Brodie's or Hummers’ Method: Oxidation Conditions Determine the Structure of Graphene Oxide

Synthesis and studies of graphite oxide started more than 150 years ago and turned into a boom by the measurements of the outstanding physical properties of graphene. A series of preparation protocols emanated trying to optimize the synthesis of graphene oxide in order to obtain a less defective material, as source for graphene. However, over-oxidation of the carbon framework hampered establishing structure-property relationships. Here, the fact that two different synthetic methods for graphene oxide preparation lead to very similar types of graphene oxide with a preserved graphene lattice is demonstrated. Either sodium chlorate in nitric acid (similar to Brodie's method) or potassium permanganate in sulfuric acid (similar to Hummers’ method) treatment are possible; however, reaction conditions must be controlled. With a preserved carbon lattice analytical differences between the samples relate to the altered on-plane functionality. Consequently, terming preparation protocols “according to Brodie's/Hummers’ method” is not sufficient.     

纳米金/β-环糊精复合修饰碳糊电极测定亚硝酸盐

本文研究了亚硝酸盐(NO_2~-)在纳米金和β-环糊精复合修饰碳糊电极(AuNPs-β-CD/CPE)上的电化学行为。实验结果表明,与裸CPE相比,AuNPs-β-CD/CPE对NO_2~-的电化学氧化有显著的促进作用,其氧化峰电流显著增加。同时用循环伏安法(CV)、计时电流法(CA)测定了NO_2~-在AuNPs-β-CD/CPE上的电极反应动力学参数,用线性扫描伏安法(LSV)法测得NO_2~-氧化峰电流与其浓度在6.0×10-6~8.0×10-3 mol·L-1范围内呈良好的线性关系,检出限(S/N=3)为5.7×10-7 mol·L-1。将该传感器应用于水样的检测,相对标准偏差在0.15%~1.40%之间,回收率达99.3%~104.0%,检测结果符合定量测定要求。     

Preparation of PTFE Nanosphere with the Assistant of Modified Multi-Walled Carbon Nanotubes

PTFE nanospheres have been obtained with the assistant of different multi-walled carbon nanotubes (MWNTs) by means of a simple preparation method. The results show that the PTFE nanospheres possess the best dispersion stability using the fluorocarbon-modified MWNTs as the assistant. The products are characterized by field-emission scanning electron microscopy and X-ray photoelectron spectroscopy, respectively.     

Synthesis and design of polyurethane and its nanocomposites derived from canola-castor oil: Mechanical,thermal and shape memory properties

The recent global pandemic and its tremendous effect on the price fluctuations of crude oil illustrates the side effects of petroleum dependency more evident than ever. Over the past decades, both academic and industrial communities spared endless efforts in order to replace petroleum-based materials with bio-derived resources. In the current study, a series of shape memory polymer composites (SMPC's) was synthesized from epoxidized vegetable oils, namely canola oil and castor oil fatty acids (COFA's) as a 100% bio-based polyol and isophorone diisocyanate (IPDI) as an isocyanate using a solvent/catalyst-free method in order to eventuate polyurethanes (PU's). Thereafter, graphene oxide (GO) nanoplatelets were synthesized and embedded in the neat PU in order to overcome the thermomechanical drawbacks of the neat matrix. The chemical structure of the synthesized components, as well as the dispersion and distribution levels of the nanoparticles, was characterized. In the following, thermal and mechanical properties as well as shape memory behavior of the specimens were comprehensively investigated. Likewise, the thermal conductivity was determined. This study proves that synthesized PU's based on vegetable oil polyols, including graphene nanoparticles, exhibit proper thermal and mechanical properties, which make them stand as a potential candidate to compete with traditional petroleum-based SMPC's.     

Carbon Paste Composite with Co3O4 as a New Electrochemical Sensor for the Detection of Allura Red by Reduction

The detection of Allura red (AR) by electrochemical reduction using a different electrode from the conventional mercury electrode is presented. A carbon paste with cobalt (II, III) oxide composite electrode (CoO_x/CPE) is reported for the first time for the detection of AR. Moreover, others dyes such as tartrazine (TZ), sunset yellow (SY), amaranth (AM), Ponceaut 4‐R (P‐4R), and Sudan (SD) as well as pharmaceutical agents such as paracetamol (PMC) that are present in samples that contained AR did not show a reduced signal between 0.0 and ?0.3 V, which is the potential range where AR reduction was observed. The surface electroactivity was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The presence of CoO_X increased the cathodic peak current for AR by more than 50 % and 65 % via CV and square wave voltammetry (SWV), respectively, compared with an unmodified carbon paste electrode. Under the optimal parameters, (pH=3.0, accumulation time (t_ACC)=60 s and accumulation potential (E_ACC)=0.50 V), the detection limit for AR was 0.05 μmol L^?1. The new sensor was sensitive and stable for the detection of AR. Moreover, it was easily manufactured and very convenient for food samples such as soft and isotonic drinks as well as chili sauce.     

Atomic-Scale Dispersed Fe-Based Catalysts Confined on Nitrogen-Doped Graphene for Li-S Batteries: Polysulfides with Enhanced Conversion Efficiency

Lithium-sulfur batteries have been considered as potential electrochemical energy-storage devices owing to their satisfactory theoretical energy density. Nonetheless, the inferior conversion efficiency of polysulfides in essence leads to fast capacity decay during the discharge/charge cycle. In this work, it is successfully demonstrated that the conversion efficiency of lithium polysulfides is remarkably enhanced by employing a well-distributed atomic-scale Fe-based catalyst immobilized on nitrogen-doped graphene (Fe@NG) as a coating of separator in lithium-sulfur batteries. The quantitative electrocatalytic efficiency of the conversion of lithium polysulfides is determined through cyclic voltammetry. It is also proven that the Fe-N_X configuration with highly catalytic activity is quite beneficial for the conversion of lithium polysulfides. In addition, the adsorption and permeation experiments distinctly indicate that the strong anchoring effect, originated from the charge redistribution of N doping into the graphene matrix, inhibits the movement of lithium polysulfides. Thanks to these advantages, if the as-prepared Fe@NG catalyst is combined with polypropylene and applied as a separator (Fe@NG/PP) in Li-S batteries, a high initial capacity (1616 mA h g⁻¹ at 0.1 C), excellent capacity retention (93 % at 0.2 C, 70 % at 2 C), and superb rate performance (820 mA h g⁻¹ at 2 C) are achieved.     

Amides and Heparin‐Like Polymer Co‐Functionalized Graphene Oxide Based Core @ Polyethersulfone Based Shell Beads for Bilirubin Adsorption

Excessive bilirubin in the body of patient with liver dysfunction or metabolic obstruction may cause jaundice with irreversible brain damage, and new type of adsorbent for bilirubin is under frequent investigation. Herein, graphene oxide based core @ polyethersulfone‐based shell beads are fabricated by phase inversion method, amides and heparin‐like polymer are introduced to functionalize the core‐shell beads. The beads are successfully prepared with obvious core‐shell structure, adequate thermostability and porous shell. Clotting times and protein adsorption are investigated to inspect the hemocompatibility property of the beads. The adsorption of bilirubin is systematically investigated by evaluating the effects of contacting time, initial concentration and temperature on the adsorption, which exhibits improved bilirubin adsorption amount for the beads with amides contained cores or/and shells. It is worth believing that the amides and heparin‐like polymer co‐functionalized core‐shell beads may be utilized in the field of hemoperfusion for bilirubin adsorption.