Binary Heterojunction Research Articles

Exploring the Enhanced Catalytic Activity of Pt Nanoparticles Generated on the Red Phosphorus/Graphitic Carbon Nitride Binary Heterojunctions in the Photo-assisted Hydrolysis of Ammonia Borane.

Ammonia borane (AB) holds great promise for chemical hydrogen storage, but its slow dehydrogenation kinetics under ambient conditions requires a suitable catalyst to facilitate hydrogen production from AB. Here, we fabricated binary red phosphorus/graphitic carbon nitride (RP/g-CN) heterojunctions decorated with Pt nanoparticles (NPs, denoted Pt/RP/g-CN) with a facile ultrasound-assisted two-step protocol as a photo-assisted catalyst for the hydrolysis of AB (HAB). The heterojunction established through intimate P-O-N bonds was proven to have improved photophysical properties such as a lower electron-hole recombination and enhanced visible light utilization compared to the pristine components. With the incorporation of Pt NPs, the optical properties of RP/g-CN heterojunctions were further improved through Schottky junction formation between semiconductors and Pt NPs, enabling a superb hydrogen gas (H2) generation rate of 142 mol H2·mol Pt-1·min-1 under visible light irradiation. Even though g-CN is a well-known host material for many metal NPs, here we discovered that the interaction of Pt NPs with RP in the ternary heterojunction structure is more favorable than that of g-CN, stressing the key role of RP as a support material in the designed ternary heterostructure. The band alignment of the ternary heterojunction catalyst along with the flow of charge carriers was also studied and shown to be a type-II heterojunction structure without hole migration, namely, a complex type-II heterojunction. Several scavenger experiments were also conducted to explain the mechanism of the photo-assisted HAB. To the best of our knowledge, this is the first example of a dual mechanism proposed for the visible light-assisted HAB. While the majority of the H2 was believed to be produced on the Pt NPs surface with the traditional B-N bond dissociation mechanism, the strong oxidizing action of OH• radicals formed by the heterojunction photocatalyst was also speculated to account for the 33% increase in the activity upon visible light irradiation through another mechanism.

Enhanced photocatalytic degradation of imidacloprid by a simple Z-type binary heterojunction composite of long afterglow with metal-organic framework

Imidacloprid (IMC) is a widely used nicotine-based pesticide that can cause severe harm to water resources. To address this issue, a simple binary heterojunction photocatalyst was constructed to degrade IMC under visible light. Furthermore, the catalyst was able to continue degrading approximately 15% of IMC within 5 h under dark. The possible photocatalytic degradation intermediate's structure and low toxicity were verified by mass spectrometry and zebrafish embryo experiments, respectively. The catalyst also exhibited good stability. Therefore, a simple photocatalyst with excellent performance and low toxicity of degradation products was successfully developed for IMC pesticide removal in water.

The effect of Ni and Co co-catalysts on the catalytic activity of mesoporous graphitic carbon nitride/black phosphorus/molybdenum disulfide heterojunctions in solar-driven hydrogen evolution

In this work, a ternary heterojunction photocatalyst composed of mesoporous graphitic carbon nitride, black phosphorus, and molybdenum disulfide (m-CN/BP/MoS2) was firstly fabricated for the visible-light-driven hydrogen evolution reaction (HER) via water splitting. The photocatalytic activity of m-CN/BP/MoS2 photocatalyst was further improved by incorporating Ni and Co co-catalysts, denoted as m-CN/BP/MoS2-Y (Y: Ni, Co). The final quaternary nanocomposites were experimentally demonstrated in the form of mixed heterojunctions (type-I, type-II, and Schottky junctions) to manipulate the photogenerated carriers with the aim of reducing their recombination rate and increasing the light-harvesting ability of the pristine components. To find the best combination of different semiconductors in the heterojunction to ensure the highest photocatalytic HER activity, the loading ratio of each component was optimized one-by-one by considering the rate of HER under the same conditions. The photocatalytic HER activity of m-CN/BP/MoS2-Ni (5 wt%) and m-CN/BP/MoS2-Co (0.5 wt%) photocatalysts reached up to 21.668 mmol g−1 and 29.179 mmol g−1 for 8 h in the presence of triethanolamine electron donor under visible light irradiation, which were about 11 and 15 times higher than that of m-CN/BP binary heterojunctions, 4 and 5 times higher than that of m-CN/BP/MoS2 ternary heterojunctions, respectively. Ni or Co co-catalysts enhanced charge separation and thus increasing the rate of H2 evolution owing to their suitable d-band levels. This present study supplies a strategy to design efficient photocatalysts for solar fuel production without using non-noble metal cocatalysts.

Binary heterojunctions of Mg/Al-LDH and carbon-based matrixes derived from self-assembly synthesis for inhibition of pyrene photopolymerizing: Elucidation of LDHs protecting bitumen against UV aging

Layered double hydroxides (LDHs) have been found to protect bitumen against UV aging that was a culprit to shorten service life of new paved roads and burden environment with toxic volatiles in case of repaving roads time and again. Utilizing LDHs to improve the UV resistance to bitumen is desirable but the corresponding mechanism is still not be clarified. In this work, a simple self-assembly strategy is used to synthesize binary-heterojunction catalysts consisting of Mg/Al-LDH and carbon-based matrixes, aiming at obtaining copious mesopores and tailoring photocatalytic routes. The specific surface areas of the binary-heterojunction catalysts reached 193.94 and 156.31 m2/g for Mg/Al-LDH@biocarbon and Mg/Al-LDH@g-C3N4, respectively. It was found that the as-synthesized catalyst of Mg/Al-LDH@g-C3N4 was an outstanding inhibitor in photopolymerizing polycyclic aromatics, which was verified by photochemical experiments using pyrene (PY) as a target. The Mg/Al-LDH@g-C3N4 enabled to decrease the proportion of exciplex of PY to 8.63% upon UV irradiation, while the proportion was as high as 39.81% in the absence of Mg/Al-LDH@g-C3N4. The test results revealed that photogenerated holes and photogenerated electrons were responsible for accelerating the photodegradation process of PY and suppressing the photopolymerization of PY molecules, respectively. The binary-heterojunction Mg/Al-LDH@g-C3N4 showed its outstanding photocatalytic activities under UV irradiation, including avoiding PY molecules from degradation and macromolecular polymerization, which was attributed to the new channel for electron-hole recombination and built-up photocatalytic routes between Mg/Al-LDH and g-C3N4. This work provided a perspective for tailoring promising protective agents for bitumen anti-UV aging through building reasonable photocatalytic routes for heterogeneous structures.

Using waste silver metal in synthesis of Z-scheme Ag@WO3-CeO2 heterojunction to increase photodegradation and electrochemical performances

Design of a Z-scheme heterojunction structure is eco-friendly due to its multi-nanocatalyst performances like wastewater treatment, antibacterial and electrochemical activity. Herein, Ag was extracted from waste batteries in a nitric acid leaching manner. Also, WO3 nanorods and WO3-CeO2 were synthesized by the surfactant-assisted hydrothermal acidic and sol–gel methods, respectively. Silver nanoparticles were doped by wet impregnation method to prepare ternary (Ag@WO3-CeO2) and binary (Ag@WO3 and Ag@CeO2) heterojunctions. The band gap of the prepared Ag@WO3-CeO2 was remarkably diminished in comparison with the rest of the sample (from 2.73 to 2.59 eV). The Langmuir-Hinslewood model showed that ternary systems can degrade methylene blue twice as much as WO3-CeO2 and seven times more than single-component systems. This was due to the presence of silver as a mediator for the transfer of photogenerated electrons between two semiconductors. Also, methylene blue was degraded by more than 90.8% efficiency. Electrochemical impedance spectroscopy (EIS) analysis confirmed that the charge transfer resistance of Ag@WO3-CeO2 was decreased by more than 50%. The results of bactericidal activeness confirmed elevated inhibition capability of Ag@WO3-CeO2 towards E.coli with 99% degradation. X-ray fluorescence (XRF) results confirmed that 98% of silver can be re-extracted after 5 photocatalytic uses which is a material with green technology.

2D/2D NiAl LDH integrated graphitic carbon nitride with robust interfacial contact for driving photocatalytic hydrogen production

Photocatalytic hydrogen production is promising for generating carbon-free energy through water splitting. Efficient photocatalytic materials with high photochemical efficiency are crucial for creating well-structured photocatalytic systems. Layered Double Hydroxides (LDHs) have gained significant scientific attention due to their unique electronic structure, compositional flexibility, and tunable band gap, which make them highly active for photocatalytic hydrogen evolution. However, the high surface energy of LDHs can lead to layer deactivation and reduce their efficiency as standalone photocatalysts. Herein, a novel design of two-dimensional (2D) g-C3N4 with 2D NiAl LDH to construct morphologically 2D/2D binary heterojunction composite with strong electrostatic interactions has been investigated. Different characterization techniques, such as XRD, FESEM, EDX, UV–Vis spectra, and PL were conducted to assess its photo-physical properties. The introduction of 15% NiAl LDH led to a significant increase in hydrogen production, reaching 28.13 µmol h−1, which is 3.75 and 9 times higher than pure g-C3N4 and NiAl LDH, respectively. The improved photocatalytic performance was attributed to the efficient charge transfer facilitated by the formation of Type-II heterojunction system. The interface junction observed in 2D/2D g-C3N4/NiAl LDH restricts charge recombination and extends its lifetime to carry out photocatalytic reactions. Furthermore, the effective integration of NiAl LDH onto g-C3N4 observed from FESEM and EDX prevents the deactivation of LDH nanoplates, supplying abundant reaction-active sites to expedite the photo-redox reaction. Significantly, the incorporation of transition metals, such as Ni and Al, into the LDH brucite layer enhances the optical properties, allowing for better utilization of light and further improving photocatalytic hydrogen production. This work provides valuable insights into the development of 2D/2D morphologically-engineered nanohybrids for driving photocatalytic hydrogen production.

Construction of a Ce‐UiO‐66/MCo2O4 Heterojunction for Photocatalytic Cr(VI) Detoxification Through a p‐n Junction Formation Mechanism

AbstractHeterojunction engineering in catalyst structures is a promising approach to solve some restrictions in photocatalyst design, such as a narrow photoabsorption range and rapid recombination of photogenerated charge carriers. In this work, MCo2O4 (M=Mn, Zn, Fe) was synthesized using a template method. The porous MCo2O4 was composited by Ce‐UiO‐66 to form a heterojunction structure. The resultant material Ce‐UiO‐66/MCo2O4 had a hierarchically porous architecture and was used as a photocatalyst for Cr(VI) reduction. The coupling of Ce‐UiO‐66 and MCo2O4 resulted in a p‐n junction mechanism for charge carrier transfer. The Ce‐UiO‐66/MCo2O4 heterojunctions exhibited high Cr(VI) reduction ability under visible light irradiation over 120 min. The highest Cr(VI) photoreduction rate of the heterojunction is 14 times that of Ce‐UiO‐66. The binary heterojunction maintains high photoreduction efficiency (100 %) of Cr(VI) after four cycling tests showing excellent photocatalytic stability.

BaSnO3-SnO2 heterojunction mesoporous photoanode for quantum dot-sensitized solar cells

Mesoporous photoanodes, as quantum dot adsorption framework and electron transfer paths, are the key components in efficient quantum dot-sensitized solar cells (QDSSCs). Binary heterojunction mesoporous photoanodes hold promise for facilitating electron transport due to the heterojunction potential, when compared to conventional mono-component mesoporous photoanodes. In this work, we construct a binary mesoporous photoanode with enhanced mesoporous and electron transport using a BaSnO3-SnO2 heterojunction, and then fabricated CdSe/CdS co-sensitized QDSSCs. The charge extraction, open-circuit voltage decay, electrochemical impedance spectroscopy, and intensity-modulated voltage/photocurrent spectroscopy measurements demonstrated that, in contrast to the BaSnO3 mesoporous photoanode, the BaSnO3-SnO2 mesoporous photoanode could effectively reduce charge recombination and extend the electron lifetime, thus promoting charge collection in the QDSSCs. Based on these merits, the BaSnO3-SnO2 mesoporous photoanode-based solar cells yielded a power conversion efficiency of 3.14%, resulting in a ca. 11% increase in power conversion efficiency, compared to the reference BaSnO3 solar cells.

Black Phosphorus/WS2-TM (TM: Ni, Co) Heterojunctions for Photocatalytic Hydrogen Evolution under Visible Light Illumination

Black phosphorus (BP) has recently emerged as a versatile photocatalyst owing to its unique photophysical properties and tunable bandgap. Nonetheless, the rapid recombination of the photogenerated charges of pristine BP samples has significantly hindered its practical applications in photocatalysis. Herein, we report, for the first time, the effect of transition metal nanoparticles (Ni and Co) as co-catalysts on the photocatalytic activity of BP/tungsten disulfide (WS2) binary heterojunctions (BP/WS2-TM (TM: Ni, Co)) in the hydrogen evolution reaction (HER) under visible light irradiation (λ > 420 nm). Ternary heterojunctions named BP/WS2-TM (TM: Ni, Co) were synthesized via a chemical reduction method, leading to the formation of an S-scheme heterojunction, in which BP acts as a reduction catalyst and WS2 serves as an oxidation catalyst. BP/WS2-Ni and BP/WS2-Co performed substantial amounts of hydrogen generation of 9.53 mmol h−1g−1 and 12.13 mmol h−1g−1, respectively. Moreover, BP/WS2-Co exhibited about 5 and 15 times higher photocatalytic activity compared to the binary BP/WS2 heterojunctions and pristine BP, respectively. The enhanced photocatalytic activity of the heterojunction catalysts is attributed to the extended light absorption ability, enhanced charge separation, and larger active sites. This study is the first example of photocatalytic hydrogen evolution from water by using Ni- and Co-doped binary BP/WS2 heterojunctions.

Tailoring the redox ability of carbon nitride quantum dots/reduced graphene oxide-black phosphorus (CNQDs@rGOBP) ternary heterojunctions for photodegradation of organic pollutants

The direct utilization of solar energy in chemical transformations has paved the way for widespread use of photocatalysis for degradation. However, the state-of-the-art photocatalytic systems for various applications have not yet reached the desired level due to poor visible-light absorption and the high-cost requirements of the developed photocatalysts. Recently, the combination of different semiconductors via band engineering has been regarded as a highly efficient strategy to construct metal-free photocatalysts. In this study, a novel ternary heterojunction photocatalyst was fabricated by decorating reduced graphene oxide/black phosphorus binary heterojunctions (rGOBP) with carbon nitride quantum dots (CNQDs) via the ultrasound-assisted liquid exfoliation method. Different ratios of rGOBP binary and CNQDs@rGOBP ternary heterojunctions were prepared to investigate how the content is correlated synergistically to the coupling of the materials at their interfaces, thus possessing a superior photophysical properties. Combining the polar functional groups of as-synthesized rGO and CNQDs with the non-bonding electrons of BP on the surface led to the formation of a chemically stable photocatalyst with high catalytic performance. Harmonizing the salient features of each material boosted the degradation efficiency of organic pollutants 2.5 times in aqueous media compared to their pristine components. The photocatalytic performance of CNQDs@rGOBP heterojunctions was screened by studying different pollutants and catalyst concentrations. Moreover, the photogenerated charge migration pathway was proved by considering the results of the scavenger experiments and changes in the work functions of materials. A nonclassical type-I heterojunction, occurring at the farthest charges of band edges, was proposed as the underlying mechanism behind the superior photocatalytic activity of CNQDs@rGOBP ternary heterojunctions.

Solution-processed Bi2S3/BiVO4/TiO2 ternary heterojunction photoanode with enhanced photoelectrochemical performance

Abstract TiO2 is an important component of photoelectric devices. How to broaden the light absorption of TiO2 and accelerate the separation of photo-generated electrons and holes is the focus of the current research. Building heterojunction with narrow band gap semiconductor and TiO2 is one of the important measures to improve its photoelectric performance. We prepared BiVO4/TiO2 binary heterojunction by the simple hydrothermal method and analyzed the effect of BiVO4 precursor solution concentration on the microstructure and photoelectric performance of the heterojunction. BiVO4/TiO2 binary heterojunction can effectively improve the photoelectric performance of TiO2, and the transient current density reaches 85 μA/cm2. To further boost the photocurrent of BiVO4/TiO2, Bi2S3 was in situ grown on the heterojunction to form Bi2S3/BiVO4/TiO2 ternary heterojunction. The results show that the band gap of Bi2S3/BiVO4/TiO2 composites is significantly narrowed compared with that of TiO2. The light absorption has been expanded to the visible range, and the photogenerated current density is also greatly boosted (0.514 mA/cm2). This Bi2S3/BiVO4/TiO2 ternary heterojunction accelerates the separation of photo-carriers and improves the photoelectric performance of the device. The possible transport mechanism of photo-carriers in ternary heterojunction is analyzed. The current study provides an effective strategy for in situ construction of novel multicomponent heterojunction and provides a basis for the application of Bi2S3/BiVO4/TiO2 in the optoelectronic field.

Hierarchical UiO-66(−NH2)/CuInS2 S-Scheme Photocatalyst with Controlled Topology for Enhanced Photocatalytic N2 Fixation and H2O2 Production

The fabrication of defect rich S-scheme binary heterojunction system with enhanced space charge separation and mobilization is a pioneering approach for improving photoreduction efficiency towards the production of value added chemicals. Herein, we have rationally fabricated an atomic sulfur defect-rich hierarchical UiO-66(-NH2)/CuInS2 n-p heterojunction system by uniform dispersion of UiO-66(-NH2) (UN66) nanoparticles over the surface of hierarchical CuInS2 nanosheets under mild conditions. The designed heterostructures are characterized by using different structural, microscopic, and spectroscopic techniques. The hierarchical CuInS2 (CIS) component shows surface sulfur defects leading to creation of more surface exposed active sites with improved absorption of visible light and augmented diffusion of charge carriers. The photocatalytic performance of prepared UiO-66(-NH2)/CuInS2 heterojunction materials is explored for N2 fixation and O2 reduction reactions (ORR). The optimal UN66/CIS20 heterostructure photocatalyst exhibited outstanding N2 fixation and O2 reduction performances with yields of 398 and 4073 μmol g-1 h-1 under visible light illumination, respectively. An S-scheme charge migration pathway coupled with improved radical generation ability accounted for the superior N2 fixation and H2O2 production activity. This research work furnishes a new perspective on the synergistic effect of atomic vacancy and an S-scheme heterojunction system toward enhanced photocatalytic NH3 and H2O2 production using a vacancy-rich hierarchical heterojunction photocatalyst.

Nitrogen and sulphur co-doped carbon quantum dot integrated bismuth oxide nanocomposite for photocatalytic degradation and electrochemical sensing applications

This study developed a novel nitrogen and sulphur co-doped carbon quantum dot-modified bismuth oxide binary composite (N,S-CQD- Bi2O3) through a hydrothermal method. The binary composite was successfully evaluated for its solar light-assisted photocatalytic abatement of toxic refractory pollutants such as dyes (rhodamine B, xylenol orange and sunset yellow), pesticides (2,4-D and diuron) and pharmaceutical drug (tetracycline). It was also successfully applied for the electrochemical detection of aniline molecules. The structural, morphological, optical, and electrochemical properties of the developed photocatalyst were investigated by XRD, FESEM, TEM, UV–vis DRS, XPS, PL, CV, amperometry and impedance techniques. Among the three different weight percentage binary composites, the 5% N,S-CQD-Bi2O3 displayed maximum photocatalytic performance. In all cases, the binary heterojunction exhibited a degradation efficiency of over 90% by converting the harmful compounds into less harmful ones. The scavenger experiments showed the roles of ˙OH and O2−˙ radicals in the photodegradation. The improved photocatalytic behaviour was ascribed to the Z-scheme heterojunction formation, enhancements in visible light absorption, improved surface morphology and efficient separation and transfer of electron-hole pairs. The electrochemical detection method yields a LOD of 0.25 nM within the linear range of 5–35 nM. Real sample analysis of aniline also produces excellent results with outstanding reproducibility.

Preparation and visible light catalytic degradation of magnetically recyclable ZnFe2O4/BiOBr flower-like microspheres

The construction of a binary heterojunction is a crucial method for solving the low separation efficiency and photon utilization of BiOBr (BOB) photogeneration carriers. In this study, magnetic recyclable ZnFe2O4/BiOBr (ZFB) heterojunction microspheres containing oxygen vacancies were prepared using a two-step solvothermal method. The results of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis show that ZnFe2O4 (ZFO) induces the growth of a nanolayer structure on the surface of BOB, the diffraction peak intensity ratio of I(102)/I(110) increases, and the specific surface area increases significantly. The analysis of photoelectric characteristics indicates that compared with BOB, ZFB has a smaller bandgap, a larger visible response range, and a higher photogenerated carrier migration and separation efficiency. ZFB can significantly degrade the activated benzene ring in organic molecules, with the degradation efficiency of Rhodamine B (RhB), norfloxacin (NOR), and sulfadiazine (SDZ) reaching 99.04 %, 91.70 %, and 86.64 %, respectively. Under the magnetic recovery, the five-cycle degradation performance retention rate reaches more than 92 %. Holes and superoxide radicals are the main active substances of ZFB photocatalytic materials for degradation of micropollutants. This research provides an idea for the preparation of a green and efficient photocatalytic material with high recyclable efficiency, which can simultaneously degrade various micropollutants in organic wastewater.

Novel F-modification of g-C3N4/ZnAl–LDHs binary heterojunction with notable 2D/2D configuration for efficient visible-light-driven photocatalytic elimination of organic pollutants

Novel F-modification of g-C3N4/ZnAl–LDHs binary heterojunction with notable 2D/2D configuration for efficient visible-light-driven photocatalytic elimination of organic pollutants

Metal-free g-C3N5 photocatalyst coupling MXenes Ti3C2 for tetracycline degradation: Insight for electron transfer mechanism, degradation mechanism and photothermal effect

At present, nitrogen-rich graphitic carbon nitride (g-C3N5) has emerged as an alternative for traditional graphitic carbon nitride (g-C3N4), due to better visible-light utilization efficiency and abundant surface functional groups. In this paper, a g-C3N5/MXenes (Ti3C2) binary heterojunction was prepared and used as a photocatalyst in environmental remediation. In tetracycline (TC) degradation, g-C3N5/Ti3C2 displayed better performance than those of the reference photocatalysts, including g-C3N5, g-C3N4, Ti3C2 and g-C3N4/Ti3C2. The underlying electron (e-) transfer mechanism was investigated in detail. Besides higher visible-light harvest, better separation efficiency of photo-induced charge carrier and lower surface resistance, an internal-electric-field was established at the interface between g-C3N5 and Ti3C2, and the driving force for e- transfer was 93.9 mV. hole (h+), 1O2, •OH and •O2- were involved into TC degradation, where h+ played a dominating role due to the high e- transfer efficiency. Benefiting from the good photothermal effect, g-C3N5/Ti3C2 could efficiently transfer solar energy to thermal energy, leading to the high temperature of catalyst surface and acceleration of the surface degradation reaction rate. This work provided a possibility to construct a g-C3N5-based visible-light photocatalyst to efficiently degrade the persistent organic contaminants.

Study on g-C3N4/BiVO4 Binary Composite Photocatalytic Materials

Recent studies have shown that the composite of semiconductor photocatalytic materials and g-C3N4 can effectively inhibit photocatalytic carrier recombination and enhance the adsorption performance of the composite photocatalytic materials, so that the composite photocatalyst has stronger photocatalytic activity. In this paper, three kinds of graphitic carbon nitride photocatalyst g-C3N4 with different morphologies were prepared using the same precursor system by the chemical cracking method. After characterization and application, the sample with the most significant photocatalytic activity was selected and the g-C3N4/BiVO4 heterostructure was synthesized by the simple solvent evaporation method, then the photocatalytic experiment was carried out. The results show that, when the content of BiVO4 in the composite sample is 1%, the photocatalytic activity of RhB was the highest, and the degradation rate could reach 90.4%. The kinetic results showed that the degradation of RhB was consistent with the quasi-primary degradation kinetic model. The results of the photocatalytic cycle experiment show that the photocatalytic performance remains unchanged and stable after four photocatalytic cycles. The existence of a g-C3N4/BiVO4 binary heterojunction was confirmed by UV/Visible diffuse reflection (UV-DRS) and photoluminescence (PL) experiments. Owing to the Z-type charge process between BiVO4 and g-C3N4, efficient carrier separation was achieved, thus enhancing the photocatalytic capacity. This work provides a new idea for the study of heterojunction photocatalytic materials based on g-C3N4.

Construction of CoMoO4/g-C3N4 binary heterojunction photocatalyst with improving photocatalytic performance for ciprofloxacin under visible light

Construction of CoMoO4/g-C3N4 binary heterojunction photocatalyst with improving photocatalytic performance for ciprofloxacin under visible light

Robust construction of CdSe nanorods@Ti3C2 MXene nanosheet for superior photocatalytic H2 evolution

With energy shortage and environmental pollution, photocatalytic hydrogen production is one of the most important ways to convert solar energy into chemical energy, and its key technology lies in the development of efficient, highly stable and low-cost photocatalysts. In this study, binary heterojunction photocatalysts consisting of CdSe nanorods and Ti3C2 MXene nanosheet were constructed via a one-step in situ hydrothermal method. When the content of Ti3C2 MXene was 10 wt%, a maximum photocatalytic H2 production rate of 763.2 μmol g−1 h−1 was achieved, which was 6 times higher than that of pure CdSe and no noticeable decline of the photocatalytic activity was observed after five recycling cycles. Based on XPS, UPS, in-situ XPS, KPFM, DFT theoretical calculations and photocatalytic experiments, the mechanism of charge transfer and photocatalytic hydrogen production in CdSe-MXene composites were proposed. This work not only presents the potential of earth-abundant MXene materials in the construction of high efficiency and low-cost photocatalysts for hydrogen production, but also opens avenues to fabricate more MXene-based composites for solar energy conversion.

Creation of an internal electric field in SnO2@ZnS-ZnSn(OH)6 dual-type-II heterojunctions for efficient NO photo-oxidation

Well-designed heterojunction photocatalysts are promising high-performance materials, effective in inducing charge transfer to achieve a particular migration path and long-lasting carriers. However, the traditional binary heterojunction photocatalysts still show low-efficiency charge separation. Herein, we report a direct dual-type-II SnO2@ZnS-ZHS (ZHS = ZnSn(OH)6) ternary heterojunction, obtained by a facile in-situ face-to-face growth approach. Experimental results and density functional theory calculations reveal that the carrier dynamics of SnO2@ZnS-ZHS, with dual-type-II mechanisms, enables the photogenerated holes (h+) of SnO2 to migrate to the valence bands of ZHS and ZnS. This ensures that SnO2@ZnS-ZHS has twice as much oxidizing potential to produce enough hydroxyl radicals (·OH) to participate in NO oxidation reactions. With a unique dual-type-II ternary structure, SnO2@ZnS-ZHS shows the highest NO removal rate (44.5%) after 30 min, which is 23.5, 29.7 and 15.9 times higher than the values shown by the single components ZHS, SnO2 and ZnS, respectively. A reaction mechanism is proposed. The improved photocatalytic activity shows the advantages of the SnO2@ZnS-ZHS heterostructure as a promising candidate for ternary heterojunction design.