Efficient Hydrogen Generation and Total Nitrogen Removal for Urine Treatment in a Neutral Solution Based on a Self-Driving Nano Photoelectrocatalytic System

Abstract

Urine is the main source of nitrogen pollution, while urea is a hydrogen-enriched carrier that has been ignored. Decomposition of urea to H2 and N2 is of great significance. Unfortunately, direct urea oxidation suffers from sluggish kinetics, and needs strong alkaline condition. Herein, we developed a self-driving nano photoelectrocatalytic (PEC) system to efficiently produce hydrogen and remove total nitrogen (TN) for urine treatment under neutral pH conditions. TiO2/WO3 nanosheets were used as photoanode to generate chlorine radicals (Cl•) to convert urea-nitrogen to N2, which can promote hydrogen generation, due to the kinetic advantage of Cl–/Cl• cyclic catalysis. Copper nanowire electrodes (Cu NWs/CF) were employed as the cathode to produce hydrogen and simultaneously eliminate the over-oxidized nitrate-nitrogen. The self-driving was achieved based on a self-bias photoanode, consisting of confronted TiO2/WO3 nanosheets and a rear Si photovoltaic cell (Si PVC). The experiment results showed that hydrogen generation with Cl• is 2.03 times higher than in urine treatment without Cl•, generating hydrogen at 66.71 μmol h−1. At the same time, this system achieved a decomposition rate of 98.33% for urea in 2 h, with a reaction rate constant of 0.0359 min−1. The removal rate of total nitrogen and total organic carbon (TOC) reached 75.3% and 48.4% in 2 h, respectively. This study proposes an efficient and potential urine treatment and energy recovery method in neutral solution.

Urea catalytic oxidation for energy and environmental applications

“…289,290 The removal efficiency of total nitrogen (TN) and total organic carbon (TOC) have become important indicators for urea/urine wastewater remediation. [291][292][293] p-UOR and e-UOR have recently emerged as promising approaches for urea/urine wastewater remediation. [294][295][296] At 60 min, the amount of N 2 reached 806 mmol, with an FE of 77.9%, demonstrating that N 2 was the primary product of urine degradation (97.5%).…”

“…289,290 The removal efficiency of total nitrogen (TN) and total organic carbon (TOC) have become important indicators for urea/urine wastewater remediation. 291–293 p-UOR and e-UOR have recently emerged as promising approaches for urea/urine wastewater remediation. 294–296 Shen et al employed a photoelectrochemical cell system that Cl˙ and ˙HO facilitate the conversion of urea–nitrogen into N 2 while degrading organics into CO 2 .…”