Removal of Neutral Red from Aqueous Solution by Ni/Al Layered Double Hydroxide (LDH)

Sorption is a common treatment for removing organic pollutants from the natural environments [1]. Dyes and pigments are widely used, mostly in the textiles, paper, plastics, leather, food and cosmetic industry to color products. Most of the dyes, such as neutral red, are toxic and must be removed before discharging into receiving streams since their effluents can reduce light penetration and photosynthesis. Neutral red is a cationic dye that is used extensively for nuclear counterstaining in biological research [2]. Neutral red attracts noteworthy attention to innovate effective techniques for its removal. Layered double hydroxides (LDHs), which first were reported in the mid-19th century, are mixed-metal hydroxides that consist of octahedral double hydroxyl layers with exposed positive surface charges and interlayer anions [3]. LDHs have biological, pharmaceutical, and environmental applications [4]. The general known formula of LDH is [M1-x2+ Mx3+(OH)2] x+Ax/mm- nH2O, where M2+ and M3+ are divalent and trivalent cations, respectively, each with an ionic radius similar to that of Ni2+. Among the various types of LDH species, a hydrotalcite-like compound consisting of an Mg Al–, Ni Al–, or Mg Ni Al–CO3 double hydroxides with carbonate as interlayer anions, is commonly used for a variety of applications. However, they seem to be less effective at binding hydrophobic organic compounds (HOCs), such as pesticides or phenols, because of their strongly hydrophilic surface. Hence, current study was devoted to synthesize Ni/Al LDH via free hydrothermal method. As-obtained Ni-Al LDH was used to investigate their applications as an adsorbent for the adsorption of neutral red from aqueous solution. Effects of various experimental conditions such as pH, contact time and initial dye concentration, on the adsorption were evaluated through a batch equilibrium technique. In addition, the adsorption isotherms, kinetics and thermodynamics have been performed. The results are promising for further application of magnetic hollow spheres as an efficient low cost and recyclable adsorbent for dye removal.