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The key factor for efficient photoelectrochemical (PEC) water splitting is to design a semiconductor as photoanode with high carrier separation. Piezoelectric polarization is a considerable method to improve the carriers separation efficiency via providing a powerful built-in electric field. Herein, we synthesized WO3/CdS type II heterojunction and firstly explored the influence of CdS phase transition from sphalerite β-CdS to wurtzite α-CdS on piezoelectric polarization for WO3/CdS. Benefited from the asymmetric structure of α-CdS, fluctuation swings can be seen in the LSV curves of WO3/α-CdS due to piezoelectric polarization under ultrasound. The photocurrent density of WO3/α-CdS are enhanced with the increase of ultrasound frequency and the maximum of 2.13 mA/cm2 at 1.23 V vs. RHE, which is 1.61 times before ultrasound. The outstanding PEC performances of WO3/α-CdS under ultrasonic conditions are contributed to carrier separation driven by enhancing internal electric field between heterojunction, the built-in electric field inside the α-CdS and ballast carriers participating in water splitting reaction. This work provides a promising strategy for improving carrier separation efficiency in photoelectrodes via piezoelectric polarization.

The sliding-rolling mixed motion behavior degrades the ball screw’s precision at different levels. Based on the sliding-rolling mixed motion between ball and screw/nut raceway, the ball screw’s precision loss considering different given axial loading and rotational speed working conditions was investigated. Since creep and lubrication relate to sliding and rolling motion wear, the creep and lubrication characteristics are analyzed under different working conditions. Besides, the precision loss was calculated considering the sole influence of sliding behavior between ball and screw and compared with the results from other current models. Finally, research on precision loss owing to the sliding-rolling mixed motion behavior was realized under given working conditions, and suitable wear tests were carried out. The analytical results of precision loss are in good agreement with the experimental test conclusions, which is conducive to better predicting the law of precision loss in stable wear period.

Microwave-assisted catalytic oxidation technology has become an effective technology for rapid removal of organic pollutants in wastewater. In this research, the removal of methyl orange (MO) from aqueous solution by CuFe2O4 loaded on carbon nanotubes (CuFe2O4/CNTs) under microwave irradiation was studied. The effects of different loadings (1:2, 1:4, 1:8) of CuFe2O4 on the dielectric loss, magnetic loss, dielectric loss factor, magnetic loss factor, and reflection loss of composite materials were studied. The results showed that the microwave adsorption performance was improved by loading CuFe2O4 on CNTs. These different composites were further characterized by SEM, FTIR, and XRD techniques. In addition, this article also studied the effects of different microwave irradiation time, pH, and ionic factors on the degradation of MO. In particular, the mechanism of MO degradation by composite materials under different pH conditions was also studied in detail. The results showed that the removal rate reaches 97% with 5 min under the best conditions, and the composite material had good anti-interference performance. This study may provide a new option to degrade organic dye in wastewater treating.

CoFe-NiOOH is developed for the first time as a ternary polymetallic surface oxygen evolution cocatalyst to enhance the photoelectrochemical (PEC) water splitting performance of BiVO4-based photoan...

Although overlay coatings deposited via plasma transferred arc welding (PTAW) can effectively prolong the service life and improve the performance of components, cracks and pores tend to occur in the high-hardness and wear-resistant coating during the deposition process. Further treatment is thus necessary to improve the coating quality. Herein, PTAW-deposited Ni-based overlay coating was remelted using plasma transferred arc (PTA) under different remelting currents (RCs). The microstructure and phase composition of the coatings were investigated via metallographic microscopy and x-ray diffraction. The hardness, surface quality, and wear resistance of the coatings were also tested. The results show that PTA remelting could effectively eliminate the defects and improve the coating properties when the RC was controlled within a given interval (100-120 A). The type and content of the hard phase in the remelted coating were increased to enhance the microhardness and wear resistance. However, remelting with excessive currents resulted in the agglomeration and growth of the hard phases, which negatively affected the coating hardness and wear resistance. The proper use of PTA remelting technology to treat PTAW-deposited overlay coating is an effective approach for eliminating the coating defects and enhancing the coating properties.

Sum-frequency generation (SFG) vibrational spectroscopy is a second-order nonlinear optical spectroscopy technique. Owing to its interfacial selectivity, SFG vibrational spectroscopy can provide interfacial molecular information, such as molecular orientations and order, which can be obtained directly, or molecular density, which can be acquired indirectly. Interfacial molecular behaviors are considered the basic factors for determining the tribological properties of surfaces. Therefore, owing to its ability to detect the molecular behavior in buried interfaces in situ and in real time, SFG vibrational spectroscopy has become one of the most appealing technologies for characterizing mechanisms at friction interfaces. This paper briefly introduces the development of SFG vibrational spectroscopy and the essential theoretical background, focusing on its application in friction and lubrication interfaces, including film-based, complex oil-based, and water-based lubricating systems. Real-time detection using SFG promotes the nondestructive investigation of molecular structures of friction interfaces in situ with submonolayer interface sensitivity, enabling the investigation of friction mechanisms. This review provides guidance on using SFG to conduct friction analysis, thereby widening the applicability of SFG vibrational spectroscopy.

The combination of sliding/rolling motion can influence the degree of precision degradation of ball screw. Precision degradation modeling and factors analysis can reveal the evolution law of ball screw precision. This paper presents a precision degradation model for factors analysis influencing precision due to mixed sliding-rolling motion. The precision loss model was verified through the comparison of theoretical models and experimental tests. The precision degradation due to rolling motion between the ball and raceway accounted for 29.09% of the screw precision loss due to sliding motion. Additionally, the total precision degradation due to rolling motion accounted for 21.03% of the total sliding precision loss of the screw and nut, and 17.38% of the overall ball screw precision loss under mixed sliding-rolling motion. In addition, the effects of operating conditions and structural parameters on precision loss were analyzed. The sensitivity coefficients of factors influencing were used to quantitatively describe impact degree on precision degradation.

Using hydrogen as an energy source has gained broad interest because of its eco-friendly, renewable, high energy density, and sustainable nature. It is important to note that hydrogen generation by...

The development of non-noble bifunctional electrocatalysts with low cost, high performance and stability for overall water splitting is particularly important for solving energy problems in future. In this paper, a micron spherical NiO–CoFe2O4 film composed of nanosheets was synthesized on Ni foam (NF) as a high-efficiency bifunctional electrode through one-pot hydrothermal method. The NiO–CoFe2O4/NF owns excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity and stability due to the combination effect between NiO and CoFe2O4, good electrical conductivity of three-dimensional (3D) porous Ni foam and unique flower-spherical structure of NiO–CoFe2O4/NF. In alkaline solution, HER and OER only need low overpotential of 97 mV and 157 mV to reach 10 mA cm−2 current density, respectively. In addition, NiO–CoFe2O4 is used as both anode and cathode to overall water splitting in an alkaline electrolyte requires 1.54 V to realize a current density of 10 mA cm−2. The work provides an easy way for the preparation of bifunctional electrocatalysts for overall water splitting.

There has been great demand for high-efficiency, low-cost, and abundant photoelectrode materials for photoelectrochemical (PEC) systems. Here, we studied the PEC performance of ternary sulfide photoelectrodes (ZnIn2S4 and CuInS2) with the same nanostructure and applied bidirectional p-n heterojunctions with energy levels that were well matched to the unassisted tandem PEC cell device. Moreover, ZnIn2S4/CuInS2 and CuInS2/ZnIn2S4 were used as a photoanode and photocathode, respectively, in the unassisted tandem PEC cell device, which achieved a relatively high photocurrent density of 0.06 mA cm-2. This work provides new ideas for the design and manufacture of high-efficiency unassisted tandem PEC cell devices.

It is significant to design an electrode with high carrier separation and transport efficiency in a photoelectrochemical water splitting system. In this study, we utilized a facile H2O2 etching method for modulating S-vacancies in a TiO2/MoS2 nanostructure to enhance photoelectrochemical performance. The as-prepared TiO2/MoS2 with S-vacancies demonstrates an increased photocurrent density of 1.56 mA cm−2 at 1.23 V vs. RHE, which is 2.14 times higher than that of pristine TiO2 (0.73 mA cm−2 at 1.23 V vs. RHE). An appropriate energy level alignment between TiO2 and MoS2 and defect modulation are demonstrated in this study. The photo-generated electrons and holes are effectively separated and transported due to the built-in electric field in TiO2/MoS2. Moreover, the surface oxygen production reaction is enhanced due to its plenty exposed reaction active sites. This study demonstrates the synergistic effects of S-vacancies and built-in electric field in enhancing the carrier separation and transport properties. Furthermore, this study provides a universal strategy in designing high quality photoelectrodes in the photoelectrochemical system.

The predicaments of poor carrier separation and light absorption need to be overcome in order to maximize the preeminent performances of WO3 in photoelectrochemical (PEC) water splitting. Hence, we firstly prepared a 2D WO3/PANI core–shell hybrid heterojunction with high light absorption efficiency by a simple hydrothermal and photo-assisted electro-deposition method. A photocurrent density of 0.499 mA cm−2 at 1.23 V vs. RHE is achieved by the as-prepared hybrid heterojunction, which is about 2.35 folds higher than that of bare WO3 (0.212 mA cm−2). Moreover, the PEC stability is significantly enhanced to 87% from 60% with the deposition of organic PANI. PEC and optical measurements demonstrate that the significant PEC properties are attributed to improved photogenerated carrier separation efficiency (ηsep) and injection efficiency (ηinj) as well as broadened light absorption due to the synergistic action of the photosensitivity effect and extended space charge region (SCR), including a built-in electric field and depletion layer, in which the lifetime of photogenerated carriers is significantly improved with depletion layers of greater widths. This work can provide a favorable example for the development of more efficient hybrid photoanodes.

The two-dimensional semiconductor photocatalytic material has excellent photocatalytic H2 evolution activity. In order to further improve the hydrogen production activity of g-C3N4, this study improved the preparation process of g-C3N4 and obtained a new photocatalyst (name H-CN) with a higher absorption range, larger specific surface area, and faster hydrogen production activity. Compared with the originally prepared g-C3N4, the H-CN absorption range has been improved, and the utilization of visible light has reached 650 nm. When the doping amount of Pt cocatalyst was 1.0 wt%, the H-CN demonstrates excellent photocatalytic hydrogen production activity, with a hydrogen production rate of 4.3 mmol h−1·g−1, which was 7.0 times higher than that pure 1.0 wt% Pt/g-C3N4. The fluorescence spectroscopy of H-CN showed better separation of carriers and longer lifetime. This study has guiding significance for the preparation of subsequent ultra-thin nanosheet photocatalysts and the establishment of high-efficiency photocatalytic systems.

Designing low-cost and high-performance photoelectrodes with improved light harvesting and charge separation rates is significant in photoelectrochemical water splitting. Here, a novel TiO2/Cu2O/Al/Al2O3 photoelectrode is manufactured by depositing plasmonic nanoparticles of the non-noble metal Al on the surface of a TiO2/Cu2O core/shell heterojunction for the first time. The Al nanoparticles, which exhibit a surface plasmon resonance (SPR) effect and are substantially less expensive than noble metals such as Au and Ag, generate hot electron–hole pairs and amplify the electromagnetic field at the interface under illumination. The as-prepared TiO2/Cu2O/Al/Al2O3 photoelectrodes have an extended absorption range and enhanced carrier separation and transfer. Their photocurrent density of 4.52 mA·cm−2 at 1.23 V vs. RHE represents an 1.84-fold improvement over that of TiO2/Cu2O. Specifically, the ultrathin Al2O3 passivation layer spontaneously generated on the surface of Al in air could act as a protective layer to significantly increase its stability. In this work, the synergistic effect of the heterojunctions and the SPR effect of the non-noble metal Al significantly improve the photoelectrode performance, providing a novel concept for the design of electrodes with good properties and high practicability.

Hydrophilic polymer coatings can improve the surface characteristics of artificial implants. However, because they are used in vivo, they inevitably come into contact with biomolecules that affect their interfacial tribological properties. In this paper, the friction behaviors of poly(vinylphosphonic acid) (PVPA)-modified Ti6Al4V and polytetrafluorethylene balls were analyzed using albumin, globulin, aggrecan, and hyaluronic acid as lubricants. The interaction properties and dynamic adsorption characteristics of the biomolecules and PVPA molecules were explored by a quartz crystal microbalance to identify the cause of the friction difference. It was found that protein molecules disturbed the superlubricity of the PVPA-phosphate-buffered saline system because of the formation of a stable adsorption film, which replaced the interfacial characteristics of the PVPA coating. Polysaccharides, with their excellent hydration properties and polymer structure, had an unstable dynamic interaction or zero adsorption with PVPA molecules, and hardly changed the superlubricity of the PVPA and phosphate-buffered-saline system. The influence mechanism of the specific friction of proteins and polysaccharides was analyzed. Interactions were observed among different biomolecules. Polysaccharides can potentially reduce protein adsorption. The result of the synergistic regulation of the friction coefficient for PVPA-modified Ti6Al4V is approximately 0.017. The results of this study will provide a theoretical basis for the use of polymer coatings in vivo.

Ball screw mechanisms (BSMs) are used as accuracy transmission components in a wide range of industries and are characterized by their high accuracy. More specifically, the positioning accuracy of BSM has a significant effect on the accuracy of machine tool. Based on the macro-micro multiscale method, an exponential prediction model for the BSM positioning accuracy was developed considering time-varying working conditions (load and rotational speed) and feed modes. Since the accuracy degradation is mainly caused by wear, a microscopic approach was proposed to describe the positioning accuracy retention and the microscopic wear process was investigated. The sliding contact of the asperities between the ball and raceway was analyzed, and the microscopic wear behavior of the asperities was determined. Considering the time-varying working conditions, the BSM positioning accuracy characteristics were obtained under the normal feed mode by conducting suitable tests. The exponential wear model used the wear index to describe the wear status based on the positioning accuracy measurement. The accuracy loss value and the prediction index of positioning accuracy were determined based on an exponential model, and the effective lifetime of the BSM was predicted. Finally, the exponential prediction model was used in negative/positive skew feed distribution, and the effective lifetime determined.

In this paper, numerical simulation and finite element analysis were applied to optimize the important parameters including V-type joint and current frequency for high-frequency induction welding. The coupling of the 3D harmonic electromagnetic field and 3D transient temperature field was analyzed by establishing the physical file of the electromagnetic field and temperature field in high-frequency induction welding. The influence of important welding parameters on the temperature field distribution in the welding area was obtained by using a single control variable method. In the temperature field, the size of the V-type joint determines the heating efficiency, and the current frequency affects the heat produced by the eddy current. The numerical simulation results were verified by the analysis of the actual production experimental results and a good process parameter group was summarized. The shape of the slit between the different V-type joint parameters and the centerline of the squeeze roll showed that the relationship of the welding image and the welding quality and provided a solution for real-time online monitoring of welding quality.

The SnO2 quantum dots (SnO2QDs)/ZnS nanosheets (ZnSNs) heterojunction was fabricated via an in-situ synthetic method at room temperature. Rhodamine B, potassium dichromate, and tetracycline were used to discuss the photocatalytic activities of the as-prepared samples under the visible light illumination. The photocatalytic mechanism of the as-prepared samples was also proposed. The experimental results indicate that the degradation efficiency of the as-prepared SnO2QDs/ZnSNs heterojunction first increases and then decreases with increasing the usage of ZnSNs. When the mass ratio of SnO2QDs to ZnSNs is 1: 2 in 180 min, the asprepared samples have the highest degradation efficiency of 89.1% for rhodamine B, 97.7% for potassium dichromate, and 83.8% for tetracycline, which are much higher than 51.7%, 26.8%, and 0.9% of pure SnO2QDs as well as 37.9%, 87.1%, and 19.1% of pure ZnSNs, respectively. After it is repeatedly degraded for 3 times, it possesses the degradation efficiency of 62.5% for rhodamine B, which increases by 200.5% in comparison with 20.8% of the pure SnO2QDs. Moreover, the enhanced photocatalytic performances of the as-prepared hybrids are attributed to the formation of heterojunction between the SnO2QDs and ZnSNs. In addition, hydroxyl radicals and superoxide anion radicals play major roles during the photocatalytic degradation process, while holes play a minor role.

Despite the impressive development of CH3NH3PbI3(MAPbI3)-based perovskite solar cells (PSCs) in device efficiency, they are limited by their low stability due to the moisture-induced degradation of...

Enhancing the response to visible light and inhibiting recombination of photogenerated electrons and holes is a key point for strongly improved self-cleaning performances of TiO2 self-cleaning films. In this work, TiO2 thin film doping with three different ions (Fe3+, Al3+, Ce3+) on glass substrate respectively by sol–gel method to explore the effect of ions on self-cleaning performance of TiO2 thin films. All the prepared samples are characterized by XRD, SEM, UV-Vis and water contact angle tester. Moreover, the self-cleaning mechanism of doping TiO2 thin film is discussed. The water contact angle of TiO2 thin film doping with 9% Fe (molar ratio), 5% Ce and 5% Al are reach at 0°, respectively. In comparison with the water contact angle of pure TiO2 thin film (2.5°), TiO2 thin film doping with metal ions exhibit better self-cleaning property.

In order to enhance the photoelectrochemical (PEC) performance of tungsten oxide (WO3), it is critical to overcome the problems of narrow visible light absorption range and low carrier separation efficiency. In this work, we firstly prepared the 2D plate-like WO3/CuWO4 uniform core-shell heterojunction through in-situ synthesis method. After modification with the amorphous Co-Pi co-catalyst, the ternary uniform core-shell structure photoanode achieved a photocurrent of 1.4 mA/cm2 at 1.23 V vs. RHE, which was about 6.67 and 1.75 times higher than that of pristine WO3 and 2D uniform core-shell heterojunction, respectively. Furthermore, the onset potential of 2D WO3/CuWO4/Co-Pi core-shell heterojunction occurred a negatively shifts of about 20 mV. Experiments illuminated that the enhanced PEC performance of WO3/CuWO4/Co-Pi photoanode was attributed to the broader light absorption, reduced carrier transfer barrier and increased carrier separation efficiency. The work provides a strategy of maximizing the advantages of core-shell heterojunction and co-catalyst to achieve effective PEC performance.

Harmonic drives are the core components to enable movement in industrial robots. Unfortunately, the deformation of flexspline causes obvious partial axial load on gear engagement. This synthetic error leads to a series of additional problems, such as the deterioration of transmission quality, and the reduction of both precision and fatigue life. This study focuses on a harmonic drive with a double circular-arc tooth profile. A coordinate transformation is carried out based on the kinematics of harmonic drives. On this basis, the conjugate tooth profile of a circular spline is derived. A simulation model is developed based on the motion relationship for harmonic transmission. The effect of inhomogeneity of the load distribution on the surface of the gear teeth was investigated using the partial axial-load index. The effect of different factors on the partial axial load is analyzed. To reduce the effect of partial axial load of flexspline, we select a suitable material and wall thickness. For a certain practical range, both tooth width and chamfering of the flexspline teeth help reduce the partial axial load and increase the flexspline length. These conclusions enable improvements of future designs of reliable flexspline.

This study presents a closed-loop recycling process for carbon fibers using supercritical n-butanol. In the reclamation process, to achieve the highest composite recovery efficiency, the degradation of the carbon fiber-reinforced epoxy resin composites was conducted at various experimental feedstock ratios (ratio of composite waste to n-butanol), then the reclaimed carbon fiber (RCF) was characterized using various methods to develop an understanding of the changes in the properties and morphologies. In the remanufacturing process, in order to evaluate the reusability of the RCFs and the feasibility of the closed-loop recycling process for carbon fibers, the RCFs were mixed with new epoxy resin and polypropylene to remanufacture the composites, and then the mechanical properties of remanufacture composites were tested. The results show that, under an optimized process, the maximum recovery efficiency (feedstock ratio) of the composite was 0.1 g/ml. The impact of reclamation process on RCF lies in the degradation of tensile properties and the removal of sizing agent, which leads the change of the interfacial bonding strength between RCF and new resin, and eventually results in an impact on the performance of remanufacture composites. Compared with the virgin carbon fiber-reinforced composites, the improvement in the RCF-reinforced polypropylene properties and insubstantial variations in the tensile properties of the RCF validate the potential of the closed-loop recycling process for carbon fibers.

In this paper, we successfully prepare hydrophobic surface of ZnO/ZnS nanorods arrays modified by stearic acid. The morphology, microstructure, optical transmittance and self-cleaning property are examined by SEM, XRD, UV-vis and water contact angle measurements, respectively. The ZnO/ZnS core/shell nanoarrays shows a higher value of water contact angle in compare with that of pure ZnO nanorods arrays. After treatment by stearic acid, the resulting ZnO/ZnS nanostructure exhibits the best hydrophobicity with water droplets about 146.5 . The results show that the surface hydrophobicity of ZnO/ZnS nanoarrays can be improved by using stearic acid with low-surface-energy.

PurposeThe purpose of this paper is to study the effects of Cl−and direct stray current on the soil corrosion of three grounding grid materials.Design/methodology/approachThe electrochemical corrosion properties of three grounding grid materials, which include the Q235 steel, Q235 galvanized flat steel and copper, were measured by means of the weak polarization curve method and electrochemical impedance spectroscopy; the corrosion rate of specimens was calculated using the weight loss method; and the specimen surfaces were characterized using the scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction analysis.FindingsResults showed that both factors, Cl−and direct stray current, can accelerate the corrosion rate of grounding grid materials. The magnitude of DC stray current density affected the mass transfer type and response frequency of the anode and cathode reaction of grounding materials, while the Cl−contents of the soil only affect the mass transfer rate of the electrode material from the electrochemical impedance spectroscopy diagrams. The electric field generated by the DC stray current caused Cl−directed migration. The larger the DC stray current density, the greater the diffusion process and the greater the weight loss rate of the grounding grid materials that would have a logarithmic relationship with the Cl−content at the same DC stray current density. The corrosion resistance of the three materials is copper > Q235 galvanized flat steel > Q235 flat steel.Originality/valueThe paper provides information regarding the relationship among Cl−, direct stray current and corrosion of three grounding grid materials by means of electrochemical impedance spectroscopy. Meanwhile the weight loss rate is the logarithmic relationship with the Cl−content, which is useful for understanding the corrosion mechanism of Q235 steel, Q235 galvanized flat steel and copper under the condition of Cl−and direct stray current in soil.

Solar energy is a clean and sustainable energy source. Natural photosynthesis has existed for millions of years, which can convert solar energy into chemical energy needed by living things. Inspired by natural photosynthesis, scientists have developed a series of artificial photosynthetic systems that can use solar energy efficiently for humans. Conjugated microporous polymers (CMPs) are a new class of materials that can be used in artificial photosynthetic systems. This review illustrates the light-harvesting capability and the energy transfer phenomena within the supramolecular structure of CMPs to provide guidelines for the rational design of these polymers with excellent photocatalytic properties and systematically discusses the applications of these materials in the field of photocatalysis including photocatalytic water splitting, CO2 reduction, organic conversion, environmental remediation, and medical health. Finally, this review points out the major challenges in this topic and suggests the next feasible development direction.

The vast Carbon Fiber Reinforced Polymer (CFRP) waste accumulated is pressing for its recycling. A novel recycling approach, which integrated carbon fiber reclamation and composite additive manufacturing, is proposed to process the CFRP waste into three Dimensional (3D) parts. In the experiments, the CFRP waste was recycled by supercritical n-butanol to yield reclaimed Carbon Fibers (rCFs). The rCFs were ground by a ball mill, mixed with Poly-Ether-Ether-Ketone (PEEK) powder and then extruded to the composite filament. The filament was fed to the Fused Deposition Modeling (FDM) printer to fabricate 3D parts. Mechanical and electrical properties of the parts were investigated and compared with that of pure PEEK. The results illustrate that the additive manufacturing-based approach offers a potential strategy to reuse the CFRP waste and rapidly fabricate the rCF reinforced plastics with complex geometry and function.

A p-type Co–ZnFe2O4 film with a one-dimensional (1D) rod-like morphology is fabricated for the first time on fluorine-doped tin oxide (FTO) through a hydrothermal reaction and sintering treatment. The p-type Co–ZnFe2O4 is obtained by doping Co ions into n-type ZnFe2O4, in which Zn sites are substituted by Co. Compared with the n-type ZnFe2O4, the light absorption edge of Co–ZnFe2O4 is clearly shifted from 589 to 624 nm, and the positions of the valence/conduction band of Co–ZnFe2O4 meet the thermodynamic requirements for water splitting. The photocurrent density of p-type Co–ZnFe2O4 is −0.22 mA cm−2 at 0 V vs. the reversible hydrogen electrode (RHE), which is enhanced 7.33-times vs. that of n-type ZnFe2O4 (−0.03 mA cm−2 at 0 V vs. RHE). This work provides useful insights into tuning the p–n character of semiconductors to realize efficient photoelectrochemical (PEC) water splitting.

Adequate light absorption and effective charge separation and transfer are deemed to be the contributing factors to achieve high photoelectrochemical (PEC) water splitting on photoanodes. Herein, in this work, a Mo-WO3/Fe-WO3 homojunction was fabricated firstly by coating Fe doped WO3 (Fe-WO3) on Mo doped WO3 (Mo-WO3) via a two-step hydrothermal method, and then Bi2S3 nanoparticles (NPs) were further introduced onto the surface of Mo-WO3/Fe-WO3 to construct a multi-junction structure. In this Mo-WO3/Fe-WO3/Bi2S3 photoanode, the Bi2S3 NPs as the primary light absorber improve the light utilization efficiency. Moreover, the Fe-WO3/Bi2S3 heterojunction is formed due to their well-matched bands, which could facilitate charge separation and transfer; meanwhile, the internal built-in electric field at the interface of the Mo-WO3/Fe-WO3 homojunction would hinder the recombination of electron–hole pairs. Notably, the homojunction can further promote carrier transfer because of its unique property of eliminating the lattice mismatch. As expected, the Mo-WO3/Fe-WO3/Bi2S3 photoanode yields a significantly enhanced photocurrent of 2.55 mA cm−2 at 1.23 V vs. RHE, which is 8.23 times that of the WO3 photoanode. Thus, constructing a multi-junction structure with a ladder staggered alignment by integrating a homojunction and a heterojunction is believed to be an effective strategy to improve the PEC performance of WO3 photoanodes.

An understanding of the high photocatalytic performance reported for MoS2/BiOI nanocomposite is far from satisfactory. Here, the interfacial interaction and electronic properties of a MoS2/BiOI heterostructure were investigated systematically for the first time by first-principle calculations incorporating a semi-empirical dispersion-correction scheme. Our results confirm the reasonable existence of van der Waals interactions and a favorable Z-scheme mechanism, based on the typical interfacial cohesive energy and the energy level lineup at the interface. Analyzing the charge density differences and work functions, the built-in electric field is formed along the direction from MoS2 to BiOI after the interface equilibrium, and facilitates the separation of photoinduced electron–hole pairs in the interface. Additionally, it can be inferred that the incorporation of MoS2 into BiOI increases the carrier mobility and improves light harvesting, in agreement with the previously reported experimental data. Our work provides an insight into the mechanism of the enhanced visible-light photocatalytic activity of a MoS2/BiOI heterostructure, and helps to design other new heterostructure combinations.

The development and utilization of low-cost and efficient electrocatalysts for overall water splitting is of great significance for future energy supplies. Herein, a Co-doped NiCu mixed oxide film on Ni foam as a bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is synthesized by a facile solvothermal method using methanol as a reactant followed by annealing in air and it exhibits remarkably enhanced HER and OER activities. The well-constructed surface and porous skeleton structure with a large volume provide a large number of catalytically active sites during the electrochemical reaction. Notably, CuO plays an important role in improving the catalytic activity of the electrode; meanwhile, Co doping is beneficial for increasing the conductivity and activating the Ni sites at lower overpotentials via the charge transfer effect. Accordingly, the optimized CuO-NiO/Ni foam electrode exhibits a comparatively low overpotential of 38 mV and 172 mV at 10 mA cm-2 for the HER and OER in 1.0 M KOH, respectively. Moreover, the electrode shows excellent long-term stability for 1000 cyclic voltammetric cycles in both the HER and OER. A self-assembled overall water splitting device using this electrode as both the anode and cathode achieves a current density of 10 mA cm-2 at a low cell voltage of 1.51 V. This study is promising and provides a simple method for depositing a multimetal mixed oxide on a metal substrate resulting in an efficient bifunctional electrocatalyst, holding great significance for future energy applications.

A strategy is proposed for modifying BiVO4 photoanode with CoNiO2 as a novel water oxidation cocatalyst to enhance PEC water splitting performance. The results show that CoNiO2 has the following functions: reducing photogenerated charge recombination centers; providing trapping sites to promote charge separation; improving the stability of the overall system; providing more active sites; and offering a lower overpotential. The BiVO4/CoNiO2 photoanode has a higher photocurrent density (1.16 mA cm-2 at 1.23 V vs. RHE), a lower onset potential (∼0.06 V vs. RHE), a larger IPCE (34.37%) and ABPE (0.163%), better stability and good rates of hydrogen evolution (0.0148 μmol cm-2 min-1) and oxygen evolution (0.0076 μmol cm-2 min-1). The strategy provides promising prospects for achieving efficient PEC water splitting performance using water oxidation cocatalysts.

The progress of two-dimensional (2D) MXene-derived QDs (MQDs) is in the early stages, but the materials have aroused great interest due to their high electrical conductivity, abundant active catalytic sites, easily tunable structure, satisfactory dispersibility, remarkable optical properties, good biocompatibility, manifold functionalizations, and so on. However, up to now, there is still no review paper on MQDs. Herein, the research advances of MQDs, including their synthetic routes (top-down and bottom-up methods), properties (structural, electronic, optical and magnetic properties), functionalizations (surface modifications, heteroatom doping and the construction of composites) and applications (sensing, biomedical, catalysis, energy storage and optoelectronic devices etc.), are critically highlighted, and the future prospects and challenges of MQDs are discussed. This review will serve as a one-stop point for comprehending the most advanced developments of MQDs, and will hopefully enlighten researchers to employ MQDs for satisfying the growing requirements of the diverse applications.

Metal-free black phosphorus (BP) nanosheets have emerged as a promising photocatalyst. Herein, early transition-metal carbide and nitride (MXene) decorated BP (Ti3C2Tx/TiO2–BP) nanohybrids were constructed by a hydrothermal method, in which TiO2 was produced in the hydrothermal process. The optimized Ti3C2Tx/TiO2–BP nanohybrids exhibited a higher visible-light photodegradation efficiency of rhodamine B (99.09%) and tetracycline hydrochloride (92.70%) pollutants than that of pristine BP (12.75% and 9.35%, respectively). Diverse characterization techniques and density functional theory calculations have revealed that such enhanced photocatalytic performance was due to the synergistic effect of BP and Ti3C2Tx/TiO2, which could markedly improve the stability of BP, increase visible light absorption, prolong the photoexcited electron lifetime, accelerate the photoinduced electron transfer and hinder the electron–hole (e−–h+) pair recombination. Meanwhile, the mechanism analysis indicated that ˙O2− radicals played a leading role in the photocatalytic process. This study will motivate great interest in using 2D MXenes as co-catalysts to enhance the activity of BP for its applications.

Developing cost-effective and robust cocatalysts to substitute conventional Pt-group noble metals may be a great challenging stratagem for effective photoelectrochemical (PEC) water splitting. It i...

Designing and fabricating photoelectrodes with low carrier recombination, high carrier transfer, and high light-capture capability is of great significance for achieving effective photoelectrochemical (PEC) water splitting. Herein, for the first time, 2D nonstoichiometric WO3-x nanoflakes (NFs) were vertically grown by hydrothermal synthesis on 1D WO3 nanorods (NRs) obtained by a hydrothermal method and high-temperature annealing (HTA). In this 1D HTA-WO3 /2D WO3-x photoanode, the 2D WO3-x NFs with active areas could maximize light harvesting, and the unique 1D/2D homojunction structure could improve the carrier-separation efficiency. At the same time, the 1D WO3 NRs with high aspect ratio were more beneficial to charge transfer after HTA. As expected, the 1D HTA-WO3 /2D WO3-x photoanode yielded an enhanced photocurrent density of 0.98 mA cm-2 at 1.23 V versus reversible hydrogen electrode, which is approximately 3.16 times that of pristine WO3 . The improvement could be attributed to the synergistic effect of HTA and the homojunction structure in the 1D HTA-WO3 /2D WO3-x photoanode, which could effectively improve carrier separation and transfer. Furthermore, this work may provide a promising strategy for the design and fabrication of semiconductor-based photoelectrodes.

One of the crucial challenges in enhancing the photoelectrochemical (PEC) water splitting performance of BiVO4 photoanode is to improve the charge separation and transfer efficiency. Therefore, in this paper, a novel multilayer gradient W-doped BiVO4 photoanode is fabricated for improved performances in solar water splitting. Firstly, different amounts of W mono-doped BiVO4 photoanodes are prepared, and the W (5%)-doped BiVO4 photoanode reaches highest photocurrent density of 0.61 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE). Compared with the photocurrent density of the pure BiVO4 photoanode (0.28 mA cm−2), the enhancement can be attributed to the doped W which acts as an electron donor that could reduce the surface charge transfer resistance and facilitate charge transfer. Furthermore, multilayer gradient W-doped BiVO4 photoanodes are prepared to enhance PEC performances. The BVO-530 achieves a photocurrent density of 1.17 mA cm−2 at 1.23 V versus RHE due to the multilayer gradient structure which forms a diffusion path for electron–holes caused by the gradual increase in the Fermi level. The mechanisms of multilayer gradient W-doped BiVO4 photoanodes are discussed in detail based on PEC measurements. This work provides a new strategy for designing and fabricating photoanode systems to enhance the charge separation and transport for efficient water splitting.

A novel polysaccharide-bonded soft abrasive tool is proposed for the green machining of single-crystal sapphire. The composition and manufacturing process of the new abrasive tool are described whi...

Effects of surface texturing on the normal contact stiffness of joint surfaces had been investigated by experiments in many previous researches; however, there are relatively few theoretical models in this regard. The rough surface with surface texturing can be divided into two parts: the textured zone and the remaining zone, and their theoretical models are established respectively in this research considering surface morphology and material properties. For the textured zone, micro textures are modeled theoretically based on the three-dimensional topographic data obtained via a VK-X250 type laser profilometer from KEYENCE. For the remaining zone, the model of normal contact stiffness is established based on the fractal theory for the surface topography description and elastoplastic deformation of surface asperities, and the structure function method is used to calculate the fractal dimension of rough surface profiles. In the experiment, the normal contact stiffness of specimens is obtained under different normal loads, and the test results are compared with the theoretical predictions. The result shows that the predictions of proposed theoretical model are in good agreement with the experimental data. For the joint surfaces with Sa > 2.69 μm, the normal contact stiffness can be effectively increased through proper surface texturing.

Contact stiffness and backlash model of harmonic reducer is related to robot’s positioning accuracy and vibration characteristics. Harmonic reducer tooth pair height is typically less than 1 mm. Thus, backlash and contact stiffness measurement and modeling are relatively complex. In this paper, contact stiffness and backlash model is proposed by establishing a relationship between fractal parameters and tooth contact load. Non-contact optical profiler and RMS method are combined to obtain fractal roughness parameters of real machined tooth surface. Finally, the effect of rough tooth surface and contact force fractal parameters on contact stiffness and gear backlash is studied. The results indicate that surface topography parameters and contact force have significant effects on contact stiffness and backlash. By increasing the fractal dimension, a decrease of gear backlash and contact stiffness is observed. However, the opposite is true for the fractal roughness parameter. Lastly, an increase in contact force improves the contact stiffness.

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp2 carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

Efficient charge separation and transport as well as fast surface reaction kinetics all play a vital role in the efficiency of solar water splitting. Herein, we first design and fabricate a highly efficient Pt/CuWO4/Co3O4 photoanode system for photoelectrochemical water splitting. CuWO4 is selectively decorated with Pt nanoparticles and Co3O4 on the inner and outer surfaces, respectively. The Pt underlayer serves as an electron capture layer to collect electron from CuWO4 to facilitate water reduction, while the p-type Co3O4 onto n-type CuWO4 not only constructs p-n heterojunction reducing the charge recombination at the interface of CuWO4/Co3O4, but also that Co3O4 can be used as cocatalyst to accelerate the surface water oxidation. This novel ternary Pt/CuWO4/Co3O4 structure exhibits a prominently enhanced photocurrent of 4.4 mA/cm2 at 1.23 V vs. RHE. These results demonstrate that synergistic effect of spatially separated cocatalysts and p-n heterojunctions in photoelectrode could effectively achieve improve photoelectrochemical performance for water splitting.

Herein, the high surface area and efficient visible light (VSL) induced photocatalyst, namely 2D/0D g-C3N4/CdS-nitrogen doped hollow carbon spheres (NHCs) composites have been prepared. Firstly, the physicochemical, photoelectric and electronic structures (including band structure, density of state and charge density difference) properties of the obtained samples were studied. Then, the photocatalytic experiments indicated that the g-C3N4/CdS-NHCs composites performed a markedly improved VSL photocatalytic performance and photostability for cloxacillin antibiotic degradation compared with pure g-C3N4, CdS and g-C3N4/CdS heterojunction. The enhanced photocatalytic performance of g-C3N4/CdS-NHCs composites could ascribe to the synergy between g-C3N4/CdS heterojunction and NHCs, which obviously improved the specific surface area, the absorption of VSL, the transfer rate of electrons and the separation efficiency of photogenerated electron-hole pairs of the photocatalysts. Finally, the mechanism analysis showed that active substances h+, O2−, and OH worked together in the photocatalytic process, which attack the β-lactam, thiazolidine ring and amide group should be the fatal act for CLX mineralization.

The photoelectrochemical (PEC) water splitting properties can be enhanced by broadening the light absorption region and improving the separation of photogenerated carriers. In this paper, a novel ZnO/In2S3/Co–Pi ternary composite photoanode system is provided, by building the ZnO/In2S3 heterojunction to broaden the light absorption region and improve the separation and transfer of photogenerated electron–hole pairs in bulk, and by using the Co–Pi cocatalyst to increase the separation of photogenerated electron–hole pairs between the ZnO/In2S3 heterojunction surface and electrolyte. This ternary composite photoanode system exhibits a negative shifted onset potential and a higher photocurrent density of about 2.4 mA/cm2 at 1.23 V (vs. RHE), which is 3 and 2.18 times compared with bare ZnO nanorod and ZnO/In2S3 heterojunction, respectively. The results show that the ZnO/In2S3/Co–Pi ternary composite photoanode has an excellent potential application for PEC water splitting.

The presence of large amounts of contaminants in the environment would result in ecological and health hazards. The photocatalytic technologies have been developed to use sunlight to remove contaminants in recent years. Researchers are primarily focused on developing high-performance photocatalysts. This review discusses the effects of surfactant on the structural morphology, physicochemical properties and contaminant removal performance of photocatalysts. The mechanism and synthesis method of surfactant-assisted photocatalysts are reviewed. Meanwhile, the effects of surfactant type, surfactant concentration, solution pH, synthesis method and calcination temperature on the photocatalysts are also discussed in detail. In addition, we summarized the recent advances and the application of surfactant-assisted photocatalysts in the environmental remediation. Finally, the future researches on surfactant-assisted photocatalysts are also proposed. This review provides new insights into the use of surfactants to prepare photocatalysts with well-defined shape and excellent performance to enhance photocatalytic efficiency for removing pollutants.