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This work synthesized a novel CuS/KTa0.75Nb0.25O3 (KTN) heterojunction composite and firstly applied it in photocatalytic and piezocatalytic reduction of N2 to NH3. XRD, Raman, XPS, SEM, and TEM analyses indicate that CuS nanoparticles closely adhered to the surface of KTN nanorods, which facilitates the migration of electrons between the two semiconductors. Mott-Schottky and valence band XPS analysis shows that KNbO3 shows a higher conduction band than CuS, indicating that CuS mainly acts as electron trappers to capture the photogenerated electrons from KTN. Because of the great enhanced spatial separation of photogenerated charge carriers, the CuS/KTN presents much higher performance than pure KNT, which is further confirmed by 1H NMR analysis of the reaction solution. An interesting finding is that synthesized CuS/KTN not only performs well under light irradiation but also can work in an ultrasonic bath, indicating its great potential in photo/piezocatalytic conversion of N2 to NH3. The optimal 10 %CuS/KTN shows an NH3 production rate of 36.2 μmol L−1 g−1 h−1 under ultrasonic vibration, which reaches 7.4 times that of KTN. The electrons generated by KTN through the piezoelectric effect can be captured by CuS, which endows the electrons a longer life to participate in the reaction, thereby improving the catalytic reaction performance.

This work was designed to prepare a novel NiS/KNbO3 p-n heterojunction composite for efficient photocatalytic nitrogen fixation under simulated sunlight. The NiS/KNbO3 photocatalyst was prepared through a two-step hydrothermal method. X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analyses proved that NiS nanoparticles were closely decorated on the surface of KNbO3 nanorods, to facilitate the migration of electrons between the two semiconductors. Mott-Schottky analysis indicated that the Femi level of KNbO3 is higher than that of NiS. Thus, the electron migration from KNbO3 to NiS occurs naturally. This migration elevates the band potential of NiS, makes NiS/KNbO3 form a type-II photocatalyst, and generates an internal electric field in the composite. The synergetic effect of the internal electric field and the type-II band structure endows NiS/KNbO3 with high efficiency in the spatial separation of photogenerated electron-hole pairs, verified by electrochemical impedance spectroscopy and transient photocurrent experiments. Therefore, NiS/KNbO3 presents good efficiency in photocatalytic N2 reduction with an NH3 production rate of 155.6 μmol·L−1·g−1·h−1, which is 1.9 and 6.8 times higher than those of KNbO3 and NiS, respectively. UV–visible diffuse reflectance spectroscopy and N2-adsorption experiments were also performed to investigate the effect of light absorption and surface area on the photocatalytic reaction. Nevertheless, compared with the great promotion effect in charge separation, the contribution of the two factors can be ignored.

The transformation of CO2 into cyclic carbonates via atom-economical cycloadditions with epoxides has recently attracted tremendous attention. On one hand, though many heterogeneous catalysts have been developed for this reaction, they typically suffer from disadvantages such as the need for severe reaction conditions, catalyst loss, and large amounts of soluble co-catalysts. On the other hand, the development of heterogeneous catalysts featuring multiple and cooperative active sites, remains challenging and desirable. In this study, we prepared a series of porous organic catalysts (POP-PBnCl-TPPMg-x) via the copolymerization metal-porphyrin compounds and phosphonium salt monomers in various ratios. The resulting materials contain both Lewis-acidic and Lewis-basic active sites. The molecular-level combination of these sites in the same polymer allows these active sites to work synergistically, giving rise to excellent performance in the cycloaddition reaction of CO2 with epoxides, under mild conditions (40 °C and 1 atm CO2) in the absence of soluble co-catalysts. POP-PBnCl-TPPMg-12 can also efficiently fixate CO2 under low-CO2-concentration (15% v/v N2) conditions representative of typical CO2 compositions in industrial exhaust gases. More importantly, this catalyst shows excellent recyclability and can easily be separated and reused at least five times while maintaining its activity. In view of their heterogeneous nature and excellent catalytic performance, the obtained catalysts are promising candidates for the transformation of industrially generated CO2 into high value-added chemicals.

This work synthesized a novel Ag2S/K-g-C3N4 photocatalyst which was effective in photocatalytic hydrogen production under simulated sunlight and visible light. Systematic investigation including TG, XRD, FT-IR, DRS, XPS, N2-adsorption, SEM, TEM, PL, and photoelectrochemical analyses was executed to examine the structure, optical property and charge separation efficiency of the as-prepared photocatalysts. Result indicated that potassium was successfully doped into the g-C3N4 framework via direct heating the mixture of melamine and potassium iodide at 520 °C, which increases the BET surface area, broadens the visible light response region, and elevates the separation efficiency of electron-hole pairs. The modification of Ag2S nanoparticles on the optimal K-g-C3N4 sample further improves the surface charge separation efficiency via a type-II mechanism, which was believed to be the key role in photocatalytic reaction. The best Ag2S/K-g-C3N4 hybrid shows a photocatalytic H2 generation rate of 868 and 96 μmol·g−1·h−1 under simulated sunlight and visible light, respectively. This value is 2.7 and 1.3 times greater than that of g-C3N4 and K-g-C3N4, respectively. Meanwhile, the Ag2S/K-g-C3N4 displayed high photocatalytic stability. A probable mechanism of the synthesized photocatalyst was also suggested.

Photocatalysis and photoelectrocatalysis have been recognized as promising strategies to simultaneously address energy crisis and environmental pollution. Semiconductor-based photocatalysts and photoelectrocatalysts often suffer from shortcomings including the serious recombination of photogenerated charge carriers and sluggish kinetics of surface reaction, which can be overcome by the surface modification with suitable cocatalysts. Nevertheless, it is often difficult to simultaneously achieve all the good characteristics of an ideal cocatalyst with a single-component material. Thus, hybrid nanostructures consisting of different components have been fabricated as robust cocatalysts, which compensate the disadvantages of mono-component cocatalysts and produce synergistic effects for improved photocatalytic and photoelectrochemical (PEC) performance. In this review, the developments of hybrid cocatalysts over semiconductor-based photocatalysis and photoelectrocatalysis are described. The functions and architectures of hybrid cocatalysts are also discussed, and the synergistic principles of different components in these cocatalysts are elucidated. Furthermore, the applications of hybrid cocatalysts in various photocatalytic/PEC reactions are summarized and finally, the remaining challenges and future perspectives of hybrid cocatalysts are also presented.

This paper reports the synthesis of a NiO loaded KNbO3 nanocomposite via a photodeposition method and its application in photocatalytic N2 fixation for the first time. Results indicated that the NiO/KNbO3 composite displayed superior photocatalytic efficiency in NH3 production under simulated sunlight illumination. The optimal NiO/KNbO3 sample showed an NH3-generation rate of 470.6 μmol g−1 h−1, which reaches 4.8 times that of pristine KNbO3. Various characterization techniques including powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflection spectroscopy (DRS), transient photocurrent, electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) were applied to reveal the mechanism behind the high photoactivity of NiO/KNbO3. The addition of NiO nanoparticles showed a slight effect on the specific surface area and the optical properties of KNbO3, but elevated the charge separation efficiency which was verified to be the key role in affecting the photocatalytic reaction. The introduced NiO fabricated a p–n heterojunction structure with KNbO3 and hence achieved enhanced efficiency in separating electrons and holes via a type-II mechanism. The cycling test further demonstrated that the NiO/KNbO3 sample has high photocatalytic stability, indicating its good potential in photocatalytic nitrogen fixation.

Large-scale production of H2 through water electrolysis is limited by the lack of efficient and crust-abundant low-cost electrocatalysts. Here, MoSe2 and N-doped carbon (NC) is successfully constructed into a double-shelled hierarchical hollow nanobox. The obtained NC@MoSe2 is demonstrated to be an active catalyst for hydrogen evolution reaction (HER). The NC@MoSe2 delicately combine the structural and functional advantages of two-dimensional layered transition metal dichalcogenides (TMDs) and NC, which yield the striking synergistic effect to endow them with extremely enhanced electrochemical activity to efficiently catalyze the evolution of H2. Remarkably, the NC@MoSe2 with the optimum thickness of MoSe2 shell can exhibit a fairly low onset potential of 61 mV, an extremely small overpotential of 164 mV vs. RHE at 10 mA cm−2, a greatly reduced Tafel slope of 55 mV dec−1, and a higher exchange current density of 0.102 mA cm−2. Specifically, this is mainly beneficial from the abundant exposed active edges from the edge-terminated ultrathin MoSe2 nanosheets with small size, the overall hierarchical hollow architecture and strong electronic coupling between MoSe2 and NC layer. Density functional theory (DFT) calculation results have well supported the experimental observations, revealing the strong synergistic effect between NC and MoSe2, thus the increased carrier density around the Fermi level and reduced hydrogen adsorption free energy (ΔGH*) for MoSe2 composited with NC.

Novel SnSe/g-C3N4 photocatalysts were one-step synthesized via a microwave heating assisted process in 35 min with SnSe and melamine as precursors. The as-synthesized SnSe/g-C3N4 worked very well in H2 evolution via photocatalysis. Under simulated sunlight, the best SnSe/g-C3N4 sample displayed a H2-production velocity of 1064 μmol g−1 h−1, which is 1.8 folds faster than that of neat g-C3N4. Similar promotion effect was also observed under visible light. To reveal the nature behind the high photoactivity, a thorough investigation was performed. XRD and XPS experiments proved the binary constitution of the composite. DRS experiment demonstrated that the addition of SnSe improved the photoabsorption performance. N2-adsorption analysis showed that the SnSe/g-C3N4 photocatalyst presented similar surface area as g-C3N4. TEM experiments showed that some bulk SnSe were spontaneously decomposed to nanoparticles and finely dispersed in g-C3N4 during the microwave heating process. These SnSe nanoparticles were believed to be the active phase and constructed a heterojunction structure with g-C3N4, resulting in the enhanced charge separation. This conclusion was considered as the key factor leading to the high H2-evolution performance and was further confirmed by the PL, EIS, and PC experiments. The present work provides a feasible and rapid method for the construction of g-C3N4 based photocatalysts.

The present work reports a novel CdS/KTa0.75Nb0.25O3 (KTN) composite photocatalyst which was synthesized via a facile deposition method. The photocatalytic reaction in Na2S solution indicated that the as-synthesized composite presented excellent performance in water splitting under simulated sunlight and visible light. A thorough investigation was performed to reveal the origin of the high performance. X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) experiments proved that CdS nanopartilces were uniformly dispersed on the surface of KTN naocubes. UV–visible diffuse reflection spectroscopy (DRS) analysis indicated that the addition of CdS improved the ability to absorb visible light. N2-adsorption analysis showed that the difference in surface area of the CdS/KTN composites was very small. Photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and transient photocurrent response (PC) analyses suggested that the added CdS greatly elevated the charge separation efficiency, which was considered as the key character of the composite. On the basis of the characterization results and the band structure of the two semiconductors, it is deduced that the CdS/KTN composite works according to a type-II mechanism under simulated sunlight. The optimal sample demonstrated a H2-generation rate of 1252 μmol·g−1·h−1, which is 260 and 48 times higher than that of KTN and CdS, respectively. Under visible light, photosensitization mechanism works in the composite. The synergetic effect of CdS and KTN in H2 production was also observed. Meanwhile, the composite also presented high photocatalytic stability. Considering the high activity and stability, the CdS/KTN may have potential application in photocatalytic H2 generation.

A novel KTa0.75Nb0.25O3 (KTN)/g-C3N4 composite photocatalyst was fabricated through microwave heating for realizing the efficient photocatalytic H2 evolution. The energy-efficient preparation method allowed g-C3N4 to be formed in-situ on KTN surface in thirty five minutes. The binary constitution of the KTN/g-C3N4 composite was verified by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. UV–visible diffuse reflection spectroscopy (DRS) experiments suggested that the photoabsorption performance was increased after the introduction of KTN. N2-adsorption analysis indicated that the addition of KTN slightly increased the surface area of g-C3N4. Photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS) and transient photocurrent response (PC) analyses confirmed that the KTN/g-C3N4 composite displayed longer lifetime of photoexcited charge carriers than g-C3N4, owing to the suitable band potentials and the close contact of KTN and g-C3N4. This property was believed to the key characteristic of the composite, which led to its excellent photocatalytic performance. Under simulated sunlight irradiation, the optimal KTN/g-C3N4 catalyst presented a photocatalytic H2-generation rate of 1673 μmol·g−1·h−1, 2.5 and 2.4 times higher than that of KTN and pure g-C3N4, respectively. Under visible light irradiation, the value was determined to be 86.2 μmol·g−1·h−1, which achieved 9.3 times that of g-C3N4.

This work synthesized a novel CuS/KTa

This work was designed to prepare a novel NiS/KNbO

This paper is designed for elevating the photocatalytic H2-evoultion performance of g-C3N4 through the modification of AgNbO3 nanocubes. Via the microwave heating method, g-C3N4 was in-situ formed on AgNbO3 surface to fabricate a close contact between the two semiconductors in forty minutes. X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) experiments were performed to confirm the binary structure of the synthesized AgNbO3/g-C3N4 composite. N2-adsorption and visible diffuse reflection spectroscopy (DRS) analyses indicated that the addition of AgNbO3 to g-C3N4 showed nearly negligible influence on the specific surface area and the optical property. Photoluminescence (PL) spectroscopy experiment suggested that the AgNbO3/g-C3N4 displayed reduced PL emission and longer lifetime of photoexcited charge carriers than g-C3N4, which could be ascribed to the suitable band potential and the intimate contact of g-C3N4 and AgNbO3. This result was also confirmed by the transient photocurrent response experiment. The influence of the enhanced charge separation was displayed in their photocatalytic reaction. AgNbO3/g-C3N4 sample showed enhanced performance in photocatalytic H2-generation under visible light illumination. The H2-evolution rate is determined to be 88 μmol·g−1·h−1, which reaches 2.0 times of g-C3N4. This study provides a feasible and rapid approach to fabricate g-C3N4 based composite.

This work was designed to synthesize an efficient photocatalyst for photocatalytic H2 evolution via the decoration of carbon on an optimal KTa1−xNbxO3 solid solution. The C/KTa1−xNbxO3 composite was fabricated via a two-step hydrothermal process, and investigated by various techniques, including N2 adsorption, X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy(TEM), X-ray photoelectron spectroscopy (XPS), UV − vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), transient photocurrent response (PC) an electrochemical impedance spectroscopy (EIS). The catalytic performance of the composite was investigated via photocatalytic H2 evolution and rhodamine B (RhB) degradation under irradiation of simulated sunlight. Results indicate that the formation of KTa1−xNbxO3 solid solution improves the bulk charge separation, and consequently leads to the high photocatalytic activity. KTa0.75Nb0.25O3 solid solution presents the fastest rate for H2 evolution. The loading of a thin carbon layer on the KTa0.75Nb0.25O3 nanocube can further fasten the process. The optimal composite sample displays a H2 evolution rate of 1776 μmol·g−1·h−1, which is 2.44 and 9.40 times that of KTa0.75Nb0.25O3 and KTaO3, respectively. The load carbon thin layer enhances the surface area and hinders the surface charge recombination via trapping the electrons, which is believed to be the main reason for the excellent performance. Additionally, the synthesized C/KTa0.75Nb0.25O3 composite also presents good photoactivity in RhB degradation. This work affords a practical approach for the design and preparation of highly efficient photocatalysts via bulk doping and surface modification simultaneously.

This paper was designed to realize the efficient photoreduction of N2 to NH3 over a novel ternary MoS2/C-ZnO composite which was prepared via a combination of hydrothermal and photodeposition methods. The as-prepared composite was characterized by multiple techniques including X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption, transient photocurrent response (PC), and electrochemical impedance spectroscopy (EIS). The obtained results indicated that carbon was not doped into the ZnO lattice but loaded on the surface of ZnO and acted as an electron trapper to hamper the recombination of charge carriers. The thermal treatment of C-ZnO can modify the carbon content and thus improves the charge separation efficiency. The optimal calcination temperature is determined to be 300 °C. Photodeposition of MoS2 nanoparticles on the C-ZnO-300 sample can further i...

Photocatalytic conversion of CO2 into CH4 represents an appealing approach to alleviate the world's continued reliance on fossil fuels and global warming resulting from increasing CO2 concentrations in the atmosphere. However, its practical application is greatly limited by serious electron-hole recombination in the photocatalysts and the production of CO and H2 as side reactions. Herein, for the first time, it is demonstrated that the photocatalytic reduction of CO2 to CH4 can be significantly improved through the simultaneous alloying and hydriding of metal cocatalysts. The isolation of Cu and H atoms in Pd lattices play three roles in the enhancement of CO2 to CH4 conversion: 1) Cu atoms provide catalytic sites to reduce CO2 into CO and then to CH4 to suppress H2 evolution; 2) H atoms improve the electron-trapping ability of cocatalysts; and 3) H atoms accelerate the reduction of CO to CH4 , which is the rate-limiting procedure in the conversion of CO2 into CH4 . Arising from the synergistic interplay between Pd-H and Cu-CO sites, C3 N4 -Pd9 Cu1 Hx (15 mg) achieves 100 % selectivity for CH4 production with an average rate of 0.018 μmol h-1 under visible-light irradiation. This work provides insights into the design of a cocatalyst for highly selective CO2 conversion through lattice engineering at atomic precision.

Photocatalytic conversion of CO2 to value-added fuels, a promising route to address the depletion of fossil fuels and concomitant global warming, can be improved by cocatalysts through promoting the electron-hole separation and offering catalytic active sites for the surface reactions. However, the enhancement of the photocatalytic performance is greatly determined by the surface and interface structures of cocatalysts. Herein, for the first time, we demonstrate that the photocatalytic activity in the CO2 reduction can be optimized through crystalline phase design of cocatalysts. In this work, Ru nanocrystals in face-centered cubic (fcc) and hexagonal close-packed (hcp) phases are in-situ grown on C3N4 nanosheets to form different C3N4-Ru hybrid structures, respectively. It was found that the hcp Ru achieved higher average CO and CH4 production rate but lower H2 production rate in comparison with fcc Ru. As revealed by the experimental characterizations combined with theory simulations, the phase-dependent photocatalytic performance is resulted from the different surface reaction behaviors on the fcc and hcp Ru cocatalysts. The adsorption energy of CO2 molecules on the dominated (10 1 ¯ 1) face of hcp Ru is higher than that on the dominated (111) face of fcc Ru. As a result, the stronger interaction between CO2 molecules and the surface of hcp Ru contributes to the enhanced photocatalytic activity and selectivity of C3N4-hcp Ru in reduction of CO2. This work highlights the importance in the crystalline phase engineering in cocatalyst for enhanced CO2 photoreduction.

Carbon-doped KNbO3 photocatalyst was synthesized for the first time via a simple combination of hydrothermal and post-calcination processes with glucose as the carbon source. The synthesized sample had excellent performance in photocatalytic hydrogen production under simulated sunlight. Various techniques were applied to investigate the origin of the extraordinary photocatalytic activity. X-ray diffraction and Ar+ sputtering X-ray photoelectron spectroscopy analyses proved that carbon atom was successfully doped into the lattice of KNbO3. Scanning electron microscopy and N2 adsorption analysis indicated that the particle size of KNbO3 was decreased due to the doping of carbon, which resulted in the increase of the BET surface area. UV–vis diffuse reflectance spectroscopy experiment verified that the carbon doping extended the light absorption region to visible light. Both the changes in surface area and optical property are beneficial to the photocatalytic reaction. However, the stronger H2 generation rate of carbon-doped KNbO3 was mostly attributed to the enhanced separation efficiency of electron-hole pairs due to the presence of carbon dopant. The promotion effect is closely correlated with the content of carbon dopant. C-KNbO3 sample calcined at 350 °C displayed the highest hydrogen generation rate of 211 μmol g−1 h−1, which is 42 times higher than that of pure KNbO3. Additionally, the synthesized carbon-doped KNbO3 also presented good photoactivity under visible-light illumination. This study provides a feasible way for the synthesis of other similar photocatalysts with high efficiency.

A AgBr/DyVO4 composite photocatalyst was synthesized by a hydrothermal method for the first time. The physical and chemical structure and optical properties of the composite catalysts were investigated by XRD, XPS, SEM, TEM and UV–Vis. It was found that the prepared photocatalyst is a ternary composite of DyVO4, AgBr and Ag. A photodegradation experiment and a cyclic test verified that the composite catalyst has high activity and stability, indicating that the photocatalyst has a wide application potential. The optimal AgBr/DyVO4 sample can degrade 85% of RhB (20 ppm) under visible light irradiation for 12 min. The degradation rate reaches 0.290 min−1, which is 14.5 times higher than that of AgBr. The high activity can be ascribed to the coupling effect between AgBr, DyVO4 and Ag, which leads to high separation efficiency of electrons and holes.

Simulation of randomly rough bioparticle surface is crucial to better understand and control interface behaviors and membrane fouling. Pursuing literature indicated a lack of effective method for simulating random rough bioparticle surface. In this study, a new method which combines Gaussian distribution, Fourier transform, spectrum method and coordinate transformation was proposed to simulate surface topography of foulant bioparticles in a membrane bioreactor (MBR). The natural surface of a foulant bioparticle was found to be irregular and randomly rough. The topography simulated by the new method was quite similar to that of real foulant bioparticles. Moreover, the simulated topography of foulant bioparticles was critically affected by parameters correlation length (l) and root mean square (σ). The new method proposed in this study shows notable superiority over the conventional methods for simulation of randomly rough foulant bioparticles. The ease, facility and fitness of the new method point towards potential applications in interface behaviors and membrane fouling research.

This paper was designed for the first time to improve the photocatalytic activity of KNbO3 via carbon doping and MoS2 decoration simultaneously. The efficient photocatalytic hydrogen production was realized on the MoS2/C-KNbO3 composite under simulated sunlight irradiation in the present of methanol and chloroplatinic acid. The optimal composite presents a H2 production rate of 1300 μmol·g−1·h−1, which reaches 260 times that of pure KNbO3. Characterization results of the synthesized composite indicates that the introduction of a small amount of carbon into the KNbO3 lattice greatly hinders the recombination of electron-hole pairs. The decoration of MoS2 further induces the separation of charge carriers via trapping the electron in the conduction band of C-KNbO3, which is proven by the EIS and transient photocurrent response analyses. The remarkably enhanced separation efficiency of electron-hole pairs is believed to be the origin of the excellent photocatalytic performance, though other changes in surface area and optical property may also contribute the photocatalytic process. This study provides a feasible way for the design and preparation of novel photocatalysts with high efficiency.

High-performance KNbO3/g-C3N4 composite was prepared via a feasible method and first applied in photocatalytic H2 production from water–methanol solution under irradiation of visible light. The structure and optical property of the synthesized composite were investigated by various techniques, including XRD, XPS, FT-IR, TEM, SEM, DRS, PL, and an electrochemical method. Results indicated that the combining of KNbO3 with g-C3N4 did not affect the optical absorption. However, strong interaction between the two semiconductors was observed, which promotes the fabrication of a heterojunction structure and subsequently improves the separation of photogenerated electrons and holes. Hence, KNbO3/g-C3N4 photocatalyst displayed obviously higher photoactivity than pristine g-C3N4. The photocatalytic hydrogen production rate for the optimal KNbO3/g-C3N4 composite (7.4 wt% KNbO3/g-C3N4) is 180 μmol g cat −1 h−1, which is about 3.0 times that of pristine g-C3N4. Cycling tests further proved that KNbO3/g-C3N4 showed good photocatalytic stability. Additionally, the effect of hole sacrificial agent on the photocatalytic activity was also investigated. The KNbO3/g-C3N4 sample showed better performance in the presence of methanol than triethanolamine or EDTA-Na.

This study focused on developing indicators to predict adhesive membrane fouling in a membrane bioreactor (MBR). Thermodynamic interactions between membrane surface and foulants in various interaction scenes were comprehensively evaluated. It was revealed that, the total interaction energy in contact could be considered as a critical value affecting adhesion of foulants. Surface hydrophilicity cannot be simply represented by water contact angle. Statistical analysis showed that membrane acid-based (AB) surface tension, Lifshitz-Van der waals (LW) surface tension, total tension, zeta potential and water contact angle had no apparent correlation with adhesive fouling, suggesting the infeasibility of these parameters as fouling predictors. It was found that, interaction between two identical membrane surface in water (Δ G sws ) and membrane surface electron donor tension (γ − ) strongly correlated with adhesive fouling, and could be reliable indicators to predict adhesive fouling. This study identified the relationships of series membrane surface properties with adhesive fouling in MBRs.

A novel NiMoO4/g-C3N4 composite with heterojunction structure was prepared via a simple mixing–calcination method and used as a photocatalyst for rhodamine B (RhB) degradation and hydrogen generation under visible light irradiation. Multiple techniques, such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy, were applied to investigate the physical and photo properties of the catalysts. Results indicated that the synthesized NiMoO4/g-C3N4 composite can produce hydrogen 4.4 times faster than pure g-C3N4 under visible light irradiation. When the composite was applied in photodegradation of RhB, it was found that the introduction of NiMoO4 nanorods into g-C3N4 can promote the photoabsorption performance and the adsorption of RhB, both of which benefit the photocatalytic reaction. Nevertheless, more important is the formed heterojunction between NiMoO4 and g-C3N4 efficiently retards the recombination of electron-hole pairs, which subsequently significantly promotes the photocatalytic activity. The degradation rate of the optimal NiMoO4/g-C3N4 reaches 0.044 min−1, which is 4.0 times that of pure g-C3N4. The proposed mechanism for the enhanced visible-light photocatalytic activity of NiMoO4/g-C3N4 composite is further evidenced by photoluminescence spectroscopy and photocurrent experiments.

This work synthesized a novel Ag

The present work was designed to synthesize Ag/KNbO3 nanocomposite for efficient photocatalytic conversion of N2 to NH3. KNbO3 was prepared in a low KOH concentration solution at 260 °C, while Ag n...

The present work reports a novel CdS/KTa

Photocatalytic conversion of CO2 to CH4 is beneficial in alleviating global warming and advancing a low-carbon economy. However, it is a challenge to develop semiconductor-based photocatalysts with high CO2 conversion efficiency, resulting from electron–hole recombination in bulk semiconductors as well as the low adsorption and activation ability of stable CO2 molecules on the semiconductor surface. The combination of metal cocatalysts with semiconductors is a promising route to improve the photocatalytic performance in CO2 reduction. Herein, we demonstrate that the photocatalytic performance in the reduction of CO2 to CH4 can be greatly promoted by introducing high-index faceted cocatalysts. In this work, PtCu alloy concave nanocubes with (730) facets were loaded on C3N4 nanosheets, which act as cocatalysts greatly enhancing the photocatalytic activity and selectivity in CH4 production in comparison with (100) facet enclosed PtCu nanocubes. As revealed by experimental characterization combined with density functional theory calculations, the (730) high-index facet has more low-coordinated metal active sites to increase the adsorption and activation of CO2, while the introduction of Cu to Pt leads to synergistic effects between the two metals for high selectivity towards the desired CH4. This work highlights the rational facet design of cocatalysts for enhanced photocatalytic performance in CO2 conversion.

The utilization of a metal cocatalyst is a promising route to improve the solar-to-chemical conversion efficiency of semiconductor-based photocatalysts. The efficiency of the improvement is greatly dependent on the architectural structure of the metal cocatalysts, especially the catalytically active sites on the surface of the cocatalysts. In this article, Pd nanosheets with different sizes have been hybridized with TiO2 nanosheets to disclose how the edge of Pd cocatalysts influences the photocatalytic performance of TiO2–Pd hybrid structures in the reduction of CO2 to fuels. It was found that the highest photocatalytic activity was realized by small Pd nanosheets with the highest edge density on the TiO2 nanosheets. The reason is that the edges of the nanosheets act as the highly active sites for the CO2 reduction reaction. To further verify the edge-dependent photocatalytic performance, Pd nanorings were also deposited on the TiO2 nanosheets, which further improve the photocatalytic activity as compared with original nanosheets resulting from the additional edge sites exposed on the side of the hollow interior in the rings. This work underlines the importance in the edge engineering on the surface of cocatalysts in realizing high-performance photocatalytic applications.

As a C1 feedstock, CO2 has the potential to be uniquely highly economical in both a chemical and a financial sense. Porous materials bearing particular binding and active sites that can capture and convert CO2 simultaneously are promising candidates for CO2 utilization. In this work, a bipyridine-constructed polymer featuring a high surface area, a hierarchical porous structure, and excellent stability was synthesized through free-radical polymerization. After metalation, the resultant catalysts exhibited superior activities in comparison with those of their homogeneous counterparts in the cycloaddition of CO2 to epoxides. The high performance of the heterogeneous catalysts originates from cooperative effects between the CO2 -philic polymer and the embedded metal species. In addition, the catalysts showed excellent stabilities and are readily recyclable; thus, they are promising for practical utilization for the conversion of CO2 into value-added chemicals.

While the adsorptive fouling in membrane bioreactors (MBRs) is highly dependent of the surface morphology, little progress has been made on modeling biocake layer surface morphology. In this study, a novel method, which combined static light scattering method for fractal dimension (Df) measurement with fractal method represented by the modified two-variable Weierstrass-Mandelbrot function, was proposed to model biocake layer surface in a MBR. Characterization by atomic force microscopy showed that the biocake surface was stochastic, disorder, self-similarity, and with non-integer dimension, illustrating obvious fractal features. Fractal dimension (Df) of sludge suspension experienced a significant change with operation of the MBR. The constructed biocake layer surface by the proposed method was quite close to the real surface, showing the feasibility of the proposed method. It was found that Df was the critical factor affecting surface morphology, while other factors exerted moderate or minor effects on the roughness of biocake layer.

The aim of this work was to synthesize, characterize and evaluate the photocatalytic activity of AgI/Bi5O7I composite photocatalyst under visible light irradiation. The photocatalyst was prepared by a simple one-step ionic reaction between Bi5O7I microrods and AgNO3 solutions, and was characterized by various techniques including X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The characterizations indicate that AgI particles were closely anchored on Bi5O7I micronods. During the photocataytic reaction, the composite was actually an Ag-AgI-Bi5O7I ternary system. The plasmonic effect of the formed Ag nanoparticles improved the visible light absorption performance, which benefits the photocatalytic reaction. However, more important was the formed heterojunction structure in the composite, which efficiently promoted the separation of electron-hole pairs by a plasmonic Z-scheme mechanism, and ultimately enhanced the photocatalytic activity. The optimal AgI/Bi5O7I composite showed a RhB degradation rate of 0.046 min−1, which was 3.83 and 6.57 times higher than those of Bi5O7I and AgI, respectively. This work may provide some insight into the design of novel and highly efficient Z-scheme visible-light photocatalysts.

A novel method was developed to construct membrane surface morphology in this study. The method was based on fractal geometry theory, and involved a modified Weierstrass-Mandelbrot (WM) function for modeling surface topography. With MATLAB programming, membrane surface could be graphically modeled. It was found that the fractal dimension (Df) and cutoff frequency (Ls) were the two key parameters affecting the topography, and the membrane surface constructed by this method could be very close to the real situation. The method was then applied in interaction energy assessment regarding membrane fouling in a membrane bioreactor. The procedure which combines membrane surface topography construction, surface element integration (SEI) method and the composite Simpson's rule was theoretically proposed. The surface properties of foulant and membrane were experimentally measured. Accordingly, a membrane surface was reconstructed for interaction energy assessment. With these data, quantitatively assessing interfacial interactions between foulant particles and a nearly-real rough membrane surface is expected to be firstly realized. This study provided a complete solution for quantitative assessment of interaction energies between a foulant particle and rough membrane surface.

The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance.

Effects of both membrane and sludge foulant surface zeta potentials on interfacial interactions between membrane and sludge foulant in different interaction scenarios were systematically investigated based on thermodynamic methods. Under conditions in this study, it was found that zeta potential had marginal effects on total interfacial interaction between two infinite planar surfaces, and the total interfacial interaction between foulant particles and membrane would be more repulsive with increase of absolute value of zeta potential. Adhesion of foulant particles on membrane surface should overcome an energy barrier. There exists a critical zeta potential below which energy barrier would disappear. Results also showed that rough surface membrane corresponded to significantly low strength of interfacial interactions. This study not only provided a series of methods to quantitatively assess the interfacial interactions between membrane and sludge foulants, but also reconciled the contradictory conclusions regarding effects of zeta potential in literature, giving important implications for membrane fouling mitigation.

Though sludge foaming often occurs and thus causes serious membrane fouling in membrane bioreactors (MBRs), the fouling mechanisms related with the foaming phenomenon have not been well addressed, hindering better understanding and solving foaming problem. In this work, it was interestingly found that, the foulants during the foaming period possessed extremely high specific filtration resistance (SFR) (over 1016 m kg−1) and strong adhesion ability to membrane surface. Chemical characterization showed that the proteins (178.57 mg/L) and polysaccharides (209.21 mg/L) in the foaming sample were about 6.4 times and 5.4 times of those in the supernatant sample, suggesting existence of a mechanism permitting continuous production of these foulants in the MBR during the foaming period. It was revealed that the fouling caused by foams was associated with gel layer filtration process, and the extremely high SFR can be interpreted by chemical potential change in the gel filtration process depicted in Flory-Huggins theory. Meanwhile, analyses by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed that the strong adhesion ability stemmed from the high interaction energy between the foaming foulants and membrane surface. In addition, 16S rDNA gene sequencing identified that the abundance of the foaming related bacteria species in the sludge suspension during the foaming period was more than 10 times of that during the non-foaming period. This study offered new mechanism insights into foaming fouling in MBRs.

Theoretical investigation of the static and kinetic behaviors of H and H2 on metal surface plays a key role in the development of hydrogenation catalysts and new materials with high H2 storage capacity. Based on the density functional theory (DFT) calculation of H and H2 adsorption on Pt(111), H(a) adatom strongly interacts with surface Pt, while H2 weakly adsorbs on Pt(111). H(a) adatoms stably occupy the face-centered cubic sites on Pt(111) which agrees with the experimental LERS observations. By using kinetic Monte Carlo (kMC) simulation, the qualitative effects of the kinetic parameters on the H2 TDS spectra indicate that the H2 desorption peaks shift to the low temperature with increasing pre-exponential factor and decreasing desorption barrier. Simultaneously, the desorption peaks shift downwards and broaden to two peaks with the increase of the lateral interaction energy among H(a) adatoms. Using the kMC simulation based on DFT calculation, the predicted H2 TDS spectra are well consistent with the experimental ones. It unanimously proves that the two peaks of TDS spectra are derived from the lateral interactions among H(a). This work provides the intrinsic kinetics of H(a) and H2 on Pt(111) at an atomic level, and gives insight into the development of hydrogenation catalysts.