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To achieve a conductive hydrogel with favourable mechanical and electrical properties, an oriented Mxene-SNF (MSNF) conductive hydrogel was developed using the directional freezing technique. This process involved combining silk fibroin nanofibers (SNF) rich in β-sheet structures with MXene nanosheets to establish an oriented internal cross-linked network. The study investigated the influence of various factors on the hydrogel's mechanical and electrical properties. Results demonstrated that the hydrogel's mechanical properties were influenced by SNF content, MXene content and internal structure. Optimal mechanical properties and favourable electrical conductivity were achieved when the SNF mass fraction was 10%, the MXene mass fraction was 10%, and the internal structure was oriented. The obtained oriented MSNF hydrogel displayed a tensile strain of 80% ± 3%, a tensile stress of 0.89 ± 0.03 MPa, and an elastic modulus of 3.41 ± 0.05 MPa, roughly twice that of the human forearm skin. It maintained a stable resistance response at 0–70% tensile strain. To demonstrate its stability and durability, the hydrogel underwent 500 cycles within the 30–50% tensile strain interval. Therefore, the conductive hydrogel exhibits the potential to be attached to different parts of the human body for real-time monitoring of human movement. Its strain-sensing potential holds value in the field of flexible wearable sensors. [ABSTRACT FROM AUTHOR]

Advances in ultrasound-assisted photocatalyst synthesis and piezo-photocatalysis have shown great potential in enhancing the efficiency of photocatalytic reactions. This minireview provides a comprehensive overview of these innovative techniques, which leverage the unique properties of ultrasound waves and light activation to enhance photocatalysis. The underlying principles and mechanisms are discussed, alongside their diverse applications such as water splitting, CO2 conversion, water purification, and volatile organic compound (VOC) removal. The advantages of ultrasound assistance, including shortened reaction times, enhanced product yield, and attainment of uniform photocatalytic material morphology, are highlighted. By shedding light on the substantial contributions of ultrasound-assisted photocatalyst synthesis and piezo-photocatalysis, this minireview serves to advance the realms of sustainable and efficient chemical processes. [ABSTRACT FROM AUTHOR]

The intrinsic high X-ray attenuation and insignificant biological toxicity of Bi-based nanomaterials make them a category of advanced materials in oncology. Bi-based two-dimensional nanomaterials have gained rapid development in cancer diagnosis and treatment owing to their adjustable bandgap structure, high specific surface area and strong NIR absorption. In addition to the single functional cancer diagnosis and treatment modalities, Bi-based two-dimensional nanomaterials have been certified for accomplishing multi-imaging guided multifunctional synergistic cancer therapies. In this review, we summarize the recent progress including controllable synthesis, defect engineering and surface modifications of Bi-based two-dimensional nanomaterials for cancer diagnosis and treatment in the past ten years. Their medical applications in cancer imaging and therapies are also presented. Finally, we discuss the potential challenges and future research priorities of Bi-based two-dimensional nanomaterials. [ABSTRACT FROM AUTHOR]

The pollution and damage caused by antibiotics in water have aroused serious concern. Metal–organic frameworks (MOF), which have been hotly investigated as a novel kind of sensing materials, have been tentatively applied to the detection of antibiotics in recent years. In this work, four new Zn(II)/Cd(II) coordination polymers, [Cd(opda)(mbib)(H2O)] (1), [Cd(opda)(pbib)(H2O)] (2), [Cd(ppda)(mbib)] (3), and [Zn2(mpda)2(mbib)2]·2H2O (4), (H2opda = 1,2-phenylenediacetic acid, H2mpda = 1,3-phenylenediacetic acid, H2ppda = 1,4-phenylenediacetic acid, mbib = 1,3-bis(imidazolyl)benzene, pbib = 1,4-bis(imidazolyl)benzene), have been synthesized using bis(imidazole) and phenylenediacetate isomers under hydrothermal conditions. The flexible pda and bib ligands in 1–3 afford 2D (4,4)-connected layers, which are further stacked in an offset fashion with an ABAB sequence to propagate into a 3D supramolecular architecture through strong C–H⋯π and C–H⋯O interactions. In contrast, the flexible cis-conformation mpda and mbib ligands in 4 can be seen as "V"-type building blocks, linking Zn(II) atoms to form a 1D loop chain. The structural diversity of these complexes is mainly attributed to the different coordination modes and isomer conformations of the flexible phenylenediacetic acid and bis(imidazole) ligands. The application of the fluorescence properties of the four complexes for detecting the antibiotics cefixime (CEF) and tetracycline (TEC) and the related mechanisms have been researched. Complexes 1–4 exhibit high quenching percentages in low-concentration aqueous solutions, with values of 94.9%, 97.8%, 95.5%, and 97.2% (toward CEF) and 97.7%, 96.7%, 96.4%, and 97.4% (toward TEC), respectively. Compared with 1–3, complex 4 has a higher quenching percentage, which may be because 4 is a 3D porous supramolecular network. The detection limits of complexes 1–4 have been measured to be 0.278 μM, 0.379 μM, 0.52 μM, and 0.171 μM (for CEF) and 0.384 μM, 0.189 μM, 0.421 μM, and 0.137 μM (for TEC), which surpass/approach those of most of the reported MOF-based fluorescent sensing materials. Systematic analysis of the sensing mechanism reveals that photoinduced electron transfer and the inner filter effect contribute to the realization of the sensing process. [ABSTRACT FROM AUTHOR]

It is significant to directly use solar energy for selective H2O2 production and subsequent water purification through a Fenton reaction that converts H2O2 into highly active free radicals. Nevertheless, the efficiency of such a promising route is still unsatisfactory due to the low sunlight utilization, poor selectivity towards H2O2 production, and the requirement of additional Fe-based co-catalysts in the Fenton reaction. Here we present a fascinating design to synthesize a metal-free photocatalyst for highly selective H2O2 production and efficient water purification via a Fenton-like cascade reaction. A BP/OPCN heterojunction is constructed for the first time by assembling 2D oxygen-enriched porous g-C3N4 (OPCN) with 2D black phosphorus (BP), which can effectively promote the visible light response and charge separation. Further investigation reveals that the surface oxygen groups and nanopores of the OPCN are critical both in increasing the active sites and in enhancing the selectivity of H2O2 production. The highest H2O2 production rate of BP/OPCN reaches a remarkable value of 3463 μmol h−1 g−1, which is much higher than that of reported g-C3N4-related materials. The large amount of H2O2 produced in situ over BP/OPCN can subsequently undergo a Fenton-like cascade reaction to degrade organic pollutants in wastewater in only one step. This work demonstrates an efficient photocatalytic approach to produce H2O2 and purify wastewater, while discovering the fundamental roles of the surface chemistry and physical structure of the photocatalyst. [ABSTRACT FROM AUTHOR]

Bismuth halide based semiconductors have attracted increasing attention as the next generation photodetectors because of their excellent photoelectric performance, environmental friendliness, and high-element-abundance characteristics. However, it is still challenging to prepare a thin film under normal conditions because of the instability of BiI3. In this work, we use a room temperature elemental powder reaction in ambient conditions for the easy preparation of Cu incorporated perovskite-like CuBiI4 on a large scale. The crystalline and photoelectric characteristics of the resulting CuBiI4 thin films with different initial Cu content have been investigated by X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence spectroscopy (PL), and transient surface photovoltage (TSPV) studies. The CuBiI4 based photodetectors were first assembled, which showed a striking improvement in the responsivity of the photodetectors compared with pure binary BiI3. Particularly, the responsivity of the photodetector with a 1 : 1 molar ratio of copper to bismuth is 106 times larger than that with an initial molar ratio of 0 : 1 (pure BiI3). A possible mechanism for such an improvement was preliminarily discussed by taking advantage of the Hall effect measurements. Our work not only provides a universal synthetic strategy for preparing high quality Bi-based perovskite-like photoelectric materials but also presents a novel Bi-based photodetector material. [ABSTRACT FROM AUTHOR]

Prominent piezochromic materials play a vital role in the development of damage detection devices and smart sensors. However, compared to other external stimuli (such as light, pH and temperature), understanding of intermolecular interactions and piezochromic properties based on multicomponent molecular hybrid materials is still limited and examples are quite rare. Herein, we choose 4-bis(1-cyano-2-phenyl-ethenyl)benzene (DCSB, A) as the core chromophore to self-assemble with two small organic molecules (tetrafluorohydroquinone (B) and 2,3,5,6-tetrafluoro-4-hydroxy-benzoic (C)), for the sake of studying their relationship between solid-state molecular arrangement and piezochromic luminescence. The as-prepared samples (two new co-crystals: A-5B and A-2C) present tunable multiple hydrogen bonds, molecular packing, and photophysical properties (such as PL colors, lifetimes, PLQYs and aggregation-induced-emission (AIE) properties) compared to pristine DCSB. Moreover, these two co-crystals exhibit prominent piezochromic properties and fluorescence quenching phenomena towards specific environmental stimuli (applied pressure and vapor fumigation) due to collapse of inner supramolecular architectures. Furthermore, the mechanism of visible piezochromic behavior has been confirmed by in situ IR micro-spectroscopy. Therefore, this work not only illustrates the relationship between molecular configuration/packing and photophysical properties of new AIE-based co-crystals, but also develops potential applications in multiple optical sensors towards pressure and detrimental vapor (NH3). [ABSTRACT FROM AUTHOR]

Different from band edge alignment, the Fermi level mismatch induced by band bending can manipulate charge collection at the ITO/(CH3NH3)1−xCuxPbI3 heterojunctions. In this work, we employed a feasible spin-coating process to prepare copper defect compensation in CH3NH3PbI3. The related work function was shown to shift with the copper doping density by Kelvin probe force microscopy (KPFM). Next, we applied transient surface photovoltage (TSPV) spectroscopy and first-order series reactions simulations to confirm that interface charge recombination at the ITO/perovskite junction can be eliminated through Cu+ doping. Nanoelectric photoconductive AFM analysis showed enhanced charge transfer and a higher photovoltage at the ITO/Cu-perovskite junction. Owing to efficient Fermi level alignment, the ITO/(CH3NH3)1−xCuxPbI3/PCBM/Ag devices displayed high power conversion efficiencies of 15.14 ± 0.67% at ambient conditions for inverted perovskite solar cells without any hole transport layer. [ABSTRACT FROM AUTHOR]

Luminescent metal–organic frameworks (MOFs) have received much attention due to their structural tunability and broad range of light-emitting applications. The fluorescence emission of such inorganic–organic hybrids can be significantly tuned by the encapsulation of guest species such as cations, anions, vapors, and dyes. In contrast, the phosphorescence tunability for MOFs has rarely been reported. In this study, an anionic MOF [CdLi(IPA)2](Me2NH2) (IPA = isophthalic acid, Me2NH2 = dimethylamine), denoted as AMOF-1, was prepared via a solvothermal method. The as-synthesized MOF exhibited green long-lasting phosphorescence (LLP). The single-crystal structural analysis revealed that the AMOF-1 channels were lined with the π-electron-rich phenyl rings of IPA and were occupied by exchangeable (Me2NH2)+ guest cations. Based on a facile cation exchange with Mn2+ at different concentrations, the LLP performance of AMOF-1 could be further adjusted across an unusually wide range from blue to violet, white, yellow, orange and red. Furthermore, the reversible changes in the LLP emission indicated that AMOF-1 could also serve as a Cu2+-responsive “on–off” phosphorescent switch. Therefore, this study not only provides a facile way to develop a new type of multi-color LLP materials, but also a strategy to obtain a cation-responsive sensor based on an anionic MOF. [ABSTRACT FROM AUTHOR]

Molecular self-assemblies based on a solution system and solid-state reaction have been largely developed and achieved great success during last few decades; however, the knowledge on the molecular recognition and potential formation of orderly molecular hybrids in the vapor phase is quite limited and examples are still rare. Herein, we confirmed that the molecular recognition organized by intermolecular π–π interaction can be achieved based on a facile vapor deposition process. Through a continuous heating–cooling process of the self-assembled units (such as dibenzothiophene and tetracyanobenzene), the obtained co-crystalline hybrids present an orderly one-dimensional (1D) hollow tubular structure, which also features a high fluorescence quantum yield (47%), optical waveguide, and two-photon emission properties. A combination of crystal morphology prediction and experimental observation deduced that the 1D micro-sized tubular co-crystals were formed based on a growth mechanism of random aggregation. Moreover, this strategy based on vapor-phase molecular recognition can be further extended to the construction of other 1D co-crystal systems. Therefore, this study supplies a facile and environmentally friendly way to prepare high-quality 1D co-crystals towards potential photonic and photofunctional applications. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-8 directly exhibits unexpected white-light emission and near-infrared (NIR) phosphorescence, due to the host–guest interaction and the alternation of electron-density distribution, as confirmed by both experimental and computational studies. [ABSTRACT FROM AUTHOR]

Two novel luminescent three-dimensional coordination polymers [Eu2(tpphz)(oba)3]·nH2O (n = 5.5 for 1, n = 3.5 for 2; H2oba = 4,4′-dicarboxydiphenyl ether) have been hydrothermally synthesized by in situ generation of tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine (tpphz) ligand from 2-(4-pyridine)-imidazo-[4,5-f]1,10-phenanthroline precursor. Both complexes are rare examples of eight-connected self-penetrating networks. The porous nature of the structures is further supported by gas adsorption measurements. [ABSTRACT FROM AUTHOR]

Understanding the intrinsic behaviour of perovskite solar cells is as important as breaking a new PCE record. In particular, the essential mechanisms (e.g. the effect of moisture, oxygen or temperature) behind their chemical instability remain controversial. In this work, we unconventionally and specially fabricate a robust CH3NH3PbI3 perovskite solar cell device in ∼70% relative humidity (RH) with an un-optimized PCE of 8.76%, because our main aim is to understand the essential mechanisms, not the efficiency, which drastically relies on the device assembling technique. Such a device exhibits excellent chemical and performance stability, with more than 72% of the initial PCE still maintained after 250 days storage under 40 ± 3% RH conditions without any encapsulation. In addition, the mechanism underlying the chemical and device stability is fully understood from the charge carrier dynamics and variation of the perovskite crystal. These high RH conditions may facilitate a slight and rapid decomposition/separation of CH3NH3PbI3 to form a PbI2 passivation layer as a moisture defender, which on the contrary plays a crucial role in stabilizing the PCE of CH3NH3PbI3 mesoporous solar cells. This PbI2 insulation layer made the CH3NH3PbI3/ZnO p–n junction a CH3NH3PbI3/PbI2/ZnO p–i–n junction, and maintained good junction quality. Another key factor contributing to the high stability lies in the formation of regular nano-sized ZnO arrays. Consequent transient photovoltaic (TPV) tests revealed that not only fresh CH3NH3PbI3, but also pure PbI2 thin films and CH3NH3PbI3 thin films stored for a long time, all possess a long minority carrier life time. In particular, the stored CH3NH3PbI3/ZnO thin films still maintain a relatively fast photogenerated carrier transfer stability compared with the fresh CH3NH3PbI3/ZnO thin film. We demonstrated the relatively positive role of a moderate amount of PbI2 in perovskite solar cells. This robust device fabrication and TPV measurements give a new perspective for understanding the heterojunction quality and PCE variation in perovskite solar cell fabrication. [ABSTRACT FROM AUTHOR]

The development of molecule-based solid-state materials with novel photofunctional and optoelectronic properties has received much attention recently. In this sense, the construction of two-component molecular systems (such as cocrystals) provides an effective way to adjust and optimize the molecular stacking, aggregation state and related performances. In this work, 2,5-diphenyloxazole (DPO) was chosen as a photoactive model system to study the structure–property relationship of its cocrystals. It was found that the as-prepared new cocrystals exhibited tunable fluorescence properties, up-conversion emission and thermal stability relative to the pure DPO solid. Moreover, the cocrystal based on DPO and hydroquinone has exhibited a pump-enhanced luminescence effect. The measurement of dielectric constants also suggests that the co-crystallization strategy can be applied in modulating the permittivity for the development of new materials in electro-optical applications. Therefore, this work provides a detailed picture on the relationship between the molecular stacking and optoelectronic properties of new DPO cocrystals and gives an alternative to achieve tunable fluorescence, up-conversion emission and dielectric properties. [ABSTRACT FROM AUTHOR]

Fabrication of a monocrystalline silicon based heterojunction film at room-temperature in a time-efficient manner is desirable for energy and environmental considerations. In this report, a gas–solid phase direct elemental reaction (DER) route to realize this aim by firstly depositing an elemental copper layer on a monocrystalline silicon surface followed by a reaction with iodine vapor is described. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoelectrochemical measurements, and the transient photovoltage (TPV) technique. The novelty of the current work lies in the following three aspects: (1) formation of an in situ CuI/Si quasi-bulk-heterojunction at room temperature is assisted by the infiltrated elemental copper layer being completely transformed into a γ phase copper iodide (γ-CuI) thin film; (2) the virgin monocrystalline silicon is pretreated to ensure a pyramidally patterned rough surface which facilitates the construction of quasi-bulk-heterojunction thin films and enhances their chemical stability and mechanical stability; (3) the photovoltaic performance and mechanism of the resulting CuI/Si quasi-bulk-heterojunction based solar cell was detected and evaluated for the first time by a combination of photoelectrochemical and TPV techniques, which demonstrates that the intensity of the interface electric field as well as the open circuit potential can be adjusted by tuning the amount of CuI coated on the pyramidally patterned n-Si substrate. [ABSTRACT FROM AUTHOR]

The energy conversion efficiency of a photoelectrochemical system is intimately connected to a number of processes, including light absorption, charge excitation, separation and transfer processes. Of these processes, the charge transfer rate at the electrode|electrolyte interface is the slowest and, hence, the rate-limiting step causing charge accumulation. Such an understanding underpins efforts focused on applying highly active electrocatalysts, which may contribute to the overall performance by augmenting surface charge accumulation, prolonging charge lifetime or facilitating charge transfer. How the overall effect depends on these individual possible mechanisms has been difficult to study previously. Aiming at advancing knowledge about this important interface, we applied first-order serial reactions to elucidate the charge excitation, separation and recombination kinetics on the semiconductor|electrocatalyst interfaces in air. The study platform for the present work was prepared using a two-step Mo-doped BiVO 4 film modified with an ultrathin Fe-doped NiO nanosheet, which was derived from an Fe-doped α-Ni(OH) 2 nanosheet by a convenient precipitation and ion-exchange method. The simulation results of the transient surface photovoltage (TSPV) data showed that the surface charge accumulation was significantly enhanced, even at an extremely low coverage (0.12-120 ppm) using ultra-thin Fe-NiO nanosheets. Interestingly, no improvement in the charge separation rate constants or reduction of recombination rate constants was observed under our experimental conditions. Instead, the ultra-thin Fe-NiO nanosheets served as a charge storage layer to facilitate the catalytic process for enhanced performance.

Fabrication of a monocrystalline silicon based heterojunction film at room-temperature in a time-efficient manner is desirable for energy and environmental considerations. In this report, a gas-solid phase direct elemental reaction (DER) route to realize this aim by firstly depositing an elemental copper layer on a monocrystalline silicon surface followed by a reaction with iodine vapor is described. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoelectrochemical measurements, and the transient photovoltage (TPV) technique. The novelty of the current work lies in the following three aspects: (1) formation of an in situ CuI/Si quasi-bulk-heterojunction at room temperature is assisted by the infiltrated elemental copper layer being completely transformed into a γ phase copper iodide (γ-CuI) thin film; (2) the virgin monocrystalline silicon is pretreated to ensure a pyramidally patterned rough surface which facilitates the construction of quasi-bulk-heterojunction thin films and enhances their chemical stability and mechanical stability; (3) the photovoltaic performance and mechanism of the resulting CuI/Si quasi-bulk-heterojunction based solar cell was detected and evaluated for the first time by a combination of photoelectrochemical and TPV techniques, which demonstrates that the intensity of the interface electric field as well as the open circuit potential can be adjusted by tuning the amount of CuI coated on the pyramidally patterned n-Si substrate.