The coupled processes of coprecipitation and ultrasonic spray pyrolysis (USP) were used to synthesize Fe₃O₄-Au hybrid nanostructures. The first coprecipitation method enabled the synthesis of Fe₃O₄ nanoparticles by mixing iron salts’ ions (Fe²⁺ and Fe³⁺) and ammonia as the base, and USP was used as the coating process of the Fe₃O₄ nanoparticles with Au. The formatted hybrid nanostructures consist of Fe₃O₄ nanoparticles that have Au on their surface in the form of gold nanoparticles (AuNPs). AuNPs have a crystalline structure and range in size from 10 to 200 nm. Additional characterization techniques, including ICP-OES, TEM, SEM, EDS, DLS, zeta potential, and room temperature magnetic hysteresis loops, were used to determine the chemical, physical, and magnetic properties of the Fe₃O₄ nanoparticles and hybrid nanostructures. It was found that USP produces separate AuNPs too (not just on the Fe₃O₄ surface), suggesting a bimodal formation of AuNPs. The zeta potential of the Fe₃O₄ nanoparticles showed poor stability (−15 mV), indicating a high tendency to aggregate, and the zeta potential of the hybrid nanostructures was also very low (≅0), which, comparatively means even worse stability. The saturation magnetization of the Fe₃O₄ nanoparticles was 35 emu/g, which is relatively lower than that of bulk Fe₃O₄, while the saturation magnetization of the hybrid nanostructures was significantly lower (0.1 emu/g) compared to the Fe₃O₄ nanoparticles.

Gold nanoparticles (AuNPs) were synthesised using ultrasonic spray pyrolysis (USP) with the addition of polyvinylpyrrolidone (PVP) as a stabilising agent and subsequently dried via lyophilisation. The resulting dried AuNPs were redispersed in ethanol and homogenised to ensure uniform dispersion. This AuNP dispersion was then deposited onto a ceramic substrate—aluminum oxide (Al₂O₃)—using plasma jet printing. Comprehensive characterisation of the dispersion, AuNPs, and the resulting printed lines was performed using the following methods: inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), measurements of dispersion viscosity and printed line roughness. ICP-OES confirmed consistent gold content in the AuNP dispersion, while the SEM and EDS analyses revealed predominantly spherical AuNPs with minimal aggregation and similar size distributions. TEM, SAED, and STEM/EDS confirmed that the crystalline structure and elemental composition of the AuNPs had diverse morphologies and strong gold signals. The UV-Vis, DLS, and zeta potential measurements indicated moderate colloidal stability, and thermogravimetric analysis (TGA) verified the AuNPs dispersion’s composition. The AuNP dispersion exhibited thixotropic behaviour favourable for printing applications, while confocal microscopy confirmed smooth, uniform printed traces, with an average surface line roughness of 1.65 µm. The successful use of plasma printing with the AuNP dispersion highlights its potential for functional material applications in electronics.

Gold nanoparticles (AuNPs) were synthesised using ultrasonic spray pyrolysis (USP) with the addition of polyvinylpyrrolidone (PVP) as a stabilising agent and subsequently dried via lyophilisation. The resulting dried AuNPs were redispersed in ethanol, and homogenised to ensure uniform dispersion. This AuNPs` dispersion was then deposited onto a ceramic substrate (Al2O3) using plasma jet printing. Comprehensive characterisation of the dispersion, AuNPs and the resulting printed line were performed using: ICP-OES, SEM/TEM/EDS, UV-Vis, DLS, measurements of dispersion viscosity and printed line roughness. ICP-OES confirmed consistent gold content in the AuNPs` dispersion, while the SEM and EDS analyses revealed predominantly spherical AuNPs with minimal aggregation and similar size distributions. TEM, SAED, and STEM/EDS confirmed the crystalline structure and elemental composition of the AuNPs, with diverse morphologies and strong gold signals. The UV-VIS, DLS, and zeta potential measurements indicated moderate colloidal stability, and TGA verified the AuNPs dispersion’s composition. The AuNPs` dispersion exhibited thixotropic behaviour favourable for printing applications, while confocal microscopy confirmed smooth, uniform printed traces, with an average surface line roughness of 1.65 µm. The successful use of plasma printing with the AuNPs` dispersion highlights its potential for functional material applications in electronics.

A dispersion of gold nanoparticles (AuNPs) was printed onto an alumina (Al₂O₃) substrate using a plasma jet printer, followed by post-printing sintering to form conductive traces, thus creating a printed circuit board (PCB). The resulting PCB was characterised through direct current (DC) resistance measurements and broadband scattering parameter (S-parameter) analysis, and the results were benchmarked against a commercial ENIG-plated copper microstrip fabricated on an RO4350B laminate. In addition, full-wave electromagnetic simulations were performed, to evaluate the intrinsic radiofrequency (RF) behaviour of the printed microstrip architecture up to 40 GHz. The experimental results demonstrated that the plasma-printed AuNPs microstrip exhibited predictable impedance behaviour and low insertion loss across the 0–20 GHz range, with a measured insertion loss of − 2.86 dB at 20 GHz, compared to − 2.13 dB for the ENIG PCB. The AuNPs PCB exhibited an effective electrical conductivity of 9.7 × 10⁶ S/m, compared to 7.0 × 10⁷ S/m for the ENIG PCB. While the printed lines showed higher DC resistance due to material and structural differences, the RF insertion-loss difference per unit of length remained modest; 0.01 dB/cm difference at 10 GHz and 0.110 dB/cm difference at 20 GHz, indicating good matching between AuNPs PCB and commercially available PCBs. Furthermore, the close agreement between the simulations and measurements validates the suitability of the AuNPs PCB for further microwave applications. These findings highlight the potential of plasma-printed AuNPs conductors on ceramic substrates as a promising additive manufacturing approach for high-frequency interconnects and emerging mm-wave electronic systems.

The integration of advanced materials, additive manufacturing processes, and simulation-driven design is becoming increasingly important in the development of high-frequency electronic and machinery components. In this work, a simulation-driven design methodology is presented for gold nanoparticles-based (AuNPs) conductive structures intended for implementation on low-temperature co-fired ceramic (LTCC) substrates. The approach incorporates both electromagnetic performance requirements and manufacturing constraints associated with already developed printed conductive materials. As a representative application, a microstrip coupled-line band-pass filter operating in the Ku-band frequency range is designed using full-wave electromagnetic simulations. The geometry is optimized while considering realistic limitations related to conductor thickness, minimum feature size, and effective electrical conductivity of AuNPs based conductive layers. The AuNPs are produced via ultrasonic spray pyrolysis (USP), liophilizied, dispered in a solvent, plasma printed on a Al2O3 substrate and sintered. The resulting properties thus deviate from bulk gold. The optimized structure of the AuNPs LTCC filter exhibits a center frequency of approximately 15 GHz with a bandwidth of about 1 GHz. Simulated S-parameter results demonstrate efficient signal transmission within the passband and strong attenuation outside the operating frequency range.

This study presents the development and characterization of a polymer-immobilized silver nanoparticle (AgNP) composite for potential application in water remediation and metal recycling. AgNPs were synthesized by ultrasonic spray pyrolysis (USP) using silver nitrate as a precursor and polyvinylpyrrolidone (PVP) as a stabilizing agent, followed by incorporation into a sodium alginate matrix to form separable alginate/AgNP beads. The nanoparticles were characterized by scanning and transmission electron microscopy (SEM, TEM), energy-dispersive X-ray spectroscopy (EDS), selected-area electron diffraction (SAED), dynamic light scattering (DLS), and zeta-potential measurements. The AgNPs were predominantly spherical and crystalline, with a TEM observed average diameter of approximately 90 nm and most particles between 50 and 125 nm. A PVP surface layer of up to approximately 10 nm was observed. DLS measurements showed a hydrodynamic diameter of 159.6 nm. AgNP incorporation into the alginate matrix was confirmed by microscopy and elemental analysis. AgCl formation inside parts of the composite was observed, indicating chemical transformation of silver and the possibility of affected stability and performance due to interactions with the surrounding environment. The dried composite exhibited a low specific surface area of 0.05 m²/g and a pore size of approximately 2 nm, indicating limited accessible porosity. Results indicate a required further optimization of AgNP loading and alginate structure, with preliminary tests of microplastic (MP) interactions with alginate/AgNP beads showing a limited interaction under the tested conditions. The developed composite provides a basis for multifunctional water treatment materials targeting microbial, metallic, organic, and MP contaminants and subsequent metal recycling.