Triboelectrification induced self-powered microbial disinfection using nanowire-enhanced localized electric field

The study addresses the urgent need for efficient inactivation of air-transmitted pathogens, which contribute to diseases such as pneumonia, asthma, and influenza. Conventional HEPA filtration imposes high pressure drops and does not inactivate captured microbes, posing risks during filter replacement. Alternatives like UV radiation and photocatalysis suffer from low throughput and high energy demands. Electroporation, which relies on strong localized electric fields to disrupt microbial membranes/capsids, has shown promise in liquids using nanowire-modified electrodes but is limited by transport to the nanowire tip and dependence on external power supplies. Fast airflow in building ventilation (~m/s) further challenges air-phase electroporation. The research proposes a self-powered, rapid air disinfection system that overcomes transport limitations by charging and trapping microbes and powers electroporation using vibration-driven triboelectric nanogenerators (V-TENGs).

The paper contextualizes limitations of existing air disinfection methods: HEPA filters separate but do not inactivate pathogens and create high pressure drops; UV- and photocatalysis-based systems often require long treatment times, have low throughput, or high energy consumption. Prior nanowire-assisted electroporation has demonstrated bacterial disinfection in water using Ag/CuO/ZnO/ZnO nanowires at low voltages through field enhancement at wire tips. TENG-powered disinfection has also been shown in water (wave-driven ball-in-ball TENG, hand-powered systems), but not in air and not for viruses. A performance comparison with literature shows previously reported air disinfection approaches either need long contact times (>10–30 min) at moderate airflow or achieve shorter treatment times (≥10 s) at much lower airflow rates (0.05–0.7 m/s), whereas the proposed system achieves complete inactivation in 0.025 s at 2 m/s.

System design: A resonance-vibration-driven (RV) air disinfection system integrates (i) a contact-separation-type vibration-driven TENG (V-TENG), (ii) a rectifying power management circuit, and (iii) a three-electrode disinfection filter (macro-mesh negative electrode; integrated positive Cu3P nanowire-modified copper plate and ground electrodes).

• Resonance matching: The V-TENG middle layer mass and spring constants were designed so its resonance frequency matches typical building ventilator vibration (~30 Hz; f = (1/2π)√(k/m)) to maximize amplitude and power.
• Disinfection filter: Air first passes a four-layer stainless-steel macro-mesh negative electrode (5 mm × 5 mm pores) to impart negative charge to microbes via contact electrification. It then flows between parallel positive (Cu3PNW-modified Cu plates) and ground electrodes separated by 1 cm, establishing a background field (~100 V/cm). Charged microbes are electrostatically trapped onto the nanowire-modified positive surface where highly localized fields (>10^7–10^8 V/m) at nanowire tips induce electroporation.

Electrode fabrication:

• Macro-mesh negative electrode: Stainless-steel foil (0.5 mm) cut to 6 cm × 6 cm with 5 mm × 5 mm square pores; 1–4 layers spaced by 5 mm in an acrylic holder.
• Positive electrode (Cu3PNW-Cu): Two-step process. (1) Electrochemical anodization of Cu foil (6 × 2 cm; 0.5 mm thick) in 3.0 M NaOH at 5 mA/cm^2 for 30 min to grow vertically aligned Cu(OH)2 nanowires (~5 µm length; ~50 nm diameter). (2) Phosphidation using sodium hypophosphite at 120 °C (downstream of furnace center at 300 °C) for 90 min under Ar to convert to Cu3P while retaining NW morphology (black surface). For nanoparticle control, phosphidation at 180 °C for 2 h yields Cu3P nanoparticles.
• Ground electrode: Stainless steel, 6 × 2 cm. Three positive and three ground electrodes integrated in parallel with 1 cm spacing.

V-TENG construction and operation:

• Structure: Acrylic three-layer device (top/middle/bottom). Al (4 × 4 cm, 25 µm thick) on top/bottom; middle has Al covered with 80 µm PFA film (4 × 4 cm). Middle layer mass: 20 g. Four springs (82.712 N/m each) create 2 mm gaps. Closed acrylic frame ensures durability.
• Operation: Mounted on shaker (1–40 Hz sweep; fixed 30 Hz), amplitudes 100–500 µm. AC output from top/middle and bottom/middle contacts; rectified to DC. Outputs measured with oscilloscope.

Prototype duct and testing:

• Acrylic duct cross-section 6 × 6 cm, length 1.4 m (laminar flow). Bioaerosols generated via nebulizer (Philips) from high-titer bacterial or viral feed; humidity set to 30% via second nebulizer. Airflow 0.5–2 m/s via compressed gas. Sensors monitored airflow, humidity, particle concentration, and pressure drop.
• Microbes: Escherichia coli (ATCC 15597), Bacillus subtilis (ATCC 23857), and bacteriophage MS2 (ATCC 15597-B1). E. coli and B. subtilis cultured to log phase; MS2 prepared via PEG precipitation.
• Quantification: After passing through the system, 0.5 m^3 of airflow was bubbled into 500 mL sterile DI water. Bacteria quantified by spread plating; MS2 by double agar layer. Log removal efficiency = −log10(C/C0). Triplicate plating and serial dilutions were performed. Intermittent aerosol tests toggled nebulizer on/off (5 min each) at 2 m/s and 30% RH.

Measurements and simulations:

• V-TENG outputs: Frequency sweep, amplitude dependence, post-rectification open-circuit voltage and short-circuit current; load-dependent power density (10^4–10^8 Ω).
• Contact efficiency: Ansys Fluent simulations for particle–mesh interactions across 1–4 mesh layers and different geometries (macro-mesh, slope, column) for particle diameters 10^−2–10 µm.
• Electric field: COMSOL simulations for a 9×9 NW array (5 µm length, 50 nm diameter), driven by ~100 V DC to estimate field enhancement at tips.
• Charge per microbe: Electrometer measurements of charge retained on the negative electrode with and without microbes; calculated charge per E. coli and per MS2 using simulation-derived contact efficiency (Eq. 3).
• Cu2+ release: ICP-MS of water capturing 0.5 m^3 airflow post-treatment. Intracellular ROS: DCFH-DA fluorescence compared with 0.1 mM H2O2 control.
• SEM/TEM morphology: SEM for E. coli and B. subtilis; TEM with negative staining for MS2 before/after treatment.
• Pressure drop: Compared macro-mesh system vs HEPA filter at 0.5–2 m/s.

• Self-powered rapid disinfection: >99.99% inactivation (>4.1 log removal; no detectable live organisms) of E. coli (Gram-negative), B. subtilis (Gram-positive; 3.9–>4.1 log), and MS2 bacteriophage achieved at airflow rates up to 2 m/s corresponding to 0.025 s treatment time.
• Low pressure drop: 2, 6, 13, and 24 Pa at 0.5, 1.0, 1.5, and 2.0 m/s, respectively. HEPA yielded ~105 Pa at 0.5 m/s and ≥200 Pa at 1.0 m/s (sensor limit).
• V-TENG performance: Peak resonance at 30 Hz. Output voltages (Vpp) at 30 Hz: 130, 162, 182, and 227 Vpp for 100, 200, 300, and 500 µm amplitudes. After rectification: 104 V open-circuit voltage, 62 µA short-circuit current. Maximum power density 125 W/m^2 at 10^6 Ω load.
• Robust disinfection across conditions: Complete inactivation at amplitudes 200–400 µm; at 100 µm, >3.7 log removal at 2 m/s. Effective over humidity 30–80%. Effective for intermittent aerosols (on/off 5 min cycles): no live microbes detected when powered. Complete inactivation across wide concentration ranges (E. coli 10^2–10^8 CFU/m^3; MS2 10^3–10^9 PFU/m^3).
• Necessity of charging and nanowires: Charge-model (with macro-mesh negative electrode) achieved >3.9 log removal at 2 m/s; no-charge-model achieved ~0.5 log. Cu3PNW electrodes enabled >3.9 log removal; Cu3PNP electrodes yielded <0.15 log under identical conditions.
• Contact efficiency: Four-layer macro-mesh achieved >99.1% contact for virus-sized (0.02–0.1 µm) and >99.6% for bacteria-sized (0.5–4 µm) particles; fewer layers reduced contact and disinfection.
• Microbe charging: Single-particle charges after mesh contact: E. coli ~6.1×10^−10 C; MS2 ~7.2×10^−12 C (vs <10^−15 C before contact).
• Electric field: Simulations showed localized fields >10^8 V/m at Cu3PNW tips under ~100 V DC, sufficient for electroporation; nanoparticles did not achieve sufficient fields.
• Mechanism specificity: Radical scavengers (IPA, BQ) had no effect; intracellular ROS generation was <3% of H2O2 control; Cu2+ release ~2 µg/L (well below 1000 µg/L drinking water standard); negligible temperature rise and insufficient contact time for thermal or mechanical killing. SEM/TEM showed electroporation pores (~100 nm) in bacteria and damaged MS2 capsids with internal staining, confirming electroporation as the primary mechanism.
• Performance vs literature: Achieves complete disinfection in 0.025 s at 2 m/s, outperforming prior methods that either require long times at moderate airflow or short times at low airflow.

The study demonstrates that coupling a resonance-matched vibration-driven triboelectric nanogenerator with a rationally designed three-electrode filter overcomes the transport-limited nature of nanowire-assisted electroporation in air. The macro-mesh negative electrode imparts substantial negative charge to airborne microbes with high contact efficiency, enabling rapid electrostatic trapping on a nanowire-modified positive electrode where intense localized fields cause electroporation. This integrated charging–trapping–electroporation sequence enables complete inactivation of representative bacteria and a virus at high airflow rates with minimal pressure drop and without external power. Comparative tests and simulations confirm the essential roles of the mesh charging step and nanowire geometry. Mechanistic controls exclude oxidative, ionic, thermal, or purely mechanical contributions, aligning observed morphological changes with electroporation. Relative to existing air disinfection technologies, the system achieves markedly shorter treatment times at higher throughputs, indicating strong relevance for ventilation-based air sanitation.

A self-powered resonance-vibration-driven air disinfection system using Cu3P nanowire-enhanced localized electric fields effectively inactivates airborne bacteria and viruses at high airflow (2 m/s) within 0.025 s while maintaining very low pressure drops. The V-TENG provides sufficient electrical output from ambient mechanical vibrations, eliminating the need for external power. The macro-mesh charging and nanowire-enabled electroporation are key to overcoming transport limitations and achieving rapid, efficient disinfection. This proof-of-concept indicates strong potential for integration into building ventilation systems for indoor air safety.

The work presents a proof-of-concept prototype tested in a laboratory duct that simulates building ventilation; field deployment in actual ventilation systems was not reported. Disinfection efficacy was demonstrated on model organisms (E. coli, B. subtilis, and MS2) rather than a broad panel of human pathogens. The reported log-removal values are constrained by initial microbial concentrations in challenge aerosols. Performance depends on achieving resonance with available mechanical vibrations (e.g., ~30 Hz ventilator vibrations).