Photooxidative Degradation of Aromatic Carboxylic Acids in Water: Influence of Hydroxyl Substituents

Abstract

The UV/H 2 O 2 process was applied for the degradation of aromatic carboxylic acids (ACAs). Benzoic acid, salicylic acid, gentisic acid, and gallic acid are chosen as typical water pollutants representing ACAs with the increased number of hydroxyl groups. The effect of the structural characteristics of ACAs and UV/H 2 O 2 process parameters on their degradation kinetics was investigated by a statistical/empirical approach employing the design of experiments and response surface methodology. Different optimal conditions for maximal degradation rates were established, while degradation rates followed the decreasing order benzoic acid > salicylic acid > gentisic acid > gallic acid with the increasing number of hydroxyl groups. The inversed order was established in the case of mineralization kinetics. Structurally influenced degradation pathways of studied ACAs, with the shared sequence related to the preferable hydroxylation position at the benzene ring, are reflected in the observed changes in the biodegradability and toxicity toward Vibrio fischeri during UV/H 2 O 2 treatment.

Diclofenac removal by simulated solar assisted photocatalysis using TiO2-based zeolite catalyst; mechanisms, pathways and environmental aspects

“…The portion of adsorbed organics on the catalyst surface exhibited much lower toxicity than that present in the bulk (Fig. 9), supporting the above assumption that by-products adsorbed might be lower C-atom aliphatics, which are usually less toxic than aromatics [33,50].…”

Prediction of key structural features responsible for aromaticity of single-benzene ring pollutants and their photooxidative intermediates

“…S1, Supplementary material). Initial pH values (adjusted by 0.1 M NaOH or H 2 SO 4 ) and [H 2 O 2 ] were determined as optimal within the investigated range for each studied pollutant in previous studies using RSM modeling approach [28][29][30][31][32][33] and are summarized in Table S2 (Supplementary material). The duration of each experiment depended on the pollutant structure and ranged from 16 to 105 min in order to decrease parent pollutant concentration to a quarter (t 3/4 (PP)) of the initial value.…”

“…The duration of each experiment depended on the pollutant structure and ranged from 16 to 105 min in order to decrease parent pollutant concentration to a quarter (t 3/4 (PP)) of the initial value. Samples were taken from the reactor in the predefined treatment periods: t 0 , t 1/2 (PP) (time required to decrease parent pollutant concentration to a half of the initial value) and t 3/4 (PP), using determined degradation rates [28][29][30][31][32][33], and thereafter were immediately analyzed. All experiments were performed in triplicates and averages were reported; the reproducibility was >95%.…”

“…quinones. According to the degradation mechanism of studied aromatics by HO Å , the main reactive species in the applied photooxidative treatment, the formation of various dihydroxybenzene (DHB) derivatives occurs, with or without parent substituents [28][29][30][31]. The presence of DHBs is often associated with the presence of benzoquinones (BQ) as well [42].…”

Oxidative degradation of salicylic acid by sprayed WO3 photocatalyst

“…These methods are unable for the wastewater treatment, because they have limited applicability [2,3]. Advanced oxidation processes (AOP) are effective techniques for the degradation of organic compounds; where OC are finally converted into the form of CO 2 and H 2 O. AOP is based on the generation and utilization of hydroxyl radicals ( • OH) to decompose the OC [1,4]. Salicylic acid is a pollutant present in wastewaters of pharmaceutical industry, paper milling, and cosmetic industries, etc.…”