Organic Geochemistry And Photodegradation Of Organic Pollutants In The Environment

Polycyclic aromatic hydrocarbons (PAHs) belong to a class of organic contaminants of great environmental concern. They have grasped much attention due to their carcinogenic potential and ubiquitous presence in the environment. Various forms of PAHs in coals or from coal combustion may affect human, especially indoor coal combustion. In the meantime, PAHs in raw coal can reduce or even poison the activity of catalysts in the refinery, making the stockpile of liquid product unstable. Many literatures concluded that most of the PAHs come from fossil-fuel combustion. However, their pollution from raw coal were usually neglected.The abundances of sixteen polycyclic aromatic hydrocarbons (PAHs) on the priority list of U.S. Environmental Protection Agency (USEPA) have been determined in fourteen Chinese and American coals. The ranks of the samples range from lignite, bituminous coal, anthracite to natural coke. The results show that the total PAHs content ranged from0.31to57.6μg/g coal (on a dry basis). It varied with coal rank and is highest in the maturity range of bituminous coal rank. High-molecular-weight (HMW) PAHs are predominant in low-rank coals, but low-molecular-weight (LMW) PAHs are predominant in high-rank coals. The Low-sulfur coals have a higher PAHs content than high S coals. It may be explained by an increasing connection between disulfide bonds and PAHs in high-S coal. In addition, it leads us to conclude that the PAH content of coals may be related to the depositional environment. Fly ash and bottom ash samples were collected from a coal-fired power plant located in Anhui province, China. In the fly ashes, the Σ16PAH (total amount of16PAHs) and the CPAHs (total amount of eight carcinogenic PAHs) levels varied from0.93to2.08μg/g,0.26to0.87μg/g, respectively. In the bottom ashes, Σ16PAH and the CPAHs levels varied from2.83to5.32μg/g,1.76to3.76μg/g, respectively. The CPAHs levels of some ashes, especially for the bottom ashes, are above the limits regulated by several countries, indicating that this type of coal combustion product need special treatment before landfill. Fly ashes were dominated by medium molecular weight (MMW)PAHs and low molecular weight (LMW) PAHs, while bottom ashes were abundant in the5-and6-ring PAHs species. Thirty-three soil samples were collected from the Luling, Liuer, and Zhangji coal mines, in the Huaibei and Huainan areas, Anhui Province, China, in2007. The sum of16US-EPA PAHs ranged from0.13to3.54μg/g (dry weight basis) with a mean concentration of0.84μg/g. Among the three sampling sites selected around the coal mines, the site at the Luling Coal Mine revealed maximum concentration of PAHs, while minimum concentration was observed at the site at Zhangji Coal Mine. In general, low molecular weight PAHs were predominant. Gob pile and coal preparation plant are the sources of PAHs pollution in surface soils in the vicinity of coal mines. The crops in rice paddies may adsorb some PAHs and reduces the PAHs content in soils from paddyfields. Vertical distribution of PAHs in two soil profiles indicates that PAHs contamination in soil profiles tends to occur high in the surface soils and markedly decreases with soil depth. For all depths, PAHs showed a similar distribution pattern, which is an indicator of a similar origin. Total B[a]P equivalent concentration (B[a]Peq) was found to be maximum at the Luling area, while it was minimum at Liuer zones.Organic pollutants in water have been causing serious environmental problems. Photocatalytic degradation of these pollutants using solar energy is an attractive solution to this global problem. We propose to develop a series of highly efficient visible light nano-photocatalyst of niobates and tantalates as well as improving their photo-activity by doping.Based on this viewpoint, nitrogen doped KNbO3micro/nanostructures was synthesized. Photocatalytic experiment results showed that1) different morphology and particle size of KNbO3can cause the change of recombination rate of photogenerated chargers and specific surface area, thus have a significant influence on the photocatalytic activity;2) The as prepared N-cube exhibited greatly enhanced activity in the visible-light photocatalytic degradation of varies of organic contaminants and photocatalytic reduction and oxidation of water for H2and O2 generation, which were mainly attributed to the improved surface area and increased optical absorption properties arises from the N2p levels above the O2p levels of the valence band. A mechanism for the photodegradation of organic contaminants by the N-cube photocatalyst under visible light is also proposed. The visible-light-sensitive photocatalyst of Ag1.4K0.6Ta4O11nanoplates was synthesized by a facile molten-salt method. The Ag1.4K0.6Ta4011nanoplates exhibited high photocatalytic activity on photodegradation of PCP and RhB. In addition, the activity of the Ag1.4K0.3Ta4O11nanoplates is improved significantly by the modification with lanthanum ions. The optimal modifying content is lmol%corresponding to the highest photodegradation percentages for photodegradation. On the other hand, the5%La3+modifying content exhibited highest photocatalytic activity for H2evolution. The enhancement of photocatalytic activity after La3+modification is attributed to the formation of nanowires, which further promote charge separation and transfer capability in the La3+modified Ag1.4K0.6Ta4O11nanocomposites.