Dendritic CuSe with Hierarchical Side-Branches: Synthesis, Efficient

Research Article pubs.acs.org/journal/ascecg

Dendritic CuSe with Hierarchical Side-Branches: Synthesis, Efficient Adsorption, and Enhanced Photocatalytic Activities under Daylight Meng Li Liu,† Bin Bin Chen,† Rong Sheng Li,‡ Chun Mei Li,‡ Hong Yan Zou,*,‡ and Cheng Zhi Huang*,†,‡ †

Education Ministry Key Laboratory on Luminescence and Real-Time Analytical Chemistry, College of Chemistry and Chemical Engineering, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400716, China ‡ Chongqing Key Laboratory of Biomedical Analysis (Southwest University), Chongqing Science & Technology Commission, College of Pharmaceutical Science, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400716, China S Supporting Information *

ABSTRACT: Dendritic copper selenides (CuSe) with hierarchical sidebranches are synthesized on a large scale through a one-pot rapid, facile, and green hydrothermal route in which natural kiwi juice is employed as the reducing and coating reagent. Importantly, the CuSe have high specific surface area and excellent photocatalytic activity toward model dye malachite green (MG). The degradation rate of MG on the dendritic CuSe reaches 97% within 30 min under natural daylight irradiation. The high degradation capabilities are mainly attributed to a synergetic effect of the hierarchical side-branched structure with the strong adsorption of MG and the natural daylight-driven photocatalytic activity producing highly reactive oxygen. Thus, the dendritic CuSe will have a broad application prospect, which can be used for the treatment of the dye-contaminated wastewater. KEYWORDS: Dendritic CuSe, Hydrothermal synthesis, Adsorption, Photocatalysis, Dye degradation

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INTRODUCTION

strong adsorption and natural daylight-driven photocatalytic activities remains highly desirable. Copper selenides (CuSe), owing to their superiorities in localized surface plasmon resonance, tunable electronic properties, and photothermal transduction efficiency, are a rising star family with current available applications in photoacoustic imaging, solar cells, and photothermal therapy.14−18 In addition, CuSe have also proven to be excellent photocatalysts in solar energy conversion and environmental remediation because of their low cost, environmental friendliness, and good photocatalytic activity.12,19,20 In general, the catalytic behavior of nanoparticles is highly dependent on particle size, morphology, and dispersion quality. Many approaches have been conducted on preparing various sizes and new morphologies of CuSe, such as flowers,21 tubes,22 and hollow spheres.23 In a previous study, our group synthesized watersoluble size-controlled Cu2−xSe nanocrystals for enhancing chemiluminescence. 24 Moreover, the nonstoichiometric Cu2−xSe nanocrystals can easily be internalized by cancer cells for photothermal therapy.15 Unfortunately, their small size with low active surface area is not beneficial to the adsorption of organic dyes. However, the dendritic CuSe with side-branches

Organic dyes have been widely used in the production of printing ink, paint, textile fabrics, building materials, and plastics due to their gorgeous color and strong colorability.1,2 However, only a small dose of organic dyes reaching natural water can directly damage human health by irritating the skin or causing acute poisoning or chronic damage in organisms.1,3 Meanwhile, the dyes existing in water can hamper the incoming sun rays and gas dissolution which influence the photosynthetic activity of aquatic plants, resulting in the destruction of the aquatic ecosystem.4 Therefore, it is urgent to treat toxic dyecontaminated wastewater to minimize the threat to the environment. With this in mind, numerous nanomaterials have been developed for the treatment of the dye-contaminated wastewater. Nitrogen-rich core/shell magnetic structures have been prepared for selective adsorption and separation of anionic dyes.1 Graphene oxide and nanocomposite hydrogels have also been developed for highly efficient removal of dyes.5−8 The complex synthesis and modification processes are the main challenges in current studies, which limit their large-scale production and further industrial applications.9−11 Besides, traditional photocatalytic degradation of dyes is conducted under strong UV or visible light irradiation.12,13 Therefore, developing a new type of nanomaterial on a large scale with © 2017 American Chemical Society

Received: January 13, 2017 Revised: February 19, 2017 Published: March 27, 2017 4154

DOI: 10.1021/acssuschemeng.7b00126 ACS Sustainable Chem. Eng. 2017, 5, 4154−4160

Research Article

ACS Sustainable Chemistry & Engineering

is converted to concentration through the standard curve method. The adsorption efficiency of the dye is calculated by

and large specific surface area would combine the advantages of both adsorption and photocatalytic techniques: on the one hand, dendritic CuSe acts as an adsorbent and concentrates the pollutants; on the other hand, the CuSe photocatalyst can also decompose the pollutants, thus regenerating the catalyst in situ. In this work, we develop a one-pot green hydrothermal route to prepare hierarchical side-branched dendritic CuSe at least at gram level by using natural kiwi juice as the reducing and coating reagent. Due to their optical band gap of 1.57 eV and high specific surface areas, the natural daylight-driven photocatalytic activity and adsorption capacity of dendritic CuSe are investigated by degradation of MG. The degradation rate reaches 97% in a short time using dendritic CuSe, indicating that the dendrite CuSe can be used as a desirable candidate for environmental remediation.

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⎛ c⎞ η = ⎜1 − ⎟ × 100% c0 ⎠ ⎝

(1)

where c0 and c are the concentrations of dye at reaction times 0 and t, respectively. The amount of adsorbed dye per gram CuSe at equilibrium, qe (mg/g), is obtained by

qe = (c0 − c)V /W

(2)

where V is the volume of the solution and W is the weight of adsorbent used. Photoactivity Studies Using Dendritic CuSe. CuSe (20 mg) is dissolved in the mixture solution of 8 mL of water and 1 mL of MG solution (300 μM) in a clear drying round-bottom flask. It is stirred magnetically for 5 min in the dark to establish the adsorption/ desorption equilibrium between the dye and the photocatalyst surface. Then, 1 mL of hydrogen peroxide (30%) is added into the reaction solution at room temperature. Next, the reaction mixture is put in the natural daylight. Finally, absorbance intensity of the MG is measured by a UV-3600 spectrophotometer, and the degradation efficiency is calculated as eq 1.

EXPERIMENTAL SECTION

Materials. Domestic kiwis are purchased from Yonghui Supermarket (Beibei, Chongqing). Copper(II) sulfate pentahydrate (CuSO4·5H2O) is obtained from Ruijinte Chemical Group Co., Ltd. (Tianjin, China). Selenium dioxide (SeO2) is from Aladdin Reagent Co., Ltd. (Shanghai, China). Instruments. The UV−vis absorption spectrum of CuSe is recorded with a Hitachi U-3010 spectrophotometer (Tokyo, Japan). The surface elements of CuSe are measured using an ESCALAB 250 X-ray photoelectron spectroscope (XPS). Infrared spectrum of CuSe is scanned through a 8400S Fourier transform infrared (FT-IR) spectrometer (Hitachi, Japan). Scanning electron microscope (SEM) images of CuSe are captured with an S-4800 SEM (Hitachi, Japan). Xray powder diffraction (XRD) data of CuSe are determined using a Bruker ADVANCE D8 diffractometer. High-resolution TEM (HRTEM) images and selected area electron diffraction (SAED) patterns of CuSe are obtained with a Tecnai G2 F20 field emission transmission electron microscope (FEI, USA). The elemental composition of CuSe is determined by an energy dispersive X-ray spectroscopy (EDX) used in combination with a scan electron microscope (Hitachi, Japan). The specific surface area of dendritic CuSe is obtained with an ASAP-2020 physisorption apparatus (Mike, USA). The electron spin resonance (ESR) measurements are achieved with a Bruker ESR-300E spectrometer operating in the X-band at room temperature. Synthesis of Dendritic CuSe with Kiwi Juice. The preparation of dendritic CuSe is very simple. At first, kiwis are cut into small pieces and then squeezed to obtain light green kiwi juice. The as-collected juice is further purified through a 0.45 μm filter membrane to obtain the colorless solution after centrifugation at 12 000 rpm for 5 min.25 After that, 1.0 mL of the kiwi juice is mixed with the prepared mixture of 1.0 mL of CuSO4·5H2O (0.3 M) and 1.0 mL of SeO2 (0.3 M). Finally, the mixture is transferred into a polytetrafluoroethylene autoclave in which 7.0 mL of deionized water is further added. To obtain a high yield of dendritic CuSe, influencing factors, such as reaction time, reaction temperature, and the molar ratios of SeO2 and CuSO4, are taken into consideration. The synthesis process of CuSe is monitored at 1 h intervals for 6 h, and the reaction temperatures are adjusted from 115 to 190 °C. Moreover, the molar ratios of SeO2 and CuSO 4 are adjusted from 3:1 to 1:3 by keeping the SeO 2 concentration constant at 0.3 M and changing CuSO4 concentrations from 0.1 to 0.9 M. Eventually, the dendritic CuSe are synthesized on a large scale at 130 °C in a DHG series heating and drying oven for 3 h. After five repeated natural precipitation and suspension processes, the resulting products are dried by lyophilization to obtain dendritic CuSe powder for further application. Adsorption Studies Using Dendritic CuSe. Kinetic studies on the adsorption of MG by dendritic CuSe are carried out in the dark over a range of initial concentrations with a fixed weight (2 mg/mL) of the CuSe samples to obtain the adsorption isotherms of MG on the adsorbent. The absorbance of the MG at 616 nm is measured to determine the equilibrium concentration. The determined absorbance

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RESULTS AND DISCUSSION Synthesis and Characterization of Dendritic CuSe. The morphology of the dendritic CuSe is displayed in Figure 1a,b,

Figure 1. Morphology and structure of CuSe. (a,b) SEM images; (c,d) HRTEM images; (e) SAED pattern; (f) XRD of dendritic CuSe.

which shows the high yield and good uniformity achieved with this hydrothermal approach. Further observation by HRTEM reveals that the dendritic CuSe are composed of primary stem and secondary side-branches (Figure 1c). The lattice fringe with a spacing of 0.19 nm matches well with the (220) interplanar spacing of the CuSe (Figure 1d).26 The SAED pattern indicates that the CuSe dendrites are of singlecrystalline nature (Figure 1e). Meanwhile, the XRD spectrum of the CuSe shows the sharp diffraction peaks at 26.44, 27.94, 31.08, 45.58, 49.84, 56.28, and 69.98°, which can be index to (101), (102), (006), (110), (108), (116), and (208) planes of hexagonal CuSe (Figure 1f).12 The corresponding EDX spectrum (Figure S1) of dendritic CuSe shows that Cu and Se elements are coexistent in the dendritic CuSe. The atom percentage ratio is 50.32:49.68 for Cu and Se, which is consistent with the stoichiometric composition of CuSe. The XPS spectrum displays C 1s, O 4155


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reaction proceeds, the monomer concentration in some areas is depleted by the continuous growth of CuSe trees. If the reaction time is long enough, the monomer concentration should drop to such a level that the reaction process is dominated by quasi-equilibrium or equilibrium conditions, and the thermodynamically stable sheet structure is formed. Dendritic scales are typically associated with the thermal processes. The changes of the dendritic CuSe patterns can be observed with the reaction temperature increasing from 115 to 190 °C (Figure 3). The branch array is developed better at 160

1s, and N 1s peaks at 284.73, 531.53, and 399.53 eV, respectively, and the other two peaks at 932.48 and 54.73 eV are due to Cu 2p and Se 3d, respectively (Figure 2a).27,28 The

Figure 2. Elemental analysis and optical properties of CuSe. (a) XPS; (b) FT-IR; (c) UV−vis; (d) (ahν)2−hν curve of dendritic CuSe.

Cu 2p spectrum (Figure S2a) has a peak in the range of 940 to 945 eV, which is due to a large number of Cu2+ that exists in the dendrites.29 Moreover, the Se 3d spectrum (Figure S2b) suggests the presence of Se (−II), and the other peak at 58−60 eV corresponds to the high oxidation state of Se.29,30 Moreover, the FT-IR spectrum (Figure 2b) exhibits characteristic absorption bands of N−H/O−H (3412 cm−1), CO (1636 cm−1), C−N (1412 cm−1), and C−O−C (1076 cm−1).31 The high-resolution XPS spectra (Figure S3) further confirm C−N, CO, and C−O−C bonds exist in the CuSe. Carbon, oxygen, and nitrogen elements come from the organic substances in the kiwi juice, such as proteins, sugars, etc., whereas Cu and Se are due to the introduction of CuSO4·5H2O and SeO2. Moreover, the dendritic CuSe has a wide absorption band from UV−vis− NIR region (Figure 2c), causing a strong light-harvesting capability. After being dried, a large scale of the black powder can be obtained, indicating the high yield (at least at gram level) of this proposed method (inset image in Figure 2c). As shown in Figure 2d, the optical band gap energy of dendritic CuSe is found to be as low as 1.57 eV, which is lower than that of many other photocatalysts.12,19 Therefore, their low band gap and high light-harvesting capability are responsible for the good photocatalytic activity of dendritic CuSe. Dependent Factors of Structure and Morphology of Dendritic CuSe. It is known that the reaction time, temperature, and molar ratio of Cu/Se have significant effects on the formation and morphology of dendritic crystals.32 The growth of the dendritic nanostructure is carefully followed by a time-dependent process. As the reaction proceeded, the initial CuSe experiences a morphological evolution and converts to perfect dendrites with high density of secondary branches within 3 h (Figure S4), whereas the dendritic morphology is destroyed with longer reaction time. We believe that the observations here imply an evolution from non-equilibrium to equilibrium. At the early stage (e.g., within 3 h), the reaction process is dominated by a non-equilibrium condition, and a dendritic morphology is always formed. As the replacement

Figure 3. Effect of reaction temperature on the synthesis of the CuSe: (a) 115 °C; (b) 130 °C; (c) 145 °C; (d) 160 °C; (e) 175 °C; (f) 190 °C. Reaction time is 3 h. The molar ratio of SeO2 and CuSO4 is 1:1. Scale bar, 2 μm.

°C than that in 130 °C (Figure S5), which is in accordance with the characteristic of dendrite growth due to a high growth driving force.33 It is generally believed that the growth temperature and the supersaturation determine the growth rate of surface planes and the final morphology of the crystals,34 and higher temperatures favor the epitaxial growth of singlecrystal nanostructures. Moreover, the different molar ratios of SeO2 and CuSO4 also influence the shape of dendritic CuSe. When the molar ratio of SeO2 and CuSO4 is 3:2 and 1:1, the dendritic growth of CuSe with developed branch arrays occurs (Figure S6). These indicate that, by controlling the molar ratio of the precursors in the solution, a CuSe dendrite with well-defined morphology can be realized. Components of kiwi juice are very complex, which are not only rich in vitamin C (Vc) and carbohydrate (glucose, sucrose, and fructose) but have many trace ingredients, such as organic phenol, amino acids, protein, and minerals, etc.35,36 When the Vc is added individually, the irregular CuSe are synthesized, which shows that the Vc can act as a reducing agent in the synthesis process in accordance with the previous reports (Figure S7a).25,37,38 However, when the carbohydrates (glucose, sucrose, and fructose) are added, the dendritic CuSe are prepared successfully (Figure S7b−d), revealing that the carbohydrates may act as the reducing and coating reagents to improve the stability in the synthesis process of metal nanoparticles.25,37,38 Moreover, the CuSe prepared using 4156


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dosage. The decoloring degree of MG is 48% when the amount of dendritic CuSe just is 5 mg. When CuSe is 20 mg, the adsorption efficiency is 68% and is maintained at a relatively stable level. The enhanced adsorption activity with increasing amount of CuSe before saturation is attributed to the fact that a more active surface area can be used to adsorb the pollutant. The saturated adsorption capacity of the CuSe sample for MG is 3.72 mg/g when CuSe is 20 mg, indicating that the dendritic CuSe can adsorb the MG in the solution efficiently. The contact time required to reach equilibrium is an important parameter for dye removal. By changing the contact time from 0 to 40 min, the dye can be removed rapidly in the first 5 min (Figure 4c). The accumulation of dye molecules on the adsorption sites of the CuSe nanomaterials increases with the contacting time, but a plateau appears which might be a result of the strong repulsive forces between the dye molecules and CuSe. In comparison to other similar materials for dye degradation (Table 1), the dendritic CuSe synthesized by using kiwi juice shows comparable adsorption and good photocatalytic activities even under daylight within a short time. The high adsorption rate with no visible light irradiation (Figure S10) toward MG during the degradation process is due to the high specific surface areas (6.08 m2/g) measured by the N2 adsorption method, porousness (Figure S11), rich branch structure of CuSe, and strong interaction of anionic dye with CuSe. In addition, to study the adsorption mechanism, the relationship between the amount of dye adsorbed and the dye remaining in solution is given in Figure 4d. The equilibrium adsorption data are analyzed by the famous Langmuir and Freundlich isotherm models (Figure S12):44,45

the separated components are different compared with the dendritic CuSe obtained using kiwi juice, indicating that the other ingredients that exist in the kiwi juice also make a contribution to the formation of dendritic CuSe. The effects of different fruits (such as imported kiwi, pear, orange, and watermelon) on the formation and morphology of CuSe are investigated. The synthesis processes are consistent with dendritic CuSe obtained by using kiwi juice. It shows that the imported kiwi can also prepare dendritic CuSe (Figure S8a), but the other three kinds of fruits cannot synthesize dendritic CuSe (Figure S8b−d), indicating that the ingredients that exist in the fruit juice have a significant influence on the formation of dendritic CuSe. Adsorption Effect of MG Using Dendritic CuSe. The chemical structure (Figure S9) of MG has rich cationic atoms (e.g., N+), which is favorable for staying on the surface of CuSe with a negative charge (−16.6 mV, Figure 4a) through

Figure 4. Adsorption process of the dendritic CuSe toward MG. (a) Zeta-potential of CuSe; (b) degradation rate of MG against the qualities; (c) degradation rate of MG against the degradation time; (d) adsorption isotherms for the adsorption of MG on CuSe adsorbent.

ce/qe = 1/KLqm + ce/qm

(3)

log qe = log KF + log ce/n

(4)

where qe is the equilibrium adsorption capacity of adsorbent (mg/g), ce is the equilibrium concentration of dye (mg/L), qm is the maximum amount of dye adsorbed (mg/g), KL is the constant that refers to the bonding energy of adsorption (L/ mg), KF is the constant related to the adsorption capacity of the adsorbent (mg1−n Ln g−1), and n is the constant related to the adsorption intensity and adsorption capacity. Isotherm results of the adsorption process of MG with CuSe are shown in Table 2. On the basis of the squared correlation coefficient values, the

electrostatic interaction. The strong electrostatic interaction between MG and dendritic CuSe makes a good contribution to the highly efficient adsorption for MG. As can be seen in Figure 4b, the dye adsorption efficiency increases with increasing CuSe

Table 1. Comparison of Adsorption and Photocatalysis Abilities of the Dendritic CuSe with Similar Material Prepared by Conventional Reducing Agent in the Literaturesa material CuSe0.7S0.3 nanoflakes Cu2−xSe-g-C3N4 heterojunctions CuSe nanoparticles Fernwort-like CuSe CuSe nanoflakes Cu2−xSe nanocrystals rosalike CuSe/TiO2 structures dendritic CuSe a

reducing agent

organic dyes

light source

adsorption rate (%) nearly 0 nearly 0

99 96

15 120

39 40

10/13 25

76/87 97/96 99 >50%

90/90 10/12 25 120

41 42 19 20

nearly 100%

70

43

97

30

this work

Se and S powder Vc

MB MB

Xe lamp Xe lamp

hydrazine hydrate polyvinylpyrrolidone Se powder mercaptopropionic acid Se powder

MB/RhB MG/RhB MB RhB

UV light sunlight Xe lamp

ACA

Xe lamp

kiwi juice

MG

daylight

68

photocatalytic degradation rate (%)

degradation time (min)

refs

MB represents methylene blue; RhB represents Rhodamine-B, and ACA represents anthracene-9-carboxylic acid. 4157


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exhibit a stable photocatalytic activity and emphasize the chemical stability of the dendritic CuSe. The photocatalytic activity of the photocatalyst always relies on the active species such as photogenerated holes, •OH radicals and •O2− in the photocatalytic process. Therefore, in order to verify the existence of these reactive species, a series of radical trapping experiments using isopropyl alcohol (IPA, 2 mM), ethylenediaminetetraacetate (EDTA, 2 mM), and pbenzoquinone (BQ, 2 mM), which are known as effective •OH, hole, and •O2− scavengers for photocatalytic reactions, respectively, are conducted to investigate the species involved in the process of photocatalytic degradation. Figure 5b shows that the holes, •O2−, and •OH radicals indeed function during the catalytic process. Meanwhile, the ESR technique is used to detect oxygen-related radicals in the degradation process (Figure 5c,d). The results suggest that CuSe has catalytic activity to accelerate the decomposition of H2O2 to yield •O2− and •OH radicals, thereby accelerating the MG degradation. A brief description of the photocatalytic mechanism can be described as follows:

adsorption data are well simulated with the Freundlich isotherm model. Table 2. Equilibrium Adsorption of MG Using Dendritic CuSe model parameter value

qm 14.28

Langmuir model KL R2 0.151 0.946

KF 5.33

Freundlich model 1/n R2 0.426 0.998

Photocatalytic Activity under Daylight and Possible Mechanism. After the dark adsorption equilibrium for MG on CuSe in the first 5 min, the amount of dye remaining in solution rapidly decreases from 32 to 3% (Figure 5a) under

CuSe + hν → h+ + e−

(6)

H 2O2 + h+ → •OOH + H+

(7)

H 2O2 + e− → •OH + OH−

(8)

•

OOH → •O−2 + H+

Because the CuSe has broad absorption in the region of 200− 1300 nm and a relatively narrow band gap (1.57 eV), the electrons (e−) in the valence band (VB) would be stimulated to the conduction band (CB) by catching the photon energy (hν) under daylight irradiation, and the corresponding holes (h+) are generated in the VB at the same time (eq 6). Excitation in the band gap region as low as 1.57 eV can promote the valence band electron to the conduction band for the CuSe. Under normal circumstances, electron−hole recombination is a relatively fast process unless either the electron or hole is trapped.12,19,20 In our work, the electrons can be easily excited just under daylight irradiation. Then the photogenerated electrons and holes, instead of recombination, would be captured by H2O2 molecules to generate oxidants (eqs 7−9), which benefits the catalytic reaction. Finally, the oxidants such as •OH radicals and •O2− degrade MG molecules into smaller molecules such as CO2, H2O, etc.19,47,48 The degradation of MG relies on the highly efficient adsorption and photocatalysis of dendritic CuSe. A fast 68% decrease in the initial MG concentration is observed within 5 min by adsorption of dendritic CuSe, which is due to high specific surface area and strong electrostatic interaction with MG of dendritic CuSe; therefore, adsorption is the main degradation approach. Meanwhile, the dendritic CuSe acting as the photocatalyst can photocatalytically degrade MG. Therefore, the high degradation capabilities of dendritic CuSe are attributed to a synergetic effect of the strong adsorption and the natural daylight-driven photocatalytic activity.

Figure 5. Photocatalysis process of the dendritic CuSe. (a) Adsorption and photocatalysis process of the CuSe; (b) photocatalytic degradation of MG over CuSe, the mixture of CuSe and H2O2, and the mixture of CuSe and H2O2 with the addition of EDTA, BQ, and IPA, respectively; (c,d) ESR spectra of dendritic CuSe under irradiation (red and blue line) and in the dark (black line).

daylight irradiation, which suggests the great enhancement of catalytic activities. The photodegradation of MG can be considered as a pseudo-first-order reaction ln(c0/c) = kt

(9)

(5) −1

where k is the degradation rate constant (min ). As shown in Figure S13, the dendritic CuSe with H2O2 under daylight shows high photocatalytic activity with a high reaction rate constant of k = 0.08 min−1 (Figure S14), which is higher than those of only CuSe or only H2O2. Although the MG acting as a good photosensitizer can easily take up the photons and undergo photolysis under direct sunlight irradation (after 30 h of effective irradiation, the degradation rate of MG is up to 50%),46 the MG is hardly degraded in our work for photocatalysis exposed to daylight indoors within a short time (30 min) (Figure S13). Therefore, it is indicated that the degradation of MG is due to the photocatalytic activity of dendritic CuSe, rather than photolytic degradation of MG. The stability of CuSe is further investigated by collecting and reusing it for five cycles under the same conditions. After five recycles for the degradation of MG, the dendritic CuSe does not exhibit significant loss of activity (Figure S15). The results

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CONCLUSIONS In summary, a facile large-scale synthesis of hierarchical sidebranched dendritic CuSe is successfully developed in this work. Natural kiwi juice is used to be the green reducing and capping reagent. Compared with previously reported methods, this work is easier, more green, and effective to synthesize dendritic 4158


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CuSe with milder conditions, shorter time, and better stability. The dendritic CuSe performs excellent degradation of MG by combining the effect of highly efficient adsorption and natural daylight-driven photocatalysis. Therefore, the dendritic CuSe will have broad applications, such as in the treatment of dyecontaminated wastewater.

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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.7b00126. Details of EDX, XPS, and TEM measurements in this work, UV−vis spectra, N 2 adsorption isotherms, Langmuir and Freundlich isotherm parameters, degradation kinetics curves, plot of ln(c/c0) versus photocatalysis time, and cyclic experiments (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel: (+86)-23-68254659. *E-mail: [email protected]. Tel: (+86)-23-68254659. ORCID

Bin Bin Chen: 0000-0001-7533-0686 Hong Yan Zou: 0000-0002-7245-1893 Cheng Zhi Huang: 0000-0002-1260-5934 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 (21375109), Fundamental Research Funds for the Central Universities (XDJK2016C177), and Doctoral Scientific Research Foundation (20710930).

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REFERENCES

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Dendritic CuSe with Hierarchical Side-Branches: Synthesis, Efficient

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