Green Energy&Environment

Endeavors on the development of efficient and sustainable supported metal catalysts for chemical synthesis on solid-liquid interfaces

Chao Yang, Lifeng Cui

2023, 8(1): 1-3. doi: 10.1016/j.gee.2022.03.004

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Supported metal catalysts, particularly for precious metals, have gained increasing attention in green synthetic chemistry. They can make metal-catalyzed organic synthesis more sustainable and economical due to easy separation of product with less metal residue, as well as reusability of the high-cost catalysts. Although great effort has been spent, the precise catalytic mechanism of supported metal-catalyzed reactions has not been clearly elucidated and the development of efficient and stable recyclable catalysts remains challenging. This highlight reveals a “molecular fence” metal stabilization strategy and discloses the metal evolution in Pd-catalyzed C-C bond formation reactions using N-heterocyclic carbene (NHC)-functionalized hypercrosslinked polymer support, wherein the polymeric skeleton isolates or confines the metal species involved in the catalytic reactions, and NHC captures free low-valent metal species in solution and stabilizes them on the support via strong metal-support coordination interaction. This strategy creates a novel route for the development of supported metal catalysts with high stability and provides insights into the reaction mechanism of heterogeneous catalysis.

Selective capture of Tl₂O from flue gas with formation of p-n junction on V₂O₅-WO₃/TiO₂ catalyst under working conditions

Jianjun Chen, Rongqiang Yin, Gongda Chen, Junyu Lang, Xiaoping Chen, Xuefeng Chu, Junhua Li

2023, 8(1): 4-9. doi: 10.1016/j.gee.2021.12.001

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Thallium (Tl) compounds, highly toxic to biology, are usually released into flue gas during fossil/minerals combustion, and further distributed in water and soil. In this work, we fundamentally investigated the capture of gaseous Tl₂O by industrial V₂O₅-WO₃/TiO₂ catalyst under working condition in Tl-containing flue gas. Experimental and theoretical results indicated that the Tl₂O has significant electron-feeding capacity and easily donate electron to unoccupied orbitals of TiO₂, leading to dismutation of Ti 2p and inartificial formation of p-n junction on TiO₂ surface, which prompted Tl₂O selectively interacted with TiO₂ in flue gas. Herein, we proposed and verified an effective way to capture gaseous Tl₂O, which offered almost the best choice to eliminate Tl emission from flue gas and expanded the function of the TiO₂-based catalyst. The formation of p-n junction on commercial V₂O₅-WO₃/TiO₂ catalyst under working condition was revealed for the first time, which can be a valuable reference for both heterocatalysis and electro/photocatalysis.

Catalytic conversion of lignocellulosic biomass into chemicals and fuels

Weiping Deng, Yunchao Feng, Jie Fu, Haiwei Guo, Yong Guo, Buxing Han, Zhicheng Jiang, Lingzhao Kong, Changzhi Li, Haichao Liu, Phuc T.T. Nguyen, Puning Ren, Feng Wang, Shuai Wang, Yanqin Wang, Ye Wang, Sie Shing Wong, Kai Yan, Ning Yan, Xiaofei Yang, Yuanbao Zhang, Zhanrong Zhang, Xianhai Zeng, Hui Zhou

2023, 8(1): 10-114. doi: 10.1016/j.gee.2022.07.003

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In the search of alternative resources to make commodity chemicals and transportation fuels for a low carbon future, lignocellulosic biomass with over 180-billion-ton annual production rate has been identified as a promising feedstock. This review focuses on the state-of-the-art catalytic transformation of lignocellulosic biomass into value-added chemicals and fuels. Following a brief introduction on the structure, major resources and pretreatment methods of lignocellulosic biomass, the catalytic conversion of three main components, i.e., cellulose, hemicellulose and lignin, into various compounds are comprehensively discussed. Either in separate steps or in one-pot, cellulose and hemicellulose are hydrolyzed into sugars and upgraded into oxygen-containing chemicals such as 5-HMF, furfural, polyols, and organic acids, or even nitrogen-containing chemicals such as amino acids. On the other hand, lignin is first depolymerized into phenols, catechols, guaiacols, aldehydes and ketones, and then further transformed into hydrocarbon fuels, bioplastic precursors and bioactive compounds. The review then introduces the transformations of whole biomass via catalytic gasification, catalytic pyrolysis, as well as emerging strategies. Finally, opportunities, challenges and prospective of woody biomass valorization are highlighted.

Carbon materials toward efficient potassium storage: Rational design, performance evaluation and potassium storage mechanism

Daping Qiu, Yanglong Hou

2023, 8(1): 115-140. doi: 10.1016/j.gee.2022.05.007

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Potassium-ion batteries (PIBs) are potential “Beyond Li-ion Batteries” candidates for their resource advantage and low standard electrode potential. To date, the research on PIBs is in its early stages, the most urgent task is to develop high-performance electrode materials and reveal their potassium storage mechanism. For PIBs anode materials, carbon with tunable microstructure, excellent electrochemical activity, nontoxicity and low price is considered as one of the most promising anode materials for commercialization. Although some breakthrough works have emerged, the overall electrochemical performance of the reported carbon anode is still far away from practical application. Herein, we carry out a comprehensive overview of PIBs carbon anode in terms of three aspects of rational design of structure, performance evaluation criteria and characterization of potassium storage mechanism. First, the regulation mechanism of key structural features of carbon anode on its potassium storage performance and the representative structural regulation strategies are introduced. Then, in view of the undefined performance evaluation criteria of PIBs carbon anode, a reference principle for evaluating the potassium storage performance of carbon anode is proposed. Finally, the advanced characterization techniques for the potassium storage mechanism of carbon anode are summarize. This review aims to provide guidance for the development of practical PIBs anode.

Electrochemical synthesis of FeN_x doped carbon quantum dots for sensitive detection of Cu²⁺ ion

Siyuan Sun, Weijie Bao, Fan Yang, Xingru Yan, Yang Sun, Ge Zhang, Wang Yang, Yongfeng Li

2023, 8(1): 141-150. doi: 10.1016/j.gee.2021.04.005

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A novel strategy was developed to fabricate FeN_x-doped carbon quantum dots (Fe-N-CQDs) to detect Cu²⁺ ions selectively as a fluorescence probe. The Fe-N-CQDs were synthesized by an efficient electrolysis of a carbon cloth electrode, which was coated with monoatomic iron-anchored nitrogen-doped carbon (Fe-N-C). The obtained Fe-N-CQDs emitted blue fluorescence and possessed a quantum yield (QY) of 7.5%. An extremely wide linear relationship between the Cu²⁺ concentration and the fluorescence intensity was obtained in the range from 100 nmol L^-1 to 1000 nmol L^-1 (R² = 0.997), and the detection limit was calculated as 59 nmol L^-1. Moreover, the Fe-N-CQDs demonstrated wide range pH compatibility between 2 and 13 due to the coordination between pyridine nitrogen and Fe³⁺, which dramatically reduced the affection of the protonation and deprotonation process between H⁺ and Fe-N-CQDs. It is notable that the Fe-N-CQDs exhibited a rapid response in Cu²⁺ detection, where stable quenching can be completed in 7 s. The mechanism of excellent selective detection of Cu²⁺ was revealed by energy level simulation that the LUMO level of Fe-N-CQDs (-4.37 eV) was close to the redox potential of Cu²⁺, thus facilitating the electron transport from Fe-N-CQDs to Cu²⁺.

Poly(ionic liquid)-crosslinked graphene oxide/carbon nanotube membranes as efficient solar steam generators

Jiangjin Han, Zhiyue Dong, Liang Hao, Jiang Gong, Qiang Zhao

2023, 8(1): 151-162. doi: 10.1016/j.gee.2021.03.010

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Graphene oxide (GO) is regarded as a promising candidate to construct solar absorbers for addressing freshwater crisis, but the easy delamination of GO in water poses a critical challenge for practical solar desalination. Herein, we improve the stability of GO membranes by a self-crosslinking poly (ionic liquid) (PIL) in a mild condition, which crosslinks neighbouring GO nanosheets without blemishing the hydrophilic structure of GO. By further adding carbon nanotubes (CNTs), the sandwiched GO/CNT@PIL (GCP) membrane displays a good stability in pH = 1 or 13 solution even for 270 days. The molecular dynamics simulation results indicate that the generation of water nanofluidics in nanochannels of GO nanosheets remarkably reduces the water evaporation enthalpy in GCP membrane, compared to bulk water. Consequently, the GCP membrane exhibits a high evaporation rate (1.87 kg m^-2 h^-1) and displays stable evaporation rates for 14 h under 1 kW m^-2 irradiation. The GCP membrane additionally works very well when using different water sources (e.g., dye-polluted water) or even strong acidic solution (pH = 1) or basic solution (pH = 13). More importantly, through bundling pluralities of GCP membrane, an efficient solar desalination device is developed to produce drinkable water from seawater. The average daily drinkable water amount in sunny day is 10.1 kg m^-2, which meets with the daily drinkable water needs of five adults. The high evaporation rate, long-time durability and good scalability make the GCP membrane an outstanding candidate for practical solar seawater desalination.

Titanium-rich TS-1 zeolite for highly efficient oxidative desulfurization

Risheng Bai, Yue Song, Ge Tian, Fei Wang, Avelino Corma, Jihong Yu

2023, 8(1): 163-172. doi: 10.1016/j.gee.2021.03.006

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The exploration of highly efficient catalysts based on nano-sized Ti-rich titanosilicate zeolites with controllable active titanium species is of great importance in zeolite catalytic reactions. Herein, we reported an efficient and facile synthesis of nano-sized Ti-rich TS-1 ( MFI ) zeolites by replacing tetrabutyl orthotitanate (TBOT) with tetrabutyl orthotitanate tetramer (TBOT-tetramer) as the titanium source. The introduced TBOT-tetramer slowed down the zeolite crystallization process, and accordingly balanced the rate of incorporating Ti and the crystal growth and inhibited the massive formation of anatase species. Notably, the prepared Ti-rich TS-1 zeolite sample had a Si/Ti as low as 27.6 in contrast to conventional one with a molar ratio of 40. The TBOT-tetramer endowed the titanosilicate zeolites with enriched active titanium species and enlarged external surface area. It also impeded the formation of anatase species, resulting in superior catalytic behavior toward the oxidative desulfurization of dibenzothiophene compared with the conventional TS-1 zeolite counterpart prepared with TBOT.

Cerium-tungsten oxides supported on activated red mud for the selective catalytic reduction of NO_x

Qiuzhun Chen, Dong Wang, Chuan Gao, Bin Wang, Shengli Niu, Gaiju Zhao, Yue Peng, Junhua Li, Chunmei Lu, John Crittenden

2023, 8(1): 173-182. doi: 10.1016/j.gee.2021.03.008

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Activated red mud (RM) has been proved to be a promising base material for the selective catalysis reduction (SCR) of NO_x. The inherent low reducibility and acidity limited its low-temperature activity. In this work, molybdenum oxide, tungsten oxide, and cerium oxide were used to reconfigure the redox sites and acid sites of red mud based catalyst. When activated red mud was reconfigured by cerium-tungsten oxide (Ce-W@RM), the NO_x conversion kept above 90% at 219-480 ℃. The existence of Ce³⁺/Ce⁴⁺ redox electron pairs provided more surface adsorbed oxygen (O_α) and served as a redox cycle. Positive interactions between Ce, W species and Fe oxide in red mud occurred, which led to the formation of unsaturated chemical bond and promoted the activation of adsorbed NH₃ species. WO₃ and Ce₂(WO₄)₃ (formed by solid-state reaction between Ce and W species) could provide more Brønsted acid sites (W-O modes of WO₃, WO or W-O-W modes of Ce₂(WO₄)₃). CeO₂ species could provide more Lewis acid sites. The Langmuir-Hinshelwood (L-H) routes and Eley-Rideal (E-R) routes occurred in the low-temperature SCR reaction on the Ce-W@RM surface. NH₄⁺ species on Brønsted acid sites, NH₃ species on Lewis acid sites, bidentate nitrate and bridging nitrate species were key active intermediates species.

Ionic liquids-SBA-15 hybrid catalysts for highly efficient and solvent-free synthesis of diphenyl carbonate

Songlin Wang, Qiying Zhang, Chengxing Cui, Hongying Niu, Cailing Wu, Jianji Wang

2023, 8(1): 183-193. doi: 10.1016/j.gee.2021.02.010

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Diphenyl carbonate (DPC) is one of the versatile carbonates, and is often used for the production of polycarbonates. In recent years, the catalytic synthesis of DPC has become an important topic but the development of a highly active metal-free catalyst is a great challenge. Herein, a series of ionic liquids-SBA-15 hybrid catalysts with different functional groups have been developed for the synthesis of DPC under solvent-free condition, which are effective and clean instead of the metal-containing catalysts. It is found that in the presence of [SBA-15-IL-OH]Br catalyst, methyl phenyl carbonate (MPC) conversion of 80.5% along with 99.6% DPC selectivity is achieved, the TOF value is thrice higher than the best value reported by using transition metal-based catalysts. Moreover, the catalyst displays remarkable stability and recyclability. This work provides a new idea to design and prepare eco-friendly catalysts in a broad range of applications for the green synthesis of carbonates.

Visible-light degradation of azo dyes by imine-linked covalent organic frameworks

Hongbo Xue, Sen Xiong, Kai Mi, Yong Wang

2023, 8(1): 194-199. doi: 10.1016/j.gee.2020.09.010

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Covalent organic frameworks (COFs) are nanoporous crystalline polymers with densely conjugated structures. This work discovers that imine-linked COFs exhibit remarkable photodegradation efficiency to azo dyes dissolved in water. Visible light generates different types of radicals from COFs, and superoxide radicals break N＝N bonds in dye molecules, resulting in 100% degradation of azo dyes within 1 h. In contrast, these dyes cannot be degraded by conventionally used photocatalysts, for example, TiO₂. Importantly, the COF photocatalysts can be recovered from the dye solutions and re-used to degrade azo dyes for multiple times without loss of degradation efficiency. This work provides an efficient strategy to degrade synthetic dyes, and we expect that COFs with designable structures may use as new photocatalysts for other important applications.

3D flower-like mesoporous Bi₄O₅I₂/MoS₂ Z-scheme heterojunction with optimized photothermal-photocatalytic performance

Sijia Song, Zipeng Xing, Ke Wang, Huanan Zhao, Peng Chen, Zhenzi Li, Wei Zhou

2023, 8(1): 200-212. doi: 10.1016/j.gee.2021.03.013

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3D flower-like hierarchical mesoporous Bi₄O₅I₂/MoS₂ Z-scheme layered heterojunction photocatalyst was fabricated by oil bath and hydrothermal methods. The heterojunction with narrow band gap of ~1.95 eV extended the photoresponse to near-infrared region, which showed obvious photothermal effect due to the introduction of MoS₂ with broad spectrum response. MoS₂ nanosheets were anchored onto the surface of flower-like hierarchical mesoporous Bi₄O₅I₂ nanosheets, thereby forming efficient layered heterojunctions, the solar-driven photocatalytic efficiency in degradation of highly toxic dichlorophenol and reduction of hexavalent chromium was improved to 98.5% and 99.2%, which was ~4 and 7 times higher than that of the pristine Bi₄O₅I₂, respectively. In addition, the photocatalytic hydrogen production rate reached 496.78 μmol h^-1 g^-1, which was ~6 times higher than that of the pristine Bi₄O₅I₂. The excellent photocatalytic performance can be ascribed to the promoted photothermal effect, as well as, the formation of compact Z-scheme layered heterojunctions. The 3D flower-like hierarchical mesoporous structure provided adequate surface active-sites, which was conducive to the mass transfer. Moreover, the high stability of the prepared photocatalyst further promoted its potential practical application. This strategy also provides new insights for fabricating layered Z-scheme heterojunctions photocatalysts with highly photothermal-photocatalytic efficiency.

Efficient quantum dot sensitized solar cells via improved loading amount management

Wei Wang, Yiling Xie, Fangfang He, Yuan Wang, Weinan Xue, Yan Li

2023, 8(1): 213-223. doi: 10.1016/j.gee.2021.04.002

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High light-harvesting efficiency and low interfacial charge transfer loss are essential for the fabrication of high-efficiency quantum dot-based solar cells (QDSCs). Increasing the thickness of mesoporous TiO₂ films can improve the loading of pre-synthesized QDs on the film and enhance the absorbance of photoanode, but commonly accompanied by the increase in the unfavorable charge recombination due to prolonged electron transmission paths. Herein, we systematically studied the influence of the balance between QD loading and TiO₂ film thickness on the performance of QDSCs. It is found that the relative thin photoanode prepared by the cationic surfactant-assisted multiple deposition procedure has achieved a high QD loading which is comparable to that of the thick photoanode commonly used. Under AM 1.5G illumination, Zn-Cu-In-Se and Zn-Cu-In-S based QDSCs with optimized 11.8 μm photoanodes show the PCE of 10.03% and 8.53%, respectively, which are comparable to the corresponding highest PCE of Zn-Cu-In-Se and Zn-Cu-In-S QDSCs (9.74% and 8.75%) with over 25.0 μm photoanodes. Similarly, an impressive PCE of 6.14% was obtained for the CdSe based QDSCs with a 4.1 μm photoanode, which is slightly lower than the best PCE (7.05%) of reference CdSe QDSCs with 18.1 μm photoanode.

Scalable solid-phase synthesis of defect-rich graphene for oxygen reduction electrocatalysis

Chunxiao Dong, Li Yang, Cheng Lian, Xiaoling Yang, Yihua Zhu, Hongliang Jiang, Chunzhong Li

2023, 8(1): 224-232. doi: 10.1016/j.gee.2021.03.012

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Defect-engineered carbon materials have been emerged as promising electrocatalysts for oxygen reduction reaction (ORR) in metal-air batteries. Developing a facile strategy for the preparation of highly active nanocarbon electrocatalysts remains challenging. Herein, a low-cost and simple route is developed to synthesize defective graphene by pyrolyzing the mixture of glucose and carbon nitride. Molecular dynamics simulations reveal that the graphene formation is ascribed to two-dimensional layered feature of carbon nitride, and high compatibility of carbon nitride/glucose systems. Structural measurements suggest that the graphene possesses rich edge and topological defects. The graphene catalyst exhibits higher power density than commercial Pt/C catalyst in a primary Zn-air battery. Combining experimental results and theoretical thermodynamic analysis, it is identified that graphitic nitrogen-modified topological defects at carbon framework edges are responsible for the decent ORR performance. The strategy presented in this work can be can be scaled up readily to fabricate defective carbon materials.

Self-assembly synthesis of phosphorus-doped tubular g-C₃N₄/Ti₃C₂ MXene Schottky junction for boosting photocatalytic hydrogen evolution

Kelei Huang, Chunhu Li, Xiuli Zhang, Liang Wang, Wentai Wang, Xiangchao Meng

2023, 8(1): 233-245. doi: 10.1016/j.gee.2021.03.011

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Establishing highly effective charge transfer channels in carbon nitride (g-C₃N₄) to enhance its photocatalytic activity is still a challenging issue. Herein, the delaminated 2D Ti₃C₂ MXene nanosheets were employed to decorate the P-doped tubular g-C₃N₄ (PTCN) for engineering 1D/2D Schottky heterojunction (PTCN/TC) through electrostatic self-assembly. The optimized PTCN/TC exhibited the highest hydrogen evolution rate (565 μmol h^-1 g^-1), which was 4.3 and 2.0 -fold higher than pristine bulk g-C₃N₄ and PTCN, respectively. Such enhancement may be primarily attributed to the phosphorus heteroatom doped and unique structure of 1D/2D g-C₃N₄/Ti₃C₂ Schottky heterojunction, enhancing the light-harvesting and charges’ separation. One-dimensional pathway of g-C₃N₄ tube and built-in electric field of interfacial Schottky effect can significantly facilitate the spatial separation of photogenerated charge carriers, and simultaneously inhibit their recombination via Schottky barrier. In this composite, metallic Ti₃C₂ was served as electrons sink and photons collector. Moreover, ultrathin Ti₃C₂ flake with exposed terminal metal sites as a co-catalyst exhibited higher photocatalytic reactivity in H₂ evolution compared to carbon materials (such as reduced graphene oxide). This work not only proposed the mechanism of tubular g-C₃N₄/Ti₃C₂ Schottky junction in photocatalysis, but also provided a feasible way to load ultrathin Ti₃C₂ as a co-catalyst for designing highly efficient photocatalysts.

Direct production of hydrogen peroxide over bimetallic CoPd catalysts: Investigation of the effect of Co addition and calcination temperature

Hamidreza Nazeri, Alireza Najafi Chermahini, Zahra Mohammadbagheri, Mirko Prato

2023, 8(1): 246-257. doi: 10.1016/j.gee.2021.03.014

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A series of CoPd/KIT-6 bimetallic catalysts with various Co:Pd molar ratios at different calcination temperatures were prepared and used for the direct synthesis of H₂O₂ from H₂ and O₂. These catalysts were characterized by nitrogen adsorption-desorption, low and wide-angle X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), elemental mapping and energy-dispersive X-ray (EDX) methods. It was found that the particle size, electronic interactions, morphology, and textural properties of these catalysts as well as their catalytic activity in the reaction of H₂ with O₂ were affected by Co addition and different calcination temperatures. Also, the results showed that while the H₂O₂ selectivity depends on Pd²⁺ species, the H₂ conversion is related to Pd⁰ active sites. Among these catalysts, CoPd/KIT-6 calcined at 350 ℃ ( CoPd/KIT-350 catalyst) showed the best catalytic activity with 50% of H₂O₂ selectivity and 51% conversion of H₂.

Bimetallic AgNi nanoparticles anchored onto MOF-derived nitrogen-doped carbon nanostrips for efficient hydrogen evolution

Dandan Chen, Cheng Han, Qiuhong Sun, Junyang Ding, Qi Huang, Ting-Ting Li, Yue Hu, Jinjie Qian, Shaoming Huang

2023, 8(1): 258-266. doi: 10.1016/j.gee.2021.04.003

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Hydrogen energy has long been recognized as a clean alternative to conventional fossil fuels, which can be applied in a wide range of transportation and power generation applications. The rational design and engineering of high-performance and robust catalysts for hydrogen evolution reaction (HER) shows not a great significance but a challenge for efficient electrochemical water splitting. Herein, a new type of Ni-based Ni-ABDC precursor has been obtained, which leads to the formation of N-doped porous carbon nanomaterials uniformly coated with well-proportioned bimetallic AgNi alloys via a stepwise strategy. To their credit, all samples of AgNi/NC-X are structurally calcined from the pristine AgNi-ABDC-X by tuning the different concentration of AgNO₃, which means all of them maintain the vermicelli-like morphology compared with Ni-ABDC . The series of AgNi/NC-X materials can be regarded as effective electrocatalysts for HER both in acidic and alkaline media, but an acid-leaching phenomenon is observed. Among them, the as-prepared AgNi/NC-2 exhibits a low overpotential of 103 mV at the current density of 10 mA cm^-2 and decent durability with a high retention rate of 90.9% after 10 h in 1.0 mol L^-1 KOH electrolyte. The compelling HER properties of AgNi/NC-2 can be attributed to the synergistic effect between the hierarchical carbon materials, partial N-doping and abundant AgNi alloys. Meanwhile, this study provides a practicable method for the development of efficient HER electrocatalysts for energy applications, which can be conveniently prepared through the reasonable introduction of active components in the crystalline inorganic-organic precursors.

Polysulfide nanoparticles-reduced graphene oxide composite aerogel for efficient solar-driven water purification

Fantao Meng, Yuang Zhang, Shufen Zhang, Benzhi Ju, Bingtao Tang

2023, 8(1): 267-274. doi: 10.1016/j.gee.2021.04.004

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Along with the environmental pollution, the scarcity of clean water seriously threatens the sustainable development of human society. Recently, the rapid development of solar evaporators has injected new vitality into the field of water purification. However, the industry faces a considerable challenge of achieving comprehensive purification of ions, especially the efficient removal of mercury ions. In this work, we introduce an ideal mercury-removal platform based on facilely and cost-effectively synthesized polysulfide nanoparticles (PSNs). Further development of PSN-functionalized reduced graphene oxide (PSN-rGO) aerogel evaporator results in achieving a high evaporation rate of 1.55 kg m^-2 h^-1 with energy efficiency of 90.8% under 1 sun. With the merits of interconnected porous structure and adsorption ability, the photothermal aerogel presents overall purification of heavy metal ions from wastewater. During solar desalination, salt ions can be rejected with long-term stability. Compared with traditional water purification technologies, this highly efficient solar evaporator provides a new practical method to utilize clean energy for clean water production.

Mechanochemical synthesis of oxygenated alkynyl carbon materials with excellent Hg(II) adsorption performance from CaC₂ and carbonates

Yingjie Li, Songping Li, Xinyi Xu, Hong Meng, Yingzhou Lu, Chunxi Li

2023, 8(1): 275-282. doi: 10.1016/j.gee.2021.04.007

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Adsorptive removal of heavy metal ions from wastewater is very important, and the key is the development of efficient sorbents. In this work, oxygenated alkynyl carbon materials (OACMs) were synthesized via mechanochemical reaction of CaC₂ and a carbonate (CaCO₃, Na₂CO₃, or NaHCO₃) at ambient temperature. The resultant OACMs are micro mesoporous carbon nanomaterials with high specific area (>648 m² g^-1), highly crosslinked texture, and rich alkynyl and oxygenated groups. The OACMs exhibit excellent Hg(II) adsorption due to the soft acid-soft base interaction between alkynyl and Hg(II), and OACM-3 derived from CaC₂ and NaHCO₃ has the saturated Hg(II) adsorbance of 483.9 mg g^-1 along with good selectivity and recyclability. The adsorption is mainly chemisorption following the Langmuir mode. OACM-3 also shows high adsorbance for other heavy metal ions, e.g. 256.6 mg g^-1 for Pb(II), 232.4 mg g^-1 for Zn(II), and 198.7 mg g^-1 for Cu(II). This work expands the mechnochemical reaction of CaC₂ with carbonates and possibly other oxyanionic salts, provides a new synthesis approach for functional alkynyl carbon materials with excellent adsorption performance for heavy metal ions, as well as a feasible approach for CO₂ resource utilization.

High piezo/photocatalytic efficiency of Ag/Bi₅O₇I nanocomposite using mechanical and solar energy for N₂ fixation and methyl orange degradation

Lu Chen, Wenqian Zhang, Junfeng Wang, Xiaojing Li, Yi Li, Xin Hu, Leihong Zhao, Ying Wu, Yiming He

2023, 8(1): 283-295. doi: 10.1016/j.gee.2021.04.009

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In this work, Ag/Bi₅O₇I nanocomposite was prepared and firstly applied in piezo/photocatalytic reduction of N₂ to NH₃ and methyl orange (MO) degradation. Bi₅O₇I was synthesized via a hydrothermal-calcination method and shows nanorods morphology. Ag nanoparticles (NPs) were photo deposited on the Bi₅O₇I nanorods as electron trappers to improve the spatial separation of charge carriers, which was confirmed via XPS, TEM, and electronic chemical analyses. The catalytic test indicates that Bi₅O₇I presents the piezoelectric-like behavior, while the loading of Ag NPs can strengthen the character. Under ultrasonic vibration, the optimal Ag/Bi₅O₇I presents high efficiency in MO degradation. The degradation rate is determined to be 0.033 min^-1, which is 4.7 folds faster than that of Bi₅O₇I. The Ag/Bi₅O₇I also presents a high performance in piezocatalytic N₂ fixation. The piezocatalytic NH₃ generation rate reaches 65.4 μmol L^-1 g^-1 h^-1 with water as a hole scavenger. The addition of methanol can hasten the piezoelectric catalytic reaction. Interestingly, when ultrasonic vibration and light irradiation simultaneously act on the Ag/Bi₅O₇I catalyst, higher performance in NH₃ generation and MO degradation is observed. However, due to the weak adhesion of Ag NPs, some Ag NPs would fall off from the Bi₅O₇I surface under long-term ultrasonic vibration, which would greatly reduce the piezoelectric catalytic performance. This result indicates that a strong binding force is required when preparing the piezoelectric composite catalyst. The current work provides new insights for the development of highly efficient catalysts that can use multiple energies.

Mechanism of CO₂ reduction in carbonylation reaction promoted by ionic liquid additives: A computational and experimental study

Kai-Lun Bi, Bao-Hua Xu, Wei-Lu Ding, Li-Jun Han, Lin Ji

2023, 8(1): 296-307. doi: 10.1016/j.gee.2021.04.008

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The Ru-catalyzed carbonylation of alkenes with CO₂ as a C1 surrogate and imidazole chlorides as the promotor is investigated by a combination of computational and experimental study. The conversion rate of CO₂ to CO is positively correlated with the efficiency of both hydroesterification and hydroformylation, which is found facilitated in the presence of chloride additives with a decreasing order of BmimCl ~ B3MimCl > BmmimCl ~ LiCl. Taking the hydroesterification with MeOH as a representative example, BmimCl bearing C-H functionality at the C² site of the cation assists the reduction of CO₂ to CO as a hydrogen donor medium, with the anion and cation acting in a synergistic fashion. Subsequent insertion of CO₂ into the formed Ru-H bond with the assistance of chloride anion produces the Ru-COOH species, which ultimately accelerates the activation of CO₂.

Micropores regulating enables advanced carbon sphere catalyst for Zn-air batteries

Jingsha Li, Shijie Yi, Ranjusha Rajagopalan, Zejie Zhang, Yougen Tang, Haiyan Wang

2023, 8(1): 308-317. doi: 10.1016/j.gee.2021.03.003

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Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction (ORR) electrocatalysts with low cost and high catalytic activity. Herein, N-doped carbon spheres (N-CS) with rich micropore structure have been synthesized by a facile two-step method, which includes the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process. During the preparation, zinc chloride (ZnCl₂) was utilized as a catalyst to promote polymerization and provide a hypersaline environment. In addition, the morphology, defect content and activity area of the resultant N-CS catalysts could be regulated by controlling the content of ZnCl₂. The optimum N-CS-1 catalyst demonstrated much better catalytic activity and durability towards ORR in alkaline conditions than commercial 20 wt% Pt/C catalysts, of which the half-wave potential reached 0.844 V vs. RHE. When applied in the Zn-air batteries as cathode catalysts, N-CS-1 showed a maximum power density of 175 mW cm^-2 and long-term discharging stability of over 150 h at 10 mA cm^-2, which outperformed 20 wt% Pt/C. The excellent performance could be due to its ultrahigh specific surface area of 1757 m² g^-1 and rich micropore channels structure. Meanwhile, this work provides an efficient method to synthesize an ultrahigh surface porous carbon material, especially for catalyst application.

Manipulating the ion-transference and deposition kinetics by regulating the surface chemistry of zinc metal anodes for rechargeable zinc-air batteries

Miao He, Chaozhu Shu, Ruixing Zheng, Wei Xiang, Anjun Hu, Yu Yan, Zhiqun Ran, Minglu Li, Xiaojuan Wen, Ting Zeng, Jianping Long

2023, 8(1): 318-330. doi: 10.1016/j.gee.2021.04.011

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Aqueous zinc-air battery (ZAB) has attractive features as the potential energy storage system such as high safety, low cost and good environmental compatibility. However, the issue of dendrite growth on zinc metal anodes has seriously hindered the development of ZAB. Herein, the N-doped carbon cloth (NC) prepared via magnetron sputtering is explored as the substrate to induce the uniform nucleation of zinc metal and suppress dendrite growth. Results show that the introduction of heteroatoms accelerates the migration and deposition kinetics of Zn²⁺ by boosting the desolvation process of Zn²⁺, eventually reducing the nucleation overpotential. Besides, theoretical calculation results confirm the zincophilicity of N-containing functional group (such as pyridine N and pyrrole N), which can guide the nucleation and growth of zinc uniformly on the electrode surface by both promoting the redistribution of Zn²⁺ in the vicinity of the surface and enhancing its interaction with zinc atoms. As a result, the half-cell assembled with magnetron sputtered carbon cloth achieves a high zinc stripping/plating coulombic efficiency of 98.8% and long-term stability of over 500 cycles at 0.2 mA cm^-2. And the Coulombic efficiency reached about 99.5% at the 10th cycle and maintained for more than 210 cycles at a high current density of 5.0 mA cm^-2. The assembled symmetrical battery can deliver 220 plating/stripping cycles with ultra-low voltage hysteresis of only 11 mV. In addition, the assembled zinc-air full battery with NC-Zn anode delivers a high special capacity of about 429 mAh g_Zn^-1 and a long life of over 430 cycles. The effectiveness of surface functionalization in promoting the transfer and deposition kinetics of Zn²⁺ presented in this work shows enlightening significance in the development of metal anodes in aqueous electrolytes.

High tension cyclic hydrocarbons synthesized from biomass-derived platform molecules for aviation fuels in two steps

Zhanchao Li, Yizhuo Wang, Qing Li, Liqing Xu, Hong Wang

2023, 8(1): 331-337. doi: 10.1016/j.gee.2021.04.012

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Abstract:
Synthesizing ring structure aviation fuels from biomass-derived platform molecules is challenging, especially for bridged ring structure aviation fuels which are typically achieved from fossil-derived chemicals. Herein, we report the synthesis of a series of ring structure biofuels in two steps by a combination of a solvent-free Michael-cyclization reaction and a hydrodeoxygenation (HDO) reaction from lignocellulose-derived 5,5-dimethyl-1,3-cyclohexanedione. These biofuels are obtained with high overall yields up to 90%, which exhibit high densities of 0.81 g cm^-3-0.88 g cm^-3 and high volumetric neat heat of combustion (VNHOC) values of 36.0 MJ L^-1-38.6 MJ L^-1. More importantly, bridged-ring structure hydrocarbons can also be achieved in two steps by a combination of a Robinson annulation reaction and an HDO reaction to afford the final products at high overall yields up to 90%. The bridged-ring structure products have comparable high densities and high VNHOC values to the best artificial fuel JP-10 (0.94 g cm^-3 and 39.6 MJ L^-1). The results demonstrate a promising way for the synthesis of high-density aviation fuels with different fuel properties at high yields.

Techno-economic assessment of a chemical looping splitting system for H₂ and CO Co-generation

Hao Peng, Zichen Di, Pan Gong, Fengling Yang, Fangqin Cheng

2023, 8(1): 338-350. doi: 10.1016/j.gee.2022.02.012

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Abstract:
The natural gas (NG) reforming is currently one of the low-cost methods for hydrogen production. However, the mixture of H₂ and CO₂ in the produced gas inevitably includes CO₂ and necessitates the costly CO₂ separation. In this work, a novel double chemical looping involving both combustion (CLC) and sorption-enhanced reforming (SE-CLR) was proposed towards the co-production of H₂ and CO (CLC-SECLR_HC) in two separated streams. CLC provides reactant CO₂ and energy to feed SECLR_HC, which generates hydrogen in a higher purity, as well as the calcium cycle to generate CO in a higher purity. Techno-economic assessment of the proposed system was conducted to evaluate its efficiency and economic competitiveness. Studies revealed that the optimal molar ratios of oxygen carrier (OC)/NG and steam/NG for reforming were recommended to be 1.7 and 1.0, respectively. The heat integration within CLC and SECLR_HC units can be achieved by circulating hot OCs. The desired temperatures of fuel reactor (FR) and reforming reactor (RR) should be 850 ℃ and 600 ℃, respectively. The heat coupling between CLC and SECLR_HC units can be realized via a jacket-type reactor, and the NG split ratio for reforming and combustion was 0.53:0.47. Under the optimal conditions, the H₂ purity, the H₂ yield and the CH₄ conversion efficiency were 98.76%, 2.31 mol mol^-1 and 97.96%, respectively. The carbon and hydrogen utilization efficiency respectively were 58.60% and 72.45% in terms of the total hydrogen in both steam and NG. The exergy efficiency of the overall process reached 70.28%. In terms of the conventional plant capacity (75×103 t y^-1) and current raw materials price (2500 $ t^-1), the payback period can be 6.2 years and the IRR would be 11.5, demonstrating an economically feasible and risk resistant capability.

2023 Vol. 8, No. 1

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