Graphite and graphene oxide electrodes for lithium ion batteries

Sustainable mining of natural vein graphite via acid-extraction from waste attached to rock pieces of vein banks

A procedure based on acid extraction using a mixture of conc. sulfuric and nitric acids (8:1) to recover graphite attached to rock pieces of the vein contact zones of graphite mines, is developed as a sustainable mining practice. When the extracted graphite is heated at 600 °C for 15 min, it is converted to a highly expanded form resembling worm-like structures. The unique properties of this graphite and expanded graphite are presented by characterizing using FT-IR, Raman, SEM-EDX and XRD. This expanded graphite has the oil absorption capacity of 120 g of oil per 1 g of expanded graphite, making it the material so far known to have the highest oil absorption capacity. For comparison purpose, properties of ball-milled graphite powder which was obtained from the middle of the vein is prepared and characterized. However, the ball-milled graphite does not expand upon heat-treatment at 600 °C for 15 min. The acid-extracted graphite (AEG) has lower purity than that of ball-milled graphite (BMG), but heat-treatment increases the purity of the AEG while BMG shows opposite results. The purity of AEG has increased considerably upon heat-treatment by lowering the O wt% (weight percentage) by 6.07% to half of its original value while increasing C wt% by 8.05%. On the contrary, the C wt% of BMG has decreased by 3.71% and O wt% increased by 3.84%. The increase of purity upon heat treatment of AEG is due to the removal of some carbon and sulfur impurities as their volatile oxides. The ball-milled graphite absorbs carbon dioxide from the atmosphere when heat-treated at 600 °C. As such, the ball-milled graphite powder can be used to extract carbon dioxide from the atmosphere. The crystallite size of AEG is 1.25 times larger than that of BMG and it has been increased by 8 and 2.9 times, respectively, upon heat-treatment at 600 °C for 15 min. This is a clear evidence to expanded nature of AEG compared to BMG.

Adsorptive removal of aflatoxin B1 from contaminated peanut oil via magnetic porous biochar from soybean dreg

The contamination of mycotoxin in edible oil has always been a major threat to human health. In this study, magnetic soybean dreg-based biochar SDB-6-K-9@Fe₃O₄ was prepared via co-precipitation and used to remove aflatoxin B1 (AFB1) from contaminated oil. The adsorbent characterization results revealed that the Fe₃O₄ was successfully loaded to the SDB-6-K-9. The 0.45SDB-6-K-9@Fe₃O₄ had paramagnetic properties with a saturation magnetization of 45.15 emu/g, which could be quickly separated from the peanut oil using an external magnet. The maximum adsorption capacity of peanut oil contaminated with 200 ng/mL AFB1 by 50 mg 0.45SDB-6-K-9@Fe₃O₄ for 2 h reached 0.1354 mg/g, while the removal process minimally affected the quality of the oil. The adsorption behavior results followed a pseudo-second-order kinetic and fitted well with the Freundlich model. The excellent adsorption removal efficiency and facile magnetic separation of the adsorbents provide a simple and efficient method for removing contaminants from the oil.

Fabrication of flexible composite film based on xylan from pulping process for packaging application

To realize the application of xylan based film in food and drug packaging, the poor mechanical property and film-forming property of xylan based film must be overcome. Herein, a good oxygen barrier composite film with desired mechanical properties was prepared based on carboxymethly xylan (CMX), chitosan (CS), and graphene oxide (GO). The results of scanning electron microscope revealed the composite film had a dense and continuous structure, which will endow the composite film with excellent mechanical property. As expected, the composite film with the 0.5% mass fraction of GO exhibited best mechanical property, among which the tensile stress, tensile strain, and Young's modulus of the composite film reached 50.81 MPa, 47.61%, and 1.39 GPa, respectively. The oxygen barrier properties of the composite films significantly increased with the addition of graphene oxide due to the dense, stacked multilayer structure. In addition, these composite films exhibited good antibacterial properties. Therefore, these films show great promise in the field of food packaging and wound dressing due to their excellent mechanical, oxygen barrier and antibacterial properties.

An electrochemical aptasensor based on tetrahedral DNA nanostructures as a signal probe carrier platform for sensitive detection of patulin

In this work, we proposed an electrochemical aptasensor for patulin (PAT) based on tetrahedral DNA nanostructures (TDNs) and thionine (Thi)-labeled Fe₃O₄ nanoparticles (Fe₃O₄NPs)/rGO signal amplification strategy. The rigid structure of TDNs could effectively improve the binding efficiency. Fe₃O₄NPs/rGO with excellent electrical conductivity and large specific surface area was used as a label material, which could load more Thi and accelerate electron transfer. Besides, the unique catalytic properties of Fe₃O₄NPs could achieve active signal amplification. Once PAT existed, PAT aptamer was released from the capture probe, thereby introducing Fe₃O₄NPs/rGO with Thi onto the electrode surface. Therefore, a noticeable increase in Thi current intensity was observed. Under the optimized conditions, the proposed aptasensor showed superior performance with a linear range from 5 × 10^-8 to 5 × 10^-1 μg mL^-1 and a detection limit of 30.4 fg mL^-1. The obtained sensor showed reliable specificity, stability and reproducibility, and was successfully applied to the determination of real samples.

Detoxification of Aflatoxin B1 by magnetic graphene composite adsorbents from contaminated oils

Safety concerns pertaining towards fungal occurrence in oil commodities have been a significant threat to human health. In this research, magnetic composite adsorbents were fabricated for the removal of aflatoxin B₁ (AFB₁) from contaminated oils. To this goal, graphene oxides (GO) were synthesized using Hummer's method, and graphenes (rGO) were obtained by the reduction of GO by sodium borohydride. Thereafter, magnetic graphene oxides (MGO) and magnetic graphenes (MrGO) were prepared by coprecipitation of iron oxides on GO and rGO nanosheets, respectively. The as-prepared MGO and MrGO were characterized by SEM, TEM, FT-IR, XRD, VSM, and nitrogen adsorption-desorption techniques. Results showed that MGO had two-dimensional layered nanostructure with many wrinkles on its surface, and the Fe₃O₄ nanoparticles were essentially encapsulated onto the composite. The adsorption behaviors for the composite adsorbents especially for the removal of AFB₁ from contaminated oils were systematically explored by varying adsorbent dosage, contact time, adsorption temperature and initial AFB₁ concentration. The MGO adsorbent could have great potential in the application of AFB₁ removal from contaminated oils, with the merits of facile magnetic separation and high removal efficiency. However, the removal process also causes a loss of the triglyceride, pigment, and beneficial micronutrients in the oil feedstocks.

Preparation and characterization of hierarchical porous carbons derived from solid leather waste for supercapacitor applications

Utilization of crust leather waste (CLW) as precursors for the preparation of hierarchical porous carbons (HPC) were investigated. HPCs were prepared from CLW by pre-carbonization followed by chemical activation using KOH at relatively high temperatures. Textural properties of HPC's showed an extent of micro-and mesoporosity with maximum BET surface area of 716m(2)/g. Inducements of graphitic planes in leather waste derived carbons were observed from X-ray diffraction and HR-TEM analysis. Microstructure, thermal behavior and surface functional groups were identified using FT-Raman, thermo gravimetric analysis and FT-IR techniques. HPCs were evaluated for electrochemical properties by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) by three electrode system. CLC9 sample showed a maximum capacitance of 1960F/g in 1M KCl electrolyte. Results achieved from rectangular curves of CV, GCD symmetric curves and Nyquist plots show that the leather waste carbon is suitable to fabricate supercapacitors as it possess high specific capacitance and electrochemical cycle stability. The present study proposes an effective method for solid waste management in leather industry by the way of converting toxic leather waste to new graphitic porous carbonaceous materials as a potential candidate for energy storage devices.