Thermodynamic study of the interactions of salicylic acid and granular activated carbon in solution at different pHs

Abstract

The inappropriate use of pain medication has led to the appearance of salicylic acid molecules (aspirin's metabolite excretion) in surface water, which causes problems for the environment. The adsorption process using activated carbon is one of the processes that is used for the removal of organic compounds present in the aqueous phase; however, the percentage of removal depends on the physicochemical properties of the adsorbent and the adsorbate such as: pore size, surface area, surface chemistry, molecular size and solubility. In this work, we have studied the adsorbent-adsorbate interactions through the determination of the immersion enthalpy of the activated carbon in salicylic acid aqueous solutions; due to the solute and activated carbon surface have functional groups capable of ionized with the pH, the adsorption study was carried out at pH 2, 7, and 11. The activated carbons selected for the study were a granular activated carbon and a reduced activated carbon to 1173 K; as the immersion liquid were used salicylic acid aqueous solutions with concentrations between 0.072 mmol/ l and 0.72 mmol/ l, the solutions at pH 2 and 11 were prepared with HCl and NaOH solutions, respectively. It was determined that the immersion enthalpy is between À7.39 J /g and À22.5 J/g for the reduced activated carbon and between À7.63 J/g and À16.73 J/g for the granular activated carbon.

Selected pharmaceuticals removal using algae derived porous carbon: experimental, modeling and DFT theoretical insights

“…During the adsorption on PCLD@NaOH at pH 3, the aspirin and ketoprofen molecules are in their neutral forms. 14,23,64 They can form strong H-bonds with oxygen-containing surface functional groups present in PCLD@NaOH and be not repelled by the surface positive charge. 65 Accordingly, they presented their highest aspirin adsorption at pH 3.4, which was close to the original pH of the aspirin solution.…”

Microwave assisted green synthesis of Fe2O3/biochar for ultrasonic removal of nonsteroidal anti-inflammatory pharmaceuticals

“…At pH 3.2, the SA, Nap, and Keto molecules are in their neutral forms. [49][50][51][52] They can form strong H-bonds with oxygen-containing surface functional groups present in the surface of Fe 2 O 3 /biochar and be not repelled by the surface positive charge. 53 Accordingly, they revealed their maximum removal at pH 3.2.…”

“…Hence, the removal of SA, Nap, and Keto in molecular form was favorable to the Fe 2 O 3 /biochar, while the adsorption of the anionic form of SA, Nap, and Keto was unfavorable. [49][50][51][52]54 In addition, the acidic and basic surface functions of the prepared adsorbent were determined according to the Boehm. Thus, 0.5 g of the powder was mixed with 50 mL of one of the three bases solutions NaHCO 3 (0.05 M), Na 2 CO 3 (0.05 M) and NaOH (0.05 M) to identify the organic acid surface groups (-COOH), (-COO-) and (-OH), respectively, as described elsewhere.…”

Green Microalgae Scenedesmus Obliquus Utilization for the Adsorptive Removal of Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) from Water Samples

“…As shown in Table 1, the pKa 1 (carboxylic group) and pKa 2 (phenol group) values of salicylic acid are 3.0 and 13.6, respectively and the pKa (carboxylic group) value of ibuprofen is 4.9. In the case of salicylic acid, diprotic species (neutral) are dominant (about 90%) at pH values below 2, monoprotic species (negative) are dominant at pH values between 4 and 13 and completely dissociated species (negative) are dominant (about 70%) at pH values above 13 [69] (see Figure S1a (Supplementary Information) [69,70]). The carboxylic group of ibuprofen is not charged at low solution pH (equal or below to pKa).…”

“…The carboxylic group of ibuprofen is not charged at low solution pH (equal or below to pKa). However, as the solution pH increases from 3 to 7, the carboxylic group begins to dissociate and almost all ibuprofen molecules are negatively charged when the solution pH is above 7 [70,71] (see Figure S1b (Supplementary Information) [69,70]). Thus, at the pH of adsorption experiments (pH 7), electrostatic repulsive interactions between the negatively charged surface of Scenesdesmus obliquus and the negatively charged ibuprofen and salicylic acid and ibuprofen species cannot be disregarded.…”