Laser Direct Writing of Sol-Gel-Derived Vacancy-Rich Functional Oxide Semiconductors.

Fabricating micro/nanostructures of oxide semiconductors with oxygen vacancies (OVs) is crucial for advancing miniaturized functional devices. However, traditional methods for the synthesis of semiconductor metal oxides (SMOs) with OVs usually involve thermal treatment, such as annealing or sintering, under anaerobic conditions. Herein, a multiphoton-induced femtosecond laser (fs) additive manufacturing method is reported for directly writing micropatterns with high resolution (∼1 µm) and abundant OVs in an atmospheric environment at room temperature (25 °C). The interdigitated functional devices fabricated by these micropatterns exhibit both photosensitivity and gas sensitivity. Additionally, this method can be applied to flexible and rigid substrates. The proposed method realizes the high-precision fabrication of SMOs with OVs, enabling the future heterogeneous integration of oxide semiconductors on various substrates, especially flexible substrates, for various device applications, such as soft and wearable electronics/optoelectronics.

Highly Sensitive Chemiresistive H2S Detection at Subzero Temperature over the Sb-Doped SnO2@g-C3N4 Heterojunctions under UV Illumination.

NASA has detected H2S in the persistently shadowed region of the lunar South Pole through NIR and UV/vis spectroscopy remotely, but in situ detection is generally considered to be more accurate and convincing. However, subzero temperatures in space drastically reduce chemisorbed oxygen ions for gas sensing reactions, making gas sensing at subzero temperature something that has rarely been attempted. Herein, we report an in situ semiconductor H2S gas sensor assisted by UV illumination at subzero temperature. We constructed a g-C3N4 network to wrap the porous Sb doped SnO2 microspheres to form type II heterojunctions, which facilitate the separation and transport of photoinduced charge carriers under UV irradiation. This UV-driven technique affords the gas sensor a fast response time of 14 s and a response value of 20.1 toward 2 ppm H2S at -20 °C, realizing the sensitive response of the semiconductor gas sensor at subzero temperature for the first time. Both the experimental observations and theoretical calculation results provide evidence that UV irradiation and the formation of type II heterojunctions together promote the performance at subzero temperature. This work fills the gap of semiconductor gas sensors working at subzero temperature and suggests a feasible method for deep space gas detection.

Enhanced Photocatalytic H2 Evolution Performance of the Type-II FeTPPCl/Porous g-C3N4 Heterojunction: Experimental and Density Functional Theory Studies.

It is of great significance to improve the photocatalytic performance of g-C3N4 by promoting its surface-active sites and engineering more suitable and stable redox couples. Herein, first of all, we fabricated porous g-C3N4 (PCN) via the sulfuric acid-assisted chemical exfoliation method. Then, we modified the porous g-C3N4 with iron(III) meso-tetraphenylporphine chloride (FeTPPCl) porphyrin via the wet-chemical method. The as-fabricated FeTPPCl-PCN composite revealed exceptional performance for photocatalytic water reduction by evolving 253.36 and 8301 µmol g-1 of H2 after visible and UV-visible irradiation for 4 h, respectively. The performance of the FeTPPCl-PCN composite is ∼2.45 and 4.75-fold improved compared to that of the pristine PCN photocatalyst under the same experimental conditions. The calculated quantum efficiencies of the FeTPPCl-PCN composite for H2 evolution at 365 and 420 nm wavelengths are 4.81 and 2.68%, respectively. This exceptional H2 evolution performance is because of improved surface-active sites due to porous architecture and remarkably improved charge carrier separation via the well-aligned type-II band heterostructure. Besides, we also reported the correct theoretical model of our catalyst through density functional theory (DFT) simulations. It is found that the hydrogen evolution reaction (HER) activity of FeTPPCl-PCN arises from the electron transfer from PCN via Cl atom(s) to Fe of the FeTPPCl, which forms a strong electrostatic interaction, leading to a decreased local work function on the surface of the catalyst. We suggest that the resultant composite would be a perfect model for the design and fabrication of high-efficiency heterostructure photocatalysts for energy applications.

Sponge-like loose and porous SnO2 microspheres with rich oxygen vacancies and their enhanced room-temperature gas-sensing performance.

Structure and surface modification of semiconductor materials are of great importance in gas sensors. In this study, a facile citric acid-assisted solvothermal method via a precise calcination process was leveraged to synthesize sponge-like loose and porous SnO2 microspheres with rich oxygen vacancies (denoted as LP-SnO2-Ov). When this material was used in a gas sensor, it exhibited an extremely high response to 10 ppm hydrogen sulfide gas at room temperature (Ra/Rg = 9688), which was 54 times higher than that of commercial SnO2. Furthermore, the response time of LP-SnO2-Ov was 5 s, while the recovery time was 177 s. Moreover, it displayed such high selectivity and stability for hydrogen sulfide gas that its properties remained almost unchanged after 1 month. This method paves a new way to fabricate materials possessing a sponge-like loose and porous structure with oxygen vacancies, which is promising for many other scientific fields such as lithium-ion batteries and photocatalysis.

Vertically grown CeO2 and TiO2 nanoparticles over the MIL53Fe MOF as proper band alignments for efficient H2 generation and 2,4-DCP degradation.

The design of highly efficient photoca talysts for clean energy production and environmental remediation are the grand challenges of scientific research. Herein, TiO2@MIL53Fe and CeO2@MIL53Fe composite photocatalysts are synthesized via solvothermal technique. The SEM and TEM micrographs reveal that TiO2 and CeO2 nanoparticles are vertically grown onto the surface of MIL53Fe MOF. Further, HRTEM micrograph confirmed the formation of heterojunction. It has been investigated that the resultant TiO2@MIL53Fe and CeO2@MIL53Fe photocatalysts exhibit remarkably improved visible light activities for H2 production and 2,4-dichlorophenol (2,4-DCP) degradation in comparison to the bare MIL53Fe photocatalyst. The enhanced photoactivities of the fabricated TiO2@MIL53Fe and CeO2@MIL53Fe photocatalysts are attributed to significantly promoted charge separation as confirmed via the surface photo voltage (SPV) and photoluminescence (PL) results. Further, the photocatalysts exhibit high stability and reusability as confirmed via the recyclable tests. This work will promote the design of MOF-based efficient photocatalysts for clean energy production and environment purification.

A rational design of g-C3N4-based ternary composite for highly efficient H2 generation and 2,4-DCP degradation.

In this work, g-C3N4 based ternary composite (CeO2/CN/NH2-MIL-101(Fe)) has been fabricated via hydrothermal and wet-chemical methods. The composite showed superior photoactivities for H2O reduction to produce H2 and 2,4-dichlorophenol (2,4-DCP) degradation. The amount of H2 evolved over the composite under visible and UV-visible irradiations is 147.4 µmol·g-1·h-1 and 556.2 µmol·g-1·h-1, respectively. Further, the photocatalyst degraded 87% of 2,4-DCP in 2 hrs under visible light irradiations. The improved photoactivities are accredited to the synergistic-effects caused by the proper band alignment with close interfacial contact of the three components that significantly promoted charge transfer and separation. The 2,4-DCP degradation over the composite is dominated by OH radical rather than h+ and O2- as investigated by scavenger trapping experiments. This is further supported by the electron para-magnetic resonance (EPR) study. This work provides new directions for the development of g-C3N4 based highly efficient ternary composite materials for clean energy generation and pollution control.

Fabrication of BiFeO3-g-C3N4-WO3 Z-scheme heterojunction as highly efficient visible-light photocatalyst for water reduction and 2,4-dichlorophenol degradation: Insight mechanism.

In this work, a Z-scheme BiFeO3-g-C3N4-WO3 (BFO-CN-WO) photocatalyst has been synthesized via a wet chemical method and utilized in photocatalysis for hydrogen generation and 2,4-dichlorophenol (2,4-DCP) degradation under visible light irradiation. The resultant photocatalyst showed 90 µmol·h-1 g-1 H2 evolution activity and 63% 2,4-DCP degradation performance, which is 12 and 4.2 times higher than the pristine g-C3N4 respectively. The fascinating photocatalytic performance is attributed to the strong interfacial contact between g-C3N4 and the coupled BiFeO3 and WO3 component, which greatly improved the visible light absorption and charge carriers' separation. The designed Z-scheme heterojunction is a successful strategy for enhancing the separation efficiency of photo-induced charge carriers at the interface while retaining outstanding redox ability. During 2,4-DCP degradation, LC/MS technique was used to detect the reaction intermediates. According to the LC/MS results, several new intermediates such as 2,3-dichloro-6-(2,4-dichlorophenoxy)phenol (m/z = 306), 2,4-dichlorophenyl hydrogen carbonate (m/z = 207), 2,4-dichlorobenzen-1,3-diol (m/z = 177) and phenyl hydrogen carbonate (m/z = 137) were detected. Based on these intermediates, 2,4-DCP degradation pathway is proposed. The fluorescence (FL) and electron paramagnetic resonance (EPR) results reveal that the •OH plays an important role in the 2,4-DCP degradation. The fabricated photocatalyst can be utilized in the field of photocatalysis for practical applications.

A Bi2Te3 Topological Insulator as a New and Outstanding Counter Electrode Material for High-Efficiency and Endurable Flexible Perovskite Solar Cells.

Inverted flexible perovskite solar cells (PSCs) typically employ expensive metals as the counter electrodes, which are brittle and corrodible by perovskite, leading to a sharp performance drop under continuous bending, air exposure, thermal stress, or light illumination and eventually retard the commercialization. Herein, a low-cost Bi2Te3 counter electrode was employed by using a simple thermal evaporation process. The resultant device achieved an excellent power conversion efficiency of 18.16%, which was among the highest reported efficiencies, much higher than the reference Ag PSC (15.90%). The improvement should be attributed to the intrinsic suppressed electron backscattering in a Bi2Te3 topological insulator. Simultaneously, the Bi2Te3 device obtained a significantly improved mechanical flexibility and long-term operational stability. The present strategy will help to open up a new avenue for future commercialization of flexible photovoltaic applications.

Experimental and DFT Studies of Au Deposition Over WO3/g-C3N4 Z-Scheme Heterojunction.

A typical Z-scheme system is composed of two photocatalysts which generate two sets of charge carriers and split water into H2 and O2 at different locations. Scientists are struggling to enhance the efficiencies of these systems by maximizing their light absorption, engineering more stable redox couples, and discovering new O2 and H2 evolutions co-catalysts. In this work, Au decorated WO3/g-C3N4 Z-scheme nanocomposites are fabricated via wet-chemical and photo-deposition methods. The nanocomposites are utilized in photocatalysis for H2 production and 2,4-dichlorophenol (2,4-DCP) degradation. It is investigated that the optimized 4Au/6% WO3/CN nanocomposite is highly efficient for production of 69.9 and 307.3 µmol h-1 g-1 H2 gas, respectively, under visible-light (λ > 420 nm) and UV-visible illumination. Further, the fabricated 4Au/6% WO3/CN nanocomposite is significant (i.e., 100% degradation in 2 h) for 2,4-DCP degradation under visible light and highly stable in photocatalysis. A significant 4.17% quantum efficiency is recorded for H2 production at wavelength 420 nm. This enhanced performance is attributed to the improved charge separation and the surface plasmon resonance effect of Au nanoparticles. Solid-state density functional theory simulations are performed to countercheck and validate our experimental data. Positive surface formation energy, high charge transfer, and strong non-bonding interaction via electrostatic forces confirm the stability of 4Au/6% WO3/CN interface.