Design of a comprehensive experiment for the degradation of nitrogenous organic pollutants by DNA-AuNCs
[Objective]This paper outlines a comprehensive experiment designed to investigate the degradation of nitrogenous organic pollutants by DNA-AuNCs.Organic pollutants,especially nitro-containing organic ones such as nitrophenols and azo dyes are difficult to degrade towing to their stable structures.These pollutants can be absorbed by humans,posing significant risks to both human health and the environment.Therefore,finding efficient ways to remove nitrogen-containing organic pollutants from the environment has become a key research focus.Nitrophenol compounds,with their low electron cloud density in the benzene ring,are challenging to oxidize directly.A more eco-friendly approach is to transform nitrophenol into aminophenol via reduction.Sodium borohydride(NaBH4)is a simple and safe reducing agent.However,the mixture of nitrophenol and NaBH4 struggles to react quickly,highlighting the need for an effective catalyst to improve the reaction rate.Gold nanoclusters(AuNCs),rapidly developing nanomaterials,have attracted significant attention owing to their excellent surface effect,quantum size effect,unique fluorescence characteristics,and high catalytic activity.AuNCs prepared using DNA as a template have been widely used in the catalytic and biosensing fields thanks to the excellent DNA biocompatibility and its high degree of programmability in terms of length,charge,and sequence.[Methods]With DNA-functionalized AuNCs as catalysts,we investigated their catalytic degradation ability for nitrogenous organic pollutants.This was based on a standard model catalytic reaction of 4-nitrophenol(4-NP)and methyl orange dye pollutants.For instance,4-nitrophenol is a nonbiodegradable noxious organic pollutant.Its reduction product,4-aminophenol,serves as an important intermediate in numerous fields.The catalytic reduction of 4-NP to 4-AP followed the Langmuir-Hinshelwood mechanism.When 4-NP was mixed with NaBH4,the color of the mixture turned yellow,and the characteristic absorption peak of 4-NP at 400 nm decreased with the addition of DNA-AuNCs.Eventually,the solution became colorless after the reaction,providing a simple method for tracking the process through spectroscopic measurements.Several factors influencing the catalytic performance were systematically studied,including different DNA-AuNC templates,dosage,pH,and additives.We analyzed the kinetic and thermodynamic properties of the catalyst by examining the reaction rates at different temperatures.[Results]Our experimental results showed that DNA-AuNCs prepared with an oligocytosine chain as a template exhibited superior catalytic performance.Furthermore,the catalytic activity of DNA-AuNCs was higher under neutral pH and high-temperature conditions.By determining the activation energy(Ea)from the reaction rate constants(k)at different temperatures,we also calculated the activation enthalpy(ΔH).These results indicated that the catalytic reaction was endothermic,with the reaction rate constant increasing as the temperature increased.Moreover,among all variants,C20-AuNCs demonstrated the fastest reaction rate and the smallest activation energy.This indicates that C20-AuNCs need to overcome a low reaction energy barrier in the catalytic degradation of pollutants.[Conclusions]Our comprehensive experiment aligns with the cutting-edge trends of science and technology,including nanotechnology,organic pollutant degradation,and other societal hot spots.It integrates theoretical knowledge from multiple fields,such as nanomaterials,spectroscopy,and catalysis.The experiment also employs a variety of experimental equipment and methods,thereby broadening students'academic visions and cultivating scientific research literacy and innovation skills.
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