THÔNG TIN TÀI LIỆU
Journal of Science: Advanced Materials and Devices (2018) 44e50 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Green engineered synthesis of Ag-doped CuFe2O4: Characterization, cyclic voltammetry and photocatalytic studies B.S Surendra Department of Chemistry, East West Institute of Technology, Bengaluru 560 091, India a r t i c l e i n f o a b s t r a c t Article history: Received 17 December 2017 Received in revised form 25 January 2018 Accepted 27 January 2018 Available online February 2018 Ag-doped CuFe2O4 nanoparticles (ACNPs) with cubic and tetragonal spinel structures were synthesized by the Jatropha-oil assisted combustion method and their properties were well characterized The ACNPs catalyst was synthesized based on the CuFe2O4 nanoparticles by the incorporation of Ag atoms, which showed an excellent (97%) photocatalytic activity as compared to the host CuFe2O4 (85%) under UV-light for the decomposition of Malachite green (MG) dye Electrochemical properties of CNPs were studied by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) Our study provides some new insights into the design of materials for multifunctional long-term applications The prepared photocatalysts exhibited reusability with an excellent efficiency © 2018 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Jatropha-oil AgeCuFe2O4 CuFe2O4 CV and EIS Photocatalysis Introduction The non-edible plant seed cakes are the most abundant renewable biomasses and sustainable alternative source for chemicals The non-edible plant seeds like, Jatropha, Pongamia, Simarubha etc were used in the production of biodiesel by extracting the oil During this process, it released huge amount of seed cake, which contains little oil, proteins, carbohydrates, fiber and inorganic compounds [1e5] Therefore, it has been used for extracting the smaller percentage of oil and used as a fuel for the synthesis AgeCuFe2O4 using the combustion method Nowadays many industries and laboratories use carcinogenic coloring reagents, releasing waste water and thus causing a lot of problems to the environment Mainly the dye discharge into water from industries is extremely toxic to microorganisms, aquatic life and human habitats [6e10] Most of the semiconductor photocatalysts used for the treatment of organic pollutants can utilize ultraviolet radiations due to their intrinsic limitations of band gap (> 3.1 eV) To deal with this issue, we need to develop a photocatalyst that efficiently extends its visible light response in catalytic activities for environmental remediation This has become a great task and one of the most dynamic research topics in photocatalysis [11e13] In this regard, spinel ferrites MFe2O4 (M ¼ Mn, Zn, Cu etc.) E-mail address: surendramysore2010@gmail.com Peer review under responsibility of Vietnam National University, Hanoi and their related structures have been researched for their photocatalysis and magnetic properties [14e16] Also, ferrite nanoparticles have attracted growing attention due to their technological importance in high density magnetic storage, telecommunication equipment, gas sensors, and etc [17,18] Doping adds intentional defects into the host particles that may have a reflective effect in a photocatalysis reaction Potential toxicity of metals is one of the fundamental concerning issues while deciding the doping substances However, Ag metal possesses an ecofriendly, antimicrobial and antioxidant property, which affects the properties of CuFe2O4 nanoparticles by doping of Ag, therefore a combination of these two may yield an excellent photocatalytic activity A material that possesses properties like good stability, high reactivity and ability to be magnetically separated can be applied in a wide range of fields In the present investigation, Ag-doped CuFe2O4 and host CuFe2O4 photocatalysts were fabricated by the combustion method and the properties were well characterized by various techniques These photocatalysts are promising for multifunctional applications Experimental 2.1 Extraction of Jatropha oil The Jatropha oil was extracted by Soxhlet extraction method [19] using methanol as a solvent Run down the process using https://doi.org/10.1016/j.jsamd.2018.01.005 2468-2179/© 2018 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 heating mantle till up to 45 cycles at 70 C followed by distillation of solvent and finally crude oil was collected The chemical composition of extracted Jatropha oil was analyzed using BTH/QL1/ 161 instrument and the details were given in Table 2.2 Synthesis of Ag-doped CuFe2O4 nanoparticles (ACNPs) The CuFe2O4 NPs was prepared by using stoichiometric amounts of analytic grade Cu (NO3)2$3H2O and Fe (NO3)3$9H2O and an optimal amount of extracted Jatropha oil was used as a green fuel The above mentioned materials were taken in a crucible with minimum quantity of double distilled water and magnetic stirrer, mixed thoroughly to attain homogeneity and placed in a preheated muffle furnace maintained at 450 ± 10 C The highly porous brownish black final product was obtained However, in ACNPs preparation, the optimum amounts of Ag(NO3) (2 wt%) [20] were obtained by using Jatropha oil as a green fuel, and the same procedure was followed to get the final product 45 Results and discussion 3.1 PXRD analysis The PXRD patterns of the prepared ACNPs and CNPs are shown in Fig The PXRD pattern shows the major reflection peaks indexed as (220), (311), (111), (400), (200), (422), (511) and (440), and these peaks well matched with JCPDS card No 034-0425 having the cubic and tetragonal spinel structures [21] In ACNPs, the existence of the extra peaks indicated that the Ag has been incorporated in the host CuFe2O4 NPs The crystallization process proceeded along the (311) and (440) crystal planes and the intensity of these planes was found to be minimum for the CNPs as compared to the ACNPs Scherer's method was employed to observe the variation in crystallite size for the prepared ACNPs [22] The estimated results showed that the average crystallite size is ~16 and ~20 nm for the prepared CNPs and ACNPs, respectively 3.2 Morphological studies 2.3 Characterization The phase investigation of the prepared materials was carried out in Shimadzu Powder X-ray diffractometer (PXRD) using nickel filter in the range 20e70 with Cu Ka (1.541 Å) radiation at a scan rate of 2 minÀ1 Using AXIS ULTRA from AXIS 165, the surface morphology was studied using SEM, Hitachi e 3000 FT-IR studies were performed with a Spectrum-1000 (Perkin Elmer) spectrophotometer UVeVisible absorption was recorded using Shimadzu UV 2600 UVeVisible Spectrophotometer The surface area and pore diameter were obtained by BrunnereEmmeteTeller (BET) method using Quanta chrome Nova-1000 surface analyzer under a liquid nitrogen temperature regime 2.4 Photocatalytic activity studies The photocatalytic decomposition of dye was carried out under UV-light for the synthesized ACNPs and CNPs by degrading Malachite green (MG) dye Here, 30 mg of synthesized ACNPs dispersed in 250 ml of MG dye solution was taken in a glass reactor During the experiment, ml of dye solution was pipetted out at regular intervals until a complete decomposition of the dye solution and finally the adsorption was observed using UVeVisible spectrophotometer In order to check the endurance of the synthesized ACNPs, the experiment was repeated by using the same photocatalyst after washing and drying it with fresh dye The concentration of MG was analyzed by monitoring the absorbance at 617 nm Fig shows the SEM micrographs of the ACNPs and CNPs prepared by the combustion method In this method, the temperature was uniformly distributed and transferred to the interior of the sample, which made the evolution of gases and release of enormous amount of heat to form spinel ferrites [23] Fig 2(a) shows the spinel structure with porous flakes and agglomeration of particles, whereas in case of the Ag-doped sample it showed the change in morphology by the formation of numerous trapped pores, and spherical shaped agglomerations were observed [Fig 2(b)] When ferric nitrate was mixed with copper ferrite in the presence of Jatropha oil extract, the Cu2ỵ and Fe2ỵ ions distributed uniformly and formed a complex structure with active fatty acids like oleic acid (Fig 3) After the complex structure reacted with proteins at a low temperature to form the superstructure When subjected to heat treatment, this network underwent slow decomposition In summary, fatty acid molecules that interacted with divalent Cu2ỵ cations forming bridges between two hydroxyl groups from two different chains came in close contact This polymeric binding was responsible for the conjugation of all these families of compounds present in the oil extract and expected to get different structures 3.3 FT-IR studies In order to confirm the phase transformation of the prepared Ag-doped CNPs and CNPs, the FT-IR spectra were recorded in the Table Percentage composition of acid present in Jatropha oil Parameters Results Color Methyl esters of Caproic acid Caprylic acid Capric acid Lauric acid Myristic acid Palmitic acid Stearic acid Oleic acid Linoleic acid Linolenic acid Arachidonic acid Behenic acid Erucic acid Lignoceric acid Yellow colored liquid Nil Nil Nil Nil Nil 10.82% 7.14% 51.56% 18.05% 3.80% Nil 5.67% Nil Nil Fig PXRD studies of the synthesized ACNPs and host CNPs 46 B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 Fig SEM micrographs of the synthesized ACNPs and host CNPs Fig The probable mechanism of formation of the ACNPs and host CNPs range of 400e4000 cmÀ1 (Fig 4) The two prominent absorption bands of metaleoxygen bond correspond to the vibration of tetrahedral and octahedral complexes The bond observed at ~528 cmÀ1 was attributed to the stretching vibration of the tetrahedral group Cu2ỵeO2 and the bond observed at ~418 cm1 was attributed to the octahedral complex Fe3ỵeO2 vibrations [24,25] Both the samples showed peaks at ~1400 cmÀ1, which were attributed to the OeH bending vibration of adsorbed water molecules The bond around 1100 cmÀ1 due to CeC bending frequencies and that may correspond to the fuel Jatropha oil 3.4 Electrochemical studies Cyclic voltammetry (CV) was examined to study the electrochemical properties of the synthesized Ag-doped CNPs and CNPs modified with carbon paste electrode The CV experiments were carried out with a conventional three electrode system in M NaNO3 electrolyte, and the results are shown in Fig It is worth noting that the synthesized Ag-doped CNPs modified the electrode Fig FT-IR spectra of the synthesized ACNPs and host CNPs B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 47 Fig CV plots for the prepared ACNPs and host CNPs possess redox peak with an enhanced peak current as compared to the host CNPs, and this can be ascribed to its good photocatalytic activity From the above explanation, it is clear that the capacitances of the samples follow the order: the Ag-doped CNPs > the host CNPs Fig shows typical EIS (Electrochemical Impendence Spectroscopy) Nyquist plots of the prepared Ag-doped CNPs and CNPs The arc radius of the EIS spectra reflects the interface layer resistance arising outside the electrode The smaller the arc radius, the higher the charge transfer effectiveness The arc radii for the Agdoped CNPs and CNPs were found to be and 14 U, respectively This suggests that the Ag-doped CNPs has a lower charge transfer resistance than that of the CNPs, which can accelerate the interfacial charge-transfer process The smaller charge-transfer resistance provides more contribution to the enhanced photocatalytic activity via the easy transfer of charge Thus, the Ag-doped CNPs possess a smaller arc radius with an enhanced photocatalytic activity as compared to the host CNPs 3.5 Diffuse reflectance spectroscopy (DRS) analysis Fig shows the DRS of the Ag-doped CNPs and CNPs to find energy band gap The spectra are plotted in terms of F(R)n Fig Wood and Tauc's plot to find band gap and the variation of the band gap of the ACNPs and host CNPs Inset shows the transmittance vs wavelength of the ACNPs and host CNPs (equivalent to the absorption coefficient) in Y-axis and energy in Xaxis KubelkaeMunk equation [26] at any wavelength is represented as follows: FRị ẳ Rị2 2R (1) where R is the absolute reflectance of the sample and F(R) is KubelkaeMunk function The optical band gap represents the electron excitation from the valance band to conduction, which is determined by the following relation: (F(R) hy)n ¼ A(hy À Eg), (2) where n ¼ for a direct allowed transition, n ¼ 1/2 for an indirect allowed transition, A is the constant and hy is the photon energy In order to get the direct band gap, the linear part of the curve was extrapolated to (F(R) hy)2 ¼ The band gap energy (Eg) values are estimated from the plot and found to be 1.6 and 2.15 eV for the Ag-doped CNPs and host CNPs, respectively The expected changes in the band gap values in the Ag-doped CNPs are due to the increase of carrier concentrations, leading to the BursteineMoss effect [27] 3.6 BET analysis Fig Impedance plot of the synthesized ACNPs and host CNPs The N2 adsorptionedesorption measurement at a liquid nitrogen temperature of 77 K was used to study the porosity and textural properties of the synthesized Ag-doped CNPs and CNPs The combustion-derived products usually have a large surface area due to liberation of heat (exothermicity) During combustion reaction, the temperature is just enough to form nuclei but too short for grain growth The BET surface area of the Ag-doped CNPs and CNPs were found to be 15 m2/g and 30 m2/g, respectively, as shown in Fig The large surface area of the formed sample is due to the uniform distribution of nanosized particles as observed in the SEM images, and the same may also be supported by the XRD analysis Inset of Fig shows the average pore diameter and isotherms for the Ag-doped CNPs and CNPs, respectively It is clear that all isotherm curves reach a plateau as the relative pressure reaches unity [28] This indicates that the materials prepared have no pores in the macropore region (i.e., 500 Å) and means pores are in the mesopore region, and the sample is mesoporous 48 B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 of dispersion of particles per volume, the increase in number of active sites as compared to other samples Hence, the particle size also plays an important role in the catalytic activity [29] It was found that the photo-decolorization of MG for CNPs (GCR) was 97%, whereas it was only 85% for CNPs (Fig 9c) As band gap decreases there will be an increase in the redox potential of the photo-excited electronehole pairs, thus significantly increasing the activity of the photocatalyst Fig Nitrogen adsorption and desorption isotherms and pore volume distribution curves (inset) of the synthesized ACNPs and host CNPs 3.7 Photocatalytic activity The photocatalytic decomposition of MG dye was carried out for the prepared Ag-doped CNPs and CNPs (Fig 9a and b) The Agdoped CNPs photocatalyst displays the best performance due to the uniform structure with less particle size, the increase in amount 3.7.1 Mechanism of MG dye decolorization The mechanism involved in the photocatalytic activity of MG dye under UV light is proposed in Fig 10 On the surface of the photocatalyst, oxygen molecules (O2) and water molecules (H2O) are absorbed easily owing to the porous spinel structures under UV light irradiation These molecules are not only adsorbed on the outer surface but also adsorbed on the internal surface of the CNPs As mentioned above, the porous structure is mainly responsible for the absorption of the aforementioned molecules and the capture of incident light When CNPs absorb photons with sufficient energy, these electrons (eÀ) jump into the conduction band (CB) from the valence band (VB), leaving behind the same number of holes (hỵ) in the VB If these photogenerated electrons and holes become free, they automatically move towards the surface of the CNPs and are got captured by absorbed O2, OHÀ Of course, the absorbed MG molecules can also capture the carriers to ionize it After that, a lot of superoxide radicals (OÀ ) and hydroxyl radicals (OH ) are formed These produced active radicals react with the ionized MG molecules to decompose them into the harmless H2O, CO2, and mineral Fig (a) % decomposition of MG under UV light for the synthesized host CNPs; (b) % decomposition of MG under UV light for the synthesized ACNPs; and (c) Spectral absorbance of MG with the variation of irradiation time under UV irradiation B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 49 Fig 10 Mechanism for the photocatalytic decomposition of MG under UV light irradiation À 2À acids (NOÀ , NO3 , or SO4 ) [30e32] During this step, partial strong oxidizing holes (hỵ) can also directly participate in the decomposition of the MG molecules According to the results obtained, the self decomposition of MG molecules is very negligible [6] [7] Conclusion The present work demonstrated the efficient ability of preparing the Ag-doped CNPs with enhanced photocatalytic properties by using the Jatropha-oil assisted low temperature combustion method The PXRD analysis clearly confirms the formation of cubic and tetragonal phases with an average crystallite size of around 12 nm The energy band gap (Eg) values of the Ag-doped CNPs and host CNPs samples were found to be 1.6 and 2.15 eV, respectively The electrochemical properties of the synthesized samples possess the redox peak with an enhanced peak current, and the arc radii of the Ag-doped CNPs and CNPs were found to be and 14 U respectively This indicates that the Ag-doped CNPs has a lower charge transfer resistance with enhanced photocatalytic activity The photocatalytic activity of the Ag-doped CNPs is highly active towards the photodecolorization of MG with a very high yield (97%), due to the smaller crystalline size, the lesser band gap, and the presence of more number of active sites These synthesized photocatalysts are also recoverable and recyclable [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] References [18] [1] N Ali, A.K Kurchania, S Babel, Bio-methanisation of Jatropha curcas defatted waste, J Eng Technol Res (3) (2010) 038e043 [2] Raphael M Jingura, Downmore Musademba, 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the synthesized ACNPs; and (c) Spectral absorbance of MG with the variation of irradiation... gases and release of enormous amount of heat to form spinel ferrites [23] Fig 2(a) shows the spinel structure with porous flakes and agglomeration of particles, whereas in case of the Ag-doped sample... Nil Fig PXRD studies of the synthesized ACNPs and host CNPs 46 B.S Surendra / Journal of Science: Advanced Materials and Devices (2018) 44e50 Fig SEM micrographs of the synthesized ACNPs and
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