Freestanding Graphitic Carbon Nitride Photonic Crystals for Enhanced Photocatalysis

Graphitic carbon nitride (g‐C₃N₄) has attracted tremendous attention in photocatalysis due to its extraordinary features, such as good thermal and chemical stability, metal‐free composition, and easy preparation. However, the photocatalytic performance of g‐C₃N₄ is still restricted by the limited surface area, inefficient visible light absorption, and high recombination rate of photoinduced charge carriers. Herein, a facile synthesis to produce freestanding g‐C₃N₄ photonic crystals (PCs) by crack‐free, highly ordered colloid crystals templating is reported. The PC structure succeeded from the silica opals induces bicontinuous framework, stronger optical absorption, and increase in the lifetime of photoexcited charge carriers compared to that of the bulk g‐C₃N₄, while the chemical structure remains similar to that of the bulk g‐C₃N₄. As such, the g‐C₃N₄ PCs have a much higher photodegradation kinetic of methyl orange and photocatalytic hydrogen production rate which is nearly nine times the rate of bulk g‐C₃N₄.     

Recent Progress of Heterojunction Ultraviolet Photodetectors: Materials,Integrations, and Applications

Ultraviolet photodetectors (UV PDs) with “5S” (high sensitivity, high signal‐to‐noise ratio, excellent spectrum selectivity, fast speed, and great stability) have been proposed as promising optoelectronics in recent years. To realize high‐performance UV PDs, heterojunctions are created to form a built‐in electrical field for suppressing recombination of photogenerated carriers and promoting collection efficiency. In this progress report, the fundamental components of heterojunctions including UV response semiconductors and other materials functionalized with unique effects are discussed. Then, strategies of building PDs with lattice‐matched heterojunctions, van der Waals heterostructures, and other heterojunctions are summarized. Finally, several applications based on heterojunction/heterostructure UV PDs are discussed, compromising flexible photodetectors, logic gates, and image sensors. This work draws an outline of diverse materials as well as basic assembly methods applied in heterojunction/heterostructure UV PDs, which will help to bring about new possibilities and call for more efforts to unleash the potential of heterojunctions.     

Nanoimprint Lithography Facilitated Plasmonic-Photonic Coupling for Enhanced Photoconductivity and Photocatalysis

Imprint lithography has emerged as a reliable, reproducible, and rapid method for patterning colloidal nanostructures. As a promising alternative to top-down lithographic approaches, the fabrication of nanodevices has thus become effective and straightforward. In this study, a fusion of interference lithography (IL) and nanosphere imprint lithography on various target substrates ranging from carbon film on transmission electron microscope grid to inorganic and dopable polymer semiconductor is reported. 1D plasmonic photonic crystals are printed with 75% yield on the centimeter scale using colloidal ink and an IL-produced polydimethylsiloxane stamp. Atomically smooth facet, single-crystalline, and monodisperse colloidal building blocks of gold (Au) nanoparticles are used to print 1D plasmonic grating on top of a titanium dioxide (TiO₂) slab waveguide, producing waveguide-plasmon polariton modes with superior 10 nm spectral line-width. Plasmon-induced hot electrons are confirmed via two-terminal current measurements with increased photoresponsivity under guiding conditions. The fabricated hybrid structure with Au/TiO₂ heterojunction enhances photocatalytic processes like degradation of methyl orange (MO) dye molecules using the generated hot electrons. This simple colloidal printing technique demonstrated on silicon, glass, Au film, and naphthalenediimide polymer thus marks an important milestone for large-scale implementation in optoelectronic devices.     

A Review of Surface Plasmon Resonance‐Enhanced Photocatalysis

In the past decade, the surface plasmon resonance of Ag and Au nanoparticles has been investigated to improve the efficiency of photocatalytic processes. The photocatalytic production of fuels is particularly interesting for its ability to store the sun's energy in chemical bonds that can be released later without producing harmful byproducts. This Feature Article reviews recent work demonstrating plasmon‐enhanced photocatalytic water splitting, reduction of CO₂ with H₂O to form hydrocarbon fuels, and degradation of organic molecules. Focus is placed on several possible mechanisms that have been previously discussed in the literature. A particular emphasis is given to several aspects of these mechanisms that are not fully understood and will require further investigation.     

半导体材料的化学功能—光催化技术与环境保护

半导体材料的光催化效应可将光能转化为化学，在环保化工和太阳能利用方面有巨大应用潜力。文章介绍光催化技术的基本原理，实施方法以及在环保领域内的应用前景。对光催化技术实用化过程中的几个重要问题进行了讨论。     

Evidence and Effect of Photogenerated Charge Transfer for Enhanced Photocatalysis in WO3/TiO2 Heterojunction Films: A Computational and Experimental Study

Semiconductor heterojunctions are used in a wide range of applications including catalysis, sensors, and solar‐to‐chemical energy conversion devices. These materials can spatially separate photogenerated charge across the heterojunction boundary, inhibiting recombination processes and synergistically enhancing their performance beyond the individual components. In this work, the WO₃/TiO₂ heterojunction grown by chemical vapor deposition is investigated. This consists of a highly nanostructured WO₃ layer of vertically aligned nanorods that is then coated with a conformal layer of TiO₂. This heterojunction shows an unusual electron transfer process, where photogenerated electrons move from the WO₃ layer into TiO₂. State‐of‐the‐art hybrid density functional theory and hard X‐ray photoelectron spectroscopy are used to elucidate the electronic interaction at the WO₃/TiO₂ interface. Transient absorption spectroscopy shows that recombination is substantially reduced, extending both the lifetime and population of photogenerated charges into timescales relevant to most photocatalytic processes. This increases the photocatalytic efficiency of the material, which is among the highest ever reported for a thin film. In allying computational and experimental methods, this is believed to be an ideal strategy for determining the band alignment in metal oxide heterojunction systems.     

Construction of Self‐Healing Internal Electric Field for Sustainably Enhanced Photocatalysis

The construction of internal electric field is generally considered an effective strategy to enhance photocatalytic performance due to its significant role in charge separation. However, static internal electric field is prone to be saturated either by inner or outer shield effect, and thus its effect on the improvement of photocatalysis can easily vanish. Here, the self‐healing internal electric field is proposed and successfully endowed to a designed helical structural composite microfiber polyvinylidene fluoride/g‐C₃N₄ (PVDF/g‐C₃N₄) based on the bioinspired simple harmonic vibration. Importantly, the saturation and recovery of internal electric field are characterized by transient photovoltage and photoluminescence. The results indicate that the internal electric field could be saturated within about 10 min and refreshed with the assistance of rebuilt piezoelectric potential. The lifetime of photogenerated carriers is about 10^?4 s and the number of effective carriers is greatly increased in the presence of self‐healing internal electric field. The results provide direct experimental evidence on the role of self‐healing internal electric field in charge transfer behavior. This work represents a new design strategy of photocatalysts, and it may open up new horizons for solving energy shortage and environmental issues.     

Enhanced Photocurrent Performance of Flexible Micro-Photodetector Based on PN Nanowires Heterojunction using All-Laser Direct Patterning

UV micro-photodetectors (mPDs) have received significant attention owing to the increasing demand for application in wearable healthcare devices. However, mPDs often suffer from tiny signals owing to their small size. Although this problem can be overcome by using low-dimensional nanomaterials with high surface-to-volume ratios, such as nanowires (NWs), selective synthesis of functional NWs on the desired position of the specific substrate is challenging. This study introduces, for the first time, the laser-induced hydrothermal growth (LIHG) process, in which a strongly focused laser beam generates a localized high-temperature field, enabling the localized growth of CuO NWs on the desired position of the specific substrate. Also, an all-laser direct patterning process for the fabrication of a flexible mPD based on a p-CuO NW/n-ZnO NW heterojunction is demonstrated. The PN NWs heterojunction exhibits remarkable photocurrent enhancement compared to a homojunction with a single semiconductor material. Furthermore, the all-laser direct patterning process of the flexible PN NWs heterojunction can be applied for the fabrication of other flexible optoelectronic applications.     

Improved Photocatalytic Performance of Heterojunction by Controlling the Contact Facet: High Electron Transfer Capacity between TiO2 and the {110} Facet of BiVO4 Caused by Suitable Energy Band Alignment

Charge separation at the interface of heterojunctions is affected by the energy band alignments of the materials that compose the heterojunctions. Controlling the contact crystal facets can lead to different energy band alignments owing to the varied electronic structures of the different crystal facets. Therefore, BiVO₄‐TiO₂ heterojunctions are designed with different BiVO₄ crystal facets at the interface ({110} facet or {010} facet), named BiVO₄‐110‐TiO₂ and BiVO₄‐010‐TiO₂, respectively, to achieve high photocatalytic performance. Higher photocurrent density and lower photoluminescence intensity are observed with the BiVO₄‐110‐TiO₂ heterojunction than those of the BiVO₄‐010‐TiO₂ heterojunction, which confirms that the former possesses higher charge carrier separation capacity than the latter. The photocatalytic degradation results of both Rhodamine B and 4‐nonylphenol demonstrate that better photocatalytic performance is achieved on the BiVO₄‐110‐TiO₂ heterojunction than the BiVO₄‐010‐TiO₂ heterojunction under visible light (≥422 nm) irradiation. The higher electron transfer capacity and better photocatalytic performance of the BiVO₄‐110‐TiO₂ heterojunction are attributed to the more fluent electron transfer from the {110} facet of BiVO₄ to TiO₂ caused by the smaller interfacial energy barrier. This is further confirmed by the selective deposition of Pt on the TiO₂ surface as well as the longer lifetime of Bi⁵⁺ in the BiVO₄‐110‐TiO₂ heterojunction.     

Piezotronic Effect Enhanced Plasmonic Photocatalysis by AuNPs/BaTiO3 Heterostructures

Piezopotential‐assisted catalysis is of great significance for low cost and efficient catalysis processes. Here, Au_x/BaTiO₃ plasmonic photocatalysts are fabricated by precipitating Au nanoparticles on piezoelectric BaTiO₃ nanocubes through a chemical approach. The Au nanoparticles (<8 nm) are decorated uniformly on the surface of BaTiO₃, which endows the heterostructure with a wide light absorption from 300 to 600 nm. The photocatalytic properties of the heterostructures are investigated in detail toward methyl orange (MO) degradation. The Au content, piezoelectric potential of the BaTiO₃ substrate, and surface plasmon resonance (SPR) are confirmed to be vital to the photocatalytic activity. The Au₄/BaTiO₃ shows an optimum photocatalytic performance for a complete degradation of MO in 75 min under full spectrum light irradiation with auxiliary ultrasonic excitation. The piezoelectric field originating from the deformation of BaTiO₃ further enhances the separation of photon‐generated carriers induced by SPR and promotes the formation of hydroxyl radicals, which results in a strong oxidizing ability of organic dyes. This work introduces the piezotronic effect to enhance plasmonic photocatalysis with Au_x/BaTiO₃ heterostructures, which is ready to extend to other catalytic systems and offers a new option to design high‐performance catalysts for pollutant treatment.     

Hollow Mesoporous Metal Organic Framework Single Crystals Enabled by Growth Kinetics Control for Enhanced Photocatalysis

The tailored design of hollow mesoporous metal−organic framework (MOF) single crystals to realize the unimpeded mass transport and long-range carrier migration for advanced photoelectric applications is attractive while being a major challenge. Here, a kinetically mediated micelle assembly strategy is presented to synthesize hollow UiO-66(Ce) single crystals in 1,3,5-trimethylbenzene (TMB)-H₂O emulsion system with Pluronic F127/P123 as dual surfactants. This synthesis features the employment of modulator acetic acid, which can coordinate growth kinetics of MOFs, allowing the nucleation of MOF on block polymer micelles and transforming the self-assembly of block polymer/MOF composite monomicelles from water to TMB/H₂O emulsion interface and the growth of MOF from aggregation to oriented attachment, and thus ensuring the formation of hollow mesoporous UiO-66(Ce) single crystals. Moreover, a precise control in cavity diameter from ≈0 to ≈600 nm, mesopore structure from close to radial and dendritic can be achieved by tuning the amount of TMB and the ratio of F127/P123. As a result, the hollow mesoporous UiO-66(Ce) single crystals with large radial mesopores (≈25 nm) and high surface area (≈1061 m2 g) exhibit excellent photocatalytic performance for H₂ generation owing to enhanced permeability and suppressed electron-hole combination.     

Symmetry Breaking in Monometallic Nanocrystals toward Broadband and Direct Electron Transfer Enhanced Plasmonic Photocatalysis

Metallic nanocrystals manifest themselves as fascinating light absorbers for applications in plasmon-enhanced photocatalysis and solar energy harvesting. The essential challenges lie in harvesting the full-spectrum solar light and harnessing the plasmon-induced hot carriers at the metal–acceptor interface. To this end, a cooperative overpotential and underpotential deposition strategy is proposed to mitigate both the challenges. Specifically, by utilizing both ionic additive and thiol passivator to introduce symmetry-breaking growth over gold icosahedral nanocrystals, the microscopic origin can be attributed to the site-specific nucleation of stacking faults and dislocations. By adopting asymmetric crystal shape and unique surface facets, such nanocrystals attain high activity toward photocatalytic ammonia borane hydrolysis, arising from combined broadband plasmonic properties and enhanced direct transfer of hot electrons across the metal–adsorbate interface.     

Enhanced Photocatalytic Hydrogen Evolution from Organic Ternary Heterojunction Nanoparticles Featuring a Compact Alloy-Like Phase

Organic semiconductor nanoparticles (NPs) are attractive photocatalysts to produce hydrogen from water splitting. Herein, a ternary strategy of incorporating crystalline n-type molecule IDMIC-4F into the host system made of p-type polymer PM6 and n-type molecule ITCC-M is demonstrated. ITCC-M and IDMIC-4F form compact alloy-like composite with shorter lattice spacing in the ternary p/n heterojunction NPs, resulting in enhanced exciton dissociation and charge transfer characteristics. As the result, an unprecedented hydrogen evolution rate (HER) of 307 mmol h⁻¹ g⁻¹ and a maximum apparent quantum efficiency of 5.9% at 600 nm are achieved in the optimized ternary NPs (PM6:ITCC-M:IDMIC-4F = 1:1.3:0.2), which is among the highest HER from organic photocatalysts to the best of the authors’ knowledge. The alloy-like composite also improves the operational stability of ternary NP photocatalysts. This study shows that synergizing two compatible n-type small molecules to form alloy-like composite is a promising approach to design novel organic photocatalysts for boosting the photocatalytic hydrogen evolution efficiency.     

Optoelectronic Synapses and Photodetectors Based on Organic Semiconductor/Halide Perovskite Heterojunctions: Materials,Devices, and Applications

Both photodetectors (PDs) and optoelectronic synaptic devices (OSDs) are optoelectronic devices converting light signals into electrical responses. Optoelectronic devices based on organic semiconductors and halide perovskites have aroused tremendous research interest owing to their exceptional optical/electrical characteristics and low-cost processability. The heterojunction formed between organic semiconductors and halide perovskites can modify the exciton dissociation/recombination efficiency and modulate the charge-trapping effect. Consequently, organic semiconductor/halide perovskite heterojunctions can endow PDs and OSDs with high photo responsivity and the ability to simulate synaptic functions respectively, making them appropriate for the development of energy-efficient artificial visual systems with sensory and recognition functions. This article summarizes the recent advances in this research field. The physical/chemical properties and preparation methods of organic semiconductor/halide perovskite heterojunctions are briefly introduced. Then the development of PDs and OSDs based on organic semiconductor/halide perovskite heterojunctions, as well as their innovative applications, are systematically presented. Finally, some prospective challenges and probable strategies for the future development of optoelectronic devices based on organic semiconductor/halide perovskite heterojunctions are discussed.     

Stress-Triggered Mechanoluminescence in ZnO-Based Heterojunction for Flexible and Stretchable Mechano-Optics

Owing to the forthcoming global energy crisis, the search for energy-saving materials has intensified. Over the past two decades, mechanically induced luminescent materials have received considerable attention as they can convert waste into useful components, for instance, the conversion from stress into light. However, this material features many constraints that limit its widespread application. Herein, a strategy to improve the mechanoluminescence (ML) of ZnO by embedding it in a ZnF₂:Mn²⁺ matrix is introduced. Upon dynamic excitation via an external stress, the reddish-yellow ML is confirmed to originate from the ⁴T₁ (4G) → ⁶A₁ (6S) transition of the optically active Mn²⁺ center. Moreover, the sample with the strongest ML contains the appropriate amount of ZnF₂ (ZnF₂:ZnO = 7:3). By performing density functional theory calculations, a possible ML-enhancement mechanism is elucidated, which indicates the formation of a ZnF₂/ZnO:Mn²⁺ heterojunction. Considering the unique characteristics of ML, its promising applications are demonstrated in various mechano-optics scenarios, including flexible and stretchable optoelectronics, advanced self-powered displays, e-skins/e-signatures, and anti-counterfeiting, without the use of external light/electric-incentive sources. The study significantly increases the variety of ML materials and is expected to strengthen the foundation for the future development of smart mechanically controlled devices and energy-saving systems.     

Piezophototronic Effect Enhanced Photoresponse of the Flexible Cu(In,Ga)Se2 (CIGS) Heterojunction Photodetectors

The Cu(In,Ga)Se₂ (CIGS) heterojunction, as a mature and high efficiency thin‐film solar cell, is rarely studied as a photodetector, especially in flexible substrates. In this paper, the structure of an ITO/ZnO/CdS/CIGS/Mo heterojunction is grown on the polyimide (PI) substrate to form a flexible CIGS heterojunction photodetector. The photodetector can work in a very wide band ranging from 350 to 1200 nm with responsivity up to 1.18 A W^?1 (808 nm), detectivity up to 6.56 × 10¹⁰ Jones (cmHz^1/2 W^?1), and response time of 70 (/88) ms, respectively. Moreover, the piezophototronic effect is first used to investigate performance modulation of this device by effectively controlling the separation and transport of carriers at the interface of CdS/ZnO. Interestingly, by externally applying a 0.763% tensile strain, the photoresponsivity and detectivity of the photodetector exhibit a decrease from 1.18 to 0.88 A W^?1, and from 6.56 × 10¹⁰ to 4.81 × 10¹⁰ Jones, respectively, while under a –0.749% externally static compressive strain, the photoresponsivity could be enhanced by ≈75.4% with a maximum of 2.07 A W^?1, and the detectivity is improved by ≈66.1% with its peak value up to 10.9 × 10¹⁰ Jones. Meanwhile, the response time can be modulated from 99(/116) to 41.3(/42.6) ms. This work suggests that the CIGS heterojunction has great potential in novel applications for piezophototronic sensors and also gives a hint to modulate the performance of other multilayer heterostructures via the piezotronic effect.     

Defect-Engineering Bismuth-Based Homologous Schottky Heterojunction for Metabolic Regulation-Augmented Sonodynamic Tumor Therapy

Sonodynamic therapy demonstrates tremendous potential in biomedicine due to its non-invasiveness, deep tissue penetration, and spatiotemporal controllability. However, the lack of favorable nanosonosensitizers with prominent reactive oxygen species generation capability and green chemical constituents remains a significant challenge for its broad biomedical applications. Herein, a homologous bismuth-based nanosonosensitizer (Bi-HJ) is designed and fabricated by direct defect engineering for combinational tumor therapy. Specifically, self-derived Schottky heterojunction and oxygen vacancies are concurrently constructed in Bi-HJ, which prominently promotes the separation of ultrasound-triggered electron–hole pairs and improves the charge utilization efficiency. With the porous structure, Bi-HJ is loaded with a metabolic regulation drug atovaquone to block the mitochondrial respiration for oxygen-economized sonodynamic tumor suppression. The strong near-infrared absorption of Bi-HJ imparted by oxygen vacancies allows the implementation of photothermal therapy. Accordingly, Bi-HJ rationally combines two therapeutic modalities and metabolic regulation function, as well as computed tomography imaging ability, thus achieving effective tumor theranostics in vitro and in vivo. Therefore, this study provides new insight into the fabrication of homologous nanosonosensitizers without the introduction of other constituents for synergistically enhanced tumor therapy.     

Modulating the Photocatalytic Activity of Graphene Quantum Dots via Atomic Tailoring for Highly Enhanced Photocatalysis under Visible Light

Precise control over doping of photocatalysts is required to modulate their photocatalytic activity in visible light‐driven reactions. Here, a single precursor‐employing bottom‐up approach is developed to produce different heteroatom‐doped graphene quantum dots (GQDs) with unique photocatalytic activities. The solvothermal reaction of a norepinephrine precursor with redox active and condensable moieties effectively produces both nitrogen/sulfur codoped GQDs (NS‐GQDs) and nitrogen‐doped GQDs (N‐GQDs) by simply varying solvents (from dimethyl sulfoxide to water) under microwave irradiation. As‐prepared NS‐GQDs and N‐GQDs show similar lateral sizes (3–4 nm) and heights (1–2 nm), but they include different dopant types and doping constitution and content, which lead to changes in photocatalytic activity in aerobic oxidative coupling reactions of various amines. NS‐GQDs exhibit much higher photocatalytic activity in reactions under visible light than N‐GQDs and oxygen‐doped GQDs (O‐GQDs). The mechanism responsible for the outstanding photocatalytic activity of NS‐GQDs in visible light‐driven oxidative coupling reactions of amines is also fully investigated.     

Nanoscaling and Heterojunction for Photocatalytic Hydrogen Evolution by Bimetallic Metal-Organic Frameworks

Using sunlight to manufacture hydrogen offers promising access to renewable clean energy. For this, low-cost photocatalyst with effective light absorption and charge transfer are crucial, as current top-performing systems often involve precious metals like Pd and Pt. An integrated organic–inorganic photocatalyst based on the cheap metals of iron and nickel are reported, wherein the metal ions form strong metal-sulfur bonds with the organic linker molecules (2,5-dimercapto-1,4-benzenedicarboxylic acid, H₄DMBD) to generate 2D coordination sheets for promoting light absorption and charge transport. The 2D sheets are further modified through ionic metal-carboxylate moieties to allow for functional flexibility. Thus, high-surface-area thin nanosheets of this 2D material, with an optimized Fe/Ni ratio (0.25:1.75), and in heterojunction with CdS nanosheet, achieve a stable photocatalytic hydrogen evolution rate of 12.15 µmol mg⁻¹ h⁻¹. This work synergizes coordination network design and nano-assembly as a versatile platform for catalyzing hydrogen production and other sustainable processes.