NO is the main precursor of photochemical smog. Since the SCR system of marine diesel engines has many disadvantages, this paper proposes an effective wet method to remove NO from the exhaust gases of marine diesel engines. Experiments were performed in a bubble column reactor to study the absorption of NO using sodium persulfate (Na 2 S 2 O 8 )/urea ((NH 2 ) 2 CO) solutions from a simulated gas stream. The effects of various operating parameters on NO removal were investigated, including reaction temperature, urea concentration, Na 2 S 2 O 8 concentration and the initial pH value of Na 2 S 2 O 8 /urea solutions. The experimental results showed that the NO removal efficiency increased with increasing reaction temperature (25–80 °C) and increasing Na 2 S 2 O 8 concentration (0.01–0.2 mol/L). When the concentration of urea was higher than 0.5 mol/L at 60 °C, 1 mol/L at 70 °C or 2 mol/L at 80 °C, the NO removal efficiency increased with the increase of urea concentration (0.1–4 mol/L). The highest NO removal efficiency was 99.7%, occurring at 80 °C when the concentrations of Na 2 S 2 O 8 and urea were 0.1 mol/L and 4 mol/L, respectively, and the concentration of nitrate was 14.93 mg/L. The optimal urea conditions were well below the legal limit of 60 mg/L. The NO removal efficiency increased with the increase of initial pH value within the herein investigated range of 7–9. All the experimental data showed that the novel system not only achieved effective NO removal efficiency, but also reduced the nitrate in wastewater, which could thus be applied to denitrification of marine engine exhaust gases.
Xiuyong Chen,Jianhui Yuan,Jing Huang,Kun Ren,Yi Liu,Shaoyang Lu,Hua Li
This study aims to further enhance the anti-corrosion performances of Al coatings by constructing superhydrophobic surfaces. The Al coatings were initially arc-sprayed onto steel substrates, followed by deposition of polyurethane (PU)/nano-Al 2 O 3 composites by a suspension flame spraying process. Large-scale corrosion-resistant superhydrophobic PU/nano-Al 2 O 3 -Al coatings were successfully fabricated. The coatings showed tunable superhydrophilicity/superhydrophobicity as achieved by changing the concentration of PU in the starting suspension. The layer containing 2.0 wt.%PU displayed excellent hydrophobicity with the contact angle of ∼151° and the sliding angle of ∼6.5° for water droplets. The constructed superhydrophobic coatings showed markedly improved anti-corrosion performances as assessed by electrochemical corrosion testing carried out in 3.5 wt.% NaCl solution. The PU/nano-Al 2 O 3 -Al coatings with superhydrophobicity and competitive anti-corrosion performances could be potentially used as protective layers for marine infrastructures. This study presents a promising approach for fabricatiing superhydrophobic coatings for corrosion-resistant applications.
In harsh marine environments, the long-term protection performance of organic coatings is not ideal. Based on this, a strategy for constructing a triple-functional nano-pigment was proposed. Zinc oxide (ZnO) grown on boron nitride (BN) with polydopamine (PDA) as an interface layer (PDA-BN@ZnO nano-pigment) was prepared. This strategy not only avoided the accumulation of BN but also improved the interface compatibility between nano-pigment and silicon-epoxy resin. Characterization analyses validated that ZnO had been successfully grown onto PDA-modified BN nanosheets . Polarisation curves obtained in the solution phase showed that compared with the Al-alloy immersed in pure 3.5 wt% NaCl solution, the introduction of PDA-BN@ZnO caused i corr to decrease from 2.11 × 10 −5 A/cm 2 to 9.47 × 10 −9 A/cm 2 . Combined with the significant enhancement of the low-frequency impedance modulus (|Z| 0.01 Hz ) of the scratched PDA-BN@ZnO/SE coatings, the effective corrosion inhibition of the prepared nano-pigment was demonstrated. In addition, |Z| 0.01Hz of PDA-BN@ZnO/SE composite coating after immersion for 60 days was as high as 10 10 Ω·cm 2 with only about 0.3 orders of magnitude lower than the initial value. The excellent protective properties of the composite coating were due to the synergistic effects of improved barrier properties, chloride ion retention and corrosion inhibition.
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