Yangjian Cheng,Zhibin Ke,Xiaojing Bian,Jianhua Zhang,Zhen Huang,Yuancai Lv,Minghua Liu
The recovery of precious metals is a project with both economic and environmental significance. In this paper, how to use bacterial mineralization to selectively recover gold from multi-ionic aqueous systems is presented. TheBacillus licheniformisFZUL-63, isolated from a landscape lake in Fuzhou University, was shown to selectively mineralize and precipitate gold from coexisting ions in aqueous solution. The removal of Au(III) almost happened in the first hour. Scanning electron microscope with X-ray energy dispersive spectroscopy (SEM/EDS-mapping) results and fourier transform infrared spectroscopy (FTIR) data show that the amino, carboxyl, and phosphate groups on the surface of the bacteria are related to the adsorption of gold ions. X-ray photoelectron spectroscopy (XPS) results implied that Au(III) ions were reduced to those that were monovalent, and the Au(I) was then adsorbed on the bacterial surface at the beginning stage (in the first hour). X-ray diffraction (XRD) results showed that the gold biomineralization began about 10 h after the interaction between Au(III) ions and bacteria. Au(III) mineralization has rarely been influenced by other co-existing metal ions. Transmission electron microscope (TEM) analysis shows that the gold nanoparticles have a polyhedral structure with a particle size of ~20 nm. TheBacillus licheniformisFZUL-63 could selectively mineralize and recover 478 mg/g (dry biomass) gold from aqua regia-based metal wastewater through four cycles. This could be of great potential in practical applications.Keywords:selective biomineralization;recovery of Au(III);AuNP;Bacillus licheniformisFZUL-63;aqua regia-based metal wastewater
A series of Co@N-C materials are synthesized from pyrolysis of ZIF-67 at different temperatures and employed as catalyst for electrochemical reduction of CO 2 (CO 2 RR) to syngas. Through a systematical investigation of the relationship between structure of Co@N-C catalysts and their catalytic activity, it could be found that the Co species exposed on the material surface mainly promote the hydrogen evolution reaction (HER) process to produce H 2 , while the Co particles packaged by N-C skeleton provide electrons and transfer them to CO 2 molecule through the Co -N- C skeleton, promoting the CO 2 reduction reaction. Following this thinking, the pristine Co@N-C materials are treated by aqua regia to remove the surface exposed Co species. After acid treatment, the affinity of H species sharply decreases, and adsorption of CO 2 and transfer of electron to CO 2 are successfully improved. The acid-treated Co@N-C catalysts exhibit improved catalytic activity, faradic efficiency of CO, and stability in CO 2 RR process. Among all these catalysts, the obtained Co@N-C-700-A shows highest CO 2 reduction activity and stability, achieving a specific current of 25 A∙g (cat) −1 and a productivity of 0.266 mol (CO) h −1 ∙ g(cat) −1 at a mild potential of -0.57 V vs. RHE. The ratio of CO/H 2 in products could be adjusted in the range of 1/4 to 1.5/1.
Breaking the limitation of smooth silver nanowires (Ag NWs) in forming sufficient “hot spots” is a crucial step to push them into practical surface enhancement Raman scattering (SERS)-based detection. Herein, Ag NWs with various etched configurations were developed by utilizing different amounts of aqua regia as etchant at room temperature . Compared with the smooth Ag NWs, more electromagnetic “hot spots” were enabled by the etched one, which exhibited better sensitivity and uniformity in SERS signals. The limit of detection (LOD) for 2-naphthalenethiol (2-NAT) obtained from the optimized substrate could reach 8.3 × 10 −10 mol/L and the relative standard deviation (RSD) was 6.8%. The maximum enhancement factor (EF) value obtained as 3.34 × 10 6 was even three times higher than that of the smooth one. Finally, an ultra-sensitive detection of thiram with a lowest detectable concentration of 4 × 10 −8 mol/L was facilitated by the optimal etched Ag NWs.
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