Correlação estrutura-desempenho do ZnO na fotodegradação de poluentes e na redução eletroquímica de CO2 em CO

Abstract

Anthropogenic activities generate excessive amounts of organic and inorganic pollutants, which are often released into water, air, and soil without adequate treatment. Heterogeneous photocatalysis has emerged as a promising approach for the photodegradation of organic contaminants, while electrocatalysis offers an efficient pathway for the electrochemical reduction of CO2. In this study, the effect of synthesis temperature and amine functionalization on the physicochemical properties and performance of zinc oxide (ZnO) was investigated in photo and electrocatalytic processes applied to:(i) the degradation of organic pollutants and (ii) the electrochemical reduction of CO2. The ZnO samples were tested for the photodegradation of pharmaceuticals (Amiloride and Ciprofloxacin) and dyes (Methylene Blue and Rhodamine B). The ZnO sample synthesized at 100 °C exhibited superior photocatalytic performance compared to those obtained at higher synthesis temperatures. This result can be attributed to the synergy between the Zn(OH)2/ZnO structural phases combined with the higher specific surface area of the material. (ii)The ZnO sample was modified with monoethanolamine, and its characterization revealed that the functionalization led to materials with distinct morphology and surface groups.The amino-functionalized sample, ZnO/Met-100, exhibited superior performance in the electrochemical reduction of CO2 to CO, achieving a Faradaic efficiency of approximately 90% for CO at current densities exceeding -100 mA cm-2.This result is attributed to the presence of amino groups on the ZnO surface, which enhance CO2 adsorption and increase selectivity toward CO formation. The in situ FTIR spectroscopy study enabled the monitoring of reaction intermediates and the proposal of a possible reaction mechanism. Electrochemical impedance spectroscopy (EIS) results confirmed that the presence of amino groups on the functionalized ZnO significantly reduced the charge-transfer resistance, thereby facilitating the kinetics of the electrocatalytic process. The stability of the amino-functionalized ZnO was investigated under electrochemical operating conditions, demonstrating excellent durability over 100 h of continuous operation in a membrane electrode assembly (MEA) cell. The system operated at a current density of 50 mA cm-2, maintaining a Faradaic efficiency above 70% and a total cell potential of approximately 2.7 V. These results reinforce the viability of the material for sustainable electrocatalytic applications.