Yang Liu,Luyao Fan,Bingxin Zhang,Zhenbo Xu,Thanapop Soteyome,Lei Yuan
Biofilms formed by Bacillus licheniformis usually serve as a continuous bacterial contamination in the dairy industry. The purpose of this study was to explore how 1% organic acids (citric acid, phenyllactic acid, malic acid , and butyric acid) and their 1% organic peroxyacids (peroxycitric acid, peroxyphenyllactic acid, peroxymalic acid, and peroxybutyric acid) can inactive the planktonic and biofilm cells of B. licheniformis . Results demonstrated that the number of B. licheniformis planktonic cells was increased from 4 to 6.46 Log CFU mL −1 when treated with water. Organic peroxyacids, especially peroxyphenyllactic acid (PPA), obviously inactivated planktonic cells of B. licheniformis by a range of 3.32–4.14 Log CFU mL −1 . Moreover, organic peroxyacids could also decrease the cell surface hydrophobicity of bacteria, and effectively control the Ca 2+ -mediated biofilm formation by B. licheniformis in 96-well plates (reduction of OD values by 0.14–0.33) and on stainless steel (reduction of cell counts by 1.20–2.49 Log CFU cm −2 ). The low minimum biofilm eradication concentration of PPA (0.125%) also suggests its strong biofilm inactivation activity, which could serve as a novel and environmentally friendly biofilm control agent in the dairy industry.
Dissolved cobalt ions (Co 2+ ) are an excellent catalyst for activating peroxymonosulfate (PMS) to generate SO 4 − for the degradation of organic pollutants, but fairly high level of Co 2+ is generally required, which may cause secondary pollution due to its toxicity. Herein, we demonstrate a novel strategy for this catalytic oxidation treatment in which the required Co 2+ addition is very small, being much less than the emission limit of 17 μmol L −1 . This new strategy is based on the much enhanced catalytic effect by the addition of small organic acids (SOAs). In a typical case, all the added diclofenac (30 μmol L −1 ) was degraded in 20 min by using 2 μmol L −1 Co 2+ , 0.15 mmol L −1 PMS and 0.5 mmol L −1 acetate with a degradation rate constant of 0.482 min −1 , which was about 10 times higher than that (0.048 min −1 ) of equivalent Co 2+ -PMS system without acetate. The formation of SO 4 − was greatly enhanced by introducing acetate, and this novel system is universal for enhanced degradation of various organic pollutants. Similarly, formate, propionate, and butyrate also exhibited enhancing effects on the catalytic ability of Co 2+ . The enhancement mechanism of SOAs on catalytic activation of PMS by low-level Co 2+ was also proposed.
Varied metallophthalocyanine intercalated layered double hydroxides (LDHs) as bifunctional hybrid catalysts for selective epoxidation have been prepared and characterized. Systematic characterizations suggested the successful intercalation of the metallophthalocyanines into the interlayer of ZnAl LDHs. The synthesized hybrid exhibited excellent catalytic activity in the selective epoxidation of various olefins through O 2 /isobutaldehyde system. The basicity of the hybrid benefits to the selectivity of epoxide, and the bifunctional roles of the catalyst in the reaction have been discussed and verified by a series of controlled experiments. On the basis of obtained results, a probable mechanism of the epoxidation by the hybrid has been proposed and detailedly investigated. Under the catalysis of metallophthalocyanines intercalated LDHs in the presence of O 2 /isobutaldehyde, the production of epoxide undergoes two reaction paths. And two types of intermediates, namely acylperoxy radical and peroxyacid, are formed in the reaction, and the former is predominant.
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