Controlled synthesis of core-mesoporous shell from biomass sustainable N-doped hollow carbonaceous nanospheres

Encompassing ecological and economic concerns, the utilization of biomass to produce carbonaceous materials has attracted intensive research and industrial interest. Using nitrogen containing precursors could realize an in situ and homogeneous incorporation of nitrogen into the carbonaceous materials with a controlled process. Herein, N-doped hollow core-disordered mesoporous shell carbonaceous nanospheres （HCDMSs） were synthesized from glucosamine hydrochloride （GAH）, an applicable carbohydrate-based derivative. The obtained HCDMSs possessed controlled size （-450-50 nm） and shell thickness （-70-10 nm）, suitable nitrogen contents （-6.7-4.4 wt.%）, and Brunauer-Emmett-Teller （BET） surface areas up to 770 m^2.g^-1. These materials show excellent electrocatalytic activity as a metal-free catalyst for the oxygen reduction reaction （ORR） in both alkaline and acidic media. Specifically, the prepared HCDMS-1 exhibits a high diffusion-limited current, and superior durability and better immunity towards methanol crossover and CO poisoning for ORR in alkaline solution than a commercial 20 wt.% Pt/C catalyst.

Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits.Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities.In addition,plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment.Here,we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide(VO_(2))hybrids,exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots.Polarization-and wavelength-dependent pump–probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas.The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant,antenna-mediated local heating on a picosecond time scale.The hybrid,nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO_(2) film without antennas,enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range.The hybrid solution of antennas and VO_(2) provides a conceptual framework to merge the field localization and phase-transition response,enabling precise,nanoscale optical memory functionalities.

The SBA-15/SO_3H nanoreactor as a highly efficient and reusable catalyst for diketene-based,four-component synthesis of polyhydroquinolines and dihydropyridines under neat conditions

An efficient diketene ring-opening synthesis of polyhydroquinoline derivatives using SBA-15 sulfonic acid modified mesoporous substrates a green and reusable catalyst in a single-pot four-component coupling reaction of diketene,alcohol,enamine,and aldehydes is reported.Dihydropyridine derivatives based on neat adduct of diketene,alcohols and aldehydes using SBA-15/SO_3H nanoreactor as catalyst via a four-component reactions are also synthesized.The advantages of the present method include the use of a small amount catalyst,simple procedure with an easy filterable work-up,waste-free,green and direct synthetic method with an excellent yield of products with efficient use of catalyst and a short reaction time.

Comparative Analysis of Ti,Ni,and Au Electrodes on Characteristics of TiO_2 Nanofibers for Humidity Sensor Application

The effect of metal （Ti, Ni, and Au） electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contacts on SiO2 layer thermally grown on silicon substrate. The separation between the electrodes was 90 μm for all sensors. The sensors were tested from 40% to 90% relative humidity （RH） by AC electrical characterization at room temperature. When sensors are switched between 40% and 90% RH, the corresponding response and recovery time are 3 s and 5 s for Ti-electrode sensor, 4 s and 7 s for Ni-electrode sensor, and 7 s and 13 s for Au-electrode sensor. The hysteresis was 3%, 5% and 15% for sensitivity of Ti, Ni, and Au-electrode sensors are Ti-, Ni-, and Au-electrode sensor, respectively. The 7.53 MΩ/%RH, 5.29 MΩ/%RH and 4.01 MΩ/%RH respectively at 100 Hz. Therefore Ti-electrode sensor is found to have linear response, fast response and recovery time and higher sensitivity as compared with those of Ni- and Au-electrode sensors. Comparison of humidity sensing properties of sensors with different electrode material may propose a compelling route for designing and optimizing humidity sensors.

Carrier transport mechanisms in semiconductor nanostructures and devices

Semiconductor nanostructures have gained importance due to their potential application in future nano- electronic devices. For such applications, it is extremely important to understand the electrical properties of semi- conductor nanostructures. This review presents an overview of techniques to measure the electrical properties of individual and clusters of semiconductor nanostructures using microcopy based techniques or by fabricating metal- lic electrical contacts using lithography. Then it is shown that current-voltage （I-V） characteristics can be used to determine the conduction mechanism in these nanostructures. It has been explained that various material paramet- ers can be extracted from I-V characteristics. The frequently observed conduction mechanism in these nanostruc- tures such as thermally activated conduction, space charge limited current （SCLC）, hopping conduction, Poole Frenkel conduction, Schottky emission and Fowler Nordheim （FN） tunneling are explained in detail.

Germinant ZnO nanorods as a charge-selective layer in organic solar cells

A facile method was introduced and demonstrated to synthesize zinc oxide(ZnO) nanorods(NRs) as an electron transporting layer(ETL) for organic solar cells(OSCs).Hydrothermal synthesis of the NRs showed a constant growth rate of 5.5 nm min-1 from germination to sub-micrometer length.The properties were characterized using scanning electron microscopy(SEM),transmission electron microscopy(TEM),absorption spectrophotometry and so on.Based on these measurements,the germinant growth mechanism and its corresponding orientation characteristics were investigated.As an ETL of the OSCs,ZnO NRs enhance the charge extraction from the active layer due to their increased interfacial surface area,but there is an optimal length because of the shunt path formation and UV absorption of long ZnO NRs.As a re sult,the OSC with the ZnO NRs as ETL shows power conversion efficiency(PCE) up to 6.2%.The J-V characteristics and incident photon-to-current conversion efficiency(IPCE) measurement also reveal that the efficiency enhancement is an assembly of individual results from optical,physical and electrical characteristic of the ZnO NRs.

Humidity Effect on Transport Properties of Titanium Dioxide Nanoparticles

Rutile TiO2 nanoparticles were synthesized using co-precipitation method with an average diameter of 30 nm TiO2 nanoparticle device was then fabricated on glass substrate.Aluminum electrodes were defined using photolithography and vacuum evaporation.A suspension of TiO2 nanoparticles was prepared in isopropanol using ultrasonic agitation.The nanoparticles were deposited between the electrodes.The device was tested by AC electrical measurements at 40%-90%relative humidity（RH）.The impedance of the TiO2nanoparticles decreases by about 80 times with the increase in RH from 40%to 90%at 100 Hz.The response time and the recovery time were 4 s and 5 s,respectively between 40%and 90%RH.At 100 Hz,the sensitivity of the aluminum electrode TiO2 nanoparticle device in the range of 40%—90%RH was17 MΩ/%RH.Complex modulus analysis also confirms the increase in DC conductivity of TiO2 nanoparticles as RH increases.

Controlled growth of crossed ultralong carbon nanotubes by gas flow

Carbon nanotubes(CNTs)work as the promising components of miniature electromechanical systems due to their ecellent performances from individual to bundle scales.But it's challenging to achieve precise patterning at nanoscale resolution with controlled position and orientation.Here,we demonstrate a fluidic strategy to interlace one-dimensional(1D)ultralong CNTs into the crossed pattern in a one-step in-situ process.Semi-circular substrates of different diameters were placed in front of the growth substrate to change the path and momentum of gas flow.Such flow perturbation caused by substrates could be markedly reflected within a micro-channel reactor,which led to formation of crossed utralong CNTs at definite positions.Furthermore,precise control over the crossing angle as well as the diameter distribution of CNTs was achieved by varying the CNT length and diameter of semi-circular substrates.Our strategy has offered a feasible route for production of crossed ultralong CNTs and will contribute to multidimensional fluidic assembly of flexible nanomaterals.

Nanotechnology for Water Treatment: Is It the Best Solution Now?

INTRODUCTION Preservation of the freshwater resources is a big challenge for a healthy civilized world.Although water consumption increased more than twice the population increase rate,drinking water pollution and freshwater shortage increased dramatically during the last decades(Kar et al.,2012;Mueller and Nowack,2010).Only 0.01%of freshwater resources are suitable for human needs(Rashid et al.,2019),even in the areas of abundant freshwater(Yeston et al.,2006).By 2050,over 5 billion of the world population will be under severe fresh water supply conditions due to climate change and urbanization exacerbate(Sealy,2019;Oves et al.,2015;Kar et al.,2012).Currently,one billion people drink unhygienic water,especially in developing countries which leads to severe waterborne diseases which might cause death(Aminiyan et al.,2018).Twelve million people die every year due to this problem(Zhao et al.,2019;Oves et al.,2015).

Diketene-based neat four-component synthesis of the dihydropyrimidinones and dihydropyridine backbones using silica sulfuric acid(SSA)

Heterocyclic skeleton building blocks to afford dihydropyrimidinones and dihydropyridines based on neat adducts of diketene, alcohols and aldehydes via silica sulfuric acid （SSA） catalyzed ring opening of diketene in four-component Biginelli-type and Hantzsch-type reactions are presented.

Warpage and Shrinkage Optimization of Injection-Molded Plastic Spoon Parts for Biodegradable Polymers Using Taguchi, ANOVA and Artificial Neural Network Methods

In this study, it is attempted to give an insight into the injection processability of three self-prepared polymers from A to Z. This work presents material analysis, injection molding simulation, design of ex- periments alongside considering all interaction effects of controlling parameters carefully for green biodegradable polymeric systems, including polylactic acid （PLA）, polylactic acid-thermoplastic poly- urethane （PLA-TPU） and polylactic acid-thermoplastic starch （PLA-TPS）. The experiments were carried out using injection molding simulation software Autodesk Moldflov~~ in order to minimize warpage and volumetric shrinkage for each of the mentioned systems. The analysis was conducted by changing five significant processing parameters, including coolant temperature, packing time, packing pressure, mold temperature and melt temperature. Taguchi＇s [.27 （35） orthogonal array was selected as an efficient method for design of simulations in order to consider the interaction effects of the parameters and reduce spu- rious simulations. Meanwhile, artificial neural network （ANN） was also used for pattern recognition and optimization through modifying the processing conditions. The Taguchi coupled analysis of variance （ANOVA） and ANN analysis resulted in definition of optimum levels for each factor by two completely different methods. According to the results, melting temperature, coolant temperature and packing time had significant influence on the shrinkage and warpage. The ANN optimal level selection for minimiza- tion of shrinkage and/or warpage is in good agreement with ANOVA optimal level selection results. This investigation indicates that PLA-TPU compound exhibits the highest resistance to warpage and shrink- age defects compared to the other studied compounds.