Frontiers of Chemical Science and Engineering

ISSN 2095-0179

ISSN 2095-0187(Online)

CN 11-5981/TQ

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Tailoring electrical conductivity of two dimensional nanomaterials using plasma for edge electronics: A mini review
Aswathy Vasudevan, Vasyl Shvalya, Aleksander Zidanšek, Uroš Cvelbar
Front. Chem. Sci. Eng.    2019, 13 (3): 427-443.
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Since graphene has been discovered, two-dimensional nanomaterials have attracted attention due to their promising tunable electronic properties. The possibility of tailoring electrical conductivity at the atomic level allows creating new prospective 2D structures for energy harvesting and sensing-related applications. In this respect, one of the most successful way to manipulate the physical properties of the aforementioned materials is related to the surface modification techniques employing plasma. Moreover, plasma-gaseous chemical treatment can provide a controlled change in the bandgap, increase sensitivity and significantly improve the structural stability of material to the environment as well. This review deals with recent advances in the modification of 2D carbon nanostructures for novel ‘edge’ electronics using plasma technology and processes.

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Dealumination and desilication for Al-rich HZSM-5 zeolite via steam-alkaline treatment and its application in methanol aromatization
Yuehua Fang, Fan Yang, Xuan He, Xuedong Zhu
Front. Chem. Sci. Eng.    2019, 13 (3): 543-553.
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The hierarchical HZSM-5 was prepared via dealumination and desilication of commercial Al-rich HZSM-5, and characterized by X-ray diffraction, 27Al magic-angle spinning nuclear magnetic resonance, inductively coupled plasma mass spectrometry, scanning electron microscope, transmission electron microscope, N2 adsorption-desorption, NH3 temperature-programmed desorption, performed thermogravimetric and Raman spectrum. The results showed that partial framework of HZSM-5 was removed after steam treatment at 0.15 MPa, 500°C for 3 h. HZSM-5 with high specific surface area and much mesoporosity was obtained by the subsequent alkaline treatment. The regulation of acid quantity was achieved by altering the concentration of alkaline. Dealumination and desilication of Al-rich HZSM-5 zeolites became more effective using a combination of steam and alkaline treatments than using alkaline treatment alone. Methanol aromatization reaction was employed to evaluate the catalytic performance of treated HZSM-5 at 0.15 MPa, 450°C and MHSV of 1.5 h−1. The results indicated that after steam treatment, HZSM-5 further treated with 0.2 mol/L NaOH exhibits the best catalytic performance: the selectivity of aromatics reached 42.1% and the lifetime of catalyst attained 212 h, which are much better than untreated HZSM-5.

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Molecular tailoring to improve polypyrrole hydrogels’ stiffness and electrochemical energy storage capacity
Evelyn Chalmers, Yi Li, Xuqing Liu
Front. Chem. Sci. Eng.    2019, 13 (4): 684-694.
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This research looks at ways of tailoring and improving the stiffness of polypyrrole hydrogels for use as flexible supercapacitor electrodes. Molecules providing additional cross-linking between polypyrrole chains are added post-polymerisation but before gelation, and are found to increase gel stiffness by up to 600%, with the degree of change dependent on reactant type and proportion. It was also found that addition of phytic acid led to an increase in pseudocapacitive behaviour of the hydrogel, and thus a maximum specific capacitance of 217.07 F·g1 could be achieved. This is an increase of 140% compared to pristine polypyrrole hydrogels produced by this method.

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Review of plasma-assisted reactions and potential applications for modification of metal–organic frameworks
Tingting Zhao, Niamat Ullah, Yajun Hui, Zhenhua Li
Front. Chem. Sci. Eng.    2019, 13 (3): 444-457.
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Plasma catalysis is drawing increasing attention worldwide. Plasma is a partially ionized gas comprising electrons, ions, molecules, radicals, and photons. Integration of catalysis and plasma can enhance catalytic activity and stability. Some thermodynamically unfavorable reactions can easily occur with plasma assistance. Compared to traditional thermal catalysis, plasma reactors can save energy because they can be operated at much lower temperatures or even room temperature. Additionally, the low bulk temperature of cold plasma makes it a good alternative for treatment of temperature-sensitive materials. In this review, we summarize the plasma-assisted reactions involved in dry reforming of methane, CO2 methanation, the methane coupling reaction, and volatile organic compound abatement. Applications of plasma for modification of metal–organic frameworks are discussed.

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Two-dimensional SnS2 nanosheets on Prussian blue template for high performance sodium ion batteries
Glenn J. Sim, Kakui Ma, Zhixiang Huang, Shaozhuan Huang, Ye Wang, Huiying Yang
Front. Chem. Sci. Eng.    2019, 13 (3): 493-500.
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Three-dimensional Prussian blue (PB) nanostructures was obtained via a one-step hydrothermal method. Subsequently, two-dimensional tin disulfide (SnS2) nanosheets were grown onto PB through a facile hydrothermal synthesis. The as prepared SnS2/PB is further employed as the anode of sodium ion batteries (SIBs). SnS2/PB nanoarchitecture delivers a specific capacity of 725.7 mAh∙g−1 at 50 mA∙g−1. When put through more than 200 cycles, it achieved a stable cycling capacity of 400 mAh∙g−1 at 200 mA∙g−1. The stable Na+ storage properties of SnS2/PB was attributed to the synergistic effect among the conductive PB carbon, used as the template in this work. These results obtained potentially paves the way for the development of excellent electrochemical performance with stable performance of SIBs.

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Mass transport mechanisms within pervaporation membranes
Yimeng Song, Fusheng Pan, Ying Li, Kaidong Quan, Zhongyi Jiang
Front. Chem. Sci. Eng.    2019, 13 (3): 458-474.
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Pervaporation is an energy-efficient membrane technology for separating liquid molecules of similar physical properties, which may compete or combine with distillation separation technology in a number of applications. With the rapid development of new membrane materials, the pervaporation performance was significantly improved. Fundamental understanding of the mass transport mechanisms is crucial for the rational design of membrane materials and efficient intensification of pervaporation process. Based on the interactions between permeate molecules and membranes, this review focuses on two categories of mass transport mechanisms within pervaporation membranes: physical mechanism (solution-diffusion mechanism, molecular sieving mechanism) and chemical mechanism (facilitated transport mechanism). Furthermore, the optimal integration and evolution of different mass transport mechanisms are briefly introduced. Material selection and relevant applications are highlighted under the guidance of mass transport mechanisms. Finally, the current challenges and future perspectives are tentatively identified.

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Mechanistic understanding of Cu-based bimetallic catalysts
You Han, Yulian Wang, Tengzhou Ma, Wei Li, Jinli Zhang, Minhua Zhang
Front. Chem. Sci. Eng.    2020, 14 (5): 689-748.
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Copper has received extensive attention in the field of catalysis due to its rich natural reserves, low cost, and superior catalytic performance. Herein, we reviewed two modification mechanisms of co-catalyst on the coordination environment change of Cu-based catalysts: (1) change the electronic orbitals and geometric structure of Cu without any catalytic functions; (2) act as an additional active site with a certain catalytic function, as well as their catalytic mechanism in major reactions, including the hydrogenation to alcohols, dehydrogenation of alcohols, water gas shift reaction, reduction of nitrogenous compounds, electrocatalysis and others. The influencing mechanisms of different types of auxiliary metals on the structure-activity relationship of Cu-based catalysts in these reactions were especially summarized and discussed. The mechanistic understanding can provide significant guidance for the design and controllable synthesis of novel Cu-based catalysts used in many industrial reactions.

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Low-k integration: Gas screening for cryogenic etching and plasma damage mitigation
Romain Chanson, Remi Dussart, Thomas Tillocher, P. Lefaucheux, Christian Dussarrat, Jean François de Marneffe
Front. Chem. Sci. Eng.    2019, 13 (3): 511-516.
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The integration of porous organo-silicate low-k materials has met a lot of technical challenges. One of the main issues is plasma-induced damage, occurring for all plasma steps involved during interconnects processing. In the present paper, we focus on porous SiOCH low-k damage mitigation using cryogenic temperature so as to enable micro-capillary condensation. The aim is to protect the porous low-k from plasma-induced damage and keep the k-value of the material unchanged, in order to limit the RC delay of interconnexion levels while shrinking the microchip dimension. The cryogenic temperature is used to condense a gas inside the porous low-k material. Then, the etching process is performed at the temperature of condensation in order to keep the condensate trapped inside the material during the etching. In the first part of this work, the condensation properties of several gases are screened, leading to a down selection of five gases. Then, their stability into the porous structure is evaluated at different temperature. Four of them are used for plasma damage mitigation comparison. Damage mitigation is effective and shows negligible damage for one of the gases at –50°C.

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A non-lithographic plasma nanoassembly technology for polymeric nanodot and silicon nanopillar fabrication
Athanasios Smyrnakis, Angelos Zeniou, Kamil Awsiuk, Vassilios Constantoudis, Evangelos Gogolides
Front. Chem. Sci. Eng.    2019, 13 (3): 475-484.
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In this work, we present plasma etching alone as a directed assembly method to both create the nanodot pattern on an etched polymeric (PMMA) film and transfer it to a silicon substrate for the fabrication of silicon nanopillars or cone-like nanostructuring. By using a shield to control sputtering from inside the plasma reactor, the size and shape of the resulting nanodots can be better controlled by varying plasma parameters as the bias power. The effect of the shield on inhibitor deposition on the etched surfaces was investigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The fabrication of quasi-ordered PMMA nanodots of a diameter of 25 nm and period of 54 nm is demonstrated. Pattern transfer to the silicon substrate using the same plasma reactor was performed in two ways: (a) a mixed fluorine-fluorocarbon-oxygen nanoscale etch plasma process was employed to fabricate silicon nanopillars with a diameter of 25 nm and an aspect ratio of 5.6, which show the same periodicity as the nanodot pattern, and (b) high etch rate cryogenic plasma process was used for pattern transfer. The result is the nanostructuring of Si by high aspect ratio nanotip or nanocone-like features that show excellent antireflective properties.

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Cryptosporidium parvum oocyst directed assembly of gold nanoparticles and graphene oxide
Sona Jain, Zhicheng Huang, Brent R. Dixon, Syed Sattar, Juewen Liu
Front. Chem. Sci. Eng.    2019, 13 (3): 608-615.
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Understanding the interactions between inorganic nanomaterials and biological species is an important topic for surface and environmental chemistry. In this work, we systematically studied the oocysts of Cryptosporidium parvum as a model protozoan parasite and its interaction with gold nanoparticles (AuNPs) and graphene oxide (GO). The as-prepared citrate-capped AuNPs adsorb strongly on the oocysts leading to a vivid color change. The adsorption of the AuNPs was confirmed by transmission electron microscopy. Heat treatment fully inhibited the color change, indicating a large change of surface chemistry of the oocysts that can be probed by the AuNPs. Adding proteases such as trypsin and proteinase K partially inhibited the color change. DNA-capped AuNPs, on the other hand, could not be adsorbed by the oocysts. GO was found to wrap around the oocysts forming a conformal shell reflecting the shape of the oocysts. Both citrate-capped AuNPs and GO compromised the membrane integrity of the oocysts as indicated by the propidium iodide staining experiment, and they may be potentially used for inactivating the oocysts. This is the first example of using nanomaterials to probe the surface of the oocysts, and it suggests the possibility of using such organisms to template the assembly of nanomaterials.

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Cube-octameric silsesquioxane (POSS)-capped magnetic iron oxide nanoparticles for the efficient removal of methylene blue
Ali Akbari, Nasser Arsalani, Bagher Eftekhari-Sis, Mojtaba Amini, Gholamreza Gohari, Esmaiel Jabbari
Front. Chem. Sci. Eng.    2019, 13 (3): 563-573.
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Octavinyl polyhedral oligomeric silsesquioxane (POSS) was polymerized on the surface of Fe3O4 nanoparticles (NPs) and then the NPs were functionalized with carboxylic acid groups using thiol-ene click reactions with thioglycolic acid. The as-prepared Fe3O4@POSS-COOH magnetic hybrid NPs had mesoporous structures with an average particle diameter of 15 nm and a relatively high specific surface area of 447 m2∙g−1. Experimental results showed that 4 mg of Fe3O4@POSS-COOH NPs efficiently adsorbed and removed methylene blue from water at 5 min. This is due to the presence of both carboxylic acid and pendant vinyl groups on the Fe3O4@POSS-COOH NPs. These NPs could be easily withdrawn from water within a few seconds under moderate magnetic field and showed high stability in acid and alkaline aqueous mediums.

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Magnetic-porous microspheres with synergistic catalytic activity of small-sized gold nanoparticles and titania matrix
Kadriye Özlem Hamaloğlu, Ebru Sağ, Çiğdem Kip, Erhan Şenlik, Berna Saraçoğlu Kaya, Ali Tuncel
Front. Chem. Sci. Eng.    2019, 13 (3): 574-585.
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Fe3O4 nanoparticles immobilized on porous titania in micron-size range were decorated with small-sized gold nanoparticles and used as a plasmonic catalyst for the reduction of 4-nitrophenol. Monodisperse-porous magnetic titania microspheres were synthesized with bimodal pore-size distribution by the sol-gel templating method. Small-sized gold nanoparticles obtained by the Martin method were attached onto the aminated form of the magnetic titania microspheres. A significant enhancement in the catalytic activity was observed using the gold nanoparticle-decorated magnetic titania microspheres compared to gold nanoparticle-decorated magnetic silica microspheres because of the synergistic effect between small-sized gold nanoparticles and titania. The synergistic effect for gold nanoparticle-attached magnetic titania microspheres could be explained by surface plasmon resonance-induced transfer of hot electrons from gold nanoparticles to the conduction band of titania. Using the proposed catalyst, 4-nitrophenol could be converted to 4-aminophenol in an aqueous solution within 0.5 min. The 4-nitrophenol reduction rates were 2.5–79.3 times higher than those obtained with similar plasmonic catalysts. The selection of micron-size, magnetic, and porous titania microspheres as a support material for the immobilization of small-sized gold nanoparticles provided a recoverable plasmonic catalyst with high reduction ability.

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Effect of TiO2 loading on the morphology and CO2/CH4 separation performance of PEBAX-based membranes
Navid Azizi, Mojgan Isanejad, Toraj Mohammadi, Reza M. Behbahani
Front. Chem. Sci. Eng.    2019, 13 (3): 517-530.
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Membranes have attracted much attention as economical methods for industrial chemical processes. The effects of the titanium dioxide nanoparticle load on the morphology and CO2/CH4 separation performance of poly (ether-block-amide) (PEBAX-1657) mixed matrix membranes (MMMs) were investigated from pressures of 3–12 bar and temperatures of 30°C–60°C. The PEBAX membranes were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, atomic force microscopy and tensile strength analysis. The incorporation of TiO2 nanoparticles into the polymeric MMMs improved the CO2/CH4 gas separation performance (both the permeability and selectivity) of the membranes. The CO2 permeability and ideal CO2/CH4 selectivity values of the nanocomposite membrane loaded with 8 wt-% TiO2 were 172.32 Barrer and 24.79, respectively whereas those of the neat membrane were 129.87 Barrer and 21.39, respectively.

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Linking renewables and fossil fuels with carbon capture via energy storage for a sustainable energy future
Dawid P. Hanak, Vasilije Manovic
Front. Chem. Sci. Eng.    2020, 14 (3): 453-459.
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Renewable energy sources and low-carbon power generation systems with carbon capture and storage (CCS) are expected to be key contributors towards the decarbonisation of the energy sector and to ensure sustainable energy supply in the future. However, the variable nature of wind and solar power generation systems may affect the operation of the electricity system grid. Deployment of energy storage is expected to increase grid stability and renewable energy utilisation. The power sector of the future, therefore, needs to seek a synergy between renewable energy sources and low-carbon fossil fuel power generation. This can be achieved via wide deployment of CCS linked with energy storage. Interestingly, recent progress in both the CCS and energy storage fields reveals that technologies such as calcium looping are technically viable and promising options in both cases. Novel integrated systems can be achieved by integrating these applications into CCS with inherent energy storage capacity, as well as linking other CCS technologies with renewable energy sources via energy storage technologies, which will maximise the profit from electricity production, mitigate efficiency and economic penalties related to CCS, and improve renewable energy utilisation.

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Photothermal materials for efficient solar powered steam generation
Fenghua Liu, Yijian Lai, Binyuan Zhao, Robert Bradley, Weiping Wu
Front. Chem. Sci. Eng.    2019, 13 (4): 636-653.
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Solar powered steam generation is an emerging area in the field of energy harvest and sustainable technologies. The nano-structured photothermal materials are able to harvest energy from the full solar spectrum and convert it to heat with high efficiency. Moreover, the materials and structures for heat management as well as the mass transportation are also brought to the forefront. Several groups have reported their materials and structures as solutions for high performance devices, a few creatively coupled other physical fields with solar energy to achieve even better results. This paper provides a systematic review on the recent developments in photothermal nanomaterial discovery, material selection, structural design and mass/heat management, as well as their applications in seawater desalination and fresh water production from waste water with free solar energy. It also discusses current technical challenges and likely future developments. This article will help to stimulate novel ideas and new designs for the photothermal materials, towards efficient, low cost practical solar-driven clean water production.

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Plasma-electrochemical synthesis of europium doped cerium oxide nanoparticles
Liangliang Lin, Xintong Ma, Sirui Li, Marly Wouters, Volker Hessel
Front. Chem. Sci. Eng.    2019, 13 (3): 501-510.
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In the present study, a plasma-electrochemical method was demonstrated for the synthesis of europium doped ceria nanoparticles. Ce(NO3)3·6H2O and Eu(NO3)3·5H2O were used as the starting materials and being dissolved in the distilled water as the electrolyte solution. The plasma-liquid interaction process was in-situ investigated by an optical emission spectroscopy, and the obtained products were characterized by complementary analytical methods. Results showed that crystalline cubic CeO2:Eu3+ nanoparticles were successfully obtained, with a particle size in the range from 30 to 60 nm. The crystal structure didn’t change during the calcination at a temperature from 400°C to 1000°C, with the average crystallite size being estimated to be 52 nm at 1000°C. Eu3+ ions were shown to be effectively and uniformly doped into the CeO2 lattices. As a result, the obtained nanophosphors emit apparent red color under the UV irradiation, which can be easily observed by naked eye. The photoluminescence spectrum further proves the downshift behavior of the obtained products, where characteristic 5D07F1,2,3 transitions of Eu3+ ions had been detected. Due to the simple, flexible and environmental friendly process, this plasma-electrochemical method should have great potential for the synthesis of a series of nanophosphors, especially for bio-application purpose.

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Dual enzyme activated fluorescein based fluorescent probe
Maria L. Odyniec, Jordan E. Gardiner, Adam C. Sedgwick, Xiao-Peng He, Steven D. Bull, Tony D. James
Front. Chem. Sci. Eng.    2020, 14 (1): 117-121.
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A simple dual analyte fluorescein-based probe (PF3-Glc) was synthesised containing β-glucosidase (β-glc) and hydrogen peroxide (H2O2) trigger units. The presence of β-glc, resulted in fragmentation of the parent molecule releasing glucose and the slightly fluorescent mono-boronate fluorescein (PF3). Subsequently, in the presence of glucose oxidase (GOx), the released glucose was catalytically converted to D-glucono-δ-lactone, which produced H2O2 as a by-product. The GOx-produced H2O2, resulted in classic H2O2-mediated boronate oxidation and the release of the highly emissive fluorophore, fluorescein. This unique cascade reaction lead to an 80-fold increase in fluorescence intensity.

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A boronic acid-based fluorescent hydrogel for monosaccharide detection
Suying Xu, Adam C. Sedgwick, Souad A. Elfeky, Wenbo Chen, Ashley S. Jones, George T. Williams, A. Toby A. Jenkins, Steven D. Bull, John S. Fossey, Tony D. James
Front. Chem. Sci. Eng.    2020, 14 (1): 112-116.
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A boronic acid-based anthracene fluorescent probe was functionalised with an acrylamide unit to incorporate into a hydrogel system for monosaccharide detection. In solution, the fluorescent probe displayed a strong fluorescence turn-on response upon exposure to fructose, and an expected trend in apparent binding constants, as judged by a fluorescence response where D-fructose>D-galactose>D-mannose>D-glucose. The hydrogel incorporating the boronic acid monomer demonstrated the ability to detect monosaccharides by fluorescence with the same overall trend as the monomer in solution with the addition of D-fructose resulting in a 10-fold enhancement (≤0.25 mol/L).

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Special issue on “Fluorescent probes”
Adam C. Sedgwick, Tony D. James
Front. Chem. Sci. Eng.    2020, 14 (1): 1-3.
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Detection and monitoring prostate specific antigen using nanotechnology approaches to biosensing
Grant Perry, Fernando Cortezon-Tamarit, Sofia I. Pascu
Front. Chem. Sci. Eng.    2020, 14 (1): 4-18.
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Prostate cancer has a high incidence in men and remains the second cause of mortality due to cancer worldwide. As the development of the disease is greatly correlated to age, the identification of novel detection methods reliable, efficient, and cost effective is a matter of significant importance in the ageing population of western societies. The detection of the prostate specific antigen (PSA) in blood samples has been the preferred method for the detection and monitoring of prostate cancer over the past decades. Despite the indications against its use in massive population screening, PSA still remains the best studied biomarker for prostate cancer and the detection of its different forms and incorporation in multiplexed designs with other biomarkers still remains a highly valuable indicator in the theranostics of prostate cancer. The latest developments in the use of nanomaterials towards the construction of PSA biosensors are reviewed hereby. The incorporation of gold nanoparticles, silica nanoparticles and graphene nanostructures to biosensing devices has represented a big leap forward in terms of sensitivity, stability and miniaturization. Both electrochemical and optical detection methods for the detection of PSA will be reviewed herein.

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Current understanding and applications of the cold sintering process
Tong Yu, Jiang Cheng, Lu Li, Benshuang Sun, Xujin Bao, Hongtao Zhang
Front. Chem. Sci. Eng.    2019, 13 (4): 654-664.
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In traditional ceramic processing techniques, high sintering temperature is necessary to achieve fully dense microstructures. But it can cause various problems including warpage, overfiring, element evaporation, and polymorphic transformation. To overcome these drawbacks, a novel processing technique called “cold sintering process (CSP)” has been explored by Randall et al. CSP enables densification of ceramics at ultra-low temperature (≤300°C) with the assistance of transient aqueous solution and applied pressure. In CSP, the processing conditions including aqueous solution, pressure, temperature, and sintering duration play critical roles in the densification and properties of ceramics, which will be reviewed. The review will also include the applications of CSP in solid-state rechargeable batteries. Finally, the perspectives about CSP is proposed.

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Improvement in growth yield of single-walled carbon nanotubes with narrow chirality distribution by pulse plasma CVD
Bin Xu, Toshiro Kaneko, Toshiaki Kato
Front. Chem. Sci. Eng.    2019, 13 (3): 485-492.
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A pulse plasma chemical vapor deposition (CVD) technique was developed for improving the growth yield of single-walled carbon nanotubes (SWNTs) with a narrow chirality distribution. The growth yield of the SWNTs could be improved by repetitive short duration pulse plasma CVD, while maintaining the initial narrow chirality distribution. Detailed growth dynamics is discussed based on a systematic investigation by changing the pulse parameters. The growth of SWNTs with a narrow chirality distribution could be controlled by the difference in the nucleation time required using catalysts comprising relatively small or large particles as the key factor. The nucleation can be controlled by adjusting the pulse on/off time ratio and the total processing time.

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Impacts of CO2 and H2S on the risk of hydrate formation during pipeline transport of natural gas
Solomon A. Aromada, Bjørn Kvamme
Front. Chem. Sci. Eng.    2019, 13 (3): 616-627.
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Evaluation of maximum content of water in natural gas before water condenses out at a given temperature and pressure is the initial step in hydrate risk analysis during pipeline transport of natural gas. The impacts of CO2 and H2S in natural gas on the maximum mole-fractions of water that can be tolerated during pipeline transport without the risk of hydrate nucleation has been studied using our novel thermodynamic scheme. Troll gas from the North Sea is used as a reference case, it contains very negligible amount of CO2 and no H2S. Varying mole-fractions of CO2 and H2S were introduced into the Troll gas, and the effects these inorganic impurities on the water tolerance of the system were evaluated. It is observed that CO2 does not cause any distinguishable impact on water tolerance of the system, but H2S does. Water tolerance decreases with increase in concentration of H2S. The impact of ethane on the system was also investigated. The maximum mole-fraction of water permitted in the gas to ensure prevention of hydrate formation also decreases with increase in the concentration of C2H6 like H2S. H2S has the most impact, it tolerates the least amount of water among the components studied.

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Preface to the CSCST-25 Special IssueŽ1)
Xiaolei Fan, Jiawei Wang
Front. Chem. Sci. Eng.    2019, 13 (4): 629-631.
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Synthesis and properties of water-soluble 1,9-dialkyl-substituted BF2 azadipyrromethene fluorophores
Dan Wu, Gonzalo Durán-Sampedro, Donal F. O’Shea
Front. Chem. Sci. Eng.    2020, 14 (1): 97-104.
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Bis-alkylsulfonic acid and polyethylene glycol (PEG)-substituted BF2 azadipyrromethenes have been synthesized by an adaptable and versatile route. Only four synthetic stages were required to produce the penultimate fluorophore compounds, containing either two alcohol or two terminal alkyne substituents. The final synthetic step introduced either sulfonic acid or polyethylene glycol groups to impart aqueous solubility. Sulfonic acid groups were introduced by reaction of the bis-alcohol-substituted fluorophore with sulfur trioxide, and a double Cu(I)-catalyzed cycloaddition reaction between the bis-alkyne fluorophore and methoxypolyethylene glycol azide yielded a neutral bis-pegylated derivative. Both fluorophores exhibited excellent near-infrared (NIR) photophysical properties in methanol and aqueous solutions. Live cell microscopy imaging revealed efficient uptake and intracellular labelling of cells for both fluorophores. Their simple synthesis, with potential for last-step structural modifications, makes the present NIR-active azadipyrromethene derivatives potentially useful as NIR fluorescence imaging probes for live cells.

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Metal-organic framework UiO-66 membranes
Xinlei Liu
Front. Chem. Sci. Eng.    2020, 14 (2): 216-232.
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Metal-organic frameworks (MOFs) have emerged as a class of promising membrane materials. UiO-66 is a prototypical and stable MOF material with a number of analogues. In this article, we review five approaches for fabricating UiO-66 polycrystalline membranes including in situ synthesis, secondary synthesis, biphase synthesis, gas-phase deposition and electrochemical deposition, as well as their applications in gas separation, pervaporation, nanofiltration and ion separation. On this basis, we propose possible methods for scalable synthesis of UiO-66 membranes and their potential separation applications in the future.

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Deep eutectic ionic liquids based on DABCO-derived quaternary ammonium salts: A promising reaction medium in gaining access to terpyridines
Muhammad Faisal, Azeem Haider, Quret ul Aein, Aamer Saeed, Fayaz Ali Larik
Front. Chem. Sci. Eng.    2019, 13 (3): 586-598.
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Owing to the directional H-bonding, coordination and p-stacking abilities, terpyridines have been widely used as supramolecular tectons in molecular architectures, skeletons in molecular devices and metallopolymers, and are gaining importance in medicinal chemistry. In this paper, we have synthesized, characterized and applied deep eutectic ionic liquids (DEILs) based on 1,4-diazabicyclo[2.2.2]octane; triethylenediamine (DABCO)-derived quaternary ammonium salts for the preparation of terpyridines. These DEILs were synthesized through N-alkylation of DABCO with haloalkanes (1-bromopentane or 1-bromoheptane) followed by mixing and heating with methanol or polyethylene glycol as a hydrogen bond donor. The synthesized DEILs were structurally characterized by IR and NMR. The formation of deep eutectic solvent was confirmed by freezing point depression, it composition was investigated through phase diagram, and its thermal stability was determined through differential scanning calorimetry, derivative thermogravimetry and thermal gravimetric analysis studies. Further, these DEILs were investigated for their effectiveness towards synthesis of 2,2':6',2"-terpyridine, 3,2':6',3"-terpyridineand 4,2':6',4"-terpyridine derivatives through Kröhnke reaction. The results show that these three types of terpyridines can be obtained in reasonable yields (80%-97%) by the one-pot reaction of 2-, 3- or 4-acetylpyridine with a variety of aromatic aldehydes in the presence of DEIL as a reaction medium, sodium hydroxide as a base and ammonium acetate as a cyclizing agent. This methodology is highly efficient and cost-effective for synthesis of symmetrical as well as unsymmetrical terpyridines. Importantly, these DEILs can be reused several times without an obvious loss of activity and are non-toxic, low-volatile, biodegradable and highly thermally stable. Therefore, these DEILs as a non-conventional reaction medium for the synthesis of terpyridines provides appealing opportunities to be investigated in the domain of green synthesis.

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Modeling of oil near-infrared spectroscopy based on similarity and transfer learning algorithm
Yifei Wang, Kai Wang, Zhao Zhou, Wenli Du
Front. Chem. Sci. Eng.    2019, 13 (3): 599-607.
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Near-infrared spectroscopy mainly reflects the frequency-doubled and total-frequency absorption information of hydrogen-containing groups (O‒H, C‒H, N‒H, S‒H) in organic molecules for near-infrared lights with different wavelengths, so it is applicable to testing of most raw materials and products in the field of petrochemicals. However, the modeling process needs to collect a large number of laboratory analysis data. There are many oil sources in China, and oil properties change frequently. Modeling of each raw material is not only unfeasible but also will affect its engineering application efficiency. In order to achieve rapid modeling of near-infrared spectroscopy and based on historical data of different crude oils under different detection conditions, this paper discusses about the feasibility of the application of transfer learning algorithm and makes it possible that transfer learning can assist in rapid modeling using certain historical data under similar distributions under a small quantity of new data. In consideration of the requirement of transfer learning for certain similarity of different datasets, a transfer learning method based on local similarity feature selection is proposed. The simulation verification of spectral data of 13 crude oils measured by three different probe detection methods is performed. The effectiveness and application scope of the transfer modeling method under different similarity conditions are analyzed.

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Diversity-oriented synthesis of blue emissive nitrogen heterocycles and their conjugation with carbon nano-onions
Viviana Maffeis, Lisa Moni, Daniele Di Stefano, Silvia Giordani, Renata Riva
Front. Chem. Sci. Eng.    2020, 14 (1): 76-89.
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The search for new fluorescent molecules for possible applications as functional p-electron systems and their conjugation with different nanomaterials is nowadays of paramount importance to broaden the availability of materials with different properties. Herein we present a diversity-oriented approach to heterocyclic luminophores based on a multicomponent Ugi reaction followed by a Pd-mediated cascade sequence. The new molecules are coupled to carbon nano-onions, and hybrid systems represent the first example of blue emitters conjugated with these carbon nanoparticles.

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GO-modified flexible polymer nanocomposites fabricated via 3D stereolithography
Chi Him Alpha Tsang, Adilet Zhakeyev, Dennis Y.C. Leung, Jin Xuan
Front. Chem. Sci. Eng.    2019, 13 (4): 736-743.
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Graphene oxide (GO) induced enhancement of elastomer properties showed a great deal of potential in recent years, but it is still limited by the barrier of the complicated synthesis processes. Stereolithography (SLA), used in fabrication of thermosets and very recently in “flexible” polymers with elastomeric properties, presents itself as simple and user-friendly method for integration of GO into elastomers. In this work, it was first time demonstrated that GO loadings can be incorporated into commercial flexible photopolymer resins to successfully fabricate GO/elastomer nanocomposites via readily accessible, consumer-oriented SLA printer. The material properties of the resulting polymer was characterized and tested. The mechanical strength, stiffness, and the elongation of the resulting polymer decreased with the addition of GO. The thermal properties were also adversely affected upon the increase in the GO content based on differential scanning calorimetry and thermogravimetric analysis results. It was proposed that the GO agglomerates within the 3D printed composites, can result in significant change in both mechanical and thermal properties of the resulting nanocomposites. This study demonstrated the possibility for the development of the GO/elastomer nanocomposites after the optimization of the GO/“flexible” photoreactive resin formulation for SLA with suitable annealing process of the composite in future.

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