Photocatalytic preconcentration of Bi on TiO2 nanoparticles and their determination by ETAAS

VILLAFAÑE GASTON; BAZAN, VANESA; MARATA, ARIEL; LARA, RODOLFO; PABLO PACHECO

Mendoza

Simposio; 15 Rio Symposium on Atomic Spectrometry; 2019

Bismuth (Bi) is an element that in small quantities can alter the properties of metallurgical materials. Copper smelters impose significant fines for the presence of concentrations above Bi to 0.05% in Cu concentrates and can absolutely reject those that exceed that value. Knowing the concentration of Bi allows to identify the quality of the mineral to be extracted 1 . Bi-level analysis of traces requires the development of new methods for selective separation, concentration, purification and determination. In this context, solid phase micro extraction (µSPE) has been proposed. The search for new adsorbents, as is the case with some nanomaterials, has been decisive for this evolution. One of the main problems in µSPE methods is the aggregation of sorbent materials. This deficiency is overcome by applying dispersive solid phase microextraction techniques (D-µSPE) 2 . This procedure allows more efficient contact between the analytes and the sorbent. Recently,titanium dioxide nanoparticles (NP-TiO 2 ) have been used as a solid sorbent due to their physical and chemical properties, low cost, non-toxicity, high specific surface area and high adsorption capacity. NP-TiO 2 are also used in photocatalytic processes, where due to their greater surface area in relation to volume, they have greater catalytic activity. Under irradiation of a specific wavelength, metals are adsorbed on the surface of TiO 2 as Pd 3 . Inthe present work NP-TiO 2 for the D-µSPE of Bi ions was implemented. In thismethodology, a homemade mini-photoreactor was used, where the NP-TiO 2 wereirradiated with UVA in the presence of a sacrificial agent ethanol, generating a selective photocatalytic adsorption of Bi on NP-TiO 2 by decomposition of the ethanol. After adsorption, the sample is centrifuged, where the supernatant was removed and the Bi is eluted with nitric acid 5% by sonication, then centrifuged again and its concentration in the eluate was determined by electrothermal atomic absorption spectrometry (ETAAS) with a reduced temperature program, without the pyrolysis stage. The study of significant variables was carried out through a reduced factorial design where the following factorswere included: amount of NP-TiO 2 , volume of ethanol, UVA exposure time and sonication time. The optimization stage was performed using the response surface method, implementing a Box-Behnken design. The procedure allowed the determination of Bi with detection and quantification limits of 3.4 and 1 .3 ng L -1 respectively. The relative standard deviation was 4.5% for a Bi solution of 0.50 µg L -1 , with a preconcentration factor (PF) of 100 when 30 mL of sample was treated with 10 mg of NP-TiO 2 and eluted with 0.5 mL of HNO 3 . The method was applied to the determination of Bi in previously digested copper mineral samples, which was framed in the parameters of green chemistry by decreasingreagent use, obtaining quantitative recoveries.