In-Situ Synthesis and High-Efficiency Photocatalytic Performance of

Oct 10, 2018 - School of Biology and Biological Engineering, South China University of Technology, Guangzhou, 510006, P. R. China. §. School of Chemi...
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Cite This: Inorg. Chem. 2018, 57, 13289−13295

In-Situ Synthesis and High-Efficiency Photocatalytic Performance of Cu(I)/Cu(II) Inorganic Coordination Polymer Quantum Sheets Shixiong Li,† Zhentao Feng,† Yun Hu,† Chaohai Wei,*,† Haizhen Wu,‡ and Jin Huang§ †

School of Environment and Energy, South China University of Technology, Guangzhou, 510006, P. R. China School of Biology and Biological Engineering, South China University of Technology, Guangzhou, 510006, P. R. China § School of Chemistry and Pharmacy, Guangxi Normal University, Guilin, 541004, P. R. China ‡

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S Supporting Information *

ABSTRACT: Two-dimensional (2D) materials ultrathin quantum sheets have the advantage of elevating the catalysis performance and prominent edge effects, but most of them belong to element single valence materials. In this paper, the ultrathin Cu(I)/Cu(II) inorganic coordination polymer quantum sheet (ICPQS) {[CuII(H2O)4][CuI4(CN)6]}n is synthesized by controlling the appropriate molar ratio of raw material, reaction time, and temperature. Transmission electron microscopy (TEM) and atomic force microscope (AFM) analysis show that this ICPQS has a thickness of ∼0.2 nm. Due to the fact that about 58.16% of the Cu(I)/Cu(II) is occupied in molecular structure and most of the metal active sites are fully utilized, this ICPQS can accelerate the photocatalytic degradation of methylene blue (MB) (K = 2.5 mg·L−1·min−1 at pH 3) and organic compounds in coking wastewater and biotreated coking wastewater. Basing on mixed valences, the ICPQS can use visible light to promote energy transfer and increase quantum efficiency, paving the way for developing the next-generation monolayer 2D mixed valence photocatalysts. beneficial to improve catalytic performance.21−27 So, the QSs with strong visible light absorption can avoid the above disadvantages of traditional photocatalysts. QS, such as graphene,28,29 MoS2, and WS230−33 could be imparted with not only the intrinsic characteristic of two-dimensional materials but also quantum confinement and prominent edge effects. These characteristics are invaluable in the field of photocatalysts. Although many 2D materials and quantum sheets have been developed and studied in recent years,22−35 they are mainly derived from inorganic and organic single valence materials. It is necessary to develop novel two-dimensional materials and study the effect of multivalent/multisite quantum sheets on the photoquantum efficiency. The outermost electron arrangement of Cu is 3d104S1, which tends to lose one or two electrons and becomes 3d10 and 3d9. The −CN has well-coordinated C and N atoms, which is very easy to coordinate with Cu(I)/Cu(II) to form two-dimensional structure. In this paper, an ultrathin Cu(I)/Cu(II) inorganic coordination polymer quantum sheet (ICPQS) {[CuII(H2O)4][CuI4(CN)6]}n is synthesized in situ by combining the surfactant and ultrasonic wave. This ICPQS has a high photocatalytic performance in photocatalytic degradation of methylene blue (MB) and actual industrial coking wastewater and biotreated coking wastewater.

1. INTRODUCTION Environmental pollution and energy shortages seriously restrict the development of society. The development of efficient photocatalysts for environmental purification and energy conversion has attracted the attention of scientists.1−5 The improvements of photocatalytic oxidation technology need to regulate the active sites and energy level of the photocatalysts from the photocatalytic mechanism and improve the photoquantum efficiency. TiO2-based photocatalyst can effectively photocatalytically degrade organic pollutants in water, but it has a large band gap (Eg = 3.0−3.2 eV), and only 4% of the ultraviolet light in the sunlight could meet this energy requirement for photocatalytic reaction.6−9 The coordination polymers (CPs) are considered to be very promising functional materials, some of which have been studied for magnetic,10 fluorescent,11 pollutants degradation,12 and hydrogen evolution.13 Metal− organic frameworks (MOFs) are one type of CPs. The density functional theory (DFT) calculations showed that MOFs are typically semiconductors or insulators with a band gap between 1.0 and 5.5 eV. Thus, only some MOFs can utilize visible light to catalyze the degradation of organic pollutants.14−16 Additionally, for both traditional catalysts and MOFs catalysts, their catalytically active sites are located only on the surface,17−20 which not only wastes most of the catalyst material but also reduces the effective use of the catalysts. Two-dimensional (2D) material quantum sheets (QSs) can completely expose surface atoms and/or active sites, which is © 2018 American Chemical Society

Received: July 3, 2018 Published: October 10, 2018 13289

DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295

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Inorganic Chemistry

2. RESULTS AND DISCUSSION In-Situ Synthesis and Structure Determination of {[CuII(H2O)4][CuI4(CN)6]}n. In the previous research work, we found that −CN could be synthesized in situ under solvothermal or hydrothermal conditions (relatively high temperature of 120 °C and autogenous pressure), under which the reduction of the Cu(II) center to Cu(I) accompanies the reaction.36,37 So, the Cu(I)/Cu(II) materials can be synthesized in situ by controlling the appropriate molar ratio of raw material, reaction time, and temperature. The solvothermal reaction of CuCl2·2H2O and K3[Fe(CN)6] in pH 5 water solution at 150 °C generates a violet lump of inorganic coordination polymer {[CuII(H2O)4][CuI4(CN)6]}n (1). The magnetic measurements (Figure S1) show that the χmT value of 2.04 cm3 K mol−1 at 300 K is slightly higher than that expected for an isolated divalent high-spin Cu(II) system. This indicates that there is a single electron in 1. To gain further insight into the evidence that Cu(II) ions are also present in 1, X-ray photoelectron spectroscopy (XPS) analysis of 1 is also performed. XPS did not provide valuable information about Cu(IV) ions, but it further determines the possibility of magnetic contamination having a 3d9 configuration (Figure S2 and Figure S3). Both Cu(I) and Cu(II) signals are observed: Cu(II) has a main peak at 935.1 eV (peak II) with a shakeup satellite (peak III) at higher binding energies, and Cu(I) has a characteristic peak at 932.5 eV (peak I) with no satellite peak. The Fourier transform infrared (FT-IR) spectrum (Figure S4) of 1 shows a strong peak at 2107 cm−1, which is a feature of the CN vibration, it falls in the normal ranges of complexes36,38−42 containing −CN, confirming the presence of the −CN group. An X-ray single-crystal diffraction analysis43 reveals that 1 crystallizes in monoclinic system, P21/c space group. The coordination environment of Cu(I)/Cu(II) in 1 is shown in Figure 1a.

and all the atoms are in a plane, forming a two-dimensional monolayer structural framework: [CuI4(CN)6]2−n. The C−N distance falls in the range of 1.129(5)−1.148(5) Å and the Cu−N distances fall in the range of 1.946(4)−1.990(3) Å (Cu(2)−N(1) = 1.990(3) Å; Cu(1)−N(3) = 1.946(4) Å; Cu(1)−N(2) = 1.971(4) Å), and the Cu−C distances fall in the range of 1.898(4)−1.913(4) Å (Cu(1)−C(1) = 1.898(4) Å; Cu(2)−C(3)A = 1.898(4) Å; Cu(2)−C(2)B = 1.913(4) Å). The bond angles of N(2)−Cu(1)−N(3) and C(2)B−Cu(2)− C(3)A are 106.71(15)° and 131.87(15)°, respectively. These bond angles and bond distances are comparable to those in other cyanide bridged copper(I) complexes.36,38−42 The Cu(II) ions in 1 are coordinated by four coordinated water molecules, forming a single ion countercation: [CuII(H2O)4]2+n. This countercation forms a two-dimensional inorganic coordination polymer {[CuII(H2O)4][CuI4(CN)6]}n (1) with [CuI4(CN)6]2−n (Figure 1b). Scanning electron microscopy also confirms that its morphology is a two-dimensional sheet structure (Figure 1(c) and 1(d)). All the atoms in this countercation are not in the two-dimensional monolayers structural framework; instead, owing to the introduction of water molecules, a two-dimensional sandwich structure (Figure S5a) is formed by O−H···N and O−H···C hydrogen bonds (Figure S5b) to link two monolayers [CuI4(CN)6]2−n. Since the Cu(I) ions in 1 are three-coordinated, the Cu(II) is four-coordinated and in the sandwich, so 1 can be generalized as a single ion multisites Cu(I)/Cu(II) 2D material. The surface area of 1 is determined using the BET technique and its specific surface area (Figure S6a) is 35.6 m2·g−1. Photoelectric Response and Photocatalytic Performance of 1. The UV−visible diffuse reflectance (UV−vis DRS) (Figure S7) shows that 1 has over 50% absorbance in the visible range (400−800 nm). The cyclic voltammetry curve (Figure S8) shows that the bandgap (eV) of 1 is 2.46 eV. The HOMO = −5.29 eV and LUMO = −2.83 eV of 1 can be calculated by the following formula:44,45 EHOMO/eV = −4.44 − Eonset(Ox); ELUMO/eV = −4.44 − Eonset(Red). Therefore, 1 is a very good photocatalyst with visible light response, which photocatalytically degrades MB in comparison with MoS2 QS in solutions at pH 3−9. The amount of their photocatalytic degradation of MB is greater than adsorption (Figure S9). Under the condition of pH 3, the rate constants of photocatalytic degradation of MB in unit time are 1.7 mg·L−1·min−1 and 0.5 mg·L−1·min−1, respectively. There is a good linear relationship between ln(C0/Ct) and time (t) for 1, indicating that the MB photocatalytic degradation reaction conforms to the first-order kinetic reaction. By using the linear regression equation of ln(C0/Ct) and t, the reaction kinetic equations and their related parameters at different initial concentrations can be obtained (Table S4). The zeta potential vs pH (Table S5) of 1 and MoS2 QS show that their zeta potentials at pH 3 are 62.93 mV and 33.51 mV, respectively. According to the effect of pH on quantum efficiency, the larger the surface charge, the higher the photocatalytic quantum efficiency.46 The powder of 1 after the photocatalysis is collected, and the powder X-ray diffraction (PXRD) test shows that its structure remained unchanged (Figure S10a). The electronic spray ionization mass spectra (ESI-MS) results show that there are four signals (Figure S11) attributed to [C16H18N3S]+, [C16H22N3SO]+, [C6H9N2SO8]+, and [C4H6NO6]+. So, the possible photocatalytic mechanism and degradation pathways are shown in Figure 2. The above test shows that 1 has higher performance in photocatalytic degradation of MB and it can be predicted

Figure 1. (a) Coordination environment of Cu(I)/Cu(II) of 1 from X-ray crystallographic data at 50% ellipsoid probability; (b) 2D polyhedral stacking layer viewing along the a-axis; (c and d) SEM images of 1.

Its empirical formula is C6H8Cu5N6O8, which consists of four Cu(I) ions, one Cu(II) ion, six cyano (−CN) ions, and four coordinated water molecules. Among them, Cu(I)/Cu(II) occupies about 58.16%. The Cu(I) ions in 1 are coordinated by three −CN ions, the center Cu(I) ions are three-coordinated, 13290

DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295

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Figure 2. Possible photocatalytic degradation MB mechanism of 1.

that the photocatalytic performance of its QS will be better than 1. Synthesis and Photocatalytic Performance of ICPQS. The synthesis of the ICPQS is similar to that of 1, except that 2 mL of 50 mg·L−1 sodium dodecyl benzenesulfonate is added after the hydrothermal reaction is completed. After ultrasound treatment for 30 min, the suspension is collected and centrifuged at 10,000 rpm. Solid-phase amorphous phase quantum sheets are obtained (Figure S10b). Transmission electron microscopy (TEM) reveals that the ultrathin quantum sheets become thinner (Figure S12). The energy-dispersive X-ray spectroscopy (EDS) mapping (Figure 3) results and EDS spectra

Figure 4. (a−b) the AFM image and (c−d) the corresponding height profile of ICPQS.

as the coexistence of inorganic metal cations and anions in wastewater.47 The Na+, K+, Mg2+, Ca2+, Ba2+, and Fe3+ cations and Cl−, NO3−, HCO3−, CO32−, SO42−, and PO43− anions are common inorganic ions in wastewater.47,48 They might affect the performance of photocatalysts for the degradation of organic pollutants. The coexistence experiments of ICPQS at pH = 7 indicate that these cations have different effects on the photocatalytic degradation of MB (Figure S15). Na+, K+, Mg2+, and Ca2+, in the range of 0.001−1.000 mmol·L−1, have an inhibitory effect on the ICPQS photocatalytic degradation of MB. The inhibition effects increase with their concentration. This phenomenon can be attributed to the influence of the presence of Cl− ions in the solution. It is well-known that I− is an excellent scavenger for free radicals.47,49 Cl and I are in the same main group, and their extranuclear electrons are arranged in the same way, which makes Cl a similar free radical scavenger. Therefore, Cl− can also remove the free radicals generated during the ICPQS photocatalytic process and inhibit the MB degradation rate. Ba2+ has different effects in the photocatalytic degradation of MB by ICPQS, which significantly inhibits the photocatalytic degradation of MB at 0.001−1.000 mmol·L−1. But when the concentration of Ba2+ is lower than 0.001 mmol·L−1, Ba2+ is able to promote the photocatalytic degradation of MB, probably due to the precipitation of the catalytic decomposition intermediates with Ba2+, saving additional free radicals to react with MB. Fe3+ enhanced the degradation of MB with the increase of concentrations. This may be due to the existence of two different photocatalytic degradation processes of MB in the reaction system in which ICPQS and Fe3+ coexist:50 i.e. photogenerated holes by ICPQS and •OH produced by Fe(OH)2+, which cocatalyze the degradation of MB. Since Fe(OH)2+ can absorb light and become activated, in the reaction system in which Fe3+ exists, as the concentration of Fe3+ increases in the range of 0.001−1.000 mol·L−1, the rate of photocatalytic degradation of MB also increases. The anions coexistence experiment at pH 7 indicates that these anions have different effects on the photocatalytic degradation of MB (Figure S16). Cl−, which displays an inhibition effect on the catalytic degradation of MB, has been discussed above. CO32−, SO42−, and PO43− also inhibit the photocatalytic

Figure 3. (a−e) EDS mapping results.

(Figure S13) for C, N, O, and Cu confirm that the ICPQS structure is consistent with its crystal structure. And atomic force microscopy (AFM) shows that this ICPQS has a thickness of ∼0.2 nm (Figure 4). The surface area of ICPQS is 132.5 m2·g−1 (Figure S6b); this also indirectly shows that polymer 1 is stripped into quantum sheets. Although 1 and MoS2 QS can photocatalytically decompose 85% and 15% of MB in 25 min with the respective degradation rates reaching 1.7 and 0.3 mg·L−1·min−1, the ICPQS can photocatalytically decompose nearly 100% of MB in 20 min (Figure S14) with a degradation rate of 2.5 mg·L−1·min−1. Influence of the Inorganic Ions on the Photocatalytic Performance. In practical industrial applications, photocatalytic degradation might be affected by many factors, such 13291

DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295

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Inorganic Chemistry degradation of MB by ICPQS in the concentration range of 0.001−1.000 mol·L−1, and the inhibition effects increased with increasing concentrations. It is clear that PO43− shows stronger inhibition than CO32−, SO42−, and Cl− on the photocatalytic degradation of MB by ICPQS. The zeta potential test indicates that the pHPZC of the ICPQS is 7.5. Therefore, when the pH of the reaction solution is lower than 7.5, the surface of the ICPQS is positively charged. Therefore, anions such as Cl−, CO32−, SO42−, and PO43− can be adsorbed on the surface of the ICPQS and block the active sites; this leads to a decrease in the reaction rate. Since PO43− has three negative charges, it exhibits a stronger adsorption capacity on the surface of ICPQS than Cl−, CO32−, and SO42−, so it shows a stronger inhibitory effect on MB photocatalytic degradation. However, NO3− and HCO3− did not show a strong inhibitory effect on the rate of photocatalytic degradation of MB by ICPQS. On the contrary, both NO3− and HCO3− slightly enhance the degradation of MB at low concentrations (0.100 mmol·L−1), it is adsorbed on the surface of the ICPQS and inhibits the photocatalytic degradation rate of MB. HCO3− slightly inhibits the photocatalytic degradation of MB by ICPQS in the range of 0.001−1.000 mmol·L−1, which may be attributable to the adsorption of HCO3− to the ICPQS surface as well. It has also been reported that HCO3− is an effective free radical scavenger that reacts with •OH to form • CO3−,51 which is a weak oxidizing reagent that hardly reacts with other organic compounds. Therefore, HCO3− only displays a slight inhibition effect on the degradation of MB by ICPQS. Despite the inhibition effects observed with certain cations or anions, these inorganic ions coexistence experimental results in general suggest that ICPQS could efficiently photodegrade MB in complex ion matrices. So the ICPQS has a potential application value in catalytic degradation of organics in industrial wastewater. Photocatalytic Coking Wastewater and Biotreated Coking Wastewater. Coking wastewater is a typical industrial organic wastewater, which has the characteristics of complex composition, extreme toxicity, and high organic strength.52,54 Phenolic compounds, which represent around 80% of the total organic carbon (TOC), are the main organic contaminants in the coking wastewater.55 After biotreatment, organic compounds in the coking wastewater are substantially oxidized into oxygen-rich organics, for which a further biochemical treatment is almost impossible; however, it still contains many hazardous compounds, such as phenolic compounds, compounds with nitrogen heterocyclic rings, amine compounds, and polycyclic aromatic hydrocarbons (PAHs).53−55 A further treatment is needed to reduce the environmental danger and decrease the burden of water reuse. The performance of ICPQS for photocatalytic degradation of industrial coking wastewater and the biotreated coking wastewater are investigated. The amount of TOC photocatalytically degraded by this ICPQS in the coking wastewater (Figure 5) is greater than adsorption (Figure S17). It can be clearly seen from Figure 4 that upon the color change from dark brown to orange, the TOC and pH reduce from 1350 mg·/L−1 and 11.98 to 120 mg·L−1 and 2.86 in 10 h, respectively. When the pH value is less than 2,

Figure 5. ICPQS photocatalytic degradation of organic pollutants in coking wastewater.

the ICPQS structure will be destroyed, so no further study on its performance on photocatalytic degradation of coking wastewater is pursued. The amount of TOC photocatalytic degraded by this ICPQS in the biotreated coking wastewater (Figure 6) is

Figure 6. ICPQS photocatalytic degradation of organic pollutants in biotreated coking wastewater.

greater than adsorption (Figure S18) as well. It can be clearly seen from Figure 5 that the TOC reduces from 35.97 mg·L−1 to 18.57 mg·L−1 in 2 h. Furthermore, in the following 3 h, the photocatalytic reaction is difficult to proceed further, which indicates that ICPQS is the only photocatalytic degraded part of the organic compounds in the biotreated coking wastewater. The pH reduced from 7.45 to 7.16 in 5 h, which also indicates that some of the organic compounds in the biotreated coking wastewater were photocatalytically degraded to produce some hardly degradable acidic substances. To investigate the performance stability of this ICPQS, recycling experiments of organic compounds decomposition in biotreated coking wastewater are performed, and the corresponding results (Figure S19) show that the efficiency of the ICPQS photocatalyst is nearly 100% for the first cycle and remains above 97% even after five cycles. Characterization of Coking Wastewater and Biotreated Coking Wastewater by 3D Fluorescence Spectroscopy. The excitation emission matrix spectrum (EEMs) 13292

DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295

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Inorganic Chemistry obtained by three-dimensional (3D) fluorescence spectroscopy is used to evaluate the performance of photocatalytic degradation of organic compounds by ICPQS. There are five fluorescence peaks (Figure S20a) at Ex/Em 225/300, 276/300, 310/ 430, 495/530, and 267/599 nm for the raw coking wastewater. The peaks at Ex/Em 225/300 and 276/300 nm correspond to tyrosine-like substances,56 which may be related to phenols, PAHs, and soluble microbial metabolites in coking wastewater. The peaks at Ex/Em 310/430 and 495/530 nm correspond to humus-like substances,56 which may be related to humic acidlike substances and PAHs in coking wastewater. The peak at Ex/Em 267/599 nm corresponds to fulvic acid-like substances,56 which may be related to aromatic hydroxycarboxylic acids-like substances and soluble microbial metabolites in coking wastewater. It can be clearly seen (Figure S20b−f) that the peaks at Ex/Em 225/300 and 276/300 nm undergo significant changes after 10 h of photocatalytic treatment using ICPQS. This shows that ICPQS mainly photocatalytic degrades phenol-like substances. The EEMs of some typical organic compounds in wastewater (Figure S21) further indicate that the ICPQS is mainly photocatalytic degrading phenol-like substances. Similarly, there are three fluorescence peaks (Figure S20a) at Ex/Em 295/ 360, 330/375, and 360/420 nm from the biotreated coking wastewater. The peak at Ex/Em 295/360 at 330/375 nm disappeared after 1 h of photocatalysis. According to the EEMs of some typical organic compounds in wastewater (Figure S22), two classes of substances that are expected to disappear are anilines-like and quinolones-like substances.56 It also shows that the humic acid-like substance is hardly photocatalyzed in the biotreated coking wastewater based on the above phenomenon and description. The above results show that ICPQS has high photocatalytic performances and thus a very good potential in the application of photocatalytic degradation of organic pollutants.

40 kV and 150 mA, respectively; 2θ is 5° to 50°. The crystal structure of 1 is analyzed by a Bruker APEX-II CCD. The X-ray photoelectron spectroscopy (XPS) test analysis of 1 is performed on a Kratos Axis Ultra DLD system with a base pressure of 10−9 Torr. The elemental analysis (C, O, H, and N) of the structure of 1 is carried out using a PerkinElmer 240 elemental analyzer. The IR spectrum of 1 is measured on KBr pellets using Nicolet 5DX Fourier Transform infrared spectroscopy. The Zeta potential of 1 and MoS2 QS at pH 3−9 are measured using a Zetasizer (ZEN 3600, Malvern, UK). The UV−vis diffuse reflectance spectrum (UV−vis DRS) of 1 in the range of 220−800 nm is measured using a UV-2700 instrument with BaSO4 as a reference. The atomic force microscopy (AFM) images of ICPQS are obtained by using a SHIMDZU SPM-9500J3 device. Transmission electron microscopy (TEM) images and energy dispersive spectroscopy (EDX) of ICPQS are taken with a JEOL ARM200F microscope (JEOL, Tokyo, Japan). The surface areas of 1 and ICPQS are determined using the BET technique (AUTOCHEM II 2920). The electrochemical cyclic voltammetry of 1 is conducted on a CHI 410B Electrochemical Workstation with Pt disk coated with the polymer film, Pt plate, and Ag/Ag+ electrode as working electrode, counter electrode, and reference electrode, respectively, in a 0.100 mol·L−1 tetrabutylammonium hexafluorophosphate (Bu4NPF6) acetonitrile solution. The electrochemical potential is calibrated against Fc/Fc+. The concentration of MB in the solution during photocatalytic degradation is measured by UV−vis 2550 at 664 nm. The visible light photocatalytic experiment of 1 is carried out under 800 W xenon lamp, and the radiated light passes through the filter to completely remove any radiation below 420 nm and is measured by a UV irradiation meter (Model UV-A, Photoelectric Instrument Factory of Beijing Normal University). The irradiation intensity is about 15.5 mW·m−2. According to the K3[Fe(C2O4)3] measurement quantum yield method, when λ > 420 nm, the average quantum yield is 1.11. The concentrations of coking wastewater and biotreated coking wastewater are expressed as total organic carbon (TOC), which are determined using a TOC analyzer (TOC-VCPH, Shimadzu, Japan). The pH values of the MB solution, coking wastewater, and biotreated coking wastewater are measured using a pH meter (STARTER 3000, OHAUS, Shanghai). The 3D fluorescence measurements of coking wastewater and biotreated coking wastewater are performed using a fluorescence spectrophotometer (F-7000, Hitachi, Japan), with a emission scan and excitation wavelength range of 200−600 nm. The slit width and scanning speed of excitation and emission are maintained at 5 and 1200 nm·min−1, respectively.

3. CONCLUSION In summary, we have successfully synthesized a single ion multisites Cu(I)/Cu(II) inorganic coordination polymer 2D material: {[CuII(H2O)4][CuI4(CN)6]}n (1). Importantly, due to the fact that about 58.16% of the Cu(I)/Cu(II) is occupied in molecular structure and most of the metal active sites are fully utilized, the obtained ultrathin quantum sheets of 1 showed exceptionally high visible light absorption property and photocatalytic activities. The successful synthesis of novel quantum sheets based on mixed valence paves the way for the development of next-generation monolayer 2D material photocatalysts for capturing a broader range of the solar spectrum for environmental decontamination.

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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.inorgchem.8b01795. Synthesis details, X-ray crystallography, structural figures, photocatalytic experiments and data, IR spectra, magnetic spectra, XPS spectra, N2 adsorption−desorption isotherms of 1 and ICPQS, UV−vis DRS spectra, cyclic voltammetry spectrum, TEM images, EDS image, XRD patterns, and crystallographic tables (PDF)

4. MATERIALS AND METHODS Methylene blue (MB), CuCl2·2H2O, and K3[Fe(CN)6] are purchased from Energy Chemical Co., Ltd. (Shanghai, China). All solvents and chemicals in this paper are commercial reagents and can be used without further purification. Industrial coking wastewater and biotreated coking wastewater (Table S6) is collected from Shaoguan steel plant, Shaoguan City, Guangdong Province, China. Inorganic metal cations (Na+, K+, Ca2+, Mg2+, Ba2+ and Fe3+) are used as their chloride salts, and inorganic anions (NO3−, HCO3−, Cl−, CO32−, SO42−, and PO43−) are used as their sodium salts. All these inorganic salts are analytical grade and are purchased from Energy Chemical Co., Ltd. (Shanghai, China). Powder X-ray diffraction (XRD) is performed using Rigaku’s D/max 2500 X-ray diffractometer with Cu Kα radiation (λ = 0.15604 nm); the tube voltages and tube current of the sample characterization test are

Accession Codes

CCDC 1837267 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 13293

DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295

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Inorganic Chemistry ORCID

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Shixiong Li: 0000-0002-6600-1749 Author Contributions

Shixiong Li and Chaohai Wei designed and conceived the experiments of this paper; Shixiong Li conducted all experiments and analyzed the data obtained; Jin Huang and Zhentao Feng characterized and analyzed the SEM, TEM, AFM, and Sbet of ICPQS. Haizhen Wu contributed reagents/materials/ analysis tools needed for the experiment and participated in the discussion of the data; Shixiong Li wrote this paper under the guidance of Chaohai Wei. All authors of this paper participated in analysis, interpretation, and review of the results, and provided valuable input during the writing of the paper. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the Research and Development Foundation of Applied Science and Technology of Guangdong Province, China (No. 2015B020235005); the Guangdong Science and Technology of Guangdong Province, China (No. 2017A020216001 and No. 2015A020215008); and the National Natural Science Foundation of China (No. 51878290, No. 51778238, and No. 21777047).

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DOI: 10.1021/acs.inorgchem.8b01795 Inorg. Chem. 2018, 57, 13289−13295