In-situ generated Ni3Si2O5(OH)4 on mesoporous heteroatom

Subscriber access provided by Kaohsiung Medical University

Article

In-situ generated Ni3Si2O5(OH)4 on mesoporous heteroatom-enriched carbon derived from natural bamboo leaves for high performance supercapacitors Qiushi Wang, Yifu Zhang, Hanmei Jiang, Tao Hu, and Changgong Meng ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00556 • Publication Date (Web): 20 Jun 2018 Downloaded from http://pubs.acs.org on June 21, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Energy Materials

In-situ Generated Ni3Si2O5(OH)4 on Mesoporous Heteroatom-enriched Carbon Derived from Natural Bamboo Leaves for High Performance Supercapacitors Qiushi Wang, Yifu Zhang*, Hanmei Jiang, Tao Hu, Changgong Meng School of Chemistry, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, PR China *Corresponding author. E-mail address: [email protected], [email protected]

Abstract Hybrids consisting of mesoporous carbon and uniform sized, regular morphology and even distributed metal silicate has been a challenge, although they are a potential promising material for electrochemical supercapacitor. In this work, we have synthesized a hybridized supercapacitor electrode of layered nickel silicate Ni3Si2O5(OH)4 nanoparticles on the porous carbon derived from calcined natural bamboo leaves (C-SiO2). The good combination of C-SiO2 and in-situ generated layered nickel silicate, which turned out to be an outstanding electrode, perform high specific surface area, multi-porous structure, good electrical conductivity and prominent electrochemical performance. For instance, the obtained C-NiSi-3 showed 132.4 F g−1 at a current density of 0.5 A g−1 and significantly maintained 100% after 10000 cycles. Furthermore, a flexible all-solid-state asymmetric supercapacitor device was assembled by C-NiSi-3 and Ni(OH)2. The device was suited to various bending angles and achieved a high capacitance (693.8 F cm−2 at the current density of 4 mA cm−2) and an energy density of 30.0 Wh kg−1. The results presented in this work reveal that C-NiSi material is a promising candidate for fabricating supercapacitors with both a high performance, bending mechanical properties and relatively low cost.

Keywords: Bamboo leaves; mesoporous carbon material; Nickel silicate; in-situ synthesis; all-solid-state supercapacitor; high energy density

1

ACS Paragon Plus Environment

ACS Applied Energy Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1.

Page 2 of 30

Introduction Nowadays, there has been an ever urgent and increasing demand to novel energy storage devices

with high power and energy density due to the growing electricity consumption of electronic devices and electric vehicles1. Among various energy storage devices, supercapacitors (SCs) are the emerging energy storage devices, which stand out due to their very high power density, rapid charging-discharging rate, high rate capability, and super-long cycle life compared to conventional capacitors and Li-ion batteries. Basing on the energy storage mechanisms, SCs can be categorized into two types: pseudocapacitors and electrical double-layer capacitors (EDLCs). The former takes advantage of the reversible Faradaic reactions under certain potentials at the interface of electrode (such as metal oxides/sulfides2-13, conducting polymers14-18, etc.) and electrolyte. On the other hand, the later (most are carbon materials, such as activated carbon (AC)19, mesoporous carbon, carbon nanotubes, graphene nanosheets and bio-derived carbon20-22) primarily stores electrical energy by electrostatic accumulation in the electric double-layer at electrode/electrolyte interfaces2,

23

. By comparison, pseudocapacitors show a higher

specific capacitance and energy density than EDLCs capacitors because of their fast and reversible faradaic processes in connection with electroactive species24. However, in most cases, the poor electrical conductivity of pseudocapacitors bring a huge resistance that leads to the detected specific capacitances less than the theoretical value. Besides, an easy structural damage during the redox process results a poor cycling stability, which hinders their practical applications. The EDLCs capacitors show a limited energy storage capacity and low rate capability limit their applications only to some certain niche markets. As a traditional material, silicate, as mesoporous materials and/or zeolites are usually used for various applications including catalysis, separation, and the controlled release of medicines

25-29

. Among

these silicon materials, metal silicate has drawn attention for their remarkable abilities of electrochemical properties and applied in catalysis30-34 and batteries35-37. There are also a few reports of metal silicate such as manganese silicate38 and cobalt-nickel silicate39-40 that used for supercapacitor. However, the poor cycling stability or low capacitance hinders the application of metal silicate, resulting in rapid capacity fading and insufficient capacitance when used in SCs. This situation is due to the low electronic conductivity and sluggish ion diffusion that limit the electrons transfer of the metal silicates, thereby forming a major barrier for application in electrochemical devices. To solve this problem, some methods have been employed to improve the capacitance and elevating the cycling stability. Combining the nanoparticles with carbon materials such as graphene, carbon nanotube and bio-material based carbon41-42 2


Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


has been proved to be an effective way to relieve the situation. Nevertheless, due to the unique surface of the participants, it is not easy to acquire a firm conjunction and might lead to an increased resistance which can be a problem for applied in SC. Thus, it is necessary to develop a new strategy to open up the possibility of combining metal silicate and carbon materials that used for applications of energy devices43. Herein, we combine the carbon materials (C-SiO2) that derived from bamboo leaves and the layered nickel silicate to fabricate a SC electrode using in-situ growing method. First, we prepare a rather stable and porous carbon material through directly calcinate the bamboo leaves under N2 protection. Then, layered nickel silicate Ni3Si2O5(OH)4 nanoparticles are grown on the C-SiO2 by utilizing the silicon species inherent in the carbon as a silicon source via a facile hydrothermal method. The layered structure and low crystalline feature of layered nickel silicate facilitate charge transfer; meanwhile, the porous structure, high surface area reactive sites of C-SiO2 promote the electrochemical reaction at the interface of electrode and electrolyte. Besides, C-SiO2 acts as the supporting material for Ni3Si2O5(OH)4 to adapt to the large volume changes during redox reaction process and elevate the structural stability during long-term repeated charge-discharge cycles, which results in an evolutionary cycle performance and an outstanding rate capability44-45. In the liquid electrolyte based three-electrode test, the composite C-NiSi-3 shows a specific capacitance of up to 132.4 F g−1 at the current density of 0.5 A g−1 achieved in a 3 M KOH aqueous solution. Moreover, we also assemble the all-solid-state asymmetric SC (ASC) by employing Ni(OH)2 as the counter electrode. The combined ASC exhibits an excellent electrochemical performance with the highest energy density of 30.0 Wh kg−1. The device simultaneously shows a flexible behavior without sacrificing obvious electrochemical performance when bending to different angles and a good cyclic performance.

2.

Experimental section

2.1. Material preparation All chemicals in this work were purchased from Sinopharm Chemical Reagent Co., Ltd and used without any further purification. Fresh bamboo leaves were collected locally (Dalian City) and thoroughly washed with a large amount of de-ionized (DI) water to eliminate physical contaminants on the surface. Then, the cleaned bamboo leaves were dried at 60 °C for 12 h. Subsequently, the dried bamboo leaves

3



were first carbonized at 600 °C for 2 h with a heating rate of 1 °C min−1 in a tube furnace under a high-purity N2 atmosphere. During the following acid treatment, the obtained products were mixed with an amount of 1.0 M hydrochloric acid (HCl, 36.5 wt%) and stirred for 12 h to remove the metal species inside the products. The acid-treated products were washed with DI water for several times until pH ≈7 and centrifugated, dried at 60 °C for 12 h. The as-prepared product was named as C-SiO2. According to ICP-AES, the constitution of C and SiO2 is 76.7 % and 23.3 %. The final product was synthesized by a simple hydrothermal method. Typically, 0.04 g C-SiO2 was mixed with a certain amount of Nickel (II) acetate tetrahydrate (Ni(OAc)2·4H2O) and 20 mL H2O and transferred into a steel autoclave with Teflon lining for hydrothermal treatment at 180 °C for 24 h. The resultant products were centrifuged, washed with ethanol and deionized water repeatedly for 3 times and then dried under 60 °C for 12 h. To get optimal experiment conditions, we regulated the molar ratio of Ni to Si by controlling the concentration of Ni(OAc)2·4H2O to 0.1/1, 0.3/1, 0.5/1, 0.8/1, 1/1, 1.2/1 and named as C-NiSi-1, C-NiSi-2, C-NiSi-3, C-NiSi-4, C-NiSi-5 and C-NiSi-6. An ICP-AES test was used to quantify the nickel species existed in sample C-NiSi-1, C-NiSi-2, C-NiSi-3, C-NiSi-4, C-NiSi-5 and C-NiSi-6. By excluding the silicon species reacted with nickel species, the rest silicon are the residual SiO2. After the test, the reacted silicon are 0.22, 0.66, 1.02, 2.35, 2.43 and 2.64 wt% in sample C-NiSi-1, C-NiSi-2, C-NiSi-3, C-NiSi-4, C-NiSi-5 and C-NiSi-6. Due to the SiO2 in SiO2-C is 23.3%, the residual silicon is 23.08, 22.64, 22.28, 20.95, 20.87 and 20.66 wt% in sample C-NiSi-1, C-NiSi-2, C-NiSi-3, C-NiSi-4, C-NiSi-5 and C-NiSi-6. By comparison of the reacted and unreacted silicon in the sample, it could be seen that the nickel ions only reacted with the amorphous silicon existed in the C-SiO2 in a certain depth on the surface. And the residual SiO2 can immobilized the nickel silicate on the carbon basement.

2.2. Characterization The morphologies and structures of the resulting products were measured by field-emission scanning electron microscope (FE-SEM, NOVA NanoSEM 450, FEI) and transmission electron microscopy (TEM) and high-resolution TEM (HRTEM, FEI Tecnai F30, FEI). Samples for SEM observation were sputtered for 90s with gold in order to get better morphology of the surface, and the samples were dispersed in pure ethanol with ultrasonication before TEM characterization. An energy-dispersive X-ray spectrometer (EDS) and elemental mapping were recorded by a scanning electron microscope (SEM, QUANTA450, FEI). The crystalline structure of the products were analyzed by X-ray diffraction (XRD) technique by a X-ray 4


Page 4 of 30

Page 5 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


diffractometer using Cu Kα radiation (λ=1.5418 Å) in the 2 theta range from 4 ° to 80 °. Fourier-transform infrared spectra (FTIR) were collected using a Nicole Avatar 360 FTIR spectrometer (USA) with data acquisition software OMNIC 5.0 in the range of 4000-400 cm−1, samples were analyzed by KBr disk method. Raman spectra were obtained using a Thermo Scientific spectrometer (DXR Smart Raman, Thermo Fisher). N2 adsorption/desorption was determined by Brunauer-Emmet-Teller (BET) method using Quantachrome Autosorb-iQ-C at a heating rate of 10 °C min −1 and the samples were degassed at 250 °C for 12 h. The mass percentage of Ni in the composites was determined by dissolving the composites in HF solutions and using inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Optima2000DV, PerkinElmer). The X-ray photoelectron spectroscopy (XPS) measurements were performed on ESCALAB 250Xi electron spectrometer. The spectra was excited using Al Kα radiation with a pass energy of 20 eV. 2.3 Electrochemical characterization The electrochemical performances of single electrode were carried out in a three-electrode system. Working electrodes were prepared using as-prepared active materials (C-NiSi), polyvinylidene difluoride (PVDF) and carbon black in a weight ratio of 8:1:1. A small amount of N-methyl-2-pyrrolidone (NMP) was then added as a solvent to make a homogeneous mixture. The mixed slurry was then coated onto a nickel foam (1 cm2) current collector and heated at 80 °C for 12 h to remove organic solvent. The resultant foils were made by pressing on the Ni-grids at 10 MPa for 10 minutes. The typical loading of the electroactive material on current collector is 3-5 mg cm-2 for the electrochemical evaluation. Electrochemical characterization was performed in a three-electrode system using 3 M KOH electrolyte, where a carbon rod and a mercuric-oxide-electrode (Hg-HgO) were used as the counter and reference electrodes, respectively. In addition, a C-NiSi-based solid-state asymmetric supercapacitor (ASC) was also electrochemically characterized. The solid-state ASC was fabricated using Ni(OH)2 electrode as the positive electrode and C-NiSi electrode as the negative electrode. The positive electrode material Ni(OH)2 was prepared according to the previous article46 as depicted in SI. The electrode was prepared by mixing 80 wt% C-NiSi material, 10 wt% polyvinylidene difluoride (PVDF) and 10 wt% carbon black in a small amount of N-methyl-2-pyrrolidone (NMP). The mixtures were coated on nickel foam (current collector) in an active area of 1.25 cm × 0.8 cm and heated at 80 °C for 12 h to remove organic solvent. The electrodes were further pressed under 10 MPa for 10 minutes. The polyvinyl alcohol (PVA)/KOH gel electrolyte 5



Page 6 of 30

was prepared by mixing 3.04 g PVA with 4.26 g KOH in 30 mL H2O and heated at 80 °C under stirring for 2 h until it became homogeneously clear. When it is cooling naturally, the electrodes and the separator were soaked in the gel for 5 min, then taken out from the gel, and assembled together. Afterward, the ASC device was pressed by mechanical stress. Electrochemical performance of ASC device was evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge performance (GCD) and electrochemical impedance spectroscopy (EIS) measurements. The specific capacitance of a single electrode was calculated from the GCD curves based on the following equation: C = (I·∆t)/(m·∆U)

(1)

where, C (mF·g−1) represents specific capacitance; I (A) corresponds to discharge current; ∆t (s) denotes discharge time; m (g) refers to the mass of active material in the working electrode; ∆U (V) represents the potential drop during discharge process. The specific capacitance, energy density, and power density of ASC was calculated from the GCD curves based on the following equation: Cs = (I·∆t)/(Stotal active area·∆U)

(2)

Cv = (I·∆t)/(Vtotal volume·∆U)

(3)

Cm= (I·∆t)/( mtotal mass·∆U)

(4)

Em = Cm U2/2×3600

(5)

Ev = Cv U2/2×3600

(6)

Pm = Em/△T

(7)

Pv = Ev/△T

(8)

where Cs, Cv and Cm was the areal, volume and mass capacitance of the asymmetric supercapacitor, respectively; the Stotal active area, Vtotal volume and mtotal mass represents the total active area, total volume and total mass of activate materials of the asymmetric supercapacitor. The areal capacitance (Cs, mF cm-2) of the electrodes was calculated from the surface area of the electrode (1 cm2). The volume capacitance (Cv, F cm−3) of the electrodes was calculated from the total volume of the electrode (including the volume of current collectors). The mass capacitance Cm (mF·g−1) was calculated by replacing the areal capacitance with the total mass of both of the electrodes. The mass ratio of the positive to negative electrode is adjusted by using the equation below m+C+=m−C− (Q+=Q−)

6


Page 7 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Where m stands for the mass of activated electrode material, Q and C is the specific capacitance. According to the previously reported work47-49, the respective masses of the two electrodes are adjusted to optimize the performance of device, because the specific capacitance of Ni(OH)2 differs from C-Ni3Si2O5(OH)4. Em (mWh kg−1) and Ev (mWh cm−3) are the mass and volume energy density of the asymmetric supercapacitor. Pm (mW kg−1) and Pv (mW cm−3) are the mass and volume power density of the asymmetric supercapacitor. All electrochemical tests of the ASC device were performed in a two electrode configuration at ambient temperature.

3.

Results and discussion The synthesis strategy is schematically illustrated in Figure 1. First, the C-SiO2 are easily prepared

by a calcination method. The dried and cleaned bamboo leaves are calcinated in a tube furnace under N2 protection. For the typical synthesis of C-NiSi, a hydrothermal treatment of C-SiO2 with various of concentrations of nickel solution is processed. During which, Ni2+ reacts with the amorphous silicon species inside the C-SiO2 by forming Ni3Si2O5(OH)4. Meanwhile, the continuous consumption of silicon species results in an in-situ grown Ni3Si2O5(OH)4 on the surface of the carbon. By precisely tuning the Ni2+ concentration, a layered structure Ni3Si2O5(OH)4 decorated carbon material can be synthesized.

Figure 1. A schematic illustration of the formation of the complex C-NiSi.

The natural air-dried bamboo leave exhibits a slightly wrinkled and rough surface with biologic macropores (40~60 µm) (Figure S1). The shrink may be attributed to the evaporation of water during the drying process. It can be observed from the cross section (Figure S1c-d), the vessels inherent the bamboo leaves which play an important role in water and nutrient transportation that shaped a stereoscopic distinct lamellar morphology. After calcination, it can be seen that the C-SiO2 shows a crapy surface and a more multiporous structure (Figure S2a-b) on the flank that inherited from the original structure of the bamboo

7



leaves. The longitudinal section image (Figure S2c) of the C-SiO2 display a large amount of perforations on the vessel wall (Figure S2c-d). The C-SiO2 has numerous macropores with a diameter from a few micrometers to a few hundred nanometers, which can not only facilitate the electrolyte ions to fast diffuse into the inner micropores but also serve on the ion-buffering reservoir of electrode materials, particularly at high charging rates50. Meanwhile, a nonuniform transparent structure is also observed clearly from the TEM images of C-SiO2 (Figure S2g-h), indicating a hierarchical porous structure existed. No clear lattice fringe is found in the enlarged HRTEM image of the edge (Figure S2i), in accordance with the XRD data that the carbon is amorphous discussed below. After hydrothermal treatment with Ni2+, C-NiSi still retain the shape of C-SiO2 but decorated with layered structure of Ni3Si2O5(OH)4. From the TEM images (Figure 2a-c) of the C-NiSi-3, the main structure of C-NiSi-3 is composed of a main structure of C-SiO2 and well dispersed layered structure of Ni3Si2O5(OH)4 grown on the surface of the C-SiO2. The length of the layered structures is up to 150-250 nm and width of 130-230 nm. As shown in inset in Figure 1b, it was observed that the layered Ni3Si2O5(OH)4 was composed of several layers with a porous microstructure, which may explain the electrolyte with improved capacitance characteristics. The typical HRTEM (Figure 2d) reveal the low crystallization in weak intensity of lattice fringes with the spacings of 0.736, 0.263 and 0.244 nm, which are attributed to the interplanar distance of the (002), (200) and (202) crystal planes of Ni3Si2O5(OH)4-JCPDS no. 49-1859, respectively. Furthermore, the selected area electron diffraction (SAED) also proves the weak diffraction of the patterns of the Ni3Si2O5(OH)4 (inset in Figure 2d).

8


Page 8 of 30

Page 9 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. TEM images of C-NiSi-3 (a-c) and the inset in (a) a high-resolution TEM (HRTEM) image of the Ni3Si2O5(OH)4 and selected area electron diffraction (d).

Typical field-emission scanning electron microscopy (FE-SEM) images of C-NiSi-3 are shown in Figure 3a-d. FE-SEM reveal that this sample consists of closely aggregated nickel silicate nanosheets on the surface and pores of C-SiO2. The nickel silicate nanosheets generated on the surface of carbon are in order and possess highly interconnected structures that generated pores. In the structure of Ni3Si2O5(OH)4 as shown in Figure S3a, all the atoms are settled in layers along the c axis and each silicon atom has a tetrahedral environment with four oxygen atoms. The nickel atom in the interlayer space link with oxygen atoms by electrostatic attraction and the SiO4 tetrahedra are connected each other via oxygen bridges. The insets in Figure S3c-d show the enlarged image of nanosheets, indicating they own a layered structure, which is similar to the previous reported51-52.

9



Figure 3. (a-d) SEM images of C-NiSi-3 and the enlarged image.

To further investigate the structural composition of the product, energy dispersive spectroscopy (EDS) microanalysis and element mapping are performed. Figure S4 and Figure 4 show the element mappings of the C-SiO2 and C-NiSi-3, respectively. Element mapping results suggest the uniform distribution of the component elements including C, O, N, Ni (in C-NiSi-3), Si, S and P both in the C-SiO2 and C-NiSi-3. Furthermore, in order to analyze and confirm the structure of the products and Ni/Si atomic ratio, inductively coupled plasma atomic emission spectrometry was performed as well. Notably, the Ni/Si atomic ratio was 0.044, which is smaller than the ideal ratio in the formula Ni3Si2O5(OH)4. This can be probably explained by that the nickel ions reacts with the silicon on the surface of C-SiO2. The results of element mapping also prove the presence and well spatial distribution of Ni3Si2O5(OH)4 in the prepared C-NiSi-3.

10


Page 10 of 30

Page 11 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. The corresponding EDS mapping of C-NiSi-3.: (a) SEM image, (b) C-K, (c) O-K, (d) N-K, (e) Ni-K, (f) Si-K, (g) S-K, (h) P-K and (i) EDS of C-NiSi-3.

The compositions and microstructures of the as-synthesized samples are also characterized by XRD, FTIR, Raman and N2 adsorption-desorption. As shown in Figure 5A(a), the weak and broad peak observed in the pattern of basement of C-SiO2 can be ascribed to the amorphous nature of the carbon. As expected, after the hydrothermal treatment with Ni2+, five diffraction peaks at 12°, 24°, 33°, 36° and 60° appear and correspond to the lattice plane of (002), (004), (200), (202) and (060) of Ni3Si2O5(OH)4, respectively (JCPDS no. 49-1859), which is similar to the previous report

39

. The diffraction peaks of

Ni3Si2O5(OH)4 shifts a little compared with the pure nickel silicate hydroxide, which might be caused by the influence of C-SiO2. Due to the small amount of Ni species used and the low crystalline of the layered nickel silicate, the XRD patterns of the C-NiSi-1 and C-NiSi-2 show no obvious peaks of the layered

11



nickel silicate. As the amount of Ni species is increased, the diffraction intensity of the samples increased slightly.

Figure 5. (A) XRD pattern of (a) C-SiO2, (b) C-NiSi-1, (c) C-NiSi-2, (d) C-NiSi-3, (e) C-NiSi-4, (f) C-NiSi-5 and (g) C-NiSi-6. (B) FTIR spectra of (a) C-SiO2 and (b) C-NiSi-3. (C) Raman spectra of the (a) C-SiO2 and (b) C-NiSi-3. (D) N2 adsorption-desorption isotherms of (a) C-SiO2 and (b) C-NiSi-3, insert pore size distribution curves.

Figure 5B shows the FTIR spectra of C-SiO2 and C-NiSi-3. In Figure 5B (b), the broad band at 3427 cm−1 are related to the hydrogen-bonded hydroxyl groups of adsorbed water molecules; while the narrow peak at 3677 cm−1 is attributed to the stretching mode of -OH in Ni3Si2O5(OH)4 53. The band at 1616 cm−1 also indicates the presence of hydroxyl groups. The bands located at 1106 and 804 cm−1 correspond to stretching vibration of the Si-O bonds54. Bands at 1458 and 879 cm−1 are attributed to the stretching vibration of C-N and C-S, respectively55. The band at 669 cm−1 is ascribed to lattice vibration of Ni-O bond in the layered nickel silicate56. In Figure 5B(a), a strong adsorption peak at 1081 cm−1 is due to the asymmetric Si-O-Si bond stretching vibration and the band at 801 cm−1 is assigned to the symmetrical Si-O-Si network bond stretching vibrations57. The band at 464 cm−1 is ascribed to the deformation

12


Page 12 of 30

Page 13 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


vibration of silica skeleton58. Comparing the FTIR patterns of C-NiSi-3 and C-SiO2, it is obvious to find that the absorptions of 464 and 801 cm−1 disappear, and the peak at 1081 shifts to 1106 cm−1, which may be attributed to the formation of Si-O-Ni bonds. The differences in FTIR spectra further prove the formation of Ni3Si2O5(OH)4. The Raman spectra of C-SiO2 and C-NiSi-3 are provided in Figure 5C. Evidently, all the Raman spectra exhibit two typical peaks, the D band and the G band. The D band locates at around 1340 cm−1 originates from the structural defects and disorder of the samples, and the G band at around 1590 cm−1 represents for the in-plane vibration of sp2 carbon atoms both in chains and rings. As is well-known, the relative intensity ratio of the D band (ID) to G band (IG) indicates the degree of graphitization and the amount of disorder in graphitic materials59. In, Figure 3C, the value of ID/IG is 0.81 for both C-NiSi-3 and C-SiO2, indicating the degree of graphitization is unchanged during hydrothermal treatment. However, comparing the intensities of peaks of D band and G band of C-NiSi-3 with C-SiO2, it is obvious to observe the intensities are reduced. This result demonstrates that the generation of layered nickel silicate on C-SiO2 covers some of the structural defects. To better understand the mesoporous structure of the products, we measure N2 adsorption-desorption isotherms (Figure 5D) of the C-SiO2 and C-NiSi-3, and the corresponding porous properties of the products are summarized in Table 1. As illustrated in Figure 5D, the N2 adsorption-desorption isotherms are close to a combination form of type I and type IV according to the International Union of Pure and Applied Chemistry (IUPAC) classification, proving the coexistence of micropores and mesopores formed in the products

60

. Specifically, the isothermals of all the products show a steep increase in a relatively

low pressure (

In-situ generated Ni3Si2O5(OH)4 on mesoporous heteroatom

Recommend Documents