Gaseous mercury capture by copper-activated nanoporous carbon

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Gaseous mercury capture by copper-activated nanoporous carbon nitride Dongjing Liu, Cheng Lu, and Jiang Wu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01708 • Publication Date (Web): 03 Jul 2018 Downloaded from http://pubs.acs.org on July 4, 2018

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Gaseous mercury capture by copper-activated nanoporous carbon nitride

Dongjing Liu 1*, Cheng Lu 2, Jiang Wu 2*

1

School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013,

China 2

College of Energy and Mechanical Engineering, Shanghai University of Electric

Power, Shanghai 200090, China

1

ACS Paragon Plus Environment

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ABSTRACT: Graphitic carbon nitride (g-C3N4) as a two-dimensional layered carbon material with exceptional electronic, thermal, and catalytic property has attracted increasing research attention. A porous g-C3N4 nanosheet (PCNN) has been synthesized via a facile two-step thermal etching oxidation approach and applied in low-temperature elemental mercury (Hg0) removal. PCNN exhibits good reactivity towards Hg0 adsorption at temperatures of 40-200 °C, CuO-impregnation can prominently enhance the Hg0 capture performance of PCNN on account of the intimate interaction of CuO and PCNN. Temperature has positive effect on Hg0 capture ability of PCNN and CuO/PCNN. Hg0 is mainly oxidized by the chemisorbed oxygen species which are generated from the O-C-N of g-C3N4 and the lattice oxygen of CuO, CuO-modification can efficiently activate g-C3N4 with significantly improved Hg0 capture ability presumably owing to the Mott-Schottky effect at the interface of CuO and g-C3N4.

INTRODUCTION Due to the extreme toxicity and bioaccumulation of methyl mercury transformed from emitted mercury which is mainly derived from coal-fired power plants (~24% of global anthropogenic sources of mercury emissions)

1–3

, China and

America promulgated national mercury emission standards to restrict mercury releasing from coal-fired power plants in 2011

4, 5

. Mercury in coal-fired flue gas

usually presents in three forms, such as elemental mercury (Hg0), oxidized mercury (Hg2+), and particle-bound mercury (HgP)

6, 7

. Among these mercury species, Hg0

2


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vapor is most likely to escape from existing air pollution control devices owing to its high volatility and almost insolubility in water 8, 9. What is more, Hg0 is the dominant mercury species in coal-fired flue gas and it has a long lifespan in the atmosphere 10, which makes it a global environmental pollutant. In 2017, more than 120 countries signed the Minamata Convention on Mercury to protect human health and the environment from the adverse effects of mercury from anthropogenic sources

11

.

Therefore, effective and economical technologies for mercury emission control of coal-fired power plants are urgently needed. Recently, the re-emission of mercury from the flue gas desulfurization (FGD) utility becomes a serious issue, mercury emission control before the FGD device is thereby a feasible solution. A wide range of sorbents or catalysts have been applied for Hg0 capture from flue gas, such as noble metals (Pd, Pt, Au)

12–14

, transition metal

oxides (Fe2O3 15, CuO 16, Mn2O3 17, CeO2 18, V2O5 19), and carbonaceous materials 20. Among them activated carbon is the most widely used sorbents for mercury capture from coal-fired power plants so far 21–24. However, the application of activated carbon for mercury adsorption is restrained attributed to its higher operation cost, poorer mercury capture capacity, and slower adsorption rate

25–27

. Recently, graphitic carbon

nitride (g-C3N4), a two-dimensional layered carbon material, has attracted incremental research interest owing to its accessible nanoporous structures, chemical and thermal stability, and facile synthesis route 28. Since g-C3N4 was first reported as a metal-free polymeric catalyst in 2009 29, it has gained worldwide attention and widely applied in many fields, especially in environmental decontamination, for instance, wastewater

3


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treatment

30, 31

, NO removal

32, 33

, CO2 reduction

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34, 35

. g-C3N4 may promise as a

potential sorbent for mercury capture from coal-derived flue gas as well. In this work, three types of graphitic carbon nitrides are synthesized via direct thermal polycondensation of dicyandiamide and mixed dicyandiamide with ammonium carbonate, two-step thermal condensation of the mixture of dicyandiamide and ammonium carbonate. The as-fabricated g-C3N4 is then tested in a bench-scale vertical fixed-bed quartz reactor for gaseous mercury capture at temperatures of 40-200 °C. The resultant porous g-C3N4 and porous g-C3N4 nanosheet display good potential towards mercury removal and outperform bulk g-C3N4. The three kinds of g-C3N4 are subsequently modified with CuO via incipient-wetness impregnation approach to further improve their Hg0 capture abilities. The effect of temperature on Hg0 capture performances of pristine and CuO-activated g-C3N4 is investigated; the manner of chemical modification or activation of g-C3N4 by using CuO towards enhanced Hg0 capture ability is then elucidated with the Mott-Schottky effect. EXPERIMENTAL Synthesis of g-C3N4 Bulk g-C3N4 (BCN) is attained via direct thermal condensation of dicyandiamide at high temperature. Briefly, 10 g of dicyandiamide (Aladdin Reagent, Inc., China) are put into a capped alumina crucible and heated in static air at 550 °C for 2 h with a ramp rate of 5 °C/min, the resultant blocky yellow products are ground into powders which are bulk g-C3N4 (denoted as BCN) 31. Porous g-C3N4 (PCN) is obtained via thermal polymerization of the mixture of

4


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dicyandiamide (Aladdin Reagent, Inc., China) and ammonium carbonate (foaming agent, Aladdin Reagent, Inc., China). Briefly, 5 g of dicyandiamide and 10 g of ammonium carbonates are firstly well mixed together and put into a covered alumina crucible which is then heated in static air at 550 °C for 2 h at a heating rate of 5 °C/min, the resulting blocky yellow products are ground into powders which are porous g-C3N4 (named as PCN) 36. Porous g-C3N4 nanosheet (PCNN) is fabricated by heating treatment of the as-synthesized PCN once more. Typically, 5 g of PCN are placed into an open alumina crucible and heated in static air at 550 °C for 3 h with a heating rate of 5 °C/min; the final products are pale yellow porous g-C3N4 nanosheet (labeled as PCNN) 37. Fabrication of CuO/g-C3N4 The CuO-modified g-C3N4 is prepared via pore volume impregnation approach. Firstly, 0.1 g of Cu(NO3)2·3H2O (Aladdin Reagent, Inc., China) are dissolved in 0.5 g of deionized water, 0.3 g of as-synthesized g-C3N4 (i.e. BCN, PCN, and PCNN) are subsequently put into the aforementioned solution and dried at 70 °C over night, the generated mixtures are then placed into an open alumina crucible and heated in static air at 200 °C for 2 h with a ramp rate of 5 °C/min, the yielding products are denoted as CuO/BCN, CuO/PCN, and CuO/PCNN respectively (nominal weight percentage of CuO is 10%).

5


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Sample Characterization X-ray diffraction (XRD) patterns are measured on a Bruker D8 Advance equipment. Fourier transform infrared spectroscopy (FTIR) spectra are examined with a FTIR-8400S spectrometer at room temperature with specimen embedded in a KBr wafer. The nitrogen adsorption-desorption isotherms are tested at 77 K on a Beishide 3H-2000PS4

apparatus,

the

pore

size

distribution

is

estimated

with

Barrett-Joyner-Halenda (BJH) method using desorption branch of nitrogen isotherm. The field emission scanning electron microscopy (FESEM) photos are detected on a Phillips XL-30 FEG/NEW instrument operating at 5 kv; the high resolution transmission electron microscopy (HRTEM) images are acquired on a Phillips Model CM200 device. X-ray photoelectron spectroscopy (XPS) data are attained on a RBD upgraded PHI-5000C ESCA system (Perkin Elmer) with Mg Kα radiation (hν=1253.6 eV) or Al Kα radiation (hν=1486.6 eV), the X-ray anode runs at 250 W and the high voltage is kept at 14.0 kV with a detection angle at 54°, the pass energy is fixed at 23.5, 46.95 or 93.90 eV to ensure sufficient resolution and sensitivity, the base pressure of the analyzer chamber is about 5×10-8 Pa. Mercury Capture The mercury adsorption experimental system has been described in detail elsewhere

38–40

, firstly, about 50 mg of specimens are loaded in a vertical fixed-bed

quartz reactor (8 mm of inner diameter, 700 mm of length) and heated up to the desired temperatures, then the nitrogen flow (1.2 L/min) containing Hg0 vapor (~50 µg/m3) produced by a mercury generator (PS Analytical ltd., Kent, UK) at 50 °C are

6


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continuously charged into the reactor, the Hg0 concentration is measured by an on-line mercury analyzer (Lumex, RA-915-M, Russia), and the mercury conversion can be calculated by the following formula,

η Hg =

Cin -Cout ×100% Cin

(1)

, where ηHg denotes the mercury removal efficiency (%), Cin and Cout denote the inlet and outlet mercury concentration (µg/m3), respectively. The PCNN and CuO/PCNN after mercury adsorption at 120 °C refer to the spent PCNN and CuO/PCNN respectively. RESULTS AND DISCUSSIONS Characterization Analysis The XRD patterns of g-C3N4 and CuO/g-C3N4 are presented in Figure 1, typical graphitic stacking carbon nitride structures in all specimens are confirmed by two characteristic peaks, one intense band at 27.2° is the interlayer stacking reflection signals of (002) lattice planes of aromatic systems, another weak band at 12.8° relates to the (001) lattice planes of planar structural packing motif of tri-s-triazine units 41, 42. The peak intensity of PCN is prominently weaker than that of BCN and PCNN, indicating a lower condensation degree and crystallinity of PCN. The peaks at 35.4°, 38.6°, 48.6°, 53.6°, 61.2°, 66.1°, 68.0° are assigned to CuO [PDF#65-2309]. The crystalline sizes are estimated from calculation of the (-111) lattice plane of CuO based on Debye-Scherrer equation [D(hkl)=0.89λ/βcosθ] 43, the CuO crystalline sizes in CuO/BCN, CuO/PCN, CuO/PCNN are 20.68 nm, 24.99 nm, 20.37 nm relatively (Table 1), the smallest CuO crystalline size is achieved in CuO/PCNN probably 7


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attributed to the well dispersion of CuO grains on PCNN resulting from the biggest surface area of PCNN compared to BCN and PCN, whereas CuO/PCN possesses the biggest CuO crystalline size likely attributed to the poor dispersion of CuO particles on PCN with the lowest surface area. The FTIR spectra of g-C3N4 and CuO/g-C3N4 are displayed in Figure 2. The broad peaks between 3500 cm-1 and 3000 cm-1 stemmed from N-H stretches are detected in all specimens except BCN and CuO/BCN

44

, suggesting partial

hydrogenation of some nitrogen atoms in PCN, CuO/PCN, PCNN, and CuO/PCNN. The sharp peak at 2354 cm-1 in all specimens originates form the O=C=O asymmetrical stretching vibration of adsorbed CO2 on sorbent surface

45

. The weak

band at 2147 cm-1 in all specimens is assigned to the cyano C≡N terminal groups, and the set of bands between 1750 cm-1 and 890 cm-1 are the characteristic signals of s-triazine derivatives 44, 46, such as trigonal C-N(-C)-C (full condensation) or bridging C-NH-C units, and these bands of PCNN, CuO/PCNN are obviously sharper than that of BCN, CuO/BCN, PCN, CuO/PCN presumably owing to the more ordered packing of hydrogen-bond cohered long strands of polymeric melon units survived from thermal etching oxidation in the layers of porous g-C3N4 nanosheets. The sharp band at 810 cm-1 stems from heptazine ring system 46. The nitrogen adsorption-desorption isotherms of g-C3N4 (BCN, PCN, PCNN) are shown in Figure 3. PCNN presents significantly larger nitrogen uptake than that of BCN and PCN, and exhibits type Ⅳ isotherm with a clear hysteresis loop at higher relative pressure implying the presence of abundant mesoporous structures in PCNN

8


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47

. The BET surface area, micropore volume, mesopore volume and average pore size

of PCNN are 25 m2/g, 0.013 cm3/g, 0.302 cm3/g and 35 nm relatively (Table 1) which are all much bigger than that of BCN and PCN. After impregnating with CuO, the BET surface area, micropore volume, mesopore volume and average pore size all decrease, especially for PCN remarkably drops from 3 to 1 m2/g, 0.002 to 0.001 cm3/g, 0.020 to 0.001 cm3/g, 32 to 12 nm respectively, the probable reason is that the internal pore structures of PCN may be blocked by CuO particles. The FESEM images of PCNN and CuO/PCNN are depicted in Figure 4, pristine PCNN consists of big nanoplate structures with thickness of ~50 nm and length of above 1 µm; after involvement of CuO, PCNN surface becomes more impact and smooth probably resulting in the decline of surface area, pore volume and average pore size, however, numerous small nanoplate structures with diameter of 200-500 nm are detected. The HRTEM images of PCNN and CuO/PCNN are displayed in Figure 5, PCNN exhibits fluffy and transparent feature, suggesting the ultrathin nanosheet structure of PCNN with thickness of few nanometers and lateral sizes of several micrometers (Figure 5a), additionally, massive nanopores with uniform diameter of ~26 nm present on PCNN surface (Figure 5b), suggesting the successful production of nanoporous carbon nitride by using ammonium carbonate as foaming agent. After loading with CuO, the fluffy and transparent feature of PCNN is still preserved (Figure 5c), the lattice fringes with interplanar distance of 0.232 nm are attributed to the (111) crystallographic plane of CuO

48

, and CuO is well integrated with g-C3N4 (Figure

5d).

9


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Mercury Capture Performance The Hg0 capture performances of pure and CuO-modified g-C3N4 at 120 °C are displayed in Figure 6. PCN and PCNN show better activity towards Hg0 adsorption compared to BCN presumably due to their mesoporous structures with bigger pore sizes above 32 nm. The Hg0 removal efficiency of PCN can swiftly go up to ~75.0% within 2 min, then slightly drop to ~64.0% and stay at this value with time elapsed; the Hg0 removal efficiency of PCNN gradually rises up to ~45.0% within 20 min, then slightly reduces to ~42.0% (drops by only 6.7%) and keeps at this value over 100 min. BCN presents relatively poorer activity towards Hg0 adsorption, though the Hg0 removal efficiency can sharply reach up to ~61.0% within 5 min, it will gradually reduce with time elapsed and remain at only ~15.0% after mercury adsorption over 100 min. The Hg0 capture ability of BCN and PCNN can be greatly enhanced by modifying with 10 wt% CuO, the Hg0 removal efficiency rises up to 69.3% and 90.1% relatively after mercury adsorption over 100 min, probably attributed to the intimate interaction of CuO with BCN and PCNN. However, the Hg0 capture ability of PCN decreases by incorporating with 10 wt% CuO, the Hg0 removal efficiency drops from 63.9% to 49.5% after mercury adsorption over 100 min plausibly due to the significant reduction of BET surface area and pore volume. Additionally, PCNN exhibits a relatively stable activity towards Hg0 adsorption at 120 °C over 10 h on nitrogen stream, the Hg0 removal efficiency gradually grows up to ~45.0% within 20 min, it slightly reduces with time elapsed and finally stays at ~35.0% (Figure 7) for a long period. CuO/PCNN presents outstanding Hg0 capture ability at 120 °C over 10 h

10


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on nitrogen stream, the Hg0 removal efficiency at first gradually rises up to ~90.0% within 100 min and then remains at this value with time elapsed, the probable reason is owing to the intimate interface contact between CuO and PCNN deriving from the uniform dispersion of smaller CuO particles on PCNN. The effect of temperature on Hg0 removal efficiency of PCNN and CuO/PCNN is presented in Figure 8. Temperature shows positive effect on Hg0 capture ability of PCNN and CuO/PCNN. The Hg0 removal efficiency of PCNN is below 50.0% when temperature is at or below 120 °C; it gradually increases from 42.9% to 61.9% with temperature rising from 120 °C to 200 °C. Previous studies revealed that physisorption and chemisorption process are the two major types of Hg0 capture processes on sorbent surface

49

. The Hg0 removal efficiency at or below 120 °C is

relatively lower presumably owing to the lower Hg0 vapor diffusion and physisorption rate at lower temperatures. Lee et al

50

and Tan et al

51

disclosed that higher

temperature facilitates chemisorption process ascribed to the decreased activation energy barrier, which leads to higher Hg0 removal efficiency than adsorption at lower temperatures. Thus, the enhancement of temperature is favorable for Hg0 capture on account of the enhanced chemisorption of Hg0 over PCNN

52

. CuO/PCNN displays

excellent Hg0 capture ability in 40-200 °C temperature range with Hg0 removal efficiency of all above 89.0% probably due to the increased active sites for Hg0 oxidation originated from CuO incorporation, additionally, PCNN of two-dimensional nanosheet morphology possesses the advantage of bigger specific surface area and thinner layer structure for exposing abundant active sites and shortening bulk

11


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diffusion distance for Hg0 adsorption and oxidation

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53, 54

. The Hg0 removal efficiency

of CuO/PCNN mainly grows with incremental temperatures, it slightly fluctuates between 89.2% and 94.7% when temperature is at or below 120 °C and significantly rises up to above 97.0% when temperature is above 120 °C also attributed to the enhanced Hg0 diffusion and chemisorption rate over CuO/PCNN, the Hg0 removal efficiency reaches its highest value of 98.9% at 160 °C. Mercury Capture Mechanism To explore the mechanism of Hg0 capture by pristine carbon nitrides and CuO-activated carbon nitrides, the surface elemental valences of spent PCNN and CuO/PCNN are examined by XPS technique (shown in Figure 9 and 10). As can be seen from Figure 9a, the characteristic signals of C, N, and O elements are detected in the full spectra survey of spent PCNN. The C 1s spectrum (Figure 9c and d) shows two major peaks, one centered at ~288.6 eV corresponds to the signal of N-C=N structure, while another centered at ~285.8-286.0 eV relates to the reflection of C-(N)3 structure

55

. The N 1s spectrum can be fitted into three dominant peaks (Figure 9e

and f), the peaks at ~398.6-398.8 eV and ~399.4-399.8 eV belong to the occurrence of sp2-bonded nitrogen involved in triazine rings (C-N=C) and tertiary nitrogen groups (C-(N)3) correspondingly; the peaks at ~400.6-401.0 eV are ascribed to the presence of amino functional groups (C-N-H), deriving from the defective condensation of heptazine substructures

56

. The O 1s spectrum exhibits two feature

peaks (Figure 9g and h), the bands at ~534.0-534.2 eV are attributed to the oxygen in adsorbed water or carbonates, while the bands at ~532.6-532.8 eV are assigned to the

12


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chemisorbed oxygen in O-C-N structure likely derived from the heating treatment in the presence of air

57

, which contributes to Hg0 oxidation capture. The surface C/N

atomic ratio of spent PCNN is 1.23 in a semi-quantitative fashion, suggesting that PCNN is a carbon-rich and nitrogen-poor carbon nitride. As for Cu 2p spectrum (Figure 9b), the bands at ~953.8 eV and ~935.6 eV belong to the characteristic peak of Cu2+ in CuO, the peak at ~933.4 eV results from the reflection of Cu+ in Cu2O

58, 59

; the coexistence of Cu2+ and Cu+ in spent

CuO/PCNN implies that CuO is partially reduced into Cu2O on account of CuO participating in the redox reaction of mercury capture. The Hg 4f XPS spectra of spent PCNN and CuO/PCNN are shown in Figure 10, the peaks at 102.7 eV and 102.4 eV belong to Si 2p electron

60, 61

, the signals at 104.6 eV and 105.4 eV are ascribed to

oxidized mercury (HgO) 62, 63, the presence of HgO species indicates that the adsorbed Hg0 vapor is oxidized by the active sites (chemisorbed oxygen) on the surface of PCNN and CuO/PCNN. What is more, the distinctive peaks of elemental mercury (Hg0) at ~99.9 eV did not detected 64, suggesting that the chemical adsorption of Hg0 vapor dominates the mercury capture processes. Recently, the catalysis mechanism of metal/carbon nitride has been well developed by Xinhao Li and Markus Antonietti; they reported that there is a Mott-Schottky effect in the catalytic reactions over metal/carbon nitride complex 65, 66. Carbon nitride with covalently sp2 bonded atoms of carbon and nitrogen shows unique and versatile properties, its electronic state is fairly sensitive to the substances it contacts, and electrons can be donated to the carbon nitride, or vice versa

13


67

. Metals

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with a relatively higher Fermi level than that of carbon nitride, would donate electrons spontaneously to carbon nitride (i.e. carbon nitride would accept electrons from metals) until their Fermi levels reach equilibrium, this electron transfer phenomenon is the so-called Mott-Schottky effect 68. Such a Schottky barrier will obviously result in electron redistribution at the interface of metals and carbon nitride and enrich the positive charges on the side of metallic elements, the more oxidative area thus forms on the side of the metals accordingly, which is favorable for catalytic oxidation reactions 69, 70. In our case, the chemisorbed oxygen produced from O-C-N in PCNN surface serves as the active sites for Hg0 oxidation over pure PCNN. CuO-impregnation could produce new active sites for Hg0 oxidation. Firstly, CuO releases lattice oxygen to generate suboxide Cu2O, the lattice oxygen will further migrate onto CuO surface to form surface chemisorbed oxygen which is active for Hg0 oxidation, then the Hg0 vapor is oxidized by the chemisorbed oxygen yielding HgO; secondly, the produced Cu2O probably donate electrons spontaneously to g-C3N4 to regenerate CuO attributed to the above-mentioned Mott-Schottky effect. The Schottky barrier at the interface of CuO and g-C3N4 could modify the electron density of the Cu2+ ions and thus the adsorption energy of gaseous mercury, the CuO-modulated g-C3N4 would also be activated by the Schottky barrier and endowed with higher activity for mercury capture. The proposed Mott-Schottky catalysis modal can well elucidate the excellent Hg0 capture ability of CuO/PCNN; in addition, the ultrathin two-dimensional nanosheet structure of PCNN promotes the interface contact of CuO and g-C3N4,

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which thereby facilitates the Mott-Schottky effect of CuO/PCNN for Hg0 oxidation. Therefore, the good capacity of lattice oxygen storage of CuO due to the redox couple of Cu2+/Cu+ and the unique two-dimensional planar structure of PCNN predominantly contribute to the excellent Hg0 capture ability of CuO/PCNN. CONCLUSIONS PCN and PCNN exhibit much better Hg0 capture ability compared to BCN due to their mesoporous structures. CuO-impregnation can effectively promote the Hg0 capture ability of BCN and PCNN but weaken the Hg0 capture ability of PCN on account of the significantly reduced surface area and pore volume. Temperature shows promotional effect on Hg0 capture ability of PCNN and CuO/PCNN, the Hg0 removal efficiency mainly increases with incremental temperatures, and CuO/PCNN performs stably with respect to Hg0 adsorption at 120 °C over 10 h on nitrogen stream, probably attributed to the intimate contact of CuO and PCNN resulting from the well dispersion of smaller CuO particles on PCNN. CuO-impregnation can efficiently activate g-C3N4 towards greatly promoted mercury capture ability because of the Mott-Schottky effect at the interface of CuO and g-C3N4. AUTHOR INFORMATIONS Corresponding Authors *Email: [email protected] (D. Liu); [email protected] (J. Wu). Notes The authors declare no competing financial interest.

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ACKNOWLEDGEMENTS This work was partially sponsored by National Natural Science Foundation of China (21237003, 50806041), Natural Science Foundation of Shanghai (18ZR1416200). References (1) Marcia, M. N. Mercury and health. Science 2013, 341 (6153), 1430. (2) Krabbenhoft, D. P.; Sunderland, E. M. Global change and mercury. Science 2013, 341(6153), 1457-1458. (3) Li, B.; Zhang, Y.; Ma, D.; Shi, Z.; Ma, S. Mercury nano-trap for effective and efficient removal of mercury (Ⅱ) from aqueous solution. Nature Communications 2014, 5(5), 5537. (4) Li, H.; Zhu, L.; Wang, J.; Li, L.; Shih, K. Development of nano-sulfide sorbent for efficient removal of elemental mercury from coal combustion fuel gas. Environmental Science & Technology 2016, 50(17), 9551-9557. (5) Liu, Y.; Li, H.; Liu, J. Theoretical prediction the removal of mercury from flue gas by MOFs. Fuel 2016, 184, 474-480. (6) Galbreath, K. C.; Zygarlicke, C. J. Mercury speciation in coal combustion and gasification flue gases. Environmental Science & Technology 1996, 30, 2421-2426. (7) Yao, H.; Luo, G.; Xu, M.; Kameshima, T.; Naruse, I. Mercury emission and species during combustion of coal and waste. Energy & Fuels 2006, 20(5), 1946-1950. (8) Driscoll, C. T.; Mason, R. P.; Chan, H. M.; Jacob, D. J.; Pirrone, N. Mercury as a global pollutant: Sources, pathways, and effects. Environmental Science &

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effects of activated carbon’s oxygen functional groups for elemental mercury adsorption using temperature programmed desorption method. Fuel 2017, 200, 100-106. (25) Jampaiah, D.; Ippolito, S. J.; Sabri, Y. M.; Reddy, B. M.; Bhargava, S. K. Highly efficient nanosized Mn and Fe codoped ceria-based solid solutions for elemental mercury removal at low flue gas temperatures. Catalysis Science & Technology 2015, 5, 2913-2924 (26) Sabri, Y. M.; Ippolito, S. J.; Bhargava, S. K. Support layer influencing sticking probability: enhancement of mercury sorption capacity of gold. Journal of Physical Chemistry C 2013, 117 (16), 8269-8275. (27) Liu, Y.; Kelly, D. J. A.; Yang, H.; Lin, C. C. H.; Kuznicki, S. M.; Xu, Z. Novel regenerable sorbent for mercury capture from flue gases of coal-fired power plant. Environmental Science & Technology 2008, 42 (16), 6205-6210. (28) Wang, X.; Blechert, S.; Antonietti, M. Polymeric graphitic carbon nitride for heterogeneous photocatalysis. ACS Catalysis 2012, 2, 1596-1606 (29) Wang, X.; Maeda, K.; Thomas A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst hydrogen production from water under visible light. Nature Materials 2009, 8(1), 76-80. (30) Xiao, J.; Xie, Y.; Cao, H.; Wang, Y.; Guo, Z.; Chen, Y. Towards effective design of active nanocarbon materials for integrating visible-light photocatalysis with ozonation. Carbon 2016, 107, 658-666. (31) Xiao, J.; Xie, Y.; Cao, H.; Wang, Y.; Guo, Z.; Zao, Z. g-C3N4-triggered super

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synergy between photocatalysis and ozonation attributed to promoted radical ·OH generation. Catalysis Communications 2015, 66, 10-14. (32) Dong, G.; Yang, L.; Wang, F.; Zang, L.; Wang, C. Removal of nitric oxide through visible light photocatalysis by g-C3N4 modified with perylene imides. ACS Catalysis 2016, 6, 6511-6519. (33) Dong, G.; Ho, W.; Li, Y.; Zhang, L. Facile synthesis of porous graphene like carbon nitride (C6N9H3) with excellent photocatalytic activity for NO removal. Applied Catalysis B: Environmental 2015, 174, 477-485. (34) Tang, J.; Zhou, W.; Guo, R.; Huang, C.; Pan, W. Enhancement of photocatalytic performance in CO2 reduction over Mg/g-C3N4 catalysts under visible light irradiation. Catalysis Communications 2018, 107, 92-95. (35) He, Y.; Zhang, L.; Teng, B.; Fan, M. New application of Z-scheme Ag3PO4/g-C3N4 composite in converting CO2 to fuel. Environmental Science & Technology 2015, 49(1), 649-656. (36) Xiao, J.; Xie, Y.; Nawaz, F.; Wang, Y.; Du, P.; Cao, H. Dramatic coupling of visible light with ozone on honeycomb-like porous g-C3N4 towards superior oxidation of water pollutants. Applied Catalysis B Environmental 2016,183, 417-425. (37) Xiao, J.; Han, Q.; Xie, Y.; Yang, J.; Su, Q.; Chen, Y.; Cao, H. Is C3N4 chemically stable toward reactive oxygen species in sunlight-driven water treatment? Environmental Science & Technology 2017, 51, 13380-13387. (38) Liu, D. J.; Zhou, W. G.; Wu, J. Effect of Ce and La on the activity of CuO/ZSM-5 and MnOx/ZSM-5 composites for elemental mercury removal at low temperature.

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diffraction, solid-state NMR spectroscopy, and theoretical calculations-structural characterization of a carbon nitride polymer. Chemistry - A European Journal 2007, 13(17), 4969-4980. (47) Dong, F.; Sun, Y.; Wu, L.; Fu, M.; Wu, Z. Facile transformation of low cost thiourea into nitrogen-rich graphitic carbon nitride nanocatalyst with high visible light photocatalytic performance. Catalysis Science & Technology 2012, 2, 332-1335. (48) Svintsitskiy, D. A.; Kardash, T. Y.; Stonkus, O. A.; Slavinskaya, E. M.; Stadnichenko, A. I.; Koscheev, S. V.; Chupakhin, A. P.; Boronin, A. I. In situ XRD, XPS, TEM, and TPR study of highly active in CO oxidation CuO nanopowders. Journal of Physical Chemistry C 2013, 117(117), 14588-14599. (49) Cai, J.; Shen, B.; Li, Z.; Chen, J.; He, C. Removal of elemental mercury by clays impregnated with KI and KBr. Chemical Engineering Journal 2014, 241, 19-27. (50) Lee, S. J.; Seo, Y. C.; Jurng, J.; Tai, G. L. Removal of gas-phase elemental mercury by iodine- and chlorine-impregnated activated carbons. Atmospheric Environment 2004, 38, 4887-4893. (51) Tan, Z.; Sun, L.; Xiang, J.; Zeng, H.; Liu, Z.; Hu, S.; Qiu, J. Gas-phase elemental mercury removal by novel carbon-based sorbents. Carbon 2012, 50, 362-371. (52) Liu, Z.; Yang, W.; Xu, W.; Liu, Y. Removal of elemental mercury by bio-chars derived from seaweed impregnated with potassium iodine. Chemical Engineering Journal 2018, 339, 468-478. (53) Niu, P.; Zhang, L.; Liu, G.; Cheng, H. Graphene-like carbon nitride nanosheets for improved photocatalysis activities. Advanced Functional Materials 2012, 22,

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study

on

Hg0

removal

from

flue

23


gas

over

columnar

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Figure 1. XRD patterns of (a) g-C3N4 and (b) CuO/g-C3N4

Figure 2. FTIR spectra of g-C3N4 and CuO/g-C3N4

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Energy & Fuels

Figure 3. Nitrogen adsorption-desorption isotherms of g-C3N4

Figure 4. FESEM images: (a) and (b) PCNN, (c) and (d) CuO/PCNN

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Figure 5. HRTEM images: (a) and (b) PCNN, (c) and (d) CuO/PCNN

Figure 6. Hg0 capture performance of g-C3N4 and CuO/g-C3N4 at 120 °C: (a) BCN (b) CuO/BCN (c) PCN (d) CuO/PCN (e) PCNN (f) CuO/PCNN

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Energy & Fuels

Figure 7. Hg0 capture performance of PCNN and CuO/PCNN at 120 °C over 10 h

Figure 8. Effect of temperature on Hg0 removal efficiency of PCNN and CuO/PCNN

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Figure 9. XPS spectra: (a), (c), (e), (g) spent PCNN; (b), (d), (f), (h) CuO/PCNN

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Figure 10. Hg 4f XPS spectra of (a) spent PCNN and (b) spent CuO/PCNN

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Page 32 of 32

Table 1. Textural property of g-C3N4 and CuO/g-C3N4, crystalline size estimated from (-111) lattice plane of CuO for CuO/g-C3N4 Total Surface

Micropore Mesopore

Pore

Crystalline

pore samples

area (m2/g）

volume 3

volume

volume

diameter

size

(cm3/g)

(cm3/g)

(nm)

(nm)

(cm /g) BCN

5

0.033

0.002

0.031

25

-

PCN

3

0.022

0.002

0.020

32

-

PCNN

25

0.315

0.013

0.302

35

-

CuO/BCN

2

0.006

0.001

0.005

15

20.68

CuO/PCN

1

0.002

0.001

0.001

12

24.99

CuO/PCNN

23

0.147

0.003

0.144

26

20.37

32


Gaseous mercury capture by copper-activated nanoporous carbon

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