Cover illustration
(Yingying Jian, Danyao Qu, Lihao Guo, Yujin Zhu, Chen Su, Huanran Feng, Guangjian Zhang, Jia Zhang, Weiwei Wu, Ming-Shui Yao, pp. 505‒517)
Ti3C2Tx MXene, a two-dimensional (2D) materials with ultra-thin structure, has been fabricated as gas sensors working at room temperature with various thickness. In this work, two critical features towards reducing gases (NH
The global energy market is in a transition towards low carbon fuel systems to ensure the sustainable development of our society and economy. This can be achieved by converting the surplus renewable energy into hydrogen gas. The injection of hydrogen (≤10% v/v) in the existing natural gas pipelines is demonstrated to have negligible effects on the pipelines and is a promising solution for hydrogen transportation and storage if the end-user purification technologies for hydrogen recovery from hydrogen enriched natural gas (HENG) are in place. In this review, promising membrane technologies for hydrogen separation is revisited and presented. Dense metallic membranes are highlighted with the ability of producing 99.9999999% (v/v) purity hydrogen product. However, high operating temperature (≥300 °C) incurs high energy penalty, thus, limits its application to hydrogen purification in the power to hydrogen roadmap. Polymeric membranes are a promising candidate for hydrogen separation with its commercial readiness. However, further investigation in the enhancement of H2/CH4 selectivity is crucial to improve the separation performance. The potential impacts of impurities in HENG on membrane performance are also discussed. The research and development outlook are presented, highlighting the essence of upscaling the membrane separation processes and the integration of membrane technology with pressure swing adsorption technology.
This study explored the feasibility of integrating an adsorption and solvent scrubbing process for post-combustion CO2 capture from a coal-fired power plant. This integrated process has two stages: the first is a vacuum swing adsorption (VSA) process using activated carbon as the adsorbent, and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent. The results showed that the adsorption process could enrich CO2 in the flue gas from 12 to 50 mol-% with a CO2 recovery of >90%, and the concentrated CO2 stream fed to the solvent scrubber had a significantly lower volumetric flowrate. The increased CO2 concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber, bringing the size of the absorber from uneconomically large to readily achievable domain. In addition, the VSA process could also remove most of the oxygen initially existed in the feed gas, alleviating the downstream corrosion and degradation problems in the absorption section. The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO2 capture and thus accelerate the deployment of such technologies to reduce carbon emissions.
In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO2 adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72– 3078.99 m2·g−1) and high micropore percentage (61.60%–76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO2 adsorption capacity up to 5.96 and 3.92 mmol·g−1 at 0 and 25 °C, respectively. In addition, the CO2/N2 selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO2 adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO2 capacity of the NACs has a linear correlation (R2 = 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO2/N2 selectivity, and pyrrole-N and hydroxy groups contribute more to the CO2 adsorption. In situ Fourier transform infrared spectra analysis indicates that CO2 is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO2 diffusion. The CO2 adsorption kinetics for NACs at room temperature and in pure CO2 is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model.
Working temperature, sensitivity, and selectivity are some of the characteristics of the applied gas sensors. How to design and fabricate an ideal gas sensor working at room temperature is still challenging and attracting lots of interest. Two-dimensional (2D) materials with ultra-thin structure have been demonstrated as a family of ideal candidates to achieve this goal. Among them, Ti3C2Tx MXene, a kind of layered sheet synthesized by selectively etching MAX phases materials, shows remarkable potential to be the sensitive materials solely or in a composite. However, their designing rules are still lacking critical thinking from the viewpoint of the intrinsic property of Ti3C2Tx MXene based materials. In this article, two critical features, i.e., the thickness of the sensitive materials, and the scope of the analytes, are elaborated towards Ti3C2Tx MXene based gas sensors after characterizing the performance of sensing reducing gases (NH3 and CO) and oxidizing gas (NO2). First, the thinner the Ti3C2Tx MXene sensitive layer, the better the sensitivity. Second, the Ti3C2Tx MXene based gas sensor is not suitable for strong and moderate oxidation gas due to its ease of oxidation. These two rules are demonstrated, and could be considered with priority both in the future researches and practical applications.
The coal fly ash produced by gasification is estimated to be over 80 million ton per year in China by 2021. It has mainly been disposed as solid waste by landfill. There is lack of study focused on its utilization. In this paper, the coal fly ash produced by gasification was at first analyzed and then applied to synthesize zeolite as an adsorbent. The effects of synthesis conditions on the cation exchange capacity (CEC) of zeolite were investigated. The results from X-ray diffraction and scanning electron microscope indicated that the crystallinity of the synthesized zeolite is the most important factor to affect the CEC. When the synthesized zeolite with the highest CEC (275.5 meq/100 g) was used for the adsorption of Cr(VI) from aqueous solution, the maximum adsorption capacity for Cr(VI) was found to be 17.924 mg/g. The effects of pH, contact time and initial concentration on the adsorption of Cr(VI) were also investigated. The adsorption kinetics and isotherms can be well described by the pseudo-second-order model and Langmuir isotherm model, respectively.
Metal ions including Fe3+, Ca2+, Mg2+, Ni2+, Co2+ and Cu2+ are commonly found in the leaching solution of laterite-nickel ores, and the pre-removal of Fe3+ is extremely important for the recovery of nickel and cobalt. Di(2-ethylhexyl)phosphate acid (D2EHPA) showed high extraction rate and selectivity of Fe3+ over other metal ions. The acidity of the aqueous solution is crucial to the extraction of Fe3+, and the stoichiometry ratio between Fe3+ and the extractant is 0.86:1.54. The enthalpy for the extraction of Fe3+ using D2EHPA was 19.50 kJ/mol. The extraction of Fe3+ was ≥99% under the optimized conditions after a three-stage solvent extraction process. The iron stripping effects of different reagents showed an order of H2C2O4>NH4HCO3>HCl>NaCl>NaHCO3>Na2SO3. The stripping of Fe was ≥99% under the optimized conditions using H2C2O4 as a stripping reagent.
In this work, an adsorbent, which we call MnPT, was prepared by combining MnO2, polyethylenimine and tannic acid, and exhibited efficient performance for Cu(II) and Cr(VI) removal from aqueous solution. The oxygen/nitrogen-containing functional groups on the surface of MnPT might increase the enrichment of metal ions by complexation. The maximum adsorption capacities of MnPT for Cu(II) and Cr(VI) were 121.5 and 790.2 mg·g−1, respectively. The surface complexation formation model was used to elucidate the physicochemical interplay in the process of Cu(II) and Cr(VI) co-adsorption on MnPT. Electrostatic force, solvation action, adsorbate–adsorbate lateral interaction, and complexation were involved in the spontaneous adsorption process. Physical electrostatic action was dominant in the initial stage, whereas chemical action was the driving force leading to adsorption equilibrium. It should be noted that after adsorption on the surface of MnPT, Cr(VI) reacted with some reducing functional groups (hydroxylamine-NH2) and was converted into Cr(III). The adsorption capacity declined by 12% after recycling five times. Understanding the adsorption mechanism might provide a technical basis for the procedural design of heavy metal adsorbents. This MnPT nanocomposite has been proven to be a low-cost, efficient, and promising adsorbent for removing heavy metal ions from wastewater.
Particle deposition during crossflow filtration is significantly influenced by the operating conditions, in particular the permeate flux and crossflow velocity. However, there is a lack of detailed knowledge about how deposit layer structures and distributions depend on operating parameters. This study uses a microfluidic visualisation filtration system to examine the influence of operating conditions on the deposition process during crossflow ultrafiltration from a microscopic perspective. Increasing the permeate flux caused an increasing amount of deposition and a thicker deposit layer. Higher crossflow velocities reduced the extent of deposition. The degree of deposition varied over a range of operating conditions due to the altered hydrodynamic forces exerted on the particles, which can be examined by the deposition probability according to an existing model. Building on this, an empirical correlation between the deposition probability and volume of deposition as a function of filtration time was developed, which gave good agreement with experimental results. The effect of solution conditions was also involved in this correlation as a interaction energies. This could be useful for predicting the dynamic deposition process during crossflow filtration over a range of operating and solution conditions.
A two-stage leaching process, namely, high-pressure acid leaching-atmospheric acid leaching, was used to treat laterite ores under mild conditions. The leaching ratio of Ni was low because of adsorption and incomplete leaching. In this work, surfactants were used as additives to boost the leaching ratio of Ni. The effect of surfactant type (cationic, anionic, and nonionic surfactants) on the leaching ratio of Ni was investigated. Leaching results showed that stearyl trimethyl ammonium chloride (STAC) apparently increased the leaching ratios of valuable metals. The variation in the physicochemical properties of the lixiviant and the residue improved the leaching ratio of Ni in the presence of STAC. Kinetics analysis indicated that the leaching process was controlled by chemical reaction.
Emerging needs for the large-scale industrialization of organic solar cells require high performance cathode interlayers to facilitate the charge extraction from organic semiconductors. In addition to improving the efficiency, stability and processability issues are major challenges. Herein, we design block copolymers with well controlled chemical composition and molecular weight for cathode interlayer applications. The block copolymer coated cathodes display high optical transmittance and low work function. Conductivity studies reveal that the block copolymer thin film has abundant conductive channels and excellent longitudinal electron conductivity due to the interpenetrating networks formed by the polymer blocks. Applications of the cathode interlayers in organic solar cells provide higher power conversion efficiency and better stability compared to the most widely-applied ZnO counterparts. Furthermore, no post-treatment is needed which enables excellent processability of the block copolymer based cathode interlayer.
Dual-loop circulating fluidized bed (CFB) reactors have been widely applied in industry because of their good heat and mass transfer characteristics and continuous handling ability. However, the design of such reactors is notoriously difficult owing to the poor understanding of the underlying mechanisms, meaning it has been heavily based on empiricism and stepwise experiments. Modeling the gas-solid CFB system requires a quantitative description of the multiscale heterogeneity in the sub-reactors and the strong coupling between them. This article proposed a general method for modeling multi-loop CFB systems by utilizing the energy minimization multiscale (EMMS) principle. A full-loop modeling scheme was implemented by using the EMMS model and/or its extension models to compute the hydrodynamic parameters of the sub-reactors, to achieve the mass conservation and pressure balance in each circulation loop. Based on the modularization strategy, corresponding interactive simulation software was further developed to facilitate the flexible creation and fast modeling of a customized multi-loop CFB reactor. This research can be expected to provide quantitative references for the design and scale-up of gas-solid CFB reactors and lay a solid foundation for the realization of virtual process engineering.
A computational model for an ozone oxidation column reactor used in dyeing wastewater treatment is proposed to represent, simulate, and predict the ozone bubble process. Considering the hydrodynamics, mass transfer, and ozone oxidation reaction, coupling modeling can more realistically calculate the ozone oxidation bubble process than the splitting methods proposed in previous research. The modeling is validated and shows great consistency with experimental data. The verified model is used to analyze the effect of operating conditions, such as the initial gas velocity and the ozone concentration, and structural conditions, such as multiple gas inlets. The ozone consumption is influenced by the gas velocity and the initial ozone concentration. The ozone’s utilization decreases with the increasing gas velocity while nearly the same at different initial ozone concentrations. Simulation results can be used in guiding the practical operation of dyeing wastewater treatment and in other ozonation systems with known rate constants in wastewater treatment.
A cholesterol oxidase (COD) was hybridized with Ca2+, Zn2+, Al3+, Fe2+ and Mn2+. After precipitation with PO43– at 4 °C for 72 h, the resulting pellets were freeze-dried. In scanning electron microscopy assays, the metal-COD complexes revealed flower-like or granular structures after hybridization. Fourier transform infrared spectroscopy assay revealed the characteristic peaks of both the enzyme and metal materials. X-ray diffraction analysis indicated that COD was encapsulated in CaHPO4·2H2O-, Zn3(PO4)2·4H2O-, AlPO4-, FeP4- and Mn3(PO4)2·3H2O-based nanostructures, respectively. Differential scanning calorimetry assay indicated significant increases in thermo-denaturation temperatures from 60.5 °C to 167.02 °C, 167.02 °C, 137.70 °C, 172.85 °C and 160.99 °C, respectively. Using steroid derivatives as substrates, this enzyme could convert cholesterol, pregnenolone, dehydroepiandrosterone, ergosterol, b-sitosterol and stigmasterol to related single products. Hybridization in metal-based nanostructures could significantly enhance the initial conversion ratio and reaction stability of the enzyme. In addition, substrate selectivity could be affected by various metal materials. Briefly, using Ca2+, Zn2+, Al3+, Fe2+ and Mn2+ as hybrid raw materials could help to encapsulate COD in related metal-enzyme nanostructures, and could help to promote the stability and tolerant properties of the enzyme, while also enhancing its catalytic characteristics.
To obtain nano-hydroxyapatite/poly(lactide-co-glycolide) (n-HA/PLGA) nanocomposite with superior mechanical properties, here, lignin was chosen to surface-modify for n-HA through co-precipitation method. The different reaction conditions of reaction time, phosphorus source, and the lignin addition amount were studied by fourier transformation infrared spectra, X-ray diffraction, the intuitionistic dispersion experiment, transmission electron microscope and thermal gravimetric analysis. The reaction mechanism and the best appropriate reaction condition were obtained. More importantly, the results of electromechanical universal tester, scanning electron microscope, differential scanning calorimetric analyzer, polarized optical microscopy and dynamic mechanical analysis confirmed that the obtained n-HA could greatly increase the mechanical strength of PLGA, owing to the excellent dispersion and promotion crystallization effect. Moreover, in vitro cell culture experimental results indicated that the n-HA surface-modified by lignin was favorable to improve the cell biocompatibility of PLGA. The study suggested that the introduction of lignin was a novel method to acquire a highly dispersed n-HA, which would provide a new idea to achieve the n-HA/PLGA nanocomposite as bone materials in future, and it would pave the way towards a new application of lignin in biomedical field.
An encapsulation-structured Fe2O3@meso-ZSM-5 (Fe@MZ5) was fabricated by confining Fe2O3 nanoparticles (ca. 4 nm) within the ordered mesopores of hierarchical ZSM-5 zeolite (meso-ZSM-5), with ferric oleate and amphiphilic organosilane as the iron source and meso-porogen, respectively. For comparison, catalysts with Fe2O3 (ca. 12 nm) encapsulated in intra-crystal holes of meso-ZSM-5 and with MCM-41 or ZSM-5 phase as the shell were also prepared via sequential desilication and recrystallization at different pH values and temperatures. Catalytic phenol hydroxylation performance of the as-prepared catalysts using H2O2 as oxidant was compared. Among the encapsulation-structured catalysts, Fe@MZ5 showed the highest phenol conversion and hydroquinone selectivity, which were enhanced by two times compared to the Fe-oxide impregnated ZSM-5 (Fe/Z5). Moreover, the Fe-leaching amount of Fe@MZ5 was only 3% of that for Fe/Z5. The influence of reaction parameters, reusability, and ·OH scavenging ability of the catalysts were also investigated. Based on the above results, the structure-performance relationship of these new catalysts was preliminarily described.
In this work, a new mesoporous silicon sulfonic acid catalyst derived from silicic acid has been successfully prepared by the chemical bonding method. The physicochemical properties of mesoporous silicon sulfonic acid catalysts have been systematically characterized using various techniques. The results demonstrate that sulfonic acid groups have been grafted on silicic acid by forming a new chemical bond (Si–O–S). The mesoporous silicon sulfonic acid exhibits excellent catalytic performance and stability in the vapor phase hydroamination reaction of cyclohexene with cyclohexylamine. Cyclohexene conversion of 61% and 97% selectivity to dicyclohexylamine was maintained after running the reaction for over 350 h at 280 °C. The developed mesoporous silicon sulfonic acid catalyst shows advantages of low cost, superior acid site accessibility, and long term reactivity stability. Moreover, a possible catalytic hydroamination reaction mechanism over silicon sulfonic acid was suggested. It has been demonstrated that the sulfonic acid groups of the catalyst play an important role in the hydroamination. The present work provides a simple, efficient, and environmentally friendly method for the hydroamination of cyclohexene to valuable dicyclohexylamine, which also shows important industrial application prospects.
As the substitution of common noble catalysts in the hydrogenation of carboxylic acid, a highly effective Cu-Ni/SiO2 catalyst was prepared by a novel stepwise ammonia evaporation method. Its performance in the gas-phase hydrogenation of acetic acid was further examined. With the introduction of Ni dopant, more stable Cuδ+ sites, which can adsorb more acetic acid, were formed due to the electron transfer from Cu to Ni. This makes more Cu0 sites available for hydrogen adsorption, which was suggested as the rate-determining step in acetic acid hydrogenation. A conversion of 99.6% was successfully achieved on this new Cu/SiO2-0.5Ni catalyst, accompanied by the ethanol selectivity of 90%. The incorporation of nickel between copper nanoparticles enhances the synergistic effect between Cu0 and Cu+. It also helps mitigate the aggregation of copper nanoparticles due to the Ostwald ripening effect induced by acetic acid and enhance the stability of copper catalyst in the conversion of carboxylic acid.
A convenient and highly efficient method is described for the synthesis of N-methoxycarbazole derivatives, including those with sterically demanding, benzannulated, or strongly electron-donating or -withdrawing substituents. Various N-methoxycarbazole derivatives were directly prepared in good-to-moderate yields by the Pd2(dba)3CHCl3/9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene-catalyzed reactions of the corresponding dibromobiphenyl compounds and methoxya-mine. Based on this methodology, the first total synthesis of 3,3′-[oxybis(methylene)]bis(9-methoxy-9H-carbazole), an antimicrobial dimeric carbazole alkaloid previously isolated from the stem bark of Murraya koenigii, was achieved in 18% yield over seven steps from 1,2-dibromobenzene.
Four coaxial cylinder dielectric barrier discharge micro-plasma reactors were designed for the non-catalytic decomposition of pure CO2 into CO and O2 at low temperature and ambient pressure. The influence of segmented outer electrodes on the electrical characteristics and the reaction performance was investigated. Experimental results indicated that the introduction of segmented outer electrodes can significantly promote the decomposition of CO2. Encouragingly, the highest conversion of 13.1% was obtained at an applied voltage of 18 kV, which was a substantial increase of 39.4% compared to the traditional device. Compared with other types of dielectric barrier discharge plasma reactors, the proposed segmented outer electrode micro-plasma reactor can give a higher CO2 conversion and acceptable energy efficiency. The increase in conversion can be attributed mainly to the enhanced corona discharge caused by the fringe effect at electrode edges, the increase in energy density and the increase in the number of micro-discharges. In addition, detailed electrical characterization was performed to reveal some trends in the electrical behavior of proposed reactors.
Novel MgO-doped CaO sorbent pellets were prepared by gel-casting and wet impregnation. The effect of Na+ and MgO on the structure and CO2 adsorption performance of CaO sorbent pellets was elucidated. MgO-doped CaO sorbent pellets with the diameter range of 0.5-1.5 mm exhibited an excellent capacity for CO2 adsorption and adsorption rate due to the homogeneous dispersion of MgO in the sorbent pellets and its effects on the physical structure of sorbents. The results show that MgO can effectively inhibit the sintering of CaO and retain the adsorption capacity of sorbents during multiple adsorption-desorption cycles. The presence of mesopores and macropores resulted in appreciable change of volume from CaO (16.7 cm3∙mol−1) to CaCO3 (36.9 cm3∙mol−1) over repeated operation cycles. Ca2Mg1 sorbent pellets exhibited favorable CO2 capture capacity (9.49 mmol∙g−1), average adsorption rate (0.32 mmol∙g−1∙min−1) and conversion rate of CaO (74.83%) after 30 cycles.
Two-dimensional (2D) titanium carbide MXene Ti3C2 has attracted significant research interest in energy storage applications. In this study, we prepared Chl@Ti3C2 composites by simply mixing a chlorophyll derivative (e.g., zinc methyl 3-devinyl-3-hydroxymethyl- pyropheophorbide a (Chl)) and Ti3C2 in tetrahydrofuran, where the Chl molecules were aggregated among the multi-layered Ti3C2 MXene or on its surface, increasing the interlayer space of Ti3C2. The as-prepared Chl@Ti3C2 was employed as the anode material in the lithium-ion battery (LIB) with lithium metal as the cathode. The resulting LIB exhibited a higher reversible capacity and longer cycle performance than those of LIB based on pure Ti3C2, and its specific discharge capacity continuously increased along with the increasing number of cycles, which can be attributed to the gradual activation of Chl@Ti3C2 accompanied by the electrochemical reactions. The discharge capacity of 1 wt-% Chl@Ti3C2 was recorded to be 325 mA·h·g–1 at the current density of 50 mA·g–1 with a Coulombic efficiency of 56% and a reversible discharge capacity of 173 mA·h·g–1 at the current density of 500 mA·g–1 after 800 cycles. This work provides a novel strategy for improving the energy storage performance of 2D MXene materials by expanding the layer distance with organic dye aggregates.
