Aluminum Metal–Organic Frameworks with Photocatalytic Antibacterial Activity for Autonomous Indoor Humidity Control

Abstract

There is an increasing need to maintain the indoor humidity at a comfortable and healthy level without relying on high energy-consuming and potentially germ-infested air-conditioning systems. Water adsorbents exhibiting reversible moisture adsorption/desorption ability as well as sufficient antibacterial activity are highly expected to achieve humidity control in an autonomous and safe way. Metal−organic frameworks (MOFs) featuring high porosity and designability show potential in meeting these requirements in a singular platform. Given the low toxicity and the rich abundance of aluminum in nature, a family of isoreticular Al-terephthalate-based MOFs were systematically evaluated in terms of the static and kinetic water adsorption/ desorption and the photocatalytic bacteria-killing behavior. In particular, CAU-1-OH exhibits a desired working range (40−60% RH), a high working capacity (0.41 g g −1 ), an excellent cycle performance (500 cycles), and a high photocatalytic killing efficiency (99.94%) against Escherichia coli. As a proof of concept, the air filter prepared by coating CAU-1-OH on a commercial nonwoven fabric is capable of buffering against sudden humidity changes caused by the infiltration of outside air and effectively reducing the contamination of bioaerosol or particulate matter. The study significantly advanced the development of next-generation water adsorbents with antibacterial activity for residential humidity control.

High Water Adsorption MOFs with Optimized Pore‐Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal

“…The optimized UiO‐67‐4Me‐NH 2 ‐38 % obviously displays excellent performance with respect to these key parameters for autonomous indoor humidity control (Figure 4, Supplementary Table 4, 5). Its WC ads and WC des values are calculated to be 57.6 and 49.8 wt %, surpassing most reported MOFs having the function of indoor humidity control [2, 29–31, 55] except NU‐1500‐Cr [32] (Figure 4 b). However, UiO‐67‐4Me‐NH 2 ‐38 % manifests the best performance in practical efficiency, giving η ads of 88.2 % and η des of 76.3 %, outperforming NU‐1500‐Cr with η ads /η des =80/65 % (Figure 4 c) due to a suitable S hl for swing.…”

“…As the proportions of amino modified ligands increase from 29 % to 38, 47, 59 and 67 %, the major water uptake and release are gradually centered to take place in optimal 45–65 % RH range, of which UiO‐67‐4Me‐NH 2 ‐47 %, ‐59 % and ‐67 % MOFs display relatively low water‐uptake capacities. Therefore, the mixed‐ligand UiO‐67‐4Me‐NH 2 ‐38 % is optimized as the best candidate for the indoor humidity control application, which features ideal S‐shaped adsorption isotherms and high water‐uptake capacity with the adsorption and desorption inflection points exactly lying in the ASHRAE range among few exceptional MOF examples, [2, 29–32, 55] not significantly affected by crystal‐size variation (Figure 4 a and Supplementary Figure 52, Table 3).…”

“…To meet the criteria of high and steep water adsorption within ASHRAE range of 45-65 %RHfor moisture control, the adsorption inflection point where pore-filling starts and the desorption inflection point where water release starts should fall into this requisite range.E xcept UiO-67-4Me-NH 2 -29 %a nd UiO-67-4Me-COOH-38 %, all other mixedligand MOFs fit this requirement (Supplementary Table 2). However,the main water adsorption and desorption of UiO-67-4Me-OH-37 %a nd UiO-67-4Me-2NH 2 -38 %a re not concentrated in the preferable range of 45-65 %R H. To our delight, the water adsorption profiles of UiO-67-4Me-NH 2 -x%series MOFs can be finely tuned into this requisite range by varying the ligand ratios.A st he proportions of amino modified ligands increase from 29 %t o3 8, 47, 59 and 67 %, the major water uptake and release are gradually centered to take place in optimal 45-65 %R Hr ange,o fwhich UiO-67-4Me-NH 2 -47 %, -59 %and -67 %MOFs display relatively low water-uptake capacities.Therefore,the mixed-ligand UiO-67-4Me-NH 2 -38 %i so ptimized as the best candidate for the indoor humidity control application, which features ideal Sshaped adsorption isotherms and high water-uptake capacity with the adsorption and desorption inflection points exactly lying in the ASHRAE range among few exceptional MOF examples, [2,[29][30][31][32]55] not significantly affected by crystal-size variation (Figure 4a and Supplementary Figure 52, Table 3).…”

“…Theh igh porosity of metal-organic frameworks (MOFs) have been proven conducive to the adsorption of gases and vapors,s howing application prospect in the field of water adsorption and pollutant capture. [12][13][14][15] Many water-stable MOFs [10,[16][17][18][19][20] have been synthesized and applied to desiccation, [10] heat pumps/chillers, [16,[21][22][23] water harvesting, [24,25] desalination, [26,27] and ozone decomposition, [28] and pioneering works for autonomous indoor humidity control have been reported with MOFs of Y-shp-MOF-5, [2] Cr-soc-MOF-1, [29] BIT-66, [30] CAU-1-OH [31] and NU-1500-Cr. [32] As an ideal porous material for water adsorption-related humidity controlling application, the following criteria are prominent: [2,31] (1) high water-uptake capacity,g ood water stability,a nd low cost, (2) steep adsorption isotherms within the ASHRAE requisite range of 45-65 %R H, and (3) highly reproducible cycling performance and easy regeneration.…”

“…[12][13][14][15] Many water-stable MOFs [10,[16][17][18][19][20] have been synthesized and applied to desiccation, [10] heat pumps/chillers, [16,[21][22][23] water harvesting, [24,25] desalination, [26,27] and ozone decomposition, [28] and pioneering works for autonomous indoor humidity control have been reported with MOFs of Y-shp-MOF-5, [2] Cr-soc-MOF-1, [29] BIT-66, [30] CAU-1-OH [31] and NU-1500-Cr. [32] As an ideal porous material for water adsorption-related humidity controlling application, the following criteria are prominent: [2,31] (1) high water-uptake capacity,g ood water stability,a nd low cost, (2) steep adsorption isotherms within the ASHRAE requisite range of 45-65 %R H, and (3) highly reproducible cycling performance and easy regeneration. Moreover,t ypically S-shaped sorption isotherms at room temperature (RT) are preferred with the adsorption and desorption branches (a) featuring apronounced hysteresis,(b) concentrated in the middle of ASHRAE 45-65 %RHrange,and (c) showing high and comparable adsorption and desorption working capacities (Figure 1).…”