 1.61 h−1 and 0.79 h−1, respectively. Furthermore, we investigated the formation of intermediate products and explored the electrocatalytic denitrification mechanism: (a) the surface oxygen vacancies and high specific surface area of TiO2 nanotube arrays electrode promote the reduction of nitrate to ammonia and N2; (b) the active chlorine generated at the anode surface can effectively oxidize ammonium to N2

Mechanisms of Highly Efficient Photocatalytic Pollutant Degradation by Au/TiO2 Janus Nanoparticles

Semiconductor nanoparticles partially coated with metals have been widely used to degrade contaminants in water, but the physical mechanisms underlying degradation are poorly understood, limiting their real-world implementation. Here, we reveal the degradation mechanisms that dominate when gold-coated titanium dioxide (Au/TiO2) “Janus” nanoparticles (JNPs) are irradiated with monochromatic ultraviolet light (254 nm and 365 nm wavelengths) to degrade 1,4-dioxane, a carcinogenic model pollutant. To do so, we performed experiments with ultraviolet light at different wavelengths with and without radical quenching, extensive JNP characterization (SEM, XRD, EDS, DLS, and UV-Vis), and 3D simulations of self-propulsion and light-matter interactions. We traced the enhanced photocatalytic activity of Au-coated JNPs to both increased light absorption due to Au acting as an optical antenna, and inhibited recombination of photogenerated electrons and holes. These two effects increase the production of hydroxyl radicals, accelerating the degradation of 1,4-dioxane. The reduced electron/hole recombination is due to two factors: the Schottky barrier that forms between Au and TiO2 (which drives photogenerated electrons from TiO2 into the metal), and stoichiometric changes in the TiO2 that accompany gold sputtering which facilitate electron sequestration by the metal. In contrast, self-propulsion and surface plasmon resonance play at most a minor role

Stop-Flow Lithography for the Continuous Production of Degradable Hydrogel Achiral Crescent Microswimmers

The small size of robotic microswimmers makes them suitable for performing biomedical tasks in tiny, enclosed spaces. Considering the effects of potentially long-term retention of microswimmers in biological tissues and the environment, the degradability of microswimmers has become one of the pressing issues in this field. While degradable hydrogel was successfully used to prepare microswimmers in previous reports, most hydrogel microswimmers could only be fabricated using two-photon polymerization (TPP) due to their 3D structures, resulting in costly robotic microswimmers solution. This limits the potential of hydrogel microswimmers to be used in applications where a large number of microswimmers are needed. Here, we proposed a new type of preparation method for degradable hydrogel achiral crescent microswimmers using a custom-built stop-flow lithography (SFL) setup. The degradability of the hydrogel crescent microswimmers was quantitatively analyzed, and the degradation rate in sodium hydroxide solution (NaOH) of different concentrations was investigated. Cytotoxicity assays showed the hydrogel crescent microswimmers had good biocompatibility. The hydrogel crescent microswimmers were magnetically actuated using a 3D Helmholtz coil system and were able to obtain a swimming efficiency on par with previously reported microswimmers. The results herein demonstrated the potential for the degradable hydrogel achiral microswimmers to become a candidate for microscale applications