National Institute Of Materials Physics - Romania

The scarcity of water resources demands the development of technologies to remove contaminants from industrial wastewater in order to reclaim and reuse the water in other fields like agriculture. In this study, 3D macroporous structures are additively manufactured from commercial ZnO nanopowder to be used in the photocatalytic removal of environmental pollutants from water. Direct Ink Writing (DIW) is used for deposition of the photocatalytic 3D structures that were subsequently consolidated by Spark Plasma Sintering (SPS) using temperatures in the range 425-900 degrees C. The fabricated structures are microstructurally (XRD, nitrogen physisorption, SEM and EDX) and mechanically (uniaxial compression test) characterized and their photocatalytic efficiency is evaluated by analyzing the degradation of Rhodamine B (RhB). Reusability of the DIW structures is also evaluated for structures sintered at selected temperatures by determining the photocatalytic degradation of RhB during five consecutive cycles. The results prove that increasing sintering temperature increases grain size, decreases microporosity and BET specific surface area, generates oxygen vacancies, and improves compressive strength of the 3D structures, but overall, these changes do not significantly affect photocatalytic efficiency. 3D structures require higher catalyst loading and take longer to fully degrade the dye compared to the commercial nanoparticles, but the DIW 3D photocatalysts have some clear advantages in terms of easy removal from the water -avoiding costly post-treatment precipitation, filtration or centrifugation processes typically needed to remove the catalyst nanoparticles- and extraordinary reusability: despite the evident surface corrosion occurring during the photocatalysis, neither their photocatalytic efficiency nor mechanical resistance are reduced. This will translate into significant reductions in the total cost of the treatment and a reduction in the potential toxicity of the reclaimed water due to contamination from any residual catalyst nanoparticles. These findings highlight the potential of reusable DIW ZnO catalysts for sustainable industrial wastewater treatment.

Three methods were used to prepare poly(ortho-toluidine)/reduced graphene oxide (POT/RGO) composites: (i) the interaction of the two constituents in the solid state, (ii) the chemical polymerization of ortho-toluidine (OT) in the presence of the RGO sheets, and (iii) the electrochemical polymerization of OT in the presence of the RGO sheets. Combining the results of Raman scattering, FTIR spectroscopy, and X-ray photoelectron spectroscopy, we demonstrated the following: (i) the interaction of POT with RGO in the solid state leads to the non-covalent functionalization of RGO with POT; (ii) the chemical polymerization of OT in the presence of RGO results in the covalent functionalization of RGO with POT in emeraldine base (EB) and leucoemeraldine salt (LS) and (iii) the electrochemical polymerization of OT assisted by RGO sheets leads to the covalent functionalization of RGO with POT-LS and POT-emeraldine salt (ES). The cyclic voltammetry (CV) studies indicated that the values for the voltammetric output currents of the POT/RGO composites are superior to those reported for POT. Electrochemical studies demonstrated a (a) battery-type behavior in the case of the electrodes based on POT-ES and POT/RGO composites prepared by chemical and electrochemical polymerizations and a (b) pseudocapacitive behavior for the electrodes based on POT-EB and composites prepared by the interaction of POT-EB with RGO in the solid state. High capacitance values of up to 1197.23 and 1524.62 mF cm-2 were obtained for the symmetrical supercapacitors based on the electrodes containing the POT/RGO composites prepared by chemical and electrochemical polymerization, respectively, of OT in the presence of RGO sheets.

Organic layers based on metal phthalocyanines (MPc acting as donor) and a perylene diimide derivative compound (PDI acting as acceptor) were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on rigid and flexible substrates. Hence, blend films based on magnesium phthalocyanine (MgPc), copper phthalocyanine (CuPc), cobalt phthalocyanine (CoPc) or iron phthalocyanine (FePc) and N, N-bis-(1-dodecyl)perylene-3,4,9,10 tetracarboxylic diimide (AMC14) were obtained on indium tin oxide/glass (ITO/glass) and indium tin oxide/polyethylene terephthalate (ITO/PET) substrates. Although the investigated MPcs present low solubility in organic solvents, MAPLE technique enables their deposition as blend films. The organic layers reveal a globular morphology specific to the MAPLE process. The roughness of the blend films is related to the MPc molecular packing arrangement, the optical assessment disclosing the presence of MPc in the stable beta-form. The transmission spectra display the optical signature of both MPc and AMC14 components, their complementary absorption bands assuring the light harvesting over a wide part of the UV-Vis spectral range. The current-voltage characteristics recorded under illumination reveal the best electrical parameters for the structures based on FePc: AMC14 layer prepared on ITO/glass (V-OC=0.22 V, J(SC)=2 & times; 10(- 7) A/cm(2)) and on CuPc: AMC14 layer obtained on ITO/PET (V-OC=0.27 V, J(SC)=1.3 & times; 10(- 7) A/cm(2)). Thus, the properties of MAPLE-deposited MPc: AMC14 blend films on both rigid and flexible substrates endorse them as viable choice for applications in optoelectronic devices.

Cadmium sulfide (CdS) nanostructures were synthesized via sonochemical method with varying cadmiumto-sulfur (Cd:S) molar ratios (1:0.1, 1:0.25, 1:0.5, 1:0.75, and 1:1) to investigate the influence of stoichiometry on their structural, morphological, and optical properties. Scanning Electron Microscopy (SEM) analysis revealed that Cd-rich conditions (1:0.1) produced large, irregular agglomerates (similar to 254 nm) due to limited nucleation, whereas increasing sulfur content led to granular and anisotropic morphologies (1:0.25-1:0.75), including partially leaf-like/platelet structures (189-302 nm) driven by facet-selective S2- adsorption. Near-stoichiometric Cd:S ratios (1:1) yielded uniform, faceted nanoparticles (63-396 nm) with controlled growth. X-ray Diffraction (XRD) analysis confirmed a phase evolution from pure hexagonal (1:0.1-1:0.25) to mixed hexagonal - cubic (1:0.5), predominantly cubic (1:0.75), and re-emergent hexagonal coexistence (1:1). Crystallite sizes calculated via the Debye-Scherrer and Williamson-Hall methods ranged from 5.94 to 34.9 nm, correlating with phase stabilization and quantum confinement effects, while microstrain peaked at 8.42 x 10(-3) for the 1:0.5 sample, indicating lattice distortion during hexagonal - cubic coexistence. Ultraviolet-Visible (UV - Vis) spectroscopy showed direct band gaps between 5.18 and 5.41 eV, with the largest for the 1:0.5 sample, and indirect band gaps decreased to 3.32 eV at 1:0.25, reflecting defect-induced band distortion. Photoluminescence (PL) spectra revealed enhanced emission intensity at 547 nm for the 1:1 sample, attributed to defect-assisted recombination and improved surface passivation. Raman spectroscopy indicated phonon confinement, including suppression of the 2LO mode at intermediate compositions. Fourier-transform infrared (FTIR) spectra confirmed Cd - S bond formation and the presence of surface-capping 3-mercaptopropionic acid (3-MPA) ligands. Cd:S precursor ratio enables control over particle size, morphology, crystal phase, defect density, and optical properties, offering a versatile strategy to optimize CdS nanostructures for optoelectronic applications.[GRAPHICS].

In this study, thin films of copper oxide (CuO) were deposited on indium-doped tin oxide (ITO) layers supported on glass substrates using a simple and low-cost home-made pneumatic spray technique at 350 degrees C for different deposition times (5 min, 10 min, 15 min, 20 min). Copper chloride (CuCl22H(2)O) was used as copper source at a concentration of 0.05 mol/l. X-ray diffraction patterns revealed that the films were polycrystalline with a monoclinic structure in the preferred directions (111) and (-111). Increasing the deposition time led to an increase in grain size from 11.85 to 14.73 nm. Surface analysis by scanning electron microscopy revealed improved uniformity and horizontal growth of the CuO films with increasing roughness at a deposition time of 20 min. UV-Visible measurements showed a decrease in transmittance from 73 to 47% for the wavelength range (300-1100 nm) with increasing deposition time, accompanied by a decrease in the reflectance of the films. The energy gap (Eg) decreased from 2.17 to 2.44 eV, while the Urbach energy increased with increasing spray time from 0.145 to 0.33 eV. The prepared films had absorption coefficients greater than 5 x 10(4) cm(-1) in the visible range, which diminished in the near-infrared range. The refractive index ranged between 2.01 and 3.00, whereas the dielectric constant (epsilon(r)) increased from 3.65 to 9.17.

The glass/FTO/TiO2/Sb2S3-x/P3HT/Au solar cells were investigated, with a focus on identifying the origin of performance degradation after exposure to high relative humidity and to mild heat stress. Analyzing the photovoltaic output and Deep-Level Transient Spectroscopy (DLTS) results, we probed the evolution of defect states after thermal exposure and after long-term storage of Sb2S3-x-based devices. The DLTS analysis revealed that shallow hole traps govern the stability of the Sb2S3-x cells. Significantly, it was shown that this shallow defect is not related to chlorine in the absorber, indicating an intrinsic origin. In the broader context of Sb2S3-x photovoltaics, this study underlines the paramount importance of defect engineering towards achieving more stable and efficient Sb2S3-x solar cells.

Bi-layered ZnO/CuO nanostructured films have been examined for CO2 gas sensing applications. X-ray diffraction, Fourier transform infrared, and Raman spectroscopy confirm the formation of a hexagonal wurtzite ZnO and a monoclinic CuO. Scanning electron and atomic force microscopies' observations reveal homogeneous, dense, and quasi-porous surfaces with smooth spherical sponge-like (ZnO), rough spherical-like (CuO and ZnO/ CuO), and rough flat plate-like (for CuO/ZnO) grains morphologies with a few cracks. UV-visible spectroscopy shows greater transmittance (45-90 %) in the infrared and visible domains, while the energy bandgap decreases significantly from 3.3 eV for ZnO to 1.5 eV for the remaining films. The measurements of the sensor's electrical characteristics at room temperature, including current-voltage (I-V), sensitivity-concentration (S-C), and current-time (I-t), indicate a sensitivity to the presence of CO2 gas and that the fabricated sensor exhibits excellent sensitivity and faster response/recovery times. Indeed, the ZnO thin-film sensor recorded the highest sensitivity of 44.77 % at 31 ppm carbon dioxide concentration at room temperature. Based on the results obtained, a sensing mechanism is proposed. The findings demonstrate that metal oxide multilayered nanostructures are promising candidates for applications such as gas sensing, photocatalysis, and UV photodetection.

This work reports a systematic study concerning the synthesis of pure polyaniline ultrafine nanofibers (PANI-NFs) and their nanocomposites with oxygen-functionalized carbon nanotubes (PANI-NFs/O-MWCNTs) using diluted chemical polymerization and hydrothermal processes. We investigated the synergistic effects of various synthesis parameters, such as the concentration of the ammonium persulfate oxidant agent and growth temperature, on the physical, chemical, and electrochemical properties of the resulting products through structural, morphological, spectroscopic, and electrochemical characterization. Our study revealed the successful synthesis of thermally resistant polyaniline ultrafine nanofibers (PANI-NFs) in the form of emeraldine salt (ES), exhibiting a mean diameter in the range of 8-17 nm. The PANI-NFs and PANI-NFs/O-MWCNT nanocomposites demonstrated excellent electrochemical properties, with specific capacitances of up to 0.94-1.23 F cm(-2) and 1410-2074 F/g, respectively, and with good rate capability. These characteristics are confirmed by the relaxation time constant tau(0) (41 and 8 ms, respectively) and lower internal R-0/interfacial charge transfer R-Phi resistances of around 0.2 Omega, as well as diffusion coefficients of around 10(-7) and 3.7 x 10(-7) cm(2)/s. This breakthrough in nanofiber synthesis paves the way for practical applications in diverse domains, from high-performance energy storage to biosensing and beyond, where the unique electroactive properties of the nanocomposites can be leveraged to achieve exceptional results. Omega

Introduction This study examines the effect of multi-walled carbon nanotube (MWCNT) loading on the dielectric behavior and triboelectric performance of polysiloxane (PS)-based nanocomposites for high-efficiency triboelectric nanogenerators (TENGs).Methods Flexible PS/MWCNT films were fabricated using the doctor blading method and characterized by Raman spectroscopy and scanning electron microscopy (SEM). Broadband dielectric spectroscopy was employed to analyze frequency-dependent permittivity, interfacial polarization, and dielectric loss. TENGs were assembled in a vertical contact-separation mode using nylon as the positive triboelectric layer and evaluated under controlled temperature and humidity. Statistical error analysis (n = 3) was applied to ensure quantitative reliability.Results A co-optimal MWCNT concentration of 0.03-0.05 wt% enhanced dielectric permittivity and interfacial charge trapping, improving triboelectric output while keeping conductive losses low. Higher loadings led to nanotube aggregation and increased dielectric loss, degrading device performance.Discussion/Conclusion The study establishes a quantitative correlation between dielectric spectroscopy and triboelectric output, providing mechanistic insight into performance enhancement and degradation. This framework offers practical guidelines for designing PS-based nanocomposite TENGs for wearable electronics, self-powered sensors, and portable energy-harvesting applications.

This paper reports a method for separating the constituents of a cathode containing a composite of the type polydiphenylamine (PDPA)/multi-walled carbon nanotube grafted with carboxyl groups (PDPA/MWCNT-COOH-1) as active material in end-of-life rechargeable lithium-ion batteries (RLIB) and their reuse as active materials in the field of other energy storage devices. The materials recovered from lithium battery cathodes are characterized by FTIR spectroscopy, Raman scattering, surface-enhanced Raman scattering (SERS), and X-ray diffraction. The use of the PDPA/MWCNT-COOH-1 composite as active material in the development of new energy storage devices, such as symmetric supercapacitors, is also reported. The performance comparison of the recycled composite material (PDPA/MWCNT-COOH-1 and MWCNT-COOH) with the one synthesized from pure chemical compounds (PDPA/MWCNT-COOH-2) is shown. Values of the capacitance of symmetrical supercapacitors, having as electrode materials the composites of the type of a mixture of PDPA/MWCNT-COOH-1 and MWCNT-COOH, as well as PDPA/MWCNT-COOH-2, are equal to 136.6 mF cm-2 and 112.59 mF cm-2. Increasing the concentration of the PDPA/MWCNT-COOH-2 active material in the electrode mass from 80 wt% to 84 wt% led to variations in the capacitance values of the symmetrical supercapacitors from 112.59 mF cm-2 to 145.5 mF cm-2.