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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.

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.

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 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.

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.

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.

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.

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.

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.

Photocatalytic conversion of CO

Membrane fouling control necessitates the establishment of an effective method to assess interfacial interactions between foulants and rough surface membrane. This study proposed a new method which includes a rigorous mathematical equation for modeling membrane surface morphology, and combination of surface element integration (SEI) method and the composite Simpson's approach for assessment of interfacial interactions. The new method provides a complete solution to quantitatively calculate interfacial interactions between foulants and rough surface membrane. Application of this method in a membrane bioreactor (MBR) showed that, high calculation accuracy could be achieved by setting high segment number, and moreover, the strength of three energy components and energy barrier was remarkably impaired by the existence of roughness on the membrane surface, indicating that membrane surface morphology exerted profound effects on membrane fouling in the MBR. Good agreement between calculation prediction and fouling phenomena was found, suggesting the feasibility of this method.

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF4:Yb,Tm–BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF4:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF4:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF4:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF4:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal–semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

Highly efficient SnO 2− x /g-C 3 N 4 composite photocatalysts were synthesized using simple calcination of g-C 3 N 4 and Sn 6 O 4 (OH) 4 . The synthesized composite exhibited excellent photocatalytic performance for rhodamine B (RhB) degradation under visible light irradiation. The optimal RhB degradation rate of the composite was 0.088 min −1 , which was 8.8 times higher than that of g-C 3 N 4 . The SnO 2− x /g-C 3 N 4 composite also showed high photocatalytic activity for CO 2 reduction and photodegradation of other organic compounds. Various techniques including Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and an electrochemical method were applied to determine the origin of the enhanced photoactivity of SnO 2− x /g-C 3 N 4 . Results indicated that the introduction of SnO 2− x on g-C 3 N 4 increased its surface area and enhanced light absorption performance. More importantly, a hetero-junction structure was formed between SnO 2− x and g-C 3 N 4 , which efficiently promoted the separation of electron–hole pairs by a direct Z-scheme mechanism to enhance the photocatalytic activity. This study might represent an important step for the conversion of solar energy using cost-efficient materials.

The objective of this research was to prepare, characterize and evaluate the photocatalytic activity of Zn2SnO4/g-C3N4 composite in RhB degradation under visible light irradiation. The composite was synthesized by simple calcination of Zn2SnO4–melamine mixture, and was characterized by various techniques including Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). Characterization results indicated that the decoration of Zn2SnO4 on g-C3N4 showed nearly no effect on its light absorption performance, but promoted the surface area of the composite, which benefited the adsorption of dyes and the subsequent photocatalytic process. However, more significant was the formation of hetero-junction structure between Zn2SnO4 and g-C3N4, which efficiently promoted the separation of electron–hole pairs and enhanced the photocatalytic performance of Zn2SnO4/g-C3N4. The optimal Zn2SnO4/g-C3N4 photocatalyst showed a degradation rate of 0.038 min−1, which was 3.2 times higher than that of g-C3N4. In addition, the Zn2SnO4/g-C3N4 composite shows high stability. O2− and h+ were the main reactive species.

In this study, the fouling behaviors and surface properties of cake sludge and bulk sludge in a submerged membrane bioreactor (MBR) were investigated and compared. It was found that the specific filtration resistance (SFR) of cake sludge was about 5 times higher than that of bulk sludge. Two types of sludge possessed similar extracellular polymeric substances (EPS) content, particle size distribution (PSD) and zeta potential. However, their surface properties in terms of surface tensions were significantly different. Further analysis showed that cake sludge was more hydrophilic and had worse aggregation ability. Moreover, cake sludge surface possessed more hydrocarbon, less oxygen and nitrogen moieties than bulk sludge surface. It was suggested that, rather than EPS and PSD differences, the differences in the surface composition were the main cause of the great differences in SFR and adhesion ability between cake sludge and bulk sludge.

Graphene(GR)/SmVO 4 composite was prepared by a facile mixing-calcination method and characterized by X-ray diffraction (XRD), Raman spectroscopy, N 2 adsorption, and transmission electron microscopy (TEM) techniques. Results showed that SmVO 4 nanoparticle adhered on graphene sheet in GR/SmVO 4 composite. The photoactivity of the synthesized composite was evaluated by the photodegradation of Rhodamine (RhB). In comparison with pure SmVO 4 , the graphene/SmVO 4 system illustrated much higher photocatalytic activity due to the contribution of GR in RhB adsorption and charge separation. 2% GR/SmVO 4 exhibited the highest photocatalytic efficiency with a degradation rate of 0.62 h −1 , which is 4 and 1.6 times higher than that of SmVO 4 and N–TiO 2 , respectively.

National Natural Science Foundation of China [21003109, 51108424]; Opening-foundation of State Key Laboratory Physical Chemistry and Solid Surfaces, Xiamen University, China [201311]

A visible-light driven SiO 2 /g–C 3 N 4 composite was prepared by heating a mixture of SiO 2 and melamine. The products were characterized by X-ray diffraction, Brunauer–Emmett–Teller analysis, transmission electron microscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Results indicate that the composite only contained SiO 2 and g-C 3 N 4 . The addition of SiO 2 had minimal influence on light absorption, but the specific surface area was increased. In addition, the aggregation of g-C 3 N 4 in the SiO 2 /g-C 3 N 4 composite was weakened. The increased surface area and decreased aggregation of g-C 3 N 4 are considered as the cause of the strong activity of the SiO 2 /g-C 3 N 4 composite in RhB photodegradation.

A series of La 1− x Ce x FeO 3 ( x = 0–0.5) perovskite oxides were prepared by a sol–gel method. X-ray diffraction spectrometer (XRD), BET surface area measurements, scanning electron microscopy (SEM) images, and temperature-programmed reduction (TPR) were used to characterize their physical structures and redox properties. Catalytic methane combustion tests for La 1− x Ce x FeO 3 ( x = 0–0.5) perovskite oxides show that the activity of LaFeO 3 was highly improved due to the introduction of Ce in the A-site of the perovskite catalysts. Among all the catalysts, La 0.7 Ce 0.3 FeO 3 has the maximum oxidative performance with the corresponding T 90 as low as 510 °C. Combining with density functional theory calculation, it was suggested that the electrons of Fe ions increase in La 0.875 Ce 0.125 FeO 3 due to the introduction of Ce 4+ ion, which leads to stronger interactions with adsorbed O 2 . Correspondingly, the adsorption energy of O 2 on La 0.875 Ce 0.125 FeO 3 increases and the O O bond is activated. Thus, the Ce doped perovskite has higher oxidative activity than pure LaFeO 3 .

This paper reported novel graphitic carbon nitride (g-C 3 N 4 ) and SmVO 4 composite photocatalysts which were prepared through a simple mixing–calcination method. Multiple techniques, such as Brunauer–Emmett–Teller (BET) method, thermogravimetric/differential thermal analysis (TG–DTA), 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 photophysical properties of the catalysts. The XRD and FT-IR results indicate that the prepared sample is a two-phase composite of SmVO 4 and g-C 3 N 4 . The TG–DTA result suggests that the real g-C 3 N 4 concentration in the composite is lower than the theoretical value due to the catalysis of SmVO 4 . The DRS result shows that the addition of SmVO 4 to g-C 3 N 4 slightly changes the optical properties. The photocatalytic activity of the novel composite was investigated using rhodamine B (RhB) as a target pollutant. Results show that the g-C 3 N 4 /SmVO 4 photocatalysts exhibit a significantly enhanced photocatalytic activity in degrading RhB. The optimal SmVO 4 concentration and calcination temperature were also determined. Based on the band position, the synergetic effect of SmVO 4 and g-C 3 N 4 is the source of the enhanced photocatalytic activity, as proven by PL spectroscopy and transient photocurrent response.

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF

The structures and electronic properties of MxCe1 − xO2 − δ (M = Au, Pd, Pt, and Rh) modeling catalysts were theoretically compared. Two kinds of active oxygen species were obtained by O2 filling into or standing aside surface oxygen vacancy on MxCe1 − xO2 − δ (111). Correspondingly, tridentate and bidentate carbonates form by CO reaction with the two different oxygen species. Finally, the possible oxidative activities of four MxCe1 − xO2 − δ catalysts were evaluated by comparing the formation energy of surface oxygen vacancy, as well as the energy differences between carbonate and CO2 desorption. Our work will provide important information for the design of catalyst with high oxidation performance.

Membrane bioreactor (MBR) technology has been extensively employed for various industrial wastewater treatments due to its distinct advantages over conventional technologies. To provide present state and development trends of MBR technology used for industrial wastewater treatments, the authors reviewed and analyzed more than 300 scientific publications. They present an overview of the most recent development of MBR technology for treatment of industrial wastewaters (e.g., food processing, pulp and paper, textile, tannery, landfill leachate, pharmaceutical, oily and petrochemical wastewaters). Moreover, they discuss the operational characteristics, fouling characteristics, fouling control strategies, and costs of MBRs in industrial wastewater treatments. Based on the present information on MBR technology, the authors discuss further research aspects of MBRs in industrial wastewater treatments.

A novel photocatalyst CaBi 6 O 10 with flower-like morphology was prepared by a simple impregnation–calcination method and investigated by techniques such as XRD, Raman, SEM, BET, DRS, and density function theory (DFT). Results reveal that CaBi 6 O 10 is responsive to visible light below 537 nm (E g = 2.31 eV). In addition, CaBi 6 O 10 presents broader conduction band than Bi 2 O 3 , which favors the mobility of photo-generated electrons in CaBi 6 O 10 and contributes positively to the photocatalytic reaction. The good photoabsorption and the special electron structure were considered as the origin of the high activity of CaBi 6 O 10 in methylene blue photodegradation.

The heterogeneous catalytic oxidation of volatile organic compounds on Pd/CexLa1−xO2/monolith catalysts in the temperature range 160–230 °C has been studied, which took toluene combustion as a probe reaction. SEM, ICP-OES, XRD, laser Raman spectra, and temperature-programmed reduction (TPR) are used to characterize the Pd/CexLa1−xO2/monolith catalysts. A high activity of the catalyst with respect to the complete oxidation of toluene to carbon dioxide has been observed. The conversion of toluene approaches 100% at about 210 °C.

This article presents a novel visible-light-driven catalyst, an LaVO x composite that was prepared from La(NO 3 ) 3 and NH 4 VO 3 solutions. The visible-light-induced photocatalytic activity of this composite was evaluated by the degradation of acetone. Results indicate that the LaVO x composite exhibits high activity for acetone photodegradation. The highest acetone conversion (93.1%) was obtained with the La 1 V 1.5 O x catalyst. Its photo-activity and ability for complete oxidation could be enhanced further by doping with a small amount of the metal platinum. Physical and photophysical properties of the LaVO x composite catalysts were evaluated by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Based on the results of this investigation, the coupling effect of m-LaVO 4 and V 2 O 5 was identified as generating the high activity in catalysis.

Er3+ doped SrTiO3 ultrafine powders were prepared by solid state reaction in a molten NaCl flux. The structural properties were characterized by X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The Stokes emission spectra of Er3+ in SrTiO3: Er3+ ranging from green to near infrared region were investigated under 514.5 nm laser excitation. The green and red upconverted luminescence spectra of Er3+ were measured under excitation into the 4I9/2 level by 785 nm laser. The upconversion mechanisms were studied in detail through laser power dependence and Er3+ ion concentration dependence of upconverted emissions, and results show that excited state absorption and energy transfer process are the possible mechanisms for the upconversion. The upconversion properties indicate that SrTiO3:Er3+ may be used in upconversion phosphors.