Search Results (145)

Recently, diamond-like carbon (DLC) films have been considered for enhancing the wear resistance of rubber because rubber exhibits a high coefficient of friction and is prone to wearing out. However, the significant difference in thermal expansion coefficients between DLC films and rubber often leads to high residual stresses and poor interfacial adhesion, which limits their application in dynamic seals. In this study, Cr-C/DLC composite films were prepared using magnetron sputtering, and the effects of varying Cr contents (0.8 at.%, 1.4 at.%, 4.3 at.%, and 7.0 at.%) on interfacial adhesion and tribological properties were investigated. Scanning electron microscopy (SEM) analysis revealed no distinct demarcation lines in the composite films, indicating strong adhesion to the substrate. X-ray photoelectron spectroscopy (XPS) analysis revealed that chromium doping promoted the conversion of sp³ bonds to sp² bonds. Adhesion and tribology tests revealed that introducing a Cr-C layer with higher Cr content within the range of 0.8 at.% to 7.0 at.% enhanced the film’s adhesion, reducing the CoF value of the composite film to 0.13–0.14. Specifically, the RF80 sample (4.3 at.% Cr) exhibited excellent interfacial adhesion and optimal tribological performance, with a CoF value reduced to 0.13 and wear rate of 3.1 × 10⁻⁴ mm³/(Nm). In summary, modulating the Cr doping content can significantly enhance the interfacial adhesion strength and tribological properties of Cr-C/DLC composite films on rubber surfaces, providing an effective solution for optimizing rubber seals. Full article

Solid base catalysts hold significant promise for replacing traditional homogeneous bases with green chemical processes. However, the construction of their strong basic sites typically relies on high-temperature calcination, which often leads to the collapse of the carrier structure and high energy consumption. This study proposes a novel “carrier reducibility tuning” strategy, which involves endowing the carrier with intrinsic reducibility to induce the low-temperature decomposition of alkali precursors via a redox pathway, thereby enabling the mild construction of strong basic sites. Low-valence Cr³⁺ was doped into a mesoporous zirconia framework, successfully fabricating an MCZ carrier with a mesostructure and reducible characteristics. Characterization results indicate that a significant redox interaction between the Cr³⁺ in the carrier and the supported KNO₃ occurs at 500 °C. This interaction facilitates the complete conversion of KNO₃ into highly dispersed, strongly basic K₂O species, while Cr³⁺ is predominantly oxidized to Cr⁶⁺. This activation temperature is approximately 300 °C lower than that required for the conventional thermal decomposition pathway and effectively preserves the structural integrity of the material. In the transesterification reaction for synthesizing dimethyl carbonate, the prepared catalyst exhibits superior catalytic activity, significantly outperforming classic solid bases like MgO and other reference catalysts. Full article

Chromium-doped diamond-like carbon (DLC-Cr) nanocomposite films were successfully deposited using a high-power impulse magnetron sputtering (HiPIMS) system. The Cr content in the films was controlled by adjusting the Cr target powers. The influence of Cr content on the microstructure, mechanical properties, tribological performance, and wettability of the films was systematically investigated. The results show that the Cr content and deposition rate of the films increased with increases in the target power. The surface topography of the films evolved from smooth to rough as the Cr target increased from 10 W to 70 W. At low Cr doping rates, the film mainly exhibited an amorphous structure, whereas the nanocomposite structure was formed at proper Cr doping rates. Raman and XPS analyses revealed that Cr incorporation altered the I_D/I_G ratio and promoted the formation of Cr-C bonds, leading to a more graphitic and nanocomposite-like structure. The nanoindentation results show that an optimal Cr content enhances both hardness and elastic modulus, while higher Cr concentrations lead to a decline in mechanical strength due to more graphitization and decreasing stress. Tribological tests exhibited a significant reduction in the friction coefficient (0.21) and wear rate (0.63 × 10⁻¹⁴ m³/N·m) at a moderate Cr level. Additionally, the surface wettability evolved toward enhanced hydrophilicity with increasing Cr power, as evidenced by reduced water contact angles and increased surface energy. These findings demonstrate that controlled Cr incorporation effectively tailors the structure, stress state, and surface chemistry of DLC films, offering a tunable pathway to achieving optimal mechanical performance and tribological stability for advanced engineering applications. Full article

This study aimed to examine the influence of sputtering temperature on the bonding structure and properties of non-hydrogenated chromium/nickel co-doped diamond-like carbon (DLC) films synthesized via direct current magnetron sputtering. The Cr/Ni doping levels in the coatings were regulated by varying the shield opening above a chromium-nickel (20/80 at.%) target, resulting in a total metal co-doping concentration ranging from 6.1 to 8.9 at.%. The thickness of the Cr/Ni-DLC films ranged from 160 to 180 nm. Meanwhile, the deposition temperatures of 185 °C and 235 °C were achieved by adjusting the substrate-to-target distance. The XPS and Raman spectroscopy results indicated enhanced graphitization of the Cr/Ni-DLC films with a decrease in the synthesis temperature. XPS results indicated the formation of carbon-oxide and metal-oxide bonds, with no evidence of metal carbide formation in the doped DLC films. Furthermore, both the nanohardness and Young’s modulus demonstrated significant improvement, while the friction coefficient was reduced more than twice as the deposition temperature increased. These findings provide valuable insights into the influence of deposition temperature on Cr/Ni co-doped DLC films, highlighting their potential as advanced functional coatings. Full article

To address the premature corrosion failure of chromium-based coatings in harsh environments (e.g., high temperatures, chloride-containing solutions), this work systematically investigates how rare-earth (RE, i.e., Ce and La) elements regulate nitrogen (N) adsorption and diffusion behavior in Cr during the early stages of nitriding, a critical corrosion protection strategy, using first-principles density functional theory (DFT). Results show that RE preferentially occupies Cr substitutional site, increasing the Young’s modulus from 293.5 GPa (pristine Cr) to 344.9 GPa (Ce-doped) and 348.7 GPa (La-doped). Surface RE doping on Cr(110) significantly enhances N adsorption energy from −3.23 eV to −3.559/−3.645 eV (Ce-/La-doped), whereas subsurface doping slightly weakens the adsorption. Moreover, the energy barrier for N penetration into subsurface is reduced from 2.11 eV to 2.03/1.91 eV (Ce-/La-doped), thereby facilitating nitridation. Notably, RE is found to strongly trap vacancies and N atoms, leading to increased migration barriers and thus hindering their long-range transport. These findings demonstrate that RE exhibits a dual role during nitriding: promoting N incorporation at the surface while restricting its deep diffusion into the bulk. The study provides theoretical insights into the atomistic mechanisms by which RE elements modulate nitriding efficiency in Cr-based alloys, offering guidance for the design of RE-doped surface-modified coatings with improved corrosion resistance. Full article

Cuprate delafossite phases such as CuMnO₂ (crednerite) and CuFeO₂, as well as iron- and manganese-doped mcconnellite composites, were investigated as candidates for producing intense black ceramic pigments via conventional solid-state synthesis. Both electric kiln and fast dielectric (microwave) firing methods were employed, with mcconnellite (CuCrO₂) used as a reference pigment. Microwave firing led to a marked improvement in sample blackness compared to conventional electric firing. Among the delafossite phases, only mcconnellite subjected to microwave-assisted firing (R_Vis = 1.40%, corresponding to 98.60% visible light absorption) emerges, pending further optimization, as a promising candidate for an ultra-black ceramic pigment (R_Vis < 1%) under optimized glaze conditions (ZnO-free) and a firing temperature of 1000 °C. Considering the pigments in powder form, microwave-fired crednerite (R_Vis = 4.85%, 95.15% absorption) and iron- and iron–manganese-doped mcconnellite composites (R_Vis = 3.27% and 3.23%, respectively) appear as potential candidates for deep-black pigments (R_Vis < 3%), benefiting from the composite effect between the delafossite phase and the associated chromium spinel. Moreover, microwave-fired crednerite also demonstrates noteworthy potential for deep-black coloration in glazed samples (R_Vis = 4.27%, 95.73% absorption). Full article

In the application of ceramic dielectric filters, to achieve electromagnetic shielding of signals and subsequent integrated applications, it is necessary to carry out metallization treatment on their surfaces. The quality of metallization directly affects the performance of the filter. However, when in use, the filter may encounter harsh environmental conditions. Therefore, the surface-metallized film needs to have strong corrosion resistance to ensure its long-term stability during use. In this paper, Cu films and copper–chromium alloy films were fabricated on Si (100) substrates and BaTiO₃ ceramic substrates by HiPIMS technology. The effects of different added amounts of Cr on the microstructure, electrical conductivity, and corrosion resistance of the Cu films were studied. The results show that with an increase in Cr content, the preferred orientation of the (111) crystal plane gradually weakens, and the grains of the Cu-Cr alloy film gradually decrease. The particles on the film surface are relatively coarse, increasing the surface roughness of the film. However, after doping, the film still maintains a relatively low surface roughness. After doping with Cr, the resistivity of the film increases with the increase in Cr content. The film–substrate bonding force shows a trend of first increasing and then decreasing with the increase in Cr content. Among them, when the Cr content is 2 at.%, the film–substrate bonding force is the greatest. The Cu-Cr alloy film has good corrosion resistance in static corrosion. With the increase in Cr content, the Tafel slope of the cathode increases, and the polarization resistance R_p also increases with the increase in Cr content. After the addition of Cr, both the oxide film resistance and the charge transfer resistance of the electrode reaction of the Cu-Cr alloy film are greater than those of the Cu film. This indicates that the addition of Cr reduces the corrosion rate of the alloy film and enhances its corrosion resistance in a NaCl solution. 2 at.% Cr represents a balanced trade-off in composition. While ensuring the film is dense, uniform, and has good electrical conductivity, the adhesion between the film and the substrate is maximized, and the corrosion resistance of the Cu film is also improved. Full article

Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb₂Te₃. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XAS/XMCD) techniques to study the structure and magnetism of Cr-doped Sb₂Te₃ films. Symmetric $\theta$-2$\theta$ XRD and RSM establish a solubility window. Layered tetradymite order persists up to ∼10 at.-% Cr, while higher doping yields CrTe/Cr₂Te₃ secondary phases. STEM reveals nanocrystalline layered stacking at low Cr and loss of long-range layering at higher Cr concentrations, consistent with XRD/RSM. Magnetometry on a 6% film shows soft ferromagnetism at 5 K. XAS and XMCD at the Cr $L_{2,3}$ edges exhibits a depth dependence: total electron yield (TE; surface sensitive) shows both nominal Cr²⁺ and Cr³⁺, whereas fluorescence yield (FY; bulk sensitive) shows a much higher Cr²⁺ weight. Sum rules applied to TEY give $m_L=(0.20\pm 0.04)$${\mu }_{\mathrm{B}}$/Cr, and $m_S=(1.6\pm 0.2)$${\mu }_{\mathrm{B}}$/Cr, whereby we note that the applied maximum field (3 T) likely underestimates $m_S$. These results define a practical growth window and outline key parameters for MTI films. Full article

Chromium-doped hydroxyapatite (7CrHAp) and chromium-doped hydroxyapatite in chitosan matrix (7CrHAp-CH) coatings were synthesized in order to address the need for biomaterials with improved physico-chemical and biological properties for biomedical applications. Both chromium-doped hydroxyapatite (7CrHAp) and chromium-doped hydroxyapatite in chitosan matrix (7CrHAp-CH) coatings could represent promising materials for biomedical applications due to their superior properties. This study aims to evaluate the physico-chemical and in vitro biological properties of 7CrHAp and 7CrHAp-CH coatings to determine the impact of chitosan incorporation on the physico-chemical and biological features. The results reported in this study indicate that addition of chitosan improves surface uniformity and biological properties, highlighting their potential for uses in biomedical applications. In this study, coatings of chromium-doped hydroxyapatite (7CrHAp, with x_Cr = 0.07) and its composite variant embedded in a chitosan matrix (7CrHAp-CH) were systematically analyzed using a suite of characterization techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and metallographic microscopy (MM). The results of the XRD analysis revealed that the average crystal size was 19.63 nm for 7CrHAp and 16.29 nm for 7CrHAp-CH, indicating a decrease in crystallite size upon CH incorporation. The films were synthesized via the dip coating method using stable suspensions, whose stability was assessed through ultrasonic measurements (double-distilled water serving as the reference medium). The values obtained for the stability parameter were 2.59·10⁻⁶ s⁻¹ for 7CrHAp, 8.64·10⁻⁷ s⁻¹ for 7CrHAp-CH, and 3.14·10⁻⁷ s⁻¹ for chitosan (CH). These data underline that all samples are stable: CH is extremely stable, followed by 7CrHAp-CH (very stable) and 7CrHAp (stable). The in vitro biocompatibility of the 7CrHAp and 7CrHAp-CH coatings was evaluated with the aid of the MG63 cell line. The cytotoxic potential of these coatings towards MG63 cells was quantified using the MTT assay after 24 and 48 h of incubation. Our results highlight that both 7CrHAp and 7CrHAp-CH coatings exhibit high biocompatibility with MG63 cells, maintaining cell viability above 90% at both incubation times, thus supporting osteoblast-like cell proliferation. Furthermore, the antimicrobial efficacy of both 7CrHAp and 7CrHAp-CH samples was evaluated in vitro against the Pseudomonas aeruginosa 27853 ATCC (P. aeruginosa) reference strain. The in vitro antibacterial activity of the 7CrHAp and 7CrHAp-CH coatings was further evaluated against Pseudomonas aeruginosa 27853 ATCC (P. aeruginosa), Escherichia coli ATCC 25922 (E. coli) and Staphylococcus aureus ATCC 25923 (S. aureus) reference strains. In addition, atomic force microscopy (AFM) analysis was also used to investigate the ability of P. aeruginosa, E. coli and S. aureus cells to adhere and to develop colonies on the surfaces of the 7CrHAp and 7CrHAp-CH coatings. The results from the biological assays indicate that both coatings exhibit promising antibacterial properties, highlighting their potential for being used in biomedical applications, particularly in the development of novel antimicrobial devices. Full article

The ideal crystal symmetry of the 1T-TiS₂ lattice results in a non-magnetic structure. However, recent studies have demonstrated that it may become magnetic upon substitution with transition-metal (TM) atoms. In this study, we examine the mechanisms and interactions that allow magnetic exchange through the TiS₂ matrix. Using density functional theory, we model the substitutional TM-doped TiS₂ (TM = V, Cr, or Mn) system with varying spatial distances to examine the effects on the magnetic exchange. Since pristine 1T-TiS₂ is weakly semiconducting, there is a possibility that the introduction of metallic atoms may induce an RKKY-like interaction. We find that the substitution of vanadium produces a standard exchange through the orbital interactions. However, the introduction of chromium and manganese may generate RKKY interactions with the conduction electrons. Overall, a more comprehensive understanding of how different dopants affect magnetic behavior and communicate through the lattice can enable the design of spintronic devices, which offer the potential for more energy-efficient technologies and a deeper understanding of low-dimensional systems. Full article

The CO₂ hydrogenation process is thought to be one of the feasible methods for producing methanol fuel, which might be used to fulfill future energy demands. Improving the catalytic efficiency and understanding of the process are essential elements for the viability of CO₂ conversion routes. Here, a co-precipitation method was used to synthesize Ni-Cu bimetallic catalysts supported by chromium oxide (Cr₂O₃). To examine nickel (Ni)’s promoting role, the synthesized catalysts were incorporated with different concentrations of Ni. The N₂ adsorption–desorption isotherm exposed the mesoporous nature of Cr₂O₃-based Ni-Cu catalysts. A Fourier Transform Infrared (FTIR) spectroscopy investigation revealed the effective doping of Ni-Cu metal oxides on the surface of Cr₂O₃ by instigating an FTIR absorption band in the region associated with the FTIR absorption of metal oxides. The uniform morphology and homogenous, as well as highly dispersed, form of both Ni and Cu metal were recorded using a Field Emission Scanning Electron Microscope (FESEM) and X-ray Diffraction (XRD) techniques. The surface chemistry, metal–metal, and metal–support interactions of the Ni-Cu/Cr₂O₃ catalysts were disclosed via temperature program reduction (TPR) as well as X-ray photoelectron spectroscopy (XPS). The synergism between the Ni and Cu metals was revealed using both XPS and TPR techniques, which resulted in improving the catalytic profile of Ni-Cu/Cr₂O₃ catalysts. The activity data obtained by applying a slurry reactor demonstrated the active profile of Ni for CO₂ reduction to methanol in terms of the methanol synthesis rate. The promoting role of Ni was established by observing the progressing and linear increase in methanol selectivity by Ni enrichment to the Ni-Cu/Cr₂O₃ catalysts. Structure and activity studies recognized the promoting role of Ni by experiencing metal–metal and metal–support interactions with highly dispersed metal oxides over the Cr₂O₃ support in the current case. Full article

The photocatalytic reduction of hexavalent chromium (Cr(VI)) in wastewater represents a critical environmental challenge, given its high toxicity and mobility in wastewater. Conventional optimization methods relying on repetitive batch experiments with excessive reagent consumption. Herein, we proposed a synergistic experimental–deep learning approach to realize efficient photocatalytic reduction of Cr(VI). Sludge and cellulose precursors were used to prepare N-doped porous carbon through a green fabrication method at low temperature. After optimizing the composition and experimental factors, the removal efficiency of Cr(VI) could reach 92.7% after visible light irradiation in an acidic environment. The high efficiency originated from the coupled adsorption and photocatalytic mechanism. Innovatively, after comparing three algorithms, TCN and Transformer were employed to predict the desirable removal efficiency with <5% prediction error under different reaction conditions. This work highlights the novel experimental–deep learning method for heavy metal remediation using N-doped waste-derived porous carbon. Full article

In this study, blue fluorescence carbon dots of high quantum yield (42.96%) were successfully synthesized via a one-step hydrothermal method using Pueraria residues as the precursor and urea as the nitrogen source. The preparation process was simple, was environmentally friendly, and did not use toxic chemicals, with the resulting nitrogen-doped Pueraria carbon dots (N-PCDs) exhibiting excellent dispersibility, regular morphology and stable fluorescence performance. Moreover, fluorescence quenching could be induced through electron transfer between N-PCDs and hexavalent chromium (Cr(VI)) in water, which enabled the application of N-PCDs as a fluorescent probe for sensing Cr(VI) in water, with a limit of detection (LOD) and limit of quantitation (LOQ) of 0.078 μM and 0.26 μM, respectively. The effectiveness of the proposed fluorescent probe was also validated in various water matrices, achieving stable recovery rates ranging from 98.7% to 101.5%. Furthermore, experimental investigations and theoretical calculations through density functional theory (DFT) confirmed that the underlying reaction mechanism was photoinduced electron transfer (PET). Above all, this study not only demonstrated the potential of N-PCDs as sensitive probes to sense toxic elements in the environment, but also promotes the green and scalable production of high-value carbon-based products from waste biomass. Full article

Two nitrogen-modified mesoporous MCM-41-type silicas were synthesized by the sol–gel route and post-grafting surface modification procedure, obtaining an aminopropyl-modified MCM-41 (denoted MCM-41-N) and an aminoethyl-aminopropyl-modified MCM-41 (denoted MCM-41-NN). Hexavalent chromium removal from acidified water by adsorption and reduction to Cr(III) on the solid mesophases was analyzed. The modified silicas were characterized by powder X-ray diffraction (XRD), Fourier transformed infrared spectra (FT-IR), nitrogen adsorption–desorption measurements at −196 °C, X-ray photoelectron spectroscopy (XPS), ²⁹Si solid state Nuclear Magnetic Resonance (²⁹Si-RMN), and thermogravimetric analysis (TGA). Both samples exhibited very high capacities for decreasing Cr(VI) concentrations in water, according to the Langmuir isotherm model: 129.9 mg·g⁻¹ for MCM-41-N and 133.3 mg·g⁻¹ for MCM-41-NN. The chromium speciation in the supernatant after 24 h indicates that MCM-41-N had a higher capacity to reduce Cr(VI) to the less toxic Cr(III) species than MCM-41-NN: 92.9% vs. 72.5% when the initial Cr(VI) concentration was 10 mg·g⁻¹. These differences were related to the different capacity of nitrogen atoms in MCM-41-N and MCM-41-NN to interact with the surrounding surface silanols which are required for the chemical reduction in the hexavalent species to take place, as evidenced by FT-IR and XPS analysis. Also, the Cr(III)/Cr(VI) atomic ratios on the solid’s surfaces were higher for MCM-41-N. These results highlight the characteristics that nitrogen atoms incorporated into silica matrices must possess in order to maximize the transformation of Cr(VI) into the trivalent species, thereby reducing the generation of toxic waste harmful to living organisms. Full article

Novel high-entropy perovskite oxide powders were synthesized using a sol-gel process. The B-site contained five cations: chromium, cobalt, iron, manganese, and nickel. The B-site cations were present on an equiatomic basis. The A-site cation was lanthanum, with calcium doping. The amount of A-site doping varied from 0 to 30 at%, yielding a composition of La_1−xCa_x(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O_3−δ. The resulting perovskite powders were pressurelessly sintered in air at 1400 °C for 2 h. Sintered densities were measured, and the grain structure was imaged via scanning electron microscopy to investigate the effect of doping. Samples were cut and polished, and their resistance was measured at varying temperatures in air to obtain the electrical conductivity and the mechanism that governs it. Plots of electrical conductivity as a function of composition and temperature indicate that the increased configurational entropy of the perovskite materials has a demonstrable effect. Full article