Highly selective transformation of ammonia nitrogen to N2 based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions system

Application of physicochemical techniques to the removal of ammonia nitrogen from water: a systematic review

Ammonia nitrogen is a common pollutant in water and soil, known for its biological toxicity and complex removal process. Traditional biological methods for removing ammonia nitrogen are often inefficient, especially under varying temperature conditions. This study reviews physicochemical techniques for the treatment and recovery of ammonia nitrogen from water. Key methods analyzed include ion exchange, adsorption, membrane separation, struvite precipitation, and advanced oxidation processes (AOPs). Findings indicate that these methods not only remove ammonia nitrogen but also allow for nitrogen recovery. Ion exchange, adsorption, and membrane separation are effective in separating ammonia nitrogen, while AOPs generate reactive species for efficient degradation. Struvite precipitation offers dual benefits of removal and resource recovery. Despite their advantages, these methods face challenges such as secondary pollution and high energy consumption. This paper highlights the development principles, current challenges, and future prospects of physicochemical techniques, emphasizing the need for integrated approaches to enhance ammonia nitrogen removal efficiency.

Enhanced ammonia oxidation by a photoelectrocatalysis‑chlorine system: The role of ClO• and free chlorine

The decomposition of ammonia-N to environmental-friendly N2 remains a fundamental problem for water treatment. We proposed a way to selectively and efficiently oxidize ammonia to N2 through an integrated photoeletrocatalysis‑chlorine reactions (PECCl) system based on a bifunctional TiO2 nanotube photoanode. The ·OH and HClO can be simultaneously generated on the TiO2 nanotube photoanode in this system, which can in situ form ClO· for efficient ammonia removal. Compared with electrochemical‑chlorine (EC-Cl), photocatalysis‑chlorine (PC-Cl) and photoelectrocatalysis (PEC) systems, the PEC-Cl system exhibited much higher electrocatalytic activity due to the synergetic effect of photoelectrocatalyst and electrocatalyst in bifunctional TiO2 nanotube electrode. The removal efficiency of ammonia-N and total-N reached 100.0 % and 93.3 % at 0.3 V (vs Ag/AgCl) in the PEC-Cl system. Moreover, the system was efficient under various pH conditions. The reactions between ClO-/ClO· and the N-containing intermediates contributed to the high performance of the system, which expanded the reactions from the electrode surface to the electrolyte. Furthermore, radical scavenging and free chlorine determination experiments confirmed that ClO· and free chlorine were the main active species that enabled the ammonia oxidation. This study presents new understanding on the role of active species for ammonia removal in wastewater.

Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl- Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal

High Cl- concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl- conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure-property relationship in Cl- utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 μg L-1 min-1. Mechanism investigation demonstrates the fast release of lattice Cl- as an RCS and the compensation of ambient Cl-. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl- conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L-1 with different chlorinity (3-12 g L-1 NaCl). The sustainable Cl- conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L-1 NH4+-N). The structure-property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl-.

Nanomaterials-Induced Redox Imbalance: Challenged and Opportunities for Nanomaterials in Cancer Therapy

Cancer cells typically display redox imbalance compared with normal cells due to increased metabolic rate, accumulated mitochondrial dysfunction, elevated cell signaling, and accelerated peroxisomal activities. This redox imbalance may regulate gene expression, alter protein stability, and modulate existing cellular programs, resulting in inefficient treatment modalities. Therapeutic strategies targeting intra- or extracellular redox states of cancer cells at varying state of progression may trigger programmed cell death if exceeded a certain threshold, enabling therapeutic selectivity and overcoming cancer resistance to radiotherapy and chemotherapy. Nanotechnology provides new opportunities for modulating redox state in cancer cells due to their excellent designability and high reactivity. Various nanomaterials are widely researched to enhance highly reactive substances (free radicals) production, disrupt the endogenous antioxidant defense systems, or both. Here, the physiological features of redox imbalance in cancer cells are described and the challenges in modulating redox state in cancer cells are illustrated. Then, nanomaterials that regulate redox imbalance are classified and elaborated upon based on their ability to target redox regulations. Finally, the future perspectives in this field are proposed. It is hoped this review provides guidance for the design of nanomaterials-based approaches involving modulating intra- or extracellular redox states for cancer therapy, especially for cancers resistant to radiotherapy or chemotherapy, etc.

Enhanced recovery of phosphorus from hypophosphite-laden wastewater via field-induced electro-Fenton coupled with anodic oxidation

Electrochemical recovered ferric phosphate (FePO4) precipitates from hypophosphite-laden wastewater were shown to be an efficient method for phosphorus (P) recovery. However, the influence of chloride ions (Cl-) coexisting commonly in wastewater is not known for this treatment. Herein, a field-induced electro-Fenton coupled with anodic oxidation electrochemical system consisting of a Ti-RuO2 anode, an Fe inductive electrode and an activated carbon fiber (ACF) cathode, namely Ti-RuO2/Fe/ACF(NaCl) system, was established to recover phosphorus (P) as FePO4 from hypophosphite-laden wastewater in the presence of Cl-. This system enabled a hypophosphite (H2PO2-, 1.0 mM) removal ratio of ~100% and all P was recovered within 30 min at 5.0 V under the initial solution pH of 3.0. The Faradaic efficiency and energy consumption of P recovery achieved the maximum value (~94%) and the lowest value (~16 kW h kg-1 P), respectively. Reactive oxygen species including 1O2, FeIVO2+, •O2- and •OH contribute to convert H2PO2- to PO43-, which immediately formed FePO4 with the generated Fe3+ at the optimized conditions. Therein, the contribution of non-radical 1O2 was very considerable. This system exhibited good stability. The efficiency and cost for treatment of actual hypophosphite-laden wastewater were addressed to check its applicability for P recovery.

Three-compartment membrane electrolyzer combining simultaneous desalination and oxidative degradation in treating nanofiltration concentrate

The complex organic and inorganic solutes present in nanofiltration's purification by-product (NF concentrate, NFC) pose challenges to the water processing procedure. To address this, a three-compartment membrane electrolyzer was proposed that facilitates electro-driven ion migration for crystallization alongside synchronous anodic oxidation for organic degradation. With a hydraulic retention time (HRT) of 5 min and a current exceeding 50 mA, the system effectively separated over 25 % of inorganic salts and accomplished reclamation through crystallization in the concentration compartment. Simultaneously, it achieved oxidation of pollutants by more than 35 % based on the total nitrogen index and removed upwards of 15 % of organic carbon. Notably, the efficiency of pollutant removal correlated strongly with the intensity of the current. Furthermore, this study uncovered two issues encountered during the electrochemical process: membrane fouling and electrode fouling. During concentration, metal cations readily formed organic pollution by complexing with organic pollutants, while the crystallization of inorganics on the surface of anion exchange membranes emerged as a pivotal factor hindering current enhancement, similar to the formation of deposited salt in a solution. Long HRT can lead to electrode contamination and corrosion which subsequently affect current efficiency. Energy consumption verified the feasibility of the electrolyzer for NFC processing. Based on our findings, a current intensity of 100 mA (equivalent to a density of 8 mA/cm2) was deemed optimal, striking a balance between pollutant removal and various limiting factors associated with each pollutant. Consequently, this innovative advancement in membrane electrolyzers helps in overcoming limitations in synergistic desalination, ion recovery, and organic removal, establishing a fundamental component of the abbreviated flow process for future NFC treatment.

Photo-anammox by vacuum ultraviolet tandem chlorine

Excessive ammonia (NH4+) discharge can lead to algal blooms and disrupt water sustainability, so its control is imperative. Although microbiology-triggered anammox process is promising, its application is limited due to time-consuming cultivation of specific microorganisms and need for skilled operation. To bypass these barriers, this study proposed and verified a photo-induced anammox technology that removes NH4+ and total nitrogen (TN) from water by ultraviolet (UV)/vacuum UV (VUV)/chlorine under anoxic conditions. Under the Cl/N mass ratio of 5:1, the anoxic VUV/UV/chlorine process achieved 66.8% removal of 10 mg-N/L NH4+ within 10 min along with 57.8% reduction in TN. Besides the evidence from TN loss, this study confirmed nitrogen gas (N2) as the primary degradation product at low dissolved oxygen (DO) concentration of 2.0 mg/L. The selective conversion of NH4+ into N2 was mainly attributed to reactive nitrogen species (RNS, 42.5%) and reactive chlorine species (RCS, 57.5%). The TN removal efficiency was insensitive to certain variations of pH (7.0-9.0), NH4+ concentration (1-30 mg-N/L), chloride (50-125 mg/L), and sulfate (25-100 mg/L), but sensitive to DO and bicarbonate (25-100 mg/L). Given its robustness and high efficiency, the anoxic VUV/UV/chlorine technology may serve as a potentially promising alternative for NH4+ and TN alleviation in wastewater.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co-catalyzed by Trace Amounts of Copper Ions

High-efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5-10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm-2 at 1.23 VRHE , being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm-2 ). The surface charge-separation efficiency has reached 90 % under a low bias of 0.8 VRHE . This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non-aqueous solutions. Through mechanistic studies, we find that the formation of Cu-NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu-induced coordination effect activates N-H bonds and accelerates the first rate-limiting proton-coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.

An update on sustainabilities and challenges on the removal of ammonia from aqueous solutions: A state-of-the-art review

An insightful attempt has been made in this review and the primary objective was to meticulously provide an update on the sustainabilities, advances and challenges pertaining the removal of ammonia from water and wastewater. Specifically, ammonia is a versatile compound that prevails in various spheres of the environment, and if not properly managed, this chemical species could pose severe ecological pressure and toxicity to different receiving environments and its biota. The notorious footprints of ammonia could be traced to anoxic conditions, an infestation of aquatic ecosystems, hyperactivity, convulsion, and methaemoglobin, popularly known as the "blue baby syndrome". In this review, latest updates regarding the sustainabilities, advancements and challenges for the removal of ammonia from aqueous solutions, i.e., river and waste waters, are briefly elucidated in light of future perspectives. Viable routes and ideal hotspots, i.e., wastewater and drinking water, for ammonia removal under the cost-effective options have been unpacked. Key mechanisms for the removal of ammonia were grossly bioremediation, oxidation, adsorption, filtration, precipitation, and ion exchange. Finally, this review denoted biological nutrient removal, struvite precipitation, and breakpoint chlorination as the most effective and promising technologies for the removal of ammonia from aquatic environments, although at the expense of energy and operational cost. Lastly, the future perspective, avenues of exploitation, and technical facets that deserve in-depth exploration are duly underscored.

Selective and effective oxidation of ammonium to dinitrogen in MgO/Na2SO3/K2S2O8 system

The oxidation of ammonium (NH₄⁺) to dinitrogen (N₂) with high selectivity and high efficiency is still a challenge. Herein, a novel sunlight induced persulfate (PS)-based AOPs process (MgO/Na₂SO₃/PS/hv) was proposed by introducing solid base (MgO) and hydrated electron (e_aq^-), to selectively oxidize NH₄⁺ to N₂, with high selectivity and high efficiency at a wide range of pH value. The deprotonation of NH₄⁺ into NH₃ by MgO and the generation of •OH and SO₄^-• by PS activation were responsible for the high efficiency of NH₄⁺ oxidation. The buffering capacity provided by MgO to proton released from PS activation made the NH₄⁺ oxidation possible at a wide pH range. The e_aq^- from the Na₂SO₃/hv process was the main active specie to reduce NO₂^-and NO₃^- (NO_x^-) into N₂, responsible for high N₂ selectivity of NH₄⁺ oxidation. 100% NH₄⁺ could be oxidized within 30 min, and N₂ selectivity exceeded 96% at the initial pH range of 3-11 and the initial concentration of NH₄⁺ of 30 mg N/L. This work could offer an efficient AOPs process for selective NH₄⁺ oxidation, which is promising for the chemical denitrification of wastewater ….

Nitrogen-containing wastewater fuel cells for total nitrogen removal and energy recovery based on Cl•/ClO• oxidation of ammonia nitrogen

The excess nitrogen discharge into water bodies has resulted in extensive water pollution and human health risks, which has become a critical global issue. Moreover, nitrogenous wastewater contains considerable chemical energy contributed by organic pollutants and nitrogenous compounds. Therefore, the treatment of various kinds of nitrogen-containing wastewater for nitrogen removal and energy recovery is of significance. Biological methode and advanced oxidation processes (AOPs) are the main methods for nitrogen removal. However, biological treatment is easily inhibited by high-salinity, high ammonia nitrogen (NH₃-N/NH₄⁺-N), nitrite and toxic organics in wastewater, which limits its application. AOPs mainly induce in situ generation of highly reactive species, such as hydroxyl radical (HO•), sulfate radical (SO₄•^-) and chlorine radicals (Cl•, ClO•, Cl₂•^-), for nitrogen removal. Nevertheless, HO• shows low reactivity and N₂ selectivity towards NH₃-N/NH₄⁺-N oxidation, and SO₄•^- also demonstrates unsatisfactory NH₃-N/NH₄⁺-N removal. It has been shown that Cl•/ClO• can efficiently remove NH₃-N/NH₄⁺-N with high N₂ selectivity. The generation of Cl•/ClO• can be triggered by various techniques, among which the PEC technique shows great potential due to its higher efficiency for Cl•/ClO• generation and eco-friendly approach for pollutants degradation and energy recovery by utilizing solar energy. Cl•/ClO• oxidation of NH₃-N/NH₄⁺-N and nitrate nitrogen (NO₃^--N) reduction can be strengthened through the design of photoanode and cathode materials, respectively. Coupling with this two pathways, an exhaustive total nitrogen (TN) removal system is designed for complete TN removal. When introducing the mechanism into photocatalytic fuel cells (PFCs), the concept of nitrogen-containing wastewater fuel cells (NFCs) is proposed to treat several typical types of nitrogen-containing wastewater, achieving high-efficiency TN removal, organics degradation, toxic chlorate control, and energy recovery simultaneously. Recent research progress in this field is reviewed, summarized and discussed, and in-depth perspectives are proposed, providing new ideas for the resource treatment of nitrogen-containing wastewater.

Solution, exchangeable and fixed ammonium in natural diatomite as a simulated PRB material: effects of adsorption and bioregeneration processes

Ammonia nitrogen (NH₄⁺-N) is widely found in aquifers with strong reducibility or poor adsorptivity as a dissolved inorganic nitrogen pollutant. The application of adsorbents with effective long-term in situ bioregeneration as permeable reactive barrier (PRB) media for nitrogen removal has raised concern. In this study, the advantage of natural diatomite as a PRB material was investigated by exploring its NH₄⁺-N adsorption and desorption characteristics, and the ability of diatomite and zeolite to be loaded nitrifying bacteria was also compared. The results showed that the exchangeable ammonium from chemical-monolayer adsorption was the main form of NH₄⁺-N and was adsorbed by diatomite. Moreover, the adsorption process was limited with a maximum adsorption capacity of 0.677 mg g^-1. However, diatomite demonstrated an excellent loading of aerobic-heterotrophic microorganisms, even stronger than zeolite. Compared with zeolite reactors, a higher OD₆₀₀ value of nitrifiers, a faster NH₄⁺-N degradation rate and more abundant functional genes were observed during the bioregeneration process of diatomite. Both the solution and exchangeable ammonium forms were bioavailable, and the regeneration of diatomite was more than 80.0% after two days. Moreover, desorption-biodegradation was systematically analysed to determine the bioregeneration mechanism of diatomite. Diatomite with good regeneration ability can be used as a competitive alternative to address sudden nitrogen pollution.

Activation of chloride by oxygen vacancies-enriched TiO2 photoanode for efficient photoelectrochemical treatment of persistent organic pollutants and simultaneous H2 generation

Photoelectrochemical (PEC) activation of chloride ions (Cl^-) to degrade persistent organic pollutants (POPs) is a promising strategy for the treatment of industrial saline organic wastewater. However, the wide application of this technology is greatly restricted due to the general photoanode activation of Cl^- with poor capability, the propensity to produce toxic by-products chlorates, and the narrow pH range. Herein, oxygen vacancies-enriched titanium dioxide (O_v-TiO₂) photoanode is explored to strongly activate Cl^- to drive the deep mineralization of POPs wastewater in a wide pH range (2-12) with simultaneous production of H₂. More importantly, nearly no toxic by-product of chlorates was produced during such PEC-Cl system. The degradation efficiency of 4-CP and H₂ generation rate by O_v-TiO₂ were 99.9% within 60 min and 198.2 μmol h^-1 cm^-2, respectively, which are far superior to that on the TiO₂ (33.1% within 60 min, 27.5 μmol h^-1 cm^-2) working electrode. DFT calculation and capture experiments revealed that O_v-TiO₂ with abundant oxygen vacancies is conducive to the activation of Cl^- to produce more reactive chlorine species, evidenced by its high production of free chlorine (48.7 mg L^-1 vs 7.5 mg L^-1 of TiO₂). The as-designed PEC-Cl system in this work is expected to realize the purification of industrial saline organic wastewater coupling with green energy H₂ evolution.

Selective oxidation of ammonia to dinitrogen gas by facile Co2+/PMS/chloridion process through reactive chlorine radicals

The selective oxidation of ammonia to dinitrogen gas in some special wastewater is of paramount significance, but still a challenge. In this study, chlorine radical (Cl•)-mediated oxidation process was developed to realize the selective oxidation of NH₄⁺-N to N₂, in which Cl• was generated in Co²⁺/peroxymonosulfate (PMS)/chloridion (Cl^-) system. The effect of various operational parameters on the efficiency and selectivity of ammonia oxidation to N₂ was investigated, such as PMS concentration, Co²⁺ concentration, Cl^- concentration and pH value. The experiment results showed that Cl•-mediated NH₄⁺-N oxidation reaction exhibited high NH₄⁺-N removal efficiency and considerable selectivity to N₂ in the range of pH from 2.0 to 6.5. The removal efficiency of NH₄⁺-N was 90.39%, and the selectivity of NH₄⁺-N to N₂ achieved up to 97.16%. The possible mechanism for high efficient and selective oxidation of NH₄⁺-N to N₂ was tentatively proposed. The process developed in this study could provide a novel technology for the treatment and selective oxidation of ammonium in some special types of ammonium-containing wastewater.

Boosting generation of reactive oxygen and chlorine species on TNT photoanode and Ni/graphite fiber cathode towards efficient oxidation of ammonia wastewater

Photoelectrocatalytic (PEC) process combining the merits of photocatalysis and electrocatalysis is considered as a promising ammonia oxidation technology for water treatment. However, some key issues, such as the limited in situ generation of oxidants on photoanode, slow mass transfer problem and generation of nitrate/nitrite by-products hinder the further application of PEC process in the treatment of ammonia pollutant. In this study, the graphite felt (GF) cathodes modified by different transition metals (Ni, Fe, Mn, Co, Cu) were screened by physicochemical and photoelectrochemical characterizations. The results show that the Ni-GF cathode with more Ni⁰ uniformly distributed on the GF surface had the best electrocatalytic activity to generate H₂O₂. The PEC system composed of 10.0 wt% Ni-GF cathode and optimized titania nanotubes (TNTs) photoanode selectively converted about 96.1% ammonia to N₂ within 90 min. Compared with the single TNTs photoanode system, the ammonia oxidation reaction rate constant of the synergistic PEC oxidation system was increased by about two times, which demonstrated the role of the oxidants simultaneously generated on both anode and cathode. The in situ generated reactive oxygen-based oxidants and chlorine-based oxidants interacted together, and ClO• acted a leading role in the ammonia oxidation which were confirmed by quenching and probe experiments. In addition, the contributions of •OH and ClO• were significantly improved in the synergistic PEC oxidation system, compared with the single TNTs photoanode system. Furthermore, the nitrate by-products generated by the ammonia oxidation were further reduced on the Ni-GF cathode. The large amount of active chlorine and active oxygen generated on the electrode diffused into the bulk, effectively overcoming the mass transfer limitation of direct oxidation. Therefore, the developed TNTs photoanode/Ni-GF cathode system can continuously and efficiently convert ammonia to N₂ without the formation of nitrate/nitrite by-products.

CeO2 modified carbon nanotube electrified membrane for the removal of antibiotics

Electrified carbon nanotube membranes (ECM) are used as electroactive porous materials for the degradation of micropollutants. It integrated design of both electrochemical processes and filtration functions. In this study, CeO₂ modified carbon nanotube electrified membrane (CeO₂@CNT membrane) was prepared and activate NaClO towards degradation of antibiotics. As CeO₂ with face-centered cubic (Fcc) fluorite structure was loaded onto the CNT sidewalls, the CeO₂@CNT membrane showed a higher over potential and a smaller equivalent polarization resistance compared to ECM. More reactive oxygen species (ROS) and reactive chlorine species (RCS) were generated by CeO₂@CNT membrane due to faster electron transfer at the solid-liquid interface. Thus, the removal efficiencies of DCF, SMX, CIP, TC and CBZ were more than 91.2%, 91.3%, 94.4%, 99.3% and 89.4% by the CeO₂@CNT membrane with NaClO, respetively. And the apparent reaction rate constant (k) of the CeO₂@CNT membrane was 2.9 times of that of ECM. The selective capping experiments and density functional theory (DFT) calculation showed that the oxygen vacancies of CeO₂ contributed to the generation of ‧OH, and the generation of ClO‧ and ‧O₂^- would mainly occur on Lewis acid sites of CeO₂. In addition, the CeO₂@CNT membrane showed a reasonable stability to treat actual water samples and reduced disinfection byproducts (DBPs) formation, suggesting that it can potentially be combined with the conventional chlorine disinfection to degrade antibiotics in water.

Highly selective electrocatalytic reduction of nitrate to nitrogen in a chloride ion-free system by promoting kinetic mass transfer of intermediate products in a novel Pd-Cu adsorption confined cathode

The mass transfer on the catalyst surface has a great influence on the selectivity of electrocatalytic nitrate reduction to nitrogen. In this study, a Pd-Cu adsorption confined nickel foam cathode is designed in the absence of both proton exchange membranes and chloride ions. The repulsion of the cathode enables intermediate products such as nitrite to accumulate in the confined region, resulting in an increase in the possibility of a second-order reaction to form nitrogen. The system can obtain more than 92% continuous N₂ selectivity when it is used to treat 200 mg L^-1 NO₃^--N under a current density of 8 mA cm^-2, which is not only higher than those of semiconfined and nonconfined systems but also significantly better than the results obtained by Pd-Cu directly modified cathodes prepared by electrodeposition or impregnation. It is found that a high initial nitrate concentration and low current density are more beneficial for the accumulation of intermediates on Pd-Cu catalysts, thus improving the formation of nitrogen. A mechanism study reveals that the intermediates can completely occupy the active sites on the surface of Pd, avoiding the generation of active hydrogen, and therefore inhibiting the first-order reaction to produce ammonia. Moreover, the reducibility of Pd-Cu can also be gradually improved under the function of the cathode so that the system exhibits good stability. This study demonstrates an environmentally friendly and promising method for total nitrogen removal from industrial wastewater with high conductivity.

Integrating Reactive Chlorine Species Generation with H2 Evolution in a Multifunctional Photoelectrochemical System for Low Operational Carbon Emissions Saline Sewage Treatment

Conventional wastewater treatment plants (WWTPs) suffer from high carbon emissions and are inefficient in removing emerging organic pollutants (EOPs). Consequently, we have developed a low operational carbon emissions multifunctional photoelectrochemical (PEC) system for saline sewage treatment to simultaneously remove organic pollutants, ammonia, and bacteria, coupled with H₂ evolution. A reduced BiVO₄ (r-BiVO₄) photoanode with enhanced PEC properties, ascribed to constructing sufficient oxygen vacancies and V⁴⁺ species, was synthesized for the aforementioned technique. The PEC/r-BiVO₄ process could treat saline sewage to meet local WWTPs' discharge standard in 40 min at 2.0 V vs Ag/AgCl and completely degrade carbamazepine (one of EOPs), coupled with 633 μmol of H₂ production; 93.29% reduction in operational carbon emissions and 77.82% decrease in direct emissions were achieved by the PEC/r-BiVO₄ process compared with large-scale WWTPs, attributed to the restrained generation of CH₄ and N₂O. The PEC system activated chloride ions in sewage to generate numerous reactive chlorine species and facilitate ^•OH production, promoting contaminants removal. The PEC system exhibited operational feasibility at varying pH and total suspended solids concentrations and has outstanding reusability and stability, confirming its promising practical potential. This study proposed a novel PEC reaction for reducing operational carbon emissions from saline sewage treatment.

Solar-Driven Catalytic Urea Oxidation for Environmental Remediation and Energy Recovery

The water-energy nexus is highly related to sustainable societal development. As one of the most abundant biowastes discharged into the environment, mild abatements and green conversions of urea wastewater have been widely investigated. Due to abundant sources, global distribution, and easy control, light-based catalytic strategies have become alternative on-site treatment approaches. After comprehensively surveying the recent progress, recent achievements of urea oxidation under light irradiation are reviewed herein. Several typical light-promoted systems employed in urea conversion, including photocatalysis, photo-electrocatalysis, photo-biocatalysis, and photocatalytic fuel cells, are meticulously introduced and discussed, from catalyst designs and medium conditions to established mechanisms. To realize the goal of sustainability, the chemical energy in urea-rich water could be utilized for the value-added production of hydrogen fuel and electricity. Finally, based on current developments, existing challenges are enumerated and developmental prospects in the future of light-driven urea conversion technologies are proposed.

Persulfate-enhanced continuous flow three-dimensional electrode dynamic reactor for treatment of landfill leachate

Compared with sequencing batch reactor, continuous flow dynamic reactors are more conducive to promotion and application. In this study, the ability of a three-dimensional (3D) electrode dynamic reactor to remove pollutants in the landfill leachate was investigated, in which landfill leachate entered through continuous flow. Either increased of current density or the decreased of flow rate was conducive to the removal of pollutants. The optimal process parameters for current density and flow rate were 16 mA cm^-2 and 0.75 L h^-1, respectively. When the current density was constant at 16 mA cm^-2 and the flow rate was kept at 0.75 L h^-1, 60.02% of total organic carbon (TOC), 96.50% of chroma, 64.98% of chemical oxygen demand (COD) and 99.46% of ammonia nitrogen (NH₃-N) were removed. The characteristic peaks of refractory organic pollutants were reduced by 97.95%. After the reaction, the biological oxygen demand (BOD)/COD was increased from 0.24 to 0.32. As one of the emerging trace organics in landfill leachate, 85.90% of ibuprofen (IBU) was removed. The results showed that the 3D electrode dynamic reactor constructed in this study could reduce the TOC, refractory trace organic pollutant, NH₃-N and chroma in the landfill leachate. The 3D electrode dynamic reactor constructed in this research has application potential in the field of landfill leachate treatment.

Optimized titania nanotubes photoanode mediated photoelectrochemical oxidation of ammonia in highly chlorinated wastewater via Cl-based radicals

Efficient removal of low-concentration ammonia from chlorinated wastewater is a challenge for decentralized wastewater treatment due to its notorious environmental effect and lethal influence on aquaculture. Photoelectrocatalytic (PEC) oxidation process is considered as an efficient and environment-friendly approach, whereas a low-cost and stable photoanode is crucial. In this study, TiO₂ nanotubes (TNTs) photoanode (Ar-TNT-500 °C) with excellent physicochemical and photoelectrochemical properties was prepared by optimizing the parameters of anodization, including the voltage/times of anodization and the atmosphere/temperature of heat treatment. During the synthesis, the electrochemical and heat treatment processes promoted the formation of oxygen vacancies (O_V) on the TNTs surface and enhanced its electrocatalytic activity. The optimized Ar-TNT-500 °C photoanode could selectively convert ammonia to N₂ (86%) and a small amount of nitrate (14%). Radical quenching and probe experiments confirmed that the ClO produced by rapid quenching of OH and Cl by free chlorine dominated the selective degradation of ammonia in the synergistic process of photocatalysis and electrocatalysis. The cycle of chlorine-based radicals (ClO and Cl) and Cl^- provided a continuous and efficient ammonia oxidation system, because chlorine-based radicals could efficiently and selectively oxidize ammonia and reduce the production of toxic (per) chlorate.

Simultaneous removal of organics and ammonia using a novel composite magnetic anode in the electro-hybrid ozonation-coagulation (E-HOC) process toward leachate treatment

To achieve simultaneous organics and ammonia (NH₄⁺-N) removal toward leachate treatment, this study designed a composite anode (CA⁺), in which iron powders were attracted to RuO₂-IrO₂/Ti tube surface by an inserted magnet and utilized in electro-hybrid ozonation-coagulation (E-HOC). The E-HOC (CA⁺) resulted in higher chemical oxygen demand (COD) and NH₄⁺-N removal with most content of CO₂/H₂O and gaseous N in product compared with E-HOC (Fe⁺), electrolysis ozonation and single ozonation. Reactive chlorine species (RCS) and coagulants were co-produced by compositing RuO₂-IrO₂/Ti and Fe powders, resulting in multiple reactions including electrocoagulation, ozone oxidation, synergistic between ozone and coagulants (SOC), electrolytic chloride and synergistic oxidation between active chlorine and ozone (SCO) occurred. Hydroxyl radical (•OH) generated through SOC reaction was promoted due the RCS generation in E-HOC. The interaction between •OH and Cl^-/ClO^- also contributed to enhanced Cl•/ClO• production. Consequently, synergy of chlorine, coagulants and ozone enhanced reactive species generation which contributed to favorable organics and NH₄⁺-N removal. Enhanced •OH and RCS are also attributed to conversion of bio-refractory organics like polyphenol, polycyclic aromatics and S-containing to biodegradable ones, e.g., aliphatic compounds and CHO. This study provides an easily operating strategy for leachate treatment with high content organics and NH₄⁺-N.

Enhanced removal of ammonia nitrogen from rare earth wastewater by NaCl modified vermiculite: Performance and mechanism

Wastewater from rare earth mining (WREM) is very harmful to environment and human health due to its high concentration of ammonia nitrogen (NH₃-N). It is therefore necessary and urgent to find a low-cost and convenient technique to remove high concentration of NH₃-N from WREM. In this study, Natural powdered vermiculite (NV) was modified with seven sodium chloride (NaCl) solutions, and seven kinds of sodium chloride modified vermiculite (Na-V) were obtained. The NH₃-N adsorption performance of Na-V is greatly improved compared with NV. Among them, vermiculite modified with 180 g/L NaCl yielded the highest ammonium adsorption capacity (Q_m, 11.569 mg/g), which was 63.43% higher than NZ (Q_m, 7.079 mg/g). The characterizations of 180-Na-V confirmed the removal mechanism of NH₃-N that the improved capacity of modified vermiculite was attributed to its higher mesoporous volume and ion-exchange capacity, which are the result of sodium-ion exchange and Interlayer effect from high concentration of NaCl. The adsorption isotherms and kinetics were respectively best consistent with Langmuir model and the pseudo-second-order (PSO) model. The adsorption capacity (3.808 mg/g) of vermiculite after 5 cycles could still maintain 75.09% of the initial adsorption capacity (5.071 mg/g). A large amount of Na-V had little effect on pH of water, which meet the requirements of practical application. Including pH, dosage, coexisting ions, the effects of other factors on ammonium adsorption were also determined. This study provides a new method for vermiculite to remove high concentration of NH₃-N.

From Photocatalysis to Photo-Electrocatalysis: An Innovative Water Remediation System for Sustainable Fish Farming

In this study, the effects of photo-electrocatalysis (PEC) were evaluated as an innovative application of conventional photocatalysis (PC) to remediate water in a recirculating system for rainbow trout (Oncorhynchus mykiss) culture, in relation to fish welfare and health, with a multidisciplinary approach. Three tanks were employed, equipped with conventional biological filters as a control system, and three tanks equipped with the PEC purification system. The concentrations of ammonia, nitrite and nitrate ions in water were monitored, and the fish’s oxidative damage and stress response were evaluated in parallel. The water of the PEC-treated experimental group showed lower ammonia (TAN) and nitrite concentrations and higher nitrate concentration, possibly deriving from TAN oxidation through PEC, also leading to gaseous N2. Histological analysis did not reveal any pathological alteration in the gills and liver of both groups. The superoxide dismutase (sod1), glutathione reductase (GR), glutathione peroxidase (GPx1), and Tumor necrosis factor (TNFα) gene expressions were significantly higher in the control group than in the PEC-treated group, while the Heat shock protein 70 (Hsp70) expression did not show any difference in the two groups. These results indicate that the use of PEC filters has a positive effect on water quality, compared to the use of conventional biological filters, inducing a high level of welfare in O. mykiss.

Removal of ammonia and phenol from saline chemical wastewater by ionizing radiation: Performance, mechanism and toxicity

Saline chemical wastewater containing ammonia and toxic organic pollutants has been a challenge for conventional wastewater treatment technology. Advanced treatment is thus required. In this study, the removal of ammonia and phenol in saline chemical wastewater by radiation was investigated in detail. The results showed that chloridion in saline chemical wastewater could be transferred to •Cl and •ClO by radiation, which promoted ammonia oxidation, but inhibited phenol degradation. Solution pH affected the types of reactive species, which further affected the removal of ammonia and phenol. When ammonia and phenol co-existed in saline chemical wastewater, the removal efficiency of ammonia was depressed compared to that in the absence of phenol. Similarly, the phenol removal efficiency was also depressed in the presence of ammonia when the solution pH was lower than 7.0. Interestingly, the phenol removal efficiency was improved with increase of either chloridion concentration (2-8 g/L) or dose (2-5 kGy), which was attributed to the formation of intermediate nitrogen-centered radicals that can react with phenol. In addition, the intermediate products of phenol degradation under different conditions were identified. The acute toxicity of saline chemical wastewater after radiation treatment was evaluated. The results of this study could provide an insight into the removal of ammonia and phenol from saline chemical wastewater by radiation technology.

Modulating anion defect in La0.6Sr0.4Co0.8Fe0.2O3-δ for enhanced catalytic performance on peroxymonosulfate activation: Importance of hydrated electrons and metal-oxygen covalency

Perovskite oxides are promising catalysts in peroxymonosulfate (PMS) activation for wastewater treatment, attributed to their flexible structures. In this study, halogen anion (F^- or Cl^-) was doped in La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (LSCF) for PMS activation, showing that appropriate anion doping enhances the catalytic performances. La_0.6Sr_0.4Co_0.8Fe_0.2O_2.75-δCl_0.25 (LSCFCl_0.25) exhibits a superior catalytic activity to pristine LSCF and La_0.6Sr_0.4Co_0.8Fe_0.2O_2.75-δF_0.25 (LSCFF_0.25), attributed to the strong surface acidity, sufficient oxygen vacancies, and improved B-site metal-oxygen bonding. The rich acidic sites favor PMS adsorption on the catalyst surface. The sufficient hydrated electrons (e_aq^-) in the oxygen vacancies participated in the generation of free radicals (SO₄^•- and O₂^•-) and singlet oxygen (¹O₂). The enlarged B-site metal-oxygen covalency could boost the electron transfer between PMS and Co^(III)/Fe^(III), and thus accelerate the redox reaction. SO₄^•- and ¹O₂ are the dominating species for the degradation. This study deepens the catalytic mechanism and uncovers the active sites of perovskite catalysts for PMS activation, providing an inspiring modification strategy to improve the catalytic performances.

Iron Phosphide Precatalyst for Electrocatalytic Degradation of Rhodamine B Dye and Removal of Escherichia coli from Simulated Wastewater

Electrocatalysis using low-cost materials is a promising, economical strategy for remediation of water contaminated with organic chemicals and microorganisms. Here, we report the use of iron phosphide (Fe2P) precatalyst for electrocatalytic water oxidation; degradation of a representative aromatic hydrocarbon, the dye rhodamine B (RhB); and inactivation of Escherichia coli (E. coli) bacteria. It was found that during anodic oxidation, the Fe2P phase was converted to iron phosphate phase (Fe2P-iron phosphate). This is the first report that Fe2P precatalyst can efficiently catalyze electrooxidation of an organic molecule and inactivate microorganisms in aqueous media. Using a thin film of Fe2P precatalyst, we achieved 98% RhB degradation efficiency and 100% E. coli inactivation under an applied bias of 2.0 V vs. reversible hydrogen electrode in the presence of in situ generated reactive chlorine species. Recycling test revealed that Fe2P precatalyst exhibits excellent activity and reproducibility during degradation of RhB. High-performance liquid chromatography with UV-Vis detection further confirmed the electrocatalytic (EC) degradation of the dye. Finally, in tests using Lepidium sativum L., EC-treated RhB solutions showed significantly diminished phytotoxicity when compared to untreated RhB. These findings suggest that Fe2P-iron phosphate electrocatalyst could be an effective water remediation agent.

Coupling photocatalytic and electrocatalytic oxidation towards simultaneous removal of humic acid and ammonia-nitrogen in landscape water

Aiming to bring photocatalytic and electrocatalytic oxidation processes into solving practical issue of organics and ammonia-nitrogen pollution in landscape water that resulting in algae bloom and eutrophication, this work firstly investigates photocatalytic oxidation of humic acid and electrochemical oxidation of ammonia upon optimization of each process parameters, respectively. The platinum modified titania (Pt/TiO₂) exhibits improved activity than pure titania and CuO_x, MnO_x and NiO_x modified titania for decomposition of humic acid. As an application-oriented study, this work has developed a simple and effective brushing and annealing method for immobilization of TiO₂ and Pt/TiO₂ onto ceramic foam for further application. In addition, the RuO₂-IrO₂/Ti electrode presents the best electrocatalytic activity compared with RuO₂/Ti and IrO₂/Ti electrodes in terms of ammonia oxidation, and the ammonia conversion pathways have been studied. Lastly, an integrated and enlarged reactor system employing optimized photocatalytic ceramic foam and stable electrodes has been developed for simultaneous oxidation of humic acid and ammonia-nitrogen in water circulated flow condition, based on cooperative production of reactive oxidant species between photocatalysis and electrocatalysis. The results show that coupled photocatalytic and electrocatalytic oxidation is a promising approach for treatment of organic matter and inorganic ammonia nitrogen in landscape water.

Nitrate Removal in an Electrically Charged Granular-Activated Carbon Column

Nitrate removal from groundwater remains a challenge. Here, we report on the development of a flow-through, electrically charged, granular-activated carbon (GAC)-filled column, which effectively removes nitrate. In this system, the GAC functioned as an anode, while a titanium sheet acted as a cathode. The high removal rate of nitrate was achieved through a combination of electrosorption and electrochemical transformation to N₂. The column could be readily regenerated in situ by reversing the polarity of the applied potential. We demonstrate that in the presence of chloride, the mechanism responsible for the observed nitrate removal involves a combination of electroadsorption of nitrate to the anodically charged GAC, electroreduction of nitrate to ammonium, and the oxidation of ammonium to N₂ gas by reactive chlorine and other oxidative radicals (with nearly 100% N₂ selectivity). Given the ubiquitous presence of chloride in groundwater, this method represents a ready, green, and sustainable treatment process with significant potential for the remediation of contaminated groundwater.

Optimization and Modeling of Ammonia Nitrogen Removal from High Strength Synthetic Wastewater Using Vacuum Thermal Stripping

Waste streams with high ammonia nitrogen (NH3-N) concentrations are very commonly produced due to human intervention and often end up in waterbodies with effluent discharge. The removal of NH3-N from wastewater is therefore of utmost importance to alleviate water quality issues including eutrophication and fouling. In the present study, vacuum thermal stripping of NH3-N from high strength synthetic wastewater was conducted using a rotary evaporator and the process was optimized and modeled using response surface methodology (RSM) and RSM–artificial neural network (ANN) approaches. RSM was first employed to evaluate the process performance using three independent variables, namely pH, temperature (°C) and stripping time (min), and the optimal conditions for NH3-N removal (response) were determined. Later, the obtained data from the designed experiments of RSM were used to train the ANN for predicting the responses. NH3-N removal was found to be 97.84 ± 1.86% under the optimal conditions (pH: 9.6, temperature: 65.5 °C, and stripping time: 59.6 min) and was in good agreement with the values predicted by RSM and RSM–ANN models. A statistical comparison between the models revealed the better predictability of RSM–ANN than that of the RSM. To the best of our knowledge, this is the first attempt comparing the RSM and RSM–ANN in vacuum thermal stripping of NH3-N from wastewater. The findings of this study can therefore be useful in designing and carrying out the vacuum thermal stripping process for efficient removal of NH3-N from wastewater under different operating conditions.

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

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.

Selective oxidation of pharmaceuticals and suppression of perchlorate formation during electrolysis of fresh human urine

Urine comprises only a small (~1%) volumetric fraction of municipal wastewater, but represents a dominant source of pharmaceuticals, many of which may pass through conventional wastewater treatment and pose risks to aquatic ecosystems. Point-source treatment of source-separated urine presents a unique opportunity to degrade pharmaceuticals before dilution with wastewater, and electrochemical advanced oxidation processes are one increasingly investigated option. However, they often lead to the formation of oxidation byproducts including chlorate, perchlorate at very high concentrations. Here, we show that the high urea content of fresh human urine suppresses the formation of oxychlorides by inhibiting formation of HOCl/OCl^‒ during electrolysis, while still enabling pharmaceutical degradation due to the slow rate of urea oxidation by ^•OH. This results in improved performance compared to equivalent treatment of hydrolyzed aged urine. This electrochemical oxidation scheme is shown to degrade the model contaminants cyclophosphamide and sulfamethoxazole with surface-area-to-volume-normalized pseudo-first-order rate constants greater than 0.08 cm/min in authentic fresh human urine. It results in ~100 × decrease in pharmaceutical concentrations in 2 h while generating ~1000 × lower oxychloride byproduct concentrations in synthetic fresh urine than synthetic hydrolyzed aged urine matrixes. Importantly, this proof-of-principle shows that simple and safe electrochemical methods can be used for point-source-remediation of pharmaceuticals in fresh human urine (before storage and hydrolysis), without formation of significant oxychloride byproducts.

Study on adsorption of ammonia nitrogen by iron-loaded activated carbon from low temperature wastewater

In order to improve the adsorption efficiency of ammonia nitrogen in low temperature wastewater, the modified activated carbon (Fe-AC) was prepared by impregnation-calcination modification of Fe(NO₃)₃. The characterization results indicated that the total pore volume, specific surface area and the point of zero charge of activated carbon increased after modification. A better adsorption effect was achieved under neutral condition than under alkaline or acidic condition. The effect of Ca²⁺ on competitive adsorption of NH₄⁺ was greater than that of Na⁺ when both cations were present. Pseudo-first-order kinetic model was confirmed to be consistent with Fe-AC adsorption kinetic data, and Langmuir model was consistent with adsorption isotherm data. The adsorption thermodynamics demonstrated that the ammonia nitrogen adsorption process by Fe-AC was spontaneous and low-temperature was helpful to improve the adsorption capacity. The mechanism of adsorption of ammonia nitrogen by Fe-AC was the comprehensive effect of physical adsorption and chemical adsorption, which was the essential reason for improving the adsorption efficiency of ammonia nitrogen by Fe-AC at a low temperature. This research offered a new way for the modification of activated carbon and a new method for the removal of ammonia nitrogen at a low temperature.

A new electrochemical method for simultaneous removal of Mn2+and NH4+-N in wastewater with Cu plate as cathode

In this study, a new electrochemical method was used to simultaneously efficient removal of Mn²⁺ and NH₄⁺-N in wastewater with Cu plate as cathode. The effects of various reaction parameters on the concentrations of Mn²⁺, NH₄⁺-N and by-products (NO₃^--N and NO₂^--N, free chlorine and residual chlorine), as well as the removal mechanism were investigated. The results showed that the removal efficiencies of Mn²⁺ and NH₄⁺-N were 99.1% and 92.9%, and the concentrations of NO₃^--N, NO₂^--N, free chlorine and residue chlorine were 0.73 mg/L, 0.15 mg/L, 0.13 mg/L and 0.63 mg/L reacting for 3 h at room temperature, respectively, when the current density was 10 mA/cm², the mass ratio of ClO^- and Cl^- was 1:1, the initial pH was 9. The concentrations of Mn²⁺, NH₄⁺-N and by-products in wastewater met the integrated wastewater discharge standard (GB8978-1996). In addition, spherical manganese oxide was deposited on the anode plate, and spherical manganese oxide collapsed over electrolysis time. Manganese was mainly removed in the form of MnO, Mn(OH)₂ and MnO₂. NH₄⁺-N was mainly oxidized to N₂. Economic evalution revealed that the treatment cost was 2.93 $/m³.

A ClO-mediated photoelectrochemical filtration system for highly-efficient and complete ammonia conversion

The ability to convert excess ammonia in water into harmless N₂ is highly desirable for environmental remediation. We present a chlorine-oxygen radical (ClO)-mediated photoelectrochemical filtration system for highly efficient and complete ammonia removal from water. The customized photochemical device comprised a Ag-functionalized TiO₂nanotube array mesh photoanode and a Pd-Cu co-modified nickel foam (Pd-Cu/NF) cathode. Under illumination, holes generated at the anode catalyzed the conversion of H₂O and Cl^- to HOand Cl, respectively. In turn, these radicals then reacted further, yielding ClO, which selectively decomposed ammonia. The cathode enabled further reduction of anodic byproducts such as NO₃^- to N₂. The complete oxidation of all dissolved ammonia was achieved within 15 min reaction under neutral conditions, where N₂ was the dominant product. The impact of key parameters was assessed, which enabled the discovery of optimal reaction conditions and the proposal of the underlying working mechanism. The flow-through configuration demonstrated a 5-fold increase of ammonia oxidation rate compared to the conventional batch reactor. The role of ClO in the oxidation of ammonia was verified with electron paramagnetic resonance and scavenger studies. This study provided greater mechanistic insights into photoelectrochemical filtration technology and demonstrated the potential of future nanotechnology for removing ammonia.

Efficient urine removal, simultaneous elimination of emerging contaminants, and control of toxic chlorate in a photoelectrocatalytic-chlorine system

Urine, which is an important waste biomass resource, is the main source of nitrogen in sewage and contains large quantities of emerging contaminants (ECs). In this study, we propose a new method to efficiently remove urine, simultaneously eliminate ECs, and control the generation of toxic chlorate during urine treatment using a photoelectrocatalytic-chlorine (PEC-Cl) system. A type-II heterojunction of WO₃/BiVO₄ was used as a photoanode to generate chlorine radicals (Cl•) by decreasing the oxidation potential of WO₃ valence band for the highly selective conversion of urine to N₂ and the simultaneous degradation of ECs in an efficient manner. The method presented surprising results. It was observed that the amount of toxic chlorate was significantly inhibited by circumventing the over-oxidation of Cl^- by holes or hydroxyl radicals (•OH). Moreover, the removal of urea nitrogen reached 97% within 90 min, while the degradation rate of trimethoprim in urine was above 98.6% within 60 min, which was eight times more than that in the PEC system (12.1%). Compared to the bare WO₃ photoanode, the toxic chlorate and nitrate generated by the WO₃/BiVO₄ heterojunction photoanode decreased by 61% and 44%, respectively. Thus, this study provides a safe, efficient, and environmentally-friendly approach for the disposal of urine.

Near-Infrared Light-Triggered Chlorine Radical (. Cl) Stress for Cancer Therapy

Free radicals with reactive chemical properties can fight tumors without causing drug resistance. Reactive oxygen species (ROS) has been widely used for cancer treatment, but regrettably, the common O₂ and H₂ O₂ deficiency in tumors sets a severe barrier for sufficient ROS production, leading to unsatisfactory anticancer outcomes. Here, we construct a chlorine radical (^. Cl) nano-generator with SiO₂ -coated upconversion nanoparticles (UCNPs) on the inside and Ag⁰ /AgCl hetero-dots on the outside. Upon near-infrared (NIR) light irradiation, the short-wavelength emission UCNP catalyzes ^. Cl generation from Ag⁰ /AgCl with no dependence on O₂ /H₂ O₂ . ^. Cl with strong oxidizing capacity and nucleophilicity can attack biomolecules in cancer cells more effectively than ROS. This ^. Cl stress treatment will no doubt broaden the family of oxidative stress-induced antitumor strategies by using non-oxygen free radicals, which is significant in the development of new anticancer agents.