Carbon-based nanoparticles (CNPs) have demonstrated great potential in biomedical applications because of their unique physical and chemical properties, and excellent biocompatibility. Herein, we have studied two types of CNPs with gadolinium (Gd) impurities (Gd-CNPs), which were prepared by microwave synthesis (MWS) and hydrothermal synthesis (HTS), for potential applications as photoluminescent (PL) labels and contrast agents in magnetic resonance imaging (MRI). The prepared Gd-CNPs were investigated by means of transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy, UV–visible absorption spectroscopy, and magnetic-resonance relaxometry, which allowed us to reveal specific features and functional properties of the prepared samples. While the TEM data showed similar size distributions of both types of Gd-CNPs with mean sizes of 4–5 nm, the optical absorption spectroscopy showed higher absorption in the visible spectral region and stronger PL in the red and near-infrared (NIR) spectral regions for the MWS samples in comparison with those prepared by HTS. Under green light excitation the former samples exhibited the bright red-NIR PL with quantum efficiency of the order of 10%. The proton relaxometry measurements demonstrated that the HTS samples possessed longitudinal and transverse relaxivities of about 42 and 70 mM⁻¹s⁻¹, whereas the corresponding values for the MWS samples were about 8 and 13 mM⁻¹s⁻¹, respectively. The obtained results can be useful for the selection of appropriate synthesis conditions for carbon-based nanoparticles for bimodal bioimaging applications.

Gd-doped carbon nanoparticles are characterized spectroscopically to reveal new possibilities for controlling the optical and MRI contrast properties of these nanoparticles for biomedical applications.

Zinc oxide (ZnO) nanostructures with deposited silver (Ag) nanoparticles (NPs) exhibit exceptional opportunities for highly sensitive molecular diagnostics by means of the Surface-Enhanced Raman Scattering (SERS). Here we use the well known method of the hydrothermal synthesis of arrays of ZnO nanorods (NRs), followed with deposition of Ag-NPs by facile photochemical reduction under UV-light illumination to obtain ZnO-NRs/Ag-NPs hybrid structures with superior SERS activity. SERS spectra of a probe analyte, i.e. Rhodamine R6G molecules sorbed in an optimized ZnO-NRs/Ag-NPs structures, are detected in a wide range of the analyte concentration from 10-6 to 10-14 M. Numerical simulations of the light scattering in ZnO-NRs/Ag-NPs structures allow us to show that the wedge-like morphology of ZnO-NRs plays a crucial role in the 3D electromagnetic enhancement of the SERS signal, which can be as high as 3•108 for the lowest analyte concentration. The revealed high SERS activity of the obtained ZnO/Ag hybrid nanostructures together with the simplicity of their preparation open new prospects for their application in analytical chemistry, sensorics and photonics.

A composite based on θ-Al₂O₃ microspheres coated with graphene oxide (GO) and reduced graphene oxide (RGO) was prepared and evaluated as a sorbent for the removal of synthetic dyes from aqueous solutions. GO was synthesized by a modified Hummers’ method and deposited onto alumina microspheres via ultrasound-assisted treatment under various conditions, followed by supercritical reduction to obtain the Al₂O₃_RGO composite. The structure, morphology, and composition of the materials were characterized by Raman spectroscopy, SEM, TGA/DSC, FTIR, and XRD, revealing the formation of mono- and few-layer GO/RGO coatings on the substrate surface. Adsorption tests for cationic methylene blue (MB) dye and anionic methyl orange (MO) dye demonstrated that the alumina substrate was inactive, whereas GO- and RGO-coated microspheres exhibited high adsorption efficiency for MB and partial uptake of MO from water solutions. In mixed-dye solutions, both Al₂O₃_GO and Al₂O₃_RGO composites showed selectivity toward MB, and the RGO-based composite demonstrated enhanced MB adsorption at low concentrations. The results highlight GO/RGO-coated θ-Al₂O₃ microspheres as convenient and selective composite sorbents for water purification processes.

Anthropogenic contamination of water resources poses a critical global challenge for designing efficient adsorption-based water treatment processes. This work provides a systematic adsorption study of six graphene-based sorbents with different C/O ratios and surface chemistries for the removal of four representative cationic and anionic dyes and two broad-spectrum antibiotics (amoxicillin and norfloxacin) from aqueous solutions, including their mixtures in model wastewater. Overoxidized graphene oxide demonstrates high removal efficiencies for cationic dyes, with maximum sorption capacities of 155 mg/g for methylene blue and 175.5 mg/g for brilliant green. In contrast, under-oxidized graphene oxide shows even higher capacities for several dyes, reaching 369, 444 and 488 mg/g for methylene blue, brilliant green and Congo red, respectively. Thermally reduced graphene oxide combines partial reduction of carbon framework with residual oxygen functionalities and achieves sorption capacities of 153 mg/g for methylene blue and 209 mg/g for methyl orange. All graphene-based sorbents also effectively remove antibiotics, with maximum sorption capacities in the range of 322–487 mg/g. Adsorption kinetics and equilibrium are described using pseudo-second-order and nonlinear Langmuir and Sips models, enabling quantitative comparison of sorbent performance. The effectiveness of the graphene-based sorbents is further validated under near-real conditions in river water purification experiments, where dyes were present at extremely low concentrations (1 ppm). These results demonstrate that controlled oxidation and reduction of graphene oxide provide an effective route for tailoring sorbent selectivity and adsorption performance in wastewater treatment applications.