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Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX

Specific Recovery and In Situ Reduction of Precious Metals from Waste To Create MOF Composites with Immobilized Nanoclusters Chao Wu,§ Xiangyang Zhu,§ Zhe Wang, Jian Yang, Yongsheng Li, and Jinlou Gu* Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China S Supporting Information *

ABSTRACT: Incorporation of active metal (especially precious metal) nanocomponents into metal−organic frameworks (MOFs) could capacitate MOFs with enhanced or new properties for innovative industrial applications. Despite increasing numbers of reports of precious metal nanoparticles/MOFs, developing such composites with low cost and high metal loading is still highly desirable. Herein, we demonstrated a novel and facile method to convert precious metal waste to wealth via using thiourea modified MOFs of UiO-66TU as a proof of principle to recover and immobilize precious metals. The new MOFs exhibited excellent selectivity which allowed for precious metals to be isolated from the waste electronic and electrical equipment (WEEE), which commonly contain different metal species. UiO-66-TU extracts a representative precious metal of Au effectively in a wide pH range, and the maximum Au adsorption capacity could approach 326 mg g−1. Through a simple reduction treatment, the adsorbed Au ions could be converted to well-dispersed Au nanoclusters (NCs, size below 1.8 nm) embedded in the MOFs, resulting in useful Au NCs/MOF composites. The merits of low cost and considerable Au loading, combined with the good stability of the Zr based MOFs, make the currently prepared Au NCs/UiO-66-TU composites potentially promising for various applications.

1. INTRODUCTION Metal−organic frameworks (MOFs), constructed from linking organic units with metal inorganic complexes, have rapidly grown in varieties and developed into fascinating porous crystalline materials.1 Apart from the large surface area, high porosity, and tailorable chemistry, MOFs also combined the advantages of regular pore structure and elasticity in the interconnecting organic linkers.2 Through playing a role as host matrices for the functionalization with active species, MOFs could provide opportunities to develop promising composite materials which exhibit enhanced or new behaviors compared with the pristine MOFs.3−7 Various functional materials have been integrated with MOFs to meet the specific applications. In particular, the incorporation of metal nanocomponents (MNs) into MOFs draws great attention owing to the benefits of unique properties (such as optical, electrical, magnetic, and catalytic properties) shown by metal nanomaterials.8−13 Meanwhile, MNs immobilization within pores of MOFs could reduce MNs aggregation by the confinement effect. With the additional advantages from active materials, these composites hold great potential for innovative industrial uses in a wide range of technologically crucial fields. However, some metals, especially precious metals, are expensive, and their incorporation will lead to high cost for MOF composites. This could be a key limitation for practical utilization. Therefore, developing a low cost strategy for introduction of precious MNs in MOFs is of great significance for the applications of the MOF composites. © XXXX American Chemical Society

It has been well reported that with the increased use in hitech fields, considerable amounts of precious metals have been found in the wastewater of various industries.14 Direct discharge of these wastes leads to the loss of critical resources and may simultaneously cause serious metal contamination to the environment. A number of reports highlight the adsorption and recovery of such metals from waste.15−18 Owing to the outstanding characteristics, MOFs exhibit great potential in environmental remediation, and many studies have investigated them as adsorbents for purifying water.19−25 Very recently, we have explored the specific adsorption of target compounds on MOFs by taking advantage of the active groups displayed on metal nodes or organic ligands.26,27 It is reasonable to suppose that MOFs with specific sites could selectively extract precious metals from wastewater. If nanoparticles could form in situ, the obtained materials might be desirable MOF composites with much lower cost. In the current work, we successfully fused these concepts and turned waste to wealth. Thiourea modified zirconium-based MOFs (UiO-66-TU) were designed as a matrix to exemplify the recovery of precious metals and subsequent immobilization of MNs (Scheme 1). It is well-known that there are significant interactions between sulfur atoms and the precious metals, such Received: Revised: Accepted: Published: A

July 11, 2017 September 4, 2017 November 8, 2017 November 8, 2017 DOI: 10.1021/acs.iecr.7b02839 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

66-TU (0.4 g L−1) was employed to recover precious metals from the simulated waste for 6 h. The pH values of the test solutions were adjusted by adding negligible volumes of 100 mmol L−1 HNO3 or 100 mmol L−1 NaOH aqueous solutions. The adsorption experiments were carried out at a pH between 1 and 7 to evaluate the influence of pH values on Au recovery. The adsorption kinetic experiments were carried out at pH 4, and the concentrations of Au3+and the adsorbent were adjusted to 0.15 g L−1 and 0.2 g L−1, respectively. The mixtures were shaken at 180 rpm at 25 °C. After adsorption for a predetermined time (10 min to 6 h), the mixture was centrifuged, and residual Au concentrations in the supernatants were measured by ICP-OES. Batch recovery experiments of Au3+ onto UiO-66-TU, UiO-66, and UiO-66-NH2 were carried out for 3 h with 0.2 g L−1 adsorbents concentrations, the concentrations of Au3+ were adjusted between 5 and 800 mg L−1, and the pH was 4. Then, the residual Au3+ in the supernatant was determined by ICP-OES. In Situ Au NCs Formation. To convert the Au3+ adsorbed UiO-66-TU to Au NCs/MOF composites, sodium borohydride (NaBH4, 10 mM) was used to reduce the precious metal ion for 0.5 h. After that, the resultant material (donated as Au NCsUiO-66-TU) was washed with water three times and dried under vacuum overnight.

Scheme 1. Schematic Illustration for the Synthesis of UiO66-TU

as Au−S.28−30 Compared with the mercapto groups, thiourea groups are stable and have been employed to synthesize a variety of precious metal recovery materials.31−35 UiO-66 is composed of Zr6O4(OH)4 clusters and p-phthalic acid (PTA), and its excellent thermostability and chemical stability could bear the treatments of functionalization and precious metals.36,37 Thanks to the strong affinity and open cavities, selective recovery could be achieved, and the maximum extraction capacity of UiO-66-TU approached 326 mg g−1 for Au. After simple treatment, the adsorbed Au ions could be converted to well-dispersed nanoclusters (NCs) embedded in the MOFs, resulting in low cost MOF composites.

2. EXPERIMENTAL DETAILS Synthesis of UiO-66, UiO-66-NH2, and UiO-66-TU. UiO-66 and UiO-66-NH2 particles were synthesized according to the literature with a slight modification.36,37 Briefly, ZrCl4 (233 mg, 1 mmol), PTA (166 mg, 1 mmol), or BDC-NH2 (181 mg, 1 mmol), acetic acid (1.2 g, 20 mmol), and 0.16 mL HCl (37%, 2 mmol) were dissolved in 20 mL of DMF, which was subsequently sealed in a Pyrex vial at 120 °C for 24 h. After that, UiO-66 or UiO-66-NH2 was collected by centrifugation. Subsequently, these solid products were soaked in 20 mL of DMF containing 0.5 mL of HCl at 100 °C for 6 h to clear the free PTA or BDC-NH2 and the trapped modulator of acetic acid.38 Then, the obtained particles were washed with acetone several times and dried under vacuum overnight at 100 °C. The preparation of UiO-66-TU involved two steps: chloromethylation of UiO-66 followed by thiourea functionalization (Scheme 1). (1) UiO-66 was chloromethylated based on the reported procedure.39 Briefly, UiO-66 (200 mg), AlCl3· 6H2O (482 mg, 2 mmol), and MeOAcCl (108 mg, 1 mmol) were added to 16 mL of MeNO2. The mixture was refluxed at 100 °C for 6 h, and the obtained powder was washed with acetone and H2O. (2) The resultant material was dispersed in 20 mL of deionized water followed by adding thiourea (228 mg, 3 mmol). The mixture was stirred under reflux at 100 °C.33,40 After that, UiO-66-TU was collected by centrifugation and washed with deionized water. Finally, the powder was dried in a vacuum oven overnight at 100 °C. Recovery Experiments. Different concentrations of Au3+ solutions were obtained via diluting the stock solution of Au3+ (2 g L−1). Before adsorption, the UiO-66-TU, UiO-66, and UiO-66-NH2 were placed in a vacuum oven overnight at 100 °C and kept in a desiccator. ICP-OES was used to determine the Au concentration in solutions. To evaluate the potential of UiO-66-TU for selective extraction of precious metals from wastewater, an aqueous solution containing Na+ (100 mg L−1), K+ (100 mg L−1), Ca2+ (100 mg L−1), Al3+ (100 mg L−1), Fe3+ (100 mg L−1), Sn2+ (100 mg L−1), Cu2+ (100 mg L−1), Zn2+ (100 mg L−1), Ni2+ (100 mg L−1), and Au3+ (20 mg L−1) was prepared to construct a simulated waste sample. HNO3 aqueous solution (0.1 M) was added to make the mixture of metal ions dissolve. Then UiO-

3. RESULTS AND DISCUSSION Characterization of UiO-66-TU. The highly crystallized UiO-66 was synthesized via the solvothermal method with a slight modification, and the integration of the thiourea into MOFs was performed by a two-step procedure, including chloromethylation of UiO-66, followed by thiourea functionalization using the reported strategy (Scheme 1).39,40 As shown in Figure 1, both patterns of parent and modified UiO-66 show

Figure 1. XRD patterns of (a) the simulated UiO-66 structure, (b) the synthesized UiO-66, (c) UiO-66-TU, and (d) Au clusters immobilized UiO-66-TU (denoted as Au NCs-UiO-66-TU). The peaks between 10 and 50° are magnified four times.

the similar Bragg diffraction peaks in agreement with the simulated UiO-66. This confirms that the synthesized UiO-66 possesses the characteristic structure of UiO-66, and meanwhile UiO-66-TU retains the good crystallinity in the ligand modification process. The textural properties of the MOFs were examined by the N2 sorption technique. The adsorption− desorption curves for both UiO-66 and UiO-66-TU were inconsistent with the previous observation for UiO-66 structures (Figure 2).36,37 The surface area for UiO-66 and UiO-66-TU was calculated to be 1282 m2 g−1 and 958 m2 g−1 (Table 1), respectively. The slight decreases in surface area and pore volume between UiO-66 and UiO-66-TU can be ascribed to the occupation of the functional groups in the cages of B

DOI: 10.1021/acs.iecr.7b02839 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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attributed to carboxylate groups, and the peak at 1660 cm−1 has been associated with the trapped DMF in the cavities.37 In contrast, the DMF peak becomes unobservable after the modification procedure (Figure 3b). Meanwhile, it is observed that UiO-66-TU has four characteristic absorption bands at 1643, 1254, 2936, and 3382 cm−1. These bands, assigned to the CN, bending and stretching vibrations of C−H and N−H bonds, respectively, confirm that the thiourea groups have been successfully grafted onto UiO-66.40−42 Selective Extraction of Precious Metals from Simulated Waste Water. In some waste electronic and electrical equipment (WEEE), although precious metals account for more than 80% of the total intrinsic value, their amount is less than 5 wt %.43 Specific extraction of them in the presence of an excess of coexisting metals appears to be an essential capability for precious recovery materials. Motivated by the previous discoveries on the strong affinity of thiourea groups modified adsorbents toward precious metals,31−33,40,44 the UiO-66-TU are thus anticipated to achieve selective precious metals recovery. Au was selected because it is the major precious metal in the WEEE.45 To investigate the potential of the thiourea functionalized MOFs as a low-energy, high selectivity recovery media, an aqueous solution containing K+, Na+, Ca2+, Cu2+, Al3+, Ni2+, Fe3+, Zn2+, Sn2+, and Au3+ (all chlorides) was applied as a simulated waste to diffuse into UiO-66-TU for 6 h under ambient conditions. 0.1 M HNO3 was added to the solution to dissolve these metals.15 After adsorption, the concentrations of residual metals were determined by ICPOES. More than 95% of Au ions could be isolated from the solution, while only small percentages of other metals were adsorbed (Figure 4). This result demonstrates the significant binding selectivity of UiO-66-TU crystals for precious metal ions.

Figure 2. N2 adsorption−desorption isotherms of (a) as-synthesized UiO-66, (b) UiO-66-TU, and (c) Au NCs-UiO-66-TU.

Table 1. Textural Parameters of UiO-66, UiO-66-TU, and Au NCs-UiO-66-TU samples

SBET (m2 g−1)

VP (cm3 g−1)

UiO-66 UiO-66-TU Au NCs-UiO-66-TU

1285 958 517

0.71 0.57 0.33

frameworks. From TGA data, it can be found that the assynthesized UiO-66 is stable in air up to 500 °C (Figure S1, black line, Supporting Information). On the contrast, the UiO66-TU and Au NCs-UiO-66-TU (Figure S1, red and blue line, Supporting Information) show an additional weight loss (7.5% and 12.4%) between 350 and 480 °C. It might be due to the partial decomposition of functional thiourea groups from BDC ligands in MOFs. Therefore, the modified UiO-66 should be stable in air up to approximately 350 °C. When the temperature reaches 650 °C, the organic components completely burn out, and the residues are identified to be ZrO2. The preserved weight percentage at 650 °C for UiO-66 is 43.6%, while that for functionalized sample is 39.9%. This difference verifies the presence of additional organic units in the obtained UiO-66-TU originating from the ligand modification. Additionally, a reported method was utilized to quantitatively calculate the substitutional ratio of the linkers by thiourea.27 According to the values of weight loss at 350 and 650 °C, it is calculated that the number of BDC in each UiO-66 unit is approximately 5.1. Meanwhile, the S content in the UiO-66-TU is calculated to be about 0.86 mmol g−1 according to ICP analysis. Therefore, it is calculated that the substitutional ratio of linkers by thiourea was approximately 27%. FT-IR spectra were collected to evaluate the functionalization of UiO-66 with thiourea groups. As shown in Figure 3, the intense peaks of UiO-66 at 1580 and 1400 cm−1 should be

Figure 4. Percentage metal ions recovery from simulated wastewater by UiO-66-TU.

Effects of pH on Au3+ Recovery. The pH value is one of the critical factors in precious metal recovery from water, which could affect both the adsorbent structure and the distribution of pollutant species. The extraction of Au3+ from aqueous solution onto UiO-66-TU results in a pH value between 1 and 7 (Figure S2). It could be observed that UiO-66-TU works effectively over a wide range of pH, and at pH 4 it presents the highest adsorption capacity for Au3+. The further increasing of pH to 7 results in reduction in the uptake amount and would be harmful for the isolation of Au3+ due to the deposit of it at a higher pH value. Adsorption Kinetics for Au3+ Recovery. To explore the adsorption kinetics of Au3+ onto UiO-66-TU, 0.15 g L−1 initial concentration of Au3+ solution was used at 25 °C and pH 4. Figure 5a shows the time-dependent adsorption curve. The precious metal is rapidly adsorbed during the first 30 min, and

Figure 3. FT-IR spectra of (a) parent UiO-66 and (b) UiO-66-TU. (The black stars represent the stretching modes of carboxylate groups.) C


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Supporting Information). Because of the relatively higher correlation coefficients (R2) of the Langmuir model (Figure S7 and Table S3, Supporting Information), it suggests that the Langmuir model is more representative. Meanwhile, it can be found that the maximum adsorption capacities of Au3+ over UiO-66 and UiO-66-NH2 are 53.6 and 114.8 mg g−1, respectively (Table S3, Supporting Information). This result illustrates that UiO-66-TU could greatly improve the adsorption capacities of Au3+ in comparison to UiO-66 and UiO-66-NH2. A comparison of the adsorption capacities of Au3+ by various materials is shown in Table 2. The thiourea

Figure 5. (a) The influence of contact time on Au3+ adsorption over UiO-66-TU and (b) the corresponding plots of the pseudo-secondorder kinetics model (25 °C, pH = 4, Cinitial = 0.15 g L−1, Cadsorbent = 0.2 g L−1).

Table 2. Comparison of the Adsorption Capacities of Au onto Various Adsorbents

the adsorption equilibrium is reached in approximately 90 min. Based on these results, a shaking time of 180 min was selected in the following experiments to ensure the full equilibrium. To further understand the kinetics, two commonly used kinetic models, pseudo-first-order model (Figure S3, Supporting Information) and pseudo-second-order model (Figure 5b), were applied.46−48 The kinetic parameters and correlation coefficients (R2) are calculated and tabulated in Table S1 (Supporting Information). It could be found that the pseudosecond-order model exhibits a more suitable fit according to the higher correlation coefficients (R2). Furthermore, the equilibrium adsorption capacities (qe) are much closer to the experimental data. These results suggest that the Au 3+ adsorption process could be described by the pseudo-secondorder kinetic model, which assumed that the adsorption limiting step might be a chemisorption process via sharing of electrons between the adsorbate and adsorbent.49,50 Adsorption Isotherm for Au3+ Recovery. The adsorption isotherm of Au3+ onto UiO-66-TU was assessed at as a function of the equilibrium concentration in aqueous phase at 25 °C (Figure 6a). Subsequently, to analyze the equilibrium

qmax (mg g−1)

adsorbents

refs

UiO-66-TU

326

2-(3-(2-aminoethylthio)propylthio)ethanaminemodified CoFe2O4 thiolated mesoporous silica porous carbon taurine modified cellulose glycine modified chitosan resin aliquat-336-impregnated alginate capsule 3-amino-1,2-propanediol functionalized polystyrene resin

37.4

this work 18

195 90.6 34.5 170 191.9 278.6

53 54 55 56 57 58

modified MOFs exhibit better extraction capability than many reported adsorbents,18,53−58 which indicates the great potential of UiO-66-TU for dealing with wastewater containing precious metal ions. It should be pointed out that this maximum adsorption capacity is larger than amount of the sulfur content (0.86 mmol g−1) in frameworks. This suggests that the Au−S bonding was not the only interaction between UiO-66-TU and Au3+. On the basis of the species distribution diagrams, Au3+ ions exist mostly in the acidic medium in the form of chloro-complexes such as AuCl4−.59 From Figure S8 (Supporting Information) the point of zero charge of the UiO-66-TU is found to be around 5.5, which means that the surface of the MOFs remains positively charged below pH 5. Therefore, the electrostatic interaction between UiO-66-TU and AuCl4− might also play a role for Au recovery. Furthermore, due to the existence of the protonated amine groups in UiO-66-TU (Scheme 1), it is reasonable to assume that the anion exchange reaction was also involved in the adsorption process.60 Characterization of Au NCs Immobolized UiO-66-TU. After the recovery process, the Au3+ adsorbed MOF was reduced by NaBH4 to create Au nanocomponents within the porous matrix.61 The obtained Au NCs could be stabilized by the soft functional components suspended in the cavities, though they have a high surface free energy. As shown in Figure 1c and 1d, both UiO-66-TU and Au NCs-UiO-66-TU show the similar XRD patterns, suggesting that the Au adsorption and subsequent reduction did not change the structure of UiO-66TU. For Au NCs-UiO-66-TU, no diffraction peaks corresponding to crystalline Au (2θ = 38 and 44) could be observed in the high-angle region.62,63 It is therefore deduced that the particle size of the encapsulated Au species is probably too small to be detected by X-ray diffraction. The N2 adsorption−desorption curve for Au NCs-UiO-66TU exhibits typical I isotherm (Figure 2c), further affirming

Figure 6. (a) Isotherms for the adsorption Au3+ adsorption over UiO66-TU and (b) the corresponding plots of the Langmuir model (25 °C, pH = 4, t = 3 h, Cadsorbent = 0.2 g L−1).

adsorption characteristics, the Langmuir and Freundlich isotherm models were used. As shown in Figure 6b, Figure S4, and Table S2 (Supporting Information), the comparatively higher correlation coefficients (R2) of the Langmuir model suggests that, compared with the Freundlich model, the Langmuir model is more eligible. Because the surface of adsorbents is homogeneous assumed by the Langmuir model, the active adsorption sites of UiO-66-TU are distributed homogeneously on its surface.51,52 Meanwhile, the maximum adsorption capacity of Au3+ over UiO-66-TU was calculated to be 326 mg (1.65 mmol) g−1. To further compare the adsorption property of UiO-66-TU with UiO-66 and UiO-66NH2, we performed adsorption isotherms of Au ions onto the latter two MOFs. UiO-66-NH2 was successfully synthesized with good crystalline and high surface area (Figures S5 and S6, D


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To further explore the valence change of the Au species during the in situ reduction process, the XPS spectra of Au 4f electrons (Figure 9) were collected before and after NaBH4

that after Au immobilization the structure integrity of UiO-66TU was not destroyed. Moreover, it can be found that after Au immobilization, the surface area and pore volume are decreased (Table 1), owing to the Au NCs occupation in the cages of the frameworks. The TGA curve of Au NCs-UiO-66-TU features a more preserved weight percentage at 650 °C (48.3%) compared to that of UiO-66-TU (Figure S1, Supporting Information), which also evidence the successful loading of Au species. From the UV−vis spectrum (Figure S9, Supporting Information), no characteristic peak at 520 nm of Au NCsUiO-66-TU could be detected, which is usually assigned to the surface plasmon resonance band of Au nanoparticles with large size.64,65 This observation suggests that the diameter of the obtained Au NCs is below 2 nm, in good agreement with the XRD deduction.64,65 UiO-66 MOFs exhibit as well-dispersed cubic microcrystals with a mean diameter of ca. 200 nm as the SEM image illustrated (Figure S10a, Supporting Information). Meanwhile, the morphologies stay intact after the thiourea modification and in situ generation of Au NCs in MOFs (Figures S10b and c, Supporting Information). TEM images of Au NCs-UiO-66-TU were recorded (Figure 7), showing that the average diameter of Au NCs is less than 1.8 nm, and they are well dispersed, clearly demonstrating that Au NCs/MOF composites have been successfully developed.

Figure 9. XPS spectra of Au 4f electrons of UiO-66-TU-Au ions (a) before and (b) after NaBH4 treatment.

reduction. The Au 4f XPS spectrum of the untreated UiO-66TU-Au displays Au3+ (90.1 and 86.4 eV) and Au+ peaks (88.8 and 85.1 eV), ascribed to Au 4f7/2 and Au 4f5/2 binding energy.71,72 No Au0 signals could be detected before reduction. It suggests that the intermediate might be the UiO-66-TU-Au+/ Au3+ complex due to the strong Au−S bonding to specifically capture Au ions. After in situ reduction with NaBH4, the typical XPS peaks of Au0 appear at 87.8 (Au 4f7/2) and 84.14 eV (Au 4f5/2), respectively.71−73 Meanwhile, the intensities of Au3+ and Au+ XPS peaks clearly decrease. The appearance of Au0 could be assigned to the interior gold atoms of nanoclusters in Au NCs-UiO-66-TU, while Au3+ and Au+ are associated with the gold atoms on the surface of the nanoclusters. Therefore, the abundant S groups in UiO-66-TU could not only provide strong specific Au−S bonding interaction but also effectively confine the Au ions in MOFs cages and facilitate them in situ transformation to gold nanoclusters.

Figure 7. (a) TEM image of Au NCs-UiO-66-TU and (b) the corresponding magnified TEM image.

XPS was further employed to investigate the interaction between S and Au atoms and the status of Au species in UiO66-TU. As shown in Figure 8a, the S 2p signal in the XPS

4. CONCLUSIONS In summary, we report a novel and facile method to convert precious metal waste to wealth via using thiourea modified MOFs as a precious metal recovery matrix. The new MOFs of UiO-66-TU present remarkable selectivity which allows for precious metals to be recovered from the complex mixture of various metal ions. UiO-66-TU extract a representative precious metal of Au effectively in a wide pH range with the best adsorption performance at pH 4. The maximum Au adsorption capacity could approach 326 mg g−1. Through a simple reduction treatment, the adsorbed Au ion could be converted to well-dispersed Au NCs (size below 1.8 nm) embedded in the MOFs, resulting in economical Au NCs/MOF composites. The present study provides a new insight into the design of MNs/ MOF composites with low cost and high metal loading, which could be potentially promising for applications in a wide range of technologically crucial fields.

Figure 8. XPS spectra of S 2p electrons of UiO-66-TU (a) before and (b) after Au ions adsorption.

spectra could be deconvoluted into two peaks at 164.8 and 163.6 eV, ascribed to S 2p3/2 and S 2p1/2 bonding energy of S atoms in the thioether group.66,67 After Au ions adsorption, these bands shift to 164.6 and 163.3 eV (Figure 8b). The core level shifts might be due to the formation of Au−S bonding by the interaction of the Au groups and reactive sulfur in the thioether groups.68−70 This result elucidates that the S groups within UiO-66-TU plays a vitally important role in Au(III) adsorption. E


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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/acs.iecr.7b02839. TGA data, effect of pH values on Au recovery, plots of pseudo-first-order kinetics model and Freundlich isotherm model, XRD pattern and N2 adsorption− desorption isotherm of UiO-66-NH2, adsorption isotherms for Au3+ over UiO-66 and UiO-66-NH2, Zeta potential, UV−vis spectrum, SEM images, Tables S1, S2 and S3 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86-21-64252599. Fax: +86-21-64250740. E-mail: [email protected]. ORCID

Jinlou Gu: 0000-0002-3190-573X Author Contributions §

C.W. and X.Z. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of China (51072053, 51372084), the Innovation Program of Shanghai Municipal Education Commission (13zz040), the Nano-Special Foundation for Shanghai Committee of Science and Technology (12 nm0502600), and the 111 Project (B14018).

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REFERENCES

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