boron and phthalic-acid

Phthalic acid esters (PAEs) are a group of endocrine disruptors commonly used as plasticizers. The present study compares the electrochemical oxidation of PAEs at boron-doped diamond (BDD) anode with that at Pt anode. Both the degradation and the mineralization processes of PAEs became much slower when using the Pt anode compared with that using the BDD anode. Moreover, the degradation rates of PAEs decreased at the BDD anode but increased at the Pt anode with increasing alkyl chain length. This was attributed to the different oxidation mechanisms at the two anodes. The BDD electrode has an inert surface that holds a large amount of strong oxidants as free hydroxyl radicals ((*)OH), causing electrophilic attack by (*)OH to be the main reaction. Therefore, degradation of PAEs became slower on the BDD anode due to there being less available electronic energy as the alkyl chain length increased. However, adsorbed oxidants (PtO(x)(+1)) with low oxidation ability tended to form on the surface of the active Pt anode. Therefore, PAEs with longer alkyl chains promote faster degradation owing to their stronger hydrophobicity. Detection of intermediates in the GC/MS tests confirmed the above conclusion, in which oxidation of dimethyl phthalate on BDD occurred on the aromatic ring at first, while the alkyl chain was preferentially attacked on the Pt anode.

Topics: Boron; Diamond; Electrodes; Electrolysis; Environmental Restoration and Remediation; Esters; Phthalic Acids; Platinum

The enhancement on degradation of two typical organic pollutants, phenol (Ph) and phthalic acid (PA) on boron-doped diamond (BDD) electrode is particularly investigated in this study. Results show that ultrasound (US) has remarkable influence on electrochemical (EC) oxidation of the two pollutants including degradation efficiency, EC oxidation energy consumption, mass transport and electrochemical reaction. With US, the enhancement on degradation efficiency and decreasing of EC oxidation energy consumption of Ph are more obvious. US can also efficiently reduce the average electrochemical oxidation energy consumption (AE), decreasing by 74 and 69% for Ph and PA, respectively. Mass transport process can be greatly accelerated by US. The mass transport coefficients of Ph and PA both reach 2.0 x 10(-5)ms(-1) in ultrasound-assisted electrochemical (US-EC) process, from 5.4 x 10(-6) and 6.7 x 10(-6) ms(-1) in EC, increasing by 270 and 199%, respectively. The reaction amount of Ph decreases by 79% with US, from 6.49 x 10(-10) to 1.39 x 10(-10) mol cm(-2). For PA, the reaction amount decreases from 1.25x10(-11) to 3.11 x 10(-12) mol cm(-2) with US. The oxidation peak current increases by 32% for Ph. While for PA, there is no direct oxidation happened in US-EC process.

Topics: Boron; Diamond; Electrochemical Techniques; Electrodes; Oxidation-Reduction; Phenol; Phthalic Acids; Ultrasonics