I. Abstract of the Paper’s Core Research

This study employs aerosol jet printing of silver nanoink to fabricate an interconnected three-dimensional silver mesh with a 70 μm period and a maximum thickness of 20 μm. Subsequently, a hydrothermal process is used to grow zinc oxide nanorods—2 μm in length and 200 nm in diameter—perpendicular to the mesh surface. The system undergoes comprehensive characterization across multiple dimensions, including microstructural morphology, optoelectronic properties, and photocatalytic degradation performance. The key findings are as follows:

One-step fabrication of three-dimensional hierarchical heterogeneous catalytic structures

Five-layer cyclic aerosol printing yields a highly three-dimensional silver mesh; its interwoven framework provides an abundance of growth sites, while zinc oxide nanorods are uniformly and vertically coated, forming a hierarchical open‑pore structure that increases the pollutant adsorption and light‑absorption surface area by several folds compared to planar films.

Ag–ZnO Schottky junction suppresses carrier recombination.

Silver–localized surface plasmon resonance (LSPR) enhances ultraviolet light absorption, while the built-in electric field at the metal–semiconductor interface efficiently separates photogenerated electrons and holes, significantly reducing recombination losses and generating abundant hydroxyl and superoxide radicals to boost oxidative degradation efficiency.

Broad-spectrum, high-efficiency dye-degrading performance

Under a 365 nm UV light source, the degradation rates of four dyes—methylene green, malachite green, methyl orange, and methylene blue—at a concentration of 10 ppm reached 99.09%, 99.01%, 98.68%, and nearly 100%, respectively, within 150 minutes, outperforming the conventional stainless-steel-supported ZnO catalytic system.

Excellent cycling stability against photo‑corrosion

After four consecutive cycles of photocatalytic testing, the degradation efficiency for all four dyes remained at 93.51%–97.3%, with photodegradation losses of only 2.7%, thereby addressing the key challenges of powder‑type catalysts—namely, their easy leaching and rapid activity decay.

The digital grid size is precisely adjustable.

The number of aerosol‑printing layers and the grid spacing are freely programmable; the more printing cycles, the greater the thickness of the silver scaffold and the higher the density of nanorod loading, leading to a corresponding increase in catalytic activity. The process can be standardized for large‑scale batch production.

II. Complete Preparation Process via Aerosol Printing Combined with Hydrothermal Synthesis

1) Commercial silver nanoparticle ink is diluted with deionized water and subjected to ultrasonic dispersion to eliminate particle agglomeration.

2) The aerosol jetting device controls the carrier gas and sheath gas flow rates, enabling layered cyclic printing of a 70-μm-periodic three-dimensional silver mesh, with each layer featuring line widths of 14 μm.

3) Sintering on a 240°C hot plate for 20 minutes to form a continuous, highly conductive metallic framework;

4) Zinc nitrate and hexamethylenetetramine are used to prepare a hydrothermal precursor solution, enabling the in-situ growth of vertically aligned ZnO nanorods at low temperature.

5) UV–Vis spectroscopy was used to monitor changes in the absorbance of the dye during photocatalytic degradation, and degradation kinetics and cycling stability were evaluated.

III. Core Advantages of the Three‑Five Aerosol Process (Compared with Lithography, Stainless Steel Mesh, and Vacuum Coating)

Digitally customized three-dimensional mesh with a flexible, adjustable structure.

CAD allows direct modification of the mesh period and the number of printed layers, making it easy to adjust the scaffold thickness and specific surface area, whereas stainless steel mesh specifications are fixed and cannot be customized.

Maskless localized deposition, reducing precious-metal consumable usage.

Only the catalytic functional area is coated with silver lines; the entire surface is sputtered, resulting in substantial material waste from metal sheet substrates and a significant reduction in R&D costs.

High-aspect-ratio three-dimensional interconnect scaffold with a specific surface area far exceeding that of planar substrates.

Multi-layer stacking creates a three-dimensional cross‑linked network, providing an abundance of nucleation sites for zinc oxide, with a nanorod loading density far exceeding that of a single‑layer film.

Formed at ambient temperature and pressure, with no vacuum chamber required.

The equipment features no vacuum or high-temperature coating modules, resulting in a low process‑entry barrier and enabling rapid lab‑scale prototyping as well as seamless integration with roll‑to‑roll production lines for mass manufacturing.

The substrate exhibits broad compatibility, enabling fabrication on both glass and flexible substrates.

Not limited to rigid substrates, the technology can be extended to flexible catalytic thin films, enabling compatibility with curved‑surface water‑treatment reactors.

IV. Five Core Technological Innovations of This Study

Innovation 1: Aerosol Direct-Printing of Three-Dimensional Silver Grids as a Photocatalytic Growth Substrate

AJP additive manufacturing is employed as a photocatalytic support, replacing commercial stainless steel wire meshes and sputtered silver films, thereby enabling free customization of the mesh architecture.

Innovative Synergistic Catalytic Mechanism of a Hierarchical Ag–ZnO Schottky Heterojunction

By leveraging the plasmonic light-absorption effect of silver and interfacial charge separation, this approach fundamentally suppresses electron–hole recombination, thereby overcoming the bottleneck in catalytic efficiency inherent to pure zinc oxide.

Innovative Multi‑Layer Printing–Based Standardized Process for Regulating Catalytic Activity

Establish quantitative relationships among print cycle count, silver scaffold thickness, nanorod loading, and degradation efficiency, thereby defining a reusable process window.

Innovative, four‑component, solid‑supported, highly stable catalytic system; easy to recover with no secondary pollution.

Unlike nanopowder catalysts, the solid grid‑type membrane can be removed directly, enabling simple filtration and separation, with extremely low loss during four‑cycle operation.

Innovative all‑solution, mild preparation route—no high‑vacuum or complex processing steps.

Aerosol deposition at ambient temperature combined with low-temperature hydrothermal treatment—entirely conducted without high‑temperature or high‑pressure equipment—lowers the barrier to scaling up the production of catalytic materials.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Powdered zinc oxide catalysts are difficult to recover, potentially leading to secondary nanopollution of water bodies.

✅ Three-dimensional silver mesh–supported ZnO nanorods; the entire thin film can be directly removed and reused without the need for filtration or centrifugation.

Challenge 2: The conventional stainless steel mesh substrate is flat, resulting in a low loading of nanorods and weak light‑trapping capability.

✅ A three-dimensional cross‑linked aerosol mesh with multi‑level porosity, significantly enhancing load density and light scattering–absorption performance.

Challenge 3: In pure zinc oxide, photogenerated carriers recombine severely, resulting in a slow degradation rate.

✅Silver – The semiconductor Schottky junction separates charges, the plasmonic effect broadens the light-absorption range, and the yield of free radicals is significantly enhanced.

Challenge 4: The metal substrate has a fixed specification, making it impossible to tailor the catalytic specific surface area on demand.

✅ Aerosol-based digital printing, with customizable grid spacing and stack layer count, enabling rapid iteration to optimize the catalytic structure.

Challenge 5: The fabrication of metal grids via lithography and vacuum deposition is costly and involves lengthy processing steps.

✅ Maskless direct writing allows a single batch of samples to be completed in just a few hours, eliminating the need for the entire process of photoresist coating, exposure, and evaporation deposition.

VI. Future Diversified Industrial Application Scenarios

1 Organic Wastewater Treatment Equipment for the Textile Printing and Dyeing Industry

Modular aerosol‑silver/zinc oxide catalytic filter, continuously degrades dye‑contaminated wastewater, and is reusable to reduce operation and maintenance costs.

2 Small-scale domestic wastewater treatment unit

Flexible and rigid catalytic thin films for the in-situ degradation of trace organic pollutants in kitchens and bathrooms.

3 Ecological Restoration of Surface Water in Outdoor Environments

Lightweight photocatalytic mesh panels are deployed in waterways to degrade pesticides and organic dye pollutants.

4 Photocatalytic Hydrogen Evolution Reaction Substrate

A three-dimensional heterogeneous structure with a high specific surface area simultaneously enables coupled pollutant degradation and solar-driven hydrogen production.

5. Research and Development Platform for Novel Photocatalytic Materials in Higher Education Institutions

Aerosol-based rapid fabrication of various metal mesh supports enables high-throughput screening of diverse semiconductor–catalyst composite systems.

Image and Text Guide

Figure 1. A complete workflow for AJP-printed Ag 3D lattices combined with hydrothermally grown ZnO nanorods.

Figure 1(a) illustrates a two-step fabrication process: In the first step, AJP is employed—atomized silver ink is passed through a virtual impactor to remove oversized aerosols, then focused by sheath gas into a 200 μm nozzle with a stand-off of 1–3 mm, enabling printing onto a glass substrate. In the second step, low-temperature hydrothermal synthesis is carried out: a 0.1 M zinc nitrate solution mixed with hexamethylenetetramine (HMT) is heated in an oil bath at 80 °C, allowing vertical ZnO nanorods to grow in situ on the Ag mesh. Figures 1(b/c/d) show white-light interferometry‑based 3D surface profiles, revealing that after 1, 3, and 5 printing passes, the mesh thickness increases from ~5 μm to ~13 μm and then to ~21.6 μm. Figure 1(e) presents a bar graph of the mesh thickness along the scanning direction: after five printing passes, the thickness reaches approximately 20 μm, with a line width of about 14 μm and a pitch of 70 μm.

Figure 2. XRD and Raman spectra of the Ag mesh / ZnO NRs / ZnO NRs@Ag mesh.

Figure 2(a–c): XRD—The Ag mesh exhibits FCC Ag (111)/(200)/(220)/(311) peaks at 38.14°, 44.38°, 64.46°, and 77.46°; the bare ZnO nanorods display a hexagonal wurtzite structure; after composite formation, both sets of peaks are observed simultaneously, with no significant shift in peak position or full width at half maximum for the Ag peaks—indicating that the hydrothermal process does not disrupt the crystallinity of Ag. Figure 2(d): Raman—The Ag mesh shows Ag–Ag and Ag–O vibrational modes at 1360 and 1602 cm⁻¹, respectively; ZnO exhibits a dominant E₂(high) peak at 437 cm⁻¹, along with a weaker E₁(low) peak at 568 cm⁻¹, which is attributed to intrinsic defects such as oxygen vacancies and zinc interstitials.

Figure 3. Top-view FESEM of Ag grid and ZnO NRs at different printing counts.

Figure 3(a–c): Top-view FESEM images of Ag grids printed by AJP once, three times, and five times—after one print, the grid lines are continuous but relatively narrow with minimal overspray; with three and five prints, the line width and thickness increase progressively, reaching a thickness of approximately 20 μm and a line width of about 14 μm after five prints, with a grid pitch of 70 μm. Figures 3(d–f) show ZnO nanorods grown on the three types of Ag grids: insets (highlighted in yellow) reveal that the nanorods are uniformly and densely aligned perpendicular to the substrate, with an average diameter of ~200 nm. As the number of printing passes increases and the Ag surface becomes rougher, the number of ZnO nucleation sites rises, leading to denser coverage.

Figure 4. FESEM and EDS images of ZnO NRs on Ag grids, viewed from the side, after five printing cycles.

Figure 4(a/b/d): FESEM images of the sample tilted at 40°. At low magnification, ZnO nanorods are uniformly coated on the Ag mesh scaffold; at high magnification, the nanorods are observed to grow vertically from the mesh surface, forming a dense “brush-like” layer with an average length of ~2 μm. Figure 4(c): EDS spectrum showing the strongest Zn Kα peak, followed by O Kα; the Ag Lα peak originates from the mesh. The elemental composition is 75.47% Zn, 13.90% O, and 10.63% Ag, confirming the successful integration of ZnO nanorods with the Ag mesh.

Figure 9. Photocatalytic degradation performance and cycling stability of ZnO NRs@Ag networks

Figure 9(a/b): Methylene blue (MB) degradation: ZnO nanorods on Ag meshes printed five times exhibit the highest activity, achieving nearly 100% degradation within 150 minutes; three and one prints rank next. Figure 9(c/e): Kinetic curves for the degradation of four 10 ppm dyes (MO/MGO/MG/MB): MGO and MG are almost completely degraded within 90 minutes, while MB and MO approach complete degradation by 150 minutes. Figure 9(d): Langmuir–Hinshelwood first-order fitting: R² = 0.76–0.90. Figure 9(f): After four cycles, the degradation rates of all four dyes remain above 90%, demonstrating resistance to photodegradation and reusability.