P-nitrophenol electro-oxidation on a btma(+)-bentonite-modified electrode

Abstract

Phenol and its derivatives arc regarded as 'priority pollutants' and p-nitrophenol (p-NP), in particular, is of great interest due to its toxicity and frequent presence in waste waters and fresh waters. Straightforward, inexpensive methods to identify p-NP in water, however, is lacking. In the present study, an electrochemical technique using clay-modified electrodes to measure p-NP was investigated as a potentially promising method to fill that gap. A glassy carbon electrode (GCE) was modified with a thin layer of Na-enriched bentonite and a series of benzyltrimethylammonium (BTMA(+))-bentonites (BTMA(+)-B) in order to confirm these materials as p-NP electrosensitive. A series of organobentonites was synthesized using different BTMA(+)/bentonite ratios. The materials obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and a low-temperature nitrogen adsorption-desorption method. A monolayer arrangement of BTMA(+) within the interlamellar region of beidellite-rich smectite was confirmed. Deterioration of the textural properties was observed with increase of BTMA(+). loading. The electro-oxidation of p-NP in an acidic medium on BTMA(+)-B-modified GCE was investigated. The cyclic voltammetry method with a three-electrode cell was used. The reference electrode was Ag/AgCl in 3 M KCl and a Pt foil was the counter electrode. For each electrochemical measurement, a different BTMA(+) loading in BTMA(+)-B was used as the material for GCE coating and applied as the working electrode. The electrochemical activity of BTMA(+)-B-based electrodes increased with BTMA(+) loading. The results confirmed that the organophylic character of the BTMA(+)-B-modified surface was the main influence on the electrochemical activity of the BTMA(+)-B-based GCE; the influence of textural properties was almost negligible. The increased electrode activity toward p-NP was achieved by the adsorption of p-NP on the electrode surface, the process that commonly precedes the electro-oxidation. The present study showed that synthesized materials could potentially be used in an electrochemical test for the presence of p-NP in water solutions.