Dec 2019, Volume 13 Issue 4

Cover illustration

  • (Evelyn Chalmers, Yi Li, Xuqing Liu, pp. 684-694)

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    Xiaolei Fan, Jiawei Wang
    Xiaowen Zhu, Di Xu, Jing-Kang Wang
    Fenghua Liu, Yijian Lai, Binyuan Zhao, Robert Bradley, Weiping Wu

    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.

    Tong Yu, Jiang Cheng, Lu Li, Benshuang Sun, Xujin Bao, Hongtao Zhang

    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.

    Jianwei Lu, Lan Lan, Xiaoteng Terence Liu, Na Wang, Xiaolei Fan

    A strategy of intensifying the visible light harvesting ability of anatase TiO2 hollow spheres (HSs) was developed, in which both sides of TiO2 HSs were utilised for stabilising Au nanoparticles (NPs) through the sacrificial templating method and convex surface-induced confinement. The composite structure of single Au NP yolk-TiO2 shell-Au NPs, denoted as Au@Au(TiO2, was rendered and confirmed by the transmission electron microscopy analysis. Au@Au(TiO2 showed enhanced photocatalytic activity in the degradation of methylene blue and phenol in aqueous phase under visible light surpassing that of other reference materials such as Au(TiO2 by 77% and Au@P25 by 52%, respectively, in phenol degradation.

    Sidra Rama, Yan Zhang, Fideline Tchuenbou-Magaia, Yulong Ding, Yongliang Li

    Carbon capture is widely recognised as an essential strategy to meet global goals for climate protection. Although various CO2 capture technologies including absorption, adsorption and membrane exist, they are not yet mature for post-combustion power plants mainly due to high energy penalty. Hence researchers are concentrating on developing non-aqueous solvents like ionic liquids, CO2-binding organic liquids, nanoparticle hybrid materials and microencapsulated sorbents to minimize the energy consumption for carbon capture. This research aims to develop a novel and efficient approach by encapsulating sorbents to capture CO2 in a cold environment. The conventional emulsion technique was selected for the microcapsule formulation by using 2-amino-2-methyl-1-propanol (AMP) as the core sorbent and silicon dioxide as the shell. This paper reports the findings on the formulated microcapsules including key formulation parameters, microstructure, size distribution and thermal cycling stability. Furthermore, the effects of microcapsule quality and absorption temperature on the CO2 loading capacity of the microcapsules were investigated using a self-developed pressure decay method. The preliminary results have shown that the AMP microcapsules are promising to replace conventional sorbents.

    Evelyn Chalmers, Yi Li, Xuqing Liu

    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.

    Huixin Zhang, Jinying Liang, Bangwang Xia, Yang Li, Shangfeng Du

    The modification of Pt/C catalyst by using ionic liquids to improve their catalyst activities has been reported by many researchers, but their practical behavior in operating fuel cells is still unknown. In this work, we study the ionic liquid modified Pt/C nanoparticle catalysts within cathodes for proton exchange membrane fuel cells. The influence of the ionic liquid amount, adsorption times and dispersing solvents are investigated. The experiment results show the best performance enhancement is achieved through two-time surface modification with 2 wt-% ionic liquid solution. The mechanisms are explored with the attribution to the high oxygen solubility in the ionic liquid enabling an improved oxygen diffusion in micropores and to good hydrophobicity facilitating water expelling from the active sites in fuel cell operation.

    Sainab Omar, Suzanne Alsamaq, Yang Yang, Jiawei Wang

    The work studied a non-catalytic upgrading of fast pyrolysis bio-oil by blending under supercritical conditions using methanol, ethanol and isopropanol as solvent and hydrogen donor. Characterisation of the bio-oil and the upgraded bio-oils was carried out including moisture content, elemental content, pH, heating value, gas chromatography-mass spectrometry (GCMS), Fourier transform infrared radiation, 13C nuclear magnetic resonance spectroscopy, and thermogravimetric analysis to evaluate the effects of blending and supercritical reactions. The GCMS analysis indicated that the supercritical methanol reaction removed the acids in the bio-oil consequently the pH increased from 2.39 in the crude bio-oil to 4.04 after the supercritical methanol reaction. The ester contents increased by 87.49% after the supercritical methanol reaction indicating ester formation could be the major deacidification mechanism for reducing the acidity of the bio-oil and improving its pH value. Simply blending crude bio-oil with isopropanol was effective in increasing the C and H content, reducing the O content and increasing the heating value to 27.55 from 17.51 MJ·kg1 in the crude bio-oil. After the supercritical isopropanol reaction, the heating value of the liquid product slightly further increased to 28.85 MJ·kg1.

    Songshan Jiang, Helen Daly, Huan Xiang, Ying Yan, Huiping Zhang, Christopher Hardacre, Xiaolei Fan

    Microwave (MW) assisted catalyst-free hydrolysis of fibrous cellulose (FC, cellulolysis) at 200°C promoted a cellulose conversion of ca. 37.2% and quantitative production of valuable C5/C6 sugars (e.g., glucose) and the according platform biochemicals (e.g., 5-hydroxymethylfurfural), corresponding to an overall selectivity of 96.5%. Conversely, conventional hydrothermal cellulolysis under similar conditions was not effective, even after 24 h, carbonising the FC. Based on the systematic study of MW-assisted cellulolysis, the specific interaction between water molecules and macroscopic FC under the MW irradiation was proposed, accounting for the interpretation of the experimental observation. The kinetic energy of water molecules under the MW irradiation facilitated the C–C (in the non-hindered surface –CH2OH groups) and C–O–C bond breaking (inside the cellulose cavities) in FC, producing primary cellulolysis products of xylose, glucose and cellobiose.

    Bilyaminu Suleiman, Qinghua Yu, Yulong Ding, Yongliang Li

    A form stable NaCl-Al2O3 (50-50 wt-%) composite material for high temperature thermal energy storage was fabricated by cold sintering process, a process recently applied to the densification of ceramics at low temperature ˂ 300°C under uniaxial pressure in the presence of small amount of transient liquid. The fabricated composite achieved as high as 98.65% of the theoretical density. The NaCl-Al2O3 composite also retained the chloride salt without leakage after 30 heating-cooling cycles between 750°C–850°C together with a holding period of 24 h at 850°C. X-ray diffraction measurements indicated congruent solubility of the alumina in chloride salt, excellent compatibility of NaCl with Al2O3, and chemical stability at high temperature. Structural analysis by scanning electron microscope also showed limited grain growth, high density, uniform NaCl distribution and clear faceted composite structure without inter-diffusion. The latent heat storage density of 252.5 J/g was obtained from simultaneous thermal analysis. Fracture strength test showed high sintered strength around 5 GPa after 50 min. The composite was found to have fair mass losses due to volatilization. Overall, cold sintering process has the potential to be an efficient, safe and cost-effective strategy for the fabrication of high temperature thermal energy storage materials.

    Chi Him Alpha Tsang, Adilet Zhakeyev, Dennis Y.C. Leung, Jin Xuan

    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.

    Hui Shang, Pengfei Ye, Yude Yue, Tianye Wang, Wenhui Zhang, Sainab Omar, Jiawei Wang

    Hydrodesulfurization (HDS) of thiophene, as a gasoline model oil, over an industrial Ni-Mo/Al2O3 catalyst was investigated in a continuous system under microwave irradiation. The HDS efficiency was much higher (5%–14%) under microwave irradiation than conventional heating. It was proved that the reaction was enhanced by both microwave thermal and non-thermal effects. Microwave selective heating caused hot spots inside the catalyst, thus improved the reaction rate. From the analysis of the non-thermal effect, the molecular collisions were significantly increased under microwave irradiation. However, instead of being reduced, the apparent activation energy increased. This may be due to the microwave treatment hindering the adsorption though upright S-bind (η1) and enhancing the parallel adsorption (η5), both adsorptions were considered to favor to the direct desulfurization route and the hydrogenation route respectively. Therefore, the HDS process was considered to proceed along the hydrogenation route under microwave irradiation.

    Xin Gao, Dandan Shu, Xingang Li, Hong Li

    Microwave-induced film evaporation separation process has been reported recently to separate the polar/nonpolar mixture. However, the efficiency of the separation is still too low for practical applications, which requires further enhancement via different strategies such as optimization design of evaporator structure. In addition the depth understanding of the separation mechanisms is great importance for better utilization of the microwave-induced separation process. To carry out these investigations, a novel microwave-induced falling film evaporation instrument was developed in this paper. The improvement of the enhancement effect of microwave-induced separation was observed based on the improved film evaporator. The systematic experiments on microwave-induced separation with different binary azeotropic mixtures (ethanol-ethyl acetate system and dimethyl carbonate (DMC)-H2O system) were conducted based on the new evaporator. For the ethanol-ethyl acetate system, microwave irradiation shifted the direction of evaporation separation at higher ethanol content in the starting liquid mixture. Moreover, for DMC-H2O system microwave-induced separation process broke through the limitations of the traditional distillation process. The results clearly demonstrated the microwave-induced evaporation separation process could be commendably applied to the separation of binary azeotrope with different dielectric properties. Effects of operating parameters are also investigated to trigger further mechanism understanding on the microwave-induced separation process.

    Ying Yan, Peng Huang, Huiping Zhang

    Carbon molecular sieve membrane (CMSM)/paper-like stainless steel fibers (PSSF) has been manufactured by pyrolyzing poly (furfuryl alcohol) (PFA) coated on the metal fibers. PFA was synthesized using oxalic acid dihydrate as a catalyst and coated on microfibers by dip coating method. For the purpose of investigating the effects of final carbonization temperature, the composites were carbonized between 400°C and 800°C under flowing nitrogen. The morphology and microstructure were examined by X-ray diffraction, Fourier transforms infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, N2 adsorption and desorption, Raman spectra and X-ray photoelectron spectra. The consequences of characterization showed that the CMSM containing mesopores of 3.9 nm were manufactured. The specific surface area of the CMSM/PSSF fabricated in different pyrolysis temperature varies from 26.5 to 169.1 m2∙g1 and pore volume varies from 0.06 to 0.23 cm3∙g1. When pyrolysis temperature exceeds 600°C, the specific surface, pore diameter and pore volume decreased as carbonization temperature increased. Besides, the degree of graphitization in carbon matrix increased with rising pyrolysis temperature. Toluene adsorption experiments on different structured fixed bed that was padded by CMSM/PSSF and granular activated carbon (GAC) were conducted. For the sake of comparison, adsorption test was also performed on fixed bed packed with GAC. The experimental results indicated that the rate constant k′ was dramatically increased as the proportion of CMCM/PSSF composites increased on the basis of Yoon-Nelson model, which suggested that structured fixed bed padded with CMSM/PSSF composite offered higher adsorption rate and mass transfer efficiency.

    Nikolaos Rakovitis, Nan Zhang, Jie Li, Liping Zhang

    The increasing demand of goods, the high competitiveness in the global marketplace as well as the need to minimize the ecological footprint lead multipurpose batch process industries to seek ways to maximize their productivity with a simultaneous reduction of raw materials and utility consumption and efficient use of processing units. Optimal scheduling of their processes can lead facilities towards this direction. Although a great number of mathematical models have been developed for such scheduling, they may still lead to large model sizes and computational time. In this work, we develop two novel mathematical models using the unit-specific event-based modelling approach in which consumption and production tasks related to the same states are allowed to take place at the same event points. The computational results demonstrate that both proposed mathematical models reduce the number of event points required. The proposed unit-specific event-based model is the most efficient since it both requires a smaller number of event points and significantly less computational time in most cases especially for those examples which are computationally expensive from existing models.

    Jin Zhao, Guice Yao, Dongsheng Wen

    Water/oil flow characteristics in a water-wet capillary were simulated at the pore scale to increase our understanding on immiscible flow and enhanced oil recovery. Volume of fluid method was used to capture the interface between oil and water and a pore-throat connecting structure was established to investigate the effects of viscosity, interfacial tension (IFT) and capillary number (Ca). The results show that during a water displacement process, an initial continuous oil phase can be snapped off in the water-wet pore due to the capillary effect. By altering the viscosity of the displacing fluid and the IFT between the wetting and non-wetting phases, the snapped-off phenomenon can be eliminated or reduced during the displacement. A stable displacement can be obtained under high Ca number conditions. Different displacement effects can be obtained at the same Ca number due to its significant influence on the flow state, i.e., snapped-off flow, transient flow and stable flow, and ultralow IFT alone would not ensure a very high recovery rate due to the fingering flow occurrence. A flow chart relating flow states and the corresponding oil recovery factor is established.

    Daniil Marinov

    Reactions of atoms and molecules on chamber walls in contact with low temperature plasmas are important in various technological applications. Plasma-surface interactions are complex and relatively poorly understood. Experiments performed over the last decade by several groups prove that interactions of reactive species with relevant plasma-facing materials are characterized by distributions of adsorption energy and reactivity. In this paper, we develop a kinetic Monte Carlo (KMC) model that can effectively handle chemical kinetics on such heterogenous surfaces. Using this model, we analyse published adsorption-desorption kinetics of chlorine molecules and recombination of oxygen atoms on rotating substrates as a test case for the KMC model.

    Abdolhamid Hatefi-Mehrjardi, Amirkhosro Beheshti-Marnani, Zarrin Es'haghi

    A p-type transition metal dichalcogenide (WS2) was synthesized and hybridized with graphene oxide via a simple hydrothermal method. The as-prepared material was used to modify a glassy carbon electrode for the fabrication of a simple, stable, and repeatable methylene blue-labeled “signal-off” aptasensor used for the sensitive determination of very low amounts of sodium diclofenac (DCF). The synthetic material, modification process, and role of WS2 in the current response enhancement were studied by X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, Hall effect, cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Subsequently, a wide linear range of DCF concentration (0.5–300 nmol/L), very low limit of detection (0.23 nmol/L), and good selectivity were obtained using the differential pulse voltammetry method with the assembled aptasensor. Finally, the fabricated aptasensor was successfully developed for physiological real samples with significant recoveries.

    Yingying Zhao, Mengfan Wu, Zhiyong Ji, Yuanyuan Wang, Jiale Li, Jianlu Liu, Junsheng Yuan

    The desulfurization by seawater and mineral carbonation have been paid more and more attention. In this study, the feasibility of magnesia and seawater for the integrated disposal of SO2 and CO2 in the simulated flue gas was investigated. The process was conducted by adding MgO in seawater to reinforce the absorption of SO2 and facilitate the mineralization of CO2 by calcium ions. The influences of various factors, including digestion time of magnesia, reaction temperature, and salinity were also investigated. The results show that the reaction temperature can effectively improve the carbonation reaction. After combing SO2 removal process with mineral carbonation, Ca2+ removal rate has a certain degree of decrease. The best carbonation condition is to use 1.5 times artificial seawater (the concentrations of reagents are 1.5 times of seawater) at 80°C and without digestion of magnesia. The desulfurization rate is close to 100% under any condition investigated, indicating that the seawater has a sufficient desulfurization capacity with adding magnesia. This work has demonstrated that a combination of the absorption of SO2 with the absorption and mineralization of CO2 is feasible.

    Shenghua Ye, Gaoren Li