1. Introduction
With accelerating urbanization and improved building airtightness, indoor air quality (IAQ) has become a central issue in public health and human settlement environment research. The World Health Organization (WHO) has stated that approximately 38% of global respiratory diseases are related to indoor pollution exposure [1]. In the post-pandemic era, the clarification of aerosol transmission mechanisms has elevated air disinfection from an “auxiliary measure” to a “key technology for interrupting the transmission chain” [2]. Traditional air purification devices mostly focus on single functions and are prone to efficiency bottlenecks or secondary pollution in complex multi-pollutant scenarios. In recent years, the rapid iteration of semiconductor ultraviolet light-emitting diode (UV-C LED) technology has provided a physical foundation for building safe, efficient, and multi-target synergistic indoor air comprehensive purification systems. Based on recent domestic and international field measurement data and literature research, this paper systematically reviews the technical principles, application effectiveness, and development pathways of UV-C LED coupled photocatalysis and HEPA filtration.
2. Characteristics and Health Hazards of Indoor Air Pollutants
Indoor air pollutants are mainly divided into three categories:
(1) Biological pollutants: Bacteria, viruses, fungal spores, and allergens. Droplets (diameter >5 μm) settle quickly and have short transmission distances; aerosols (diameter ≤5 μm) can remain suspended in air for hours to days, penetrate deep into the respiratory tract, and significantly increase the probability of cross-infection [3].
(2) Particulate matter pollution: PM2.5, PM10, and ultrafine particles (UFPs, <0.1 μm). Long-term exposure can induce oxidative stress, damage the alveolar-capillary barrier, and is associated with cardiovascular diseases and neurodegenerative disorders [3].
(3) Chemical pollutants: Formaldehyde, benzene series compounds, TVOCs, and ozone. These mainly originate from building materials, furniture, and cleaning agents. Even low-concentration long-term exposure can cause eye and nose irritation, headaches, and immune system dysfunction.
These three types of pollutants often exhibit “coexistence-synergistic” characteristics. For example, particulate matter can act as a carrier for VOCs and pathogens, while ozone reacting with unsaturated VOCs can generate secondary organic aerosols (SOA), further reducing environmental comfort and health safety. Therefore, single purification technologies struggle to meet the modern indoor space demand for multi-target synergistic control of “biological–particulate–chemical” pollution.
3. Principles and Technical Advantages of UV-C LED Disinfection Technology
3.1 Germicidal Mechanism
UV-C band (100–280 nm) photons possess high energy (4.43–12.4 eV) and are strongly absorbed by microbial nucleic acids, inducing the formation of cyclobutane pyrimidine dimers (CPDs) and other photoproducts between adjacent pyrimidine bases. This blocks DNA/RNA replication and transcription, achieving broad-spectrum inactivation [4]. Numerous in vitro studies show that the UV-C inactivation dose (D90) for SARS-CoV-2, influenza virus, Mycobacterium tuberculosis, and drug-resistant bacteria generally ranges between 3–15 mJ/cm².
3.2 Comparison with Traditional Mercury Lamps
Low-pressure mercury lamps and UV-C LEDs (260–280 nm) are the two mainstream deep-ultraviolet light sources. The former relies on mercury vapor discharge, contains 5–20 mg of mercury, requires several minutes of warm-up, has a lifespan of 6,000–10,000 hours, and its 254 nm radiation easily produces ozone. In contrast, UV-C LEDs use semiconductor p-n junction electroluminescence, offering mercury-free environmental protection, millisecond-level start/stop, and a lifespan of ≥25,000 hours (L70). Through optical design, they effectively suppress ozone generation. UV-C LEDs also feature a narrow spectrum (full width at half maximum 10–15 nm), enabling precise matching with microbial absorption peaks and reducing ineffective energy consumption. Their chip-level packaging supports array arrangements and micro-optical integration, facilitating uniform irradiation and safe human-machine coexistence design. In terms of environmental protection, response speed, lifespan, and design flexibility, UV-C LEDs are becoming the preferred solution for intelligent, portable, and highly reliable ultraviolet disinfection applications.
4. Synergistic Mechanism of UV-C LED Coupled Photocatalysis and HEPA Filtration
Single technologies have inherent limitations: HEPA is ineffective against gaseous pollutants and prone to microbial growth; photocatalysis has limited degradation rates for high-concentration VOCs and may generate intermediate by-products; UV-C direct irradiation only acts on aerosols flowing through the light path and has limited inactivation effect on surface-adhered pollutants. The coupling of the three can form a closed-loop system of “interception–inactivation–mineralization.”
4.1 HEPA Physical Interception Layer
High-efficiency particulate air filters (HEPA, H13/H14 grade) achieve ≥99.97% removal efficiency for the most penetrating particle size (MPPS) of 0.3 μm. Through diffusion, interception, and inertial impaction mechanisms, they efficiently capture bacterial carriers, fungal spores, allergens, and PM2.5. However, dust accumulation increases pressure drop, and humid environments may turn the filter media into a breeding ground for microorganisms.
4.2 UV-C LED In-situ Disinfection Layer
Positioned upstream or midstream of the HEPA filter, it directly inactivates airborne pathogens in the airflow. Simultaneously, periodic irradiation of the HEPA filter surface inhibits biofilm formation and extends filter replacement cycles. Field measurements show that under wind speed of 0.5 m/s and irradiation dose ≥5 mJ/cm², the equipment can achieve 3-log inactivation rates of 99.2%–99.9% against Escherichia coli, Staphylococcus aureus, and MS2 bacteriophage [5, 6].
5. Conclusion
With advantages such as mercury-free operation, long lifespan, instant start/stop, and precise spectrum, UV-C LED is gradually replacing traditional ultraviolet light sources and becoming the core disinfection component in indoor air purification equipment. Coupling with HEPA filtration and modified photocatalysis technology enables the construction of a three-stage synergistic system of “physical interception–ultraviolet inactivation–catalytic mineralization,” simultaneously addressing biological, particulate, and chemical pollution. This significantly improves purification efficiency and human-machine coexistence safety across multiple scenarios. Future efforts must focus on breakthroughs in photothermal management, catalyst stability, standardized testing, and safe application of 275 nm far-UVC, driving indoor air governance from “single purification” toward an “intelligent, whole-domain, health-oriented” systematic engineering approach.
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