Photoelectrochemical reduction of nitrates with visible light by nanoporous Si photoelectrode

Electrochemical Mechanisms and Optimization System of Nitrate Removal from Groundwater by Polymetallic Nanoelectrodes

Zn-Cu-TiO₂ polymetallic nanoelectrodes were developed using Ti electrodes as the substrate. The reaction performance and pollutant removal mechanism of the electrodes were studied for different technological conditions by analyzing the electrochemical properties of the electrodes in the electrochemical system, using Ti, TiO₂, Cu-TiO₂, and Zn-Cu-TiO₂ electrodes as cathodes and Pt as the anode. The Tafel curve was used for measuring the corrosion rate of the electrode. The Tafel curve resistance of the Zn-Cu-TiO₂ polymetallic nanoelectrode was the smallest, so the Zn-Cu-TiO₂ nanoelectrode was the least prone to corrosion. The electrode reaction parameters were determined using cyclic voltammetry (CV). Zn-Cu-TiO₂ polymetallic nanoelectrodes have the lowest peak position and the highest electrochemical activity. The surface area of the electrode was determined by the time-current (CA) method, and it was found that the Zn-Cu-TiO₂ polymetallic nanoelectrode had a larger surface area and the highest removal rate of nitrate. The Ti, TiO₂, Cu-TiO₂, and Zn-Cu-TiO₂ electrodes also had higher removal rates for real groundwater, and the differences between the removal rates of nitrates for deionized water and real groundwater decreased as removal time increased. The Zn-Cu-TiO₂ polymetallic nanoelectrode exhibited the highest removal rate for real groundwater. This study reveals the reaction mechanism of the cathode reduction of nitrate, which provides the basis for constructing electrochemical reactors and its application in treating nitrate-contaminated groundwater. A mathematical model of optimized working conditions was created by the response surface method, and optimum time, NaCl concentration, and current density were 93.39 min, 0.22 g/L, and 38.34 mA/cm², respectively. Under these optimal conditions, the nitration removal rate and ammonium nitrogen generation in the process solution were 100% and 0.00 mg/L, respectively.

Engineering a Kesterite-Based Photocathode for Photoelectrochemical Ammonia Synthesis from NOx Reduction

Ammonia is a key chemical feedstock for industry as well as future carbon-free fuel and transportable vector for renewable energy. Photoelectrochemical (PEC) ammonia synthesis from NO_x reduction reaction (NO_x RR) provides not only a promising alternative to the energy-intensive Haber-Bosch process through direct solar-to-ammonia conversion, but a sustainable solution for balancing the global nitrogen cycle by restoring ammonia from wastewater. In this work, selective ammonia synthesis from PEC NO_x RR by a kesterite (Cu₂ ZnSnS₄ [CZTS]) photocathode through loading defect-engineered TiO_x cocatalyst on a CdS/CZTS photocathode (TiO_x /CdS/CZTS) is demonstrated. The uniquely designed photocathode enables selective ammonia production from NO_x RR, yielding up to 89.1% Faradaic efficiency (FE) (0.1 V vs reversible hydrogen electrode (RHE)) with a remarkable positive onset potential (0.38 V vs RHE). By tailoring the amount of surface defective Ti³⁺ species, the adsorption of reactant NO₃ ^- and ^* NO₂  intermediate is significantly promoted while the full coverage of TiO_x also suppresses NO₂ ^- liberation as a by-product, contributing to high ammonia selectivity. Further attempts on PEC ammonia synthesis from simulated wastewater show good FE of 64.9%, unveiling the potential of using the kesterite-based photocathode for sustainably restoring ammonia from nitrate-rich wastewater.

Fabrication of an amorphous metal oxide/p-BiVO4 photocathode: understanding the role of entropy for reducing nitrate to ammonia

Entropy regulation makes an amorphous metal oxide/p-BiVO4 heterostructure a desirable catalyst for the NO3− reduction reaction in a photoelectrochemical system.

Simultaneous nitrate reduction and acetaminophen oxidation using the continuous-flow chemical-less VUV process as an integrated advanced oxidation and reduction process

This work was aimed at investigating the performance of the continuous-flow VUV photoreactor as a novel chemical-less advanced process for simultaneously oxidizing acetaminophen (ACT) as a model of pharmaceuticals and reducing nitrate in a single reactor. Solution pH was an important parameter affecting the performance of VUV; the highest ACT oxidation and nitrate reduction attained at solution pH between 6 and 8. The ACT was oxidized mainly by HO while the aqueous electrons were the main working agents in the reduction of nitrate. The performance of VUV photoreactor improved with the increase of hydraulic retention time (HRT); the complete degradation of ACT and ∼99% reduction of nitrate with 100% N2 selectivity achieved at HRT of 80min. The VUV effluent concentrations of nitrite and ammonium at HRT of 80min were below the drinking water standards. The real water sample contaminated with the ACT and nitrate was efficiently treated in the VUV photoreactor. Therefore, the VUV photoreactor is a chemical-less advanced process in which both advanced oxidation and advanced reduction reactions are accomplished. This unique feature possesses VUV photoreactor as a promising method of treating water contaminated with both pharmaceutical and nitrate.

High performance nanoporous silicon photoelectrodes co-catalyzed with an earth abundant [Mo3S13]2− nanocluster via drop coating

Earth abundant [Mo₃S₁₃]²⁻ nanoclusters efficiently enhance a nanoporous silicon photoelectrode for hydrogen generation.