Biosynthesis of zinc sulfide quantum dots using waste off-gas from a metal bioremediation process

Abstract

Dissimilatory reduction of sulfate, mediated by various species of sulfate-reducing bacteria (SRB) and a few characterized species of archaea, can be used to remediate acid mine drainage (AMD). Hydrogen sulfide (H 2 S/HS À ) generated by SRB removes toxic metals from AMD as sulfide biominerals. For this, SRB are usually housed in separate reactor vessels to those where metal sulfides are generated; H 2 S is delivered to AMD-containing vessels in solution or as a gas, allowing controlled separation of metal precipitation and facilitating enhanced process control. Industries such as optoelectronics use quantum dots (QDs) in various applications, e.g. as light emitting diodes and in solar photovoltaics. QDs are nanocrystals with semiconductor bands that allow them to absorb light and re-emit it at specific wavelength couples, shifting electrons to a higher energy and then emitting light during the relaxation phase. Traditional QD production is costly and/or complex. We report the use of waste H 2 S gas from an AMD remediation process to synthesize zinc sulfide QDs which are indistinguishable from chemically prepared counterparts with respect to their physical and optical properties, and highlight the potential for a empirical process to convert a gaseous "waste" into a high value product.

Synthesis of Copper Sulfide Nanoparticles Using Biogenic H2S Produced by a Low-pH Sulfidogenic Bioreactor

“…In this system, the sulfide generated can be partially re-oxidized to elemental sulfur by using sulfide-oxidizing bacteria, while the solid product is removed and applied as fertilizer [24]. However, relatively little is known about the synthesis of metallic nanoparticles using biogenic H 2 S. The synthesis of nanoparticles of ZnS from a sulfate solution was recently reported by feeding biogenic H 2 S from the off-gas generated from a sulfidogenic metal remediation process [3]. The present study examined whether the H 2 S produced from this low-pH sulfidogenic reactor, set up for the removal of copper and sulfate from an acidic mine water, can be used to fabricate CuS nanoparticles.…”

“…The H 2 S produced by the low-pH sulfidogenic bioreactor was removed in a stream of OFN with a flow rate of 150 mL·min −1 extracting 0.1% (v/v) H 2 S. The gas stream was fed into 100 mL serum bottles containing 100 mL of 2 mM CuSO 4 in 50 mM of citrate buffer (pH 6.0), which were subsequently sealed, and head space air was displaced by passing nitrogen through the solution [3]. The copper solutions were sparged by this gas stream for 5, 15, 30, 45, and 60 min, with shaking between dosing, and then stored in the dark at 4 • C for characterization of the nanoparticles.…”

“…Recently, H 2 S produced by a sulfidogenic metal remediation process was used to produce zinc sulfide quantum dots possessing optical properties analogous to those prepared commercially [3]. Biogenic production of metallic sulfide nanoparticles has been reported by using a range of different biological [8] and chemical approaches, including aqueous solutions [9], aqueous gels [10], and wet chemical routes using complexing agents [11].…”

“…These compounds are readily transferred through waste gas streams from bioreactors to other reactor vessels for offline metal precipitation [3]. However, few successful applications using low-pH sulfidogenic reactors have been demonstrated for sulfate reduction in, and metal removal from, AMD [4][5][6].…”

Enhancement of Photosynthetic Productivity by Quantum Dots Application

“…A first report [60] showed that the characteristics and the light emitting properties of ZnS quantum dots made by use of bacterially made waste H 2 S left over from the metal bioremediation process [50,51] were comparable to those made by "classical" methods, which required more complex procedures. As a potential synthesis method at scale, this shows potential for commercial QD production and introduces the possibility to use these biogenic ZnS QDs to promote algal growth for the applications described above and also to provide algal feedstock as a nutrient source for other processes (e.g.…”