Surface conversion of ZnO nanorods to ZIF-8 to suppress surface defects for a visible-blind UV photodetector

Metal-Organic Framework-Based Photodetectors

The unique and interesting physical and chemical properties of metal-organic framework (MOF) materials have recently attracted extensive attention in a new generation of photoelectric applications. In this review, we summarized and discussed the research progress on MOF-based photodetectors. The methods of preparing MOF-based photodetectors and various types of MOF single crystals and thin film as well as MOF composites are introduced in details. Additionally, the photodetectors applications for X-ray, ultraviolet and infrared light, biological detectors, and circularly polarized light photodetectors are discussed. Furthermore, summaries and challenges are provided for this important research field.

Metal-Organic Frameworks Meet Metallic Oxide on Carbon Fiber: Synergistic Effect for Enhanced Photodegradation of Antibiotic Pollutant

Photodegradation shows a potential strategy for alleviating the excessive antibiotics crisis. The synergistic effect of various metal compounds immobilized on conductive substrates has been considered for wastewater treatment. However, developing a facile and universal approach for rational design and enhancing photocatalytic properties has endured extreme challenges. Herein, we develop a strategy to facilitate the photocatalytic reactions by designing a composite architecture of ZIF-8 ligand binding to the in-situ synthesis ZnO seed layer on carbon fiber. In this architecture, the dissolution and release of the seed layer in the excessive 2-Methylimidazole methanol solution were used as the binder to enhance the interplay between organic ligand and substrate. As an evaluated system for antibiotic contaminants, the photodegradation of tetracycline hydrochloride was performed with a removal efficiency of 88.47% (TC = 50 mg/L, pH = 4, 0.08 g of photocatalyst, illumination within 100 min). Moreover, the photocatalyst exhibited a steady photocatalytic activity (75.0%) after five cycles. The present work demonstrated a strategy for enhancing the photocatalytic performances of carbon fiber and accordingly provided useful perception into the design of the synergistic structure.

Hybrid ZnO Flowers-Rods Nanostructure for Improved Photodetection Compared to Standalone Flowers and Rods

Different Zinc Oxide (ZnO) morphologies have been used to improve photodetector efficiencies for optoelectronic applications. Herein, we present the very novel hybrid ZnO flower-rod (HZFR) morphology, to improve photodetector response and efficiency when compared to the prevalently used ZnO nanorods (NRs) and ZnO nanoflowers (NFs). The HZFR was fabricated via sol-gel microwave-assisted hydrothermal methods. HZFR achieves the benefits of both NFs, by trapping a greater amount of UV light for the generation of e-h pairs, and NRs, by effectively transporting the generated e-h pairs to the channel. The fabricated photosensors were characterized with scanning electron microscopy, X-ray diffraction, photoluminescence, and a Keithley 4200A-SCS parameter analyzer for their morphology, structural characteristics, optical performance, and electrical characteristics, respectively. The transient current response, current-voltage characteristics, and responsivity measurements were set as a benchmark of success to compare the sensor response of the three different morphologies. It was found that the novel HZFR showed the best UV sensor performance with the fastest response time (~7 s), the highest on-off ratio (52), and the best responsivity (126 A/W) when compared to the NRs and NFs. Hence, it was inferred that the HZFR morphology would be a great addition to the ZnO family for photodetector applications.

High-efficient photocatalytic degradation of commercial drugs for pharmaceutical wastewater treatment prospects: A case study of Ag/g-C3N4/ZnO nanocomposite materials

Pharmaceutical drugs' removal from wastewater by photocatalytic oxidation process is considered as an attractive approach and environmentally friendly solution. This report aims to appraise the practical application potential of Ag/g-C₃N₄/ZnO nanorods toward the wastewater treatment of the pharmaceutical industry. The catalysts are synthesized by straightforward and environmentally-friendly strategies. Specifically, g-C₃N₄/ZnO nanorods heterostructure is constructed by a simple self-assembly method, and then Ag nanoparticles are decorated on g-C₃N₄/ZnO nanorods by a photoreduction route. The results show that three commercial drugs (paracetamol, amoxicillin, and cefalexin) with high concentration (40 mg L^-1) are significantly degraded in the existence of a small dosage of Ag/g-C₃N₄/ZnO nanorods (0.08 g L^-1). The Ag/g-C₃N₄/ZnO nanorods photocatalyst exhibits degradation performance of paracetamol higher 3.8, 1.8, 1.3 times than pristine g-C₃N₄, ZnO nanorods, and g-C₃N₄/ZnO nanorods. Furthermore, Ag/g-C₃N₄/ZnO nanorods have an excellent reusability and a chemical stability that achieved paracetamol degradation efficiency of 78% and remained chemical structure of the photocatalyst after five cycles. In addition, the photocatalytic mechanism explanation and comparison of photocatalytic drugs' degradation ability have also been discussed in this study.

A Highly Permeable Mixed Matrix Membrane Containing a Vertically Aligned Metal-Organic Framework for CO2 Separation

Delicately regulating the distribution morphology of a filler is an effective strategy to promote the separation performance of mixed matrix membranes (MMMs). Herein, we describe a highly permeable metal-organic framework (MOF)-based MMM comprising vertically aligned ZIF-8 (V-ZIF-8) and polysulfone (PSF). The V-ZIF-8 is distributed uniformly within the PSF matrix. With this unique distribution morphology of ZIF-8, the shortest gas transport pathways are formed in the membrane. Meanwhile, the molecular-sieving pores of ZIF-8 can allow CO₂ to pass through and crowding out N₂. The obtained V-ZIF-8/PSF membrane shows a high CO₂ permeability of 89.7 Barrer and a CO₂/N₂ selectivity of 30.0 that is stable over a period of 50 h. The CO₂ permeability is enhanced about 11.8 times than that of the pure PSF membrane. The results prove that the vertically aligned distribution morphology of an MOF in a polymer matrix is an effective method to improve the separation performance of a membrane, providing a new concept for designing more advanced membranes.

ZnO@ZIF-8 core–shell heterostructures with improved photocatalytic activity

ZnO@ZIF-8 heterostructures with ZnO as the core and ZIF-8 as the shell were successfully fabricated and completely degraded methylene blue in ∼4.5 min under solar light irradiation.

NiOx nanoparticles obtained from hydrothermally treated NiC2O4 as an electron blocking layer for organic photodetectors

A room-temperature p-type NiO_x film synthesized from a NiC₂O₄ precursor via hydrothermal treatment is employed as an electron blocking layer (EBL) to fabricate organic photodetectors (OPDs). A simple and efficient calcine process at 375 °C in air decomposes the NiC₂O₄ particles into NiO_x, removes organic components and crystal water, and releases CO₂ gas. Our experimental results indicate that this gaseous by-product prevents the agglomeration of NiO_x, which yields smaller nanoparticles (5-10 nm). The formation of an EBL at room temperature improves device performance. After optimization, the performance parameters obtained, including dark current density, responsivity, specific detectivity and response, are 1.13 × 10^-7 A cm^-2, 0.74 A W^-1, 3.86 × 10¹² Jones, and 0.5/8 ms, respectively. Additionally, the dark current is reduced by more than an order of magnitude after the insertion of the NiO_x layer. The proposed simple and easy method for producing an EBL could be beneficial for the commercial low-temperature and large-area preparation of OPDs.

Atomic-Thin ZnO Sheet for Visible-Blind Ultraviolet Photodetection

The atomic-thin 2D semiconductors have emerged as plausible candidates for future optoelectronics with higher performance in terms of the scaling process. However, currently reported 2D photodetectors still have huge shortcomings in ultraviolet and especially visible-blind wavelengths. Here, a simple and nontoxic surfactant-assisted synthesis strategy is reported for the controllable growth of atomically thin (1.5 to 4 nm) ZnO nanosheets with size ranging from 3 to 30 µm. Benefit from the short carbon chains and the water-soluble ability of sodium dodecyl sulfate (SDS), the synthesized ZnO nanosheets possess high crystal quality and clean surface, leading to good compatibility with traditional micromanufacturing technology and high sensitivity to UV light. The photodetectors constructed with ZnO demonstrate the highest responsivity (up to 2.0 × 10⁴ A W^-1 ) and detectivity (D* = 6.83 × 10¹⁴ Jones) at a visible-blind wavelength of 254 nm, and the photoresponse speed is optimized by the 400 °C annealing treatment (τ_R  = 3.97 s, τ_D  = 5.32 s), thus the 2D ZnO can serve as a promising material to fill in the gap for deep-UV photodetection. The method developed here opens a new avenue to controllably synthesize 2D nonlayered materials and accelerates their applications in high-performance optoelectronic devices.

Molecular Sieve Based on a PMMA/ZIF-8 Bilayer for a CO-Tolerable H2 Sensor with Superior Sensing Performance

Semiconductor sensors equipped with Pd catalysts are promising candidates as low-powered and miniaturized surveillance devices that are used to detect flammable hydrogen (H₂) gas. However, the following issues remain unresolved: (i) a sluggish sensing speed at room temperature and (ii) deterioration of sensing performance caused by interfering gases, particularly, carbon monoxide (CO). Herein, a bilayer comprising poly(methyl methacrylate) (PMMA) and zeolitic imidazolate framework-8 (ZIF-8) is utilized as a molecular sieve for diode-type H₂ sensors based on a Pd-decorated indium-gallium-zinc oxide film on a p-type silicon substrate. While the PMMA effectively blocks the penetration of CO gas molecules into the sensing entity, the ZIF-8 improves sensing performances by modifying the catalytic activity of Pd, which is preferable for splitting H₂ and O₂ molecules. Consequently, the bilayer-covered sensor achieves outstanding CO tolerance with superior sensing figures of merit (response/recovery times of <10 s and sensing response of >5000% at 1% H₂).

High-Performance Photovoltaic Hydrogen Sensing Platform with a Light-Intensity Calibration Module

Although battery-free gas sensors (e.g., photovoltaic or triboelectric sensors) have recently appeared to resolve the power consumption issue of conventional chemiresistors, severe technical barriers still remain. Especially, their signals varying under ambient conditions such as light intensity restrict the utilization of these sensors. Insufficient sensing performances (low response and slow sensing rate) of previous battery-free sensors are also an obstacle for practical use. Herein, a photovoltaic hydrogen (H₂)-sensing platform having constant sensing responses regardless of light conditions is demonstrated. The platform consists of two photovoltaic units: (1) a palladium (Pd)-decorated n-IGZO/p-Si photodiode covered with a microporous zeolitic imidazolate framework-8 (ZIF-8) film and (2) a device with the same configuration, but without the Pd catalyst as a reference to calibrate the base current of sensor (1). The platform after calibration yields accurate response values in real time regardless of unknown irradiance. Besides, the sensing performances (e.g., sensing response of 1.57 × 10⁴% at 1% H₂ with a response time <15 s) of our platform are comparable with those of the conventional resistive H₂ sensors, which yield unprecedented results in photovoltaic H₂ sensors.

Zero-biased deep ultraviolet photodetectors based on graphene/cleaved (100) Ga2O3 heterojunction

In this paper, fast response, zero-biased, solar-blind UV photodetectors based on graphene/β-Ga₂O₃ heterojunctions were fabricated by transferring a monolayer graphene onto fresh cleaved β-Ga₂O₃ (100) single crystal substrate. At zero bias, the photo responsivity at 254 nm and the UV/visible rejection ratio (R₂₃₅ nm/R₄₀₀ nm) and the response time are obtained to be 10.3 mA/W and 2.28 × 10² and 2.24 μs, respectively, for the graphene/β-Ga₂O₃ (100) detector. The fast response and the high sensitivity can be attributed to the high mobility and UV transparency of graphene top-electrode and the low defect density of the β-Ga₂O₃ (100) cleaved surface. Such zero-biased detectors are very promising for next-generation solar-blind UV photodetection.