Dispersion of Manganese Dioxide Particles Using Anionic Technol PG and Sodium Cholate in the Preparation for Application as Films on Substrates

Abstract

Manganese dioxide (MnO2) is widely used in cosmetics and self-cleaning materials because of the high refractive index and photocatalytic activity of this compound. In the present work, the surfaces of MnO2 particles were coated with a commercially available anionic phospholipid mixture, Technol PG, and sodium cholate(SC). These coated particles were readily dispersed in water and subsequently applied as films onto glass substrates by drop-casting.

Manganese dioxide (MnO2; Figure 1a) has numerous uses, including in catalytic systems intended to promote the oxidation of water, electrochemical energy storage and conversion units, and cosmetics.^1,2 In many of these applications, it is important to coat the surfaces of MnO2 particles^3–10 and the coating of metal oxide surfaces with phospholipids such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine has been reported. ¹¹ However, the use of commercially available phospholipids would be preferable with regard to establishing practical applications.

Figure 1.

(a) Structure of manganese dioxide (MnO2). (b) Molecular structure of PG and composition of Technol PG. Molecular structure of sodium cholate (SC).

This study examined the feasibility of using Technol PG (Figure 1b) mixed with sodium cholate (SC; Figure 1c) for the surface coating of MnO₂. Technol PG is a mixture of anionic phosphatidyl glycerols that can be obtained commercially from the Yokozeki Company and is less expensive than conventional anionic phosphatidyl glycerols. Previously, our group demonstrated that mixtures of Technol PG and SC allowed the effective dispersion of bioactive compounds such as fullerene, ¹² resveratrol, ¹³ and cannabidiol. ¹⁴ These prior studies confirmed that MnO₂ particles could also be dispersed using this mixture of Technol PG and SC. In a typical experiment, MnO₂ particles were dispersed in water at 0.1 wt% together with Technol PG powder (5.0 wt%) and SC (2.0 wt%) after which the suspension was ultrasonicated for 2 min. In the absence of Technol PG and SC, the MnO₂ particles were observed to precipitate. In contrast, after mixing with the Technol PG and SC, these particles remained dispersed in the aqueous medium. The particle sizes were subsequently evaluated by dynamic light scattering (DLS). The bare MnO₂ particles produced a peak in the particle size distribution at approximately 91 nm while the value after the addition of the Technol PG and SC was 44 nm. When we measure zeta potentials of the dispersions before and after mixing with Technol PG and SC, their zeta potentials were –29.7  ±  0.4 mV and −32.6  ±  0.44 mV, respectively. In addition, phase-contrast microscopy revealed that large aggregate of MnO₂ particles (Figure 2a) became smaller after mixing with Technol PG and SC (Figure 2b). This result suggests that the aggregation of the MnO₂ particles was suppressed by surface coating. This surface modification was helpful with regard to forming MnO₂-based films on substrates. In the case that uncoated MnO₂ particles were drop-cast onto a glass substrate, a film exhibiting poor transparency was obtained and the particles were readily removed from the substrate by manual abrasion. In sharp contrast, drop-casting of the coated MnO₂ particles gave a film having higher transparency. In addition, these particles were not easily dislodged when the substrate surface was rubbed. These data confirm that the use of Technol PG and SC could be helpful with regard to preparing films of MnO₂ particles on substrates.

Figure 2.

Phase-contrast microscopy of manganese dioxide (MnO2) (0.1 wt%) without (a) and with (b) the mixture of Technol PG (5.0 wt%) and sodium cholate (SC) (2.0 wt%).

In summary, this work demonstrated a means of coating MnO₂ nanoparticle surfaces with Technol PG and SC. The coated nanoparticles were readily dispersed in water and were found to form films on glass substrates. Because MnO₂ has practical applications as a water oxidation catalyst, this process could lead to the design of a variety of self-cleaning surfaces in future.

Experimental

Technol PG was obtained from the Yokozeki Company while SC was purchased from TCI. MnO₂ particles were purchased from Sigma-Aldrich. Zeta potentials were measured by a Malvern Panalytical Zetasizer Nano ZSP.

The surface coating of MnO₂ particles was performed by mixing Technol PG (5.0 wt%) and SC (2.0 wt%) with MnO₂ (0.1 wt%) in water using ultrasonication for 2 min.

Supplemental Material

sj-jpg-1-npx-10.1177_1934578X231163386 - Supplemental material for Dispersion of Manganese Dioxide Particles Using Anionic Technol PG and Sodium Cholate in the Preparation for Application as Films on Substrates

Supplemental material, sj-jpg-1-npx-10.1177_1934578X231163386 for Dispersion of Manganese Dioxide Particles Using Anionic Technol PG and Sodium Cholate in the Preparation for Application as Films on Substrates by Noriyuki Uchida, Masayoshi Yanagi and Hiroki Hamada in Natural Product Communications