In-situ Synthesis of Ag Nanoparticles for High Efficient Reduction of Methylene Blue

Organic dyes in wastewater have become a critical problem due to their nonbiodegradable nature and high toxicity and may have negative effects on human and animal health. For example, the methylene blue (MB), one of the most commonly used organic dyes, can interfere with the photosynthesis and oxygen exchange of aquatic organisms. Thus far, different methods have been developed to address this issue and remove methylene blue from the waste water like adsorption, oxidation, reduction, membrane filtration, and photocatalytic degradation. Among the aforesaid methods, the nanocatalytic reduction of MB into its reduced form, i.e. leucomethylene blue, is more desirable because it has been reported to have many applications in different industrial areas.[۱] Herein, we report a rapid, facile, room temperature and one stepsynthesis for the water soluble Ag nanoparticles (AgNPs) and simultaneous fast and efficient catalytic reduction of MB. In this study, the reduction of MB by sodium borohydride (NaBH۴) in the presence of in situ synthesized AgNPs as a homogeneous catalyst at ۲۵°C was conducted and it’s catalytic activity towards the reduction of MB was studied. The controlled reduction reaction was carried out in which ۲۰۰ μL of freshly prepared ۰.۳ M NaBH۴ as a reducing agent was added into ۳ mL (۱۰ mg/L) MB solution followed by the addition of ۱۰ μL of ۷.۵ mM AgNO۳ solution as a catalyst. As soon as Ag+ was added, AgNPs were synthesized in situ in the solution due to the presence of NaBH۴ and played role of nanocatalyst, the color of MB solution changed from blue to colorless less than ۳۰ sec. To obtain spectral data and measurement of reduction of MB, UV–Vis absorption spectrophotometer equipped with a diode-array detector was used. The removal efficiency of MB without the catalysts was low, reached about ۵% (for MB and NaBH۴) within ۳۰min. In the presence of the AgNPs, the MB removal was greatly improved and occurred quickly at the first ۲۰ s and the removal efficiency of ۹۵% obtained. Therefore, the results showed in situ synthesis of AgNPs is an very efficient homogeneous nanocatalyt for the reduction of MB.