Sodium tetraborate 10 hydrate

Watermelon rinds (WMR) were collected as a waste material (to be discarded) from the shopping centers, Doha-Qatar. Collected rinds were washed with distilled water to eliminate any dirt. All chemicals used were of the analytical grade. Sodium hydroxide, sulfuric acid, nitric acid, sodium carbonate, hydrochloric acid, and sodium tetraborate-10-hydrate were the products of Sigma-Aldrich (Darmstadt, Germany). Adsorbate tested was acridine orange dye (AO, Fluka Chemicals, Germany). Ultrapure water (18.2 MΩ) was used to prepare and dilute dye solutions. A stock solution of 100 mg/L of AO was made in deionized water. The pH of dye solutions was attuned using a mixture of sodium tetraborate-10-hydrate (Na₂B₄O₇.10H₂O, 50 mM) and 0.1 M NaOH or 0.1 M HCl. All experimental runs were carried out at room temperature.

The chemicals used were of the analytical grade and were used as acquired with no additional purification. Sodium hydroxide, sodium tetraborate–10–hydrate and hydrochloric acid were purchased from Sigma–Aldrich (Eschenstrasse, Taufkirchen, Germany). Rose bengal (RB) was a product of BDH Laboratory Supplies (Poole, UK). Values of pH were adjusted as previously mentioned [10 (link)]. Pure water was used for diluting the RB dye solutions to 1000 ppm. Pineapple leaves (PAL) were used after drying as will be described in their method of preparation.