Quasi-two-dimensional α-molybdenum oxide thin film prepared by magnetron sputtering for neuromorphic computing

Two-dimensional (2D) layered materials have attracted intensive attention in recent years due to their rich physical properties, and shown great promise due to their low power consumption and high integration density in integrated electronics. However, mostly limited to mechanical exfoliation, large scale preparation of the 2D materials for application is still challenging. Herein, quasi-2D α-molybdenum oxide (α-MoO₃) thin film with an area larger than 100 cm² was fabricated by magnetron sputtering, which is compatible with modern semiconductor industry. An all-solid-state synaptic transistor based on this α-MoO₃ thin film is designed and fabricated. Interestingly, by proton intercalation/deintercalation, the α-MoO₃ channel shows a reversible conductance modulation of about four orders. Several indispensable synaptic behaviors, such as potentiation/depression and short-term/long-term plasticity, are successfully demonstrated in this synaptic device. In addition, multilevel data storage has been achieved. Supervised pattern recognition with high recognition accuracy is demonstrated in a three-layer artificial neural network constructed on this α-MoO₃ based synaptic transistor. This work can pave the way for large scale production of the α-MoO₃ thin film for practical application in intelligent devices.

An all-solid-state synaptic transistor with about 4 orders conductance modulation is fabricated based on the α-MoO₃ thin film. A three-layer artificial neural network with high recognition accuracy was constructed based on this synaptic transistor.     

α-Fe2O3 hollow meso–microspheres grown on graphene sheets function as a promising counter electrode in dye-sensitized solar cells

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets. Herein, we demonstrate a facile solvothermal route under controlled conditions to successfully fabricate 3D α-Fe₂O₃ hollow meso–microspheres on the graphene sheets (α-Fe₂O₃/RGO HMM). Attributed to the combination of the catalytic features of α-Fe₂O₃ hollow meso–microspheres and the high conductivity of graphene, α-Fe₂O₃/RGO HMM exhibited promising electrocatalytic performance as a counter electrode in dye-sensitized solar cells (DSSCs). The DSSCs fabricated with α-Fe₂O₃ HMM displayed high power conversion efficiency of 7.28%, which is comparable with that of Pt (7.71%).

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets.     

Energy-saving electrolytic γ-MnO2 generation: non-noble metal electrocatalyst gas diffusion electrode as cathode in acid solution

γ-MnO₂, which is commercially used as an electrode material in batteries, is produced using large amounts of energy and leads to the production of high pollution as a secondary product. Ideally, this material should be fabricated by energy efficient, non-polluting methods at a reasonable cost. This study reports the green fabrication of γ-MnO₂ into a gas diffusion electrode with Pt-free catalysts in acid solution. Cobalt oxide nanoparticles were deposited on few-layer graphene sheets produced via a simple sintering and ultrasonic mixing method, leading to the fabrication of cobalt oxide/few-layer graphene. Co₃O₄ nanoparticles are irregularly shaped and uniformly distributed on the surface of the few-layer graphene sheets. Characterization was conducted by X-ray diffraction, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy. Electrochemical characterization revealed the performance of cobalt oxide/few-layer graphene gas diffusion electrode in an electrolyte of 120 g L⁻¹ manganese sulfate + 30 g L⁻¹ sulfuric acid at 100 A m⁻² at 80 °C. The cobalt oxide/few-layer graphene gas diffusion electrode exhibited a lower cell voltage of 0.9 V and higher electric energy savings of approximately 50% compared with traditional cathodes (copper and carbon).

Co₃O₄/FLG was used as a nanocatalyst to catalyze the ORR in the electrodeposition of MnO₂. The proposed Co₃O₄/FLG nanocomposite GDE exhibited a high activity of 0.9 V at a current density of 100 A m⁻².     

Two-dimensional β-MoO3@C nanosheets as high-performance negative materials for supercapacitors with excellent cycling stability

MoO₃ has gained a great deal of attention as a promising electrode material in energy storage devices. In particular, the low dimensional MoO₃ nanosheets coated with carbon layers are desirable electrode materials in supercapacitors. However, the fabrication or construction of β-MoO₃ with a special morphology is difficult. Here, we report a simple solvothermal treatment method to synthesize two-dimensional β-MoO₃@C (2D β-MoO₃@C) nanosheets. When used as electrode materials for supercapacitors, the as-prepared material displays an ultra-long lifespan with a 94% retention ratio after 50 000 cycles at 2 A g⁻¹. The excellent cycling stability is mainly attributed to the unique 2D nanosheet structure and the presence of the carbon layer on the surface of the nanosheet. Specifically, the presence of the carbon layer increases the electric conductivity of MoO₃, which facilitates a good access point for electrolyte ions and short ion diffusion paths. In addition, MoO₃ that has been coated with a carbon layer can maintain a good structural stability due to the carbon layer restricting the volume expansion of MoO₃ during the charge procedure. We believe that the present work opens a new way for designing the 2D layered materials with unique architectures for supercapacitor applications.

MoO₃ has gained a great deal of attention as a promising electrode material in energy storage devices.     

Sucrose-templated interconnected meso/macro-porous 2D symmetric graphitic carbon networks as supports for α-Fe2O3 towards improved supercapacitive behavior

In this study, ultrahigh electrochemical performance for interconnected meso/macro-porous 2D C@α-Fe₂O₃ synthesized via sucrose-assisted microwave combustion is demonstrated. Hematite (α-Fe₂O₃) synthesized via the same approach gave an encouraging electrochemical performance close to its theoretical value, justifying its consideration as a potential supercapacitor electrode material; nonetheless, its specific capacitance was still low. The pore size distribution as well as the specific surface of bare α-Fe₂O₃ improved from 145 m² g⁻¹ to 297.3 m² g⁻¹ after it was coated with sucrose, which was endowed with ordered symmetric single-layer graphene (2D graphene). Accordingly, the optimized hematite material (2D C@α-Fe₂O₃) showed a specific capacitance of 1876.7 F g⁻¹ at a current density of 1 A g⁻¹ and capacity retention of 95.9% after 4000 cycles. Moreover, the material exhibited an ultrahigh energy density of 93.8 W h kg⁻¹ at a power density of 150 W kg⁻¹. The synergistic effect created by carbon-coating α-Fe₂O₃ resulted in modest electrochemical performance owing to extremely low charge transfer resistance at the electrode–electrolyte interface with many active sites for ionic reactions and efficient diffusion process. This 2D C@α-Fe₂O₃ electrode material has the capacity to develop into a cost-effective and stable electrode for future high-energy-capacity supercapacitors.

In this study, ultrahigh electrochemical performance for interconnected meso/macro-porous 2D C@α-Fe₂O₃ synthesized via sucrose-assisted microwave combustion is demonstrated.     

The preparation of a difunctional porous β-tricalcium phosphate scaffold with excellent compressive strength and antibacterial properties

Porous β-tricalcium phosphate (β-Ca₃(PO₄)₂, β-TCP) scaffolds are widely applied in the field of bone tissue engineering due to their nontoxicity, degradability, biocompatibility, and osteoinductivity. However, poor compressive strength and a lack of antibacterial properties have hindered their clinical application. In order to address these disadvantages, graphene (G) and silver nanoparticles were introduced into β-TCP through a two-step method. In the synthesis process, G-β-TCP was prepared via an in situ synthesis method, and then silver nanoparticles and HAp particles were coated on the surface of the G-β-TCP scaffold in an orderly fashion using dopamine as a binder. From the results of characterization, when the content of graphene was 1 wt% of β-TCP, the G-β-TCP scaffold had the highest compression strength (127.25 MPa). And core–shell G-β-TCP-Ag-HAp not only had reduced cytotoxicity via the continuous release of Ag⁺, but it also achieved long-term antibacterial properties. Besides, the material still showed good cell activity and proliferation.

Silver nanoparticles and HAp particles were orderly coated on the surface of G-β-TCP scaffold. So the composite had good compression strength and antibacterial property.     

Raman spectroscopy-in situ characterization of reversibly intercalated oxygen vacancies in α-MoO3

This work reports on the in situ strategy to reversibly generate or suppress oxygen vacancies on α-MoO₃ which were probed by Raman spectroscopy. Reversible changes in two features of the α-MoO₃ Raman spectrum could be correlated to the generation of oxygen vacancies: displacement of the T_b band frequency and the intensity decrease of the symmetrical stretching (ν_s) band. These two features could be used to qualitatively describe oxygen vacancies. Raman results also indicate that oxygen vacancies are located in the interlayer region of the α-MoO₃ lattice. This observation is corroborated by in situ X-ray diffraction, which also indicates the absence of nonstoichiometric phase transitions.

This work reports on the in situ strategy to reversibly generate or suppress oxygen vacancies on α-MoO₃ which were probed by Raman spectroscopy.     

Parameter optimization and degradation mechanism for electrocatalytic degradation of 2,4-diclorophenoxyacetic acid (2,4-D) herbicide by lead dioxide electrodes

2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most commonly used herbicides in the world. In this work, the electro-catalytic degradation of 2,4-D herbicide from aqueous solutions was evaluated using three anode electrodes, i.e., lead dioxide coated on stainless steel 316 (SS316/β-PbO₂), lead dioxide coated on a lead bed (Pb/β-PbO₂), and lead dioxide coated on graphite (G/β-PbO₂). The structure and morphology of the prepared electrodes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The process of herbicide degradation was monitored during constant current electrolysis using cyclic voltammetry (CV). In this study, the experiments were designed based on the central composite design (CCD) and were analyzed and modeled by response surface methodology (RSM) to demonstrate the operational variables and the interactive effect of three independent variables on 3 responses. The effects of parameters including pH (3–11), current density (j = 1–5 mA cm⁻²) and electrolysis time (20–80 min) were studied. The results showed that, at j = 5 mA cm⁻², by increasing the reaction time from 20 to 80 min and decreasing the pH from 11 to 3, the 2,4-D herbicide degradation efficiency using SS316/β-PbO₂, Pb/β-PbO₂ and G/β-PbO₂ anode electrodes was observed to be 60.4, 75.9 and 89.8%, respectively. Moreover, the results showed that the highest COD and TOC removal efficiencies using the G/β-PbO₂ electrode were 83.7 and 78.5%, under the conditions pH = 3, electrolysis time = 80 min and j = 5 mA cm⁻², respectively. It was also found that G/β-PbO₂ has lower energy consumption (EC) (5.67 kW h m⁻³) compared to the two other studied electrodes (SS316/β-PbO₂ and Pb/β-PbO₂). The results showed a good correlation between the experimental values and the predicted values of the quadratic model (P < 0.05). Results revealed that the electrochemical process using the G/β-PbO₂ anode electrode has an acceptable efficiency in the degradation of 2,4-D herbicide and can be used as a proper pretreatment technique to treat wastewater containing resistant pollutants, e.g., phenoxy group herbicides (2,4-D).

Optimization of process parameters by the CCD method and electrocatalytic degradation and the electrochemical degradation mechanism of 2,4-D using modified electrode anodes were investigated.     

The effects of deposition time and current density on the electrochemical performance of flexible and high-performance MnO2@PFG composite electrodes

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG). The paper fiber between graphene sheets could be used as a flexible substrate for MnO₂ nanoparticles, and the microscopic morphologies and electrochemical performances of the MnO₂@PFG electrodes were tuned via regulating the deposition current densities and deposition times. 3D graphene on PFG served as a highly conductive backbone with a high surface area for the deposition of the MnO₂ nanoparticles, which provided high accessibility to electrolyte ions for shortening the diffusion paths. The MnO₂-10-600 s@PFG composite electrode achieved a maximum specific capacitance of 878.6 mF cm⁻² with an MnO₂ loading mass of 3.62 mg cm⁻² (specific capacitance of 187.7 F g⁻¹) at a current density of 0.5 mA cm⁻² in a 1 M NaSO₄ aqueous solution. Additionally, the MnO₂-10-600 s@PFG composite material with the most favorable composite ratio exhibited the highest energy density of 61.01 mW h cm⁻², maximum power density of 1249.78 mW cm⁻², excellent capacitance retention with no more than 7% capacitance loss after 10 000 cycles and good mechanical flexibility (about 91.06% of its original capacitance after 500 bending times). By combining the electric double layer capacitance of graphene networks with the pseudocapacitance of the MnO₂ nanostructures, the flexible electrode showed much enhanced electrochemical capacitance behaviors with robust tolerance to mechanical deformation; thus, it is promising for being woven into textiles for wearable electronics.

A novel composite electrode has been fabricated by the direct deposition of MnO₂ onto graphene networks surrounding a paper fiber (PFG).     

Free-standing graphene/bismuth vanadate monolith composite as a binder-free electrode for symmetrical supercapacitors

Preparation of new types of electrode material is of great importance to supercapacitors. Herein, a graphene/bismuth vanadate (GR/BiVO₄) free-standing monolith composite has been prepared via a hydrothermal process. Flexible GR sheets act as a skeleton in the GR/BiVO₄ monolith composites. When used as a binder-free electrode in a three-electrode system, the GR/BiVO₄ composite electrode can provide an impressive specific capacitance of 479 F g⁻¹ in a potential window of −1.1 to 0.7 V vs. SCE at a current density of 5 A g⁻¹. A symmetrical supercapacitor cell which can be reversibly charged–discharged at a cell voltage of 1.6 V has been assembled based on this GR/BiVO₄ monolith composite. The symmetrical capacitor can deliver an energy density of 45.69 W h kg⁻¹ at a power density of 800 W kg⁻¹. Moreover, it ensures rapid energy delivery of 10.75 W h kg⁻¹ with a power density of 40 kW kg⁻¹.

A symmetrical supercapacitor with a high energy density has been assembled based on a free-standing GR/BiVO₄ monolith composite.     

MnO2/ZnCo2O4 with binder-free arrays on nickel foam loaded with graphene as a high performance electrode for advanced asymmetric supercapacitors

ZnCo₂O₄ nanosheets were successfully arrayed on a Ni foam surface with graphene using a hydrothermal method followed by annealing treatment; then MnO₂ nanoparticles were electrodeposited on the ZnCo₂O₄ nanosheets to obtain a synthesized composite binder-free electrode named MnO₂/ZnCo₂O₄/graphene/Ni foam (denoted as MnO₂/ZnCo₂O₄/G/NF). After testing the binder-free composite electrode of MnO₂/ZnCo₂O₄/G/NF via cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy testing, we found that it exhibited ultrahigh electrochemical properties, with a high specific areal capacitance of 3405.21 F g⁻¹ under a current density of 2 A g⁻¹, and wonderful cycling stability, with 91.2% retention after 5000 cycles. Moreover, an asymmetric supercapacitor (ASC) based on MnO₂/ZnCo₂O₄/G/NF//G/NF was successfully designed. When tested, the as-designed ASC can achieve a maximum energy density of 46.85 W h kg⁻¹ at a power density of 166.67 W kg⁻¹. Finally, the ASC we assembled can power a commercial red LED lamp successfully for more than 5 min, which proves its practicability. All these impressive performances indicate that the MnO₂/ZnCo₂O₄/graphene composite material is an outstanding electrode material for electrochemical capacitors.

Schematic illustration of formation process of MnO₂/ZnCo₂O₄/G/NF composite electrode.     

MOF-derived (MoS2, γ-Fe2O3)/graphene Z-scheme photocatalysts with excellent activity for oxygen evolution under visible light irradiation

Constructing Z-scheme heterojunctions is considered as an effective strategy to obtain catalysts of high efficiency in electron–hole separation in photocatalysis. Unfortunately, suitable heterojunctions are difficult to fabricate because the direct interaction between two semiconductors may lead to unpredictable negative effects such as electron scattering or electron trapping due to the existence of defects which causes the formation of new substances. Furthermore, the van der Waals contact between two semiconductors also results in bad electron diffusion. In this work, a MOF-derived carbon material as a Z-scheme photocatalyst was synthesized via one-step thermal treatment of MoS₂ dots @Fe-MOF (MIL-101). Under visible light irradiation, the well-constructed Z-scheme (MoS₂, γ-Fe₂O₃)/graphene photocatalyst shows 2-fold photocatalytic oxygen evolution activity (4400 μmol g⁻¹ h⁻¹) compared to that of γ-Fe₂O₃/graphene (2053 μmol g⁻¹ h⁻¹). Based on ultraviolet photoelectron spectrometry (UPS), Mott–Schottky plot, photocurrent and photoluminescence spectroscopy (PL) results, the photo-induced electrons from the conduction band of γ-Fe₂O₃ could transport quickly to the valence band of MoS₂via highly conductive graphene as an electron transport channel, which could significantly enhance the electron–hole separation efficiency as well as photocatalytic performance.

The heterojunction between MoS₂ and γ-Fe₂O₃ was constructed via linking by in situ formed graphene, which resulted in a good photocatalyst for the oxygen evolution reaction, showing O₂ evolution activity of 4400 μmol g⁻¹ h⁻¹.     

Rapid synthesis of vertically aligned α-MoO3 nanostructures on substrates

We report a new procedure for large scale, reproducible and fast synthesis of polycrystalline, dense, vertically aligned α-MoO₃ nanostructures on conducting (FTO) and non-conducting substrates (Si/SiO₂) by using a simple, low-cost hydrothermal technique. The synthesis method consists of two steps, firstly formation of a thermally evaporated Cr/MoO₃ seed layer, and secondly growth of the nanostructures in a highly acidic precursor solution. In this report, we document a growth process of vertically aligned α-MoO₃ nanostructures with varying growth parameters, such as pH and precursor concentration influencing the resulting structure. Vertically aligned MoO₃ nanostructures are valuable for different applications such as electrode material for organic and dye-sensitized solar cells, as a photocatalyst, and in Li-ion batteries, display devices and memory devices due to their high surface area.

We report a procedure for large scale, reproducible and fast synthesis of polycrystalline, dense, vertically aligned α-MoO₃ nanostructures on conducting (FTO) and non-conducting substrates (Si/SiO₂) by using a simple, low-cost hydrothermal technique.     

Study of molar properties of GO after doping with transition metals for photodegradation of fluorescent dyes

We synthesized graphene oxide (GO) doped with transition metal ions and characterized it using XPS, FT-IR, TGA/DTG, XRD, SEM, AFM, ICP-OES, UV/vis, and Raman spectroscopy. An intrinsic viscosity [η] of 0.002–0.012 g% @ 0.002 aq-GO was determined for viscosity average molecular weight (M_v) of GO at 288.15, 298.15, and 308.15 K. Mark–Houwink (M–H) constants k (cm³ g⁻¹) and a (cm³ mol g⁻²) were calculated for 5–15 mg/100 mL polyvinylpyrrolidone (PVP), using 29, 40, 55 kg mol⁻¹ as markers for calculating M_v by fitting the [η] to the Mark–Houwink–Sakurada equation (MHSE). We obtained 48 134.19 g mol⁻¹M_v at 298.15 K, and the apparent molar (V_ϕm, cm³ mol⁻¹), limiting molar volumes (V⁰_GO)_{G$\stackrel{⃑}{O}$0}, enthalpy (ΔH_m, J mol⁻¹), entropy (ΔS_m, J mol⁻¹ K⁻¹), viscosity (η_m, mPa s mol⁻¹), surface tension (γ_m, mN m⁻¹ mol⁻¹), friccohesity (σ_m, scm⁻¹ mol⁻¹), fractional volume (ϕ_m, cm³ mol⁻¹), isentropic compressibility (K_sϕ,m, 10⁻⁴ cm s² g⁻¹ mol), infer GO molar consistency throughout the chemical processes. Molar properties (MPs) infer a GO monodispersion producing negative electrons (e⁻) and positive holes (h⁺) under sunlight. The transition metal ions (Fe²⁺, Mn²⁺, Ni²⁺, Cr³⁺, TMI) doped onto GO (TMI-GO), can photodegrade methylene blue (MB) in 60 min compared with 120 min using GO alone. The 4011 C atoms, 688 hexagonal sheets, 222 π-conjugations, and 4011 FE were calculated from the 48 134.19 g mol⁻¹. The functional edges are the negative and positive holes generating centres of the GO 2D sheets.

We synthesize and characterise graphene oxide doped with transition metal ions, and calculate the Mark–Houwink constants, determining methylene blue degradation efficiency.     

A hybrid composite of H2V3O8 and graphene for aqueous lithium-ion batteries with enhanced electrochemical performance

Aqueous rechargeable lithium-ion batteries (ARLBs) are regarded as a competitive challenger for large-scale energy storage systems because of their high safety, modest cost, and green nature. A kind of modified composite material composed of H₂V₃O₈ nanorods and graphene sheets (HVO/G) has been effectively made by a one-step hydrothermal method and following calcination at 523 K. XRD, SEM, TEM, and TG are used to determine the phase structures and morphologies of the composite materials. Owing to the advantage of the layered structure of H₂V₃O₈ nanorods, the excellent conductivity of the graphene sheets, and the 3D network structure of the modified composite, the ARLBs with HVO/G can deliver an adequate specific capacity of 271 mA h g⁻¹ at 200 mA g⁻¹ and have a retention rate of 73.4% after 50 cycles. The average discharge capacity of ARLB with HVO/G as anode has a considerable improvement over that of HVO/CNTs and HVO, whatever the current rate used. Moreover, we find that the diffusion coefficient of lithium-ion increases by an order of magnitude through the theoretical calculation for HVO/G ARLB. The new ARLB with HVO/G electrode is a potential energy storage system with great advantages, such as simple preparation, easy assembly process, excellent safety and low-cost environmental protection.

Aqueous rechargeable lithium-ion batteries (ARLBs) are regarded as a competitive challenger for large-scale energy storage systems because of their high safety, modest cost, and green nature.     

Synthesis of 1,3-dicarbonyl-functionalized reduced graphene oxide/MnO2 composites and their electrochemical properties as supercapacitors

A novel 1,3-dicarbonyl-functionalized reduced graphene oxide (rDGO) was prepared by N-(4-aminophenyl)-3-oxobutanamide interacting with the epoxy and carboxyl groups of graphene oxide. The high-performance composite supercapacitor electrode material based on MnO₂ nanoparticles deposited onto the rDGO sheet (DGM) was fabricated by a hydrothermal method. The morphology and microstructure of the composites were characterized by field-emission scanning electron microscopy, transmission electron microscopy, Raman microscopy and X-ray photoelectron spectroscopy. The obtained results indicated that MnO₂ was successfully deposited on rDGO surfaces. The formed composite electrode materials exhibit excellent electrochemical properties. A specific capacitance of 267.4 F g⁻¹ was obtained at a current density of 0.5 A g⁻¹ in 1 mol L⁻¹ H₂SO₄, while maintaining high cycling stability with 97.7% of its initial capacitance after 1000 cycles at a current density of 3 A g⁻¹. These encouraging results are useful for potential energy storage device applications in high-performance supercapacitors.

A novel functionalized reduced graphene oxide and MnO₂ composite was prepared as a supercapacitor electrode material.     

One-pot mechanochemical exfoliation of graphite and in situ polymerization of aniline for the production of graphene/polyaniline composites for high-performance supercapacitors

Graphene/polyaniline composites have attracted considerable attention as high-performance supercapacitor electrode materials; however, there are still numerous challenges for their practical applications, such as the complex preparation process, high cost, and disequilibrium between energy density and power density. Herein, we report an efficient method to produce graphene/polyaniline composites via a one-pot ball-milling process, in which aniline molecules act as both the intercalator for the exfoliation of graphite and the monomer for mechanochemical polymerization into polyaniline clusters on the in situ exfoliated graphene sheets. The graphene/polyaniline composite electrode delivered a large specific capacitance of 886 F g⁻¹ at 5 mV s⁻¹ with a high retention of 73.4% at 100 mV s⁻¹. The high capacitance and rate capability of the graphene/polyaniline composite can contribute to the fast electron/ion transfer and dominantly capacitive contribution because of the synergistic effects between the conductive graphene and pseudocapacitive polyaniline. In addition, a high energy density of 40.9 W h kg⁻¹ was achieved by the graphene/polyaniline-based symmetric supercapacitor at a power density of 0.25 kW kg⁻¹, and the supercapacitor also maintained 89.1% of the initial capacitance over 10 000 cycles.

Efficient ball-milling production of graphene/polyaniline composites as supercapacitor electrodes with enhanced capacitive contribution, rate capability, and specific capacitance.     

Fabrication of an (α-Mn2O3:Co)-decorated CNT highly sensitive screen printed electrode for the optimization and electrochemical determination of cyclobenzaprine hydrochloride using response surface methodology

A new chemically optimized screen-printed electrode modified with a cobalt-doped α-Mn₂O₃ nanostructure on carbon nanotube paste (α-Mn₂O₃:Co@CNTs) has been constructed for the recognition of cyclobenzaprine hydrochloride. The prepared paste is based on the incorporation of oxide ion conductors, such as the α-Mn₂O₃ nanostructure with cobalt and ion pairs (tetraphenyl borate coupled with the drug), as electroactive species in the screen-printed electrode to increase the sensor surface area and decrease electrical resistance. The central composite design is a useful methodology for the estimation and modeling of the exact optimum parameters specifically designed for this process. This is a good way to graphically clarify the relationship between various experimental variables and the slope response. The proposed sensor, α-Mn₂O₃:Co@CNTs, possesses very good sensitivity and the ability to recognize the drug over the concentration range of 1 × 10⁻⁶ to 1 × 10⁻² mol L⁻¹ at 25 ± °C with a detection limit of 2.84 × 10⁻⁷ mol L⁻¹. It exhibits a reproducible potential and stable linear response for six months at a Nernstian slope of 58.96 ± 0.76 mV per decade. The proposed electrode approach has been successfully applied in the direct determination of the drug in its pure and dosage forms.

A new chemically optimized screen-printed electrode modified with a cobalt-doped α-Mn₂O₃ nanostructure on carbon nanotube paste (α-Mn₂O₃:Co@CNTs) has been constructed for the recognition of cyclobenzaprine hydrochloride.     

Preparation and characterization of an edible metal–organic framework/rice wine residue composite

In this communication, using rice wine residue (RWR) as the support, an edible γ-cyclodextrin-metal–organic framework/RWR (γ-CD-MOF/RWR) composite with a macroscopic morphology was synthesized. The obtained edible composite is promising for applications in drug delivery, adsorption, food processing, and others.

An edible metal–organic framework/rice wine residue composite was made with large surface area for potential applications in drug delivery, adsorption, food processing, and others.

As a typical class of porous materials, metal–organic frameworks (MOFs) have attracted increasing attention since being first proposed by Yaghi and co-workers.¹ Over the past two decades, owing to their large surface area, ultrahigh porosity and tunable pore size,² MOFs have exhibited great prospects for gas storage and separation,^3,4 catalysis,^5–8 sensors,⁹ drug delivery,^10–12etc. Among numerous reported MOFs, γ-cyclodextrin-MOF (γ-CD-MOF), which is connected by the (γ-CD)₆ units of alkaline earth metal ions, was initially synthesized and reported by Stoddart et al.^13,14 in the 2010s. Owing to the –OCCO– groups derived from γ-CD, this kind of MOF is edible and therefore opens a new path for preparing green, biocompatible and edible MOF materials.^13,15,16 For example, Stoddart et al.¹¹ reported a co-crystallization approach to trap ibuprofen and lansoprazole inside γ-CD-MOF, and the resultant composite microspheres can be used for sustained drug delivery. Zhang et al.¹⁷ proposed a strategy to graft cholesterol over the surface of γ-CD-MOF to form a protective hydrophobic layer to improve its water stability. Many researchers succeeded in preparing oral delivery medicine with high drug loading and an enhanced therapeutic effect by combining the drug molecules with γ-CD-MOF.^16,18–20 These works present the excellent application prospects of γ-CD-MOF in the medical field.Since MOFs possess so many attractive advantages, extensive studies have focused on combining MOFs with many other functional materials (metal nanoparticles, quantum dots, carbon matrices and polyoxometalates, etc.) by means of the synergistic effect, leading to the formation of novel composites designed for targeted applications.^21–28 However, these reported composites were still presented as loose powders, which may not be convenient for the applications. Therefore, the question of how to prepare MOFs-based composites for larger particles at low cost is of great significance. On the other hand, as a traditional alcoholic beverage, rice wine has been popular in southern China and some other Asian nations for thousands of years.²⁹ The rice wine lees or rice wine residue (RWR) is a by-product of the fermentation process of rice wine. It is a mixture of proteins, amino acids and polysaccharides. It is traditionally a health food in some Asian nations.³⁰ The edibility, extensive source, low cost and specific macroscopic shape make RWR a potential functional material for further use of MOFs.Herein, a facile and environmental-friendly strategy has been developed to realize the growth of γ-CD-MOF on rice wine residue, resulting in the formation of an edible MOF/RWR composite in the shape of rice grains. The material characterization confirmed the obtained composite possesses the characteristics of MOF. Except for the edible γ-CD-MOF/RWR, other MOF/RWR composites (HKUST-1, ZIF-67 and MIL-100(Fe)/RWR composites; shown in Fig. S1^†) were prepared to demonstrate the universality of this synthesis strategy.The synthesis procedure of the γ-CD-MOF/RWR composite is schematically illustrated in Fig. 1. The rice wine residue was soaked in deionized water for 12 h and then washed with deionized water three times before vacuum freeze-drying. Similar to the synthesis of γ-CD-MOF powder,¹⁵ KOH was dissolved into water. Then certain amounts of the aforementioned dry rice wine residue were soaked into the K⁺-containing solution for 2 h in order to absorb the sufficient potassium ions. K⁺ was then linked by the coordination of –OCCO– units in γ-CD and RWR with the three-dimensional interconnected network. After vapor diffusion of MeOH and some other procedures described in the synthesis of γ-CD-MOF powder (seen in ESI), the γ-CD-MOF/RWR composite (Fig. 2) was obtained. This method is convenient as no extra binders are needed during the whole process. The same procedure was employed to prepare the RWR composites with other MOFs (HKUST-1, ZIF-67 and MIL-100(Fe)). And the syntheses are briefly described in the ESI. The images of the obtained composites are shown in Fig. S1.^†Open in a separate windowFig. 1Schematic illustration of the synthesis procedure of γ-CD-MOF/RWR composite.Open in a separate windowFig. 2Digital photo of the γ-CD-MOF/RWR composite.The rice wine residue, of which the elemental analysis is shown in Table S1,^† is mainly composed of polysaccharides and proteins. Thus, a broad peak at around 22.2° in the XRD patterns of rice wine residue can be observed (Fig. S2^†), which is due to its poor crystallinity.³¹ The XRD patterns of γ-CD-MOF and γ-CD-MOF/RWR composite samples are shown in Fig. 3a. The characteristic peaks at 5.6°, 6.9°, 13.3°, 16.6°, 20.6° and 23.2°, observed from the XRD patterns of γ-CD-MOF, agree with the previously reported works.^32,33 Meanwhile, compared with γ-CD-MOF, the γ-CD-MOF/RWR composite shows similar characteristic peaks with lower intensity, indicating a lower crystallinity of the MOF within the composite. Fig. 3b shows the FT-IR spectra of different samples. Compared with the rice wine residue, the peaks in regions 1 and 2 of γ-CD-MOF and γ-CD-MOF/RWR can be ascribed to the stretching vibration of –CH₂ and –C–O–C– of the MOF, respectively.^15,34 These results further confirm the formation of the γ-CD-MOF in the γ-CD-MOF/RWR composite.Open in a separate windowFig. 3XRD patterns (a) and FT-IR spectra (b) of γ-CD-MOF/RWR composite, γ-CD-MOF and RWR.The SEM images were collected to further investigate the micromorphology of the as-prepared samples. As shown in Fig. 4a, a three-dimensional layered network structure and rich macropores of the rice wine residue rough surface can be seen. γ-CD-MOF (Fig. 4b) exhibits a uniform body-centered cubic shape with an average size of 4.27 μm, which is in accordance with the reported works.^15,35,36 Meanwhile, the images of the γ-CD-MOF/RWR composite (Fig. 4c and d) show that the cubic γ-CD-MOF crystals are well dispersed on the surface of the rice wine residue and even partially integrated into the framework of the rice wine residue. Compared with the pristine γ-CD-MOF, some γ-CD-MOF in γ-CD-MOF/RWR is not an intact cubic structure, exhibiting a significantly different morphology. This suggests a synergistic effect between the MOF crystals and the rice wine residue during the growth of MOF crystals, rather than a simple physical mixture of the two materials. The thermal stability of the γ-CD-MOF/RWR composite was investigated via TGA analysis. As shown in Fig. S3,^† the decomposition temperature of γ-CD-MOF/RWR composite slightly increased compared with those of pristine γ-CD-MOF and rice wine residue. Moreover, the γ-CD-MOF/RWR composite was stable in water, methanol and ethanol (shown in Fig. S4^†) even under mild stirring. These results indicate an improved physiochemical stability of γ-CD-MOF after the incorporation of rice wine residue. This finding further confirms the synergistic effect between them.Open in a separate windowFig. 4SEM images of rice wine residue (a), γ-CD-MOF (b) and γ-CD-MOF/RWR composite (c and d). Fig. 5a shows the nitrogen sorption isotherms of the γ-CD-MOF and γ-CD-MOF/RWR composite. Both pristine γ-CD-MOF and γ-CD-MOF/RWR exhibit typical type-I isotherms, demonstrating their microporous structures. The pore size distributions of pure γ-CD-MOF and γ-CD-MOF/RWR (Fig. 5b) confirm the existence of micropores (between 1 and 2 nm). The calculated Brunauer–Emmett–Teller (BET) surface areas, micropore volume and total pore volume are listed in 35,37 The specific surface area of the γ-CD-MOF/RWR composite is 651 m² g⁻¹, which is significantly higher than that of the pure rice wine residue (10.8 m² g⁻¹). Thus, the increase in the specific surface area of γ-CD-MOF/RWR composite can be attributed to the growth of γ-CD-MOF on the RWR support. Therefore, γ-CD-MOF/RWR composite inherits both the high porosity of γ-CD-MOF and the macroscopic morphology of rice wine residue, which should contribute to its practical applications.Open in a separate windowFig. 5N₂ adsorption and desorption isotherms (a) and pore size distributions (b) of γ-CD-MOF/RWR composite and corresponding comparative samples.Summary of the BET areas (S_BET), micropore volume (V_micro) and total pore volume (V_tot) of γ-CD-MOF, γ-CD-MOF/RWR composite and pure rice wine residue

Three-dimensional graphene oxide cross-linked by benzidine as an efficient metal-free photocatalyst for hydrogen evolution

The use of low-cost photocatalysts to split water into H₂ fuel via solar energy is highly desirable for the production of clean energy and a sustainable society. Here three-dimensional graphene oxide (3DG) porous materials were prepared by cross-linking graphene oxide (GO) sheets using aromatic diamines (benzidine, 2,2′-dimethyl-4,4′-biphenyldiamine, 4,4′-diaminodiphenylmethane) that reacted with the carboxyl groups of the GO sheets at room temperature. The prepared 3DG porous materials were used as efficient metal-free photocatalysts for the production of H₂via water splitting under full-spectrum light, where the photocatalytic activity was highly dependent on the cross-linker and the 3DG reduction level. It was also found that the 3DG prepared with benzidine as the linker demonstrated a significantly higher H₂ evolution rate than the 3DGs prepared using 2,2′-dimethyl-4,4′-biphenyldiamine and 4,4′-diaminodiphenylmethane as the cross-linkers. The photoactivity was further tuned by varying the mass ratio of GO to benzidine. Among the prepared 3DG materials, 3DG-3, with an intermediate C/O ratio of 1.84, exhibited the highest H₂ production rate (690 μmol g⁻¹ h⁻¹), which was significantly higher than the two-dimensional GO (45 μmol g⁻¹ h⁻¹) and the noncovalent 3DG synthesized by a hydrothermal method (128 μmol g⁻¹ h⁻¹). Moreover, this study revealed that the 3DG photocatalytic performance was favored by effective charge separation, while it could be further tuned by changing the reduction level. In addition, these results could prompt the preparation of other 3D materials and the application of new types of photocatalysts for H₂ evolution.

Three-dimensional graphene oxide covalently linked by benzidine works as an efficient metal-free photocatalyst for H₂ evolution.