Anisotropic Polymer Adsorption on Molybdenite Basal and Edge Surfaces and Interaction Mechanism With Air Bubbles.

Lei Xie,Qingxia Liu,Hao Zhang,Xin Cui,Qi Liu,Jingyi Wang,Jun Huang,Xiaogang Wang,Hongbo Zeng

doi:10.3389/fchem.2018.00361

Lei Xie, Qingxia Liu + Show 7 more

Open Access

https://doi.org/10.3389/fchem.2018.00361

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Abstract

The anisotropic surface characteristics and interaction mechanisms of molybdenite (MoS2) basal and edge planes have attracted much research interest in many interfacial processes such as froth flotation. In this work, the adsorption of a polymer depressant [i.e., carboxymethyl cellulose (CMC)] on both MoS2 basal and edge surfaces as well as their interaction mechanisms with air bubbles have been characterized by atomic force microscope (AFM) imaging and quantitative force measurements. AFM imaging showed that the polymer coverage on the basal plane increased with elevating polymer concentration, with the formation of a compact polymer layer at 100 ppm CMC; however, the polymer adsorption was much weaker on the edge plane. The anisotropy in polymer adsorption on MoS2 basal and edge surfaces coincided with water contact angle results. Direct force measurements using CMC functionalized AFM tips revealed that the adhesion on the basal plane was about an order of magnitude higher than that on the edge plane, supporting the anisotropic CMC adsorption behaviors. Such adhesion difference could be attributed to their difference in surface hydrophobicity and surface charge, with weakened hydrophobic attraction and strengthened electrostatic repulsion between the polymers and edge plane. Force measurements using a bubble probe AFM showed that air bubble could attach to the basal plane during approach, which could be effectively inhibited after polymer adsorption. The edge surface, due to the negligible polymer adsorption, showed similar interaction behaviors with air bubbles before and after polymer treatment. This work provides useful information on the adsorption of polymers on MoS2 basal/edge surfaces as well as their interaction mechanism with air bubbles at the nanoscale, with implications for the design and development of effective polymer additives to mediate the bubble attachment on solid particles with anisotropic surface properties in mineral flotation and other engineering processes.

Highlights

It is evident that the adsorption of carboxymethyl cellulose (CMC) is more difficult than guar gum most likely due to the negatively charged carboxyl groups of CMC that could induce stronger electrostatic repulsion with the negatively charged MoS2 basal plane (Lu et al, 2015; Xie et al, 2017d)
As compared to the formation of a compact polymer layer on the basal plane at 100 ppm CMC, the polymer adsorption on the edge plane at the same concentration was almost negligible, which coincided with water contact angle results
Direct force measurements between CMC functionalized atomic force microscope (AFM) tip and MoS2 showed about one order of magnitude higher adhesion on the basal plane than on the edge surface, which could be attributed to their difference in surface hydrophobicity and surface charge

Summary

Introduction

Molybdenite (MoS2), the most important mineral source of molybdenum, has exhibited excellent characteristics and functionality in a broad range of biomedical and engineering applications, such as hydrogen evolution catalysis (Jaramillo et al, 2007; Karunadasa et al, 2012; Li et al, 2016; Liu et al, 2016), friction and lubrication (Chhowalla and Amaratunga, 2000; Lee et al, 2010; Sheehan and Lieber, 2017), and clinical devices (Liu et al, 2014; Yin et al, 2014). Understanding the anisotropic surface properties and interaction mechanisms of MoS2 basal and edge planes with air bubbles is of both fundamental and practical importance

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