Ultralow Resistance Two-Stage Electrostatically Assisted Air Filtration by Polydopamine Coated PET Coarse Filter.

Airborne particulate matters (PM) pose serious health threats to the population, and efficient filtration is needed for indoor and vehicular environments. However, there is an intrinsic conflict between filtration efficiency, air resistance, and service life. In this study, a two-stage electrostatically assisted air (EAA) filtration device is designed and the efficiency-air resistance-filter life envelope is significantly improved by a thin coating of polydopamine (PDA) on the polyethylene terephthalate (PET) coarse filter by in situ dopamine polymerization. The 8 mm thick EAA PDA-140@PET filter has a high filtration efficiency of 99.48% for 0.3 µm particles, low air resistance of 9.5 Pa at a filtration velocity of 0.4 m s-1 , and steady performance up to 30 d. Compared with the bare PET filter, the penetration rate for 0.3 µm particles is lowered by 20×. The coated PDA is of submicron thickness, 10-3  × the gap distance between filter fibers, so low air resistance could be maintained. The filter shows steadily high filtration efficiency and an acceptable increase of air resistance and holds nearly as many particles as its own weight in a 30 day long-term test. The working mechanism of the EAA coarse filter is investigated, and the materials design criteria are proposed.

Gaseous formaldehyde removal: A laminated plate fabricated with activated carbon, polyimide, and copper foil with adjustable surface temperature and capable of in situ thermal regeneration.

Formaldehyde is one of the most common indoor air pollutants in Chinese residences. This study introduces a novel laminated plate with adjustable surface temperature to remove gaseous formaldehyde. The plate is fabricated with activated carbon, polyimide, and copper foil via thermal compression. The plate can be regenerated in situ by applying a direct current to the copper foil. Adsorption-regeneration cycle tests were conducted to evaluate the plate's formaldehyde removal performance. The overall removal efficiency of the fabricated laminated plate with glue mass fraction of 25% and thickness of 1.5 mm was about 30% at the face velocity of 0.8-1.2 m/s. The pressure drop was about 5 Pa. Its removal ability can be regenerated in situ in 8 minutes by increasing the surface temperature to 80°C. The fabricated laminated plate showed good durability after 52 cycles of adsorption-regeneration tests. The results indicate that the proposed laminated plate can enhance the purifying efficiency and enlarge the life span of ordinary, cheap sorbents. It makes cheap materials with low performance suitable for air purification.

Electrostatic Polydopamine-Interface-Mediated (e-PIM) filters with tuned surface topography and electrical properties for efficient particle capture and ozone removal.

Ambient particulate matter (PM) poses severe environmental health risks to the public globally, and efficient filtration technologies are urgently needed for air ventilation. In this contribution, to overcome the efficiency-resistance trade-off for fibrous filtration, we introduced an electrostatic polydopamine-interface-mediated (e-PIM) filter utilizing a combined effect of particle pre-charging and filter polarizing. After delineating the PM-fiber interactions in electrostatic filtration, we designed a composite fiber structure and fabricated the filters by a two-step dip-coating. The surface topography and electrical potential of the polyester (PET) coarse substrates were regulated by successively coating polydopamine (PDA) layers and manganese oxide clusters. By this means, an 8-mm-thick Mn-P @ P-100 filter possessed improved efficiency of 96.05%, 97.60%, and 99.14% for 0.3-0.5 µm, 0.5-1 µm, and 1-3 µm particles, the ultralow air resistance of 10.4 Pa at a filtration velocity of 0.5 m/s, and steady ozone removal property. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. Compared with the pristine PET substrates, the efficiency for 0.3-0.5 µm particles expanded 12 times. We expect e-PIM filters and the filtration prototype will be potential candidates as effective and low-cost air cleaning devices for a sustainable and healthy environment.