Colorimetric cutoff indication of relative humidity based on selectively functionalized mesoporous silica

[Display omitted] •Novel colorimetric turn-on RH indicator based on mesoporous SiO2-dye was synthesized.•Influence of diameters of pores on humidity indicating function has been studied.•Color change for non-functionalized mesoporous SiO2 indicator was gradual.•Cutoff color change was achieved via selective functionalization of mesoporous SiO2.•Capillary condensed water from humid air has been used as reaction trigger. We present a novel – cutoff concept of colorimetric indication of relative humidity based on dye dissolution in condensed water in capillaries of selectively functionalized mesoporours host SiO2 material. Consistently high levels of indoor air humidity induces mold and algae growth which represent a potential risks for human health and have deteriorating effect on walls as well. Simple localized humidity detection of high humidity with naked eye especially at places with low air circulation, where growth of mold usually starts first, is therefore highly desirable. The reporting dye was integrated in the non-functionalized mesoporous silica matrix with different pore diameters and selective-functionalized mesoporous silica material. After exposure to the environment of different air humidities the dye dissolved in water causing color change of adsorbent. With the use of adsorbents with different mesopore diameters high ability to tune the value of relative humidity when complete capillary condensation occurred was achieved. Materials with pore diameters of 3.0 nm, 3.5 nm and 7.0 nm exhibit gradual color change when reaching relative humidity up to 55, 79 and 88 RH % respectively. After selective methylation of the material with 7.0 nm pore diameter, non-gradual cutoff color change was achieved. Sample exhibited color change at narrow range of relative humidity (cutoff color change). Due to selective functionalized outer surface the dye dissolution occur only in condensed water in pores and therefore provide colorimetric indication only in this range. Selectively modified silica material has a great potential for a straightforward detection of high humid environment.