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Magnetically recoverable noble metal nanoparticles are promising catalysts for chemical reactions. However, the chemical synthesis of these nanocatalysts generally causes environmental concern due to usage of toxic chemicals under extreme conditions. Here, Pd/Fe3O4, Au/Fe3O4 and PdAu/Fe3O4 nanocomposites are biosynthesized under ambient and physiological conditions by Shewanella oneidensis MR-1. Microbial cells firstly transform akaganeite into magnetite, which then serves as support for the further synthesis of Pd, Au and PdAu nanoparticles from respective precursor salts. Surface-bound cellular components and exopolysaccharides not only function as shape-directing agent to convert some Fe3O4 nanoparticles to nanorods, but also participate in the formation of PdAu alloy nanoparticles on magnetite. All these three kinds of magnetic nanocomposites can catalyze the reduction of 4-nitrophenol and some other nitroaromatic compounds by NaBH4. PdAu/Fe3O4 demonstrates higher catalytic activity than Pd/Fe3O4 and Au/Fe3O4. Moreover, the magnetic nanocomposites can be easily recovered through magnetic decantation after catalysis reaction. PdAu/Fe3O4 can be reused in at least eight successive cycles of 4-nitrophenol reduction. The biosynthesis approach presented here does not require harmful agents or rigorous conditions and thus provides facile and environmentally benign choice for the preparation of magnetic noble metal nanocatalysts.

Bimetallic nanoparticles are generally believed to have improved catalytic activity and stability due to geometric and electronic changes. In this work, biogenic-Pd (bio-Pd), biogenic-Pt (bio-Pt), and biogenic-PdPt (bio-PdPt) nanoparticles were synthesized by Shewanella oneidensis MR-1 in the absence or presence of quinone. Compared with direct microbial reduction process, the addition of anthraquinone-2,6-disulfonate (AQDS) could promote the reduction efficiency of Pd(II) or/and Pt(IV) and result in decrease of particles size. All kinds of nanoparticles could catalyze 4-nitrophenol reduction by NaBH and their catalytic activities took the following order: bio-PdPt (AQDS) ∼ bio-PdPt > bio-Pd (AQDS) > bio-Pd > bio-Pt (AQDS) ∼ bio-Pt. Moreover, the bio-PdPt (AQDS) nanoparticles could be reused for 6 cycles. We believe that this simple and efficient biosynthesis approach for synthesizing bimetallic bio-PdPt nanocatalysts is important for preparing active and stable catalysts.

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An anaerobic/aerobic moving-bed biofilm (A/O-MBBR) reactor system was constructed, and the treatment efficiency of aqueous antibiotics in wastewater was investigated. The effects of antibiotics on the microbial communities in the A/O-MBBR were also investigated. Under the optimized reaction conditions, removal of tetracycline antibiotics (TCs) was studied in a series of experiments. When a low concentration of tetracycline (TC) was added to the reactor system, high removal efficiency of conventional pollutants (TC concentration decreased from 10 turn to 2.8 μg L) was achieved. When mixed TCs (50 μg L) were added to the system, the removal efficiencies of chlortetracycline (CTC), TC and oxytetracycline (OTC) reached 52.03, 41.79, and 38.42%, respectively. TC degradation was decreased to 21.16% when the antibiotic concentration was 500 μg L; exposure to this TC concentration destroyed the community structure of the activated sludge bacteria in the reactor. The products of the biodegradation analysis revealed the possible degradation pathways functioning in the experimental A/O-MBBRs.

The current study was conducted to appraise the PM2.5 and PM10 concentration in Dalian-China and Faisalabad-Pakistan. Study was conducted for the period of one year at different stations in both cities and the results were compared according to set standards of NEQS(Pakistan), CNAAQS(China), NAAQS(USEPA) and WHO (World Health Organization). The PM2.5 concentrations in Faisalabad is variable from 22 to 49 μg/m 3 (Average 36.5 μg/m 3), whereas PM10 variation is from 109 to 164.3 μg/m 3 (148.3 μg/m 3). The PM2.5 concentrations in Dalian varied from 5.5 to 93.3 μg/m 3 (29.1 μg/m 3), whereas PM10 values varied from 10.5 to 101.1 μg/m 3 (Average 45.9 μg/m 3). Both the average PM2.5 concentration in Faisalabad, in winter season is higher than the dry summer season. Both PM2.5 and PM10 concentrations were found significantly different in winter and summer seasons. The variations were considerably higher in Dalian comparing to those of Faisalabad. On average basis Faisalabad showed more PM concentrations comparing to Dalian, even higher than permissible limits set by NEQS and USEPA. Whereas the values representing Dalian are within the limits set by CNAAQS and WHO.

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