Screening of Seawater Compound Bioflocculant Producing Bacterial Strains and Optimization of Their Culture Medium

Compared with single bioflocculant,compound bioflocculant(CBF)normally has more stable and higher flocculation efficiencies.In order to produce a new compound bioflocculant,four bacterial strains with relative high rate of flocculation were selected from the coastal zone sediment,all of which were determined as Pseudomonas sp.by 16S rRNA sequencing.Through compounding,the ideal proportion of compound bioflocculant consisting of two bacterial strains(F5∶M5)was determined as 1∶2,resulting in 6%increase in terms of flocculation rate.The significant fermentation factors in culture media and their limitations were investigated via single factor experiments and Plackett⁃Burman design,obtaining four key variables,MgSO_(4),(NH_(4))_(2)SO_(4),sucrose and peptone,which were further optimized by response surface methodology(RSM)for their optimal concentrations.Finally,the ideal culture medium was determined,containing(NH_(4))_(2) SO_(4)0.523 g,MgSO_(4)3.7 g,sucrose 12.82 g,K_(2)HPO_(4)4 g,KH_(2)PO_(4)3 g,NaCl 33 g,and deionized water 1 L.The flocculation rate of experimental data(88.92)agreed well with the model prediction,which was 16.60 higher than original rate.

Straightforward construction of hollow polyoxometalate-based metal-organic framework via pseudo-homoepitaxial growth

Hollow structures are significant for shortening diffusion path and promoting active center exposure.Single-crystalline hollow polyoxometalate-based metal-organic frameworks(POM@MOFs)with increased adsorption performance and catalytic activity were synthesized through a straightforward pseudo-homoepitaxial growth strategy within only 1.5 min.The strategy ingeniously exploits favorable characteristics of well-matched lattice/structure but acid stability difference between MOF and POM@MOF to construct a pseudo-homoepitaxial structure.Specifically,the MOF single crystals are used as seeds to perform epitaxial growth of the lattice/structure-matched POM@MOF under appropriate conditions.Interestingly,the MOF seeds collapse spontaneously during epitaxial growth,affording regular hollow POM@MOF single crystals.Because the acid stability of the POM@MOF is much higher than that of the MOF,it is speculated that the hollow structure formation may be related to the acid released from the epitaxial POM@MOF growth.And the pseudo-homoepitaxial POM@MOF growth strategy based on structural matching but stability difference avoids additional template removal process in conventional hollow MOF preparation and ensures hollow single crystal construction.