Synthesis and characterization of new nitrogen‐ and oxygen‐rich cyclohexanone–formaldehyde resin for fast Cd(II) adsorption in aqueous solution

A new structure of cyclohexanone–formaldehyde resin (CFR) was synthesized via in situ condensation reaction of 2,4,6‐tris(p‐formylphenoxy)‐1,3,5‐triazine (TFPA) with CFR. TFPA was prepared by the reaction of cyanuric chloride and p‐hydroxybenzaldehyde and its structure was confirmed using spectroscopic methods and elemental analysis. The structural, thermal and morphological properties of the nitrogen‐ and oxygen‐rich CFR were studied using Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis and field emission scanning electron microscopy. After characterization, the resin was used as an adsorbent for Cd(II) due to the high level of nitrogen and oxygen in its structure. The effects of various parameters such as pH, concentration and time on the adsorption process were studied. The maximum adsorption capacity of cadmium at pH 8 in 5 min was 83.61 mg L^?1. The adsorption isotherm was applied to the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. Comparing the correlation coefficient (R²), the Langmuir model was fitted well. Pseudo‐first‐order, pseudo‐second‐order, Elivich and intra‐particle diffusion models of adsorption kinetics were explored. The pseudo‐second‐order model can better explain the adsorption kinetics that shows adsorption being dependent on the number of active sites of the adsorbent. © 2019 Society of Chemical Industry     

Liquefied Sunshine: Transforming Renewables into Fertilizers and Energy Carriers with Electromaterials

It has become apparent that renewable energy sources are plentiful in many, often remote, parts of the world, such that storing and transporting that energy has become the key challenge. For long-distance transportation by pipeline and bulk tanker, a liquid form of energy carrier is ideal, focusing attention on liquid hydrogen and ammonia. Development of high-activity and selectivity electrocatalyst materials to produce these energy carriers by reductive electrochemistry has therefore become an important area of research. Here, recent developments and challenges in the field of electrocatalytic materials for these processes are discussed, including the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the nitrogen reduction reaction (NRR). Some of the mis-steps currently plaguing the nitrogen reduction to ammonia field are highlighted. The rapidly growing roles that in situ/operando and quantum chemical studies can play in new electromaterials discovery are also surveyed.     

Crystalline order and mechanical properties of as‐electrospun and post‐treated bundles of uniaxially aligned polyacrylonitrile nanofiber

This study investigates the crystalline order and mechanical properties of as‐electrospun and posttreated polyacrylonitrile nanofibers. To keep the nanofibers under tension during the posttreatment, a modified method of preparing bundles such as multifilament yarn was used in which the alignment of the nanofibers and linear density of the bundles were controlled successfully. An increase in the nanofibers' diameter from 240 to 500 nm led to the E modulus, ultimate strength, and elongation at break of the bundles rising from 836 MPa, 45 MPa, and 38% to 1915 MPa, 98 MPa, and 120%, respectively. The crystallinity index (%) and coherence length of the nanofiber bundles were evaluated through wide‐angle X‐ray diffraction. The mechanical properties and crystalline order of the nanofiber bundles were both increased as a result of the posttreatment. Wide‐angle X‐ray diffraction patterns of annealed bundles showed equatorial diffraction from the (101 0) reflection at ～ 5.1 Å and from the (112 0) reflection at ～ 3 Å. The values of the coherence length, crystallinity index (%), ultimate strength, and E modulus of the bundles prepared from 240‐nm nanofibers increased from negligible, 2%, 1109 MPa, and 48 MPa to 54 Å, 35%, 2235 MPa, and 95 MPa after annealing at 85°C in a mixture of water (95 wt %) and N,N‐dimethylformamide (5 wt %), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

On the prediction of shrinkage defects by thermal criterion functions

The goal of the present study is to predict the formation of solidification induced defects in castings by thermal criteria functions. In a criterion function method, the heat transfer equation is firstly solved, and then the susceptibility of defect formation at every point in the casting is predicted by computing a local function, criterion function, using results of the thermal analysis. In the first part of the paper, some famous criteria functions, in particular, the Pellini and Niyama criteria, are analyzed and their shortcomings are discussed in details. Then, a new criterion function is suggested to decrease the shape-dependency issue of the former criteria. The feasibility of the new method is studied by comparing numerical results against some archived experimental data.     

Bubble dynamics at boiling incipience in subcooled upward flow boiling

Bubble dynamics in water subcooled flow boiling was investigated through visualization using a high-speed camera. The test section was a vertical rectangular channel, and a copper surface of low contact angle was used as a heated surface. Main experimental parameters were the pressure, mass flux and liquid subcooling. Although all the experiments were conducted under low void fraction conditions close to the onset of nucleate boiling, no bubbles stayed at the nucleation sites at which they were formed. Depending on the experimental conditions, the following two types of bubble behavior were observed after nucleation: (1) lift-off from the heated surface followed by collapsing rapidly in subcooled bulk liquid due to condensation, and (2) sliding along the vertical heated surface for a long distance. Since the bubble lift-off was observed only when the wall superheat was high, the boundary between the lift-off and the sliding could be determined in terms of the Jakob number. Based on the present experimental results, discussion was made for the possible mechanisms governing the bubble dynamics.     

Reinforcing epoxy nanocomposites with functionalized carbon nanotubes via biotin–streptavidin interactions

We report on the preparation of nanocomposites consisting of biofunctionalized single-walled carbon nanotubes (BF-SWCNTs) reinforcing an ultraviolet curable epoxy polymer by means of biotin–streptavidin interactions. The as-produced laser ablation SWCNTs are biofunctionalized via acid oxidization based purification process and non-covalent functionalization using surfactant, followed by grafting the resulting nanotubes with biomolecules. The biotin-grafted nanotubes are capable of interacting with epoxy groups in presence of streptavidin molecules by which chemical bridges between BF-SWCNTs and epoxy matrix are formed. The biomolecules grafted to the nanotubes surface not only facilitate the load transfer, but also improve the nanotube dispersion into the epoxy matrix, as observed by optical imaging and scanning electron microscopy. Mechanical characterization on the nanocomposite microfibers demonstrates considerable enhancement in both strength (by 76%) and modulus (by 93%) with the addition of only 1 wt.% of BF-SWCNTs. The electrical measurements reveal a clear change in electrical conductivity of nanocomposite microfibers reinforced with 1 wt.% of BF-SWCNTs in comparison to the microfibers containing solely purified carbon nanotubes. These multifunctional nanocomposite materials could be used to fabricate macro and microstructures for a wide variety of applications such as high strength polymer nanocomposite and potential easily-manipulated biosensors.     

Extraction and characterization of rice straw cellulose nanofibers by an optimized chemomechanical method

In this study, a chemomechanical method was performed to extract nanofibers from rice straw. This procedure included swelling, acid hydrolysis, alkali treatment, bleaching, and sonication. X‐ray diffractometer was employed to investigate the effect of acid hydrolysis conditions and other chemical treatments on the chemical structure of the extracted cellulose fibers. It was concluded that by increasing the acid concentration and hydrolysis time, the crystallinity of the extracted fibers was increased. The optimum acid hydrolysis conditions were found to be 2M and 2 h for the acid concentration and hydrolysis time, respectively. The chemical compositions of fibers including cellulose, hemicelluloses, lignin, and silica were determined by different examinations. It was noticed that almost all the silica content of fibers was solubilized in the swelling step. Moreover, the achieved results showed that the cellulose content of the alkali treated fibers was increased around 71% compared to the raw materials. ATR‐FTIR was applied out to compare the chemical structure of untreated and bleached fibers. The dimensions and morphology of the chemically and mechanically extracted nanofibers were investigated by scanning electron microscopy, field emission scanning electron microscopy, and transmission electron microscopy. The results of the image analyzer showed that almost 50% of fibers have a diameter within a range of 70–90 nm and length of several micrometers. The thermal gravimetric analyses were performed on the untreated and bleached fibers. It was demonstrated that the degradation temperature was increased around 19% for the purified fibers compared to raw materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40063.     

Polyphenol-Induced Adhesive Liquid Metal Inks for Substrate-Independent Direct Pen Writing

Surface patterning of liquid metals (LMs) is a key processing step for LM-based functional systems. Current patterning methods are substrate specific and largely suffer from undesired imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand-written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand-written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise.