Strategy for Multifunctional Hollow Shelled Triple Oxide MnâCuâAl

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Strategy for multifunctional hollow shelled triple oxide Mn-CuAl nanocomposite synthesis via microwave-assisted technique Nivedhini Iswarya Chandrasekaran, Meena Kumari, Harshiny Muthukumar, and Matheswaran Manickam ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03339 • Publication Date (Web): 21 Nov 2017 Downloaded from http://pubs.acs.org on November 22, 2017

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ACS Sustainable Chemistry & Engineering

Strategy for multifunctional hollow shelled triple oxide Mn-Cu-Al nanocomposite synthesis via microwave-assisted technique Nivedhini Iswarya Chandrasekaran, Meena Kumari, Harshiny Muthukumar, Manickam Matheswaran* Department of Chemical Engineering, National Institute of Technology, Tiruchirappalli, India-620015 * Corresponding author email ID: [email protected] Tel: +91-431-2503120 Fax: + 91-431-2500133

Abstract A facile route for assembling a hollow shelled triple Mn-Cu-Al oxide nanomaterials (HMCA) using the microwave-assisted reduction technique is demonstrated, the energy and environmental applications such as supercapacitor and photocatalyst are investigated. During the reaction time, the MnO2, CuO and Al2O3 formed a shell layer over the core SiO2 and assembled as a hollow geometrical nanostructure with uniform size densely populated hairy outer appearance. We have shown the resultant HMCA exhibited the synergistic effects of nanocomposite and thereby revealed a distinctive collection of physical and chemical properties such as improved electrochemical capacitive performance capacities, enhanced photocatalytic activities, and increased adsorption. These features collectively confirmed the potential of HMCA as an attractive material for resourceful applications in environmental and energy storage issues.

Keyword: Hollow shell nanostructure, Photocatalyst, Supercapacitor, Mn-Cu-Al oxide, Indigo carmine.

Introduction As a distinctive class of functional materials, hollow nano/microstructures have attracted immense interest for their structural description and huge potential in multitude applications including drug delivery, catalysis, adsorption and energy storage and conversion systems. Recently, many functional materials have successfully engineered into hollow structures with varied morphologies such as hollow spheres, polyhedron and tubes. However, most of the reported hollow structures are constructed by single shell component with one composition that limits the chances for adjusting the properties. In itself, it is highly enviable to design hollow structures with complexity, such as several shells or compositions. Many theoretical and experimental efforts have been initiated by developing hollow metal oxide nanomaterials with several compositions for the reduced charge and mass

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transfer transportation length1. Various metal oxides such as MnO2, CuxO, Al2O3, ZnO, and TiO2 play different roles due to the abundant availability, environmental pollution free, economic and eco-friendly in nature2–5. The transition metal oxides with narrow band gap have proved to be an adaptable material for catalyst application. Manganese oxides are a guaranteed candidate for various applications like pseudocapacitor, catalyst and sensor because of its low cost, high surface area, good chemical stability, strong oxidizing ability and excellent charge storage capacity6. Copper oxide nanomaterial possesses lower surface potential barrier than in its metallic state, which affects electron field emission properties. Accordingly, it finds application as a potential field emitter, an efficient catalytic agent, as well as good gas sensing materials7. By simultaneously taking the advantages of both MnO2 and CuO, composite nanostructure with high porous structure has used as a perfect material for the catalytic purpose. Nevertheless, this kind of composition is seriously suffers from recombination effects. In order to overcome the drawback, another material has effectively used to trap the electrons efficiently. Aluminium oxide performs a vibrant part in several fields as a catalyst or a catalyst carrier by the virtue of excellent properties such as high thermal stability, resistance to corrosion and so on8. Hence, the advancement of the catalytic application by using such composite is highly desirable. Combinations of these metal and metal oxides have been studied for different applications and processes such as electrochemical energy storage device9, dye-sensitized solar cell10, catalyst11, drug delivery, imaging12, biomedical application13etc. Larsson et al. have found that the CuMn2O4/Al2O3 shows excellent catalytic properties for ethanol oxidation14. Photocatalyst role is to remove pollutant from water using solar energy. Nature of photocatalyst should be nontoxic, easily separable, low cost, environmental friendly and stability. Recently many hollow complex composite catalyst has been prepared successfully for application of photodegradation15,16. However, there are some problems with these hollow composite materials including (1) high recombination rate, (2) low surface area and (3) poor mass diffusions. Hence, it is necessary to scrutinize a hollow shelled triple oxide structure with modified optical, textural and electrical properties to endorse the photocatalytic behavior. Supercapacitor, an energy storage device possesses long cycle life, fast chargedischarge rate, high power capability and low maintenance cost. Apart from the assistance, it also has less environmental impact than batteries. The specific capacitance of supercapacitors depends on electrode material, particularly pseudocapacitor materials based on redox behavior affords high specific capacitance. Hollow nanostructures electrodes with a single ACS Paragon Plus Environment

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material include many drawbacks like low density, high surface-volume ratio and tunable structure with large void space, etc. In spite of incorporating multi advantages, the composite material should chosen to obtain hollow nanocomposite. Till date, plentiful novel hollow nanocomposite has been developed using various synthesizing procedures for energy storage application17–19. Specifically, the approach based on microwave-assisted technique is very powerful and has been well developed20,21. Microwave-assisted synthesis is a fast, facile and quiet energy saving technique to generate nanomaterials22. Moreover, the reaction time is very less and delivers a controlled particle size distribution and its dispersion. In this work, a hollow shelled triple Mn-Cu-Al oxide (HMCA) material has prepared by microwave-assisted successive reduction method. The physiochemical characterizations of nanoparticles (NPs) such as size, shape, surface area and band energy are analyzed. These HMCA were used as electrodes of supercapacitors. The specific capacitance of the symmetric supercapacitor is 131.7 Fg-1 at a current density of 0.5 Ag-1. The photodegradation of Indigo carmine (IC) was also performed. As-synthesized HMCA exhibits high surface area, the appropriate band gap that is more useful for photodegradation of IC. Moreover, the used catalyst is successfully recovered and reused for five more times without loss in selectivity. The effect of different operating conditions such as catalyst loading, initial pH, and initial concentration of IC on degradation efficiency is studied. To our knowledge, this work first report on the triple oxide hollow structure in the combination of MnO2, CuO, and Al2O3 for supercapacitor and photodegradation process.

Experimental section Preparation of hollow shelled triple oxide photocatalyst Silica nanoparticles were prepared using modified Stober method

23

by hydrolysis of

TEOS in presence of CTAB for about 2 hours in the solution comprised of water, ethanol and ammonia maintained at room temperature with pH 11. The obtained precipitate was separated from the solution by centrifuging and washed with ethanol; finally dried at 50oC for 4h. Silica sol was prepared by dispersing 0.5 g of the prepared SiO2 NPs in 250 mL of Millipore water using ultrasonicator (20 min, room temperature). Whereas SiO2@MnO2 (SM) was prepared by treating the silica sol with MnSO4.H2O (0.05M) and Urea (0.015M) in a programmable microwave oven (MJ3286BFUM, LG Co., Ltd.). The oven was heated to 120oC for 5 min by microwave irradiation and kept at the same temperature for 1 h. The obtained precipitate was centrifuged and washed with ethanol followed by furnace treatment for about 2 h maintained 200oC. Further, SiO2@MnO2@CuO (SMC) Sol was treated in the microwave with 0.05 M of



Cu(NO3)2.3H2O and 0.015 M of urea followed by centrifugation and drying process. Finally, HMCA NPs were obtained by treating SMC sol with Al(NO3)2.9H2O salt (0.01 M) and urea (0.015 M) in the microwave, and the final products were collected at the same condition as mentioned previously.

Results and discussion Formation mechanism of Mn-Cu-Al nanocomposite The core SiO2 has synthesized in the normal room temperature by following modified Stober method. Size and shape of the core have been controlled by using CTAB, a stabilizing agent. Slow hydrolysis of urea leads to the formation of OH- and CO32-. First, the nascent precursor Mn2+ attached to the surface of SiO2, form a coordination compound with the hydroxyl group generated from hydrolysis of urea. As a result, MnO2 form a shell layer over core SiO2. Further, the introduction of Cu2+ ions made it to adsorb on the surface of SiO2@MnO2 owing to the electrostatic interaction between oxides and metal cations. These Cu2+ ions will combine with OH ions from hydrolysis of urea to form Cu(OH)2 and HNO3. The dehydration of Cu(OH)2 results in formation of CuO on SiO2@MnO2. In addition, Al3+ ions from Al(NO3)3 forms a complex conjugate with CuO results in formation of Al2O3. In this formation procedure, successive treatment with urea provides the alkaline environment, which favors for dissolution of core SiO2. Finally, hollow nanostructures have been achieved with triple oxide materials24,25. Core: + + → Shell: + + . + → @ @ + + . 3 + → @ @ @ @ + + . 9 + → @ @ @ Intermediate reaction: . → + + 3 + 6 → [ ] + 3 [ ] + 2 → + 2 → + 2 + → @


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Characterization part To determine the chemical composition and crystalline phase of the nanostructure, XRD analysis has performed and shown in Fig.1(a). The spectrum of S provides the sharp amorphous peak at 21.70, indicates the uniformity of SiO2 nanospheres. All diffraction peaks in SM (29.960 (220), 36.940 (222), 56.780 (511), 73.650 (533)) other than 21.7 0 denotes the cubic structure of MnO2 belongs to JCPDS No: 13-0162)26. Further, the peaks present in the spectrum of SMC at 49.120 (-202), 66.310 (022) and 68.380 (220) in addition to the previous peaks corresponds to the monoclinic system matching with the JCPDS.No: 01-111727. This result indicates the formation of CuO and the presence of additional peaks with reduced intensity proves that CuO layer forms an outer layer over MnO2. Finally, the XRD spectrum of HMCA has specific peaks at 25.560 (012), 37.250 (110), 45.710 (202) corresponds to the rhombohedral system matches with Al2O3 of JCPDS.No: 77-2135. This result indicates the nanostructures are formed in a pattern of core-shell-shell type. In the final product, this core disappeared completely. The FT-IR spectra of S, SM, SMC and HMCA vibrations have clearly shown in (Fig.1(b)). The Spectrum of S shows the characteristic vibrations at 1045, 789 and 542 cm-1 corresponds to Si–O–Si, Si–O and O–Si–O bonds respectively28. Whereas vibrations occurred at 962 and 1,645 cm-1 have been contributed by stretching of non-bridging oxygen atoms present in unreacted Si–OH group and weak bending vibration of H–O–H due to moisture. The wave numbers 2923 cm-1 and 1479 cm-1 shows the head and tail group vibrations of CTAB29. After successive coating over S, the characteristic vibration intensity of SiO2 (1045 and 789 cm-1) and CTAB (1479 cm-1) decreases in SM and SMC are shown clearly in Fig.1(b). Whereas this vibration is absent in HMCA once again proves the disintegration of core SiO2. N2 adsorption and desorption were conducted to describe the specific surface area and porous nature of the prepared nanostructure. Fig.1(c) demonstrates the N2 adsorptiondesorption isotherms and the respective pore size distribution of all samples. It matches with the type-II isotherm and H4 type hysteresis loop. The calculated specific surface area was about 24.125 m2g-1, 94.298 m2g-1, 201.84 m2g-1 and 310.369 m2g-1 for S, SM, SMC, and HMCA respectively. The pore size distribution obtained from Barrett-Joyner-Halenda (BJH) method for HMCA has shown in inset of Fig. 1(c) indicates the average pore width of 10.2 nm and pore volume of 0.41960 cm³g-1 of HMCA. The results clearly depict that the mesopores will stimulate the fast diffusion of reactant and products during the photocatalytic



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reaction. The increase in surface area is believed to increase the catalytic activity of the nanoparticles. The recombination rate of electron-hole pair generated during photoirradiation can be studied from the photoluminescence (PL) spectrum. Fig.1(d) provides the PL spectrum of S, SM, SMC, and HMCA respectively. When samples are excited at 230 nm, the intense near edge band emission peak appears at 237 nm for S sample. This peak is absent in SM, SMC, HMCA. Whereas the intensity of emission peaks seen at 273 nm and 282 nm follows the sequence of S > SM > SMC > HMCA respectively. Pure SiO2 shows the maximum intensity means a high recombination rate. In HMCA, the PL intensity is suppressed very much while comparing other S, SM, SMC catalyst. This reduced PL intensity shows the suppressed recombination rate, results in high photocatalytic nature. This reduced recombination rate reveals the better charge transfer nature of HMCA catalyst30. Means, the catalyst supports for the

formation

of

more

hydroxyl

radicals,

which

are

very

advantageous

for

photodegradation31. The near band edge emission peak of SiO2 is absence in HMCA catalyst once again proves the hollow nature. The morphology of the prepared nanostructure of S, SM, SMC and HMCA has shown in Fig.2(a-d). The micrograph clearly shows that the prepared particles are non-agglomerated, monodisperse and uniformity in appearance. Observing from S to HMCA NPs, the surface smoothness is reduced, and relatively the hairy like appearance increases on its surface, this modification is because of the subsequent coating at various stages. In addition, the core size had been decreasing from S to SMC. Finally, the core was completely disappeared in HMCA shown clearly in fig.2(e), which forms a hollow shelled appearance. This unique design with hairy appearance and hollow structure plays a vibrant role in adsorption as well as the photocatalytic degradation. The obtained EDS spectrum of the HMCA material has shown in Fig.2(f) provides the elemental composition details. The peaks shown in the spectrum corresponds to the element O, Mn, Al, Cu, respectively. Table.S1 (seen in supporting information) provides the weight and atomic percentage of the individual element present in the materials. High crystalline region (shell) and low crystalline region (hairy morphology) with the clear interface are observed in the HRTEM images (Figs. 2(g)). It possesses lattice distance of 0.47 nm (Fig.2(h)) which corresponds to (1 1 0) plane of the Al2O3. The selected area electron diffraction (SAED) pattern (Fig.2(i)) of a hollow nanocomposite material is well indexed to the monoclinic system of CuO that matches with the JCPDF no: 01-1117. Fig.2(j) provides the multi-elemental EDS mapping of a Mn, O, Cu and Al respectively. Apparently, the map corresponds to Mn, O and Cu confirmed the bright spots, resultant of ACS Paragon Plus Environment

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uniform distribution of the elements form shell layers. The mapping result is consistent with the EDS spectrum shown in fig.2(f). XPS spectrum for HMCA NPs has shown in Fig. 3(a). The presence of Cu, Mn, O and Al are clearly visible in the wide spectrum. The peak at 1096, 770 and 84 are contributed by Cu 2s, Mn 2s, and Mn 3s respectively. The high-resolution XPS spectrum (Fig 3(b)) shows the presence of broad peaks around 934.7 eV and 952 eV corresponds to Cu 2p 3/2 and Cu 2p 1/2, states, respectively presents in the typical spectrum of CuO. The detailed Spectrum of Al 2p shows the peak at 71.1 eV and 76.9 eV are owing to the presence of Al2O3 showed in Fig 3(c). The Mn 2p XPS spectrum (Fig 3(d)) exhibits peaks at 645.16 eV and 656.08 eV, corresponding to the Mn 2p 3/2 and Mn 2p 1/2 spin-orbit peaks of MnO2. While the peak position at 534.36 eV belongs to O1s has shown clearly in (inset of Fig.3 (a)). Performance studies of photocatalyst As a control experiment, the IC (60 ppm) degradation has been performed in photolysis (without a catalyst under Sunlight and UV light) and dark condition (with 7.5 mg/L of catalyst) maintained at pH 9 for 120 min (experimental details are given in supporting information). Fig.S1(a) (supporting information) depicts the IC degradation efficiency of photolysis process, which is very less when compared with a degradation profile of the dark condition process in presence of various catalysts. The IC degradation efficiency using photolysis processes is observed to be 6.12 % and 8.74 % respectively for 120 min in the presence of sunlight and UV light. Whereas in dark condition, the IC degradation efficiency of various catalysts (S, SM, SMC, HMCA) are 13.62 %, 21.912 %, 33.135 %, 46.08 % respectively. The increased IC degradation efficiency under the dark condition is owing to the adsorption nature of catalysis. The surface area of catalyst plays a major role in adsorption. Since adsorption is a function of surface area and directly proportional to it32. As seen in the chart, the order of degradation efficiency in dark condition for the different catalyst is HMCA > SMC > SM > S. The results once again prove the BET surface area calculated from N2 adsorption and desorption isotherms for the various catalyst. The photocatalytic degradation behavior of different catalyst (7.5 mg/L) in the presence of sunlight and UV light has been tested on IC (60 ppm) at pH 9 for 120 min. Fig. S1(b) (supporting information) clearly shows degradation behavior of HMCA is 95.729 %, 89.236 % respectively in the presence of sunlight and UV light. The photocatalytic degradation order of different catalyst is same as seen in dark condition. It is clearly noticeable that efficiency of the photocatalyst in presence of sunlight is higher when compared to UV light. Here in SMC and HMCA the presence of both MnO2 and CuO layer ACS Paragon Plus Environment


facilities the material to absorb UV as well as visible light. Therefore, the degradation percentage is high when compared to SM and S. Particularly; HMCA is a very active catalyst when compared to SMC. Because, the HMCA not only utilizes the broad energy of sunlight (UV and Visible) to excite an electron from the valence band to the conduction band in MnO2 and CuO layers, and also prevents the recombination rate due to the presence of Al2O3 layer. Since this Al2O3 facilitates many number electron to stay in the conduction band, such that dissolved oxygen in aqueous solution makes use of this electron for degrading IC33. Except the catalyst SM, all other catalyst works better in Sunlight when compared to UV light. This because the intensity of UV rays from Sunlight is less when compared to the intensity of UV light used for degradation purpose.34 Thus the MnO2 is very active in UV light since the band gap is 3.4 eV. For other catalysts, sunlight seems better because which provide a broad range of energy. Mainly the photocatalytic degradation of S is slightly higher when compared to the dark condition. Here the adsorption nature is predominantly high when compared with photocatalytic behavior. From this, we can conclude that the physicochemical property of HMCA enhances the formation of more number of hydroxyl radicals results in higher photocatalytic degradation efficiency. The effect of various parameters such as catalyst loading, initial pH, and IC concentrations in the presence of sunlight illumination is studied further to determine the degradation efficiency of HMCA. Photocatalyst mechanism. Fig.S2 (supporting information) provides the UV-VisNIR diffuse reflectance spectra of MnO2, CuO, Al2O3 and HMCA nanomaterials. For the purpose of understanding the light absorption property of nanoparticles seen in HMCA nanocomposites, nanoparticles (MnO2, CuO, Al2O3) were prepared by treating related precursor (0.05M) respectively with urea (0.015M) in the microwave (120oC, 1h). The HMCA nanocomposite possesses a broad range of absorption in both ultraviolet and visible region. Clearly, it was shown from the graph that the expanded absorption range of HMCA was due to MnO2 and CuO materials. To further analyse the photocatalytic mechanism, tauc plot (fig. 4(a)) was drawn for αℎν versus photon energy ℎν based on equation (1). αℎν = #ℎν − %&' ( → (1) where α, ν, h, %' , are absorption coefficient, light frequency, Plank’s constant, band gap of material and proportionality coefficient respectively35. The obtained band gap of MnO2, CuO, and Al2O3 is 2.13 eV, 1.72 eV and 4.8 eV respectively. By using equation (2) and (3), the valence band and conduction band edges of MnO2, CuO, Al2O3 are estimated.


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%*+ = χ − %, − 0.5%&' → (2) %/+ = χ − %, + 0.5%&' → (3) Where %*+ , %/+ are conduction band and valence band edges respectively. χ is the absolute electronegativity of the semiconductor oxide materials, calculated by taking geometric average of atoms in the compound. The electronegativity χ of MaXb compound is 3

determined by (χ10 χ2& 456 36. %, is the energy of free electron on hydrogen scale (4.5 eV). The conduction band and valence band edges of MnO2 are calculated as 0.385 eV and 2.515 eV, whereas for CuO, it is placed in 0.53 eV and 2.25 eV respectively. For Al2O3, the conduction band and valence band edges are positioned at 0.81 eV and 5.61 eV respectively as shown in fig.4(b). Type 1 heterojunction is seen between band structure of MnO2 and CuO. The possibilities of electron-hole recombination took place in this type 1 straddling heterojunction. To prevent this recombination, the electron is efficiently trapped by using Al2O3. Under illumination of light, the photogenerated electrons in MnO2 and CuO are excited from valence band to conduction band by leaving holes in the valence band. The photogenerated electrons transferred from MnO237 conduction band to CuO conduction band, likewise, the holes transfer taken place from the valence band of MnO2 to CuO valence band. Now the photoinduced electron and hole were enriched in conduction and valence band of CuO respectively. Further, the photogenerated electrons get trapped in Al2O3, which acts a photo inert support and provide the path for oxygen (from aqueous solution) to utilize this electron to produce reactive oxygen species. Moreover, it forms the dye cation radicals and facilities for dye degradation upon light excitation38. Hence, the presence of Al2O3 makes the catalyst more stable and active on degradation. The recombination of electron-hole pairs are effectively prevented by Al2O3 and provide a path for H2O to form hydroxyl radicals (••OH) by utilizing holes in the valence band of CuO. These highly active oxygen species (•O ) and hydroxyl radicals (••OH) helps in rapid degradation of IC. Nanostructure with a combination of wide and narrow bandgap system separates the photogenerated electron-holes pair efficiently and thereby increases the charge carrier lifetime. The effective separation electronhole pair and its improved lifetime are the reason for enhanced photocatalytic degradation ability of HMCA catalyst. + ℎν → ĥ/+ + 9*+ ĥ /+ + → H + •OH



9*+ + → •O

The EPR spectra for HMCA are shown in Fig.4(c) obtained as the effect of light irradiation at room temperature in air. There is no signal seen in EPR spectrum of HMCA in dark condition. The existence of prominent resonance bands, corresponding to Mn cations and Cu cations are clearly distinguished in the spectrum under light irradiation. It is noted clearly that the sextuplet characteristics centered at g∥=1.99 and g⊥=1.98 were because of hyperfine interactions of Mn4+ elements (I = 5/2)39. Cu ions (I = 3/2) showed 4-fold hyperfine-structure lines, indicating Cu2+ ions with g∥=2.4 and g⊥=2.01. The strong DMPO•OH production is observed upon UV illumination is shown in fig.4(c) (inset). It was clearly noted that there are no distinct EPR peaks in the dark condition. Increased intensity proves the availability of many numbers of free radicals. This provides information regarding the improved separation of photogenerated charge carriers and the decreased recombination rate of the electron-hole pair as well as the lengthen lifetime of the charge carriers40. Therefore, it was clearly known that •OH radicals play a prominent role in the degradation process. Effect of operating parameters. The effect of initial solution pH (3-11) on IC (60 ppm) degradation using 7.5 mg/L of HMCA catalyst was studied and shown in Fig.4(d). The maximum IC degradation percentage is observed as 98.89 % at pH 11 for 120 min. It apparently shows that the degradation percentage increases with pH up to 9 and above that, there is no significant increase in the efficiency. It indicates the electrostatic interactions between the substrate and HMCA NPs, depends on the suspension pH41. Enforcement of the reaction rate under alkaline condition has been attributed because of increased hydroxyl ions, which induces more hydroxyl radical formation, that responsible for degradation process of dye42. However, at high pH (11), the hydroxyl radicals have been rapidly scavenged and they don’t have an opportunity to react with dyes43. Therefore, the increase in degradation percentage with respect to the pH is slightly less when compared to pH 9. Fig.4(e) shows the effect of HMCA photocatalyst loading (2.5 mg/L – 10 mg/L) on the degradation of IC (60 ppm) at pH 9. The degradation percentage increases with catalyst loading up to 7.5 mg/L. The number of absorbed photon increases along with catalyst amount, therefore a number of electrons available in conduction band raise the generation of hydroxyl radicals44. The number of generated hydroxyl radicals is directly proportional to the IC degradation percentage. There are no significant changes have been noted in degradation percentage by further increasing catalyst loading beyond 7.5 mg/L. This owing to the presence of more HMCA NPs form a denser solution, which hinders the illumination area on


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photocatalyst. The opacity increases with a reduction in radiation passage through the reactor. The result depicts that 7.5 mg/L of the catalyst is adequate to degrade the IC. The initial concentration of reactant plays a vital role in the photodegradation of dyes. The effect of IC concentration (20 ppm-100 ppm) on degradation using 7.5 mg/L of catalyst loading at pH-9 under sunlight light illumination is studied. The degradation efficiency decreases with increase in IC concentration are shown in fig.4(f). At higher concentration of IC, the degradation rate is getting slow. For the lower concentration of IC (20 ppm), the degradation rate has observed to be very quickly. At higher concentration, the number of available sites of catalyst gets blocked by IC which results in the decreased photocatalytic surface area, therefore the degradation efficiency also decreasing45,46. Reusability and Photoelectrochemical test. The photoelectrochemical measurement for several on and off cycles of irradiation was carried out with the four synthesized samples coated on FTO electrode as a working electrode (details in supporting information). Fig.4(g) provides the photocurrent-potential plots of all samples. The electron-hole separation plays a vital role in the photocatalytic reaction. The higher value of photocurrent means the longer living photogenerated electron-hole pairs, hence higher photodegrading activity47. The graph shows that HMCA possess an excellent photocurrent intensity of 52.86 µA.cm-1 when comparing to SMC (33.41 µA.cm-1), SM (19.67 µA.cm-1), and S (10.78 µA.cm-1) respectively. Here the current increased sharply while upon light irradiation. Subsequently, current returns quickly to the dark current state when the light turned off. Comparing with other samples HMCA possesses larger carrier concentration during light irradiation, hence many numbers of electron-hole pairs generated for charge transfer method. The order of photocurrent intensity is HMCA > SMC > SM > S are in good agreement with the result of photodegradation. The increased photocurrent density indicates the enhanced photoinduced electron-hole separation efficiency, which attributed to the junction between layers. This clearly justifies the interfacial charge between all layers in HMCA exist while on light illumination. The catalyst stability test has been conducted to determine the stability of HMCA photocatalyst at the multiple uses (Fig.4(h)). The five repeated experiments were carried out to learn the stability of the catalyst. Each time the catalyst was removed from the solution through centrifugation process and dried at 100 0C for next use. Initial run provides 95.72 % of IC degradation efficiency. Similarly, the 2nd, 3rd, 4th and 5th run affords 93.63 %, 90.43 %, 86.21 %, and 73.57 % of IC degradation efficiency respectively. It has been clearly observed



that 23.13 % of decrease in degradation efficiency after the fifth cycle when compared to the first cycle. This owing to surface leaching happened at the time of photocatalytic reaction attributes to the loss of active support sites48. Moreover, successive heat treatment after every cycle decreases the surface area, which results in partial aggregation. In addition to this, catalyst losses also occur during centrifugation process results in reduced photoreactivity. The catalyst will effectively work up to four cycles. Electrochemical capacitance performance The cyclic voltammetry of prepared electrode materials at a constant scan rate of 50 mVs-1 in a potential window of -0.2 to 0.8 V is described in fig.5(a) (for experimental details see supporting information). As shown, the distinct redox peaks occurred during anodic and cathodic sweeps proves the faradaic pseudocapacitance reaction on the electrode surface. The CV curve of S doesn’t show any peaks whereas SM shows the redox peaks at the potential (0.3 V-cathodic, 0.58 V-anodic) particularly the peak at 0.3 V is assigned for electrochemical reduction of MnO249. In SMC, the redox peaks seen at (0.3 V, 0.1 V - anodic) and ( 0.05 V, 0.35 V- cathodic) corresponds to a multi-step electrochemical reaction because of Mn2+/Mn3+ and Cu

2+

/Cu1+. The peaks were maintained well, indicating the high reversible capacity of

MnO2 and CuO in SMC. There is no change in the peak position of HMCA comparing with SMC proves the electrochemical inactive nature of Al2O3, which do not contribute in the CV curves under our experimental conditions. There is little evolution in HMCA when comparing with SMC confirming the stability of electrode due to the presence of Al2O3. Thus, plenty of charges can be stored in HMCA when comparing with other electrodes. With the increase in scan rate from 20 to 100 mVs-1, the CV curve shape has been developed with a slight shift in peak positions occupies large areas. Hence, the specific capacitance of HMCA electrode verses scans rate shows in Fig.S3 (supporting information). Fig.5(b) shows the galvanostatic charge-discharge behaviorism within potential window 0.98 V at current density 0.5 Ag-1. The specific capacitance values are calculated based on the mass of active material loaded in the electrode. HMCA shows the greater the specific capacitance of 319.81 Fg-1 at the current density of 0.5 Ag-1 when compared to SMC (273.46 Fg-1), SM (186.17 Fg-1), S (50.48 Fg-1) respectively. The specific capacitance as a function of current density is shown in fig.5(c). Furthermore, the electrochemical stability over cycling is evaluated at a current density of 1 Ag-1 by repeated charging and discharging for 1000 cycles shown in fig.5(d). The specific capacitance of 304.09 Fg-1 for the first cycle gradually decreases to a value 292.54 Fg-1 at last cycles, shows the capacitance retention of 96.11 % to that of the initial value. On the other hand, there is a loss in capacitance of 89.34 ACS Paragon Plus Environment

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%, 94.68 %, and 68.26 % respectively for SMC, SM, and S over 1000 cycles. The capacitance retention of HMCA is only 78.14 % when increasing the current density from 1 to 10 Ag-1 for 100 cycles (Fig.S4 of supporting information). To further study the structural integrity of the HMCA, the residual electrolyte was removed from the electrode materials after cycling process using dimethyl carbonate. The SEM image of HMCA after cycles is shown in fig.5(e). Based on the images, HMCA is surrounded by binder and carbon black is seen well. As well, the structural modification is clearly seen in TEM images shown in fig. 5(f and g). Still, the porous morphology was maintained well after cycling process is a great benefit for structural stability. Nyquist plots and the corresponding impedance data were analyzed using equivalent circuit (inset) are shown in fig. 6. The intercept of the spectra in real axis at higher frequency range provides the internal resistance (=> ), which is the sum of the ionic resistance of the electrolyte, intrinsic resistance of substrate and contact resistance at active material–current collector interface50. The semicircle region in the impedance plot at high-frequency region corresponds to interfacial charge transfer resistance =?@ due to the faradic reaction and double layer capacitance (AB ). The slope angled at 45 º in low-frequency region provides information regarding Warburg resistance (CD ) of electrolyte, results of ion diffusion from the electrolyte to electrode surface51. The (E ) is the faradaic pseudocapacitance. The inset in Fig. 6 shows the Nyquist plot of S electrodes. Table.S2 (seen in supporting information) provides the impedance parameter for the S, SM, SMC, HMCA nanocomposites, calculated from the equivalent circuit using complex nonlinear least squares (CNLS) fitting method. The different => value of electrodes shows the difference in conductivity and morphology of the materials. The electrode material with high intrinsic resistance possesses low conductivity52. However, the => value of HMCA is lower than other electrode material owing to the synergistic effect of MnO2, CuO and Al2O3 in the HMCA nanocomposites. Further, this synergistic effect is again confirmed from =?@ value. =?@ Value of the electrode is associated with the amount of ion transfer into the electrode surface and it is inversely proportional to each other. This reduced =?@ is because of hollow structure surface interface character which decreases the polarization of electrode and thus might increase the specific capacity of electrodes53. Depends on the ions diffusion path length and barrier of ion movement, the Warburg region of electrode remains. The low capacitor’s diffusive resistance (CD ) of the electrolyte in HMCA is the reason for the short diffusion path length of ions, which is cause for the high capacitance of HMCA electrode materials54. The large values of =?@ and CD in S,



SM electrode materials are the reason for low capacitance value for the corresponding electrode. The results confirm the better performance HMCA electrode when compared with S, SM and SMC electrodes. To test the HMCA electrode in a real application, symmetric supercapacitor was constructed by using HMCA electrodes and 1 M Na2SO4 aqueous electrolyte. The cyclic voltammetry curve as a function of voltage for designed supercapacitor (Fig.7(a)) shows an ideal behavior of quasi-rectangular curve at various scan rates. This rectangular curve at a voltage ranging from 0.025 to 1.87 V indicates faster charging and discharging behavior with high rate capability. Fig.7(b) shows the galvanostatic charge-discharge behavior of assembled supercapacitor at different current density. From the curve, it is clearly noted that potential is almost proportional to the time, which indicates the quick I-V responses and supreme capacitive nature. The specific capacitance is calculated to be 131.7 Fg-1 at a current density of 0.5 Ag-1. From Ragone plot Fig.7(c), the maximum specific energy density and power density is measured as

62.26 Whkg-1 and 5.5 kWkg-1 respectively for our symmetric

supercapacitor, which is much higher than those of reported symmetrical supercapacitor55–60. In addition to that, the designed supercapacitor exhibits a long-term cycling stability at current density 0.5 Ag-1 for 3000 cycles (fig.7(d). The graph clearly depicts that the specific capacitance is increased gradually in initial cycling stages and start to decrease. At final cycling test, the capacitance retains 83.48 % of its initial value representing a minimal damage occurs in electrodes due to continuous redox reaction. These results offer the convincing evidence that HMCA symmetric supercapacitor device holds considerable promise for the realistic application.

Conclusion In this work, a new type of hollow shelled triple HMCA NPs has been synthesized by a facile microwave-assisted approach using successive reduction with urea. The obtained hollow shelled triple nanostructure has been investigated by using various analytical techniques. TEM micrograph has revealed the spherical structure of nanoparticles with uniform sized, densely populated hairy outer surface. The incorporation of multiple oxides not only increases the surface area of particles but also increases the light absorption range, which improves the capacity of photodegradation of IC. The higher degradation efficiency of IC (60 PPM) has been observed as 95.72% under the condition of solution pH 9 with 7.5 mg/L of HMCA catalyst. HMCA can be reused effectively, though the degree of efficiency slightly decreases with the increase in cycle number. In addition, for the application of


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supercapacitor, the combination of the pseudocapacitance of metal oxides improves the electrochemical performance. The morphology of HMCA shows the different surface interface conditions, which play major roles in ion intercalation/extraction. The fabricated symmetric supercapacitor device can be reversibly charged and discharged at an operation voltage of 1.85 V. Moreover, the device delivers the maximum energy density of 62.26 Whkg-1 at a power density of 461.25 Wkg-1, and a long-term stability retains 83.48 % of initial capacitance after 3000 cycles. These results demonstrate the potential of properly designed complex hollow nanostructures in energy storage and catalytic application.

Acknowledgements The authors are grateful to Department of Science and Technology (NO.SB/FT/CS047/2012) and Department of Biotechnology (BT/PR6080/GBD/27/503/ 2013) Government of India for the financial assistance. Also, authors sincerely thank Dr. M. C. Santhosh Kumar, Department of physics for providing for PL recording and A.V. Karthikeyani, Indian Oil Corporation, R&D Centre, for BET results.

Associated Content: Supporting Information: Chemicals and characterization details, experimental procedure (photocatalyst, photoelectrochemical, electrochemical measurements), formation of hollow nanostructures, performance studies of photocatalyst, UV-Vis absorption spectra, specific capacitance at various scan rate, capacitance retention of HMCA electrode at various current density, CV graph of HMCA electrode at various scan rate, table containing elemental composition details, calculated impedance value for various electrode from impedance spectra.

References (1)

Liu, R.; Li, D.; Wang, C.; Li, N.; Li, Q.; Lu, X.; Spendelow, J. S.; Wu, G. Core-shell structured hollow SnO 2-polypyrrole nanocomposite anodes with enhanced cyclic performance for lithium-ion batteries. Nano Energy 2014, 6, 73–81, DOI 10.1016/j.nanoen.2014.03.010.

(2)

Ren, G.; Hu, D.; Cheng, E. W. C.; Vargas-Reus, M. A.; Reip, P.; Allaker, R. P. Characterisation of copper oxide nanoparticles for antimicrobial applications. Int. J. Antimicrob. Agents 2009, 33 (6), 587–590, DOI 10.1016/j.ijantimicag.2008.12.004.

(3)

Hwa, K.-Y.; Subramani, B. Synthesis of zinc oxide nanoparticles on graphene–carbon nanotube hybrid for glucose biosensor applications. Biosens. Bioelectron. 2014, 62, 127–133, DOI 10.1016/j.bios.2014.06.023.



(4)

Ocakoglu, K.; Zafer, C.; Varlikli, C.; Icli, S. Preparation of dye sensitized titanium oxide nanoparticles for solar cell applications. Mater. Sci. Semicond. Process. 2013, 16 (6), 1688–1694, DOI 10.1016/j.mssp.2013.05.010.

(5)

Shin, J.; Anisur, R. M.; Ko, M. K.; Im, G. H.; Lee, J. H.; Lee, I. S. Hollow manganese oxide nanoparticles as multifunctional agents for magnetic resonance imaging and drug delivery. Angew. Chemie - Int. Ed. 2009, 48 (2), 321–324, DOI 10.1002/anie.200802323.

(6)

Wei, W.; Cui, X.; Chen, W.; Ivey, D. G. Manganese oxide-based materials as electrochemical supercapacitor electrodes. Chem. Soc. Rev. 2011, 40 (3), 1697–1721, DOI 10.1039/C0CS00127A.

(7)

Zhao, Y. X.; Burda, C. Development of plasmonic semiconductor nanomaterials with copper chalcogenides for a future with sustainable energy materials. Energy Environ. Sci. 2012, 5 (2), 5564–5576, DOI 10.1039/c1ee02734d.

(8)

Md Jani, A. M.; Losic, D.; Voelcker, N. H. Nanoporous anodic aluminium oxide: Advances in surface engineering and emerging applications. Prog. Mater. Sci. 2013, 58 (5), 636–704, DOI 10.1016/j.pmatsci.2013.01.002.

(9)

Zhou, W.; Zhu, J.; Cheng, C.; Liu, J.; Yang, H.; Cong, C.; Guan, C.; Jia, X.; Fan, H. J.; Yan, Q.; et al. A general strategy toward graphene@metal oxide core–shell nanostructures for high-performance lithium storage. Energy Environ. Sci. 2011, 4 (12), 4954–4961, DOI 10.1039/c1ee02168k.

(10)

Qi, J.; Dang, X.; Hammond, P. T.; Belcher, A. M. Highly efficient plasmon-enhanced dye-sensitized solar cells through metal@ oxide core--shell nanostructure. ACS Nano 2011, 5 (9), 7108–7116, DOI 10.1021/nn201808g.

(11)

Li, G.; Tang, Z. Noble metal nanoparticle@metal oxide core/yolk-shell nanostructures as catalysts: Recent progress and perspective. Nanoscale 2014, 6 (8), 3995–4011, DOI 10.1039/C3NR06787D.

(12)

Kim, J.; Piao, Y.; Hyeon, T. Multifunctional nanostructured materials for multimodal imaging, and simultaneous imaging and therapy. Chem. Soc. Rev. 2009, 38 (2), 372– 390, DOI 10.1039/b709883a.

(13)

Salgueiriño-Maceira, V.; Correa-Duarte, M. A. Increasing the complexity of magnetic core/shell structured nanocomposites for biological applications. Adv. Mater. 2007, 19 (23), 4131–4144, DOI 10.1002/adma.200700418.

(14)

Larsson, P. O.; Andersson, A. Oxides of copper, ceria promoted copper, manganese and copper manganese on Al2O3 for the combustion of CO, ethyl acetate and ethanol. ACS Paragon Plus Environment

Page 16 of 30

Page 17 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


Appl. Catal. B Environ. 2000, 24 (3–4), 175–192. (15)

Wu, S.; Shen, X.; Zhu, G.; Zhou, H.; Ji, Z.; Chen, K. Synthesis of ternary Ag / ZnO / ZnFe 2 O 4 porous and hollow nanostructures with enhanced photocatalytic activity. Appl. Catal. B Environ. 2016, 184, 328–336, DOI 10.1016/j.apcatb.2015.11.035.

(16)

Fang, S.; Xin, Y.; Ge, L.; Han, C.; Qiu, P.; Wu, L. Facile synthesis of CeO2 hollow structures with controllable morphology by template-engaged etching of Cu2O and their visible light photocatalytic performance. Appl. Catal. B Environ. 2015, 179, 458– 467, DOI 10.1016/j.apcatb.2015.05.051.

(17)

Zhu, C.; Chou, S.; He, S.; Liao, W.; Chen, C. Synthesis of core/shell metal oxide/polyaniline nanocomposites and hollow polyaniline capsules. Nanotechnology 2007, 18 (27), 275604, DOI 10.1088/0957–4484/18/27/275604.

(18)

Liu, R.; Mahurin, S. M.; Li, C.; Unocic, R. R.; Idrobo, J. C.; Gao, H.; Pennycook, S. J.; Dai, S. Dopamine as a carbon source: The controlled synthesis of hollow carbon spheres and yolk-structured carbon nanocomposites. Angew. Chemie - Int. Ed. 2011, 50 (30), 6799–6802, DOI 10.1002/anie.201102070.

(19)

Yu, J.; Zhang, J.; Liu, S. Ion-Exchange Synthesis and Enhanced Visible-Light Photoactivity of CuS / ZnS Nanocomposite Hollow Spheres. 2010, 1, 13642–13649, DOI 10.1021/jp101816c.

(20)

Zhou, X.; Shi, J.; Liu, Y.; Su, Q.; Zhang, J.; Du, G. Microwave-assisted synthesis of hollow CuO-Cu2O nanosphere/graphene composite as anode for lithium-ion battery. J. Alloys Compd. 2014, 615, 390–394, DOI 10.1016/j.jallcom.2014.07.013.

(21)

Dou, P.; Tan, F.; Wang, W.; Sarreshteh, A.; Qiao, X.; Qiu, X.; Chen, J. One-step microwave-assisted synthesis of Ag/ZnO/graphene nanocomposites with enhanced photocatalytic activity. J. Photochem. Photobiol. A Chem. 2015, 302, 17–22, DOI 10.1016/j.jphotochem.2014.12.012.

(22)

Li, X.; Sun, P.; Yang, T.; Zhao, J.; Wang, Z.; Wang, W.; Liu, Y.; Lu, G.; Du, Y. Template-free microwave-assisted synthesis of ZnO hollow microspheres and their application in gas sensing. CrystEngComm 2013, 15 (15), 2949–2955, DOI 10.1039/c2ce26539g.

(23)

Kobayashi, Y.; Katakami, H.; Mine, E.; Nagao, D.; Konno, M.; Liz-Marzán, L. M. Silica coating of silver nanoparticles using a modified Stöber method. J. Colloid Interface Sci. 2005, 283 (2), 392–396, DOI 10.1016/j.jcis.2004.08.184.

(24)

Liu, J.; Song, J.; Xiao, H.; Zhang, L.; Qin, Y.; Liu, D.; Hou, W.; Du, N. Synthesis and thermal properties of ZnAl layered double hydroxide by urea hydrolysis. Powder ACS Paragon Plus Environment


Technol. 2014, 253, 41–45, DOI 10.1016/j.powtec.2013.11.007. (25)

Zeng, H.-Y.; Deng, X.; Wang, Y.-J.; Liao, K.-B. Preparation of Mg-Al hydrotalcite by urea method and its catalytic activity for transesterification. AIChE J. 2009, 55 (5), 1229–1235, DOI 10.1002/aic.11722.

(26)

Anandan, S.; Chen, C.; Wu, J. J. Sonochemical synthesis and characterization of turbostratic MnNi ( OH ) 2 layered double hydroxide nanoparticles for supercapacitor applications. RSC Adv. 2014, 4 (98), 55519–55523, DOI 10.1039/C4RA10816G.

(27)

Devamani, R. H. P.; Alagar, M. Synthesis and Characterisation of Copper II Hydroxide Nano Particles. Nano Biomed. Eng. 2013, 5 (3), 116–120, DOI 10.5101/nbe.v5i3.

(28)

Al-Oweini, R.; El-Rassy, H. Synthesis and characterization by FTIR spectroscopy of silica aerogels prepared using several Si (OR) 4 and R’’ Si (OR’) 3 precursors. J. Mol. Struct. 2009, 919 (1–3), 140–145, DOI 10.1016/j.molstruc.2008.08.025.

(29)

Siva, C.; Ramya, R.; Baraneedharan, P.; Nehru, K.; Sivakumar, M. Fabrication, physiochemical and optoelectronic characterization of SiO 2/CdS core-shell nanostructures. J. Mater. Sci. Mater. Electron. 2014, 25 (3), 1202–1208, DOI 10.1007/s10854–014–1710–z.

(30)

Pan, X.; Yang, M.-Q.; Fu, X.; Zhang, N.; Xu, Y.-J. Defective TiO 2 with oxygen vacancies: synthesis, properties and photocatalytic applications. Nanoscale 2013, 5 (9), 3601–3614, DOI 10.1039/c3nr00476g.

(31)

Bai, X.; Wang, L.; Zhu, Y. Visible photocatalytic activity enhancement of ZnWO4 by graphene hybridization. ACS Catal. 2012, 2 (12), 2769–2778, DOI 10.1021/cs3005852.

(32)

Su, J.; Zhang, Y.; Xu, S.; Wang, S.; Ding, H.; Pan, S.; Wang, G.; Li, G.; Zhao, H. Highly efficient and recyclable triple-shelled Ag@ Fe 3 O 4@ SiO 2@ TiO 2 photocatalysts for degradation of organic pollutants and reduction of hexavalent chromium ions. Nanoscale 2014, 6 (10), 5181–5192, DOI 10.1039/C4NR00534A.

(33)

Khanchandani, S.; Srivastava, P. K.; Kumar, S.; Ghosh, S.; Ganguli, A. K. Band gap engineering of ZnO using core/shell morphology with environmentally benign Ag2S sensitizer for efficient light harvesting and enhanced visible-light photocatalysis. Inorg. Chem. 2014, 53 (17), 8902–8912, DOI 10.1021/ic500518a.

(34)

Parrish, J. A.; Fitzpatrick, T. B.; Shea, C.; Pathak, M. A. Photochemotherapy of vitiligo: Use of orally administered psoralens and a high-intensity long-wave ultraviolet light system. Arch. Dermatol. 1976, 112 (11), 1531–1534, DOI ACS Paragon Plus Environment

Page 18 of 30

Page 19 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


10.1001/archderm.1976.0163035000700. (35)

Wang, G.; Huang, B.; Lou, Z.; Wang, Z.; Qin, X.; Zhang, X.; Dai, Y. Valence state heterojunction Mn 3 O 4/MnCO 3: Photo and thermal synergistic catalyst. Appl. Catal. B Environ. 2016, 180, 6–12, DOI 10.1016/j.apcatb.2015.06.010.

(36)

Xu, Y.; Schoonen, M. A. A. The absolute energy positions of conduction and valence bands of selected semiconducting minerals. Am. Mineral. 2000, 85 (3–4), 543–556.

(37)

Niu, M.; Huang, F.; Cui, L.; Huang, P.; Yu, Y.; Wang, Y. Hydrothermal synthesis, structural characteristics, and enhanced photocatalysis of SnO2/$α$-Fe2O3 semiconductor nanoheterostructures. ACS Nano 2010, 4 (2), 681–688, DOI 10.1021/nn901119a.

(38)

Li, Z.; Sheng, J.; Wang, Y.; Xu, Y. Enhanced photocatalytic activity and stability of alumina supported hematite for azo-dye degradation in aerated aqueous suspension. J. Hazard. Mater. 2013, 254–255, 18–25, DOI 10.1016/j.jhazmat.2013.03.055.

(39)

Ferrante, R. F.; Wilkerson, J. L.; Graham, W. R. M.; Weltner Jr, W. ESR spectra of the MnO, MnO2, MnO3, and MnO4 molecules at 4 K. J. Chem. Phys. 1977, 67 (12), 5904–5913, DOI 10.1063/1.434797.

(40)

Liu, B.; Li, X.; Zhao, Q.; Liu, J.; Liu, S.; Wang, S.; Tadé, M. Insight into the mechanism of photocatalytic degradation of gaseous o-dichlorobenzene over flowertype V 2 O 5 hollow spheres. J. Mater. Chem. A 2015, 3 (29), 15163–15170, DOI 10.1039/C5TA02295A.

(41)

Chen, W.; Ruan, H.; Hu, Y.; Li, D.; Chen, Z.; Xian, J.; Chen, J.; Fu, X.; Shao, Y.; Zheng, Y. One-step preparation of hollow ZnO core/ZnS shell structures with enhanced photocatalytic properties. CrystEngComm 2012, 14 (19), 6295–6305, DOI 10.1039/C2CE25591J.

(42)

Sadollahkhani, A.; Kazeminezhad, I.; Lu, J.; Nur, O.; Hultman, L.; Willander, M. Synthesis, structural characterization and photocatalytic application of ZnO@ ZnS core-shell nanoparticles. RSC Adv. 2014, 4 (70), 36940–36950, DOI 10.1016/j.cej.2014.02.065.

(43)

Alkaim, A. F.; Aljeboree, A. M.; Alrazaq, N. A.; Baqir, S. J.; Hussein, F. H.; Lilo, A. J. Effect of pH on adsorption and photocatalytic degradation efficiency of different catalysts on removal of methylene blue. Asian J. Chem. 2014, 26 (24), 8445–8448, DOI 10.14233/ajchem.2014.17908.

(44)

Muthukumar, H.; Manickam Matheswaran. Amaranthus spinosus Leaf Extract Mediated FeO Nanoparticles: Physicochemical Traits, Photocatalytic and Antioxidant ACS Paragon Plus Environment


Activity. ACS Sustain. Chem. Eng 2015, 3, 3149−3156, DOI 10.1021/acssuschemeng.5b00722. (45)

Harshiny, M.; Iswarya, C. N.; Matheswaran, M. Biogenic synthesis of iron nanoparticles using Amaranthus dubius leaf extract as a reducing agent. Powder Technol. 2015, 286, 744–749, DOI 10.1016/j.powtec.2015.09.021.

(46)

Shet, A.; K, V. S. Photocatalytic degradation of phenol using Ag core-TiO 2 shell ( Ag @ TiO 2 ) nanoparticles under UV light irradiation. Environ. Sci. Pollut. Res. 2016, 23 (20), 20055–20064, DOI 10.1007/s11356–015–5579–z.

(47)

Xiang, Q.; Yu, J.; Jaroniec, M. Preparation and enhanced visible-light photocatalytic H2-production activity of graphene/C3N4 composites. J. Phys. Chem. C 2011, 115 (15), 7355–7363, DOI 10.1021/jp200953k.

(48)

Adhikari, S.; Sarkar, D.; Madras, G. Highly efficient WO 3-ZnO mixed oxides for photocatalysis. RSC Adv. 2015, 5 (16), 11895–11904, DOI 10.1039/C4RA13210F.

(49)

Zeng, C.; Gao, C.; Yuan, L.; Liang, T.; Yang, R.; Zhang, W.; Nie, S. Water Evaporation-Induced Self-Assembly of Hierarchical CuO/MnO 2 Composite Nanospheres and their Applications in Lithium-Ion Batteries. Nano 2017, 12 (2), 1750022, DOI 10.1142/S1793292017500229.

(50)

Qiu, K.; Lu, Y.; Zhang, D.; Cheng, J.; Yan, H.; Xu, J.; Liu, X.; Kim, J.-K.; Luo, Y. Mesoporous, hierarchical core/shell structured ZnCo 2 O 4/MnO 2 nanocone forests for high-performance supercapacitors. Nano Energy 2015, 11, 687–696, DOI 10.1016/j.nanoen.2014.11.063.

(51)

Yan, J.; Fan, Z.; Wei, T.; Qian, W.; Zhang, M.; Wei, F. Fast and reversible surface redox reaction of graphene-MnO 2 composites as supercapacitor electrodes. Carbon N. Y. 2010, 48 (13), 3825–3833, DOI 10.1016/j.carbon.2010.06.047.

(52)

Naderi, H. R.; Norouzi, P.; Ganjali, M. R. Electrochemical study of a novel high performance supercapacitor based on MnO 2/nitrogen-doped graphene nanocomposite. Appl. Surf. Sci. 2016, 366, 552–560, DOI 10.1016/j.apsusc.2016.01.058.

(53)

Pang, H.; Wei, C.; Li, X.; Li, G.; Ma, Y.; Li, S.; Chen, J.; Zhang, J. Microwaveassisted synthesis of NiS2 nanostructures for supercapacitors and cocatalytic enhancing photocatalytic H2 production. Sci. Rep. 2014, 4, 3577, DOI 10.1038/srep03577.

(54)

Dong, X. C.; Xu, H.; Wang, X. W.; Huang, Y. X.; Chan-Park, M. B.; Zhang, H.; Wang, L. H.; Huang, W.; Chen, P. 3D graphene-cobalt oxide electrode for highperformance supercapacitor and enzymeless glucose detection. ACS Nano 2012, 6 (4), ACS Paragon Plus Environment

Page 20 of 30

Page 21 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


3206–3213, DOI 10.1021/nn300097q. (55)

Dubal, D. P. .; Suarez-Guevara, J. .; Tonti, D. .; Enciso, E. .; Gomez-Romero, P. . A high voltage solid state symmetric supercapacitor based on graphene-polyoxometalate hybrid electrodes with a hydroquinone doped hybrid gel-electrolyte. J. Mater. Chem. A 2015, 3 (46), 23483–23492, DOI 10.1039/c5ta05660h.

(56)

Xia, H.; Shirley Meng, Y.; Yuan, G.; Cui, C.; Lu, L. A Symmetric RuO2⁄RuO2 Supercapacitor Operating at 1.6 V by Using a Neutral Aqueous Electrolyte. Electrochem. Solid-State Lett. 2012, 15 (4), A60–A63, DOI 10.1149/2.023204esl.

(57)

Jagadale, A. D.; Kumbhar, V. S.; Dhawale, D. S.; Lokhande, C. D. Performance evaluation of symmetric supercapacitor based on cobalt hydroxide [Co (OH) 2] thin film electrodes. Electrochim. Acta 2013, 98, 32–38, DOI 10.1016/j.electacta.2013.02.094.

(58)

Padmanathan, N.; Selladurai, S.; Razeeb, K. M. Ultra-fast rate capability of a symmetric supercapacitor with a hierarchical Co 3 O 4 nanowire/nanoflower hybrid structure in non-aqueous electrolyte. RSC Adv. 2015, 5 (17), 12700–12709, DOI 10.1039/C4RA13327G.

(59)

Kumar, A.; Sanger, A.; Kumar, A.; Mishra, Y. K.; Chandra, R. Performance of High Energy Density Symmetric Supercapacitor Based on Sputtered MnO2 Nanorods. ChemistrySelect 2016, 1 (13), 3885–3891, DOI 10.1002/slct.201600757.

(60)

Wang, Q.; Yan, J.; Wang, Y.; Wei, T.; Zhang, M.; Jing, X.; Fan, Z. Three-dimensional flower-like and hierarchical porous carbon materials as high-rate performance electrodes for supercapacitors. Carbon N. Y. 2014, 67, 119–127, DOI 10.1016/j.carbon.2013.09.070.



FIGURES

S SM SMC HMCA

Transmittance (%)

♣ 533

10

20

30

40

60

70

80

500

1000

350 300 250

5

3

5

10

15

20

25

30

35

γ (C-H)-CTAB 3000

3500

4000

d

4

0

2500

S SM SMC HMCA

c 6

2

200

2000

S SM SMC HMCA

Intensity(a.u.)

400

1500

b

Wavenumber (cm-1)

7

3

dV/dlog(D) Pore Volume (cm /g)

450

50

2θ (degree)

500

δ (CH3)-CTAB

‘γγ (O-Si-O)

S

‘a’ γ (Si-O-Si)

♣ 533

SM

γ (Si-O)

♣ 533

♦220 ♦ 220

♣511

♦ 022

♣511

♦ 022

#202

♦ 202

♣ 222

♣511

JCPDS No: 13-0162

♣ 222

*220

JCPDS No: 01-1117

♦202

♣ 222

SMC #110

#012 ♣ 220

Intensity (a.u)

HMCA

a

JCPDS No: 77-2135

Quantity Adsorbed (cm³/g STP)

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

Page 22 of 30

40

Pore Diameter (nm)

150 100 50 0 0.0

0.2

0.4

0.6

0.8

1.0

300

Relative Pressure (P/Po)

400

500

600

Wavelength(nm)

Fig.1. (a) XRD pattern of synthesized materials. (b) FTIR spectra of synthesized materials. (c) N2 adsorption-desorption isotherm of synthesized materials and the inset shows pore size distribution plot of HMCA nanocomposites. (d) Room temperature PL excitation and emission spectra of synthesized materials.


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Fig.2. TEM micrographs of S (a), SM (b), SMC (c) and HMCA(d and e). (f) EDS Spectra of HMCA nanocomposites. (g) SAED pattern of HMCA nanocomposites. (h) and (i) HR-TEM



images of HMCA nanocomposites. (j) STEM image of HMCA to be analyzed for EDS mapping.

O 1s

5

5x10

Mn 2p

534.36 eV

a

b Cu 2p

Mn 2p 3/2

5

525

5

3x10

530

O 1s

535

540

545

Binding Energy (eV)

Mn 2p

5

2x10

5

Intensity (a.u.)

Intensity (a.u.)

4x10

645.168 eV

Mn 2p 1/2

656.08 eV

HMCA

1x10

0 1200

1000

800

600

400

200

0 630

635

640

645

650

655

660

665

670

Binding Energy (eV)

Binding Energy (eV) Cu 2p

c

Al 2p

d

Cu 2p 3/2

71.10 eV

Intensity (a.u.)

934.70 eV

Intensity (a.u.)

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

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Cu 2p 1/2 952 eV

925

930

935

940

945

950

955

Binding Energy (eV)

960

965

970

975

76.90 eV

66

68

70

72

74

76

78

80

Binding Energy (eV)

Fig.3. (a) XPS survey spectra of HMCA nanocomposites with O 1s (inset). High resolution scans of (b) Mn 2p, (c) Cu 2p, and (d) Al 2p of HMCA nanocomposites.


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Fig.4. (a) tauc plot of MnO2, CuO and Al2O3. (b) Reaction mechanism of HMCA photocatalysis. (c) EPR spectra for HMCA nanocatalyst recorded in dark and after illumination of light. Inset (DMPO spin trapping EPR spectra for DMPO•OH radicals under light irradiation with HMCA nanocatalyst. (d) Degradation behavior of HMCA photocatalyst on IC (60 ppm) at different pH. (e) Effect of Catalyst (HMCA) loading on IC (60 PPM) degradation at pH 9. (f) Degradation behavior of Catalyst (HMCA-7.5 mg /L) on various IC concentrations at pH 9. (g) Degradation profile on reusability of HMCA catalysis. (h) Current - potential plot of HMCA catalysis.


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Fig 5. (a) Cyclic voltammogram of synthesized nanostructures in 1M Na2SO4 electrolyte at 50 mVs-1. (b) Galvanostatic charge-discharge bahaviour of electrodes at 0.5 Ag-1. (c) Specific capacitance of various nanostructures electrodes at different current densities, (d) Cycling performance of the nanocomposites electrodes at 1 Ag-1(inset shows the charge-discharge curve at middle cycles of SMC electrode). SEM (e) and TEM (f and g) images of HMCA nanocatalyst after 1000 cycling process.



-25

-120

S

-100 -80

-20

SM SMC HMCA

-60 -40

Z" (Ohm)

-20

-15

0

Cdl

20

40

60

80

100

120

CF

-10 Rs

Rct

Zw W

-5

0 2

4

6

8

10

12

14

16

18

20

Z' (Ohm)

Fig 6. Electrochemical impedance spectrum of the electrodes in frequency range from 0.1 Hz to 100 kHz (inset show the equivalent circuit and Nyquist plot of S electrodes).

10

Specific current (Ag-1)

6 4

a

b

2.0

0.5 Ag-1 1 Ag-1

1.5

Potential (V)

-1 5 mVs -1 10 mVs -1 20 mVs -1 50 mVs -1 100 mVs

8

2 0

2 Ag-1 4 Ag-1 5Ag-1 6 Ag-1

1.0

0.5

-2 -4 -6

0.0

0.0

0.5

1.0

1.5

0

2.0

200

400

Potential (V)

40

30

80 2.0

70 60 50 40

1000

10000

1.5 1.0 0.5 0.0 10000

20

Power Density (W/kg)

1000

90

30

20 100

800

d

100

Potential (V)

50

Capacitance retention (%)

c

600

Time (s)

110 60

Energy Density (Wh/kg)

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

Page 28 of 30

12500

15000

17500

20000

Time (S)

10 0

500

1000

1500

2000

2500

3000

Cycle Numbers

Fig 7. (a) Cyclic voltammetry curves of symmetric supercapacitor measured at different scan


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rates. (b) Charge-discharge curves at different densities. (c) Ragone plot of the symmetric supercapacitor. (d) Capacitance retention versus cycle number at current density of 0.5 Ag-1 (inset is charge-discharge curve of symmetric supercapacitor).

Table of Contents (TOC) Graphic

Synopsis: HMCA is a promising material in both energy storage and photocatalytic applications.




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