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Polypyrrole (PPy) composite coatings have been effectively synthesized in the presence of TiO2 and V-TiO2 nanoparticles on carbon steel by electrochemical method in aqueous oxalic acid solutions. These coatings were characterized by different surface analysis methods. TEM results confirmed that the size of V-TiO2 nanoparticles (11.91 ± 1.03 nm) was smaller than that of TiO2 nanoparticles (17.22 ± 2.84 nm), therefore increasing the interaction between PPy composite coatings and metal surface. The electrical conductivity measurement was carried out to examine the electrical properties of TiO2/PPy and V-TiO2/PPy composite coatings. Besides, the electrochemical behaviors of these coatings were also studied in 0.1 M HCl solution by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. Results showed that the V-TiO2/PPy composite coatings exhibited better anti-corrosion performance than TiO2/PPy composite coatings. The exceptional anti-corrosion performance of PPy composite coatings was associated with the synergistic effect of the increase in physical barrier, prevention of charge transport by TiO2 nanoparticles and the complex passive film on the metal surface.

Healthy indoor air quality (IAQ) is essential to the productivity and wellbeing of building occupants. In order to study the indoor air quality in residential buildings in Xi'an in the cold climate zone, this study selected seven natural ventilation (NV) and three mechanical ventilation (MV) samples to evaluate the levels of fine particulate matter (PM2.5) and carbon dioxide (CO2) through long-term monitoring. The results showed that it is worth studying the ventilation options in January with the lowest outdoor temperature of −0.78 °C, and the highest PM2.5 pollution of 149 μg/m3. The monthly average operation duration of the MV showed an obvious seasonal distribution, which was consistent with the degree of outdoor pollution. Compared with NV, the short-term operation of MV cannot significantly improve indoor air quality, but better results can be achieved after increasing the operation duration. When outdoor pollution is serious, the mean daily operation duration of MV recommended in this study is greater than 9 h. The probability of excessive CO2 concentration (above 1000 ppm) of MV was 26%, which is higher than that of NV (9%). The CO2 concentration increased with the increase in the MV operation duration, and the indoor CO2 concentration was proportional to the temperature difference between indoor and outdoor. The control and operation of the MV system should consider the influence of PM2.5 and CO2 simultaneously. Long-term operation of the MV system combined with short-term NV may be a ventilation strategy suitable for IAQ control of residential buildings in Xi'an.