PVP Film on Water for a Green and Rapid

May 17, 2016 - this work, a green, selective, simple, easy, cheap and energy efficient way to recover Au ion from a mimic waste stream containing Au, ...
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Research Article pubs.acs.org/journal/ascecg

Preparation of Floating Au/PVP Film on Water for a Green and Rapid Extraction of Gold Ion Minyue Li, Qidi Sun, and Chang-jun Liu* Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, 92 Wei Jin Road, Tianjin 300072, People’s Republic of China S Supporting Information *

ABSTRACT: Currently, the demand for gold is ever increasing while the reserve of gold ore is very limited. The extraction of gold ion from various waste effluents is now a very important way for a sustainable gold supply. In this work, a green, selective, simple, easy, cheap and energy efficient way to recover Au ion from a mimic waste stream containing Au, Zn, Fe and Cu ions has been developed using a room temperature electron reduction with argon glow discharge as the electron source. Metal ions with sufficiently high standard electrode potentials can be reduced by such electron reduction. A selective reduction of gold ion has been thereby established, where other metal ions remain in the solution. With the addition of poly(vinylpyrrolidone) (PVP), an Au/PVP floating film is rapidly formed on the surface of water within a few minutes. This makes the collection of the recovered gold very easy with very high recovery yield. The gold recovery yield reaches 87.19% in 60 s and 99.96% in 480 s under the reaction conditions tested. KEYWORDS: Au, PVP, Floating film, Selective recovery, Electron reduction

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INTRODUCTION

Recently, we developed a room temperature electron reduction for the selective reduction of noble metal ions using non-hydrogen (like argon) glow discharge as the electron source. The room temperature electron reduction uses energetic electron as the reducing agent. It is the greenest way to reduce metal ions. Glow discharge is a kind of cold plasma phenomena formed by applying a voltage to a metal electrode normally in a tube with another grounded metal electrode. When the applied voltage exceeds a certain value, the gas in the tube will be ionized to form the glow discharge. The glow discharge is usually operated at low pressure.15−20 A colored light can be observed with glow discharge. The color depends on the gas used. Glow discharge is extensively employed in neon light, fluorescent lamp, surface clean and treatment and others. Especially, a plenty of energetic electrons exist in glow discharge. These electrons can be used as excellent reducing agent for the reduction of metal ions with positive standard electrode potentials (in non-hydrogen glow discharges) at room temperature.17−20 The larger the value of the standard electrode potential is, the easier it is for the metal ion to be reduced (or to accept electrons). For example, the standard electrode potentials of [AuCl4]−/Au, Au+/Au and Au3+/Au are 1.00, 1.69 and 1.50 V, respectively, whereas those for Cu2+/Cu, Zn2+/Zn and Fe3+/Fe are +0.337, −0.763 and −0.04 V, respectively.20 This means that Au ions will be

Besides jewelry, gold has many important applications in electronic, sensor, photothermal conversion, catalyst and others.1−3 The demand for gold is rapidly increasing. However, the reserve of Au ore is very limited. The gold mining causes deforestation and serious pollutions to water and land. Recovery of gold from mine tailing, industrial waste, sewage sludge, obsolete electronic equipment and leaching residue is becoming an important way for a sustainable gold supply. The gold content of these wastes is sometimes higher than that that found in some gold ores.4,5 Therefore, the development of highly efficient and eco-friendly methods to extract gold from these waste streams has attracted great attention.4,6−9 Currently, most of the methods used to recover gold from aqueous solutions involve adsorption4,10−13 and extraction.6 However, highly selective separation is always a significant challenge because other metal ions such as ferric, copper and zinc ions often coexist with gold ion in the waste streams. Complex and time-consuming operations with use of various chemicals and the generation of wastewater are normally required for the existing recovery methods.14 Therefore, new separation processes that must be easy, fast, selective, effective and efficient are immediately needed with use of less toxic chemicals. In addition, no matter for adsorption or extraction, it will be great if the recovered gold can be made floating on the surface of the solution, with which collection will be quite easy. Unfortunately, there have been no literature reports of floating gold on water, which is not surprising because it is not easy to make gold float. © XXXX American Chemical Society

Received: February 12, 2016 Revised: May 10, 2016

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DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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measured using inductively coupled plasma optical emission spectrometry (ICP-OES; VISTA-MPX, Varian).

preferentially reduced by the electrons and it will make the selective recovery of gold possible. Previous studies have demonstrated that the electron reduction can reduce gold ions effectively and efficiently into gold nanoparticles within the solution.16 It requires neither hydrogen (because hydrogen is not safe and costs a lot for the production, transportation and storage) nor chemical reducing agent (that is usually hazardous and expensive). It does not require an expensive setup. It can be operated more quickly. Electron reduction should be very promising for the recovery of gold ion. However, the collection of obtained gold nanoparticles from solution is very difficult. Therefore, green electron reduction has not been employed for the recovery of gold ion. In this work, poly(vinylpyrrolidone) (PVP), a cheap and nontoxic surfactant, was added to the gold ion containing solution for room temperature electron reduction. A floating gold nanoparticle/PVP composite can be easily and rapidly formed on the water surface during the electron reduction, making the recovery of gold ions possible.

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RESULTS AND DISCUSSION To demonstrate the formation of the unique floating Au/PVP film on water, solutions with various concentrations of HAuCl4 and PVP were prepared and subjected to room temperature electron reduction. After only a few seconds of reduction, a floating metallic film can be observed on the surface of the solution. Morphology and Characterization of Au/PVP Film. Photos (Figure 1a,d,g,j) were taken of a solution of HAuCl4 (4

EXPERIMENTAL METHODS

Reagents and Materials. Analytical grade chemicals including chloroauric acid (Tianjin Delan Fine Chemical Plant), PVP (SigmaAldrich), copper sulfate (Tianjin Bodi Chemical Industry Co. Ltd.), iron(III) chloride (Tianjin Kemiou Chemical Reagent Co. Ltd.) and zinc sulfate (Alfa Aesar) were used to prepare the test solutions with distilled water. Room Temperature Electron Reduction. For the formation of Au/PVP floating film with the electron reduction, a solution of chloroauric acid and PVP was placed in a quartz boat. For the selective reduction of gold ion (to recover gold), CuSO4, ZnSO4 and FeCl3 were added into the solution of chloroauric acid (to mimic a waste stream) with PVP. The boat was then placed into the discharge chamber that contained two stainless steel electrodes (o.d. 30 mm). The pressure in the discharge tube was then evacuated to ∼200 Pa and the glow discharge was generated by applying 1000 V to the electrode using a high voltage amplifier (Trek, 20/20B). The applied power was ∼20 W. The signal input for the high voltage amplifier was supplied by a function/arbitrary waveform generator (Hewlett-Packard, model 33120A) with a 100 Hz square wave. Ultra high pure grade argon (>99.999%) was used as the plasma-forming gas. Characterization. The bulk temperature of the electron reduction was decided by thermal image obtained using infrared imaging (Ircon, 100PHT). The thermal image (shown in Figure S1 in the Supporting Information) confirms the room temperature operation of the electron reduction. For transmission electron microscopy (TEM) analyses, the samples were prepared by directly loading the Au/PVP films onto copper grids. TEM analyses were performed on a FEI Tecnai G2 F20. The system was operated at 200 kV. Samples for Fourier transform infrared spectroscopy (FTIR) analyses were prepared by mixing the Au/PVP films or PVP with KBr and then forming pellets. Infrared spectra were obtained on a Thermo Nicolet’s Nexus 870 system at room temperature under air. The measurements were conducted in the transmission mode. Scanning electron microscopy (SEM) analyses were conducted on a FEI Nanosem 430. The X-ray diffraction (XRD) patterns were recorded on a Rigaku D/Max-2500 V/PC diffractometer with a Cu Kα radiation source (λ = 0.154 056 nm) at a scanning speed of 4°/min. X-ray photoelectron spectroscopy (XPS) analyses were carried out on a PerkinElmer PHI-1600 spectrometer with monochromatic Mg Kα (1253.6 eV) radiation. The C 1s peak (284.6 eV) was used as a reference to calibrate binding energies. Kinetic Analysis. Selective reduction using room temperature electron reduction was analyzed by metal ion concentrations in the test solution before and after the electron reduction. The recovery yield (η) for each metal ion was calculated based on the changes in the metal ion concentrations. The metal ion concentration in solution was

Figure 1. Floating Au/PVP films formed from the solution of HAuCl4 (4 mM) and PVP (9 mM). (a) Photo, (b) SEM image and (c) TEM image of the sample with reduction time of 30 s; (d) photo, (e) SEM image and (f) TEM image of the sample with reduction time of 60 s; (g) photo, (h) SEM image and (i) TEM image of the sample with reduction time of 180 s; (j) photo, (k) SEM image and (l) TEM image of the sample with reduction time of 360 s. The white bar represents 1 μm in SEM images (b,e,h,k) and 100 nm in TEM images (c,f,i,l).

mM) and PVP (9 mM). At 30 s, a floating film with some black “fibers” is formed. From scanning electron microscopy (SEM) image (Figure 1b), the floating film contains small pores. However, from transmission electron microscopy (TEM) image (Figure 1c), the film is composed of nanoparticles (with size from several nanometers to several tens of nanometers). These nanoparticles aggregate in a unique way with some kind of branches, leading to the formation of pores in SEM image or fibers in the photo. The observed branch structures are characteristics of electric discharges,21 which confirm the electron reduction mechanism. The results shown in Figure 1 suggest a rapid nucleation of gold nanoparticles with room temperature electron reduction. The formed gold nanoparticles show a slow growth because of the room temperature operation. Aggregation of gold nanoparticles is observed. With the increasing reduction time, the composite film of aggregated metallic nanoparticles is finally B

DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering formed with more ordered pores and larger thickness (Figure 1). Function of PVP. PVP is a homopolymer. Its monomer has a hydrophilic cyclic amide group and the nitrogen and oxygen atoms have a strong affinity for gold, silver, platinum and palladium.22 It is generally accepted that PVP acts as a capping agent and also a stabilizing agent for these metal nanoparticles.23,24 Adding PVP can help to recover the gold nanoparticles more effectively by forming the stable floating Au/PVP film. The PVP solution itself is stable under the glow discharge. Neither floating film nor aggregate can be observed on the water surface when the pure PVP solution is discharge treated, as illustrated in Figure S3 with the PVP concentration of 180 mM. However, in the presence of gold ions, even a trace amount of PVP can lead to a formation of small floating fragments or small floating chips of Au/PVP. Regarding the influence of the PVP concentration on the formation of the floating Au/PVP film that covers the whole surface, it depends on the ratio of PVP to HAuCl4 and the time of the electron reduction. Under the reduction time applied in this study (up to 480 s), the minimum ratio of PVP to HAuCl4 is 1.00 within the concentration of metal ions tested to form such large floating film. Below this minimum ratio, the formed floating film cannot cover the whole solution surface with the electron reduction up to 480 s. If no PVP is added, no stable floating film can be observed under the electron reduction, as above addressed. According to the Fourier transform infrared spectroscopy (FTIR) analyses (Figure 2), the glow discharge

Figure 3. Floating Au/PVP films formed from the solution of HAuCl4 (4 mM), CuSO4 (4 mM) and PVP (9 mM). (a) Photo, (b) SEM image and (c) TEM image of the sample with reduction time of 30 s; (d) photo, (e) SEM image and (f) TEM image of the sample with reduction time of 60 s; (g) photo, (h) SEM image and (i) TEM image of the sample with reduction time of 180 s; (j) photo, (k) SEM image and (l) TEM image of the sample with reduction time of 360 s. The white bar represents 1 μm in SEM images (b,e,h,k) and 100 nm in TEM images (c,f,i,l).

that Cu2+ could also be reduced. This would adversely affect a separation. The compositions of the bulk phase and the surfaces of the floating films were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results are shown in Figure 4. The XRD patterns (Figure 4a) of the sample in the presence of Cu2+ show weak peaks for metallic gold. The weak peaks suggest the particles are quite small (close to 3 nm). No peak can be assigned to copper species in the XRD patterns. We took the film out of the solution and dried it under air for XPS analyses. Part of results is shown in Figure 4b that shows two weak peaks at 931.9 and 952.7 eV. The two peaks can be assigned to the binding energy of Cu2+.27−29 It means that the obtained floating film does not contain metallic copper. Cu ions are not reduced finally with the electron reduction. The trace Cu2+ in the film is the adsorbed copper species. This confirms the selective reduction of Au ions has been achieved. Therefore, the particles shown in the TEM images (Figure 3) are obviously aggregates of gold nanoparticles. The selective reduction of gold ion has also been confirmed with aqueous solutions of HAuCl4, CuSO4, ZnSO4, FeCl3 and PVP. All the experiments show us an interesting result that, with room temperature electron reduction, a thin floating film on the surface of the aqueous solution is obtained, making it easier to separate gold from the mixture. Compared with other work of preparing metallic thin films,30 this method does not need to prepare gold nanoparticle in advance. It means this method can improve the efficiency greatly. Especially, the obtained floating Au/PVP film can totally adhere to various substrates after taking it out of the solution. It can be easily bent on soft substrate without damage (as shown in Figure S2a in the

Figure 2. FTIR spectra of PVP, discharge treated PVP and Au/PVP.

has no influence on PVP molecule. Compared with pure PVP, the peak intensity at wavenumber of 1288 cm−1 is enhanced for the curve of Au/PVP, due to NCO complex vibration.25,26 The peak that reflects the CO bond shifts from 1663 to 1659 cm−1.25,26 The CN absorption peak of pure PVP at 1019 cm−1 is split into two peaks at 1018 and 1047 cm−1.25,26 This suggests interactions between gold nanoparticle and PVP. Influence of Cu Ion. With the addition of Cu2+, similar but uniform floating films are also formed rapidly with room temperature electron reduction. Figure 3 presents images of the floating films from a solution of HAuCl4 (4 mM), CuSO4 (4 mM) and PVP (9 mM). Compared to Figure 1, the addition of Cu2+ induces a change in the sizes of metallic nanoparticles and nanoparticle aggregates, which are obviously smaller than those without Cu2+. They are more significantly affected by reduction time. The standard electrode potential of Cu2+/Cu is 0.337 V. Although the value is less than that of Au ion/Au, it is possible C

DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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Figure 5. Recovery yield of gold with time.

Au3+ in the solution, the reduction rate reduces. Because electrons are supplied continuously in our method, we suppose that their concentration does not influence the reaction rate. The reaction rate can be expressed by eq 2. rAu = −

(2)

In the equation, α represents reaction order and k represents rate constant. On the basis of eq 2, we can get an integral eq 3. 1 1 (α − 1)kt = α − 1 − α − 1 CAu CAu0 (3)

Figure 4. (a) XRD patterns of the thin films for the same reduction time. (b) XPS spectra (Cu 2p) of the film from a mixture of HAuCl4 (4 mM), CuSO4 (4 mM) and PVP (9 mM) after 360 s of reduction.

A curve was made based on the experimental results and eq 3, as shown in Figure 6. From this curve, we find out that α is 1.69

Supporting Information). It suggests this kind of new film materials can have potential photonic and electronic applications (for example, sensors). Especially, the resistance of the Au/PVP film is changeable with the change of aggregation status. Moreover, the obtained Au/PVP film is very stable. As shown in Figure S2b, when the film is moved into a big vessel with distilled water, its shape does not change but the location of the floating film is totally controllable. The nice stability is very important for the future applications. The floating Au/PVP film can be a new reaction interface between air (or other gases) and liquid with gold nanoparticles as the catalyst. Kinetic Analysis. An aqueous solution containing HAuCl4 (0.2 mM), CuSO4 (0.2 mM), ZnSO4 (0.2 mM), FeCl3 (0.2 mM) and PVP (4.5 mM) was employed for kinetic analysis. The recovery yield (η) for each metal ion was calculated based on the changes in the metal ion concentrations: C − Ci η= 0 × 100% C0

dCAu α = kCAu dt

Figure 6. Kinetic analysis.

(1)

and k is 7.25 × 10−3 ppm−0.69·s−1. This suggests that the reaction is not an elementary reaction. It is a complicated reaction. Moreover, because the electron reduction is a rapid process, the rate-limiting step for the recovery is the formation of Au/PVP composites. Figure 5 shows that recovery yields of Zn2+ and Fe3+ fluctuate near 0. It means these two metal ions are not reduced. As mentioned above, Cu2+ is reduced a little at the very beginning. However, with the increasing reduction time, the reduced copper species become Cu2+ again. The electron reduction was also tested with different concentrations. Figure S4 shows the recovery amount with

where C0 and Ci are the metal ion concentrations in the test solution before and after the formation of the floating Au/PVP film by the electron reduction. The metal ion concentrations in solution were measured using ICP-OES. Figure 5 shows the recovery yield varies with the reduction time. In 60 s, the recovery yield rises from 0 to 87.19%. The recovery yield reaches 99.75% when reduction time is 360 s. For 480 s, the recovery yield reaches 99.96%. A rapid recovery has been established. Considering the recovery process as a whole reaction, at the early stage the reaction rate is very high. With the decrease of D

DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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modeling of biofunctional gold nanoparticles for systemic circulation and biological sustainability. ACS Sustainable Chem. Eng. 2015, 3 (12), 3175−3187. (2) Wang, C.; Yang, M.; Flytzani-Stephanopoulos, M. Single gold atoms stabilized on nanoscale metal oxide supports are catalytic active centers for various reactions. AIChE J. 2016, 62 (2), 429−439. (3) Zhu, B.; Li, X.-S.; Liu, J.-L.; Liu, J.-B.; Zhu, X. B.; Zhu, A.-M. Insitu regeneration of Au nanocatalysts by atmospheric-pressure air plasma: Significant contribution of water vapor. Appl. Catal., B 2015, 179, 69−77. (4) Xiong, Y.; Adhikari, C. R.; Kawakita, H.; Ohto, K.; Inoue, K.; Harada, H. Selective recovery of precious metals by persimmon waste chemically modified with dimethylamine. Bioresour. Technol. 2009, 100 (18), 4083−4089. (5) Kakumazaki, J.; Kato, T.; Sugawara, K. Recovery of gold from incinerated sewage sludge ash by chlorination. ACS Sustainable Chem. Eng. 2014, 2 (10), 2297−2300. (6) Han, S.; Balasubramanian, R. Multidentate ionic surfactant mediated extraction and dispersion of gold nanoparticles in organic solvents. Langmuir 2014, 30 (30), 9063−9070. (7) Nguyen, V. T.; Lee, J.-C.; Jeong, J.; Kim, B.-S.; Cote, G.; Chagnes, A. Extraction of gold (III) from acidic chloride media using phosphonium-based ionic liquid as an anion exchanger. Ind. Eng. Chem. Res. 2015, 54 (4), 1350−1358. (8) Shen, J.; Ma, W. L.; Yu, L.; Li, J.-B.; Tao, H.-C.; Zhang, K.; Zeng, H. Q. Size-dependent patterned recognition and extraction of metal ions by a macrocyclic aromatic pyridone pentamer. Chem. Commun. 2014, 50, 12730−12733. (9) Yin, Y. G.; Liu, J. F.; Jiang, G. B. Sunlight-induced reduction of ionic Ag and Au to metallic nanoparticles by dissolved organic matter. ACS Nano 2012, 6 (9), 7910−7919. (10) Park, S.; Lee, J. C.; Kim, B. S.; Lee, J. H. Collection of high purity gold from wastewater using ZnO nanopowders synthesized by solution combustion method. J. Mater. Sci. 2005, 40 (19), 5327−5330. (11) Elshehy, E. A.; El-Safty, S. A.; Shenashen, M. A.; Khairy, M. Design and evaluation of optical mesocaptor for the detection/ recovery of Au (III) from an urban mine. Sens. Actuators, B 2014, 203, 363−374. (12) Wang, H. X.; Ding, J.; Lee, B.; Wang, X. G.; Lin, T. Polypyrrolecoated electrospun nanofibre membranes for recovery of Au (III) from aqueous solution. J. Membr. Sci. 2007, 303 (1−2), 119−125. (13) Dhandayuthapani, B.; Mallampati, R.; Sriramulu, D.; Dsouza, R. F.; Valiyaveettil, S. PVA/gluten hybrid nanofibers for removal of nanoparticles from water. ACS Sustainable Chem. Eng. 2014, 2 (4), 1014−1021. (14) Salminen, J.; Blomberg, P.; Mäkinen, J.; Räsänen, L. Environmental aspects of metals removal from waters and gold recovery. AIChE J. 2015, 61, 2739−2748. (15) Wang, W.; Wang, Z. Y.; Yang, M. M.; Zhong, C.-J.; Liu, C.-J. Highly active and stable Pt (111) catalysts synthesized by peptide assisted room temperature electron reduction for oxygen reduction reaction. Nano Energy 2016, 25, 26−33. (16) Wei, Z. H.; Liu, C.-J. Synthesis of monodisperse gold nanoparticles in ionic liquid by applying room temperature plasma. Mater. Lett. 2011, 65 (2), 353−355. (17) Wang, Z.-J.; Xie, Y. B.; Liu, C.-J. Synthesis and characterization of noble metal (Pd, Pt, Au, Ag) nanostructured materials confined in the channels of mesoporous SBA-15. J. Phys. Chem. C 2008, 112 (50), 19818−19824. (18) Liu, C.-J.; Zhao, Y.; Li, Y. Z.; Zhang, D.-S.; Chang, Z.; Bu, X.-H. Perspectives on electron-assisted reduction for preparation of highly dispersed noble metal catalysts. ACS Sustainable Chem. Eng. 2014, 2 (1), 3−13. (19) Yan, J. M.; Pan, Y. X.; Cheetham, A. G.; Lin, Y.-A.; Wang, W.; Cui, H. G.; Liu, C.-J. One-step fabrication of self-assembled peptide thin films with highly dispersed noble metal nanoparticles. Langmuir 2013, 29 (52), 16051−16057. (20) Wang, Z. J.; Zhao, Y.; Cui, L.; Du, H. Y.; Yao, P.; Liu, C.-J. CO2 reforming of methane over argon plasma reduced Rh/Al2O3 catalyst: a

various Au initial concentrations at the same reduction time (480 s). The result shows our method can be used for a broad concentration range. To obtain a certain recovery yield, only the time for electron reduction needs adjusted.

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CONCLUSION We have confirmed in this work that the room temperature electron reduction is excellent for the recovery of gold from the Au3+ containing solution via the formation of floating Au/PVP film on the solution. A simple, rapid, easy and green recovery has been achieved with high selectivity. Compared with the existing methods,4−14,31−33 the electron reduction for the recovery of gold has several obvious advantages. For most of the reported methods,4−14,31−33 adsorption or extraction cannot be avoided. It took several hours or even longer to reach a suitable recovery yield with the use of chemicals. Further complex operation is needed to convert the adsorbed or extracted gold into the useful product. It will lead to an extra cost with the use of hazardous chemicals. In addition to the waste generated, the production and transportation of these chemicals cost a lot and generate pollutions with intense energy input. The electron reduction way just needs some small input of electricity with the use of PVP and cheap gas like argon (in China). No other chemical is needed. The electron reduction with glow discharge as the electron source just needs simple setup (as shown in Figure S1a). The glow discharge has been industrially applied for the surface treatment of cloth, cell phone screens, glass and others in a large scale. The glow discharge based room temperature electron reduction is ready for a practical application of gold recovery from various waste streams. In addition, the room temperature electron reduction can be also applied for the recovery of other noble metal ions with similar high standard electrode potentials as that of gold ion.18,20

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b00305. Photos of glow discharge for electron reduction, the Au/ PVP film moved onto the plastic and the clean water, thermal image for temperature measurement of electron reduction, image of pure PVP after exposure to the glow discharge and figure of recovery amount of gold with initial concentration for the same reduction time (480 s) (PDF).

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AUTHOR INFORMATION

Corresponding Author

*C.-j. Liu. E-mail: [email protected]. Tel: +86 22 27406490. Fax:+86 22 27406490. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (#91334206), which is much appreciated. REFERENCES

(1) Goshisht, M. K.; Moudgil, L.; Khullar, P.; Singh, G.; Kaura, A.; Kumar, H.; Kaur, G.; Bakshi, M. S. Surface adsorption and molecular E

DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering case study of alternative catalyst reduction via non-hydrogen plasmas. Green Chem. 2007, 9, 554−559. (21) Pan, Y.-X.; Cong, H.-P.; Men, Y.-L.; Xin, S.; Sun, Z.-Q.; Liu, C.J.; Yu, S.-H. Peptide self-assembled biofilm with unique electron transfer flexibility for highly efficient visible-light-driven photocatalysis. ACS Nano 2015, 9 (11), 11258−11265. (22) Huang, S. X.; Ma, H. Y.; Zhang, X. K.; Yong, F. F.; Feng, X. L.; Pan, W.; Wang, X. N.; Wang, Y.; Chen, S. H. Electrochemical synthesis of gold nanocrystals and their 1D and 2D organization. J. Phys. Chem. B 2005, 109 (42), 19823−19830. (23) Xiao, C. F.; Chen, S. M.; Zhang, L. Y.; Zhou, S. Q.; Wu, W. T. One-pot synthesis of responsive catalytic Au@ PVP hybrid nanogels. Chem. Commun. 2012, 48, 11751−11753. (24) Vial, S.; Pastoriza-Santos, I.; Pérez-Juste, J.; Liz-Marzán, L. M. Plasmon coupling in layer-by-layer assembled gold nanorod films. Langmuir 2007, 23 (8), 4606−4611. (25) Udayabhaskar, R.; Mangalaraja, R. V.; Manikandan, D.; Arjunan, V.; Karthikeyan, B. Room temperature synthesis and optical studies on Ag and Au mixed nanocomposite polyvinylpyrrolidone polymer films. Spectrochim. Acta, Part A 2012, 99, 69−73. (26) Khanna, P. K.; Singh, N.; Kulkarni, D.; Deshmukh, S.; Charan, S.; Adhyapak, P. V. Water based simple synthesis of re-dispersible silver nano-particles. Mater. Lett. 2007, 61 (16), 3366−3370. (27) Nakai, I.; Sugitani, Y.; Nagashima, K.; Niwa, Y. X-ray photoelectron spectroscopic study of copper minerals. J. Inorg. Nucl. Chem. 1978, 40 (5), 789−791. (28) Bhide, V. G.; Salkalachen, S.; Rastog, A. C.; Rao, C. N. R.; Hegde, M. S. Depth profile composition studies of thin film CdS: Cu2S solar cells using XPS and AES. J. Phys. D: Appl. Phys. 1981, 14, 1647−1656. (29) Hussain, Z.; Salim, M. A.; Khan, M. A.; Khawaja, E. E. X-ray photoelectron and auger spectroscopy study of copper-sodiumgermanate glasses. J. Non-Cryst. Solids 1989, 110 (1), 44−52. (30) Liu, C.; Li, Y.-J.; Wang, M.-H.; He, Y.; Yeung, E. S. Rapid fabrication of large-area nanoparticle monolayer films via waterinduced interfacial assembly. Nanotechnology 2009, 20 (6), 065604. (31) Gurung, M.; Adhikari, B. B.; Kawakita, H.; Ohto, K.; Inoue, K.; Alam, S. Recovery of Au (III) by using low cost adsorbent prepared from persimmon tannin extract. Chem. Eng. J. 2011, 174 (2−3), 556− 563. (32) Park, S.; Lee, J. C.; Lee, D. W.; Lee, J. H. Photocatalytic ZnO nanopowders prepared by solution combustion method for noble metal recovery. J. Mater. Sci. 2003, 38 (22), 4493−4497. (33) Huang, J. L.; Huang, D. P.; Liu, Y.; Chen, H. M.; Jing, X. L.; Sun, D. H.; Li, Q. B. Rapid Au recovery from aqueous solution by a microorganism-mediated, surfactant-directed approach: Effect of surfactants and SERS of bio-Au. Chem. Eng. J. 2015, 267, 43−50.

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DOI: 10.1021/acssuschemeng.6b00305 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX