Pb-MOF electrosynthesis based on recycling of lead-acid battery electrodes for hydrogen sulfide colorimetric detection

Abstract

Spent lead-acid batteries are environment emerging contaminants and very harmful to health. In this work, we developed one-pot electrochemical method of recycling lead electrodes for the preparation of Pb metal–organic framework, using 1,3,5-benzenetricarboxylic acid as organic ligand (Pb(btc)-1). In H2S solution, a color change can be observed on the Pb(btc)-1 surface, which is caused by PbS formation and, therefore, it was studied as a smart compound for H2S quantification. Colorimetric techniques, as diffuse reflectance and digital image (DI) analysis obtained on a smartphone, were used for H2S quantification. The grayscale and RGB color histograms were obtained from the recorded images and treated by partial least squares (PLS) regression method directly on a smartphone, or using the MATLAB® software. The colorimetric techniques showed greater sensitivity, resulting in a limit of detection of 0.11 mmol.L-1, which is slightly lower than the DI using MATLAB® software (0.21 mmol.L-1). The accuracies of the colorimetric techniques were similar and present feasible values when compared to Horwitz criteria. Thus, the H2S sensor ends the lead-acid battery recycling cycle, giving a colorimetric device by a low energy processing of the lead electrode.