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Nitrate Removal via Formate Radical-induced Photochemical Process
摘要： Removal of excess nitrate is critical to balance the nitrogen cycle in aquatic systems. This study investigated a novel denitrification process by tailoring photochemistry of nitrate with formate. Under UV light irradiation, short-lived radicals (i.e., HO·, NO2· and CO3·-) generated from nitrate photolysis partially oxidized formate to highly reductive formate radical (CO2·-). CO2·- further reduced nitrogen intermediates generated during photochemical denitrification (mainly NO·, HNO, and N2O) to gas-phase nitrogen (i.e., N2O and N2). The degradation kinetics of total dissolved nitrogen was mainly controlled by the photolysis rates of nitrate and nitrite. The distribution of final products was controlled by the reaction between CO2·- and N2O. To achieve a simultaneous and complete removal of dissolved nitrogen (i.e., nitrate, nitrite, and ammonia) and organic carbon, the formate-to-nitrate stoichiometry was determined as 3.1 ± 0.2 at neutral pH in deionized water. Solution pH impacted the removal rates of nitrate and nitrite, but not that of total dissolved nitrogen or formate. The presence of dissolved organic matter at levels similar to groundwater had a negligible impact on the photochemical denitrification process. A high denitrification efficiency was also achieved in a synthetic groundwater matrix. Outcome from this study provides a potential denitrification technology for decentralized water treatment and reuse facilities to abate nitrate in local water resources.
关键词： denitrification,water treatment,nitrate removal,photochemical process,formate radical
更新于2025-09-10 09:29:36
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Selective reduction of nitrate to nitrogen gas by novel Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation
摘要： The nitrate reduction by Fe-based materials has been extensively studied, however, the selectivity of nitrate reduction to nitrogen gas is very low, which hinders the application of this technology. In this study, a novel Cu2O-Cu0@Fe0 composite was synthesized and a strategy of Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation as reducers for the nitrate reduction was established to improve the selective reduction of nitrate (NO3?) to nitrogen gas (N2). The Cu2O-Cu0@Fe0 composite was synthesized by simple chemical replacement and O2 oxidation process and characterized by SEM, EDS, XRD and XPS. The nitrate removal efficiency of 100% and the N2 selectivity of 95.4% were achieved in Cu2O-Cu0@Fe0/HCOOH/UV system when the initial nitrate concentration was 50 mg N/L and the reduction time was 60 min. The nitrate reduction efficiency was low by the role of alone or combinations of Cu2O-Cu0@Fe0 composite, HCOOH or UV radiation. The quick reduction of nitrate to nitrite was due to the synergistic effect of electrons from the galvanic-type cell consisting of Fe0 as anode and Cu0 as cathode, photoelectrons from Cu2O under UV radiation and CO2?? produced mainly via photochemical reaction between HCOOH and UV radiation. The subsequent conversion of nitrite to N2 was caused by CO2??, which was responsible for the high efficient reduction of nitrate to nitrogen gas in the Cu2O-Cu0@Fe0/HCOOH/UV system. Finally, the denitrification mechanism of the Cu2O-Cu0@Fe0/HCOOH/UV system was tentatively proposed.
关键词： Denitrification,Galvanic-type cell,Cuprous oxide,Nitrate reduction
更新于2025-09-10 09:29:36
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Rational construction of direct Z-scheme doped perovskite/palygorskite nanocatalyst for photo-SCR removal of NO: Insight into the effect of Ce incorporation
摘要： V-Ti oxide catalyst has been widely employed in selective catalytic reduction (SCR) of NOx in industry. However, considerable cost and high reaction temperatures are commonly required. Alternatively, photo-SCR working at low temperature has attracted widespread interest. In the present work, Pr1(cid:1)xCexFeO3/palygorskite (Pal) nanocomposite was synthesized by an in situ sol-gel method. Results indicate that Pr1(cid:1)xCexFeO3 remain as a perovskite solid solution uniformly immobilized on the surface of Pal when x is less than 0.05. CeO2 co-precipitates with Pr1(cid:1)xCexFeO3 when x is beyond 0.05, leading to an enhanced charge separation induced by the formation of intimate direct Z-scheme heterostructure of Pr1(cid:1)xCexFeO3/CeO2, which is unraveled by the photoluminescence spectroscopy and Mott-Schottky analysis and further verified by the DFT calculations. Under visible light irradiation, the influence of the doping amount of Ce (from 0.05 to 0.5) on the NO conversion and N2 selectivity was investigated. The Pr0.7Ce0.3FeO3/Pal was found to achieve the highest NO conversion rate of 92% and 99% N2 selectivity. In addition, the SO2 and H2O resistance experiment show that the doping of Ce could benefit the formation of cerium sulphate which prevents NH3 from being sulfated by SO2 while Pal prevents the catalysts from being corroded by H2O, respectively.
关键词： Direct Z-scheme,Photo-SCR,Palygorskite,Denitrification,CeO2,Perovskite
更新于2025-09-10 09:29:36
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Highly efficient total nitrogen and simultaneous total organic carbon removal for urine based on the photoelectrochemical cycle reaction of chlorine and hydroxyl radicals
摘要： Urine is a major nitrogen and COD source and threatens the aqueous environment, leading to eutrophication and energy consumption. However, the conventional technologies encounter the bottleneck due to the high load of nitrogen and organics in urine. Here we propose an innovative idea for complete transformation of urea-nitrogen to N2 and simultaneous degradation of organics to CO2 with the assistance of chlorine and hydroxyls radicals (Cl? and HO?) in photoelectrochemical cell system. This idea reveals circulation process of these two radicals: photoexcited holes from WO3 anode oxidize chloride and hydroxyl ions to Cl? and HO? radicals under illumination, these radicals convert urea-nitrogen to N2 or slight nitrate, and then slight nitrate is selectively reduced to N2 on a novel Pd/Au modified porous metallic sheet. TN analysis of a simulated urea solution of 30 mg L-1 demonstrated that N2 and CO2 are the primary oxidation products of the urea, and the urea-N was completely stripped (99.45%) in 90 min. Meanwhile, with the detection of EPR spectrum, organics can be transformed to CO2 by OH? in this cyclic system. Significantly, the feasibility of actual urine treatment was also investigated, indicating great denitrification efficiency (99.37%) and TOC removal efficiency (50.91%), respectively. This work sheds light upon a new economical, efficient, and environment-friendly means of urine sewage treatment.
关键词： urine,hydroxyl radicals,denitrification,chlorine radicals,photoelectrochemical
更新于2025-09-09 09:28:46