Facilitated Unidirectional Electron Transmission by Ru Nano Particulars Distribution on MXene Mo2C@g-C3N4 Heterostructures for Enhanced Photocatalytic H2 Evolution.

Precious metals exhibit promising potential for the hydrogen evolution reaction (HER), but their limited abundance restricts widespread utilization. Loading precious metal nanoparticles (NPs) on 2D/2D heterojunctions has garnered considerable interest since it saves precious metal consumption and facilitates unidirectional electron transmission from semiconductors to active sites. In this study, Ru NPs loaded on MXenes Mo2C by an in-site simple strategy and then formed 2D/2D heterojunctions with 2D g-C3N4 (CN) via electrostatic self-assembly were used to enhance photocatalytic H2 evolution. Evident from energy band structure analyses such as UV-vis and TRPL, trace amounts of Ru NPs as active sites significantly improve the efficiency of the hydrogen evolution reaction. More interestingly, MXene Mo2C, as substrates for supporting Ru NPs, enriches photoexcited electrons from CN, thereby enhancing the unidirectional electron transmission. As a result, the combination of Ru-Mo2C and CN constructs a composite heterojunction (Ru-Mo2C@CN) that shows an improved H2 production rate at 1776.4 µmol∙g-1∙h-1 (AQE 3.58% at 400 nm), which is facilitated by the unidirectional photogenerated electron transmission from the valence band on CN to the active sites on Ru (CN→Mo2C→Ru). The study offers fresh perspectives on accelerated unidirectional photogenerated electron transmission and saved precious metal usage in photocatalytic systems.

Modulating the pore and electronic structure for targeted recovery of platinum: Accelerated kinetic and reinforced coordination.

Adsorption for recovery of low-concentration platinum (Pt) from the complex composition of acidic digestates was challenging because of slow kinetic and poor affinity. It was expected to be overcome by the improvement of pore size distribution and adsorption site activity. Herein, a series of Prussian blue etchings (PBE) with porosity-rich and activity-high cyano (CN) was synthesized to recover low-concentration Pt. The N2 isotherm results showed that the pore structure evolved from mesoporous to microporous. The Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations results revealed that the modulation of electronic structure converted FeII to FeIII in [FeII(CN)6]4-. The coexistence of micro- and meso-pore structures provided channels to accelerate adsorption and ensured PtII enrichment. The regulation of Fe valence state activated CN, which reinforced the strength of coordination interaction between Pt and Fe-CN- at N-atom. The adsorption rate and maximum capacity of PBE1 were 4.4 and 2.5 times higher than those of PB, respectively, due to the dual efficacy of accelerated kinetic and reinforced coordination. This study systematically analyzes the pivotal role of pore and electronic structure modulation in adsorption kinetic and affinity, which provides a novel strategy for PtII targeted recovery.

Surface reconstructed Fe@C1000 for enhanced Fenton-like catalysis: Sustainable ciprofloxacin degradation and toxicity reduction.

The Fe-based catalysts typically undergo severe problems such as deactivation and Fe sludge emission during the peroxymonosulfate (PMS) activation, which commonly leads to poor operation and secondary pollution. Herein, an S-doped Fe-based catalyst with a core-shell structure (Fe@CT, T = 1000°C) was synthesized, which can solve the above issues via the dynamic surface evolution during the reaction process. Specifically, the Fe0 on the surface of Fe@C1000 could be consumed rapidly, leaving numerous pores; the Fe3C from the core would subsequently migrate to the surface of Fe@C1000, replenishing the consumed active Fe species. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated that the reaction surface reconstructed during the PMS activation, which involved the FeIII in-situ reduction by S species as well as the depletion/replenishment of effective Fe species. The reconstructed Fe@C1000 achieved near-zero Fe sludge emission (from 0.59 to 0.08-0.23 mg L-1) during 5 cycles and enabled the dynamic evolution of dominant reactive oxygen species (ROS) from SO4·- to FeIVO, sustainably improving the oxidation capacity (80.0-92.5% in following four cycles) to ciprofloxacin (CIP) and reducing the toxicity of its intermediates. Additionally, the reconstructed Fe@C1000/PMS system exhibited robust resistance to complex water matrix. This study provides a theoretical guideline for exploring surface reconstruction on catalytic activity and broadens the application of Fe-based catalysts in the contaminants elimination.

Adsorptive decontamination of antibiotics from livestock wastewater by using alkaline-modified biochar.

Efficient abatement of antibiotics from livestock wastewater is in urgent demand, but still challenging. In this study, alkaline-modified biochar with larger surface area (130.520 m2 g-1) and pore volume (0.128 cm3 g-1) was fabricated and explored for the adsorption of different types of antibiotics from livestock wastewater. Batch adsorption experiments demonstrated that the adsorption process was mainly determined by chemisorption and was heterogeneous, which could be moderately affected by the variations of solution pH (3-10). Furthermore, the computational analysis based on density functional theory (DFT) indicated that the -OH groups on biochar surface could serve as the dominant active sites for antibiotics adsorption due to the strongest adsorption energies between antibiotics and -OH groups. In addition, the antibiotics removal was also evaluated in multi-pollutants system, where biochar performed synergistic adsorption towards Zn2+/Cu2+ and antibiotics. Overall, these findings not only deepen our understandings on the adsorption mechanism between biochar and antibiotics, but also promote the application of biochar in the remediation of livestock wastewater.

Spontaneous FeIII/FeII redox cycling in single-atom catalysts: Conjugation effect and electron delocalization.

The mechanism of spontaneous FeIII/FeII redox cycling in iron-centered single-atom catalysts (I-SACs) is often overlooked. Consequently, pathways for continuous SO4 ·-/HO⋅ generation during peroxymonosulfate (PMS) activation by I-SACs remain unclear. Herein, the evolution of the iron center and ligand in I-SACs was comprehensively investigated. I-SACs could be considered as a coordination complex created by iron and a heteroatom N-doped carbonaceous ligand. The ligand-field theory could well explain the electronic behavior of the complex, whereby electrons delocalized by the conjugation effect of the ligand were confirmed to be responsible for the FeIII/FeII redox cycle. The possible pyridinic ligand in I-SACs was demonstrably weaker than the pyrrolic ligand in FeIII reduction due to its shielding effect on delocalized π orbitals by local lone-pair electrons. The results of this study significantly advance our understanding of the mechanism of spontaneous FeIII/FeII redox cycling and radical generation pathways in the I-SACs/PMS process.

Evaluation of potassium ferrate activated biochar for the simultaneous adsorption of copper and sulfadiazine: Competitive versus synergistic.

Combined pollution caused by organic pollutants and heavy metals pose a significant challenge to the adsorption process. In this study, iron-modified biochar (Fe-BC) was prepared by using ferrate (K2FeO4) and wheat stalk as the precursors for the adsorption of copper (Cu2+) and sulfadiazine (SDZ), especially under combined pollution scenarios. Iron modification not only enlarged the surface area but also loaded iron oxide nanoparticles on biochar surface. Accordingly, Fe-BC exhibited better adsorption capability of Cu2+ and SDZ than the pristine biochar (BC). The corresponding maximum adsorption capacities of Fe-BC700 were 46.85 mg g-1 and 45.43 mg g-1 towards Cu2+ and SDZ, respectively. Interestingly, the adsorption was elevated in binary-pollutants system, suggesting a synergistic effect, which was probably attributed to the mutual bridging effects and complexation between Cu2+ and SDZ. The loaded iron oxide particles could serve as a physical barrier to separate the adsorptions of Cu2+ and SDZ and thus inhibited the competitive adsorption. Meanwhile, theoretical calculation demonstrated that sulfonamide group was the most probable binding site. Columns packed with Fe-BC700 showed better performances for Cu2+ and SDZ removal in binary system (635.73 BV for Cu2+ and 4846.26 BV for SDZ) than in single systems (571.60 BV for Cu2+ and 3572.06 BV for SDZ), which was consistent with batch adsorption experiments. These results demonstrated the potential application of Fe-BC700 for simultaneous adsorption of Cu2+ and SDZ and provided a cost-effective way for the remediation of organic and inorganic pollutants.

Mutual-activation between Zero-Valent iron and graphitic carbon for Cr(VI) Removal: Mechanism and inhibition of inherent Side-reaction.

The low reactivity of zero-valent iron (ZVI) usually limits its application for pollutant remediation. Therefore, a microscopic galvanic cell (mGC) with short-circuited cathode and anode was synthesized to intensify its galvanic corrosion. The prepared mGC exhibited 7.14 times higher Fe(II) release performance than ordinary nanoscale-ZVI (nZVI), rendering efficient Cr(VI) removal performance. Density functional theory (DFT) revealed mutual-activation of the cathode and anode due to close proximity, dramatically enhancing the galvanic corrosion of Fe(0) in mGC. The corrosion potential of mGC was measured as -0.77 V, which was 100 mV more negative than nZVI. The released electrons and surface-bond Fe(II) from anode in mGC was proved to be the dominant reductive species. More importantly, Cr(VI) reduction was slightly inhibited by hydroxyl radicals generated by a series of inherent side-reactions in the system, which could be well eliminated by low concentrations of 4-acetamido phenol. This study provides a promising strategy for ZVI activation, and sheds light on its environmental applications.

Oxygen vacancies-enriched CoFe2O4 for peroxymonosulfate activation: The reactivity between radical-nonradical coupling way and bisphenol A.

Oxygen vacancies (OV) play a vital role in catalytic activity. Herein, a series of MOF-derived CoFe2O4 nanomaterials with OV tuned by a simple thermal aging strategy are prepared for peroxymonosulfate (PMS) activation. Remarkably, the stability, structural and catalytic properties show dependence on the annealing temperature. The abundant surface OV and functional groups on CoFe2O4 were verified as active sites to boost catalytic activity. Based on the density functional theory (DFT) calculations, (1 1 1), (2 2 2) and (4 2 2) planes exposed at higher temperatures facilitate catalytic performance, ascribed to the intense surface adsorption energy. The quenching and electron paramagnetic resonance (EPR) experiments indicate catalysis degradation is a radical-nonradical coupling process. The reactivity between reactive oxygen species (ROS) and bisphenol A and the radical-nonradical dual degradation pathways are systematically explored by combined DFT and HPLC-MS.

Sulfonic-Group-Grafted Ti3C2Tx MXene: A Silver Bullet to Settle the Instability of Polyaniline toward High-Performance Zn-Ion Batteries.

Polyaniline (PANI) is a promising cathode material for Zn-ion batteries (ZIBs) due to its intrinsic conductivity and redox activity; however, the achievements of PANI in high-performance ZIBs are largely hindered by its instability during the repeated charge/discharge. Taking advantage of the high conductivity, flexibility, and grafting ability together, a surface-engineered Ti3C2Tx MXene is designed as a silver bullet to fight against the deprotonation and swelling/shrinking issues occurring in the redox process of PANI, which are the origins of its instability. Specifically, the sulfonic-group-grafted Ti3C2Tx(S-Ti3C2Tx) continuously provides protons to improve the protonation degree of PANI and maintains the polymer backbone at a locally low pH, which effectively inhibits deprotonation and brings high redox activity along with good reversibility. Meanwhile, the conductive and flexible natures of S-Ti3C2Tx assist the fast redox reaction of PANI and concurrently buffer its corresponding swelling/shrinking. Therefore, the S-Ti3C2Tx-enhanced PANI cathode simultaneously achieves a high discharge capacity of 262 mAh g-1 at 0.5 A g-1, a superior rate capability of 160 mAh g-1 at 15 A g-1, and a good cyclability over 5000 cycles with 100% coulombic efficiency. This work enlightens the development of versatile MXene via surface engineering for advanced batteries.

Synergistic Adsorption and Oxidation of Ciprofloxacin by Biochar Derived from Metal-Enriched Phytoremediation Plants: Experimental and Computational Insights.

Biochar is a promising candidate for the adsorptive removal of organic/inorganic pollutants, yet its role in metal-free catalyzed advanced oxidation processes still remains ambiguous. In this work, five biochar samples (PPBKx, where x represents the pyrolysis temperature) were prepared by using metal-enriched phytoremediation plant residue as the feedstock. Notably, PPBK exhibited a high specific surface area (as high as 1090.7 m2 g-1) and outstanding adsorption capacity toward ciprofloxacin (CIP, as much as 1.51 ± 0.19 mmol g-1). By introducing peroxymonosulfate (PMS, 5 mM) as the chemical oxidant, over 2 mmol g-1 CIP was synergistically adsorbed and oxidized within 30 min although PMS itself could not oxidize CIP efficiently, suggesting the formation of reactive oxidative species. Theoretical calculations revealed that PMS anions preferentially adsorbed on the activated C atoms adjacent to the graphitic N dopant, where the carbon matrix served as the electron donor, instead of as an electron mediator. The adsorbed PMS possessed a smaller molecular orbital energy gap, indicating that it was much easier to be activated than free PMS anions. Surface-bound reactive species were elucidated to be the dominant contributor through chemical quenching experiments and electrochemical characterizations. The catalytic activity of PPBK700 could be greatly retained in repeated oxidations because of the stable N species, which serve as the active catalytic sites, while the CIP adsorption was greatly deteriorated because of the diminishing active adsorption sites (carbon matrix edge) caused by the partial oxidation of PMS. This work not only provides a facile and low-cost approach for the synthesis of functional biochar toward environmental remediation but also deepens the understanding of biochar-catalyzed PMS activation and nonradical oxidation.

Enhanced Microbial Chromate Reduction Using Hydrogen and Methane as Joint Electron Donors.

Hydrogen and methane commonly co-exist in aquifer. Either hydrogen or methane has been individually utilized as electron donor for bio-reducing chromate. However, little is known whether microbial chromate reduction would be suppressed or promoted when both hydrogen and methane are simultaneously supplied as joint electron donors. This study for the first time demonstrated microbial chromate reduction rate could be accelerated by both hydrogen and methane donating electrons. The maximum chromate reduction rate (4.70 ±â€¯0.03 mg/L·d) with a volume ratio of hydrogen to methane at 1:1 was significantly higher than that with pure hydrogen (2.53 ±â€¯0.02 mg/L·d) or pure methane (2.01 ±â€¯0.02 mg/L·d) as the sole electron donor (p < 0.01). High-throughput 16S rRNA gene amplicon sequencing detected potential chromate reducers (e.g., Spirochaetaceae, Delftia and Azonexus) and hydrogenotrophic bacteria (e.g., Acetoanaerobium) and methane-metabolizing microorganisms (e.g., Methanobacterium), indicating that these microorganisms might play important roles on microbial chromate reduction using both hydrogen and methane as electron donors. Abundant hupL and mcrA genes responsible for hydrogen oxidation and methane conversion were harbored, together with chrA gene for chromate reduction. More abundant extracellular cytochrome c and intracellular NADH were detected with joint electron donors, suggesting more active electron transfers.

Degradation of antibiotics in multi-component systems with novel ternary AgBr/Ag3PO4@natural hematite heterojunction photocatalyst under simulated solar light.

Abatement of antibiotics from aquatic systems is of great importance but remains a challenge. Herein, we prepared ternary AgBr/Ag3PO4@natural hematite (AgBr/Ag3PO4@NH) heterojunction composite via a simple route for the photocatalytic degradation of antibiotic pollutants. By adjusting the dose of Ag species, four products with different Ag content (denoted as Ag0.5BrPFe, Ag1BrPFe, Ag1.5BrPFe, and Ag2BrPFe) were developed. Among them, Ag1.5BrPFe exhibited the best photocatalytic activity. Four antibiotics (i.e. ciprofloxacin (CIP), norfloxacin (NOR), sulfadiazine (SDZ), and tetracycline (TTC)) could be degraded with synthesized Ag1.5BrPFe in multi-component systems. Water matrix indexes including solution pH, coexisting anions, humic acids exhibited distinct effects on the degradation process. The results revealed that the degradation process was accelerated at acidic conditions while depressed at basic conditions. Superoxide radical and hole were detected by in situ electron spin resonance technique and played the dominant roles. The degradation pathway TTC was tentatively established followed with the identification of the degradation intermediates and computational analysis. This work would shed light on the photocatalytic degradation mechanism of organic pollutants by the AgBr/Ag3PO4@NH composite.

Biodegradation of 2-hydroxyl-1,4 naphthoquinone (lawsone) by Pseudomonas taiwanensis LH-3 isolated from activated sludge.

2-hydroxy-1,4 naphthoquinone (lawsone) is widely used and induces environmental pollutions during its production and application. In the present study, a lawsone-degrading bacterium strain, LH-3 was successfully isolated from the activated sludge. Based on the 16S rRNA gene analysis, the strain LH-3 phylogenetically belonged to the Pseudomonas taiwanensis. It could degrade 200 mg L-1 lawsone completely in 9 h with an inoculum quantity of 1% (v/v). The effects of environmental conditions on the degradation process and the degradation pathway were systematically investigated. LH-3 could maintain its high degradation efficiency under high salt condition. The identified intermediates of salicylic acid, 2-hydroxy-4-oxo-chroman-2-carboxylic acid, and catechol elucidated the potential degradation pathway. Furthermore, the immobilized LH-3 strain cells prepared with alginate gel and biochar performed excellent stability in nine successive degradation runs. It could sucessfully survive in laboratory scale sequencing batch reactor and become to be the dominant species. This study clearly revealed that LH-3 could serve as an attractive candidate for the microbial remediation of lawsone-containing wastewater.

Selective removal of cesium by ammonium molybdophosphate - polyacrylonitrile bead and membrane.

The selective removal of radionuclides with extremely low concentrations from environmental medium remains a big challenge. Ammonium molybdophosphate possess considerable selectivity towards cesium ion (Cs+) due to the specific ion exchange between Cs+ and NH4+. Ammonium molybdophosphate - polyacrylonitrile (AMP-PAN) membrane was successfully prepared for the first time in this study. Efficient removal of Cs+ (95.7%, 94.1% and 91.3% of 1mgL-1) from solutions with high ionic strength (400mgL-1 of Na+, Ca2+ or K+) was achieved by AMP-PAN composite. Multilayer chemical adsorption process was testified through kinetic and isotherm studies. The estimated maximum adsorption capacities even reached 138.9±21.3mgg-1. Specifically, the liquid film diffusion was identified as the rate-limiting step throughout the removal process. Finally, AMP-PAN membrane could eliminate Cs+ from water effectively through the filtration adsorption process.

Natural ageing process accelerates the release of Ag from functional textile in various exposure scenarios.

Natural ageing process occurs throughout the life cycle of textile products, which may possess influences on the release behavior of additives such as silver nanoparticles (Ag NPs). In this study, we assessed the releasability of Ag NPs from a Ag NPs functionalized textile in five different exposure scenarios (i.e. tap water (TW), pond water (PW), rain water (RW), artificial sweat (AS), and detergent solution (DS) along with deionized water (DW) as reference), which were very likely to occur throughout the life cycle of the textile. For the pristine textile, although the most remarkable release was found in DW (6-15 µg Ag/g textile), the highest release rate was found in RW (around 7 µg Ag/(g textile·h)). After ageing treatment, the total released Ag could be increased by 75.7~386.0% in DW, AS and DS. Morphological analysis clearly showed that the Ag NPs were isolated from the surface of the textile fibre due to the ageing treatment. This study provides useful information for risk assessment of nano-enhanced textile products.

Remediation of radiocesium-contaminated liquid waste, soil, and ash: a mini review since the Fukushima Daiichi Nuclear Power Plant accident.

The radiation contamination after the Fukushima Daiichi Nuclear Power Plant accident attracts considerable concern all over the world. Many countries, areas, and oceans are greatly affected by the emergency situation other than Japan. An effective remediation strategy is in a highly urgent demand. Though plenty of works have been carried out, progressive achievements have not yet been well summarized. Here, we review the recent advances on the remediation of radiocesium-contaminated liquid waste, soil, and ash. The overview of the radiation contamination is firstly given. Afterwards, the current remediation strategies are critically reviewed in terms of the environmental medium. Special attentions are paid on the adsorption/ion exchange and electrically switched ion exchange methods. Finally, the present review outlines the possible works to do for the large-scale application of the novel remediation strategies.

Facet-Controlling Agents Free Synthesis of Hematite Crystals with High-Index Planes: Excellent Photodegradation Performance and Mechanism Insight.

Hematite (α-Fe2O3) crystals with uniform size and structure are synthesized through very facile one-pot hydrothermal methods without any additive. The as-synthesized sub-micrometer-sized α-Fe2O3 crystals with small surface areas perform superb visible light photodegradation activities, even much better than most other α-Fe2O3 nanostructures with large surface areas. Profound mechanism analyses reveal that the microwave-assisted hydrothermal (Mic-H) synthesized α-Fe2O3 is enclosed by 12 high-index {2-15} facets. The structure and the low unoccupied molecular orbital (LUMO) of the high-index planes result in the excellent photocatalytic activity. This is the first report on the formation of {2-15} plane group of hematite, and the synthesis of the hematite particles with the {2-15} planes is very simple and no any facet-controlling agent is used. This study may pave the way to further performance enhancement and practical applications of the cheap hematite materials.

Facile synthesis of α-Fe2O3 nanodisk with superior photocatalytic performance and mechanism insight.

Intrinsic short hole diffusion length is a well-known problem for α-Fe2O3 as a visible-light photocatalytic material. In this paper, a nanodisk morphology was designed to remarkably enhance separation of electron-hole pairs of α-Fe2O3. As expected, α-Fe2O3 nanodisks presented superior photocatalytic activity toward methylene blue degradation: more than 90% of the dye could be photodegraded within 30 min in comparison with a degradation efficiency of 50% for conventional Fe2O3 powder. The unique multilayer structure is thought to play a key role in the remarkably improved photocatalytic performance. Further experiments involving mechanism investigations revealed that instead of high surface area, ·OH plays a crucial role in methylene blue degradation and that O·2- may also contribute effectively to the degradation process. This paper demonstrates a facile and energy-saving route to fabricating homogenous α-Fe2O3 nanodisks with superior photocatalytic activity that is suitable for the treatment of contaminated water and that meets the requirement of mass production.

Selective removal of cesium from aqueous solutions with nickel (II) hexacyanoferrate (III) functionalized agricultural residue-walnut shell.

A novel nickel (II) hexacyanoferrate (III) functionalized agricultural residue-walnut shell (Ni(II)HCF(III)-WS) was developed to selectively remove cesium ion (Cs(+)) from aqueous solutions. This paper showed the first integral study on Cs(+) removal behavior and waste reduction analysis by using biomass adsorption material. The results indicated that the removal process was rapid and reached saturation within 2h. As a special characteristic of Ni(II)HCF(III)-WS, acidic condition was preferred for Cs(+) removal, which was useful for extending the application scope of the prepared biomass material in treating acidic radioactive liquid waste. The newly developed Ni(II)HCF(III)-WS could selectively remove Cs(+) though the coexisting ions (Na(+) and K(+) in this study) exhibited negative effects. In addition, approximately 99.8% (in volume) of the liquid waste was reduced by using Ni(II)HCF(III)-WS and furthermore 91.9% (in volume) of the spent biomass material (Cs-Ni(II)HCF(III)-WS) was reduced after incineration (at 500°C for 2h). Due to its relatively high distribution coefficient and significant volume reduction, Ni(II)HCF(III)-WS is expected to be a promising material for Cs(+) removal in practice.

Nickel oxide grafted andic soil for efficient cesium removal from aqueous solution: adsorption behavior and mechanisms.

An andic soil, akadama clay, was modified with nickel oxide and tested for its potential application in the removal of cesium from aqueous solution. Scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and powder X-ray diffraction (XRD) results revealed the nickel oxide was successfully grafted into akadama clay. N2 adsorption-desorption isotherms indicated the surface area decreased remarkably after modification while the portion of mesopores increased greatly. Thermogravimetric-differential thermal analysis (TG-DTA) showed the modified akadama clay had better thermostability than the pristine akadama clay. Decreases in cation exchange capacity (CEC) and ζ-potential were also detected after the modification. Adsorption kinetic and isotherm studies indicated the adsorption of Cs+ on the modified akadama clay was a monolayer adsorption process. Adsorption capacity was greatly enhanced for the modified akadama clay probably due to the increase in negative surface charge caused by the modification. The adsorption of Cs+ on the modified akadama clay was dominated by an electrostatic adsorption process. Results of this work are of great significance for the application of akadama clay as a promising adsorbent material for cesium removal from aqueous solutions.