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Aero-gel based cerium doped iron oxide solid solution for ultrafast removal of arsenic Prashant Kumar Mishra, Parveen Gahlyan, Rakesh Kumar, and Pramod Kumar Rai ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02006 • Publication Date (Web): 26 Jun 2018 Downloaded from http://pubs.acs.org on July 2, 2018

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ACS Sustainable Chemistry & Engineering

Aero-gel based cerium doped iron oxide solid solution for ultrafast removal of arsenic Prashant Kumar Mishra,a*,b Parveen Gahlyanb , Rakesh Kumarb and Pramod Kumar Raia* a

Environment Safety Group, Centre for Fire, Explosive and Environment Safety, Timarpur, Delhi110054, India b ∗

Department of Chemistry, University of Delhi, Delhi-110007, India

Author for correspondence ([email protected]) and ([email protected])

Prashant Kumar Mishra (email i.d.: [email protected]) Parveen Gahlyan (email i.d.: [email protected]) Rakesh Kumar (email i.d.: [email protected]) Pramod Kumar Rai (email i.d.: [email protected])

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Abstract: A solid solution of aero-gel based cerium doped iron oxide nanoparticles have been utilized for the first time for ultra sonic wave assisted adsorptive removal of arsenic from aqueous medium. The FE-SEM and HR-TEM images revealed a novel morphology of hollow architectures with irregular distribution in sizes in which the particles are interconnected with each other in a long range network. The HR-XRD analysis indicated the cubic fluorite type structure with Fm-3m space group which is retained even after adsorption of As(III). The Raman study and Lebail refinement confirmed the formation of solid solution of Fe and Ce oxide nanoparticles. The room temperature ferromagnetism was observed for CeO2 NPs (Ms 0.0209 emu g-1) which is attributed to higher concentration of oxygen vacancies and increased (Ms 0.0287 emu g-1) after doping of iron. The adsorption pattern of As(III) is well defined by Redlich-Peterson isotherm while the adsorption is governed by pseudo second order kinetics. The HR-XPS and diffuse reflectance spectroscopy revealed the formation of variable oxidation state of metal ions which facilitate the oxidation of As(III) (more toxic) to As(V) (less toxic) during adsorption process. The effective removal of arsenic (more than 80 %) was observed within 2.5 min of initial adsorption process and approximately 99 % removal was achieved within 10 min of adsorption. The adsorption capacity of our best adsorbent was found to be 263 mg g-1. The effect of pH and interfering ions on adsorption capacities of synthesized adsorbents revealed its efficacy over the wide range of pH. Key words: Novel morphology; Ferromagnetism; Oxygen vacancy; Arsenic removal; Cerium oxide NPs.


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Introduction Arsenic is a metalloid element and naturally present in earth crust, widely distributed throughout the environment and extremely toxic in its inorganic form.1 The long term consumption of arsenic through drinking water and food can cause several chronicle disease including cardiovascular, neurotoxicity and diabetes.2 According to WHO, Bangladesh and India are one of the most affected countries dealing with arsenic exposure, approximately 45 million people in Bangladesh are at risk of being exposed with arsenic.3,4 Results from mass health study revealed that more than 400 people in Bangladesh have lost their life due to arsenic poisoning from 2000 to 2009 and many are still suffering from skin lesions and cancer.4 The new regulations of Environmental Protection Agency (EPA) in 2001 attuned the standard for arsenic in drinking water from 50 ppb to 10 ppb.5 This new regulation has embarked severe water contamination through arsenic in the many regions of United State of America (USA) and England.2-6 The extensive literature survey exposed that nanotechnology is pioneering technique for designing ideal adsorbents which provide large interface for adsorbate because of abundant surface active sites, facile mass transportation and aptitude to modify their surface charge transport properties.7 Among the several methodologies for decontamination of water, adsorption has been considered as one of the cheapest and frequently used techniques due to its ease of application, higher efficiency and wide availability.4 There are myriads of adsorbents that have been applied and extensively explored for removal of arsenic ranging from simple form of graphene, activated carbon to transition metal oxides based composites. Among the numerous available adsorbents, rare earth metal oxides are more attractive; particularly cerium oxide based composites enjoy a wide range of applications. The ability of ceria to interconvert between +3 and +4 oxidation states at certain environmental conditions is the fascinating property and one can utilize it during adsorption process to increase the efficacy of adsorbents. In addition, ceria is relatively cheaper than other rare earth metals and exhibited good adsorption capacities towards arsenic tainted water.8 However, CeO2 nanoparticles alone is extremely fine and often pass through ordinary filters. Therefore, it is recommended that the application of ceria based composites will be more suitable for remediation of water. Doping or impregnation of other metals on CeO2 NPs such as Fe, Ti, Ni, Mn etc., are advantageous and definitely improve the efficiency of CeO2 nanoparticles based adsorbent due to synergistic effect.9 Cerium oxide modified carbon,10 Cerium exchanged Zeolite,11 hydrous cerium oxide4,12 and ceria modified chitosan13 demonstrated the excellent arsenic adsorption over the wide range of pH. Recently, cerium oxide or hydroxide ACS Paragon Plus Environment


based adsorbents doped with Fe in its various form, catch more attention for arsenic removal. Ce-Fe metal oxide with CNT14, CeO2 and Fe3O4-incorporated microcapsule,15 Fe-Ce alkoxide16 and Ce-Fe mixed oxide NPs17 have been utilized for the removal of arsenic. Though, these articles revealed the better performance of ceria towards arsenic decontamination and showed good efficiency yet, lacked in terms of practical applicability and ultrafast removal of arsenic. In addition, the time taken to attain equilibrium was too slow for the above mentioned articles e.g. Li et al, hydrous CeO2 NPs12 and Chen et al, Ce–Fe mixed oxide decorated multi walled carbon nanotubes14 took 120 and 300 min respectively to reach equilibrium while Setyono and co-workers study on multi-metal oxide incorporated microcapsules demonstrated15 equilibrium in 60 min. Yu et al and Chen et al adsorbents i.e., Cerium oxide modified activated carbon10 and nanostructured hollow iron–cerium alkoxide16 took 60 min and 200 min, respectively to attain equlibrium for removal of As(III) from aqueous media. In the present study, we have demonstrated an aero-gel based solid solution of cerium doped iron oxide nanoparticles in which ceria is replaced from its lattice by iron creating high concentration of oxygen vacancies and defects, which significantly increased the performance of our material for removal of arsenic. The dynamic equilibrium was obtained within 10 min of initiating the adsorption process with maximum adsorption capacity of 263 mg g-1 which is highest amongst any other cerium based adsorbents to the best of our knowledge. The ultrafast removal and high adsorption capacity of Fe@Ce oxide nanoparticles are attributed to two major factors (i) Aero-gel based solid solution, which has benefit to create ultra fine size, novel morphology, highly porous network, low density and high surface area comprised nanomaterial18 and (ii) Ultrasonic irradiation enhanced adsorption process by virtue of acoustic cavitations which is the configuration, development and collapse of micrometrical bubbles created by proliferation of pressure wave through a liquid and conversion of sound energy into kinetic energy which enabled the mass diffusion over the interface of adsorents.19-20 Experimental The aero-gel based oxalate route has been employed for the synthesis of CeO2 NPs as reported in our previous article.18 The solid solution of iron doped cerium oxide nanoparticles were synthesized using Cerium nitrate hexahydrate, FeCl3 (10 % and 20 %) w/w and oxalic acid (stoichiometric amount). Initially cerium nitrate hexahydrate was dissolved in ethanol, and toluene solution, then 10% and 20% w/w FeCl3 solution (in ethanol) was mixed with cerium nitrate hexahydrate solution. Afterwards, the ethanol dissolved oxalic acid solution ACS Paragon Plus Environment

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was mixed drop-wise with cerium nitrate hexahydrate and FeCl3 solution. The ration of ethanol and toluene were kept at 1:1.8. A reddish yellow dense solution was formed which is placed in parr reactor and super-critically dried, finally red color ultra fine low dense Fe@Ce oxide NPs were collected and further used for arsenic removal. The reaction involved during synthesis can be represented as given below.

Result and Discussion Nitrogen adsorption desorption isotherm of CeO2, [email protected] oxide and [email protected] oxide indicates the highest uptake of nitrogen and maximum surface area for CeO2 NPs (Fig 1). The surface area of CeO2 NPs was decreased from 268 to 87 m2 g-1 (Table 1), due to reduction in mesopore and micropores along with addition of iron in the matrix of CeO2 NPs. The average pore sizes of adsorbents were found to be 8-10 nm range. The bulk density of CeO2 NPs was estimated around 0.049 g cm-3, which is much lower than the actual density of CeO2 (7.132 g cm-3). Furthermore, the doping of iron increases the bulk density from 0.049 g cm-3 to 0.073 g cm-3 (Table 1) which is still approximately 100 times less than the actual bulk density of cerium oxide. The lower bulk density helps for thoroughly dispersion of adsorbent in aqueous medium and consequently enhances the efficiency of material. The morphology of our best prepared adsorbent ([email protected] oxide NPs) has been observed using FE-SEM and HR-TEM analysis (Fig 2). The HR-TEM images (Fig 2a-2c) indicate a heterogeneous hollow architecture of interconnected nanoparticles with the appearance of some solid nanoparticles within it. The particles form a long range network, which is quite rare for cerium based composites and significantly enhances the efficacy of material during adsorption. The reason for formation of hollow architecture maybe due to Ostwald ripening16. However, the actual reason for obtaining these type of architecture by assembling process is still challenge in nano-material research. The SAED image ascribed the polycrystalline nature of [email protected] oxide NPs and the (hkl) values are well matched with HR-XRD pattern. The FE-SEM images (Fig S1) depicted porous network of interconnected nanoparticles. However, due to charged nature and extremely less density of material the clear estimation of surface morphology from FE-SEM is difficult. The interconnected network enables the diffusion of pollutant very smooth and quick, which is the main reason for observing the super-quick dynamic equilibrium and superior performance of Fe@Ce oxide NPs. The HR-XRD pattern of CeO2 ACS Paragon Plus Environment


NPs indicated the diffraction peaks at plane (111), (200), (220) and (311) with Fm-3m space group and face centred cubic (fcc) crystal structure (JCPDS #34-0394), (Fig 3a). After doping of iron, the HR-XRD analysis displayed the same reflections as cubic ceria and indicating the formation of homogeneous solid solution. A single phase for solid solution of Fe@Ce oxide NPs is formed because of replacement of Ce3+ or Ce4+ by Fe3+ or Fe2+. The solid solution can be represented as Ce1-xFexO2-y, indicating that electrical neutrality is achieved by the Ovacancy formation mechanism.22 The crystallite sizes of all adsorbents were calculated using Scherrer's equation (1) and listed in Table (2).

Table 2 clearly indicates the variation in crystallite size and lattice parameters with increase in concentration of iron. Due to smaller size of Fe3+ (0.64 Å) and Fe2+ (0.77 Å) as compare to Ce3+ (1.01 Å) and Ce4+ (0.92 Å) cations, the lattice parameters are decreased.23,24 Furthermore, the stability of all adsorbents have been investigated after adsorption of As(III). Fig 3b clearly represents the same reflections as cubic ceria after adsorption of As(III), which indicates that all adsorbents are quite stable even after adsorption of As(III). Raman spectrum of pure and iron doped cerium oxide nanoparticles are represented by Fig 4. The raman mode in pure CeO2 NPs is positioned at 460 cm-1 (F2g) with pronounced asymmetry, characteristic for ultra fine nanocrystal of ceria. Another raman mode nearby 600 cm-1 originates from intrinsic oxygen vacancies.25-27 Fig 4 clearly indicates the shift in raman spectrum after doping of iron towards lower energy side and the full width at half maximum (FWHM) for F2g exhibits broadening after increasing the concentration of iron in the matrix of ceria. There could be two plausible reason responsible for this (i) The lattice expansion or reduction by substitution of Fe2+/Fe3+ in the matrix of ceria and (ii) The presence of oxygen vacancies. Moreover, the raman spectrum also confirmed the HR-XRD results, as the perfect solid solution is formed because no raman mode is observed for iron oxide phases. The inset of Fig 4 indicates no change in F2g mode after adsorption of As(III) which confirmed the structural stability of adsorbent. We also observed room temperature ferromagnetism for CeO2 NPs (Fig 5) and it is worth to mention that the Ms value for our CeO2 NPs is quite high as compare to many other reports which indicates the presence of large oxygen vacancies in our material. C. N. Rao et al suggested that cerium can have multiple valence state (Ce3+ and Ce4+) and oxygen vacancies which lead to create magnetic moments by nearest neighbouring interaction i.e., exchange of (Ce4+-O-Ce3+) for Ce-ions.28-30 After doping of iron oxide, the Ms value increases gradually ACS Paragon Plus Environment

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which is quite obvious as iron is magnetic in nature (Table 3). The higher value of Ms is consequence of strong interaction of nearest neighbouring ions i.e., (Ce4+-O-Fe3+) or (Ce3+-OFe2+) as compare to (Ce4+-O-Ce3+). Moreover, when the concentration of either Fe3+or Fe2+ is increased, the amount of (Ce4+-O-Fe3+) or (Ce3+-O-Fe2+) interactions are also increased, which causes the increment of ferromagnetism in samples. UV-visible diffuse reflectance spectra of CeO2 NPs and iron doped cerium oxide NPs are represented in Fig S2. The DRS study indicates three maximum splits (Fig S2), bands at 232 and 292 nm are attributed to arise from 4f-5d transition of Ce 3p-ion,32 while band at 330 nm is due to charge transfer transition from O2- in O 2p to Ce4+ in Ce 4f.32,33 After doping of iron, a new hump in the range of 500 to 600 nm wavelength was also observed which is consistent from previous studies and accredited to the presence of Fe2+ and Fe3+ ions. From the Tauc plots of these samples ((ahn)2 (eV/cm)2 Vs hv (eV)), the band gaps were calculated and found to be decreased after doping of iron from 3.001 eV to 2.476 eV. (Fig S3a, Fig S3b and Fig S3c) and Table 3. Adsorption isotherms The adsorption isotherm models such as Langmuir, Freundlich, and Redlich-Peterson (R-P) were used to analyze the adsorption pattern of As(III). The linear form of these models can be expressed by equation (2), (3) and (4). (2) (3) (4) Where, Ce is equilibrium concentration of adsorbate in mg L-1 and Qe is the adsorbed amount of pollutant at equilibrium in mg g-1 and Qm is maximum adsorbed amount of pollutant in mg g-1. The langmuir fitted curve was plotted between Qe Vs Ce for the adsorption of As(III), (Fig S4a). Values of Qm and b were calculated using the slope and intercept of linear plot (R2 ≥ 0.99). The maximum adsorption capacity was found to be 263 mg g-1 for [email protected] oxide NPs (Table 4). KF and n are Freundlich constants and can be calculated from graph LnQe Vs LnCe, (Fig S4b). The values of n were found to be > 1 for all adsorbents and suggested the favorable adsorption of As(III). The R-P isotherm models predict the adsorption by considering the value of α, when α tends to zero; the adsorption would be heterogeneous, while, when α tends to 1; the adsorption would be monolayer.34 The optimum values of ɑ ACS Paragon Plus Environment


(calculated by trial and error method) were found in the range of 0.84-0.92 (closer to 1) for all adsorbents which indicated that the adsorption of As(III) followed monolayer pattern more precisely than heterogeneous. Moreover, the correlation coefficients (R2) for R-P isotherm were found to be in the range of 0.995-0.998 for all adsorbents. Hence R-P is the best fitted model in our study for adsorption of As(III) on CeO2 NPs, [email protected] and [email protected] oxide NPs (Fig 6a). Kinetics models The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to examine the adsorption mechanism and rate controlling steps (chemical reactivity and diffusion control) and can be represented by equation (5) and (6).35 (5)

+

(6)

Where, Qt is the amount of adsorbate adsorbed at time t and Qe is the equilibrium adsorption capacity in mg g-1. k1 and k2 are the rate constants for first and second order kinetics respectively. The adsorption data revealed that pseudo second order model was best fitted (R2 close to 1) (Fig S5) than pseudo first order. The values of all kinetic parameters are given in Table (5). Intra particle diffusion model can be represented by equation (7) (7) Where, Kd is the intraparticle diffusion rate constant determined by using the slope of plot Qt Vs t0.5, C is the thickness of boundary layer which can be estimated by intercept of equation (8). Intraparticle diffusion is a slow step progression and it can be considered as rate limiting step if the plot of Qt Vs t0.5 is linear and passes through the origin. However, Fig 6b portrayed the two lines for all adsorbents over variable concentrations of As(III). This indicates that some other mechanism are also involved along with intraparticle diffusion for adsorption of As(III).14 The diffusion constant Kd is calculated from the regression of the second line which is relatively slow process and could be rate limiting step. The first line depicted the surface adsorption step, which is extremely fast and cannot be the rate limiting step. The values of Kd and C for all adsorbents are given in Table (5). The overall adsorption process of As(III) is


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possibly controlled by more than one steps which includes, intraparticle diffusion, outer diffusion and adsorption of adsorbate i.e., As(III) onto active sites of adsorbents. Effect of pH The removal efficiency of all our adsorbent as a function of pH for the removal of As(III) is portrayed through Fig 7a. The optimum pH range for removal of As(III) was found between 6-9, which follows the trend with earlier reports.14,36 The adsorption behavior of As(III) is accredited to dissimilar arsenic speciation and the adsorbent surface charge. The speciation in arsenic (As(III)) species and equilibrium constant are given below,14 H3AsO3

H2AsO3- + H+, pKa = 9.23

H2AsO3-

HAsO32- + H+, pKa= 12.1

The point of zero charge (PZC) of all synthesized adsorbents were found in the range of 7.5 8.5 pH. This indicated that below PZC the adsorbent surface is positevely charged while above PZC, the adsorbent surface is negatively charged. Since As(III) mainly existed in the non-ionic form between pH 4-9, hence not a much deviation is observed in adsorption capacities of all adsorbents in this range. However, at pH 2 the adsorption capacities were decreased in significant amount due to partial dissolution of iron and ceria in acidic condition.37 Moreover, at pH greter than 9 H3AsO3 existed in its ionic form i.e., H2AsO3- and the adsorbent surface charge would be negative because pH > PZC, which lead to cause electrostatic repulsion between adsorbate and adsorbent consequently large decrease in adsorption capacities were observed above pH 9. Effect of competing ions Many co-existing anions such as (Cl-, F-, NO3-, SO42-, PO43-) are also present in ground water along with arsenic. These anions will surely compete with As(III) on surface active binding sites of adsorbent and may interfere the removal efficiency by altering the electrostatic charge on surface of adsorbents.14,35 Fig 7b reveals that Cl-, F- did not affect the percentage removal of As(III) while SO42- and NO3- slightly decreased the efficiency of all adsorbents. However, the presence of phosphate ions decreased the percentage removal of As(III) at a great extent. This can be explained on the basis of three major factors: (i) electrostatic attraction between adsorbents and phosphate ions, (ii) surface complexation of phosphate ions on adsorbents and (iii) isostructural towards H3AsO3 ions.37



Effect of Contact time The effect of contact time study revealed some astounding behavior for removal of As(III) using our synthesized adsorbents. The graph plotted between Concentration (Ct mg L-1) Vs Contact time (min) revealed that almost 75 to 80 % removal of As(III) was achieved during first 2.5 min of adsorption process and more than 98 % removal of As(III) was obtained when the concentration lie between 1-25 mg L-1. Moreover, the equilibrium was achieved within 10 min of initial adsorption process (highlighted by green color in Fig 7c), which is remarkable and attributed to novel morphology, high concentration of oxygen vacancies, small particle size, high surface area and extremely low bulk density of all adsorbents. It is clear from the Fig 6c and from the adsorption isotherms that the most efficient adsorbent for arsenic removal is [email protected] oxide NPs. This is due to synergistic effect of iron doping on cerium oxide NPs which comprehensively enhanced the physical and chemical property of adsorbent. The experiments have been carried out to check the potential leakage of Fe and Ce during adsorptive removal of As(III) using [email protected] oxide NPs. The results illustrated that extremely small amounts of Fe and Ce i.e., ≤ 9 ppb and ≤ 4 ppb respectively, were present in the water body system after 4 h of adsorption process, such a low concentration of metals are non-toxic. Therefore, we can conclude that there is no risk of further contamination of water via the leakage of adsorbent. We have also performed the FE-SEM-EDAX elemental mapping after adsorption of As(III) for both iron doped cerium oxide (Fig S6a and Fig S6b). The adsorption of As(III) represented by blue dots in Fig S6a and S6b was homogeneously occurred as distribution of arsenic is almost everywhere in both samples. Though it is very difficult to compare our findings with others due to various environmental conditions and removal process yet some iron and cerium oxide based adsorbents are listed in Table 6 and indicates the superior performance of our adsorbents. There are many factors which considerably affect the performance of our adsorbents over others such as extremely low density, small particles size, novel morphology, high surface area, large number of defects, high concentration of oxygen vacancies and variable oxidation state of metals which collectively facilitates the overall adsorption process of arsenic. Besides, ultra-sonication enables the mass diffusion of pollutant over the interface of adsorbent and formation of micrometrical bubbles and conversion of sound energy into kinetic energy are significantly contribute for ultrafast removal of As(III) using Fe@Ce oxide NPs.


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Removal mechanism of As(III) HR-XPS analysis has been widely utilized for determining the elemental composition and oxidation state of composites. We have also used this technique to elucidate the adsorption mechanism of As(III). The survey spectra of our best prepared adsorbent i.e., [email protected] oxide NPs before and after adsorption of As(III) is given in Fig 8a. The significant changes in peak positions of Ce 3d and Fe 2p is easily recognizable. Moreover, a new peak around (4446) eV was also observed which is accredited to As(III). This indicates that As(III) was transferred onto the surface of [email protected] during adsorption process.36 The XPS spectra of Ce 3d metal before adsorption of As(III) indicates the two sets of doublets (i) 3d3/2 at 901±0.2 eV and 905.4±0.3 eV and (ii) 3d5/2 at 882.6±0.2 eV and 885.5±0.3 eV these peaks correspond to both oxidation state of cerium metal i.e., Ce3+ and Ce4+ (Fig 8b).36,38,40,41 After adsorption the lowering of binding energies are observed for Ce 3d metal as the doublets are found around (i) 3d3/2 899.52±0.2 eV and 903.92 ±0.2 eV and (ii) 3d5/2 at 881.18±0.2 eV and 884.0±0.2 eV, these peaks also correspond to both oxidation state of ceria (Fig 8c). The calculation of relative percentage content using area under curve for Ce3+ is 55% before adsorption of As(III). However, the content of Ce3+ is increased from 55 % to 63.6 % after adsorption of As(III). Which is probably due to transfer of electron from As(III) to Ce4+ ions during adsorption process. The XPS for Fe 2p metal before and after adsorption of As(IIII) is portrayed by Fig 8d and Fig 8e. The binding energies for Fe 2p are consistent with previous literature indicating the presence of both Fe2+ and Fe3+ ions.31,36,14 The binding energies of 725.23±0.3 eV and 711.63±0.1 eV were assigned to Fe 2p1/2 and Fe 2p3/2, respectively, while the binding energies of 710.06±0.2 eV and 724.06±0.2 eV were accredited to Fe2+ and Fe3+ respectively.1,14,16,35 After adsorption the shift in binding energies were observed, the peaks at 708±0.1 eV, 710.32±0.2 eV and 722.19±0.2 eV were accredited to Fe2+ ions, while 713.82±0.1 eV and 724.51±0.32 eV, correspond to Fe3+ ions.30 The relative percentage content of Fe3+ was found to be 56.5 % before adsorption of As(III) and percentage calculation for Fe3+ after adsorption was found nearby 39 %. This large decreased in content of Fe3+ indicated the possible reduction of Fe3+ to Fe2+ after adsorption of As(III). This phenomenon is accredited to the redox reaction occurring between iron and arsenic ions during adsorption process. The XPS for As 3p metal ions also confirmed the redox reaction between adsorbent and pollutant. Fig 8f clearly reveals the presence of both As(V) and As(III) metal ions as binding energies for As 3p reveals the peaks around 44.8±0.3 eV and 46.6 ±0.1 eV, which correspond to As(III) and As(V), respectively.36,39 The As(V) content (61.5 %) was found to be larger than As(III) content and validate our assumption for ACS Paragon Plus Environment


reduction of Ce4+ and Fe3+ metals ions by transferring of electrons from As(III) during adsorption process. From the above discussion, it is clear that the removal of As(III) by [email protected] metal oxide NPs can be divided into two part (i) The presence of Ce(IV) and Fe(III) ions in [email protected] oxide NPs leads to effectual oxidation of As(III) (more toxic) to As(V) (less toxic) (ii) The formed As(V) can then be more easily adsorbed on [email protected] oxide NPs by formation of monodentate and bidentate complexes (Fig 9). Conclusion In summary, an aero-gel techniqe has been successfuly employed for the synthesis of solid solution of Fe@Ce oxide NPs for arsenic removal in aqeous media. The HR-XRD and Raman study revealed the successful doping of iron in the matrix of CeO2 NPs, and all adsorbents were quite stable even after adsorption of As(III). The FE-SEM and HR-TEM analysis indicated a novel hollow achitecture of interconnected nanoparticles which could be the main reason for superior performance of our adsorbents. The ferromagnetic behaviour for non-magnetic CeO2 NPs was observed at room temperature and the magnetism was found around 0.0209 emu g-1. Such a high magnetism was accredited to presence of high concentration of oxygen vacancies. The ultra fast removal of arsenic contaminated water was achieved over the wide pH range (2-10) at variable environmetal conditions. The adsorption pattern of As(III) can be well described by Redlich-Petreson isotherm followed by pseudo second order kinetics. The intraparticle diffusion model expalined pore diffusion as a rate limiting step during adsorption of As(III). The EDAX elemental mapping indicated the homogeneous adsoprtion of As(III). The XPS study before and after adsorption of As(III) portrayed the presence of dual oxidation state of both ceria and iron metals and the mechanism for removal of As(III) was majorly governed by oxidation, adsorption and surface complexation. It is concluded that our adsorbents are potentially useful and efficient for effective and ultrafast removal of arsenic from water. The synthesized materials contain astounding physical properties such as, novel morphology of hollow shaped interconnected nanoparticles, defects, oxygen vacancies, high surface area, extremely low bulk density, room temperature ferromagnetism and variable oxidation states of metal ions, which can be utilized in the field of sensor, remediation of atmosphere from toxic gases and biomedical applications.


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Acknowledgement Authors are thankful to Rajeev Narang, Director CFEES, Delhi for giving permission to carry out and publish this work. Authors are also thankful to Dr. Govind Gupta (NPL Delhi) for performing HR-XPS analysis and University Science Instrumentation Centre (USIC) for performing FE-SEM and HR-TEM analysis. Supporting Information: The details of material characterization, sample preparation, instruments and procedure for adsorption studies have been given in electronic supporting information (ESI). References : 1.

Guo, S.; Sun, W.; Yang. W.; Xu, Z.; Li, Q.; Shang, J. K. Synthesis of Cu2O nanospheres decorated with TiO2 nanoislands, their enhanced photoactivity and stability under visible light illumination, and their post-illumination catalytic memory. ACS Appl. Mater. Interfaces. 2015, 7, 26291-26300. DOI 10.1021/am500131b.

2.

Dai, M.; Zhang, M.; Xia, L.; Li, Y.; Liu, Y.; Song, S. Combined Electrosorption and Chemisorption of As(V) in Water by Using Fe-rGO@AC Electrode ACS Sustainable Chem. Eng. 2017, 5 (8), 6532-6538. DOI 10.1021/acssuschemeng.7b00633

3.

Gomaa, H.; Khalifa, H.; Selim, M. M.; Shenashen, M. A.; Kawada, S.; Alamoudi, A. S.; Azzam, A. M.; Alhamid, A. A.; El-Safty, S. A. Selective, Photoenhanced Trapping/Detrapping of Arsenate Anions Using Mesoporous Blobfish Head TiO2 Monoliths.

ACS

Sustainable

Chem.

Eng.

2017,

5

(11),

10826-10839.

DOI 10.1021/acssuschemeng.7b02766. 4.

Sakthivel, T. S.; Das, S.; Prat, C. J.; Seal, S. One-pot synthesis of a ceria–graphene oxide composite for the efficient removal of arsenic species. Nanoscale. 2017, 9, 33673374. DOI 10.1039/C6NR07608D.

5.

Setyono D.; Valiyaveettil. S. Chemically Modified Sawdust as Renewable Adsorbent for Arsenic Removal from Water. ACS Sustainable Chem. Eng. 2014, 2 (12), 27222729. DOI 10.1021/sc500458x.

6.

Doshi, R. K.; Mukherjee R.; Diwekar U. M. Application of Adsorbate Solid Solution Theory To Design Novel Adsorbents for Arsenic Removal Using CAMD. ACS Sustainable Chem. Eng. 2018, 6 (2), 2603-2611. DOI 10.1021/acssuschemeng.7b04094.



7.

Page 14 of 36

Krishnamoorthy, K.; Veerpandian, M.; Zhang, L. H.; Yun, K.; Kim, S. J. Surface chemistry of cerium oxide nanocubes: Toxicity against pathogenic bacteria and their mechanistic

study.

J.

Ind.

Eng.

Chem.

2014,

20,

3513-3517.

DOI

10.1016/j.jiec.2013.12.043. 8.

Hu, J. S.; Zhong, L. S.; Song, W. G.; Wan, L. J. Synthesis of hierarchically structured metal oxides and their application in heavy metal ion removal. Adv. Mater. 2008, 20, 2977-2982. DOI 10.1002/adma.200800623.

9.

Hua, M.; Zhang, S.; Pan, B.; Zhang, W.; Lv, L.; Zhang, Q. Heavy metal removal from water/wastewater by nanosized metal oxides: a review. J. Hazard. Mater. 2012, 211212, 317-331. DOI 10.1016/j.jhazmat.2011.10.016

10. Yu, Y.; Zhang, C.; Yang, L.; Chen, J. P. Cerium oxide modiﬁed activated carbon as an efﬁcient and effective adsorbent for rapid uptake of arsenate and arsenite: material development and study of performance and mechanisms. Chem. Eng. J. 2017, 315, 630638. DOI 10.1016/j.cej.2016.09.068. 11. Haron, M. J.; Rahim, F. A.; Abdullah, A. H.; M. Hussein, Z.; Kassim, A. Sorption removal of arsenic by cerium-exchanged zeolite P. Mater. Sci. Eng. B, 2008, 149, 20420. DOI 10.1016/j.mseb.2007.11.028. 12. Li, R.; Li, Q.; Gao, S.; Shang, J. K. Exceptional arsenic adsorption performance of hydrous cerium oxide nanoparticles: Part A. Adsorption capacity and mechanism. Chem. Eng. J. 2012, 185-186, 127-135. DOI 10.1016/j.cej.2012.01.061. 13. Zhang, L.; Zhu, T.; Liu, X.; Zhang, W. Simultaneous oxidation and adsorption of As(III) from water by cerium modified chitosan ultrafine nanobiosorbent. J. Hazard. Mater. 2016, 308, 1-10. DOI 10.1016/j.jhazmat.2016.01.015. 14. Chen, B.; Zhu, Z.; Ma, J.; Qiua, Y.; Chen, J. Surfactant assisted Ce–Fe mixed oxide decorated multiwalled carbon nanotubes and their arsenic adsorption performance. J. Mater. Chem. A. 2013, 1, 11355-11367. DOI 10.1039/C3TA11827D. 15. Setyono, D.; Valiyaveettil, S. Multi-metal oxide incorporated microcapsules for efficient As(III) and As(V) removal from water. RSC. Adv. 2014, 4, 53365-5373. DOI

10.1039/C4RA09030F. 16. Chen, B.; Zhu, Z.; Liu, S.; Hong, J.; Ma, J.; Qiu, Y.; Chen, J. Facile hydrothermal synthesis of nanostructured hollow iron–cerium alkoxides and their superior arsenic ACS Paragon Plus Environment

Page 15 of 36 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


adsorption performance. ACS Appl. Mater. Interface. 2014, 6 (16), 14016-14025. DOI 10.1021/am503343u. 17. Sahu, U. K.; Sahu, M. K.; Mohapatra, S. S.; Patel, R. K. Removal of As (V) from aqueous solution by Ce-Fe bimetal mixed oxide. J Environ. Chem. Eng. 2016, 4, 28922899. DOI 10.1016/j.jece.2016.05.041. 18. Mishra, P. K.; Saxena, A.; Rawat, A. S.; Dixit, P. K.; Kumar, R.; Rai, P. K. Surfactantfree one-pot synthesis of low-density cerium oxide nanoparticles for adsorptive removal of arsenic species. Environ. Prog. Sustainable Energy. 2018, 37, 221-231. DOI 10.1002/ep.12660. 19. Dastkhoon, M.; Ghaedi, M.; Asfaram, A.; Goudarzi, A.; Langroodi, S. M.; Tyagi, I.; Agarwal, S. Gupta, V. K. Ultrasound assisted adsorption of malachite green dye onto ZnS:Cu-NP-AC: optimization.

equilibrium Sep.

isotherms

Purif.

and

Technol.

kinetic 2015,

studies–response 156,

780-788.

surface DOI

10.1016/j.seppur.2015.11.001. 20. Dil, E. A.; Ghaedi, M.; Asfaram, A.The performance of nanorods material as adsorbent for removal of azo dyes and heavy metal ions: application of ultrasound wave, optimization and modeling. Ultrason. Sonochem. 2017, 34, 792-802. DOI 10.1016/j.ultsonch.2016.07.015. 21. Saxena, A.; Mangal, H.; Rai, P. K.; Rawat, A. S.; Datta, M. Adsorption of diethylchlorophosphate on metal oxide nanoparticles under static conditions. J. Hazard. Mater. 2010, 180, 566-576. DOI 10.1016/j.jhazmat.2010.04.071. 22. Dhannia, T.; Jayalekshmi, S.; Kumar, M. C. S.; Rao, T. P.; Bose, A. C. Effect of iron doping and annealing on structural and optical properties of cerium oxide nanocrystals. J. Phys. Chem. Solids, 2010, 71, 1020-1025. DOI 10.1016/j.jpcs.2010.04.011. 23. Lv, H.; Tu, H.; Zhao, B.; Wu, Y.; Hu, K. Synthesis and electrochemical behavior of Ce1-xFex02-δ as a possible SOFC anode materials. Solid State Ionics, 2007, 177, 34673472. DOI 10.1016/j.ssi.2006.09.010. 24. Gayen, A.; Priolkar, K. R.; Shukla, A. K.; Ravishankar, N.; Hegde, M. S. Oxide-ion conductivity in CuxCe1− xO2− δ (0≤ x≤ 0.10). Mater. Res. Bull. 2005, 40, 421-431. DOI 10.1016/j.materresbull.2004.12.006.



Page 16 of 36

25. Acharya, S. A.; Gaikwad, V. M.; D'Souza, S. W.; Barman, S. R. Gd/Sm dopantmodified oxidation state and defect generation in nano-ceria. Solid State Ion. 2014, 260, 21-29. DOI 10.1016/j.ssi.2014.03.008. 26. Wheeler, D. W.; Khan, I. A. Raman spectroscopy study of cerium oxide in a cerium–5 wt.%

lanthanum

alloy.

Vib

Spectrosc.

2014,

70,

200-206.

DOI

10.1016/j.vibspec.2013.12.006. 27. Gu, H.; Soucek, M. D. Preparation and characterization of monodisperse cerium oxide nanoparticles in hydrocarbon solvents. Chem. Mater. 2007, 19, 1103-1110. DOI 10.1021/cm061332r. 28. Alla, S. K.; Devarakonda, K. K.; Komarala, E.V.P.; Mandal R. K.; Prasad, N. K. Ferromagnetic Fe-substituted cerium oxide nanorods: synthesis and characterization. Mater. Des. 2017, 114, 584-590. DOI 10.1016/j.matdes.2016.11.105. 29. Dimri, M. C.; Khanduri, H.; Kooskora, H.; Subbi, J.; Heinmaa, I.; Mere, A.; Krustok, J.;Stern R. Ferromagnetism in rare earth doped cerium oxide bulk samples. Phys. Status Solidi. A. 2012, 209 (2), 353-358. DOI 10.1002/pssa.201127403. 30. Sundaresan, A.; Rao, C. N. R. Ferromagnetism as a universal feature of inorganic nanoparticles. Nano Today, 2009, 4, 96-106. DOI 10.1016/j.nantod.2008.10.002. 31. Gupta, P.; Nagarajan, R. Fine tuning bifunctional properties of Y0.5Gd0.5BO3 by doping with Ce3+ and co-doping with Li+,Ca2+ and Al3+ following an epoxide mediated gel approach. Mater. Today Chem. 2018, 7, 15-24. DOI 10.1016/j.mtchem.2017.11.003. 32. Ho, C.; Yu, J. C.; Kwong, T.; Mak, A. C.; Lai, S. Morphology-controllable synthesis of mesoporous Ceo2 nano- and microstructures. Chem. Mater. 2005, 17, 4514-4522. DOI 10.1021/cm0507967. 33. Choudhury, B.; Chetri, P.; Choudhury, A. Annealing temperature and oxygen-vacancydependent variation of lattice strain, band gap and luminescence properties of CeO2 nanoparticles.

J.

Exp.

Nanosci.

2015,

10,

103-114.

DOI

10.1080/17458080.2013.801566. 34. Porkodi, K.; Kumar, K. V. Equilibrium, kinetics and mechanism modeling and simulation of basic and acid dyes sorption onto jute fiber carbon: eosin yellow, Malachite green and crystal violet single component systems. J. Hazard. Mater. 2007, 143, 311-327. DOI 10.1016/j.jhazmat.2006.09.029. ACS Paragon Plus Environment

Page 17 of 36 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


35. Yazdani, M. R.; Bhatnagar, A.; Vahala, R. Synthesis, characterization and exploitation of nano-TiO2/feldspar embedded chitosan beads towards UV-assisted adsorptive abatement of aqueous arsenic (As). Chem. Eng. J. 2017, 316, 370-382. DOI 10.1016/j.cej.2017.01.121. 36. Yu, X.; Tong, S.; Ge, M.; Zuo, J.; Cao, C.; Song, W. One-step synthesis of magnetic composites of cellulose@iron oxide nanoparticles for arsenic removal. J. Mater. Chem. A. 2013, 1, 959-965. DOI 10.1039/C2TA00315E. 37. Guan, X. H.; Dong, H. R.; Ma, J.; Jiang, L. Removal of arsenic from water: Effects of competing anions on As(III) removal in KMnO4–Fe(II) process. Water Res. 2009, 43, 3891-3899. DOI 10.1016/j.watres.2009.06.008. 38. Uhart, A.; Ledeuil, J. B.; Gonbeau, D.; Dupin, J. C.; Bonino, J. P.; Ansart, F.; Esteban, J. An Auger and XPS survey of cerium active corrosion protection for AA2024-T3 aluminum

alloy.

Appl.

Surf.

Sci.

2016,

390,

751-759.

DOI

10.1016/j.apsusc.2016.08.170. 39. Yu, L.; Ma, Y.; Ong, C. N.; Xie, J.; Liu, Y. Rapid adsorption removal of arsenate by hydrous cerium oxide–graphene composite. RSC Adv. 2015, 5, 64983-64990. DOI 10.1039/C5RA08922K. 40. Chen, J.; Wang, J.; Zhang, G.; Wu, Q.; Wang, D. Facile fabrication of nanostructured cerium-manganese binary oxide for enhanced arsenite removal from water. Chem. Eng. J . 2018, 334, 1518-1526. DOI 10.1016/j.cej.2017.11.062. 41. Mishra, P. K.; Kumar, R.; Rai, P. K. Surfactant free one pot synthesis of CeO2, TiO2 and Ti@Ce oxide nanoparticles for ultra fast removal of Cr(VI) from aqueous media. Nanoscale, 2018, 10, 7257-7269. DOI 10.1039/C7NR09563E. 42. Sahu, T. K.; Arora, S.; B, Avishek.; Iyer, P. K.; Qureshi, M. Efficient and rapid removal of environmental malignant Arsenic (III) and industrial dyes using reusable, recoverable ternary iron oxide-ormosil-graphene oxide composite. ACS Sustainable Chem. Eng. 2017, 5 (7), 5912-5921. DOI 10.1021/acssuschemeng.7b00632. 43. Tucek, J.; Prucek, R.; Kolarik, J.; Zoppellaro, G.; Petr, M.; Filip J.; Sharma, V. K.; Zboril, R. Zero-valent iron nanoparticles reduce arsenites and arsenates to As(0) firmly embedded in core shell superstructure – challenging strategy of arsenic treatment under anoxic conditions. ACS Sustainable Chem. Eng. 2017, 5 (4), 3027-3038. DOI 10.1021/acssuschemeng.6b02698.



44. Yu, X.; Tong, S.; Ge, M.; Zuo, J.; Cao, C.; Song, W. One-step synthesis of magnetic composites of cellulose@iron oxide nanoparticles for arsenic removal. J. Mater. Chem. A, 2013, 1, 959-965. DOI 10.1039/C2TA00315E. 45. Tian, Na.; Tian, X.; M, L.; Yang, C.; Wang, Y.; Wang, Z.; Zhang, Lide. Welldispersed magnetic iron oxide nanocrystals on sepiolite nanofibers for arsenic removal. RSC Adv. 2015, 5, 25236-25243. DOI 10.1039/C5RA01592H. 46. Sua, H.; Yea, Z.; Hmidi, N. High-performance iron oxide–graphene oxide nanocomposite adsorbents for arsenic removal. Colloid. Surf. A Physicochem. Eng. Asp. 2017, 522, 161-172. DOI 10.1016/j.colsurfa.2017.02.065.


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Caption for Figures Fig 1 Adsorption-desorption isotherms of CeO2, [email protected], and [email protected] oxide NPs. Fig 2 HR-TEM (a-b) SAED (c) and FE-SEM (d) images of [email protected] oxide NPs Fig 3(a) HR-XRD spectra with Le-Bail refinement for CeO2, [email protected] and [email protected] oxide NPs. (b) HR-XRD spectra of CeO2, [email protected] and [email protected] oxide NPs after adsorption of As(III). Fig 4 Raman spectra of CeO2, [email protected], [email protected] oxide NPs Fig 5 M-H curve of pure CeO2 and iron impregnated ([email protected]) and ([email protected]) oxide NPs. Fig 6 (a) Redlich-Peterson isotherm for removal of As(III) using CeO2, [email protected] and [email protected] oxide NPs (b) Intra-Particle diffusion model for removal of As(III) using CeO2, [email protected] and [email protected] oxide NPs. Fig 7(a) Effect of pH on adsorption capacity of CeO2, [email protected], and [email protected] oxide NPs.(b) Effect of ions on adsorption capacity of CeO2, [email protected], and [email protected] oxide NPs.(c) Effect of Contact time for the removal of As(III) on CeO2, [email protected], and [email protected] oxide NPs. Fig 8 (a) XPS survey spectra of [email protected] oxide NPs before and after adsorption of As(III). (b) Ce 3d high resolution core level XPS spectra of [email protected] oxide NPs before adsorption of As(III). (c) Ce 3d high resolution core level XPS spectra of [email protected] oxide NPs after adsorption of As(III). (d) Fe 2p high resolution XPS spectra of [email protected] oxide NPs before adsorption of As(III). (e) Fe 2p high resolution XPS spectra of [email protected] oxide NPs after adsorption of As(III). Fig 9 Removal mechanism of As(III) using [email protected] oxide NPs.



Adsorption-desorption isotherms of CeO2, [email protected], and [email protected] oxide NPs. Figure 1

HR-TEM (a-c) and SAED (d) images of [email protected] oxide NPs . Figure 2


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(a) HR-XRD spectra with Le-Bail refinement for CeO2, [email protected] and [email protected] oxide NPs.

(b) HR-XRD spectra of CeO2, [email protected] and [email protected] oxide NPs after adsorption of As(III). Figure 3 ACS Paragon Plus Environment


Raman spectra of CeO2, [email protected], [email protected] oxide NPs Figure 4

M-H curve of pure CeO2 and iron impregnated ([email protected]) and ([email protected]) oxide NPs. Figure 5


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(a) Redlich-Peterson isotherm for removal of As(III) using CeO2, [email protected] and [email protected] oxide NPs.

(b) Intraparticle diffusion model for removal of As(III) using CeO2, [email protected] and [email protected] oxide NPs. Figure 6 ACS Paragon Plus Environment


(a) Effect of pH on adsorption capacities of CeO2, [email protected] and [email protected] oxide NPs.

(b) Effect of competing ions on adsorption capacities of CeO2, [email protected] and [email protected] oxide NPs. Figure 7


Page 24 of 36

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(c) Effect of Contact time for the removal of As(III) on CeO2, [email protected] and [email protected] oxide NPs. Figure 7



(a) XPS survey spectra of [email protected] oxide NPs before and after adsorption of As(III).

(b) Ce 3d high resolution core level XPS spectra of [email protected] oxide NPs before adsorption of As(III).

(c) Ce 3d high resolution core level XPS spectra of [email protected] oxide NPs after adsorption of As(III). Figure 8 ACS Paragon Plus Environment

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(d) Fe 2p high resolution core level XPS spectra of [email protected] oxide NPs before adsorption of As(III).

(e) Fe 2p high resolution core level XPS spectra of [email protected] oxide NPs after adsorption of As(III). Figure 8



(f) XPS spectrum of As(III) adsorbed on Fe@Ce oxide NPs. Figure 8


Page 28 of 36

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Removal mechanism of As(III) using [email protected] oxide NPs. Figure 9



Caption for Tables Table 1 Surface area and pore size distribution of CeO2, [email protected] and [email protected] oxide NPs. Table 2 Summary of the crystallographic details from the Le-Bail refinements of the HRXRD patterns of the CeO2, [email protected] and [email protected] oxide NPs. Table 3 The parameters of Ms, and Hc for CeO2, [email protected] and [email protected] oxide NPs. Table 4 Langmuir, Freundlich, Redlich Peterson, isotherms parameters for adsorption of As(III). Table 5 Kinetics parameters for the removal of As(III) of CeO2, [email protected] and [email protected] oxide NPs. Table 6 Adsorbents and their physical characteristics for the removal of As(III).


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Table 1 Surface area and pore size distribution of CeO2, [email protected] and [email protected] oxide nanoparticles.

Sample

Surface area (N2 BET) (m2 g-1)

Pore size (4V/A) by BET adsorption (nm)

Mesopore volume (N2 -BJH) (cm3 g-1)

Cumulative desorption pore volume (N2 -BJH) (cm3 g-1)

Bulk Density (g cm-3)

CeO2

268.18

4.3

0.60

0.58

0.049

[email protected]

142.30

5.1

0.48

0.48

0.059

[email protected]

87.5

5.5

0.15

0.15

0.073

Table 2 Summary of the crystallographic details from the Le-Bail refinements of the PXRD patterns of the CeO2, [email protected] and [email protected] oxide NPs.

Crystal System Space Group a (Å) Cell Volume (Å3) Z Radiation 2θ range Rp (%) Rwp (%) G.O.F. Crystallite size at (111) (nm)

CeO2 Cubic

[email protected] Cubic

[email protected] Cubic

5.431(9) 160.19(12) 8 CuKα 20-70° 12.23 11.02 1.08 5.5

5.415(18) 158.77(21) 8 CuKα 20-70° 18.92 15.68 1.05 6.3

5.422(14) 159.39(16) 8 CuKα 20-70° 17.56 14.99 1.03 7.4



Page 32 of 36

Table 3 The parameters of Ms and Hc and Band gap for CeO2, [email protected] and [email protected] oxide NPs. Sample CeO2 [email protected] [email protected]

Ms (emu g-1) 0.0209 0.0253 0.0287

Hc (kOe) 4.889 3.770 3.763

Band Energy (eV) 3.001 2.557 2.457

Table 4 Langmuir, Freundlich, Redlich Peterson, isotherms parameters for adsorption of As(III).

Models

Langmuir

Freundlich

RedlichPeterson

Parameters

CeO2

[email protected]

[email protected]

Qm b R2

195.6 0.31 0.98

256.4 0.42 0.99

263.15 0.46 0.99

KF n R2

12.2 4.0 0.75

75.3 2.4 0.79

40.34 2.47 0.80

qmon bRP α R2

108.4 0.007 0.84 0.99

160.9 0.005 0.86 0.99

200.4 0.006 0.92 0.99


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Table 5 Kinetics parameters for the removal of As(III) of CeO2, [email protected] and [email protected] oxide NPs.

Adsorbents

Second order kinetic parameters

Intra particle diffusion kinetics parameters

K2(g mg-1 min-1) 7.2x10-2 95.0 Qe (mg g-1) 2 R 1.00

Kd(mg g-1 min-0.5)1.9x10-1 90.89 C (mg g-1) 2 R 0.92

[email protected]

K2(g mg-1 min-1) Qe(mg g-1) R2

7.8x10 97.9 1.00

Kd(mg g-1min-0.5) 9.7x10-1 C (mg g-1) 95.8 R2 0.79

[email protected]

K2(g mg-1 min-1) 10.5 x10-2 Qe (mg g-1) 97.9 R2 0.99

Kd(mg g-1 min-0.5) 5.3x10-1 C (mg g-1) 96.9 R2 0.91

CeO2



Page 34 of 36

Table 6 Adsorbents and characteristics for the removal of As(III). Adsorbents

Synthesis

Size (nm)

Surface area (m2 g-1)

CeO2-MnO Ce-Fe metal oxides with CNT CeO2 & Fe3O4 incorporated Microcapsul Fe-Ce alkoxide

Precipitation CoPrecipitation Surfactant assisted

70-90 7

116.9 216.3

10-30

Hydrothermal

Ce-CNB (Cerium modified chitosan) CeO2

Model Fitted

References

Freundlich Langmuir & Freundlich Freundlich

13 14

-

Adsorption capacity (mg g-1) As(III) 34.8 28.7 16.2 32

10

217.5

206

Langmuir & Freundlich

16

Precipitation

165

-

57.5

Langmuir

17

Aero-gel

3.1

257.0

71.9

18

Hydrous CeO2

Precipitation

4

198.0

171

RedlichPeterson ReidlichPeterson

Ce-Mn binary oxide CeO2

CoPrecipitation

-

157

97.7 80.7

Langmuir & Freundlich

39

ORMOSILFe3O4-RGO

Modified Hummer's and CoPrecipitation Thermal procedure

7

127.3

38

Langmuir

42

70

25

150

Langmuir

43

OSF-nZVI

15

38

Cellulose@Fe2O3

CoPrecipitation

5-100

113

23.16

Langmuir

44

Fe2O3@Sepiolite

Thermal decomposition

9

300

50.35

Langmuir

45

FeOx–GO

Modified Hummer's and CoPrecipitation

5

341

147

Langmuir

46

3-5 11-15 15-23

268 142 87

195.6 256.4 263.1

RedlichPeterson

In this study

CeO2 [email protected] [email protected]

Aero-gel


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(TOC) Graphic Synopsis: Aero-gel based solid solution of Fe@Ce oxide NPs can be used for highly efficient and ultrafast removal of As(III) from aqueous medium.



Synopsis: Aero-gel based solid solution of Fe@Ce oxide NPs can be used for highly efficient and ultrafast removal of As(III) from aqueous medium. 254x190mm (96 x 96 DPI)


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Aero-Gel Based Cerium Doped Iron Oxide Solid ... - ACS Publications

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