*H migration-assisted MvK mechanism for efficient electrochemical NH3 synthesis over TM-TiNO.

The electrochemical NH3 synthesis on TiNO is proposed to follow the Mars-van Krevelen (MvK) mechanism, offering more favorable N2 adsorption and activation on the N vacancy (Nv) site, compared to the conventional associative mechanism. The regeneration cycle of Nv represents the rate-determining step in this process. This study investigates a series of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt)-TiNO to explore the *H migration (from TM to TiNO)-promoted Nv cycle. The screening results indicate that Ni-TiNO exhibits strong H2O decomposition for *H production with 0.242 eV and low *H migration resistance with 0.913 eV. Notably, *H migration from Ni to TiNO significantly reduces the Nv formation energy to 0.811 eV, compared to 1.387 eV on pure TiNO. Meanwhile, in the presence of *H, Nv formation takes precedence over Tiv and Ov. Lastly, electronic performance calculations reveal that the collaborative function provided by Ni and Nv enables highly stable and efficient NH3 synthesis. The *H migration-assisted MvK mechanism demonstrates effective catalytic cycle performance in electrochemical N2 fixation and may have potential applicability to other hydrogenation reactions utilizing water as a proton source.

Promoted photocatalytic N2 fixation to ammonia over floatable TiO2/Bi/Carbon cloth through relay pathway.

The floatable photocatalyst at N2-water interface allows the adequate supply of N2 reactant and the utilization of photothermal energy for photocatalytic N2 fixation, however, the presence of non-volatile NO3- product poses a challenge to the stability as it easily covers the catalytic active sites. Herein, a floatable TiO2/Bi/CC (Carbon cloth) photocatalyst was designed, in which the non-volatile NO3- can be transformed to the volatile NH3 via the newly synergistic relay photocatalysis pathway (N2 â†’ NO3- â†’ NH3) between TiO2 (N2 â†’ NO3-) and Bi (NO3- â†’ NH3). Attractively, the spontaneous NO3- â†’ NO2- step occurs on Bi component to promote the relay pathway performing. Therefore, TiO2/Bi/CC system displays better long-term stability than TiO2/CC, and moreover, it achieves a higher NH3 yield of 8.28 mmol L-1 h-1 g-1 (i.e. 4.14 mmol h-1 m-2) than that 1.46 mmol L-1 h-1 g-1 for TiO2/Bi powder. Importantly, the N2 fixation products by TiO2/Bi/CC effectively promote lettuce growth and enhance lettuce nutrient contents, which further validates the feasibility of this system in large-scale application of crop cultivation.

Few-Layer Meets Crystalline Structure: Collaborative Efforts for Improving Photocatalytic H2O2 Generation over Carbon Nitride.

Although the conversion of O2 and H2O to H2O2 over graphite carbon nitride (g-C3N4) has been realized by means of the photocatalytic process, the catalytic activity of pristine g-C3N4 is still restricted by the rapid charge recombination and inadequate exposure of the active site. In this work, we propose a straightforward strategy to solve these limitations by decreasing the thickness and improving the crystallinity of g-C3N4, resulting in the preparation of few-layered crystalline carbon nitride (FL-CCN). Benefiting from the minimal thickness and highly ordered in-plane triangular cavities within the structure, FL-CCN processes an extended π-conjugated system with a reduced charge transfer resistance and expanded specific surface area. These features accelerate the efficiency of photogenerated charge separation in FL-CCN and contribute to explore of its surface active sites. Consequently, FL-CCN exhibits a significantly improved H2O2 evolution rate (63.95 µmol g-1 h-1), which is 7.8 times higher than that of pristine g-C3N4 (8.15 µmol g-1 h-1), during the photocatalytic conversion of O2 and H2O. This systematic investigation offers valuable insights into the mechanism of photocatalytic H2O2 generation and the development of efficient catalysts.

Z-scheme heterojunction photocatalyst formed by MOF-derived C-TiO2 and Bi2WO6 for enhancing degradation of oxytetracycline: Mechanistic insights and toxicity evaluation in the presence of a single active species.

In the work, Bi2WO6/C-TiO2 photocatalyst was successfully synthesized for the first time by loading narrow bandgap semiconductor Bi2WO6 on MOF-derived carboxyl modified TiO2. The phase structure, morphology, photoelectric properties, surface chemical states and photocatalytic performance of the prepared photocatalysts were systematically investigated using various characterization tools. The degradation efficiency of oxytetracycline by 6BT Z-scheme heterojunction photocatalyst under visible light could reach 93.6 % within 100 min, which was related to the high light harvesting and effective separation and transfer of photo-generated carriers. Furthermore, the effects of various environmental factors in actual wastewater were further investigated, and the results showed that 6BT exhibited good adaptability, durability and resistance to interference. Unlike most works, the degradation system with a different single active species were designed and constructed based on their formation mechanism. In addition, for the first time, a positive study was conducted on the priority attack sites, intermediate products, and degradation pathways for the photocatalytic degradation of oxytetracycline by a single active species through HPLC-MS and Fukui index calculations. The toxicity changes of intermediate products produced in three different single active species oxidation systems were evaluated using toxicity assessment software tools (T.E.S.T.), Escherichia coli growth experiments, and wheat growth experiments. Among them, the intermediate products formed through O2- oxidation had the lowest toxicity and the main active sites it attacked were the 20C, 38O, 18C, 41O, and 55O atoms with high f+ values in the oxytetracycline molecular structure. This work provided the insight into the role of each active species in the degradation of antibiotics and offered new ideas for the design and synthesis of efficient and eco-friendly photocatalysts.

Single atom supported on MXenes for the alkaline hydrogen evolution reaction: species, coordination environment, and action mechanism.

The electrochemical hydrogen evolution reaction (HER) in alkaline media provides an environmentally friendly industrial application approach to replace traditional fossil energy. The search for efficient, low-cost, and durable active electrocatalysts is central to the development of this area. Transition metal carbides (MXenes) have been emerging as a new family of two-dimensional (2D) materials that have great potential in the HER. Herein, density functional theory calculations are performed to systematically explore the structural and electronic properties and alkaline HER performances of Mo-based MXenes, as well as the influence of species and the coordination environment of single atoms on the improvement of the electrocatalytic activity of Mo2Ti2C3O2. The results show that Mo-based MXenes (Mo2CO2, Mo2TiC2O2, and Mo2Ti2C3O2) exhibit excellent H binding ability, while slow water decomposition kinetics hinders their HER performance. Replacing the O-terminal of Mo2Ti2C3O2 with a Ru single-atom (RuS-Mo2Ti2C3O2) could promote the decomposition of water owing to the stronger electron-donating ability of the atomic state Ru. In addition, Ru could also improve the binding ability of the catalyst to H by adjusting the surface electron distribution. As a result, RuS-Mo2Ti2C3O2 exhibits excellent HER performance with a water decomposition potential barrier of 0.292 eV and a H adsorption Gibbs free energy of -0.041 eV. These explorations bring new prospects for single atoms supported on Mo-based MXenes in the alkaline hydrogen evolution reaction.

Alkali-assisted engineering of ultrathin graphite phase carbon nitride nanosheets with carbon vacancy and cyano group for significantly promoting photocatalytic hydrogen peroxide generation under visible light: Fast electron transfer channel.

Exfoliating bulk graphite phase carbon nitride (g-C3N4) into 2D nanosheets is considered to be an effective method to enhance its photocatalytic activity. However, optical absorption capacity of the exfoliated g-C3N4 nanosheets are lower than that of the original bulk g-C3N4 due to the quantum size effect. Here, the ultrathin graphite phase carbon nitride nanosheets containing both carbon vacancy and cyano group (UCNS580) were prepared by two-step calcination in air with the assistance of KOH. The formation and position of carbon vacancy and cyano group were first investigated and determined. The simultaneous introduction of carbon vacancy and cyano group not only improved light absorption range and intensity of g-C3N4 nanosheets, but also more importantly constructed a fast transfer channel for photogenerated electrons, further enhancing the separation efficiency and migration ability of photogenerated carriers. The cyano group as the accumulation center of photogenerated electrons and the oxygen adsorption center increased the proportion of one-step two-electrons reaction path to efficiently generate H2O2. As a result, UCNS580 exhibited highly boosted H2O2 generation activity, its H2O2 production yield for 6 h reached 939 µmol/L and the formation rate was up to 4167 µM h-1 g-1, which was in priority in the reported literature under the same conditions.

In Situ Formation ZnIn2 S4 /Mo2 TiC2 Schottky Junction for Accelerating Photocatalytic Hydrogen Evolution Kinetics: Manipulation of Local Coordination and Electronic Structure.

Regulating electronic structures of the active site by manipulating the local coordination is one of the advantageous means to improve photocatalytic hydrogen evolution (PHE) kinetics. Herein, the ZnIn2 S4 /Mo2 TiC2 Schottky junctions are designed to be constructed through the interfacial local coordination of In3+ with the electronegative O terminal group on Mo2 TiC2 based on the different work functions. Kelvin probe force microscopy and charge density difference reveal that an electronic unidirectional transport channel across the Schottky interface from ZnIn2 S4 to Mo2 TiC2 is established by the formed local nucleophilic/electrophilic region. The increased local electron density of Mo2 TiC2 inhibits the backflow of electrons, boosts the charge transfer and separation, and optimizes the hydrogen adsorption energy. Therefore, the ZnIn2 S4 /Mo2 TiC2 photocatalyst exhibits a superior PHE rate of 3.12 mmol g-1 h-1 under visible light, reaching 3.03 times that of the pristine ZnIn2 S4 . This work provides some insights and inspiration for preparing MXene-based Schottky catalysts to accelerate PHE kinetics.

Enhanced nitrate reduction by metal deposited g-C3N4/rGO/TiO2 Z-schematic photocatalysts: Performance and mechanism comparison of Pd-Cu and Ag.

Deposition of bimetals on Z-scheme photocatalysts has been reported to improve the nitrate nitrogen (NO3-) reduction properties. However, it is not clear whether bimetal deposition possesses advantage over single metal deposition and what is the different reaction mechanisms. In this work, the g-C3N4(Pd-Cu)/rGO/TiO2 and g-C3N4(Ag)/rGO/TiO2 composites with bimetallic Pd-Cu and single metal Ag deposited on the graphitic carbon nitride/reduced graphene oxide/titanium dioxide (g-C3N4/rGO/TiO2) Z-scheme photocatalyst were prepared, and their photocatalytic NO3- reduction properties and the mechanisms under visible light irradiation were studied. The results showed that the NO3- and total nitrogen (TN) removal efficiencies of g-C3N4(Pd-Cu)/rGO/TiO2 were 57.78% and 20.1%, respectively, 1.15 and 1.72 times higher than those of g-C3N4(Ag)/rGO/TiO2. This can be ascribed to that Pd-Cu enriched more electrons and absorbed more NO3- molecules due to the different charge densities, and the NO3- reduction process were enhanced by the staged NO3-→NO2- and NO2-→N2/NH4+ processes on Cu and Pd. The effects of reductive species were demonstrated to be photogenerated electrons > ·OH (·CO2-) > ·O2- in g-C3N4(Ag)/rGO/TiO2, while it was photogenerated electrons > ·O2- > ·OH (·CO2-) in g-C3N4(Pd-Cu)/rGO/TiO2, which may be caused by the better O2 reduction property of the latter. Finally, the cyclic experiment proved the good stability of both materials. This work provided some reference for design of metal deposited Z-scheme photocatalysts for various reduction reactions.

Efficient elimination of nonylphenol and 4-tert-octylphenol by weak electrical stimulated anaerobic microbial processes.

The investigation into the degradation of alkylphenol pollutants (APs) has become a hotspot due to their harmful effects on the environment and human health. In this study, microbial electrolysis cells (MECs) were used to degrade nonylphenol (NP) and 4-tert-octylphenol (4-tert-OP). The study found that the degradation rates of NP and 4-tert-OP for a 6-day period were 83.6% and 96.3%, respectively, which were 30.53% and 26.7% higher than those of the group without applied voltage. The double layer area in the degradation of 4-tert-OP was larger than that of NP, and the resistance exhibited by 4-tert-OP (87.47 Ω) in MEC was lower than that of NP (99.42 Ω). Meanwhile, NP had a greater effect on the bioenzyme activity than 4-tert-OP. GC-MS analysis showed that the degradation pathways of both pollutants mainly included oxidation and hydroxylation reactions. Furthermore, the microbial community analysis indicated that the main functional bacteria in NP degradation were Citrobacter, Desulfovibrio and Advenella, and those in 4-tert-OP degradation were Stenotrophomonas, Chryseobacterium, Dokdonella, and the key microbiomes underlying the cooperative relationship. The biotoxicity test indicated that the toxicity of residual substances was significantly reduced. Therefore, the MEC system is efficient and environmentally friendly and has broad application prospects in phenol refractory organics.

Spatial variability and risk assessment of heavy metals in the soil surrounding solid waste from coking plants in Shanxi, China.

Heavy metal pollution in the soil surrounding solid wastes from coking plants poses potential threats to human health and has attracted widespread attention. This study is the first to assess the spatial variability and risks of heavy metals in the soil surrounding solid waste from coking plants. The results showed that the concentrations of Cu, Ni, Pb, and Cd in the soil were much higher than the background value of the soil. Solid waste had a clear influence on the contents of Ni, Cd, Mn, Pb, and Cr in the soil. The ecological risk assessment of heavy metal pollution demonstrated that the pollution degree of Cu, Pb, and Cd was more serious than others, and the ecological risk of heavy metals was mainly caused by Cd in the soil. The human health risk assessment showed that adults and children near coking plants might face carcinogenic risk from exposure to Cr. This study can provide a theoretical basis for the prevention and management of soil heavy metal pollution surrounding solid waste in coking plants.

Enhanced nonsacrificial photocatalytic generation of hydrogen peroxide under visible light using modified graphitic carbon nitride with doped phosphorus and loaded carbon quantum dots: Constructing electron transfer channel.

The photocatalytic production of H2O2 by graphite-phase carbon nitride (g-C3N4) using water and oxygen is a promising and sustainable method. Nevertheless, the yield of H2O2 produced by the pristine g-C3N4 is still far from satisfactory owing to limited optical absorption, rapid photogenerated electron-hole recombination and poor surface electron migration. Therefore, p-P1CN/CQDs25 was designed and synthesized by doping phosphorus (P) and loading carbon quantum dots (CQDs) to modify porous g-C3N4 (p-CN) via a facile method. Herein, P acted as an electron transfer bridge to induce electrons into CQDs, while CQDs acted as an electron trapping material to capture and stabilize photogenerated electrons. Moreover, CQDs could enhance their optical absorption due to its unique optical properties. Notably, p-P1CN/CQDs25 presented highly boosted H2O2 generation activity, its H2O2 production yield for 5 h was up to 494 µM/L and the formation rate constant Kf in the first hour was 238 µM h-1 without adding sacrificial agents and without bubbling oxygen under visible light, which took precedence among the reported results under the same conditions. It should be noted that the composite p-P1CN/CQDs25 also possessed low H2O2 decomposition behavior based on the effect of CQDs stabilizing electrons. In addition, the possible mechanism of photocatalytic H2O2 generation for p-P1CN/CQDs25 was also proposed. Our research provided a new idea for the design of novel photocatalysts to efficient generation of H2O2.

Efficient visible-light-driven degradation of tetracycline by a 2D/2D rGO-Bi2WO6 heterostructure.

Constructing heterostructures has been a simple yet effective strategy for improving the photocatalytic performance of individual semiconductor photocatalysts. However, the poor quality of the contacted interface coupled with the narrow and overlapping light absorption scope between heterocomponents limits potential improvement. Herein, a 2D/2D rGO-Bi2WO6 heterostructure with face-to-face compact contact interface and UV to NIR light absorption ability was synthesized to overcome the aforementioned limitations. The as-prepared 2 wt%-rGO-Bi2WO6 with a high contact interface quality exhibits the highest kinetic rate of (5.53 ± 0.75) × 10-2 L mg-1 min-1 toward tetracycline (TC) degradation, which is 2.4 times higher than that of pristine Bi2WO6 and 2.1 times higher than that of the 2 wt%-rGO-Bi2WO6 composite with a poor interface quality. Moreover, approximately 30% of TC can be mineralized with a 2 wt%-rGO-Bi2WO6 presented system after 120 min. The subsequent Escherichia coli culture and liquid chromatography-mass spectrometry were employed to detect the biotoxicity variation of degradation intermediates and the possible transformation pathways of TC, respectively. Finally, the reactive species trapping results indicate that photogenerated holes and superoxide radical anions play dominant roles during the TC degradation process. This work provides a facile and effective method to fabricate an efficient heterojunction photocatalyst for pollutant degradation.

Two-dimensional/two-dimensional heterojunction-induced accelerated charge transfer for photocatalytic hydrogen evolution over Bi5O7Br/Ti3C2: Electronic directional transport.

Regulating electron density at the active site by electronic directional transport from special channels is an effective strategy to accelerate the reaction rate in photocatalytic water splitting. Here, a novel two dimensional/two dimensional (2D/2D) Bi5O7Br/Ti3C2 heterojunction with special interfacial charge transfer channel was fabricated successfully via in-situ growth of Bi5O7Br on the surface of ultrathin Ti3C2 by using a convenient hydrolysis method. The electrostatic attraction between Bi3+ cations and electronegative Ti3C2 ensures the construction of 2D/2D heterojunction and a strong intimate interface contact between Ti3C2 and Bi5O7Br, which establishes an electronic transport channel, and shortens the charge transport distance, assuring excellent bulk-to-surface and interfacial charge transfer abilities. Meanwhile, X-ray photoemission spectroscopy (XPS) and density functional theory (DFT) calculation revealed that the local electron density at the Ti3C2 active sites is remarkably increased because of the transfer of interfacial electrons from Bi5O7Br to Ti3C2, which is a key factor for enhancing the photocatalytic performance. Thus, the resultant Bi5O7Br/Ti3C2 exhibits significant improvement on the performance of photocatalytic hydrogen evolution under visible light irradiation. The hydrogen evolution reaction rate obtained on the optimized Bi5O7Br/Ti3C2 composite is 1.97 times higher than that of pristine Bi5O7Br. This work provides a new protocol for the construction of 2D/2D heterojunction photocatalytic systems and regulating electron density by electronic directional transporting.

Mechanism, electrochemistry and biotoxicity analysis of the biodegradation of sulfadiazine on Nickel(â ¡)/Manganese(â ¡)-modified graphite felt bioanode.

Sulfadiazine (SDZ) is one of the most representative sulfonamides antibiotics, and its biodegradation has become a research hotspot in recent years. The present study innovatively adopted a microbial fuel cells with a Nickel (Ⅱ) and Manganese (Ⅱ)-decorated graphite felt bioanode (Ni(Ⅱ)/Mn (Ⅱ)-MFCs) to remove SDZ. The results demonstrated that the Ni(Ⅱ)/Mn (Ⅱ)-MFCs exhibited improved electrochemical performance, with a higher power density (742.98 ± 58.33 mW/m2) compared to the control MFCs (678.34 ± 52.87 mW/m2), an overall lower anode potential, and a larger double layer area (cyclic voltammetry). After 5 months of operation, approximately 97.95% of 30 mg/L SDZ was degraded within 120 h, which was 11.46% higher than that of the control MFCs. Moreover, SDZ and its byproducts could be better mineralized in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs than the control, and the biotoxicity of SDZ towards Escherichia coli and Vibro qinghaiensis sp. Q67 could be greatly decreased after treatment with the modified MFCs. Based on the metabolites, we hypothesized that the chemical reactions hydroxylation, ammoxidation, SO2-extrusion, sulfur-reduction, etc. played a significant role in SDZ biodegradation. A microbial community analysis revealed that Dechloromonas (2.37%), Denitratisoma (5.32%) and Lentimicrobium (26.35%) were the dominant functional microbes in the Ni(Ⅱ)/Mn (Ⅱ)-MFCs. This study may provide insights and a theoretical basis for the biodegradation of sulfonamides and thus may facilitate further investigations and relevant findings.

Elucidating the microbial ecological mechanisms on the electro-fermentation of caproate production from acetate via ethanol-driven chain elongation.

Electro-fermentation (EF) is an attractive way to implement the chain elongation (CE) process, by controlling the fermentation environment and reducing the dosage of external electron donors (EDs). However, besides the coexistence performance of external EDs and electrode, applications of EF technology on the fermentation broth containing both EDs and electron acceptors during CE process, are all still limited. The current study investigated the contribution of EF to caproate production, under different acetate: ethanol ratios (RA/E). The effect of multiple EDs, both from ethanol and the bio-cathode, on caproate production, was also assessed. A proof-of-concept, based on experimental data, was presented for the EF-mediated ethanol-driven CE process. Experimental results showed that ethanol, together with the additional electron donors from the bio-cathode, was beneficial for the stable caproate production. The caproate concentration increased with the decrease of RA/E, while the bio-cathode further contributed to 10.7%-26.1 % increase of caproate concentration. Meanwhile, the hydrogen partial pressure tended to 0.10 ± 0.01 bar in all controlled EF reactors, thus favoring caproate production. This was attributed to the increased availability EDs, i.e., hydrogen and ethanol, generated by the electrode and electrochemically active bacteria (EAB), which might create multiple additional pathways to achieve caproate production. Molecular ecological networks analysis of the key microbiomes further revealed underlying cooperative relationships, beneficial to the chain elongation process. The genus Clostridium_sensu_stricto, as the dominant microbial community, was positively related to acetogens, EAB and fermenters.

Ammonia-nitrogen removal from water with gC3N4-rGO-TiO2 Z-scheme system via photocatalytic nitrification-denitrification process.

Photocatalytic removal of NH3-N is expected to be an alternative to the biological method that accompanied with high energy consumption and secondary pollution. However, NH3-N is always oxidized into nitrate and nitrite during the photocatalytic processes, which also need to be removed from the water. Herein, the g-C3N4/rGO/TiO2 Z-scheme photocatalytic system was prepared and used for the NH3-N removal. The results showed the rate constant of NH3-N conversion on it was 0.705 h-1, 1.7 times as high as that on g-C3N4/TiO2, and most of the NH3-N were converted into gaseous products. And the experiment result indicated NH3-N and NO3- in water could enhance the removal of each other. According to the results, the main reaction mechanism is speculated as: ·OH radicals and ·O2- radicals were generated on TiO2 and oxidized the NH3-N into NO3-, and the latter was reduced into non-toxic N2 on the conduction band of g-C3N4. Finally, NH3-N removal performance for actual coking wastewater was investigated, and the stability of the photocatalyst was tested. This work provides some theoretical basis for the two-step degradation of pollutants by Z-scheme photocatalytic system.

Mini art review for zero valent iron application in anaerobic digestion and technical bottlenecks.

Zero valent iron (ZVI) has been used extensively to control environmental pollution owing to its strong reducibility and low cost. Herein, we evaluate the impact of ZVI (iron scrap and ZVI powder with different scales) on anaerobic digestion (AD) reactor performance improvement and syntrophic relationship stimulation among various microbial groups in the methanogenesis process. In recent studies, ZVI addition significantly enhanced methane and volatile fatty acid (VFA) yields and alleviated excessive acidification, ammonia accumulation, and odorous gas production. Further, we reviewed the changes in enzyme activity and microbial metabolism after the addition of ZVI throughout the reaction process. Certain innovative technologies, such as bioelectrochemical system assistance and combined usage of conductive materials, may improve AD performance compared to the use of ZVI alone, the mechanism of which has been discussed from various viewpoints. Furthermore, the primary technical bottlenecks, such as poor mass transfer efficiency in dry AD and high ZVI dosage, have been illustrated, and syntrophic methanogenesis regulated by ZVI addition can be further studied by conducting theoretical research.

Fabrication of ternary AgBr/BiPO4/g-C3N4 heterostructure with dual Z-scheme and its visible light photocatalytic activity for Reactive Blue 19.

A plasmonic photocatalyst of AgBr/BiPO4/g-C3N4 was prepared. X-ray powder diffraction, Scanning electron microscope, Transmission electron microscopy, Fourier infrared spectroscopy, Ultraviolet Visible diffuse reflectance spectroscopy and photoluminescence emission spectra have been employed to determine the structure, morphology and optical property of the as-prepared AgBr/BiPO4/g-C3N4 composite and analysis the reasons for improving photocatalytic efficiency. The optimal doping ratio of AgBr was 10 wt% by degrading 20 mg/L of Reactive Blue 19 (RB19) under visible light (λ > 420 nm), and 10 wt%AgBr/BiPO4/g-C3N4 degraded 20 mg/L of RB19 to 2.59% at 40 min, which is ascribed to synergistic effects at the interface of AgBr, BiPO4 and g-C3N4. The effect of catalyst dosage, initial concentration and initial pH of RB19 solution on photocatalytic efficiency was investigated. Four cycles of experiments were conducted. Finally, through the trapping experiment, we found that the main active factor for degrading RB19 in the photocatalytic process is O2-. The possible photocatalytic mechanism of AgBr/BiPO4/g-C3N4 was discussed in connection with the synergistic effect of Ag and active substances at the AgBr/BiPO4/g-C3N4 interface.

Photocatalytic reduction of Cr(VI) by WO3@PVP with elevated conduction band level and improved charge carrier separation property.

Photocatalytic reduction of heavy metal ions is a green and promising technology which requires electrons with enough negative energy levels as well as efficient separation property from photo-generated holes of photocatalysts. For WO3, the low conduction band edge and the severe photo-generated charge carrier recombination limited its application in photocatalytic reduction of pollutants. In this work, we prepared WO3@PVP with PVP capped WO3 by a simple one-step hydrothermal method, which showed an elevated energy band structure and improved charge carrier separation property. XRD, SEM, TEM, XPS, DRS, and the photocurrent density test were carried out to study the properties of the composite. Results demonstrated monoclinic WO3 with a size of ∼100-250 nm capped by PVP was obtained, which possessed fewer lattice defects inside but more defects (W5+) on the surface. Moreover, the results of the photocatalytic experiment showed the kinetic constant of Cr(VI) reduction process on WO3@PVP was 0.532 h-1, which was 3.1 times higher than that on WO3 (0.174 h-1), demonstrating WO3@PVP with good photocatalytic capability for Cr(VI) reduction. This can be attributed to the improved charge carrier separation performance, the improved adsorption capacity and the elevated conduction band edge of WO3@PVP. More importantly, the energy band structure of WO3@PVP was proved elevated with a value as high as 1.14 eV than that of WO3 nanoparticles, which enables WO3@PVP a promising material in the photocatalytic reduction reaction of heavy metal ions from wastewater.

Uncovering the Key Role of the Fermi Level of the Electron Mediator in a Z-Scheme Photocatalyst by Detecting the Charge Transfer Process of WO3-metal-gC3N4 (Metal = Cu, Ag, Au).

Z-scheme photocatalytic system shows superiority in degradation of refractory pollutants and water splitting due to the high redox capacities caused by its unique charge transfer behaviors. As a key component of Z-scheme system, the electron mediator plays an important role in charge carrier migration. According to the energy band theory, we believe the interfacial energy band bendings facilitate the electron transfer via Z-scheme mechanism when the Fermi level of electron mediator is between the Fermi levels of Photosystem II (PS II) and Photosystem I (PS I), whereas charge transfer is inhibited in other cases as energy band barriers would form at the semiconductor-metal interfaces. Here, this inference was verified by the increased hydroxyl radical generation and improved photocurrent on WO3-Cu-gC3N4 (with the desired Fermi level structure), which were not observed on either WO3-Ag-gC3N4 or WO3-Au-gC3N4. Finally, photocatalytic degradation rate of 4-nonylphenol on WO3-Cu-gC3N4 was proved to be as high as 11.6 times than that of WO3-gC3N4, further demonstrating the necessity of a suitable electron mediator in Z-scheme system. This study provides scientific basis for rational construction of Z-scheme photocatalytic system.