Synthesis of Large MesoporousâMacroporous and High Pore Volume

Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Synthesis of Large Mesoporous−Macroporous and High Pore Volume, Mixed Crystallographic Phase Manganese Oxide, Mn2O3/ Mn3O4 Sponge Andrew G. Meguerdichian,† Alireza Shirazi-Amin,‡ Ehsan Moharreri,† Laura A. Achola,‡ Steven C. Murphy,‡ John Macharia,‡ Wei Zhong,† Tahereh Jafari,† and Steven L. Suib*,†,‡,§ †

Institute of Materials Science, University of Connecticut, U-3136, 97 N. Eagleville Road, Storrs, Connecticut 06269, United States Department of Chemistry, University of Connecticut, U-3060, 55 N. Eagleville Road, Storrs, Connecticut 06269, United States § Department of Chemical & Biomolecular Engineering, University of Connecticut, U-3222, 191 Auditorium Road, Storrs, Connecticut 06269, United States ‡

S Supporting Information *

ABSTRACT: The controlled synthesis of mixed crystallographic phase Mn2O3/ Mn3O4 sponge material by varying heating rates and isothermal segments provides valuable information about the morphological and physical properties of the obtained sample. The well-characterized Mn2O3/Mn3O4 sponge and applicability of difference in reactivity of H2 and CO2 desorbed during the synthesis provide new developments in the synthesis of metal oxide materials with unique morphological and surface properties. We report the preparation of a Mn2O3/Mn3O4 sponge using a metal nitrate salt, water, and Dextran, a biopolymer consisting of glucose monomers. The Mn2O3/Mn3O4 sponge prepared at 1 °C·min−1 heating rate to 500 °C and held isothermally for 1 h consisted of large mesopores−macropores (25.5 nm, pore diameter) and a pore volume of 0.413 mL/g. Furthermore, the prepared Mn2O3/Mn3O4 and 5 mol %−Fe-Mn2O3/Mn3O4 sponges provide potential avenues in the development of solid-state catalyst materials for alcohol and amine oxidation reactions.

1. INTRODUCTION Hausmannite, Mn 3O 4 , is one crystallographic phase of manganese oxides used in applications such as adsorption,1,2 batteries and energy storage,3,4 and electrocatalytic reactions in oxygen evolution or oxygen reduction reactions.5−7 The crystal phase Mn3O4 belonging to the spinels, which can be rewritten in general form as AB2X4 or more specifically MnO·Mn2O3, shows that the principle oxidation states include 2+ and 3+.8−10 The cations “A” and “B” refer to species in the tetrahedral and octahedral coordination environments, and “X” represents an anion which may include oxygen (O), sulfur (S), selenium (Se), or tellurium (Te).8−10 The material has been synthesized via diverse methodologies including hydrothermal,2,4 electrochemical,11 low-temperature preparation,1,6 and film deposition on substrates.7,12 Moreover, the application of biological materials in the synthesis of manganese oxides has been employed in the preparation of crystal phases such as MnO2, cryptomelane, and birnessite structured materials.13−16 In design of the synthesis method, research has been used to prepare Mn3O4 to have certain advantages over other preparation routes. One advantage commonly discussed is template-free preparations; however, a strong reducing agent is employed, such as hydrazine to produce the Mn3O4 crystal phase.4,5 A second advantage is the ability to control the crystal phase of manganese oxide to obtain β-MnO2, MnO, Mn2O3, or Mn5O8.2,7,17 While the chemistry and chemical properties of the final material are critical for applications and © XXXX American Chemical Society

successful use of the desired manganese oxide crystal phase, there is increasing importance to develop a synthetic process that is safe, allows for control over surface properties (surface area, pore size, and pore volume), and produces a thermally stable material that exists in the literature.1,3,8,12,18 To vary the surface properties of a sample, foams have been synthesized, which can be composed of metals, ceramics, or glass materials for applications in catalysis, batteries, and engineering applications.19,20 The synthesis of ceramic (phosphate and oxide) foams included several approaches such as using biological materials,21 coating foam substrates,22−26 and preparation of manganese oxide foam materials.27,28 However, the properties of the foams have proven advantageous in applications and successful demonstration of their superior qualities in batteries and electrochemistry,21,28 electrocatalysis,27 and energy storage.22,23,25 Examples of properties advantageous for these applications are high thermal stability, porosity (microporous, mesoporous, or macroporous), and chemical composition of the material including the presence of dopants or intercalated species.21−23,25,27,28 Sponges, another class of porous materials, have been discussed in the literature as having distinct properties compared to foams based on the organization and structure of the pores in Received: March 8, 2018

A

DOI: 10.1021/acs.inorgchem.8b00613 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry the material.19,29 While the pore structure of foams is more random with imprecise cellular compartments on the sample surface, their applicability in chemical and materials science has led to significant developments such as electrochemical energy storage in which the morphological and porous network of the sample contributed to excellent storage properties of the sample.30−32 A literature review shows that facile synthesis methods (i.e., hydrothermal) and controlling the crystallographic phase of manganese oxide (MnO, MnO2, Mn2O3, Mn3O4) have been reported to produce a material readily applied to an application to demonstrate activity. In addition, control over surface properties such as surface area, pore size, and pore volume are integral parts of the literature by preparing either supports or commercial supports containing sponges. The current study is distinguished from the literature as the synthetic method allowed for the preparation of a mixed crystallographic phase manganese oxide (Mn2O3/Mn3O4) sponge material that expands during synthesis using facile methods without the use of a hydrothermal apparatus or strong oxidants (potassium persulfate) or reductants.4,5,33,34 Previous studies have supported what makes the prepared material in this study as a sponge.35−37 Additionally, the reaction time was minimized to a two-day period, which avoided extensive solution preparation and thorough washing of the final sample.33,34 The material properties obtained from the prepared Mn2O3/Mn3O4 sponge have not been observed in other sponge-like or foam-like materials as the pores or “cells” are not of the same size (not monomodal pore size distribution) and are easily observable in micrographic analyses and tuned based on synthesis conditions.33,34 As a result, a concentration on preparing large pore size and pore volume manganese oxide sponge material without carbon support, using a facile and environmentally friendly synthetic method (via carbohydrates), has not been reported (Table 1). Therefore, the purpose of this

and benzylamine to imines as the literature has supported its multifunctional purposes in catalysis.38,39

2. EXPERIMENTAL SECTION 2.1. Preparation of Manganese Oxide, Mn2O3/Mn3O4 Dextran Assisted Sponge. All chemicals and reagents in this research analysis were used as received without any purification. The Mn2O3/Mn3O4 material is synthesized using a modified procedure reported by Walsh et al. and shown in Figure 1.37 In a Coors-Tek casserole crucible dish, approximately 1.43 g (0.0057 mol) of manganese nitrate tetrahydrate, Mn(NO3)2·4H2O (Sigma-Aldrich) is dissolved in 0.67 g (0.0372 mol) of deionized water. One gram of Dextran (Mr = 100 000, Sigma-Aldrich) is added to the solution and manually mixed to produce a homogeneous pink paste. Dextran was used, which exhibits a unique phenomenon called “viscoelasticity” in which the biopolymer increases the viscosity of a sample.40,41 The paste is aged overnight leading to the following calcination procedures: (a) heating rate; 0.5 °C, 1 °C, 5 °C, 10 °C·min−1 to 500 °C, isothermal for 1 h and (b) applying the heating rate that maximized surface properties (1 °C·min−1), varying isothermal segment; no isothermal, 1 and 3 h isothermal. The calcination temperature of 500 °C was applied based on the thermal decomposition of Dextran (Supporting Information, S1) in which the biopolymer is completely decomposed by this temperature. The 5 mol %−Fe-Mn2O3/ Mn3O4 sample is prepared in the same manner; however, 0.115 g of Fe(NO3)3·9H2O is added after the Mn(NO3)2·4H2O. We recommend that the experimenter place the casserole crucible dish in a porcelain shallow-form evaporating dish to contain the product during calcination. 2.2. Organic Catalytic Reactions. Alcohol esterification of 1octanol was performed as a reaction that the prepared Mn2O3/Mn3O4 sponge can perform. The reaction was performed by using 100 mg of the prepared catalyst and 0.03 mol of 1-octanol at 150 °C, refluxed with 130 mL·min−1 air flow for 48 h. A second catalytic application was performed for the oxidation of two amines (aniline and benzylamine). The oxidation of aniline was performed using 93 mg of aniline, 50 mg of Mn2O3/Mn3O4 sponge, and 6 mL of toluene, refluxed at 110 °C for 8 h. Another catalytic oxidation was performed using 53 mg of benzylamine, 50 mg of Mn2O3/Mn3O4 sponge, and 6 mL of toluene, refluxed at 110 °C for 24 h. Yields and conversion were determined using a gas chromatography−mass spectrometry (GC-MS) instrument. 2.3. Catalyst Characterization. The characterization of the prepared Mn2O3/Mn3O4 sponge was completed by first using X-ray diffraction (XRD) measurements on a Rigaku Ultima IV instrument with Cu Kα radiation (1.5406 Å) where the beam voltage is 40 kV with a beam current of 45 mA. Measurements were conducted at a scan rate of 1°·min−1 and between 5° and 75°. A Rietveld refinement based on XRD was completed to quantify the amount of each crystal phase present in the sample. To confirm the presence of both crystal phases of Mn2O3 and Mn3O4, high-resolution transmission electron microscopy (HRTEM) was conducted on a FEI, Talos F200X microscope with an operating voltage of 200 kV and the ability to conduct energy dispersive X-ray spectroscopy (EDS). Thermogravimetric analysis−mass spectrometry analyses were performed on a Netzsch instrument, which presented thermal stability of the prepared Mn2O3/Mn3O4 sponge at a 10 °C·min−1 heating rate up to 900 °C, in air (45 mL·min−1 air and 5 mL·min−1 argon) and in argon (50 mL·min−1). Scanning electron microscopy (SEM) was performed on a field emission instrument (FE-SEM, JEOL 6335F) with elemental dispersive X-ray spectroscopy (EDS) to confirm particle morphology and large cell porosity of the prepared sample. Surface properties (surface area, pore diameter, pore volume) were determined using a Quantachrome Nova 2000e instrument via the BET method and degassed for 3 h at 120 °C. Quantification of these properties was determined using DFT analysis on the adsorption branch of the isotherm. The parameters used for DFT analysis included studying relative pressures between 0 and 1 and treating the adsorbent as a zeolite. X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI model 590 XPS to study the different manganese and oxygen environments in the Mn2O3/ Mn3O4 sponge. Another technique used in the identification of manganese oxidation states present was electron paramagnetic

Table 1. Literature Comparison of Manganese Oxide, Mn3O4 on Synthesis Conditions and Physicochemical Properties material description

surface area, (m2/g)

pore diameter, (nm)

pore volume, mL/g

sponge

90

16

0.38

nanorods

33

3.7

0.053

sponge

102

10

NRa

crystals from MOF nanotubes

160

23

0.649

42

3.72

0.08

a

comments

reference

Dextran template aqueous media; calcined 500 °C hydrothermal; PEG-400; 300 °C, N2 for 5 h use of ethanol amine; centrifuge 8000 rpm 5 min use of ionic liquids

this work

reduction from MnO2

2

33

62

63

NR = not reported in literature article.

study will be to first successfully synthesize a manganese oxide sponge using Dextran, a polysaccharide composed of glucose monomer units.37 The synthesis will be varied via (1) heating rate and (2) isothermal segment during the calcination to understand how these factors affect the porosity of the material. The sample with maximized surface properties (prepared at 1 °C· min−1 to 500 °C, isothermal 1 h) and 5 mol %−Fe-Mn2O3/ Mn3O4 will be applied to understand their catalytic application toward (1) oxidation of 1-octanol and (2) oxidation of aniline B


Article

Inorganic Chemistry

Figure 1. Schematic drawing of synthesis methodology for Mn2O3/Mn3O4 sponge illustrating (A) sample preparation and (B) aging/calcination steps. resonance (EPR). The measurements were conducted at 298 K with a X-Band (9 GHz) Bruker EMX spectrometer. The sample was loaded into a quartz tube (3 mm outer diameter, 2 mm inner diameter). Lastly, cyclic voltammetry (CV) was also applied to the prepared Mn2O3/ Mn3O4 sponge to observe the redox behavior of the manganese. The analysis was conducted using a CHI Electrochemical Workstation. The measurements were conducted using an electrochemical cell, purged with argon gas. The reference electrode was Ag/AgCl in saturated KCl, and the counter electrode was a glassy carbon electrode. The electrolyte solution consisted of 0.1 M KOH (Sigma-Aldrich, reagent grade, 90%, flakes) in deionized water. To conduct the electrochemistry measurements, the following parameters were used: (A) voltage scanned, −1.3 to 0.6 V; (B) scan rate, 0.01 V·s−1, and (C) sampling interval, 0.001 V. Additional parameters utilized to conduct the measurement included a quiet time of 2 s and sensitivity of 0.001 A·V−1. Ink preparation, based on a previously reported procedure,42 consisted of 2 mg of Cabot carbon black, 2 mg of Mn2O3/Mn3O4 sponge catalyst, which were mixed with 800 and 200 μL of distilled deionized water and ethanol, respectively. The addition of 75 μL of Nafion along with sonication for 30−60 min was performed. From this solution, 10 μL was dropped onto the electrode surface and dried before conducting the analysis. To support the results obtained from the characterization of the Mn2O3/Mn3O4 sample, thermogravimetric analysis (TGA) was completed on the Dextran biopolymer using a TA Instruments Q500 instrument. Parameters for the measurement included using air and heating rate of 10 °C·min−1 to 900 °C. Second, temperature programmed desorption-mass spectrometry (TPD-MS) was completed to demonstrate that CO2 and H2 are the most significant gases being desorbed from the decomposition of Dextran. The analysis was completed using 100 mg of Dextran, packed in a quartz tube with quartz wool in a programmable tube furnace (Thermolyne 79300) at 5 °C·min−1 to 500 °C, in air at 50 mL·min−1. Additionally, the experimental setup consisted of a MKS eVision PPT residual gas analyzer (RGA) and quadrupole mass spectrometry detector. The results of the TGA and TPD-MS analysis of Dextran are provided in the Supporting Information.

3. RESULTS XRD analyses were performed to determine crystal structure of the synthesized MnOx sponge material and whether other crystal phases of manganese oxide were present. Figure 2A illustrates that the synthesized MnOx is crystalline and can be indexed according to the crystal phases of Mn2O3 and Mn3O4 after being calcined to 500 °C. The patterns were indexed according to International Center for Diffraction Data (ICDD) Journal of Crystal Powder Diffraction File (JCPDF) Card no. 01-071-0636, Quality: S, for Mn2O3 and Card no. 01-080-0382, Quality: S, for Mn3O4. The molar ratio of Mn2O3/Mn3O4 presented in the manuscript was determined using a Rietveld Refinement based on XRD within the PDXL software and the previously mentioned ICDD JCPDF Cards. On the basis of our analysis of this method, we were able to determine the molar ratio to be 44% Mn2O3 and 56% Mn3O4. Moreover, the HR-TEM image in Figure2B presents crystal lattices from each phase of Mn2O3 and Mn3O4 such as (400) and (202) or (206), respectively. The physical state and property of the sample postcalcination are illustrated in Figure 2C in which the sample expands out of the crucible after being calcined to 500 °C. Likewise, the XRD of the 5 mol %−Fe-Mn2O3/Mn3O4 sample is presented in Figure 2D along with the physical imagery of the sample in Figure 2E, postcalcination. To confirm the complete decomposition of the Dextran biopolymer, postcalcination, TGA-MS analyses were performed in air and argon (Figure 3A,B) atmospheres from room temperature to 900 °C. The TGA-MS data in air confirm that the Mn2O3/Mn3O4 sponge is thermally stable with less than 2 wt % decomposition by 900 °C with no significant mass spectrometry signals of species being desorbed during the analysis. However, Figure 3B demonstrates that the Mn2O3/ Mn3O4 sponge has ∼5 wt % loss by 900 °C in which the weight loss corresponds with the mass spectrometry signal, m/z = 32. Supporting data were incorporated into the study using C


Article

Inorganic Chemistry Figure 2. continued

Mn2O3/Mn3O4 sponge prepared at 1 °C·min−1 heating rate, isothermal for 1 h.

Figure 3. Thermogravimetric analysis-mass spectrometry (TGA-MS) of Mn2O3/Mn3O4 prepared at 1 °C·min−1 to 500 °C, isothermal for 1 h. Analysis conducted in (A) air (45 mL·min−1 air, 5 mL·min−1, argon) and (B) argon atmosphere (50 mL·min−1).

temperature programmed desorption-mass spectrometry (TPDMS) analyses of the gases produced through the thermal decomposition of Dextran (Supporting Information, S2). SEM micrographs in Figure 4 of the Mn2O3/Mn3O4 sponge illustrated differences in particle morphology with respect to applied heating rate of the prepared gel with Dextran. Support for the morphological result that the prepared material is reflective of

Figure 2. (A) XRD patterns of Mn2O3/Mn3O4 sponge using Dextran, prepared at 1 °C·min−1 heating rate, isothermal for 1 h. Patterns are indexed according to Mn2O3 JCPDS Card No. 01-071-0636, Quality: S and Mn3O4 JCPDS Card No. 01-080-0382, Quality: S. (B) HR-TEM image of Mn2O3/Mn3O4 sponge with diffraction planes identified. Images in (C) illustrate the postcalcined sample’s unique physical property of expanding out of the crucible. (D) XRD pattern for 5 mol %−Fe-Mn2O3/Mn3O4 along with (E) physical images of 5 mol %−Fe-

Figure 4. SEM images of samples at varied heating rates: (A) 0.5 °C; (B) 1 °C; (C) 2 °C; (D) 5 °C; and (E) 10 °C·min−1. D


Article

Inorganic Chemistry a sponge sample was mentioned by Gibson and Ashby in which the samples contain “cells” or pores observable in micrograph imaging.43 In Figure 4A−E, several resultant effects of heating rate (up to 500 °C) are observed on the particle morphology of the Mn2O3/Mn3O4 sponge materials. At relatively low heating rates (0.5 and 1 °C·min−1, Figure 4, panels A and B, respectively), a high degree of porosity is observed in the overall Mn2O3/ Mn3O4 sponge morphology. However, at higher heating rates (5 and 10 °C·min−1, Figure 4D,E, respectively), lower degrees of porosity are observed. Alternatively, Figure 5A,B illustrates the

Figure 5. SEM images of samples at varied isothermal segments: (A) no isothermal; (B) 3 h isothermal.

Figure 7. N2 adsorption (A) isotherms and (B) pore size analyses of Mn2O3/Mn3O4 sponge at varied heating rates. Units for heating rate are °C·min−1.

sponge morphology of the prepared Mn2O3/Mn3O4 sponge at variable isothermal segments at 500 °C. More specifically, these sponges in the variable heating rate and isothermal synthesis experiments are sheet-like as observed in the SEM micrographs. Likewise, the SEM image in Figure 6 illustrates the incorporation of 5 mol %−Fe-Mn2O3/Mn3O4 throughout the structure. Figure 6 of the EDX analysis demonstrates that the iron was distributed throughout the analyzed sample area. N2 adsorption analysis using the BET method demonstrated the degree of porosity and adsorption properties (surface area, pore size and pore volume) of the prepared samples using N2 gas as the adsorbent. In general, the isotherms in Figures 7A and 8A exhibited a type II isotherm where either nonporous or macroporous sites are present on the prepared Mn2O3/Mn3O4 sponge. The isotherm hysteresis for both sets of samples are classified as type H3 and H4 where H4 is particularly observed for the lowest heating rate of 0.5 °C·min−1. The H3 isotherm hysteresis provides information about the types of pores present in the sample as consisting of flexible groupings of particles without a limit to adsorption. However, H4 isotherm hysteresis reveals that micropores are primarily present in the sample as

Figure 8. N2 adsorption (A) isotherms and (B) pore size analyses of Mn2O3/Mn3O4 sponge at varied isothermal conditions. Units for isothermal conditions are hours.

Figure 6. SEM images and EDX mapping of 5 mol %−Fe-Mn2O3/Mn3O4 prepared sample. E


Article

Inorganic Chemistry there is a more pronounced uptake in N2 at lower relative pressures. In general the prepared samples had surface areas varying between 52 m2/g to 86 m2/g and have large mesoporous pore diameters (25.5 nm) and some macroporosity present. However, the pore volumes varied significantly between 0.124 mL/g to 0.413 mL/g. Tables 2, 3, and 4 demonstrate that the Table 2. Summary of N2 Adsorption Properties in Mn2O3/ Mn3O4 − Varied Heating Rates entry

heating rate (OC/min)

surface area (m2/g)

pore diameter (nm)

pore volume (mL/g)

fitting error (%)

1 2 3 4 5

0.5 1 2 5 10

54 68 68 86 72

25.5 25.5 25.5 25.5 25.5

0.124 0.413 0.333 0.379 0.297

0.469 0.923 0.685 0.621 0.625

Degassing conditions for N2 adsorption were 3 h at 120 °C. Isothermal variation samples were prepared at 1 °C·min−1, based on the data collected. cFitting error determined based on the DFT model. a b

Figure 9. N2 adsorption (A) isotherms and (B) pore size distribution analyses of Mn2O3/Mn3O4 sponge with and without 5 mol %-Fe dopant.

Table 3. Summary of N2 Adsorption Properties in Mn2O3/ Mn3O4 Sponges − Varied Isothermal Segments

sample exhibited a broad peak in the XPS analysis demonstrating the wide variety of oxygen environments in the mixed oxide crystallographic material. Figure 10C of the high resolution XPS spectrum of O1s emphasizes different types of oxygen species in the prepared manganese oxide sponge sample. Furthermore, the presented data in Figure 10C support previous literature results that lattice oxygen (528−530 eV) and chemisorbed oxygen (531−532 eV) species are present.44−49 The EPR spectra obtained in Figure 11 for the synthesized Mn2O3/Mn3O4 sponge revealed a broad curvature. Literature examples have revealed that the obtained spectrum does not particularly identify the oxidation state of manganese present in the prepared sample. For example, the confirmation of Mn2+ in undoped OMS-2 demonstrated the expected sextet of peaks in the hyperfine structure when completing EPR analysis.50 However, upon doping with vanadium, the EPR spectrum drastically changed as these individual peaks became less apparent.50 Therefore, the present sample could have a variety of oxidation states present for manganese such as 2+ and 3+. Another challenge in peak broadening is in (1) electron mobility from different manganese or metal species present and (2) the presence of Mn3+ which is d4 electron configuration (generally problematic for even number of electrons) and experiences spin−spin coupling interactions with short relaxation times.51−53 Broadening can also be due to self-quenching due to high concentration of paramagnetic species. Electrochemical analyses using CV revealed the redox behavior of the sample undergoing oxidation and reduction events. The literature supplements the redox data presented in Figure 12 by identifying the occurrence of redox events such as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).54,55 The application of the prepared 5 mol %−Fe-Mn2O3/Mn3O4 sponge at 1 °C·min−1 heating rate to 500 °C, isothermal for 1 h toward alcohol oxidation exhibited increased conversion (58% conversion) and overall better activity toward the reaction than the sample without iron dopant (Table 5). Another catalytic application explored (Table 6) aniline oxidation demonstrated the prepared 5 mol %−Fe-Mn2O3/Mn3O4 catalyst was able to oxidize aniline and benzylamine within the 24-h time period. Moreover, the catalytic reaction is one opportunity for further development in the application of the prepared Mn2O3/Mn3O4 sponge.

entry

isothermal duration (h)

surface area (m2/g)

pore diameter (nm)

pore volume (cc/g)

fitting error (%)

1 2 3

0 1 3

63 68 52

25.5 25.5 25.5

0.307 0.413 0.269

0.662 0.923 0.718

Degassing conditions for N2 adsorption were 3 h at 120 °C. Isothermal variation samples were prepared at 1 °C·min−1, based on the data collected. cFitting error determined based on the DFT model. a b

Table 4. Summary of N2 Adsorption Properties of Pure and 5 mol %−Fe-Mn2O3/Mn3O4 Sponges entry

sample

1

nondoped Mn2O3/ Mn3O4 sponge 5 mol %−FeMn2O3/Mn3O4

2

surface area (m2/g)

pore diameter (nm)

pore volume (mL/g)

fitting error (%)

68

25.5

0.413

0.923

84

25.5

0.230

0.470

current Mn2O3/Mn3O4 sponge prepared at 1 °C·min−1 heating rate with 1 h isothermal segment had the greatest pore volume. The pore size analysis in Figures 7B and 8B also demonstrated that while the pore diameter for all samples was approximately 25.5 nm, the distribution of pores was widespread and generally in the large mesoporous−macroporous range. Incorporation of the 5 mol %−Fe-Mn2O3/Mn3O4 sample demonstrated a significant decrease in pore volume from 0.413 mL/g to 0.230 mL/g, which was also reflected in the relative volume of adsorbed N2 in the isotherm (Figure 9A,B; Table 4). XPS analyses performed on the Mn2O3/Mn3O4 sponge (Figure 10) demonstrated several different manganese and oxygen environments in the tested sample. In particular, the survey spectrum (Figure 10A) demonstrated peaks corresponding to C1s (284 eV), O1s (530 eV), and Mn2p (640 eV). The high resolution XPS spectrum for Mn2p (Figure 10B) exhibited regions designated for the Mn2+ and Mn3+ species in the synthesized sample at ∼642 and 653 eV. The regions observed for Mn2+ and Mn3+ in the prepared Mn2O3/Mn3O4 sponge are similar to those previously reported.44−49 Moreover, the O1s F


Article

Inorganic Chemistry

Figure 10. X-ray photoelectron spectroscopy (XPS) of prepared Mn2O3/Mn3O4 sponge: (A) survey spectrum, (B) Mn2p, (C) O1s, and (D) C1s spectra peaks.

(Supporting Information, S2). However, the XRD for the undoped sample demonstrated the potential for preferential orientation in the Mn3O4 crystal phase as demonstrated in intensities among (1 k l) and (2 0 l) planes being different than reported in the PDF card. The possibility of obtaining a lowangle peak in the prepared sponge was investigated; however, this sample was unable to produce such an observation. Potential reasons for this occurrence have been supported in the literature that well-ordered mesoporous structures are able to produce a peak at low 2θ values.56,57 While the observation of two crystal phases of metal oxides in the same material provides a unique aspect to the present study, the physical form of the sample, postsynthesis, provides more information into the preparation process. Figure 2C,E illustrates this unique property in which the sample expands from the crucible and forms a dome-shaped structure. TPD-MS analyses provided information about potential gases being desorbed from the sample during the synthetic process (Supporting Information, S2). The two primary gases desorbed from Dextran, H2, and CO2 have distinctly different roles in the calcination procedure. H2 is likely to react with the manganese in the sample, whereas CO2 is likely not to react. Therefore, the gas bubbles of reactive H2 produced during the decomposition of Dextran also react with the oxidized Mn2O3 to produce the slightly reduced Mn3O4. However, CO2, which is not very reactive in the presented conditions, as compared to H2, most likely does not remain in the sample crucible, but rather escapes into the environment. Alternatively, the role of CO2 could be hypothesized to provide the expanded physical form postheat treatment of the room temperature gel. Another explanation for the expanded MnOx product is in manganese’s relatively high coefficient of thermal expansion

Figure 11. Electron paramagnetic resonance (EPR) of prepared Mn2O3/Mn3O4 sponge.

Figure 12. Cyclic voltammetry (CV) of prepared Mn2O3/Mn3O4 sponge to demonstrate redox behavior of manganese.

4. DISCUSSION The presented data of the mixed crystallographic phase Mn2O3/ Mn3O4 sponge provide important insights into the synthesis of manganese oxide sponges. XRD analyses demonstrated the mixed crystallographic phases of the oxidized Mn2O3 and slightly reduced Mn3O4. The presence of these two structural forms of manganese oxides occurred via in situ reduction of the Mn2O3 crystal phase using H2 from the decomposition of Dextran

Table 5. Esterification Results of Prepared Mn2O3/Mn3O4 Catalyst with 1-Octanol

entry 1 2 3

catalyst none Mn2O3/Mn3O4 sponge 5 mol %−Fe-Mn2O3/Mn3O4 sponge

conversion

pentanoic acid octyl ester

hexanoic acid octyl ester

heptanoic acid octyl ester

octanoic acid octyl ester

TON

TOF

0 43 58

0 4 6

0 11 15

0 27 29

0 1 8

N/A 25 34

N/A 0.5 0.7

G


Article

Inorganic Chemistry Table 6. Oxidation of Aniline Results using Prepared Mn2O3/Mn3O4 Catalyst

entry

catalyst

substrate

conversion

selectivity, A

TON

TOF

1 2 3

none 5 mol % Fe−Mn2O3/Mn3O4 sponge 5 mol % Fe−Mn2O3/Mn3O4 sponge

aniline aniline benzyl amine

0 20 50

0 100 100

N/A 4 10

N/A 0.5 1.2

(CTE), 22 × 10−6/K as compared to other transition metals such as pure chromium (4.9−8.2 × 10−6/K), pure iron (12−13 × 10−6/K), and pure cobalt (12−14 × 10−6/K).58 As a result, the increased presence and eventual reactivity of H2 with respect to temperature, from the decomposition of Dextran, coupled with the relatively high CTE, potentially allowed for the dome-shaped sample to be produced, postcalcination. Despite the unique properties in the physical form, the Mn2O3/Mn3O4 sponge demonstrated the expected properties in thermal stability as the initially prepared gel was calcined to 500 °C, the temperature at which all of the Dextran biopolymers would be decomposed. However, the sample lost ∼6 wt % in the TGA-MS analysis under argon atmosphere in which the significant species desorbed from the sample included m/z = 32 or O2. SEM analyses of the prepared samples at varying heating rates and isothermal conditions provided additional information into the material properties and synthetic methodology. Figure 4 illustrates the variations in porosity of the Mn2O3/Mn3O4 sample at varying heating rates in which the greatest number of pores and distribution of pores can be qualitatively observed in Figure 4B. A potential explanation for the differentiation in porosity between the samples in Figure 4A−E is based on (A) the rate at which gases desorbed, and (B) the ability of these desorbed gases to be trapped in the prepared sample instead of escaping to the atmosphere. Figure 4A illustrates the presence of pores throughout the imaged sample area; however, these pores are randomly scattered throughout the area, whereas Figure 4B shows pores that are more distributed throughout the sample area. As the heating rate increased, the number of pores in the imaged areas qualitatively decreased, therefore demonstrating the increased rate of gases produced from the decomposition of Dextran and fewer gas molecules being trapped in the prepared sample. One potential explanation is that increased heating rates (10 °C·min−1) decomposed the Dextran faster thereby desorbing the gases from the gel sample at a greater rate. As the gases were desorbed faster, the Dextran became nonexistent after a short time since the sample was brought to 500 °C in a shorter time than one experiencing a slower heating rate.

Therefore, the increased heating rate sample was unable to trap the gas bubbles at a high production rate, thereby leading to a sample without significant pores in the imaging analysis. Additional support for the heating rate discussion is in the N2 adsorption data based on pore volumes obtained for the individual samples. The data suggest that a relatively low heating rate of 1 °C·min−1 produced the greatest pore volume of 0.413 mL/g. The explanation for this ocurrence not only originates from the rate at which gaseous bubbles are produced, but also from bubble coalescence during the calcination heat treatment. For example, one inference is that the lowest and highest heating rates did not produce the greatest pore volumes since the gas bubbles being produced did not have the opportunity to coalesce or form larger bubbles with others nearby. Table 2 demonstrates this occurrence as the pore volumes obtained between the lower heating rates 0.5 °C·min−1 and 1 °C·min−1 illustrate a significant increase in pore volumes with heating rate (0.124 mL/g and 0.413 mL/g). However, the pore volume of 0.413 mL/g generally decreases thereafter with increasingly applied heating rate demonstrating the interaction between bubbles to form larger voids in the sample becoming less likely. Another potential explanation for the porosity of the samples in Figure 4A−E is in the additional experiments completed in Figure 5A,B, where the isothermal segment at 500 °C was varied. Figure 5A,B suggests that the isothermal segment at 500 °C impacts the porosity of the sample obtained, postcalcination treatment. Moreover, the isothermal segment allows the pores to develop and gases to slowly dissipate from the sample. Figure 5A justifies this claim as little or no pores are qualitatively observed in the sample when no isothermal segment was applied. However, Figure 5B demonstrates the presence of some pores in the sample, justifying that gases were present, but the amount of time at 500 °C was too elongated. A potential explanation for this was that a narrow and particular time segment is granted for gases to be soluble and preserved in the prepared aqueous gel. This observation could also be related to the viscosity of the gel and potentially, related to the concentration of Dextran used in the synthesis.41 H


Article

Inorganic Chemistry The N2 adsorption data in Table 3 support the observations made in the variable isothermal segment analyses. Table 3 suggests several potential hypotheses why the pore volume varies with respect to the time duration at which the sample is held isothermally at 500 °C. One potential explanation is that the gas in the prepared sample over time dissipates out of the sample. A factor affecting the diffusion of gas through the sample may be the relatively low viscosity of the prepared Mn(NO3)2·4H2O/ Dextran gel, which was unable to preserve the gas bubbles in the sample. Additionally, bubble coalescence, or the joining of two or more bubbles to form a larger bubble could have a narrow time frame in which this event would occur. Evidence of the diversity of oxidation states and redox behavior present in the prepared Mn2O3/Mn3O4 sample was observed by CV analysis. The CV analysis suggests that a quasireversible redox transition (peaks A and E) could lead the reader to understand that the Mn2+ ↔ Mn3+ redox transition had occurred. Additionally, redox peaks at B and D also indicate that high oxidation states of manganese (4+, 6+) could potentially be observed. However, these species are quite acidic relative to Mn2+ and Mn3+, which as a result would react very strongly in the basic medium prepared for this experiment. This could lead to a possible reason why the peaks observed at B and D are quasireversible in the CV analysis. The catalytic data present an application of the prepared Mn2O3/Mn3O4 sponges investigated in this study. The mechanism for the conversion of alcohols to a variety of functional groups and driving forces for N−C coupling reactions has previously been demonstrated in the literature.59−61 The presented data show that the Mn2O3/Mn3O4 and 5 mol %−FeMn2O3/Mn3O4 perform the catalytic reaction. Potential explanations for the activity in this material toward the present catalytic reaction are that (1) large mesopores-macropores are present and (2) the mixed phase nature of catalyst provides Mn2+ and Mn3+ both playing an essential role in driving oxidation reaction.

■

AUTHOR INFORMATION

Corresponding Author

*Fax: +1 860 486 2981. Tel: +1 860 486 2797. E-mail: steven. [email protected]. ORCID

Ehsan Moharreri: 0000-0002-3585-2962 Steven L. Suib: 0000-0003-3073-311X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical, Biological, and Geological Sciences under Grant DE-FGO286ER13622.A000. The authors would like to acknowledge the Institute of Materials Science (IMS) for financial support for this research along with the use of the Bioscience Electron Microscopy Laboratory of the University of Connecticut (UConn) and use of FEI Nova NanoSEM 450 and Oxford EDS purchased through NSF Grant No. 1126100. Additionally, S.L.S. would like to acknowledge that HR-TEM studies were performed using the facilities in the UConn/Thermo Fisher Scientific Center for Advanced Microscopy and Materials Analysis (CAMMA). The authors would like to thank Dr. Wubin Sui (Zaozhuang University, Department of Chemistry and Chemical Engineering) and Dr. Caterina Riccardi (Dr. Kumar’s research group at UConn) for helpful discussions regarding the characterization and catalytic application of the prepared Mn2O3/Mn3O4 sponge in this study.

■

5. CONCLUSIONS The catalyst synthesis design factors such as heating rate and isothermal segment during the preparation of mixed crystallographic phase Mn2O3/Mn3O4 were successfully investigated. The control of these factors during the synthesis procedure proved to impact the surface and material properties (surface area, pore size, and pore volume) along with the general morphology of the prepared metal oxide sponge. Unlike previous literature that report a heating rate of 5 °C·min−1, our analysis demonstrated that the sponge prepared at a 1 °C·min−1 heating rate with an isothermal segment of 1 h produced a welldistributed porous material, most representative of a sponge. Additionally, the material prepared exemplified unique porosity including large pore size (25.5 nm) and large pore volume (0.413 mL/g) unlike previously reported MnOx samples in the literature (Table 1). The material was then utilized toward the oxidation of 1-octanol and amines (aniline and benzylamine) to demonstrate its ability to catalyze this organic reaction.

■

Thermogravimetric analysis (TGA) and temperatureprogrammed desorption-mass spectrometry (TPD-MS) measurements of Dextran (PDF)

REFERENCES

(1) Guo, S.; Sun, W.; Yang, W.; Xu, Z.; Li, Q.; Shang, J. K. Synthesis of Mn3O4/CeO2 Hybrid Nanotubes and Their Spontaneous Formation of a Paper-Like, Free-Standing Membrane for the Removal of Arsenite from Water. ACS Appl. Mater. Interfaces 2015, 7, 26291−26300. (2) Bai, Z.; Sun, B.; Fan, N.; Ju, Z.; Li, M.; Xu, L.; Qian, Y. Branched Mesoporous Mn3O4 Nanorods: Facile Synthesis and Catalysis in the Degradation of Methylene Blue. Chem. - Eur. J. 2012, 18, 5319−5324. (3) Luo, Y.; Fan, S.; Hao, N.; Zhong, S.; Liu, W. An UltrasoundAssisted Approach to Synthesize Mn3O4/RGO Hybrids with High Capability for Lithium Ion Batteries. Dalt. Trans. 2014, 43, 15317− 15320. (4) Lee, J. W.; Hall, A. S.; Kim, J.-D.; Mallouk, T. E. A Facile and Template-Free Hydrothermal Synthesis of Mn3O4 Nanorods on Graphene Sheets for Supercapacitor Electrodes with Long Cycle Stability. Chem. Mater. 2012, 24, 1158−1164. (5) Bag, S.; Roy, K.; Gopinath, C. S.; Raj, C. R. Facile Single-Step Synthesis of Nitrogen-Doped Reduced Graphene Oxide-Mn3O4 Hybrid Functional Material for the Electrocatalytic Reduction of Oxygen. ACS Appl. Mater. Interfaces 2014, 6, 2692−2699. (6) Luo, Z.; Irtem, E.; Ibáñez, M.; Nafria, R.; Martí-Sánchez, S.; Genç, A.; de la Mata, M.; Liu, Y.; Cadavid, D.; Llorca, J.; et al. Mn3O4 @ CoMn2O4−CoXOY Nanoparticles: Partial Cation Exchange Synthesis and Electrocatalytic Properties toward the Oxygen Reduction and Evolution Reactions. ACS Appl. Mater. Interfaces 2016, 8, 17435−17444. (7) Ramírez, A.; Hillebrand, P.; Stellmach, D.; May, M. M.; Bogdanoff, P.; Fiechter, S. Evaluation of MnOX, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of Water. J. Phys. Chem. C 2014, 118, 14073−14081.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00613. I


Article

Inorganic Chemistry (8) Chen, Z.; Jiao, Z.; Pan, D.; Li, Z.; Wu, M.; Shek, C.; Wu, C. M. L.; Lai, J. K. L. Recent Advances in Manganese Oxide Nanocrystals: Fabrication, Characterization, and Microstructure. Chem. Rev. 2012, 112, 3833−3855. (9) O’Neill, H. S. C.; Navrotsky, A. Simple Spinels: Crystallographic Parameters, Catio Radii, Lattice Energies, and Cation Distribution. Am. Mineral. 1983, 68, 181−194. (10) Sickafus, K. E.; Wills, J. M.; Grimes, N. W. Structure of Spinel. J. Am. Ceram. Soc. 1999, 82, 3279−3292. (11) Koza, J. A.; Schroen, I. P.; Willmering, M. M.; Switzer, J. A. Electrochemical Synthesis and Nonvolatile Resistance Switching of Mn3O4 Thin Films. Chem. Mater. 2014, 26, 4425−4432. (12) Tian, Z.-Y.; Mountapmbeme Kouotou, P.; Bahlawane, N.; Tchoua Ngamou, P. H. Synthesis of the Catalytically Active Mn3O4 Spinel and Its Thermal Properties. J. Phys. Chem. C 2013, 117, 6218− 6224. (13) Zhou, L.; He, J.; Zhang, J.; He, Z.; Hu, Y.; Zhang, C.; He, H. Facile In-Situ Synthesis of Manganese Dioxide Nanosheets on Cellulose Fibers and Their Application in Oxidative Decomposition of Formaldehyde. J. Phys. Chem. C 2011, 115, 16873−16878. (14) Ching, S.; Roark, J. L.; Duan, N.; Suib, S. L. Sol−Gel Route to the Tunneled Manganese Oxide Cryptomelane. Chem. Mater. 1997, 9, 750−754. (15) Ching, S.; Petrovay, D. J.; Jorgensen, M. L.; Suib, S. L. Sol−Gel Synthesis of Layered Birnessite-Type Manganese Oxides. Inorg. Chem. 1997, 36, 883−890. (16) Brock, S. L.; Duan, N.; Tian, Z. R.; Giraldo, O.; Zhou, H.; Suib, S. L. A Review of Porous Manganese Oxide Materials. Chem. Mater. 1998, 10, 2619−2628. (17) Qiao, L.; Swihart, M. T. Solution-Phase Synthesis of Transition Metal Oxide Nanocrystals: Morphologies, Formulae, and Mechanisms. Adv. Colloid Interface Sci. 2017, 244, 199−266. (18) Moharreri, E.; Hines, W. A.; Biswas, S.; Perry, D. M.; He, J.; Murray-Simmons, D.; Suib, S. L. Comprehensive Magnetic Study of Nanostructured Mesoporous Manganese Oxide Materials and Implications for Catalytic Behavior. Chem. Mater. 2018, 30, 1164−1177. (19) Banhart, J. Light-Metal Foams-History of Innovation and Technological Challenges. Adv. Eng. Mater. 2013, 15, 82−111. (20) Jiang, B.; He, C.; Zhao, N.; Nash, P.; Shi, C.; Wang, Z. Ultralight Metal Foams. Sci. Rep. 2015, 5, 13825. (21) Zhou, Y.; Rui, X.; Sun, W.; Xu, Z.; Zhou, Y.; Ng, W. J.; Yan, Q.; Fong, E. Biochemistry-Enabled 3D Foams for Ultrafast Battery Cathodes. ACS Nano 2015, 9, 4628−4635. (22) Kundu, M.; Liu, L. Direct Growth of Mesoporous MnO 2 Nanosheet Arrays on Nickel Foam Current Collectors for HighPerformance Pseudocapacitors. J. Power Sources 2013, 243, 676−681. (23) Li, Y.; Cao, D.; Wang, Y.; Yang, S.; Zhang, D.; Ye, K.; Cheng, K.; Yin, J.; Wang, G.; Xu, Y. Hydrothermal Deposition of Manganese Dioxide Nanosheets on Electrodeposited Graphene Covered Nickel Foam as a High-Performance Electrode for Supercapacitors. J. Power Sources 2015, 279, 138−145. (24) He, S.; Chen, W. High Performance Supercapacitors Based on Three-Dimensional Ultralight Flexible Manganese Oxide Nanosheets/ carbon Foam Composites. J. Power Sources 2014, 262, 391−400. (25) Huang, M.; Zhao, X. L.; Li, F.; Zhang, L. L.; Zhang, Y. X. Facile Synthesis of Ultrathin Manganese Dioxide Nanosheets Arrays on Nickel Foam as Advanced Binder-Free Supercapacitor Electrodes. J. Power Sources 2015, 277, 36−43. (26) Xu, P.; Ye, K.; Cao, D.; Huang, J.; Liu, T.; Cheng, K.; Yin, J.; Wang, G. Facile Synthesis of Cobalt Manganese Oxides Nanowires on Nickel Foam with Superior Electrochemical Performance. J. Power Sources 2014, 268, 204−211. (27) Baktash, E.; Zaharieva, I.; Schröder, M.; Goebel, C.; Dau, H.; Thomas, A. Cyanamide Route to Calcium−manganese Oxide Foams for Water Oxidation. Dalt. Trans. 2013, 42, 16920. (28) Lu, K.; Xu, J.; Zhang, J.; Song, B.; Ma, H. General Preparation of Three-Dimensional Porous Metal Oxide Foams Coated with NitrogenDoped Carbon for Enhanced Lithium Storage. ACS Appl. Mater. Interfaces 2016, 8, 17402−17408.

(29) Banhart, J. Manufacture, Characterisation and Application of Cellular Metals and Metal Foams. Prog. Mater. Sci. 2001, 46, 559−632. (30) Chen, W.; Rakhi, R. B.; Hu, L.; Xie, X.; Cui, Y.; Alshareef, H. N. High-Performance Nanostructured Supercapacitors on a Sponge. Nano Lett. 2011, 11, 5165−5172. (31) Dubal, D. P.; Holze, R.; Gomez-Romero, P. Development of Hybrid Materials Based on Sponge Supported Reduced Graphene Oxide and Transition Metal Hydroxides for Hybrid Energy Storage Devices. Sci. Rep. 2015, 4, 7349. (32) Chabot, V.; Higgins, D.; Yu, A.; Xiao, X.; Chen, Z.; Zhang, J. A Review of Graphene and Graphene Oxide Sponge: Material Synthesis and Applications to Energy and the Environment. Energy Environ. Sci. 2014, 7, 1564. (33) Wang, L.; Asheim, K.; Vullum, P. E.; Svensson, A. M.; VullumBruer, F. Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries. Chem. Mater. 2016, 28, 6459−6470. (34) Liu, Z.; Wu, D.; Guo, X.; Fang, S.; Wang, L.; Xing, Y.; Suib, S. L. Robust Macroscopic 3D Sponges of Manganese Oxide Molecular Sieves. Chem. - Eur. J. 2017, 23, 16213−16218. (35) Walsh, D.; Wimbush, S. C.; Hall, S. R. Use of the Polysaccharide Dextran as a Morphological Directing Agent in the Synthesis of HighTc Superconducting YBa2Cu3O7‑δ Sponges with Improved Critical Current Densities. Chem. Mater. 2007, 19, 647−649. (36) Su, B.-L.; Vantomme, A.; Surahy, L.; Pirard, R.; Pirard, J.-P. Hierarchical Multimodal Mesoporous Carbon Materials with Parallel Macrochannels. Chem. Mater. 2007, 19, 3325−3333. (37) Walsh, D.; Arcelli, L.; Ikoma, T.; Tanaka, J.; Mann, S. Dextran Templating for the Synthesis of Metallic and Metal Oxide Sponges. Nat. Mater. 2003, 2, 386−390. (38) Cai, J.; Liu, J.; Willis, W. S.; Suib, S. L. Framework Doping of Iron in Tunnel Structure Cryptomelane. Chem. Mater. 2001, 13, 2413−2422. (39) Carrillo, A. J.; Serrano, D. P.; Pizarro, P.; Coronado, J. M. Improving the Thermochemical Energy Storage Performance of the Mn2O3 /Mn3O4 Redox Couple by the Incorporation of Iron. ChemSusChem 2015, 8, 1947−1954. (40) De Vuyst, L. Heteropolysaccharides from Lactic Acid Bacteria. FEMS Microbiol. Rev. 1999, 23, 153−177. (41) Figgs, G. P. Dextran: Chemical Structure, Applications and Potential Side Effects; Nova Publishers: New York, NY, 2014. (42) Meguerdichian, A. G.; Jafari, T.; Shakil, M. R.; Miao, R.; Achola, L. A.; Macharia, J.; Shirazi-Amin, A.; Suib, S. L. Synthesis and Electrocatalytic Activity of Ammonium Nickel Phosphate, [NH4]NiPO4 ·6H2O, and β-Nickel Pyrophosphate, β-Ni2P2O7: Catalysts for Electrocatalytic Decomposition of Urea. Inorg. Chem. 2018, 57, 1815−1823. (43) Gibson, L. J.; Ashby, M. F. Cellular Solids: Structure and Properties; 2nd ed.; Cambridge University Press: Cambridge, U.K., 1997. (44) Wang, Y.; Cui, J.; Luo, L.; Zhang, J.; Wang, Y.; Qin, Y.; Zhang, Y.; Shu, X.; Lv, J.; Wu, Y. One-Pot Synthesis of NiO/Mn2O3 Nanoflake Arrays and Their Application in Electrochemical Biosensing. Appl. Surf. Sci. 2017, 423, 1182−1187. (45) Moses Ezhil Raj, A.; Victoria, S. G.; Jothy, V. B.; Ravidhas, C.; Wollschläger, J.; Suendorf, M.; Neumann, M.; Jayachandran, M.; Sanjeeviraja, C. XRD and XPS Characterization of Mixed Valence Mn3O4 Hausmannite Thin Films Prepared by Chemical Spray Pyrolysis Technique. Appl. Surf. Sci. 2010, 256, 2920−2926. (46) Wang, W.; Geng, J.; Kuai, L.; Li, M.; Geng, B. Porous Mn2O3: A Low-Cost Electrocatalyst for Oxygen Reduction Reaction in Alkaline Media with Comparable Activity to Pt/C. Chem. - Eur. J. 2016, 22, 9909−9913. (47) Li, Y.; Wan, Y.; Li, Y.; Zhan, S.; Guan, Q.; Tian, Y. LowTemperature Selective Catalytic Reduction of NO with NH3 over Mn2O3-Doped Fe2O3 Hexagonal Microsheets. ACS Appl. Mater. Interfaces 2016, 8, 5224−5233. (48) Li, Z.-Y.; Shaheer Akhtar, M.; Bui, P. T. M.; Yang, O.-B Predominance of Two Dimensional (2D) Mn2O3 Nanowalls Thin Film for High Performance Electrochemical Supercapacitors. Chem. Eng. J. 2017, 330, 1240−1247. J


Article

Inorganic Chemistry (49) Li, Y.; Qu, J.; Gao, F.; Lv, S.; Shi, L.; He, C.; Sun, J. In Situ Fabrication of Mn3O4 Decorated Graphene Oxide as a Synergistic Catalyst for Degradation of Methylene Blue. Appl. Catal., B 2015, 162, 268−274. (50) Genuino, H. C.; Meng, Y.; Horvath, D. T.; Kuo, C.-H.; Seraji, M. S.; Morey, A. M.; Joesten, R. L.; Suib, S. L. Enhancement of Catalytic Activities of octahedral Molecular Sieve Manganese Oxide for Total and Preferential CO Oxidation through Vanadium Ion Framework Substitution. ChemCatChem 2013, 5, 2306−2317. (51) Dyrek, K.; Che, M. EPR as a Tool To Investigate the Transition Metal Chemistry on Oxide Surfaces. Chem. Rev. 1997, 97, 305−332. (52) Kalapsazova, M.; Ivanova, S.; Kukeva, R.; Simova, S.; Wegner, S.; Zhecheva, E.; Stoyanova, R. Combined Use of EPR and 23Na MAS NMR Spectroscopy for Assessing the Properties of the Mixed Cobalt− nickel−manganese Layers of P3-NaYCo1−2XNiXMnXO2. Phys. Chem. Chem. Phys. 2017, 19, 27065−27073. (53) Duan, L.; Sun, B.; Wei, M.; Luo, S.; Pan, F.; Xu, A.; Li, X. Catalytic Degradation of Acid Orange 7 by Manganese Oxide octahedral Molecular Sieves with Peroxymonosulfate under Visible Light Irradiation. J. Hazard. Mater. 2015, 285, 356−365. (54) de Groot, M. T.; Koper, M. T. M. Redox Transitions of Chromium, Manganese, Iron, Cobalt and Nickel Protoporphyrins in Aqueous Solution. Phys. Chem. Chem. Phys. 2008, 10, 1023−1031. (55) Gorlin, Y.; Jaramillo, T. F. Investigation of Surface Oxidation Processes on Manganese Oxide Electrocatalysts Using Electrochemical Methods and Ex Situ X-Ray Photoelectron Spectroscopy. J. Electrochem. Soc. 2012, 159, H782−H786. (56) Poyraz, A. S.; Kuo, C.-H.; Biswas, S.; King’ondu, C. K.; Suib, S. L. A General Approach to Crystalline and Monomodal Pore Size Mesoporous Materials. Nat. Commun. 2013, 4, 2952. (57) Ishii, Y.; Nishiwaki, Y.; Al-zubaidi, A.; Kawasaki, S. Pore Size Determination in Ordered Mesoporous Materials Using Powder X-Ray Diffraction. J. Phys. Chem. C 2013, 117, 18120−18130. (58) Chapter 2: Thermal Expansion. In ASM Ready Reference: Thermal Properties of Metals; Cverna, F., Ed.; ASM International: Materials Park, OH, 2002; p 9. (59) Biswas, S.; Mullick, K.; Chen, S.-Y.; Gudz, A.; Carr, D. M.; Mendoza, C.; Angeles-Boza, A. M.; Suib, S. L. Facile Access to Versatile Functional Groups from Alcohol by Single Multifunctional Reusable Catalyst. Appl. Catal., B 2017, 203, 607−614. (60) Mukherjee, A.; Angeles-Boza, A. M.; Huff, G. S.; Roth, J. P. Catalytic Mechanism of a Heme and Tyrosyl Radical-Containing Fatty Acid α-(Di)oxygenase. J. Am. Chem. Soc. 2011, 133, 227−238. (61) Biswas, S.; Dutta, B.; Mullick, K.; Kuo, C.-H.; Poyraz, A. S.; Suib, S. L. Aerobic Oxidation of Amines to Imines by Cesium-Promoted Mesoporous Manganese Oxide. ACS Catal. 2015, 5, 4394−4403. (62) Peng, L.; Zhang, J.; Xue, Z.; Han, B.; Li, J.; Yang, G. Large-Pore Mesoporous Mn3O4 Crystals Derived from Metal−organic Frameworks. Chem. Commun. 2013, 49, 11695. (63) Bai, Z.; Fan, N.; Ju, Z.; Guo, C.; Qian, Y.; Tang, B.; Xiong, S. Facile Synthesis of Mesoporous Mn3O4 Nanotubes and Their Excellent Performance for Lithium-Ion Batteries. J. Mater. Chem. A 2013, 1, 10985.

K


Synthesis of Large MesoporousâMacroporous and High Pore Volume

Recommend Documents

Synthesis of Large MesoporousâMacroporous and High Pore Volume