Supporting carbon quantum dots on NH2-MIL-125 for enhanced photocatalytic degradation of organic pollutants under a broad spectrum irradiation

Accepted Manuscript Full Length Article Supporting carbon quantum dots on NH2-MIL-125 for enhanced photocatalytic degradation of organic pollutants under a broad spectrum irradiation Qingjuan Wang, Guanlong Wang, Xiaofei Liang, Xiaoli Dong, Xiufang Zhang PII: DOI: Reference:

S0169-4332(18)32940-4 https://doi.org/10.1016/j.apsusc.2018.10.165 APSUSC 40733

To appear in:

Applied Surface Science

Received Date: Revised Date: Accepted Date:

30 July 2018 15 October 2018 19 October 2018

Please cite this article as: Q. Wang, G. Wang, X. Liang, X. Dong, X. Zhang, Supporting carbon quantum dots on NH2-MIL-125 for enhanced photocatalytic degradation of organic pollutants under a broad spectrum irradiation, Applied Surface Science (2018), doi: https://doi.org/10.1016/j.apsusc.2018.10.165

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Supporting carbon quantum dots on NH2-MIL-125 for enhanced photocatalytic degradation of organic pollutants under a broad spectrum irradiation

QingjuanWang#, GuanlongWang#, Xiaofei Liang, Xiaoli Dong, Xiufang Zhang* School of Light Industry and Chemical Engineering, Dalian Polytechnic University, Dalian, China, 116034 *Corresponding authors. Tel.: +86 411 86323508; fax: +86 411 86323736. E-mail address: [email protected], [email protected] #Co-first authors：These authors contributed equally to this study

Abstract The rapid recombination of photoinduced electron-holes and the low utilization of solar energy have become two disadvantages limiting the performance of current photocatalysts. In this work, a novel composite photocatalyst, in which the carbon quantum dots (CQDs) were supported on the NH2-MIL-125 (a kind of metal-organic frameworks (MOFs)), was designed and constructed. The CQDs could not only serve as electron-acceptors for promoting the photoinduced charge separation in NH2-MIL-125, but also act as the spectrum converter (convert near-infrared light into visible light) to realize the enhanced light absorption by NH2-MIL-125. The NH2-MIL-125 supported CQDs (CQDs/NH2-MIL-125) displayed significantly enhanced photocatalytic activity compared with NH2-MIL-125 for Rhodamine B (RhB) degradation, regardless of the light source varied from the full-spectrum, visible light or even near-infrared light. Moreover, the photocatalytic efficiency of CQDs/NH2-MIL-125 was influenced by the CQDs content, and the composite with 1% CQDs loading exhibited the best performance. The excellent photocatalytic performance of CQDs/NH2-MIL-125 is attributed to the enhanced photoinduced charge separation and improved utilization efficiency of light energy. This work is expected to provide an attractive strategy for constructing high-efficiency photocatalyts towards environmental remediation. Keywords: MOFs; carbon quantum dots; visible light; near-infrared light; RhB

1. Introduction Photocatalysis has emerged as a promising technology for environmental remediation, chemical synthesis and water splitting, et.al, since it could directly convert the solar energy into chemical energy without producing secondary pollution [1-3]. Conventional photocatalysis focuses on the TiO2 and its modified semiconductor [4]. However, their photocatalytic efficiency was usually restricted by the fast recombination of photogenerated electron-holes [5, 6] and narrow spectrum absorption [7, 8]. Consequently, constructing novel, robust photocatalysts with extended spectrum response is highly desirable. Metal-organic frameworks (MOFs), composed of metal clusters and organic linkers, possess several characteristics such as large specific surface area, well-defined porous structure and facile functionalization [9-11]. Benefiting from these interesting properties, MOFs have attracted extensive interest in various catalytic fields since MOFs could exhibit more exposed surface active sites and the interfacial reaction between MOFs and reactants would be promoted. Especially, some MOFs have been discovered as a promising candidate for photocatalysis, for which the organic linker acts as valence band while the uncoordinated metal cluster serves as the conduction band [12, 13]. A variety of MOFs such as Ti, Cu or Fe-based MOFs have been explored for photocatalytic application [13-15]. Among these MOFs, the MIL-125(Ti) is an attractive candidate for photocatalysis due to its low toxicity, high thermal stability and good photocatalytic activity [16, 17]. Moreover, it was proposed that modifying the organic linkers of MIL-125(Ti) with -NH2 groups could greatly reduce the bandgap of MIL-125(Ti) and extend its spectrum absorption range to the visible-light region [18, 19]. The visible light response was mainly ascribed to the conjugated πelectron transition from the amine containing chromophores to the Ti-oxo clusters. Besides changing the light absorption properties of MOFs via linker functionalization, current studies also pursued to enhance the photocatalytic performance of MOFs through promoting their photoinduced charge separation.

Therefore, various modification methods were reported: (1) noble metals deposition, such like Au, Pt, and Pd with small sizes can be uniformly deposited onto MOFs [20, 21]; (2) combination of semiconductor, such as the CdS and g-C3N4 [22, 23]; (3) decoration with other functional materials such as RGO and Gr [24-26]. As a novel carbon nanomaterial, CQDs possess the advantages of low cost, low toxicity, facile functionalization, good electron conductivity and tunable fluorescence emissions [27-29]. In particular, the upconversion luminescence property of CQDs allows them to directly harvest the near infrared part of solar energy and convert them to visible light [30]. Hence, supporting CQDs on MOFs may greatly improve the photocatalytic efficiency of MOFs through two pathways: on one hand, the anchored CQDs with good electro-conductivity could facilitate the effective separation of photogenerated electron-holes [31, 32]; on the other hand, due to the upconversion luminescence function of CQDs, it is possible for them to convert near-infrared light into the visible light excited by NH2-MIL-125, thus largely boosting its light utilization efficiency [33, 34]. Moreover, considering the high specific surface area of MOFs, they are ideal supporters with plentiful anchoring sites for CQDs deposition. However, to the best of our knowledge, constructing the MOFs supported CQDs for enhanced photocatalytic performance has not been reported yet. Herein, for the first time, we report a facile method to support CQDs onto NH2-MIL-125 frameworks (CQDs/NH2-MIL-125) through a solvent-deposition method. It is expected that the anchored CQDs allow for fully exploitation of the solar light and inhibit the recombination of the photoinduced charge carriers in NH2-MIL-125.

The

morphology,

structure

and

optical

properties

of

CQDs/NH2-MIL-125 composites were systematically characterized. Rhodamine B (RhB), as a typical dye, was chosen to evaluate the photocatalytic activity of CQDs/NH2-MIL-125. Furthermore, the possible photocatalytic mechanism of CQDs/NH2-MIL-125 was explored and elucidated.

2. Experimental Section

2.1. Materials RhB (positively charged dye ), N, N dimethyl formamide ( DMF), methylalcohol, acetone, titaniumisopropylate (TTIP), 2-aminoterephthalic acid, ascorbic acid, polyethylene glycol. All solvents (DMF, methanol, etc.) were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. These chemicals were used without further purification or treatment. 2.2. Sample Preparation The NH2-MIL-125(Ti) was prepared via a facile hydrothermal method. According to the previously reported work [35], 25 mL DMF and 25 mL methyl alcohol were mixed and followed by adding 7 mM 2-aminoterephthalic acid after stirring for 10 min, then 3.5 mL TTIP added, and stirring for another 30 min, the precursor solution was transferred into a 80mL Teflon-lined stainless steel autoclave and heated at 150 °C for 16 h in an electric oven. After reaction, the products were collected by centrifugation and washed with acetone and methylalcohol for several times. The samples were then dried overnight at 105 ℃. To realize the sample activation, the as-synthesized solid was heated in air at 200 °C for 12 h. In the typical synthetic procedure of CQDs, 1.5 g of ascorbic acid was dispersed in mixed solution containing 9 mL ultra-pure water and 30 mL polyethylene glycol, and then the ascorbic acid was dissolved for 1 min in the microwave. The gained carbon quantum dots aqueous solution was transferred for twice dialysis. Each dialysis lasted for 24 hours, and finally the pure carbon quantum dots solution were achieved. The

catalysts

of

CQDs/NH2-MIL-125

composites

were

prepared

by

solvent-deposition method. The loading amount of CQDs for all samples was X wt% (X=0.5, 1, 2). Typically, a certain amount of CQDs and NH2-MIL-125 were homogeneously dispersed into the 100 mL distilled water and low temperature constant temperature bath at 90 ℃ for 3 h. The NH2-MIL-125 with different CQDs content was denoted as the NH2-MIL-125-X. The synthetic routine of the CQDs/NH2-MIL-125 composites is shown in Fig. 1. Fig. 1.

2.3. Characterizations The crystallinity and structure of the photocatalytic samples were illustrated by X-ray diffractometer (XRD) spectra (Shimadzu LabX-6000) with Cu Ka radiation at 40 kV and 30 mA. Infrared spectra were collected on a JASCO FTIR-6100. Samples were diluted with KBr and compressed into thin disk-shaped pellets. Reflectance UV spectra of powdered samples were collected using a Shimadzu UV-2600 photospectrometer. The reference was BaSO4 . Nitrogen adsorption-desorption isotherms measurements were performed using a BELSORP-max system (BEL Japan, Inc.). Transmission electron microscopy (TEM) images were obtained using a Hitachi H-800 electron microscope, operated at 200 kV. XPS results were measured by X-ray photoelectron spectrometer (AXIS ULTRA). Photoluminescence (PL) spectra of CQDs/NH2-MIL-125 were obtained on a Fluorescence Spectrometer (LS 55, PerkinElmer, America). Electrochemical impedance spectroscopy (EIS) tests were performed with an electrochemical station (CHI660D, Shanghai Chenhua Ltd., China) in a three-electrode system, which is composed of the CQDs/NH2-MIL-125 (working electrode), Pt (counter electrode), saturated calomel electrode (SCE) (reference electrode), and 0.01 mol L−1 Na2SO4 (electrolyte).

2.4. Photocatalytic performance tests. The photocatalytic performance of CQDs/NH2-MIL-125 was evaluated using RhB as the model pollutant. A certain amount (40 mg) of photocatalyst was dispersed in 80 mL solution of RhB (10 mg﹒L-1) under rigorous stirring. Before irradiation, the mixture was stirred for 40 min in the dark to reach the adsorption-desorption equilibrium. The reaction was initiated under the irradiation of a 300 W Xe lamp. For visible light or near-infrared light irradiation, the light was passed through a glass filter which could shield the light with wavelength lower than 420 nm or 700 nm. A suitable volume of the solution was separated every 20 min and centrifuged to obtain the sample after reaction. The concentrations of samples were calculated based on the absorbance measured at 554 nm on a UV-vis spectrophotometer (Shimadzu, UV-2450).

3. Results and Discussion 3.1. Characteristics. The XRD patterns of as-prepared NH2-MIL-125 and CQDs/NH2-MIL-125 composites materials are shown in Fig. 2. Fig. 2 shows that the XRD pattern of NH2-MIL-125 is in good agreement with that reported in the previous works [36, 37], indicating that the NH2-MIL-125 is successfully synthesized. After the loading of CQDs, a typical “bread” peak forms at about 26° (2θ), which corresponds to the (002) peak of the carbon material. As the amount of CQDs increases, the intensity of the characteristic peaks of NH2-MIL-125 decreases gradually, meaning the coverage of CQDs on the surface of NH2-MIL-125. Fig. 2.

The morphologies CQDs/NH2-MIL-125 are displayed in Fig. 3(a). It is found the CQDs/NH2-MIL-125 exhibits a disc-like morphology with the diameters of 2 μm and thickness of 300 nm. Moreover, the border of this composite displays a cotton-like shape instead of the smooth crystal structure (Fig. 3(b)). However, No CQDs could be observed on NH2-MIL-125 from the images due to the resolution limit of the SEM (Fig. 3(a) and low magnification of TEM (Fig. 3(b)). As shown in Fig. 3(c), the average size of as-prepared CQDs is approximately 2 nm. Hence, the high-resolution TEM (HR-TEM) was further performed to confirm the presence of CQDs onNH2-MIL-125. The HRTEM of CQDs/NH2-MIL-125 shows that the particles with clear lattice fringes are deposited on the surface of NH2-MIL-125 (Fig. 3(d)).The lattice distance of these particles is around 0.195 nm, corresponding to the (002) plane of the carbon materials. The above results confirm that the CQDs were successfully loaded on the surface of NH2-MIL-125. Fig. 3.

Fig. 4 displays the N2 adsorption-desorption isotherms of the NH2-MIL-125 and NH2-MIL-125-1.The specific surface area of NH2-MIL-125 and NH2-MIL-125-1 are

calculated to be 487 m2/g and 198 m2/g, respectively. A significant decline of the BET surface area of NH2-MIL-125 may be attributed to deposition of CQDs, which sacrifice the BET value of NH2-MIL-125. The high specific surface area of NH2-MIL-125 makes it possible for high loading of CQDs. Moreover, the high specific surface area is beneficial for photocatalysis because it could promote the photocatalytic interfacial reaction between catalysts and reactant, and expose more active sites to participate in the reaction. Fig. 4.

The electronic structure and chemical composition of the prepared samples were characterized by XPS. As shown in Fig 5(a), XPS spectrum of NH2-MIL-125 was divided into four notable peaks at 284.6, 285.05, 285.7, and 288.9 eV, which correspond to C=C, C-N, C-C, and C=O, respectively [38, 39]. Compared with it, only the peaks at 284.6, 285.7 and 288.9 eV are found in the CQDs/NH2-MIL-125 composite, corresponding to C=C, C-C and C=O, respectively. These peaks may belong to the carbon-containing function groups of MOFs and CQDs. In addition, the carbon content of NH2-MIL-125(Ti)-1 is 13.2% higher than that of NH2-MIL-125, confirming the existence of CQDs on NH2-MIL-125. Fig. 5(b) shows the symmetric peaks at 458.8 eV and 464.2 eV in the Ti2p spectrum for Ti2p3/2 and Ti2p1/2 [40], implying that the Ti(IV) exists in the titanium oxo-cluster. Unexpectedly, the characteristic peaks of Ti shifted after the deposition of CQDs, which may be ascribed to the possible formation of Ti-O-C bond [24]. The characteristic peaks in O1s XPS spectra of these two materials (Fig. 5(c)) refer to the oxygen atoms included in the titanium oxo-cluster and the C=O bond. Fig. 5.

3.2. The DRS and bandgap of CQDs/ NH2-MIL-125. Fig. 6 shows the DRS spectra of CQDs/NH2-MIL-125. Obviously, the NH2-MIL-125 shows the main absorption peak at around 400 nm and the absorption edge to 530 nm, demonstrating the good visible response of the NH2-MIL-125.

Compared with it, the CQDs/NH2-MIL-125 displays better response in the region of visible light and even the near-infrared light, which should attributed to the optical absorption properties of CQDs. Moreover, according to the (αhv)2-hv curve and eq.1, the bandgaps of different composite were calculated and were shown in the inset figure of Fig. 6. The bandgap of NH2-MIL-125, NH2-MIL-125-0.5, NH2-MIL-125-1 and NH2-MIL-125-2 were 2.43 eV, 2.42 eV, 2.35 eV and 2.33 eV, respectively. The results indicate that depositing CQDs on NH2-MIL-125 could lower its bandgap and extend its light absorption range. αhv = A (hv-Eg)n/2

(1)

Fig. 6.

3.3. Photocatalytic performance of CQDs/NH2-MIL-125. The photocatalytic performances of the NH2-MIL-125 and CQDs/NH2-MIL-125 composites are evaluated using RhB as the model pollutant. As can be seen from Fig 7(a), before light irradiation, less than 30% RhB was removed by NH2-MIL-125 and CQDs/NH2-MIL-125, owing to the adsorption of RhB on MOFs. Moreover, it is clear the RhB adsorption decreases gradually with the increase of CQDs deposition, which is consistent with the BET results that the CQDs/NH2-MIL-125 composites with higher CQDs content possesses lower specific surface area. Under full-spectrum irradiation, the NH2-MIL-125-1 showed the best photocatalytic activity with almost 100% RhB removal within 120 min, followed by NH2-MIL-125-2, NH2-MIL-125-0.5 and NH2-MIL-125.These results suggest that the CQDs deposition improves the photocatalytic activity of NH2-MIL-125, which is probably attributed to the enhanced electron-holes separation caused by CQDs. However, the excess CQDs would cover the surface of MOFs and block the light penetration, leading to the declined photocatalytic efficiency. The above results also suggest that the specific surface area of NH2-MIL-125 composites plays an insignificant role in photocatalysis, as the NH2-MIL-125-1 with lower specific surface area displays the best photocatalytic activity. To further clarify the function of CQDs, the photocatalytic activity of CQDs/NH2-MIL-125 was evaluated under visible light irradiation (λ>420 nm). It was

found the photocatalytic activity of CQDs/NH2-MIL-125 still followed the same order (NH2-MIL-125-1>NH2-MIL-125-2>NH2-MIL-125-0.5>NH2-MIL-125) as that under full-spectrum (Fig. 7(b)), but their photocatalytic efficiency decreased, as longer time was required to achieve 100% RhB removal on NH2-MIL-125-1 than that under full-spectrum. In this case, it is inferred that the enhanced photocatalytic activity of NH2-MIL-125 not only results from the effective separation of electron-holes, but also originates from the enhanced light utilization by MOFs, because it was reported the CQDs are capable of converting near-infrared light into visible light [28], which could excite MOFs to produce more electron-holes. The upconversion property of NH2-MIL-125 was further examined by evaluating its performance under near-infrared light (λ>700 nm). As expected, the NH2-MIL-125-1 still displays the best performance (40% RhB removal) among these NH2-MIL-125 composites (Fig. 7(c)), while the NH2-MIL-125 alone nearly exhibits no RhB removal. This result confirms the CQDs could absorb the near-infrared photons and then convert them into visible-light for MOFs excitation. The stability of photocatalysis was investigated by testing the photocatalytic performance of NH2-MIL-125-1 for RhB degradation in seven consecutive cycles under irradiation of full-spectrum. As shown in Fig. 7(d), the RhB removal on NH2-MIL-125-1 maintains almost 100% after 7 cycles under full-spectrum irradiation, indicating that the CQDs/NH2-MIL-125 could maintain good stability in long-term run without performance decay. Fig. 7.

3.4. The photocatalytic mechanism of CQDs/NH2-MIL-125 As mentioned before, the enhanced charge separation and light absorption are two possible reasons responsible for the excellent photocatalytic performance of CQDs/NH2-MIL-125. To verify this hypothesis, The PL measurements were employed to detect the separation efficiency of photogenerated charge carriers in CQDs/NH2-MIL-125.

Under

the

excitation

wavelength

of

438

nm,

CQDs/NH2-MIL-125 composite materials exhibit a broad and strong peak centered at

550 nm, which is assigned to the fluorescence emission caused by the recombination of photogenerated electron-holes. Commonly, the lower emission intensity means more effective separation of photogenerated electron-holes. Notably, after introducing CQDs to NH2-MIL-125, the composites emit fluorescence with a significant quenching and the emission intensity was obviously reduced, indicating a more effective

separation

of photoexcited

electron-holes

in CQDs/NH2-MIL-125

composites. This result proves that CQDs act as effective electron reservoirs and can hinder the recombination of photoinduced carriers in NH2-MIL-125 under illumination. However, when the CQDs content was higher than 1%, the separation efficiency of electron-holes declined, suggesting the excess CQDs deposition was unfavorable for the charge separation. This phenomenon is consistent with the results of photocatalytic performance tests. Furthermore, the EIS spectra were conducted to examine the electron transfer resistance of CQDs/NH2-MIL-125. Commonly, the diameter of semicircle in EIS spectra equals to the charge transfer resistance (R ct) of catalysts. As shown in Fig. 8(b), the Rct values of CQDs/NH2-MIL-125 composites are lower than that of NH2-MIL-125, and the Rct value follows the order of NH2-MIL-125-1700 nm) and then relaxed by emitting upcoversion PL at visible-light regions (around 500 nm). As is depicted in Fig. 6, the adsorption edge of NH2-MIL-125 reaches 530 nm. Hence, the emitting visible light from CQDs could be excited by the NH2-MIL-125. The unique upconversion function of CQDs is beneficial for enhancing the light energy utilization by NH2-MIL-125, which could be excited to generate more photoinduced charge carriers. Fig. 8.

Based on the above results, the possible mechanism for the high photocatalytic

performance of the CQDs/NH2-MIL-125 composites is proposed (Fig. 9). NH2-MIL-125 is a kind of photocatalyst active in visible light region, but its photocatalytic performance is still limited by the rapid recombination of charge carriers. After introducing the CQDs, firstly, CQDs can convert a fraction of near-IR light into a visible light, which then excites NH2-MIL-125 to generate more electron–hole pairs. Secondly, CQDs with good electro-conductivity facilitates the electron transfer from the CB ofNH2-MIL-125 to the CQDs, leading to the effective separation of photogenerated electron-holes. Thirdly, the high specific surface area of NH2-MIL-125 makes it an ideal supporter to disperse CQDs and enlarges their contact interface. Hence, the electron transfer between NH2-MIL-125 and CQD could be further facilitated. The electrons on CQDs would then react with O2 to produce the O2•−, which could further react with H2O to produce the •OH. Meanwhile, the left holes on NH2-MIL-125 reacted with OH− and generated the •OH as well. As a result, all these reactive radicals and holes contributed to the dye degradation and the photocatalytic RhB degradation on CQDs/NH2-MIL-125 was largely improved. The possible mechanism for the photocatalytic degradation of RhB in our experiment is proposed as follows from eq.2 to eq.9. CQDs/NH2-MIL-125+hv →CQDs/NH2-MIL-125 + e- + h+

(2)

e− + O2 → O2•−

(3)

O2•− + H2O → HO2• + •OH

(4)

HO2• + H2O → H2O2 + •OH

(5)

H2O2 → 2•OH

(6)

h+ + OH− →•OH

(7)

•

OH + RhB (dye) → CO2 + H2O

(8)

h+ + RhB (dye) → CO2 + H2O

(9) Fig. 9.

4. Conclusions In this work, the CQDs/NH2-MIL-125 composite photocatalysts were successfully synthesized via a simple solvent-deposition method. The NH2-MIL-125 with large

specific surface area provided an ideal platform for CQDs distribution. Under the irradiation

of

full-spectrum,

visible

light

or

near-infrared

light,

the

CQDs/NH2-MIL-125 exhibited enhanced photocatalytic activity for RhB removal compared with NH2-MIL-125 alone, and the CQDs/NH2-MIL-125 with 1% CQDs content showed the best photocatalytic efficiency. The superior photocatalytic activity of CQDs/NH2-MIL-125 composites is mainly owing to effective separation of photogenerated electron-holes and enhanced light energy utilization. This work provides insight into constructing highly efficient photocatalyst with wide-spectrum response for contaminants elimination.

Acknowledgment This work was supported by the National Science Fund of China (Project No. 21577008) and Fundamental Research Funds for Central Universities (Project No. 2016J004).

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Figure captions Fig. 1. The synthetic routine of CQDs/NH2-MIL-125. Fig. 2. XRD patterns of NH2-MIL-125 and CQDs/NH2-MIL-125 composite materials. Fig. 3. (a) SEM and (b) TEM of CQDs/NH2-MIL-125; (c) TEM image of CQDs; (d) HR-TEM of CQDs/NH2-MIL-125. Fig. 4. N2 adsorption-desorption isotherm of NH2-MIL-125 and CQDs/NH2-MIL-125. Fig. 5. XPS spectra of (a) C 1s, (b) Ti 2p and (c) O 1s for (A) NH2-MIL-125 (B) CQDs/NH2-MIL-125. Fig. 6. DRS spectra of NH2-MIL-125, NH2-MIL-125-0.5, NH2-MIL-125-1 and NH2-MIL-125-2; inset figure of it is bandgap energy of photocatalysts. Fig. 7. The photocatalytic performances of NH2-MIL-125 and CQDs/NH2-MIL-125 composites for the degradation of RhB under the irradiation of (a) the full spectrum (b) visible light (λ>420 nm) and (c) near-infrared light (λ>700 nm); (d) the photocatalytic stability test of NH2-MIL-125-1. Fig. 8. (a) PL spectra and (b) EIS spectra of NH2-MIL-125, NH2-MIL-125-0.5, NH2-MIL-125-1 and NH2-MIL-125-2; (c) the upconversion PL spectra of CQDs. Fig. 9. The possible photocatalytic mechanism of the CQDs/NH2-MIL-125.

NH2-MIL-125

CQDs/NH2-MIL-125

Intensity (a.u.)

Fig. 1.

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Fig. 9.

Graphical abstract

Highlights 1.

The carbon quantum dots were supported on NH2-MIL-125 through a facile method.

2.

CQDs/NH2-MIL-125 displayed enhanced photocatalytic removal of RhB.

3.

CQDs/NH2-MIL-125 was capable of removing RhB under near-infrared light.

4.

CQDs serve as both electron-acceptor and light converter for efficiency increase.