Porphyrin/MgCl2/Silica Gel Composite as a Cobalt-free Humidity Indicator

Abstract

In order to develop cobalt-free humidity indicator, the composite consisted of porphyrin, MgCl2, and silica gel was prepared. The composite exhibited a reversible color change from green to purple under dry and humid conditions, respectively.

Surface treatment of silica nanoparticles for stable and charge-controlled colloidal silica

“…13,14 SiO 2 (silica) nanoparticles are being utilized in a wide range of industrial applications, including as thickening agents, desiccants, toothpaste additives, and adsorbents. [15][16][17][18] With the increase in the demand for and production of nanomaterials, the general public will have a higher possibility of being exposed to engineered nanomaterials. Thus, the Working Party on Manufactured Nanomaterials (WPMN) of the Organization for Economic Cooperation and Development (OECD) selected 14 nanomaterials to analyze for potential human health risks.…”

Quantitative Analysis for a Color-Change of Humidity Indicator by Microscopic Absorption Spectrometry

“…As has been reported, 5 1 can be prepared from 3 (Method B in Scheme 3). In Method B, a 2-propanol solution (10 cm 3 ) of 3 (0.7 μmol) and an aqueous solution (2 cm been adsorbed on SiO2, the solvent was evaporated.…”

“…4 Recently, we reported on porphyrin-SiO2-MgCl2 composites (1) as a humidity indicator using dichloro(tetraphenylporphyrinato)phosphorus chloride (3a). 5 The pH change arose from the reaction of MgCl2 with a silanol group of SiO2 under dry conditions to form a Si-O-Mg bond along with the release of a proton (Eq. (1) in Scheme 2), 6 and turned to neutral under humid conditions by hydrolysis of the Si-O-Mg to Si-OH and Mg(OH)2 (Eq.…”

Paper-Based Humidity Sensors as Promising Flexible Devices, State of the Art, Part 2: Humidity-Sensor Performances

“…Their development primarily followed a directive issued by the European Community (EC), in 1998, which classified products containing cobalt (II) chloride from 0.01 wt.% to 1 wt.% as toxic. Studies have shown that there is a fairly large range of materials that can also change color when exposed to a moisture [157][158][159][160][161][162][163][164][165][166][167]. For example, Matushima et al [159][160][161] presented a series of reports on reversible humidity-sensitive indicator films prepared from the combination of a dye with a sugar-based hydrogel, e.g., agarose or k-carrageenan, that undergo reversible color changes due to the appearance of an aggregated form of the dye at high humidity and its subsequent disintegration at low humidity.…”