Surface Micropore Research Articles

Unravelling the properties of microzonal carbon from waste hard rubber by selective thermal transformation via conventional heating and microwave irradiation

Concerns regarding resource limitations and environmental pollution have led humankind towards a circular economy, where the primary objective is to convert waste into resources. In solidarity with the principles of the circular economy, for the first time, we have reported the synthesis of microzonal carbon by microrecycling of waste hard rubber using a conventional furnace (500 °C - 1500 °C; for 20min) and a microwave furnace (500 °C - 950 °C; for 5min). Microzonal carbon has been unveiled here as a hybrid carbon structure composed of ordered and disordered carbons. This study reveals the aspects of micorzonal carbon and analogises the effectiveness and performance of two different heating methods by way of various material characterisations. The overall analysis summarises that due to selective and rapid heating mechanism, the rate of change of structural properties of microzonal carbon, such as d-spacing (d002), crystallite size (Lc), and ID/IG band ratio, as well as the surface morphology, takes place rapidly in microwave heating than conventional heating. And it has been found that with the rise of temperature, the features of microzonal carbon become more prominent, such as the number of ordered carbon zone and mesopore volume increased, while micropore volume, surface area and interlayer spacing decreased. These evolving adjustments of features with temperature eventually ended up producing near-spherical shaped agglomerated microzonal carbon, with approximately 35–45 nm size. Waste hard rubber can have negative impacts on the environment unless they are disposed of properly. Synthesis of microzonal carbon via microrecycling of waste hard rubber can protect the environment from harsh consequences of waste hard rubber and ensure material sustainability to some extent or another. Therefore, microrecycling of waste hard rubber can fabricate a new horizon in the field of renewable carbon material synthesis, in the form of microzonal carbon.

Tailoring the hierarchical porous nitrogen-doped carbon structures loaded single-atomic Ni catalyst for promoting CO2 electrochemical reduction at low CO2 concentration

Although direct reduction of exhaust gases into CO can enable significant economic benefits, the poor activity of CO2 reduction reaction (CO2RR) at low CO2 concentration seriously impedes its application. Herein, a series of Ni single atom sites/nitrogen doped porous carbon materials with different pore sizes were prepared to explore the effect of porosity on the local CO2 concentration in the electrocatalytic process of CO2RR. The results of characterization and experiments demonstrate that surface micropores generated by KOH activation are the key to creating the high local concentration of CO2 around active sites, helping facilitate the reaction kinetics at low CO2 concentration. Therefore, when the reaction is conducted under 20% diluted CO2 condition, the optimal activated macroporous sample exhibits up to nearly 1.3-fold higher faradaic efficiency of CO (FE(CO)) and a 1.7-fold higher of partial current density of CO (jCO) than similar samples without activation. These results offer new insight for designing efficient electrocatalysts for low-concentration CO2 reduction by constructing advanced porous structures.

Improvement of n-Butene Yield in Dimethyl Ether-to-Olefin Reaction Using Ferrierite Zeolite Catalysts

Various ferrierite zeolites were investigated as catalysts for the dimethyl ether (DME)-to-olefin (DTO) reactions to efficiently synthesize n-butene, such as 1-butene, trans-2-butene, and cis-2-butene except for iso-butene using a fixed-bed flow reactor. Twenty P-loaded ferrierite zeolites with different structural parameters and acidic properties were prepared by the impregnation method by varying the P content and the temperature of air calcination as a pretreatment. The zeolites were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, and NH3 temperature-programmed desorption (NH3-TPD). Micropore surface area, external surface area, total pore volume, micropore volume, and weak and strong acid sites affected the DTO reaction behavior. A high n-butene yield (31.2 C-mol%) was observed, which is higher than the previously reported maximum yield (27.6 C-mol%). Multiple regression analysis showed that micropore surface area and strong acid sites had a high correlation with n-butene yield. Based on our findings, we explained the reaction mechanism for selective n-butene synthesis except for iso-butene in the DTO reaction by the dual cycle model.

A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

The study of water vapor adsorption (WVA) isotherms on shales is crucial to comprehend the adsorption–desorption behavior and deposit mechanism of water in shale pore systems. To systematically investigate the relationship between fractal dimension and WVA in shale reservoirs, a new Dent-fractal (DF) model was developed and the ability of different adsorption models to match with WVA experimental data was evaluated. The role of shale pore structure heterogeneity controlling the amount of WVA is also discussed. The results indicate that WVA on shale involves the monolayer–multilayer adsorption and capillary condensation. On the one hand, the GAB and Dent and DF models were found to be the best models for fitting and predicting WVA isotherms in Longmaxi shale. On the other hand, the DLP and DS models had the worst fitting qualities for WVA adsorption data. The pore structure of micropores has a more significant effect on WVA adsorption than that of meso-macropores. The larger surface and pore volume of micropores can provide more adsorption sites and space, which is favorable for WVA. In low-Rh conditions, the higher surface area, the pore surface complexity rises, resulting in higher water vapor monolayer adsorption. Under high-Rh conditions, for shale reservoirs with a highly heterogeneous pore structure, the relationship between the heterogeneous pore structure of the shale and the amount of water adsorbed in multiple layers is not obvious due to the formation of clusters of water molecules.

Preparation of a High-Silicon ZSM-5 Molecular Sieve Using Only Coal Gangue as the Silicon and Aluminum Sources.

The traditional preparation of ZSM-5 molecular sieves relies on chemical reagents to provide silicon and aluminum sources, which are limited as raw materials and cannot be commonly used in production practice. Using coal gangue as the raw material and using medium-temperature chlorination roasting and the pressure acid leaching process to control the silicon-aluminum ratio [n(Si/Al)] of coal gangue, a ZSM-5 molecular sieve was prepared using the alkali melting hydrothermal method. The pressure acid leaching process solved the limitation that kaolinite and mica cannot simultaneously be activated. Under optimal conditions, the n(Si/Al) of the coal gangue increased from 6.23 to 26.14 and complied with the requirements for the synthesis n(Si/Al) of a ZSM-5 molecular sieve. The effect of n(Si/Al) on the preparation of the ZSM-5 molecular sieve was studied. Finally, spherical granular ZSM-5 molecular sieve material with a microporous specific surface area of 169.6329 m2/g, an average pore diameter of 0.6285 nm, and a pore volume of 0.0988 cm3/g was prepared. Providing ideas for the high-value utilization of coal gangue, it is significant for solving the problem of coal gangue solid waste, as well as the problem of ZSM-5 molecular sieve feed stock.

Effect of α-Al2O3 Additive on the Surface Micro-Arc Oxidation Coating of Ti6Al4V Alloy.

α-Al2O3 nanoparticles can enter a micro-arc oxidation coating and participate in the coating-formation process through chemical reaction or physical-mechanical combination in the electrolyte. The prepared coating has high strength, good toughness and excellent wear and corrosion resistance. In this paper, 0, 1, 3 and 5 g/L of α-Al2O3 nanoparticles were added to a Na2SiO3-Na(PO4)6 electrolyte to study the effect on the microstructure and properties of a Ti6Al4V alloy micro-arc oxidation coating. The thickness, microscopic morphology, phase composition, roughness, microhardness, friction and wear properties and corrosion resistance were characterized using a thickness meter, scanning electron microscope, X-ray diffractometer, laser confocal microscope, microhardness tester and electrochemical workstation. The results show that surface quality, thickness, microhardness, friction and wear properties and corrosion resistance of the Ti6Al4V alloy micro-arc oxidation coating were improved by adding α-Al2O3 nanoparticles to the electrolyte. The nanoparticles enter the coatings by physical embedding and chemical reaction. The coatings' phase composition mainly includes Rutile-TiO2, Anatase-TiO2, α-Al2O3, Al2TiO5 and amorphous phase SiO2. Due to the filling effect of α-Al2O3, the thickness and hardness of the micro-arc oxidation coating increase, and the surface micropore aperture size decreases. The roughness decreases with the increase of α-Al2O3 additive concentration, while the friction wear performance and corrosion resistance are improved.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

Ti-6Al-4V intervertebral fusion cage with compatible stiffness, enhanced fatigue life, and osteogenic differentiation

The 3D-printed Ti-6Al-4V intervertebral fusion cage is fabricated to be biocompatible with improved stiffness, fatigue life, and osteogenic differentiation, which are greatly enhanced by heat treatment and surface modification. The flexible cage’s life, which exceeds the standard dynamic fatigue requirement of 5 × 106 cycles based on the ASTM F2077 and F2267 test methods, is achieved by heat treatment at 800 ℃ in argon atmosphere, shot peening, and adjusting the α to β phase ratio to increase mechanical toughness. Surface modification via sandblasting and chemical etching removes the surface oxide layer and forms submicron pores on the surface of the cage, which significantly boosts cell proliferation, differentiation, and osteoblast mineralization. This work exhibits a novel design of Ti-6Al-4V intervertebral fusion cage with biocompatible stiffness, enhanced fatigue life, and improved osteogenic differentiation achieved by reducing residual stress, modifying surface micro-pores, and optimizing microstructure.

Characterization of both anionic and cationic surfactant-modified natural zeolite and its application for removal of metal-ions from aqueous medium

Natural zeolite from Nor Koghb deposit (Armenia) was modified by anionic surfactant sodium dodecyl sulfate and cationic surfactant cetyltrimethylammonium bromide; and the modified samples were used for the removal of metal-ions from aqueous medium. The surface and textural characteristics of both natural and modified zeolites were studied by nitrogen adsorption/desorption isotherms and FTIR methods. The specific surface area, microporous surface area, volume of macro- and microporous both for natural and surfactant-modified zeolites were determined. It was shown that the surfactant-modified zeolites are effective adsorbents for the removal of metal-ions from aqueous medium. It was established that the optimal conditions of Co2+, Ni2+, Fe2+, Cu2+, Zn2+, Mn2+, and Pb2+ metal-ions adsorption are as follows: mMe2+=50 mg/l, Vsolution=500 ml, mSMZ=0.7 g, pH=6.5, T=298 K. Under these conditions, it is possible to remove the 88.27% Co2+, 87.54% Fe2+, 81.37% Ni2+, 76.49% Cu2+, 58.79% Zn2+, 29.32% Mn 2+, 23.49% Pb2+ and 75% Cr(VI) from single-component system. In the multi-component system, the effectiveness of metal-ions removal is lower. From presented study, it is allowed that due to the low cost, industrial quantities availability of the natural Armenian zeolite and the high efficiency of their surfactant-modified samples as metal-ions removal sorbents, as well as easy and non-valuable process of modification, they can find wide application as effective adsorbents for purification of wastewaters.

TS-1 with Abundant Micropore Channel-Supported Au Catalysts toward Improved Performance in Gas-Phase Epoxidation of Propylene

The gas-phase propylene epoxidation reaction catalyzed by Au/TS-1 has attracted great attention due to its clean and efficient merits. However, high conversion of propylene (>10%) and high selectivity of propylene oxide (PO) (>90%) often cannot be obtained at the same time. Although a variety of TS-1 supports with different microstructures have been developed to improve the catalytic performance, few have met the above criteria. In this work, we have reported a silane-assisted strategy to prepare TS-1-CTES zeolites containing abundant micropore channels, which showed both high propylene conversion (13.3%) and high PO selectivity (92.7%). The silane, (3-chloropropyl) triethoxysilane (CTES), not only participates in constructing the MFI framework but also serves as a spatial filling agent to build secondary micropore channels. Ar physisorption characterization exhibited the increased micropore volume and surface area of the as-synthesized TS-1-CTES, which benefit molecule diffusion. XPS results showed an enriched Ti concentration on the surface of TS-1-CTES and a decreased electron density of Ti atoms. A few more Au nanoparticles were proved to be distributed inside the TS-1-CTES crystal compared with those inside TS-1. The optimized distribution of Au and Ti active sites in Au/TS-1-CTES enhanced their synergistic catalytic effects. The PO formation rate remained relatively stable for 24 h, superior to traditional Au/TS-1. The construction of a micropore-rich TS-1 structure opens a way for the reasonable design and manufacture of the Au/TS-1 catalyst, for the gas-phase epoxidation of propylene.

Evolution of pore structures and fractal characteristics of coal-based activated carbon in steam activation based on nitrogen adsorption method

To investigate the structures and fractal characteristics of micro- and mesopores during steam activation, a series activated carbons were prepared from Datong bituminous coal by physical activation at 750 and 850 °C. Low-temperature nitrogen adsorption and Frenkel-Halsey-Hill model were employed to determine the fractal dimensions of pore structures. The results demonstrate that micro- and mesopore structures were fully developed during steam activation, and activation at 750 °C was conducive to the development of pore structures, especially mesopores. The samples had similar pore size distributions that the micropore diameters mainly centered at 0.4–0.8 nm and 1.2–1.8 nm, and the mesopores mainly distributed in the range of 2–9 nm. The variation of surface and structure fractal dimensions for activated carbons with different burn-offs indicated that the surface roughness and structure complexity changed during activation process. The fractal dimensions of micropore surface (D1) and micropore structure (D2) had positively linear correlation with Smic/SBET and Vmic/Vtot, respectively. While the mesopore surface fractal dimensions (D1’) have a negative association with Sext/SBET, and the structure fractal dimensions (D2’) have a negative but weak association with Vmes/Vtot.

Improvement of Core–Shell Lightweight Aggregate by Modifying the Cement–EPS Interface

To improve the interfacial compatibility between cement matrix and expanded polystyrene (EPS) in core-shell lightweight aggregates (CSLA), the effects of sodium silicate, polyvinyl acetate (PVA) emulsion, vinyl acetate-ethylene (VAE) emulsion, acrylic acid, and acetic acid on the cement-EPS interface were investigated. The density of the interface was studied by scanning electron microscopy (SEM), and the effect of interfacial agents on the hydration process of cement was studied by the heat of hydration and induction resistivity. The macroscopic properties of the interface of the CSLA were characterized by the "leak-white" rate, drop resistance, and numerical crushing strength. The results show that the sodium silicate densifies the interface by generating hydration products on the EPS surface. At the same time, organic acid enhances the interfacial properties of EPS and cement by increasing the surface roughness, and allowing hydration products to grow in the surface micropores. In terms of the cement hydration process, both interfacial agents delay the cement hydration. Above all, with comprehensive interface properties, "leak-white" rate, and mechanical properties, VAE emulsion and sodium silicate can achieve the best performance with a final crushing resistance of 5.7 MPa, which had a 46% increase compared with the reference group.

Влияние примеси метана при разложении ацетилена на размер и морфологию частиц образующейся сажи

The paper studied the effect of acetylene or its methane mixture pressure at decomposition in the laboratory cylindrical reactor with spark ignition to obtain the acetylene soot. Size range of the formed particles and their surface morphology were determined by scanning and transmission electron microscopy. Specific surface area distributions over the pore radii and evaluation of the acetylene soot samples particle size were identified using the adsorption method of limited evaporation. All the experimental methods used confirmed significant decrease in the acetylene soot particle size at the increase in the acetylene initial pressure during its decomposition. Accordingly, the particles specific outer surface increased, but the microporous specific surface of the particles outer shell practically was not changing. Methane present in the mixture with acetylene in decomposition significantly increased the particles size and reduced both the specific outer surface and the microporous surface of the soot particles shell. It is shown that the proposed method for analyzing distributions of the acetylene soot specific surface area over the pore radii makes it possible to estimate with high accuracy particle sizes, total soot specific surface area and contribution of various factors forming this surface

Development of a Zeolite H-ZSM-5-Based D-μSPE Method for the Determination of Organophosphorus Pesticides in Tea Beverages

In this study, a novel dispersive micro-solid phase extraction (D-μSPE) technique with H-ZSM-5 zeolite as an adsorbent was developed for the determination of 21 trace pesticides in tea beverages. The adsorption and desorption of H-ZSM-5 zeolites were investigated based on structural characteristics and adsorption properties similar to those of H-beta zeolites. In combination with the properties of the adsorbates, it was explained that the adsorption reaction occurred on the microporous surface and mesopores of H-ZSM-5. Based on optimal parameters, the beverage samples were extracted by 50 mg of zeolite within 1 min. The zeolite was eluted with 2 mL of an acetonitrile-water mixture after separation, and the eluent was filtered prior to HPLC-MS/MS analysis. The D-μSPE protocol demonstrated acceptable accuracy and precision, with recoveries between 62.1% and 106.6% and relative standard deviations of 1.4% to 12.6%, as validated by analytical reliability. The correlation coefficient in the linear range of 0.2–50 ng·mL−1 was greater than 0.98, with limits of detection of 0.05–0.1 ng·mL−1 and limits of quantification of 0.1–0.2 ng·mL−1. The matrix effects ranged from 76.2% to 112.7%. The results indicate that the novel D-μSPE technique based on H-ZSM-5 is a rapid, simple, green and economical method for the determination of pesticide residues in tea beverages. The proposed method achieved simultaneously low adsorbent dosage, 20-fold enrichment factor, rapid pre-concentration in 12 min, minimal organic wastes, and effective reduction of matrix interference.

Characterization of physicochemical properties of activated carbons prepared from penicillin mycelial residues and its adsorption properties for VOCs

In this study, adhering to the concept of "treat waste with waste", the physicochemical properties of activated carbons (ACs) prepared from penicillin mycelial residues (PMR) was characterized, and the adsorption performance of ACs for VOCs was explored. The results showed that AC230–1 exhibited the largest specific surface area (2187.50 m2/g), while AC290–0.5 exhibited the largest microporous surface area (1624.81 m2/g). With the increase of KOH ratio, microporous surface area of ACs decreased gradually, and the pore size distribution of ACs gradually developed to large micropores and mesopores. XRD and Raman results showed that AC290–0.5 had better graphite microcrystalline structure and stability. FT-IR results showed that ACs had similar surface functional groups, and XPS results indicated that AC290–0.5 contained more CO, C-OH, and abundant N-containing functional groups, which could effectively improve the adsorption capacity of ACs for VOCs. AC290–0.5 exhibited the highest dichloromethane (DCM) saturation adsorption capacity (204.83 mg/g), trichloroethylene (TCE) saturation adsorption capacity (732.59 mg/g) and chlorobenzene (CLB) saturation adsorption capacity (735.90 mg/g). The Y–N model could perfectly fit the adsorption breakthrough curve of ACs for VOCs, and adsorption kinetics indicated that the adsorption of ACs for VOCs was mainly physical adsorption. The microporous and surface chemical group of AC were the main factors that determined its adsorption capacity for VOCs.

Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure

Adsorption agents are an important class of solid hydrogen storage materials. Attributed to their high specific surface area and adjustable nanopore structure, activated carbon nanofibers have attracted extensive attention in the application of solid hydrogen storage. The research in this field mostly focuses on applications with a hydrogen pressure condition of 30 to 300 bar, while there have been few systematic studies on the hydrogen storage performance of these materials under ambient pressure. In this study, polyacrylonitrile-based activated carbon nanofibers were constructed by electrospinning technology and ultrasonic-assisted activation technology for the application of atmospheric hydrogen storage. Their nanopore structure was revealed to be mainly composed of micropores, and the relative contents of micropore volume and ultramicropore volume were 77.92% to 88.3% and 22.34% to 24.68%, respectively. Attributed to the synergy of rich microporous structure and surface chemical structure, the atmospheric hydrogen storage density of activated carbon nanofibers could reach 2.64 wt% at 77 K and 1 bar. After the optimization analysis of adsorption isotherm models, the Multisite-Langmuir model was found as more suitable for accurately describing the atmospheric hydrogen adsorption process of activated carbon nanofibers. Cited as: Yu, J., Lin, T., Li, J., Zhang, W., Bao, W., Zhu, B. Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure. Capillarity, 2023, 6(3): 49-56. https://doi.org/10.46690/capi.2023.03.02

Evaluation of selenite reduction under salinity and sulfate stress in anaerobic membrane bioreactor.

Current microbial reduction technologies have been proven to be suitable for decontaminating industrial wastewaters containing high concentrations of selenium (Se) oxyanions, however, their application is strictly limited by the elemental Se (Se0) accumulation in the system effluents. In this work, a continuous-flow anaerobic membrane bioreactor (AnMBR) was employed for the first time to treat synthetic wastewater containing 0.2mM soluble selenite (SeO3 2-). The SeO3 2- removal efficiency by the AnMBR was approachable to 100% in most of the time, regardless of the fluctuation in influent salinity and sulfate (SO4 2-) stress. Se0 particles were always undetectable in the system effluents, owing to their interception by the surface micropores and adhering cake layer of membranes. High salt stress led to the aggravated membrane fouling and diminished content ratio of protein to polysaccharide in the cake layer-contained microbial products. The results of physicochemical characterization suggested that the sludge-attached Se0 particles presented either sphere- or rod-like morphology, hexagonal crystalline structure and were entrapped by the organic capping layer. According to the microbial community analysis, increasing influent salinity led to the diminished population of non-halotolerant Se-reducer (Acinetobacter) and increased abundance of halotolerant sulfate reducing bacteria (Desulfomicrobium). In the absence of Acinetobacter, the efficient SeO3 2- abatement performance of the system could still be maintained, as a result of the abiotic reaction between SeO3 2- and S2- generated by Desulfomicrobium, which then gave rise to the production of Se0 and S0.

Adsorption of Carotene from Crude Palm Oil by Activated Achalla Clay

High costs of imported bleaching earths have led to the need for alternative local sources. The effectiveness of acid-activated Achalla clay in crude palm oil bleaching was examined. The clay sample was collected, sun-dried, manually ground, and activated with the hydrochloric acid solution. Characterization of the raw and activated clay samples was carried out using X-ray fluorescence (XRF), Scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analyses. The factors that were varied during the bleaching process were temperature, contact time, and adsorbent dosage. The adsorption kinetics, adsorption isotherm, and thermodynamics studies were also investigated. The XRF, SEM, and FTIR characterization results showed that the clays were kaolinites with some significant increase in the number of microporous surfaces and some changes in the functional groups. The results also indicated that the process performance improved at higher temperatures. The highest bleaching efficiency of the bleaching process was 85.6%. The pseudo-first-order model described the adsorption process from the experimental data with higher correlation coefficients than the pseudo-second-order, first-order, and Intra-particle diffusion models. The equilibrium isotherm data were described better by the Temkin model than Langmuir and Freundlich models due to higher R2 values. The enthalpy and entropy values were determined to be 26,968.12 J/mol and 78.2273 J/mol respectively. The Gibb’s free energy was found to vary between -1.428.39 to 1,700.70 J/mol. The results of the thermodynamic parameters showed that it was a spontaneous chemical adsorption process and endothermic. This study has revealed that acid-activated Achalla clay can be used for the bleaching of crude palm oil at higher temperatures.

Systematic Thiol Decoration in a Redox-Active UiO-66-(SH)2 Metal-Organic Framework: A Case Study under Oxidative and Reductive Conditions.

The practical applicability of thiolated metal-organic frameworks (MOFs) remains challenging due to their low crystallinity and transient stability. Herein, we present a one-pot solvothermal synthesis process using varying ratios of 2,5-dimercaptoterephthalic acid (DMBD) and 1,4-benzene dicarboxylic acid (100/0, 75/25, 50/50, 25/75, and 0/100) to prepare stable mixed-linker UiO-66-(SH)2 MOFs (ML-U66SX). For each variant, the effects of different linker ratios on the crystallinity, defectiveness, porosity, and particle size have been discussed in detail. In addition, the impact of modulator concentration on these features has also been described. The stability of ML-U66SX MOFs was investigated under reductive and oxidative chemical conditions. The mixed-linker MOFs were used as sacrificial catalyst supports to highlight the interplay of template stability on the rate of the gold-catalyzed 4-nitrophenol hydrogenation reaction. The release of catalytically active gold nanoclusters originating from the framework collapse decreased with the controlled DMBD proportion, resulting in a 59% drop in the normalized rate constants (9.11-3.73 s-1 mg-1). In addition, post-synthetic oxidation (PSO) was used to further probe the stability of the mixed-linker thiol MOFs under harsh oxidative conditions. Following oxidation, the UiO-66-(SH)2 MOF underwent immediate structural breakdown, unlike other mixed-linker variants. Along with crystallinity, the microporous surface area of the post-synthetically oxidized UiO-66-(SH)2 MOF could be increased from 0 to 739 m2 g-1. Thus, the present study delineates a mixed-linker strategy to stabilize the UiO-66-(SH)2 MOF under harsh chemical conditions through meticulous thiol decoration.

Encapsulation of Redox p-Benzoquinone into Microporous Carbon Frameworks by a Diamine Covalent-Grafted Strategy for Aqueous Hybrid Supercapacitors

Aqueous hybrid supercapacitors (AHSs) with a wide operating voltage and intrinsic safety are emerging as promising energy storage devices, while their energy densities are still greatly restricted by carbon-based negative electrodes. Developing a high-performance redox system for carbon electrodes is one of the potential strategies to realize the practical utilization of AHSs. Herein, we present a covalent-grafted strategy to encapsulate redox p-benzoquinone (PBQ) into microporous carbon frameworks by using p-phenylenediamine (PPD) as a bridging agent. Both experimental and theoretical analysis reveal that the diamine groups from PPD play a vital role in chemically bonding PBQ with the microporous surfaces of carbon materials, which deliver a great deal of electronic delocalization throughout the redox-active sites and conductive carbon regions. As such, the obtained carbon electrodes grafted by the redox PBQ and PPD species facilitate charge transfer and consequently exhibit excellent charge storage performances. These are highlighted by an extremely high specific capacitance of 377 F g–1 at a current density of 0.5 A g–1 and 276 F g–1 at 100 A g–1 with a superior rate capability of 73%. Impressively, the assembled AHSs based on covalently grafted carbon electrodes (AC-PPD-PBQ) and NiCoAl-layered double hydroxides/carbon nanotubes (NiCoAl-LDH@CNT) demonstrate a maximum energy density of 70.9 W h kg–1 with a wide voltage window of 1.8 V and good cycling stability with 84.4% of initial capacitance after 5000 cycles. This work provides insights into the fabrication of high-performance carbon electrodes by encapsulating redox species into microporous frameworks.