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2019, 34(3): .

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Preparation and characterization of spinnable mesophase pitches: A review

SHI Jing-li, MA Chang

2019, 34(3): 211-219.

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Mesophase pitch-based carbon fibers have a higher modulus and thermal conductivity than other carbon fibers. A good spinnable mesophase pitch is key to prepare high performance carbon fibers. In this paper, the preparation and characterization of mesophase pitches are reviewed. Spinnable mesophase pitches have been prepared from petroleum pitch or coal tar pitch by heat and catalytic polycondensation. Sometimes, hydrogenation, catalytic polymerization and co-carbonization were used to modify the chemical structure of the pitch before polycondensation. Traditional characterization of mesophase pitch include the softening point, rheology properties, optical anisotropy, average molecule weight and chemical structure. With the rapid progress of characterization techniques, other characterization of the microstructure is possible, such as high resolution MALDI ToF MS which gives the elemental formula of thousands of molecular constituents, which helps improve our understanding of the molecular structure of spinnable mesophase pitches.

Research progress of the application of graphene-based materials in the treatment of water pollutants

MENG Liang, SUN Yang, GONG Han, WANG Ping, QIAO Wei-chuan, GAN Lu, XU Li-jie

2019, 34(3): 220-237.

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Graphene-based nanomaterials have attracted increasing attention in different areas, such as material science, chemical engineering and environmental science. In recent years, it and its derivatives (e.g. graphene oxide, reduced graphene oxide) have been considered promising functional materials in water pollution control because of their many unique properties. Recent intense research on the development of graphene-based composite materials has expanded their application to water treatment. Progress in the use of graphene, graphene oxide and graphene-based composite materials in water pollutant treatment is reviewed, including their use as adsorbents, photocatalysts, and the oxidant and oxidant (e.g. H₂O₂, peroxymonosulfate) activators in electrocatalysis. Water pollutants are heavy metal ions, dyestuffs, some inorganic nutrients and the emerging environmental pollutants. Not only are the mechanisms of the use of graphene and its derivatives in different treatment processes considered, but the effects of important factors on the removal efficiency of pollutants are analyzed, such as environmental factors (e.g. pH, pollutant concentration), the properties of the materials (e.g. particle size, surface charge) and the concentration and morphology of the material. Current problems of using graphene-based composite materials in water treatment are summarized and future research directions are proposed.

Hierarchically-organized C₆₀crystals obtained from a liquid/liquid interfacial precipitation method by using 1,2,3,4-tetrahydronaphthalene as a solvent

ZHANG Lin-wen, ZHOU Sheng-ju, CHEN Meng-jun, YIN Ke-yang, LI Hong-guang

2019, 34(3): 238-246. doi: 10.1016/S1872-5805(19)60013-2

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C₆₀ crystals have potential applications in the optoelectronics, photoconducting devices and templated synthesis fields. However, their preparation is complex. A simple liquid-liquid interfacial precipitation method was used to fabricate hierarchically-organized C₆₀ crystals with various topographic characteristics, using 1,2,3,4-tetrahydronaphthalene as a good solvent, and isopropanol, ethanol or methanol as a poor solvent. Results indicate that the morphology and shape of the as-prepared C₆₀ crystals vary according to the solvent combination and the ratio of good to poor solvents. The SEM images of fractured surfaces and XRD patterns of the crystals reveal that the crystals are formed by the hierarchical organization of C₆₀ molecules at the molecular level to nanocrystals that are assembled into micrometer crystals. The crystals are composed solely of C₆₀ molecules, without polymerization and solvents, which are arranged in a face-centered cubic lattice. The surface roughness is increased by post washing with ethanol. The methodology described here is advantageous over the high-temperature conversion and solvent annealing methods reported previously.

Activated carbons prepared by the KOH activation of a hydrochar from garlic peel and their CO₂ adsorption performance

HUANG Ge-ge, LIU Yi-fei, WU Xing-xing, CAI Jin-jun

2019, 34(3): 247-257. doi: 10.1016/S1872-5805(19)60014-4

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Biomass is regarded as a promising low-cost precursor for the preparation of activated carbons. However, direct carbonization of biomass usually produces a low-surface-area or even non-porous carbons that are useless for CO₂ capture. In this work, garlic peel was first transformed to a hydrochar by hydrothermal carbonization and then chemically activated by KOH to obtain activated carbons with high-surface-areas and large pore volumes. The microstructure and morphology of the activated carbons were characterized by N₂ adsorption, SEM and XRD. Results indicate that their surface area and pore volume are mainly determined by the activation temperature and KOH/hydrochar mass ratio. Activated carbon (AC-28) obtained by KOH activation with a KOH/hydrochar ratio of 2 at 800℃ has a well-developed porosity with a surface area and pore volume of 1262 m²/g and 0.70 cm³/g, respectively, while a reduction of the activation temperature to 600℃ (AC-26) results in a material whose corresponding values are 947 m²/g and 0.51 cm³/g. Although AC-26 exhibits a much lower surface area and pore volume compared with AC-28, it has the larger CO₂ uptake of up to 4.22 mmol/g at 25℃ and 1 bar due to its higher microporosity of up to 98% and abundant narrow micropores, implying that the microporosity is one of the main factors for CO₂ capture besides the traditionally-believed surface area and pore volume. The isosteric heat of CO₂ adsorption indicates that the affinity between the activated carbon and CO₂ molecules increases with the volume of narrow micropores less than 0.8 nm and the number of surface oxygen-containing functional groups.

Co-carbonization of brominated petroleum pitch, coal tar pitch and benzoyl chloride to prepare cokes

DONG Ya-wei, XING Guo-zheng, JIN Li-e, LI Ping, CAO Qing

2019, 34(3): 258-266. doi: 10.1016/S1872-5805(19)60015-6

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After the quinoline insoluble fraction was removed, petroleum pitch (PP) was brominated under ultraviolet light irradiation for 3 to 9 h with a bromine to PP mass ratio of 1:20 to prepare brominated PPs (BPPs). Synthetic pitches (SPs) were produced from these BPPs by mixing them with refined coal tar pitch (RCTP) using a solvent (5 wt% benzoyl chloride)-assisted mixing method, using different mass ratios of BPP/RCTP, and BPPs with different irradiation times. The SPs were carbonized to prepare semicokes. The properties and carbonization behavior of the SPs were investigated by FT-IR spectrometry, ¹H NMR, thermogravimetry and viscometry, and the optical texture of the semicokes was examined by polarized-light microscopy, X-ray diffraction and scanning electron microscopy. Results indicate that converting PP into BPPs increases its reactivity with RCTP, which is beneficial for developing an ordered texture during carbonization. A high-quality coke with a highest yield of 50.1 wt% was prepared from the optimum SP made from BPP brominated for 6 h and a mass ratio of BPP to RCTP of 1:9.

Adsorption of tetrabromobisphenol A in aqueous solutions by porous carbon nanospheres

DUAN Fei-fei, QIN Lei, CHEN Chao-qiu, YANG Yong-zhen, QIN Yong, LIU Xu-guang

2019, 34(3): 267-274.

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Porous carbon nanospheres (PCNs) were prepared by a hydrothermal method using glucose as the precursor. The structure and morphology of the PCNs were characterized by FT-IR, TGA and SEM. The PCNSs can be well dispersed in water and settle within 12 h, which is beneficial for separation from solutions. The adsorption of tetrabromobisphenol A (TBBPA) in aqueous solutions by PCNs was investigated. Results indicate that the maximum adsorption capacity of PCMSs for TBBPA is 10.91 mg/g at 293 K. The adsorption kinetics and isotherm are well described by a pseudo-second-order kinetic model and the Langmuir model, respectively. The adsorption is favorable under neutral conditions. PCNs is a promising adsorbent for water treatment.

Effect of the graphene content on the microstructures and properties of graphene/aluminum composites

WANG Jian, GUO Li-na, LIN Wan-ming, CHEN Jin, LIU Chun-lian, CHEN Shao-da, ZHANG Shuai, ZHEN Tian-tian

2019, 34(3): 275-285. doi: 10.1016/S1872-5805(19)60016-8

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A graphite mold was filled with a mixed powder of aluminum and graphene. It was evacuated to 2×10^-1 Pa, pre-pressed under 10 MPa, heated to 450℃ where it was kept for 5 min, pressed again under 40 MPa, heated to 600℃ where it was kept for another 5 min to prepare graphene/aluminum (G/Al) composites. The effect of the graphene content on the microstructure, and thermal, electrical, mechanical and anticorrosive properties of the composites was investigated. Results indicate that when the graphene content is 0.5 wt.%, it is uniformly dispersed at grain boundaries in the Al matrix. Compared to pure Al the resulting composite has thermal and electrical conductivities that are respectively 7.1% and 4% higher, tensile strength and hardness that are 30.6% and 44% higher, and a corrosion resistance that is 31% higher. When the graphene content exceeds 0.5 wt.%, it agglomerates at grain boundaries in the Al matrix, leading to a decrease of all the above-mentioned properties.

Preparation and oxidation resistance of Si-B co-doped pitch-based carbon fibers

DU Li, DONG Zhi-jun, YUAN Guan-ming, CONG Ye, ZHU Hui, LI Xuan-ke, LUO Yong-ming

2019, 34(3): 286-295.

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Si-B co-doped pitch-based carbon fibers were prepared from mixtures of polyborosilicane (PSNB) and petroleum pitch with a PSNB content of 3 to 10 wt% to improve their oxidation resistance. The composition, microstructure, mechanical properties and oxidation resistance of the fibers were investigated. Results show that with increasing PSNB content in the pitch, the tensile strength and Young's modulus decrease gradually, but the oxidation resistance increases significantly. For fibers prepared by carbonization at 1400℃, the weight loss is 25% after oxidation at 600℃ for 240 min and 60% after oxidation at 650℃ for 140 min. However, these values are 46% and 99% of the respective values for the un-doped carbon fibers. The B₂O₃ generated during oxidation of the Si-B co-doped carbon fibers has a good fluidity, and as a result a continuous glass film is formed on the surface of the fibers, which effectively inhibits carbon oxidation.

Evolution of functional groups during the preparation of cellulose-based carbon fibers characterized by nanoscale infrared spectroscopy

SONG Yun-jia, CHEN Cong-jie, WU Qi-lin

2019, 34(3): 296-301.

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The evolution of functional groups during the preparation of cellulose-based carbon fibers (CFs) was investigated by nanoscale infrared spectroscopy (Nano IR) of the fiber cross-section and surface. The cross-sections of cellulose-based fibers at different stages of low-temperature pyrolysis from room temperature to 600℃ were obtained by an ultra-thin sectioning technique. The infrared spectra and maps of the functional groups at different locations on the cross-section and the surface of a fiber were obtained by the Nano IR. Results showed that C-O and CO groups were distributed evenly on the fiber surface, but -OH groups were unevenly distributed. The -OH group concentration was higher near the surface than in the inner area, but CO groups were distributed evenly on the fiber cross-section. The number of both -OH and CO groups started decreasing at 150℃ and levelled off at 300 and 600℃, respectively. Pyrolysis reactions proceeded from the outer to the inner part of the fiber, indicating that the skin and core were not pyrolyzed simultaneously. I_D/I_G values from Raman spectroscopy also confirmed the structural heterogeneity in the cross-section at the different pyrolysis temperatures examined. This study is useful to effectively optimize the preparation parameters of CFs with improved properties.

A crystalline Si solar cell using a carbon nanotube thin film as the back electrode

ZHANG Ze-lin, ZHAO Ke, CUI Xian, YAO You-wei, WEI Jin-quan

2019, 34(3): 302-306.

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Due to their outstanding charge collecting and transport ability, carbon nanotubes (CNTs) can be used as electrode materials in solar cells. Here, we replaced the aluminum back electrode in a crystalline silicon (c-Si) solar cell with a CNT thin film to form a c-Si/CNT film solar cell. The c-Si/CNT solar cell had a high short-circuit current density of 35.5 mA cm^-2, which is higher than that using aluminum as the back electrode, indicating that CNTs can be used as hole transport materials in silicon-based solar cells. The power conversion efficiency of the c-Si/CNT solar cell was increased from 7.1% to 10.9% by dropping a few drops of a dilute HF solution (5 wt%) at the interface of the c-Si and the CNT film. This is because HF etches away the oxide layer on the c-Si surface, increases the interfacial contact area between the CNT film and the c-Si and decreases the recombination rate of electron/hole pairs.

2019 Vol. 34, No. 3

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