In order to develop efficient visible light driven photocatalysts for environmental applications, novel polymeric g-C₃N₄ layered materials with high surface areas are synthesized efficiently from an oxygen-containing precursor by directly treating urea in air between 450 and 600 °C, without the assistance of a template for the first time. The as-prepared g-C₃N₄ materials with strong visible light absorption have a band gap around 2.7 eV. The crystallinity and specific surface areas of g-C₃N₄ increases simultaneously when the heating temperatures increases. The g-C₃N₄ materials are demonstrated to exhibit much higher visible light photocatalytic activity than that of C-doped TiO₂ and g-C₃N₄ prepared from dicyanamide for the degradation of aqueous RhB. The large surface areas, layered structure and band structure in all contributed to the efficient visible light photocatalytic activity. The efficient synthesis method for g-C₃N₄ combined with efficient photocatalytic activity is of significant interest for environmental pollutants degradation and solar energy conversion in large scale applications.

Continuous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during the high-pollution fall and winter seasons at Xi'an, Shaanxi Province, China from September 2003 through February 2004. Battery-powered mini-volume samplers collected PM_2.5 samples daily and PM₁₀ samples every third day. Samples were also obtained from the plumes of residential coal combustion, motor-vehicle exhaust, and biomass burning sources. These samples were analyzed for OC/EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. OC and EC levels at Xi'an are higher than most urban cities in Asia. Average PM_2.5 OC concentrations in fall and winter were 34.1±18.0 μg m⁻³ and 61.9±;33.2 μg m⁻³, respectively; while EC concentrations were 11.3±6.9 μg m⁻³ and 12.3±5.3 μg m⁻³, respectively. Most of the OC and EC were in the PM_2.5 fraction. OC was strongly correlated (R>0.95) with EC in the autumn and moderately correlated (R=0.81) with EC during winter. Carbonaceous aerosol (OC×1.6+EC) accounted for 48.8%±10.1% of the PM_2.5 mass during fall and 45.9±7.5% during winter. The average OC/EC ratio was 3.3 in fall and 5.1 in winter, with individual OC/EC ratios nearly always exceeding 2.0. The higher wintertime OC/EC corresponded to increased residential coal combustion for heating. Total carbon (TC) was associated with source contributions using absolute principal component analysis (APCA) with eight thermally-derived carbon fractions. During fall, 73% of TC was attributed to gasoline engine exhaust, 23% to diesel exhaust, and 4% to biomass burning. During winter, 44% of TC was attributed to gasoline engine exhaust, 44% to coal burning, 9% to biomass burning, and 3% to diesel engine exhaust.

The immobilization of a photocatalyst on a proper support is pivotal for practical environmental applications. In this work, graphitic carbon nitride (g-C₃N₄) as a rising visible light photocatalyst was first immobilized on structured Al₂O₃ ceramic foam by a novel in situ approach. Immobilized g-C₃N₄ was applied for photocatalytic removal of 600 ppb level NO in air under real indoor illumination of an energy-saving lamp. The photocatalytic activity of immobilized g-C₃N₄ was gradually improved as the pyrolysis temperature was increased from 450 to 600 °C. The optimized conditions for g-C₃N₄ immobilization on Al₂O₃ supports can be achieved at 600 °C for 2 h. The NO removal ratio could reach up to 77.1%, exceeding that of other types of well-known immobilized photocatalysts. Immobilized g-C₃N₄ was stable in activity and can be used repeatedly without deactivation. The immobilization of g-C₃N₄ on Al₂O₃ ceramic foam was found to be firm enough to overwhelm the continuous air flowing, which can be ascribed to the special chemical interaction between g-C₃N₄ and Al₂O₃. On the basis of the 5,5′-dimethyl-1-pirroline-N-oxide electron spin resonance (DMPO ESR) spin trapping and reaction intermediate monitoring, the active species produced from g-C₃N₄ under illumination were confirmed and the reaction mechanism of photocatalytic NO oxidation by g-C₃N₄ was revealed. The present work could provide new perspectives for promoting large-scale environmental applications of supported photocatalysts.

Simultaneous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during winter and summer seasons at 2003 in 14 cities in China. Daily PM_2.5 samples were analyzed for OC and EC by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance protocol. Average PM_2.5 OC concentrations in the 14 cities were 38.1 μg m⁻³ and 13.8 μg m⁻³ for winter and summer periods, and the corresponding EC were 9.9 μg m⁻³ and 3.6 μg m⁻³, respectively. OC and EC concentrations had summer minima and winter maxima in all the cities. Carbonaceous matter (CM), the sum of organic matter (OM = 1.6 × OC) and EC, contributed 44.2% to PM_2.5 in winter and 38.8% in summer. OC was correlated with EC (R²: 0.56–0.99) in winter, but correlation coefficients were lower in summer (R²: 0.003–0.90). Using OC/EC enrichment factors, the primary OC, secondary OC and EC accounted for 47.5%, 31.7% and 20.8%, respectively, of total carbon in Chinese urban environments. More than two thirds of China's urban carbon is derived from directly emitted particles. Average OC/EC ratios ranged from 2.0 to 4.7 among 14 cities during winter and from 2.1 to 5.9 during summer. OC/EC ratios in this study were consistent with a possible cooling effect of carbonaceous aerosols over China.