Efficient Removal and Recovery of Ag from Wastewater Using Charged Polystyrene-Polydopamine Nanocoatings and Their Sustainable Catalytic Application in 4-Nitrophenol Reduction

Abstract

This study addresses the long-standing challenges of removing and recovering trace silver (Ag) ions from wastewater while promoting their sustainable catalysis utilization. We innovatively developed a composite material by combining charged sulfonated polystyrene (PS) with a PDA coating. This composite serves a dual purpose: effectively removing and recovering trace Ag + from wastewater and enabling reused Ag for sustainable applications, particularly in the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The PS−PDA demonstrated exceptional selectivity to trace Ag + recycling, which is equal to 14 times greater than the commercial ion exchanger. We emphasize the distinct roles of different charged functional groups in Ag + removal and catalytic reduction performance. The negatively charged SO 3 H groups exhibited the remarkable ability to rapidly enrich trace Ag ions from wastewater, with a capacity 2−3 times higher than that of positively-N + (CH 3 ) 3 Cl and netural-CH 2 Clmodified composites; this resulted in an impressive 96% conversion of 4-NP to 4-AP within just 25 min. The fixed-bed application further confirmed the effective treatment capacity of approximately 4400 L of water per kilogram of adsorbent, while maintaining an extremely low effluent Ag + concentration of less than 0.1 mg/L. XPS investigations provided valuable insights into the conversion of Ag + ions into metallic Ag through the enticement of negatively charged SO 3 H groups and the in situ reduction facilitated by PDA. This breakthrough not only facilitates the efficient extraction of Ag from wastewater but also paves the way for its environmentally responsible utilization in catalytic reactions.

Improving the Anticorrosion and Self-Healing Properties of the Epoxy Coating Using the Mn–Zn2SiO4/PDA Composite

“…PDA is a bioinspired material that draws inspiration from mussel adhesive proteins. − The structure contains catechol and primary amine groups, , which impart it excellent adhesion to metal substrates, , metal coordination, , and antioxidant capabilities. , The abundant modifiable sites in its structure enable PDA to undergo chelation with metals, making it suitable for the modification of various functional materials. , Additionally, PDA exhibits an abundance of planar conjugated structures and donor–acceptor configurations, which contribute to its broad absorption spectra and excellent electrochemical properties. , The remarkable adaptability, strong adhesion to substrates, environmentally friendly degradation, and self-healing capabilities make PDA a promising material for corrosion-resistant modification. Li et al applied a PDA anticorrosion coating on the surface of N80 steel through PDA self-polymerization and assembly.…”

Copper sulfide-incorporated layered porous sulfur-doped graphitic carbon nitride nanosheets for an efficient catalytic reduction of 4-nitrophenol

“…3 Yet, the viable pathway of reduction of 4-NP to less toxic and readily reducible 4-aminophenol (4-AP), which is the essential intermediate product, finds applications in the dyeing industry (disperse, direct, sulfur, and acid dyes), medicine industry (vitamin B1, paracetamol and analgesic drugs), rubber industry (as an antioxidant), and photosensitive materials. 3–7 Among diverse methods of 4-AP production (sulfide-based reduction, iron powder reduction, and electrochemical reduction), iron powder reduction is a standard method in the chemical industry. However, this approach demands considerable amounts of iron powder and acid, resulting in an expensive and high iron content method that makes it challenging to manage, posing risks of environmental pollution if handled poorly.…”