Theoretical design of direct Z-scheme SnC/PtSe2 heterostructure with enhanced photocatalytic performance and tunable optoelectronic properties

Recently, direct Z-scheme heterostructures have attracted much attention because of their outstanding electronic properties and excellent photocatalytic performance. In this article, the electronic, optical and photocatalytic properties of SnC/PtSe₂ heterojunction are systematically explored via first-principles calculations. Evidence suggests that a Type-Ⅱ band alignment as well as an indirect bandgap of 1.35 eV can be observed in the SnC/PtSe₂ heterojunction. The combined influence of the built-in electric field from SnC to PtSe₂ and the band bending causes a Z-scheme carrier migration mechanism. At biaxial strains of −3%–5%, the band edge positions of the heterojunction are able to cross the redox potential of water. The light absorption coefficient of 4.21 × 10⁵ cm⁻¹ and the energy conversion efficiency of 42.32% demonstrate that the photon energy can be utilized by the heterostructure efficiently. Furthermore, the absorption coefficient in the visible range can be significantly increased under tensile strain. Hence, there are reasons to believe that SnC/PtSe₂ heterostructure has tremendous potential for application in the field of photocatalytic water decomposition.     

Interfacial charge transfer in WS<Subscript>2</Subscript> monolayer/CsPbBr<Subscript>3</Subscript> microplate heterostructure

Integration of heterogenous materials produces compelling physical phenomena and increased performance of optoelectronic devices. In this work, we integrate CsPbBr₃ microplate with WS₂ monolayer to investigate the interfacial carrier transfer mechanism in the heterojunction. The quenching of photoluminescence (PL) emission from CsPbBr₃ and WS₂ after heterostructure formation indicates efficient charge transfer in the junction. Low-temperature PL spectra reveal that the decreasing PL of WS₂ arises from the vanishing of biexcitons. Photodetection based on the WS₂/CsPbBr₃ heterostructure is demonstrated. The higher performance from the junction further certifies the occurrence of charge transfer in the heterojunction.     

Ultrasound-engineered synthesis of WS2@CeO2 heterostructure for sonocatalytic degradation of tylosin

The main aim of the present investigation was the intercalation of WS₂ nanosheets in the structure of ceria (CeO₂) to be used for the efficient catalytic destruction of tylosin (TYL) as a macrolide antibiotic in water. As-synthesized heterostructured catalyst was placed in a sono-reactor (40 kHz and 300 W) in order to degrade TYL through the sonocatalysis. 15 wt% WS₂/CeO₂ was chosen for performing the systematic experiments. Decreasing the concentration of TYL, along with increasing the WS₂/CeO₂ dosage led to reduced degradation efficiency. The water hardness was demonstrated to be a suppressive agent on the sonocatalysis of the target pollutant. As-generated holes, OH, and also O₂⁻ were responsible for the degradation of TYL. Increasing the ultrasound power and operating temperature enhanced the degradation efficiency. The degradation rate boosted up when the temperature was raised from 10 °C (0.0107 1/min) to 40 °C (0.0165 1/min). Moreover, the lowest activation energy (E_a) for sonocatalytic degradation was obtained as 10.81 kJ/mol. The sonocatalytic activity of WS₂/CeO₂ in the sono-reactor encountered insignificant change within five consecutive operational runs (~15% reduction). The mechanism and pathways of the sonocatalytic decomposition of TYL are also proposed.     

First-principles study of nitrogen defect g-C3N4/WS2 heterojunction on photocatalytic activity

In this work, first-principles density functional theory simulations have been performed to investigate the influence of nitrogen (N) defect on the supercell structure, electronic structure and photocatalytic properties of g-C₃N₄/WS₂ heterojunctions. Analyses of calculated binding energies and the lattice mismatch ratios led us to confirm that N-deficient g-C₃N₄ and WS₂ were in parallel contact and form a stable heterojunction. Furthermore, the work functions, molecular dynamics simulations, charge density differences, band structures, DOS, electronic and optical properties and absorption spectra of different g-C₃N₄/WS₂ heterojunctions have been analyzed in detail. It is revealed that the compositing of N-deficient g-C₃N₄ with WS₂ improves the separation of photoinduced electron-hole pairs. N-defect enhances the visible light absorption of the heterojunction, due to the introduction of impurity energy levels. Moreover, the introduction of defect species further improves the photocatalytic performance of g-C₃N₄/WS₂ heterojunction in the visible region.     

Preparation and photocatalytic activity of CeO2/TiO2 interface composite film

The CeO₂/TiO₂ and TiO₂/CeO₂ interface composite films were prepared on glass substrates by the sol-gel process via dip-coating and calcining technique. The scanning electron microscopy (SEM) revealed that the TiO₂ layer has a compact and uniformity glasslike surface with 200 nm in thickness, and the CeO₂ layer has a coarse surface with 240 nm in thickness. The X-ray diffractometer (XRD) analysis showed that the TiO₂ layer is made up of anatase phase, and the CeO₂ layer is structured by cubic fluorite phase. Through a series of photo-degradation experiments, the relationship of the photocatalytic activity with the constituents of the films was studied. In virtue of the efficient interfacial charge separation via the process of electron transfer from TiO₂ to CeO₂, the photocatalytic activity of the CeO₂/TiO₂ composite film is high. Contrarily, the photocatalytic activity of the TiO₂/CeO₂ composite film is low, due to its inert surface made up of CeO₂ with broad bandwidth. Apart from the effect of the film structure, the effect of film thickness on photocatalytic activity was also discussed.     

The ν2 infrared band of 1-phosphapropyne CH3CP

The Fourier transform infrared spectrum of 1-phosphapropyne CH₃CP has been recorded in the region 1470–1580 cm⁻¹ with a resolution of 0.01 cm⁻¹, and the ν₂ band centered at 1558.7416(28) cm⁻¹ was analyzed. The 689 observed transitions with J′ and K′ values up to 69 and 8, respectively, were assigned. A set of the spectroscopic constants determined for the upper v₂ = 1 state reproduced the experimental wavenumbers with an rms error of 0.0025 cm⁻¹. No significant perturbations were observed. The ν₂ + ν₈ − ν₈ hot band, centered at 1553.5492(35) cm⁻¹, was also analyzed. The upper state constants determined from the 341 observed transitions with J′ and K′ values up to 53 and 6, respectively, reproduced the experimental wavenumbers with an rms error of 0.0047 cm⁻¹.     

Ultrasonically assisted surface modified CeO2 nanospindle catalysts for conversion of CO2 and methanol to DMC

This study developed a facile and effective approach to engineer the surface properties of cerium oxide (CeO₂) nanospindle catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. CeO₂ nanospindles were first prepared by a simple precipitation method followed by wet chemical redox etching with sodium borohydride (NaBH₄) under high intensity ultrasonication (ultrasonic horn, 20 kHz, 150 W/cm²). The ultrasonically assisted surface modification of the CeO₂ nanospindles in NaBH₄ led to particle collisions and surface reduction that resulted in an increase in the number of surface-active sites of exposed Ce³⁺ and oxygen vacancies. The surface modified CeO₂ nanospindles showed an improvement of catalytic activity for DMC formation, yielding 17.90 mmol·g_cat⁻¹ with 100 % DMC selectivity. This study offers a simple and effective method to modify a CeO₂ surface, and it can further be applied for other chemical activities.     

The visible absorption spectrum of S2O

The visible absorption spectrum of S₂O vapor has been studied by spectrographic and laser optoacoustic techniques. Magnetic rotation spectroscopy was used to establish the triplet-singlet nature of the transition. Vibrational analysis gave ν′₁ = 1089, ν′₂ = 505, and ν′₃ = 332 cm⁻¹.     

A feasible sonochemical approach to synthesize CuO@CeO2 nanomaterial and their enhanced non-enzymatic sensor performance towards neurotransmitter

A nanostructured and high conductive cupric oxide (CuO NPs) with hierarchical CeO₂ sheets-like structure was synthesized by a facile sonochemical approach. Furthermore, CuO/CeO₂ nanostructure is synthesized by high-intensity ultrasonic probe (Ti-horn, 50 kHz and 100 W) at ambient air. Moreover, the synthesized CuO/CeO₂ material was characterized by various analytical techniques including FESEM, EDX, XRD and electrochemical methods. Then, the synthesized CuO/CeO₂ composite was applied for the electrocatalytic detection of dopamine using CV and DPV techniques. In addition, the CuO/CeO₂ modified electrode has good electrocatalytic performance with high linear range from 0.025 to 98.5 µM towards the determination of dopamine drug and high sensitivity of the CuO/CeO₂ modified drug sensor was calculated as 16.34 nM and 4.823 μA·µM⁻¹·cm⁻², respectively. Moreover, a repeatability, reproducibility and stability of the CuO@CeO₂ mixture modified electrode were analyzed towards the determination of dopamine biomolecule. Interestingly, the real time application of CuO@CeO₂ modified electrode was established in different serum and drug samples.     

Characteristics of a type-II n-MoS2/p-Ge van der Waals heterojunction

A few-atomic-layer molybdenum disulfide (MoS₂) film on Si/SiO₂ substrates grown by metal-organic chemical vapor deposition was investigated. The few-atomic-layer MoS₂ film was subsequently transferred onto a (100) p-Ge substrate to build a van der Waals n-p heterojunction. The as-grown few-atomic-layer MoS₂ film and the MoS₂/Ge heterostructure were characterized atomic force microscopy, spectroscopic ellipsometry, high-resolution scanning transmission electron microscopy, Raman spectroscopy analyses, photoluminescence (PL) measurements at room temperature (RT, 300 K), and type-II band alignment of the heterostructure determined by ultraviolet photoelectron spectroscopy. The RT-PL measurements showed dominant peaks at 1.96 and 1.8 eV for the as-grown MoS₂ and red-shifted PL peaks for that transferred onto Ge. We examined the electrical characteristics of the few-atomic-layer MoS₂ by forming a type-II band alignment van der Waals heterojunction with a highly doped p-Ge. The heterojunction solar cell exhibited an open-circuit voltage of 0.15 V and a short-circuit current density of 45.26 μA/cm². The external quantum efficiency measurements showed a spectral response up to approximately 500 nm owing to the absorption by the few-atomic-layer MoS₂ film.     

Fabrication and efficient visible light-induced photocatalytic activity of Bi2MoO6/BiPO4 composite

Novel Bi₂MoO₆/BiPO₄ composites with heterojunction structure were fabricated by a one-step hydrothermal method. The photocatalytic properties of Bi₂MoO₆/BiPO₄ composites were evaluated by photocatalytic degradation of rhodamine B (Rh B) under visible light irradiation (λ>420 nm). The results showed that Bi₂MoO₆/BiPO₄ photocatalysts showed much higher photocatalytic activity for the Rh B degradation than the pure BiPO₄ and Bi₂MoO₆ under visible light. The best photocatalytic performance of Bi₂MoO₆/BiPO₄ with about 98.0% Rh B degradation located at molar ratio of 2:1 under visible light illumination for 30 min. The enhanced photocatalytic activity could be mainly ascribed to the formation of heterojunction interface in Bi₂MoO₆/BiPO₄ composites, which is beneficial to the transfer and separation of photogenerated electron–hole pairs, as well as the strong visible light absorption resulting from the sensitization role of Bi₂MoO₆ to BiPO₄. It was also observed that the photodegradation of Rh B is chiefly attributed to the oxidation action of the generated O₂⁻ radicals and the action of h_vb⁺ through direct hole oxidation process.     

TiO2 Nanobelts Decorated with In2S3 Nanoparticles as Photocatalysts with Enhanced Full‐Solar‐Spectrum (UV–vis–NIR) Photocatalytic Activity toward the Degradation of Tetracycline

Herein, ultradispersed In₂S₃ nanoparticle (NP)/TiO₂ nanobelt (NB) heterostructures with an intimate interfacial coupling effect are synthesized from the consideration of combining the visible/near‐infrared photoabsorption property of In₂S₃ with the excellent UV photocatalytic property of TiO₂. In this process, the 1D TiO₂ NBs not only perform as the support to form the heterostructure, but are also employed as a dispersant to confine the aggregation of In₂S₃ NPs. As expected, the obtained In₂S₃ NP/TiO₂ NB heterostructure gives rise to a prominently strong optical absorption in the full solar region of 300–1800 nm, and thus displays a desired photocatalytic degradation of tetracycline in full utilization of all solar energy, compared with that of pristine In₂S₃ and TiO₂. Besides, the In₂S₃ NP/TiO₂ NB heterostructure photocatalysts have no selectivity and can effectively degrade other different kinds of organic pollutants, including cationic dyes (methyl blue and rhodamine B) and colorless chemical pollutants (phenol and salicylic acid). The exceptional photocatalytic enhancement is due to the synergistic interactions of heterojunction with the strong interfacial coupling effect, the In₂S₃ extended light absorption, efficient photogenerated e^?/h⁺ pair separation, and fully exposed reactive sites induced by uniform packing of the ultrasmall In₂S₃.     

g-C3N4/SnS2异质结构:一类有潜力的光解水催化剂

采用第一性原理方法研究了层间耦合作用对g-C₃N₄/SnS₂异质结构的电子结构和吸光性质的影响.发现g-C₃N₄/SnS₂是一类典型的范德瓦异质结构,能有效吸收可见光,其价带顶和导带底与水的氧化还原势匹配,且由于电荷转移而导致的界面处极化场有利于光生载流子的分离.这些理论研究结果表明g-C₃N₄/SnS₂异质结构是一类非常有潜力的光解水催化材料.     

Free-standing WS<Subscript>2</Subscript><Emphasis Type="Strikethrough">-</Emphasis>MWCNTs hybrid paper integrated with polyaniline for high-performance flexible supercapacitor

As two-dimensional layered nanomaterials, the tungsten disulfide (WS₂) nanosheets can be used as building blocks of paper-like electrodes for high-performance FSs. However, poor conductivity and mechanical property of WS₂ nanosheets (NSs) paper greatly hinders their capacitance and/or rate performance. To solve these problems, we fabricated the WS₂-multiwalled carbon nanotubes (MWCNTs)/polyaniline (PANI) composite papers based on liquid exfoliation and electrochemical deposition for high-performance flexible supercapacitors. The WS₂-MWCNTs/PANI with conductive PANI chains linked WS₂ NSs and MWCNTs takes the advantages of high-electronic double-layer capacitance originated from the internal surface areas of MWCNTs and effective pseudocapacitance generated by exfoliated WS₂ NSs and PANI. Electrochemical studies showed that the gravimetric-specific capacitance of WS₂-MWCNTs/PANI can reach ~760.1 F/g at a current density of 1 A/g. A symmetric flexible solid-state supercapacitor was also assembled and studied. The WS₂-MWCNTs/PANI-assembled FS device also has an excellent area specific capacitance of 1158.7 mF/cm² at a current density of 0.5 mA/cm² together with a high-capacity retention of ~82.5% after 2000 cycles.     

Thin Film Solar Cell Based on ZnSnN2/SnO Heterojunction

In this article, we report the growth of zinc‐tin nitride (ZnSnN₂) thin films as a potential absorber for photovoltaic applications by fabricating a heterojunction of n‐ZnSnN₂/p‐SnO. The performance of the heterojunction has been monitored through selective deposition of top electrode with different materials (Ni/Au or Al). The electron‐transfer process from the ZnSnN₂ layer to the cathode is facilitated by selecting metal electrode with relatively low work function, which also boosts up the electron injection or/and extraction. The diode exhibits a good J–V response in the dark with a rectification ratio of 3 × 10³ at 1.0 V and an ideality factor of 4.2 in particular with Al as the top electrode. Under illumination, the heterostructure solar cell demonstrates a power conversion efficiency of ≈0.37% with an open circuit voltage of 0.25 V and a short circuit current density of 4.16 mA cm^?2. The prime strategies, on how to improve solar cell efficiency concerning band offsets and band alignment engineering are also discussed.     

Spectroscopic studies of interfacial structures of CeO2-TiO2 mixed oxides

We have investigated the geometric and electronic structures of the cerium oxide (CeO₂)-titanium dioxide (TiO₂) mixed oxides with various Ce/TiO₂ weight ratios prepared by the sol-gel method in detail by means of X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (XPS), Raman spectroscopy excited by 325 and 514.5 nm lasers, and scanning electron microscope (SEM). Existence of cerium effectively inhibits the phase transition of TiO₂ from the anatase phase to the rutile phase. XRD peaks of TiO₂ anatase attenuate continuously with the increasing amount of CeO₂ in the mixed oxide, but the XRD peaks of cubic CeO₂ appear only after the weight ratio of Ce/TiO₂ reaches 0.50. The average crystalline sizes of TiO₂ anatase and cubic CeO₂ in CeO₂-TiO₂ mixed oxides are smaller than those in the corresponding individual TiO₂ anatase and cubic CeO₂. Raman spectroscopy excited by the 514.5 nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.70 whereas Raman spectroscopy excited by the 325 nm laser detects CeO₂ after the weight ratio of Ce/TiO₂ reaches 0.90. XPS results demonstrate that Ti exists in the form of Ti⁴⁺ in the CeO₂-TiO₂ mixed oxide. Ce is completely in the form of Ce³⁺ in the mixed oxides with a 0.05 weight ratio of Ce/TiO₂. With the increasing weight ratio of Ce/TiO₂, Ce⁴⁺ dominates. On basis of these results, we proposed that CeO₂ initially nucleates at the defects (oxygen vacancies) within TiO₂ anatase, forming an interface bridged with oxygen between CeO₂ and TiO₂ anatase. At the interface, Ce species cannot substitute Ti⁴⁺ in the lattice of TiO₂ anatase whereas Ti⁴⁺ can substitute Ce⁴⁺ in the lattice of cubic CeO₂. The decreasing concentration of oxygen vacancies, the Ti-O-Ce interface, and the decreasing average crystalline size of TiO₂ anatase act to inhibit the phase transformation of TiO₂ anatase. With the increasing amounts of CeO₂, the CeO₂ clusters continuously grow and form cubic CeO₂ nanocrystals. Spectroscopic results strongly demonstrate that the surface region of CeO₂-TiO₂ mixed oxide is enriched with TiO₂.     

Ultrasonically prepared photocatalyst of W/WO3 nanoplates with WS2 nanosheets as 2D material for improving photoelectrochemical water splitting

A sonochemical treatment has been an emerged technique as an interesting method for fabricating different photocatalysts with unique photoelectrochemical (PEC) properties. This study investigated the PEC performance of WO₃ with WS₂ nanosheets as a 2D material before calcination (WO₃/WS₂-90) and after calcination (WO₃/WS₂-450) prepared with sonochemical treatment. The WS₂ nanosheets were prepared from a liquid exfoliation phase with few-layer nanosheets, approximately 6.5 nm in thickness. The nanosheets were confirmed by UV–Vis spectroscopy and atomic force microscopy. Further, XPS, RAMAN, and SEM-EDAX analyses indicated that, following calcination of the WO₃/WS₂ electrode, the WS₂ nanosheets initially transformed to 2D-WO₃. After depositing the WS₂ nanosheets on the WO₃, the photocurrent density increased substantially. The WO₃/WS₂-450 films after calcination showed a photocurrent density of 5.6 mA.cm⁻² at 1.23 V vs. Ag/AgCl, which was 3.1 and 7.2 times higher, respectively than those of the WO₃/WS₂-90 before calcination and pure WO₃. Mott-Schottky and electrochemical impedance spectroscopy analyses confirmed the fabrication of the WO₃/WS₂ photoanode after calcination. The deposition of WS₂ nanosheets onto pure WO₃ increased the donor concentration (24-fold), reduced the space charge layer (4.6-fold), and decreased the flat band potential (1.6-fold), which could all help improve the photoelectrochemical efficiency. Moreover, the incorporation of WO₃ with WS₂ nanosheets as a 2D material (WO₃/WS₂-450) enhanced the incident photon current efficiency (IPCE) by 55%. In addition, the applied-bias photon-to-current conversion efficiency of the WO₃/WS₂-450 films was approximately 2.26% at 0.75 V (vs. Ag/AgCl), which is 5.6 and 9 times higher, respectively than those of WO₃/WS₂-90 and pure WO₃.     

Heterojunction between crystalline silicon and nanocomposite coupled ZnO·SnO2 and optimization of its photovoltaic performance

In this work coupled ZnO·SnO₂ nanocomposite has been used as heterojunction partner to Si for photovoltaic application and its performance is optimized. The interface defect more than 10¹² cm⁻² reduces the short circuit current density, fill factor and efficiency of the device. In addition, the best device performance is observed at the vicinity of 280K. The junction of the device has a dark saturation current density and ideality factor of the order of 10⁻⁴ Acm⁻² and 21 respectively. In addition, four different organic materials are used as back surface field layer (BSL) to the same device and performance is improved. The best conversion efficiency and open circuit voltage as high as 4.1% and 0.591 V respectively are obtained for the device with CuSCN as BSL. Consequently, a range of combined values of the energy band gap and electron affinity of the BSL materials are examined for optimal device performance.     

NH4PO3/SiO2 composite as electrolyte for intermediate temperature fuel cells

NH₄PO₃/SiO₂ composite based electrolyte with SiO₂ as supporting matrix was prepared. A thermogravimetric analysis was performed. Its electrochemical properties were investigated by an impedance spectroscopy within the temperature range of 100–300 °C under dry and humid atmospheres. The maximum conductivity is 6 mS cm^− 1 at 300 °C under dry N₂ and 0.1 S cm^− 1 at 200 °C under humid N₂.     

圆盘状Bi2WO6-BiPO4异质结的水热合成及光催化性能 (cited: 1)

采用水热法制备Bi₂WO₆-BiPO₄异质结光催化剂．利用模拟太阳光照射下的罗丹明B降解实验评价了Bi₂WO₆-BiPO₄复合物的光催化性能．结果表明,Bi₂WO₆-BiPO₄光催化活性比Bi₂WO₆和BiPO₄高得多．当Bi₂WO₆与BiPO₄的摩尔比为1:1时复合光催化剂对罗丹明B的降解率最高．Bi₂WO₆-BiPO₄催化活性增强主要归结为两者之间形成了有效的异质结结构,其内建电场能够促进光生载流子的分离．同时,Bi₂WO₆的加入增强了其对可见光的吸收．研究表明O₂· ^-和h⁺在光催化降解过程中是主要的活性物种