Heterojunction Materials Research Articles

Construction of high-performance g-C3N4/MoS2 heterojunction humidity sensor and investigation of its application

In the paper, a g-C3N4/MoS2 humidity sensor with high response, low hysteresis and fast response/recovery for skin health status detection was prepared. The synthesis of g-C3N4/MoS2 heterojunction materials increases the interfacial barrier and improves the sensitivity of sensor. The edge unsaturated bonds and S defects of g-C3N4/MoS2 composites together enhance the adsorption of H2O, which in turn improves the sensitivity of sensor. The consequent acceleration of electron transfer between the material surface and water molecules led to an improvement in the response/recovery speed and humidity hysteresis. The N-H on the composite surface promotes the formation of physically adsorbed water layer and enhances the sensor recovery capability. The g-C3N4/MoS2 sensor shows high sensitivity (204875 Ω/%RH), fast response/recovery speed (11/9 s), and low hysteresis (2.0 %) at the 11 %-95 % RH range. In this study, the sensors were successfully used for the detection of skin health conditions, providing a viable solution for skin detection.

Z-scheme metal organic framework/Ag@AgCl heterojunction photocatalysts with elevated photocatalytic N2 fixation activity

As one of the most consumed chemical reagents, ammonia (NH3) has a wide range of applications in many fields. The demand for ammonia may continue to increase with the advancement of technology and the acceleration of industrialization. The traditional high energy consumption and high pollution ammonia synthesis methods (Haber-Bosch) need to be optimized and improved to reduce environmental pollution and energy dependence. In this work, a series of Z-scheme NM/Ag@AgCl heterojunctions were prepared as catalysts for the research of photocatalytic nitrogen fixation. By in-situ photodeposition, Ag@AgCl was uniformly distributed on the NM surface, and the interfaces of different substances were tightly bonded. The SPR effect that generated by Ag nanoparticles significantly enhanced the light energy absorption performance of heterojunction materials. In the ESR spectra, the signal peak intensity of NM/Ag@AgCl was higher than that of NM under light condition. Constructing of heterojunction was beneficial to the formation of Ti3+. The strong built-in electric field among NM and AgCl promoted the generation of Z-scheme heterojunction. NM/Ag@AgCl had sufficient redox potential to overcome thermodynamic barriers and drive the catalytic reaction. Without adding any sacrificial reagent, the ammonia production of NM/Ag@AgCl-3 reached 76.7 µmol g−1 h−1 under full spectrum radiation. The rate of ammonia formation of NM/Ag@AgCl was almost seven times than that of NM. The synergistic effect between NM and Ag@AgCl optimized the photogenerated carrier separation path. This work provided a new vision for the practical application of efficient photocatalytic N2 reduction.

Construction of Ag2O/WO3-based hollow microsphere p-n heterojunction for continuous detection of ppb-level H2S gas sensor

Three-dimensional (3D) hierarchical hollow microsphere WO3 and Ag2O/WO3 heterojunction materials were prepared by a simple hydrothermal method for a highly sensitive continuous response H2S gas sensor. The results show that compared with the original WO3 (Ra/Rg=12.5, 10 ppm, 70℃), the sensor based on Ag2O/WO3 has excellent H2S sensing performance at 60℃. Including ultra-high sensitivity (Ra/Rg=207.12, 10 ppm), continuous detection of different concentrations of H2S gas (0.05–50 ppm), fast response capability (15 s), low detection limit (50 ppb), high selectivity and reliable stability. The study of gas sensing mechanism shows that the synthesized 3D hierarchical hollow microsphere structure provides more channels for gas diffusion and transmission. The dispersion of Ag2O nanoparticles (NPs) on the surface of WO3 provides more reactive sites for gas adsorption. At the same time, the charge transfer is promoted by constructing Ag2O/WO3 p-n heterojunction. Sulfurization of Ag2O improved the response value and selectivity to H2S gas. These factors together determine the superior performance of the prepared Ag2O/WO3 H2S-based sensor.

Effect of Metal-Organic Frameworks with Different Ligand Structures (ZIF-11 & ZIF-23) on the Optoelectronic Performance of Perovskite Photodetectors.

Crystal engineering using passivation to reduce perovskite defects is crucial to improving the quality of perovskite crystals and optoelectronic properties. Because of their unique properties, metal-organic framework materials have been used as an emerging and effective passivator for perovskite materials and optoelectronic devices. This paper focuses on the differences in the optoelectronic properties of zeolite imidazolium ester framework materials (ZIF-11 & ZIF-23) doped with different conjugated ring ligands for perovskite photodetectors. This paper proposes a simple and effective method to dope zeolite imidazolium ester framework nanoparticles (ZIF-11 & ZIF-23) into organic-inorganic perovskite MAPbI3 films. The crystalline quality of the perovskite films was improved after doping with ZIF-11 and ZIF-23. Meanwhile, the performance of the planar photoconductive devices was significantly improved. The photoresponsivity of the photodetector doped with ZIF-23 was 0.185A/W, and the detectivity was 4.22 × 1012 Jones. The photoresponsivity of the photodetector doped with ZIF-23 was 0.164 A/W, and the detectivity was 3.27 × 1012 Jones. The devices maintained long-time operational stability, operating without significant degradation for 480 s under the 1.2 V bias voltage operating condition. In addition, we observed a significant suppression of the ion migration process in ZIF-23 for a voltage-controlled ion migration process. The potential application of perovskite and MOF heterojunction materials for image information acquisition and storage is demonstrated.

Construction of CdS/ZnO/TiO2 ternary heterojunction with hierarchical structure as photo-anode for enhancing photo-electrochemical performance

Composition and microstructure expert a significant impact on the photoelectric properties of the photo-anode. In this work, CdS/TiO2 and CdS/ZnO/TiO2 heterojunction materials were prepared using a simple and low-cost hydrothermal method. Their microstructure, crystallinity, elemental presence state and photoelectron-chemical performance of the heterojunction materials were investigated by SEM, XRD, XPS and Electrochemical workstation. The hydrothermal growth time of CdS has a significant impact on the structure and performance of heterojunctions. As the CdS deposition time increase, the photocurrent density of CdS/TiO2 shows a trend of first increasing and then decreasing. We optimized the process parameters of CdS/TiO2, and the optimal growth time for CdS is 6h. The transient photocurrent density value of CdS/TiO2 heterojunction is 0.15 mA/cm2. Depositing ZnO onto TiO2 to construct a hierarchical ZnO/TiO2 heterojunction can improve light absorption and accelerate carrier separation efficiency. The photoelectric performance of CdS/ZnO/TiO2 was compared with CdS/TiO2 and pure TiO2. The photocurrent density of CdS/ZnO/TiO2 is 1.5 mA/cm2, which is significantly larger than that of pure TiO2 and CdS/TiO2. This is due to the formation of a heterojunction between TiO2 and ZnO, which promotes the separation of carriers and ultimately improves the photoelectric performance of the CdS/ZnO/TiO2 ternary heterojunction. The fabricated CdS/ZnO/TiO2 heterojunction showed high photocurrent, which indicated a new candidate for photoelectric device.

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

Boosted charge separation in porphyrin-based MOFs/CdS photocatalyst via interfacial −N−Cd− bridge bond construction

The high interfacial charge transfer barrier has been a main thermodynamic obstacle for improving the catalytic efficiency of heterojunction materials. Optimizing the interfacial environment is an effective strategy to achieve high catalytic efficiency. Herein, the coordinate bond (−N−Cd−) is designed to connect the hafnium porphyrin−metal organic framework (HT) and CdS nanoparticles, which is systematically analyzed by the 1H NMR, FTIR, Raman and DRS, respectively. The optimized 15HT1.5 H/CdS6 composite featuring interfacial bridge bonds, exhibits an H2 production up to 11.9 mmol·g−1·h−1, which is 28.5, 52.8 and 7 times greater than pure CdS, HTH, and mechanically mixed sample without interfacial chemical bonds connected, respectively. Mechanistic study suggests that the coordination bonds between HT and CdS serve as the directional carrier transfer bridges, significantly improving interfacial charge separation and chemical stability. Moreover, the formed Z-scheme charge transfer mechanism also endows the composite with high redox ability. This strategic construction of interfacial chemical bonds within heterojunction provides an effective pathway for improving interfacial charge transfer in the heterojunction photocatalysts.

Synthesis of visible-light-driven heterojunction graphitic carbon nitride (g-C3N4/Feo/TiP) material: An efficient photocatalytic agent for degradation of rhodamine 6G from wastewater

In this study, a novel and cost-effective photocatalytic material based on graphitic carbon nitride (g-C3N4) heterojunctions incorporating zero-valent iron (Feo) and titanium phosphate (TiP) was successfully synthesized via chemical reduction method. Various characterization techniques including UV–visible Diffuse Reflectance Spectroscopy, Fourier Transform Infrared Spectroscopy, X-Ray diffraction, Scanning Electron Microscopy, and Energy Dispersive Spectrum were employed to analyze the ternary photocatalyst g-C3N4/Feo/TiP. The study focused on investigating the degradation mechanism of Rhodamine 6G (Rh6G) in aqueous solution under visible light irradiation using synthesized g-C3N4/Feo/TiP heterojunction material. Remarkably, optimal photocatalytic activity was achieved at pH 3, wherein 98 % degradation of 50 mL of Rh6G (10 ppm) was attained within 60 min under visible light irradiation. This activity was consistent across a wide pH range from 3 to 11. This happens due to the exceptional enhancement of hydroxyl radicals, higher photocurrent response and photo-excited holes via Z-scheme of heterojucntion mechanism from g-C3N4/Feo/TiP material compared to g-C3N4 (60 %), TiP (75 %), and Feo/TiP (85 %) against Rh6G. The extraordinary degradation arises due to more visible light absorption capability and enhanced separation of photo-excited electrons and holes through Z-scheme heterojucntion mechanism. This report show the promising clean environmental application prospect of synthesized heterojucntion photocatalyst against organic pollutants from wastewater.

In2O3[sbnd]Co3O4 p-n heterojunction sensors: Comparison of efficient interfaces and gas sensing enhancement mechanism through two strategies

The fabrication of heterostructure has been considered as a great potential to improve the gas sensing performances due to its flexible features at the interface. The p-n heterojunction composites with Co3O4 modified In2O3 were synthesized through physical mixing calcination process and hydrothermal method for the effectiveness comparison as gas sensors for detecting of ethanol. The morphology, microstructure, and surface element state of the heterojunction materials were investigated. Furthermore, the forbidden band width and the active oxygen species were analyzed on account of the efficient interface for the heterojunction materials. The gas response of heterojunction sensor by the physical mixing calcination method exhibits an outstanding response of 5585 towards 100 ppm of ethanol gas, which was about 10 times higher than that by two-step hydrothermal method. Moreover, it shows improved adsorption and desorption kinetics with response time of 8 s and 15 s, respectively at the operating temperature of 280 °C. It also reveals a distinct selectivity to ethanol with better reproducibility, the humidity-dependent stability and ambient retention over a period of 30 days with rendering 94 %. Combined with the in-situ infrared diffuse reflection spectrum analysis and Hall effect test from the perspective of catalytic and electrical properties, we inferred the gas sensing enhancement mechanism involved in In2O3Co3O4 p-n heterojunction with the design of proof-of-concept demonstration by surface modification, which could provide an approach to explore the effect of heterojunction interface through the variable method.

Synergistic enhancement of photocatalytic hydrogen peroxide production activity in CN/rBOB composite through double field effect

Herein, a novel rod-like bismuth bromide oxide (rBOB) was prepared by using a Bi3+ delayed-release strategy and H+ capping competition effect. And rBOB was combined with graphite carbon nitride (CN) to construct S-scheme heterojunction material (CN/rBOB). This work focused on the regulation mechanism of the rod-like morphology of rBOB and the photocatalytic H2O2 production (PHP) performance of CN/rBOB under the action of an external magnetic field. The results showed that the magnetic field can significantly increase the photocurrent response and intrinsic carrier concentration of the catalyst. And the magnetic field action improved the PHP of CN/rBOB from 1.81 to 3.31 mmol·g−1·h−1. This "internal electric field-external magnetic field" synergistic tuning obviously improves the efficiency of photogenerated carrier separation and transport to the surface active sites, which is a simple and useful strategy to construct high-quality photocatalytic systems.

Synthesis of type-II SrTiO3/ZnO heterojunction material for photocatalytic degradation of methylene blue under sunlight

This work presents the synthesis of ZnO, SrTiO3, and SrTiO3/ZnO catalysts by simple hydrothermal method. The obtained materials were characterized by X-Ray Diffraction (XRD), Fourier transformation infrared spectra (FT-IR), scanning electron microscopy (SEM), Energy-dispersive X-ray (EDS) and element mapping images, Photo-luminescence spectroscopy (PL), and Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS). The photocatalytic activity of the synthesized materials was assessed by degradation of methylene blue (MB) under sunlight. In particular, SrTiO3/ZnO displayed outstanding photocatalytic activity compare to individual catalysts. Our findings have revealed an improvement of photogenerated charge separation and the dominating role of the holes and electrons in the degradation of MB.

Fabrication and improved photocatalytic performance of 2D/0D structured g-C3N4/WO3 composite materials

In this work, WO3 quantum dots grow in situ on the synthesized ultra-thin g-C3N4 nanosheets, ultimately forming a type of tightly bound 2D/0D Z-type heterojunctions. It was found that WO3 quantum dots were closely combined with g-C3N4 nanosheets through SEM and TEM measurements. XRD, IR, and XPS characterization proved a g-C3N4/WO3 heterojunction material was formed. The construction of g-C3N4/WO3 heterojunctions enhanced visible light absorption, improved carrier separation efficiency, and reduced charge transfer resistance. Photocatalytic hydrogen production tests showed that the hydrogen production rate of 20% g-C3N4/WO3 composite materials was 2.8 times that of the original g-C3N4, and the hydrogen production amount within 3 h was 3.7 times that of the original g-C3N4. Photocatalytic degradation of Rhodamine B and 4-chlorophenol under visible light irradiation showed that compared with g-C3N4, the photocatalytic degradation efficiency of 20% g-C3N4/WO3 composite materials was enhanced. The results reveal that the special structured g-C3N4/WO3 composite materials have excellent photocatalytic activity, which can not only efficiently produce hydrogen but also efficiently degrade organic pollutants, providing an important reference for solving energy crises and environmental problems.

Construction of oxygen-doped g-C3N4/BiOCl (S-scheme) heterojunction: Efficient degradation of tetracycline in wastewater

Graphitic phase carbon nitride (g-C3N4) demonstrates significant promise in the photocatalytic degradation of organic pollutants, but the rapid recombination of photogenerated electron-hole pairs seriously restricts its degradation capacity. In this study, an innovative heterostructural anion regulation strategy based on g-C3N4 was proposed to significantly enhance the degradation performance of tetracycline. Initially, we regulated the electron configuration of g-C3N4 through O doping to optimize the active sites at the reaction interface. Subsequently, the S-scheme heterojunction was constructed by introducing BiOCl to stimulate the pumping effect and form efficient build-in electric field electron channels. The oxygen-doped g-C3N4/BiOCl (OCN/BiOCl) heterojunction material obtained through aforementioned modification exhibited a degradation efficiency of 89.33 % towards 20 mg·L−1 tetracycline (90 min light reaction, 30 min dark reaction), which was 2.5 times that of conventional g-C3N4 catalyst. In particular, density functional theory calculations and ultraviolet photoelectron spectroscopy jointly revealed the unique chemical environment and electronic structure between OCN and BiOCl due to the formation of the build-in electric field, thereby providing enhanced pathways for the migration of photogenerated currents. Meanwhile, the heterostructure significantly reduced the transport distance of photo-induced charge and minimizes the internal transmission resistance. It enhances the efficiency of separating photogenerated electrons and hole pairs, which is the key mechanism for greatly improving the photocatalytic degradation performance of OCN/BiOCl materials. In summary, the hetero-anion regulation strategy proposed in this study addresses the issue of rapid recombination of photogenerated charges in g-C3N4, providing a new perspective for efficient control of organic pollutants in the environment driven by g-C3N4 photocatalyst.

Fabrication of 0D/2D amorphous NixB/ZnIn2S4 S-scheme for enhanced photocatalytic hydrogen evolution performance

The design and synthesis of low-cost hydrogen evolution photocatalysts with high carrier separation capability and visible light responsiveness are key factors in increasing hydrogen production. In this work, zero-dimensional (0D) amorphous nickel boride (NixB) was synthesized using a reduction method. Subsequently, a 0D/2D amorphous NixB/ZnIn2S4 S-scheme heterojunction was fabricated through electrostatic attraction. This heterojunction exhibited stronger visible light responsiveness and enhanced photogenerated carrier separation performance. The morphology, composition, elemental, structural, and light absorption capacities of the as-synthesized composites were researched by SEM, TEM, XRD, XPS, and UV–vis DRS. The ability to separate photogenerated carriers were evaluated through photoelectrochemical experiments. The hydrogen evolution rate of NixB/ZnIn2S4 (2208 μmol h−1 g−1) increased 25 times than that of single ZnIn2S4 in sacrificial solution, and the apparent quantum yield (AQY) at 400 nm was 14.25 %. This study gives evidence of the great preponderance of S-scheme heterojunction and multidimensional material co-construction in improving hydrogen precipitation.

Assembly of S-Scheme heterojunctions In2S3/Zr-bcu-22bipy44dc and In2S3/PCN-224: Polishing band states to boost highly efficient photochemical scavenging of X-, K- and KN-types reactive dyes and Cr(VI)

Remarkable capability in utilizing visible light and the low CB potential makes In2S3 appealing in assembling MOFs-based heterojunctions. To achieve dual-functional photocatalytic decontamination of Cr(VI) and dyes via low-energy light, the focus remains on assembly of advanced heterostructures based on water-stable Zr-MOFs and In2S3. Herein, Zr-bcu-22bipy44dc and PCN-224 were deployed to fabricate two novel heterojunctions In2S3/Zr-bcu-22bipy44dc (IS/2244) and In2S3/PCN-224 (IS/P224), respectively. Indeed, IS/2244–2 and IS/P224–2 (with 50 % mass ratio of Zr-MOFs) exhibit the optimized optical-electronic properties. The new findings confirm that IS/P224–2, assembled from visible light-sensitive PCN-224, displays higher photocatalytic REDOX abilities than IS/2244–2 in degrading X-, K- and KN-types reactive dyes (RR2, RB13 and RB21) and reducing Cr2O72- ions. The elimination efficiencies of IS/P224–2 towards RR2, RB13, RB21 and Cr(VI) have reached 93.9 %, 95.8 %, 89.4 % and 98.0 % under 500 W xenon lamp, providing accelerated kinetic rates of 7.32, 14.04, 40.2 and 23.67 times of PCN-224, 112.8, 19.95, 10.58 and 3.38 times of In2S3, 5.04, 1.02, 1.39 and 1.78 times of IS/2244–2, respectively, which have been well maintained even after four photocatalytic cycles. More prominently, its performance has surpassed that of some reported MOFs-based materials and other photocatalysts. Mechanism studies have confirmed the potential active radical species, carriers transfer path and S-Scheme talents of two heterojunction materials. This study offers a feasible avenue to design low-energy light-driven bifunctional photocatalysts for water environment remediation.

MoS2/MXene Van der Waals heterojunction-based electrochemiluminescence sensor for triple negative breast cancer detection

The van der Waals heterojunction is able to combine the advantages of different materials and has potential to be used in biosensing researches. In this study, we developed a novel van der Waals heterojunction by combining MXene and MoS2 nanosheets for the electrochemiluminescence (ECL) sensing applications. This van der Waals heterojunction material not only possessed the superior conductivity of MXene, but also regulated the electron transport. Additionally, the incorporation of MoS2 nanosheets into the MXene interlayers significantly enhances the material stability. Meanwhile, nitrogen-rich quantum dots (N dots) were synthesized as ECL tags with an impressive nitrogen content of up to 75 %. By integrating the ECL response of N dots within the van der Waals heterojunction, we established a highly efficient sensing system for miRNA-373, which overexpressed in triple negative breast cancer tissues. The van der Waals heterojunction-based biosensor can enhance the ECL signal of N dots effectively to detect miRNA-373 from 1 fM to 1 μM. Consequently, the developed sensing system holds promise for the early detection of metastasis of the triple-negative breast cancer, paving the way for the effective clinical interventions.

Er-Doped BiVO4/BiFeO3 Nanocomposites Synthesized via Sonochemical Process and Their Piezo-Photocatalytic Application.

In this work, Er-doped BiVO4/BiFeO3 composites are prepared using the sonochemical process with a difference of rare earth loading compositions. The crystallinity and chemical and morphological structure of as-synthesized samples were investigated via X-ray diffraction, Raman scattering, and electron microscopy, respectively. The diffuse reflectance technique was used to extract the optical property and calculate the optical band gap of the composite sample. The piezo-photocatalytic performance was evaluated according to the decomposition of a Rhodamine B organic compound. The decomposition of the organic compound was achieved under ultrasonic bath irradiation combined with light exposure. The Er-doped BiVO4/BiFeO3 composite heterojunction material exhibited significant enhancement of the piezo-photocatalytic activity under both ultrasonic and light irradiation due to the improvement in charge generation and separation. The result indicates that Er dopant strongly affects the phase transformation, change in morphology, and alternation in optical band gap of the BiVO4 matrix. The incorporation of BiFeO3 in the composite form with BiVO4 doped with 1%Er can improve the photocatalytic performance of BiVO4 via piezo-induced charge separation and charge recombination retardment.

Tailored Polymeric Carbon Nitride Coupled with Bi2O3 for Constructing Z‐Scheme Heterojunction with Enhanced Photocatalytic Activity

AbstractThe great demand for visible‐light‐induced catalysts with high photocatalytic performance has stimulated extensive interest in constructing g‐C3N4‐based Z‐Scheme heterojunctions. In this research work, the g‐C3N4/Bi2O3 Z‐Scheme heterojunction by precipitation‐hydrothermal method was constructed, and characterized by various techniques. The g‐C3N4/Bi2O3‐1 composite exhibited a transient photocurrent response approximately 7 and 5 times higher than that of bare g‐C3N4 and Bi2O3, respectively, and showed higher visible photocatalytic activity with 99.8 % degradation of methylene blue (MB) within 75 min. Meanwhile, the pH effect on the photocatalytic degradation of MB was investigated. Radicals trapping experiments showed that •OH free radical played a predominant role for the degradation of MB, EPR analysis confirmed the presence of superoxide radicals, which combined with the band structure of the composites, confirmed the Z‐Scheme of the heterojunction. A possible mechanism for photocatalytic degradation of MB dyes in g‐C3N4/Bi2O3‐1 composites was also proposed. This study provided a new avenue for the development of novel g‐C3N4‐based Z‐Scheme heterojunction materials with prospective applications in the fields of energy and environment.

Simultaneously Utilizing Excited Holes and Electrons for Piezoelectric-Enhanced Photoproduction of H2O2 from S-Scheme 2D S-Doped VOx/g-C3N4 Nanostructures.

2D/2D step-scheme (S-scheme) piezo-photocatalysts for the production of fine chemicals, such as hydrogen peroxide (H2O2), have attracted significant attention of global scientists owing to the efficiency in utilizing surface piezoelectric effects from 2D materials to overcome rapid charge recombination in photocatalytic processes. In this research, we reported the fabrication of 2D S-doped VOx deposited on 2D g-C3N4 to produce H2O2 via the piezo-photocatalytic process with high production yields at 20.19 mmol g-1 h-1, which was 1.75 and 4.87 times higher than that from solely piezo-catalytic and photocatalytic H2O2 generation. The finding pointed out that adding sulfur (S) to VOx can help to improve the catalytic outcomes by modifying the electronic properties of pristine VOx. In addition, when coupled with g-C3N4, the presence of S limits the formation of graphene in the VOx/g-C3N4 composites, causing shielding effects and pushing the cascade reactions toward water generation in the materials. Besides, the research also sheds light on the charge transport between g-C3N4 and S-VOx under irradiation and how the composites work to trigger the formation of H2O2. The presence of S in the composite systems enhances charge transfer between two semiconductors by strengthening the internal electric fields (IEF) to drive electrons moving in one direction, as demonstrated by density functional theory (DFT) calculations. Moreover, the formation of H2O2 significantly relies on the reduction of oxygen to generate oxygenic radical species at the g-C3N4 sites. Meanwhile, S-VOx provides oxidative sites in the composites to oxidize water molecules to directly or indirectly generate H2O2 or O2, which will further participate in the reactions to produce the final products. This study confirms the validation of S-scheme piezo-photocatalysts, thus encouraging further research on developing heterojunction materials with high catalytic efficiency, which can be used in practical conditions.

Two-Dimensional Sc2CCl2/XSe2(X=Mo, Pt) van der Waals Heterojunctions: Promising Photocatalytic Hydrogen Evolution Materials.

In the field of photocatalysis, new heterojunction materials are increasingly explored to achieve efficient energy conversion and environmental catalysis under visible light and sunlight. This paper presents a study on two newly constructed two-dimensional van der Waals heterojunctions, Sc2CCl2/MoSe2 and Sc2CCl2/PtSe2, using density-functional theory. The study includes a systematic investigation of their geometrical structure, electronic properties, and optical properties. The results indicate that both heterojunctions are thermodynamically, kinetically, and mechanically stable. Additionally, Bader charge analysis reveals that both heterojunctions exhibit typical type II band properties. However, the band gap of the Sc2CCl2/MoSe2 heterojunction is only 1.18 eV, which is insufficient to completely cross the reduction and oxidation (REDOX) potential of 1.23 eV, whereas the band gap of Sc2CCl2/PtSe2 heterojunction is 1.49 eV, which is theoretically capable for water decomposition. The subsequent calculation of the Sc2CCl2/PtSe2 heterojunction demonstrate excellent hole carrier mobility and high efficiency light absorption in the visible light range, facilitating the separation of photogenerated electrons and holes. More importantly, Sc2CCl2/PtSe2 vdW type II heterojunction can achieve full water decomposition from pH 1 to pH 4, and its thermodynamic feasibility is confirmed by Gibbs free energy results. The aim of this study is to develop materials and analyses that will result in optoelectronic devices that are more efficient, stable, and sustainable.