Specific Area Research Articles

Palladium nanocrystals immobilized on boron and nitrogen codoped mesoporous carbon spheres as efficient methanol oxidation electrocatalysts

The development of cost-effective and high-performance electrocatalysts is crucial for the widespread application of direct methanol fuel cell. Herein, a convenient and robust method is developed to the controllable fabrication of Pd nanocrystals in situ immobilized on boron and nitrogen codoped mesoporous carbon spheres (Pd/BNMCS) as anode catalysts for the methanol oxidation reaction. The as-derived Pd/BNMCS hybrids are equipped with a series of useful structural features, such as large specific surface area, abundant mesoporous channels, presence of plentiful B and N atoms, well-dispersive Pd nanoparticles, and good electrical conductivity. As a consequence, the optimized Pd/BNMCS catalyst demonstrates superior electrocatalytic methanol oxidation properties in terms of a large electrochemically active surface area, high mass/specific activities, and reliable long-term stability, which are significantly better than those of traditional carbon black and undoped mesoporous carbon sphere supported Pd catalysts. This study highlights the potential of heteroatom codoped mesoporous carbon matrixes in the construction of advanced noble metal electrocatalysts for practical fuel cell applications.

Laccase immobilized on amino modified magnetic biochar as a recyclable biocatalyst for efficient degradation of trichloroethylene

Bioremediation of trichloroethylene (TCE) contaminated groundwater has recently attracted considerable attention. In this study, laccase was immobilized on amino modified magnetic pine biochar (MBC-NH2) by adsorption-crosslinking-covalent binding method, and its application in the degradation of TCE was evaluated. MBC-NH2 was obtained from pine sawdust by calcination, magnetic modification and amino modification. MBC-NH2 had high specific surface area (71.3 m2/g), rich surface functional groups and good magnetism. Under the conditions of 25 °C, pH = 4, glutaraldehyde (GA) concentration of 7 %, crosslinking time of 1 h, laccase concentration of 0.75 mg/mL, and immobilization time of 7 h, the loading capacity of laccase on MBC-NH2 carrier was as high as 782 mg/g. Compared with free laccase, immobilized laccase showed higher pH stability and thermal stability, and its activity remained 48.5 % after being reused for 10 times, and 80.8 % after being stored at 4 °C for 30 days. The immobilized laccase exhibited a good degradation effect on TCE. At 25 °C, pH = 4, immobilized laccase concentration of 0.35 g/L, and initial TCE concentration of 10 mg/L, the degradation efficiency of TCE by immobilized laccase was as high as 92.1 % within 48 h. In addition, the degradation products of TCE were analyzed, and the results showed that immobilized laccase could degrade TCE into non-toxic products through epoxidation, hydroxylation, and dechlorination. The immobilized laccase biocatalyst prepared in this study can achieve efficient degradation of TCE, which provides a feasible solution for chlorinated pollution of water resources. These research results are of great significance for the synthesis of biocatalysts for the efficient degradation of chlorinated hydrocarbons.

Ultrasonic-Assisted Synthesis of Lead Citrate as Precursor for Preparation of Lead Oxide from Lead Sulfate

ABSTRACT In this study, an efficient method of lead recovery from lead sulfate in spent lead-acid batteries assisted by ultrasonic is developed using the citric acid–sodium citrate solution. Ultrasonic-assisted technology is employed to enhance the kinetics of lead sulfate leaching. Initially, the predominance area of the lead citrate complexes was analyzed. The study was conducted to evaluate the effect of ultrasonic-assisted technology on the kinetic behavior of lead sulfate within the citric acid–sodium citrate solution, thereby unveiling the differences between ultrasonic-assisted leaching and the non-ultrasonic-assisted leaching. Kinetic study indicated that the employment of ultrasonic-assisted technology could effectively reduce the apparent activation energy during the desulfurization process, decreasing the energy initially required from 43.27 kJ/mol to 35.15 kJ/mol. Furthermore, the ultrasonic-assisted leaching led to successful preparation of lead citrate precursor, characterized by a smaller particle size and larger specific surface area. Systematic investigations were performed on the thermal decomposition process of these precursors and the effects of calcination temperature and holding time on the properties of calcination products. It was revealed that pure porous lead oxide powder with a purity of 99.9% could be produced successfully under the conditions of calcination temperature at 350°C and holding time of 1 h. The research provides an innovative process for the efficient recovery of lead from spent lead acid batteries.

Synthesis of heterogeneous nanocomposite catalyst ZrO2@SBA-15 for formic acid production from hemicelluloses

Heterogeneous nanocomposite ZrO2@SBA-15 catalysts containing 10 wt. % of zirconium oxide were synthesized by two methods: co-condensation and incipient wetness impregnation. The silica support and catalysts were characterized by X-ray diffraction, gas adsorption, FTIR-spectroscopy and other physicochemical methods. As a result of zirconia introduction into the silica wall, the mesostructured of SBA-15 is preserved, but the specific surface area and pore Volume are reduced. It was established that during one-stage co-condensation synthesis, the particle fibers shorten and stick together. The catalysts were tested in the process of catalytic hydrolysis-oxidation of hemicelluloses of aspen wood. The optimal formic acid synthesis conditions were determined: 150°С, 3 h. The highest formic acid yield obtained over the catalyst obtained by co-condensation under best reaction conditions was 28.4 wt. %.

Characterization and Greenhouse Trial of Zn Bio-Chelates Derived from Spent Coffee Grounds

The conversion of spent coffee grounds (SCG) into hydrochars has been the subject of extensive research in recent years, aimed at evaluating their potential for biofortifying foods and mitigating the plant toxicity linked to SCG. This study aimed to assess the physicochemical characterization and the impact of incorporating both activated (ASCG and AH160) and functionalized SCG (ASCG-Zn), as well as SCG-derived hydrochars (AH160-Zn), on cucumber yield and plant zinc content. The following physicochemical properties were analyzed: specific surface area, pH and electrical conductivity, polyphenols, and nuclear magnetic resonance. The by-products activated and functionalized with zinc were applied to cucumber crops grown in a greenhouse across multiple harvests. The activation of both SCG and H160 reduced the specific surface area of the particles. However, when these by-products were functionalized, their Zn content increased significantly, up to 7400 ppm. Concerning polyphenol content, the activated products showed levels ranging from 3.5 to 4.9 mg GAE/g. Regarding cumulative production, the treatments that showed the highest yields were the by-products activated and functionalized with Zn reaching 25 kg. Incorporating these by-products notably raised the Zn content in cucumbers, reaching 0.1 mg Zn per 100 g of fresh weight. The activated by-products demonstrated the highest Zn utilization efficiency.

A N-heterocyclics induced π-π interaction strategy to synthesis hyper-crosslinked polymers with enhanced porosity for xenon adsorption

Hyper-crosslinked polymers (HCPs) with large specific surface areas play an important role in gas adsorption and separation. However, the method to enhance the specific surface area of HCPs and gas adsorption performance without changing the polyaromatic hydrocarbons (PAHs) monomer structure and reaction condition is still missing. Here, we present a general and facile N-heterocyclics induced π-π interaction strategy to increase the specific surface area of HCPs by simply adding N-heterocyclics during the Friedel-Crafts alkylation reaction. The specific surface areas of HCP (tetraphenylmethane based HCPs, TPMBPy-TCM) increased up to 7.78 times compared to the one without adding N-heterocyclics. The crosslinking and stacking of PAHs was influenced by the π-π stacking between the N-heterocyclic complexes and PAHs. More importantly, N-heterocyclics coordinated with Lewis acids have lower electron density and do not react with PAHs in the Friedel-Crafts alkylation reaction, which can be removed easily from HCPs. The HCPs obtained shown good xenon adsorption performance with Xe uptake of 3.63 mmol/g, which is the highest value for organic adsorbents reported in literature. This work provides new insight into the preparation of high-performance HCPs.

Research on 4N8 High-Purity Quartz Purification Technology Prepared Using Vein Quartz from Pakistan

This study investigates the potential of two quartz vein ores from the Hunza District, Gilgit-Baltistan, Pakistan, as raw materials to obtain 4N8 high-purity quartz (HPQ) sand. Various quartz purification processes were examined, including ore calcination, water quenching, flotation, sand calcination, acid leaching, and chlorination roasting. Analytical techniques such as optical microscopy, Raman spectroscopy, and inductively coupled plasma spectroscopy were employed to analyze the microstructure, inclusion characteristics, and chemical composition of both the quartz raw ore and the processed quartz sand. Microscopic observation reveals that the PK-AML quartz raw ore has relatively high purity, the secondary fluid inclusions are arranged in a directional–linear manner or developed along crystal micro-cracks, and most intracrystalline regions exhibit low inclusion contents, while the PK-JTLT quartz raw ore contains a certain number of melt inclusions. The two processed quartz sand samples exhibit a smooth surface with extremely low fluid inclusion content. A comparative analysis of different purification processes shows that quartz sand calcination has a higher impurity removal rate than ore calcination. After crushing the raw ore into sand, the particles become finer with a larger specific surface area. Quartz sand calcination maximally exposes the inclusions and lattice impurity elements within the quartz, facilitating subsequent impurity removal through acid leaching. Following the processes of crushing, ultrasonic desliming, flotation, sand calcination, water quenching, acid leaching, and chlorination roasting, the SiO2 content of PK-AML processed quartz sand is 99.998 wt.%, with only a small amount of Ti and Li remaining, and a total impurity element content of 20.83 µg·g−1. This meets the standard requirements for crucible preparation in industrial applications, making this vein quartz suitable for producing high-end HPQ products. In contrast, the overall purity of PK-JTLT quartz is lower, and the high contents of impurity elements such as Li, Al, and Ti are difficult to remove via purification experiments. The SiO2 content of PK-JTLT processed quartz sand is 99.991 wt.%, which is applied to higher-quality glass products such as photovoltaic glass, electronic glass, and optical glass, thus presenting broad prospects for application.

Highly active Cu2O/CoCo-PBA S-scheme heterojunction for enhanced visible-light-driven hydrogen evolution

Prussian blue analogues is a unique class of organic-inorganic hybrid materials that have garnered significant attention in the field of photocatalysis due to their large specific surface area and abundant active sites. However, their potential is limited by the challenge of photogenerated charge carrier recombination. To address this issue, we successfully synthesized a tightly coupled Cu2O/CoCo-PBA S-scheme heterojunction catalyst using ultrasound-assisted and thermal treatment methods, aiming to reduce the recombination of photogenerated charge carriers. In this system, CoCo-PBA serves as the electron donor, while Cu2O acts as the electron acceptor. The closely coupled interface between these materials shortens the electron transfer distance. Under 10 W white light irradiation, the Cu2O/CoCo-PBA composite photocatalyst demonstrated remarkable hydrogen evolution activity, with a hydrogen production rate of 5.98 mmol⋅g⁻¹⋅h⁻¹, which is 6.4 times that of CoCo-PBA alone. This S-scheme heterojunction strategy lays the groundwork for the design and large-scale application of highly active visible-light-driven photocatalysts.

Sonochemical preparation of powerful S-scheme Zr(HPO4)2/g-C3N4 heterojunction for photocatalytic degradation of rhodamine B under natural solar radiations

An effective Zr(HPO4)2/g-C3N4 S-scheme heterojunction was synthesized by sonochemical coupling of Zr(HPO4)2 nanoparticles as an oxidative photocatalyst [EVB = +3.0 eV] with g-C3N4 nanosheets as an effective reductive photocatalyst [ECB = −1.25 eV] for photocatalytic degradation of rhodamine B dye under natural solar radiation of 1000 W power. The physicochemical properties of the as-synthesized heterojunctions were investigated by X-ray diffraction [XRD], N2-adsorption-desorption isotherm, diffuse reflectance spectrum [DRS], photoluminescence [PL], scanning electron microscope [SEM], X-ray photoelectron spectroscope [XPS], and high resolution transmission electron microscope [HRTEM]. The experimental results implied the agglomeration of Zr(HPO4)2 nanoparticles on g-C3N4 sheets which reduced the specific surface area of the solid specimen from 88 to 21 m2/g. The significant increase in the photocatalytic degradation rate of RhB dye with introducing Zr(HPO4)2 nanoparticles implied that Zr(HPO4)2 plays a crucial role in reducing the band gap energy and remarkable increasing in the rate of electron-hole separation. The photocatalytic experiments implied that incorporation of 5 wt% Zr(HPO4)2 on g-C3N4 sheets destroyed 98 % of RhB dye during 3 h of light illumination with pseudo-first-order rate of 0.048 min−1. The remarkable enhancement in the photocatalytic performance of Zr(HPO4)2/g-C3N4 heterojunctions was ascribed to successful generation of an effective S-scheme heterojunction with strong redox power, utilizing of both hydroxyl and superoxide radicals in the degradation process and limiting the electron-hole recombination rate. Based on scavenger experiments and terephthalic acid PL analysis, the S-scheme pathway was chosen as the proposed mechanism for photocatalytic charge transfer. The as-synthesized Zr(HPO4)2/g-C3N4 heterojunction with exceptional redox power is considered a novel candidate for destructing organic pollutants that exist in industrial wastewater.

Biomass-Derived-Carbon-Supported Spinel Cobalt Molybdate as High-Efficiency Electrocatalyst for Oxygen Evolution Reaction.

Ananas comosus leaves were converted to a porous graphitized carbon (GPLC) material via a high-temperature pyrolysis method by employing iron salt as a catalyst. A cobalt molybdate (CoMoO4)-and-GPLC composite (CoMoO4/GPLC) was then prepared by engineering CoMoO4 nanorods in situ, grown on GPLC. N2 adsorption-desorption isothermal curves and a pore size distribution curve verify that the proposed composite possesses a porous structure and a large specific surface area, which are favorable for charge and reactant transport and the rapid escape of O2 bubbles. Consequently, the as-synthesized CoMoO4/GPLC shows low overpotentials of 289 mV and 399 mV to afford the current densities of 10 mA cm-2 and 100 mA cm-2 towards the oxygen evolution reaction (OER), which is superior to many CoMoO4-based catalysts in previous studies. In addition, the decrease in current density is particularly small, with a reduction rate of 3.2% after a continuous OER procedure for 30 h, indicating its good stability. The excellent performance of the CoMoO4/GPLC composite proves that the GPLC carrier can obviously impel the catalytic activity of CoMoO4 by improving electrical conductivity, enhancing mass transport and exposing more active sites of the composite. This work provides an effective strategy for the efficient conversion of waste ananas comosus leaves to a biomass-derived-carbon-supported Co-Mo-based OER electrocatalyst with good performance, which may represent a potential approach to the development of new catalysts for OER, as well as the treatment of waste biomass.

Preparation of a MIL-125/MoS2/SiO2 Ternary Nanohybrid and Its Smart Electrorheological Behavior.

In this work, a kind of ternary hybrid material, MIL-125/MoS2/SiO2, was prepared by a solvothermal and Stöber method. In this system, MIL-125, as the matrix material, not only furnishes a large specific surface area for MIL-125/MoS2/SiO2, thereby providing a basis for stronger interfacial polarization, but also effectively enhances the antisettlement ability of the electrorheological fluids (ERFs). Different characterizations, such as scanning electron microscopy, transmission electron microscopy, XRD, XPS, FT-IR, BET, electron mapping, etc., were used to analyze the ternary nanohybrid. The ERFs prepared by combining the different advantages of the three materials in the hybrid system were studied by a HAAKE high-speed rotary rheometer. In addition, the combination of MoS2 and SiO2 provides suitable electrical conductivity and dielectric properties for the system to promote the generation of interface polarization, ensuring that the entire system exhibits stronger electrorheological behavior without electrical breakdown and thus obtains higher shear stress.

The Influence of Thermal Treatment of Activated Carbon on Its Electrochemical, Corrosion, and Adsorption Characteristics

Activated carbons can be applied in various areas of our daily life depending on their properties. This study was conducted to investigate the effect of thermal treatment of activated carbon on its properties, considering its future use. The characteristics of activated carbon heat-treated at temperatures of 1500, 1800, and 2100 °C based on its future use are presented. The significant effect of the treatment temperature on morphological, adsorption, electrochemical, and corrosion properties was proved. Increasing the temperature above 1800 °C resulted in a significant decrease in the specific surface area (from 969 to 8 m2·g−1) and material porosity—the formation of mesopores (20–100 nm diameter) was observed. Simultaneously, adsorption capability, double layer capacity, and electrochemically active surface area also decreased, which helped to explain the shape of cyclic voltammograms recorded in 2,4-dichlorophenoxyacetic acid and in supporting electrolytes. However, a significant increase in corrosion resistance was found for the carbon material treated at a temperature of 2100 °C (corrosion current decreased by 23 times). Comparison of morphological, adsorption, corrosion, and electrochemical characteristics of the tested activated carbon, its applicability as an electrode material in electrical energy storage devices, and materials for adsorptive removal of organic compounds from wastewater or as a sensor in electrochemical determination of organic compounds was discussed.

Spontaneous combustion coal gangue-based composite cement: Compressive performance and environmental benefits under grinding kinetics control

This study aims to tackle the environmental pressure of spontaneous combustion coal gangue by using its active silica-alumina content to create eco-friendly composite cement through a low-energy process. The Divas-Aliavden grinding kinetics equation was established, and powder characteristics were analyzed using particle size distribution, the Rosin-Rammler-Bennett model, and fractal dimension theory. The compressive performance of the coal gangue-based composite cement was tested. A comprehensive evaluation model linked grinding time, powder characteristics, compressive performance, and energy consumption, while also analyzing hydration products and environmental impact. Results showed that initial grinding stages had larger particle sizes and higher energy utilization efficiency. As grinding progressed, energy consumption increased. A grinding time of 35 min achieved optimal balance between energy efficiency and compressive performance, improving particle distribution uniformity and complexity. The compressive performance of the composite cement reached 95 % of ordinary Portland cement after 28 days of curing. The evaluation model indicated that specific surface area, d50, and fractal dimension are key factors influencing energy efficiency, determining energy consumption and particle distribution during grinding. Environmental assessment revealed that substituting 30 % of cement with coal gangue could reduce CO2 emissions by 250 kg CO2/t, achieving a reduction rate of 29.5 %. This study supports the large-scale application of spontaneous combustion coal gangue, contributing to efficient resource utilization and environmental protection.

Nanoscale pore structure and fractal characteristics of lacustrine shale: A case study of the Upper Cretaceous Qingshankou shales, Southern Songliao Basin, China.

The Upper Cretaceous Qingshankou Formation's lacustrine shales in the Songliao Basin are among China's most promising shale oil reservoirs. To elucidate their pore and fractal characteristics, a comprehensive set of analyses encompassing total organic carbon (TOC), X-ray diffraction (XRD), and low-temperature N2 adsorption (LTNA), Rock-Eval pyrolysis experiments and two-dimensional nuclear magnetic resonance (2D-NMR) were conducted. Using the Frenkel-Halsey-Hill (FHH) method, fractal dimensions (D) were calculated, and their relationship with pore metrics and shale compositions were explored. Two distinct fractal dimensions, D1 (0 < P/P0 < 0.5) and D2 (0.5 <P/P0 <1.0), were derived from LTNA isotherms via the FHH approach. D1 values fluctuated between 2.5715 and 2.7551 (mean 2.6564), while D2 spanned from 2.3247 to 2.4209 (mean 2.3653). Notably, D1 consistently surpassed D2, signifying that smaller pores exhibit greater homogeneity compared to their larger counterparts. D1 gradually increases with the increase of clay content. A direct correlation was observed between pore volume (PV), specific surface area (SSA), and D (both D1 and D2), whereas the association between average pore diameter (APD) and D was inverse. Both D1 and D2 escalated with diminishing TOC, 2D-NMR solid organic matter (OM), S1 content and 2D-NMR light oil. Intriguingly, D1 showed a stronger association with key pore and "sweet spot" parameters, highlighting its utility in assessing pore structural complexity and shale oil potential. This study illustrates how fractal theory enhances our understanding of pore structures and the shale oil enrichment process for the lacustrine shale.

Emerging Horizons in Gas Sensing: Exploring the Potential of MXenes and MBenes.

This review article is focused on the development and application of two types of emerging two-dimensional (2D) materials, namely MXenes and MBenes, in the field of gas detection. Owing to its excellent electrical conductivity, specific surface area, and tunable surface functionality, MXenes have demonstrated high sensitivity and rapid response in detecting a variety of gases, such as volatile organic compounds (VOCs), nitrogen dioxide (NO2), and ammonia (NH3). MBenes are relatively newly discovered materials with excellent electronic stability and gas adsorption capabilities. Both of these materials demonstrate significant potential in improving sensor selectivity and stability through surface functionalization and heterostructure designs. However, despite the impressive gas detection performance of these materials, challenges remain in achieving long-term stability, cost-effectiveness, and commercialization. We summarize the prominent research insights on these materials and offer an outlook on future research directions and potential applications. With ongoing research and technological advancements, MXenes and MBenes are anticipated to have a substantial impact in critical areas such as environmental monitoring and industrial safety.

Exploration of Changes in Coal Pore Characteristics and Gas Adsorption Characteristics Based on Influence of Stress

As the mining depth increases, the effect of stress on the gas adsorption of coal gradually becomes significant. There are significant differences in the pore volume, specific surface area, and adsorption characteristics of coal before and after stress. In this study, the porosity variation characteristics of coal were studied using axial and confining pressure loading processes, and volumetric stress was introduced to characterize the pore variation law of coal under triaxial stress. By calculating the stress values at different burial depths, gas isothermal adsorption experiments were conducted on coal under different stress effects. The Langmuir equation, D-A equation, and Freundlich empirical formula were used to fit the adsorption experimental results. Combining experiments and models to predict the adsorbed and free gas content under stress, we described the gas adsorption law of coal under different stress effects.

Effects of indigenous microorganisms on the CO2 adsorption capacity of coal

The adsorption capacity of coal is a crucial criterion for CO2 sequestration in deep unminable coal seams. Previous studies have documented how indigenous microorganisms interact with supercritical carbon dioxide (ScCO2) in coal. But how these interactions affect the adsorption capacity were rarely investigated. In this study, we treated bituminous coal samples with ScCO2-H2O and ScCO2-H2O-microorganism interactions in high-pressure reactors for 120 days at 35 °C and 10 MPa, respectively. After the treatments, we characterized both coal pore types and structures. The comparisons between two different post-treatments indicate that no significant change in coal pore types but notable alterations in pore structures are observed. Specifically, the treated coal with microorganisms exhibits a significant increase in micropore specific surface area (SSA) and surface roughness than the one without them. However, changes in meso/macropore structures and overall pore complexity of the coal sample treated with microorganisms were less pronounced than in coal sample treated with ScCO2-H2O alone. FTIR spectra analysis indicated that the absorption peak intensity of oxygen-containing groups and aliphatic functional groups in the sample treated with microorganisms decreased much more significantly than the sample treated without microorganisms. The CO2 adsorption capacity slightly increased in all treated samples at equilibrium pressures below 2.5 MPa. Above this pressure, the coal sample treated with microorganisms maintained a higher CO2 adsorption capacity, while the sample treated without microorganisms exhibited lower CO2 adsorption capacity compared to untreated coal sample. The increased SSA and the reduced oxygen-containing functional groups of coal after the treatment exerted antagonistic effects on CO2 adsorption. These findings suggest that indigenous microorganisms in coal seams affect CO2 adsorption through antagonistic effects, necessitating site-specific microbial assessments.

Flexible Hybrid Membrane with Synergistic Exciton Dynamics for Excessive 280 h of Durably Piezo-Photocatalytic H2O-to-H2 Conversion.

Solar-driven H2O-to-H2 conversion is a feasible artificial photoconversion technology for clean energy production. However, low photon utilization efficiency has become a major obstacle limiting the practical application of this technology. Herein, a metal atomic replacement (Sb→Ni) is conducted to disintegrate bulk Sb2S3 nanorods and synchronously grow the NiS nanolayers, and a flower-like Sb2S3-NiS nanocomposite with high BET specific surface area and synergistic exciton dynamics is constructed for simulated solar (SSL)-driven H2O-to-H2 conversion. The optimal Sb2S3-NiS nanocomposite is compounded with polyvinylidene fluoride (PVDF) to prepare a flexible PVDF/Sb2S3-NiS (PSN) hybrid membrane with stable structure and excellent recyclability via an electrospinning method. Due to the synergistically interacted organic-inorganic interface and high porosity, it is conducive to the exposure of effective active sites, exciton conduction and mass transfer and exchange, thereby an outstanding alkaline (Ph=13.0) H2O-to-H2 conversion activity with a 0.06% of solar-to-hydrogen efficiency and over 280 h (70 cycles) of durable recycling is achieved under the collaborative drives of SSL and weak ultrasound (40 Hz). This study raises a state-of-the-art membrane material for solar-driven panel reaction technology.

In-Depth Characterization of Natural Clays from Southeast Albania

Clays have been exploited in the manufacture of diverse products from ceramics to paints, pharmaceuticals, plastics, cosmetics, and more. Thus, they can be used in many industrial applications, showing good adsorbent ability thanks to their lamellar structure, high cation exchange capacity, pore size distribution, and large surface area. For this reason, considerable attention has been paid to their in-depth characterization, for further integration in sectors such as biomedicine, construction, remediation, aerospace, and nanotechnology. For this aim, two samples of natural clays, ALO1 and PRE4, from the southeast part of Albania, were subject to a multi-methodological characterization, with the aim of addressing the use of such geomaterials in possible sensing applications. X-ray fluorescence analysis, morphological characterization of the samples, and energy-dispersive system spectroscopy pointed to an extreme mineralogical variety, with kaolinite in AL01 and montmorillonite in PRE4 as the most abundant phases. This fact was further confirmed by powder X-ray diffraction, showing a quartz content of 20%, a kaolinite content of 64%, and a muscovite content of 16% for ALO1; meanwhile, for PRE4, we found a content of quartz of 45%, a content of montmorillonite of 34.9%, and a content of clinochlore of 20%. Infrared spectroscopy and thermal analyses confirmed the presence of hydroxyl groups in both samples, suggesting a higher content in ALO1. Measurement of N2 adsorption isotherms on the clay samples yields specific surface areas of 87 m2/g for PRE4 and 32 m2/g for ALO1, pore volumes of 0.721 cm3/g for PRE4 and 0.637 cm3/g for ALO1, and similar pore sizes in the range of 6–12 nm. Electrochemical analysis highlighted a good conductivity of ALO1 and PRE4 when used for the modification of commercial carbon-based screen-printed electrodes. In detail, higher currents were registered by differential pulse voltammetry for the electrodes modified with the clays with respect to bare electrodes, as well as good repeatability of the measurements. In addition, a comparative study with nanomaterials, known for their good conductivity, was achieved, using carbon black and gold nanoparticles as a reference, showing that the conductivity of the clays was lower than but not so different from those of the reference materials.

Novel design of hollow carbon nanocage modified with nanotubes as a bifunctional electrocatalyst for high performance Zn–air batteries

Microcavities play a crucial role as microreactors in the transport of molecular/ionic guests and the exposure of active sites, thus significantly influencing the electrocatalytic performance. This study prepares Co/N-codoped hollow carbon (HT-CoN/C) with surface-distributed carbon nanotubes by pyrolysis of PDA-coated Zn/Co bimetallic ZIF (BM-ZIF@PDA). Benefiting from the hierarchical porous structure, high specific surface area (307.17 m2 g−1) and abundant Co clusters, the HT-CoN/C exhibits remarkable bifunctional oxygen electrocatalytic activity with an overpotential of the ORR/OER processes (ΔE = 0.703 V). The density functional theory (DFT) calculations also verify that the configuration of C-coated N-coordinated Co clusters (Co4-Nx) affect the electrocatalytic activity of ORR and OER, illustrating the source of the excellent oxygen electrocatalytic activity of HT-CoN/C. The aqueous rechargeable zinc-air battery (RZAB) using HT-CoN/C as the air electrode is characterized by a superior peak power density (175 mW cm−2), a prolonged cycle life (1230 cycles/410 h at 5.0 mA cm−2) and a high open-circuit voltage (1.47 V). Meanwhile, the flexible solid-state RZAB assembled by the HT-CoN/C also exhibits a higher peak power density (117 mW cm−2) and an excellent bending performance. This work is extremely valuable for the design and synthesis of Co/N co-doped carbon electrocatalysts.