Fabrication of a Biomass-Derived Activated Carbon-Based Anode for High-Performance Li-Ion Batteries.

Porous carbons are highly attractive and demanding materials which could be prepared using biomass waste; thus, they are promising for enhanced electrochemical capacitive performance in capacitors and cycling efficiency in Li-ion batteries. Herein, biomass (rice husk)-derived activated carbon was synthesized via a facile chemical route and used as anode materials for Li-ion batteries. Various characterization techniques were used to study the structural and morphological properties of the prepared activated carbon. The prepared activated carbon possessed a carbon structure with a certain degree of amorphousness. The morphology of the activated carbon was of spherical shape with a particle size of ~40-90 nm. Raman studies revealed the characteristic peaks of carbon present in the prepared activated carbon. The electrochemical studies evaluated for the fabricated coin cell with the activated carbon anode showed that the cell delivered a discharge capacity of ~321 mAhg-1 at a current density of 100 mAg-1 for the first cycle, and maintained a capacity of ~253 mAhg-1 for 400 cycles. The capacity retention was found to be higher (~81%) with 92.3% coulombic efficiency even after 400 cycles, which showed excellent cyclic reversibility and stability compared to commercial activated carbon. These results allow the waste biomass-derived anode to overcome the problem of cyclic stability and capacity performance. This study provides an insight for the fabrication of anodes from the rice husk which can be redirected into creating valuable renewable energy storage devices in the future, and the product could be a socially and ethically acceptable product.

Zinc Oxide/Phosphorus-Doped Carbon Nitride Composite as Potential Scaffold for Electrochemical Detection of Nitrofurantoin.

Herein, we present an electrocatalyst constructed by zinc oxide hexagonal prisms/phosphorus-doped carbon nitride wrinkles (ZnO HPs/P-CN) prepared via a facile sonochemical method towards the detection of nitrofurantoin (NF). The ZnO HPs/P-CN-sensing platform showed amplified response and low-peak potential compared with other electrodes. The exceptional electrochemical performance could be credited to ideal architecture, rapid electron/charge transfer, good conductivity, and abundant active sites in the ZnO HPs/P-CN composite. Resulting from these merits, the ZnO HPs/P-CN-modified electrode delivered rapid response (2 s), a low detection limit (2 nM), good linear range (0.01-111 µM), high sensitivity (4.62 µA µM-1 cm2), better selectivity, decent stability (±97.6%), and reproducibility towards electrochemical detection of NF. We further demonstrated the feasibility of the proposed ZnO HPs/P-CN sensor for detecting NF in samples of water and human urine. All the above features make our proposed ZnO HPs/P-CN sensor a most promising probe for detecting NF in natural samples.

Low-Temperature Ethanol Sensor via Defective Multiwalled Carbon Nanotubes.

This paper focuses on the fabrication of defective-induced nanotubes via the catalytic chemical vapor deposition method and the investigation of their properties toward gas sensing. We have developed defective multi-walled carbon nanotubes with porous and crystalline structures. The catalyst layer used in CNTs' growth here was based on 18 and 24 nm of Ni, and 5 nm of Cr deposited by the dc-sputtering technique. The CNTs' defects were characterized by observing the low graphite peak (G-band) and higher defect peaks (D-band) in the Raman spectrum. The defectives sites are the main source of the sensitivity of materials toward different gases. Thus, the current product was used for sensing devices. The device was subjected to various gases such as NO, NO2, CO, acetone, and ethanol at a low operating temperature of 30 °C and a concentration of 50 ppm. The sensor was observed to be less sensitive to most gas while showing the highest response towards ethanol gas. The sensor showed the highest response of 8.8% toward ethanol at 30 °C of 50 ppm, and a low response of 2.8% at 5 ppm, which was investigated here. The signal repeatability of the present sensor showed its capability to detect ethanol at much lower concentrations and at very low operating temperatures, resulting in reliability and saving power consumption. The gas sensing mechanism of direct interaction between the gas molecules and nanotube surface was considered the main. We have also proposed a sensing mechanism based on Coulomb dipole interaction for the physical adsorption of gas molecules on the surface.

Structural Transition-Induced Raman Enhancement in Bioinspired Diphenylalanine Peptide Nanotubes.

Semiconducting materials are increasingly proposed as alternatives to noble metal nanomaterials to enhance Raman scattering. We demonstrate that bioinspired semiconducting diphenylalanine peptide nanotubes annealed through a reported structural transition can support Raman detection of 10-7 M concentrations for a range of molecules including mononucleotides. The enhancement is attributed to the introduction of electronic states below the conduction band that facilitate charge transfer to the analyte molecule. These results show that organic semiconductor-based materials can serve as platforms for enhanced Raman scattering for chemical sensing. As the sensor is metal-free, the enhancement is achieved without the introduction of electromagnetic surface-enhanced Raman spectroscopy.

Removal of Heavy Metal Ions from Wastewater Using Hydroxyethyl Methacrylate-Modified Cellulose Nanofibers: Kinetic, Equilibrium, and Thermodynamic Analysis.

The objective of this work was to fabricate modified cellulose nanofibers (CNFs) for the removal of heavy metal ions (Cd2+ and Pb2+) from wastewater. Cellulose was modified with 2-hydroxyethyl methacrylate (HEMA) via grafting copolymerization using the microwave-assisted technique in the presence of ceric ammonium nitrate (CAN) as an initiator. Prepared cellulose-graft-(2-hydroxyethyl methacrylate) (HEMA/C) copolymers were characterized using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Different factors affecting the graft yield, such as irradiation time, monomer concentrations, and initiator concentrations, were investigated. Furthermore, cellulose-graft-(2-hydroxyethyl methacrylate) copolymer nanofibers (HEMA/CNF) were fabricated by electrospinning using N,N-dimethylacetamide-LiCl as a solvent. Electrospun nanofiber copolymers were characterized using SEM and thermogravimetric analysis (TGA). Operating parameters, including time, starting metal concentrations, and adsorbent concentration, were analyzed at a pH of 5.6 for the two metal ions. The best-fit model of adsorption energy was the pseudo-second-order model, and adsorption isotherms at equilibrium were well described by the Langmuir and Freundlich models. The negative values of ΔG and positive values of ΔH and ΔS suggest that the adsorption of Cd2+ and Pb2+ ions onto electrospun HEMA/CNF is a spontaneous, endothermic, and favorable reaction.

Monitoring Food Spoilage Based on a Defect-Induced Multiwall Carbon Nanotube Sensor at Room Temperature: Preventing Food Waste.

We have developed an electronic nose based on carbon nanotubes (CNTs) synthesized by using a plasma-enhanced chemical vapor deposition, aiming to be a convenient monitoring device for food spoilage. The prepared CNTs showed a crystalline structure and smooth surface with a diameter of 11.3 nm and a length of ∼10 µm. The Raman spectrum showed that the CNTs fabricated were multiwalled carbon nanotubes (MWCNTs). The characteristic graphite peak (G) observed at 1595 cm-1 in the Raman spectrum showed low intensity as compared to the defect peak (D) observed at 1330 cm-1, which referred to defect-induced points in CNTs. The CNTs were used to fabricate a sensor for ethylene gas produced by banana fruits for in situ measurements at room temperature. The sensor demonstrated good performance toward detecting the produced gas. The gas sensing signal was used as early indicators of the spoilage to help prevent food waste. The calibration curve was shown for the sensor responses evaluated at ripening days over 5 days. The sensor showed a response of 3.2% on the first day and increased to ∼7.0% by the third day and then gradually decreased. This sensor is appropriate for detecting the spoilage of food because it shows a good sensing response to a low level of produced gas from a single banana. Insight into food spoilage status of a specific level of gas shows its potential to be applied for quality assurance of food. The sensor sensitivity toward ethylene produced by a banana was confirmed based on the sensor response toward chemical ethylene gas.

Binder-Free Electrode Based on ZnO Nanorods Directly Grown on Aluminum Substrate for High Performance Supercapacitors.

Herein, for the first time, the growth of ZnO nanorods directly on aluminum (Al) substrate via a low temperature (80 °C) wet chemical method, and used as binder-free electrode for supercapacitors were reported. XRD pattern and HRTEM images showed that high crystalline nanorods grown on Al substrate with c-axis orientation. Morphological studies revealed that the nanorods possessed well defined hexagon phase with length and diameter of ~2 µm and 100-180 nm, respectively. Raman spectrum of ZnO nanorods showed that the characteristic E2H mode corresponds to the vibration associated with the oxygen atoms of ZnO. The optical properties of ZnO nanorods studied using Room-temperature PL spectra revealed a near-band-edge (NBE) peak at ~388 nm emission and deep level (DLE) at ~507 nm. Electrochemical measurements showed that ZnO nanorods on Al substrate exhibited remarkably enhanced performance as electrode for supercapacitors with a value of specific capacitance of 394 F g-1 measured with scan rate of 20 mV s-1. This unique nanorods structures also exhibited excellent stability of >98% capacitance retention for 1000 cycles that were measured at 1A g-1. The presented easy and cost-effective method might open up the possibility for the mass production of binder-free electrodes for efficient electrochemical energy storage devices.

Flower-Like ZnO Nanorods Synthesized by Microwave-Assisted One-Pot Method for Detecting Reducing Gases: Structural Properties and Sensing Reversibility.

In this work, flower-like ZnO nanorods (NRs) were successfully prepared using microwave-assisted techniques at a low temperature. The synthesized NRs exhibited a smooth surface and good crystal structure phase of ZnO. The sharp peak of the XRD and Raman spectrum confirmed the high crystallinity of these ZnO NRs with a pure wurtzite structure. The nanorods were ~2 µm in length and ~150 nm in diameter, respectively. The electron diffraction pattern confirmed that the single crystal ZnO nanorods aligned along the [001] plane. The NRs were applied to fabricate a gas sensor for reducing gases such as CH4, CO, and H2. The sensor showed a good performance and sensitivity toward the target gases. However, its response toward CH4 and CO was higher compared to H2 gas. Although the operating temperature was varied from room temperature (RT) up to 350°C, the sensor did not show a response toward any of the target gases in the range of RT-150°C, but dramatic enhancement of the sensor response was observed at 200°C, and up to higher temperatures. This behavior was ascribed to the activity of the smooth surface and the reactivity of surface oxygen species with the targeted gases. The sensor response was measured at various gas concentrations, where the calibration curve was shown. The gas sensing mechanism was described in terms of the reaction of the gases with the transformed oxygen species on the surface of the oxides.

Synthesis of mesoporous SnO2/NiO nanocomposite using modified sol-gel method and its electrochemical performance as electrode material for supercapacitors.

In this research work, SnO2, NiO and SnO2/NiO nanocomposites were synthesized at low temperature by modified sol-gel method using ultrasonication. Prepared samples were investigated for their properties employing various characterization techniques. X-ray diffraction (XRD) patterns confirmed the purity and phase of the samples as no secondary phase was detected. The average crystallite size of the nanocomposites was found to decrease from 19.24 to 4.53 nm with the increase in NiO concentration. It was confirmed from SEM micrographs that the material has mesoporous morphology. This mesoporous morphology resulted in the increase of the surface to mass ratio of the material, which in turn increases the specific capacitance of the material. The UV-Visible spectra showed the variation in the band gap of SnO2/NiO at different weight ratio ranging from 3.49 to 3.25 eV on increasing NiO concentration in the samples. These composites with different mass ratio of SnO2 and NiO were also characterized by FT-IR spectroscopy that showed shifting of the peaks centered at 545 cm-1 in the spectra for NiO/SnO2 nanocomposite. The analysis of the electrochemical performance of the material was done with the help of cyclic voltammetry and Galvanostatic charge-discharge. The specific capacitance of the synthesized samples with different concentration of SnO2 and NiO was analyzed at different scan rates of 5 to 100 mV/s. Interestingly, 7:1 mass ratio of NiO and SnO2 (SN7) nanocomposite exhibited a maximum specific capacitance of ~ 464 F/g at a scan rate of 5 mV/s and good capacitance retention of 87.24% after 1,000 cycles. These excellent electrochemical properties suggest that the SnO2/NiO nanocomposite can be used for high energy density supercapacitor electrode material.

Correction to 'Photocatalytic inactivation of Escherichia coli under UV light irradiation using large surface area anatase TiO2 quantum dots'.

[This corrects the article DOI: 10.1098/rsos.191444.].

Fabrication of TiO2-Nanotube-Array-Based Supercapacitors.

In this work, a simple and cost-effective electrochemical anodization technique was adopted to rapidly grow TiO2 nanotube arrays on a Ti current collector and to utilize the synthesized materials as potential electrodes for supercapacitors. To accelerate the growth of the TiO2 nanotube arrays, lactic acid was used as an electrolyte additive. The as-prepared TiO2 nanotube arrays with a high aspect ratio were strongly adhered to the Ti substrate. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the TiO2 nanotube arrays were crystallized in the anatase phase. TEM images confirmed the nanotublar-like morphology of the TiO2 nanotubes, which had a tube length and a diameter of ~16 and ~80 nm, respectively. The electrochemical performance of the TiO2 nanotube array electrodes was evaluated using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD) measurements. Excellent electrochemical response was observed for the electrodes based on the TiO2 nanotube arrays, as the cells delivered a high specific capacitance of 5.12 mF/cm2 at a scan rate of 100 mV/s and a current density of 100 µA/cm2. The initial capacity was maintained for more than 250 cycles. Further, a remarkable rate capability response was observed, as the cell retained 88% of the initial areal capacitance when the scan rate was increased from 10 to 500 mV/s. The results suggest the suitability of TiO2 nanotube arrays as electrode materials for commercial supercapacitor applications.

Self-assembled Cube-like Copper Oxide Derived from a Metal-Organic Framework as a High-Performance Electrochemical Supercapacitive Electrode Material.

Interest in pseudocapacitive materials, especially cuprous oxide, has grown owing to its various advantageous properties and application as electrode materials in the energy storage devices. The work presented here, a cubic Cu2O framework was synthesized using a simple and one-step modified polyol-assisted (metal-organic framework) solvothermal method. The structural configuration was rationalized by systematically studying the effect of the reaction time on the morphology and growth of the Cu2O. In addition, a range of microscopic and spectroscopic techniques was employed to further characterize the obtained cubic Cu2O. The morphological effect on the electrochemical supercapacitive performance of the obtained cubic Cu2O was also examined by cyclic-voltammetry (CV) and galvanostatic-charge-discharge (G-C-D) method. The obtained outcome shows that the cubic Cu2O synthesized using a reaction time of 12 h (Cu2O-12h; Csp ~365 Fg-1) exhibited superior capacitive performance as compared to the cubic Cu2O synthesized at 8 h (Cu2O-8h; Csp ~151 Fg-1) and 10 h (Cu2O-10h; Csp ~195 Fg-1) at the current density of 0.75 Ag-1. Furthermore, the Cu2O-12h electrode exhibits energy density of 16.95 Wh/Kg at a power density of 235.4 W/Kg and higher power density of 2678.5 W/Kg at low current density. In particular, the cube-like Cu2O-12h exhibited excellent capacitive performance and rate capability as compared to Cu2O-8h and Cu2O-10h, owing to its unique three-dimensional morphology, which facilitates the formation of various active sites for intercalation of the electrolyte during the electrochemical process. These results show the as-obtained Cu2O could be a promising supercapacaitive electrode material for various applications.

Preparation and Characterization of Developed CuxSn1-xO2 Nanocomposite and Its Promising Methane Gas Sensing Properties.

Novel materials with nanostructures are effective in controlling the physical properties needed for specific applications. The use of active and sensing materials is increasing in many applications, such as gas sensing. In the present work, we attempted to synthesize incorporated Cu2+ into the SnO2 matrix as CuxSn1-xO2 nanocomposite using a cost-effective precursor and method. It was observed that, at low concentrations of copper precursor, only SnO2 phase could be detected by X-ray diffraction (XRD). The distribution of Cu in the SnO2 matrix was further measured by elemental analysis of energy-dispersive X-ray (EDX) mapping and X-ray fluorescence (XRF). At high copper concentration, a separated monoclinic phase of CuO was formed (noted here as CuO/SnO2). The average crystallite size was slightly reduced from 5.9 nm to 4.7 nm with low doping of 0.00-5.00% Cu but increased up to 15.0 nm at high doping of 10.00% Cu upon the formation of separated SnO2 and CuO phases. The formation of Cu-SnO2 or CuO phases at low and high concentrations was also observed by photoluminescent spectra. Here, only the emission peak of SnO2 with a slight blueshift was recorded at low concentrations, while only the CuO emission peak was recorded at high concentration. The effect of Cu concentration on the sensing properties of SnO2 toward methane (CH4) gas was also investigated. It was found that the sensor embedded with 2.00% Cu exhibited an excellent sensitivity of 69.0 at 350 °C and a short response-recovery time compared with the other sensors reported here. The sensing mechanism of CuxSn1-xO2 and CuO/SnO2 is thus proposed based on Cu incorporation.

Photocatalytic inactivation of Escherischia coli under UV light irradiation using large surface area anatase TiO2 quantum dots.

In this study, high specific surface areas (SSAs) of anatase titanium dioxide (TiO2) quantum dots (QDs) were successfully synthesized through a novel one-step microwave-hydrothermal method in rapid synthesis time (20 min) without further heat treatment. XRD analysis and HR-TEM images showed that the as-prepared TiO2 QDs of approximately 2 nm size have high crystallinity with anatase phase. Optical properties showed that the energy band gap (E g) of as-prepared TiO2 QDs was 3.60 eV, which is higher than the standard TiO2 band gap, which might be due to the quantum size effect. Raman studies showed shifting and broadening of the peaks of TiO2 QDs due to the reduction of the crystallite size. The obtained Brunauer-Emmett-Teller specific surface area (381 m2 g-1) of TiO2 QDs is greater than the surface area (181 m2 g-1) of commercial TiO2 nanoparticles. The photocatalytic activities of TiO2 QDs were conducted by the inactivation of Escherischia coli under ultraviolet light irradiation and compared with commercially available anatase TiO2 nanoparticles. The photocatalytic inactivation ability of E. coli was estimated to be 91% at 60 µg ml-1 for TiO2 QDs, which is superior to the commercial TiO2 nanoparticles. Hence, the present study provides new insight into the rapid synthesis of TiO2 QDs without any annealing treatment to increase the absorbance of ultraviolet light for superior photocatalytic inactivation ability of E. coli.

A low-temperature technique and new strategy for the dual growth of carbon nanotubes and nanorods through the confinement of explosive materials inside a porous structure.

In this paper, we report a low temperature technique and new strategy for the dual growth of carbon nanotubes (CNTs) and nanorods (CNRs) with alumina nanoparticles to avoid the high temperature required for CNT and CNR production and their assembling behaviour. In this trend, X-ray diffraction and thermal analysis indicated that the porous system of aluminium species was prepared and saturated with the crystalline structure of ammonium nitrate to act as a solid explosive composite and caused alcohol decomposition inside a pressurized vessel at 250 °C. TEM images and the Raman results confirmed that the CNTs had grown at 250 °C through the decomposition of methanol inside the boehmite structure. Also, the TEM images revealed that the growth of CNTs depended on the ratio between the methanol and the solid explosive. By calcination at 600 °C, the Raman results indicated that the CNTs became more ordered and had fewer defects. In the case of changing methanol to ethanol, the results indicated that methanol was more favorable than ethanol for growing CNTs by this technique. Also, it indicated that ethanol was a good source for producing carbon nanorods. Finally, we concluded that this was probably the first time that carbon nanotubes or nanorods had been prepared at 250 °C and their aggregations prevented through their dual growth with alumina nanoparticles. This dual growth approach is a very promising strategy for building homogeneous nanocomposites based on carbon nanotubes and nanorods.

Accelerating the Photocatalytic Degradation of Green Dye Pollutants by Using a New Coating Technique for Carbon Nanotubes with Nanolayered Structures and Nanocomposites.

The present study has two aims, first to accelerate the degradation of pollutants by coating carbon nanotubes (CNTs) with nanoplatelets or nanocomposites of aluminum zinc oxides and second to fabricate an advanced photocatalyst. Accordingly, Zn-Al layered double hydroxides (LDHs) were grown in the presence of functionalized CNTs during urea hydrolysis. The presence of CNTs led to the formation of LDH nanoplatelets, and TEM images showed that the CNTs were coated with nanoplatelets. The nanoplatelets were thermally treated to form nanocomposite-coated CNTs. Raman spectra demonstrated the successful coating of CNTs with LDHs and nanocomposite. The coated CNTs were very effective in the photocatalytic degradation of industrial pollutants. A kinetics study demonstrated that the rate of photocatalytic degradation of green dye in the presence of CNTs coated with aluminum zinc oxide nanocomposite was five times faster than with the aluminum zinc oxide nanocomposite.

Light-soaking free organic photovoltaic devices with sol-gel deposited ZnO and AZO electron transport layers.

This paper investigates light-soaking effects in inverted organic photovoltaic (OPV) devices with zinc oxide (ZnO) and aluminum doped ZnO (AZO) electron transport layers (ETL), which is important for the development of low-cost and stable solar cells. The samples demonstrated high solar harvesting properties with power conversion efficiency up to 3.9%. Air-stability tests of up to 150 days were performed on devices with different Al doping levels. The devices maintained higher than 60% of the initial PCE after 50 days of open-air exposure. The light-soaking mechanism was investigated with experiments and simulations and shown to be eliminated when the Al fraction of the AZO is higher than 4%. The simulated band diagram of the OPV devices indicates that the low carrier density in the ZnO layer by virtue of depletion is the main reason of the light-soaking effect. Doping the ZnO layer as well as exposing the devices under UV irradiation will introduce additional free carriers into the ETL and reduce the width of the depletion region at both sides of the ETL.