Rapid Au recovery from aqueous solution by a microorganism-mediated, surfactant-directed approach: Effect of surfactants and SERS of bio-Au

• Microorganism-mediated, surfactant-directed approach was effective for Au recovery.
• Bio-Au-nanowire composites were obtained while Au was effectively recovered.
• Au recovery was little affected by the chain length of the Br-containing surfactant.
• The recovered bio-Au-nanowire composites could be used for SERS detection.

Gold recovery is of practical significance while functional Au nanostructures are of great interest in modern nanotechnology. In this work, highly and hierarchically branched Au nanowires (AuNWs) were produced to obtain bio-AuNW composites while the Au was effectively recovered from aqueous HAuCl4 solution by a microorganism-mediated, surfactant-directed (MSD) approach with Lactobacillus spp. cells (LSCs). Ternary coordination of the cell-surfactant-AA played an important role in recovering Au and producing the bio-AuNW composites in the cases of tetradecyl trimethyl ammonium bromide (TTAB), hexadecyltrimethylammonium bromide (CTAB) and octadecyl trimethyl ammonium bromide (OTAB). In contrast, Au recovery could not be achieved with hexadecyltrimethylammonium chloride (CTAC). Strong interaction between [AuCl4]− and the LSCs prior to addition of surfactant (except CTAC) and ascorbic acid (AA) was vital for the highly and hierarchically branched nanostructures. Furthermore, the bio-AuNW composites could serve as excellent surface-enhanced Raman spectroscopy (SERS) substrate. the SERS detection limits of toxic rhodamine 6G (R6G) and 4-mercaptobenzoic acid (MBA) with the bio-AuNW composites are down to 10−9 and 10−6 M, respectively. This work therefore exemplifies combining recovery of Au and fabrication of functional Au nanomaterials, which was environmentally benign and application-oriented.

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