In situ single iron atom doping on Bi2WO6 monolayers triggers efficient photo-fenton reaction.

Developing an efficient photocatalytic system for hydrogen peroxide (H2O2) activation in Fenton-like processes holds significant promise for advancing water purification technologies. However, challenges such as high carrier recombination rates, limited active sites, and suboptimal H2O2 activation efficiency impede optimal performance. Here we show that single-iron-atom dispersed Bi2WO6 monolayers (SIAD-BWOM), designed through a facile hydrothermal approach, can offer abundant active sites for H2O2 activation. The SIAD-BWOM catalyst demonstrates superior photo-Fenton degradation capabilities, particularly for the persistent pesticide dinotefuran (DNF), showcasing its potential in addressing recalcitrant organic pollutants. We reveal that the incorporation of iron atoms in place of tungsten within the electron-rich [WO4]2- layers significantly facilitates electron transfer processes and boosts the Fe(II)/Fe(III) cycle efficiency. Complementary experimental investigations and theoretical analyses further elucidate how the atomically dispersed iron induces lattice strain in the Bi2WO6 monolayer, thereby modulating the d-band center of iron to improve H2O2 adsorption and activation. Our research provides a practical framework for developing advanced photo-Fenton catalysts, which can be used to treat emerging and refractory organic pollutants more effectively.

Triggering Dual Two-electron Pathway for H2 O2 Generation by Multiple [Bi-O]n Interlayers in Ultrathin Bi12 O17 Cl2 towards Efficient Piezo-self-Fenton Catalysis.

Piezo-self-Fenton system (PESF) has been emerging as a promising water treatment technology but suffering from unsatisfied H2 O2 production efficiency. Herein, we rationally design a Bi12 O17 Cl2 piezo-catalyst with multiple [Bi-O]n interlayers towards highly efficient H2 O2 production. The introduction of [Bi3 O4.25 ] layers initiates dual two-electron pathway for H2 O2 generation by altering the interlayer properties. It is found that the additional [Bi3 O4.25 ] layers not only enhance the polarization electric field but also serve as active sites for triggering dual pathways of two-electron O2 reduction and H2 O oxidation reaction for H2 O2 production. Therefore, the Bi12 O17 Cl2 exhibits an ultrahigh rate of H2 O2 generation (7.76 mM h-1 g-1 ) in pure water. Based on the adequate H2 O2 yield, a PESF was constructed for acetaminophen (ACE) degradation with an apparent rate constant of 0.023 min-1 . This work not only presents a potential strategy of tuning the activity of bismuth based piezo-catalysts but also provides a good example on the construction of highly efficient PESF for environmental remediation by using natural mechanical energy.

Environmental energy enhanced solar-driven evaporator with spontaneous internal convection for highly efficient water purification.

Solar-driven interfacial evaporation for water purification is limited by the structural design of the solar evaporator and, more importantly, by the inability to separate the water from volatile organic compounds (VOCs) present in the water source. Here, we report a three-dimensional (3D) bifunctional evaporator based on N-doped carbon (CoNC/CF), which enables the separation of fresh water from VOCs by activating PMS during the evaporation process with a VOC removal rate of 99%. There is abundant van der Waals interaction between peroxymonosulfate (PMS) and CoNC/CF, and pyrrolic N is confirmed as the active site for binding phenol, thus contributing to the separation of phenol from water. With the advantageous features of sufficient light absorption, adequate water storage capacity, and spontaneous internal convection flow on its top surface, the 3D evaporator achieves a high evaporation rate under one sun (1 kW/m2) at 3.16 kg/m2/h. More notably, through careful structural design, additional energy from the environment and water can be utilized. With such a high evaporation rate and satisfactory purification performance, this work is expected to provide a promising platform for wastewater treatment.

Highly Efficient FeIII -initiated Self-cycled Fenton System in Piezo-catalytic Process for Organic Pollutants Degradation.

Piezo-catalytic self-Fenton (PSF) system has been emerging as a promising technique for wastewater treatment, while the competing O2 reductive hydrogen peroxide (H2 O2 ) production and FeIII reduction seriously limited the reaction kinetics. Here, we develop a two-electron water oxidative H2 O2 production (WOR-H2 O2 ) coupled with FeIII reduction over a FeIII /BiOIO3 piezo-catalyst for highly efficient PSF. It is found that the presence of FeIII can simultaneously initiate the WOR-H2 O2 and reduction of FeIII to FeII , thereby enabling a rapid reaction kinetics towards subsequent Fenton reaction of H2 O2 /FeII . The FeIII initiating PSF system offers exceptional self-recyclable degradation of pollutants with a degradation rate constant for sulfamethoxazole (SMZ) over 3.5 times as that of the classic FeII -PSF system. This study offers a new perspective for constructing efficient PSF systems and shatters the preconceived notion of FeIII in the Fenton reaction.

Multi-heteroatom-doping promotes molecular oxygen activation on polymeric carbon nitride for simultaneous generation of H2O2 and degradation of oxcarbazepine.

Simultaneously realizing the efficient generation of H2O2 and degradation of pollutants is of great significance for environmental remediation. However, most polymeric semiconductors only show moderate performance in molecular oxygen (O2) activation due to the sluggish electron-hole pair dissociation and charge transfer dynamics. Herein, we develop a simple thermal shrinkage strategy to construct multi-heteroatom-doped polymeric carbon nitride (K, P, O-CNx). The resultant K, P, O-CNx not only improves the separation efficiency of charge carriers, but also improves the adsorption/activation capacity of O2. K, P, O-CNx significantly increases the production of H2O2 and the degradation activity of oxcarbazepine (OXC) under visible light. K, P, O-CN5 shows a high H2O2 production rate (1858 µM h-1 g-1) in water under visible light, far surpassing that of pure PCN. The apparent rate constant for OXC degradation by K, P, O-CN5 increases to 0.0491 min-1, which is 8.47 times that of PCN. Density functional theory (DFT) calculations show that the adsorption energy of O2 near phosphorus atoms in K, P, O-CNx is the highest. This work provides a new idea for the efficient degradation of pollutants and generation of H2O2 at the same time.

n→π* Electron Transitions and Directional Charge Migration Synergistically Promoting O2 Activation and Holes Utilization on Carbon Nitride for Efficiently Photocatalytic Degradation of Organic Contaminants.

Stimulating electron transitions and promoting exciton dissociation are crucial for improving the photocatalytic performance of polymeric carbon nitride (CN) yet still challenging. Herein, a novel CN with C dopant and asymmetric structure (CC-UCN2 ) is ingeniously synthesized. The obtained CC-UCN2 not only reinforces the intrinsic π→π* electron transitions, but also successfully awakens additional n→π* electron transitions. Besides, charge centers dislocation caused by symmetry breaking induces a spontaneous polarized electric field, effectively breaking the constraints of Coulomb electrostatic interaction between electrons and holes and driving their directional migration. Along with the spatial separation of reduction and oxidation sites, CC-UCN2 shows exceptional O2 activation and holes oxidation efficiency, thus exhibits a high degradation rate constant (0.201 min-1 ) and mineralization rate (80.1%) for bisphenol A (BPA)(far outperforming pristine and other modified CNs). This work proposes a novel perspective for developing high-efficiency photocatalysts and comprehending the underlying mechanism of O2 activation and holes oxidation for pollutant degradation.

Simultaneously Achieving Fast Intramolecular Charge Transfer and Mass Transport in Holey D-π-A Organic Conjugated Polymers for Highly Efficient Photocatalytic Pollutant Degradation.

Simultaneously realizing efficient intramolecular charge transfer and mass transport in metal-free polymer photocatalysts is critical but challenging for environmental remediation. Herein, we develop a simple strategy to construct holey polymeric carbon nitride (PCN)-based donor-π-acceptor organic conjugated polymers via copolymerizing urea with 5-bromo-2-thiophenecarboxaldehyde (PCN-5B2T D-π-A OCPs). The resultant PCN-5B2T D-π-A OCPs extended the π-conjugate structure and introduced abundant micro-, meso-, and macro-pores, which greatly promoted intramolecular charge transfer, light absorption, and mass transport and thus significantly enhanced the photocatalytic performance in pollutant degradation. The apparent rate constant of the optimized PCN-5B2T D-π-A OCP for 2-mercaptobenzothiazole (2-MBT) removal is ∼10 times higher than that of the pure PCN. Density functional theory calculations reveal that the photogenerated electrons in PCN-5B2T D-π-A OCPs are much easier to transfer from the donor tertiary amine group to the benzene π-bridge and then to the acceptor imine group, while 2-MBT is more easily adsorbed on π-bridge and reacts with the photogenerated holes. A Fukui function calculation on the intermediates of 2-MBT predicted the real-time changing of actual reaction sites during the entire degradation process. Additionally, computational fluid dynamics further verified the rapid mass transport in holey PCN-5B2T D-π-A OCPs. These results demonstrate a novel concept toward highly efficient photocatalysis for environmental remediation by improving both intramolecular charge transfer and mass transport.

Self-cycled photo-Fenton-like system based on an artificial leaf with a solar-to-H2O2 conversion efficiency of 1.46.

Millions of families around the world remain vulnerable to water scarcity and have no access to drinking water. Advanced oxidation processes (AOPs) are an effective way towards water purification with qualified reactive oxygen species (ROSs) while are impeded by the high-cost and tedious process in either input of consumable reagent, production of ROSs, and the pre-treatment of supporting electrolyte. Herein, we couple solar light-assisted H2O2 production from water and photo-Fenton-like reactions into a self-cyclable system by using an artificial leaf, achieving an unassisted H2O2 production rate of 0.77 µmol/(min·cm2) under 1 Sun AM 1.5 illumination. Furthermore, a large (70 cm2) artificial leaf was used for an unassisted solar-driven bicarbonate-activated hydrogen peroxide (BAP) system with recycled catalysts for real-time wastewater purification with requirements for only water, oxygen and sunlight. This demonstration highlights the feasibility and scalability of photoelectrochemical technology for decentralized environmental governance applications from laboratory benchtops to industry.

Highly efficient removal of organic contaminant with wide concentration range by a novel self-cleaning hydrogel: Mechanism, degradation pathway and DFT calculation.

A novel carbon nitride based self-cleaning hydrogel photocatalyst (KI-PCN gel, potassium and iodine co-doped carbon nitride confined in alginate) has been successfully constructed by a facile method. Fabricated photocatalyst showed enhanced synergistic adsorption-photocatalytic degradation property on a high concentration of methylene blue (HMB) because of enhanced carrier separation efficiency and improved light adsorption capacity of KI-PCN. As expected, the KI-PCN gel showed the highest apparent rate constant value (Kapp =0.0310 min-1), which was about 38.8 and 5.8 times as that of blank hydrogel (Kapp=0.0008 min-1) and PCN gel (Kapp=0.0053 min-1), respectively. Meanwhile, KI-PCN gel can continuously adsorb low concentration of MB (LMB), and the MB-adsorbed KI-PCN gel can self-clean under light irradiation. The bench-scale experiments simulating real river showed that KI-PCN gel can effectively and continuously remove LMB (0.1-20 ppm), indicating the possibility for the removal of contaminants in natural rivers. Furthermore, the possible degradation pathways were proposed by combining the density functional calculations (DFT) and intermediates identified by liquid chromatography-mass spectrometry (LC-MS). This work proposed a new perspective to acquire a novel self-cleaning and easily recyclable photocatalyst for treatment of wide concentration range organic wastewater as well as remediation of natural waterbody.

Regulating directional transfer of electrons on polymeric g-C3N5 for highly efficient photocatalytic H2O2 production.

Graphite carbon nitride (g-C3N5) has been widely used in various photocatalytic reactions due to its higher thermodynamic stability and better electronic properties compared to g-C3N4. However, it is still challenging to endow g-C3N5 with high performance on photocatalytic hydrogen peroxide (H2O2) production. Herein, potassium and iodine are co-doped into g-C3N5 (g-C3N5-K, I) for photocatalytic production of H2O2 with high efficiency. As expected, the photocatalytic H2O2 production rate over the g-C3N5-K, I (2933.4 µM h-1) reaches to 84.22 times as that of g-C3N5. The excellent photocatalytic H2O2 production activity is mainly ascribed to the co-doping of K and I, which significantly improves the capacity of oxygen (O2) adsorption, selectivity of two-electrons oxygen reduction reaction (2e- ORR) and separation efficiency of charge carriers. The density functional theory (DFT) calculations reveal that O2 molecules are more conducive to being adsorbed on g-C3N5-K, I. Besides, the result of excited states further indicates that photo-generated electrons can be directionally driven to the adsorbed O2 molecules, which are effectively activated to form H2O2. The findings will contribute to new insights in designing and synthesizing g-C3N5 based photocatalysts for the H2O2 production.

Directing Charge Transfer in a Chemical-Bonded BaTiO3 @ReS2 Schottky Heterojunction for Piezoelectric Enhanced Photocatalysis.

The piezo-assisted photocatalysis system, which can utilize solar energy and mechanical energy simulteneously, is promising but still challenging in the environmental remediation field. In this work, a novel metal-semiconductor BaTiO3 @ReS2 Schottky heterostructure is designed and it shows high-efficiency on piezo-assisted photocatalytic molecular oxygen activation. By combining experiment and calculation results, the distorted metal-phase ReS2 nanosheets are found to be closely anchored on the surface of the BaTiO3 nanorods, through interfacial ReO covalent bonds. The Schottky heterostructure not only forms electron-transfer channels but also exhibits enhanced oxygen activation capacity, which are helpful to produce more superoxide radicals. The polarization field induced by the piezoelectric BaTiO3 can lower the Schottky barrier and thus reduce the transfer resistance of photogenerated electrons directing to the ReS2 . As a result of the synergy effect between the two components, the BaTiO3 @ReS2 exhibits untrahigh activity for degradation of pollutants with an apparent rate constant of 0.133 min-1 for piezo-assisted photocatalysis, which is 16.6 and 2.44 times as that of piezocatalysis and photocatalysis, respectively. This performance is higher than most reported BaTiO3 -based piezo-assisted photocatalysis systems. This work paves the way for the design of high-efficiency piezo-assisted photocatalytic materials for environmental remediation through using green energies in nature.

Understanding the mechanism of interfacial interaction enhancing photodegradation rate of pollutants at molecular level: Intermolecular π-π interactions favor electrons delivery.

Uncovering the interaction between photocatalyst and reaction substrate as well as subsequent electron transfer process is critical to achieve high-performance photodegradation of pollutants. Herein, based on the reduced density gradient (RDG) method, we visualize the simulation of the π-π interactions between photocatalyst (g-C3N4) and pollutant molecule (flumequine, FLU). Results revealed that π-π interactions between g-C3N4 and FLU favor electrons delivery, resulting in enhanced charge separation efficiency and direct hole oxidation of FLU. Moreover, it is found that the charge transfer rate is determined by the valence band (VB) level of g-C3N4 and EHOMO of FLU, of which the deeper VB position of g-C3N4 favors faster charge transfer, leading to further enhancement in photocatalytic degradation rate of FLU. Additionally, the possible degradation pathways of FLU were proposed by theoretical calculation and the determined intermediates. Our work afforded a new insight into pollutants degradation and the rational design of highly efficient photocatalysts.

Intimately coupled photocatalysis and biodegradation for effective simultaneous removal of sulfamethoxazole and COD from synthetic domestic wastewater.

The inefficiency of conventional biological treatment for removing sulfamethoxazole (SMX) is posing potential risks to ecological environments. In this study, an intimately coupled photocatalysis and biodegradation (ICPB) system consisting of Fe3+/g-C3N4 and biofilm was fabricated for the treatment of synthetic domestic wastewater containing SMX. The results showed that this ICPB system could simultaneously remove 96.27 ± 5.27% of SMX and 86.57 ± 3.06% of COD, which was superior to sole photocatalysis (SMX 100%, COD 4.2 ± 0.74%) and sole biodegradation (SMX 42.21 ± 0.86%, COD 95.1 ± 0.18%). Contributors to SMX removal in the ICPB system from big to small include LED photocatalysis, biodegradation, LED photolysis, and adsorption effect of the carrier, while COD removal was largely ascribed to biodegradation. Increasing initial SMX concentration inhibits SMX removal rate, while increasing photocatalyst dosage accelerates SMX removal rate, and both had no impact on COD removal. Our analysis of biofilm activity showed that microorganisms in this ICPB system maintained a high survival rate and metabolic activity, and the microbial community structure of the biofilm remained stable, with Nakamurella and Raoultella being the two dominant genera of the biofilm. This work provides a new strategy to effectively treat domestic wastewater polluted by antibiotics.

Probing the role of surface acid sites on the photocatalytic degradation of tetracycline hydrochloride over cerium doped CdS via experiments and theoretical calculations.

Surface acid site regulation of photocatalysts is a promising strategy to improve their performance. Herein, surface acid sites of cadmium sulfide were rationally regulated by cerium doping, which resulted in significantly increased photocatalytic activity for tetracycline hydrochloride (TC-HCl) degradation. The generated Brønsted acid sites were verified to favor the adsorption of organic molecules because of their strong affinity. Meanwhile, Lewis acid sites acted as the active sites for C-C bond cleavage via a nucleophilic substitution process, which was testified by the Fukui function and electrostatic potential. Besides, Ce3+ doping suppressed the recombination of electron-hole pairs, which also boosted the performance of TC-HCl degradation. Moreover, the degradation pathway of TC-HCl was deduced based on theoretical calculations and HPLC-MS results. The toxicity of pollutants and intermediates was also evaluated. This work provided new insight into the rational design and preparation of highly efficient photocatalysts for environmental purification.

Iodide-Induced Fragmentation of Polymerized Hydrophilic Carbon Nitride for High-Performance Quasi-Homogeneous Photocatalytic H2 O2 Production.

Polymeric carbon nitride (PCN) as a class of two-electron oxygen reduction reaction (2 e- ORR) photocatalyst has attracted much attention for H2 O2 production. However, the low activity and inferior selectivity of 2 e- ORR greatly restrict the H2 O2 production efficiency. Herein, we develop a new strategy to synthesize hydrophilic, fragmented PCN photocatalyst by the terminating polymerization (TP-PCN) effect of iodide ions. The obtained TP-PCN with abundant edge active sites (AEASs), which can form quasi-homogeneous photocatalytic system, exhibits superior H2 O2 generation rate (3265.4 µM h-1 ), far surpassing PCN and other PCN-based photocatalysts. DFT calculations further indicate that TP-PCN is more favorable for electron transiting from ß spin-orbital to the π* orbitals of O2 , which optimizes O2 activation and reduces the energy barrier of H2 O2 formation. This work provides a new concept for designing functional photocatalysts and understanding the mechanism of O2 activation in ORR for H2 O2 production.

Risk prediction of microcystins based on water quality surrogates: A case study in a eutrophicated urban river network.

Microcystins (MCs), the toxic by-products from harmful algal bloom (HAB), have caused world-wide concern due to their acute toxicity in freshwater ecosystems. Most studies on HAB have been conducted for shallow freshwater lakes, such as Taihu Lake in China. However, algal blooms in urban rivers located downstream of eutrophicated lakes are also a serious problem for local administrators. It is important for them to know the current and potential risk level of MCs. This environmental issue is rarely reported or discussed. Within this context, we monitored MC concentrations in the Binhu River Network (BRN) in the algal bloom season (Aug, Sep, and Oct) in 2019. To note if the MC concentrations were dangerous, we used 1.0 µg/L suggested by the World Health Organization as the standard value. The proportions of MC samples violating the standard value were 31.78% (Aug), 21.14% (Sep) and 30.77% (Oct). We also designed two statistical models to predict MC concentrations and the possibility to exceed the standard level based on 10 water quality surrogates: Artificial Neural Network (ANN) and Logistic Regression (LR) models. These two models were trained and validated by the monitoring dataset (n = 224). Both models had good performances during training and testing. Although the water quality varied diversely both in spatial and temporal scale, Cluster Analysis (CA) could detect similarities among the samples and separated them into 3 classes, with each class denoting different types of rivers based on the 10 water quality surrogates. Then the ANN and LR were applied as a function of chl-a in each class; by gradually increasing chl-a concentration, we detected chl-a thresholds in class 1, 2, 3 were 25.5, 224, and 109.5 µg/L, respectively, when MCs have a 50% possibility to exceed standard level. The threshold values provided important implications for MC management in the BRN.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review.

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

Numerical simulation of microcystin distribution in Liangxi River, downstream of Taihu Lake.

Microcystins (MCs), the algal toxins produced by cyanobacteria, raised a worldwide concern in recent decades. Limited monitoring stations for MCs make it hard to map the MC spatial distribution in certain areas. To tackle such problems, we selected Liangxi River as our research area and developed an integrated model to get spatial continuous MC data without too many sampling sites, which integrates a hydro-environment model and an artificial neural network algorithm (ANN). The ANN algorithm can estimate concentration MCs via environmental factors. In this paper, we selected chl-a, TN, TP, NO 2 - , NO 3 - , NH3 -N, and PO 4 3 - as stressors. The ANN model we established showed good performances both in train (R2  = 0.8407) and test set (R2  = 0.7543). In the hydro-environment model, by inputting river geometry and model boundary data, the spatial continuous water quality data could be simulated. The water quality data returned from the hydro-environmental model were used as input variables of the well-trained ANN model; the continuous MC data were derived. To evaluate this model on geo-mapping the MC distribution in Liangxi River, we compared the performance of this model and spatial interpolation on the test set, it turns out the integrated model showed a better performance. © 2020 Water Environment Federation PRACTITIONER POINTS: The cost of microcystin (MC) detection is too high for routine monitoring. We integrated regression method and hydro-environment model to predict MCs. Results derived from spatial interpolation are not robust in unmonitored area. The new integration model can minimize the drawback of spatial interpolation.

Effective inactivation of Microcystis aeruginosa by a novel Z-scheme composite photocatalyst under visible light irradiation.

Microcystis aeruginosa is one of the most famous harmful algae. In this work, Z-scheme g-C3N4-MoO3 (Mo-CN) composite photocatalysts were successfully synthesized to alleviate the algae pollution. The obtained composites exhibited excellent performance for the inactivation of M. aeruginosa. The optimal photocatalysts (15Mo-CN) achieved a removal efficiency of 97% for the algal cells after 3 h visible light irradiation, which was attributed to their remarkable surface properties and ingenious structure design. The physiological status of Microcystis aeruginosa were evaluated by the chlorophyll a (chla), relative electron transport rate (rETR) and maximum photochemical efficiency (Fv/Fm), and all of them decreased in different degrees. Furthermore, the as-prepared photocatalysts also show a certain activity for the removal of leaked macromolecule organic compounds during the process of algal cells inactivation. Finally, a possible mechanism on the photocatalytic inactivation of algal cells by the Z-scheme photocatalysts was deduced based on the experimental and characterization results. We believe this study would provide new insights into the development of promising technology and basic theory for remediation of algae pollution.

The surface engineering of ReS2 with cobalt for efficient performance in hydrogen evolution under both acid and alkaline conditions.

Cobalt-modified rhenium disulfide nanosheets rich in defects, obtained by following an ingenious atom substitution strategy, exhibited boosted HER performance. The 2%-Co doped ReS2 sample was highly efficient in both acid electrolyte (149 mV) and alkaline electrolyte (240 mV), achieving a current density of 10 mA cm-2 as well as superior long-term durability.