Shenyang University of Chemical Technology

Metal-organic frameworks (MOFs) have shown major promise for electrochemical dopamine (DA) sensing owing to their high surface area, tunable pores, and abundant active sites. In this work, iron-tetra(4-carboxyphenyl)porphyrin-coordinated assembly metal-organic framework (Fe-TCPP MOF material) capable of effectively catalyzing the oxidation of DA was synthesized. Subsequently, it was combined with reduced graphene oxide (rGO) with excellent electrical conductivity and perfluorosulfonic acid polymer (Nafion) with cation selectivity to construct an electrochemical sensor that could synergistically enhance the sensitivity of DA detection. The resulting Fe-TCPP/rGO/Nafion electrode detected DA from 0.1 to 3200μM with a detection limit of 0.021μM, outperforming most reported sensors. It also maintained high stability, selectivity, and interference resistance over repeated cycles, and achieved recoveries of 84.84-110.76% in real samples. Mechanistically, the porous Fe-TCPP MOF increased accessibility of catalytic sites; rGO improved charge transport and π-π adsorption; and Nafion provided cation-exchange selectivity and electrostatic preconcentration. These complementary roles yielded synergistic gains in catalytic oxidation, preconcentration, selectivity, and anti-interference. The integrated strategy offered a practical route to high-performance MOF-based DA sensors and a useful reference for developing efficient analytical materials.

A novel strain of Paracoccus sp. QD-21, which is capable of simultaneous heterotrophic nitrification and aerobic denitrification, was isolated and investigated for the potential in removal of nitrogen in wastewater treatment. The strain exhibited nitrogen removal rates of 5.55, 3.35, and 2.78mg/(L·h) for NH4+-N (100mg/L), NO2--N (100mg/L), and NO3--N (100mg/L), respectively. Notably, QD-21 maintained substantial nitrogen removal efficiency under high concentrations of inorganic nitrogen, highlighting its remarkable tolerance to complex nitrogenous conditions. Optimal nitrogen removal occurred with sodium succinate as carbon source, C/N 7:1, pH 8.41, 140rpm, 38.41°C, and inoculum size 4.56% (v/v). Analysis using molecular biology techniques revealed the presence of genes associated with the nitrification process, such as amo and hao, in QD-21. This confirms the nitrification pathway of strain: NH4+-N → NH2OH → NO2--N → NO3--N. Additionally, the presence of nirK, norB, and nosZ confirms the denitrification pathway in QD-21: NO3--N → NO2--N → NO → N2O → N2. Meanwhile, the presence of nirBD, nark, glnL, glnA, gltB, and nasA indicates that a portion of nitrogen is assimilated into biomass through the ammonia assimilation pathway, which supports cellular biosynthesis and growth at the expense of metabolic energy. Furthermore, in practical wastewater tests QD-21 achieved removal efficiencies of 75.5% for NH4+-N and 55.8% for COD. Such findings demonstrate the great potential of strain QD-21 in treating nitrogen pollution from diverse sources.