Separation Of Photoinduced Charge Carriers Research Articles

Fabrication of CdS/Zn2GeO4 heterojunction with enhanced visible-light photocatalytic H2 evolution activity

CdS/Zn2GeO4 (CG) composites were synthesized through the simple hydrothermal process. The crystal structure, morphology and light absorption property of the products were studied in detail. The CG composites showed excellent photocatalytic hydrogen production performance upon visible light illumination. Especially, the CG-3 composite displayed the highest H2 evolution rate of 1719.8 μmol h−1 g−1, which was about 3.80 and 4.28 times higher than the pure CdS and Zn2GeO4. Besides, the cyclic stability of the CG-3 composite was also excellent. The PL, photocurrent response and EIS spectra results testified that the efficient separation and transfer of photoinduced charge carriers achieved between CdS and Zn2GeO4, which could result in the promotion of photocatalytic performance. Moreover, a possible mechanism of H2 generation over CdS/Zn2GeO4 heterojunction was discussed. The practicable way to construct heterojunction composites would be helpful for the design of other systems with excellent photocatalytic property.

Biosynthesis of Ag deposited phosphorus and sulfur co-doped g-C3N4 with enhanced photocatalytic inactivation performance under visible light

Photocatalytic inactivation has been proved to be an effective strategy for controlling biohazards. Herein, the novel Ag deposited phosphorus and sulfur co-doped g-C3N4 (PSCN) composites with different Ag content were constructed via a facile calcination combining with biogenic-reduction method for inactivating Escherichia coli (E. coli). The detailed characterization results indicated that P and S elements were successfully co-doped into g-C3N4 (CN) lattice and Ag nanoparticles (NPs) were evenly deposited on the surface of PSCN with diameter range of 4–20 nm. The Ag/PSCN at depositing amount of 4 wt% (Ag/PSCN-4) achieved the strongest photocatalytic inactivation along with excellent stability, which could completely inactivate 7.0 log cells of E. coli within 60 min of visible light irradiation. This improved bactericidal performance was mainly attributed to the synergistic effects of P-S co-doped together with Ag deposition, which resulted in the increased visible light utilization, the improved separation and transfer efficiency of photo-induced charge carriers. Moreover, active species trapping experiments revealed that the generated superoxide radicals (O2−) and holes (h+) played the significant roles in photocatalytic inactivation process. Our present work presented a promising and environmentally friendly strategy to enhance the photocatalytic capacities of CN based composites for pathogens inactivation.

Photocatalytic overall water splitting by spatially-separated Rh and RhOx cocatalysts on polymeric carbon nitride nanosheets

Site-selective deposition of dual cocatalysts for H2 and O2 evolution reactions on polymeric carbon nitride (PCN) nanosheets still remains a great challenge due to the difficulty in controlling the nucleation location and growth dynamics. Herein, we report an one-step and efficient photodeposition strategy to simultaneously load Rh and RhOx nanoparticles on PCN nanosheets with desired spatial isolation. The dual cocatalysts modification can effectively accelerate the reaction kinetics and boost the separation of photoinduced charge carriers, greatly enhancing overall water photosplitting efficiency. As a result, the overall water photosplitting activity of Rh-RhOx/PCN is obviously higher than those of RhOx/PCN and Rh/PCN. This work provides a new method for loading dual cocatalysts on the PCN nanosheets with spatial isolation to achieve pure water splitting under visible light and offers promise for a wealth of innovative applications in energy conversion, catalysis and environmental protection.

Continuously Improved Photocatalytic Performance of Zn2SnO4/SnO2/Cu2O Composites by Structural Modulation and Band Alignment Modification.

Improving the photocatalytic performance of multi-component photocatalysts through structural modulation and band alignment engineering has attracted great interest in the context of solar energy utilization and conversion. In our work, Zn2SnO4/SnO2 hierarchical architectures comprising nanorod building block assemblies were first achieved via a facile solvothermal synthesis route with lysine and ethylenediamine (EDA) as directing agents, and then chemically etched in NaOH solution to enlarge the surface area and augment active sites. The etched Zn2SnO4/SnO2 hierarchical architectures were further decorated by Cu2O nanoparticles though an in situ chemical deposition method based on band alignment engineering. In comparison with unetched Zn2SnO4/SnO2, the specific surface area of Zn2SnO4/SnO2/Cu2O hierarchical architectures became larger, and the responsive region and absorbance intensity became wider and higher in the whole visible-light range. Zn2SnO4/SnO2/Cu2O hybrid photocatalysts presented enormously improved visible-light photocatalytic behaviour for Rhodamine B (RhB) decomposition. The enhancement of photocatalytic behaviour was dominantly attributed to the synergy effect of the larger specific surface area, higher light absorption capacity, and more effective photo-induced charge carrier separation and migration. A proposed mechanism for the enormously promoted photocatalytic behaviour is brought forth on the basis of the energy-band structure combined with experimental results.

Enhanced visible-light photocatalytic H2 production of hierarchical g-C3N4 hexagon by one-step self-assembly strategy

Herein, self-assembly of hierarchical multihole g-C3N4 hexagon with excellent specific surface area (129 m2/g) and nitrogen vacancies were accomplished via a one-step polymerization of hydrothermal-treated dicyandiamide and ethylene-diamine-tetra-acetic acid (EDTA). The special chelate structure of EDTA efficiently enlarged a broad visible light response range, and the concentrations of EDTA promoted the self-assembly formation of different surface morphology. The photocatalytic H2 production rate under visible light for the optimal g-C3N4 hexagon (CN-20E) reaches 5839 μmol·g−1·h−1 and its apparent quantum efficiency reaches up to 7.3% at 420 nm, which has a 102 times higher for H2 production rate than that of bulk g-C3N4 (57 μmol·g−1·h−1). Special structure of the multihole hexagon endows them with remarkably visible light absorption, fast separation of photo-induced charge carriers, large surface areas as well as the exposure of potential photocatalytic active sites, thereby dramatically improved the H2 production property. Moreover, the forming process for the specific structure and the reaction mechanism of the enhanced photocatalytic activity were proposed according to the experimental results and theoretical calculations. This work exhibits a new avenue to rehandle graphitic carbon nitride precursor to build a grafted structure for developing highly efficient g-C3N4 in the practical photocatalytic application.

Enhanced Visible-Light Photocatalytic Remediation of Tetracycline Hydrochloride by Nanostructured BiOI Homojunctions

The BiOI homojunctions were constructed between BiOI nanosheets and BiOI nanoflowers, which were prepared with a facile ultrasound-assisted solvothermal method. BiOI nanosheets were uniformly distributed on BiOI nanoflowers surface. The homojunction structure constructed between nanosheets and nanoflowers efficiently speeds up the transfer and separation of photoinduced charge carriers, which is beneficial to promote the photocatalytic activity. Compared with single BiOI, BiOI homojunctions exhibit remarkably improved photocatalytic degradation activity for tetracycline hydrochloride (TC); photodegradation rate of 69.43% for TC has been reached after being irradiated under visible light for 1[Formula: see text]h. Deeper analyses of photocatalytic degradation mechanism of TC have been conducted; the results identify that [Formula: see text] and h[Formula: see text] play important roles during the TC degradation reaction.

In Situ Construction of a Two-Dimensional Heterojunction by Stacking Bismuth Trioxide Nanoplates with Reduced Graphene Oxide for Enhanced Water Oxidation Performance.

In this study, a two-dimensional heterojunction consisting of bismuth trioxide nanoplates and layered reduced graphene oxide was synthesized using a facile In Situ growth route. A series of characterization tests indicated that the reduction of graphene oxide played a key role as an electron collector for enhancing photoinduced charge carrier separation efficiency. Thus, the as-prepared reduced graphene oxide/bismuth trioxide composite exhibited enhanced photocatalytic water oxidation, which was higher than that of pristine bismuth trioxide under simulated solar light irradiation. Furthermore, the photoelectrochemical properties of the prepared hybrid system were investigated to understand the transfer of photoinduced electrons and holes between layered reduced graphene oxide and bismuth trioxide nanoplates. Thus, this strategy provided an efficient approach for the fabrication of graphene composites containing hierarchical ternary oxides for photocatalysis.

Construction of heterostructure CoWO4/g-C3N4 nanocomposite as an efficient visible-light photocatalyst for norfloxacin degradation

The CoWO4 nanoparticles assembled with g-C3N4 nanosheets were successfully fabricated by means of a simple hydrothermal method, followed by ultrasonication. The surface topography, crystalline structure, chemical status, and optical properties of as-prepared materials are well characterized herein. These studies unveil the formation of CoWO4 nanoparticles assembled on the surface of g-C3N4 nanosheets with good crystallinity. EDX and XPS studies substantiated that there were no impurities in the synthesized photocatalyst materials. Furthermore, surface topographical (TEM) analysis affirms that CoWO4 nanoparticles were successfully anchored to g-C3N4 nanosheet. This worthy interfacial contact between CoWO4 and g-C3N4 leads the transfer and separation of photo-induced charge carriers. The effect of catalyst loading and initial substrate concentrations on photocatalytic degradation of norfloxacin by as-prepared samples were examined under visible light. We found that the rate of CoWO4 and g-C3N4 photocatalytic degradation of norfloxacin was 3.18 times and 2.69 times higher than that of pure g-C3N4 and CoWO4, respectively. Enhanced photocatalytic activity was because the synergism between CoWO4 nanoparticles and g-C3N4 nanosheets inhibit the fast recombination of photogenerated e−–h+ pairs. In addition, the radical scavenger study substantiates that OH plays dominate role for norfloxacin degradation rather than O2−. A possible mechanism responsible for photodegradation of the Z-scheme was ultimately proposed. This work can be useful in the rational design and delivery of new types of Z-scheme photocatalysts.

Interfacial charge-transfer transitions enhanced photocatalytic activity of TCNAQ/g-C3N4 organic hybrid material

Abstract Graphitic carbon nitride (g-C3N4) photocatalyst has a promising application prospect in solving environment problems and energy crisis. In order to improve the photocatalytic activity of g-C3N4, a novel TCNAQ/g-C3N4 organic hybrid photocatalyst was designed by introducing 11,11,12,12-tetracyanonaphtho-1,4-quinodimethane (TCNAQ) as an electron acceptor. Due to the interfacial charge-transfer transitions between g-C3N4 donor and TCNAQ acceptor, separation and migration of photo-induced charge carriers were promoted, while their recombination was prohibited, which led to enhanced photocatalytic performance in pollutant degradation. This work provides a strategy to produce efficient hybrid photocatalysts with high light-to-current conversions due to the interfacial charge-transfer transitions, which have potential applications in light-to-energy conversions.

Flower-like direct Z-scheme WS2/Bi2O2CO3 photocatalyst with enhanced photocatalytic activity

Novel flower-like direct Z-scheme WS2/Bi2O2CO3 photocatalyst was fabricated via a one-pot hydrothermal method. The structure, morphology, together with the optical and photoelectrochemical properties of the photocatalysts were analyzed by various techniques. The flower-like WS2/Bi2O2CO3 photocatalyst exhibited efficient removal of Lanasol Red 5B, with rate constants of 1.85 and 3.23 times higher than that of Bi2O2CO3 under UV and simulated solar irradiation, respectively. Additionally, the flower-like WS2/Bi2O2CO3 photocatalyst exhibited 95% ciprofloxacin removal efficiency within 90 min. The enhanced photocatalytic activity of optimal WS2/Bi2O2CO3 could be attributed to the synergistic effect of the effective photoinduced charge carrier separation and transfer, the enhanced light harvesting ability and larger specific surface area. Furthermore, the active species trapping and ESR experiments indicated that hole (h+), superoxide radical (•O2−) and hydroxyl radical (•OH) were main reactive species in the photocatalytic process. The WS2/Bi2O2CO3 heterojunction was speculated to follow a Z-scheme charge transfer mechanism. This facile method provides new possibilities for the fabrication of effective Bi2O2CO3-based photocatalysts for environmental remediation.

Enhanced light-driven water splitting by fast electron transfer in 2D/2D reduced graphene oxide/tungsten trioxide heterojunction with preferential facets

In this work, 2D/2D tungsten trioxide (WO3) plates/reduced graphene oxide (RGO) heterojunction was prepared by combining the (0 0 2) faceted WO3 with RGO nanosheets. An enhanced photocatalytic efficiency of O2 evolution was achieved due to the uncovering electronegative oxygen atoms, which results in the enhancement of photo-induced charge carrier separation efficiency. The 3 wt% RGO/WO3 heterojunctions display significantly the increase of O2 production, which is 3.9 and 7.3 times higher than those of WO3 nanoplates with preferential (0 0 2) facets and commercial WO3. The strategy could provide an efficient approach for the fabrication of graphene-based metal oxide hybrids with exposed facets towards high photocatalytic performance.

Improved visible light photocatalytic performance through an in situ composition-transforming synthesis of BiVO4/BiOBr photocatalyst

The monoclinic scheelite (ms) BiVO4 shows great potential applications in the photocatalyst due to its strong light absorption in the visible light region. To improve the separation of photoinduced charge carriers in BiVO4, such as election and hole, BiVO4/BiOBr photocatalyst with a high visible light activity was synthesized using an in situ chemical transformation method with BiVO4 as a matrix and hydrobromic acid (HBr) as a construction agent. The effect of the concentration of BiOBr on the formation of BiVO4/BiOBr nanocomposite was studied. BiVO4/BiOBr nanocomposite was characterized in detail and the results show that the BiVO4 and BiOBr co-present in the system and BiVO4/BiOBr nanocomposite has a well hydrophilic surface. The photocatalytic properties of such nanocomposite were investigated through studying the degradation of a pollutant model (RhB), and meanwhile, the recombination of electron and hole was evaluated by photoluminescence (PL) spectroscopy. The results reveal that incorporation of BiOBr on BiVO4 could contribute to the enhanced separation and transport of photoinduced electrons and hole, leading to improved photocatalysis performance. The BiVO4/BiOBr photocatalyst could be applied as an outstanding photocatalytic material for organic pollutants degradation.

Noble metal free CdS@CuS-NixP hybrid with modulated charge transfer for enhanced photocatalytic performance

Constructing low-cost and highly active photocatalysts is extremely desirable for converting solar energy into chemical fuels. Herein, we report a one-dimensional (1D) CdS@CuS-NixP (CCN) core-shell heterostructure catalyst for effective photocatalytic hydrogen (H2) evolution with modulated charge transfer, which exhibits remarkably higher activity than bare CdS nanowires (NWs). The evenly distributed and closely contacted CdS@CuS (CC) heteroepitaxial nanomaterial constructs a type-I heterostructure for improved photoinduced charge carrier separation. The NixP nanoparticles (NPs), which act as a cocatalyst, not only contribute to constructing three-level charge transfer by capturing the photogenerated electrons, but also provide active sites for proton reduction. In addition, the cocatalyst strategy reported here can be extended to other transition metal phosphide (TMP). Mechanistic studies suggest that the cooperative synergy of three-level charge transfer and introduction of reaction sites results in a significant enhancement of photoactivity for H2 evolution.

Compositional regulation and modification of the host CdS for efficient photocatalytic hydrogen production: Case study on MoS2 decorated Co0.2Cd0.8S nanorods

Compositional regulation and modification of CdS are effective strategies to enhance its photocatalytic activity and stability. Herein, a series of MoS2 modified Co0.2Cd0.8S nanorods (CCS) was synthesized by a hydrothermal method and used for photocatalytic hydrogen evolution reaction (HER) under visible light irradiation. The results indicated that the HER activity and stability of CdS could be substantially improved by the introduction of Co2+ into CdS lattice, which can accelerate the separation of photoinduced charge carriers and avoid the formation of high oxidation power holes (h+) due to the upward shift of the valence band edge. The HER performance of CCS could be further enhanced by the decoration of MoS2 nanosheets. CCS loaded with 5% MoS2 (wt%) showed the highest activity (2835.6 μmol·g−1·h−1), which is about 8.9 and 1.6 times higher than that of CdS and CCS. The type II heterojunction formed between CCS and the intimately contacted MoS2 accounts for the improvement as MoS2 can serve as trapping centers for photoinduced electrons (e−) and active sites for HER. This work demonstrated that the activity and the stability of CdS for photocatalytic HER could be boosted by a consolidation of CoS with the host CdS to form a solid solution and a further decoration with low-cost MoS2 cocatalyst.

Facile synthesis of cactus-shaped CdS-Cu9S5 heterostructure on copper foam with enhanced photoelectrochemical performance

In this study, we report the synthesis of cactus-shaped CdS-Cu9S5 heterostructure on copper foam (CdS-Cu9S5-CF) through a cost-effective strategy. The as-prepared CdS-Cu9S5-CF is demonstrated to be a highly efficient catalyst for photoelectrochemical (PEC) water splitting, and its high performance is attributed to its unique cactus-shaped structure, which provides abundant surface catalytic active sites, and numerous charge transfer channels, thereby enhancing the transport and separation of photoinduced charge carriers during the PEC process. The optimized 3% CdS-Cu9S5-CF (the mole ratio of CdS: Cu9S5 = 3: 100) exhibits higher photocurrent density than those of pure Cu9S5 and other CdS-Cu9S5-CF catalysts because the synergetic effects between Cu9S5 and CdS can significantly inhibit the recombination of photoinduced charge carriers during the PEC process. We believe that the new synthetic route developed in this study will enable the facile preparation of metal sulfide-based catalysts for high-efficiency PEC water splitting.

Preparation of SnO2/conjugated polyvinyl alcohol derivative nanohybrid with good performance in visible light-induced photocatalytic reduction of Cr(VI)

A new visible light-responsive SnO2/conjugated polyvinyl alcohol derivative (CPVA) nanohybrid photocatalyst was prepared by an easy-to-implement three-step method, using low cost and easily accessible SnCl4·5H2O, PVA and H2O as the source materials. The photocatalytic properties of the as-prepared SnO2/CPVA nanohybrid were examined through the reduction of aqueous Cr(VI) in the presence of citric acid and visible light (λ > 420 nm). The compositional and structural analysis of SnO2/CPVA nanohybrid after the recycle stability test was also performed. The photodegradation efficiency of Cr(VI) using SnO2/CPVA nanohybrid and other reported visible light-responsive photocatalysts (g-C3N4 and ZnFe2O4/CPVC nanocomposite) were compared. Besides, the effects of the solution pH and different water matrices (including black chromium electroplating solution, industrial cooling water, yellow sea water, and tap water) on the efficiency of photocatalytic reduction of Cr(VI) by SnO2/CPVA nanohybrid were also investigated. The results manifested that the as-prepared SnO2/CPVA nanohybrid had both high activity and good stability in photocatalytic reduction of aqueous Cr(VI) under visible light irradiation. According to the results of photoabsorption, photoluminescence, transient photocurrent response, electrochemical impedance, and Mott-Schottky characterization, it was deduced that the notable visible light-activated photocatalysis of SnO2/CPVA nanohybrid may originate from its prominent visible light-absorbing ability and the efficient electron transfer from CPVA to SnO2 (which results in the efficient separation of photoinduced charge carriers of CPVA as well as the sensitization of SnO2).

Core-shell synergy and Eu3+ doping in boosting charge transfer in Eu3+ doped TiO2-carbon core-shell nanohybrids: Sustainable synthesis and visible light-driven photocatalysis

Abstract Core-shell nanostructures have gained enormous research interest owing to a synergetic interfacial interaction resulting in enhanced functionalities, particularly optical and optoelectronic, and sometimes exotic properties. The investigation reports on a sustainable synthesis of Eu3+ doped TiO2‑carbon core-shell nanohybrids (0.5–2.0 mol% Eu3+) using a simple green-chili-based biogenic method. The crystal structure, morphology, optical properties are systematically studied using X-ray diffraction, Electron microscopy, UV–visible light absorption spectrophotometry, photocurrent and electrochemical impedance measurement. The roles of carbon shell and Eu3+ ions in boosting the photocatalytic activity of the nanohybrids are studied and analysed by evaluating their degradation performance under visible light using methylene blue (MB) and 2-cholorophenol (2-CP) as target water pollutants. 1.5 mol% Eu3+ doped core shell nanohybrid, annealed at 600 °C exhibits highest removal efficiency 91.5% and 76.8% for MB and 2-CP respectively. The analysis in correlation with the properties studied reveals that a strong core-shell interfacial coupling and Eu3+ doping boosts up the photo-induced charge carrier generation and separation that enhances degradation performance of the sample. The degradation efficiency and rate are nearly three and five times of that of bare TiO2. The work demonstrates a sustainable development of core-shell nanohybrids showing a scope for solar light-driven photocatalytic applications.

Boosting visible-light photocatalytic degradation of indomethacin by an efficient and photostable Ag3PO4/NG/WO3 composites

In our work, Z-scheme Ag3PO4/NG/WO3 composites were fabricated via a facile deposition approach, which was used in the photocatalytic degradation of indomethacin (IDM) under visible light irradiation. The as-prepared Ag3PO4-based photocatalysts were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscope, Fourier transform infrared, X-ray photoelectron spectroscopy and UV–visible diffuse reflectance spectroscopy in order to determine the chemical structure, morphological feature and optical performance. From the degradation experiments of IDM, the Ag3PO4/NG/WO3 composite exhibited the highest photocatalytic activity and stability, and its kinetics constant was ~8 times of pure Ag3PO4. Furthermore, reactive species trapping experiment, electron spin resonance, liquid chromatography-mass spectrometry, total organic carbon, photoelectrochemical measurement and photoluminescence spectra were applied to analyze the possible degradation pathways and photocatalytic mechanism of IDM. The results indicated that the visible-light photocatalytic degradation of IDM using Ag3PO4/NG/WO3 conformed to a Z-scheme photocatalysis mechanism, further facilitating the photoinduced charge carriers separation, and inhibiting the recombination of photoinduced electron-hole pairs. It also confirmed that the holes, OH and O2– radicals generated in Z-scheme system played the significant roles during the photocatalytic degradation of IDM.

Bi2MoO6/g-C3N4 of 0D/2D heterostructure as efficient photocatalyst for selective oxidation of aromatic alkanes

In the production of value-added organics, the design of efficient photocatalysts for the selective oxidation of C H bonds is crucial. In this work, zero-dimension (0D) Bi 2 MoO 6 quantum dots (QDs), two-dimension (2D) g-C 3 N 4 nanosheets (NSs), and Bi 2 MoO 6 /g-C 3 N 4 of 0D/2D heterostructure were prepared via a facile two-step process. Anchoring the Bi 2 MoO 6 QDs on g-C 3 N 4 NSs can shorten the charge-migration distance, extend the visible-light absorption range and provide active sites in abundance. The obtained Bi 2 MoO 6 /g-C 3 N 4 exhibits excellent photocatalytic activity as well as stability for the selective oxidation of toluene to benzaldehyde using green O 2 as oxidant, achieving a benzaldehyde formation rate of 850.7 μmol·g −1 ·h −1 under solvent free condition with visible light irradiation. • Bi 2 MoO 6 /g-C 3 N 4 (0D/2D) photocatalyst was prepared by a facile two-step process. • The novel structure is beneficial for the separation of photo-induced charge carriers. • It shows high activity and stability in the selective oxidation of toluene to benzaldehyde without any solvent.

Ultrathin 2D/2D ZnIn2S4/MoS2 hybrids for boosted photocatalytic hydrogen evolution under visible light

A well-connected hetero-layered ZnIn2S4/MoS2 composite was fabricated via an electrostatic self-assembly process to boost photocatalytic hydrogen evolution under visible-light irradiation. Ultrathin nanosheets contribute to efficient charge transfer by reducing electron diffusion length. In the sheet-on-sheet heterostructure, ultrathin ZnIn2S4 nanosheets (NSs) and MoS2 NSs were well connected with each other to form a large and intimate contact interface, which features an efficient separation and migration of photoinduced charge carriers. Moreover, MoS2 NSs endow the composite with abundant active sites and lowers its overpotential for water reduction. Consequently, the ultrathin hetero-layered ZnIn2S4/MoS2 composite with optimized loading of MoS2 achieves a hydrogen production rate of 4.974 mmol g−1 h−1, which is ca. 50 times as much as that of pure ZnIn2S4, and 2.2 times as much as that of its ZnIn2S4/Pt counterpart. This work provides inspiration for the fabrication of well-contacted hetero-layered structure for photocatalytic hydrogen evolution.