Surface Oxygen Content Research Articles

Activation of periodate by CNT for selective catalytic oxidation: The overlooked significant role of residual metal species as catalytic sites

Carbon nanotubes (CNTs) catalyzed activation of peroxides has been extensively investigated, while the role of residual metal species in CNT in the catalysis is largely overlooked. In the study, calcination treatment of pristine CNT at high temperatures was employed as an approach to gain an insight into the role of residual metal species as catalytic sites in promoted catalytic activation of periodate (PI). Firstly, the calcination treatment at 500–1100 °C significantly promoted PI activation by calcined CNT. By constructing the quantitative structure–activity relationships (QSARs) between several surface and bulk properties of CNT (such as total surface oxygen content, surface carbonyl group, bulk defect and residual metal species) and PI activation performance, the residual metal species were identified as the catalytic sites. Moreover, the purification method of pristine CNT in the concentrated HNO3 was confirmed to be not efficient to remove these residual metals. The calcination treatment can tune the electronic structure of residual metal species, and promote their exposure and electron donation capacity for PI activation, thus significantly improving PI activation performance. Moreover, IO3• was identified as the dominant reactive species in CNT/PI system via a line of approaches including quenching experiments, PI decomposition in the presence/absence of organic pollutants, electrochemical testes, high selectivity in degradation of organic pollutants, QSARs of substituted phenols, and analysis of degradation products of 4-bromophenol. Furthermore, the CNT/PI system exhibited a wide pH application range of 3–11, high anti-interference to bicarbonate, chloride and phosphate in water. The study advances the understanding on the residual metal species in CNT and its overlooked catalytic role in PI activation, and also provides a high-performance oxidation process for wastewater purification.

Effect of Cu doping on morphology and properties of calcium ferrite and its application as oxygen carrier in chemical looping hydrogen production

Chemical looping hydrogen production with inherent CO2 capture has been widely recognized as a clean and efficient approach to high-purity hydrogen production because of the ultra-pure H2 product without any purification facilities. It is crucial to develop oxygen carriers with better performance to improve fuel conversion and hydrogen production efficiency. The potential of Ca2Fe2O5 in steam converting has been confirmed. However, its lower oxygen transfer capacity, that is, it tends to produce lower fuel conversion in fuel reactors, which will limit its practical application. Here, we report the development of Cu-doped Ca2Fe2O5-based oxygen carriers using sol-gel technology. The effects of B-site substitution of Cu element on the morphological properties and redox properties of Ca2Fe2-xCuxO5 (x = 0, 0.1, 0.25, 0.5, 1) oxygen carriers were evaluated based on experiments and density functional theory calculations. The results show that Cu doping not only elevated the surface oxygen content and enhanced the oxygen activity of the oxygen carriers, but also increased the Fe3+ at the B-site, thus enhanced their binding ability with oxygen molecules. Vacancy formation was a rate-determining step in the chemical looping hydrogen production (CLH), and Cu-doped Ca2Fe2O5 reduced the energy of oxygen vacancy formation. In the CLH process, the doping of Cu significantly improved the hydrogen productivity and fuel conversion rate. The fuel conversion rate was positively correlated with the doping amount of Cu. When x = 1, Ca2Fe2-xCuxO5 had the maximum fuel conversion rate, and its average conversion was 54.2% more than that of undoped Ca2Fe2O5. Ca2Fe2-xCuxO5 with x = 0.25 was the most suitable for CLH with the highest H2 yield, which was 20.3% more than that of Ca2Fe2O5. Moreover, its properties remained stable over multiple redox cycles with high activity and stability for CO-CLH.

Etching physicochemical adsorption sites of biochar by steam for enhanced hydrogen storage

Enhancing the hydrogen storage capacity of carbon-based materials requires the precise synthesis of strong hydrogen adsorption sites. Consequently, this work suggests improving hydrogen storage capacity by employing H2O low-temperature etching technology. First, the simulation methods investigated the pore structure and oxygen-containing groups’ adsorption properties on hydrogen. The results showed that the oxygen-containing group could increase the adsorption energy of biochar on hydrogen, and the carboxyl group had the greatest effect. A suitable coupling of pores and oxygen-containing groups can improve the microporous region’s hydrogen storage capacity. Moreover, biochar may form a new ultra-microporous region (less than 0.5 nm) by etching it at 700 °C and 30 vol% H2O. After etching 90 min, the surface oxygen concentration remained stable at 14 at.%. In conjunction with results from mass spectrometry, we discovered that the process influencing pore growth was the heterogeneous interaction between CO and H2 to create CH4. At 25 ℃ and −196 ℃, the KSBC-30–60 showed superior hydrogen storage capacity compared to KSB. Its total adsorption capacity was 0.49 wt% and 5.28 wt%, respectively, and increased by 1.32 and 1.2 times. This study proposes a novel approach to improving hydrogen storage by etching porous carbon structures with H2O. The strategy has the potential for large-scale application and can be further utilized in the design and optimization of related carbon adsorbents.

Mechanism of one-step hydrothermal nitric acid treatment for producing high adsorption capacity porous materials from coal gasification fine slag

The increasing amount of coal gasification fine slag (CGFS) necessitates its resource utilization. CGFS, mainly composed of porous carbonaceous particles and partially fused spherical or agglomerated ash particles, is an inexpensive and high-quality raw material for preparing adsorbent materials. However, the challenge remains in developing a simple, low-cost, and environmentally friendly method to produce high-performance porous materials from CGFS. In this study, a one-step treatment method using 2 mol/L nitric acid under hydrothermal conditions was proposed for CGFS. The adsorbent material (CGFS-2 M) prepared under a solid–liquid ratio of 2:5 and an initial concentration of 200 mg/L methylene blue (MB) exhibited an equilibrium adsorption capacity as high as 210.20 mg/g. The excellent adsorption performance of CGFS-2 M can be attributed to several factors: acid leaching for mineral removal and pore formation, resulting in a specific surface area and total pore volume 2.2 and 1.6 times that of untreated CGFS, respectively, and an optimized mesoporous pore size distribution favorable for MB adsorption; optimal mineral removal and a well-defined carbon microcrystal structure providing more space for MB adsorption; nitric acid treatment increasing the surface oxygen content and hydrophilicity, enhancing its ability to remove MB. The synergistic effect of pore structure improvement and surface modification indicates a feasible research direction for enhancing the performance of CGFS-based adsorbent materials. These results provide theoretical support for the development of efficient CGFS-based adsorbents.

Influence of Laser Power and Rotational Speed on the Surface Characteristics of Rotational Line Spot Nanosecond Laser Ablation of TC4 Titanium Alloy.

The TC4 titanium alloy is widely used in medical, aerospace, automotive, shipbuilding, and other fields due to its excellent comprehensive properties. As an advanced processing technology, laser processing can be used to improve the surface quality of TC4 titanium alloy. In the present research, a new type of rotational laser processing method was adopted, by using a beam shaper to modulate the Gaussian spot into a line spot, with uniform energy distribution. The effects of the laser power and rotational speed on the laser ablation surface of the TC4 titanium alloy were analyzed. The results reveal that the melting mechanism of the material surface gradually changes from surface over melt to surface shallow melt with the increase in the measurement radius and the surface roughness increases first, then decreases and, finally, tends to be stable. By changing the laser power, the surface roughness changes significantly with the variation in the measurement radius. Because low laser power cannot provide sufficient laser energy, the measurement radius corresponding to the surface roughness peak of the microcrack area is reduced. Under a laser power of 11 W, the surface roughness reaches its peak when the measurement radius is 600 μm, which is 200 μm lower than that of a laser power of 12 W, 13 W, and 14 W. By changing the rotational speed, the centrifugal force generated by the rotation of the specimen affects the distribution and re-condensation of the molten pool of the surface. As the rotational speed increases, the shallow pit around the pit is made shallower by the filling of the pit with molten material and the height of the bulge decreases, until it disappears. The surface oxygen content of the material increases first and then decreases with the increase in the measurement radius and gradually approaches the initial surface state. Compared with a traditional laser processing spot, the rotational line spot covers a larger processing area of 22.05 mm2. This work can be used as the research basis for rotational modulation laser polishing and has significance for guiding the innovative development of high-quality and high-efficiency laser processing technology.

Predicting extinction limits of concurrent smoldering spread by a reduced analytical model

Smoldering is a flameless combustion mode occurring on the surface of charring fuels, such as wood and cigarettes. Although the smoldering process is slow and has a low temperature compared to flaming, it is easy to be initiated by a weak heat source and persists under poor oxygen conditions. Extensive work has been done for flame extinction to develop scaling models to predict the limiting oxygen concentration (LOC), but limited work is available for the smoldering extinction. This study develops a reduced analytical model to predict the extinction limits of smoldering. The model simultaneously solves smoldering propagation rate, surface temperature, and surface oxygen mass fraction as part of the solutions. The extinction limit is determined as the critical condition where solutions satisfying all governing equations cease to exist. The model provides a qualitative description and captures the essential characteristics of a previous experiment. The smoldering rate decreases with increasing fuel diameter, and a larger-diameter fuel is easier to extinguish. The mechanisms of the extinction process are investigated, showing the dominant role of radiative heat loss in the smothering limit at low airflow velocities and convective heat loss near the blowoff limit at high airflow velocities. Further analysis of the effect of oxygen concentration shows an increasing trend of LOC with fuel diameter, and the smothering branch cannot be predicted without considering the heat loss through radiation from the solid surface. Novelty and Significance StatementThe novelty of this research is the prediction of smoldering propagation rates and extinction limits across various fuel diameters using a reduced analytical model. The model is modified to accommodate a thin fuel configuration and high airflow velocity condition, where convective heat and mass transfer play a more important role. The model's significance is that it not only provides essential insights into the mechanisms but also has the capability to simultaneously determine key parameters such as spread rate, reaction temperatures, and surface oxygen concentration as part of the solutions. Additionally, this study demonstrates the model's ability to reproduce the limit conditions, including smothering/blowoff limits and limiting oxygen concentration (LOC).

Comparative analysis of Cr(VI) oxyanions adsorption on aged polyamide microplastics: Evaluating UV irradiation versus chemical aging

Microplastics (MPs) commonly undergo aging in various environmental media, affecting both their environmental behavior and Trojan-horse effect for contaminants. However, the mechanisms underlying the different impact of various aging processes on the Trojan-horse effect of polyamide (PA) MPs towards metal oxyanions remain unclear. This study explored how chemical aging and UV irradiation impact the structural characteristics and Cr(VI) adsorption of PA MPs under various influencing factors. Results showed that both aging processes enhanced the negative surface charge, surface oxygen content, and roughness of PA MPs, with FTIR correlation spectroscopy confirming an increase in O-containing functional groups. Cr(VI) adsorption onto aged PA sharply increased by 17.4 % (14 days of UV irradiation), 39.4 % (42 days of UV irradiation), and 21.7 % (chemical aging) compared to original PA. Salinity and natural organic matter had adverse effects on Cr(VI) adsorption. Spectroscopic analyses highlighted the crucial role of hydrophilic amide groups in controlling Cr(VI) adsorption onto aged PA, involving hydrogen bonding, electrostatic interactions, and reduction. Aged PA exhibited higher adsorption capacities but also greater desorption under simulated seawater and intestinal fluid, suggesting increased migration potential for Cr(VI). This study provides helpful insights into assessing the environmental risk of co-existing PA MPs and metal oxyanions, particularly considering the effect of aging processes.

Exploring oxygen migration and capacitive mechanisms: Crafting oxygen-enriched activated carbon fiber from low softening point pitch

A green pitch fiber from coal tar distillation residue, with a softening point of 190 °C, was used to make activated carbon fiber through an in-situ oxygen-doped method. Oxygen-rich pitch-based activated carbon fibers (OPACFs) were successfully created with a three-stage stabilization process using this low softening point pitch fiber. The OPACFs exhibit a moderate pore size distribution and high surface oxygen content (20.83 at%). The migration and transformation of oxygen during this process were studied. Due to the formation of stable oxygen-containing functional groups (CO), the resulting material shows excellent electrochemical performance. It achieved a specific capacitance of 334 F/g at 0.5 A/g and maintained good rate capacity (73.7 %, 0.5–50 A/g) in a 6 M KOH electrolyte. The assembled supercapacitor displayed exceptional cycle stability, retaining 91.4 % capacitance at 1 A/g after 10,000 cycles. Further investigation revealed that the specific capacitance includes both surface-controlled and diffusion-controlled capacitance, with oxygen doping significantly enhancing the latter.

Systematic Investigations of Surface Oxygen Functional Groups on Spherical Hard Carbon for Sodium-Ion Batteries

The surface activity of hard carbons and its effect on the formation of a stable solid electrolyte interface (SEI) in sodium ion batteries has gained significant interest in the scientific community over the last years. The surface of hard carbons thus plays a pivotal role within the cell, as it constitutes the interface between the bulk material and the electrolyte. Following pyrolysis of the carbon-rich precursor at high temperatures, various oxygen functional groups (OFGs) and defects, such as five- or seven-membered rings, are present on the surface of the resulting hard carbons. The influence of OFGs on the surface is however controversially discussed. On the one hand, irreversible reactions of sodium ions with OFGs lower the initial coulombic efficiency (ICE), which leads to a decreased energy density. On the other hand, OFGs may also serve as nucleation sites for the SEI leading to a more conductive interfacial phase for sodium ions. Although many approaches of additional oxygen functionalization on the surface of hard carbons have already been reported, they mostly employ harsh reaction conditions disregarding the morphological impact on the carbon surface.In our studies, oxo-functionalized polycyclic aromatic hydrocarbons (PAHs) are adsorbed on the surface to serve as model OFGs on surface oxygen deficient hard carbons. The versatility of functionalized pyrenes in combination with nondestructive adsorption enables independent investigations on the oxygen functionalization of the hard carbon surface. In the first step, native surface oxygen groups are cleaved from the pristine hard carbon through a high-temperature post-treatment in hydrogen atmosphere. Afterwards, selective re-introduction of surface OFGs is achieved through adsorption of oxo-functionalized pyrene derivatives such as 1-hydroxypyrene or 1-pyrenecarboxylic acid to simulate hydroxy or carboxylic surface functionalities. Additionally, various spatially configurations of surface OFGs can be mimicked by elongating the distance between the oxygen functionality and the pyrene backbone through a short alkyl chain (e.g. 1-pyrenebutyric acid).Our systematic approach of selectively re-introducing surface OFGs allows the discrimination between different surface OFGs and their influence on the SEI. The surface of our modified hard carbons is characterized by X-Ray photoelectron spectroscopy (XPS) and Raman spectroscopy to evaluate the oxygen content and determine the defect concentration. The electrochemical performance is assessed by rate performance tests and cyclic voltammetry in three-electrode half-cells with sodium metal as counter and reference electrode. Initial findings validate the correlation between surface oxygen functionalization determined by XPS and the electrochemical formation potential of the SEI during the first cycle. After high-temperature treatment in a hydrogen atmosphere, the surface oxygen content decreases from ~5% to 2%, leading to a significant lowering of the plateau capacity. Simultaneously, the ICE decreases from 79% to 55%. Cyclic voltammetry of deoxygenated hard carbon reveals that the SEI formation potential is shifted from ~1.0 V vs. Na towards lower potentials of ~0.3 V vs. Na indicating that different decomposition products are formed. Furthermore, rate performance is substantially deteriorated by the development of a modified SEI. Ex-situ XPS of cycled electrodes and electrochemical impedance spectroscopy are used to identify differences in the SEI composition and link them to the electrochemical performance of our spherical hard carbons.Figure: 1-Pyrenebutyric acid adsorbed on the surface of hard carbon highlighting the different possible spatially orientations of the oxygen functional group. Figure 1

Enhanced catalytic performance and antichlorine poisoning over Cu-doped cobalt oxide nanosheets for chlorobenzene oxidation

The degradation of Chlorinated volatile organic compounds (CVOCs) by catalytic oxidation forms toxic products, and catalysts may be poisoned by chlorine at low temperatures. To address this, a Cu-assisted strategy is proposed for enhancing the catalytic degradation of chlorobenzene (CB) over cobalt oxide nanosheets. The Cu-doped Co3O4 catalysts exhibited lower T90 values (temperatures with 90 % conversion) and improved stability compared to the unmodified catalyst. These results were attributed to strong metal-metal interactions between Cu species and cobalt oxide nanosheets, which showed a high specific surface area, reduced binding energy of lattice oxygen, higher surface oxygen concentration, and more surface Co3+ species. These properties promoted low-temperature catalytic activity. In addition, the disappearance of Cu2+ satellite peak after the catalyst is used, indicating that the Cu2+ also contributes to the catalytic activity. Furthermore, the in situ FTIR spectra provided details about the reaction mechanism of CB degradation over Cu-doped cobalt oxide nanosheets. The oxygen vacancy generation and the surface absorption of chlorine-containing intermediates were calculated using density functional theory calculations. This study provides new insight into novel pathways for catalyst design aimed at CB degradation.

Interfacial property enhancement of carbon fiber/epoxy composites via constructing a gradual modulus interphase with a waterborne bio‐based spiro diacetal epoxy emulsion

AbstractIn this article, to explore the utilization of bio‐based epoxy resin in the preparation of sizing agents for carbon fibers (CFs), a bio‐based epoxy emulsion (S‐P‐S) derived from spiro diacetal epoxy (SDE) resin was prepared and compared to the traditional diglycidyl ether of bisphenol A (DGEBA) based emulsion (D‐P‐D) and a mixed emulsion of S‐P‐S and D‐P‐D (S‐P‐S&D‐P‐D). The CF sized with S‐P‐S (CF‐(S‐P‐S)) showed improved surface oxygen content (22.86%) and roughness (40.9 nm), enhancing wettability and interfacial bonding between the fiber and the matrix. Nanoindentation test and AFM results showed the enhanced interfacial stiffness and a gradual modulus interphase with a thickness of 381 nm in CF‐(S‐P‐S) reinforced epoxy resin composite (CF‐(S‐P‐S)/EP). Therefore, the resulting CF‐(S‐P‐S)/EP composite possesses the best mechanical properties, with the transverse fiber bundle tensile (TFBT) strength of 27.3 ± 1.45 MPa and the interfacial shear strength (IFSS) of 85.6 ± 8.26 MPa. These results highlight the potential of the SDE‐based emulsion (S‐P‐S) to enhance the interfacial properties and mechanical performance of CF/EP composite, offering a sustainable alternative to conventional petroleum‐based epoxy resins.Highlights Emulsion (S‐P‐S) was prepared using spiro diacetal epoxy (SDE) for carbon fiber sizing. Properties of S‐P‐S sized CF (CF‐(S‐P‐S)) and its composite were evaluated. Spiro diacetal structure created a gradual modulus interphase in CF‐(S‐P‐S)/EP. The interfacial properties of the CF‐(S‐P‐S)/EP composite were greatly improved. Bio‐based SDE resin showed promise for optimizing carbon fiber composite interphase.

Multi-Objective Optimization of Laser Cleaning Quality of Q390 Steel Rust Layer Based on Response Surface Methodology and NSGA-II Algorithm.

To improve the laser cleaning surface quality of rust layers in Q390 steel, a method of determining the optimal cleaning parameters is proposed that is based on response surface methodology and the second-generation non-dominated sorting genetic algorithm (NSGA-II). It involves constructing a mathematical model of the input variables (laser power, cleaning speed, scanning speed, and repetition frequency) and the objective values (surface oxygen content, rust layer removal rate, and surface roughness). The effects of the laser cleaning process parameters on the cleaning surface quality were analyzed in our study, and accordingly, NSGA-II was used to determine the optimal process parameters. The results indicate that the optimal process parameters are as follows: a laser power of 44.99 W, cleaning speed of 174.01 mm/min, scanning speed of 3852.03 mm/s, and repetition frequency of 116 kHz. With these parameters, the surface corrosion is effectively removed, revealing a distinct metal luster and meeting the standard for surface treatment before welding.

Almond skin derived porous biocarbon nanoarchitectonics with tunable micro and mesoporosity for CO2 adsorption and supercapacitors

The careful selection of carbon precursors for chemical activation is critical in obtaining cost-effective and efficient porous activated biocarbons with multifunctional properties. Herein, we report on utilising almond skin to synthesize porous activated biocarbons via solid-state KOH activation. Through precise manipulation of the impregnation ratio of KOH to the non-porous carbon, a range of materials with intriguing properties including high surface area, large pore volume, tunable micro and mesopores, and surface functionalization with oxygen were synthesized. The optimized material ASPC5-4 displayed an extremely high surface area (3535 m2 g−1), a large pore volume (1.9 cm3 g−1), a high proportion of mesopores (96.5 %) and a notable surface oxygen content (6.93 wt %). These excellent features allowed ASPC5-4 to adsorb a record amount of CO2 at 0 °C/30 bar (39.81 mmol g−1). Another material ASPC5-2 exhibited a high content of micropores and adsorbed 5.92 mmol g−1 of CO2 at 0 °C/1 bar. ASPC5-4 also exhibited great potential as a supercapacitor electrode, displaying a high specific capacitance in both a three-electrode (354 F g−1/0.5 A g−1) and two-electrode (203 F g−1/0.5 A g−1) systems. It also demonstrated high power and energy densities of 638 W kg−1 and 47 W h kg−1, respectively.

Characteristics of graphene oxide-like materials prepared from different deashed-devolatilized coal chars and comparison with graphite-based graphene oxide, with or without the ultrasonication treatment

Deashed-devolatilized coal chars were prepared from anthracite, bituminous, subbituminous, and lignite coals, then oxidized to prepare graphene oxide (GO)-like materials that were extensively characterized and compared with a pristine graphite-based GO sample (CGO). Coal-based GO-like materials and CGO were then subjected to ultrasonication treatment for delamination, which also impacted their physicochemical properties. The surface oxygen contents of CGO and coal-based samples were ∼32 % and ∼26–35 %, respectively, that were reduced to ∼27 % and ∼21–24 %, respectively, after ultrasonication. The Fourier transform infrared and X-ray photoelectron spectroscopy spectra of all samples showed different profiles before and after the ultrasonication, suggesting a change in chemical functionalities. The Raman spectra of CGO and coal-based samples exhibited similar D and G bands with D/G intensity ratios (ID/IG) of 0.93 and 0.88–0.92, respectively. The ID/IG ratio of CGO and most of the coal-based samples increased after the ultrasonication due to creation of more defects. The main X-ray diffraction (XRD) peak for CGO and coal-based samples were observed at ∼11° and ∼22–24°, respectively. Ultrasonication of the samples resulted in a reduction of crystallite size and number of layers for all CGO and coal-based samples, confirming both splitting and delamination of carbon layers. Additionally, different coal-based samples exhibited almost overlapping XRD profiles after the ultrasonication.

VOCs (toluene) removal from iron ore sintering flue gas via LaBO3 (B = Cu, Fe, Cr, Mn, Co) perovskite catalysts: experiment and mechanism

Abstract The challenges posed by volatile organic compound (VOC) emissions in iron ore sintering flue gas are significant. La-based perovskite catalysts offer a promising solution for efficiently degrading VOCs. In this study, a series of LaBO3 (B = Cu, Fe, Cr, Mn, Co) perovskite catalysts were synthesized using the sol-gel method. The influence of various B-site elements on the catalyst’s structure and surface chemical properties was thoroughly examined. Simulations were conducted to assess the VOC reduction capabilities of these catalysts under conditions mimicking sintering flue gas composition. It was found that the crystallite size of the perovskite catalyst decreases as the ionic radius of the B-site elements increases, while the specific surface area, total pore volume, and average pore size increase correspondingly. Notably, LaCoO3 and LaMnO3 demonstrated exceptional activity, attributed primarily to their elevated surface oxygen concentration and oxygen migration capability, positioning them as highly promising materials for further development. Furthermore, a proposed mechanism elucidates the La-based perovskite catalytic reduction of toluene, wherein lattice oxygen and adsorbed oxygen undergo mutual conversion during the oxidation process. This mechanism aligns with the L-H and M-v-K models, providing a comprehensive understanding of the catalytic process.

Application of functionalized carbon nanofibers as a modifying additive to motor oil

Due to the widespread of lubricants, improving their tribological characteristics remains an important practical task. Among the promising modifying additives, carbon nanomaterials attract special attention. Such materials are found to improve the antifriction characteristics of lubricants and oils. In the present research, carbon nanofibers were synthesized via catalytic pyrolysis of a mixture of light hydrocarbons (C2-C4) over the NiCu catalyst. In order to form functional groups on the surface of carbon nanofibers, they were treated with diluted acids HCl, HNO3, and H2SO4 as well as with concentrated HNO3. The functionalized samples were comprehensively characterized by a set of physicochemical methods including atomic absorption spectroscopy, scanning and transmission electron microscopies, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, temperature-programmed desorption/oxidation, and Raman spectroscopy. As defined, the surface oxygen concentration in the samples varies from 3.5 to 16.3 at.%. It was shown that the addition of modified carbon nanofibers to a motor oil leads to an improvement in its tribological characteristics. In particular, the most effective additive was the sample treated with diluted HNO3. The motor oil with this modifying additive exhibited the heating temperature decreased by 10 °C and the contact spot area on the stationary body decreased by 20 %.

Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy

Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO2 and Al2O3 oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts.

Effects of porous structure and oxygen functionalities on electrochemical synthesis of hydrogen peroxide on ordered mesoporous carbon

Two-electron oxygen reduction reaction (2e− ORR) is a promising alternative to energy-intensive anthraquinone process for hydrogen peroxide (H2O2) production. Metal-free nanocarbon materials have garnered intensive attention as highly prospective electrocatalysts for H2O2 production, and an in-depth understanding of their porous structure and active sites have become a critical scientific challenge. The present research investigates a range of porous carbon catalysts, including non-porous, microporous, and mesoporous structures, to elucidate the impacts of porous structures on 2e− ORR activity. The results highlighted the superiority of mesoporous carbon over other porous materials, demonstrating remarkable H2O2 selectivity. Furthermore, integration of X-ray photoelectron spectroscopy (XPS) data analysis with electrochemical assessment results unravels the moderate surface oxygen content is the key to increase 2e− ORR activity. These results not only highlight the intricate interplay between pore structure and oxygen content in determining catalytic selectivity, but also enable the design of carbon catalysts for specific electrochemical reactions.

Pitch-based porous carbon via the solid–liquid synergistic oxidation of K2FeO4 for excellent electrocapacitive desalination

To address limited desalination capacity and insufficient charge efficiency for carbon materials in capacitive deionization (CDI), a solid–liquid synergistic oxidation strategy of potassium pertechnetate (VI) for pitch was proposed to construct porous carbon with a reasonable pore structure and high reactive surface. On the one hand, K2FeO4 is first utilized for the solid-phase oxidation (SPO) of pitch by a high-energy ball mill, introducing rich oxygen-containing groups such as ether bonds. Meanwhile, dehydro-condensation reactions occurred during SPO, resulting in the formation of the oxidized pitch with a high degree of condensation. Importantly, the pyrolysis yield of the oxidized pitch is as high as 46.9 % at 800 °C, almost twice that of the pristine pitch, meaning that the oxidized pitch with high polymer degree and rich C-O bridge bonds facilitates the carbon fixation and emission reduction during carbonization. On the other hand, the self-oxidation of K2FeO4 in aqueous solution forms bifunctional activators (KOH and Fe(OH)3) for the preparation of pitch-based porous carbon. Benefiting from the crosslinking structure of oxidized pitch and the multi-effective activation, the prepared porous carbon (H-CBPF) exhibits a robust layered stacking topology with a high surface area and oxygen content. Thereby, it can deliver an excellent salt adsorption capacity (SAC) of 22.1 mg g−1 with an average desalination rate of 1.89 mg g−1 min−1 and a high charge efficiency of 85 % at 1.2 V in 500 mg L-1 NaCl solution. This work opens up a green and economical route for the preparation of pitch-derived porous carbon for high-performance CDI.

Study on the adsorption mechanism of polar and non-polar VOCs by the activated carbon with surface oxygen

In this study, CO2 was converted to activated carbon by the molten salt CO2 capture and electrochemical conversion (MSCC-EC) method, and the surface oxygen content of the activated carbon was further modified for the adsorption of polar molecules (chlorobenzene) and nonpolar molecules (toluene), the role of the pore structure and surface O-containing functional groups of the adsorbents in contributing to the adsorption process was systematically investigated. The results showed that MS-AC500-10, MS-AC500-15, and MS-AC550-15 have rich pore structures with specific surface areas of 811.56 m2/g, 835.35 m2/g, 1249.104 m2/g, and surface oxygen contents of about 10 %, 15 %, 15 %, respectively. The toluene adsorption capacity of MS-AC500-10, MS-AC500-15, and MS-AC550-15 was 203.82 mg/g, 229.72 mg/g, and 358.97 mg/g, respectively, and was dominated by pore adsorption, which was positively proportional to the specific surface areas and pore volumes, the adsorption process belonged to the pseudo-first-order kinetic model. The adsorption amounts of chlorobenzene by MS-AC500-10, MS-AC500-15, and MS-AC550-15 were 287.98 mg/g, 363.11 mg/g, and 495.41 mg/g, respectively. In addition to the pore adsorption, the oxygen content on the surface of the adsorbents had a non-negligible promotion effect on the adsorption of chlorobenzene, mainly because chlorobenzene is a polar molecule, and the asymmetric electrons on its surface have strong interactions with the O-containing functional groups on the surface of the adsorbents. Moreover, the prepared adsorbents were thermally stable, and the decay rate of adsorption performance was less than 5 % after five adsorption–desorption cycles.