Study on the adsorption properties of methyl orange by natural one-dimensional nano-mineral materials with different structures

Our plain-English summary of Study on the adsorption properties of methyl orange by natural one-dimensional nano-mineral materials with different structures, by L. Wu, X. Liu, G. Lv, et al (Scientific Reports, 2021).

The study

• Authors: L. Wu, X. Liu, G. Lv, R. Zhu, L. Tian, M. Liu, Y. Li, W. Rao, T. Liu, L. Liao
• Journal: Scientific Reports
• Published: 2021;11(1):10640
• Cited by: 47 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Methyl orange (MO) is a common anionic azo dye that is harmful to the environment and biology, so it must be treated innocuously before it can be discharged. Adsorption is an effective method to remove anionic dyes. Nanotube mineral is a natural one-dimensional adsorption material, and its unique morphology and structure endow it with good adsorption capacity. Although there are many related studies, there is a lack of in-depth discussions on the influence of nanotube's composition and structure on the adsorption of dyes and other pollutants. In this paper, two kinds of natural one-dimensional silicate minerals [halloysite nanotubes (HNTs) and chrysotile nanotubes (ChNTs)] with similar morphology but slightly different compositions and crystal structures were used as adsorbents, and MO solution was used as simulate pollutants. It is the first time to discuss in depth the influence of the composition and structure of nanotube minerals on their charge properties and the adsorption performance of methyl orange dyes. It is found that HNTs and ChNTs have different adsorption capacity due to the difference of electronegativity between Al3+ and Mg2+ in the crystal, so they possess negative and positive charges respectively in near-neutral solution, which leads to the adsorption capacity of MO by ChNTs with positive charges which is greater than that of HNTs.

In plain English

This was a laboratory chemistry study. It did not examine people, animals or disease. The authors compared two natural tube-shaped minerals as materials for removing methyl orange, an industrial dye, from water. One was halloysite nanotubes, supplied by China Kaolin Co. The other was chrysotile nanotubes from Linqu County, Shandong Province, which the authors cleaned and dispersed before use. Each mineral (0.05 g) was shaken with 20 mL of dye solution at a range of concentrations for 3 hours. The measured surface charge (zeta potential) was 3.45 mV for chrysotile and minus 18.2 mV for halloysite. This meant chrysotile was positively charged and halloysite negatively charged in neutral solution. The average maximum amount of dye taken up was 13.56 mg/g for halloysite and 31.46 mg/g for chrysotile, even though chrysotile had lower surface area and smaller pores. The authors concluded that the two minerals carry different surface charges because of differences in how their crystal structures curl, and that this led to significant differences in how much dye they adsorbed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory adsorption experiment comparing two natural mineral nanotubes (no human or animal subjects)
• Who was studied: No people or animals. Two mineral samples were studied: halloysite nanotubes from China Kaolin Co., Ltd., Suzhou, China, and chrysotile nanotubes from Linqu County, Weifang City, Shandong Province, China.
• Exposure: The minerals (halloysite nanotubes and chrysotile nanotubes, 0.05 g each) were exposed to 20 mL of methyl orange dye solution at different concentrations. They were shaken for 3 hours at room temperature. This was not a study of human exposure to asbestos.
• Main results:
  • Average maximum dye adsorption capacity was 13.56 mg/g for halloysite nanotubes and 31.46 mg/g for chrysotile nanotubes.
  • Zeta potential was 3.45 mV for chrysotile nanotubes and minus 18.2 mV for halloysite nanotubes. The authors stated that halloysite particles were negatively charged and chrysotile particles positively charged in neutral solution.
  • Chrysotile nanotubes took up much more dye than halloysite nanotubes, although their specific surface area, average pore size and pore volume were far lower.
  • Dye adsorption by halloysite fitted the Temkin model best (multi-layer adsorption). Dye adsorption by chrysotile fitted the Langmuir model best (single-layer adsorption).
  • Infrared spectra indicated better dye adsorption by chrysotile nanotubes than by halloysite nanotubes.
• The authors' conclusion: The authors concluded that the two nanotube minerals, though similar in shape, carry different surface charges because of the different curling of their crystal structures. They concluded that this leads to significant differences in how they adsorb the anionic dye methyl orange.
• Limitations the authors state:
  • The wettability of the inner surface of halloysite nanotubes could not be measured directly, so the authors used boehmite as a substitute surface.
  • No crystal structure data exist for halloysite, so the authors represented its structure with that of kaolinite.

Topics

Medical terms in this study, explained in our Lexicon: Silicate, Chrysotile, Crystal Structure.

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