Kelp-inspired N–I-doped ZnO photocatalysts with highly efficient catalytic activity

Efficient N–I-doped ZnO photocatalysts with hierarchical structures are fabricated with kelp as the template. Abundant nitrogen and iodine are successfully simultaneously introduced into the bulk ZnO crystals though calcination under high temperature (600 °C). The morphology, structure, composition, and optical absorption properties of the kelp-templated ZnO are characterized by X-ray diffraction (XRD), field-emission scanning microscopy (FESEM), transmission electron microscopy (TEM), and diffuse reflectance spectra (DRS), respectively. The band gap of the kelp-templated ZnO is narrowed by the N–I coping. The photocatalytic activity under UV-irradiation of the kelp-templated ZnO is about 23.1 times and 1.1 times that of common ZnO and P25, respectively. In addition, no obvious activity of the kelp-templated ZnO is decreased, during five cycle runs. The efficient photocatalytic activity of the kelp-templated ZnO is attributed to the sufficient UV-light utilization and efficient separation of electron–hole pairs.     

Ag3PO4/BiPO4 p–n heterojunction nanocomposite prepared in room-temperature ionic liquid medium with improved photocatalytic activity

A visible-light-active Ag₃PO₄/BiPO₄ nanocomposite with a p–n heterojunction structure was fabricated via a co-precipitation hydrothermal process using 2-hydroxylethylammonium formate (RTIL) as a room-temperature ionic liquid. The resulting catalysts were characterized by various techniques. The photocatalytic activity of the photocatalysts was evaluated by the photodegradation of phthalocyanine Reactive Blue 21 (RB21) under both visible and UV light irradiations. The results reveal that the heterojunction composite prepared in RTIL noticeably exhibited an improvement in both efficiency and rate of RB21 photodegradation in comparison with pure Ag₃PO₄ and BiPO₄. The enhanced photocatalytic activity of Ag₃PO₄/BiPO₄ heterostructure prepared in RTIL is mainly ascribed to the internal electric field built at the heterojunction interface and efficient charge separation and transfer across the p–n junction. RTIL can also assist in decreasing the crystalline size, orderly distributing the particles, preventing the collapse of pore structures, and losing of composite surface area.     

WO3/TiO2 nanocomposites: Salt–ultrasonic assisted hydrothermal synthesis and enhanced photocatalytic activity

A series of WO₃/TiO₂ composite photocatalysts were fabricated via a facile salt–ultrasonic assisted hydrothermal process. The obtained samples were characterized by X-ray diffraction, scanning eletron microscopy, energy dispersive X-ray spectroscopy and UV–vis diffused reflectance spectroscopy. It was confirmed that anatase TiO₂ and monoclinic WO₃ coexisted in the composites. The photocatalytic activity of as-prepared WO₃/TiO₂ composites for degradation of Rhodamin B (RhB) under visible light irradiation was investigated. The results showed that WO₃/TiO₂ composites have a higher photocatalytic activity than those of pure TiO₂ and pure WO₃. First-principle calculations based on density functional theory were performed to explore the electronic structure and illustrate the photocatalytic mechanism of WO₃/TiO₂. The calculated energy gap was 2.53 eV, which was close to the experimental observation (2.58 eV). Due to the combination of WO₃/TiO₂, the photoinduced electrons and holes transfer between the WO₃ and TiO₂ in opposite directions, thus providing sufficient charge separation, which contributed to the photocatalytic activity enhancement.     

Highly efficient photocatalytic treatment of mixed dyes wastewater via visible-light-driven AgI–Ag3PO4/MWCNTs

A high-performance photocatalyst of AgI–Ag₃PO₄/multi-walled carbon nanotubes (MWCNTs) was fabricated by chemical precipitation method using KI, K₂HPO₄ and AgNO₃ in the presence of MWCNTs. Its structure and physical properties were characterized by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), X-ray diffraction (XRD), UV–vis absorption spectra, X-ray photo-electron spectroscopy (XPS), photoluminescence spectra (PL) and photocurrent techniques. SEM, TEM and EDS analyses verified that AgI–Ag₃PO₄ is successfully loaded on MWCNTs. AgI–Ag₃PO₄/MWCNTs possess the absorption edge of red shift and small band gap energy, and could absorb more photons in the visible region. PL and photocurrent analyses illustrated that AgI–Ag₃PO₄/MWCNTs have the lowest emission peak intensity and the highest photoelectric current, compared with Ag₃PO₄, AgI and AgI–Ag₃PO₄. By using the photocatalytic degradation of mixed dyes wastewater of Orange II and ponceau 4R as a model reaction, the photocatalytic efficiencies of Ag₃PO₄, AgI, AgI–Ag₃PO₄ and AgI–Ag₃PO₄/MWCNTs were evaluated. The reaction results showed that AgI–Ag₃PO₄/MWCNTs have strong photocatalytic activity and excellent chemical stability in repeated and long-term applications. Therefore, the prepared AgI–Ag₃PO₄/MWCNTs could act as a high-performance catalyst for the photocatalytic degradation of mixed dyes wastewater and also suggested the promising applications.     

Weak-acceptor-polyacrylonitrile/donor-polyaniline core–shell nanofibers: A novel 1D polymeric heterojunction with high photoconductive properties

A novel one-dimensional (1D) polymeric heterojunction based on weak-acceptor-polyacrylonitrile/donor-polyaniline core–shell nanofibers is designed for photoconductive devices through electrospinning followed by solution polymerization. Such 1D heterojunction can not only provide the large phase-separated nano-interface for effective charges separation between the cores and shells, but also facilitate the mass charge collection and transport along the nanofiber structure, resulting in greatly enhanced optoelectronic performance. The short 0.1 s response time upon irradiation is among the fastest values, as is the short 0.1 s time for return to the non-irradiated state. Extremely high on–off resistivity ratios (exceeding 4 × 10⁴) can be obtained under the drive voltage of only 0.01 V, indicating the energy required for electrical input is very small. Higher drive voltages (a modest 10 V) can provide a very high responsivity of 20 A W⁻¹ driven by 365 nm UV irradiation. Moreover, the as-prepared flexible photoconductive device maintains performance even after bending fatigue tests for bending angles as large as 180°.     

NiTiO3/NiFe2O4 nanocomposites: Simple sol–gel auto-combustion synthesis and characterization by utilizing onion extract as a novel fuel and green capping agent

NiTiO₃/NiFe₂O₄ nanocomposites were prepared via a simple sol–gel auto-combustion route using onion extract as a novel fuel and green capping agent. The present work focused on the synthesis and characterization of NiTiO₃/NiFe₂O₄ nanocomposites for the first time. First, a sol of NiFe₂O₄ was obtained, from metal nitrates and onion extract as reductant. Second, a sol of titanat was prepared by mixing of tetra-n-butyl orthotitanate, diethanolamin and ethanol. Then obtained sol was added to the NiFe₂O₄ sol. The molar ratio of Ti to Ni had significant effect on morphology, magnetic properties, purity and phase of nanocomposites. Nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and vibrating sample magnetometer (VSM). The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer where the optimum condition was performed in the molar ratio Ti/Ni 1:1. The photocatalytic activity of the synthesized products has been compared with the photodegradation activity of methyl orange (MO).     

Resistive switching characteristics of ZnO–graphene quantum dots and their use as an active component of an organic memory cell with one diode-one resistor architecture

We investigated the resistive switching characteristics of a polystyrene:ZnO–graphene quantum dots system and its potential application in a one diode-one resistor architecture of an organic memory cell. The log–log I–V plot and the temperature-variable I–V measurements revealed that the switching mechanism in a low-current state is closely related to thermally activated transport. The turn-on process was induced by a space-charge-limited current mechanism resulted from the ZnO–graphene quantum dots acting as charge trap sites, and charge transfer through filamentary path. The memory device with a diode presented a ∼10³ I_ON/I_OFF ratio, stable endurance cycles (10² cycles) and retention times (10⁴ s), and uniform cell-to-cell switching. The one diode-one resistor architecture can effectively reduce cross-talk issue and realize a cross bar array as large as ∼3 kbit in the readout margin estimation. Furthermore, a specific word was encoded using the standard ASCII character code.     

Novel Christmas Branched Like NiO/NiWO4/WO3 (p–p–n) Nanowire Heterostructures for Chemical Sensing

Establishing a platform comprising different nanostructured oxides is an emerging idea to develop highly sensitive and selective sensing devices. Herein, novel 3D-heterostructures (p–p–n) consisting of 1D nanowires of NiO and WO₃ along with their intermediate reactive product, i.e., NiWO₄ seed, are produced by a two-steps vapor phase growth method. In-depth morphological and structural investigations describing the growth mechanism of these heterostructures are presented. Finally, the p–p–n heterostructures are integrated into conductometric sensing devices and their performances are investigated toward different gases. It is observed that by modulating the charge-carrier transport with temperature, the heterostructure sensors exhibit selective behavior toward different gas analytes. Indeed, at 300 °C, the heterostructure sensors show relatively selective behavior toward NO₂, while at 400 °C, high selectivity toward VOCs is observed. The improvement in sensing performances is mainly based on charge carrier transport through the two interfaces (one at WO₃/NiWO₄ (n–p) and the other at NiWO₄/NiO (p–p)) and the modulation of charge carriers in the electron depletion layer of WO₃ and hole accumulation layer of NiO and NiWO₄. The remarkable performance of these complex heterostructures with low ppb-level detection limits makes them excellent candidates for chemical/ gas sensing applications in e-noses.     

Controlled Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag Core–Shell Composite Nanoparticles with High Electrical Conductivity

The presented method provides an easy processing route to synthesize Fe₃O₄/Ag core–shell composite nanoparticles. Their structures were characterized by x-ray diffraction and transmission electron microscopy. The average size of the Fe₃O₄ core and Ag shell was about 32.0 nm and 5.0 nm (or 28.0 nm), respectively. Furthermore, magnetic measurements showed that the composite nanoparticles exhibited typical superparamagnetic behavior, specific saturation magnetization of ca. 24.0 emu/g, and intrinsic coercivity of 106.0 Oe. At the same time, high conductivity (64.7 S/cm) of the composite nanoparticles was also observed. This method provides an opportunity to synthesize other core–shell (Fe₃O₄) nanoparticles in a single step.     

Novel hybrid self-assembly of an ultralarge ZnO macroflower and defect intensity-induced photocurrent and photocatalytic properties by facile hydrothermal synthesis using CO(NH2)2–N2H4 as alkali sources

Different flower-like ZnO nanoarchitectures were synthesized by a facile hydrothermal method using CO(NH₂)₂ and N₂H₄ as alkali sources simultaneously. A novel ultralarge ZnO macroflower was constructed by the ultrathin leaf-like nanobelts, hollow semisphere-like, sphere-like and apple-shaped nanoparticles simultaneously. The diameter of an individual flower can reach 90 µm. Meanwhile, three or five flower-like ZnO nanostructures with different diameters, lengths and tips (Planar, semi-pyramid, and/ or pyramid tips) were formed simultaneously under the same reaction condition. XRD shows that all the ZnO crystals possess the hexagonal wurtzite structure. When the samples range from S1 to S5, the crystallinity is improved. EDX shows that the Zn/ O atom ratio of S1–S5 is close to the 1:1 stoichiometric ratio, and that of S3 is almost equal to 1:1. FTIR indicates that S4 and S5 are pure. However, the surface of S1, S2 and S3 adsorbs the CO₃²⁻ group. The reflectance of S1–S4 in the range of 300–370 nm is inversely proportional to that in visible region. Meanwhile, when the grain size of S1–S4 decreases, their band gap increases. The Raman results of S1 and S5 are different from those of S4 and exhibit the higher crystal quality, which are favorable for the improvement of photocatalytic performance. S1 and S5 exhibit the highest photocatalytic performance and decompose 65% and 70% of MB within 50 min respectively. The photocatalytic activity and photocurrent strongly depend on the defect intensity of the ZnO crystals. The ZnO photocatalyst of S5 is still stable and efficient after three cycles. However, the photocatalytic activity of S1 decreases continuously, due to its unique morphology and the adsorption of intermediates. In addition, A hybrid self-assembly process of the ultralarge ZnO macroflower was proposed.