The collaborative removal of copper/nitrate via catalytic hydrogenation processes over Pd/TiO₂ catalyst

Nitrate (NO₃^-) and Cu²⁺ are common water pollutants that were frequently detected in varied waters such as metallurgical wastewater, electronic wastewater, etc. It is challenging to achieve simultaneous removal of NO₃^- and Cu²⁺. Herein, we prepared varied Pd/TiO₂ catalysts for the catalytic hydrogenation reduction of Cu²⁺ and NO₃^-, and found that single Cu²⁺ could be effectively reduced (100 %) within 15 min, while the removal of NO₃^- was ignorant. Interestingly, the catalytic reduction of NO₃^- was triggered rapidly with the presence of Cu²⁺, where Cu²⁺ was still efficiently removed. The detected NO₃^- reduction intermediate products were NO₂^-, NH₄⁺ and N₂, and the selectivity for N₂ and NH₄⁺ in the final products were 27 % and 73 %, respectively, reflecting a synergistic treatment of multiple pollutants with clean products. The active H generated on the Pd active sites and newly formed Cu species played vital roles for the reduction of Cu²⁺ and NO₃^-, respectively. The low valence Cu was regenerated by the appearance of active H and cyclically joined NO₃^- reduction. Conventional technologies for NO₃^- removal are often inhibited or compromised in the presence of Cu²⁺, whereas this study circumvents these limitations and achieves efficient simultaneous removal of both Cu²⁺ and NO₃^-, with negligible generation of the byproduct NO₂^-. This study provided a new pathway to simultaneously catalytic eliminate heavy metal and NO₃^- and insights into the promote effect of coexisted Cu²⁺ for NO₃^- elimination.