Tambov State Technical University is a state institution of higher learning in Tambov, Russia. It was founded in 1958 and specializes in technical sciences (including information and communication technologies) and chemical, electronic, and agricultural engineering.
Sunflower meal, a renewable agricultural raw material, has been used to produce biochars via hydrothermal carbonization (HTC). We have assessed the influence of biomass processing steps (HTC, carbonization, and alkaline activation), the amount of the alkaline agent, and graphene oxide (GO) additions on the physicochemical and sorption properties of the biochars. According to scanning and transmission electron microscopy data, the uncarbonized material has a disordered structure, which is determined by a considerable amount of amorphous carbon with low porosity. Carbonization opens pore spaces as a consequence of the removal of amorphous organics and formation of defects, which ensure a considerable amount of meso- and micropores. According to IR spectroscopy results, the HTC process includes active removal of thermally unstable organic compounds from the sunflower meal, and alkaline activation causes alkyl groups to appear in the composition of the material, which points to an increase in defect density in the material. These results are satisfactorily correlated with Raman spectroscopy and X-ray diffraction data. We have determined the adsorption capacity of the sunflower meal-derived biochars for Zn2+ heavy metal ions and methylene blue (MB), a synthetic organic dye. Results of comparative sorption studies in static mode show that the highest sorption capacity for Zn2+ ions and MB, 58.4 and 2301.2 mg/g, respectively, is offered by the GO-containing material. To identify the assumed adsorption mechanism, experimental kinetic data have been analyzed in terms of the pseudo-first order, pseudo-second order, Elovich, and interparticle diffusion models. The results demonstrate that Zn2+ ion and MB molecule sorption is a mixed diffusion process contributed by a pseudo-second-order reaction between the contaminant and active centers of the sorbent.
This paper is devoted to studies of the liquid-phase adsorption of an aromatic organic compound, phenol, on biochars produced from plant residues of rapeseed processing. The sorbent materials were prepared by hydrothermal carbonization of rapeseed meal (R/HTC) (grown in the Tambov region) followed by subsequent carbonization (R/HTC/C) and alkaline activation (R/HTC/C/KOH). Post-treatment of the HTC-char enables opening of the porous space of the carbon framework due to removal of amorphous organics and the formation of defects in the material structure. The physicochemical and morphological properties were investigated by scanning electron microscopy (SEM), FT‑IR spectroscopy and Raman (vibrational) spectroscopy, and X‑ray diffractometry (XRD). Adsorption studies showed that the phenol contact time differs among the materials: for the activated material within 10 min; for R/HTC and R/HTC/C within 60 min. The experimental adsorption capacity for phenol was 298 mg/g for R/HTC, 1236 mg/g for R/HTC/C and 1309 mg/g for R/HTC/C/KOH. To determine the likely adsorption mechanism, the kinetic experimental data were analyzed using pseudo-first-order and pseudo-second-order models, the Elovich model and the intraparticle-diffusion model, while the isotherms were fitted to the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. The kinetics for all materials are described by the pseudo-second-order equation with a contribution from diffusion-controlled phenol adsorption. The Elovich model confirms chemical heterogeneity of the R/HTC adsorbent surface. The maximum adsorption capacity from the Langmuir model was 434.8 mg/g for R/HTC, 1429 mg/g for R/HTC/C and 1667 mg/g for R/HTC/C/KOH. Parameters of the Dubinin–Radushkevich model indicate that the interaction between the adsorbent active sites and phenol is physical in nature.
The physical and structural characteristics of activated carbon material compacted using various binders (polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and basalt fiber (BF)) were investigated. In the first stage of the study, the following were carried out: high-temperature alkaline activation of the carbon material at 400–750°C for 2 h in an inert atmosphere; compaction, including stepwise heating at 75–190°C and pressing at 1.5–7.5 kN for 3–210 min with various binders; and preparation of experimental samples by taking specimens from different parts of the blocks obtained by compaction. In the second stage, the specific surface area and porosity were determined using an Altamira Instruments Top 200 analytical system, and the sorption capacity for removal of methylene blue (MB) dye molecules was measured with a PE-5400VI spectrophotometer. The following results were obtained: for samples with PVA, PVAc and BF binders, the specific surface area was 685–1390, 570–735, and 483–532 m2/g, respectively; porosity was 0.31–0.70, 0.21–0.35, and 0.17–0.29 cm3/g, respectively; and sorption capacity was 1450–1700, 1104–1415, and 1032–1512 mg/g, respectively. A nonlinear influence of the binder components on the overall physical and structural characteristics of the materials was established, indicating the need for further studies and more careful selection of binder components for practical applications.
When creating various microwave devices using multiresonant metamaterials and radio-absorbing coatings based on them, it is assumed that the metamaterial is placed in the form of a plane-parallel layer on a metal substrate. Therefore, for the efficient design of such metamaterials, ensuring the necessary electrophysical parameters and their periodic quasi-homogeneity, appropriate measurement tools are required to assess their quality during the design and production processes. This paper substantiates a generalized method for locally testing the complex dielectric and magnetic permeabilities, as well as the thickness of flat-layered metamaterial samples with an arbitrary number of resonant regions on a metal substrate. In the developed method, the electrophysical parameters of the metamaterial are represented as parametric functions of frequency in accordance with the generalized Drude–Lorentz dispersion models for multiresonant metamaterials, and their evaluation is carried out by minimizing the objective function constructed from the discrepancy between the experimental and calculated theoretical values of attenuation coefficients of the surface electromagnetic wave field on a discrete frequency grid. To identify resonant regions of the metamaterial, the method includes an analysis of the frequency dependence of the surface electromagnetic wave field attenuation coefficient over a wide frequency band. The determined frequency values corresponding to the resonant regions are adopted as initial approximations for the Drude–Lorentz dispersion models when minimizing the objective function. To improve the stability of the inverse problem solution, a regularization of the solution based on a parametric optimization method is introduced into the objective function. To experimentally validate the method, a sample of a flat-layered dual-resonance metamaterial based on DBSRR (dual-band split-ring resonator) elements with negative refraction regions in the frequency ranges of 7.16–8.19 GHz and 10.1–10.9 GHz was studied. Experimental verification showed that the local values of the effective electrophysical parameters of the studied metamaterial differ from the calculated ones by no more than 10
This review provides a comprehensive analysis of modern strategies for the synthesis, functionalization, and application of carbon nanotubes (CNTs) and graphene for the development of high-performance polymer composites in the field of strain sensing. The paper systematically organizes key synthesis methods for CNTs and graphene (chemical vapor deposition (CVD), such as arc discharge, laser ablation, microwave synthesis, and flame synthesis, as well as approaches to their chemical and physical modification aimed at enhancing dispersion within polymer matrices and strengthening interfacial adhesion. A detailed examination is presented on the structural features of the nanofillers, such as the CNT aspect ratio, graphene oxide modification, and the formation of hybrid 3D networks and processing techniques, which enable the targeted control of the nanocomposite’s electrical conductivity, mechanical strength, and flexibility. Central focus is placed on the fundamental mechanisms of the piezoresistive response, analyzing the role of percolation thresholds, quantum tunneling effects, and the reconfiguration of conductive networks under mechanical load. The review summarizes the latest advancements in flexible and stretchable sensors capable of detecting both micro- and macro-strains for structural health monitoring, highlighting the achieved improvements in sensitivity, operational range, and durability of the composites. Ultimately, this analysis clarifies the interrelationship between nanofiller structure (CNTs and graphene), processing conditions, and sensor functionality, highlighting key avenues for future innovation in smart materials and wearable devices.
