Spontaneous Generation of H2O2 and Hydroxyl Radical through O2 Reduction on Copper Phosphide under Ambient Aqueous Condition

Yeast-derived phosphorus for eco-friendly synthesis of Cu3P/biochar catalysts with enhanced hydrogen peroxide-based Fenton-like reaction

Transition metal phosphides (TMPs) are promising catalysts, yet challenges remain in terms of low stability and secondary pollution. Herein, we report a novel synthesis of Cu3P particles loaded on yeast-derived biochar (Cu3P/BC) using Cu2+ as a precursor and mannan-phosphate from yeast cell walls as a sustainable phosphorus source. Cu3P/BC demonstrated a significantly superior catalytic performance in Rhodamine B (RhB) degradation, exhibiting a 25.2-fold increase in RhB removal efficiency and an approximately 4-fold increase in chemical oxygen demand removal efficiency compared to biochar alone. Furthermore, the catalytic Fenton-like performance remained robust, achieving degradation efficiencies between 70.7 % and 88.6 % across three different real water matrices, highlighting the catalyst's potential for practical applications. Stability tests revealed effective performance over four cycles, and post-regeneration, the removal rate increased to 96.4 %, with copper leaching ≤0.51 mg/L. Free radical quenching experiments and electron paramagnetic resonance analysis revealed that reactive oxygen species, •OH, O2•-, and 1O2, played critical roles in the degradation of RhB. These reactive species were primarily generated through the redox cycling of Cu(II)/Cu(I), a process that facilitated H2O2 activation. Moreover, toxicity assessments indicated that while early intermediates show moderate toxicity, extended reaction times promote complete mineralization into non-toxic end products. This study offers a facile, eco-friendly method for fabricating TMP/carbon composites from yeast biomass, with significant potential for wastewater treatment.

Research on the Mechanism of Hydrogen Peroxide Synthesis from Oxygen and Water on a Boron Nitride Surface at Room Temperature

At ambient conditions, boron nitride (BN) is incapable of catalyzing the liquid-phase synthesis of hydrogen peroxide from oxygen and water. However, experiments have demonstrated that friction can significantly enhance the efficiency of this reaction. Under certain experimental conditions, the yield of hydrogen peroxide reached 8374.58 μmol/L/g. This study utilizes density functional theory (DFT) and associated experimental calculations to investigate the mechanism by which oxygen is reduced in water to form hydrogen peroxide. The application of frictional force enables the continuous generation of a substantial amount of hydrogen ions and superoxide radicals, thus facilitating the reaction. The process primarily proceeds through two pathways: O2 → •O2- → •OOH → H2O2 and O2 + 2q- + 2H+ → H2O2.

Efficient production of singlet oxygen via dioxygen activation on Cu0 decorated MoS2 facilitates the elimination of oxytetracycline

Molecular oxygen (O2), a green oxidant, is applied in advanced oxidation processes, which represents one of the current focal points in water treatment research. However, achieving efficient and economical activation of O2 remains a formidable challenge because of its spin-restricted nature. Herein, zero-valent copper (Cu0) modified molybdenum disulfide (MoS2) materials were applied as O2 activators to degrade organic pollutants. The results showed that Cu0-MoS2 could significantly enhance the activation of O2 and thus accelerate the removal of oxytetracycline (OTC). Notably, 90.0 % of OTC was eliminated within 20 min in the Cu0-F-MoS2 (Cu0-Flower-MoS2) /air system. Quenching experiments, XPS spectra, and DFT calculations confirmed •O2- and 1O2 were pivotal reactive species, with both Mo and Cu playing essential roles. Specially, O2 was activated by Cu0/Cu+ to generate •O2-, then •O2- was oxidized by Mo6+ of MoS2 into 1O2. This research offers an eco-friendly approach for eliminating organic substances by activating O2.

Oxygen Vacancy-Mediated Microflower-like Bi5O7I for Reactive Oxygen Species Generation through Piezo-Photocoupling Effect

Photocatalytic reactive oxygen species (ROS) evolution with Bi5O7I still suffers from sluggish charge carrier dynamics and limited light absorption. Herein, abundant oxygen vacancies (OVs) were introduced into the microflower-like Bi5O7I, and its ROS generation toward organic dye degradation under the synergistic effect of visible light and ultrasound irradiation was investigated. Benefiting from the broadened visible-light absorption range, stronger piezoresponse, and higher carrier transport efficiency in OV-enriched Bi5O7I (2-PEG-Bi5O7I), both its photocatalytic and piezocatalytic degradations were improved. More importantly, its piezo-photocatalytic degradation performance was greater than the sum of the corresponding photocatalysis and piezocatalysis, indicating a strong coupling effect. In addition, the piezo-photocatalytic yield of •O2- with 2-PEG-Bi5O7I was 1.5 times higher than that with Bi5O7I, and it was also 4.3 and 3.1 times higher than its single photocatalysis and piezocatalysis, respectively. Interestingly, no noticeable •OH was detected in the case of visible-light irradiation, while the piezocatalytic and piezo-photocatalytic yields of •OH were 3.6 and 5.3 μmol g-1 h-1, respectively, with OV-enriched Bi5O7I, surpassing the pristine Bi5O7I as well. This work advances the coupling effect between photocatalysis and piezocatalysis as a new strategy for efficient ROS generation and also discloses the positive role of oxygen vacancies in improving multiresponsive catalysis.

Efficient generation of singlet oxygen (1O2) by CoP/Ni2P@NF for degradation of sulfamerazine through a heterogeneous electro-Fenton process at circumneutral pH

In electro-Fenton (EF), the development of a catalytic material with wide pH application range and high interference resistance is more suitable for practical wastewater treatment. In this study, the nanoneedle-shaped CoP/Ni2P heterostructure loaded onto a nickel foam substrate (CoP/Ni2P@NF) was successfully fabricated, which was used as a cathode material for heterogeneous electro-Fenton (Hetero-EF) to degrade sulfamerazine (SMR) at circumneutral pH. The SMR degradation efficiency within 90 min went to 100% and 87% at initial pH of 6.8 and 11, respectively. Experiments and theoretical calculations demonstrated that the heterostructure of CoP/Ni2P redistributed the interfacial charge and accelerated the electron transfer, resulting in different two-electron oxygen reduction (2e-ORR) selectivity and activity than CoP and Ni2P. The ion interference and complex water quality experiment exhibited that the degradation performance remained almost unchanged, showing better anti-interference ability and complex water quality applications. Through quenching experiments and EPR tests, it is confirmed that singlet oxygen (1O2) was the major reactive oxygen species (ROS) and 1O2 was converted from hydroxyl radical (·OH) adsorbed on the catalyst surface. This study provides an efficient catalyst for the application of Hetero-EF to remove organic compounds in complex water at circumneutral pH.

Synthesis of Hydrogen Peroxide in Neutral Media by an Iron-Doped Nickel Phosphide Catalyst

The two-electron oxygen reduction reaction (2e- ORR) for electrochemical hydrogen peroxide (H2O2) synthesis has drawn much attention due to its eco-friendly, cost-effective, and highly efficient properties. Developing catalysts with excellent H2O2 production rates and selectivity is still a big challenge. In this work, an iron-doped nickel phosphide (Fe-Ni-P) catalyst was synthesized by a solvent thermal method. The synthesis temperature of 180 °C could obtain the best 2e- ORR catalyst, i.e., Fe-Ni-P-180, since the crystallization of metal phosphide under this temperature was promoted. In addition, Fe-Ni-P-180 had a high catalytic activity, high electron transfer rate, and low electrochemical resistance. The H2O2 production rate constant of Fe-Ni-P-180 was 9.99 ± 0.63 μM/(min cm2) and the Faradaic efficiency was 94.38 ± 4.68% at 0.25 V vs RHE, which increased by 57.9 and 15.4% compared with Ni-P, respectively. Fe-Ni-P-180 could work in a wide pH range of 5-9 with the optimized pH of 7, and it exhibited low specific energy consumption and great reusability. The elemental state analysis demonstrated that Niδ+, Feδ+, and Pδ- are all active species, and the doping of Fe increases the crystallization of metal phosphide.

Boosted H2O2 utilization and selective hydroxyl radical generation for water decontamination: Synergistic roles of dual active sites in H2O2 activation

H2O2 as a green oxidant plays a crucial role in numerous green chemical reactions. However, how to improve its activation and utilization efficiency as well as regulate the distribution of ROS remains a pressing challenge. In this work, a sulfur quantum dots (SQDs) modified zero-valent iron (SQDs@ZVI) was delicately designed and prepared, whose iron sites can coordinate with strongly electronegative sulfur atoms to construct highly reactive Fe-S dual active sites, for high-efficient selective H2O2 activation and utilization with potent •OH production. Experimental tests, in situ FTIR/Raman spectra and theoretical calculations demonstrated that SQDs modulates the local coordination structure and electronic density of iron centers, thus effectively enhancing its Fenton reactivity and promoting the rate-limiting H2O2 adsorption and subsequent barrierless dissociation of peroxyl bonds into •OH via the formation of bridged S-O-O-Fe complexes. Consequently, substantial generated surface-bound •OH induced by the highly reactive Fe-S dual sites enabled excellent degradation of miscellaneous organic pollutants over a broad pH range (3.0-9.0). The developed device-scale Fenton filter realized durable performance (up to 200 h), verifying the vast potential of SQDs@ZVI with diatomic sites for practical application. This work presents a promising strategy to construct metal-nonmetal diatomic active sites toward boosting selective activation and effective utilization of H2O2, which may inspire the design of efficient heterogeneous Fenton reaction for water decontamination.

Ov-rich γ-MnO2 enhanced electrocatalytic three-electron oxygen reduction to hydroxyl radicals for sterilization in neutral media

Marine biofouling severely limits the development of the marine economy, and reactive oxygen species (ROS) produced by electrocatalytic antifouling techniques could inactivate marine microorganisms and inhibit the formation of marine biofouling. Compared with an electro-Fenton reaction, a three-electron oxygen reduction reaction (3e- ORR) could generate a hydroxyl radical (˙OH) in situ without the limitation of pH and iron mud pollutants. Herein, Ov-rich γ-MnO2 is designed to enhance the 3e- ORR performance in neutral media and exhibits excellent sterilization performance for typical marine bacteria. DFT calculation reveals that Ov is beneficial to the "end-on" adsorption and activation of O2, and the Mn site could accept the electrons from *OOH and promote its further reduction to form ˙OH; Ov and Mn sites together guarantee the high 3e- ORR efficiency. In addition, liquid chromatography-tandem mass spectrometry (LC-MS/MS) proves the vast formation of ˙OH in the primary reaction stage, which is the key to sterilization. This work explores the reaction mechanism of the 3e- ORR in neutral media and provides the possibility for the application of electrocatalysis technology in the treatment of marine biofouling pollution.

Bifunctional Oxygen-Defect Bismuth Catalyst toward Concerted Production of H2O2 with over 150% Cell Faradaic Efficiency in Continuously Flowing Paired-Electrosynthesis System

The electrosynthesis of hydrogen peroxide (H2O2) from O2 or H2O via the two-electron (2e-) oxygen reduction (2e- ORR) or water oxidation (2e- WOR) reaction provides a green and sustainable alternative to the traditional anthraquinone process. Herein, a paired-electrosynthesis tactic is reported for concerted H2O2 production at a high rate by coupling the 2e- ORR and 2e- WOR, in which the bifunctional oxygen-vacancy-enriched Bi2O3 nanorods (Ov-Bi2O3-EO), obtained through electrochemically oxidative reconstruction of Bi-based metal-organic framework (Bi-MOF) nanorod precursor, are used as both efficient anodic and cathodic electrocatalysts, achieving concurrent H2O2 production at both electrodes with high Faradaic efficiencies. Specifically, the coupled 2e- ORR//2e- WOR electrolysis system based on such distinctive oxygen-defect Bi catalyst displays excellent performance for the paired-electrosynthesis of H2O2, delivering a remarkable cell Faradaic efficiency of 154.8% and an ultrahigh H2O2 production rate of 4.3 mmol h-1 cm-2. Experiments combined with theoretical analysis reveal the crucial role of oxygen vacancies in optimizing the adsorption of intermediates associated with the selective two-electron reaction pathways, thereby improving the activity and selectivity of the 2e- reaction processes at both electrodes. This work establishes a new paradigm for developing advanced electrocatalysts and designing novel paired-electrolysis systems for scalable and sustainable H2O2 electrosynthesis.

Atomically dispersed low-valent Au boosts photocatalytic hydroxyl radical production

Providing affordable, safe drinking water and universal sanitation poses a grand societal challenge. Here we developed atomically dispersed Au on potassium-incorporated polymeric carbon nitride material that could simultaneously boost photocatalytic generation of ·OH and H2O2 with an apparent quantum efficiency over 85% at 420 nm. Potassium introduction into the poly(heptazine imide) matrix formed strong K-N bonds and rendered Au with an oxidation number close to 0. Extensive experimental characterization and computational simulations revealed that the low-valent Au altered the materials' band structure to trap highly localized holes produced under photoexcitation. These highly localized holes could boost the 1e- water oxidation reaction to form highly oxidative ·OH and simultaneously dissociate the hydrogen atom in H2O, which greatly promoted the reduction of oxygen to H2O2. The photogenerated ·OH led to an efficiency enhancement for visible-light-response superhydrophilicity. Furthermore, photo-illumination in an onsite fixed-bed reactor could disinfect water at a rate of 66 L H2O m-2 per day.

Sustainable electro-Fenton simultaneous reduction of Cr (VI) and degradation of organic pollutants via dual-site porous carbon cathode driving uncoordinated molybdenum sites conversion

Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable "iron-free" EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS2 nanoarray promoter (MoS2 NA). The NPC-D/MoS2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis.

Stable Pentagonal Layered Palladium Diselenide Enables Rapid Electrosynthesis of Hydrogen Peroxide

Electrosynthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is promising for various practical applications, such as wastewater treatment. However, few electrocatalysts are active and selective for 2e- ORR yet are also resistant to catalyst leaching under realistic operating conditions. Here, a joint experimental and computational study reveals active and stable 2e- ORR catalysis in neutral media over layered PdSe2 with a unique pentagonal puckered ring structure type. Computations predict active and selective 2e- ORR on the basal plane and edge of PdSe2, but with distinct kinetic behaviors. Electrochemical measurements of hydrothermally synthesized PdSe2 nanoplates show a higher 2e- ORR activity than other Pd-Se compounds (Pd4Se and Pd17Se15). PdSe2 on a gas diffusion electrode can rapidly accumulate H2O2 in buffered neutral solution under a high current density. The electrochemical stability of PdSe2 is further confirmed by long device operational stability, elemental analysis of the catalyst and electrolyte, and synchrotron X-ray absorption spectroscopy. This work establishes a new efficient and stable 2e- ORR catalyst at practical current densities and opens catalyst designs utilizing the unique layered pentagonal structure motif.

Cu3-xP nanocrystals filled halloysite nanotubes for chemodynamic therapy of breast cancer

Copper-based Fenton-like agents have the ability to convert weakly oxidizing H2O2 into highly oxidizing hydroxyl radicals (·OH) at tumor sites during chemodynamic therapy (CDT). In this study, the interfacial attraction properties between the negatively charged OCP- in sodium phosphathynolate (NaOCP) and the positively charged environment inside the lumen of halloysite nanotubes (HNTs) were utilized to synthesize Cu3-xP nanoparticles in situ within the HNTs. The study investigated the chemical composition, morphology, and structure of Cu3-x P@HNTs. The results indicated uniform distribution of Cu3-xP particles measuring 3-5 nm within HNTs' lumen. Experiments conducted internally and externally to cells confirmed the catalytic capability of Cu3-xP@HNTs to oxidize H2O2 to ·OH. Furthermore, CP@H-CM was synthesized by enclosing Cu3-xP@HNTs in a cancer cell membrane, which selectively targets cancer cells. The experiments revealed the cytotoxicity of CP@H-CM on 4T1 cells. Additionally, the antitumor efficacy of CP@H-CM was evaluated in vivo through tumor recurrence experiments in mice. Moreover, the efficacy of CP@H-CM in repressing tumor growth was enhanced by incorporating infrared laser, indicating a synergistic photodynamic treatment for breast cancer. This study presents an efficacious and viable therapeutic approach to inhibit postoperative tumor reappearance. The implications of this approach are promising, particularly in the domain of tumor treatment and metastasis.

Phosphorus-based nanomaterials as a potential phosphate fertilizer for sustainable agricultural development

Phosphorus-based nanomaterials (PNMs) have been reported to have substantial promise for promoting plant growth, improving plant tolerance mechanisms, and increasing resistance to pathogenic organisms. Recent scientific investigation has demonstrated that utilizing PNMs can enhance plant physiological growth, photosynthetic pigments, antioxidant system, metabolism, nutrient absorption, rhizosphere secretion, and soil nutrients activation. Previous research on PNMs mostly concentrated on calcium phosphate, zeolite, and chitosan, with little systematic summarization, demanding a thorough evaluation of PNMs' broader uses. In our current review article, we address the knowledge gap by classifying PNMs according to green synthesis methods and the valence state of phosphorus while elucidating the underlying mechanisms through which these PNMs facilitate plant growth. In addition, we also targeted some strategies to improve the bioavailability of PNMs, offering valuable insights for the future design and safe implementation of PNMs in agricultural practices.

Sequential anodic oxidation and cathodic electro-Fenton in the Janus electrified membrane for reagent-free degradation of pollutants

Electrified membrane technologies have recently demonstrated high potential in tackling water pollution, yet their practical applications are challenged by relying on large precursor doses. Here, we developed a Janus porous membrane (JPEM) with synergic direct oxidation by Magnéli phase Ti4O7 anode and electro-Fenton reactions by CuFe2O4 cathode. Organic pollutants were first directly oxidized on the Ti4O7 anode, where the extracted electrons from pollutants were transported to the cathode for electro-Fenton production of hydroxyl radical (·OH). The cathodic ·OH further enhanced the mineralization of organic pollutant degradation intermediates. With the sequential anodic and cathodic oxidation processes, the reagent-free JPEM showed competitive performance in rapid degradation (removal rate of 0.417 mg L-1 s-1) and mineralization (68.7 % decrease in TOC) of sulfamethoxazole. The JPEM system displayed general performance to remove phenol, carbamazepine, and perfluorooctanoic acid. The JPEM runs solely on electricity and oxygen that is comparable to that of PEM relies on large precursor doses and, therefore, operation friendly and environmental sustainability. The high pollutant removal and mineralization achieved by rational design of the reaction processes sheds light on a new approach for constructing an efficient electrified membrane.

Au nanoparticle sensitized blue TiO2 nanorod arrays for efficient Gatifloxacin photodegradation

TiO2 nanorod arrays have been widely used in photocatalytic processes, but their poor visible light absorption and rapid carrier recombination limit their application. Both introducing oxygen vacancies and using precious metals as surface plasmon resonance (SPR) stimulators are effective strategies to enhance their photocatalytic performance. Herein, Au nanoparticle sensitized blue TiO2 nanorod arrays (Au/B-TiO2) were successfully fabricated for efficient Gatifloxacin photodegradation. The degradation efficiency of Gatifloxacin was up to 95.0%. Moreover, the corresponding reaction rate constant (Ka) was up to 0.02007 min-1. Additionally, it was suggested that Gatifloxacin could be subject to three different degradation pathways. The superior catalytic activity of Au/B-TiO2 is a result of the combined effect of the two components. Firstly, TiO2 nanorod arrays provide a larger surface area for Au deposition and act as efficient transfer channels. Secondly, the presence of oxygen vacancies in blue TiO2 nanorod arrays enhances the catalytic activity. Thirdly, Au acts as a SPR activator, providing a large number of high-energy electrons in the photocatalysis process. Lastly, the improved light capture capabilities are essential for efficient removal of Gatifloxacin. This work provides a new approach for the construction of a high-performance heterojunction photocatalyst in advanced oxidation processes.

Electrocatalytic transformation of oxygen to hydroxyl radicals via three-electron pathway using nitrogen-doped carbon nanotube-encapsulated nickel nanocatalysts for effective organic decontamination

The selective electrochemical reduction of oxygen (O₂) via 3e^- pathway for the production of hydroxyl radicals (HO) is a promising alternative to conventional electro-Fenton process. Here, we developed a nitrogen-doped CNT-encapsulated Ni nanoparticle electrocatalyst (Ni@N-CNT) with high O₂ reduction selectivity for the generation of HO^•via 3e^- pathway. Exposed graphitized N on the CNT shell, and Ni nanoparticles encapsulated within the tip of the N-CNT, played a key role in the generation of H₂O₂ intermediate (*HOOH) via a 2e^- oxygen reduction reaction. Meanwhile, those encapsulated Ni nanoparticles at the tip of the N-CNT facilitated the sequential HO^• generation by directly decomposing the electrogenerated *H₂O₂ in a 1e^- reduction reaction on the N-CNT shell without inducing Fenton reaction. Improved bisphenol A (BPA) degradation efficiency were observed when compared with conventional batch system (97.5% vs 66.4%). Trials using Ni@N-CNT in a flow-through configuration demonstrated a complete removal of BPA within 30 min (k = 0.12 min^-1) with a limited energy consumption of 0.068 kW·h·g^-1 TOC.

Low-valent copper on molybdenum triggers molecular oxygen activation to selectively generate singlet oxygen for advanced oxidation processes

Singlet oxygen (¹O₂), which is difficult to generate, plays an important role in chemosynthesis, biomedicine and environment. Molecular oxygen (O₂) is a green oxidant to produce ¹O₂ cost-effectively. However, O₂ activation is difficult due to its spin-forbidden nature. Moreover, the main products of O₂ activation are basically hydrogen peroxide (H₂O₂) and hydroxyl radical (•OH), but rarely ¹O₂. Herein, we innovatively realize the selective generation of ¹O₂ via O₂ activation by a facile molybdenum (Mo)/Cu²⁺ system. In this system, Mo firstly reduces Cu²⁺ in solution to low-valence Cu⁰/Cu⁺ on its surface. Cu⁰/Cu⁺ activates O₂ to generate superoxide radical (O₂^•-). Importantly, O₂^•- can be captured immediately and oxidized to ¹O₂ by surface-bound Mo⁶⁺ rather than reduced to H₂O₂. As a result, the Mo/Cu²⁺ system can selectively produce ¹O₂. Under air and O₂ conditions, the degradation efficiency of ibuprofen by Mo/Cu²⁺ system is 67.2 % and 76.6 %, respectively. The degradation efficiencies of bisphenol A, rhodamine B and furfuryl alcohol are 77.1 %, 87.7 % and 91.1 %, respectively. The dosages of Mo and Cu²⁺ are 0.4 g/L and 3 mM, respectively, and the reaction time is 2 h. Interestingly, the activity of Mo decreased by only 4.2 % after 4 cycles. Therefore, this study provides a green pathway to selectively generate ¹O₂ for advanced oxidation processes.

Investigation on the reaction kinetic mechanism of polydopamine-loaded copper as dual-functional catalyst in heterogeneous electro-Fenton process

Heterogeneous electro-Fenton (HEF) process has been regarded as a promising method in environmental remediation. However, the reaction kinetic mechanism of the HEF catalyst for simultaneous production and activation of H₂O₂ remained confounded. Herein, the copper supported on polydopamine (Cu/C) was synthesized by a facile method and employed as a bifunctional HEFcatalyst, and the catalytic kinetic pathways were deeply investigated by using rotating ring-disk electrode (RRDE) voltammetry based on the Damjanovic model. Experimental results substantiated that a two-electron oxygen reduction reaction (2e^- ORR) and a sequential Fenton oxidation reaction were proceeded on 1.0-Cu/C, where metallic copper played a crucial role in the fabrication of 2e^- active sites as well as utmost H₂O₂ activation to produce highly reactive oxygen species (ROS), resulting in the high H₂O₂ productivity (52.2%) and the almost complete removal of contaminant ciprofloxacin (CIP) after 90 min. The work not only expanded the idea of reaction mechanism on Cu-based catalyst in HEF process but also provided a promising catalyst for pollutants degradation in wastewater treatment.

Construction of a Novel Cascade Electrolysis-Heterocatalysis System by Using Zeolite-Encaged Ultrasmall Palladium Catalysts for H2 O2 Generation

In situ generation of hydrogen peroxide (H₂ O₂ ) has attracted extensive attention, especially in water treatment. However, traditional anthraquinones can only produce high-concentration H₂ O₂ and its transportation and storage are not convenient and dangerous. Herein, an in situ and on-demand strategy to produce H₂ O₂ by using a cascade water electrolysis together with a heterocatalysis system is provided. Beginning with water, H_2, and O₂ can be generated via electrolysis and then react with each other to produce H₂ O₂ immediately on efficient zeolite-encaged ultrasmall Pd catalysts. Significantly, the H₂ O₂ generation rate in the optimized cascade system reaches up to 0.85 mol L^-1 h^-1 g_Pd ^-1 , overcoming most of the state-of-the-art catalysts in previous literature. The confinement effect of zeolites is not only beneficial to the formation of highly dispersed metal species, promoting the H₂ O₂ generation, but also inhibits the H₂ O₂ decomposition, enhancing the production yield of H₂ O₂ . In addition, the effect of electrolytes, sizes of Pd species, as well as zeolite acidity are also systematically studied. This work provides a new avenue for H₂ O₂ generation via a highly efficient cascade electrolysis-heterocatalysis system by using zeolite-supported metal catalysts. The high catalytic efficiency and green process for H₂ O₂ generation make it very promising for further practical applications.

Dynamic coordination of two-phase reactions in heterogeneous Fenton for selective removal of water pollutants

The •OH-mediated heterogeneous Fenton reaction has been widely applied despite the limitations of low pollutant selectivity and unclear oxidation mechanism. Here we reported an adsorption-assisted heterogeneous Fenton process for the selective degradation of pollutants and systematically illustrated its dynamic coordination in two phases. The results showed that the selective removal was improved by (i) surface enrichment of target pollutants via electrostatic interactions including real adsorption and adsorption-assisted degradation and (ii) inducing the diffusion of H₂O₂ and pollutants from the bulk solution to the catalyst surface to trigger the homogeneous and surface heterogeneous Fenton reactions. Furthermore, surface adsorption was confirmed as a crucial but not necessary step for degradation. Mechanism studies demonstrated that •O₂^- and Fe³⁺/Fe²⁺ cycle increased •OH generation, which remained active in two phases within ⁓244 nm. These findings are critical for understanding the removal behavior of complex targets and expanding heterogeneous Fenton applications.

Spontaneous Formation of Low Valence Copper on Red Phosphorus to Effectively Activate Molecular Oxygen for Advanced Oxidation Process

Efficient spontaneous molecular oxygen (O₂) activation is an important technology in advanced oxidation processes. Its activation under ambient conditions without using solar energy or electricity is a very interesting topic. Low valence copper (LVC) exhibits theoretical ultrahigh activity toward O₂. However, LVC is difficult to prepare and suffers from poor stability. Here, we first report a novel method for the fabrication of LVC material (P-Cu) via the spontaneous reaction of red phosphorus (P) and Cu²⁺. Red P, a material with excellent electron donating ability and can directly reduce Cu²⁺ in solution to LVC via forming Cu-P bonds. With the aid of the Cu-P bond, LVC maintains an electron-rich state and can rapidly activate O₂ to produce ·OH. By using air, the ·OH yield reaches a high value of 423 μmol g^-1 h^-1, which is higher than traditional photocatalytic and Fenton-like systems. Moreover, the property of P-Cu is superior to that of classical nano-zero-valent copper. This work first reports the concept of spontaneous formation of LVC and develops a novel avenue for efficient O₂ activation under ambient conditions.

The development of cobalt phosphide co-catalysts on BiVO4 photoanodes to improve H2O2 production

Photoanodic hydrogen peroxide (H₂O₂) production via water oxidation is limited by low yields and poor selectivity. Herein, four variations of cobalt phosphides, including pristine CoP and Co₂P crystals, and two mixed-phase cobalt phosphides (CoP/Co₂P) with different ratios, were applied as co-catalysts on the BiVO₄ (BVO) photoanode to improve H₂O₂ production. The optimal yield and selectivity were approximately 9.6 µmol‧h^-1‧cm^-2 and 25.2 % at a voltage bias of 1.7 V vs reversible hydrogen electrode (V_RHE) under sunlight illumination, respectively. This performance is approximately 1.8 times that of pristine BVO photoanode. The roles of the Co and P sites were investigated. In particular, the Co site promotes the breaking of one HO bond in water to form OH^• radicals, which is the rate-determining step in H₂O₂ production. The P site plays an important role in the desorption of H₂O₂ formed from the catalyst, which is responsible for the recovery of fresh catalytic sites. Among the four samples, Co₂P exhibited the best performance for H₂O₂ production because it had the highest rate of OH^• formation owing to its improved accumulation property. This study offers a rational design strategy for co-catalysts for photoanodic H₂O₂ production.

Composition Engineering of Amorphous Nickel Boride Nanoarchitectures Enabling Highly Efficient Electrosynthesis of Hydrogen Peroxide

Developing advanced electrocatalysts with exceptional two electron (2e^- ) selectivity, activity, and stability is crucial for driving the oxygen reduction reaction (ORR) to produce hydrogen peroxide (H₂ O₂ ). Herein, a composition engineering strategy is proposed to flexibly regulate the intrinsic activity of amorphous nickel boride nanoarchitectures for efficient 2e^- ORR by oriented reduction of Ni²⁺ with different amounts of BH₄ ^- . Among borides, the amorphous NiB₂ delivers the 2e^- selectivity close to 99% at 0.4 V and over 93% in a wide potential range, together with a negligible activity decay under prolonged time. Notably, an ultrahigh H₂ O₂ production rate of 4.753 mol g_cat ^-1 h^-1 is achieved upon assembling NiB₂ in the practical gas diffusion electrode. The combination of X-ray absorption and in situ Raman spectroscopy, as well as transient photovoltage measurements with density functional theory, unequivocally reveal that the atomic ratio between Ni and B induces the local electronic structure diversity, allowing optimization of the adsorption energy of Ni toward *OOH and reducing of the interfacial charge-transfer kinetics to preserve the OO bond.

Self-Regulating Solar Steam Generators Enable Volatile Organic Compound Removal through In Situ H2O2 Generation

Interfacial solar steam generation for clean water production suffers from volatile organic compound (VOC) contamination during solar-to-steam conversion. Here, we present a solar steam generator based on the integration of melamine foam (MF), polydopamine (PDA), and Ag/AgCl particles. Together with the high photothermal conversion efficiency (ca. 87.8%, 1 kW/m²) achieved by the PDA thin film, the Ag/AgCl particles can efficiently activate the localized generation of H₂O₂ and •OH in situ, thus degrading the VOCs during the rapid vapor generation. The generation of H₂O₂ and •OH in situ also facilitates the creation of a buffer zone containing H₂O₂ and •OH for the rapid removal of organic pollutants in the surrounding water attracted to the solar vapor generator, demonstrating a self-cleaning steam generator toward various volatile compounds such as phenol, aniline, 2,4-dichlorophenol, and N,N-dimethylformamide in a wide range of concentrations.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Recent Progress of Electrochemical Production of Hydrogen Peroxide by Two-Electron Oxygen Reduction Reaction

Shifting electrochemical oxygen reduction reaction (ORR) via two-electron pathway becomes increasingly crucial as an alternative/green method for hydrogen peroxide (H2 O2 ) generation. Here, the development of 2e- ORR catalysts in recent years is reviewed, in aspects of reaction mechanism exploration, types of high-performance catalysts, factors to influence catalytic performance, and potential applications of 2e- ORR. Based on the previous theoretical and experimental studies, the underlying 2e- ORR catalytic mechanism is firstly unveiled, in aspect of reaction pathway, thermodynamic free energy diagram, limiting potential, and volcano plots. Then, various types of efficient catalysts for producing H2 O2 via 2e- ORR pathway are summarized. Additionally, the catalytic active sites and factors to influence catalysts' performance, such as electronic structure, carbon defect, functional groups (O, N, B, S, F etc.), synergistic effect, and others (pH, pore structure, steric hindrance effect, etc.) are discussed. The H2 O2 electrogeneration via 2e- ORR also has various potential applications in wastewater treatment, disinfection, organics degradation, and energy storage. Finally, potential future directions and prospects in 2e- ORR catalysts for electrochemically producing H2 O2 are examined. These insights may help develop highly active/selective 2e- ORR catalysts and shape the potential application of this electrochemical H2 O2 producing method.

Copper Phosphide Nanoparticles Used for Combined Photothermal and Photodynamic Tumor Therapy

Copper-based nanomaterials are widely used in near-infrared (NIR) light-mediated deep tumor treatment because of their abundant photothermal and photodynamic properties. However, copper phosphide (Cu₃P) nanoparticles (NPs) are rarely investigated. Herein, Cu₃P NPs were prepared to strengthen their local surface plasmon resonance absorption in the NIR region, exhibiting promising photothermal and photodynamic properties. After surface modification by polyethylene glycol, the formed pCu₃P NPs showed negligible influence on the viability of 4T1 cells, presenting remarkable biocompatibility. However, with 808 nm irradiation, pCu₃P NPs could induce HSP70 and HO-1 protein expression and enhance intracellular reactive oxygen species levels, leading to dramatic cell death. In 4T1 tumor-bearing mice, an intravenous injection of biocompatible pCu₃P NP could lead to remarkable aggregation in the tumor region and significantly inhibit tumor growth under 808 nm laser irradiation, presenting great potential for tumor therapy.

Highly selective electrochemical nitrate reduction using copper phosphide self-supported copper foam electrode: Performance, mechanism, and application

A highly active and selective electrode is essential in electrochemical denitrification. Although the emerging Cu-based electrode has attracted intensive attentions in electrochemical NO₃^- reduction, the issues such as restricted activity and selectivity are still unresolved. In our work, a binder-free composite electrode (Cu₃P/CF) was first prepared by direct growth of copper phosphide on copper foam and then applied to electrochemical NO₃^- reduction. The resulting Cu₃P/CF electrode showed enhanced electrochemical performance for NO₃^- reduction (84.3%) with high N₂ selectivity (98.01%) under the initial conditions of 1500 mg L^-1 Cl^- and 50 mg N L^-1 NO₃^-. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) demonstrated that electrochemical NO₃^- reduction was achieved through electron transfer between NO₃^- and Cu⁰ originated from CF. The in-situ grown Cu₃P served as the bifunctional catalyst, the electron mediator or bridge to facilitate the electron-transfer for NO₃^- reduction and the stable catalyst to produce atomic H* toward NO₂^- conversion. Meanwhile, the Cu₃P/CF remained its electrocatalytic activity even after eight cyclic experiments. Finally, a 2-stage treatment strategy, pre-oxidation by Ir-Ru/Ti anode and post-reduction by Cu₃P/CF cathode, was designed for electrochemical chemical oxygen demand (COD) and total nitrogen (TN) removal from real wastewater.

Enhanced Fenton-like catalytic activity and stability of g-C3N4 nanosheet-wrapped copper phosphide with strong anti-interference ability: Kinetics and mechanistic study

Metal-based Fenton-like catalysts usually activate H₂O₂ to produce free radicals (^•OH and O₂^•-) for the degradation of organic pollutants. However, a catalytic reaction dominated by free radicals is easily interfered with by various inorganic anions and water matrices. Herein, g-C₃N₄-wrapped copper phosphide (Cu_xP), as a highly efficient Fenton-like catalyst, was successfully synthesized by a simple low-temperature phosphidation method. The Cu_xP/g-C₃N₄ catalyst exhibited excellent catalytic ability for the removal of various organic contaminants over a wide pH range of 3-11. In addition, the catalyst exhibited strong anti-interference ability toward various inorganic anions (Cl^-, SO₄^2-, NO₃^-, F^-, H₂PO₄^-, HCO₃^- and CO₃^2-) and water matrices (lake water, river water, tap water and simulated water matrix). The reasons for this performance were analyzed by verifying the mechanism of the catalytic reaction. Compared to the pure Cu_xP catalyst, the Cu_xP/g-C₃N₄ composite possessed good catalytic stability. The enhanced and deactivated mechanisms of the Cu_xP/g-C₃N₄ catalyst were systematically analyzed by a series of characterization techniques. A possible reaction mechanism was also proposed based on the experimental results. This work provides new insights into designing highly efficient metal-based Fenton-like catalysts with strong anti-interference ability to practically treat wastewater.

Selective Electrocatalytic Reduction of Oxygen to Hydroxyl Radicals via 3-Electron Pathway with FeCo Alloy Encapsulated Carbon Aerogel for Fast and Complete Removing Pollutants

We reported the selective electrochemical reduction of oxygen (O₂ ) to hydroxyl radicals (^. OH) via 3-electron pathway with FeCo alloy encapsulated by carbon aerogel (FeCoC). The graphite shell with exposed -COOH is conducive to the 2-electron reduction pathway for H₂ O₂ generation stepped by 1-electron reduction towards to ^. OH. The electrocatalytic activity can be regulated by tuning the local electronic environment of carbon shell with the electrons coming from the inner FeCo alloy. The new strategy of ^. OH generation from electrocatalytic reduction O₂ overcomes the rate-limiting step over electron transfer initiated by reduction-/oxidation-state cycle in Fenton process. Fast and complete removal of ciprofloxacin was achieved within 5 min in this proposed system, the apparent rate constant (k_obs ) was up to 1.44±0.04 min^-1 , which is comparable with the state-of-the-art advanced oxidation processes. The degradation rate almost remains the same after 50 successive runs, suggesting the satisfactory stability for practical applications.

Fenton/Fenton-like processes with in-situ production of hydrogen peroxide/hydroxyl radical for degradation of emerging contaminants: Advances and prospects

Fenton processes based on the reaction between Fe²⁺ and H₂O₂ to produce hydroxyl radicals, have been widely studied and applied for the degradation of toxic organic contaminants in wastewater due to its high efficiency, mild condition and simple operation. However, H₂O₂ is usually added by bulk feeding, which suffers from the potential risks during the storage and transportation of H₂O₂ as well as its low utilization efficiency. Therefore, Fenton/Fenton-like processes with in-situ production of H₂O₂ have received increasing attention, in which H₂O₂ was in-situ produced through O₂ activation, then decomposed into hydroxyl radicals by Fenton catalysts. In this review, the in situ production of H₂O₂ for Fenton oxidation was introduced, the strategies for activation of O₂ to generate H₂O₂ were summarized, including chemical reduction, electro-catalysis and photo-catalysis, the influencing factors and the mechanisms of the in situ production and utilization of H₂O₂ in various Fenton/Fenton-like processes were analyzed and discussed, and the applications of these processes for the degradation of toxic organic contaminants were summarized. This review will deepen the understanding of the tacit cooperation between the in situ production and utilization of H₂O₂ in Fenton process, and provide the further insight into this promising process for degradation of emerging contaminants in industrial wastewater.

High-Temperature Synthesis of a Uranyl Peroxo Complex Facilitated by Hydrothermally In Situ Formed Organic Peroxide

Because H₂O₂ is thermally unstable, it seems to be difficult to synthesize peroxides at elevated temperatures. We describe here the in situ generation of peroxide that is incorporated in a new uranyl peroxo complex, HT-UPO1, through the hydrothermal treatment of uranyl nitrate at 150 °C in the presence of organic ligands. In this novel process, a highly conjugated aromatic carboxylate linker, (E)-4-[2-(pyridin-4-yl)vinyl]benzoic acid (HPyVB), plays a crucial role by inducing the reduction of oxygen in air to form peroxide in situ and coordinating with uranyl to promote the preferred formation of thermally stable HT-UPO1. This work expands our knowledge on the speciation and chemistry of uranyl peroxide compounds and also sheds light on the possibility of their synthesis under more harsh conditions.

Duet Fe3C and FeNx Sites for H2O2 Generation and Activation toward Enhanced Electro-Fenton Performance in Wastewater Treatment

Heterogeneous electro-Fenton (HEF) reaction has been considered as a promising process for real effluent treatments. However, the design of effective catalysts for simultaneous H₂O₂ generation and activation to achieve bifunctional catalysis for O₂ toward •OH production remains a challenge. Herein, a core-shell structural Fe-based catalyst (FeNC@C), with Fe₃C and FeN nanoparticles encapsulated by porous graphitic layers, was synthesized and employed in a HEF system. The FeNC@C catalyst presented a significant performance in degradation of various chlorophenols at various conditions with an extremely low level of leached iron. Electron spin resonance and radical scavenging revealed that •OH was the key reactive species and Fe^IV would play a role at neutral conditions. Experimental and density function theory calculation revealed the dominated role of Fe₃C in H₂O₂ generation and the positive effect of FeN_x sites on H₂O₂ activation to form •OH. Meanwhile, FeNC@C was proved to be less pH dependence, high stability, and well-recycled materials for practical application in wastewater purification.

Metal-free black-red phosphorus as an efficient heterogeneous reductant to boost Fe3+/Fe2+ cycle for peroxymonosulfate activation

In this work, a novel metal-free black-red phosphorus (BRP) was prepared from red phosphorus (RP) and applied in Fe²⁺/peroxymonosulfate (PMS) process. Compared with that of RP, the contaminant degradation performance of BRP was significantly elevated due to the enhanced electron transfer from BRP to Fe³⁺. This enhancement was mainly induced by size decrease effect, the removal of oxidation layer and the partial phase conversion. Moreoevr, BRP avoided the radical quenching reaction caused by reductant itself, whereas it was inevitable using homogeneous reductant like hydroxylamine. More importantly, the system had a superior recyclability and strong resistance to natural water. Though concurrent side-reaction between PMS and BRP occured, multiple PMS dosage could remarkedly alleviated the side-reaction, thus elevating PMS utilization efficiency. The dominant BRP oxidation products included phosphite and phosphate. Interestingly, moderate increase of Fe³⁺ concentration could efficiently reduce the by-product formation via the prompt PMS activation by regenerated Fe²⁺. Our work clarified the acceleration mechanism of Fe³⁺/Fe²⁺ cycle by BRP and proposed the control strategy of by-prodoct formation.

In Situ-Formed PdFe Nanoalloy and Carbon Defects in Cathode for Synergic Reduction-Oxidation of Chlorinated Pollutants in Electro-Fenton Process

Complete dechlorination and mineralization of chlorophenols via the reduction-oxidation-mediated electro-Fenton process with a composite bulk cathode is first proposed. The in situ formation of a PdFe nanoalloy and carbon defects as key active sites is mutually induced during the formation of a carbon aerogel-based electrode. Specifically, the PdFe nanoalloy promotes the generation of [H]_ads as reduction sites and improves the electron transfer via an electrical circuit, while the carbon defects selectively favor the 2e^- oxygen reduction pathway. Notably, this work implies a novel electrocatalytic model for the formation of ·OH via (2 + 1)e^- oxygen reduction by a consecutive reaction with carbon defects and a PdFe nanoalloy. Complete total organic carbon removal and dechlorination of 3-chlorophenol were performed after 6 h. The kinetic rate constant for removing haloacetamides (HAMs) in drinking water was 0.21-0.41 h^-1, and the degradation efficiency was self-enhanced after electrolysis for 2 h because of the increased concentration of [H⁺]. The specific energy consumption was ∼0.55 W·h·g^-1 at 100% removal of some HAMs, corresponding to a power consumption of 0.6-1.1 kW·h for complete dehalogenation per ton of drinking water in waterworks. Moreover, the PdFe alloy/CA exhibited extreme mechanical and electrochemical stability with limited iron (∼0.07 ppm) and palladium (0.02 ppm) leaching during the actual application.

Simultaneous reduction of Cr(VI) and oxidization of organic pollutants by rice husk derived biochar and the interactive influences of coexisting Cr(VI)

In this study, biochar derived from rice husk via one-spot calcination treatment at 550 °C (biochar R550), demonstrated a remarkable efficiency in the simultaneous reduction of Cr(VI) and degradation of organic pollutants. With a low Cr(VI) content (0-0.2 mM) coexisting in the biochar (10 g L^-1) system, organic pollutants (1 mM) were mostly degraded via a radical process at pH 3, additionally oxidized by Cr(VI) via an electron transfer mediated by biochar, which ultimately promoted the removal of organic pollutants. While further increasing the Cr(VI) content, the radical degradation of organic pollutants was gradually restrained, but partially replaced by the accelerated oxidization of organics by Cr(VI). On the other hand, the Cr(VI) was mainly reduced to Cr (III) by the functional groups on biochar in the absence of organic pollutants. However, the coexisted organic pollutants could take the place of biochar to reduce Cr(VI), resulting in a slight change of Cr(VI) reduction. Further studies indicated that the defective sites on biochar could enhance the reaction between organic pollutants and Cr(VI). These findings are very much interesting and innovative in the ongoing biochar research and demonstrate a new dimension of biochar potential for detoxification of multiple industrial pollutants containing Cr(VI) and organics.