M-N3 Configuration on Boron Nitride Boosts Singlet Oxygen Generation via Peroxymonosulfate Activation for Selective Oxidation.

Singlet oxygen (1O2) is an essential reactive species responsible for selective oxidation of organic matter, especially in Fenton-like processes. However, due to the great limitations in synthesizing catalysts with well-defined active sites, the controllable production and practical application of 1O2 remain challenging. Herein, guided by theoretical simulations, a series of boron nitride-based single-atom catalysts (BvBN/M, M=Co, Fe, Cu, Ni and Mn) were synthesized to regulate 1O2 generation by activating peroxymonosulfate (PMS). All the fabricated BvBN/M catalysts with explicit M-N3 sites promoted the self-decomposition of the two PMS molecules to generate 1O2 with high selectivity, where BvBN/Co possessed moderate adsorption energy and d-band center exhibited superior catalytic activity. As an outcome, the BvBN/Co-PMS system coupled with membrane filtration technology could continuously transform aromatic alcohols to aldehydes with nearly 100 % selectivity and conversion rate under mild conditions, suggesting the potential of this novel catalytic system for green organic synthesis.

Dynamic defects boost in-situ H2O2 piezocatalysis for water cleanup.

Creating efficient catalysts for simultaneous H2O2 generation and pollutant degradation is vital. Piezocatalytic H2O2 synthesis offers a promising alternative to traditional methods but faces challenges like sacrificial reagents, harsh conditions, and low activity. In this study, we introduce a cobalt-loaded ZnO (CZO) piezocatalyst that efficiently generates H2O2 from H2O and O2 under ultrasonic (US) treatment in ambient aqueous conditions. The catalyst demonstrates exceptional performance with ~50.9% TOC removal of phenol and in situ generation of 1.3 mM H2O2, significantly outperforming pure ZnO. Notably, the CZO piezocatalyst maintains its H2O2 generation capability even after multiple cycles, showing continuous improvement (from 1.3 mM to 1.8 mM). This is attributed to the piezoelectric electrons promoting the generation of dynamic defects under US conditions, which in turn promotes the adsorption and activation of oxygen, thereby facilitating efficient H2O2 production, as confirmed by EPR spectrometry, XPS analysis, and DFT calculations. Moreover, the CZO piezocatalysts maintain outstanding performance in pollutant degradation and H2O2 production even after long periods of inactivity, and the deactivated catalyst due to metal ion dissolution could be rejuvenated by pH adjustment, offering a sustainable solution for wastewater purification.

Effective green treatment of sewage sludge from Fenton reactions: Utilizing MoS2 for sustainable resource recovery.

Effectively managing sewage sludge from Fenton reactions in an eco-friendly way is vital for Fenton technology's viability in pollution treatment. This study focuses on sewage sludge across various treatment stages, including generation, concentration, dehydration, and landfill, and employs chemical composite MoS2 to facilitate green resource utilization of all types of sludge. MoS2, with exposed Mo4+ and low-coordination sulfur, enhances iron cycling and creates an acidic microenvironment on the sludge surface. The MoS2-modified iron sludge exhibits outstanding (>95%) phenol and pollutant degradation in hydrogen peroxide and peroxymonosulfate-based Fenton systems, unlike unmodified sludge. This modified sludge maintains excellent Fenton activity in various water conditions and with multiple anions, allowing extended phenol degradation for over 14 d. Notably, the generated chemical oxygen demand (COD) in sludge modification process can be efficiently eliminated through the Fenton reaction, ensuring effluent COD compliance and enabling eco-friendly sewage sludge resource utilization.

Dynamic in situ Formation of Cu2 O Sub-Nanoclusters through Photoinduced pseudo-Fehling's Reaction for Selective and Efficient Nitrate-to-Ammonia Photosynthesis.

Copper (Cu) is evidenced to be effective for constructing advanced catalysts. In particular, Cu2 O is identified to be active for general catalytic reactions. However, conflicting results regarding the true structure-activity correlations between Cu2 O-based active sites and efficiencies are usually reported. The structure of Cu2 O undergoes dynamic evolution rather than remaining stable under working conditions, in which the actual reaction cannot proceed over the prefabricated Cu2 O sites. Therefore, the dynamic construction of Cu2 O active sites can be developed to promote catalytic efficiency and reveal the true structure-activity correlations. Herein, by introducing the redox pairs of Cu2+ and reducing sugar into a photocatalysis system, it is clarified that the Cu2 O sub-nanoclusters (NCs), working as novel active sites, are on-site constructed on the substrate via a photoinduced pseudo-Fehling's route. The realistic interfacial charge separation and transformation capacities are remarkably promoted by the dynamic Cu2 O NCs under the actual catalysis condition, which achieves a milestone efficiency for nitrate-to-ammonia photosynthesis, including the targets of production rate (1.98±0.04 mol gCu -1 h-1 ), conversion ratio (94.2±0.91 %), and selectivity (98.6 %±0.55 %). The current work develops an effective strategy for integrating the active site construction into realistic reactions, providing new opportunities for Cu-based chemistry and catalysis sciences research.

A polymer tethering strategy to achieve high metal loading on catalysts for Fenton reactions.

The development of heterogenous catalysts based on the synthesis of 2D carbon-supported metal nanocatalysts with high metal loading and dispersion is important. However, such practices remain challenging to develop. Here, we report a self-polymerization confinement strategy to fabricate a series of ultrafine metal embedded N-doped carbon nanosheets (M@N-C) with loadings of up to 30 wt%. Systematic investigation confirms that abundant catechol groups for anchoring metal ions and entangled polymer networks with the stable coordinate environment are essential for realizing high-loading M@N-C catalysts. As a demonstration, Fe@N-C exhibits the dual high-efficiency performance in Fenton reaction with both impressive catalytic activity (0.818 min-1) and H2O2 utilization efficiency (84.1%) using sulfamethoxazole as the probe, which has not yet been achieved simultaneously. Theoretical calculations reveal that the abundant Fe nanocrystals increase the electron density of the N-doped carbon frameworks, thereby facilitating the continuous generation of long-lasting surface-bound •OH through lowering the energy barrier for H2O2 activation. This facile and universal strategy paves the way for the fabrication of diverse high-loading heterogeneous catalysts for broad applications.

Single-atom Mo-Co catalyst with low biotoxicity for sustainable degradation of high-ionization-potential organic pollutants.

Single-atom catalysts (SACs) are a promising area in environmental catalysis. We report on a bimetallic Co-Mo SAC that shows excellent performance in activating peroxymonosulfate (PMS) for sustainable degradation of organic pollutants with high ionization potential (IP > 8.5 eV). Density Functional Theory (DFT) calculations and experimental tests demonstrate that the Mo sites in Mo-Co SACs play a critical role in conducting electrons from organic pollutants to Co sites, leading to a 19.4-fold increase in the degradation rate of phenol compared to the CoCl2-PMS group. The bimetallic SACs exhibit excellent catalytic performance even under extreme conditions and show long-term activation in 10-d experiments, efficiently degrading 600 mg/L of phenol. Moreover, the catalyst has negligible toxicity toward MDA-MB-231, Hela, and MCF-7 cells, making it an environmentally friendly option for sustainable water treatment. Our findings have important implications for the design of efficient SACs for environmental remediation and other applications in biology and medicine.

Selective Production of CO from Organic Pollutants by Coupling Piezocatalysis and Advanced Oxidation Processes.

To date, the chemical conversion of organic pollutants into value-added chemical feedstocks rather than CO2 remains a major challenge. Herein, we successfully developed a coupled piezocatalytic and advanced oxidation processes (AOPs) system for achieving the conversion of various organic pollutants to CO. The CO product stems from the specific process in which organics are first oxidized to carbonate through peroxymonosulfate (PMS)-based AOPs, and then the as-obtained carbonate is converted into CO by piezoelectric reduction under ultrasonic (US) vibration by using a Co3 S4 /MoS2 catalyst. Experiments and DFT calculations show that the introduction of Co3 S4 not only effectively promotes the transfer and utilization of piezoelectric electrons but also realizes highly selective conversion from carbonate to CO. The Co3 S4 /MoS2 /PMS system has achieved selective generation of CO in actual complex wastewater treatment for the first time, indicating its potential practical applicability.

Switching of radical and nonradical pathways through the surface defects of Fe3O4/MoOxSy in a Fenton-like reaction.

Coexistence of radical and nonradical reaction pathways during advanced oxidation processes (AOPs) makes it challenging to obtain flexible regulation of high efficiency and selectivity for the requirement of diverse degradation. Herein, a series of Fe3O4/MoOxSy samples coupling peroxymonosulfate (PMS) systems enabled the switching of radical and nonradical pathways through the inclusion of defects and adjustment of Mo4+/Mo6+ ratios. The silicon cladding operation introduced defects by disrupting the original lattice of Fe3O4 and MoOxS. Meanwhile, the abundance of defective electrons increased the amount of Mo4+ on the catalyst surface, promoting PMS decomposition with a maximum k value up to 1.530 min-1 and a maximum free radical contribution of 81.33%. The Mo4+/Mo6+ ratio in the catalyst was similarly altered by different Fe contents, and Mo6+ contributed to the production of 1O2, allowing the whole system to attain a nonradical species-dominated (68.26%) pathway. The radical species-dominated system has a high chemical oxygen demand (COD) removal rate for actual wastewater treatment. Conversely, the nonradical species-dominated system can considerably improve the biodegradability of wastewater (biochemical oxygen demand (BOD)/COD = 0.997). The tunable hybrid reaction pathways will expand the targeted applications of AOPs.

Efficient hydrogen production from wastewater remediation by piezoelectricity coupling advanced oxidation processes.

Efficient H2 harvesting from wastewater instead of pure water can minimize fresh water consumption, which is expected to solve the problem of water shortage in H2 production process and contribute to carbon neutrality in the environmental remediation, but the inevitable electron depletion caused by electron-consuming pollutants will result in an exhausted H2 evolution reaction (HER) performance. In this paper, by coupling piezocatalysis and advanced oxidation processes (AOPs) by a MoS2/Fe0/peroxymonosulfate (PMS) ternary system, extensive types of wastewater achieved considerable H2 generation, which exceeded the yield in pure water with synchronous advanced degradation of organic pollutants. In addition, profiting from the crucial bridging role of PMS, the H2 yield in nitrobenzene wastewater after the introduction of PMS-based AOPs increased 3.37-fold from 267.7 µmol·g-1·h-1 to 901.0 µmol·g-1·h-1 because the presence of PMS both thermodynamically benefited MoS2 piezocatalytic H2 evolution and eliminated the electron depletion caused by organic pollutants. By this way, the original repressed H2 evolution performance in substrate of wastewater not only was regained but even showed a significant enhancement than that in pure water (505.7 µmol·g-1·h-1). Additionally, the cyclonic piezoelectric reactor was preliminarily designed for future industrialization. This strategy provided a valuable path for the recycling of actual wastewater by fuel production and synchronous advanced treatment.

In situ H2 O2 Generation and Corresponding Pollutant Removal Applications: A Review.

Catalytic hydrogen peroxide (H2 O2 ) generation from oxygen and water enables a sustainable environment to operate in an effective and green energy-to-chemical conversion way, which has attracted increasing interest in the fields of energy production and environment treatment. In light of this, tremendous progresses and developments have been made during the past decades in catalytic H2 O2 production for pollutant removal from three perspectives including photocatalysis, electrocatalysis or chemical activation. Herein, we critically review the state-of-the-art developments over various procedures of H2 O2 generation and its further application, with the existence of photocatalysts, electrocatalysts, and catalysts, respectively. Benefiting from extensively experimental and theoretical investigations, the performance and stability of H2 O2 generation and its utilization can be maneuvered by devising catalytic platform based on numerous catalysts with predominant electronic, chemical and physical properties, which endow the catalysts with efficient electrons transportation, abundant active sites, and sufficient oxygen adsorption for H2 O2 generation. Furthermore, this review also discusses the formation mechanism of H2 O2 by 2e-ORR and 2e-WOR, as well as its functional process of activating and removing pollutants, and summarizes the design principles of various catalysts by focusing on the formation of H2 O2 . We finally highlight the specific challenges and prospects related to the utilization of catalysts and envision the possible future development trends in the fields of pollutant removal.

Generating High-valent Iron-oxo ≡FeIV =O Complexes in Neutral Microenvironments through Peroxymonosulfate Activation by Zn-Fe Layered Double Hydroxides.

The universal limit on the pH conditions is disturbing peroxymonosulfate (PMS)-triggered high-valent iron-oxo systems in environmental applications. Here, we propose for the first time the construction of a neutral microenvironment on the surface of Zn-Fe layered double hydroxide (ZnFe-LDH) by using the amphoteric properties of zinc hydroxide, which continuously generates ≡FeIV =O over a wide pH range of 3.0-11.0 in activating PMS. The ≡Zn(OH)2 moiety offers a neutral microenvironment at the phase interface, which mitigates the self-decomposition of ≡FeIV =O by protons and the hydrolysis reaction of iron by hydroxyl groups, which is supported by the Mossbauer spectra, density functional theory calculations and designed experiments. Consequently, ZnFe-LDH/PMS can satisfy the stability in long-term experiments, selectivity under conditions with high salinity or natural organic matter and efficient treatment of actual wastewater.

Emerging Cocatalysts on g-C3 N4 for Photocatalytic Hydrogen Evolution.

Over the past few decades, graphitic carbon nitride (g-C3 N4 ) has arisen much attention as a promising candidate for photocatalytic hydrogen evolution reaction (HER) owing to its low cost and visible light response ability. However, the unsatisfied HER performance originated from the strong charge recombination of g-C3 N4 severely inhibits the further large-scale application of g-C3 N4 . In this case, the utilization of cocatalysts is a novel frontline in the g-C3 N4 -based photocatalytic systems due to the positive effects of cocatalysts on supressing charge carrier recombination, reducing the HER overpotential, and improving photocatalytic activity. This review summarizes some recent advances about the high-performance cocatalysts based on g-C3 N4 toward HER. Specifically, the functions, design principle, classification, modification strategies of cocatalysts, as well as their intrinsic mechanism for the enhanced photocatalytic HER activity are discussed here. Finally, the pivotal challenges and future developments of cocatalysts in the field of HER are further proposed.

Constructing an Acidic Microenvironment by MoS2 in Heterogeneous Fenton Reaction for Pollutant Control.

Although Fenton or Fenton-like reactions have been widely used in the environment, biology, life science, and other fields, the sharp decrease in their activity under macroneutral conditions is still a large problem. This study reports a MoS2 cocatalytic heterogeneous Fenton (CoFe2 O4 /MoS2 ) system capable of sustainably degrading organic pollutants, such as phenol, in a macroneutral buffer solution. An acidic microenvironment in the slipping plane of CoFe2 O4 is successfully constructed by chemically bonding with MoS2 . This microenvironment is not affected by the surrounding pH, which ensures the stable circulation of Fe3+ /Fe2+ on the surface of CoFe2 O4 /MoS2 under neutral or even alkaline conditions. Additionally, CoFe2 O4 /MoS2 always exposes "fresh" active sites for the decomposition of H2 O2 and the generation of 1 O2 , effectively inhibiting the production of iron sludge and enhancing the remediation of organic pollutants, even in actual wastewater. This work not only experimentally verifies the existence of an acidic microenvironment on the surface of heterogeneous catalysts for the first time, but also eliminates the pH limitation of the Fenton reaction for pollutant remediation, thereby expanding the applicability of Fenton technology.

Novel Fenton process of Co-catalyst Co9S8 quantum dots for highly efficient removal of organic pollutants.

Advanced oxidation processes (AOPs) have been widely accepted as an efficient and promising strategy for treating organic pollutants, is mainly dominated by hydroxyl radicals (•OH); however, its further practical application has been hindered by its low decomposition rate of H2O2. Hence, for the first time, we propose an eco-friendly and facile synthesis methodology synthesize water-soluble Co9S8 quantum dots (QDs) derived from commercial cobalt disulfide (CoS2), which can serve as excellent co-catalysts to dramatically enhance the decomposition rate of H2O2. It is demonstrated that the conversion rate of H2O2 into •OH is ca. 80.02% promoted by Co9S8 QDs, whereas the conventional Fenton process is ca. 34.9%. The result shows that unsaturated edged S atoms on the surface of Co9S8 play a pivotal role in this enhancement, where the number of protons will react with sulfur atoms to form H2S and expose reductive metallic active sites to accelerate the Fe3+/Fe2+ conversion. In addition, to tackle the issue for difficult recovery of liquid quantum dots, the magnetic Co9S8 QDs/Fe3O4 nanoparticles are particularly synthesized, which show excellent performance for degradation of 20 mg/L Rhodamine B (RhB). Moreover, the TOC degradation rate can remain stable at 80% even after five cycles. It is expected that this work will provide a new pathway of thinking in the Fenton process and impulse the usage of liquid quantum dots in practical AOPs application.

Defects on CoS2-x : Tuning Redox Reactions for Sustainable Degradation of Organic Pollutants.

It is important to develop self-producing reactive oxygen species (ROSs) systems and maintain the continuous and effective degradation of organic pollutants. Herein, for the first time, a system of ultrasound-treated CoS2-x mixed with Fe2+ is constructed to sustainably release singlet oxygen (1 O2 ) for the effective degradation of various organic pollutants, including dyes, phenols, and antibiotics. Ultrasonic treatment produces defects on the surface of CoS2 which promote the production of ROSs and the circulation of Fe3+ /Fe2+ . With the help of Co4+ /Co3+ exposed on the surface of CoS2-x , the directional conversion of superoxide radical (. O2- ) to 1 O2 is realized. The CoS2-x /Fe2+ system can degrade organic pollutants efficiently for up to 30 days, which is significantly better than the currently recognized CuPx system (<3 days). Therefore, CoS2-x provides a new choice for the long-term remediation of organic pollutants in controlling large area river pollution.

Designing 3D-MoS2 Sponge as Excellent Cocatalysts in Advanced Oxidation Processes for Pollutant Control.

3D-MoS2 can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D-MoS2 sponge loaded with MoS2 nanospheres and graphene oxide (GO). Exposed Mo4+ active sites on 3D-MoS2 can significantly improve the concentration and stability of Fe2+ in AOPs and keep the Fe3+ /Fe2+ in a stable dynamic cycle, thus effectively promoting the activation of H2 O2 /peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D-MoS2 system is about 50 times higher than without cocatalyst. After a 140 L pilot-scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D-MoS2 achieves a degradation rate of 120 mg L-1 antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications.

Metallic Active Sites on MoO2(110) Surface to Catalyze Advanced Oxidation Processes for Efficient Pollutant Removal.

Advanced oxidation processes (AOPs) based on sulfate radicals (SO4⋅-) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO2 as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO4⋅--based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO2, whereas the exposed active sites of Mo(IV) on MoO2 surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO2 as a cocatalyst is a promising technique for large-scale practical environmental remediation.

Hollow Fe3O4/carbon with surface mesopores derived from MOFs for enhanced lithium storage performance.

Hollow metal-organic frameworks (MOFs) and their derivatives have attracted more and more attention due to their high specific surface area and perfect morphological structure, which determine their large potential application in energy storage and catalysis fields. However, few researchers have carried out further modification on the outer shell of hollow MOFs, such as the perforation modification, which will endow hollow nanomaterials derived from MOFs with multifunctionality. In this paper, hollow MOFs of MIL-53(Fe) with perforated outer surface are successfully synthesized by using SiO2 nanospheres as the template via a self-assembly process induced by the coordination polymerization. The tightly packed mesopore structure makes the carbon outer shell of MOFs thinner, thus realizing the in-situ transformation from MOFs to hollow Fe3O4/carbon, which exhibits perfect capacity approaching 1270 mA h g-1 even after 200 cycles at 0.1 A g-1, as an anode material in lithium ion batteries (LIBs) application. This research provides a new strategy for the design and preparation of MOFs and their derivatives with multifunctionality for the energy applications.

The role of oxygen defects in metal oxides for CO2 reduction.

The abuse of fossil fuels release large amount of CO2, causing intense global warming. Using photoreduction and electroreduction to convert CO2 into highly valuable fuels such as CO and CH4 can effectively solve this problem. However, due to the limited activity and selectivity, pristine catalyst materials cannot meet the requirements of practical applications, which means that some modifications to these catalysts are necessary. In this review, a series of research reports on oxygen defect engineering have been introduced. First, the methods of preparing oxygen defects by heat treatment, doping, and photoinduction combined with influencing factors in the preparation are introduced. Subsequently, common characterization methods of oxygen defects including EPR, Raman, XPS, EXAFS, and HRTEM are summarized. Finally, the mechanisms of introducing oxygen defects to improve CO2 reduction are discussed, and include enhancing light absorption, improving CO2 adsorption and activation, as well as promoting stability of the reaction intermediates. The summary of research on oxygen defects provides guidance for researchers who focus on CO2 reduction and accelerate the realization of its industrial applications in the future.