Sustainable electrochemical integrated-hybrid process for degrading caffeine and producing green hydrogen

Abstract

Several studies prove that caffeine (CF) is a persistent chemical substance with toxic effects on the environment, thus indicating the real need for its degradation in domestic and industrial wastewaters. Thus, the development of efficient techniques for water treatment and removal of emerging pollutants of high solubility is of great importance due to the management of environmental and health risks. Within this framework, the electrochemical oxidation of organic molecules and concurrent hydrogen production employing membrane-equipped electrochemical devices might significantly increase the sustainability and commercial viability of this process. Here, we provide a method for improving operational efficiency and sustainability for removing CF from water (at the anodic reservoir) and simultaneously producing green H2 at the cathodic compartment by using Ti/TiO2-RuO2-IrO2 (DSA) and boron-doped diamond (BDD) anodes. Experimental conditions such as anode and current densities were investigated during the electrochemical treatment, determining that BDD electrode by applying 45 mA cm−2 favored the generation of a larger amount of oxidants (hydroxyl radicals and sulfate-based oxidants), and promoting a higher removal of CF and organic load, besides the greater production of green H2 (0.46 L). Analytical approaches were used for monitoring the CF concentration decay and for determining its mechanism of degradation. Differential electrochemical mass spectroscopy (DEMS) analysis was conducted to determine the composition of the gas phase produced at cathodic reservoir during the electrochemical oxidation of real water matrix containing CF in the anodic reservoir, demonstrating that only H2 is produced with high purity. This investigation allows us to establish a novel win–win strategy to decrease the electrolysis voltage and treat waste effluent to produce valuable byproducts, such as green H2.